JP3946533B2 - Solution casting method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solution casting method in which a film is formed using a dope, and more particularly to a solution casting method by multilayer casting.
[0002]
[Prior art]
A film formed from cellulose acylate, particularly cellulose triacetate having an average degree of acetylation of 57.5 to 62.5% (hereinafter referred to as TAC film) is characterized by its toughness and flame retardancy. It is used as a support. In addition, since the TAC film is excellent in optical isotropy, the TAC film is suitable for use as a protective film for a polarizing plate of a liquid crystal display device and a color filter whose market is expanding in recent years.
[0003]
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 casting 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 dope. Incidentally, when the formed film is used as a support for a photographic photosensitive material or an optical material, the flatness and slipperiness of the film are strictly required. For this reason, a method of forming a film by multi-layer casting in which a plurality of dopes with adjusted components are cast at the same time is often performed. A dope for improving flatness and slipperiness is used for the exposed layer (hereinafter referred to as the surface layer) of the multilayer film. The layer forming the main part of the film (hereinafter referred to as the base layer) uses a dope suitable for the basic properties such as the strength of the film, thereby impairing the toughness and flame retardancy of the entire film. Therefore, the flatness and slipperiness of the surface can be improved.
[0004]
[Problems to be solved by the invention]
In the solution casting method by multi-layer casting, the surface layer and the base layer exist, but the same dope (mother solution dope) is used for branching in the liquid feeding system, and in order to add a function to the surface layer side, liquid feeding of the surface layer liquid Additives may be injected in the process. The smaller the volume of the liquid feeding pipe in each layer, the better. However, the capacity (pipe length, pipe thickness) to some extent due to restrictions on the layout of the equipment with the casting section, mixing and stirring of the additive liquid, pressure loss during liquid feeding, etc. Is needed. For this reason, there is a difference in the residence time in the pipe from the relationship between the liquid feeding pipe capacity and flow rate of each layer, and there is a difference in the time for each dope to reach the casting part when changing the mother liquor dope conditions. It will occur. As a result, it takes time for the conditions of each dope to be constant, so that a product loss occurs during this time.
[0005]
It is an object of the present invention to provide a solution casting method in which product loss is reduced by reaching the casting portion at substantially the same timing when changing the dope solution conditions used for multilayer casting. .
[0006]
[Means for Solving the Problems]
As a result of intensive research, the inventors have optimized the condition switching time by combining each dope solution replacement (residence) time in multilayer casting and designing the piping volume so that the time is minimized. I found out.
[0007]
The solution casting method of the present invention comprises a dope prepared by dissolving a polymer in a solvent. On the support by casting die In the solution casting method for casting a multilayer to form a film, the multilayer is composed of a base layer and at least one first layer formed on the surface of the base layer, A base layer dope for forming the base layer and a first layer dope for forming the first layer; The dope for the base layer and the dope for the first layer are sent through the respective pumps and the respective introduction paths from these pumps to the casting die, and the time for the base layer dope to pass through the introduction path is divided into The time T2 for the first layer dope to pass through the introduction path with respect to T1 is set in a range of T1 × 0.5 ≦ T2 ≦ T1 × 2.0. In addition, The multilayer is preferably composed of a base layer and surface layers formed on both sides of the base layer.
[0008]
The multilayer casting is preferably performed by co-casting on an endless support. Alternatively, the multilayer casting is preferably performed on the endless support by sequential casting.
[0009]
For the film peeled off from the endless support, It is preferable to stretch at least uniaxially. Furthermore, it is preferable to form a film having a retardation in the thickness direction of the film formed in the range of 1 to 200 nm. Retardation (hereinafter sometimes referred to as Rth) is one of indices indicating the optical characteristic value of a film formed, and is obtained by the following formula.
Rth = {(nMD + nTD) / 2−nTH} × d
In the above equation, nMD is the refractive index in the lateral direction of the film, nTD is the refractive index in the longitudinal direction of the film, nTH is the refractive index in the thickness direction of the film, and d is the thickness of the film.
