JP2018065993A - Method for producing polyimide film, method for producing polyimide precursor, method for manufacturing laminate, and method for manufacturing surface material for display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide film which suppresses coloring and has improved transparency.SOLUTION: A method for producing the polyimide film includes the steps of: preparing a polyimide precursor solution; reducing residual monomers in the polyimide precursor solution to obtain a purified polyimide precursor; preparing a polyimide precursor composition containing the purified polyimide precursor and an organic solvent; applying the polyimide precursor composition to a support to form a polyimide precursor coating film; and heating the polyimide precursor coating film to imidize the polyimide precursor.SELECTED DRAWING: None

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 of an aromatic tetracarboxylic acid anhydride and an aromatic diamine to a dehydration ring-closing reaction (imidation reaction). . However, since polyimide resins generally show yellow or brown coloration, it has been difficult to use them in fields that require transparency, such as display applications and optical applications. Therefore, it has been studied to apply a polyimide having improved transparency to a display member. For example, Patent Document 1 discloses 1,2,4,5-cyclohexanetetracarboxylic acid, 1,2,4,5-cyclohexanetetracarboxylic acid dicarboxylic 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 compound selected from compounds having at least one phenylene group and isopropylidene group represented by a specific formula A polyimide resin obtained by reacting with an imino forming compound is disclosed, and is described as being suitable for a substrate material such as a flat panel display or a mobile phone device.

  Also, imidization methods include 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 reducing 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 excellent in heat resistance while maintaining light transmittance. ing.

JP 2006-199945 A JP 2016-27146 A JP 2014-172978 A

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 has attracted particular attention in the electronics field. Above all, transparent polyimide film with improved transparency is expected to be applied to liquid crystal displays and organic EL displays as a substitute for glass, and developed with the aim of applying it to flexible devices that take advantage of the properties of resin films. Is underway.
However, the polyimide film produced by chemical imidation has a problem that it is difficult to completely remove ammonium ions in the polyimide film, and the optical properties are deteriorated due to the influence of the remaining ammonium ions.
On the other hand, the polyimide film manufactured by thermal imidation has a problem that the polyimide film exhibits coloration due to high-temperature treatment performed during imidization.

This invention is made | formed in view of the said problem, and it aims at providing the manufacturing method of the polyimide film by which coloring was suppressed and transparency improved.
Moreover, this invention is a manufacturing method of the polyimide precursor suitable for manufacture of the said polyimide film, the manufacturing method of the laminated body which has the said polyimide film, and the manufacturing method of the surface material for displays which is the said polyimide film or the said laminated body. The purpose is to provide.

The method for producing a polyimide film of the present invention includes a step of preparing a polyimide precursor solution,
Obtaining a purified polyimide precursor by reducing residual monomers in the polyimide precursor solution; and
Preparing a polyimide precursor composition containing the purified polyimide precursor and an organic solvent;
Applying the polyimide precursor composition to a support to form a polyimide precursor coating;
A step of imidizing the polyimide precursor by heating the polyimide precursor coating film.

In the production method of the polyimide film of the present invention, the step of obtaining the purified polyimide precursor,
It is preferable from the point which collect | recovers the polyimide precursor by including the process of collect | recovering a polyimide precursor by dripping the said polyimide precursor solution to a poor solvent, and precipitating a polyimide precursor.

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

The method for producing a polyimide precursor of the present invention includes a step of preparing a polyimide precursor solution,
Reducing the residual monomer in the polyimide precursor solution.

In the method for producing a polyimide precursor of the present invention, the step of reducing the residual monomer,
It is preferable from the point which collect | recovers the polyimide precursor by including the process of collect | recovering a polyimide precursor by dripping the said polyimide precursor solution to a poor solvent, and precipitating a polyimide precursor.

The method for producing a laminate of the present invention comprises a step of producing a polyimide film by the production method of the present invention,
Forming a coating film of a composition for forming a hard coat layer containing at least one of a radical polymerizable compound and a cationic polymerizable compound on at least one surface of the polyimide film obtained by the step;
Curing the coating film.

  In the method for producing a laminate of the present invention, the radical polymerizable compound is a compound having two or more (meth) acryloyl groups in one molecule, and the cationic polymerizable compound is at least one of an epoxy group and an oxetanyl group. It is preferable that it is a compound which has 2 or more in 1 molecule from the point of the adhesiveness of a polyimide film and a hard-coat layer, and the point of the light transmittance of a laminated body, and surface hardness.

  The manufacturing method of the surface material for display of this invention includes the process of manufacturing a polyimide film with the manufacturing method of the said invention, or the process of manufacturing a laminated body with the manufacturing method of the said invention.

ADVANTAGE OF THE INVENTION According to this invention, coloring can be suppressed and the manufacturing method of the polyimide film which transparency improved can be provided.
Moreover, this invention is a manufacturing method of the polyimide precursor suitable for manufacture of the said polyimide film, the manufacturing method of the laminated body which has the said polyimide film, and the manufacturing method of the surface material for displays which is the said polyimide film or the said laminated body. Can be provided.

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

I. Manufacturing method of polyimide film The manufacturing method of the polyimide film of the present invention includes a step of preparing a polyimide precursor solution (hereinafter referred to as a polyimide precursor solution preparing step),
A step of obtaining a purified polyimide precursor by reducing residual monomer 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);
Applying the polyimide precursor composition to a support to form a polyimide precursor coating film (hereinafter referred to as polyimide precursor coating film forming process);
A step of imidizing the polyimide precursor by heating the polyimide precursor coating film (hereinafter referred to as an imidization step).

  According to the present invention, as a polyimide precursor composition, a composition obtained by re-dissolving a purified polyimide precursor is used, and in the imidation of the polyimide precursor, a thermal imide is used without using a catalyst such as an amine. 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, yellowness (YI value) and haze value of the polyimide film produced by chemical imidation decrease as the content of ammonium ions is reduced by purification. However, it is difficult to completely remove ammonium ions, and the optical characteristics are deteriorated due to the influence of the remaining ammonium ions.
Therefore, the present inventors paid attention to 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 ions can be produced. Thereby, the optical characteristic does not deteriorate due to the influence of ammonium ions. However, a polyimide film produced by thermal imidization has a problem of showing coloration by high temperature treatment. On the other hand, in the present invention, by using a polyimide precursor composition obtained by dissolving a purified polyimide precursor in an organic solvent, even if a high temperature treatment for thermal imidization is performed, coloring of the film is suppressed, An increase in the YI value can be suppressed. The coloring of the film caused by the high temperature treatment is considered to be largely influenced by oxidation of residual monomers, especially oxidation of diamine, but in the present invention, the residual monomer in the polyimide precursor composition is reduced, so that the film It is considered that the coloring of is suppressed. When the tetracarboxylic acid component or diamine component used for the synthesis of the polyimide precursor has a structure with relatively low reactivity, the unreacted monomer tends to remain, so the production method of the present invention is relatively reactive. This is particularly effective when a monomer component having a low structure is used, and particularly effective when a diamine component having a structure with relatively low reactivity is used.
Moreover, since the polyimide film obtained by chemical imidation is synthesized in a polyimide precursor (polyamic acid) and imidation of the polyimide precursor is performed in a solution, it cannot apply a temperature higher than the boiling point of the solvent, Compared to the polyimide film obtained by thermal imidization, the temperature of the thermal history until film formation is lower than when performing thermal imidization, so dimensional stability, solvent resistance, moisture absorption resistance, moisture permeability resistance, etc. There is a tendency to be inferior. On the other hand, in the production method of the present invention, a high temperature treatment is performed during the thermal imidization, so that a polyimide film with improved properties can be obtained. Since the polyimide film obtained by the production method of the present invention has good solvent resistance, it is easy to apply varnish to the surface. Therefore, for example, the polyimide film can be disposed on a desired article or a decorative portion can be provided on the polyimide film via an adhesive layer, a planarizing layer, or the like. In addition, since the polyimide film obtained by the production method of the present invention has good moisture absorption resistance or moisture permeability resistance, it can be used as a surface material of a desired article to suppress deterioration of the article due to moisture. Can do.
In addition, it is known that the polyimide film forms an ordered structure in which the arrangement of the molecular chains inside is constant, whereby the bending resistance can be improved. With regard to the arrangement of the molecular chains of the polyimide resin, it is easier to form a certain ordered structure when thermal imidization is performed than when chemical imidization is performed. Therefore, the polyimide film obtained by the production method of the present invention can easily improve bending resistance and can be suitably used for a flexible device. In addition, the bending resistance of the film tends to deteriorate due to moisture absorption of the film, but the polyimide film obtained by the production method of the present invention has good moisture absorption resistance, so that the bending resistance is reduced under high humidity. It is suppressed.

In addition, the production method of the present invention further includes 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 process). You may have.
Hereinafter, each step will be described in detail.

1. Polyimide precursor solution preparatory process The polyimide precursor solution prepared in this invention contains a polyimide precursor and a solvent, and may contain the additive etc. as needed. 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 previously 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, the residual monomer is reduced by the polyimide precursor purification step described later, that is, a component in which unreacted monomer tends to remain, that is, comparison The production method of the present invention is more effective when using at least one selected from a tetracarboxylic acid component having a structure with low mechanical reactivity and a diamine component having a structure with relatively low reactivity. When the diamine remains, the film is particularly easily colored, so that it is more effective when a diamine component having a structure with relatively low reactivity is used.

Examples of the tetracarboxylic acid component having a relatively low-reactivity structure include, for example, a tetracarboxylic acid component having an aromatic ring, and among them, a low reactivity includes an aromatic ring and a carboxyl group. Or the tetracarboxylic-acid component in which the aromatic ring which has an acid dianhydride structure has an electron-donating group is mentioned.
Moreover, the tetracarboxylic-acid component which has an aromatic ring is preferable from the point which improves the surface hardness of a polyimide film.
Examples of the tetracarboxylic acid component having an aromatic ring include pyromellitic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 2,2 ′, 3,3′-benzophenone. Tetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic 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) sulfone dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4 -Dicarbo Cyphenyl) methane dianhydride, 2,2-bis (3,4-dicarboxyphenyl) -1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis (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) fe Noxy] 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} sulfone dianhydride, bis {4- [3- (1,2-dicarboxy) phenoxy] phenyl} sulfone Anhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} sulfide dianhydride, bis {4- [3- (1,2-dicarboxy) phenoxy] phenyl} sulfide dianhydride 4 4 ′-(hexafluoroisopropylidene) diphthalic anhydride, 3,4 ′-(hexafluoroisopropylidene) diphthalic anhydride, 3,3 ′-(hexafluoroisopropylidene) diphthalic anhydride, 4,4 ′ -Oxydiphthalic anhydride, 3,4'-oxydiphthalic anhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 1, 2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3 , 6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, and the like.
Examples of tetracarboxylic acid components having an aromatic ring and an aromatic ring having a carboxyl group or an acid dianhydride structure having an electron donating group include, for example, 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] Phenyl} propane dianhydride, 4,4′-oxydiphthalic anhydride, 3,4′-oxydiphthalic anhydride, and the like.

