WO2020235601A1 - Polyamic acid solution, method for preparing same, polyamide film, laminate, method for producing said laminate, and flexible device - Google Patents

Abstract

This polyamic acid solution includes: a polyamic acid having a terminal structure represented by general formula (1); and a polyamic acid having a terminal structure represented by general formula (2). For example, a polyamic acid solution can be prepared by hydrolytically ring-opening a tetracarboxylic acid dianhydride to form a ring-opening body, and by reacting diamine with a mixture of the tetracarboxylic acid dianhydride and the ring-opening body. In general formulae (1) and (2), X is a tetravalent organic group which is a tetracarboxylic acid dianhydride residue, and Y is a divalent organic group which is a diamine residue.

Description

Polyamic acid solution and its manufacturing method, polyimide film, laminate and its manufacturing method, and flexible device

The present invention relates to a polyamic acid solution and a method for producing the same. Furthermore, the present invention relates to a polyimide film obtained from the polyamic acid solution, a laminate in which a polyimide film is closely laminated on a substrate, and a device provided with an electronic element on the polyimide film.

A glass substrate is used as a substrate for electronic devices such as flat panel displays and electronic paper, but from the viewpoint of thinning, weight reduction, flexibility, etc., replacement of glass with a polymer film is being considered. As a polymer film material for electronic devices, polyimide is suitable because it has excellent heat resistance and dimensional stability.

As a method for efficiently manufacturing an electronic device using a polyimide film substrate, a laminate in which a polyimide film is closely laminated on a rigid substrate such as glass is produced, an element is formed on the polyimide film, and then the element is formed. A method of peeling the polyimide film from the rigid substrate has been proposed. A laminate in which a polyimide film is closely laminated on a rigid substrate is formed by applying a solution of polyamic acid, which is a precursor of polyimide, on the rigid substrate and dehydrating and cyclizing (imidizing) the polyamic acid by heating. Will be done.

Polyamic acid, which is a precursor of polyimide, is obtained by an addition reaction between tetracarboxylic dianhydride and diamine. The polyamic acid solution tends to change in viscosity due to polymerization or depolymerization over time, and storage stability may not be sufficient. As an attempt to improve the storage stability of the polyamic acid solution, Patent Document 1 proposes a method of sealing the ends of the polyamic acid with a non-reactive functional group.

International Publication No. 2012/03586

Since the polyimide film used as a substrate for flexible devices and the like is required to have sufficient mechanical strength, it is preferable that the polyimide constituting the film has a high molecular weight. As a method for obtaining a high molecular weight polyimide, it is common to increase the molecular weight of the precursor polyamic acid.

However, if the molecular weight of polyamic acid is increased, the viscosity of the solution increases and the handleability decreases. In order for the high molecular weight polyamic acid solution to have a viscosity suitable for coating on a substrate, it is necessary to lower the solid content concentration of the solution, resulting in a decrease in production efficiency due to an increase in the amount of solvent used and a solution. It causes a decrease in storage stability of.

In this way, it is generally a trade-off between giving a polyimide film high mechanical properties and increasing the storage stability of the solution by lowering the viscosity and increasing the solid content of the polyamic acid solution that is the precursor thereof. There is a relationship. In view of these, it is an object of the present invention to provide a polyamic acid having a low viscosity of a solution, excellent storage stability even when the solid content concentration is high, and having sufficient mechanical strength when a polyimide film is formed.

The above problem can be solved by the polyamic acid having a predetermined terminal structure. The polyamic acid solution of one embodiment of the present invention contains a polyamic acid having a terminal structure represented by the general formula (1) and a polyamic acid having a terminal structure represented by the general formula (2). X is a tetravalent organic group which is a tetracarboxylic dianhydride residue, and Y is a divalent organic group which is a diamine residue.

The weight average molecular weight of the polyamic acid is preferably 5000 or more and 45000 or less. The water content of the polyamic acid solution is preferably 1500 ppm or less. The imidization ratio of the polyamic acid in the polyamic acid solution is preferably 5 mol% or less.

The solid content concentration of the polyamic acid solution is preferably 10% by weight or more. The ratio logη / D of the log η of the viscosity η (unit: poise) of the polyamic acid solution at the temperature of 23 ° C. to the solid content concentration D (unit: weight%) of the polyamic acid is preferably 0.12 or less.

In the above-mentioned polyamic acid solution, for example, tetracarboxylic dianhydride is hydrocyclic to form a ring-opened body, and a mixture of tetracarboxylic dianhydride and the ring-opened body thereof is reacted with diamine to form a polyamide. Obtained by polymerizing an acid. Hydrocyclic ringing of the tetracarboxylic dianhydride is carried out, for example, at a temperature of 50 to 100 ° C. in a solution containing 2 to 10 mol% of water with respect to the total amount of the tetracarboxylic dianhydride.

By water ring opening, a single ring opening represented by the following general formula (4) is produced. By water-opening, a bicyclic ring represented by the following general formula (3) may be further produced.

