WO2022064890A1 - Transparent film manufacturing method and transparent film - Google Patents

Abstract

Provided are: a transparent film manufacturing method the enables obtaining of a transparent film in which coloring is suppressed by having high productivity; and a transparent film in which coloring is suppressed.　This method or the like for manufacturing a transparent film (10) comprises: a polymer solution preparation step for preparing a polymer solution containing a nitrogen-containing polymer (11), an antioxidant (12), and methylene chloride; a film formation step for forming a film by a solution film-forming method using said polymer solution; and a heating step for bringing a heated gas having a temperature not lower than 200°C into contact with both surfaces of the film.

Description

Manufacturing method of transparent film and transparent film

The present invention relates to a method for producing a transparent film and a transparent film.

Nitrogen-containing polymers containing nitrogen atoms in their molecules are widely used as functional resins, heat-resistant resins, ultraviolet-absorbing resins, and the like. Specific examples of the nitrogen-containing polymer include polyamide or polyacrylonitrile containing a nitrogen atom in the polymer, or polyimide or polyaniline having a cyclic structure containing a nitrogen atom.

It is known that these resins are molded into a film to form an optical film. For example, a polyimide film containing an organic additive having an aromatic ring in the molecule is known. This polyimide film suppresses the generation of warpage and is used for flexible displays and the like (Patent Document 1).

International Publication No. 2016/190105

When molding the nitrogen-containing polymer into a film, the film may be colored, especially by a method involving melting. Therefore, when making an optical film that needs to be an optically transparent film, a polymer solution in which a nitrogen-containing polymer is dissolved in a solvent is used, and this polymer solution is used to form a film by a method such as solution film formation. There is a way to do it. In such a film forming method, it is effective to use methylene chloride as a solvent, which has a low boiling point and high safety.

Films made of nitrogen-containing polymers are strongly required to be dehalogenated when used in electronic components and the like. Therefore, it is necessary to heat-treat the film in order to reduce the methylene chloride in the film after the solution film formation is performed using the polymer solution composed of the nitrogen-containing polymer. However, in particular, a film made of a nitrogen-containing polymer is prone to coloring, which is presumed to be an oxidation reaction of the nitrogen portion, by heating.

An object of the present invention is to provide a method for producing a transparent film capable of obtaining a transparent film in which coloring is suppressed with high productivity, and a transparent film in which coloring is suppressed.

The present invention is a method for producing a transparent film, which comprises a polymer solution preparation step of preparing a polymer solution containing a nitrogen-containing polymer, an antioxidant, and methylene chloride, and a solution film forming method using the polymer solution. A film forming step of forming a film and a heat treatment step of bringing a heated gas having a temperature of 200 ° C. or higher into contact with each of both surfaces of the film are provided.

The heat treatment step is preferably performed by continuously transporting the film in an airtight heat treatment space formed by a drying device equipped with an air supply means and an exhaust means.

In the heat treatment step, it is preferable to treat the film in the range of 1 m ² or more and 10 m ² or less per 1 m ³ of the volume of the heat treatment space.

The heat treatment step preferably has a film transport speed within the range of 0.5 m or more and 20 m or less per minute.

In the heat treatment step, the weight per volume of methylene chloride contained in the exhaust by the exhaust means is preferably 0.1% or less with respect to the entire exhaust.

The heated gas preferably has a temperature of 270 ° C. or lower.

The heat treatment step is preferably performed within 25 minutes.

The nitrogen-containing polymer is preferably polyimide.

The antioxidant is preferably a hindered phenolic antioxidant.

The hindered phenolic antioxidant preferably has a number average molecular weight of 1000 or more.

It is preferable that the film forming process and the heat treatment process are performed continuously.

Further, the present invention is a transparent film manufactured by a film manufacturing method, and has a chromaticity b ^* of less than 2.

According to the present invention, it is possible to provide a method for producing a transparent film capable of obtaining a transparent film in which coloring is suppressed due to high productivity, and a transparent film in which coloring is suppressed.

It is a schematic diagram of an example of a film manufacturing equipment. It is a schematic diagram of an example of a roller dryer. It is explanatory drawing explaining an example of the shape of a roller dryer and a heat treatment space. It is explanatory drawing explaining an example of the heat treatment space and the arrangement of a roller. It is explanatory drawing explaining another example of the heat treatment space and the arrangement of a roller. 5 (A) shows the processing device A, FIG. 5 (B) shows the processing device B, FIG. 5 (C) shows the processing device C, and FIG. 5 (D) shows the processing device D. It is explanatory drawing explaining the thickness of a film. It is a schematic diagram of another example of a film manufacturing facility.

The method for producing a transparent film of the present invention is to form a film by a polymer solution preparation step of preparing a polymer solution containing a nitrogen-containing polymer, an antioxidant, and methylene chloride, and a solution film forming method using the polymer solution. The film forming step and the heat treatment step of bringing a heated gas having a temperature of 200 ° C. or higher into contact with each of both surfaces of the film are provided.

The film manufacturing equipment 20 shown in FIGS. 1 and 2 is an example of equipment for manufacturing the film 10. In this embodiment, this example is used. The film 10 that has undergone the heat treatment step is a transparent film. The film manufacturing equipment 20 includes a dope preparation device 22 and a film manufacturing device 23. The film manufacturing apparatus 23 includes a casting unit 37, a tenta 38, a slitter 42, a winder 43, a transmitter 44 and a roller dryer 41 shown in FIG. 2, in order from the upstream side. And a winder 45. The film 10 wound by the winder 43 is supplied to the roller dryer 41 by the feeder 44. The arrow 1 in FIG. 1 means that the process continues to the arrow 1 in FIG.

The polymer solution preparation process will be explained. The polymer solution preparation step is a step of preparing a polymer solution by dissolving the nitrogen-containing polymer 11 which is a resin in methylene chloride as a solvent. The polymer solution contains the antioxidant 12 as an additive. The nitrogen-containing polymer 11 is a resin capable of forming a transparent film. The polymer solution is prepared as the dope 21 by the dope preparation device 22.

The nitrogen-containing polymer 11 contains a nitrogen atom in the molecule and is soluble in methylene chloride. The nitrogen atom may be contained in the molecule of the polymer, and may have a nitrogen atom in the main chain or a nitrogen atom in the side chain. Further, it may have a cyclic structure containing a nitrogen atom.

As the polymer having a nitrogen atom in the main chain, for example, polyamide (PA, Polyamide), polyacrylonitrile (PAN, Polyacrylonitrile), polyaniline (PANI, polyaniline), polyamideimide (PAI, PolyamideImide) and the like are preferably used. As the polymer having a nitrogen atom in the side chain, polyacrylamide (PAM, Poly (acrylamide)) such as poly (2-propenamide), polymaleimide (Polymaleimide) and the like are preferably used. As the polymer having a cyclic structure containing a nitrogen atom, polyimide (PI, Polyimidazole), polybenzimidazole (PBI, PolybenzImidazole) and the like are preferably used. Further, a copolymer or the like with these may be used.

The nitrogen-containing polymer 11 is preferably a so-called engineering plastic having a ring such as an aromatic ring and / or an imide ring in the main chain and having excellent mechanical strength or heat resistance. Among them, when used for an optical film, polyimide is preferable because it has excellent transparency. In this embodiment, a polyimide having a ring such as an aromatic ring and / or an imide ring in the main chain is used.

Polyimide is a polymer having an imide bond, and is a polymer containing an imide ring having an imide bond in the repeating unit of the main chain of the polymer. The polyimide is preferably formed from a diamine compound and an acid anhydride compound. As the polyimide, aromatic polyimide, alicyclic polyimide, or the like can be used, and these are compounds in which the chemical structure of the portion where the acid anhydride compound and the diamine compound are linked is aromatic or alicyclic. It can be appropriately selected by using it. Aromatic compounds, alicyclic compounds, or their bonds can be replaced with fluorine, hydrocarbons, halogens, hydrophilic groups, or the like. The acid anhydride compound and the diamine compound can be selected from the viewpoint of the methylene chloride solubility or the glass transition point of the resin, or the physical properties or transparency when the film 10 is formed. Of these, alicyclic polyimide or fluorine-substituted polyimide is preferable from the viewpoint of methylene chloride solubility, film transparency, and the like.