Moreover, as a tetracarboxylic-acid component used for this invention, the tetracarboxylic-acid component which has an aliphatic ring from the point of the light transmittance of a polyimide film is preferable.
Examples of the tetracarboxylic acid component having an aliphatic ring include cyclohexanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, dicyclohexane-3,4,3 ′, 4′-tetracarboxylic dianhydride. And cyclobutane tetracarboxylic dianhydride.
In addition, the tetracarboxylic acid component mentioned above can also be used individually or in mixture of 2 or more types.

As a diamine component which has a structure with comparatively low reactivity, the diamine which has an aromatic ring, the diamine containing a silicon atom in a principal chain, etc. are mentioned, for example. Among diamines having an aromatic ring, those having low reactivity include diamines having an aromatic ring and an aromatic ring having an amino group having an electron-withdrawing group.
In addition, 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 silicon atom-free fragrance from the viewpoint of achieving both bending resistance and surface hardness. It is more preferable to use in combination with a diamine having an aromatic 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. Among them, a diamine containing one or two silicon atoms in the main chain is preferable from the viewpoint that both bending resistance and surface hardness can be easily achieved.

  Examples of the diamine having one silicon atom in the main chain include diamines represented by the following general formula (A). Moreover, as a diamine which has two silicon atoms in a principal chain, the diamine represented by the following general formula (B) is mentioned, for example.

（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 General Formula (A) and General Formula (B), each L is independently a direct bond or —O— bond, and each R ¹⁰ may independently have a substituent, oxygen Represents a monovalent hydrocarbon group having 1 to 20 carbon atoms which may contain an atom or a nitrogen atom, and each R ¹¹ may independently have a substituent, and represents an oxygen atom or a nitrogen atom. Represents a divalent hydrocarbon group having 1 to 20 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 combinations 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 to 20 carbon atoms is preferably an alkyl group having 1 to 10 carbon atoms. Specifically, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, 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 to 10 carbon atoms, and specific examples include a cyclopentyl group and a cyclohexyl group. The aryl group is preferably an aryl group having 6 to 12 carbon atoms, and specific examples 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 that may contain an oxygen atom or a nitrogen atom include an ether bond, a carbonyl bond, an ester bond, an amide bond, and an imino bond between a divalent hydrocarbon group and the monovalent hydrocarbon group described below And a group bonded by at least one bond (—NH—).
The substituent which the monovalent hydrocarbon group represented by R ¹⁰ may have is not particularly limited as long as the effects of the present invention are not impaired. For example, a halogen atom such as a fluorine atom or a chlorine atom And a hydroxyl group.

The monovalent hydrocarbon group represented by R ¹⁰ is an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 10 carbon atoms from the viewpoint of compatibility between improvement in bending resistance and surface hardness. Preferably there is. The alkyl group having 1 to 3 carbon atoms is more preferably a methyl group, and the aryl group having 6 to 10 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 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 to 20 carbon atoms is preferably an alkylene group having 1 to 10 carbon atoms. And a combination of a linear or branched alkylene group and a cyclic alkylene group.
The arylene group is preferably an arylene group having 6 to 12 carbon atoms, and examples of the arylene group include a phenylene group, a biphenylene group, and a naphthylene group, and further have a substituent for an aromatic ring described later. You may do it.
As the divalent hydrocarbon group which may contain an oxygen atom or a nitrogen atom, the divalent hydrocarbon groups are ether bonds, carbonyl bonds, ester bonds, amide bonds, and imino bonds (—NH—). A group bonded with at least one is exemplified.
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 to 6 carbon atoms or an arylene group having 6 to 10 carbon atoms from the viewpoint of compatibility between improvement in bending resistance and surface hardness. Preferably, it is more preferably an alkylene group having 2 to 4 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, even more preferably 500 or less, from the viewpoint of surface hardness and bending resistance. It is particularly preferred that

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 Sulfone, 4,4′-diaminodiphenylsulfone, 3,3′-diaminobenzophenone, 4,4′-diaminobenzophenone, 3,4′-diaminobenzophenone, 4,4′-diaminobenzanilide, 3,3′-diamino Diphenylmethane, 4,4'-diaminodiphenylmeta 3,4′-diaminodiphenylmethane, 2,2-di (3-aminophenyl) propane, 2,2-di (4-aminophenyl) propane, 2- (3-aminophenyl) -2- (4-amino) Phenyl) propane, 2,2-di (3-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 2,2-di (4-aminophenyl) -1,1,1, 3,3,3-hexafluoropropane, 2- (3-aminophenyl) -2- (4-aminophenyl) -1,1,1,3,3,3-hexafluoropropane, 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-aminophen Xyl) 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-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, 2,6-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) benzidine), 3,3′-dichloro-4,4′-diaminobiphenyl, 3,3′-dimethoxy-4,4′-diaminobiphenyl, 3,3′-di Til-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-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 2,2-bis [4- (4-amino) Phenoxy) 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) benzoyl] 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-dimethylbenzyl] benzene, 1,4-bis [4- ( 3-A Nophenoxy) -α, α-dimethylbenzyl] benzene, 1,4-bis [4- (4-aminophenoxy) -α, α-dimethylbenzyl] benzene, 4,4′-bis [4- (4-amino) Phenoxy) benzoyl] diphenyl ether, 4,4′-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] benzophenone, 4,4′-bis [4- (4-amino-α, α-dimethyl) Benzyl) phenoxy] diphenylsulfone, 4,4′-bis [4- (4-aminophenoxy) phenoxy] diphenylsulfone, 3,3′-diamino-4,4′-diphenoxybenzophenone, 3,3′-diamino- 4,4′-dibiphenoxybenzophenone, 3,3′-diamino-4-phenoxybenzophenone, 3,3′-diamino-4-biphenoxybenzophenone, , 6′-bis (3-aminophenoxy) -3,3,3 ′, 3′-tetramethyl-1,1′-spirobiindane, 6,6′-bis (4-aminophenoxy) -3,3,3 ', 3'-tetramethyl-1,1'-spirobiindane, etc., and a part or all of the hydrogen atoms on the aromatic ring of the diamine are fluoro groups, methyl groups, methoxy groups, trifluoromethyl groups, or trifluoro Diamines substituted with a substituent selected from methoxy groups can also be used.
Examples of the diamine having an aromatic ring without having a silicon atom and an amino group having an electron-withdrawing group include 3,3′-diaminodiphenyl sulfone and 3,4′-diaminodiphenyl. Sulfone, 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′- Examples include ditrifluoromethyl-4,4′-diaminobiphenyl (2,2′-bis (trifluoromethyl) benzidine), 3,3′-dichloro-4,4′-diaminobiphenyl, and the like.

Moreover, as a diamine component used for this invention, the diamine which does not have a silicon atom but has an aliphatic ring from the point of the light transmittance of a polyimide film is also preferable.
Examples of diamines that do not have a silicon atom and have 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.
In addition, the diamine component mentioned above can also be used individually or in mixture of 2 or more types.

  The solvent used for the synthesis of the polyimide precursor (polyamic acid) is not particularly limited as long as it can dissolve the above-described tetracarboxylic acid component and diamine component. For example, an aprotic polar solvent or a water-soluble alcohol 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 of 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, Y / X is preferably 0.9 or more and 1.1 or less, and 0.95 or more and 1.05 or less. Is more preferably 0.97 or more and 1.03 or less, and particularly preferably 0.99 or more and 1.01 or less. By setting it as such a range, the molecular weight (polymerization degree) of the polyamic acid obtained can be adjusted moderately.
The procedure of the polymerization reaction can be appropriately selected from known methods and is not particularly limited.

The polyimide precursor contained in the polyimide precursor solution is a polyimide precursor obtained by polymerizing the tetracarboxylic acid component described above and the diamine component described above.
The polyimide precursor preferably has a number average molecular weight or a weight average molecular weight of 10,000 or more, more preferably 20,000 or more, from the viewpoint of strength when used as 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 reduced, and therefore it is preferably 10000000 or less, and more preferably 500000 or less.
The number average molecular weight of the polyimide precursor can be determined by NMR (for example, AVANCE III manufactured by BRUKER). For example, after applying a polyimide precursor solution to a glass plate and drying at 100 ° C. for 5 minutes, 10 mg of solid content is dissolved in 7.5 ml of dimethyl sulfoxide-d6 solvent, NMR measurement is performed, and the aromatic ring is bonded. 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 an 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.

  As a polyimide precursor which the said polyimide precursor solution contains, the polyimide precursor which has a structure represented by following General formula (1) is mentioned, for example.

（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 General Formula (1), R ¹ represents a tetravalent group that is a tetracarboxylic acid residue, R ² represents a divalent group that 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 tetracarboxylic acid, and represents the same structure as a residue obtained by removing acid dianhydride structure from tetracarboxylic dianhydride. . Moreover, a diamine residue means the residue remove | excluding two amino groups from diamine.
Examples of R ¹ in the general formula (1) include residues obtained by removing four carboxyl groups or acid dianhydride structures from the above-described tetracarboxylic acid component, and R ² in the general formula (1) For example, the residue which remove | excluded two amino groups from the diamine component mentioned above is mentioned.

As the polyimide precursor 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%, the surface hardness is particularly improved. 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. Even more preferably.

Moreover, the polyimide precursor contained in the polyimide precursor solution includes an aromatic ring, and more than 50% of hydrogen atoms bonded to carbon atoms contained in the polyimide precursor are directly in the aromatic ring. A polyimide that is a hydrogen atom to be bonded is preferable from the viewpoint of improving the light transmittance of the polyimide film to be produced and improving the surface hardness. The ratio of the hydrogen atoms (number) directly bonded to the aromatic ring in 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 bonded directly to the aromatic ring, the stretching is performed at, for example, 200 ° C. or higher even after a heating step in the atmosphere. Even if it carries out, it is preferable from the point with few changes of the optical characteristic of the polyimide film produced, especially a total light transmittance and yellowness YI value. When 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide precursor are polyimides that are hydrogen atoms bonded directly to the aromatic ring, the reactivity with oxygen is low. It is estimated that the chemical structure of polyimide is difficult to change. Polyimide films are often used in devices that require high heat resistance and require processing steps involving heating, but 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide precursor are aromatic. In the case of a hydrogen atom directly bonded to the ring, there is no need to carry out these post-processes under an inert atmosphere in order to maintain transparency. is there.
Here, the ratio of the hydrogen atom (number) directly bonded to the aromatic ring in the total hydrogen atom (number) bonded to the carbon atom contained in the polyimide precursor can be determined using NMR.