[0010]
It is preferable that the polymer is a cellulose ester. The cellulose ester is more preferably cellulose acetate having an average degree of acetylation of 58.0 to 62.5%. It is preferable that the solvent contains a halogenated hydrocarbon as a main component. The halogenated hydrocarbon contained in the solvent is more preferably 70 to 95% by weight in the solvent.
[0011]
The solution casting method of the present invention includes forming a film used as a polarizing plate protective film, forming a film used as a polarizing plate, and forming a film used as an optical functional film. included.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
[polymer]
Although the polymer used for this invention is not specifically limited, It is preferable to use a cellulose ester. Among the cellulose esters, it is preferable to use cellulose acylate, and it is particularly preferable to use cellulose acetate. Further, among the cellulose acetates, it is most preferable to use cellulose triacetate having an average degree of acetylation of 57.5 to 62.5%. The degree of acetylation means the amount of bound acetic acid per unit weight of cellulose. The degree of acetylation follows the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method for cellulose acetate and the like). 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. Also, preferably 95% by weight or more, more preferably 97% by weight or more, further preferably 98% by weight or more, and most preferably 99% by weight or more of particles have a particle size of 0.1 to 4 mm. Furthermore, 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, still more preferably 80% by weight or more, and most preferably 90% by weight or more of the particles have a particle size of 2 to 3 mm. The particle shape of the cellulose acylate is preferably as close to a sphere as possible.
[0013]
[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 commercially available. The solvent may be used alone (100% by weight), or may be a mixture of alcohols having 1 to 6 carbon atoms, ketones, esters and ethers. Examples of solvents that can be used include 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.), ethers (eg, dioxane, dioxolane, tetrahydrofuran, diethyl ether, methyl-t-butyl ether), alcohols (eg, methanol, ethanol, etc.) and the like. In particular, it is preferable to use a halogenated hydrocarbon as a main component as a solvent used in the present invention because the above-mentioned polymer is easily dissolved. Specifically, it is preferable that 70 to 95% by weight in the solvent for preparing the dope is a halogenated hydrocarbon.
[0014]
[Additive]
Examples of the additive used in the present invention include a plasticizer, an ultraviolet absorber, and a matting agent. Examples of the plasticizer include phosphate esters (for example, triphenyl phosphate (hereinafter referred to as TPP), tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenyl biphenyl phosphate (hereinafter referred to as BDP), trioctyl. Phosphate, tributyl phosphate, etc.), phthalate esters (eg, diethyl phthalate, dimethoxyethyl phthalate, dimethyl phthalate, dioctyl phthalate, etc.), glycolate esters (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.
[0015]
An ultraviolet absorber may be added to the dope. For example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, nickel complex compounds, and other ultraviolet absorbers can be used. Particularly preferred ultraviolet absorbers are benzotriazole compounds and benzophenone compounds.
[0016]
A matting agent can also be added to the dope. As a matting agent, SiO ₂ TiO ₂ , BaSO _Four , CaCO _Three , Talc, kaolin and the like. In addition, inorganic fine powders such as barium sulfate, manganese colloid, titanium dioxide, barium sulfate, and silicon dioxide can also be used. Furthermore, silicon dioxide such as synthetic silica obtained by a wet method or gelation of silicic acid, titanium dioxide (rutile type or anatase type) produced by titanium slug and sulfuric acid can be used. Further, it is also possible to use those obtained by pulverizing from an inorganic substance having a relatively large particle size, for example, 20 μm or more and then classifying (vibration filtration, wind classification, etc.). Preferred matting agents include ZnO and TiO _Three , SnO ₂ , Al ₂ O _Three , In ₂ O _Three , SiO ₂ , MgO, BaO, MoO _Three And at least one crystalline metal oxide selected from the group consisting of fine particles of these composite oxides.
[0017]
In addition to the aforementioned inorganic compounds and oxides thereof, a matting agent made of a polymer compound can also be used. Examples include, but are not limited to, polytetrafluoroethylene, cellulose acetate, polystyrene, polymethyl methacrylate, polypropyl methacrylate, polymethyl acrylate, polyethylene carbonate, starch, and the like. These pulverized and classified products can also be used. Furthermore, a polymer compound synthesized by a suspension polymerization method, or a polymer compound made spherical by a spray drying method or a dispersion method can also be used.