It is preferable that the polyimide is imidized in the state of a resin. As a method for forming a polyimide film, there is a method of forming a polyamic acid obtained by reacting an acid anhydrous compound and a diamine compound into a film and imidizing it by heat. However, this method requires high heat treatment and has a large production process load. There is a risk that the resin has a large amount of hydrophilic components and the resin has high metal adhesion, or that insolubilization and coloring are likely to occur after heat treatment, making it difficult to process films for optical applications. It is preferable to use a polyimide that is imidized in the state of a resin and has solubility in methylene chloride because a solution film can be formed and a transparent and smooth film can be obtained.

The molecular weight of the polyimide is preferably in the range of 10,000 or more and 700,000 or less in terms of weight average molecular weight, and more preferably in the range of 50,000 or more and 500,000 or less. If the molecular weight is 10,000 or less, the strength of the film 10 may not be obtained, and the proportion of molecular ends that tend to be hydrophilic in polyimide increases, so that the metal adhesion of the resin may increase. If the molecular weight is 700,000 or more, it may be difficult to dissolve in methylene chloride.

Any of such polyimides can be used, but for example, it is synthesized from anhydrous pyromellitic anhydride (PMDA, Pyromellitic Dianhydride) and 4,4'-diaminodiphenyl ether (ODA, 4,4'-Oxydianiline). Polyimide, 4,4'-(hexafluoroisopropylidene) diphthalic acid dianhydride (6FDA, 4,4'-(Hexafluoroisopropylide) diphthalic Anhydride) and 2,2'-bis (trifluoromethyl) -4,4 Polyimide synthesized from'-diamino-diphenyl (TFMB, 2,2'-bis (trifluoromethyl)-[1,1'-biphenyl] -4,4'-hydride), or 1,1'-bicyclohexane -3,3', 4,4'-Tetracarboxylic acid-3,3', 4,4'-Polyimide synthesized from dianhydride (H-BPDA) and 4,4'-diaminodiphenyl ether (ODA) Etc. are preferable.

More specifically, a polyimide made of 6FDA / TFMB can be preferably used depending on the physical characteristics of the film and the like. Preferred examples of the commercially available product include Neoprim (registered trademark) manufactured by Mitsubishi Gas Chemical Company, Inc. or KPI-MX300F manufactured by Kawamura Sangyo Co., Ltd. As the polyimide, a mixture of two or more kinds may be used.

As the nitrogen-containing polymer 11, a polymer that dissolves 10% or more in mass percent concentration with respect to methylene chloride is preferably used. A resin that dissolves 15% or more is more preferably used, and a polymer that dissolves 20% or more is further preferably used. Dissolution of at least 10% of the polymer will give a smooth film 10 in solution casting.

As the nitrogen-containing polymer 11, one type may be used, or two or more types may be used. When two or more kinds are used, for example, the same kind of polymer having a different molecular weight or the same kind of polymer having a different copolymer composition is appropriately selected from the viewpoint of the solubility or drying property of the solution, or the physical properties or transparency of the film. Can be used.

Methylene chloride is used as the solvent 15. Methylene chloride can be used alone as a solvent without using other solvent components in combination. Since methylene chloride is used as the solvent 15, the nitrogen-containing polymer 11 is dissolved in the solvent in a mass ratio sufficient to form the dope 21 even at room temperature. Further, since the nitrogen-containing polymer 11 has good solubility, a film having excellent transparency can be obtained.

As the solvent 15 other than methylene chloride, any solvent containing chlorine in the molecule (hereinafter referred to as chlorine-based solvent) may be used. Examples of the chlorine-based solvent that can be used include chloroform, 1,2-dichloroethane, and 1,1,2,2-tetrachloroethane, in addition to methylene chloride.

Other components may be added to methylene chloride to prepare the solvent 15. For example, a monohydric alcohol having a carbon number in the range of 1 or more and 4 or less may be added. As such a monohydric alcohol, methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol and the like can be used. Preferably, methanol is used.

By adding the monovalent alcohol, especially when the film 10 is prepared by the solution casting method, it is extremely difficult to remove the dope 21 made of the polymer solution when it adheres to the metal lip of the casting die 36 and hardens. It is necessary in the step of peeling the film 10 from the metal support (belt 46) on which the dope 21 is spread, or the problem of sticking that causes a surface failure such as streaks in the film 10. The problem of stripping at very high loads is ameliorated.

The mixing ratio of the monohydric alcohol to the methylene chloride is preferably in the range of 0.5% or more and 10% or less in terms of the mass ratio with respect to the total solvent containing the methylene chloride and the monohydric alcohol. It is more preferably 1% or more and 5% or less, and further preferably 1% or more and 3% or less. Within this range, the transparency of the solution-formed film 10 is good. In the present invention, the monohydric alcohol added as a solvent can be measured as the amount of residual solvent in the film.

When a monohydric alcohol is added, it is preferable to use a solvent in which a citric acid ester is further added as another component to methylene chloride. The citric acid ester is represented by the following general formula (1). In the formula (1), R ¹ , R ² and R ³ are independently hydrogen (H) or a hydrocarbon group having 3 or more and 5 or less carbon atoms, and R ⁴ is hydrogen (H). ), A carbonyl group, or an acetyl group. The citric acid ester preferably contains at least a component in which R ¹ is hydrogen (H).

 

As an example of the citrate ester, in the formula (1), R ¹ and R ⁴ are hydrogen (H), R ² and R ³ are isopropyl groups, isopropyl citrate, R ¹ and R ⁴ are hydrogen (H). , R ² and R ³ are n-butyl groups, butyl citrate, R ¹ and R ⁴ are hydrogen (H), R ² and R ³ are sec-pentyl groups, sec-pentyl citrate and the like. Be done. Among these, isopropyl citrate represented by the following formula (2) is preferable.

 

One type of citric acid ester may be used, or two or more types may be mixed and used. When two or more kinds are mixed, it is recommended to use a citric acid ester which is a mixture by hydrolysis of the citric acid ester, so that the film can be peeled off from the support and promote drying while maintaining the transparency of the film when mixed. Is preferable because it can be imparted. Further, as the citric acid ester, a commercially available one may be used. As a commercially available product, isopropyl citrate (mixture) (Isopropyl Citrate (mixture)) manufactured by Tokyo Kasei Co., Ltd. can be used.

The mass ratio of the citric acid ester is preferably in the range of 0.01 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the resin, and is also within this range in this example. When the mass ratio of the citric acid ester is 0.01 parts by mass or more, the film 10 has a smoother film surface with better peelability from the support than when it is less than 0.01 parts by mass. .. When the mass ratio of the citric acid ester is 10 parts by mass or less, the white turbidity is further suppressed and the haze (cloudiness) is good and the transparent film 10 is obtained as compared with the case where the mass ratio exceeds 10 parts by mass. The mass ratio of the citric acid ester is more preferably in the range of 0.05 parts by mass or more and 5 parts by mass or less. The mass ratio of the citric acid ester in the film 10 is substantially the same as the mass ratio of the citric acid ester in the polymer solution (dope 21 described later (see FIG. 1)).

As described above, by adding the citric acid ester to the solvent and using it, drying is promoted even when alcohol is added while suppressing the decrease in haze due to the additive, and the stickability between the films 10 is achieved. Is improved.

The polymer solution contains the antioxidant 12 in addition to dissolving the nitrogen-containing polymer 11 in a solvent made of methylene chloride. The antioxidant 12 is one of the additives for the polymer solution. As the antioxidant 12, any agent can be used as long as it can prevent oxidation in the polymer solution or the film 10 after film formation. Since the film 10 is less colored after the heat treatment step, a hindered phenol-based antioxidant or a phosphoric acid-based antioxidant can be preferably used.

As the antioxidant 12, one having a relatively large molecular weight is preferably used. This is because volatilization in the heat treatment process is suppressed, and there is less contamination in the process and stains on the film. The preferable molecular weight is preferably 300 or more, more preferably 500 or more, and further preferably 1000 or more from the viewpoint of effects and the like. On the other hand, the upper limit is preferably 2000 or less, more preferably 1500 or less, still more preferably 1200 or less, from the viewpoint of solubility in the polymer solution or transparency of the film after film formation. By setting the molecular weight of the antioxidant to a certain level, it is possible to suppress the volatilization of the antioxidant when the film 10 is heated.