Among the polyimide precursors, among others, from the viewpoint of improving the light transmittance and surface hardness of the polyimide film to be produced, the polyimide precursor contains an aromatic ring, and (i) a fluorine atom, (ii) an aliphatic ring, and ( iii) It preferably contains at least one selected from the group consisting of aromatic rings connected by a sulfonyl group or an alkylene group optionally 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 is improved. Although the surface hardness is increased, the rigid aromatic ring skeleton tends to increase the absorption wavelength to a long wavelength, and the transmittance in the visible light region tends to decrease.
When the polyimide precursor or polyimide contains (i) a fluorine atom, the light transmittance of the polyimide film is improved because the electronic state in the polyimide skeleton can be hardly transferred.
When the polyimide precursor or polyimide contains (ii) an aliphatic ring, the polyimide film has light transmittance because the transfer of charge in the skeleton can be inhibited by breaking the π-electron conjugation in the polyimide skeleton. improves.
Including the structure in which (iii) aromatic rings are connected to the polyimide precursor or polyimide by a sulfonyl group or an alkylene group which may be substituted with fluorine, by cutting off the π-electron conjugation in the polyimide skeleton, The light transmittance of a polyimide film improves from the point which can inhibit the movement of an electric charge.

As the polyimide precursor contained in the polyimide precursor solution, among them, 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) and the number of carbon atoms (C) measured on the surface of the polyimide precursor by X-ray photoelectron spectroscopy is 0.00. It is preferably 01 or more, and more preferably 0.05 or more. On the other hand, if the fluorine atom content is too high, the inherent heat resistance of the polyimide may be lowered, so the ratio (F / C) of the number of fluorine atoms (F) to the number of carbon atoms (C) is 1 or less. Preferably, it is preferably 0.8 or less.
In the present invention, the ratio of each atom as measured by X-ray photoelectron spectroscopy (XPS) is determined from the value of atomic% of each atom measured using an X-ray photoelectron spectrometer (for example, Thermo Scientific Thea Probe). be able to.

Further, the polyimide precursor having the structure represented by the general formula (1), from the viewpoint of surface hardness and optical transparency of the polyimide film to be produced is improved, tetracarboxylic acid residue of R ^1, and R ² It is preferable that at least one of the diamine residues includes 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) because the surface hardness and light transmittance of the polyimide film to be produced are improved. Is preferably 100 mol%, the total of the tetracarboxylic acid residue having an aromatic ring and fluorine atom and the diamine residue having an aromatic ring and fluorine atom is preferably 50 mol% or more, and 60 mol% More preferably, it is more preferably 75 mol% or more.

In addition, as the polyimide precursor obtained using at least one selected from the above-described tetracarboxylic acid component having a relatively low-reactivity structure and diamine component having a relatively low-reactivity structure, the general formula ( 1) A polyimide having a structure represented by 1) and having a structure having relatively low reactivity in at least ^one of the tetracarboxylic acid residue of R ¹ and the diamine residue of R ² in the general formula (1) A precursor is mentioned. Among these tetracarboxylic acid residue of the R ^1, from the viewpoint of surface hardness of the polyimide film, it is preferable to contain the tetracarboxylic acid residue having an aromatic ring. In addition, 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. From the viewpoint of bending resistance of the polyimide film, a silicon atom is contained in the main chain. A diamine residue that preferably contains a diamine residue that does not have a silicon atom and has an aromatic ring and a diamine residue that contains a silicon atom in the main chain from the viewpoint of achieving both surface hardness and bending resistance It is more preferable to contain in combination.

As the tetracarboxylic acid residue having an aromatic ring in R ¹ of the general formula (1), among them, pyromellitic dianhydride residue from the viewpoint of surface hardness and bending resistance and light transmittance 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride residue, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride residue, 4,4 ′-(hexafluoroisopropyl Ridene) diphthalic anhydride residue, 3,4 ′-(hexafluoroisopropylidene) diphthalic anhydride residue, 3,3 ′-(hexafluoroisopropylidene) diphthalic anhydride residue, 4,4′- At least one selected from the group consisting of an oxydiphthalic anhydride residue and a 3,4'-oxydiphthalic anhydride residue is preferred, and 4,4 '-(hexafluoroisopropylidene) diphthalic anhydride residue, 3, '-(Hexafluoroisopropylidene) diphthalic anhydride residue, 3,3'-(hexafluoroisopropylidene) diphthalic anhydride residue, 4,4'-oxydiphthalic anhydride residue, and 3,4 More preferred is at least one selected from the group consisting of residues of '-oxydiphthalic anhydride.

In addition, 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 From the point of light transmittance, cyclohexanetetracarboxylic dianhydride residue, cyclopentanetetracarboxylic dianhydride residue, dicyclohexane-3,4,3 ′, 4′-tetracarboxylic dianhydride residue, At least one selected from the group consisting of cyclobutanetetracarboxylic dianhydride residues is preferred.

From the viewpoint of surface hardness, bending resistance, and light transmittance, in R ¹ in the general formula (1), a tetracarboxylic acid residue having a suitable aromatic ring and a tetracarboxylic acid having an aliphatic ring described above are used. The total content of acid residues is preferably 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more. Moreover, from the point that the effect of the present invention is more effectively exhibited, the content ratio of the tetracarboxylic acid residue having the above preferred aromatic ring in R ¹ in the general formula (1) is 50 mol. % Or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more.
R ¹ in the general formula (1) may contain other tetracarboxylic acid residues different from the tetracarboxylic acid residue having an aromatic ring and the tetracarboxylic acid residue having an aliphatic ring. Good. The other tetracarboxylic acid residue is preferably 10 mol% or less of the total amount of R ¹ , more preferably 5 mol% or less, still more preferably 3 mol% or less, especially 1 It is preferable that it is below mol%.

Among R ² in the general formula (1), the diamine residue containing a silicon atom in the main chain is preferably a diamine residue having one or two silicon atoms in the main chain, and the silicon atom in the main chain. It is preferable that it is the diamine residue which has two from the point of a light transmittance, a bending tolerance, and the 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). The amino acid may be appropriately selected from residues obtained by removing two amino groups from the diamine, 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 are preferred.
More specifically, 1,3-bis (3-aminopropyl) tetramethyldisiloxane residue, 1,3-bis (4-aminobutyl) tetramethyldisiloxane, 1,3-bis (5-aminopentyl) ) Tetramethyldisiloxane and the like are preferable from the viewpoint of easy availability and compatibility between light transmittance and surface hardness.

As the diamine residue having no silicon atom and having an aromatic ring in R ² of the general formula (1), among others, from the viewpoint of light transmittance, surface hardness and bending resistance, 4, 4 '-Diaminodiphenylsulfone residue, 3,4'-diaminodiphenylsulfone 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 preferred.

（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 General Formula (2), R ^a and R ^b each independently represent a hydrogen atom, an alkyl group, or a perfluoroalkyl group.)

As R ² 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. Among them, the light transmittance point, surface hardness and bending resistance are preferred. From the viewpoint, at least one selected from a trans-cyclohexanediamine residue and a trans-1,4-bismethylenecyclohexanediamine residue is preferable.

From the viewpoint of surface hardness, bending resistance, and light transmittance, R ² in the general formula (1) contains 50 mol of a diamine residue having no silicon atom and having an aromatic ring or an aliphatic ring. The diamine residue containing 1 or 2 silicon atoms in the main chain is preferably 10 mol% or more and 50 mol% or less. From the point that the effect of the present invention is more effectively exhibited, R ² in the general formula (1) has 50 mol% or more and 90 mol% of a diamine residue having no silicon atom and having an aromatic ring. The diamine residue containing one or two silicon atoms in the main chain is preferably 10 mol% or more and 50 mol% or less.
R ² in the general formula (1) is a diamine residue different from a diamine residue having an aromatic ring or an aliphatic ring and a diamine residue containing one or two silicon atoms in the main chain. It may be included. The other diamines is preferably from 10 mol% of the total amount of R ^2, further preferably 5 mol% or less, preferably more or less further 3 mol%, particularly 1 mol% or less Preferably there is. Examples of the other diamine residue include a diamine residue that does not have a silicon atom and does not have an aromatic ring or an aliphatic ring.

As a preferred embodiment in the present invention from the viewpoint of surface hardness, bending resistance, and light transmittance, in the general formula (1), R ¹ is a tetracarboxylic acid residue having an aromatic ring or an aliphatic ring. Represents a certain tetravalent group, R ² represents a divalent group which is a diamine residue, and 10 mol% or more and 50 mol% or less of the total amount of R ² is one or two silicon atoms in the main chain The case is a diamine residue having 50 mol% or more and 90 mol% or less 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 exhibits a preferable glass transition temperature to be 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.

In the polyimide precursor used in the present invention, the structure represented by the general formula (1) is preferably 95% or more, and 98% or more of the total number of repeating units of the polyimide precursor. More preferably, it is 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 effects of the present invention are not impaired. Examples of the structure different from the structure represented by the general formula (1) include a structure derived from a tricarboxylic acid such as when trimellitic anhydride is used, and a dicarboxylic acid such as when terephthalic acid is used. The structure of origin is mentioned.

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. Thereby, since the residual monomer in the polyimide precursor composition mentioned later can be reduced, coloring of the polyimide film by oxidation of a residual monomer can be suppressed and transparency can be improved.
In the present invention, the residual monomer may include one or more selected from the group consisting of tetracarboxylic dianhydride, tetracarboxylic acid, and diamine used for producing the polyimide precursor. Furthermore, 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 including 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 further dropped into a poor solvent to obtain a polyimide precursor. By precipitating again, the step of recovering the polyimide precursor again is preferably performed once or more, more preferably repeated twice or more. Among them, it is preferable to perform the step of recovering the polyimide precursor again once or twice from the viewpoint of sufficiently reducing the residual monomer, suppressing the coloring of the polyimide film, and the production efficiency. It is more preferable.
In addition, although the polyimide precursor collect | recovered is normally solid and a form changes with molecular weights of a polyimide precursor, it is a fibrous form or a powder form, for example.

The poor solvent used in the polyimide precursor purification step may be appropriately selected from solvents 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. In addition, the poor solvent is a solvent in which the solubility of each of the tetracarboxylic acid component and the diamine component used for the production of the polyimide precursor is 0.1 g / 100 g or more at 25 ° C. 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 cyclohexanone; and mixed solvents thereof. Is mentioned. Among these, water and a mixed solvent of water and alcohols are preferable as the poor solvent from the viewpoint of easy isolation of the polyimide precursor and compatibility with a good solvent described later.
In addition, when performing the process which collect | recovers a polyimide precursor again, the same solvent may be sufficient as each poor solvent used for each process, and a different solvent may be sufficient as it.

The good solvent used in the polyimide precursor purification step is preferably a solvent in which the solubility of the polyimide precursor is 20 g / 100 g or more at 25 ° C. Examples of the good solvent include N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, 1,2-dimethyl-2- An organic solvent containing a nitrogen atom such as imidazolidinone; γ-butyrolactone; and a mixed solvent thereof. The good solvent is preferably an organic solvent containing a nitrogen atom from the viewpoint of solubility of the polyimide precursor and compatibility with the poor solvent, and N-methyl-2-pyrrolidone (NMP), N, N- Amides such as dimethylformamide and N, N-dimethylacetamide are more preferred. In the present invention, the organic solvent is a solvent containing carbon atoms.
In addition, when performing the process of collect | recovering a polyimide precursor again twice or more, the good solvent used for each process may be the same solvent, respectively, and a different solvent may be sufficient as it.

