JP7009902B2 - A method for manufacturing a polyimide film, a method for manufacturing a polyimide precursor, a method for manufacturing a laminate, and a method for manufacturing a surface material for a display. - Google Patents

Description

The present invention relates to a method for producing a polyimide film, a method for producing a polyimide precursor, a method for producing a laminate, and a method for producing a surface material for a display.

Generally, a polyimide resin is a highly heat-resistant resin obtained by subjecting a polyamic acid (polyamic acid) obtained by a condensation reaction between an aromatic tetracarboxylic acid anhydride and an aromatic diamine to a dehydration ring-closing reaction (imidization reaction). .. However, since the polyimide resin is generally colored yellow or brown, it is difficult to use it in fields where transparency is required, such as display applications and optical applications. Therefore, it is being studied to apply a polyimide having improved transparency to a display member. For example, Patent Document 1 describes 1,2,4,5-cyclohexanetetracarboxylic acid and 1,2,4,5-cyclohexanetetracarboxylic acid as polyimide resins having high heat resistance, high transparency and low water absorption. At least one acyl-containing compound selected from the group consisting of anhydrides and reactive derivatives thereof, and at least one selected from compounds having at least one phenylene group and an isopropridene group represented by a specific formula. A polyimide resin obtained by reacting with an imino-forming compound is disclosed, and it is described that it is suitable for a substrate material such as a flat panel display and a mobile phone device.

Further, as the imidization method, there are chemical imidization and thermal imidization. In chemical imidization, a catalyst such as an amine is generally used to accelerate the reaction. Therefore, there is a problem that ammonium ions are generated from the catalyst as the reaction proceeds, and the optical properties of the polyimide film are deteriorated due to the influence of the generated ammonium ions. Therefore, Patent Document 2 proposes to reduce the content of ammonium ions in the polyimide layer by performing a purification step after chemical imidization.

On the other hand, Patent Document 3 proposes a copolymerized polyimide obtained by thermally imidizing a copolymerized polyimide precursor having a specific structure as a polyimide resin having excellent heat resistance while maintaining light transmittance. ing.

Japanese Unexamined Patent Publication No. 2006-199945 Japanese Unexamined Patent Publication No. 2016-27146 Japanese Unexamined Patent Publication No. 2014-172978

As described above, the polyimide film is superior in heat resistance and the like as compared with other resin films, and is a material that is particularly attracting attention in the field of electronics. Above all, the transparent polyimide film with improved transparency is expected to be applied to liquid crystal displays, organic EL displays, etc. as a material to replace glass, and was developed with the aim of applying it to flexible devices that take advantage of the characteristics of resin films. Is underway.
However, the polyimide film produced by chemical imidization has a problem that it is difficult to completely remove the ammonium ions in the polyimide film and the optical characteristics are deteriorated due to the influence of the residual ammonium ions.
On the other hand, the polyimide film produced by thermal imidization has a problem that the polyimide film exhibits coloring due to the high temperature treatment performed at the time of imidization.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a polyimide film in which coloring is suppressed and transparency is improved.
Further, the present invention is a method for producing a polyimide precursor suitable for producing the polyimide film, a method for producing a laminate having the polyimide film, and a method for producing the polyimide film or a surface material for a display which is the laminate. The purpose is to provide.

The method for producing a polyimide film of the present invention comprises a step of preparing a polyimide precursor solution containing a polyimide precursor containing a diamine residue containing a silicon atom in the main chain .
A step of obtaining a purified polyimide precursor by reducing residual monomers in the polyimide precursor solution, and
A step of preparing a polyimide precursor composition containing the purified polyimide precursor and an organic solvent, and
A step of applying the polyimide precursor composition to a support to form a polyimide precursor coating film, and a step of forming the polyimide precursor coating film.
The step of imidizing the polyimide precursor by heating the polyimide precursor coating film is included.

In the method for producing a polyimide film of the present invention, the step of obtaining the purified polyimide precursor is
It is preferable to include a step of recovering the polyimide precursor by dropping the polyimide precursor solution into a poor solvent to precipitate the polyimide precursor, because it is easy to recover the purified polyimide precursor.

In the method for producing a polyimide film of the present invention, the polyimide film is used.
Contains polyimide, does not contain ammonium ions,
The total light transmittance measured according to JIS K7361-1 is 90% or more.
The haze value according to JIS K-7105 is 2.0 or less, and
It is preferable that the yellowness calculated in accordance with JIS K7373-2006 is 5.0 or less from the viewpoint of suppressing the coloring of the polyimide film and improving the transparency.

The method for producing a polyimide precursor of the present invention comprises a step of preparing a polyimide precursor solution containing a polyimide precursor containing a diamine residue containing a silicon atom in the main chain .
A step of reducing residual monomers in the polyimide precursor solution is included.

In the method for producing a polyimide precursor of the present invention, the step of reducing the residual monomer is
It is preferable to include a step of recovering the polyimide precursor by dropping the polyimide precursor solution into a poor solvent to precipitate the polyimide precursor, because it is easy to recover the purified polyimide precursor.

The method for producing a laminate of the present invention includes a step of producing a polyimide film by the production method of the present invention.
A step of forming a coating film of a composition for forming a hard coat layer containing at least one of a radically polymerizable compound and a cationically polymerizable compound on at least one surface of the polyimide film obtained by the above step.
Includes a step of curing the coating film.

In the method for producing a laminate of the present invention, the radically polymerizable compound is a compound having two or more (meth) acryloyl groups in one molecule, and the cationically polymerizable compound is at least one of an epoxy group and an oxetanyl group. It is preferable that the compound has two or more of the above in one molecule from the viewpoint of adhesion between the polyimide film and the hard coat layer, light transmission of the laminate, and surface hardness.

The method for manufacturing a surface material for a display of the present invention includes a step of manufacturing a polyimide film by the manufacturing method of the present invention, or a step of manufacturing a laminate by the manufacturing method of the present invention.

According to the present invention, it is possible to provide a method for producing a polyimide film in which coloring is suppressed and transparency is improved.
Further, the present invention is a method for producing a polyimide precursor suitable for producing the polyimide film, a method for producing a laminate having the polyimide film, and a method for producing the polyimide film or a surface material for a display which is the laminate. Can be provided.

It is a figure for demonstrating the method of a static bending test.

I. Method for Producing Polyimide Film The method for producing a polyimide film of the present invention includes a step of preparing a polyimide precursor solution (hereinafter referred to as a polyimide precursor solution preparation step).
A step of obtaining a purified polyimide precursor by reducing residual monomers in the polyimide precursor solution (hereinafter referred to as a polyimide precursor purification step).
A step of preparing a polyimide precursor composition containing the purified polyimide precursor and an organic solvent (hereinafter referred to as a polyimide precursor composition preparation step) and
A step of applying the polyimide precursor composition to a support to form a polyimide precursor coating film (hereinafter referred to as a polyimide precursor coating film forming step).
A step of imidizing the polyimide precursor by heating the polyimide precursor coating film (hereinafter referred to as an imidization step) is included.

According to the present invention, as the polyimide precursor composition, a composition obtained by redissolving the purified polyimide precursor is used, and in the imidization of the polyimide precursor, a thermal imide without using a catalyst such as amine is used. By performing the conversion, it is possible to provide a polyimide film in which coloring is suppressed and transparency is improved.

As shown in Comparative Examples 2 and 3 described later, the polyimide film produced by chemical imidization has a lower yellowness (YI value) and haze value as the content of ammonium ions is reduced by purification. However, it is difficult to completely remove the ammonium ions, and the optical properties are deteriorated due to the influence of the remaining ammonium ions.
Therefore, the present inventors have focused on a polyimide film produced by thermal imidization. Since thermal imidization can be performed without using a catalyst such as amine, a polyimide film containing no ammonium ion can be produced. As a result, the optical characteristics do not deteriorate due to the influence of ammonium ions. However, the polyimide film produced by thermal imidization has a problem that it exhibits coloring by high temperature treatment. On the other hand, in the present invention, by using the polyimide precursor composition in which the purified polyimide precursor is dissolved in an organic solvent, the coloring of the film is suppressed even if the high temperature treatment for thermal imidization is performed. It is possible to suppress an increase in the YI value. It is considered that the coloring of the film due to the high temperature treatment is greatly affected by the oxidation of the residual monomer, especially the oxidation of the diamine. However, in the present invention, the residual monomer in the polyimide precursor composition is reduced, so that the film is colored. It is considered that the coloring of the film is suppressed. When the tetracarboxylic acid component or the diamine component used for the synthesis of the polyimide precursor has a structure having a relatively low reactivity, the unreacted monomer tends to remain, so that the production method of the present invention is relatively reactive. It is particularly effective when a monomer component having a low structure is used, and particularly effective when a diamine component having a relatively low reactivity structure is used.
Further, in the polyimide film obtained by chemical imidization, since the synthesis of the polyimide precursor (polyimide acid) and the imidization of the polyimide precursor are performed in the solution, the temperature above the boiling point of the solvent cannot be applied. Since the temperature of the heat history until film formation is lower than that in the case of thermal imidization, it has better dimensional stability, solvent resistance, moisture absorption resistance, moisture permeability resistance, etc. than the polyimide film obtained by thermal imidization. Tends to be inferior. On the other hand, in the production method of the present invention, high temperature treatment is performed at the time of thermal imidization, so that a polyimide film having improved these properties can be obtained. The polyimide film obtained by the production method of the present invention has good solvent resistance, so that varnish can be easily applied to the surface. Therefore, for example, the polyimide film can be placed on a desired article via an adhesive layer, a flattening layer, or the like, or a decorative portion can be provided on the polyimide film. Further, since the polyimide film obtained by the production method of the present invention has good moisture absorption resistance or moisture permeability resistance, deterioration of the article due to moisture can be suppressed by using it as a surface material of a desired article. Can be done.
Further, it is known that the arrangement of molecular chains inside the polyimide film forms a constant ordered structure, whereby bending resistance can be improved. Regarding the arrangement of the molecular chains of the polyimide resin, it is easier to form a constant ordered structure in the case of thermal imidization than in the case of chemical imidization. Therefore, the polyimide film obtained by the production method of the present invention can easily improve bending resistance and can be suitably used for flexible devices. Further, the bending resistance of the film tends to be deteriorated by the moisture absorption of the film, but since the polyimide film obtained by the production method of the present invention has good moisture absorption resistance, the bending resistance under high humidity is lowered. It is suppressed.

Further, the production method of the present invention further comprises a step of stretching at least one of the polyimide precursor coating film and the imidized coating film obtained by imidizing the polyimide precursor coating film (hereinafter referred to as a stretching step). You may have.
Hereinafter, each step will be described in detail.

1. 1. Polyimide precursor solution preparation step The polyimide precursor solution prepared in the present invention contains a polyimide precursor and a solvent, and may contain additives and the like, if necessary. The polyimide precursor solution used in the present invention can be obtained, for example, by reacting a tetracarboxylic acid component and a diamine component in a solvent. Alternatively, a polyimide precursor solution may be prepared by dissolving a pre-synthesized solid polyimide precursor in a solvent.

The tetracarboxylic acid component and the diamine component used in the present invention are not particularly limited, but in the present invention, since the residual monomer is reduced by the polyimide precursor purification step described later, the component in which the unreactive monomer is likely to remain, that is, the comparison. The production method of the present invention is more effective when at least one selected from a tetracarboxylic acid component having a low reactivity structure and a diamine component having a relatively low reactivity structure is used, and above all, unreacted. Since the film is particularly liable to be colored when the diamine of the above remains, it is more effective when a diamine component having a structure having a relatively low reactivity is used.

Examples of the tetracarboxylic acid component having a structure having a relatively low reactivity include a tetracarboxylic acid component having an aromatic ring, and among them, a tetracarboxylic acid component having a low reactivity has an aromatic ring and a carboxyl group. Alternatively, a tetracarboxylic acid component in which the aromatic ring having an acid dianhydride structure has an electron donating group can be mentioned.
Further, the tetracarboxylic acid component having an aromatic ring is preferable from the viewpoint of improving the surface hardness of the polyimide film.
Examples of the tetracarboxylic acid component having an aromatic ring include pyromellitic acid dianhydride, 3,3', 4,4'-benzophenone tetracarboxylic acid dianhydride, 2,2', 3,3'-benzophenone. Tetracarboxylic acid dianhydride, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride, 2,2', 3,3'-biphenyltetracarboxylic acid dianhydride, 2,2-bis (3) , 4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, bis (3, 4-Dicarboxyphenyl) sulfonate dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4) -Dicarboxyphenyl) methane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) 2,3-Dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 1,3-bis [(3,4-dicarboxy) benzoyl] benzene dianhydride, 1 , 4-bis [(3,4-dicarboxy) benzoyl] benzene dianhydride, 2,2-bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} propane dianhydride, 2, 2-Bis {4- [3- (1,2-dicarboxy) phenoxy] phenyl} propane dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} ketone dianhydride, Bis {4- [3- (1,2-dicarboxy) phenoxy] phenyl} ketone dianhydride, 4,4'-bis [4- (1,2-dicarboxy) phenoxy] biphenyl dianhydride, 4, 4'-bis [3- (1,2-dicarboxy) phenoxy] biphenyl dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} ketone dianhydride, bis {4- [3- (1,2-dicarboxy) phenoxy] phenyl} ketone dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} sulfonate dianhydride, bis {4- [3 -(1,2-Dicarboxy) phenoxy] phenyl} sulfonate dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} sulfide dianhydride, bis {4- [3- ( 1,2-dicarboxy) phenoxy] phenyl} sulfide Dianoxide, 4,4'-(hexafluoroisopropyridene) diphthalic acid anhydride, 3,4'-(hexafluoroisopropyridene) diphthalic acid anhydride, 3,3'-(hexafluoroisopropyridene) diphthalic acid anhydride , 4,4'-oxydiphthalic acid anhydride, 3,4'-oxydiphthalic acid anhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid Dinohydrate, 1,2,5,6-naphthalenetetracarboxylic acid dianhydride, 1,2,3,4-benzenetetracarboxylic acid dianhydride, 3,4,9,10-perylenetetracarboxylic acid ternate Examples thereof include anhydrides, 2,3,6,7-anthracenetetracarboxylic acid dianhydride, 1,2,7,8-phenanthrentetracarboxylic acid dianhydride and the like.
Examples of the tetracarboxylic acid component having an aromatic ring and having an electron-donating group in the aromatic ring having a carboxyl group or an acid dianhydride structure include bis (3,4-dicarboxyphenyl) ether dianhydride. , 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride , 2,2-bis {4- [3- (1,2-dicarboxy) phenoxy] phenyl} propane dianhydride, 2,2-bis {4- [4- (1,2-dicarboxy) phenoxy] Examples thereof include phenyl} propane dianhydride, 4,4'-oxydiphthalic anhydride, and 3,4'-oxydiphthalic anhydride.

Further, as the tetracarboxylic acid component used in the present invention, a tetracarboxylic acid component having an aliphatic ring is also preferable from the viewpoint of light transmission of the polyimide film.
Examples of the tetracarboxylic acid component having an aliphatic ring include cyclohexanetetracarboxylic acid dianhydride, cyclopentanetetracarboxylic acid dianhydride, and dicyclohexane-3,4,3', 4'-tetracarboxylic acid dianhydride. , Cyclobutanetetracarboxylic acid dianhydride and the like.
The above-mentioned tetracarboxylic acid component may be used alone or in combination of two or more.

