JP2003221450A - Method for preparing dope and solution film-forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a film in which the variation of retardation is suppressed by a simple method. <P>SOLUTION: A solvent is sent from a solvent tank 11 to a temperature- adjusting tank 13. The temperature of the solvent is controlled at a constant temperature in a range of 20-35°C in the temperature-adjusting tank 13. The solvent having a constant temperature is sent to a solution tank 15. A polymer in an amount of 19 wt.% relative to the solvent is sent to the solution tank 15 by a meter 16. A plasticizer is sent from a plasticizer tank 17 to the solution tank 15. These are stirred in the solution tank 15 at 80 rpm for 30 minutes by a Maxblend (R) type stirring blade 20 to obtain a crude solution 22. The crude solution 22 is heated by a heater 29 and cooled by a cooler 30 to obtain a dope 41. The film formed from the dope 41 has a deviation of retardation in a thickness direction relative to the target value of 3% or less, providing a film having uniform optical properties. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a dope preparation method for obtaining a dope by dissolving a polymer in a solvent, and a solution film formation method for forming a film using the dope.

[0002]

2. Description of the Related Art Cellulose acylate, especially 57.5-
A film formed of cellulose triacetate having an average acetylation degree of 62.5% (hereinafter referred to as TAC film) is used as a support for a photographic light-sensitive material because of its toughness and flame retardancy. Further, since the TAC film has excellent optical isotropy, it is suitable for use as a protective film for a polarizing plate or a color filter of a liquid crystal display device, which has been expanding in the market in recent years.

The TAC film is generally produced by a solution casting method. The solution casting method can produce a film having excellent optical properties and physical properties, as compared with other production methods such as a melt casting method. In the solution film-forming method, a polymer is dissolved in a solvent (mainly an organic solvent) to prepare a dope, and then the dope is cast on a support such as a band or a drum to form a film.

[0004]

When the film formed from the above-mentioned dope is used as an optical material such as an optical compensation film for liquid crystal display, retardation in the thickness direction of the film is an important characteristic. . Since this retardation affects the viewing angle and the tint, it is necessary to suppress the variation as much as possible. It is known that the retardation of the film produced by the solution casting method is sensitively affected by the process conditions in the casting process, stretching process and drying process. Therefore, these conditions are strictly controlled so that a cellulose ester film having a desired retardation can be produced. However, even if these process conditions are strictly controlled, variations in film retardation occur,
It was a manufacturing problem.

The present invention is directed to a method for preparing a dope which suppresses variations in retardation that cannot be controlled only by the process conditions of casting, stretching and drying, and a solution film-forming method for forming a film using the dope. I will provide a.

[0006]

The above-mentioned dope is produced by stirring a solvent (mainly an organic solvent) and a solute solid content (polymer and additives) in a tank to dissolve the solute solid content in the solvent. . Usually, the dissolution tank has a structure with a jacket for keeping heat, but the inventors of the present invention have conducted diligent research and found that the temperature of the solvent added for preparing the solution varies depending on the season and the temperature difference between day and night. I found that it was not constant.

In a dissolution tank into which raw materials (polymer solid content, organic solvent) are charged, when the temperature of the solvent at the time of starting the dissolution of the polymer is lower than 15 ° C., the film is reduced as the temperature is lowered. It was found that the retardation value (Rth) was low. That is, it was found that by maintaining the temperature of the solvent in the range of 20 to 35 ° C., a dope capable of reducing the deviation of the Rth of the film formed from the target can be prepared.

The dope preparation method of the present invention is a method of preparing a dope by dissolving a polymer in a solvent, wherein the dope is prepared by dissolving the polymer in the solvent.
After keeping the temperature of the solvent in the range of 20 to 35 ° C,
Initiate the dissolution. When the dope is prepared by dissolving the polymer in the solvent, the polymer and the solvent are stirred using a stirring blade having a paddle-shaped lower portion and a lattice-shaped upper portion, thereby improving the stirring efficiency. Is improved and the stirring time can be reduced. In addition, this is also preferable because undissolved substances in the dope can be reduced.

The dope preparation method of the present invention is a method of preparing a dope by dissolving a polymer in a solvent, wherein when the polymer is dissolved in the solvent, the polymer and the solvent have a paddle-shaped lower part. , The upper part is agitated with a grid-shaped stirring blade.

The time for stirring by the stirring blade is 30 to 9
It is preferably within the range of 0 min. The rotation speed of the stirring blade is preferably in the range of 10 to 100 rpm.

Before preparing the dope, it is preferable to charge 15.0 to 25.0% by weight of the polymer with respect to the solvent. In addition, before preparing the dope, it is preferable to charge 5.0 to 15.0% by weight of the plasticizer into the solvent with respect to the polymer. The polymer is preferably a cellulose ester. Furthermore, the cellulose ester is more preferably cellulose acetate having an average acetylation degree of 58.0 to 62.5%.