  In the said polyimide precursor refinement | purification process, when dripping the solution containing a polyimide precursor to a poor solvent, the solid content concentration of the solution containing a polyimide precursor is from the point of removing the point of a yield and an impurity efficiently. 0.5 mass% or more and 30 mass% or less is preferable, and 1 mass% or more and 10 mass% or less is more preferable.

  In the said polyimide precursor refinement | purification process, when dripping the solution containing a polyimide precursor to a poor solvent, the quantity of the poor solvent with respect to 1 mass part of polyimide precursor is from the point of removing a point of a yield and an impurity efficiently. 50 mL or more and 500 mL or less is preferable.

  In the said polyimide precursor refinement | purification process, the method of collect | recovering a polyimide precursor is not specifically limited, For example, the method by filtration is mentioned. As a filtration method, for example, known methods such as vacuum filtration, pressure filtration, and centrifugal filtration can be applied, and there is no particular limitation. Moreover, it does not specifically limit as a filter used for filtration, The thing of the hole diameter and material which can remove impurities, such as a residual monomer, and can collect | recover a polyimide precursor can be selected suitably.

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

  The organic solvent used for the polyimide precursor composition is not particularly limited as long as it can dissolve the purified polyimide precursor obtained by the polyimide precursor purification step. Examples of the organic solvent include N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, 1,3-dimethyl-2-imidazolidinone. And organic solvents containing nitrogen atoms such as γ-butyrolactone, and mixed solvents thereof. As the organic solvent, an organic solvent containing a nitrogen atom is preferably used, and among them, N, N-dimethylacetamide, N-methyl-2-pyrrolidone or a combination thereof is preferably used. The organic solvent is preferably N, N-dimethylacetamide, N-methyl-2-pyrrolidone or a combination thereof from the viewpoint of suppressing distortion of the polyimide film.

  The polyimide precursor composition may contain an additive as necessary. Examples of the additive include inorganic particles, a silica filler for facilitating winding, and a surfactant that improves film-forming properties and defoaming properties.

The polyimide precursor composition preferably has a moisture content of 1000 ppm or less from the viewpoint of improving the storage stability of the polyimide precursor composition and improving the productivity.
In addition, the moisture content of a polyimide precursor composition can be calculated | required using a Karl Fischer moisture meter (For example, Mitsubishi Chemical Corporation make, trace moisture measuring device CA-200 type).

  Although the method for preparing the polyimide precursor composition is not particularly limited, as described above, in order to make the water content 1000 ppm or less, the organic solvent to be used was dehydrated or the water content was controlled. In the above, it is preferable to handle in an environment with a humidity of 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. and a sample amount of 0.8 ml.
Moreover, when preserve | saving the said polyimide precursor composition, it is preferable to preserve | save at -5 degrees C or less from the point which suppresses deterioration of the said composition.

4). Polyimide precursor coating film forming step In the step of applying the polyimide precursor composition to a support to form a polyimide precursor coating film, the support used 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 having a mirror-finished surface, and the like can be given. The shape of the support is selected depending on the coating method, and may be, for example, a plate shape, a drum shape, a belt shape, a sheet shape that can be wound around a roll, or the like.

The application means is not particularly limited as long as it can be applied at a desired film thickness, and for example, a known one such as a die coater, comma coater, roll coater, gravure coater, curtain coater, spray coater, lip coater or the like can be used. .
Application may be performed by a single-wafer coating apparatus or a roll-to-roll coating apparatus.

  After the polyimide precursor composition is applied 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, imidization of the polyamic acid can be suppressed.

  Although drying time should just be adjusted suitably according to the film thickness of a polyimide precursor coating film, the kind of solvent, drying temperature, etc., Usually, it is 5 minutes-120 minutes, Preferably you may be 10 minutes-60 minutes. preferable. When exceeding an upper limit, it is unpreferable from the surface of the production efficiency of a polyimide film. On the other hand, when the value is below the lower limit, the appearance of the resulting polyimide film may be affected by rapid solvent drying.

The method for drying the solvent is not particularly limited as long as the solvent can be dried at the above temperature. For example, an oven, a drying furnace, a hot plate, infrared heating, or the like can be used.
When high management of optical properties is required, the atmosphere during drying of the solvent is preferably an inert gas atmosphere. The inert gas atmosphere is preferably a nitrogen atmosphere, the oxygen concentration is preferably 100 ppm or less, and more preferably 50 ppm or less. When heat treatment is performed in the atmosphere, the film may be oxidized and colored, or the performance may deteriorate.

5). Imidization process In the manufacturing method of this invention, the polyimide precursor is imidized by heating the said polyimide precursor coating film.
In the said manufacturing method, when it has an extending process, an imidation process may be performed with respect to the polyimide precursor in the said polyimide precursor coating film before an extending process, and the said polyimide precursor coating film after an extending process It may be performed on the polyimide precursor in the inside, or may be performed on both the polyimide precursor in the polyimide precursor coating film before the stretching step and the polyimide precursor present 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, more preferably 100 ° C. or higher. On the other hand, the temperature rise end temperature is preferably 250 ° C. or higher. From the standpoints of optical properties, hygroscopicity, dimensional stability, solvent resistance, etc., it is preferable that the temperature rise end temperature is within the range of the glass transition temperature ± 30 ° C. of the polyimide imidized with the polyimide precursor. The transition temperature is more preferably within a range of ± 20 ° C., and the glass transition temperature of polyimide is more preferably within a range of ± 15 ° C. If the imidization temperature is too high, the polyimide film may be colored by oxidation within the skeleton of the polyimide or polyimide precursor. If the imidization temperature is too low, imidization may not proceed sufficiently. is there.

The rate of temperature increase is preferably selected as appropriate depending on the film thickness of the polyimide film to be obtained. When the film thickness of the polyimide film is thick, it is preferable to decrease the temperature increase rate.
From the viewpoint of the production efficiency of the polyimide film, it is preferably 5 ° C./min or more, more preferably 10 ° C./min or more. On the other hand, the upper limit of the heating rate is usually 50 ° C./min, preferably 40 ° C./min or less, more preferably 30 ° C./min or less. It is preferable to set the temperature increase rate from the viewpoint that the appearance defect and strength reduction of the film can be suppressed, and the whitening associated with the imidization reaction can be controlled, and the light transmittance is improved.

  The temperature rise may be continuous or stepwise, but it is preferable to make it continuous from the viewpoint of controlling the appearance of the film, suppressing the decrease in strength, and controlling the whitening associated with the imidization reaction. Moreover, in the above-mentioned whole temperature range, the temperature rising rate may be constant or may be changed in the middle.

The atmosphere at the time of temperature increase in imidation is preferably an inert gas atmosphere. The inert gas atmosphere is preferably a nitrogen atmosphere, the oxygen concentration is preferably 500 ppm or less, more preferably 200 ppm or less, and even more preferably 100 ppm or less. When heat treatment is performed in the atmosphere, the film may be oxidized and colored, or the performance may deteriorate.
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, there is little influence of oxygen on the optical properties, and an inert gas atmosphere is not used. In addition, a polyimide having a high light transmittance can be obtained.

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

Especially, it is more preferable that the imidation ratio of a polyimide precursor shall be 50% or more before an extending process. Even if the imidization rate is 50% or more before the stretching step, the film is stretched after the step, and then heated at a higher temperature for a certain period of time to perform imidization. Whitening is suppressed. In particular, from the point that the surface hardness of the polyimide film is improved, it is preferable that the imidization rate is 80% or more in the imidization step before the stretching step, and the reaction is allowed to proceed to 90% or more, further 100% Is preferred. By stretching after imidization, it is presumed that the surface hardness is improved because a rigid polymer chain is easily oriented.
The imidation rate can be measured by analyzing the spectrum by infrared measurement (IR).

In order to obtain a final polyimide film, it is preferable to proceed the reaction to 90% or more, further 95% or more, and further 100%.
In order to advance the reaction to 90% or more, further 100%, it is preferable to hold at a temperature rising end temperature for a certain period of time. Minutes are preferred.

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 it has the said extending | stretching process, it is preferable from the point which the surface hardness of a polyimide film improves including the process of extending | stretching the coating film after imidation especially.

In the production method of the present invention, the step of stretching 101% or more and 10000% or less when the initial dimension before stretching is 100% is preferably performed while heating at 80 ° C. or more.
The heating temperature during stretching is preferably in the range of glass transition temperature ± 50 ° C. of the polyimide or polyimide precursor, and preferably in the range of glass transition temperature ± 40 ° C. If the stretching temperature is too low, the film may not be deformed and the orientation may not be sufficiently induced. On the other hand, if the stretching temperature is too high, the orientation obtained by stretching is relaxed by the temperature, and there is a possibility that sufficient orientation cannot be obtained.
The stretching step may be performed simultaneously with the imidization step. Stretching the film after imidization after imidation rate of 80% or more, further 90% or more, even more 95% or more, and particularly substantially 100% imidation improves the surface hardness of the polyimide film. It is preferable from the point.

  The draw ratio of the polyimide film is preferably 101% or more and 10,000% 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.

  There is no restriction | limiting in particular in the fixing method of the polyimide film at the time of extending | stretching, It selects according to the kind etc. of extending | stretching apparatus. Moreover, there is no restriction | limiting in particular in the extending | stretching method, For example, it can extend | stretch through a heating furnace using the extending | stretching apparatus which has conveyance apparatuses, such as a tenter. The polyimide film may be stretched only in one direction (longitudinal stretching or lateral stretching), or may be stretched in two directions by simultaneous biaxial stretching, sequential biaxial stretching, oblique stretching, or the like.

7). Polyimide film The polyimide film obtained by the production method of the present invention contains at least a polyimide obtained by imidizing the above-described polyimide precursor, and further contains other components unless the effects of the present invention are impaired. Is also good. Examples of other components include the same additives as those 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 an 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 is one in which a decrease in optical properties due to the influence of ammonium ions is suppressed. Furthermore, since the polyimide film obtained by the production method of the present invention is obtained by using a polyimide precursor composition with reduced residual monomer, the coloring of the film due to oxidation of the residual monomer is suppressed, and the transparent film is transparent. Is improved.
In the present invention, 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 ammonium ions in the polyimide film into water. Specifically, a test piece of polyimide film having a weight of about 0.4 g is put in a polypropylene bag, immersed in 50 mL of ultrapure water in the bag, and sealed with a heat sealer. It is put in a 60 ° C. water bath and allowed to stand for 1 hour or longer to elute ammonium ions in the polyimide film. The ion concentration of the obtained eluate is measured with an ion chromatograph (for example, Thermo Fisher Scientific Co., Ltd., ICS-3000), and the amount of ammonium ions per gram of the test piece is calculated.