Examples of the diamine component having a structure having a relatively low reactivity include a diamine having an aromatic ring, a diamine containing a silicon atom in the main chain, and the like. Among the diamines having an aromatic ring, those having low reactivity include diamines having an aromatic ring and the aromatic ring having an amino group having an electron-withdrawing group.
Further, a diamine having an aromatic ring is preferable from the viewpoint of improving the surface hardness, and a diamine containing a silicon atom in the main chain and a diamine having no silicon atom in the main chain are aromatic from the viewpoint of achieving both bending resistance and surface hardness. It is more preferable to use it in combination with a diamine having a group ring.

The diamine containing a silicon atom in the main chain is not particularly limited as long as it is a diamine component containing one or more silicon atoms in the main chain. For example, a diamine containing only one silicon atom in the main chain and a main chain. Examples thereof include a diamine containing two or more silicon atoms in the chain and containing a siloxane structure. Of these, a diamine containing one or two silicon atoms in the main chain is preferable because it is easy to achieve both bending resistance and surface hardness.

Examples of the diamine having one silicon atom in the main chain include a diamine represented by the following general formula (A). Examples of the diamine having two silicon atoms in the main chain include diamines represented by the following general formula (B).

（一般式（Ａ）及び一般式（Ｂ）において、Ｌはそれぞれ独立して、直接結合又は－Ｏ－結合であり、Ｒ^１０はそれぞれ独立して、置換基を有していても良く、酸素原子又は窒素原子を含んでいても良い炭素数１以上２０以下の１価の炭化水素基を表す。Ｒ^１１はそれぞれ独立して、置換基を有していても良く、酸素原子又は窒素原子を含んでいても良い炭素数１以上２０以下の２価の炭化水素基を表す。）

(In the general formula (A) and the general formula (B), L may be an independent direct bond or an —O— bond, and R ¹⁰ may be independent and have a substituent, and oxygen may be used. It represents a monovalent hydrocarbon group having 1 or more and 20 or less carbon atoms which may contain an atom or a nitrogen atom. R ¹¹ may independently have a substituent and may contain an oxygen atom or a nitrogen atom. It represents a divalent hydrocarbon group having 1 or more and 20 or less carbon atoms which may be contained.)

Examples of the monovalent hydrocarbon group represented by R ¹⁰ include an alkyl group having 1 to 20 carbon atoms, an aryl group, and a combination thereof. The alkyl group may be linear, branched or cyclic, and may be linear or a combination of branched and cyclic.
The alkyl group having 1 or more and 20 or less carbon atoms is preferably an alkyl group having 1 or more and 10 or less carbon atoms, and specifically, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and the like. Examples thereof include a t-butyl group, a pentyl group and a hexyl group. The cyclic alkyl group is preferably a cycloalkyl group having 3 or more carbon atoms and 10 or less carbon atoms, and specific examples thereof include a cyclopentyl group and a cyclohexyl group. The aryl group is preferably an aryl group having 6 or more carbon atoms and 12 or less carbon atoms, and specific examples thereof include a phenyl group, a tolyl group and a naphthyl group. Further, the monovalent hydrocarbon group represented by R ¹⁰ may be an aralkyl group, and examples thereof include a benzyl group, a phenylethyl group and a phenylpropyl group.
Examples of the hydrocarbon group which may contain an oxygen atom or a nitrogen atom include an ether bond, a carbonyl bond, an ester bond, an amide bond, and imino, which are a divalent hydrocarbon group described later and the monovalent hydrocarbon group. Examples include groups bonded by at least one of the bonds (-NH-).
The substituent that the monovalent hydrocarbon group represented by ^R10 may have is not particularly limited as long as the effect of the present invention is not impaired, and for example, a halogen atom such as a fluorine atom or a chlorine atom. , Hydrocarbons and the like.

The monovalent hydrocarbon group represented by R ¹⁰ is an alkyl group having 1 or more and 3 or less carbon atoms or an aryl group having 6 or more carbon atoms and 10 or less carbon atoms from the viewpoint of improving bending resistance and compatibility with surface hardness. It is preferable to have. The alkyl group having 1 or more and 3 or less carbon atoms is more preferably a methyl group, and the aryl group having 6 or more and 10 or less carbon atoms is more preferably a phenyl group.

Examples of the divalent hydrocarbon group represented by R ¹¹ include an alkylene group having 1 to 20 carbon atoms, an arylene group, and a group in combination thereof. The alkylene group may be linear, branched or cyclic, and may be linear or a combination of branched and cyclic.
The alkylene group having 1 or more and 20 or less carbon atoms is preferably an alkylene group having 1 or more and 10 or less carbon atoms. Examples thereof include a group obtained by combining a cyclic or branched alkylene group with a cyclic alkylene group.
The arylene group is preferably an arylene group having 6 or more carbon atoms and 12 or less carbon atoms, and examples of the arylene group include a phenylene group, a biphenylene group, a naphthylene group and the like, and further have a substituent for an aromatic ring described later. You may be doing it.
As the divalent hydrocarbon group which may contain an oxygen atom or a nitrogen atom, the divalent hydrocarbon groups are ether-bonded, carbonyl-bonded, ester-bonded, amide-bonded, and imino-bonded (-NH-). Examples include at least one bonded group.
The substituent that the divalent hydrocarbon group represented by R ¹¹ may have is the same as the substituent that the monovalent hydrocarbon group represented by R ¹⁰ may have. Good.

The divalent hydrocarbon group represented by R ¹¹ is an alkylene group having 1 or more and 6 or less carbon atoms or an arylene group having 6 or more and 10 or less carbon atoms from the viewpoint of improving bending resistance and achieving both surface hardness. It is preferably present, and more preferably it is an alkylene group having 2 or more and 4 or less carbon atoms.

The molecular weight of the diamine containing a silicon atom in the main chain is preferably 1000 or less, more preferably 800 or less, still more preferably 500 or less, and even more preferably 300, from the viewpoint of surface hardness and bending resistance. The following is particularly preferable.

Examples of the diamine having no silicon atom and having an aromatic ring include p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4 , 4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl Sulfon, 4,4'-diaminodiphenylsulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzanilide, 3,3'-diamino Diphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-di (3-aminophenyl) propane, 2,2-di (4-aminophenyl) propane, 2- (3-amino Phenyl) -2- (4-aminophenyl) propane, 2,2-di (3-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2,2-di (4-amino) Benzene) -1,1,1,3,3,3-hexafluoropropane, 2- (3-aminophenyl) -2- (4-aminophenyl) -1,1,1,3,3,3-hexa Fluoropropane, 1,1-di (3-aminophenyl) -1-phenylethane, 1,1-di (4-aminophenyl) -1-phenylethane, 1- (3-aminophenyl) -1- (4) -Aminophenyl) -1-phenylethane, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, 1 , 4-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminobenzoyl) benzene, 1,3-bis (4-aminobenzoyl) benzene, 1,4-bis (3-aminobenzoyl) benzene , 1,4-Bis (4-aminobenzoyl) benzene, 1,3-bis (3-amino-α, α-dimethylbenzyl) benzene, 1,3-bis (4-amino-α, α-dimethylbenzyl) Benzene, 1,4-bis (3-amino-α, α-dimethylbenzyl) benzene, 1,4-bis (4-amino-α, α-dimethylbenzyl) benzene, 1,3-bis (3-amino-) α, α-ditrifluoromethylben Jill) Benzene, 1,3-bis (4-amino-α, α-ditrifluoromethylbenzyl) benzene, 1,4-bis (3-amino-α, α-ditrifluoromethylbenzyl) benzene, 1,4- Bis (4-amino-α, α-ditrifluoromethylbenzyl) benzene, 2,6-bis (3-aminophenoxy) benzonitrile, 2,6-bis (3-aminophenoxy) pyridine, N, N'-bis (4-Aminophenyl) terephthalamide, 9,9-bis (4-aminophenyl) fluorene, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-ditrifluoromethyl-4,4' -Diaminobiphenyl (2,2'-bis (trifluoromethyl) benzene), 3,3'-dichloro-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 3, 3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-bis (3-aminophenoxy) biphenyl, 4,4'-bis (4-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) ) Phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoxy) phenyl] sulfide, bis [4 -(3-Aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether, bis [4- (4-aminophenoxy) phenyl ] Ether, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [3- (3- (3-) Aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3 -Hexafluoropropane, 1,3-bis [4- (3-aminophenoxy) benzoyl] benzene, 1,3-bis [4- (4-aminophenoxy) benzoyl] benzene, 1,4-bis [4- ( 3-Aminophenoxy) Benzene] Benzene, 1,4-bis [4- (4-aminophenoxy) benzoyl] benzene, 1,3-bis [4- (3-aminophenoxy) -α, α-dimethylbenzyl] benzene , 1,3-Bis [4- (4-Aminophenoxy) -α, α-di Methylbenzyl] benzene, 1,4-bis [4- (3-aminophenoxy) -α, α-dimethylbenzyl] benzene, 1,4-bis [4- (4-aminophenoxy) -α, α-dimethylbenzyl] ] Benzene, 4,4'-bis [4- (4-aminophenoxy) benzoyl] diphenyl ether, 4,4'-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] benzophenone, 4,4 '-Bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] diphenyl sulfone, 4,4'-bis [4- (4-aminophenoxy) phenoxy] diphenyl sulfone, 3,3'-diamino- 4,4'-Diphenoxybenzophenone, 3,3'-diamino-4,4'-dibiphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-biphenoxybenzophenone, 6,6'-bis (3-aminophenoxy) -3,3,3', 3'-tetramethyl-1,1'-spirobiindan, 6,6'-bis (4-aminophenoxy) -3,3, 3', 3'-tetramethyl-1,1'-spirobiindan, etc., and some or all of the hydrogen atoms on the aromatic ring of the diamine are fluorogroups, methyl groups, methoxy groups, trifluoromethyl groups, or tris. Diamines substituted with a substituent selected from the fluoromethoxy group can also be used.
Examples of the diamine in which the aromatic ring having an aromatic ring without a silicon atom and having an electron-withdrawing group has an electron-withdrawing group include 3,3'-diaminodiphenylsulfone and 3,4'-diaminodiphenyl. Sulfur, 4,4'-diaminodiphenylsulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzanilide, 1,3-bis ( 3-Aminobenzoyl) benzene, 1,3-bis (4-aminobenzoyl) benzene, 1,4-bis (3-aminobenzoyl) benzene, 1,4-bis (4-aminobenzoyl) benzene, 1,3- Bis (3-amino-α, α-ditrifluoromethylbenzyl) benzene, 1,3-bis (4-amino-α, α-ditrifluoromethylbenzyl) benzene, 1,4-bis (3-amino-α, α-Ditrifluoromethylbenzyl) benzene, 1,4-bis (4-amino-α, α-ditrifluoromethylbenzyl) benzene, 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl (2,2) ''-Bis (trifluoromethyl) benzidine), 3,3'-dichloro-4,4'-diaminobiphenyl and the like can be mentioned.

Further, as the diamine component used in the present invention, a diamine having no silicon atom and having an aliphatic ring is also preferable from the viewpoint of light transmission of the polyimide film.
Examples of the diamine having no silicon atom and having an aliphatic ring include trans-cyclohexanediamine, trans-1,4-bismethylenecyclohexanediamine, and 2,6-bis (aminomethyl) bicyclo [2,2,1]. ] Heptane, 2,5-bis (aminomethyl) bicyclo [2,2,1] heptane and the like.
The above-mentioned diamine component may be used alone or in combination of two or more.

The solvent used for synthesizing the polyimide precursor (polyamic acid) is not particularly limited as long as the above-mentioned tetracarboxylic acid component and diamine component can be dissolved, and for example, an aprotonic polar solvent or a water-soluble alcohol-based solvent is used. obtain. In the present invention, among others, N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, 1,3-dimethyl-2-imidazolidinone, etc. It is preferable to use an organic solvent containing a nitrogen atom; γ-butyrolactone or the like.

When the number of moles of the diamine component in the solvent is X and the number of moles of the tetracarboxylic acid component is Y, the Y / X is preferably 0.9 or more and 1.1 or less, and 0.95 or more and 1.05 or less. It is more preferably 0.97 or more and 1.03 or less, and particularly preferably 0.99 or more and 1.01 or less. Within such a range, the molecular weight (degree of polymerization) of the polyamic acid obtained can be appropriately adjusted.
The procedure of the polymerization reaction can be appropriately selected and used by a known method, and is not particularly limited.

The polyimide precursor contained in the polyimide precursor solution is a polyimide precursor obtained by polymerizing the above-mentioned tetracarboxylic acid component and the above-mentioned diamine component.
At least one of the number average molecular weight and the weight average molecular weight of the polyimide precursor is preferably 10,000 or more, and more preferably 20,000 or more, from the viewpoint of strength when formed into a film. On the other hand, if the average molecular weight is too large, the viscosity becomes high and the workability such as filtration may be deteriorated. Therefore, it is preferably 10,000,000 or less, and more preferably 500,000 or less.
The number average molecular weight of the polyimide precursor can be determined by NMR (for example, manufactured by BRUKER, AVANCE III). For example, a polyimide precursor solution is applied to a glass plate and dried at 100 ° C. for 5 minutes, then 10 mg of solid content is dissolved in 7.5 ml of a dimethyl sulfoxide-d6 solvent, NMR measurement is performed, and the mixture is bonded to an aromatic ring. The number average molecular weight can be calculated from the peak intensity ratio of hydrogen atoms.
The weight average molecular weight of the polyimide precursor can be measured by gel permeation chromatography (GPC). Specifically, the polyimide precursor is a N-methylpyrrolidone (NMP) solution having a concentration of 0.5% by weight, and the developing solvent is a 10 mmol% LiBr-NMP solution having a water content of 500 ppm or less. Using HLC-8120, column used: GPC LF-804 manufactured by SHODEX, measurement is performed under the conditions of a sample injection amount of 50 μL, a solvent flow rate of 0.5 mL / min, and 40 ° C. The weight average molecular weight is determined based on a polystyrene standard sample having the same concentration as the sample.

Examples of the polyimide precursor contained in the polyimide precursor solution include a polyimide precursor having a structure represented by the following general formula (1).

（一般式（１）において、Ｒ^１はテトラカルボン酸残基である４価の基を表し、Ｒ^２はジアミン残基である２価の基を表す。ｎは繰り返し単位数を表す。）

(In the general formula (1), R ¹ represents a tetravalent group which is a tetracarboxylic acid residue, R ² represents a divalent group which is a diamine residue, and n represents the number of repeating units.)

Here, the tetracarboxylic acid residue means a residue obtained by removing four carboxyl groups from the tetracarboxylic acid, and represents the same structure as the residue obtained by removing the acid dianhydride structure from the tetracarboxylic dianhydride. .. Further, the diamine residue means a residue obtained by removing two amino groups from the diamine.
Examples of R ¹ in the general formula (1) include residues obtained by removing four carboxyl groups or an acid dianhydride structure from the above-mentioned tetracarboxylic acid component, and as R ² in the general formula (1). For example, a residue obtained by removing two amino groups from the above-mentioned diamine component can be mentioned.

Among the polyimide precursors having the structure represented by the general formula (1), when the total of R ¹ and R ² in the general formula (1) is 100 mol% from the viewpoint of improving the surface hardness. In addition, the total of the tetracarboxylic acid residue having an aromatic ring and the diamine residue having an aromatic ring is preferably 50 mol% or more, more preferably 60 mol% or more, and 75 mol% or more. It is even more preferable to have.