The solvent preferably contains a halogenated hydrocarbon as a main component. The halogenated hydrocarbon contained in the solvent is 70 to 95 in the solvent.
More preferably, it is wt%.

In the solution film-forming method of the present invention, the dope obtained by the dope preparation method described in any one of the above is cast to form a film. Further, in the solution casting method of the present invention, two or more kinds of dopes are prepared by the dope preparation method described in any one of the above, and the two or more kinds of dopes are co-cast to form a film. . Furthermore, the solution casting method of the present invention prepares two or more kinds of dopes by the dope preparation method described in any one of the above, and
Films are formed by sequentially casting dopes of different types. In this case, it is preferable that the dope is continuously cast on an endless support to form a film. In addition, it is preferable to stretch at least uniaxially when forming the film.

It is preferable to form a film having a retardation in the thickness direction of the formed film in the range of 1 to 200 nm. The retardation (Rt
h) is one of the indexes showing the optical characteristic values of the film formed and is calculated by the following formula. Rth = {(nMD + nTD) / 2−nTH} × d In the above equation, nMD is the lateral refractive index of the film, n
TD is the refractive index in the vertical direction of the film, nTH is the refractive index in the thickness direction of the film, and d is the thickness of the film.
The smaller this value of Rth, the smaller the optical anisotropy, which is preferable.

In the solution film-forming method of the present invention, a film used as a polarizing plate protective film is formed, a film used as a polarizing plate is formed, and a film used as an optically functional film is formed. , Are included.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION [Polymer] The polymer used in the present invention is not particularly limited, but cellulose ester is preferably used. Among the cellulose esters, it is preferable to use cellulose acylate,
It is particularly preferable to use cellulose acetate. Further, among the cellulose acetates, it is most preferable to use cellulose triacetate having an average acetylation degree of 57.5 to 62.5%. The degree of acetylation means the amount of bound acetic acid per unit weight of cellulose.
The acetylation degree follows the measurement and calculation of the acetylation degree in ASTM: D-817-91 (test method for cellulose acetate, etc.). In the present invention, cellulose acylate particles are used, and 90% by weight or more of the particles used have a particle diameter of 0.1 to 4 mm, preferably 1 to 4 mm. Further, preferably 95% by weight or more, more preferably 97% by weight or more, further preferably 98% by weight or more, most preferably 99% by weight or more of particles of 0.1 to 4 m.
It has a particle size of m. Further, it is preferable that 50% by weight or more of the particles used have a particle diameter of 2 to 3 mm. More preferably 70% by weight or more, even more preferably 80% by weight or more, most preferably 90% by weight or more of the particles have a particle diameter of 2 to 3 mm. The particle shape of cellulose acylate is preferably as close to a sphere as possible.

[Solvent] Examples of the solvent used in the present invention include halogenated hydrocarbons, esters, ketones, ethers and alcohols, but are not particularly limited. The solvent is not particularly limited as long as it is a commercially available product. The solvent may be used alone (100% by weight) or may be used by mixing alcohols, ketones, esters and ethers having 1 to 6 carbon atoms. Examples of solvents that can be used are halogenated hydrocarbons (eg methylene chloride), esters (eg methyl acetate,
Methyl formate, ethyl acetate, amyl acetate, butyl acetate etc.), ketones (eg acetone, methyl ethyl ketone, cyclohexanone etc.),
Examples thereof include ethers (eg, dioxane, dioxolane, tetrahydrofuran, diethyl ether, methyl-t-butyl ether, etc.), alcohols (eg, methanol, ethanol, etc.) and the like. In particular, it is preferable to use a halogenated hydrocarbon as a main component as the solvent used in the present invention because the above-mentioned polymer is easily dissolved. Specifically, 70 in the solvent for preparing the dope.
It is preferred that ~ 95 wt% is a halogenated hydrocarbon.

[Additive] The additive used in the present invention includes a plasticizer, an ultraviolet absorber and the like. As the plasticizer, a phosphate ester type (for example, triphenyl phosphate (hereinafter referred to as TPP), tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc.), Phthalates (eg, diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, etc.), glycolates (eg, triacetin, tributyrin, butyl phthalyl butyl glycolate, ethyl phthalyl ethyl glycolate, methyl phthalyl) Ethyl glycolate, butyl phthalyl butyl glycolate, etc.) and other plasticizers can be used.

An ultraviolet absorber may be added to the dope. For example, an oxybenzophenone compound, a benzotriazole compound, a salicylic acid ester compound, a benzophenone compound, a cyanoacrylate compound, a nickel complex salt compound and other ultraviolet absorbers can be used. A particularly preferred ultraviolet absorber is
Examples thereof include benzotriazole compounds and benzophenone compounds.