[0018]
Furthermore, polymers synthesized from acrylic esters, methacrylic esters, vinyl esters, styrenes, olefins and the like can also be used. Further, a compound particle having a fluorine element or a silicon element in its structural formula as described in JP-A Nos. 62-14647, 62-17744, and 62-17743 can be used. Good. Moreover, what made the high molecular compound which is a 1 type, or 2 or more types of polymer of the monomer compound mentioned above into a particle | grain by various means can also be used.
[0019]
As the particle composition preferably used in the matting agent described above, polystyrene, polymethyl (meth) acrylate, polyethyl acrylate, poly (methyl methacrylate / methacrylic acid = 95/5) (molar ratio), poly (styrene / styrenesulfonic acid = 95/5) (molar ratio), polyacrylonitrile, poly (methyl methacrylate / ethyl acrylate / methacrylic acid = 50/40/10), silica, and the like, but are not limited thereto.
[0020]
As the matting agent, various inorganic compounds and polymer compounds can be used as described above, but inorganic compounds are preferably used for the dope using methylene chloride as a solvent, particularly silica (SiO 2 ₂ ) Is preferable because it is inexpensive and easily available.
[0021]
Furthermore, you may add various additives, for example, a mold release agent, a peeling accelerator, a fluorine-type surfactant, etc. to a dope as needed.
[0022]
[Solution casting method]
1 to 3 show a film casting line 10 used in the solution casting method according to the present invention, but the line used in the solution casting method according to the present invention is not limited to the illustrated one. FIG. 1 shows a film production line 10 from the preparation of a mother liquor dope from a solvent, a polymer, and the like. First, a mother liquor dope (which may be simply referred to as a dope in the following description) is prepared. In the dope preparation method, a necessary amount of solvent is sent from the solvent tank 11 to the dissolution tank 12. The solvent tank 11 is filled with the above-described solvent (even when a mixed solvent is used, in the following description, it may be simply referred to as a solvent). This solvent is fed while adjusting the liquid feed amount by a valve 13 attached between the solvent tank 11 and the dissolution tank 12.
[0023]
Next, the polymer charged in the meter 14 is fed into the dissolution tank 12 while being metered. 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 having a good film quality obtained by forming a dope thus prepared can be obtained. In addition, although it is preferable to use TAC for a polymer, it is not limited to this.
[0024]
Further, the plasticizer is sent from the plasticizer tank 15 to the dissolution tank 12. A valve 16 is attached between the plasticizer tank 15 and the dissolution tank 12, and a necessary amount of plasticizer is fed into the dissolution tank 12. In addition, although it is preferable that TPP and BDP are used for a plasticizer, it is not limited to these. In FIG. 1, the plasticizer is fed into the dissolution tank 12 as a solution in which the plasticizer is dissolved in a solvent, but the present invention is not limited to this method. When the plasticizer is liquid at normal temperature, the liquid state can be sent to the dissolution tank 12. Further, when the plasticizer is solid, it can be fed into the dissolution tank 12 using a measuring instrument. In the present invention, when the amount of the plasticizer fed into the dissolution tank 12 is 5.0 to 15.0% by weight with respect to the polymer, the plasticity of the film formed from the prepared dope is a product. The one with the most favorable flexibility is obtained.
[0025]
In the above description, the order of charging into the dissolution tank 12 is the order of solvent, polymer, and plasticizer, but the present invention is not necessarily limited to this order. For example, after a polymer is weighed and sent to the dissolution tank 12, a preferred amount of solvent can be sent. Further, the plasticizer is not necessarily sent to the dissolution tank 12 in advance, and can be mixed in a later step with a mixture of a polymer and a solvent (hereinafter, the mixture may also be referred to as a dope). It is also possible to feed the aforementioned additives other than the plasticizer into the dissolution tank 12.