Further, among the polyimide precursors contained in the polyimide precursor solution, 50% or more of hydrogen atoms bonded to carbon atoms contained in the polyimide precursor and containing an aromatic ring are directly attached to the aromatic ring. Polyimide, which is a hydrogen atom to be bonded, is preferable from the viewpoint of improving the light transmittance of the produced polyimide film and improving the surface hardness. The ratio of the hydrogen atoms (number) directly bonded to the aromatic ring to the total hydrogen atoms (number) bonded to the carbon atoms contained in the polyimide precursor is preferably 60% or more, more preferably 70%. % Or more is preferable.
When 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide precursor are hydrogen atoms directly bonded to the aromatic ring, the polyimide is stretched at, for example, 200 ° C. or higher even after being heated in the atmosphere. Even if it is carried out, it is preferable because the optical characteristics of the produced polyimide film, particularly the change in the total light transmittance and the yellowness YI value is small. When 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide precursor are polyimides, which are hydrogen atoms directly bonded to the aromatic ring, the reactivity with oxygen is low, so that the polyimide precursor to It is presumed that the chemical structure of polyimide is difficult to change. Polyimide film utilizes its high heat resistance and is often used for devices that require a processing process that involves heating. However, 50% or more of the hydrogen atoms bonded to carbon atoms contained in the polyimide precursor are aromatic. In the case of hydrogen atoms directly bonded to the ring, it is not necessary to carry out these subsequent steps in an inert atmosphere in order to maintain transparency, so there is an advantage that equipment costs and atmosphere control costs can be suppressed. be.
Here, the ratio of the hydrogen atoms (number) directly bonded to the aromatic ring to the total hydrogen atoms (number) bonded to the carbon atoms contained in the polyimide precursor can be obtained by using NMR.

The polyimide precursor contains an aromatic ring, and (i) a fluorine atom, (ii) an aliphatic ring, and (ii) an aliphatic ring, among others, from the viewpoint of improving the light transmittance and surface hardness of the produced polyimide film. iii) It is preferable to contain at least one selected from the group consisting of a structure in which aromatic rings are linked to each other with a sulfonyl group or an alkylene group which may be substituted with fluorine. When the polyimide precursor or polyimide contains at least one selected from a tetracarboxylic acid residue having an aromatic ring and a diamine residue having an aromatic ring, the molecular skeleton of the polyimide in the polyimide film becomes rigid and the orientation becomes high. Although the surface hardness is increased and the surface hardness is improved, the absorption wavelength of the rigid aromatic ring skeleton tends to be extended to a long wavelength, and the transmittance in the visible light region tends to be decreased.
When the polyimide precursor or the polyimide contains (i) a fluorine atom, it is possible to make it difficult for the electronic state in the polyimide skeleton to transfer charge, and thus the light transmittance of the polyimide film is improved.
When the (ii) aliphatic ring is contained in the polyimide precursor or the polyimide, the light transmission of the polyimide film is improved because the π-electron conjugation in the polyimide skeleton can be cut off to inhibit the transfer of charge in the skeleton. improves.
When the polyimide precursor or the polyimide contains a structure in which (iii) aromatic rings are linked to each other by a sulfonyl group or an alkylene group which may be substituted with fluorine, the π electrons in the polyimide skeleton are cut off from the conjugation of the π electrons in the skeleton. The light transmittance of the polyimide film is improved because the transfer of charge can be inhibited.

Among the polyimide precursors contained in the polyimide precursor solution, a polyimide precursor containing a fluorine atom is preferable from the viewpoint of improving the light transmittance of the produced polyimide film and improving the surface hardness.
The content ratio of fluorine atoms in the polyimide precursor is such that the ratio (F / C) of the number of fluorine atoms (F) to the number of carbon atoms (C) measured on the surface of the polyimide precursor by X-ray photoelectron spectroscopy is 0. It is preferably 01 or more, and more preferably 0.05 or more. On the other hand, if the content ratio of fluorine atoms is too high, the heat resistance inherent in polyimide may deteriorate. Therefore, the ratio (F / C) of the number of fluorine atoms (F) to the number of carbon atoms (C) is 1 or less. It is preferably 0.8 or less, and more preferably 0.8 or less.
In the present invention, the ratio of each atom measured by X-ray photoelectron spectroscopy (XPS) is determined from the value of the atomic% of each atom measured using an X-ray photoelectron spectroscope (for example, Thetera Probe of Thermo Scientific). be able to.

Further, the polyimide precursor having the structure represented by the general formula (1) has a tetracarboxylic acid residue of R ¹ and R ² from the viewpoint of improving the surface hardness and light transmittance of the polyimide film to be produced. It is preferable that at least one of the diamine residues in the above contains an aromatic ring and a fluorine atom.
The polyimide precursor having the structure represented by the general formula (1) is the sum of R ¹ and R ² in the general formula (1) from the viewpoint of improving the surface hardness and light transmittance of the produced polyimide film. Is 100 mol%, the total of the tetracarboxylic acid residue having an aromatic ring and a fluorine atom and the diamine residue having an aromatic ring and a fluorine atom is preferably 50 mol% or more, preferably 60 mol%. The above is more preferable, and it is even more preferable that the content is 75 mol% or more.

Further, as the polyimide precursor obtained by using at least one selected from the above-mentioned tetracarboxylic acid component having a relatively low reactivity structure and the diamine component having a relatively low reactivity structure, the above-mentioned general formula ( A polyimide having a structure represented by 1) and having a relatively low reactivity structure in at least one of the tetracarboxylic acid residue of R ¹ and the diamine residue of R ² in the general formula (1). Examples include precursors. Above all, the tetracarboxylic acid residue of R ¹ preferably contains a tetracarboxylic acid residue having an aromatic ring from the viewpoint of the surface hardness of the polyimide film. Further, the diamine residue of R ² preferably contains a diamine residue having an aromatic ring from the viewpoint of the surface hardness of the polyimide film, and from the viewpoint of bending resistance of the polyimide film, a silicon atom is added to the main chain. It is preferable to contain a diamine residue to be contained, and from the viewpoint of achieving both surface hardness and bending resistance, a diamine residue having no silicon atom and having an aromatic ring and a diamine residue having a silicon atom in the main chain Is more preferable to be contained in combination.

Among the tetracarboxylic acid residues having an aromatic ring in R ¹ of the general formula (1), the pyromellitic dianhydride residue is found in terms of surface hardness, bending resistance, and light transmission. , 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride residue, 2,2', 3,3'-biphenyltetracarboxylic acid dianhydride residue, 4,4'-(hexafluoroisopropi) Liden) Diphthalate Anhydride Residue, 3,4'-(Hexafluoroisopropylidene) Diphthalate Anhydride Residue, 3,3'-(Hexafluoroisopropylidene) Diphthalate Anhydride Residue, 4,4'- At least one selected from the group consisting of oxydiphthalic anhydride residues and 3,4'-oxydiphthalic anhydride residues is preferable, and 4,4'-(hexafluoroisopropylidene) diphthalic anhydride residues, 3,4'-(Hexafluoroisopropylidene) diphthalate anhydride residue, 3,3'-(hexafluoroisopropyridene) diphthalate anhydride residue, 4,4'-oxydiphthalate anhydride residue, and At least one selected from the group consisting of 3,4'-oxydiphthalic anhydride residues is more preferable.

Further, as R ¹ of the general formula (1), a tetracarboxylic acid residue having an aliphatic ring is preferable from the viewpoint of improving the light transmittance of the polyimide film, and among them, surface hardness and bending resistance, and bending resistance, and From the viewpoint of light transmission, cyclohexanetetracarboxylic acid dianhydride residue, cyclopentanetetracarboxylic acid dianhydride residue, dicyclohexane-3,4,3', 4'-tetracarboxylic acid dianhydride residue, At least one selected from the group consisting of cyclobutanetetracarboxylic acid dianhydride residues is preferred.

In terms of surface hardness, bending resistance, and light transmission, in ^R1 in the general formula (1), the tetracarboxylic acid residue having the above-mentioned suitable aromatic ring and the tetracarboxylic acid having the aliphatic ring described above are used. The total content of the acid residues is preferably 50 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more. Further, from the viewpoint that the effect of the present invention is more effectively exhibited, the content ratio of the tetracarboxylic acid residue having the above-mentioned suitable aromatic ring in ^R1 in the general formula (1) is 50 mol. % Or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more.
In addition, even if R ¹ in the general formula (1) contains a tetracarboxylic acid residue having an aromatic ring and another tetracarboxylic acid residue different from the tetracarboxylic acid residue having an aliphatic ring. good. ^The other tetracarboxylic acid residue is preferably 10 mol% or less, more preferably 5 mol% or less, still more preferably 3 mol% or less, and particularly 1 It is preferably mol% or less.

As the diamine residue containing a silicon atom in the main chain in R ² of the general formula (1), a diamine residue having one or two silicon atoms in the main chain is preferable, and a silicon atom in the main chain is preferable. It is preferable that the diamine residue has two of them in terms of light transmission, bending resistance and surface hardness. The diamine residue having one or two silicon atoms in the main chain is at least one selected from the group consisting of the diamine represented by the general formula (A) and the diamine represented by the general formula (B). It may be appropriately selected from the residues obtained by removing two amino groups from the diamine of the above, and among them, two amino groups from at least one diamine selected from the group consisting of diamines represented by the general formula (B). Residues excluding the above are preferred.
More specifically, 1,3-bis (3-aminopropyl) tetramethyldisiloxane residue, 1,3-bis (4-aminobutyl) tetramethyldisiloxane, 1,3-bis (5-aminopentyl). ) Tetramethyldisiloxane or the like is preferable from the viewpoint of easy availability, light transmission and surface hardness.

Among the diamine residues in R ² of the general formula (1) that do not have a silicon atom and have an aromatic ring, 4, 4 are among them from the viewpoint of light transmission, surface hardness and bending resistance. '-Diaminodiphenyl sulfone residue, 3,4'-diaminodiphenyl sulfone residue, 2,2-bis (4-aminophenyl) propane residue, 2,2-bis (4-aminophenyl) hexafluoropropane residue , And at least one selected from the group consisting of divalent groups represented by the following general formula (2) is preferable.

（一般式（２）において、Ｒ^ａ及びＲ^ｂはそれぞれ独立に、水素原子、アルキル基、またはパーフルオロアルキル基を表す。）

(In the general formula (2), Ra and R ^b independently represent ^a hydrogen atom, an alkyl group, or a perfluoroalkyl group.)

As ^R2 of the general formula (1), a diamine residue having an aliphatic ring is also preferable from the viewpoint of improving the light transmittance of the polyimide film, and among them, the point of light transmission, surface hardness and bending resistance. From the point of view, at least one selected from the straights-cyclohexanediamine residue and the trans-1,4-bismethylenecyclohexanediamine residue is preferable.

From the viewpoint of surface hardness, bending resistance, and light transmission, 50 mol of diamine residues having no silicon atom and having an aromatic ring or an aliphatic ring in ^R2 in the general formula (1). % Or more and 90 mol% or less, and preferably 10 mol% or more and 50 mol% or less of diamine residues containing one or two silicon atoms in the main chain. From the viewpoint that the effect of the present invention is more effectively exhibited, in ^R2 in the general formula (1), the diamine residue having no silicon atom and having an aromatic ring is 50 mol% or more and 90 mol% or more. It is preferable that the number of diamine residues containing one or two silicon atoms in the main chain is 10 mol% or more and 50 mol% or less.
In addition, ^R2 in the general formula (1) contains a diamine residue having an aromatic ring or an aliphatic ring and a diamine residue different from a diamine residue containing one or two silicon atoms in the main chain. It may be included. The other diamine is preferably 10 mol% or less, more preferably 5 mol% or less, still more preferably 3 mol% or less, and particularly 1 mol% or less of the total amount of R ² . It is preferable to have. Examples of the other diamine residues include diamine residues having no silicon atom and having no aromatic ring or aliphatic ring.

In the above general formula (1), R ¹ is a tetracarboxylic acid residue having an aromatic ring or an aliphatic ring as a preferred embodiment in the present invention in terms of surface hardness, bending resistance, and light transmission. Representing a tetravalent group, R ² represents a diamine residue, and 10 mol% or more and 50 mol% or less of the total amount of R ² has one or two silicon atoms in the main chain. The diamine residue having, 50 mol% or more and 90 mol% or less may be a diamine residue having no silicon atom and having an aromatic ring or an aliphatic ring.

In the structure represented by the general formula (1), n represents the number of repeating units and is 1 or more.
The number of repeating units n in the polyimide precursor can be appropriately selected depending on the structure so that the polyimide film shows a preferable glass transition temperature described later, and is not particularly limited.
The average number of repeating units is usually 10 or more and 2000 or less, and more preferably 15 or more and 1000 or less.

Further, the polyimide precursor used in the present invention preferably has a structure represented by the general formula (1) of 95% or more, preferably 98% or more, of the total number of repeating units of the polyimide precursor. More preferably, it is even more preferably 100%.
The polyimide precursor used in the present invention may have a structure different from the structure represented by the general formula (1) in a part thereof as long as the effect of the present invention is not impaired. As a structure different from the structure represented by the general formula (1), for example, a structure derived from tricarboxylic acid such as when trimellitic acid anhydride is used, or a dicarboxylic acid such as when terephthalic acid is used. The structure of origin can be mentioned.

2. 2. Polyimide precursor purification step The production method of the present invention includes a polyimide precursor purification step of obtaining a purified polyimide precursor by reducing residual monomers in the polyimide precursor solution. As a result, the residual monomer in the polyimide precursor composition described later can be reduced, so that the coloring of the polyimide film due to the oxidation of the residual monomer can be suppressed and the transparency can be improved.
In the present invention, the residual monomer includes one or more selected from the group consisting of tetracarboxylic dianhydride, tetracarboxylic acid, and diamine used for producing the polyimide precursor. Further, these derivatives may be contained.

The polyimide precursor purification step in the present invention is not particularly limited as long as it is a step capable of reducing residual monomers in the polyimide precursor solution. Examples of the polyimide precursor purification step include a step of recovering the polyimide precursor by dropping the polyimide precursor solution into a poor solvent to precipitate the polyimide precursor. In the polyimide precursor purification step, in order to further reduce impurities such as residual monomers, a solution obtained by dissolving the recovered polyimide precursor in a good solvent is added dropwise to a poor solvent to obtain a polyimide precursor. It is preferable to repeat the step of recovering the polyimide precursor once or more by precipitating it again, and more preferably to repeat it twice or more. Above all, from the viewpoint of sufficiently reducing the residual monomer, suppressing the coloring of the polyimide film, and the production efficiency, the step of recovering the polyimide precursor again is preferably performed once or twice, and repeated twice. Is more preferable.
The polyimide precursor to be recovered is usually a solid, and although the form differs depending on the molecular weight of the polyimide precursor, it is, for example, fibrous or powdery.

