JP7519812B2 - Polyamic acid, polyimide and polyimide film - Google Patents

Description

The present invention relates to polyamic acid, polyimide, and polyimide film.

In recent years, there has been a demand for more flexible display devices, and attempts have been made to replace glass substrates with plastic materials. Among plastic materials, polyimide is a material that excels in heat resistance, insulation properties, and dimensional stability, and research is being conducted into its use as an alternative material to glass substrates.

For example, Patent Document 1 proposes that introducing amide bonds into polyimide improves scratch resistance and mechanical properties as well as UV blocking properties.

Patent Document 2 proposes adding silica fine particles to polyimide to produce a film that combines mechanical strength, surface hardness, and flex resistance.

Patent Document 3 proposes producing a polyimide resin film with low residual stress, little warping, small yellowness index (YI value), and high elongation by using a polyimide having a specific chemical structural formula.

Meanwhile, Patent Document 4 also describes the development of a diamine that can synthesize polyimides with improved solubility in organic solvents and melt moldability.

Special table 2019-510847 publication International Publication No. 2016/060213 International Publication No. 2017/051827 JP 2018-118947 A

Plastic materials used in the cover windows and touch panels of flexible display devices need to be both highly hard and tough. However, these properties are usually in a trade-off relationship, and there is still a demand for polyimides that adequately meet this requirement.

The inventors discovered that this problem could be solved by introducing a polyimide containing a residue derived from a diamine having a specific chemical structure, and thus completed the present invention.

（式（１）中、Ｒ₁～Ｒ₄のいずれかが、炭素数６～１０の芳香族基、炭素数６～１０のフェノキシ基、炭素数６～１０のベンジル基及び炭素数６～１０のベンジルオキシ基から選択され、それ以外のＲ₁～Ｒ₄が水素原子である。）で示されるジアミンから誘導される残基及び屈曲性ジアミンから誘導される残基を含む、ポリアミド酸。
［２］全ジアミン残基に占める、式（１）で示されるジアミンから誘導される残基と屈曲性ジアミンから誘導される残基の合計の割合が、３０モル％以上である、［１］のポリアミド酸。
［３］全ジアミン残基に占める、式（１）で示されるジアミンから誘導される残基の割合が２０モル％以上５９モル％以下であり、屈曲性ジアミンから誘導される残基の割合が１モル％以上１０モル％以下である、［１］又は［２］のポリアミド酸。
［４］屈曲性ジアミンが、式：

で示されるジアミンから選択される１種以上である、［１］～［３］のいずれかのポリアミド酸。
［５］屈曲性ジアミンが、７．１０ｅＶ以上のイオン化ポテンシャルを有する、［１］～［４］のいずれかのポリアミド酸。
［６］ジアミン残基が、式：

で示されるジアミンから誘導される残基の１種以上を含む、［１］～［５］のいずれかのポリアミド酸。
［７］酸二無水物が、式：

で示される酸二無水物から選択される１種以上である、［１］～［６］のいずれかのポリアミド酸。
［８］酸二無水物が、２．２５ｅＶ以下の電子親和力を有する、［１］～［７］のいずれかのポリアミド酸。
［９］[１]～[８]のいずれかのポリアミド酸のイミド化物であるポリイミド。
［１０］［９］のポリイミドを含むポリイミドフィルム。
［１１］フィルム厚４０～１５０μｍでの全光線透過率が９０％以上であり、イエローインデックスが３以下である、［１０］のポリイミドフィルム。 The gist of the present invention is as follows.
[1] A polyamic acid containing an acid dianhydride residue and a diamine residue,
The diamine residue is represented by formula (1):

(in formula (1), any of R ₁ to R ₄ is selected from an aromatic group having 6 to 10 carbon atoms, a phenoxy group having 6 to 10 carbon atoms, a benzyl group having 6 to 10 carbon atoms, and a benzyloxy group having 6 to 10 carbon atoms, and the remaining R ₁ to R ₄ are hydrogen atoms) and a residue derived from a flexible diamine.
[2] The polyamic acid according to [1], in which the total ratio of residues derived from the diamine represented by formula (1) and residues derived from the flexible diamine to all diamine residues is 30 mol % or more.
[3] The polyamic acid according to [1] or [2], in which the proportion of residues derived from the diamine represented by formula (1) in all diamine residues is 20 mol % or more and 59 mol % or less, and the proportion of residues derived from the flexible diamine is 1 mol % or more and 10 mol % or less.
[4] The flexible diamine has the formula:

The polyamic acid according to any one of [1] to [3], wherein the diamine is one or more selected from the diamines represented by the formula:
[5] The polyamic acid according to any one of [1] to [4], wherein the flexible diamine has an ionization potential of 7.10 eV or more.
[6] The diamine residue is represented by the formula:

The polyamic acid according to any one of [1] to [5], which contains one or more residues derived from a diamine represented by the following formula:
[7] The acid dianhydride is represented by the formula:

The polyamic acid according to any one of [1] to [6], wherein the polyamic acid is one or more selected from the acid dianhydrides represented by the following formula:
[8] The polyamic acid according to any one of [1] to [7], wherein the acid dianhydride has an electron affinity of 2.25 eV or less.
[9] A polyimide which is an imidized product of any one of the polyamic acids [1] to [8].
[10] A polyimide film comprising the polyimide of [9].
[11] The polyimide film according to [10], having a total light transmittance of 90% or more at a film thickness of 40 to 150 μm and a yellow index of 3 or less.

The polyamic acid of the present invention provides a polyimide having high hardness and toughness. In addition to these properties, the polyamic acid of the present invention can also provide a polyimide having high transparency and low yellowness.

The present invention relates to polyamic acid, a polyimide which is an imidized product of this polyamic acid, and a polyimide film containing this polyimide. The polyamic acid is obtained by polymerizing an acid dianhydride and a diamine, and has an acid dianhydride residue derived from the acid dianhydride and a diamine residue derived from the diamine.

（ここで、Ｒ₁～Ｒ₄のいずれかが、炭素原子数６～１０の芳香族基、炭素原子数６～１０のフェノキシ基、炭素原子数６～１０のベンジル基及び炭素原子数６～１０のベンジルオキシ基から選択され、それ以外のＲ₁～Ｒ₄が水素原子である。）で示されるジアミンから誘導される残基（「式（１）のジアミン残基」ともいう。）と屈曲性ジアミンから誘導される残基（「屈曲性ジアミン残基」ともいう。）を含む。一般に、硬度と伸びは相反する特性であるところ、式（１）のジアミン残基と屈曲性ジアミン残基を併用することにより、高硬度と強靭性の両方をポリイミドにもたらすことができる。 <Diamine>
The polyamic acid of the present invention has a diamine residue represented by the formula (1):

(wherein any of R ₁ to R ₄ is selected from an aromatic group having 6 to 10 carbon atoms, a phenoxy group having 6 to 10 carbon atoms, a benzyl group having 6 to 10 carbon atoms, and a benzyloxy group having 6 to 10 carbon atoms, and the remaining R ₁ to R ₄ are hydrogen atoms) (also referred to as "diamine residue of formula (1)") and a residue derived from a flexible diamine (also referred to as "flexible diamine residue"). Generally, hardness and elongation are contradictory properties, but by using the diamine residue of formula (1) in combination with the flexible diamine residue, it is possible to impart both high hardness and toughness to the polyimide.

<<Diamine represented by formula (1)>>
In the diamine represented by formula (1), one of the two benzene rings connected by an ester bond is unsubstituted at the position other than the position where the amino group is bonded, while the other benzene ring is substituted at least at one position with a group containing an aromatic group. This structure enhances the solubility in a solvent while maintaining the rigidity of the main chain, thereby achieving both the processability of the solution and the thermal and mechanical properties of the coating film.

At least one of R ₁ to R ₄ in formula (1) is an aromatic group having 6 to 10 carbon atoms, a phenoxy group having 6 to 10 carbon atoms, a benzyl group having 6 to 10 carbon atoms, or a benzyloxy group having 6 to 10 carbon atoms, and the rest are hydrogen atoms. Here, the aromatic group includes a substituent bonded to the main skeleton via an oxygen atom, a nitrogen atom, or a carbon atom. Furthermore, the aromatic group includes a heteroaromatic group such as a pyrrole group. The aromatic group is preferably unsubstituted, but may have one or more substituents such as an alkyl group, a halogen atom (such as a fluorine atom or a chlorine atom), an amino group, a nitro group, a hydroxyl group, a cyano group, a carboxyl group, or a sulfonic acid group.