[0026]
The dissolution tank 12 is provided with a stirring blade 18 that is rotated by a motor 17. By rotating the stirring blade 18, the solvent, polymer, and plasticizer and other additives that have been fed into the dissolution tank 12 are agitated to roughly dissolve solutes such as polymer in the solvent. Let The rough dissolution means a state where the solute is not completely dissolved in the solvent. In the following description, this roughly dissolved solution is referred to as a crude solution 19. In the present invention, in order to prepare the crude solution 19, the time for stirring with the stirring blade 18 in the dissolution tank 12 is preferably 30 to 90 minutes, but is not limited to this range. If it is less than 20 minutes, the amount of solutes such as polymers dissolved is too small to be completely dissolved even by dissolution by heating described later, and the dope may not be prepared. Moreover, it is because it will become expensive if dope is prepared with the dissolution tank 12 over 120 minutes.
[0027]
From the viewpoint of cost, it is preferable to carry out a continuous batch method in which the process of forming the crude solution 19 is performed by once sending the crude solution 19 into the storage tank 20 and emptying the dissolution tank 12. The storage tank 20 is also provided with an agitating blade 22 that is rotated by a motor 21, and agitation is performed on the fed coarse solution 19 to make it uniform. The crude solution 19 in the storage tank 20 passes through the coarse filter 23 to remove impurities such as dust that are not necessary for the dope preparation. However, the coarse filter 23 is not necessarily attached. The crude solution 19 in the storage tank 20 is sent to the heater 26 through the pipe 25 by the pump 24. In addition, this process is not limited to what was illustrated.
[0028]
It is preferable that the pipe 25 is heated when the crude solution 19 is sent from the pump 24 to the heater 26. Since the dissolution of the solute such as the polymer not dissolved in the solvent in the crude solution 19 is progressed by heating the crude solution 19 when it is fed through the pipe 25, the dope is added in a short time. Can be prepared.
[0029]
Next, the dope can be prepared by dissolving the solute such as a polymer necessary for film formation by heating the crude solution 19 with the heater 26. The heating time is preferably 5 to 30 minutes and the heating temperature is preferably 60 to 120 ° C., but is 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, the necessary solute components are completely dissolved in the solvent, which is a waste of time. At the same time, the prepared dope may be altered. Further, if the heating temperature is less than 50 ° C., the dope may not be completely prepared, and if it exceeds 120 ° C., necessary solute components may be modified.
[0030]
The heater 26 includes a multi-tube heat exchanger (shell and tube method) and a static mixing stirrer (also referred to as a static mixer) having heating means provided with a tube of two or more tubes in order to efficiently prepare the dope. It is preferable to use an in-line mixer such as) in order to shorten the dope preparation time. In particular, it is more preferable to use a spiral heat exchanger from the viewpoint of heat exchange efficiency. The spiral heat exchanger is composed of two flow paths by winding two plates in a spiral shape from the center. This structure is a device that is extremely excellent in heat exchange efficiency because the heat transfer area can be increased with respect to the cross-sectional area of the flow path of the process liquid. Moreover, it is preferable to use a material having high corrosion resistance as the material of the heater 26, and more specifically, it is more preferable to use a material formed from stainless steel, titanium, Hastelloy (trade name) or the like. Thereby, it is possible to increase the speed for mass production of the dope without changing the capacity of the dissolution tank 12.
[0031]
It is preferable to send the dope prepared by the heater 26 to the cooler 27 and cool it below the boiling point of the main solvent constituting the dope in order to prepare a dope for forming a film of good quality. . In general, methylene chloride (methylene chloride) is used as the main solvent constituting the dope. In this case, it is preferable to cool the dope to a range of 30 to 38 ° C. However, in the present invention, it is not always necessary to cool the prepared dope by the cooler 27.
[0032]
In the present invention, the method for preparing the dope from the crude solution 19 is not necessarily performed by the heater 26 described above. For example, it is possible in some cases to prepare the dope simply by heating the pipe 25 and feeding the crude solution 19. Alternatively, in some cases, it is possible to prepare the dope by rapidly rotating the stirring blade 22 in the storage tank 20. The method for preparing the dope from the crude solution 19 as described above is not necessarily limited to the heating method using the heater 26 described above.