Specifically, as the hindered phenolic antioxidant, for example, the following compounds can be used. Each of these is commercially available, and the trade name, molecular weight, number of phenol groups having an antioxidant function in the molecule (hereinafter referred to as the number of phenol groups), and the like are also described. Pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] (molecular weight; 1178, number of phenol groups 4, trade name: Irganox® 1010, manufactured by BASF Japan, Inc., Alternatively, trade name; Adecastab (registered trademark) AO-60, manufactured by ADEKA), 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] (molecular weight) 643, number of phenol groups 2, trade name; Irganox (registered trademark) 1035, manufactured by BASF Japan, Inc., octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (molecular weight; 531, phenol) Group 1, trade name; Irganox (registered trademark) 1076, manufactured by BASF Japan, N, N'-hexane-1,6-diylbis [3- (3,5-di-t-butyl-4-hydroxyphenylpropane) (Amid)] (molecular weight; 637, number of phenol groups 2, trade name; Irganox (registered trademark) 1098, manufactured by BASF Japan, Inc.), benzenepropanoic acid, 3,5-bis (1,1-dimethylethyl) -4-hydroxy- , C7-C9 side chain alkyl ester (molecular weight; 390, number of phenol groups 1, trade name; Irganox (registered trademark) 1135, manufactured by BASF Japan), 1,3,5-trimethyl-2,4,6-tris (3) , 5-di-t-butyl-4-hydroxybenzyl) benzene (molecular weight; 775, number of phenol groups 3, trade name: Irganox® 1330, manufactured by BASF Japan), 4,6-bis [(octylthio) methyl ] -O-cresol (molecular weight; 425, number of phenol groups 1, trade name; Irganox (registered trademark) 1520L, manufactured by BASF Japan), triethylene glycol-bis [3- (3-t-butyl-5-methyl-4) -Hydroxyphenyl) propionate] (molecular weight; 587, number of phenol groups 2, trade name: Irganox (registered trademark) 245, manufactured by BASF Japan, Inc.), 1,6-hexanediol-bis [3- (3,5-di-t) -Butyl-4-hydroxyphenyl) propionate] (molecular weight; 639, number of phenol groups 2, trade name: Irganox (registered trademark) 259, manufactured by BASF Japan), 1,3,5-tris (3,5-di-t) -Butyl-4-hydroxybenzyl) -1,3,5-triazine-2,4,6 (1H, 3H, 5H) -trion (Molecular weight: 784, number of phenol groups 3, trade name: Irganox (registered trademark) 3114, manufactured by BASF Japan, or trade name: ADEKA STAB (registered trademark) AO-20, manufactured by ADEKA), 3,9-bis [2 -{3- (3-Tercharly butyl-4-hydroxy-5-methylphenyl) propionyloxy} -1,1-dimethylethyl] -2,4-8,10-tetraoxaspiro [5,5] undecane ( Molecular weight; 741, number of phenol groups 2, trade name; ADEKA STAB (registered trademark) AO-80, manufactured by ADEKA Corporation.

It also has a hindered phenol group and a hindered amine group, for example, bis- (1,2,2,6,6-pentamethyl-4-piperidyl) {[3,5-bis (1,1-dimethylethyl) -4- Hydroxyphenyl] methyl} butylmalonate (molecular weight; 685, number of phenol groups 1, trade name; Tinuvin® 144, manufactured by BASF Japan Ltd.) can also be used.

Phosphate-based antioxidants include 3,9-bis (octadecyloxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5,5] undecane (molecular weight; 733, trade name; adekastab). Registered trademark) PEP-8, manufactured by ADEKA Corporation) can be used.

Among these antioxidants, it has excellent solubility in methylene chloride, which is the solvent 15, and there is no crying of the additive from the solution in which the nitrogen-containing polymer 11 is dissolved in the solvent 15 to the film formed, and there is no coloring. Since the film 10 having excellent transparency can be obtained, a hindered phenol-based antioxidant can be preferably used. As the hindered phenolic antioxidant, one having no hindered amine group is preferable, and since the number of phenol groups in the molecule is 2 or more, the coloration of the film is suppressed and a transparent film can be obtained. It can be preferably used.

In some cases, additives other than the antioxidant 12 may be added. Examples of the additive other than the antioxidant 12 include various additives such as a plasticizer, an ultraviolet absorber, fine particles, an antioxidant, and a matting agent. Further, a known peeling accelerator (also referred to as a peeling reducing agent or the like) for improving the peelability may be contained as an additive. As the peeling accelerator, a so-called surfactant which is a compound having an ionic group and a hydrocarbon group is preferable, and specifically, a phosphate ester-based surfactant, a carboxylic acid or a carboxylate-based surfactant, and the like. Sulfonic acid or sulfonate-based surfactants, ammonium salt-based surfactants and the like are preferable. Of these, phosphoric acid ester-based surfactants are particularly preferable, and specifically, Plysurf (registered trademark) A208B, A208F, A208N, A219B and the like manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. can be used.

The polymer solution is prepared as a dope 21 by the film manufacturing equipment 20. The dope preparation device 22 includes a mixing tank 26, a pump 27, a filter 28, a storage tank 31, and a pump 32, which are connected by a pipe 33 in this order from the upstream side.

The mixing tank 26 is for dissolving the nitrogen-containing polymer 11 and the antioxidant 12 in the solvent 15 by mixing the nitrogen-containing polymer 11, which is the raw material of the dope 21, the antioxidant 12, and the solvent 15. .. When a monohydric alcohol or the like is contained, the solvent 15 is adjusted by mixing methylene chloride and methanol, which is a monohydric alcohol, in the mixing tank 26. The nitrogen-containing polymer 11 and the antioxidant 12 are added to the mixing tank 26 containing the solvent 15. In the present embodiment, the solvent 15 is a mixed solvent having a mass ratio of methylene chloride and methanol of 98: 2.

The nitrogen-containing polymer 11 supplied to the mixing tank 26 is a powder in this example, but the aspect of the nitrogen-containing polymer 11 is not limited to the powder, and may be, for example, flakes or pellets. The mixing tank 26 is provided with a stirring mechanism (not shown) for stirring the guided mixture of the nitrogen-containing polymer 11, the antioxidant 12, and the solvent 15, thereby promoting dissolution. The nitrogen-containing polymer 11 and the antioxidant 12 are dissolved in the solvent 15 by being mixed with the solvent 15 in the mixing tank 26 to form the dope 21. Since the antioxidant 12 has excellent solubility in the solvent 15 and also has excellent compatibility with the solution in which the nitrogen-containing polymer 11 is dissolved in the solvent 15, a film 10 having excellent transparency can be obtained.

It is also preferable that the nitrogen-containing polymer 11 supplied to the mixing tank is heat-dried before being supplied to reduce the water content of the resin. The nitrogen-containing polymer 11 may absorb moisture. For example, in polyimide, the water content may be in the range of 2% or more and 4% or less. If the solution is made while the water content of the nitrogen-containing polymer 11 is high, the solution may become cloudy or the transparency of the film 10 may deteriorate, and the resin concentration may fluctuate due to fluctuations in the water content of the resin. Drying or peeling property may vary.

The heating and drying of the nitrogen-containing polymer 11 is preferably in the range of 100 ° C. or higher and 180 ° C. or lower, and more preferably in the range of 120 ° C. or higher and 160 ° C. or lower. The heating time is preferably in the range of 5 minutes or more and 240 minutes or less, and more preferably in the range of 20 minutes or more and 180 minutes or less. The water content of the resin after heating and drying is preferably 1% or less, more preferably 0.7% or less.

The mixing tank 26 may be provided with a temperature control mechanism (not shown) for adjusting the internal temperature. The mixing tank 26 of this example also has a temperature control mechanism, and keeps the temperature of the mixture at room temperature (generally within the range of 25 ° C. or higher and 30 or lower). Depending on the type of the nitrogen-containing polymer 11, the antioxidant 12, and the solvent 15, the temperature of the mixture is adjusted by the temperature control mechanism, so that dissolution is promoted and alteration and / or foaming is suppressed. When methylene chloride is used as the solvent 15, the temperature is preferably 39 ° C. or lower under normal pressure, whereby foaming is suppressed. Further, in this case, the temperature in the mixing tank 26 is more preferably in the range of 15 ° C. or higher and 39 ° C. or lower, further preferably in the range of 15 ° C. or higher and 37 ° C. or lower, and in the range of 25 ° C. or higher and 35 ° C. or lower. Especially preferable. However, depending on the type of the nitrogen-containing polymer 11, the antioxidant 12, and the solvent 15, the mixture may be dissolved without temperature control, and in that case, the temperature control mechanism may not be provided.