The poor solvent used in the polyimide precursor purification step may be used by appropriately selecting from a solvent having a solubility of the polyimide precursor lower than that of a good solvent described later and 19 g / 100 g or less at 25 ° C. Further, the poor solvent is, among others, a solvent having a solubility of 0.1 g / 100 g or more at 25 ° C. for each of the tetracarboxylic acid component and the diamine component used in the production of the polyimide precursor, which can be the residual monomer. preferable.
Examples of the poor solvent include water; alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol and cyclohexanol; aromatic hydrocarbons such as toluene; ketones such as acetone, methyl ethyl ketone and cyclohexanol; and mixed solvents thereof and the like. Can be mentioned. Among them, water and a mixed solvent of water and alcohols are preferable as the poor solvent from the viewpoint of ease of isolation of the polyimide precursor and compatibility with a good solvent described later.
When the step of recovering the polyimide precursor is performed again, the poor solvent used in each step may be the same solvent or a different solvent.

The good solvent used in the polyimide precursor purification step is preferably a solvent having a solubility of the polyimide precursor at 25 ° C. of 20 g / 100 g or more. Examples of the good solvent include N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, 1,2-dimethyl-2-. Organic solvents containing a nitrogen atom such as imidazolidinone; γ-butyrolactone; and mixed solvents thereof and the like can be mentioned. As the good solvent, an organic solvent containing a nitrogen atom is preferable from the viewpoint of solubility of the polyimide precursor and compatibility with the poor solvent, and N-methyl-2-pyrrolidone (NMP), N, N- Amidos such as dimethylformamide and N, N-dimethylacetamide are more preferred. In the present invention, the organic solvent is a solvent containing a carbon atom.
When the step of recovering the polyimide precursor is performed twice or more, the good solvent used in each step may be the same solvent or different solvents.

In the polyimide precursor purification step, when the solution containing the polyimide precursor is dropped into a poor solvent, the solid content concentration of the solution containing the polyimide precursor is determined from the viewpoint of yield and the point of efficiently removing impurities. , 0.5% by mass or more and 30% by mass or less, and more preferably 1% by mass or more and 10% by mass or less.

In the polyimide precursor purification step, when the solution containing the polyimide precursor is dropped into the poor solvent, the amount of the poor solvent with respect to 1 part by mass of the polyimide precursor is from the viewpoint of yield and efficiently removing impurities. , 50 mL or more and 500 mL or less is preferable.

In the polyimide precursor purification step, the method for recovering the polyimide precursor is not particularly limited, and examples thereof include a method by filtration. As the filtration method, for example, known methods such as vacuum filtration, pressure filtration, centrifugal filtration and the like can be applied, and the method is not particularly limited. The filter used for filtration is not particularly limited, and a filter having a pore size and a material that can remove impurities such as residual monomers and can recover the polyimide precursor can be appropriately selected.

3. 3. Polyimide precursor composition preparation step The polyimide precursor composition prepared in the present invention contains the purified polyimide precursor obtained by the polyimide precursor purification step and an organic solvent, and is further added as necessary. Etc. may be contained.
Since the polyimide precursor composition prepared in the present invention is obtained by redissolving the purified polyimide precursor, the residual monomer is reduced.

The organic solvent used in the polyimide precursor composition is not particularly limited as long as it can dissolve the purified polyimide precursor obtained in the polyimide precursor purification step. Examples of the organic solvent include N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, and 1,3-dimethyl-2-imidazolidinone. Organic solvents containing nitrogen atoms such as γ-butyrolactone; and mixed solvents thereof and the like can be mentioned. As the organic solvent, it is preferable to use an organic solvent containing a nitrogen atom, and above all, it is preferable to use N, N-dimethylacetamide, N-methyl-2-pyrrolidone or a combination thereof. Further, as the organic solvent, N, N-dimethylacetamide, N-methyl-2-pyrrolidone or a combination thereof is preferable from the viewpoint of suppressing distortion of the polyimide film.

The polyimide precursor composition may contain an additive, if necessary. Examples of the additive include inorganic particles, a silica filler for facilitating winding, a surfactant for improving film forming property and defoaming property, and the like.

Further, it is preferable that the water content of the polyimide precursor composition is 1000 ppm or less because the storage stability of the polyimide precursor composition is improved and the productivity can be improved.
The water content of the polyimide precursor composition can be determined using a Karl Fischer Moisture Meter (for example, Mitsubishi Chemical Corporation, trace moisture measuring device CA-200 type).

The method for preparing the polyimide precursor composition is not particularly limited, but as described above, in order to have a water content of 1000 ppm or less, the organic solvent used is dehydrated or a water content controlled is used. Above, it is preferable to handle it in an environment where the humidity is 5% or less.

The viscosity of the polyimide precursor composition at 25 ° C. is preferably 500 cps or more and 100,000 cps or less from the viewpoint of forming a uniform coating film and a polyimide film.
The viscosity of the polyimide precursor composition can be measured using a viscometer (for example, TVE-22HT, Toki Sangyo Co., Ltd.) at 25 ° C. with a sample volume of 0.8 ml.
When the polyimide precursor composition is stored, it is preferably stored at −5 ° C. or lower from the viewpoint of suppressing deterioration of the composition.

4. Polyimide precursor coating film forming step The support used in the step of applying the polyimide precursor composition to a support to form a polyimide precursor coating film has a smooth surface, heat resistance and solvent resistance. There is no particular limitation as long as it is a certain material. For example, an inorganic material such as a glass plate, a metal plate whose surface is mirror-treated, and the like can be mentioned. The shape of the support is selected by the coating method, and may be, for example, a plate shape, a drum shape, a belt shape, a sheet shape that can be wound on a roll, or the like.

The coating means is not particularly limited as long as it can be coated with a desired film thickness, and for example, known ones such as a die coater, a comma coater, a roll coater, a gravure coater, a curtain coater, a spray coater, and a lip coater can be used. ..
The coating may be performed by a single-wafer coating device or a roll-to-roll coating device.

After applying the polyimide precursor composition to the support, the solvent in the coating film is dried at a temperature of 150 ° C. or lower, preferably 30 ° C. or higher and 120 ° C. or lower, until the coating film becomes tack-free. By setting the drying temperature of the solvent to 150 ° C. or lower, the imidization of the polyamic acid can be suppressed.

The drying time may be appropriately adjusted according to the film thickness of the polyimide precursor coating film, the type of solvent, the drying temperature, etc., but is usually 5 minutes to 120 minutes, preferably 10 minutes to 60 minutes. preferable. If it exceeds the upper limit, it is not preferable from the viewpoint of the production efficiency of the polyimide film. On the other hand, if it is below the lower limit, the appearance of the obtained polyimide film may be affected by the rapid drying of the solvent.

The method for drying the solvent is not particularly limited as long as the solvent can be dried at the above temperature, and for example, an oven, a drying oven, a hot plate, infrared heating, or the like can be used.
When a high degree of control of optical properties is required, the atmosphere of the solvent when it is dried is preferably an inert gas atmosphere. The inert gas atmosphere is preferably a nitrogen atmosphere, preferably an oxygen concentration of 100 ppm or less, and more preferably 50 ppm or less. Heat treatment in the atmosphere can oxidize the film, causing it to color or reduce its performance.

5. Imidization Step In the production method of the present invention, the polyimide precursor is imidized by heating the polyimide precursor coating film.
When the manufacturing method has a stretching step, the imidization step may be performed on the polyimide precursor in the polyimide precursor coating before the stretching step, or the polyimide precursor coating after the stretching step. It may be performed on the polyimide precursor inside, or on both the polyimide precursor in the polyimide precursor coating film before the stretching step and the polyimide precursor existing in the film after the stretching step. good.

The imidization temperature may be appropriately selected according to the structure of the polyimide precursor.
Usually, the temperature rise start temperature is preferably 30 ° C. or higher, and more preferably 100 ° C. or higher. On the other hand, the temperature rise end temperature is preferably 250 ° C. or higher. From the viewpoint of optical characteristics, moisture absorption, dimensional stability, solvent resistance, etc., it is preferable that the temperature rise end temperature is within the range of the glass transition temperature of the polyimide imimized with the polyimide precursor ± 30 ° C., and the polyimide glass. The transition temperature is more preferably within the range of ± 20 ° C., and the transition temperature is more preferably within the range of ± 15 ° C. of the glass transition temperature of the polyimide. If the imidization temperature is too high, the polyimide film may be colored due to oxidation in the skeleton of the polyimide or the polyimide precursor, and if the imidization temperature is too low, imidization may not proceed sufficiently. be.

The temperature rising rate is preferably appropriately selected depending on the film thickness of the obtained polyimide film, and when the film thickness of the polyimide film is thick, it is preferable to slow down the temperature rising rate.
From the viewpoint of the production efficiency of the polyimide film, the temperature is preferably 5 ° C./min or more, and more preferably 10 ° C./min or more. On the other hand, the upper limit of the temperature rising rate is usually 50 ° C./min, preferably 40 ° C./min or less, and more preferably 30 ° C./min or less. It is preferable to set the temperature rise rate from the viewpoints of suppressing poor appearance and decrease in strength of the film, controlling whitening due to the imidization reaction, and improving light transmission.

The temperature rise may be continuous or stepwise, but it is preferable to raise the temperature continuously from the viewpoints of suppressing poor appearance and strength deterioration of the film and controlling whitening associated with the imidization reaction. Further, the temperature rising rate may be constant or may be changed in the middle of the above-mentioned entire temperature range.

The atmosphere at the time of temperature rise of imidization is preferably an inert gas atmosphere. The inert gas atmosphere is preferably a nitrogen atmosphere, preferably an oxygen concentration of 500 ppm or less, more preferably 200 ppm or less, and even more preferably 100 ppm or less. Heat treatment in the atmosphere can oxidize the film, causing it to color or reduce its performance.
However, when 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide are hydrogen atoms directly bonded to the aromatic ring, the influence of oxygen on the optical properties is small, and an inert gas atmosphere is not used. A polyimide having high light transmittance can be obtained.

The heating method for imidization is not particularly limited as long as the temperature can be raised at the above temperature, and for example, an oven, a heating furnace, infrared heating, electromagnetic induction heating or the like can be used.

Above all, it is more preferable to set the imidization ratio of the polyimide precursor to 50% or more before the stretching step. By setting the imidization ratio to 50% or more before the stretching step, even when stretching is performed after the step and then heating is performed at a higher temperature for a certain period of time to perform imidization, the appearance of the film may be poor. Whitening is suppressed. Above all, from the viewpoint of improving the surface hardness of the polyimide film, it is preferable to set the imidization ratio to 80% or more, further to 90% or more, and further to 100% in the imidization step before the stretching step. Is preferable. It is presumed that the surface hardness is improved by stretching after imidization because the rigid polymer chains are easily oriented.
The imidization rate can be measured by analyzing the spectrum by infrared measurement (IR) or the like.

In order to obtain the final polyimide film, it is preferable to proceed the reaction to 90% or more, further 95% or more, and further 100% of imidization.
In order to allow the reaction to proceed to 90% or more and even 100% of imidization, it is preferable to keep the temperature at the end temperature for a certain period of time, and the holding time is usually 1 minute to 180 minutes, further 5 minutes to 150 minutes. It is preferably a minute.

6. Stretching Step The production method of the present invention may include a stretching step of stretching at least one of the polyimide precursor coating film and the imidized coating film obtained by imidizing the polyimide precursor coating film. When the stretching step is provided, it is particularly preferable to include a step of stretching the coating film after imidization from the viewpoint of improving the surface hardness of the polyimide film.

In the production method of the present invention, it is preferable to carry out the step of stretching 101% or more and 10000% or less while heating at 80 ° C. or higher when the initial dimension before carrying out stretching is 100%.
The heating temperature during stretching is preferably in the range of the glass transition temperature of the polyimide or the polyimide precursor ± 50 ° C., and preferably in the range of the glass transition temperature ± 40 ° C. If the stretching temperature is too low, the film may not be deformed and sufficient orientation may not be induced. On the other hand, if the stretching temperature is too high, the orientation obtained by stretching may be relaxed by the temperature, and sufficient orientation may not be obtained.
The stretching step may be performed at the same time as the imidization step. Stretching the imidized coating film after imidization of 80% or more, further 90% or more, further 95% or more, particularly substantially 100% imidization improves the surface hardness of the polyimide film. It is preferable from the point of view.

The draw ratio of the polyimide film is preferably 101% or more and 10000% or less, and more preferably 101% or more and 500% or less. By stretching in the above range, the surface hardness of the obtained polyimide film can be further improved.

The method for fixing the polyimide film at the time of stretching is not particularly limited, and is selected according to the type of stretching device and the like. Further, the stretching method is not particularly limited, and it is possible to stretch while passing through a heating furnace by using a stretching device having a transporting device such as a tenter. The polyimide film may be stretched in only one direction (longitudinal stretching or lateral stretching), or may be stretched in two directions by simultaneous biaxial stretching, sequential biaxial stretching, diagonal stretching, or the like.

7. Polyimide film The polyimide film obtained by the production method of the present invention contains at least the polyimide obtained by imidizing the above-mentioned polyimide precursor, and further contains other components as long as the effect of the present invention is not impaired. Is also good. Examples of other components include those similar to the additives described in the above-mentioned polyimide precursor composition.

Since the polyimide film obtained by the production method of the present invention does not use a catalyst such as amine during imidization, it does not contain ammonium ions generated from the catalyst. Therefore, the polyimide film obtained by the production method of the present invention has suppressed deterioration of optical properties due to the influence of ammonium ions. Further, since the polyimide film obtained by the production method of the present invention is obtained by using the polyimide precursor composition in which the residual monomer is reduced, the coloring of the film due to the oxidation of the residual monomer is suppressed and the film is transparent. The sex has improved.
In the present invention, the term "not containing ammonium ions" means that the ammonium ion content per 1 g of the polyimide film is less than 0.01 μg. The ammonium ion content per 1 g of the polyimide film can be measured, for example, by eluting the ammonium ions in the polyimide film into water. Specifically, a test piece of a polyimide film weighing about 0.4 g is placed in a polypropylene bag, immersed in 50 mL of ultrapure water in the bag, and sealed with a heat sealer. It is placed in a water bath at 60 ° C. and allowed to stand for 1 hour or more to elute the ammonium ions in the polyimide film. The ion concentration of the obtained eluate is measured by an ion chromatograph (for example, Thermo Fisher Scientific Co., Ltd., ICS-3000), and the amount of ammonium ion per 1 g of the test piece is calculated.

The polyimide film obtained by the production method of the present invention is produced by heating imidizing the purified polyimide precursor by reducing the residual monomer in the polyimide precursor solution.
Contains polyimide, does not contain ammonium ions,
The total light transmittance measured according to JIS K7361-1 is 90% or more.
The haze value according to JIS K-7105 is 2.0 or less, and
A polyimide film having a yellowness of 5.0 or less calculated in accordance with JIS K7373-2006 can be easily obtained.

The polyimide film obtained by the production method of the present invention can have a total light transmittance of 90% or more as measured in accordance with JIS K7361-1, and in a more preferable embodiment, it can be 91% or more. can. Since the transmittance is high as described above, the transparency is improved and the material can be used as a substitute for glass.
The polyimide film obtained by the production method of the present invention preferably has a thickness of 5 μm or more and 100 μm or less, and has a total light transmittance of 90% or more, more preferably 91%, as measured in accordance with JIS K7361-1. The above is preferable.
Further, the polyimide film obtained by the production method of the present invention preferably has a total light transmittance of 90% or more, more preferably 91% or more, as measured in accordance with JIS K7361-1 at a thickness of 50 μm ± 5 μm. Is preferable.
The total light transmittance measured according to JIS K7361-1 can be measured by, for example, a haze meter (for example, HM150 manufactured by Murakami Color Technology Laboratory). From the measured value of the total light transmittance of a certain thickness, the converted value of the total light transmittance of different thickness can be obtained by Lambertbert's law, and it can be used.