[0033]
Impurities unnecessary for film formation are removed from the dope prepared by the above-described method by passing through the filtration filter 28. That is, the components necessary for film formation must be completely dissolved in the dope immediately before passing through the filter 28 for filtering out impurities. At this time, if an insoluble solute component is present in the dope, it is removed by the filtration filter 28, and the component ratio of the solvent sent to the dissolution tank 12 and the solute such as polymer is different. This is because a dope having a composition ratio of Although FIG. 1 illustrates an example in which four filtration filters 28 are attached in parallel, the present invention is not limited to this embodiment. The dope from which impurities have been removed after passing through the filter 28 is sent to the dope tank 30 by the pump 29 to become a uniform mother liquor dope 31.
[0034]
The waste liquid after washing the filter 28 is sent to the solvent tank 32 after the filter is washed by a pipe (not shown). The waste liquid is processed by a solvent processing apparatus (not shown) and then sent to the recycle solvent tank 34 by the pump 33. The recycled solvent can be sent to the dissolution tank 12 for use as a dope preparation solvent. The recycle solvent preferably contains 0.1 to 25.0% by weight of polymer with respect to the solvent in order to prepare a uniform dope. The solvent preferably contains 0.1 to 20.0% by weight of a plasticizer with respect to the polymer.
[0035]
FIG. 2 shows a film production line 10 from the mother liquor dope 31 until the base layer dope and the surface layer dope are prepared and cast from the casting die to the casting drum. The dosing tank 30 charged with the mother liquor dope 31 may also be provided with a stirring blade 36 rotated by a motor 35. By rotating the stirring blade 36, the mother liquor dope 31 can always be kept in a uniform state. The mother liquor dope 31 is sent to the two-stage filtration filter 41 by the pump 40. The two-stage filter 41 removes fine impurities that could not be removed in the mother liquor dope preparation process described above. In addition, you may arrange | position a two-stage filtration filter so that switching is possible as needed. After the fine impurities are removed by the two-stage filter 41, the mother liquor dope 31 is sent to the static mixer 42.
[0036]
In the upstream process of the static mixer 42, the various additives described above may be fed as a solution and may be uniformly mixed in the mother liquor dope 31. The additive liquid 43 is charged into the additive liquid tank 44 and fed to the upstream portion of the static mixer 42 by the pump 45. In the figure, only one system for feeding the additive liquid is shown, but a plurality of liquid feeding systems may be provided in the present invention.
[0037]
The additive solution 43 is uniformly mixed in the mother liquor dope 31 by the static mixer 42. The mother liquor dope 31 that has become completely uniform is obtained by the pumps 50, 51, 52 by using the base layer dope, the back surface dope (hereinafter referred to as the first surface layer dope), and the front surface dope (hereinafter referred to as the second dope). (Referred to as a surface layer dope).
[0038]
The base layer dope passes through the base layer dope channel 53 and is removed from the feed block 55 to the co-casting die 56 after impurities are removed by a filter 54 provided in the middle.
[0039]
The first and second surface layer dopes are prepared by mixing and adding the surface layer additive solution 57 in-line in order to impart functions, and are sent from the feed block 55 to the co-casting die 56. The surface layer additive liquid 57 is charged in the surface layer additive liquid tank 58, and is sent to the first and second surface layer dopes by the pumps 59 and 60, respectively. The surface layer additive liquid 57 is prepared using the aforementioned additives (plasticizer, ultraviolet absorber, matting agent, etc.) and solvent. Moreover, you may mix the said polymer with this surface layer addition liquid 57 as needed. As a method for mixing the polymer, the polymer may be mixed as it is, or the polymer may be dissolved or dispersed in a liquid, and the liquid may be mixed with the surface layer additive liquid 57. By adjusting the amount of the polymer contained, the physical properties (particularly the viscosity) of the surface layer additive liquid 57 can be adjusted.
[0040]
The first and second surface layer dopes described above are sent to the filters 61 and 62 by the pumps 51 and 52 to remove impurities. Thereafter, the above-described surface layer additive solution 57 is fed into each of the flow channels 63 and 64 and then fed to the feed block 55, and then is cast from the co-casting die 56 simultaneously with the base layer dope. . In addition, static mixers 65 and 66 are provided in the flow paths 63 and 64, respectively, and the first and second surface layer dopes and the surface layer additive solution 57 are uniformly mixed. Moreover, although the form which mixes the same surface layer addition liquid 57 with the 1st and 2nd surface layer dope was illustrated in the figure, this invention is not limited to the form. A surface layer additive solution having different components may be mixed with the first and second surface layer dopes.