When various additives other than the above-mentioned antioxidant 12 are contained in the film 10, these additives may be guided to the mixing tank 26. As described above, the raw materials of the dope 21 to which the mixing tank 26 is mixed are not limited to the nitrogen-containing polymer 11, the antioxidant 12, and the solvent 15.

Depending on the raw material, impurities may be mixed in, or it may not be dissolved by stirring in the mixing tank 26 and may remain as an insoluble matter. Therefore, in this example, the dope 21 is sent from the mixing tank 26 to the filter 28 by the pump 27, and these foreign substances are removed by the filter 28. As the filter 28, a filter paper having a pore diameter of 20 μm (63LS manufactured by Toyo Filter Paper Co., Ltd.) is used, but the pore diameter and the material are not limited to this example, and the application of the film 10 or the nitrogen-containing polymer 11 and the antioxidant are prevented. It may be determined according to the type of the agent 12 and the solvent 15. The pore diameter of the filter paper used as the filter 28 is preferably in the range of 5 μm or more and 100 μm or less, more preferably in the range of 10 μm or more and 50 μm or less, and further preferably in the range of 10 μm or more and 25 μm or less.

Examples of other filters include metal filters, and the pore diameter of the metal filter is preferably in the range of 3 μm or more and 15 μm or less, more preferably in the range of 3 μm or more and 10 μm or less, and further preferably in the range of 3 μm or more and 5 μm or less. When a metal filter having such a pore size is used, a metal filter may be arranged downstream of the filter 28 and filtered in two stages. Such stepwise filtration is particularly effective in producing optical films.

A heater (not shown) may be provided between the pump 27 and the filter 28, and the heater may promote the dissolution of the undissolved portion that was not dissolved in the mixing tank 26. Further, depending on the type of the nitrogen-containing polymer 11 used, it may be difficult to dissolve in the solvent 15, and a heater may be used in such a case as well. For example, when methylene chloride is used as the solvent 15, the temperature of the dope 21 in the heater is more preferably in the range of 40 ° C. or higher and 120 ° C. or lower, further preferably in the range of 45 ° C. or higher and 90 ° C. or lower, and more preferably 60 ° C. It is particularly preferable that the temperature is in the range of 90 ° C. or lower.

The dope 21 that has been filtered by the filter 28 is guided to the storage tank 31 and stored in the storage tank 31 until it is subjected to casting. The storage tank 31 is preferably provided with a stirring mechanism (not shown), and in this example as well, the storage tank 31 is provided with a stirring mechanism having the same configuration as the stirring mechanism of the mixing tank 26. This stirring mechanism more reliably maintains the uniformity of the dope 21 until it is subjected to casting. In this example, the number of storage tanks 31 is one, but a plurality of storage tanks 31 may be used. In the case of a plurality of storage tanks 31, a plurality of storage tanks 31 may be connected in series or in parallel.

It is preferable that the mixing tank 26, the filter 28, and the storage tank 31 are each provided with a light-shielding member that shields light from the inside, and this is also provided in this example. For example, in the mixing tank 26, the tank main body for accommodating the mixture is formed of a material having a light-shielding function, and the upper portion of the tank main body is provided with a lid as a light-shielding member also having a light-shielding function. ing. With such a light-shielding member, deterioration of the nitrogen-containing polymer 11 due to light is suppressed.

The downstream end of the pipe 33 is connected to the casting die 36 of the film manufacturing apparatus 23, and the dope 21 of the storage tank 31 is sent to the casting die 36 by the pump 32. In the case of producing the film 10 having a single layer structure, the dope 21 to be cast may have a concentration of the nitrogen-containing polymer 11 of 15% or more and 30% or less at a mass percent concentration with respect to the entire dope 21. Preferably, it is set to 20% in this example. By setting it to 15% or more, it is easier to secure the viscosity of the dope (corresponding to the pressure loss (pressure loss)) from the casting die 36 as compared with the case of less than 15%. Further, by setting it to 30% or less, since the solvent 15 is methylene chloride as compared with the case where it is larger than 30%, the nitrogen-containing polymer 11 is more reliably dissolved in the solvent 15, and the dope 21 becomes more cloudy. It is definitely prevented.

The concentration of the nitrogen-containing polymer 11 in the dope 21 is more preferably in the range of 15% or more and 25% or less, and further preferably in the range of 15% or more and 23% or less in terms of mass percent concentration. When the nitrogen-containing polymer 11 is polyimide, the concentration of the polyimide is more preferably in the range of 20% or more and 30% or less in terms of mass percent concentration. The dope 21 can be cast even if the concentration of the nitrogen-containing polymer 11 is in the range of 8% or more and less than 15% by using, for example, a gisa (preferably G-type gisa).

The concentration of the nitrogen-containing polymer 11 in the dope 21 can be adjusted by adjusting the supply amounts of the solvent 15 and the nitrogen-containing polymer 11 supplied to the mixing tank 26. The concentration of the nitrogen-containing polymer 11 of the dope 21 is a mass percent concentration with respect to the entire dope 21, and is a mass ratio of the nitrogen-containing polymer 11 to the mass sum of the nitrogen-containing polymer 11 and the solvent 15. That is, when the mass of the solvent 15 is M15 and the mass of the resin is M11, it is calculated by {M11 / (M15 + M11)} × 100.

The mass percent concentration of the antioxidant 12 with respect to the dope 21 is preferably in the range of 0.01% or more and 10% or less, and is also within this range in this example. The mass percent concentration of the antioxidant 12 in the dope 21 is more preferably in the range of 0.05% or more and 5.0% or less.

Next, the film forming process will be described. The film forming step is a step of forming a film by a solution casting method. The solution casting method consists of a casting step of forming a casting film by casting a polymer solution, Dope 21 on a metal support, and a peeling step of peeling the casting film from the support to form a film. It consists of a process. The casting step and the peeling step are carried out by the casting unit 37 of the film manufacturing apparatus 23.

As shown in FIG. 1, the film manufacturing apparatus 23 includes a casting unit 37, a tenta 38, a slitter 42, a winder 43, a roller dryer 41, and a winder 45 in this order from the upstream side. .. In the present embodiment, the film 10 that has passed through the tenta 38 is once wound up. The wound film 10 is sent to the roller dryer 41 for subsequent processing.

The casting unit 37 includes a belt 46 as a support formed in an annular shape, a pair of rollers 47 that run in the longitudinal direction while supporting the belt 46, a casting die 36, and a stripping roller 48. Be prepared. At least one of the pair of rollers 47 is rotated in the circumferential direction by a drive mechanism (not shown), and this rotation causes the belt 46 wound around the pair of rollers 47 to circulate in the longitudinal direction. The flow die 36 is arranged above one of the pair of rollers 47 in this example, but may be arranged above the belt 46 between one and the other of the pair of rollers 47.

The flow-casting die 36 is a discharge unit that continuously discharges the supplied dope 21 from the discharge port 36a facing the belt 46. By continuously discharging the dope 21 to the running belt 46, the dope 21 is spread on the belt 46, and the casting film 51 is continuously formed on the belt 46 (casting step). In FIG. 1, a reference numeral PC is attached to a position (hereinafter referred to as a casting position) where the casting film 51 begins to be formed when the dope 21 comes into contact with the belt 46. The material of the belt 46 is not particularly limited, but metal is preferable, and SUS is used in this example.

The pair of rollers 47 includes a temperature controller (not shown) that adjusts the peripheral surface temperature. The temperature of the cast film 51 is adjusted via the belt 46 by the roller 47 whose peripheral surface temperature is adjusted. In the case of the so-called dry gelling method in which drying is promoted by heating the casting film 51 and then hardened (gelled) by this drying, the peripheral surface temperature of the roller 47 is, for example, in the range of 10 ° C. or higher and 30 ° C. or lower. To be inside. Further, in the case of the so-called cooling gelling method in which the casting film 51 is hardened by cooling, the peripheral surface temperature of the roller 47 is set within the range of −15 ° C. or higher and 5 ° C. or lower. Due to such gelation, the cast film 51 is hardened to the extent that it can be transported.

