JP2005187827A - Method for manufacturing dope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stably manufacturing a dope with a prescribed concentration by enhancing the solubility of a solid portion of a dope raw material into a solvent for the process of film-forming from a solution when preparing the dope. <P>SOLUTION: The solid portion including a polymer etc., and the solvent are fed into a first stirring tank 21 and are stirred for a prescribed period, and subsequently the mixture is sent to a second stirring tank 22, and the mixture is furthermore stirred there to manufacturing the dope. The second stirring tank 22 is equipped with a baffle 71. When the dope is filtered at 0.5 MPa, the mixture is completely mixed in the second stirring tank 21 to be less than 2.06 of (filtrate V1 from initiation to 30 minutes later of filter)/(filtrate V2 from initiation to 2 hours later of filter). By the above process, the polymer is completely dissolved and does not coagulate and remain around the baffle 71, and the dope having the equal mixing ratio of compositions to that of the raw materials can be prepared. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a dope, and more particularly to a method for producing a dope for forming a polymer film for use in optical applications such as a liquid crystal display device.

  Many polymer films used in the optical field are manufactured by a solution casting method. Among them, the cellulose acylate film is widely used because it has transparency and appropriate moisture permeability, has high mechanical strength, and has low dependence on humidity and temperature for dimensional stability. One. In the solution casting method, a polymer such as cellulose acylate and various additives are doped with a solvent, and then the dope is cast from a die to a casting support, and the casting film is peeled off when it has self-supporting properties. Then, this is dried in a drying step to form a film. The casting support is a drum or a band that continuously rotates.

  In many cases, impurities and gel-like substances are mixed in a dope obtained by simply stirring and mixing a polymer and an additive in a solvent. Therefore, when cast into a film in this state, these insoluble matters are mixed as foreign matter in the film, causing a surface failure of the film, etc., resulting in a decrease in commercial value or inability to use. Sometimes it ends up. Therefore, it is common to perform filtration before casting. However, since the components that should be contained in the film are filtered out together with impurities as a result of filtration, the concentration of each production lot may differ depending on the difference in the dissolved state. If dopes with different concentrations are used, the resulting film will have variations in optical properties such as mechanical strength, viscoelasticity, and birefringence, and the properties of the product will change.

  In addition, the more the foreign matter including undissolved material is contained in the dope, the faster the hole closing speed of the filter used for filtering becomes, and the life of the filter becomes shorter. The filter whose hole is blocked is replaced with another filter, but the line may be temporarily stopped during the replacement, which is regarded as a manufacturing loss. Therefore, from the viewpoint of not only the variation in the concentration of the dope but also the production loss due to the filter replacement, it is preferable to dissolve or uniformly finely disperse the undissolved material in the dope without leaving as much as possible.

Therefore, in the dope preparation, sufficient stirring or the like is performed to dissolve or finely disperse the solid component in the solvent. This stirring method, in the dissolution step of the dope by mixing cellulose acylate and a solvent, 9.8 × 10N / m / sec 2 or more ^{9.8 × 10 5 N / m /} sec 2 or less shear force Has been proposed (see, for example, Patent Document 1). In addition, in stirring with a stirring blade or the like, in order to improve the stirring efficiency, a method of stirring by providing a baffle plate inside the stirring tank is not limited to dope preparation and is widely applied.
JP 2000-273184 A (page 4-6)

  However, according to the method of Patent Document 1, as a method for dissolving the solid content in the preparation of the dope, a sufficient effect is not observed such that a gel-like substance still remains. In addition, this method does not mention the installation of baffle plates that are generally used to increase the stirring efficiency.

  On the other hand, in the preparation of the dope, the method of mixing the solvent and the solid content in a stirring tank equipped with a baffle plate and dissolving the mixture while stirring can promote the dissolution, but this method also has a problem. The baffle plate is most commonly provided on the inner peripheral surface of the agitation tank, and the problem is, for example, that the stirrer shear force is not transmitted to a part of the vicinity of the baffle plate, and the liquid flow is stagnant and the staying part The solid content in an undissolved state aggregates and adheres to and remains in the staying portion. Even if stirring continues after that, this deposit | attachment will not melt | dissolve but will accumulate. When the deposition amount increases, the raw material ratio of the obtained liquid changes from the charged raw material ratio, which causes a problem that the target dope component mixing ratio, that is, the concentration changes. In addition, when the amount of deposition increases and the deposits grow greatly, this may inhibit the rotation of the stirring blades and the stirring shaft and damage them.