[0041]
In the present invention, the dope flow paths 53, 63, 64 mean introduction paths of the respective dopes from the respective pumps 50, 51, 52 to the feed block 55. For example, the first surface layer dope flow path 63 includes all of the filters 61, the static mixer 65, and all the pipes connecting them. In the present invention, it is preferable that the time required for each dope to pass through each flow path 53, 63, 64 is substantially the same. This is because each dope branched from the mother liquor dope 31 can be cast on the casting drum 67 from the co-casting die 56 at substantially the same timing. The casting support may be a band. Thereby, even if the component of the mother liquor dope 31 is changed or the component of the mother liquor dope 31 is changed by the addition of the additive solution 43, the time for each dope after the component change to reach the co-casting die 56 is changed. Since they are almost the same, the time required for producing the film can be shortened. For the time T1 when the base layer dope passes through the flow path 53, the time T2 when the first and second surface layer dopes pass through the respective flow paths 63 and 64,
The range is preferably T1 × 0.5 ≦ T2 ≦ T1 × 2.0, and more preferably the range is T1 × 0.8 ≦ T2 ≦ T1 × 1.2.
[0042]
As a method for making the above-described T1 and T2 substantially the same, there is a method that takes into account the length of the pipe constituting the flow path and the diameter of the pipe. Alternatively, a method that considers the speed at which the dope is fed can be mentioned. In addition, a method of adjusting the average transit time T2 of the surface layer dope by providing a liquid reservoir in the channel 53 of the base layer dope may be used. However, in the present invention, the method of making the base layer dope average passage time T1 and the surface layer dope average passage time T2 substantially the same is not limited to that described above.
[0043]
The film deposition apparatus 70 constituting the film deposition line 10 is divided into a first zone 71 and a second zone 72 as shown in FIG. The dopes are simultaneously cast on the casting drum 67 from the co-casting die 56 described above. Each dope is gradually dried while being rotated by the casting drum 67, and is peeled off from the casting drum 67 by the peeling roller 73 to form a film 74. The film deposition apparatus used in the present invention is not limited to the illustrated form.
[0044]
The film 74 is dried while being conveyed by the tenter 75. At this time, it is preferable that at least one axis is stretched to a predetermined width. The film 74 sent from the tenter 75 to the second zone 72 is wound around a plurality of rollers 76 and dried in the second zone 72. The dried film 74 is taken up by a winder 77. The temperature in the second zone 72 is preferably controlled in the range of 50 to 150 ° C. for uniform drying of the film 74.
[0045]
Moreover, in FIG. 3, although each dope was cast on the casting drum 67 which is an endless support body, this invention is not limited to the form shown in figure. As shown in FIG. 4, a casting band 82 is provided in the first zone so as to span the support drums 80 and 81, and the casting band 82 is rotated by a driving device (not shown). It is also possible to provide a co-casting die 56 on the casting band 82 and cast the dopes in multiple layers simultaneously.
[0046]
FIG. 5 shows a schematic diagram of an example in which the present invention is applied to a solution casting method for sequential casting (sequential casting). In this method, a casting band 87 is provided around the support drums 85 and 86 in the first zone, and the casting band 87 is rotated by a driving device (not shown). On the casting band 87, three casting dies 88, 89, 90 are arranged. From the respective casting dies 88, 89, 90, the respective dopes (first surface layer dope, base layer dope, second surface layer dope) described above are cast to form a film.
[0047]
In the above description, all three layers are shown. However, in the present invention, the number of layers to be cast at the same time is not limited to three layers, and can be applied to any two or more layers of simultaneous casting.
[0048]
FIG. 6 shows a cross-sectional view of a main part of a film 74 formed by the solution casting method according to the present invention. It can be seen that the film 74 has surface layers 74b and 74c formed on both sides of the base layer 74a. FIG. 7 shows an example in which the solution casting method according to the present invention is applied to the formation of a two-layer film. A surface layer 95b is formed only on one side of the base layer 95a of the film 95. Although not shown, the present invention can also be applied to a solution casting method for forming a film in which another intermediate layer is formed between a base layer and a surface layer.