A drum (not shown) may be used as the support instead of the belt 46. In this case, a drive mechanism is provided on the drum, and the drum is rotated in the circumferential direction to form the cast film 51 on the peripheral surface. In this case, the peripheral surface of the drum functions as the surface of the traveling support. The material of the drum is not particularly limited, but metal is preferable, and SUS is preferable as the metal, and SUS plated with hard chrome is particularly preferable. When the drum is used as a support, the drum shall be provided with a temperature controller (not shown) for adjusting the peripheral surface temperature, and the temperature of the casting film 51 may be adjusted by adjusting the peripheral surface temperature of the drum. It is good to do it. In the case of the dry gelation method, it is preferable to use the belt 46 as the support, and in the case of the cooling gelation method, it is preferable to use the drum as the support.

Regarding the dope 21 from the flow die 36 to the belt 46, the so-called bead, a decompression chamber (not shown) may be provided upstream of the belt 46 in the traveling direction, and is also provided in this example. This decompression chamber sucks the atmosphere of the upstream area of the discharged dope 21 and decompresses this area by this suction. Further, a blower (not shown) may be provided at a position facing the belt 46 to promote the drying of the cast film 51.

The cast film 51 is hardened on the belt 46 to the extent that it can be transported to the tenta 38, and then continuously peeled off from the belt 46 in a state containing a solvent. As a result, the film 10 is formed (peeling step). The stripping roller 48 is for continuously stripping the casting film 51 from the belt 46. The stripping roller 48 supports the film 10 formed by peeling from the belt 46, for example, from below, and keeps the stripping position PP in which the cast film 51 is peeled off from the belt 46 constant. The stripping method may be either a method of pulling the film 10 to the downstream side, a method of rotating the stripping roller 48 in the circumferential direction, or the like.

When the dope 21 contains a monohydric alcohol and a citric acid ester, the casting film 51 formed on the belt 46 also contains the citric acid ester. And the citric acid ester has a carboxyl residue. Therefore, from the above-mentioned presumed action on the interaction between the hydroxyl group on the surface of the belt 46 and the dope 21, the flow-through film 51 has a small peeling load from the belt 46, and as a result, the flow-through film 51 is smooth (smooth). ) Is continuously peeled off from the belt 46. Therefore, a film 10 having excellent smoothness on the film surface can be obtained. Since the film surface is smooth, a film 10 that can be used for an optical film having strict requirements for optical characteristics can be obtained.

In the case of the dry gelation method, the stripping from the belt 46 is performed, for example, while the solvent content of the cast film 51 is in the range of 10% by mass or more and 100% by mass or less. In the present specification, the solvent content (unit;%) is a value based on the dry amount, and specifically, when the mass of the solvent 15 is M15 and the mass of the film 10 is M10, {M15. / (M10-M15)} × 100 is a percentage. In the case of the cooling gelling method, stripping is performed, for example, while the solvent content of the cast film 51 is in the range of 100% by mass or more and 300% by mass or less.

As described above, the casting unit 37 forms the film 10 from the dope 21. The belt 46 circulates between the spreading position PC and the stripping position PP, so that casting of the dope 21 and stripping of the spreading film 51 are repeatedly performed.

The film 10 stripped off and formed is guided by the tenta 38. A blower (not shown) for promoting the drying of the film 10 may be arranged in the transport path between the casting unit 37 and the tenter 38. The tenta 38 includes a clip 52 that grips the side of the long film 10, a pair of rails (not shown) and a chain (not shown). Instead of the clip 52, a pin plate (not shown) in which a plurality of pins (not shown) are arranged upright on the upper surface of the table and hold the film 10 by piercing the side portions of the film 10 with individual pins. You may use it.

The rails are installed on the side of the transport path of the film 10, and the pair of rails are arranged apart from each other. The chain is hung on a prime mover sprocket and a driven sprocket (not shown) and is movably attached along rails. The clips 52 are attached to the chain at predetermined intervals, and the rotation of the driving sprocket causes the clips 52 to circulate and move along the rails. The clip 52 starts holding the guided film 10 near the entrance of the tenter 38, moves toward the exit, and releases the holding near the exit. The clip 52 released from holding moves to the vicinity of the entrance again and holds the newly guided film 10. In this way, the clip 52 is conveyed in the longitudinal direction while gripping each side portion of the film 10.

The tenta 38 is provided with a blower 53 above the transport path of the film 10. An outlet (not shown) through which the dry gas flows out is formed on the lower surface of the blower 53, and the dry gas (for example, air) is blown out toward the passing film 10. The temperature of the dry gas from the blower 53 is preferably in the range of 40 ° C. or higher and 200 ° C. or lower. A blower having the same structure may be provided below the transport path of the film 10. Since the tenter 38 has the blower 53 as described above, the film 10 can be dried while passing through the tenta 38 (first drying step). However, the tenta 38 may not be provided.

The film 10 that has passed through the tenta 38 is sent to the slitter 42. The slitter 42 is for cutting off each side end of the film 10. This excision brings the film 10 to, for example, the desired product width. A slitter having the same configuration as the slitter 42 may be arranged at another position. For example, between the casting unit 37 and the tenta 38, and / or between the tenta 38 and the roller dryer 41. The excised side end may be guided by a crusher (not shown), crushed into chips by the crusher, and used as a raw material for a new dope 21.

The winder 43 is for winding the film 10 into a roll. The winder 43 includes a motor (not shown), and a winding core 54 is set in the winder 43. When the winding core 54 is rotated by the motor, the film 10 is wound around the winding core 54.

Next, the heat treatment process will be described. The heat treatment step is a step of bringing a heated gas having a temperature of 200 ° C. or higher into contact with each of both surfaces of the film. The heat treatment step can be performed as a drying step using a drying device (second drying step).

As shown in FIG. 2, the film 10 wound around the winding core 54 is sent to the heat treatment step, which is the next step, by the feeder 44. In this embodiment, a roller dryer 41 is used as the drying device. The roller dryer 41 is heat-insulated and airtight. The roller dryer 41 forms a heat treatment space S inside. The roller dryer 41 includes a plurality of rollers 41a in the heat treatment space S inside, and the plurality of rollers 41a support the film 10 on the peripheral surface. The film 10 is wound around the roller 41a and conveyed. In the heat treatment space S, the heat treatment step is performed by transporting the film 10 with a roll tow roll.

As shown in FIG. 3, specifically, the heat treatment space S1 formed by the processing apparatus A, which is an example of the roller dryer 41, has a height H2.0 m, a depth D4.0 m, a width W1.0 m, and a volume 8. It is a rectangular parallelepiped of ^0m3 . The drying device A includes an air supply port 55 and an exhaust port 56. The heated gas is supplied from the air supply port 55 through the air supply chamber 57, exhausted from the exhaust port 56, and discharged to the exhaust chamber 58. The film 10 is sent out from the feeder 44, advanced in the depth D direction, and wound by the winder 45. The width W direction of the processing apparatus A and the width direction of the film 10 are the same. The air supply means includes the air supply port 55 and the air supply chamber 57. Further, the exhaust means includes an exhaust port 56 and an exhaust chamber 58.

As shown in FIG. 4, in the heat treatment space S1, the plurality of rollers 41a are provided so as to have a diameter of 0.1 m and the film 10 reciprocates 5 times in the height direction with a height difference of 1 m. The path length L is about 1 m. The processing apparatus A processes the film 10 with a processing length of 10 m. The width of the film 10 is 0.7 m, and the treated area of the film 10 treated by the heat treatment space S1 is 7 m ² . The heated gas flows with each of both sides of the film 10 alongside the surface of the film 10 or against the surface of the film 10. Therefore, in the heat treatment space S1, the processing area of the film 10 per volume 1 m ³ of the heat treatment space is 0.9 m ² .

Further, the heat treatment space S1 brings the film 10 into contact with a heated gas having a specific temperature, but in order to bring the heated gas at a specific temperature into contact with the film 10, it is necessary to maintain the temperature in the heat treatment space S1. In the present embodiment, the air volume capable of maintaining the temperature of the heat treatment space S1 is about 80 m ³ / min. The air volume varies depending on the size of the roller dryer 41, that is, the volume of the heat treatment space S, the heating means, and the like.