  The present invention has been made in view of the above problems, and in the solution casting method, when preparing a dope, it improves the solubility in a solid content solvent that is a raw material of the dope, and stabilizes the dope at a predetermined concentration. An object of the present invention is to provide a method for manufacturing the same. In addition, by forming a dope obtained by this production method, a polymer film having few foreign substances and having good optical properties, and a polarizing plate using this polymer film and having good optical properties are provided. Objective.

  In order to solve the above-mentioned object, in the present invention, in a dope manufacturing method in which a polymer and a solvent are mixed in a stirring tank to obtain a dope, the polymer and the solvent are stirred by a first stirring tank provided with a first stirring member. When the dope was filtered at 0.5 MPa, the filtrate amount V1 from the start of filtration to 30 minutes elapsed was divided by the filtrate amount V2 from the start of filtration to 2 hours after filtration. And a second step of stirring the mixed solution in the second stirring tank provided with the second stirring member and the baffle member so that the value V1 / V2 is smaller than 2.06. It is structured as a feature.

  The baffle member is a plate provided on the inner wall of the second agitation tank, the lower end of the plate is located above the bottom surface inside the second agitation tank, and the upper end is higher than the liquid level of the mixed liquid. It is preferable to be located above, and in the first step, it is preferable to stir with the solvent while gradually putting the polymer into the first stirring tank.

  By this invention, the solubility with respect to the solvent of the solid content which is the raw material of dope can be improved, and the dope of a predetermined density | concentration can be manufactured stably. Moreover, by forming the dope obtained, a polymer film having few foreign substances and good optical properties, and a polarizing plate having good optical properties using this polymer film can be obtained.

  FIG. 1 is a schematic view of a solution casting apparatus as an embodiment of the present invention. The solution casting apparatus 10 includes a dope preparation device 11, a casting device 12, a drying device 15 and a winding device 16.

  The dope preparation device 11 includes first and second stirring tanks 21 and 22, a filter 25, a static mixer 26, first to third pumps P1 to P3, and a flow rate adjustment valve V1. The first to third supply sources 31 to 33 are connected to the first stirring tank 21 of the dope preparation device 11.

  The casting apparatus 12 includes a casting die 36, a backup roller 37, and a band 38. The drying device 15 includes a tenter 41 and a roller dryer 42, and the winding device 16 includes a cutter 45 and a winding unit 46. The solution casting apparatus 10 is appropriately provided with a supporting or conveying roller 47 as needed, and this roller 47 supports or conveys the polymer film 52. In FIG. 1, only a part of the used rollers is illustrated in order to avoid complexity.

  The polymer as the main component of the casting dope 51 and the film 52 is supplied from the first supply source 31, and the liquid serving as a solvent for the dope is supplied from the second supply source 32 to the first stirring tank 21 through separate liquid supply paths. Supplied. Various additives such as ultraviolet absorbers and fine particles are mainly supplied from the third supply source 33. The polymer and the solvent sent from the first and second supply sources 31 and 32 to the first stirring tank 21 are mixed in the first stirring tank 21 and stirred for a predetermined time, and the first pump P1 is used as the first preparation dope 51a. Is sent to the second stirring tank 22. In the second stirring tank 22, the first prepared dope 51a is further stirred for a predetermined time, and the mixed liquid obtained by stirring here is hereinafter referred to as a second prepared dope 51b.

  The second prepared dope 51b is sent to the filtration device 25 by the second pump P2, and foreign matters such as undissolved matter and dust are removed. The amount of the prepared dope 51b fed from the second agitation tank 22 to the filtration device 25 is controlled by the valve V1 in consideration of the filtration pressure and the film forming speed in the filtration device 25. However, the second pump and the valve V1 may be changed to a metering pump, and the liquid may be fed while controlling the flow rate of the second preparation dope 51b. In the following description, the mixture from which foreign substances have been removed by filtration with the filtration device 25 will be referred to as a third prepared dope (not shown). Subsequently, the third preparation dope, the additive from the third supply source 33 and the like are mixed in-line by the static mixer 26 to become the casting dope 51 and reach the casting die 36.

  The casting dope 51 is cast from the casting die 36 on a band 38 that is supported by the backup roller 37 and continuously runs. The backup roller 37 is provided with drive control means (not shown), and the rotational speed of the backup roller 37 is controlled by this drive control means, and the band is conveyed at a predetermined speed. The cast dope 51 cast becomes a cast film on the band, and the cast film becomes self-supporting while traveling on the band.