Further, if necessary, various additives such as a release agent, a release accelerator, a fluorine-containing surfactant, etc. are added to the dope at any stage before or after the dope is prepared. Good.

[Dope Preparation Method] FIG. 1 shows a dope preparation line 10 used in the dope preparation method according to the present invention. The dope preparation line used in the dope preparation method according to the present invention is not limited to the illustrated embodiment. Not something.
In the dope preparation method, the solvent is sent to the temperature adjustment tank 13 by first opening the valve 12 from the solvent tank 11. The water contained in this solvent is dehydrated in advance in a knitting process (not shown) so that the water content is 0.3 to
It is preferably adjusted to 1.5% by weight and stored in the solvent tank 11, but it is not limited to this range. In the temperature adjustment tank 13, the solvent is kept at a constant temperature T in the range of 15 to 35 ° C. At this time, the temperature T of the solvent
Is preferably controlled to vary within a range of ± 10% from a certain value. In addition, as a method for keeping the temperature of the solvent constant, the illustrated temperature adjustment tank 13 is used.
However, a heating device such as an in-line heater can also be used. Further, the storage tank 11 may be a tank whose temperature can be adjusted. Further, it is preferable that the pipes connecting the tanks 11 and 13 are also kept warm. Then, the required amount of solvent is sent to the dissolution tank 15 while adjusting the amount of solution sent by the valve 14.

Next, the polymer charged in the measuring device 16 is fed into the dissolution tank 15 while being measured. The polymer is preferably charged in an amount of 15.0 to 25.0% by weight with respect to the above-mentioned solvent, and a film obtained by forming a dope prepared in this manner into a film having good quality can be obtained. However, the amount of the polymer charged in the solvent in the present invention is not limited to the above range. In addition,
Although it is preferable to use TAC as the polymer, it is not limited thereto.

Further, the plasticizer is sent from the plasticizer tank 17 to the dissolution tank 15. A valve 18 is attached between the plasticizer tank 17 and the dissolution tank 15,
The required amount of plasticizer is fed into the dissolution tank 15. It should be noted that triphenyl phosphate is preferably used as the plasticizer, but the plasticizer is not limited thereto. Also,
In FIG. 1, the plasticizer is sent to the dissolution tank 15 as a solution dissolved in a solvent, but the present invention is not limited to this method. When the plasticizer is liquid at room temperature, the liquid state can be sent to the dissolution tank 15.
When the plasticizer is a solid, it can be sent to the dissolution tank 15 using a measuring instrument. In the present invention, the amount of the plasticizer sent to the dissolution tank 15 is 5.0 to 15.0% by weight based on the above-mentioned polymer.
The plastic film formed from the prepared dope has the most preferable flexibility as a product. However, in the present invention, the amount of the plasticizer fed into the dissolution tank is not limited to the above range.

Further, in the above description, the order of charging the dissolution tank 15 was the order of the solvent, the polymer and the plasticizer, but the present invention is not necessarily limited to this order. For example, it is possible to measure a polymer and send it to the dissolution tank 15 and then send a preferable amount of the solvent. Further, the plasticizer does not necessarily have to be sent to the dissolution tank 15 in advance, and can be mixed in a mixture of the polymer and the solvent (hereinafter, these mixtures may also be referred to as a dope) in a later step. Also, dissolution tank 1
It is also possible to feed the above-mentioned additives other than the plasticizer into 5.

An enlarged view of essential parts of the dissolution tank 15 will be described with reference to FIG. As described above, the solvent for adjusting the dope is injected into the dissolution tank 15 after the temperature is adjusted by the temperature adjustment tank 13 from the solvent tank 11. The dissolution tank 15 is provided with a stirring blade 20 rotated by a motor 19. Further, a jacket 21 is provided so as to enclose the dissolution tank 15. The jacket 21 is provided with a double wall, and a fluid is caused to flow between them to control the temperature of the solvent injected into the dissolution tank 15 so as to be a constant temperature T. Then, after the temperature of the solvent is controlled, the solute (polymer, additive) starts to dissolve. It should be noted that the fluid flowing inside the jacket 21 is determined depending on the temperature T of the solvent in the dissolution tank 15 and the temperature of the place where the dissolution tank is installed, whether the cooling fluid or the heat retaining fluid is supplied. .