As shown in FIG. 5, as another example of the roller dryer 41, a processing device B, a processing device C, or a processing device D can be used. In FIG. 5, since it is complicated, the reference numerals are given only to a part thereof. Further, the processing device A is also described as a reference for the processing device or the heat treatment space. Unless otherwise specified, the processing device B, the processing device C, or the processing device D has the same configuration as the processing device A. Further, in the figure, the diameter of the roller and the like are exaggerated and shown, and are different from the actual dimensions. Maintain the size, volume, treatment length, treatment area, treatment area of the film 10 per 1 m ³ of heat treatment space volume, and the temperature of the heat treatment space S of the treatment device A, the treatment device B, the treatment device C, or the treatment device D. The amount of air that can be produced is shown in Table 1.

 

One air supply port 55 and one exhaust port 56 may be arranged for each roller dryer 41, or a plurality of them may be arranged. Regardless of the number of air supply ports 55 and exhaust ports 56 arranged, the supply and exhaust of the heated gas can be adjusted to perform at a set air volume. Here, the air volume means the volume of the heated gas supplied per minute. In addition, the supply and exhaust of the heated gas can be adjusted to be performed at a set temperature. By supplying and exhausting the heated gas, it is possible to bring the heated gas at a temperature set on both sides of the film 10 into contact with each other. Further, a member for controlling the wind speed such as a net, a perforated plate, or a slit plate can be provided between the air supply port and the film of the heated gas and between the film and the exhaust port. This is because the heated gas can be uniformly brought into contact with the entire film in the processing device, and the entire inside of the processing device can be maintained at a desired temperature. In particular, it is preferable to provide a member for controlling the wind speed between the air supply port and the film because the heated gas in contact with the film can be made uniform as a whole in the apparatus.

The area of the film 10 to be processed is adjusted per 1 m ³ of the volume of the heat treatment space according to the air volume and the area of the film 10 processed by the roller dryer 41. In the film heat treatment step, it is preferable to treat the film at a ratio of 1 m ² or more of the film per 1 m ³ of the volume of the heat treatment space. It is more preferably 1.5 m ² or more, and further preferably 2.0 m ² or more. By bringing the heated air into contact with the film 10, methylene chloride in the film is reduced and dehalogenation is promoted. However, on the other hand, since the film 10 is made of a nitrogen-containing polymer, there is a possibility that coloring, which is presumed to be an oxidation reaction of the nitrogen portion, is likely to occur by heating. When the heated air comes into contact with both sides of the film 10 due to the supply and exhaust of the heated gas, the oxidation reaction of the film 10 may proceed and coloring may occur. When the film processing area per 1 m ³ of the volume of the heat treatment space is smaller than 1 m ² , the volume of the heat treatment space is large, and it is necessary to increase the air volume in order to maintain the temperature of the heated gas in contact with the film 10. A large air volume promotes the oxidation reaction of the film 10 due to the contact with the heated air, and there is a possibility that coloring is likely to occur.

Here, the area of the film 10 means the area of one side of the film 10. Therefore, the area actually processed in the heat treatment space is doubled when the front and back surfaces of the film 10 are calculated separately. Therefore, when the film is processed at a ratio of 1 m ² or more of the film per 1 m ³ of the volume of the heat treatment space, if the areas of the front and back of the film 10 are distinguished from each other, the film per 1 m ³ of the volume of the heat treatment space is used. The film will be processed at a ratio of 2 m ² or more.

On the other hand, in the heat treatment step, it is preferable to treat the film at a ratio of 10 m ² or less per 1 m ³ of the heat treatment space volume. It is more preferably 7 m ² or less, and even more preferably 5 m ² or less. The film 10 is reciprocated in the heat treatment space to the extent that it can be conveyed by a roller, a space between the reciprocating films 10 is secured, and the heated air is uniformly brought into contact with the entire film in the heat treatment process to obtain methylene chloride or chlorine in the film. Since atoms are used in optical films and the like, the number of atoms can be reduced to the extent that there is no problem. Further, the coloring of the film 10 due to the air volume can be prevented from varying in the heat treatment space.

The gas used for the heating gas is air. In this embodiment, air heated by an electric heater is used. The air may be humidity-controlled and dehumidified as the case may be. Further, noble gas such as nitrogen, helium or argon may be added and blown. Moreover, you may perform the process of blowing superheated steam and heating.

As a method of contacting the formed film 10 with a heated gas having a temperature of 200 ° C. or higher on both sides, a long film is used in an airtight heat treatment space formed by a drying device equipped with an air supply means and an exhaust means. A method of transporting 10 by roll-to-roll can be preferably used. The air supply means and the exhaust means of the drying device keep the heat treatment space at a specific temperature by supplying and exhausting the heated gas, respectively. Further, it is preferable that the drying device forming the heat treatment space is insulated. In such a heat treatment space, by continuously transporting the film 10 using a roll while supplying and exhausting the heated gas, it is possible to bring the heated air of 200 ° C. or higher into contact with each of both sides of the film 10. ..

In the heat treatment step, the temperature of the heated gas in contact with the film 10 is preferably 200 ° C. or higher, more preferably 205 ° C. or higher, still more preferably 210 ° C. or higher. When the temperature is 200 ° C. or higher, the effect of reducing the amount of methylene chloride contained in the film 10 is preferably exhibited as compared with the case where the temperature is lower than 200 ° C. On the other hand, the temperature of the heated gas in contact with the film 10 is preferably 270 ° C. or lower, more preferably 260 ° C. or lower, still more preferably 250 ° C. or lower. Continuing to supply the heated gas higher than 270 ° C. to the film 10 may cause a problem in the equipment and equipment, and the inside of the equipment may be contaminated by the volatilized material from the film.

Further, in the heat treatment step, it is preferable that the continuous transfer of the film is performed at a speed of 0.5 m / min or more. More preferably, it is 1.0 m / min or more, and even more preferably 2.0 m / min or more. The transport speed is generally constant. From the viewpoint of production efficiency and from the viewpoint of preventing the heated air from coming into contact with the film more than necessary, 0.5 m / min or more is preferable. Further, when the polymer solution preparation step, the film forming step, and the heat treatment step are continuously performed, the speeds of the film forming step and the heat treatment step can be set to be the same, and the continuous step can be performed. On the other hand, in the heat treatment step, it is preferable that the continuous transfer of the film is performed at a speed of 20 m / min or less. It is more preferably 10 m / min or less, and even more preferably 5 m / min or less. By performing at a speed of 20 m / min or less, it is possible to sufficiently bring the heated gas into contact with each of both sides of the film.

Further, in the heat treatment step, it is preferable that the weight of methylene chloride contained in the exhaust gas by the exhaust means is 1% or less with respect to the weight of a certain volume of the exhaust gas. It is more preferably 0.5% or less, still more preferably 0.1% or less. Since the weight of methylene chloride contained in the exhaust is 1% or less of the weight of a certain volume of the exhaust, there is no problem in using the amount of methylene chloride or chlorine atoms remaining in the film 10 for the optical film or the like. This is because the methylene chloride in the exhaust can be easily treated.

The weight of the film 10 that has undergone the heat treatment step is reduced to 0.1% or less of the weight of the entire film with respect to the methylene chloride remaining in the film 10. The weight of methylene chloride contained in the film 10 is a value measured by a calibration curve method by gas chromatography measurement for a film in which a film piece of the film 10 is dissolved. This is because the weight of methylene chloride remaining on the film 10 is 0.1% or less, which makes it more suitable for members for electronic components than when it is larger than 0.1%.

The longer the heat treatment step is performed on the film 10, the less methylene chloride remains on the film 10, but the longer the heat treatment step is, the more the film 10 is oxidized and colored. There is a risk. It also leads to an increase in manufacturing cost. Therefore, it is preferable that the time for the methylene chloride remaining on the film 10 to reach a weight of 0.1% or less with respect to the total weight of the film is 25 minutes or less.