  The cast film having self-supporting properties is peeled off by a roller as a film 52 and further conveyed to a downstream process. The peeled film 52 is sent to the tenter 41, where the width is regulated and the film 52 is dried while being stretched. In the tenter 41, a plurality of tenter clips (not shown) travel along a tenter track (not shown) while holding both side ends of the film 52, and the film 52 is conveyed by the travel of the tenter clip. . A pin clip or the like may be used instead of the tenter clip. The tenter clip is automatically controlled to be opened and closed by a controller (not shown), and the holding and releasing of the film 52 are controlled by the opening and closing. The tenter clip holding the film 52 travels inside the tenter 41 and is automatically controlled to release the clip and release the holding of the film 52 when reaching a predetermined holding release point near the exit.

  The film 52 of the tenter 41 is sent to a roller dryer 42 which is a next process by a supporting or conveying roller 47, and is sufficiently dried while being supported or conveyed by a plurality of rollers 42a. The film 52 after being sufficiently dried is cut and removed at both ends by the cutter 45 and wound up by the winding section 46 as a product. In addition, in order to stabilize the conveyance in the roller dryer 42, it is also possible to cut and remove both end portions of the film 52 including the portion deformed by the holding by the tenter clip before sending it into the roller dryer 42. is there.

  Further, a tank (not shown) is provided at an arbitrary position downstream of the second stirring tank 22 and upstream of the static mixer 26, where the second prepared dope 51b or the third prepared dope is retained for a predetermined time. To defoam. Thereby, the amount of bubbles in the casting dope 51 can be reduced. Further, a drum may be used as the support instead of the band, but the illustration is omitted in this embodiment.

  FIG. 2 is a schematic view showing a part of a dope preparation facility embodying the present invention. As shown in FIG. 2, both the first and second stirring tanks 21 and 22 have motors 61a and 61b, and controllers 62a and 62b are connected to the motors 61a and 61b, respectively. In the first stirring vessel 21, two stirring blades 63a and two stirring blades 63b are attached to the top and bottom of the stirring shaft 66a. Further, the stirring blade 63a and the stirring blade 63b are provided so that an angle formed when the first stirring tank 21 is viewed from above is 90 °. In the second stirring tank 22, the stirring blade 63c and the stirring blade 63d are provided in the same manner as the first stirring tank 21 with respect to the stirring shaft 66b. The motors 61a and 61b have their rotational speed and stirring power controlled by the controllers 62a and 62b, and the stirring shafts 66a and 66b are rotated by driving the motors 61a and 61b, and the stirring blades 63a to 63d are driven by the stirring shafts 66a and 66b. It rotates as the center of rotation.

  The first and second agitation tanks 21 and 22 have constant temperature tanks 68a and 68b whose temperatures are controlled by temperature controllers 67a and 67b, respectively. By controlling the temperature of the thermostatic chambers 68a and 68b, the internal liquid temperature is controlled.

  Further, a baffle plate 71 is attached to the inner wall of the second stirring tank 22. There are usually a plurality of baffle plates 71 attached to the agitation tank. In the present embodiment, there are four baffle plates, but only two of them are shown in FIG. However, the present invention is not limited to the configuration of each of the stirring tanks 21 and 22 including the number and shape of the baffle plates 71 and the mounting position.

  In addition, the polymer from the first supply source 31 and the solvent from the second supply source 32 are supplied to the first stirring tank 21 from the upper part, and after mixing in the first stirring tank, the first prepared dope 51a. Is sent from the bottom to the second agitation tank 22. The first preparation dope 51 a is supplied from the upper part of the second stirring tank 22 and sent to the filter 25 from the bottom. However, the present invention does not depend on the positions of the inlets and outlets of the respective substances in the first and second stirring tanks 21 and 22, for example, at least one of the inlet and the outlet is the first and second You may be provided in the side surface of the 2nd stirring tank 21 and 22.

  A predetermined amount of the polymer and the solvent is sent to the first stirring vessel 21 and mixed therein. Usually, after the solvent is allowed to flow into the first stirring tank 21, the polymer is allowed to flow while rotating the stirring blades 63a and 63b. At this time, first, the whole amount of the solvent may be allowed to flow in, or the polymer may be allowed to flow after flowing a predetermined amount of the solvent that can be stirred and mixed first, and then the remaining solvent may be allowed to flow. Good. In the latter case, it is more preferable to allow the solvent to flow in so as to wash away the polymer adhering to the polymer inlet or the inner wall of the first stirring tank 21 when the remaining solvent is allowed to flow.

  In addition, the present invention does not depend on the time required for the polymer and solvent to flow into the first stirring tank 21, but at least the polymer is allowed to flow gradually rather than at a time. It is preferable. The inflow speed when the mixture is gradually stirred depends on the solvent species, polymer species, stirring method and stirring conditions. However, the flow rate of the polymer flowing into the first stirring tank 21 and flowing down to the internal liquid surface is rotated once by stirring. It is preferable that the inflow speed is such that it is buried in the liquid. It is more preferable that the rotation of the stirring blades 63a and 63b is already started when the polymer starts to flow into the first stirring tank 21, and has reached a predetermined condition.