Since the polyimide film obtained by the production method of the present invention is produced by heating and imidizing a 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 in accordance with JIS K7361-1 is 90% or more,
The haze value based on JIS K-7105 is 2.0 or less,
A polyimide film having a yellowness calculated in accordance with JIS K7373-2006 of 5.0 or less 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 measured in accordance with JIS K7361-1, and in a more preferred embodiment, 91% or more. it can. Thus, since the transmittance is high, the transparency becomes good and a glass substitute material can be obtained.
The polyimide film obtained by the production method of the present invention preferably has a total light transmittance of 90% or more, and 91%, measured in accordance with JIS K7361-1, in a thickness of 5 μm to 100 μm. The above is preferable.
In addition, 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 at a thickness of 50 μm ± 5 μm, measured according to JIS K7361-1. It is preferable that
The total light transmittance measured according to JIS K7361-1 can be measured, for example, with a haze meter (for example, HM150 manufactured by Murakami Color Research Laboratory). In addition, 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 Lambert Beer's law and can be used.

Specifically, according to Lambert Beer's law, the transmittance T is
Log ₁₀ (1 / T) = kcb
(K = constant specific to substance, c = concentration, b = optical path length).
For the transmittance of the film, so even if the film thickness is changed density is also constant c assuming a constant, the above formula, Log ₁₀ using constants f (1 / T) = fb
(F = kc). Here, if the transmittance at a certain film thickness is known, a specific constant f of each substance can be obtained. Therefore, the transmittance at a desired film thickness can be obtained by substituting a constant specific to f and a target film thickness into b using the formula T = 1/10 ^{f · b} .

Moreover, it is preferable that the polyimide film obtained by the manufacturing method of this invention is 2.0 or less from the point of light transmittance, and the haze value based on JISK-7105 is 1.0 or less. More preferably, it is still 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.
The polyimide film obtained by the production method of the present invention preferably 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. Preferably, it is still more preferably 0.5 or less.
The haze value can be measured by a method based on JIS K-7105, and can be measured by, for example, a haze meter HM150 manufactured by Murakami Color Research Laboratory.
In addition, from the measured value of the haze value of a certain thickness, the haze value of a different thickness is determined by the method described above and the haze value at each wavelength measured at 5 nm intervals between 380 nm and 780 nm of a sample having a specific thickness. From the total light transmittance of each wavelength to be measured, calculate the diffuse transmittance of each wavelength, determine the converted value of the diffuse transmittance at each wavelength of different thickness according to Lambert Beer's law as well as the total light transmittance, The haze value can be calculated and used as a ratio of diffuse transmittance to total light transmittance.

The polyimide film 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, preferably 3.0 or less. Is more preferable, and it is still more preferable that it is 2.0 or less. Thus, by low yellowness, coloring of yellowishness is suppressed, light transmittance improves, and it can become a glass substitute material.
The polyimide film obtained by the production method of the present invention preferably has a yellowness (YI value) of 5.0 or less calculated in accordance with JIS K7373-2006 when the thickness is 5 μm or more and 100 μm or less. It is more preferably 0 or less, and further preferably 2.0 or less.
In addition, the polyimide film obtained by the production method of the present invention preferably has a yellowness (YI value) of 5.0 or less calculated in accordance with JIS K7373-2006 at a thickness of 50 μm ± 5 μm. It is more preferably 3.0 or less, and further preferably 2.0 or less.
In addition, yellowness (YI value) is spectrophotometric color measurement prescribed | regulated to JISZ8722 using an ultraviolet visible near-infrared spectrophotometer (for example, JASCO Corporation V-7100) based on JISK7373-2006. It can be calculated based on the transmittance measured by the method.
It should be noted that, from the measurement value of yellowness of a certain thickness, the yellowness of different thicknesses is calculated for each transmittance at each wavelength measured at 5 nm intervals between 380 nm and 780 nm of a sample with a specific thickness. Similar to the light transmittance, a conversion value of each transmittance at each wavelength of different thickness can be obtained by Lambert Beer's law, and can be calculated and used based on it.

  As a polyimide which the polyimide film obtained by the manufacturing method of this invention contains, the polyimide which has a structure represented by the following general formula (1 ') is mentioned, for example.

（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 ′), preferable R ¹ , R ² and n are the same as those in the general formula (1).
In addition, the polyimide has a structure represented by the general formula (1 ′), preferably 95% or more of the total number of repeating units of polyimide, more preferably 98% or more, and 100%. It is even more preferable.
The polyimide may have a structure different from the structure represented by the general formula (1 ′) in part as long as the effects of the present invention are 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 included include a polyamideimide structure containing a tricarboxylic acid residue such as trimellitic anhydride and a polyamide structure containing a dicarboxylic acid residue such as terephthalic acid.

  In the polyimide film obtained by the production method of the present invention, the content of the polyimide with respect to the total amount of the polyimide film is preferably 50% by mass or more, and more preferably 60% by mass or more. The upper limit of the content of the polyimide may be appropriately adjusted depending on the content component.

In addition, the polyimide is a polyimide that includes an aromatic ring and 50% or more of the hydrogen atoms bonded to the carbon atoms included in the polyimide are hydrogen atoms directly bonded to the aromatic ring. From the viewpoint of improving light transmittance and improving surface hardness. The proportion of hydrogen atoms (number) directly bonded to the aromatic ring in the total hydrogen atoms (number) bonded to carbon atoms contained in the polyimide is preferably 60% or more, and more preferably 70% or more. It is preferable that
Here, the ratio of the hydrogen atoms (number) directly bonded to the aromatic ring in the total hydrogen atoms (number) bonded to the carbon atoms contained in the polyimide is determined by high-performance liquid chromatography or gas chromatography mass of the polyimide decomposition product. It can be determined using an analyzer and NMR. For example, the sample is decomposed with an alkaline aqueous solution or supercritical methanol, and the resulting decomposition product is separated by high performance liquid chromatography, and a qualitative analysis of each separated peak is performed by a gas chromatograph mass spectrometer, NMR, etc. The ratio of hydrogen atoms (numbers) directly bonded to the aromatic ring in the total hydrogen atoms (numbers) contained in the polyimide can be determined by performing determination using high performance liquid chromatography.

Moreover, as said polyimide, especially from the point which improves the light transmittance and surface hardness of a polyimide film, it contains an aromatic ring, and (i) a fluorine atom, (ii) an aliphatic ring, and (iii) aromatic It preferably contains at least one selected from the group consisting of a structure in which group rings are connected by a sulfonyl group or an alkylene group which may be substituted with fluorine.
Moreover, as said polyimide, especially the polyimide which contains a fluorine atom from the point of the light transmittance of a polyimide film and surface hardness is preferable.

As a preferred embodiment, the ratio (F / C) of the number of fluorine atoms (F) and 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 preferable that it is 0.05 to 0.8.
The ratio (F / N) of the number of fluorine atoms (F) and 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) and the number of silicon atoms (Si) on the film surface, measured by X-ray photoelectron spectroscopy of the polyimide film, is preferably 1 or more and 50 or less. It is preferably 3 or more and 30 or less.
Here, the said ratio by the measurement of X-ray photoelectron spectroscopy (XPS) is calculated | required from the value of atomic% of each atom of the polyimide film measured using an X-ray photoelectron spectrometer (for example, Thermo Scientific Thea Probe). be able to.

The atomic% of silicon atoms (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 from 0.1 to 10, and preferably from 0.2 to 5. Further preferred.
In the present invention, each atomic concentration of the polyimide film measured by X-ray photoelectron spectroscopy (XPS) can be measured by using an X-ray photoelectron spectrometer (for example, Thermo Scientific Thea Probe).

In addition, the glass transition temperature of the polyimide film obtained by the production method of the present invention is preferably 150 ° C. or higher from the viewpoint of heat resistance, more preferably 200 ° C. or higher, and the baking temperature can be reduced. The temperature is preferably 400 ° C. or lower, and more preferably 380 ° C. or lower. Moreover, it is preferable that the polyimide film obtained by the manufacturing method of this invention has one glass transition temperature in the temperature range of 150 to 400 degreeC.
The glass transition temperature is obtained from the peak temperature of a 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 where the maximum value of the peak is maximum when there are a plurality of peaks of the tan δ curve. As the dynamic viscoelasticity measurement, for example, with a dynamic viscoelasticity measuring device RSA III (TA Instruments Japan Co., Ltd.), the measurement range is -150 ° C to 400 ° C, the frequency is 1 Hz, and the temperature rises. This can be done at a rate of 5 ° C./min. Further, the measurement can be performed with a sample width of 5 mm and a distance between chucks of 20 mm.
In the present invention, the peak of the tan δ curve refers to a peak having an inflection point that is a maximum value, and a peak width between peak valleys of 3 ° C. or more, which is derived from measurement such as noise. The fine vertical fluctuation is not interpreted as the peak.

In addition, the polyimide film obtained by the production method of the present invention has a tensile elastic modulus at 25 ° C. measured based on a test piece of 15 mm × 40 mm in accordance with JIS K7127, a tensile speed of 10 mm / min, and a distance between chucks of 20 mm. It is preferable that it is 1.8 GPa or more. Since the surface elasticity sufficient as a protective film is obtained because the tensile modulus is high, the polyimide film obtained by the production method of the present invention can be suitably used as the surface material. The tensile elastic modulus is preferably 2.0 GPa or more, and more preferably 2.4 GPa or more. The preferred tensile modulus, polyimide polyimide film contains is, in the general formula (1 ') represents a tetravalent group R ¹ is a tetracarboxylic acid residue having an aromatic ring or aliphatic ring, R ² represents a divalent 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 and 90 mol% or less is easy to achieve also when it has a structure which is a diamine residue which does not have a silicon atom and has an aromatic ring or an aliphatic ring.
The tensile elastic modulus was obtained 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) at 25 ° C. The tensile speed can be 10 mm / min, and the distance between chucks can be 20 mm. The polyimide film for obtaining the tensile modulus of elasticity preferably has a thickness of 50 μm ± 5 μm.

In addition, in the polyimide film obtained by the production method of the present invention, when the static bending test is performed according to the following static bending test method from the point of excellent moisture absorption resistance and excellent bending resistance under high humidity. The internal angle measured in the test is preferably 120 ° or more, more preferably 125 ° or more, and still more preferably 130 ° or more. The preferable inner angle represents a tetravalent group in which the polyimide contained in the polyimide film is a tetracarboxylic acid residue having R ¹ having an aromatic ring or an aliphatic ring in the general formula (1 ′), and R ² Represents a divalent 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 test piece of polyimide film cut out to 15 mm × 40 mm is bent at a half of the long side, and both ends of the long side of the test piece sandwich a metal piece (100 mm × 30 mm × 6 mm) having a thickness of 6 mm from the upper and lower surfaces. Placed between glass plates (100 mm x 100 mm x 0.7 mm) from above and below with the tape fixed so that the overlap between the top and bottom surfaces of the test piece and the metal piece is 10 mm each. 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 there is no test piece, and is fixed with tape so that the glass plate is parallel. The test piece fixed in a 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 on the specimen. Thereafter, one end of the test piece is fixed, and the internal angle of the test piece 30 minutes after the force applied to the test piece is released is measured.