Specifically, according to Lambert-Beer's law, the transmittance T is
Log ₁₀ (1 / T) = kcb
It is represented by (k = substance-specific constant, c = concentration, b = optical path length).
In the case of film transmittance, c is also a constant assuming that the density is constant even if the film thickness changes. Therefore, in the above equation, Log ₁₀ (1 / T) = fb using the constant f.
It can be expressed as (f = kc). Here, if the transmittance at a certain film thickness is known, the unique constant f of each substance can be obtained. Therefore, by substituting a constant unique to f and a target film thickness into b using the equation of T = 1/10 ^{f · b} , the transmittance at a desired film thickness can be obtained.

Further, the polyimide film obtained by the production method of the present invention preferably has a haze value based on JIS K-7105 of 2.0 or less, preferably 1.0 or less, from the viewpoint of light transmission. It is more preferably 0.5 or less, and even more preferably 0.5 or less. It is preferable that the haze value can be achieved when the thickness of the polyimide film is 5 μm or more and 100 μm or less.
Further, the polyimide film obtained by the production method of the present invention has a haze value of 2.0 or less, more preferably 1.0 or less, in accordance with JIS K-7105 at a thickness of 50 μm ± 5 μm. It is preferably 0.5 or less, and even more preferably 0.5 or less.
The haze value can be measured by a method according to JIS K-7105, and can be measured by, for example, a haze meter HM150 manufactured by Murakami Color Technology Laboratory.
From the measured value of the haze value of a certain thickness, the haze value of a different thickness is determined by the haze value at each wavelength measured at 5 nm intervals between 380 nm and 780 nm of a sample of a specific film thickness and the above method. The diffusion transmittance of each wavelength is calculated from the total light transmittance of each wavelength to be measured, and the conversion value of the diffusion transmittance at each wavelength having a different thickness is obtained according to Lambertvale's law as in the case of the above total light transmittance. The haze value can be calculated and used as the ratio of the diffuse transmittance to the total light transmittance.

Further, the polyimide film obtained by the production method of the present invention preferably has a yellowness (YI value) of 5.0 or less, preferably 3.0 or less, calculated in accordance with JIS K7373-2006. Is more preferable, and 2.0 or less is further preferable. Such low yellowness suppresses yellowish coloring, improves light transmission, and can be a substitute for glass.
The polyimide film obtained by the production method of the present invention preferably has a thickness of 5 μm or more and 100 μm or less and a yellowness (YI value) of 5.0 or less calculated in accordance with JIS K7373-2006. It is more preferably 0 or less, and further preferably 2.0 or less.
Further, the polyimide film obtained by the production method of the present invention preferably has a thickness of 50 μm ± 5 μm and a yellowness (YI value) of 5.0 or less calculated in accordance with the JIS K7373-2006. It is more preferably 3.0 or less, and further preferably 2.0 or less.
The yellowness (YI value) is based on JIS K7373-2006, and is spectrophotometrically measured according to JIS Z8722 using an ultraviolet-visible near-infrared spectrophotometer (for example, JASCO Corporation V-7100). It can be calculated based on the transmittance measured by the method.
From the measured value of the yellowness of a certain thickness, the yellowness of a different thickness is the above-mentioned total for each transmittance at each wavelength measured at 5 nm intervals between 380 nm and 780 nm of a sample of a specific film thickness. Similar to the light transmittance, the converted value of each transmittance at each wavelength having a different thickness can be obtained by Lambertvale's law, and can be calculated and used based on the converted value.

Examples of the polyimide contained in the polyimide film obtained by the production method of the present invention include a polyimide having a structure represented by the following general formula (1').

（一般式（１’）において、Ｒ^１、Ｒ^２及びｎは、前記一般式（１）と同様である。）

(In the general formula (1'), R ¹ , R ² and n are the same as those in the general formula (1).)

In the general formula (1'), suitable R ¹ , R ² and n are the same as those in the general formula (1).
Further, in the polyimide, the structure represented by the general formula (1') is preferably 95% or more, more preferably 98% or more, and 100% of the total number of repeating units of the polyimide. Is even more preferable.
The polyimide may have a structure different from the structure represented by the general formula (1') in a part thereof as long as the effect of the present invention is not impaired. Examples of the structure different from the structure represented by the general formula (1') include a polyamide structure. Examples of the polyamide structure that may be contained include a polyamide-imide structure containing a tricarboxylic acid residue such as trimellitic acid anhydride and a polyamide structure containing a dicarboxylic acid residue such as terephthalic acid.

The polyimide film obtained by the production method of the present invention preferably has a polyimide content of 50% by mass or more, more preferably 60% by mass or more, based on the total amount of the polyimide film. The upper limit of the content of the polyimide may be appropriately adjusted depending on the contained components.

Further, the polyimide is a polyimide containing an aromatic ring and in which 50% or more of hydrogen atoms bonded to carbon atoms contained in the polyimide are hydrogen atoms directly bonded to the aromatic ring. It is preferable from the viewpoint of improving the light transmission and the surface hardness. The ratio of the hydrogen atoms (number) directly bonded to the aromatic ring to the total hydrogen atoms (number) bonded to the carbon atoms contained in the polyimide is preferably 60% or more, more preferably 70% or more. Is preferable.
Here, the ratio of the hydrogen atoms (number) directly bonded to the aromatic ring to the total hydrogen atoms (number) bonded to the carbon atoms contained in the polyimide is the mass of the decomposition product of polyimide by high performance liquid chromatography or gas chromatograph. It can be determined using an analyzer and NMR. For example, the sample is decomposed with an alkaline aqueous solution or supercritical methanol, the obtained decomposition product is separated by high performance liquid chromatography, and the qualitative analysis of each separated peak is performed by a gas chromatograph mass spectrometer, NMR, etc. The ratio of hydrogen atoms (number) directly bonded to the aromatic ring can be determined from the total hydrogen atoms (number) contained in the polyimide by performing the test using high performance liquid chromatography and quantifying the amount.

Further, the polyimide contains an aromatic ring from the viewpoint of improving the light transmittance and the surface hardness of the polyimide film, and (i) a fluorine atom, (ii) an aliphatic ring, and (iii) an aromatic. It is preferable to include at least one selected from the group consisting of a structure in which group rings are linked to each other with a sulfonyl group or an alkylene group which may be substituted with fluorine.
Further, as the polyimide, a polyimide containing a fluorine atom is preferable from the viewpoint of light transmission and surface hardness of the polyimide film.

As a preferred embodiment, the ratio (F / C) of the number of fluorine atoms (F) to the number of carbon atoms (C) on the film surface measured by X-ray photoelectron spectroscopy of the polyimide film is 0.01 or more and 1 or less. It is preferably 0.05 or more and 0.8 or less.
Further, the ratio (F / N) of the number of fluorine atoms (F) to the number of nitrogen atoms (N) on the film surface measured by X-ray photoelectron spectroscopy of the polyimide film is preferably 0.1 or more and 20 or less. Further, it is preferably 0.5 or more and 15 or less.
Further, the ratio (F / Si) of the number of fluorine atoms (F) to the number of silicon atoms (Si) on the surface of the film as measured by X-ray photoelectron spectroscopy of the polyimide film is preferably 1 or more and 50 or less, and more preferably. It is preferably 3 or more and 30 or less.
Here, the above ratio measured by X-ray photoelectron spectroscopy (XPS) is determined from the value of the atomic% of each atom of the polyimide film measured using an X-ray photoelectron spectrometer (for example, Theta Probe of Thermo Scientific). be able to.

Further, the atomic% of the silicon atom (Si) on the film surface measured by X-ray photoelectron spectroscopy of the polyimide film obtained by the production method of the present invention is preferably 0.1 or more and 10 or less, and 0.2 or more and 5 or less. More preferred.
In the present invention, each atomic concentration of the polyimide film measured by X-ray photoelectron spectroscopy (XPS) can be measured using an X-ray photoelectron spectroscope (for example, Thetera Probe of Thermo Scientific).

Further, the glass transition temperature of the polyimide film obtained by the production method of the present invention is preferably 150 ° C. or higher, more preferably 200 ° C. or higher, from the viewpoint of heat resistance, and the baking temperature can be reduced. , 400 ° C or lower, and more preferably 380 ° C or lower. Further, the polyimide film obtained by the production method of the present invention preferably has one glass transition temperature in a temperature range of 150 ° C. or higher and 400 ° C. or lower.
The glass transition temperature is obtained from the peak temperature of the temperature-tan δ (tan δ = loss elastic modulus (E ″) / storage elastic modulus (E ′)) curve obtained by dynamic viscoelasticity measurement. The glass transition temperature of the polyimide film refers to the temperature of the peak at which the maximum value of the peak is the maximum when there are a plurality of peaks of the tan δ curve. As the dynamic viscoelasticity measurement, for example, the dynamic viscoelasticity measuring device RSA III (TA Instrument Japan Co., Ltd.) sets the measurement range to -150 ° C to 400 ° C, and raises the temperature at a frequency of 1 Hz. It can be performed at a speed of 5 ° C./min. Further, the sample width can be measured as 5 mm and the distance between chucks as 20 mm.
In the present invention, the peak of the tan δ curve has an inflection point which is a maximum value, and the peak width between the valleys of the peak is 3 ° C. or more, which is derived from the measurement of noise and the like. Small vertical fluctuations are not interpreted as the peak.

In addition, the polyimide film obtained by the manufacturing method of the present invention has a tensile elastic modulus at 25 ° C., which is measured by measuring a 15 mm × 40 mm test piece in accordance with JIS K7127 with a tensile speed of 10 mm / min and a chuck distance of 20 mm. It is preferably 1.8 GPa or more. Since the high tensile elastic modulus provides sufficient surface hardness as a protective film, the polyimide film obtained by the production method of the present invention can be suitably used as a surface material. The tensile elastic modulus is preferably 2.0 GPa or more, and more preferably 2.4 GPa or more. The preferable tensile elasticity represents a tetravalent group in which the polyimide contained in the polyimide film is a tetracarboxylic acid residue having an aromatic ring or an aliphatic ring in the general formula ( ¹ '). R ² represents a diamine group which is a diamine residue, and 10 mol% or more and 50 mol% or less of the total amount of R ² is a diamine residue having one or two silicon atoms in the main chain, and 50 mol. It is also easy to achieve when% or more and 90 mol% or less have a structure which is a diamine residue having no silicon atom and having an aromatic ring or an aliphatic ring.
The tensile elastic modulus was determined by cutting a test piece having a width of 15 mm and a length of 40 mm from a polyimide film using a tensile tester (for example, manufactured by Shimadzu Corporation: Autograph AG-X 1N, load cell: SBL-1KN) and at 25 ° C. The tensile speed can be measured as 10 mm / min, and the distance between chucks can be measured as 20 mm. The thickness of the polyimide film used to determine the tensile elastic modulus is preferably 50 μm ± 5 μm.

Further, in the polyimide film obtained by the production method of the present invention, since it is excellent in hygroscopicity and bending resistance under high humidity, when the static bending test is performed according to the following static bending test method. The internal angle measured in the test is preferably 120 ° or more, more preferably 125 ° or more, and even more preferably 130 ° or more. The preferable internal angle represents a tetravalent group in which the polyimide contained in the polyimide film is a tetracarboxylic ^acid residue having an aromatic ring or an aliphatic ring in the general formula ( ¹ '). Represents a diamine group which is a diamine residue, and 10 mol% or more and 50 mol% or less of the total amount of R ² is a diamine residue having one or two silicon atoms in the main chain, and 50 mol% or more. It is easy to achieve when 90 mol% or less has a structure which is a diamine residue having no silicon atom and having an aromatic ring or an aliphatic ring.
[Static bending test method]
A polyimide film test piece cut into a size of 15 mm × 40 mm is bent at the position of half of the long side, and a metal piece (100 mm × 30 mm × 6 mm) having a thickness of 6 mm is sandwiched between both ends of the long side of the test piece from the upper and lower surfaces. Arranged and fixed with tape so that the overlap margins on both ends of the test piece and the upper and lower surfaces of the metal piece are 10 mm each, sandwiched between glass plates (100 mm x 100 mm x 0.7 mm) from above and below. , The test piece is fixed in a bent state with an inner diameter of 6 mm. At that time, a dummy test piece is sandwiched between the metal piece and the glass plate where the test piece does not exist, and the glass plate is fixed with tape so as to be parallel to each other. The test piece fixed in the bent state in this way was allowed to stand for 24 hours in an environment of 60 ± 2 ° C. and 93 ± 2% relative humidity (RH), and then the glass plate and the fixing tape were removed. Release the force applied to the test piece. Then, one end of the test piece is fixed, and the internal angle of the test piece is measured 30 minutes after the force applied to the test piece is released.

Further, in the polyimide film obtained by the production method of the present invention, since it is excellent in hygroscopicity and bending resistance under high humidity, when the dynamic bending test is performed according to the following dynamic bending test method. The internal angle of the test piece is preferably 155 ° or more, and more preferably 160 ° or more. The preferable internal angle represents a tetravalent group in which the polyimide contained in the polyimide film is a tetracarboxylic ^acid residue having an aromatic ring or an aliphatic ring in the general formula ( ¹ '). Represents a diamine group which is a diamine residue, and 10 mol% or more and 50 mol% or less of the total amount of R ² is a diamine residue having one or two silicon atoms in the main chain, and 50 mol% or more. It is easy to achieve when 90 mol% or less has a structure which is a diamine residue having no silicon atom and having an aromatic ring or an aliphatic ring.
[Dynamic bending test method]
The test piece of the polyimide film cut out to a size of 20 mm × 100 mm is fixed to the endurance test system in a constant temperature and humidity chamber (manufactured by Yuasa System Equipment, planar body no-load U-shaped expansion and contraction test jig DMX-FS) with tape. .. The test piece was set so that the distance between both ends of the long side of the test piece in a bent state similar to the static bending test, that is, the bent state was 6 mm (fixed in a bent state with an inner diameter of 6 mm). Then, in an environment of 60 ± 2 ° C. and 93 ± 2% relative humidity (RH), bending is repeated 200,000 times at 90 times per minute.
Then, the test piece is removed, one end of the obtained test piece is fixed, and the internal angle of the test piece is measured 30 minutes after repeating bending 200,000 times.

Further, in the polyimide film obtained by the production method of the present invention, when the adhesion test is performed according to the following adhesion test method, the cured film does not peel off, so that the adhesion between the polyimide film and the hard coat layer does not occur. It is preferable from the viewpoint of property and the surface hardness of the laminated body in which the hard coat layer is laminated adjacent to the polyimide film. In the general formula (1'), the polyimide contained in the polyimide film represents a tetravalent group in which R ¹ is a tetracarboxylic acid residue having an aromatic ring or an aliphatic ring, and R ² is a diamine residue. Representing a certain divalent group, 10 mol% or more and 50 mol% or less of the total amount of R ² is a diamine residue having one or two silicon atoms in the main chain, and 50 mol% or more and 90 mol% or less is. , When the structure is a diamine residue having an aromatic ring or an aliphatic ring without having a silicon atom, the cured film may be peeled off when the adhesion test is performed according to the following adhesion test method. Hard to occur.
[Adhesion test method]
A composition for adhesion evaluation prepared by adding 10 parts by mass of 1-hydroxy-cyclohexyl-phenyl-ketone to 100 parts by mass of pentaerythritol triacrylate to a 40% by mass methyl isobutyl ketone solution of pentaerythritol triacrylate. A cured film having a thickness of 10 μm is formed by applying it on a test piece of a polyimide film cut into a size of 10 cm × 10 cm and irradiating it with ultraviolet rays at an exposure amount of 200 mJ / cm ² under a nitrogen stream to cure it. A cross-cut test based on JIS K 5600-5-6 is performed on the cured film, and after repeating the peeling operation with tape 5 times, the presence or absence of peeling of the cured film is observed.