  The liquid mixture is stirred for a predetermined time by the stirring blades 63a and 63b, and when the liquid mixture does not completely dissolve and reaches a predetermined state, the liquid is fed to the second stirring tank 22. When the entire amount is fed from the first stirring tank 21 to the second stirring tank 22, a polymer and a solvent for fresh preparation flow into the first stirring tank 21. The predetermined state that is not completely dissolved as described above is appropriately determined according to the affinity and solubility of the polymer used for the solvent, the solid concentration of the target dope, and the like. For example, a predetermined state is a state in which a part of the polymer is dissolved and the rest is swollen, or a part of the polymer is dissolved and the rest is dispersed as an undissolved product. Hereinafter, this preliminary stirring step in the first stirring tank 21 will be referred to as a first stirring step.

  The first stirring tank 21 is not provided with a baffle plate, so that the polymer added here does not accumulate in a part of the first stirring tank 21. That is, since the polymer is present in the solvent without forming a large mass, the contact area with the solvent is kept large, and the affinity with the solvent can be improved by stirring. Therefore, since the concentration in the mixed liquid is kept uniform throughout the liquid, the first preparation dope 51a is sent to the second stirring tank 22 in a state where the predetermined concentration in the preparation is maintained. Note that the concentration in the first preparation dope 51a is not the value of the dissolved polymer for the solvent, but the sum of the polymer dissolved in the solvent and the polymer in a state of being dispersed or swollen almost uniformly, It means the value for the solvent.

  The first prepared dope 51 a obtained by the first stirring step is further stirred in the second stirring tank 22. The stirring process in the second stirring tank 22 will be referred to as a second stirring process in the following description. Since the baffle plate 71 is attached to the second agitation tank 22, the agitation efficiency when the agitation blades are rotating at the same rotational speed is higher than that of the first agitation tank 21. Therefore, the transmission efficiency of the stirring power with respect to the liquid is higher than when stirring in the first stirring tank 21, and the level difference of the liquid level is smaller than that in the first stirring tank 21. The polymer uniformly present in the solvent in the first stirring step sufficiently contains the solvent on the surface or inside of the molecule in the first preparation dope 51a. Therefore, the polymer is quickly and completely dissolved by stirring in the second stirring tank 22.

  As described above, the present invention stirs and mixes a solid component such as a polymer and a solvent in advance in a stirring tank not provided with a baffle plate, and increases the affinity between the two in the first stirring step. After having uniform solubility or uniform dispersibility in, solid components such as polymers can be dissolved without agglomerating in the solvent by stirring in a stirring tank equipped with a baffle plate.

  The stirring power per unit liquid amount in the first stirring tank 21 is not limited at the start of stirring, but the unit at the end of stirring in the first stirring tank 21 and at the start of stirring in the second stirring tank 22. The stirring power relative to the liquid amount is preferably 2 W / liter or more and 10 W / liter or less. Further, the stirring power per unit liquid amount after the start of stirring in the second stirring tank 22 is not limited, but it is preferable to maintain the value at the start of stirring or increase it to a predetermined value. . The above-described end of stirring in the first stirring tank 21 and start of stirring in the second stirring tank are predetermined times. In this embodiment, the time is approximately 30 minutes to 300 minutes, but is not limited thereto. Is not to be done. Here, the stirring power is a value obtained by subtracting the idling power of the stirring blades 63a to 63d from the driving power of the motors 61a and 61b of the stirring tanks 21 and 22.

  If the stirring power per unit liquid volume is less than 2 W / liter, sufficient stirring efficiency cannot be obtained. That is, in the first agitation tank 21, the amount of dissolution is reduced and the uniform dispersion of the polymer is not sufficient, and sufficient affinity between the dispersed polymer and the solvent cannot be obtained. Further, in the second stirring tank 22, the polymer dispersed in the first preparation dope 51a starts to aggregate, and the aggregate may stay in the vicinity of the baffle plate. On the other hand, even if the stirring power per unit liquid volume is larger than 10 W / liter, the effect of increasing the power cannot be obtained, resulting in inefficient stirring. The stirring power per unit liquid amount is more preferably 3 W / L or more and 10 W / L or less, and further preferably 5 W / L or more and 10 W / L or less.