In addition, in the polyimide film obtained by the production method of the present invention, when the dynamic bending test is performed according to the following dynamic bending test method, it has excellent moisture absorption resistance and excellent bending resistance under high humidity. The inner angle of the test piece is preferably 155 ° or more, and more preferably 160 ° or more. The preferable inner angle represents a tetravalent group in which the polyimide contained in the polyimide film is a tetracarboxylic acid residue having R ¹ having an aromatic ring or an aliphatic ring in the general formula (1 ′), and R ² Represents a divalent 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]
Fix a polyimide film specimen cut to a size of 20 mm x 100 mm to a constant temperature and humidity chamber endurance test system (manufactured by Yuasa System Equipment Co., Ltd., planar loadless U-shaped expansion and contraction test jig DMX-FS) with tape. . The test piece was set in the same bent state as in the static bending test, that is, the distance between both ends of the long side of the bent test piece was set to 6 mm (fixed in a bent state with an inner diameter of 6 mm). Thereafter, bending is repeated 200,000 times with 90 times of bending per minute in an environment of 60 ± 2 ° C. and 93 ± 2% relative humidity (RH).
Thereafter, the test piece is removed, one end of the obtained test piece is fixed, and the inner angle of the test piece 30 minutes after measuring 200,000 times of bending is measured.

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, and the adhesion between the polyimide film and the hard coat layer From the point of the surface hardness of the laminated body which laminated | stacked the hard-coat layer adjacent to the property point and the polyimide film, it is preferable. 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. It represents a certain divalent group, 50 mol% 10 mol% or more of the total amount of R ² or less is a main one silicon atom in a chain or two with diamine residue, at least 50 mol% 90 mol% or less In the case of having a structure that is a diamine residue having no silicon atom and having an aromatic ring or an aliphatic ring, the cured film is peeled off when the adhesion test is performed according to the following adhesion test method. Hard to occur.
[Adhesion test method]
An adhesion evaluation composition prepared by adding 10 parts by mass of 1-hydroxy-cyclohexyl-phenyl-ketone to 100 parts by mass of pentaerythritol triacrylate in a 40% by mass methyl isobutyl ketone solution of pentaerythritol triacrylate A cured film having a thickness of 10 μm is formed by coating on a test piece of a polyimide film cut out to 10 cm × 10 cm and irradiating and curing ultraviolet rays at an exposure amount of 200 mJ / cm ² under a nitrogen stream. About the said cured film, the crosscut test based on JISK5600-5-6 is performed, and after peeling operation by a tape is repeatedly implemented 5 times, the presence or absence of peeling of a 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 JIS K5600-5-4 using a test pencil specified by JIS-S-6006 after the measurement sample is conditioned for 2 hours at a temperature of 25 ° C. and a relative humidity of 60%. (1999), a pencil hardness test (0.98 N load) is performed on the film surface, and the highest pencil hardness that does not cause scratches can be evaluated. For example, a pencil scratch coating film hardness tester manufactured by Toyo Seiki Co., Ltd. can be used.

The polyimide film obtained by the production method of the present invention preferably has a birefringence in the thickness direction at a wavelength of 590 nm of 0.020 or less. When the birefringence is small, the optical distortion is reduced, and therefore, when a polyimide film is used as a display surface material, it is possible to suppress a decrease in display quality of the display. The birefringence in the thickness direction at the 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. .
In addition, the birefringence of the thickness direction in wavelength 590nm of the polyimide film obtained by the manufacturing method of this invention can be calculated | required as follows.
First, the thickness direction retardation value (Rth) of a polyimide film is measured with light of 25 ° C. and a wavelength of 590 nm using a phase difference measuring device (for example, product name “KOBRA-WR” manufactured by Oji Scientific Instruments Co., Ltd.). To do. For the thickness direction retardation value (Rth), a phase difference value at 0 degree incidence and a phase difference value at an incidence angle of 40 degrees are measured, and the thickness direction retardation value Rth is calculated from these phase difference values. The retardation value at an oblique incidence of 40 degrees is measured by making light having a wavelength of 590 nm incident on the retardation film from a direction inclined by 40 degrees from the normal line 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. Said d represents the film thickness (nm) of a polyimide film.
The thickness direction retardation value is nx the refractive index in the slow axis direction in the in-plane direction of the film (the direction in which the refractive index in the film in-plane direction is maximum), and the fast axis direction in the film plane (film surface). Rth [nm] = {(nx + ny) / 2−nz} × d, where ny is the refractive index in the direction in which the refractive index in the inner direction is the minimum) and nz is the refractive index in the thickness direction of the film. 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 use, but is preferably 1 μm or more, more preferably 5 μm or more, and further more preferably 10 μm or more. preferable. On the other hand, it is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less.
If the thickness is thin, the strength is reduced and breakage is liable to occur. If the thickness is thick, the difference between the inner diameter and the outer diameter at the time of bending is increased, and the load on the film is increased.

  In addition, 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, or flame treatment.

The use of the polyimide film obtained by the production method of the present invention is not particularly limited. For example, the polyimide film can be used as a substrate or member for which a glass product such as a glass substrate has been conventionally used.
For example, since the polyimide film obtained by the production method of the present invention is suppressed in coloration and improved in transparency, it can be suitably used as a display surface material. In addition, since the polyimide film obtained by the production method of the present invention is easily improved in bending resistance, it can be used as a display that can handle curved surfaces, such as a flexible organic EL display that is thin and bent, a smartphone, a wristwatch type terminal, and the like. It can be suitably used for a portable terminal, a display device inside an automobile, a flexible panel used for a wristwatch, and the like. Moreover, the polyimide film obtained by the manufacturing method of the present invention is a solar cell panel such as 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 board, a surface protective film or a substrate material. The present invention can also be applied to a member for use, an optical waveguide member, other semiconductor-related members, and the like.

II. Production method of polyimide precursor Production method of polyimide precursor of the present invention,
Preparing a polyimide precursor solution;
Reducing the residual monomer in the polyimide precursor solution.

In the method for producing a polyimide precursor of the present invention, the step of preparing a polyimide precursor solution can be performed in the same manner as the polyimide precursor solution preparation step described in the above-described method for producing a polyimide film of the present invention.
Moreover, the process of reducing a residual monomer in the said polyimide precursor solution can be performed similarly to the polyimide precursor refinement | purification process demonstrated with the manufacturing method of the polyimide film of this invention mentioned above.
Since the polyimide precursor obtained by the production method of the present invention has a reduced residual monomer, the polyimide precursor is used for the production of a polyimide film, thereby suppressing coloring of the polyimide film due to oxidation of the residual monomer. be able to.

III. Production method of polyimide precursor composition Production method of polyimide precursor composition of the present invention,
Preparing a polyimide precursor solution;
Obtaining a purified polyimide precursor by reducing residual monomers in the polyimide precursor solution; and
And a step of preparing a polyimide precursor composition containing the purified polyimide precursor and an organic solvent.

Each said process which the manufacturing method of the polyimide precursor composition of this invention has can be performed similarly to each process demonstrated with the manufacturing method of the polyimide film of this invention mentioned above.
Since the polyimide precursor composition obtained by the production method of the present invention is obtained by re-dissolving the purified polyimide precursor, the residual monomer is reduced and no catalyst such as amine is contained. . Therefore, by using the polyimide precursor composition obtained by the production method of the present invention for the production of a polyimide film for thermal imidization, as described in the polyimide production method of the present invention described above, coloring is suppressed. Further, it is possible to obtain a polyimide film with improved transparency and further improved dimensional stability, solvent resistance, moisture absorption resistance or moisture permeability resistance, and bending resistance.

IV. The manufacturing method of a laminated body The manufacturing method of the laminated body of this invention, The process (henceforth a polyimide film manufacturing process) which manufactures a polyimide film with the manufacturing method of this invention mentioned above,
The process of forming the coating film of the composition for hard-coat layer formation containing at least 1 sort (s) of a radically polymerizable compound and a cationically polymerizable compound on the at least one surface of the polyimide film obtained by the said process (henceforth, hard-coat layer) 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).

  Since the manufacturing method of the laminate of the present invention uses the polyimide film obtained by the above-described manufacturing method of the present invention, the manufactured laminate has improved surface hardness, and further has a hard coat layer, resulting in a surface hardness. It is an improvement.

1. Polyimide film manufacturing process In the manufacturing method of the laminated body of this invention, since the manufacturing method of the polyimide film of this invention mentioned above can be used in the process of manufacturing a polyimide film, description here is abbreviate | omitted.

2. In the method for producing a laminate of the present invention, a radical polymerizable compound and a cationic 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 the composition for forming a hard coat layer containing at least one kind is formed.
The composition for forming a hard coat layer contains at least one of a radical polymerizable compound and a cationic polymerizable compound, and may further contain other components such as a polymerization initiator, a solvent, and an additive as necessary. Good.

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

The number of radical polymerizable groups contained in one molecule of the radical polymerizable compound is preferably 2 or more, and more preferably 3 or more from the viewpoint of improving the hardness of the hard coat layer.
As the radical polymerizable compound, a compound having a (meth) acryloyl group is preferable from the viewpoint of high reactivity, and further, the adhesiveness between the polyimide film and the hard coat layer, light transmittance and surface hardness. From this point, 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, a molecule called urethane (meth) acrylate, polyester (meth) acrylate, or epoxy (meth) acrylate An oligomer having a molecular weight of several hundreds to several thousands having several (meth) acryloyl groups therein can be preferably used.
In this specification, (meth) acryloyl represents each of acryloyl and methacryloyl, and (meth) acrylate represents each of acrylate and methacrylate.

  Specific examples of the radical polymerizable compound include vinyl compounds such as divinylbenzene; ethylene glycol di (meth) acrylate, bisphenol A epoxy di (meth) acrylate, 9,9-bis [4- (2- ( Meth) acryloyloxyethoxy) phenyl] fluorene, alkylene oxide modified bisphenol A di (meth) acrylate (eg ethoxylated (ethylene oxide modified) bisphenol A di (meth) acrylate), trimethylolpropane tri (meth) acrylate, tri Methylolethane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol tri (meth) acrylate, dipentaeryth Polyol polyacrylates such as tall tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, diacrylate of bisphenol A diglycidyl ether, diacrylate of hexanediol diglycidyl ether, etc. Examples thereof include epoxy acrylates, urethane acrylates obtained by the reaction of polyisocyanate and hydroxyl group-containing acrylates such as hydroxyethyl acrylate.

  A cationically polymerizable compound is a compound having a cationically polymerizable group. The cationic polymerizable group possessed by the cationic polymerizable compound is not particularly limited as long as it is a functional group capable of causing a cationic polymerization reaction, and examples thereof include an epoxy group, an oxetanyl group, and a vinyl ether group. When the cationic polymerizable compound has two or more cationic polymerizable groups, these cationic 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 2 or more, and more preferably 3 or more from the viewpoint of improving the hardness of the hard coat layer.
In addition, as the cationic polymerizable compound, among them, a compound having at least one of an epoxy group and an oxetanyl group as the cationic polymerizable group is preferable. From the viewpoint of hardness, a compound having two or more of at least one of an epoxy group and an oxetanyl group in one molecule is more preferable. Cyclic ether groups such as epoxy groups and oxetanyl groups are preferred from the viewpoint of small shrinkage accompanying the polymerization reaction. In addition, compounds having an epoxy group among the cyclic ether groups are easily available as compounds having various structures, do not adversely affect the durability of the obtained hard coat layer, and easily control the compatibility with the radical polymerizable compound. There is an advantage. Of the cyclic ether groups, the oxetanyl group has a high degree of polymerization and low toxicity compared to the epoxy group. When the obtained hard coat layer is combined with a compound having an epoxy group, a cation in the coating film is obtained. There are advantages such as speeding up the network formation obtained from the polymerizable compound and forming an independent network without leaving unreacted monomer in the film even in a region mixed with the radical polymerizable compound.