It is preferable that one or two of R ₁ to R ₄ are aromatic groups, more preferably R ₁ and/or R ₃ are aromatic groups, even more preferably R ₁ or R ₃ are aromatic groups, and particularly preferably R ₃ is an aromatic group.

Examples of the aromatic group having 6 to 10 carbon atoms include a phenyl group, a tolyl group, a methylphenyl group, a dimethylphenyl group, an ethylphenyl group, a diethylphenyl group, a propylphenyl group, a butylphenyl group, a fluorophenyl group, a pentafluorophenyl group, a chlorophenyl group, a bromophenyl group, a methoxyphenyl group, a dimethoxyphenyl group, an ethoxyphenyl group, a diethoxyphenyl group, a methoxybenzyl group, a dimethoxybenzyl group, an ethoxybenzyl group, a diethoxybenzyl group, an aminophenyl group, an aminobenzyl group, a nitrophenyl group, a nitrobenzyl group, a cyanophenyl group, a cyanobenzyl group, a phenethyl group, a phenylpropyl group, a phenylamino group, a diphenylamino group, a biphenyl group, and a naphthyl group.
Examples of the phenoxy group having 6 to 10 carbon atoms include a methylphenoxy group, an ethylphenoxy group, a propylphenoxy group, a dimethylphenoxy group, a diethylphenoxy group, a methoxyphenoxy group, an ethoxyphenoxy group, and a dimethoxyphenoxy group.
Examples of the benzyl group having 6 to 10 carbon atoms include a benzyl group, a methylbenzyl group, an ethylbenzyl group, a propylbenzyl group, a dimethylbenzyl group, a methoxybenzyl group, an ethoxybenzyl group, and a methoxybenzyl group.
Examples of the benzyloxy group having 6 to 10 carbon atoms include a methylbenzyloxy group, a benzyloxy group, an ethylbenzyloxy group, a propylbenzyloxy group, a dimethylbenzyloxy group, a methoxybenzyloxy group, and an ethoxybenzyloxy group.
Among the above, from the viewpoint of transparency, aromatic groups having 6 to 10 carbon atoms are more preferred, with a phenyl group, a tolyl group, a methylphenyl group, a dimethylphenyl group, an ethylphenyl group and a diethylphenyl group being even more preferred, and a phenyl group being particularly preferred.

The diamine residue of formula (1) may be one type or a combination of two or more types.

<<Flexible diamine>>
The flexible diamine is a diamine containing a bending group such as -O-, _-CH2- , -C( _CH3 ) _2- , -C( _CF3 ) _2- , -C(=O)-, -S(=O) _2- , -S-, etc. in the main chain, or a diamine having a structure in which the nitrogen atoms of the two amino groups and the carbon atoms bonded thereto are not aligned in a straight line if the diamine does not have a bending group. However, the flexible diamine does not include the diamine represented by formula (1). By blending a diamine having such a structure, it is possible to increase the number of binding molecular chains located across a plurality of ordered regions in the film, thereby improving the mechanical flexibility.

As a diamine containing a bending group in the main chain, a diamine having a structure in which the bending group is directly bonded to a ring structure (e.g., a benzene ring) and a ring structure (e.g., a benzene ring) is preferred. In this case, the bond angle formed by the bending group and the two ring structures is less than 180 degrees, preferably 160 degrees or less, more preferably 130 degrees or less, and usually 90 degrees or more. The bond angle can be determined by a known calculation method, for example, empirical molecular orbital methods such as the Huckel method and the extended Huckel method, ab initio molecular orbital methods such as the Hartree-Fock method, the conformational substitution interaction method, and the multi-configuration SCF method, PPP approximation, semi-empirical molecular orbital methods such as CNDO/2, INDO, MNDO, AM1, and PM3, molecular dynamics methods such as MM2, and density functional methods such as BLYP and B3LYP.