When the stirring times in the first and second stirring tanks 21 and 22 are t1 and t2 (units: minutes), respectively, it is preferable that t1 and t2 satisfy the following formulas (1) and (2).
t1 ≧ 0.2 × (t1 + t2) (1)
t2 ≧ 0.4 × (t1 + t2) (2)

  It is inappropriate that one of the stirring times t1 and t2 in the first and second stirring tanks 21 and 22 is extremely short. For example, when the stirring time t1 in the first stirring tank 21 is t1 <0.2 × (t1 + t2), the mixture is sent to the second stirring tank 22 in a state where the amount of polymer dissolved in the solvent and the degree of dispersion are insufficient. It is done. Therefore, the polymer aggregates in the second stirring tank 22 particularly in the vicinity of the baffle plate. Further, when the stirring time t2 in the second stirring tank 22 is t2 <0.4 × (t1 + t2), the stirring becomes insufficient and the polymer is not completely dissolved.

  The stirring times t1 and t2 in the first and second stirring tanks 21 and 22 are very effective as long as the values satisfy the above formulas (1) and (2), but the first and second stirring tanks 21 and 22 are respectively In the case of one by one, it is more preferable that t1 = t2 because there is no waiting time in one stirring tank and it is efficient. When t1 ≠ t2, it is also preferable to provide a plurality of first or second stirring tanks 21 and 22 in parallel in order to avoid inefficiency due to waiting time. For example, when t2 = t1 × 2, when two second stirring tanks 22 are provided for one first stirring tank 21 and are operated alternately, the first stirring time t2 of the second stirring tank 22 is long. Since the waiting time of the stirring tank 21 is eliminated, it is efficient.

  In the present embodiment, general commercially available paddle type stirring tanks are used as the first and second stirring tanks 21 and 22. The stirring tank body is a vertical cylindrical shape, and a paddle type stirrer is attached to the stirring tank body. A paddle type stirring tank is a stirring tank in which a spatula-shaped stirring blade is attached to a stirring shaft, and the substance inside the stirring tank is mixed by its rotation. However, the present invention is not limited to the paddle type stirring tank, and various known stirring tanks can be used. For example, a turbine type stirring tank, a screw type stirring tank, an anchor type stirring tank, or the like can be used.

  In the present embodiment, the baffle plate 71 provided in the second stirring tank 22 has an upper end at a position higher than the liquid level and a lower end at a position higher than the bottom. However, the present invention does not depend on the shape or the number of baffle plates 71. For example, a plurality of small baffle plates may be provided above and below to form a set, and the plurality of sets may be attached to the inner wall peripheral surface of the second stirring tank 22. Further, instead of the baffle plate 71, a cylindrical pipe or the like may be used.

  In the present embodiment, the solubility can be further improved by providing the first and second agitation tanks 21 and 22 with thermostatic baths. Since the solubility of many solids such as polymers increases as the temperature of the solvent increases, it is preferable to raise the temperature of the solvent or mixed solution within a range that does not impair the properties of the finally obtained casting dope or film. . The upper limit of the temperature rise is preferably lower than the boiling point of the solvent. When the solvent is a mixture, the upper limit of the temperature rise is preferably lower than the boiling point of the solvent having the lowest boiling point. However, it is preferable to promote dissolution by pressurizing the inside of the first and second stirring tanks 21 and 22 and stirring and mixing the solution without boiling it at a temperature equal to or higher than the boiling point of the solvent at atmospheric pressure.

  As the polymer component in the production method of the present invention, cellulose acylate is preferable, and cellulose acetate is particularly preferable. Even if the polymer is other than cellulose acylate, the present invention is applicable as long as the polymer and its precursor can be doped with a solvent to form a solution. For example, polyvinyl alcohol, modified polyvinyl alcohol, polyacrylate, polymethacrylate, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), chlorinated polyether, polyacetal, polyetheretherketone (PEEK), polyethersulfone (PES), polyimide (PI), polyamide (PA), polyamideimide (PAI), polyphenylene oxide (PPO), polyphenylenesulfone, polysulfone, polyarylate, polycarbonate (PC), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), etc. can be illustrated. Furthermore, the above-mentioned various polymers can be used in the present invention, either individually or in combination.

  Further, the present invention is not limited to the form such as the shape of the polymer, and may be, for example, a powder or a pellet. In particular, in the case of a powder, the present invention is particularly effective because it easily aggregates when mixed with a solvent. Further, the solid component flowing into the first agitation tank 21 is not limited to the polymer. In addition, for example, various additives such as a plasticizer, an ultraviolet absorber, and an ultraviolet stabilizer may be added. Is obtained. Furthermore, when adding a highly soluble thing, you may add this in the case of the mixing in the 2nd stirring tank 22. FIG.