[0049]
It is preferable that the Rth (retardation) of the film formed by any one of the solution casting methods described above is in the range of 1 to 200 nm in order to use the film in a product described later.
[0050]
The film formed by the solution casting method described above can be used as a polarizing plate protective film. A polarizing plate can be formed by pasting this polarizing plate protective film on both surfaces of a polarizing film made of polyvinyl alcohol or the like. Furthermore, it can also be used as an optical functional film such as an optical compensation film having an optical compensation sheet affixed on a film, or an antireflection film having an antiglare layer laminated on the film. It is also possible to constitute a part of the liquid crystal display device from these products.
[0051]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, the aspect of this invention is not limited to this. In addition, description was demonstrated in detail in the Example, description of the comparative example was abbreviate | omitted about the same conditions as the Example.
[0052]
[Example]
The mother liquor dope 31 was prepared using the film production line shown in FIG. As a solvent for preparing the mother liquor dope, a mixed solvent in which methylene chloride, which is a halogenated hydrocarbon, and an alcohol mixed solution (mixing ratio of methanol: n-butanol = 34: 1) are mixed at 83:17 is added to the dissolution tank 12. Liquid was sent. With respect to this mixed solvent, 20% by weight of cellulose triacetate (acetylation degree 60%) as a polymer was fed into the dissolution tank 12 by the measuring instrument 14. Further, a mixture of TPP and BDP, which is 11.0% by weight of plasticizer with respect to cellulose triacetate (TPP: BDP = 2: 1 weight mixing ratio), was fed into the dissolution tank 12. These mixtures were stirred by a motor 17 with an output of 45 kW for 30 minutes at a speed of 80 rpm to prepare a crude solution 19 and stored in the storage tank 20. Then, the mixture was sent to the heater 26 and 85 ° C. The temperature was raised to in-line and held for 10 minutes. When the obtained solution was visually confirmed, the insoluble matter of the polymer was not confirmed. This solution was passed through a filtration filter 28 to remove impurities contained in the raw material, and a mother liquor dope 31 was obtained.
[0053]
Next, the mother liquor dope 31 obtained by the above-described method was fed to the co-casting die 56 using the film production line 10 shown in FIG. The liquid 43 containing the ultraviolet absorber corresponding to 1.1% by weight with respect to the solid content weight of the mother liquor dope 31 was mixed and then made uniform by the static mixer 42. Thereafter, the dope for the base layer was fed to the co-casting die 56 by the pump 50 at 40 L / min. The dopes for the first and second surface layers were fed at 2 L / min by pumps 51 and 52. When the volume of the base layer dope channel 53 was 800 L, the average transit time T1 for the base layer dope passing through the channel 53 was 20 minutes. When the volume of each of the surface dope channels 63 and 64 is 50 L, the average transit time T2 for the first and second surface layer dopes passing through the channels 63 and 64 is 25 minutes. Met.
[0054]
Each dope under the above-described conditions was cast from a co-casting die 56 onto a casting drum 67, and the thickness of the film 74 after drying was 80 μm as a whole, and the surface layers 74b and 74c were 3 to 4 μm. . The retardation (Rth) of the obtained film 74 was 40 nm when measured at a wavelength of 632.8 nm using an ellipsometer (an ellipsometer), and a film excellent in optical anisotropy was obtained. I found out.
[0055]
[Comparative example]
The process was performed under the same conditions as in the example except that the surface layer dope channel having a volume of 90 L was used. At this time, the average transit time T2 for the first and second surface layer dopes to pass through the flow path was 45 minutes.