等が好ましい。
上記において、化学構造式の下の数値は、イオン化ポテンシャル（ｅＶ）である。イオン化ポテンシャルは、Ｇａｕｓｓｉａｎ１６Ｗを用いたＤＦＴ法により、汎関数としてＢ３ＬＹＰ、分子軌道を構成する基底関数として６－３１１＋＋Ｇ（ｄ，ｐ）を用い、各ジアミンの構造パラメータとしてＢ３ＬＹＰ／６－３１１Ｇ（ｄ）基底で最適化したものを用いて求めた値である。 The flexible diamine includes a diamine having the formula:

etc. are preferred.
In the above, the numerical value under the chemical structural formula is the ionization potential (eV). The ionization potential is a value obtained by the DFT method using Gaussian16W, B3LYP as the functional, 6-311++G(d,p) as the basis function constituting the molecular orbital, and optimizing the structural parameters of each diamine with the B3LYP/6-311G(d) basis.

From the viewpoint of colorless transparency of polyimide, it is preferable to use a flexible diamine with an ionization potential of 7.10 eV or more, such as tCHDA, 3,3'-DDS, 6F-ODA, 3FMDA, 6FAP, 6FAPB, HFBAPP, BIS-A-AS, etc. From the viewpoint of solubility, 6F-ODA, 3FMDA, 6FAP, 6FAPB, HFBAPP, BIS-A-AS, etc. are more preferable.

The flexible diamine residue may be one type or a combination of two or more types.

<<Proportion of diamine residues>>
The total ratio of the diamine residue of formula (1) and the flexible diamine residue to the total diamine residue is preferably 30 mol% or more, more preferably 35 mol% or more, from the viewpoint of achieving both high hardness and toughness in the polyimide. The total ratio of the diamine residue of formula (1) and the flexible diamine residue may be 100 mol%, but residues derived from other diamines (also referred to as "other diamine residues") can be introduced depending on the solubility and required viscosity. For example, the total of the diamine residue of formula (1) and the flexible diamine can be 30 mol% or more and 60 mol% or less, and the other diamine residue can be 40 mol% or more and 70 mol% or less, and preferably the total of the diamine residue of formula (1) and the flexible diamine can be 35 mol% or more and 55 mol% or less, and the other diamine residue can be 45 mol% or more and 65 mol% or less.

The proportion of the diamine residues of formula (1) in the total diamine residues is preferably 20 mol% or more, more preferably 27 mol% or more, and preferably 59 mol% or less, more preferably 53 mol% or less. The proportion of the flexible diamine residues in the total diamine residues is preferably 1 mol% or more, more preferably 2 mol% or more, and preferably 10 mol% or less, more preferably 8 mol% or less. If the diamine residues of formula (1) and the flexible diamine are in the above ranges, the polyimide can be sufficiently provided with both high hardness and toughness.

のジアミンが挙げられ、溶解性の点からＴＦＭＢが好ましい。 <<Other diamines>>
As the diamine from which the other diamine residue is derived, from the viewpoint of improving the main chain rigidity and colorless transparency of the polyimide, it is preferable to use a non-flexible diamine having an ion potential of 7.10 eV or more. For example, a diamine represented by the formula:

Of these, TFMB is preferred from the viewpoint of solubility.

When other diamine residues are present, the other diamine residues may be one type or a combination of two or more types.

<Acid dianhydride>
The polyamic acid of the present invention contains an acid dianhydride residue, which is a residue derived from an acid dianhydride. The acid dianhydride residue is not particularly limited and can be a residue derived from a known acid dianhydride.

等が好ましい。上記において、化学構造式の下の数値は、電子親和力（ｅＶ）である。電子親和力は、上記のＤＦＴ法により求めた値である。 As the acid dianhydride, from the viewpoints of solubility and rigidity, a compound represented by the formula:

In the above, the numerical value under the chemical structural formula is the electron affinity (eV). The electron affinity is a value obtained by the above-mentioned DFT method.

From the viewpoint of colorless transparency of polyimide, it is preferable to use an acid dianhydride having an electron affinity of 2.25 eV or less, such as CBDA, BPAF, 6FDA, etc. From the viewpoint of solubility, it is preferable to use CBDA in combination with BPAF and/or 6FDA.