In the polyimide film obtained by the production method of the present invention, the pencil hardness is preferably 2B or more, more preferably B or more, and even more preferably HB or more.
The pencil hardness of the polyimide film is determined by adjusting the humidity of the measurement sample for 2 hours under the conditions of a temperature of 25 ° C. and a relative humidity of 60%, and then using a test pencil specified by JIS-S-6006, JIS K5600-5-4. It can be performed by performing a pencil hardness test (0.98 N load) specified in (1999) on the surface of the film and evaluating the highest pencil hardness that does not damage the film. For example, a pencil scratch coating film hardness tester manufactured by Toyo Seiki Co., Ltd. can be used.

Further, the polyimide film obtained by the production method of the present invention preferably has a birefringence of 0.020 or less in the thickness direction at a wavelength of 590 nm. Since the optical distortion is reduced due to the small birefringence, it is possible to suppress the deterioration of the display quality of the display when the polyimide film is used as the surface material for the display. The birefringence index in the thickness direction at a wavelength of 590 nm is preferably smaller, preferably 0.015 or less, more preferably 0.010 or less, and even more preferably less than 0.008. ..
The birefringence in the thickness direction of the polyimide film obtained by the production method of the present invention at a wavelength of 590 nm can be obtained as follows.
First, the thickness direction retardation value (Rth) of the polyimide film is measured with light at 25 ° C. and a wavelength of 590 nm using a phase difference measuring device (for example, manufactured by Oji Measuring Instruments Co., Ltd., product name “KOBRA-WR”). do. For the thickness direction retardation value (Rth), the phase difference value incident at 0 degrees and the phase difference value incident at an angle of 40 degrees are measured, and the thickness direction retardation value Rth is calculated from these phase difference values. The retardation value of the oblique 40-degree incident is measured by injecting light having a wavelength of 590 nm onto the retardation film from a direction inclined by 40 degrees from the normal of the retardation film.
The birefringence in the thickness direction of the polyimide film can be obtained by substituting it into the formula: Rth / d. The d represents the film thickness (nm) of the polyimide film.
The thickness direction retardation value is nx for the refractive index in the slow-phase axial direction (the direction in which the refractive index is maximized in the in-plane direction of the film) in the in-plane direction of the film, and the phase-advancing axial direction (the film surface) in the film surface. When the refractive index in the inward direction (the direction in which the refractive index is minimized) is ny and the refractive index in the thickness direction of the film is nz, it is expressed as Rth [nm] = {(nx + ny) /2-nz} × d. be able to.

The thickness of the polyimide film obtained by the production method of the present invention may be appropriately selected depending on the intended use, but is preferably 1 μm or more, more preferably 5 μm or more, and further preferably 10 μm or more. preferable. On the other hand, it is preferably 200 μm or less, more preferably 150 μm or less, and further preferably 100 μm or less.
If the thickness is thin, the strength is lowered and the film is easily broken, and if the thickness is thick, the difference between the inner diameter and the outer diameter at the time of bending becomes large, and the load on the film becomes large, so that the bending resistance may decrease.

Further, the polyimide film obtained by the production method of the present invention may be subjected to surface treatment such as saponification treatment, glow discharge treatment, corona discharge treatment, ultraviolet treatment, and flame treatment.

The use of the polyimide film obtained by the production method of the present invention is not particularly limited, and for example, it can be used as a base material or a member in which a glass product such as a glass base material has been conventionally used.
For example, the polyimide film obtained by the production method of the present invention has suppressed coloring and improved transparency, and therefore can be suitably used as a surface material for a display. Further, since the polyimide film obtained by the manufacturing method of the present invention tends to improve bending resistance, as a display capable of dealing with curved surfaces, for example, a thin and bendable flexible type organic EL display, a smartphone, a wristwatch type terminal, etc. It can be suitably used for mobile terminals, display devices inside automobiles, flexible panels used for wristwatches, and the like. Further, the polyimide film obtained by the manufacturing method of the present invention is a member for an image display device such as a liquid crystal display device or an organic EL display device, a member for a touch panel, a flexible printed substrate, a solar cell panel such as a surface protective film or a substrate material. It can also be applied to members for optical waveguides, members for optical waveguides, and other semiconductor-related members.

II. Method for Producing Polyimide Precursor The method for producing the polyimide precursor of the present invention is as follows.
The process of preparing the polyimide precursor solution and
A step of reducing residual monomers in the polyimide precursor solution is included.

In the method for producing a polyimide precursor of the present invention, the step of preparing the polyimide precursor solution can be performed in the same manner as the step of preparing the polyimide precursor solution described in the above-described method for producing the polyimide film of the present invention.
Further, the step of reducing the residual monomer in the polyimide precursor solution can be performed in the same manner as the polyimide precursor purification step described in the above-described method for producing a polyimide film of the present invention.
Since the polyimide precursor obtained by the production method of the present invention has a reduced amount of residual monomers, the polyimide precursor is used in the production of the polyimide film to suppress the coloring of the polyimide film due to the oxidation of the residual monomers. be able to.

III. Method for Producing Polyimide Precursor Composition The method for producing the polyimide precursor composition of the present invention is as follows.
The process of preparing the polyimide precursor solution and
A step of obtaining a purified polyimide precursor by reducing residual monomers in the polyimide precursor solution, and
A step of preparing a polyimide precursor composition containing the purified polyimide precursor and an organic solvent is included.

Each of the steps included in the method for producing a polyimide precursor composition of the present invention can be carried out in the same manner as each step described in the above-mentioned method for producing a polyimide film of the present invention.
Since the polyimide precursor composition obtained by the production method of the present invention is obtained by redissolving the purified polyimide precursor, residual monomers are reduced and a catalyst such as amine is not contained. .. Therefore, by using the polyimide precursor composition obtained by the production method of the present invention for the production of the polyimide film to be thermally imidized, coloring is suppressed as described in the above-mentioned method for producing the polyimide of the present invention. It is possible to obtain a polyimide film having improved transparency and further improved dimensional stability, solvent resistance, moisture absorption resistance or moisture permeability resistance, and bending resistance.

IV. Manufacturing Method of Laminate The manufacturing method of the laminated body of the present invention includes a step of manufacturing a polyimide film by the above-mentioned manufacturing method of the present invention (hereinafter referred to as a polyimide film manufacturing step).
A step of forming a coating film of a composition for forming a hard coat layer containing at least one of a radically polymerizable compound and a cationically polymerizable compound on at least one surface of the polyimide film obtained by the above step (hereinafter, hard coat layer). (Referred to as a coating film forming process) and
A step of curing the coating film (hereinafter referred to as a coating film curing step for a hard coat layer) is included.

Since the method for producing the laminate of the present invention uses the polyimide film obtained by the above-mentioned production method of the present invention, the produced laminate has improved transparency and further has a hard coat layer, so that the surface hardness is increased. It is a better one.

1. 1. Polyimide film manufacturing process In the method for manufacturing a laminate of the present invention, the above-mentioned method for manufacturing a polyimide film of the present invention can be used in the step of manufacturing a polyimide film, and thus the description thereof is omitted here.

2. 2. Coating film forming step for hard coat layer In the method for producing a laminate of the present invention, a radically polymerizable compound and a cationically polymerizable compound are formed on at least one surface of the polyimide film obtained by the method for producing a polyimide film of the present invention. A coating film of a composition for forming a hard coat layer containing at least one type is formed.
The composition for forming a hard coat layer contains at least one of a radically polymerizable compound and a cationically polymerizable compound, and may further contain other components such as a polymerization initiator, a solvent and an additive, if necessary. good.

The radically polymerizable compound is a compound having a radically polymerizable group. The radically polymerizable group contained in the radically polymerizable compound may be any functional group capable of causing a radical polymerization reaction, and is not particularly limited, and examples thereof include a group containing a carbon-carbon unsaturated double bond. Specific examples thereof include a vinyl group and a (meth) acryloyl group. When the radically polymerizable compound has two or more radically polymerizable groups, these radically polymerizable groups may be the same or different from each other.

The number of radically polymerizable groups contained in one molecule of the radically polymerizable compound is preferably two or more, and more preferably three or more, from the viewpoint of improving the hardness of the hard coat layer.
As the radically polymerizable compound, a compound having a (meth) acryloyl group is preferable from the viewpoint of high reactivity, and further, from the viewpoint of adhesion between the polyimide film and the hard coat layer, light transmittance and surface hardness. From this point of view, a compound having two or more (meth) acryloyl groups in one molecule is preferable. For example, a compound called a polyfunctional acrylate monomer having 2 to 6 (meth) acryloyl groups in one molecule, or a molecule called urethane (meth) acrylate, polyester (meth) acrylate, or epoxy (meth) acrylate. Monomers having a number of (meth) acryloyl groups within and having a molecular weight of several hundred to several thousand can be preferably used.
In addition, in this specification, (meth) acryloyl represents each of acryloyl and methacryloyl, and (meth) acrylate represents each of acrylate and methacrylate.

Specific examples of the radically polymerizable compound include vinyl compounds such as divinylbenzene; ethylene glycol di (meth) acrylate, bisphenol A epoxy di (meth) acrylate, and 9,9-bis [4- (2-(2-(. Meta) acryloyloxyethoxy) phenyl] fluorene, alkylene oxide-modified bisphenol A di (meth) acrylate (for example, ethoxylated (ethylene oxide modified) bisphenol A di (meth) acrylate), trimethyl propantri (meth) acrylate, tri Methylol ethanetri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate , Polyacrylate polyacrylates such as dipentaerythritol hexa (meth) acrylates, diacrylates such as bisphenol A diglycidyl ether diacrylates, epoxy acrylates such as hexanediol diglycidyl ether diacrylates, hydroxyl groups such as polyisocinates and hydroxyethyl acrylates. Examples thereof include urethane acrylate obtained by the reaction of the contained acrylate.

The cationically polymerizable compound is a compound having a cationically polymerizable group. The cationically polymerizable group contained in the cationically polymerizable compound may be any functional group capable of causing a cationically polymerizable reaction, and is not particularly limited, and examples thereof include an epoxy group, an oxetanyl group, and a vinyl ether group. When the cationically polymerizable compound has two or more cationically polymerizable groups, the cationically polymerizable groups may be the same or different from each other.

The number of cationically polymerizable groups contained in one molecule of the cationically polymerizable compound is preferably two or more, and more preferably three or more, from the viewpoint of improving the hardness of the hard coat layer.
Further, as the cationically polymerizable compound, a compound having at least one epoxy group and an oxetanyl group as the cationically polymerizable group is preferable, and the point of adhesion between the polyimide film and the hard coat layer, the light transmittance and the surface thereof are preferable. From the viewpoint of hardness, a compound having at least one of an epoxy group and an oxetanyl group at least two in one molecule is more preferable. A cyclic ether group such as an epoxy group or an oxetanyl group is preferable because the shrinkage associated with the polymerization reaction is small. Further, among the cyclic ether groups, compounds having an epoxy group are easily available, compounds having various structures are easily available, the durability of the obtained hard coat layer is not adversely affected, and compatibility with radically polymerizable compounds is easily controlled. There is an advantage. Of the cyclic ether groups, the oxetanyl group has a higher degree of polymerization than the epoxy group and has low toxicity, and when the obtained hard coat layer is combined with a compound having an epoxy group, the cation in the coating film There are advantages such as accelerating the network formation rate obtained from the polymerizable compound and forming an independent network without leaving an unreacted monomer in the film even in a region mixed with the radically polymerizable compound.

Examples of the cationically polymerizable compound having an epoxy group include polyglycidyl ether of a polyhydric alcohol having an alicyclic ring, or a cyclohexene ring or cyclopentene ring-containing compound with an appropriate oxidizing agent such as hydrogen peroxide or peracid. Alicyclic epoxy resin obtained by epoxidation; polyglycidyl ether of aliphatic polyhydric alcohol or its alkylene oxide adduct, polyglycidyl ester of aliphatic long chain polybasic acid, homopolymer of glycidyl (meth) acrylate, An aliphatic epoxy resin such as a copolymer; a glycidyl ether produced by reacting bisphenols such as bisphenol A, bisphenol F and hydrogenated bisphenol A, or derivatives such as alkylene oxide adducts and caprolactone adducts thereof with epichlorohydrin. And novolak epoxy resin and the like, and examples thereof include glycidyl ether type epoxy resin derived from bisphenols.

Examples of the alicyclic epoxy resin include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (UVR-6105, UVR-6107, UVR-6110) and bis-3,4-epoxycyclohexylmethyl adipate. (UVR-6128) (The above is the trade name in parentheses and is manufactured by Dow Chemical Co., Ltd.).

Examples of the glycidyl ether type epoxy resin include sorbitol polyglycidyl ether (Denacol EX-611, Denacol EX-612, Denacol EX-614, Denacol EX-614B, Denacol EX-622) and polyglycerol polyglycidyl ether (Denacol EX). -512, Denacol EX-521), Pentaeryth Little Polyglycidyl Ether (Denacol EX-411), Diglycerol Polyglycidyl Ether (Denacol EX-421), Gglycerol Polyglycidyl Ether (Denacol EX-313, Denacol EX-314), Trimethylol Propanepolyglycidyl Ether (Denacol EX-321), Resoltinol Diglycidyl Ether (Denacol EX-201), Neopentyl Glycol Diglycidyl Ether (Denacol EX-211), 1,6 Hexanodiol Diglycidyl Ether (Denacol EX-) 212), Hydrodibisphenol A Diglycidyl Ether (Denacol EX-252), Ethylene Glycol Diglycidyl Ether (Denacol EX-810, Denacol EX-811), Polyethylene Glycol Diglycidyl Ether (Denacol EX-850, Denacol EX-851, Denacol EX-821), propylene glycol glycidyl ether (Denacol EX-911), polypropylene glycol glycidyl ether (Denacol EX-941, Denacol EX-920), allyl glycidyl ether (Denacol EX-111), 2-ethylhexyl glycidyl ether (Denacol). EX-121), phenylglycidyl ether (Denacol EX-141), phenol glycidyl ether (Denacol EX-145), butylphenyl glycidyl ether (Denacol EX-146), diglycidyl phthalate (Denacol EX-721), hydroquinone diglycidyl ether (Denacol EX-203), Diglycidyl terephthalate (Denacol EX-711), Glycidyl phthalimide (Denacol EX-731), Dibromophenyl glycidyl ether (Denacol EX-147), Dibromoneopentyl glycol diglycidyl ether (Denacol EX-221) (The above is the product name in parentheses and is made by Nagase Chemtex.)