Further, the film 10 preferably has a chromaticity b ^* of less than 2. The chromaticity b ^* is the value of the chromaticity b ^* using the L ^* a ^* b ^* color system measured with a spectrocolorimeter (SE7700, manufactured by Nippon Denshoku Kogyo Co., Ltd.) in accordance with JIS Z8370. Is. The smaller the value of the chromaticity b ^* , the less the yellow component in the film color. The chromaticity b ^* is preferably less than 2, more preferably less than 1.5, and even more preferably less than 1.2. It is said that the coloring of the film 10 is also caused by the combination of the nitrogen-containing polymer of the film 10 with oxygen. The film 10 is produced as a transparent film having a reduced residual methylene chloride and a chromaticity b ^* of less than 2 and less coloring by the film manufacturing method configured as described above.

The chromaticity b ^* is preferably evaluated using a value obtained by dividing the chromaticity b ^* by the thickness in consideration of the influence of the thickness of the film 10. When the unit of film thickness is μm, the chromaticity b ^* / thickness value is preferably 0.4 or less.

As shown in FIG. 6, the thickness T10 of the film 10 is in the range of 5 μm or more and 100 μm or less, more preferably 30 μm or more and 80 μm or less in this example. Not limited to this range, it may be thicker than 100 μm or thinner than 5 μm. The thickness T10 when used as an optical film is preferably in the range of 10 μm or more and 60 μm or less. For example, in a mobile display cover film application, the thickness T10 is 10 μm or more and 50 μm or less, and the thickness T10 when used as a diaphragm for earphones or the like is 5 μm. It is preferably within the range of 15 μm or more.

The film is not limited to a single-layer structure, but may be a multi-layer structure. In the case of a multi-layer structure, the number of layers is not limited to three, and may be two or four or more. The multi-layered film is obtained, for example, by co-flowing each dope forming each layer.

In the above embodiment, the film 10 that has passed through the tenta 38 is once wound up, but the film 10 that has passed through the tenta 38 may be continuously sent to the heat treatment step. In the film manufacturing facility 40 shown in FIG. 7, the film 10 is directly sent from the tenter 38 to the roller dryer 41. In this case, since the polymer solution preparation step, the film forming step, and the heat treatment step can be continuously performed, the film 10 can be manufactured with high productivity.

According to the method for producing a transparent film and the transparent film configured as described above, it is possible to obtain a transparent film in which coloring is suppressed with high productivity. When the nitrogen-containing polymer is heated, coloring that is presumed to be an oxidation reaction of the nitrogen portion is likely to occur. Further, when a film is molded using a methylene chloride solution of a nitrogen-containing polymer, it is necessary to efficiently reduce the methylene chloride remaining on the film. As a method of drying the film, heat transfer drying (roll contact) lowers the drying efficiency. Further, heating by electromagnetic radiation such as infrared rays promotes coloring of the film. It is presumed that in the film manufacturing method configured as described above, the solvent concentration on the film surface can be lowered by aeration heating on both sides of the film, and the solvent diffusion from both sides in the film can be promoted.

On the other hand, the ventilation of both sides of the film may promote the oxidation of the film. Therefore, in order to prevent oxidation of the film, it is preferable to specify the film treatment amount per volume of the heat treatment space and heat with a low air volume so as to reduce the air flow volume and perform heating efficiently. Heating with a low air volume also leads to maintenance of the drying temperature in the heat treatment space and improvement of thermal efficiency. Further, in order to maintain the drying efficiency, it is preferable to adjust the transport speed and the like so that the amount of methylene chloride in the exhaust does not increase.

In addition, since an antioxidant such as hindered phenol is added, coloring of the film is prevented. Furthermore, when the casting process and the heat treatment process are integrated, the amount of methylene chloride that accompanies the heat treatment process tends to increase, but the transport speed, air volume, etc. are adjusted to be contained in the exhaust and film. The transport speed can be adjusted so that the amount of methylene chloride does not increase. Further, since the film molding to the heat treatment step can be performed by the continuous production method, the production efficiency is improved.

Further, in addition to reducing the methylene chloride remaining on the film 10, the film 10 having a chromaticity b * of less than 2 is brought into contact with both sides of the film 10 after adjusting the temperature with a heated gas. It can be manufactured by a simple heat treatment process such as. Further, since the heat treatment step can be performed while the film 10 is conveyed by adjusting the speed, the productivity can be improved. The heat treatment step also serves as a drying step which is usually performed, and can be manufactured without adding an additional step to the conventional step. Therefore, the method for producing a transparent film is a production method capable of obtaining a transparent film in which coloring is suppressed with high productivity, and the produced film is a transparent film in which coloring is suppressed.

[Example 1] to [Example 9]
The film 10 having a single-layer structure was manufactured by the film manufacturing equipment 20, and used as Examples 1 to 9. Polyimide was used as the nitrogen-containing polymer 11.

The polyimide used was manufactured as follows. Under a nitrogen atmosphere, 1 g of isoquinoline was charged into a reaction vessel to which a vacuum pump equipped with a solvent trap and a filter was connected. Next, 375 g of γ-butyrolactone and 104 g of 2,2'-bis (trifluoromethyl) -4,4'-diaminodiphenyl (TFMB, 2,2'-Bis (trifluoromethyl) benzidine) were added to the reaction vessel. It was stirred and dissolved. Further, after adding 145 g of 4,4'-(hexafluoroisopropylidene) diphthalate dianhydride (6FDA, 4,4'-(Hexafluoroisopropylide) diphthalic anhydride) to the reaction vessel, the mixture is stirred and raised in an oil bath. The warming started. The mixture was heated and stirred at 80 ° C. for 6 hours. Then, the outside temperature was heated to 190 ° C., and the water generated by imidization was azeotropically distilled off together with toluene. After continuing heating, refluxing and stirring for 6 hours, no water was observed. Subsequently, the mixture was heated for 7 hours while distilling off toluene, and after distilling off toluene, methanol was added to reprecipitate. When the polyimide in the obtained polyimide varnish was measured by GPC, the weight average molecular weight was 360,000. The fluorine atom content of the polyimide was 31.3% by mass. Tg was 335 ° C.

As the antioxidant, any of the compounds A, B, C, D or E described below was used. The amount of the antioxidant used is described in the "Amount" column of "Additives" in Table 2. When no antioxidant was used, "None" was described in the "Additives" column of Table 2, and "-" was described in the "Amount" column.

Compound A: Pentaerythrityl-tetrax [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] (molecular weight; 1178, trade name: Irganox® 1010, manufactured by BASF Japan), Compound B: 3,9-bis (octadecyloxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5,5] undecane (molecular weight; 733, trade name; Adecastab (registered trademark) PEP-8 , Made by ADEKA), Compound C: Bis- (1,2,2,6,6-pentamethyl-4-piperidyl) {[3,5-bis (1,1-dimethylethyl) -4-hydroxyphenyl] methyl } Butyl malonate (molecular weight; 685, trade name; Tinuvin (registered trademark) 144, manufactured by BASF Japan, Inc.), compound D: 3,9-bis [2- {3- (3-tertiary butyl-4-hydroxy-). 5-Methylphenyl) propionyloxy} -1,1-dimethylethyl] -2,4-8,10-tetraoxaspiro [5,5] undecane (molecular weight; 741, trade name; Adecastab® AO-80 , Made by ADEKA)

The dope 21 containing polyimide used for the film manufacturing equipment 20 was prepared as follows. First, the polyimide was placed in a heating device and heated at 140 ° C. for 2 hours to dry the resin for dehydration. As a result, the water content before heating was 0.18% based on the entire polyimide, but it became 0.04%. Next, in the mixing tank 26, 128.3 kg of methylene chloride and 2.6 kg of methanol were mixed to prepare a solvent 15. The methanol ratio (mass ratio) in the solvent was 2%, and the volume was 100 L. The solvent 15 was stirred and 150 g of citric acid ester was added. Then, 29.9 kg of polyimide was added over 25 minutes. This was stirred to dissolve the polyimide. This was used as a dope 21 and used in the film manufacturing equipment 20. The mass ratio of each component excluding the solvent of the dope 21 containing polyimide was as follows. The mass ratio of the polyimide in the dope 21 was 18.6%.