The acid dianhydride residue may be one type or a combination of two or more types.

<Polyamic acid>
The polyamic acid of the present invention can be obtained by polymerizing an acid dianhydride and a diamine. The molar ratio of the acid dianhydride and the diamine used in the reaction can be 0.95:1 to 1.05:1, preferably 0.97:1 to 1.03:1, from the viewpoint of polymerization.

The reaction can be carried out in an organic solvent, and the organic solvent is not particularly limited as long as it is an organic solvent inert to the reaction. In order to use the polyamic acid polymerization solution as is in the imidization step, examples of the organic solvent include N,N-dimethylacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, dimethylsulfoxide, m-cresol, γ-butyrolactone, cyclopentanone, cyclohexanone, and tetrahydrofuran. Among these, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and γ-butyrolactone are preferred in terms of solubility. The organic solvent may be one type or a combination of two or more types.

During the reaction, the solids concentration of the acid dianhydride and the diamine can be 5% by mass or more, and preferably 10% by mass or more, in order to increase the reaction rate, and can be 40% by mass or less, and preferably 25% by mass or less.
From the viewpoint of improving the reaction rate, the reaction temperature can be set to 20° C. or higher, and preferably 60° C. or higher, and can be set to 100° C. or lower, and preferably 80° C. or lower.
From the viewpoints of completion of the reaction and working efficiency, the reaction time can be 1 hour or more, preferably 2 hours or more, and can be 10 hours or less, preferably 8 hours or less.

（ここで、Ａは酸二無水物残基であり、Ｂはジアミン残基であり、ジアミン残基は、上記式（１）のジアミン残基及び上記屈曲性ジアミン残基を含む）で示される繰り返し単位を含む。 The resulting polyamic acid has the formula (2):

(wherein A is an acid dianhydride residue, B is a diamine residue, and the diamine residue includes the diamine residue of the above formula (1) and the above flexible diamine residue).

The above examples and preferred examples apply to the acid dianhydride residue, the diamine residue, the diamine residue of formula (1), and the flexible diamine residue.

The polyamic acid may have a weight average molecular weight (Mw) of 50,000 or more, preferably 60,000 or more, and may have a weight average molecular weight (Mw) of 100,000 or less, preferably 80,000 or less. If the weight average molecular weight (Mw) is within this range, the viscosity of the polyamic acid falls within a range that allows easy processing.
The weight average molecular weight is a value measured by size exclusion chromatography using polystyrene as a standard.

<Polyimide>
The present invention also relates to a polyimide which is an imidized product of the polyamic acid. The polyimide contains an acid dianhydride residue and a diamine residue, and the diamine residue contains a diamine residue of formula (1) and a flexible diamine residue. The above-mentioned examples and preferred examples are applied to the acid dianhydride residue, the diamine residue, the diamine residue of formula (1) and the flexible diamine residue.

Polyimide can be obtained by imidizing polyamic acid through dehydration and ring closure. Imidization can be thermal imidization, reflux imidization, or chemical imidization using a dehydrating agent. However, chemical imidization is preferred because the ring closure reaction proceeds at low temperatures, maintaining colorless transparency, and also improving mechanical properties by facilitating the formation of partially ordered (crystalline) regions within the molecular structure.

Thermal imidization can be performed by casting a polyamic acid solution and gradually heating it, while reflux imidization can be performed by adding an azeotropic solvent (e.g., toluene, xylene, etc.) that forms an azeotrope with the water produced during the imidization reaction to the polyamic acid solution and then heating it. A reaction accelerator may be used in these imidization processes.

Chemical imidization is preferably carried out in an organic solvent using a condensing agent and a reaction accelerator. For example, a polyamic acid containing a repeating unit represented by the above formula (2) can be imidized in an organic solvent using a condensing agent and a reaction accelerator.

The organic solvent is not particularly limited as long as it is an organic solvent inert to the reaction. In order to use the polyamic acid polymerization solution as is in the imidization step, examples of the organic solvent include N,N-dimethylacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, dimethylsulfoxide, m-cresol, γ-butyrolactone, cyclopentanone, cyclohexanone, and tetrahydrofuran. Among these, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and γ-butyrolactone are preferred in terms of improving solubility. The organic solvent may be one type or a combination of two or more types.