In FIG. 2, the solvent temperature T before the solute such as a polymer is dissolved in the solvent is controlled by the temperature adjustment tank 13
And the jacket 21 provided in the dissolution tank 15. In the present invention, in controlling the solvent temperature T before dissolution, it is not always necessary to use both of them together, and the solvent whose temperature is controlled to a constant temperature T by the temperature adjustment tank 15 is sent to a dissolution tank not equipped with a jacket, Dissolution may be initiated. In addition, from the solvent tank 11 to the dissolution tank 15
After the solvent reaches a certain temperature T by a jacket 21 provided in the dissolution tank 15,
Dissolution may be initiated. Further, the temperature of the solvent injected into the dissolution tank 15 does not necessarily have to be controlled by the jacket. For example, in the case of cooling the melting tank, a cooler may be attached to the melting tank, and in the case of heating (including the case of keeping the temperature), a device equipped with a heater may be used.

A stirring blade 20 is provided in the dissolution tank 15 for dissolving a solute such as a polymer in a solvent. In the present invention, in order to efficiently dissolve the solute in the solvent, as shown in FIG. 2, the lower part has a paddle-shaped paddle portion 20a.
It is preferable to use the stirring blade 20 in which the upper portion is a lattice-shaped lattice portion 20b, and these are integrally formed. It is particularly preferable to use Max Blend (registered trademark: manufactured by Sumitomo Heavy Industries, Ltd.). As the stirring blade 20 rotates, the solvent, the polymer, and the plasticizer and other additives, which have been fed as necessary, into the dissolution tank 15 are agitated, so that the solute such as the polymer is added to the solvent. Can be roughly dissolved. The crude dissolution means a state in which the solute is not completely dissolved in the solvent. In the following description, this roughly dissolved solution is referred to as a crude solution 22.

In the present invention, the time for stirring by the stirring blade 20 in the dissolution tank 15 to prepare the crude solution 22 is preferably 30 to 90 minutes, but is not limited to this range. . If it is less than 20 minutes, the amount of solute such as polymer is too small to be completely dissolved even by the later-described heating and the dope may not be prepared. Also, if the dope is prepared in the dissolution tank 15 for more than 120 minutes, the cost will increase. The rotation speed of the stirring blade is preferably in the range of 10 to 100 rpm, but is not limited to this range. If it is less than 10 rpm, the polymer as a solid content may not be uniformly roughly dissolved in the solvent. Also, 100 rpm
The reason is that using a device with a rotation speed higher than 1 is expensive in the dope preparation.

Next, the crude solution 22 is once stored in the storage tank 23.
And the inside of the dissolution tank 15 is emptied, and the crude solution 2
From the viewpoint of cost, it is preferable to carry out the step of forming 2 in a continuous batch system. The storage tank 23 is also provided with a stirring blade 25 rotated by a motor 24, and stirs the fed crude solution 22 to make it uniform. Stirring blade 2
5 as well as the stirring blade 20 is Max Blend (registered trademark:
It is preferable to use Sumitomo Heavy Industries, Ltd., but not limited to this. The crude solution 22 in the storage tank 23 preferably passes through the coarse filtration filter 26 to remove impurities such as dust that are not necessary for dope preparation, but the coarse filtration filter 26 does not necessarily have to be attached. Crude solution 22 in storage tank 23
Is sent to the heater 29 through the pipe 28 by the pump 27. Note that this step is not limited to the illustrated one.

From pump 27 to heater 29 crude solution 22
It is preferable that the pipe 28 is heated or kept warm when the liquid is sent. Since the crude solution 22 is also heated when being sent through the pipe 28, the solute such as the polymer not dissolved in the solvent in the solution 22 progresses to dissolve, so that the dope is dissolved in a short time. Can be prepared.

Next, by heating the crude solution 22 with the heater 29, solutes such as polymers necessary for film formation can be dissolved to prepare a dope. The heating time is preferably 5 to 30 minutes and the heating temperature is preferably 60 to 120 ° C, but not limited to these ranges.
If it is less than 5 minutes, the dope may not be completely prepared, and even if it is heated for more than 30 minutes, it is a waste of time because the necessary solute components are completely dissolved in the solvent. At the same time, the quality of the prepared dope may be deteriorated. Also, if the heating temperature is less than 50 ° C,
The dope may not be completely prepared.
This is because if the temperature exceeds 0 ° C, the necessary solute components may be modified.

The heater 29 is a multi-tube heat exchanger (shell & tube type) or a double tube heat exchanger for efficiently preparing the dope.
In order to shorten the dope preparation time, it is preferable to use an in-line mixer such as a static mixing stirrer (also referred to as a static mixer) having a tube equal to or more than a heavy tube and having a heating means. Particularly, from the viewpoint of heat exchange efficiency, it is more preferable to use the spiral heat exchanger. The spiral heat exchanger has two plates wound from the center in a spiral shape.
It consists of two channels. This structure has a large heat transfer area with respect to the flow path cross-sectional area of the process liquid.
It is a device with excellent heat exchange efficiency. Also, heater 2
It is preferable to use a material having high corrosion resistance as the material of 9, and more specifically, it is more preferable to use a material formed of stainless steel, titanium, Hastelloy (trade name), or the like. As a result, it is possible to speed up the mass production of the dope without changing the capacity of the dissolution tank 15.