[0056]
As described above, in the film formation by the conventional co-casting method, when the component of the mother liquor dope 31 is changed, the base layer dope passes through the flow path for 20 minutes, and the surface layer dope flows. Since the time for passing through the road was 45 minutes, it took 25 minutes or more for each dope to stabilize during casting. However, when the three-layer simultaneous multi-layer casting is performed by co-casting using the film forming method according to the present invention, the average transit time T1 for the base layer dope to pass through the flow path is 20 minutes, and the surface layer dope is Since the average passage time T2 passing through the flow path is 25 minutes, it has been found that even if the component of the mother liquor dope 31 is changed, the time required for the casting conditions to be stable can be shortened to about 5 minutes.
[0057]
【The invention's effect】
As described above, according to the solution casting method of the present invention, a dope obtained by dissolving a polymer in a solvent is used. On the support by casting die In the solution casting method for casting a multilayer to form a film, the multilayer is composed of a base layer and at least one first layer formed on the surface of the base layer, A base layer dope for forming the base layer and a first layer dope for forming the first layer; The dope for the base layer and the dope for the first layer are sent through the respective pumps and the respective introduction paths from these pumps to the casting die, and the time for the base layer dope to pass through the introduction path is divided into Since the time T2 for the first layer dope to pass through the introduction path is set to T1 × 0.5 ≦ T2 ≦ T1 × 2.0 with respect to T1, The base layer dope and the surface layer dope delivered to the casting part through different introduction paths can reach the casting part at almost the same timing, and the stability after changing the film deposition conditions The time required for conversion can be shortened.
[Brief description of the drawings]
FIG. 1 is a view showing a part of a film deposition line used for carrying out a solution casting method according to the present invention.
FIG. 2 is a view showing a part of a film deposition line used for carrying out the solution casting method according to the present invention.
FIG. 3 is a view showing a part of a film deposition line used for carrying out the solution casting method according to the present invention.
FIG. 4 is a view showing a main part of another embodiment of a film forming line used for carrying out the solution film forming method according to the present invention.
FIG. 5 is a view showing a main part of still another embodiment of a film forming line used for carrying out the solution casting method according to the present invention.
FIG. 6 is a cross-sectional view of an essential part of a film formed by the solution casting method of the present invention.
FIG. 7 is a cross-sectional view of an essential part of another form of film formed by the solution casting method of the present invention.
[Explanation of symbols]
10 Film film production line
30 Dope tank
31 Mother liquor dope
50, 51, 52 pump
53 Dope channel for base layer
55 Feed Block
56 Co-casting die
57 Surface layer additive
63 Dope channel for surface layer
64 Dope channel for surface layer
67 Casting drum
70 Film deposition equipment
74 Film
74a Substratum
74b, 74c Surface layer
T1 Dope average transit time for base layer
T2 Surface average dope transit time

Claims (10)

In a solution casting method in which a dope prepared by dissolving a polymer in a solvent is cast on a support by a casting die to form a film,
The multilayer includes a base layer and at least one first layer formed on a surface of the base layer,
The dope is divided into a base layer dope for forming the base layer and a first layer dope for forming the first layer, and the base layer dope and the first layer dope are respectively pumped. And these pumps are sent through respective introduction paths from the casting die to the casting die,
Time T2 for the first layer dope to pass through the introduction path with respect to time T1 for the base layer dope to pass through the introduction path,
A solution casting method characterized in that T1 × 0.5 ≦ T2 ≦ T1 × 2.0 . 2. The solution casting method according to claim 1 , wherein the multilayer includes a base layer and surface layers formed on both sides of the base layer. 3. The solution casting method according to claim 1, wherein the multilayer casting is performed on the endless support by co-casting. 3. The solution casting method according to claim 1, wherein the multilayer casting is performed on an endless support by sequential casting. The solution casting method according to claim 3 or 4, wherein the film peeled from the endless support is stretched at least uniaxially. The solution casting method according to any one of claims 1 to 5 , wherein the polymer is a cellulose ester. The solution casting method according to claim 6 , wherein the cellulose ester is cellulose acetate having an average degree of acetylation of 58.0 to 62.5%. Claims 1 to 7 or 1 solution casting method according to, characterized in that film formation the film to be used as a polarizing plate protective film. Claims 1 to 7 or 1 solution casting method according to, characterized in that film formation the film to be used as a polarizing plate. The solution casting method of any one claim 1 to 7, characterized in that film formation the film used as an optical functional film.

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