Other commercially available epoxy resins include Epicoat 825, Epicoat 827, Epicoat 828, Epicoat 828EL, Epicoat 828XA, Epicoat 834, Epicoat 801 and Epicoat 801P, Epicoat 802, Epicoat 815, Epicoat 815XA, and Epicoat 816A. Epicoat 819, Epicoat 834X90, Epicoat 1001B80, Epicoat 1001X70, Epicoat 1001X75, Epicoat 1001T75, Epicoat 806, Epicoat 806P, Epicoat 807, Epicoat 152, Epicoat 154, Epicoat 871, Epicoat 191P, Epicoat YX310, Epicoat DX255, Epicoat YX8000 Etc. (The above product name is made by Japan Epoxy Resin).

Examples of the cationically polymerizable compound having an oxetanyl group include 3-ethyl-3-hydroxymethyloxetane (OXT-101) and 1,4-bis-3-ethyloxetane-3-ylmethoxymethylbenzene (OXT-121). , Bis-1-ethyl-3-oxetanylmethyl ether (OXT-221), 3-ethyl-3--2-ethylhexyloxymethyloxetane (OXT-212), 3-ethyl-3-phenoxymethyloxetane (OXT-) 211) (The product name in parentheses is the product name of Toa Synthetic), and the product names include Ethanacole EHO, Ethanacole OXBP, Ethanacole OXTP, and Ethanacole OXMA (trade name, manufactured by Ube Kosan).

As the polymerization initiator used in the present invention, a radical polymerization initiator, a cationic polymerization initiator, a radical, a cationic polymerization initiator and the like can be appropriately selected and used. These polymerization initiators are decomposed by at least one of light irradiation and heating to generate radicals or cations to promote radical polymerization and cation polymerization.

The radical polymerization initiator may be any kind as long as it can release a substance that initiates radical polymerization by at least one of light irradiation and heating. For example, examples of the photoradical polymerization initiator include imidazole derivatives, bisimidazole derivatives, N-arylglycine derivatives, organic azide compounds, titanocenes, aluminate complexes, organic peroxides, N-alkoxypyridinium salts, thioxanthone derivatives and the like. More specifically, 1,3-di (tert-butyldioxycarbonyl) benzophenone, 3,3', 4,4'-tetrakis (tert-butyldioxycarbonyl) benzophenone, 3-phenyl-5-. Isooxazolone, 2-mercaptobenzimidazole, bis (2,4,5-triphenyl) imidazole, 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name: Irgacure 651, Ciba Japan Co., Ltd.) , 1-Hydroxy-cyclohexyl-phenyl-ketone (trade name: Irgacure 184, manufactured by Ciba Japan Co., Ltd.), 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butane-1- On (trade name: Irgacure 369, manufactured by Ciba Japan Co., Ltd.), bis (η5-2,4-cyclopentadiene-1-yl) -bis (2,6-difluoro-3- (1H-pyrrole-1-yl) ) -Phenyl) Titanium) (trade name: Irgacure 784, manufactured by Ciba Japan Co., Ltd.), etc., but is not limited thereto.

In addition to the above, commercially available products can be used, specifically, Irgacure 907, Irgacure 379, Irgacure 819, Irgacure 127, Irgacure 500, Irgacure 754, Irgacure 250, Irgacure 1800, Irgacure 1870 manufactured by Ciba Japan Co., Ltd. , Irgacure OXE01, DAROCUR TPO, DAROCUR1173, Japan Siber Hegner Co., Ltd. of SpeedcureMBB, SpeedcurePBZ, SpeedcureITX, SpeedcureCTX, SpeedcureEDB, Esacure ONE, Esacure KIP150, Esacure KTO46, manufactured by Nippon Kayaku Co., of (stock) KAYACURE DETX-S, KAYACURE CTX , KAYACURE BMS, KAYACURE DMBI and the like.

Further, the cationic polymerization initiator may be any material as long as it can release a substance that initiates cationic polymerization by at least one of light irradiation and heating. Examples of the cationic polymerization initiator include sulfonic acid ester, imide sulfonate, dialkyl-4-hydroxysulfonium salt, aryl sulfonic acid-p-nitrobenzyl ester, silanol-aluminum complex, (η ⁶ -benzene) (η ⁵ -cyclopentadi). Enyl) iron (II) and the like are exemplified, and more specific examples thereof include, but are not limited to, benzointosilate, 2,5-dinitrobenzyltosylate, N-tosiphthalateimide and the like.

Examples of the agent used as both the radical polymerization initiator and the cationic polymerization initiator include aromatic iodonium salts, aromatic sulfonium salts, aromatic diazonium salts, aromatic phosphonium salts, triazine compounds, iron arene complexes and the like. More specifically, chloride, bromide, borofluoride salt, hexafluorophosphate salt, hexafluoro of iodonium such as diphenyl iodonium, ditril iodonium, bis (p-tert-butylphenyl) iodonium, and bis (p-chlorophenyl) iodonium. Iodonium salt such as antimonate salt, chloride, bromide, borofluoride salt, hexafluorophosphate salt, hexafluoroantimonate of sulfonium such as triphenylsulfonium, 4-tert-butyltriphenylsulfonium, tris (4-methylphenyl) sulfonium. Sulfonium salts such as salts, 2,4,6-tris (trichloromethyl) -1,3,5-triazine, 2-phenyl-4,6-bis (trichloromethyl) -1,3,5-triazine, 2- Examples thereof include, but are not limited to, 2,4,6-substituted-1,3,5-triazine compounds such as methyl-4,6-bis (trichloromethyl) -1,3,5-triazine. ..

The solvent used in the present invention can be appropriately selected from known solvents. Examples of the additive include antistatic agents, antiglare agents, antifouling agents, inorganic or organic fine particles for improving hardness, leveling agents, various sensitizers and the like.

As a method for forming the coating film of the hard coat layer forming composition on at least one surface of the polyimide film, for example, the hard coat layer forming composition is known on at least one surface of the polyimide film. Examples thereof include a method of coating by a coating means.
The coating means is not particularly limited as long as it can be applied with a desired film thickness, and examples thereof include the same means as those for applying the polyimide precursor composition to the support.
The coating film of the composition for forming the hard coat layer may be formed on only one surface of the polyimide film, or may be formed on both surfaces of the polyimide film.

The solvent is removed by drying the coating film of the curable composition for the hard coat layer, if necessary. Examples of the drying method include vacuum drying, heat drying, and a method of combining these drying methods. When drying at normal pressure, it is preferable to dry at 30 ° C. or higher and 110 ° C. or lower.

3. 3. Curing step of coating film for hard coat layer The radical polymerizable compound and cationically polymerizable compound contained in the curable composition are applied to the coating film to which the curable composition for hard coat layer is applied and dried as necessary. By curing the coating film by at least one of light irradiation and heating depending on the polymerizable group, at least one polymer of a radical polymerizable compound and a cationically polymerizable compound is applied to at least one surface of the polyimide film. The contained hard coat layer can be formed.

Ultraviolet rays, visible light, electron beams, ionizing radiation and the like are mainly used for light irradiation. In the case of ultraviolet curing, ultraviolet rays emitted from light rays such as ultra-high pressure mercury lamps, high pressure mercury lamps, low pressure mercury lamps, carbon arcs, xenon arcs, and metal halide lamps are used. The irradiation amount of the energy radiation source is about 50 to 5000 mJ / cm ² as the integrated exposure amount at the ultraviolet wavelength of 365 nm.
When heating, it is usually treated at a temperature of 40 ° C. or higher and 120 ° C. or lower. Further, the reaction may be carried out by leaving it at room temperature (25 ° C.) for 24 hours or more.

Further, the method for producing a laminated body of the present invention comprises, for example, a step of further forming another layer such as a gel containing urethane or acrylic resin, and a known surface treatment within a range not impairing the effect of the present invention. It may include a step of applying.

4. Laminates The laminate obtained by the production method of the present invention is a hard coat layer containing the polyimide film obtained by the above-mentioned production method of the present invention and at least one polymer of a radically polymerizable compound and a cationically polymerizable compound. Is a laminated body located adjacent to each other.
The laminate obtained by the production method of the present invention may be one in which the hard coat layer is laminated adjacent to only one surface of the polyimide film, or the hard coat layer may be laminated on both sides of the polyimide film. May be laminated adjacent to each other.
Further, the hard coat layer may be provided with functions such as antireflection property and antiglare property. The function can be imparted, for example, by subjecting the hard coat layer to a known surface treatment or by incorporating an additive such as inorganic or organic fine particles.
Further, the laminate obtained by the production method of the present invention has, in addition to the polyimide film and the hard coat layer, other layers such as a gel containing urethane, acrylic resin, etc., as long as the effects of the present invention are not impaired. May be laminated.

The overall thickness of the laminate obtained by the production method of the present invention may be appropriately selected depending on the intended use, but is preferably 10 μm or more, and more preferably 40 μm or more from the viewpoint of strength. On the other hand, from the viewpoint of bending resistance, it is preferably 300 μm or less, and more preferably 250 μm or less.
Further, in the laminated body of the present invention, the thickness of each hardcoat layer may be appropriately selected depending on the intended use, but is preferably 2 μm or more and 80 μm or less, and more preferably 3 μm or more and 50 μm or less. Further, from the viewpoint of curl prevention, a hard coat layer may be formed on both sides of the polyimide film.

In the laminate obtained by the production method of the present invention, the pencil hardness of the surface on the hard coat layer side is preferably H or more, more preferably 2H or more, and even more preferably 3H or more.
The pencil hardness of the laminate of the present invention can be measured in the same manner as the pencil hardness of the polyimide film.

The laminate obtained by the production method of the present invention preferably has a total light transmittance of 85% or more, more preferably 88% or more, and further more than 90, as measured in accordance with JIS K7361-1. % Or more is preferable. Since the transmittance is high as described above, the transparency is improved and the material can be used as a substitute for glass.
The total light transmittance of the laminate obtained by the production method of the present invention can be measured in the same manner as the total light transmittance measured according to JIS K7361-1 of the polyimide film.

The laminate obtained by the production method of the present invention preferably has a yellowness (YI value) calculated in accordance with JIS K7373-2006 of 5.0 or less, and more preferably 3.0 or less. It is preferably 2.0 or less, and even more preferably 2.0 or less.
The yellowness (YI value) of the laminate obtained by the production method of the present invention can be measured in the same manner as the yellowness (YI value) calculated in accordance with JIS K7373-2006 of the polyimide film. ..

The haze value of the laminate obtained by the production method of the present invention in accordance with JIS K-7105 is preferably 5.0 or less, more preferably 2.0 or less, from the viewpoint of light transmission. It is more preferably 1.0 or less.
The haze value of the laminate obtained by the production method of the present invention according to JIS K-7105 can be measured in the same manner as the haze value of the polyimide film.

The birefringence in the thickness direction of the laminate obtained by the production method of the present invention at a wavelength of 590 nm is preferably 0.020 or less, preferably 0.015 or less, and further 0.010 or less. Is preferable, and more preferably less than 0.008.
The birefringence of the laminate obtained by the production method of the present invention can be measured in the same manner as the birefringence in the thickness direction of the polyimide film at a wavelength of 590 nm.

The use of the laminate obtained by the manufacturing method of the present invention is not particularly limited, and for example, it can be used in the same manner as the use of the polyimide film obtained by the manufacturing method of the present invention described above.

V. Method for Manufacturing Surface Material for Display The method for manufacturing a surface material for display of the present invention is a step of manufacturing a polyimide film by the above-mentioned manufacturing method of the present invention, or a step of manufacturing a laminate by the above-mentioned manufacturing method of the present invention. including. That is, the surface material for a display obtained by the manufacturing method of the present invention is a polyimide film obtained by the manufacturing method of the present invention described above, or a laminate obtained by the manufacturing method of the present invention described above.

The display surface material obtained by the manufacturing method of the present invention is arranged and used so as to be located on the surface of various displays. The surface material for a display obtained by the manufacturing method of the present invention has improved transparency, similar to the polyimide film obtained by the manufacturing method of the present invention and the laminate obtained by the manufacturing method of the present invention. Further, since it is easy to improve bending resistance, it can be suitably used for a flexible display.

The surface material for a display obtained by the manufacturing method of the present invention can be used for various known displays, and is not particularly limited. For example, the display described in the application of the polyimide film obtained by the manufacturing method of the present invention and the like. Can be used for.

When the surface material for a display obtained by the manufacturing method of the present invention is a laminate obtained by the manufacturing method of the present invention, the outermost surface after being arranged on the surface of the display is the surface on the polyimide film side. It may be the surface on the hard coat layer side, but it is preferable to arrange the surface material for a display of the present invention so that the surface on the hard coat layer side is the surface. Further, the surface material for a display obtained by the production method of the present invention may have a fingerprint adhesion prevention layer on the outermost surface.

Further, the method of arranging the surface material for a display obtained by the manufacturing method of the present invention on the surface of a display is not particularly limited, and examples thereof include a method via an adhesive layer. As the adhesive layer, a conventionally known adhesive layer that can be used for adhering a surface material for a display can be used.

[Evaluation methods]
<Weight average molecular weight of polyimide precursor>
For the weight average molecular weight of the polyimide precursor, the polyimide precursor was prepared as an N-methylpyrrolidone (NMP) solution having a concentration of 0.5% by weight, and a 10 mmol% LiBr-NMP solution having a water content of 500 ppm or less was used as a developing solvent. Using an apparatus (HLC-8120 manufactured by Tosoh, column used: GPC LF-804 manufactured by SHODEX), measurement was performed under the conditions of a sample injection amount of 50 μL, a solvent flow rate of 0.5 mL / min, and 40 ° C., and polystyrene having the same concentration as the sample. The weight average molecular weight was determined based on the standard sample.
<Viscosity of polyimide precursor solution>
The viscosity of the polyimide precursor solution was measured using a viscometer (for example, TVE-22HT, Toki Sangyo Co., Ltd.) at 25 ° C. with a sample volume of 0.8 ml.

<Glass transition temperature>
Using the dynamic viscoelastic modulus measuring device RSA III (TA Instruments Japan Co., Ltd.), the measurement range is -150 ° C to 400 ° C, the frequency is 1 Hz, the temperature rise rate is 5 ° C / min, and the sample width is set. Dynamic viscoelastic measurement was performed with 5 mm and a chuck distance of 20 mm, and the glass transition temperature (Tg) was obtained from the peak temperature of tanδ (tanδ = loss elastic modulus (E ″) / storage elastic modulus (E ′)). rice field.

<Ammonium ion content>
The ammonium ion content in the polyimide film was determined as follows. A test piece of a polyimide film weighing about 0.4 g cut out to a weight of 5 cm × 5 cm was placed in a polypropylene bag, immersed in 50 mL of ultrapure water in the bag, and sealed with a heat sealer. By placing it in a water bath at 60 ° C. and allowing it to stand for 1 hour or more, ammonium ions in the polyimide film are eluted, and the ion concentration of the obtained eluate is measured by ion chromatograph (Thermo Fisher Scientific Co., Ltd.). The amount of ammonium ion per 1 g of the polyimide film was calculated by measuring with ICS-3000). The detection limit of ammonium ions in the eluate is 0.1 ppb.

<Total light transmittance>
It was measured by a haze meter (HM150 manufactured by Murakami Color Technology Research Institute) in accordance with JIS K7361-1.

<YI value (yellowness)>
The YI value also includes the transmittance measured by the spectrophotometric method specified in JIS Z8720 using an ultraviolet-visible near-infrared spectrophotometer (JASCO Corporation V-7100) in accordance with JIS K7373-2006. It was calculated to.