Examples of the condensing agent include acid anhydrides such as acetic anhydride, propionic anhydride, and trifluoroacetic anhydride, and phosphites such as triethyl phosphite, triethyl phosphite, tributyl phosphite, dimethyl phosphite, diethyl phosphite, and triphenyl phosphite. From the viewpoint of low boiling point of the by-product and easy removal, preferred are acetic anhydride, propionic anhydride, and trifluoroacetic anhydride, and more preferred is acetic anhydride.
The condensing agent may be one type or a combination of two or more types.
The amount of the condensing agent used may be 1 equivalent or more, preferably 2 equivalents or more, relative to the acid dianhydride, from the viewpoint of improving the reaction rate, and may be 5 equivalents or less, preferably 4 equivalents or less.

Examples of the reaction accelerator include triethylamine, diisopropylethylamine, N-methylpiperidine, pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 3-ethylpyridine, 3,5-dimethylpyridine, 3,5-diethylpyridine, isoquinoline, imidazole, 1-methylimidazole, 2-methylimidazole, and 1,2-dimethylimidazole. From the viewpoints of improving the reaction rate and maintaining colorless transparency, preferred are pyridine, 3-methylpyridine, 3-ethylpyridine, 3,5-dimethylpyridine, 3,5-diethylpyridine, isoquinoline, imidazole, 1-methylimidazole, 2-methylimidazole, and 1,2-dimethylimidazole, and more preferred are pyridine, 3-methylpyridine, 3-ethylpyridine, and isoquinoline.
The reaction accelerator may be one type or a combination of two or more types.
The amount of the reaction accelerator used may be 0.1 equivalents or more, preferably 0.2 equivalents or more, relative to the acid dianhydride, from the viewpoints of improving the reaction rate and maintaining colorless transparency, and may be 2 equivalents or less, preferably 1 equivalent or less.

The reaction temperature can be set to 0° C. or higher, preferably 60° C. or higher, and can be set to 120° C. or lower, preferably 85° C. or lower, from the viewpoints of improving the reaction rate and maintaining colorlessness and transparency.
From the viewpoints of reaction completion and working efficiency, the reaction time can be 1 hour or more, preferably 2 hours or more, and can be 4 hours or less, preferably 3 hours or less.
The reaction atmosphere is preferably a nitrogen atmosphere from the viewpoint of maintaining colorlessness and transparency.

Optionally, a terminal modifier may be added, and a process for distilling off the condensation agent and reaction promoter may be performed.

The resulting polyimide can be isolated by a known method. An example of an isolation method is reprecipitation. The resulting polyimide can also be made into a film without being isolated.

（ここで、Ａは酸二無水物残基であり、Ｂはジアミン残基であり、ジアミン残基は、上記式（１）のジアミン残基及び上記屈曲性ジアミン残基を含む）で示される繰り返し単位を含む。 The resulting polyimide has the formula (3):

(wherein A is an acid dianhydride residue, B is a diamine residue, and the diamine residue includes the diamine residue of the above formula (1) and the above flexible diamine residue).

The above examples and preferred examples apply to the acid dianhydride residue, the diamine residue, the diamine residue of formula (1), and the flexible diamine residue.

The polyimide may have a weight average molecular weight (Mw) of 50,000 or more, preferably 80,000 or more, and may have a weight average molecular weight (Mw) of 110,000 or less, preferably 100,000 or less.
The weight average molecular weight is a value measured by size exclusion chromatography using polystyrene as a standard.

The polyimide of the present invention is not limited to those produced via imidization of polyamic acid, so long as it has the above structure.

<Polyimide film>
The present invention also relates to a polyimide film comprising the above polyimide.

The polyimide film may contain additives such as photosensitizers (photoacid generators, photopolymerization initiators, photobase generators), sensitizers, adhesion agents, surfactants, leveling agents, colorants, release agents, stabilizers, plasticizers, lubricants, inorganic fillers, organic fillers, oils, fibers, fragrances, and defoamers, within the scope of the present invention.