  The present invention does not limit the solvent used for the dope, and various known solvents can be used. For example, in addition to halogen-containing organic compounds such as dichloromethane and dichloromethylene, alcohols such as methyl alcohol, ethyl alcohol, and n-butyl alcohol, various ester compounds such as methyl acetate and ethyl acetate, non-chlorine organic compounds such as acetone, Water can be used. The present invention can also be applied to a cooling dissolution method, which is one of methods for preparing a dope, and is effective in the dissolution or dispersion process.

  Furthermore, the film produced by the above dope manufacturing method and solution film-forming method can also be utilized for a polarizing plate. A polarizing plate is obtained by bonding the film 52 (refer FIG. 2) obtained by said manufacturing method as a protective film on both surfaces of the polarizing film produced with the polyvinyl alcohol (PVA) type film. The polarizing film is obtained by dyeing a polyvinyl alcohol film. As this dyeing method, a gas phase adsorption method and a liquid phase adsorption method are generally used, and both can be applied. In the present invention, dyeing was performed by liquid phase adsorption.

  For dyeing by liquid phase adsorption, iodine is used here, but the present invention is not limited to this. The polyvinyl alcohol film was immersed in an iodine / potassium iodide (KI) aqueous solution with an immersion time of 30 seconds to 5000 seconds. The aqueous solution at this time preferably has an iodine concentration of 0.1 g / liter to 20 g / liter and a potassium iodide concentration of 1 g / liter to 100 g / liter. Moreover, it is preferable that the temperature of the aqueous solution at the time of immersion is set to the range of 5 degreeC or more and 50 degrees C or less.

  The liquid phase adsorption method is not limited to the above immersion method, and a known method such as a method of applying iodine or other dye solution to a polyvinyl alcohol film or a method of spraying may be applied. Dyeing may be performed before or after the polyvinyl alcohol film is stretched, but the polyvinyl alcohol film is appropriately swelled and easily stretched by being dyed, so that the stretching step It is particularly preferable to provide a dyeing step before the step.

  It is also preferable to dye with a dichroic dye instead of iodine. Examples of dichroic dyes include dye compounds such as azo dyes, stilbene dyes, pyrazolone dyes, triphenylmethane dyes, quinoline dyes, oxazine dyes, thiazine dyes, anthraquinone dyes. it can. Water-soluble dye compounds are most preferable. Further, it is preferable that a hydrophilic functional group such as a sulfonic acid group, an amino group, or a hydroxyl group is introduced into the molecule of these dichroic dyes.

  In the step of producing a polarizing film by stretching a dyed polyvinyl alcohol film, a compound that crosslinks polyvinyl alcohol is used. Specifically, a polyvinyl alcohol film is immersed in a crosslinking agent solution in the pre-stretching step or the stretching step to contain a crosslinking agent. It may be applied instead of dipping. The polyvinyl alcohol film is sufficiently hardened by the inclusion of the crosslinking agent, and as a result, appropriate orientation is imparted. In addition, as a crosslinking agent of polyvinyl alcohol, boric acids are most preferable, but are not limited thereto.

  As the adhesive between the obtained polarizing film and the polymer film obtained from the above-mentioned dope, particularly a cellulose triacetate film, various known adhesives that can be used for bonding the polarizing film and the protective film are used. Among these, an aqueous solution of a polyvinyl alcohol polymer or a boron compound containing a modified polyvinyl alcohol having an acetoacetyl group, a sulfonic acid group, a carboxyl group, an oxyalkylene group or the like is preferable. This adhesive is preferably applied so that the thickness after drying is 0.01 μm or more and 10 μm or less, and more preferably 0.05 μm or more and 5 μm or less. Furthermore, an antireflection layer, an antiglare layer, a slippage imparting layer, an easy adhesion layer, and the like can be imparted to the surface of the cellulose acylate film layer imparted to the polyvinyl alcohol layer as a protective film.

  Furthermore, an optical compensation sheet can be stuck on the obtained cellulose acylate film and used as an optical compensation film. An antireflection film provided with an antireflection layer on the polarizing plate is obtained, and this is used as one side of the surface protective film, and twisted nematic (TN), super twisted nematic (STN), vertical alignment (VA), A transmissive, reflective, or transflective liquid crystal display device having a mode such as in-switching (IPS) or optically compensated birefringence (OCB) is obtained. Further, an optical compensation film such as a viewing angle widening film for improving the viewing angle of the liquid crystal display device, a retardation plate, and the like can be used in combination. When used in a transmissive or transflective liquid crystal display device, it is used in combination with a commercially available brightness enhancement film (a polarized light separating film having a polarization selective layer, such as D-BEF manufactured by Sumitomo 3M Co., Ltd.). In addition, a display device with higher visibility can be obtained.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated concretely, this invention is not limited to this.