Dope 21 containing polyimide
Polyimide 100.0 parts by mass Isopropyl citrate 0.50 parts by mass

The details of the casting process, peeling process and drying process were as follows. As the casting die 36 and the metal lip (die lip), those made of SUS316L or the like were used. The dope 21 was passed through the filter 28, respectively. First, it was passed through a 30 μm filter and then through a 10 μm filter. The dope 21 was delivered from the casting die at 1450 cc / min. The belt 46 was operated at 5 m / min. Therefore, the flow rate was 5 m / min. The belt 46 was a metal band made of SUS. Drying was recommended on the metal band by the film manufacturing equipment 20. After peeling in the peeling step, the film 10 was wound through the tenta 38 and the slitter 42. Winding was performed on a winding core made of FRP (Fiber-Reinforced Plastics) with a film width of 700 mm and a film length of 500 m. The thickness of this film 10 is described in the column of "thickness" of "film formation" in Table 2.

The wound film 10 was set in the delivery machine 44, and the film 10 was continuously conveyed by the roller dryer 41 to perform a heat treatment step. The types of the roller dryer 41 are described in the "heat treatment space" column of "heat treatment" in Table 2. The processing device A, the processing device B, or the processing device C is as described above (see Table 1).

In the "Temperature" column of "Heat treatment" in Table 2, the temperature of the heated gas in contact with each of both sides of the film 10 is described. As the heated gas, air heated with an electric heater was used. The temperature is a value measured by a thermocouple at the position of the outlet of the air supply port 55. The heat treatment time of the film 10 was about 15 minutes, and the transport speed of the film 10, which is the processing speed of the heat treatment, was about 0.67 m / min. The film 10 that had been heat-treated was wound up to complete the production.

Regarding the production of the film 10 and the produced film 10, the effect of reducing the methylene chloride remaining on the film 10 and the coloring of the film 10 were evaluated by the following methods and criteria. The results of each evaluation are shown in Table 2.

1. 1. Effect of reducing methylene chloride remaining on the film 10 The amount of methylene chloride remaining on the film 10 was measured as follows with respect to the film 10 produced by changing the heat treatment time. As a sample for measurement, a film piece of film 10 was dissolved in chloroform so as to be about 0.9%, and the amount of methylene chloride in the sample for measurement was measured by a calibration curve method by gas chromatography measurement. The apparatus used was gas chromatography (manufactured by Shimadzu Corporation) GC-2014, and the separation column used was INTER CAP1 (length 30 m, inner diameter 0.32 mm) manufactured by GL Science. The measurement conditions are as follows: the measurement sample is injected at an injection volume of 0.1 μL, the column temperature is 60 ° C, the oven temperature program starts measurement from 60 ° C, and the temperature rises to 120 ° C in 5 minutes and to 160 ° C in the next 5 minutes. It was a step to do. The amount of methylene chloride in the measurement sample / the concentration of the film piece in the measurement sample was determined as a percentage. Therefore, the amount of methylene chloride obtained is the mass ratio of the amount of methylene chloride to the entire film 10. The time for the residual methylene chloride to be 0.1% in the film 10 was determined and described in the column of "Time for the residual methylene chloride to be 0.1%" in Table 2.

2. 2. Coloring of Film 10 The chromaticity b ^* was measured with respect to the produced film 10. The chromaticity b ^* was measured using a spectrocolorimeter (SE7700, manufactured by Nippon Denshoku Kogyo Co., Ltd.) in accordance with JIS Z8370. As for the evaluation criteria, less than 2 is acceptable and 2 or more is unacceptable. Further, in order to consider the influence of the thickness of the film 10, the value obtained by dividing the chromaticity b ^* by the thickness of the film 10 measured above is divided into the “b ^* value / thickness” column of the “result” in Table 2. Described in.

[Comparative Example 1] to [Comparative Example 6]
A film was produced using the dope 21 to which no antioxidant was added. In Comparative Example 1, the heat treatment step was performed by treating the film 10 with a heated contact roll. The treatment with the contact roll was carried out by contacting the films for 25 minutes using a heating roll having a surface temperature of 220 ° C. In Comparative Examples 2 and 3, the heat treatment step was performed by a heater irradiating far infrared rays. The process of irradiating infrared rays was performed in 14 minutes at 220 ° C. and 9 minutes at 240 ° C. by adjusting the output and distance so that the film surface temperature of the film became the corresponding temperature. As a result, the effect of reducing the methylene chloride remaining on the film 10 and the coloring of the film 10 were evaluated by the above methods and criteria as in the examples. The results of each evaluation are shown in Table 2.

 

[Example 10] to [Example 25]
The film 10 having a single-layer structure was manufactured by the film manufacturing facility 20 or the film manufacturing facility 70, and used as Examples 10 to 25. The one using the film manufacturing equipment 20 was described as "separate process" in the "film forming process" column of Table 3, and the one using the film manufacturing equipment 70 was described as "consistent". The same polyimide as in Example 1 was used as the nitrogen-containing polymer 11, and the same compound A as in Example 1 was used as the antioxidant. The film 10 was manufactured in the same manner as in Example 1 except that the processing apparatus in the heat treatment step, the temperature of the heated gas, and the transport speed of the film 10, which is the processing speed of the heat treatment, were different. The conditions of the heat treatment process are shown in Table 3. Exhaust gas was obtained from the exhaust port 56 of the roller dryer 41, which is a treatment device in the heat treatment step, and the concentration of methylene chloride in the exhaust gas was measured. The concentration of methylene chloride is indicated by the weight of methylene chloride with respect to the total weight of the exhaust gas. Further, with respect to the production of the film 10 and the produced film 10, the effect of reducing the methylene chloride remaining on the film 10 and the coloring of the film 10 were evaluated by the above methods and criteria. The results of each evaluation are shown in Table 3.

 

10 Film 11 Nitrogen-containing polymer 12 Antioxidant 15 Solvent 20,70 Film manufacturing equipment 21 Dope 22 Dope preparation equipment 23 Film manufacturing equipment 26 Mixing tank 27, 32 Pump 28 Filter 31 Storage tank 33 Piping 36 Flowing die 36a Discharge port 37 Flowing unit 38 Tenta 41 Roller dryer 41a Roller 42 Slitter 43, 45 Winding machine 44 Distributor 46 Belt 47 Roller 48 Stripping roller 51 Flowing film 52 Clip 53 Blower 54 Winding core 55 Air supply port 56 Exhaust port 57 Supply Air chamber 58 Exhaust chamber D1 Thickness direction PC spreading position PP stripping position S1 to S4 Heat treatment space L Path length

Claims (12)

1. A polymer solution preparation step for preparing a polymer solution containing a nitrogen-containing polymer, an antioxidant, and methylene chloride,
   A film forming step of forming a film by a solution film forming method using the polymer solution, and
   A method for producing a transparent film, comprising a heat treatment step of contacting both sides of the film with a heated gas having a temperature of 200 ° C. or higher.
2. The method for producing a transparent film according to claim 1, wherein the heat treatment step is performed by continuously transporting the film in an airtight heat treatment space formed by a drying device provided with an air supply means and an exhaust means.
3. The method for producing a transparent film according to claim 2, wherein the heat treatment step treats the film within a range of 1 m ² or more and 10 m ² or less per 1 m ³ of the volume of the heat treatment space.
4. The method for producing a transparent film according to claim 2 or 3, wherein the heat treatment step is a speed in which the transport speed of the film is within the range of 0.5 m or more and 20 m or less per minute.
5. The transparent film according to any one of claims 2 to 4, wherein in the heat treatment step, the weight per volume of the methylene chloride contained in the exhaust by the exhaust means is 1% or less with respect to the entire exhaust. Method.
6. The method for producing a transparent film according to any one of claims 1 to 5, wherein the heated gas has a temperature of 270 ° C. or lower.
7. The method for producing a transparent film according to any one of claims 1 to 6, wherein the heat treatment step is performed within a time of 25 minutes or less.
8. The method for producing a transparent film according to any one of claims 1 to 7, wherein the nitrogen-containing polymer is polyimide.
9. The method for producing a transparent film according to any one of claims 1 to 8, wherein the antioxidant is a hindered phenolic antioxidant.
10. The method for producing a transparent film according to claim 9, wherein the hindered phenolic antioxidant has a number average molecular weight of 1000 or more.
11. The method for producing a transparent film according to any one of claims 1 to 10, wherein the film forming step and the heat treatment step are continuously performed.
12. A transparent film produced by the method for producing a film according to any one of claims 1 to 11, wherein the chromaticity b ^* is less than 2.
    

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