The thickness of the polyimide film is not particularly limited and can be set appropriately depending on the application. For example, it can be 40 μm or more, preferably 45 μm or more, and can be 150 μm or less, preferably 120 μm or less.

The polyimide film of the present invention is excellent in that it has both high hardness and toughness.
The high hardness refers to a tensile modulus of elasticity of 6.0 GPa or more, and more preferably 6.5 GPa or more.
The toughness may be an elongation at break of 10% or more, and more preferably 15% or more.
These measurements can be carried out by the measurement methods described in the Examples below.

According to the present invention, a polyimide film having excellent colorless transparency can be obtained.
The colorless transparency may be a yellow index of 3 or less, a total light transmittance of 90% or more, and a haze of 1 or less, and more preferably a yellow index of 2 or less, a total light transmittance of 91% or more, and a haze of 0.5 or less.
These measurements can be carried out by the measurement methods described in the Examples below.

A polyimide film can be produced by casting a solution containing polyimide onto a support and drying the resulting coating to form a film. As the solution containing polyimide, a solution containing imidized polyimide can be used.

The method for applying the solution containing polyimide is not particularly limited, and any known application method can be used, such as a spin coater, bar coater, blade coater, comma coater, lip coater, rod coater, squeeze coater, reverse coater, transfer roll coater, gravure coater, spray coater, etc.

The support is not particularly limited, and examples thereof include substrates and films such as glass, ceramics, metals (aluminum foil, etc.), and resin films (polyester films such as PET and PEN, polyimide films, polyamideimide films, polypropylene films, polystyrene films, etc.). These substrates and films may have circuits formed from copper or the like.

Additives such as photosensitizers (photoacid generators, photopolymerization initiators, photobase generators), sensitizers, adhesion agents, surfactants, leveling agents, colorants, release agents, stabilizers, plasticizers, lubricants, inorganic fillers, organic fillers, oils, fibers, fragrances, and defoamers can be added to a solution containing polyimide within the scope of the present invention to produce a polyimide film containing these additives.

The coating thickness of the polyimide-containing solution can be set according to the desired thickness of the polyimide film.

After casting the solution containing polyimide, the resulting coating film can be dried to obtain a polyimide film. The drying method is not particularly limited, and any known method can be used, such as air drying, heat drying in an oven or on a hot plate, vacuum drying, etc.

The drying temperature can be set depending on the type of organic solvent. Drying can be carried out in air, but it is preferable to carry it out in an inert atmosphere such as nitrogen to prevent discoloration.

Polyimide films can be used as a glass replacement material, such as films for touch panels, cover films and back films for displays, and base films and cover films for flexible printed wiring boards.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

The polyimide films were evaluated as follows.
<Tensile modulus (GPa), maximum strength (MPa), and breaking elongation (%)>
The polyimide film was cut into a film width of 5 mm using a sample cutter and used as the measurement sample. The measurement was performed in accordance with ASTM D882 using an "EZ-LX" measuring device manufactured by Shimadzu Corporation. The gripper distance was 30 mm, the test speed was 3 mm/min, and measurements were performed 5 to 7 times per sample, and the average of the three highest points for each characteristic was recorded as the measurement result.

<Total light transmittance (%), haze (%)>
The polyimide film was used as it was as a measurement sample. Measurements were performed in accordance with JIS K7361-1 using a haze meter NDH7000 manufactured by Nippon Denshoku Industries Co., Ltd. as a measurement device, and measurement results were obtained.

<Yellow Index (YI)>
The polyimide film was used as a measurement sample as it was, and the color was measured in accordance with ASTM E313 using a color spectrometer CM-5 manufactured by Konica Minolta, Inc. as the measurement device.

Example 1
A 50 mL sample tube was charged with 1.022 g (5.21 mmol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 0.796 g (1.74 mmol) of 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF), 19.8 mg (0.17 mmol) of trans-1,4-cyclohexanediamine (tCHDA), 1.157 g (3.61 mmol) of 2,2'-bis(trifluoromethyl)benzidine (TFMB), and 1.005 g (3.30 mmol) of 2-phenyl-4,4'-diaminobenzanilide (PHBAAB; a compound in which R ₃ is phenyl, and R ₁ , R ₂ , and R ₄ are hydrogen atoms) and dissolved in 12 g of N,N-dimethylacetamide (DMAc). This solution was maintained at 60° C. and reacted for 2 hours to obtain a polyamic acid solution.