The dope prepared by the heater 29 is sent to the cooler 30 and cooled to a temperature below the boiling point of the main solvent constituting the dope to prepare the dope for forming a film of good quality. Preferred for. In general,
Methylene chloride (methylene chloride) is used as the main solvent forming the dope.
It is preferable to cool to the range of 0 to 38 ° C. However, in the present invention, the prepared dope is cooled by the cooler 3
It is not always necessary to perform cooling by 0.

In the present invention, heating and cooling by the heater 29 and the cooler 30 can be omitted after the dope is prepared by preparing the crude solution 22 by the dissolution tank 15. When a uniform dope in which dissolution has progressed from the crude solution 22 can be obtained by stirring the stirring blade 20 in the above-described dissolution tank 15, heating and cooling can be omitted thereafter.

Impurities unnecessary for film formation are removed from the dope prepared by any of the above-mentioned methods by passing it through a filtration filter 31. Although FIG. 1 illustrates an example in which four filtration filters 31 are attached in parallel, the present invention is not limited to this mode. Filtration filter 31
The dope from which impurities have been removed through the pump is sent to the dope tank 40 by the pump 32, and the uniform dope 41
Becomes

The waste liquid after cleaning the filtration filter 31 is sent to the solvent tank 43 after filter cleaning through a pipe (not shown). The waste liquid is processed by a solvent processing device (not shown), and then sent to the recycle solvent tank 45 by the pump 44. This recycled solvent can be sent to the dissolution tank 15 and used as a solvent for dope preparation. It is preferable that the recycled solution contains 0.1 to 25.0% by weight of the polymer with respect to the solvent in order to prepare a uniform dope. Further, it is preferable that the recycled solution contains 0.1 to 20.0% by weight of the plasticizer with respect to the polymer in the solution.

Although not shown in the figure, the filtration filter 3
Before switching the No. 1, it is possible to flow the pre-prepared dope into the filter to be used newly.
It is a more preferable operation method for continuous operation at 0.

[Solution Casting Method] As shown in FIG. 3, the film casting apparatus 50 includes a band zone 51 and a drying zone 52.
Can be divided into The dope tank 40 in which the above-mentioned dope 41 is charged is connected to the film forming apparatus 50 via a pump 53 and a filter 54. Further, a stirring blade 56 rotated by a motor 55 is attached to the dope tank 40 to keep the dope 41 uniform. Also in this case, the plasticizer can be mixed with the dope 41 by controlling the plasticizer tank opening / closing valve 46 from the plasticizer tank 17. Further, additives such as other UV absorbers can be mixed. Further, as the solvent for preparing the dope 41, a commercially available solvent can be used, but the solvent recovered from the film forming apparatus 50 can be mixed and used.

In the band zone 51, the support drum 57,
A casting band 59 is provided around 58,
The casting band 59 is rotated by a driving device (not shown). A casting die 60 is provided on the casting band 59. The dope 41 is sent from the dope tank 37 by the pump 53, and after removing impurities by the filter 54, sent to the casting die 60. The casting die 60 casts the dope 41 onto the casting band 59. The dope 41 is gradually dried until it has self-supporting properties while being conveyed by the casting band 59, and is stripped from the casting band 59 by the stripping roller 61 to form a film 62.

The film 62 is dried while being conveyed by the tenter 63. At this time, it is preferable that at least one axis is stretched to a predetermined width. Also,
In FIG. 3, the dope 41 is cast on the casting band 59 which is an endless support, but the present invention is not limited to the illustrated embodiment, and can be applied to a solution film forming method in which the dope 41 is cast on a rotary drum.

The film 62 sent from the tenter 63 to the drying zone 52 has a plurality of rollers 6 in the drying zone 52.
Wrap around 4 and dry. Film 62 after drying
Is taken up by the winder 65. The temperature in the drying zone 52 is preferably controlled in the range of 50 to 150 ° C. for uniform drying of the film 62.

FIG. 3 shows a solution casting method using a single-layer casting die 60. However, the present invention
It can also be applied to other solution film forming methods. For example, a solution casting method by co-casting with a casting die 70 equipped with a multi-manifold as shown in FIG. 4 can be applied. The casting die 70 is a multi-manifold provided with a plurality of (three in FIG. 4) manifolds. Manifolds 71, 72, and 73 are filled with the dope for the back surface layer, the dope for the intermediate layer, and the dope for the surface layer, which are prepared by the above-mentioned dope preparation method, respectively, and join the respective dopes inside casting die 70. After that, the casting ribbon 74 is cast on the casting band 75 to form a film. In the present invention, the number of layers of the dope to be laminated at the time of co-casting is not limited to the illustrated three layers.