<Haze value>
It was measured by a haze meter (HM150 manufactured by Murakami Color Technology Research Institute) in accordance with JIS K-7105.

(Example 1)
(1) Synthesis of polyimide precursor solution In a 500 ml separable flask, 302.0 g of dehydrated dimethylacetamide and 2.49 g (10 mmol) of 1,3-bis (3-aminopropyl) tetramethyldisiloxane (AprTMOS). ), To a place where the solution temperature was controlled to 30 ° C, 2.22 g (5 mmol) of 4,4'-(hexafluoroisopropyridene) diphthalic acid anhydride (6FDA) was added, and the temperature rise was 2 ° C. It was gradually added so as to be as follows, and stirred with a mechanical stirrer for 4 hours. 28.8 g (90 mmol) of 2,2'-bis (trifluoromethyl) benzidine (TFMB) was added thereto, and after confirming that the solution was completely dissolved, 4,4'-(hexafluoroisopropyridene) diphthalic acid was added. 42.0 g (94.5 mmol) of anhydride (6FDA) was gradually added in several portions so that the temperature rise was 2 ° C. or lower to synthesize a polyimide precursor solution 1 in which the polyimide precursor 1 was dissolved. The molar ratio of TFMB used for polyimide precursor 1 to AprTMOS was 90:10. The viscosity of the polyimide precursor solution 1 (solid content 20% by weight) at 25 ° C. was 40150 cps, and the weight average molecular weight of the polyimide precursor 1 measured by GPC was 253000.

(2) Purification of Polyimide Precursor 5 g of the obtained polyimide precursor solution 1 (solid content 20% by weight) was diluted with 20 g of a solvent (dimethylacetamide). 100 ml of water was placed in a beaker, the mixture was stirred with a magnetic stirrer, and the diluted polyimide precursor solution 1 was added dropwise thereto at 2.5 g / min to precipitate the polyimide precursor 1. The precipitated polyimide precursor 1 was collected by filtering and washing with 10 ml of water.
Using a solution (solid content 4% by mass) in which the recovered polyimide precursor 1 was dissolved in dimethylacetamide, the polyimide precursor 1 was precipitated by the same method as described above, and the operation of recovery was repeated twice, and the white color was obtained. A fibrous purified polyimide precursor 1 was obtained.

(3) Preparation of Polyimide Precursor Composition The polyimide precursor 1 obtained by repeating the operation of precipitation and recovery three times in total is dissolved in dimethylacetamide so as to have a solid content of 25% by weight, and the polyimide precursor is prepared. Composition 1 was obtained.

(4) Preparation of Polyimide Film The polyimide precursor composition 1 was applied onto glass and dried in a circulation oven at 120 ° C. for 10 minutes. Then, the temperature was raised to 330 ° C. at a heating rate of 10 ° C./min under a nitrogen stream (oxygen concentration of 100 ppm or less), maintained at 330 ° C. for 1 hour, and then cooled to room temperature. It was peeled off from the glass to obtain the polyimide film of Example 1. When measured using the obtained polyimide film, the glass transition temperature of the polyimide was 312 ° C.

(Comparative Example 1)
In Example 1, the unpurified polyimide precursor solution 1 was used instead of the polyimide precursor composition 1 when the polyimide film was produced without purifying the polyimide precursor and preparing the polyimide precursor composition. A polyimide film of Comparative Example 1 was obtained in the same manner as in Example 1 except that it was used.

(Comparative Example 2)
In a 500 ml separable flask, put 302.0 g of dehydrated dimethylacetamide, 44.22 g (99.5 mmol) of 4,4'-(hexafluoroisopropyridene) diphthalic anhydride (6FDA), and 1,3-bis. 2.49 g (10 mmol) of (3-aminopropyl) tetramethyldisiloxane (AprTMOS) and 28.8 g (90 mmol) of 2,2'-bis (trifluoromethyl) benzidine (TFMB) were added. Subsequently, it was heated to 120 ° C. and 40 g of pyridine was added. Subsequently, 50 g of trifluoroacetic anhydride was added, and the mixture was stirred at 150 ° C. for 8 hours to synthesize a comparative polyimide resin solution A in which the comparative polyimide resin A was dissolved. The molar ratio of TFMB and AprTMOS used in the comparative polyimide resin A was 90:10.

5 g of the obtained comparative polyimide resin solution A (solid content 20% by weight) was diluted with 20 g of a solvent (dimethylacetamide). 100 ml of water was placed in a beaker, the mixture was stirred with a magnetic stirrer, and the diluted comparative polyimide resin solution A was added dropwise at 2.5 g / min to precipitate the comparative polyimide resin A. The precipitated comparative polyimide resin A was filtered and then recovered by washing with 10 ml of water. Using a solution (solid content 4% by mass) in which the recovered comparative polyimide resin A was dissolved in dimethylacetamide, the comparative polyimide resin A was precipitated by the same method as described above, and the operation of recovery was repeated twice, and the white color was obtained. A powdery purified comparative polyimide resin A was obtained.

The comparative polyimide resin A obtained by repeating the operation of precipitation and recovery three times in total was dissolved in dimethylacetamide so as to have a solid content of 25% by weight to obtain a comparative polyimide resin composition A.

The comparative polyimide resin composition A is applied onto glass, placed in an oven at 80 ° C., heated to 200 ° C. at a heating rate of 10 ° C./min under a nitrogen stream (oxygen concentration of 100 ppm or less), and at 200 ° C. After holding for 10 minutes, it was cooled to room temperature. It was peeled off from the glass to obtain a polyimide film of Comparative Example 2.

(Comparative Example 3)
Using the comparative polyimide resin solution A obtained by the same method as in Comparative Example 2, the comparative polyimide resin obtained by repeating the operation of precipitating and recovering the comparative polyimide resin A by the same method as in Comparative Example 2 a total of 6 times. A'was dissolved in dimethylacetamide so as to have a solid content of 25% by weight to obtain a comparative polyimide resin composition A'.
In Comparative Example 2, the polyimide film of Comparative Example 3 was obtained in the same manner as in Comparative Example 2 except that the comparative polyimide resin composition A'was used instead of the comparative polyimide resin composition A.

Each of the polyimide films obtained in Example 1 and Comparative Examples 1 to 3 was evaluated using the above evaluation method. The evaluation results are shown in Table 1. When the ammonium ion content is less than the detection limit value, the ammonium ion content per 1 g of the polyimide film is less than 0.01 μg.

From Table 1, the polyimide film of Example 1 obtained by the production method of the present invention does not contain ammonium ions, has a small YI value and haze, has a high total light transmittance, and is suppressed in coloring. The transparency was improved.
In Comparative Example 1, since the polyimide precursor was not purified, the YI value was higher and the yellowness was stronger than that of the polyimide film of Example 1.
In Comparative Examples 2 and 3, since the polyimide film was produced by chemical imidization using a catalyst, the polyimide film contained ammonium ions, had a higher YI value and haze than the polyimide film of Example 1, and had a total light transmittance. Was low.

In addition, the following evaluations were performed on each of the polyimide films obtained in Example 1 and Comparative Examples 1 and 2.

<Static bending test>
Hereinafter, the method of the static bending test will be described with reference to FIG.
The test piece 1 of the polyimide film cut out to 15 mm × 40 mm is bent at the position of half of the long side, and the metal pieces 2 (100 mm × 30 mm × 6 mm) having a thickness of 6 mm at both ends of the long side of the test piece 1 are sandwiched from the upper and lower surfaces. The pieces were arranged so as to be sewn, and fixed with tape so that the overlap margins between both ends of the test piece 1 and the upper and lower surfaces of the metal piece 2 were 10 mm each. The metal piece 2 to which the test piece 1 was fixed was sandwiched between glass plates (100 mm × 100 mm × 0.7 mm) 3a and 3b from above and below, and the test piece 1 was fixed in a bent state with an inner diameter of 6 mm. At that time, dummy test pieces 4a and 4b were sandwiched between the metal pieces 2 and the portion where the test piece 1 was not provided, and fixed with tape so that the glass plates 3a and 3b were parallel to each other.
The test piece fixed in the bent state in this way is allowed to stand for 24 hours in an environment of 60 ± 2 ° C. and 93 ± 2% relative humidity (RH), and then the glass plate and the tape for fixing the test piece are removed. , Released the force on the test piece. Then, one end of the test piece was fixed, and the internal angle of the test piece was measured 30 minutes after releasing the force applied to the test piece. The larger the angle of the internal angle, the better the bending resistance. If the film is completely restored unaffected by the static bending test, the internal angle will be 180 °. Further, since the static bending test is performed under high humidity of 60 ± 2 ° C. and 93 ± 2% relative humidity (RH), the better the hygroscopicity, the larger the angle of the internal angle. If the hygroscopicity is poor, the film absorbs moisture, which deteriorates the bending resistance of the film and reduces the angle of the internal angle.
The internal angles of each polyimide film were 135 ° in Example 1, 130 ° in Comparative Example 1, and 120 ° in Comparative Example 2.

<Dimensional stability>
A test piece of a polyimide film cut into a size of 5 cm × 5 cm was fired in an oven at 300 ° C. for 30 minutes, and changes in dimensions before and after firing were evaluated. The polyimide films of Example 1 and Comparative Example 1 had no change in dimensions, and the polyimide films of Comparative Example 2 had changes in dimensions.

<Solvent resistance>
A test piece of a polyimide film cut into a size of 5 cm × 5 cm was immersed in N-methyl-2-pyrrolidone (NMP) for 5 hours, and then visually observed whether the polyimide film changed. The polyimide films of Example 1 and Comparative Example 1 had only slight changes, and the polyimide films of Comparative Example 2 had changes such as distortion.

From the static bending test and the evaluation results of the dimensional stability and the solvent resistance, it was clarified that the polyimide film of Example 1 had improved hygroscopicity, dimensional stability and solvent resistance. Since thermal imidization was performed, it is considered that these properties were improved as compared with the case where chemical imidization was performed.

Moreover, as a result of evaluating the pencil hardness of the polyimide film obtained in Example 1 by the following method, it was HB.
<Pencil hardness>
After adjusting the humidity of the measurement sample for 2 hours under the conditions of a temperature of 25 ° C and a relative humidity of 60%, use a pencil scratch coating hardness tester manufactured by Toyo Seiki Co., Ltd. using a test pencil specified by JIS-S-6006. The pencil hardness test (0.98N load) specified in JIS K5600-5-4 (1999) was performed on the surface of the film to evaluate the highest pencil hardness that did not damage the film.

[Preparation of laminated body]
To a 40 wt% methyl isobutyl ketone solution of pentaerythritol triacrylate, 10 parts by weight of 1-hydroxy-cyclohexyl-phenyl-ketone (BASF, Irgacure 184) was added to 100 parts by weight of pentaerythritol triacrylate to make a hard product. A composition for forming a coat layer was prepared.
The polyimide film obtained in Example 1 was cut into a size of 10 cm × 10 cm, the composition for forming a hard coat layer was applied to the surface of the cut polyimide film, and ultraviolet rays were irradiated at an exposure amount of 200 mJ / cm ² under a nitrogen stream. It was cured to form a hard coat layer which is a cured film having a thickness of 10 μm, and a laminated body was prepared.
The hardness of the pencil hardness of the surface of the obtained laminate on the hardcourt layer side was evaluated by the same method as that of the polyimide film, and the result was 3H.

Claims (10)

A step of preparing a polyimide precursor solution containing a polyimide precursor represented by the following general formula (1), and
A step of obtaining a purified polyimide precursor by reducing residual monomers in the polyimide precursor solution, and
A step of preparing a polyimide precursor composition containing the purified polyimide precursor and an organic solvent, and
A step of applying the polyimide precursor composition to a support to form a polyimide precursor coating film, and a step of forming the polyimide precursor coating film.
A method for producing a polyimide film, which comprises a step of imidizing the polyimide precursor by heating the polyimide precursor coating film.

(In the general formula (1), R ¹ represents a tetravalent group which is a tetracarboxylic acid residue, and R ² represents a divalent group which is a diamine residue, and a diamine containing a silicon atom in the main chain. Includes residues. N represents the number of repeating units.) The step of obtaining the purified polyimide precursor is
The method for producing a polyimide film according to claim 1, which comprises a step of recovering the polyimide precursor by dropping the polyimide precursor solution into a poor solvent to precipitate the polyimide precursor. The polyimide precursor represented by the general formula (1) is
R in the general formula (1) ¹ And R ² When the total of the above is 100 mol%, the total of the tetracarboxylic acid residue having an aromatic ring and a fluorine atom and the diamine residue having an aromatic ring and a fluorine atom is 50 mol% or more.
R in the general formula (1) ² When the total of 100 mol% is taken, the diamine residue having no silicon atom and having an aromatic ring is 50 mol% or more and 90 mol% or less, and one or two silicon atoms are contained in the main chain. The method for producing a polyimide film according to claim 1 or 2, wherein the diamine residue is 10 mol% or more and 50 mol% or less. The polyimide film
Contains polyimide, does not contain ammonium ions,
The total light transmittance measured according to JIS K7361-1 is 90% or more.
The haze value according to JIS K-7105 is 2.0 or less, and
The method for producing a polyimide film according to any one of claims 1 to 3 , wherein the yellowness calculated in accordance with JIS K7373-2006 is 5.0 or less. A step of preparing a polyimide precursor solution containing a polyimide precursor represented by the following general formula (1), and
A method for producing a polyimide precursor, which comprises a step of reducing residual monomers in the polyimide precursor solution.

(In the general formula (1), R ¹ represents a tetravalent group which is a tetracarboxylic acid residue, and R ² represents a divalent group which is a diamine residue, and a diamine containing a silicon atom in the main chain. Includes residues. N represents the number of repeating units.) The step of reducing the residual monomer is
The method for producing a polyimide precursor according to claim 5 , which comprises a step of recovering the polyimide precursor by dropping the polyimide precursor solution into a poor solvent to precipitate the polyimide precursor. The polyimide precursor represented by the general formula (1) is
R in the general formula (1) ¹ And R ² When the total of the above is 100 mol%, the total of the tetracarboxylic acid residue having an aromatic ring and a fluorine atom and the diamine residue having an aromatic ring and a fluorine atom is 50 mol% or more.
R in the general formula (1) ² When the total of 100 mol% is taken, the diamine residue having no silicon atom and having an aromatic ring is 50 mol% or more and 90 mol% or less, and one or two silicon atoms are contained in the main chain. The method for producing a polyimide precursor according to claim 5 or 6, wherein the diamine residue is 10 mol% or more and 50 mol% or less. A step of manufacturing a polyimide film by the manufacturing method according to any one of claims 1 to 4 .
A step of forming a coating film of a composition for forming a hard coat layer containing at least one of a radically polymerizable compound and a cationically polymerizable compound on at least one surface of the polyimide film obtained by the above step.
A method for producing a laminate including the step of curing the coating film. The radically polymerizable compound is a compound having two or more (meth) acryloyl groups in one molecule, and the cationically polymerizable compound is a compound having at least one of an epoxy group and an oxetanyl group in one molecule. The method for producing a laminate according to claim 8 . A surface for a display including a step of manufacturing a polyimide film by the manufacturing method according to any one of claims 1 to 4 or a step of manufacturing a laminate by the manufacturing method according to claim 8 or 9 . Material manufacturing method.

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