  As the cationically polymerizable compound having an epoxy group, for example, a polyglycidyl ether of a polyhydric alcohol having an alicyclic ring, a cyclohexene ring or a cyclopentene ring-containing compound may be used with an appropriate oxidizing agent such as hydrogen peroxide or peracid. Alicyclic epoxy resin obtained by epoxidation; polyglycidyl ether of aliphatic polyhydric alcohol or alkylene oxide adduct thereof, polyglycidyl ester of aliphatic long-chain polybasic acid, homopolymer of glycidyl (meth) acrylate, Aliphatic epoxy resins such as copolymers; glycidyl esters produced by the reaction of bisphenols such as bisphenol A, bisphenol F and hydrogenated bisphenol A, or derivatives thereof such as alkylene oxide adducts and caprolactone adducts, and epichlorohydrin. Ether, and novolac epoxy resins such as a and glycidyl ether type epoxy resins derived from bisphenols are exemplified.

  Examples of the alicyclic epoxy resin include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (UVR-6105, UVR-6107, UVR-6110), bis-3,4-epoxycyclohexylmethyl adipate. (UVR-6128) (In the above, the names in parentheses are trade names, manufactured by Dow Chemical).

  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), Polyglycerol polyglycidyl ether (Denacol EX). -512, Denacol EX-521), pentaerythritol polyglycidyl ether (Denacol EX-411), diglycerol polyglycidyl ether (Denacol EX-421), glycerol polyglycidyl ether (Denacol EX-313, Denacol EX-314), Trimethylolpropane polyglycidyl ether (Denacol EX-321), resortinol diglycidyl ether (Denacol EX-201), neopentyl glycol diglyci Luether (Denacol EX-211), 1,6 hexanediol 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), phenyl glycidyl 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), di Glycidyl terephthalate (Denacol EX-711), Glycidyl phthalimide (Denacol EX-731), Dibromophenyl glycidyl ether (Denacol EX-147), Dibromoneopentylglycol diglycidyl ether (Denacol EX-221) And manufactured by Nagase ChemteX).

  Other commercially available epoxy resins include trade names such as Epicoat 825, Epicoat 827, Epicoat 828, Epicoat 828EL, Epicoat 828XA, Epicoat 834, Epicoat 801, Epicoat 801P, Epicoat 802, Epicoat 815, Epicoat 815XA, 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. (above product name, di Bread epoxy resin) and the like.

  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-oxetanyl methyl ether (OXT-221), 3-ethyl-3--2-ethylhexyloxymethyl oxetane (OXT-212), 3-ethyl-3-phenoxymethyl oxetane (OXT- 211) (the name in parentheses is a product name manufactured by Toa Gosei Co., Ltd.), and the product names Etanacol EHO, Etanacol OXBP, Etanacol OXTP, Etanacol OXMA (above, trade name, manufactured by Ube Industries).

  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 advance radical polymerization and cationic polymerization.

  Any radical polymerization initiator may be used as long as it can release a substance that initiates radical polymerization by light irradiation and / or heating. For example, examples of the photo radical polymerization initiator include imidazole derivatives, bisimidazole derivatives, N-aryl glycine 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- Isoxazolone, 2-mercaptobenzimidazole, bis (2,4,5-triphenyl) imidazole, 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name Irgacure 651, Ciba Japan Co., Ltd.) 1-hydroxy-cyclohexyl-phenyl) Ketone (trade name Irgacure 184, manufactured by Ciba Japan), 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butan-1-one (trade names Irgacure 369, Ciba Japan ( Co., Ltd.), bis (η5-2,4-cyclopentadien-1-yl) -bis (2,6-difluoro-3- (1H-pyrrol-1-yl) -phenyl) titanium) (trade name Irgacure 784 However, it is not limited to these.

  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, K YACURE DMBI, and the like.

Moreover, the cationic polymerization initiator should just be able to discharge | release the substance which starts cationic polymerization by at least any one of light irradiation and a heating. Examples of the cationic polymerization initiator include sulfonic acid ester, imide sulfonate, dialkyl-4-hydroxysulfonium salt, arylsulfonic acid-p-nitrobenzyl ester, silanol-aluminum complex, (η ⁶ -benzene) (η ⁵ -cyclopentadidiene). Enyl) iron (II) and the like are exemplified, and more specifically, benzoin tosylate, 2,5-dinitrobenzyl tosylate, N-tosiphthalimide and the like are exemplified, but not limited thereto.

  Examples of radical polymerization initiators that can be used as cationic polymerization initiators include aromatic iodonium salts, aromatic sulfonium salts, aromatic diazonium salts, aromatic phosphonium salts, triazine compounds, iron arene complexes, and the like. More specifically, iodonium chloride such as diphenyliodonium, ditolyliodonium, bis (p-tert-butylphenyl) iodonium, bis (p-chlorophenyl) iodonium, bromide, borofluoride, hexafluorophosphate salt, hexafluoro Iodonium salts such as antimonate salts, chlorides of sulfonium such as triphenylsulfonium, 4-tert-butyltriphenylsulfonium, tris (4-methylphenyl) sulfonium, bromides, borofluorides, hexaf Sulfonium salts such as orophosphate salts and hexafluoroantimonate salts, 2,4,6-tris (trichloromethyl) -1,3,5-triazine, 2-phenyl-4,6-bis (trichloromethyl) -1, 2,4,6-substituted-1,3,5 triazine compounds such as 3,5-triazine, 2-methyl-4,6-bis (trichloromethyl) -1,3,5-triazine, etc. It is not limited to these.

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

As a method of forming a 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 publicly known on at least one surface of the polyimide film. The method of apply | coating with an application | coating means is mentioned.
The application means is not particularly limited as long as it is a method capable of being applied with a target film thickness, and examples thereof include the same means as means for applying the polyimide precursor composition to a support.
In addition, the coating film of the said composition for hard-coat layer formation may be formed only in one side of a polyimide film, and may be formed in both surfaces of a polyimide film.

  The coating film of the curable composition for hard coat layer is dried as necessary to remove the solvent. Examples of the drying method include reduced-pressure drying or heat drying, and a method combining these drying methods. Moreover, when drying at a normal pressure, it is preferable to dry at 30 degreeC or more and 110 degrees C or less.

3. Hard coating layer coating film curing step The coating composition obtained by applying the hard coating layer curable composition, and drying the coating as necessary, contains a radical polymerizable compound and a cationic polymerizable compound contained in the curable composition. Depending on the polymerizable group, the coating film is cured by at least one of light irradiation and heating, so that at least one polymer of a radical polymerizable compound and a cationic polymerizable compound is formed on at least one surface of the polyimide film. A hard coat layer can be formed.

For light irradiation, ultraviolet rays, visible light, electron beams, ionizing radiation, etc. are mainly used. In the case of ultraviolet curing, ultraviolet rays emitted from light such as an ultra-high pressure mercury lamp, a high pressure mercury lamp, a low pressure mercury lamp, a carbon arc, a xenon arc, and a metal halide lamp are used. The irradiation amount of the energy ray source is about 50 to 5000 mJ / cm ² as an integrated exposure amount at an ultraviolet wavelength of 365 nm.
When heating, the treatment is usually performed at a temperature of 40 ° C. or higher and 120 ° C. or lower. Moreover, you may react by leaving it to stand for 24 hours or more at room temperature (25 degreeC).

  Moreover, the manufacturing method of the laminated body of this invention is the range which does not impair the effect of this invention, for example, the process of forming other layers, such as gel containing urethane, an acrylic resin, etc., and well-known surface treatment. The process etc. to give may be included.

4). Laminate A laminate obtained by the production method of the present invention comprises a polyimide film obtained by the production method of the present invention described above, and a hard coat layer containing at least one polymer of a radical polymerizable compound and a cationic polymerizable compound. Is a laminated body positioned 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 side of the polyimide film, or the hard coat layer on both sides of the polyimide film. May be stacked adjacent to each other.
The hard coat layer may be provided with functions such as antireflection and antiglare properties. The function can be imparted, for example, by subjecting the hard coat layer to a known surface treatment or containing an additive such as inorganic or organic fine particles.
In addition, the laminate obtained by the production method of the present invention is a layer that does not impair the effects of the present invention, in addition to the polyimide film and the hard coat layer, and other layers such as a gel containing urethane and acrylic resin. May be laminated.

The total thickness of the laminate obtained by the production method of the present invention may be appropriately selected depending on the application, 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.
In the laminate of the present invention, the thickness of each hard coat layer may be appropriately selected depending on the application, but is preferably 2 μm or more and 80 μm or less, and more preferably 3 μm or more and 50 μm or less. Moreover, you may form a hard-coat layer on both surfaces of a polyimide film from a viewpoint of curl prevention.

In the laminate obtained by the production method of the present invention, the pencil hardness of the hard coat layer side surface 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.

In the laminate obtained by the production method of the present invention, the total light transmittance measured according to JIS K7361-1 is preferably 85% or more, more preferably 88% or more, and still more 90. % Or more is preferable. Thus, since the transmittance | permeability is high, transparency becomes favorable and it can become a glass substitute material.
The said total light transmittance of the laminated body obtained by the manufacturing method of this invention can be measured similarly to the total light transmittance measured based on JISK7361-1 of the said 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, more preferably 3.0 or less. Preferably, it is 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 based on JIS K7373-2006 of the polyimide film. .

The haze value based on JIS K-7105 of the laminate obtained by the production method of the present invention is preferably 5.0 or less, more preferably 2.0 or less, from the viewpoint of light transmittance. More preferably, it is 1.0 or less.
The haze value based on JIS K-7105 of the laminate obtained by the production method of the present invention can be measured in the same manner as the haze value of the polyimide film.

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

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

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

  The display surface material obtained by the production method of the present invention is used by being disposed so as to be positioned on the surface of various displays. The surface material for display obtained by the production method of the present invention has improved transparency, like the polyimide film obtained by the production method of the present invention and the laminate obtained by the production method of the present invention, Moreover, since it is easy to improve bending tolerance, it can be used suitably for flexible displays.

  The display surface material obtained by the production 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 production method of the present invention, etc. Can be used.

  When the display surface material obtained by the production method of the present invention is a laminate obtained by the production method of the present invention, the surface that is the outermost surface after being disposed on the surface of the display is the surface on the polyimide film side The surface material for display of the present invention is preferably arranged so that the surface on the hard coat layer side is the surface. The display surface material obtained by the production method of the present invention may have a fingerprint adhesion preventing layer on the outermost surface.