FIG. 5 shows a part of the outline of an example in which the present invention is applied to a solution casting method for sequentially casting (sequential casting). In this method, a casting band 82 is provided around support drums 80 and 81 provided in the band zone, and the casting band 82 is rotated by a driving device (not shown). On the casting band 82, two casting dies 83 and 84 are arranged. Casting dies 83, 84
From the above, the dope for the back surface layer and the dope for the surface layer respectively prepared by the dope preparation method described above are cast to form a film. In the present invention, the film formation by sequential casting is not limited to the illustrated embodiment using two casting dies, and three or more casting dies may be arranged on the casting band 82. .

The Rth (retardation) of the film formed by any of the solution film forming methods described above is 1 to
The range of 200 nm is preferable for using the film in the products described later.

The film formed by the solution film forming method described above can be used as a protective film for a polarizing plate. A polarizing plate can be formed by sticking this polarizing plate protective film on both sides of a polarizing film formed of polyvinyl alcohol or the like. Further, it can also be used as an optical functional film such as an optical compensation film obtained by sticking an optical compensation sheet on the film, an antireflection film obtained by laminating an antiglare layer on the film. It is also possible to form a part of the liquid crystal display device from these products.

[0046]

The present invention will be described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto. In addition, in the description, the detailed description is given in Example 1, and the description of the same points as those in Example 1 is omitted for the other examples and comparative examples.

<Experiment 1> [Example 1] In Example 1, an experiment was conducted so that the retardation (Rth) in the thickness direction of the film was 38 nm. The dope was prepared using the dope preparation line shown in FIG. As the solvent for preparing the dope, a mixed solvent obtained by mixing methylene chloride, which is a halogenated hydrocarbon, and an alcohol mixed solution (mixing ratio of methanol: n-butanol = 8: 1) in a ratio of 82:18 was used by the temperature adjustment tank 13. The temperature T was controlled at 25 ° C. At this time, the temperature T
The fluctuation range was adjusted within ± 10%. Further, when the amount of water contained in the solvent whose temperature was adjusted was measured by gas chromatography, it was found to be 0.6% by weight in the solvent.

After that, the mixed solvent was sent to the dissolution tank 15. To the mixed solvent, 19.0% by weight of a polymer, cellulose triacetate (acetylation degree: 60%), was fed by a measuring device 16 into a dissolution tank 15. further,
10.5% by weight of TPP, which is a plasticizer with respect to cellulose triacetate, was fed into the dissolution tank 15. Using Max Blend (registered trademark) for these mixtures, the stirring blade 25 was rotated at 80 rpm by the motor 19 having an output of 45 kW.
Stir for 30 minutes at the speed of to make a crude solution 22,
After being stored in the storage tank 23, the solution was sent to the heater 29, and the temperature was increased in-line to 85 ° C. and held for 10 minutes. When the obtained solution was visually confirmed, insoluble matter of the polymer was not confirmed. The solution was passed through a filtration filter 31 to remove impurities contained in the raw material, and the dope 41
Got

Next, the dope 41 obtained by the above-mentioned method
Then, the film 62 was formed by using the film forming apparatus 50 shown in FIG. For the film formation, the dope 41 is 35
It was cast on a casting band 59 from a casting die 60 at 0 ° C. The casting was performed so that the thickness of the dried film 62 was 107 μm. After the film was dried on the casting band 59 until it had a self-supporting property, the film 62 was peeled off by the peeling roller 61 and dried while being conveyed by the tenter 63. Further, the film 62 was dried in the drying zone 52 and wound by the winder 65. Film 6 obtained
The retardation (Rth) in the thickness direction of 2 was measured using an ellipsometer (polarimeter) with a wavelength of 632.8 n.
When the value at m was measured, it was 38 nm, and it was found that the film having the target value was obtained.

Furthermore, the above experiment was repeated 4 times, for a total of 5 times.
Experiments were performed once. The temperature T of the solvent before the start of dissolution, the amount of water contained in the solvent, and the retardation in the thickness direction of the film formed were measured, and the deviation of the retardation from the target value was determined. The results of these experiments are shown later in Table 1.