[Experiment 1]
In a first stirring tank, 87 kg of dichloromethane and 13 kg of methyl alcohol were added and mixed while gently stirring. Here, 1.6 kg of triphenyl phosphate and 0.8 kg of biphenyl diphenyl phosphate were added and gently stirred until they were completely dissolved by visual observation. Furthermore, 20.6 kg of powdery cellulose triacetate (acetylation ratio 60.9%) was mixed with this liquid while stirring at a constant stirring speed while maintaining this liquid at about 35 ° C. The cellulose triacetate was charged over about 30 minutes so that the charging rate was almost constant. After the cellulose triacetate was added, the mixture was stirred for 60 minutes, and then the stirring was stopped. The stirring power immediately before stopping the stirring was 300 W, and the amount of the first prepared dope 51a obtained was 100 liters. The first stirring tank 21 has a capacity of 100 liters and an inner diameter of 450 mm, and the stirring diameter of the stirring blades 63a to 63d is 300 mm.

  The entire amount of the first prepared dope 51a obtained was sent to the second stirring tank 22 and stirred. The second stirring tank 22 is the same as the first stirring tank 21 except that the baffle plate 71 is provided. The baffle plate 71 has a width of 35 mm, and is integrally formed from the upper part close to the tank mirror part to above the liquid level. The tank mirror portion refers to the lower surface of the cylindrical container, and means a bottom surface including a curved surface at the bottom of the side wall in a cross section viewed from the side. The baffle plates 71 are attached so as to be 90 ° from each other about the stirring shaft 66b. In the second stirring tank 22, the rotation condition of stirring was set so that the stirring power at the start of stirring was 300W. In the 2nd stirring tank 22, after stirring for 120 minutes, stirring was stopped. The obtained second prepared dope 51b was filtered with a filter 25 and cast. After the cast film was peeled off, the film was dried and wound up to obtain a film 52 having a thickness of 80 μm.

[Experiment 2]
The experiment was performed in the same manner as in Experiment 1 except that the stirring power at the start of stirring in the second stirring tank 22 was 600 W.

[Experiment 3]
Stirring in the first stirring tank 21 was performed for 120 minutes after adding the cellulose triacetate, and the same as in Experiment 1 except that the stirring time in the second stirring tank 22 was 60 minutes.

[Comparative Experiment 1]
Stirring in the first stirring tank 21 was carried out for 180 minutes after the cellulose triacetate was added, and was carried out in the same manner as in Experiment 1 except that stirring in the second stirring tank 22 was not performed.

[Comparison experiment 2]
The powdery cellulose triacetate was charged not in the first stirring tank 21 but in the second stirring tank 22. Cellulose triacetate was added to the second stirring tank 22 and stirred for 180 minutes, and the final stirring power in the second stirring tank 22 was 300 W. Other conditions were the same as in Experiment 1.

[Comparative Experiment 3]
The experiment was performed in the same manner as in Experiment 1 except that the final stirring power in the first stirring tank 21 and the stirring power at the start of stirring in the second stirring tank 22 were set to 150 W.

[Comparison Experiment 4]
Stirring in the first stirring tank 21 was carried out for 150 minutes after adding the cellulose triacetate, and the same as in Experiment 1 except that the stirring time in the second stirring tank 22 was 30 minutes.

[Comparative Experiment 5]
Stirring in the first stirring tank 21 was carried out for 40 minutes after the cellulose triacetate was added, and the same as in Experiment 1 except that the stirring time in the second stirring tank 22 was 140 minutes.

  About the above experiments 1-3 and comparative experiments 1-5, evaluation was implemented regarding three items of (1)-(3) shown below, and each result is shown in Table 1.

(1) Evaluation of filter pore blockage Using a filtration device 81 as shown in FIG. 3, the second prepared dope 51 b obtained in Experiments 1 to 3 and Comparative Experiments 1 to 5 is filtered at a constant pressure, and per unit time. The amount of filtrate was measured over time. By this evaluation, the residual degree of the undissolved portion of the second preparation dope 51b was evaluated. The filtration device 81 includes a tank 82, an air source 83 that sends air to the tank 82 and applies pressure to the inside, and a valve V2 for controlling the amount of air sent to the tank. In addition, a filtrate outlet 82 a is provided at the bottom of the tank 82, and a filter 86 is provided at the outlet. A graduated cylinder 87 is installed below the filter 86. Here, as the filter 86, filter paper (filtration accuracy; # 63, manufactured by Toyo Filter Paper Co., Ltd.) is used.