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

[Evaluation method]
<Weight average molecular weight of polyimide precursor>
The weight-average molecular weight of the polyimide precursor was determined using GPC using a polyimide precursor as an N-methylpyrrolidone (NMP) solution having a concentration of 0.5% by weight, and using a 10 mmol% LiBr-NMP solution having a water content of 500 ppm or less as a developing solvent. Using a device (manufactured by Tosoh Corporation, 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., and polystyrene having the same concentration as the sample. The weight average molecular weight was determined based on a 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 amount of 0.8 ml.

<Glass transition temperature>
Using a dynamic viscoelasticity measuring device RSA III (TA Instruments Japan Co., Ltd.), the measurement range is -150 ° C to 400 ° C, the frequency is 1 Hz, the heating rate is 5 ° C / min, and the sample width is Dynamic viscoelasticity measurement is performed at 5 mm and the distance between chucks is 20 mm, and the glass transition temperature (Tg) is obtained from the peak temperature of tan δ (tan δ = loss elastic modulus (E ″) / storage elastic modulus (E ′)). It was.

<Ammonium ion content>
The ammonium ion content in the polyimide film was determined as follows. A test piece of polyimide film having a weight of about 0.4 g cut out to 5 cm × 5 cm, the weight of which was measured, was put 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 60 ° C. water bath and allowed to stand for 1 hour or longer to elute ammonium ions in the polyimide film, and the ion concentration of the resulting eluate is determined by ion chromatography (Thermo Fisher Scientific Co., Ltd.). Company, ICS-3000), and the amount of ammonium ions per gram of polyimide film was calculated. The detection limit value of ammonium ions in the eluate is 0.1 ppb.

<Total light transmittance>
Based on JIS K7361-1, it measured with the haze meter (HM150 by Murakami Color Research Laboratory).

<YI value (yellowness)>
The YI value is a transmittance measured by a spectrocolorimetric method specified in JIS Z8720 using an ultraviolet-visible near-infrared spectrophotometer (JASCO Corporation V-7100) according to JIS K7373-2006. And calculated.

<Haze value>
Based on JIS K-7105, it measured with the haze meter (HM150 made by Murakami Color Research Laboratory).

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) ) Was dissolved at a liquid temperature of 30 ° C., and 2.22 g (5 mmol) of 4,4 ′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) was added at a temperature increase of 2 ° C. The mixture was gradually added to the following and stirred with a mechanical stirrer for 4 hours. 2,2′-bis (trifluoromethyl) benzidine (TFMB) 28.8 g (90 mmol) was added thereto, and after confirming complete dissolution, 4,4 ′-(hexafluoroisopropylidene) diphthalic acid Anhydrous anhydride (6FDA) 42.0 g (94.5 mmol) was gradually added several times so that the temperature rise was 2 ° C. or less, and a polyimide precursor solution 1 in which the polyimide precursor 1 was dissolved was synthesized. The molar ratio of TFMB used for the polyimide precursor 1 and AprTMOS was 90:10. The viscosity at 25 ° C. of the polyimide precursor solution 1 (solid content 20% by weight) 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 put into a beaker, stirred with a magnetic stirrer, and the polyimide precursor solution 1 diluted there was added dropwise at 2.5 g / min to precipitate the polyimide precursor 1. The precipitated polyimide precursor 1 was filtered and recovered by washing with 10 ml of water.
Using a solution (solid content: 4% by mass) of the recovered polyimide precursor 1 in dimethylacetamide, the polyimide precursor 1 was precipitated by the same method as described above, and the operation of recovering was repeated twice more. A fibrous purified polyimide precursor 1 was obtained.

(3) Preparation of polyimide precursor composition The polyimide precursor 1 obtained by repeating the precipitation and recovery operation three times in total was dissolved in dimethylacetamide so that the solid content was 25 wt%, and the polyimide precursor was obtained. Composition 1 was obtained.

(4) Preparation of polyimide film The polyimide precursor composition 1 was applied on glass and dried in a circulating oven at 120 ° C for 10 minutes. Next, under a nitrogen stream (oxygen concentration of 100 ppm or less), the temperature was raised to 330 ° C. at a rate of temperature rise of 10 ° C./min, held at 330 ° C. for 1 hour and then cooled to room temperature. The polyimide film of Example 1 was obtained by peeling from the glass. When measured using the obtained polyimide film, the glass transition temperature of the polyimide was 312 ° C.

(Comparative Example 1)
In Example 1, without purifying the polyimide precursor and preparing the polyimide precursor composition, the polyimide precursor solution 1 that was not purified was used instead of the polyimide precursor composition 1 when the polyimide film was produced. A polyimide film of Comparative Example 1 was obtained in the same manner as Example 1 except that it was used.

(Comparative Example 2)
In a 500 ml separable flask, add 302.0 g of dehydrated dimethylacetamide, 44.22 g (99.5 mmol) of 4,4 ′-(hexafluoroisopropylidene) 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, the mixture was heated to 120 ° C. and 40 g of pyridine was added. Subsequently, 50 g of trifluoroacetic anhydride was added and 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 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 put into a beaker, stirred with a magnetic stirrer, and the comparative polyimide resin solution A diluted there was added dropwise at 2.5 g / min to precipitate the comparative polyimide resin A. The comparative polyimide resin A thus precipitated was filtered and then recovered by washing with 10 ml of water. Using a solution (solid content: 4% by mass) of the recovered comparative polyimide resin A dissolved in dimethylacetamide, the comparative polyimide resin A was precipitated by the same method as described above, and the operation of recovering was repeated twice more. A powdered purified comparative polyimide resin A was obtained.

  The comparative polyimide resin A obtained by repeating the precipitation and recovery operation 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 coated on glass, put into an oven at 80 ° C., heated to 200 ° C. at a temperature rising 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 peeled from glass and the polyimide film of the comparative example 2 was obtained.

(Comparative Example 3)
Comparative polyimide resin obtained by repeating the operation of precipitating and recovering comparative polyimide resin A by the same method as in comparative example 2 for a total of 6 times using comparative polyimide resin solution A obtained by the same method as in comparative example 2. 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, a polyimide film of Comparative Example 3 was obtained in the same manner as Comparative Example 2 except that the comparative polyimide resin composition A ′ was used instead of the comparative polyimide resin composition A.

  About each polyimide film obtained in Example 1 and Comparative Examples 1-3, it evaluated using the said 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 coloring is suppressed. 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 the polyimide film of Example 1.
In Comparative Examples 2 and 3, since a polyimide film was prepared by chemical imidization using a catalyst, the polyimide film contained ammonium ions, had a higher YI value and higher haze than the polyimide film of Example 1, and a total light transmittance. Was low.

  Moreover, the following evaluation was performed about each polyimide film obtained by Example 1 and Comparative Examples 1 and 2. FIG.

<Static bending test>
Hereinafter, the method of the static bending test will be described with reference to FIG.
The polyimide film test piece 1 cut out to 15 mm × 40 mm is bent at the half of the long side, and the metal piece 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 is sandwiched from above and below. The test piece 1 was fixed with tape so that the overlap between the upper and lower surfaces of the test piece 1 and the metal piece 2 was 10 mm each. The metal piece 2 on 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 state of being bent with an inner diameter of 6 mm. At that time, dummy test pieces 4a and 4b were sandwiched between portions of the metal piece 2 where the test piece 1 was not provided, and fixed with tape so that the glass plates 3a and 3b were parallel.
After the test piece fixed in the bent state in this manner is left to stand for 24 hours in an environment of 60 ± 2 ° C. and 93 ± 2% relative humidity (RH), the glass plate and the test piece fixing tape are removed. The force applied to the test piece was released. Thereafter, 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. In addition, it is excellent in bending tolerance, so that the angle of the said internal angle is large. When the film returns completely without being affected by the static bending test, the interior angle is 180 °. Moreover, since the static bending test is performed under high humidity of 60 ± 2 ° C. and 93 ± 2% relative humidity (RH), the angle of the inner angle increases as the moisture absorption resistance is improved. If the moisture absorption resistance is poor, the film's bending resistance deteriorates due to moisture absorption, and the angle of the inner angle becomes small.
The inner angles of the polyimide films were 135 ° in Example 1, 130 ° in Comparative Example 1, and 120 ° in Comparative Example 2.

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

<Solvent resistance>
After the polyimide film test piece cut out to 5 cm × 5 cm was immersed in N-methyl-2-pyrrolidone (NMP) for 5 hours, whether or not the polyimide film was visually observed was observed. The polyimide film of Example 1 and Comparative Example 1 had only slight changes, and the polyimide film of Comparative Example 2 had changes such as distortion.

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

Moreover, it was HB as a result of evaluating the pencil hardness of the polyimide film obtained in Example 1 by the following method.
<Pencil hardness>
After the measurement sample was conditioned for 2 hours under the conditions of a temperature of 25 ° C. and a relative humidity of 60%, a pencil scratch coating film hardness tester manufactured by Toyo Seiki Co., Ltd. A pencil hardness test (0.98N load) defined in JIS K5600-5-4 (1999) was performed on the film surface, and the highest pencil hardness without scratches was evaluated.

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

Claims (8)

Preparing a polyimide precursor solution;
Obtaining a purified polyimide precursor by reducing residual monomers in the polyimide precursor solution; and
Preparing a polyimide precursor composition containing the purified polyimide precursor and an organic solvent;
Applying the polyimide precursor composition to a support to form a polyimide precursor coating;
The process of imidating a polyimide precursor by heating the said polyimide precursor coating film, The manufacturing method of a polyimide film. Obtaining the purified polyimide precursor,
The manufacturing method of the polyimide film of Claim 1 including the process of collect | recovering a polyimide precursor by dripping the said polyimide precursor solution to a poor solvent, and precipitating a polyimide precursor. The polyimide film is
Contains polyimide, does not contain ammonium ions,
The total light transmittance measured in accordance with JIS K7361-1 is 90% or more,
The haze value based on JIS K-7105 is 2.0 or less,
The manufacturing method of the polyimide film of Claim 1 or 2 whose yellowness calculated based on JISK7373-2006 is 5.0 or less. Preparing a polyimide precursor solution;
And a step of reducing residual monomer in the polyimide precursor solution. Reducing the residual monomer,
The manufacturing method of the polyimide precursor of Claim 4 including the process of collect | recovering a polyimide precursor by dripping the said polyimide precursor solution to a poor solvent, and precipitating a polyimide precursor. The process of manufacturing a polyimide film by the manufacturing method of any one of the said Claims 1-3,
Forming a coating film of a composition for forming a hard coat layer containing at least one of a radical polymerizable compound and a cationic polymerizable compound on at least one surface of the polyimide film obtained by the step;
And a step of curing the coating film.   The radical polymerizable compound is a compound having two or more (meth) acryloyl groups in one molecule, and the cationic polymerizable compound is a compound having two or more epoxy groups or oxetanyl groups in one molecule. The manufacturing method of the laminated body of Claim 6 which exists.   The surface for a display including the process of manufacturing a polyimide film with the manufacturing method of any one of the said Claims 1-3, or the process of manufacturing a laminated body with the manufacturing method of the said Claim 6 or 7. A method of manufacturing the material.

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