[Example 2] In Example 2, an experiment was conducted such that the retardation (Rth) in the thickness direction of the film was 80 nm. The dope was prepared using the dope preparation line shown in FIG. 1 as in Example 1.
As the solvent for preparing the dope, a mixed solvent in which methylene chloride, which is a halogenated hydrocarbon, and an alcohol mixed solution (mixing ratio of methanol: n-butanol = 8: 1) were mixed at 81:19 was used by the temperature adjustment tank 13. The temperature T was controlled at 25 ° C. At this time, the fluctuation range of the temperature T was adjusted to be within ± 10%. Further, when the amount of water contained in the solvent whose temperature was adjusted was measured by the same method as in Example 1, it was found to be 0.6% by weight in the solvent.

After that, the mixed solvent was sent to the dissolution tank 15. To the mixed solvent, 19.0% by weight of a polymer, cellulose triacetate (acetylation degree: 60%), was fed by a measuring device 16 into a dissolution tank 15. further,
10.5% by weight of TPP, which is a plasticizer with respect to cellulose triacetate, was fed into the dissolution tank 15. Further, 2.6 wt% of 2-hydroxy-4-benzyloxy-benzophenone, which is an ultraviolet absorber, was fed to the dissolution tank 15 with respect to cellulose triacetate. Using Max Blend (registered trademark) for these mixtures,
The stirring blade 25 is 80 rp by the motor 19 with an output of 45 kW
After stirring at a speed of m for 30 minutes to prepare a crude solution 22, which was stored in a storage tank 23, the solution was sent to a heater 29 and heated in-line to 85 ° C. and held for 10 minutes.
When the obtained solution was visually confirmed, insoluble matter of the polymer was not confirmed. This solution is filtered through a filter 31
The impurities contained in the raw material were removed by passing through a dope 41 to obtain a dope 41.

Next, the dope 41 obtained by the above-mentioned method
Then, the film 62 was formed by using the film forming apparatus 50 shown in FIG. For the film formation, the dope 41 is 35
It was cast on a casting band 59 from a casting die 60 at 0 ° C. The casting was performed so that the thickness of the dried film 62 was 107 μm. After the film was dried on the casting band 59 until it had a self-supporting property, the film 62 was peeled off by the peeling roller 61 and dried while being conveyed by the tenter 63. Further, the film 62 was dried in the drying zone 52 and wound by the winder 65. Film 6 obtained
The retardation (Rth) in the thickness direction of 2 was measured using an ellipsometer (polarimeter) with a wavelength of 632.8 n.
When the value at m was measured, it was found to be 80 nm, and the film having the target value was obtained.

Furthermore, the above experiment was repeated 4 times, for a total of 5 times.
Experiments were performed once. The temperature T of the solvent before the start of dissolution, the amount of water contained in the solvent, and the retardation in the thickness direction of the film formed were measured, and the deviation of the retardation from the target value was determined. The results of these experiments are shown later in Table 1.

[Comparative Example 1 and Comparative Example 2] The same experiment as in Example 1 and Example 2 was performed, except that the temperature T of the solvent was 10 ° C. and the temperature was not adjusted, respectively.
As done. Then, the experiment was repeated 4 times, and a total of 5 experiments were performed. Temperature T of the solvent before the start of dissolution
And the amount of water contained in the solvent and the retardation in the thickness direction of the film thus formed were measured, and the deviation of the retardation from the target value was determined.
The results of these experiments are shown later in Table 1.

[0056]

[Table 1]

From Table 1, the solvent temperature T before dissolution is 20 to 3
It can be seen that the film formed from the obtained dope by controlling the temperature within the range of 5 ° C. has a small deviation from the target value of the retardation and the fluctuation thereof is suppressed.

<Experiment 2> The following adhesive layer and back layer were applied to the film obtained in the first experiment of Example 1 to prepare a laminated film having a three-layer structure. Adhesion layer (front surface): Gelatin 200 mg / m ² solvent 25 cc / m ² (acetone: methanol: methylene chloride = 5: 3: 2) Back layer (back surface): diacetyl cellulose 200 mg / m ² 0.01 μm silica 10 mg / m ² Solvent 25 cc / m ² (acetone: methanol: methylene chloride = 5: 3: 2)

The retardation of the thus obtained laminated film having a three-layer structure was 80 nm as measured by the above-mentioned method. It can be seen that the film formed by using the present invention has a small variation in retardation and is suitable for optical applications.

[0060]

According to the method for preparing a dope of the present invention, in the method for preparing a dope by dissolving a polymer in a solvent, the temperature of the solvent is adjusted when the dope is prepared by dissolving the polymer in the solvent. Since the dissolution is started after the temperature is kept in the range of 20 to 35 ° C., the amount of water contained in the solvent falls within a certain range, so that the dope capable of suppressing the fluctuation of the retardation of the film can be prepared.