  First, a predetermined amount of the second prepared dope 51a is put into a predetermined amount of tank 82, and then compressed air is fed into the tank 82 from above, thereby performing constant pressure filtration at 0.5 MPa. The filtrate is collected in the graduated cylinder 87. The amount of filtrate for 30 minutes from the start of filtration was set as V1, the amount of filtrate for 30 minutes from the start of filtration for 2 minutes was set as V2, and the value of V1 / V2 was determined. As the value of V1 / V2 is larger, the decrease in the filtration rate is more remarkable and the pores are more likely to be blocked. That is, as the value of V1 / V2 is larger, the solid component such as a polymer is not sufficiently dissolved.

(2) Evaluation of foreign matter contamination in film Film 52 was sandwiched between two polarizing plates stacked so that their deflection directions were orthogonal to each other, and this was used as an evaluation sample. This sample was observed with a microscope with a magnification of 50 times, and the number of bright spot foreign matters of 5 μm or more was counted. In Table 1, the number of bright spot foreign materials is a number per 55 mm ² .

(3) Evaluation of Internal Contamination of Second Stirring Tank 22 After stirring in the second stirring tank 22, the state of adhesion of aggregates and foreign matters near the baffle plate 71 was visually observed and evaluated. In Table 1, “O” is indicated for those in which no deposits were observed, “Δ” for those in which a small amount of deposits were observed, and “×” for those in which deposits were observed, together with the mass of the deposit. (Unit: g) is indicated.

  According to the results of Table 1, in Experiments 1 to 3, the V1 / V2 values are all smaller than 2.1, and the number of bright spot foreign materials in the film is less than 40, which is good. Furthermore, there is no deposit in the second stirring tank, which is very good. From Experiments 1 to 3, it can be seen that when the stirring power per unit liquid amount is in the range of 2 W / liter to 10 W / liter, the greater the value, the better the solubility.

  On the other hand, as a result of the comparative experiment, Comparative Experiment 1 was not stirred in the second stirring tank provided with the baffle plate, so that the dissolution was insufficient, the V1 / V2 value was high, and the brightness in the film was There are many point foreign objects. In Comparative Experiment 2, since the cellulose triacetate was charged in the second stirring tank equipped with the baffle plate, the solubility evaluated from the V1 / V2 value and the number of bright spot foreign materials was relatively good. A large amount of agglomerates were generated near the baffle plate of the tank. In Comparative Experiment 3, the stirring power was small, and in Comparative Experiment 4, the stirring time was short. Further, in Comparative Experiment 5, both the V1 / V2 value and the number of bright spot foreign materials in the film are relatively good values, but the first stirring is not possible because the stirring time in the first stirring tank 21 is short. Undissolved substances in the tank adhered to the vicinity of the baffle plate of the second stirring tank 22 to form aggregates.

[Experiment 4]
The cellulose triacetate films obtained in Experiments 1 to 3 were saponified by immersing them in a 2.0 normal 55 ° C. NaOH aqueous solution for 2 minutes. Using these films as protective films, three types of polarizing plates were prepared by adhering to both sides of a polarizer prepared by adsorbing iodine to polyvinyl alcohol. The obtained polarizing plates were all good with a small number of foreign substances.

It is the schematic of the solution casting apparatus which is embodiment of this invention. It is the schematic which shows a part of casting dope preparation equipment which is embodiment. It is the schematic of the filtration apparatus which implemented blockade evaluation of the filter hole by an undissolved substance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Dope preparation apparatus 21 1st stirring tank 22 2nd stirring tank 31 1st supply source 32 2nd supply source 51 Casting dope 51a 1st preparation dope 51b 2nd preparation dope 52 Film 61a, b Motor 62a, b Controller 63a- d Stirring blade 66a, b Stirring shaft P1-3 Pump

Claims (3)

In a dope manufacturing method in which a polymer and a solvent are mixed in a stirring tank to form a dope,
A first step of stirring the polymer and the solvent in a first stirring tank provided with a first stirring member to form a mixed solution;
When the dope is filtered at 0.5 MPa, the value V1 / V2 obtained by dividing the filtrate volume V1 from the start of filtration by 30 minutes and the filtrate volume V2 from the start of filtration to 2 hours is more than 2.06. To be smaller
A method for producing a dope, comprising: a second step of stirring the mixed solution into the dope by the second stirring tank including a second stirring member and a baffle member. The baffle member is a plate provided on the inner wall of the second stirring tank,
2. The dope production according to claim 1, wherein a lower end of the plate is located above a bottom surface inside the second stirring tank, and an upper end is located above the liquid level of the mixed solution. Method. 3. The method for producing a dope according to claim 1, wherein in the first step, the polymer is stirred with the solvent while being gradually put into the first stirring tank.

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