24 g of DMAc and 1.703 g of acetic anhydride were added to the obtained polyamide acid solution, and the solution was stirred until it became homogeneous. After that, 0.550 g of pyridine was added, and the solution was subjected to a chemical imidization reaction at 60°C for 2 hours to obtain a polyimide solution.

15 mg of a surface modifier (MEGAFAC R-94, manufactured by DIC Corporation) was added to 15 g of the obtained polyimide solution and stirred until homogenous. The obtained solution was applied to a soda glass plate, cast to a coating film of 500 μm, and then dried with hot air at 70°C for 30 minutes. The glass plate with the coating formed was placed in an inert gas oven and dried at 170°C in a nitrogen atmosphere for 1 hour to obtain a 50 μm polyimide film.

<Examples 1 to 12 and Comparative Examples 1 to 10>
Polyimide films of Examples 2 to 12 and Comparative Examples 1 and 2, and 4 to 8 were produced in the same manner as in Example 1, except that the types and amounts of acid dianhydrides and diamines shown in Table 1 were used. In Comparative Example 3, gelation occurred during the chemical imidization stage, making it impossible to form a film, and in Comparative Examples 9 and 10, the components were insoluble and it was impossible to produce a film. mTol used in Comparative Example 2 is a non-flexible diamine represented by the following formula, and has an ionization potential of 7.08 eV.

The properties of the resulting polyimide film were measured. The results are shown in Table 1.

As shown in Table 1, the polyimide films of the examples had a tensile modulus of 6.0 GPa or more, a breaking elongation of 10% or more, and were hard and tough. They also had good maximum strength, and had a yellow index of 3 or less, a total light transmittance of 90% or more, and a haze of 1 or less, and were excellent in terms of optical properties.

The polyamic acid of the present invention provides a polyimide having high hardness and toughness. In addition to these properties, the polyamic acid of the present invention can also provide a polyimide having high transparency and low yellowness. The polyimide, which is an imidized product of the polyamic acid of the present invention, and the polyimide film containing this polyimide have the above properties and are highly useful in industry.

Claims (9)

A polyamic acid containing an acid dianhydride residue and a diamine residue,
The diamine residue is represented by formula (1):
(in formula (1), any of R ₁ to R ₄ is selected from an aromatic group having 6 to 10 carbon atoms, a phenoxy group having 6 to 10 carbon atoms, a benzyl group having 6 to 10 carbon atoms, and a benzyloxy group having 6 to 10 carbon atoms, and the remaining R ₁ to R ₄ are hydrogen atoms) and a residue derived from a flexible diamine,
the total ratio of residues derived from the diamine represented by formula (1) and residues derived from the flexible diamine to the total diamine residues is 30 mol % or more;
A polyamic acid, in which the proportion of residues derived from a diamine represented by formula (1) is 20 mol % or more and 59 mol % or less of all diamine residues, and the proportion of residues derived from a flexible diamine is 1 mol % or more and 10 mol % or less . The flexible diamine has the formula:
2. The polyamic acid according to claim 1 , wherein the diamine is one or more selected from the group consisting of diamines represented by the formula: 3. The polyamic acid according to claim 1, wherein the flexible diamine has an ionization potential of 7.10 eV or more. The diamine residue has the formula:
4. The polyamic acid according to claim 1, which comprises one or more residues derived from a diamine represented by the formula: The acid dianhydride has the formula:
The polyamic acid according to any one of claims 1 to 4 , which is at least one selected from the group consisting of acid dianhydrides represented by the formula: The polyamic acid according to any one of claims 1 to 5 , wherein the acid dianhydride has an electron affinity of 2.25 eV or less. A polyimide which is an imidized product of the polyamic acid according to any one of claims 1 to 6 . A polyimide film comprising the polyimide according to claim 7 . 9. The polyimide film according to claim 8 , which has a total light transmittance of 90% or more at a film thickness of 40 to 150 μm and a yellow index of 3 or less.