According to the method for preparing a dope of the present invention, in the method for preparing a dope by dissolving a polymer in a solvent,
When the polymer is dissolved in the solvent, the polymer and the solvent are stirred by a paddle-shaped lower portion and a lattice-shaped stirring blade in the upper portion, so that fluctuation of retardation of the film can be suppressed. A uniform dope can be obtained.

According to the solution film-forming method of the present invention, the dope obtained by the dope-preparing method of the present invention is cast to form a film, so that the fluctuation of the retardation of the formed film is suppressed. can do.

[Brief description of drawings]

FIG. 1 is a schematic view of a dope preparation line used for carrying out a dope preparation method according to the present invention.

FIG. 2 is an enlarged view of a main part of the dope preparation line shown in FIG.

FIG. 3 is a schematic view of an apparatus used for carrying out the solution casting method according to the present invention.

FIG. 4 is a schematic view of a main part of another device used for carrying out the solution film-forming method according to the present invention.

FIG. 5 is a schematic view of a main part of another device used for carrying out the solution film-forming method according to the present invention.

[Explanation of symbols]

10 Dope preparation line 11 solvent tank 13 Temperature control tank 15 Melting tank 19 motor 20 stirring blades 20a Kamabe 20b lattice part 21 jacket 22 Crude solution 40 Dope tank 41 Dope 50 film forming equipment 51 band zone 62 films 70 Co-casting die 83, 84 Casting die

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // B29K 1:00 B29K 1:00 B29L 7:00 B29L 7:00 C08L 1:08 C08L 1:08 F Term (reference) 4F070 AA02 AA71 AC33 AC36 AC55 AC65 AE02 CA03 CA11 CB05 CB11 4F071 AA01 AA09 AC01 AC15 AE04 AF29Y AG34 AH12 BA02 BB02 BB07 BC01 BC10 4F205 AA01 AG01 AG03 AH73 GA07 GB02 GB26 GC07 GE22GW21

Claims (20)

[Claims] 1. A method for preparing a dope by dissolving a polymer in a solvent, wherein the temperature of the solvent is kept in a range of 20 to 35 ° C. when the polymer is dissolved in the solvent to prepare a dope. From the above, the dope preparation method is characterized in that the dissolution is started. 2. When the polymer is dissolved in the solvent to prepare a dope, the polymer and the solvent are stirred by a stirring blade having a paddle-like lower portion and a lattice-like upper portion. The dope preparation method according to claim 1. 3. A method for preparing a dope by dissolving a polymer in a solvent, wherein when the polymer is dissolved in the solvent, the polymer and the solvent are in a paddle-like shape in a lower part and a lattice-like shape in an upper part. A method for preparing a dope, which comprises stirring with a stirring blade. 4. The stirring time of the stirring blade is 30 to 30.
The dope preparation method according to claim 2 or 3, wherein the range is 90 min. 5. The rotating speed of the stirring blade is 10 to 100 r.
The dope preparation method according to any one of claims 2 to 4, wherein the dope is set in the range of pm. 6. The dope preparation according to claim 1, wherein 15.0 to 25.0% by weight of the polymer is charged in the solvent before preparing the dope. Method. 7. Prior to preparing the dope, 5.0 to 15.0 wt% of a plasticizer with respect to the polymer is charged in the solvent.
The method for preparing a dope according to any one of items. 8. The dope preparation method according to claim 1, wherein the polymer is a cellulose ester. 9. The cellulose ester is 58.0.
The dope preparation method according to claim 8, which is a cellulose acetate having an average acetylation degree of 62.5%. 10. The dope preparation method according to claim 1, wherein the solvent contains a halogenated hydrocarbon as a main component. 11. The dope preparation method according to claim 10, wherein the halogenated hydrocarbon contained in the solvent is 70 to 95% by weight in the solvent. 12. A solution casting method, which comprises casting the dope obtained by the dope preparation method according to claim 1 to cast a film. 13. A dope preparation method according to claim 1, wherein two or more kinds of dopes are prepared, and the two or more kinds of dope are co-cast to form a film. Solution casting method. 14. A dope preparation method according to claim 1, wherein two or more kinds of dope are prepared, and the two or more kinds of dope are sequentially cast to form a film. A solution casting method characterized by: 15. The film is formed by continuously casting the dope on an endless support.
15. The solution casting method according to any one of 1 to 14. 16. The solution film-forming method according to claim 12, wherein at least one axis is stretched when the film is formed. 17. The solution casting method according to claim 12, wherein a film having a retardation in the thickness direction of the formed film is in the range of 1 to 200 nm. . 18. The solution film-forming method according to claim 12, wherein a film used as a polarizing plate protective film is formed. 19. The solution film-forming method according to claim 12, wherein a film used as a polarizing plate is formed into a film. 20. The solution casting method according to claim 12, wherein a film used as an optically functional film is formed.