The amount of one-sided ring-opened body produced by water-opening is preferably 1 to 15 mol% based on the total amount of tetracarboxylic acid. The amount of both ring-opened bodies produced by water-opening may be 0.1 to 5 mol% with respect to the total amount of tetracarboxylic acid. The total amount of tetracarboxylic acid (total number of moles) is the number of moles of unopened tetracarboxylic dianhydride x ₁ , the number of moles of single-opened ring x _2, and the number of moles of bi-opened ring x ₃ . The total is x ₁ + x ₂ + x ₃ .

The polyamic acid solution may further contain a polyamic acid having a terminal structure represented by the general formula (5). R ¹ is a divalent organic group, and R ² is an alkyl group having 1 to 5 carbon atoms.

By reacting the alkoxysilane compound with the polyamic acid and modifying the terminal of the polyamic acid with an alkoxysilane, a polyamic acid having a terminal structure represented by the above general formula (5) is produced.

Polyimide can be obtained by the dehydration cyclization reaction of the above polyamic acid. For example, by applying a polyamic acid solution on a substrate and dehydrating and cyclizing the polyamic acid by heating to imidize, a laminate in which a polyimide film is closely laminated on the substrate can be obtained. A polyimide film can be obtained by peeling the polyimide film from the substrate.

A flexible device can be manufactured by providing an electronic element on a polyimide film. An electronic element may be provided on the polyimide film before the polyimide film is peeled from the laminate, and then the polyimide film may be peeled from the laminate.

The polyamic acid solution of the present invention has a low viscosity and is excellent in storage stability, so that it is easy to handle. The polyimide film produced by using the polyamic acid solution has excellent mechanical strength and is suitably used as a substrate for a flexible device or the like.

[Polyamic acid solution]
Polyamic acid is a polyaddition reaction product of tetracarboxylic dianhydride and diamine. The tetracarboxylic dianhydride is a compound represented by the following general formula (A), and the diamine is a compound represented by the following general formula (B). The polyamic acid has a repeating unit of the following general formula (P).

In the general formulas (A) and (P), X is a residue of tetracarboxylic dianhydride. The residue of tetracarboxylic dianhydride is a portion other than the two acid anhydride groups (-CO-O-CO-) in the compound of the general formula (A), and is a tetravalent organic group. In tetracarboxylic dianhydride, two of the four carbonyl groups bonded to X form a pair, and together with X and an oxygen atom, form a five-membered ring. In the general formulas (B) and (P), Y is a diamine residue. The residue of the diamine is a portion other than the _two amino groups (-NH ₂ ) in the compound of the general formula (B), and is a divalent organic group.

The general polyamic acid obtained by the reaction of tetracarboxylic dianhydride and diamine has a terminal structure (amine terminal) represented by the following general formula (Q) and a terminal represented by the following general formula (R). It has a structure (acid anhydride terminal).

The polyamic acid solution of the embodiment of the present invention has one characteristic in the terminal structure of the polyamic acid, and the terminal structure represented by the general formula (1) (the acid dianhydride group at the terminal is hydrocyclic. Polyamic acid) and a terminal structure represented by the general formula (2) (amine-terminated polyamic acid).

The polyamic acid solution may further contain a compound (tetracarboxylic acid) represented by the general formula (3).

X in the general formulas (1) to (3) is a residue of tetracarboxylic dianhydride, and Y is a residue of diamine.

The terminal structure of the general formula (2) is an amine terminal contained in a general polyamic acid (same as the above general formula (Q)), but the hydrocyclic ring-opened terminal structure of the general formula (1) is a tetracarboxylic acid. It is a structure not contained in polyamic acid obtained only by the reaction of dianhydride and diamine. That is, the polyamic acid solution of the embodiment of the present invention contains the polyamic acid having the terminal structure represented by the general formula (1) in addition to the polyamic acid having an amine terminal contained in the general polyamic acid. It is one of the features.

The structure of both ends of the polyamic acid molecule may be the same or different. Although it depends on the charging ratio of the raw materials and the reaction conditions, the polyamic acid is generally a mixture of a polyamic acid having the same terminal structure and a polyamic acid having a different terminal structure. That is, the polyamic acid solution contains a polyamic acid having both ends represented by the general formula (1); a polyamic acid having both ends represented by the general formula (2); and one end. It contains a polyamic acid having a structure represented by (1) and having a structure represented by (2) at the other end. The polyamic acid may contain the terminal structure (acid anhydride terminal) of the above general formula (R) in addition to the terminal structure of the general formula (1) and the terminal structure of the general formula (2).

The terminal structure of the general formula (1) is formed, for example, by the reaction of the amine terminal of the polyamic acid or the diamine with the single ring-opened ring of the tetracarboxylic dianhydride. In the polyamic acid solution, the ratio of the terminal structure of the general formula (1) to all the terminals of the polyamic acid is preferably 1 mol% or more.

The polyamic acid solution of the present embodiment preferably has a polyamic acid having a weight average molecular weight of 5000 to 45000. The water content of the polyamic acid solution may be 1500 ppm or less. The solid content concentration of the polyamic acid solution is preferably 10% by weight or more. The polyamic acid contained in the polyamic acid solution may be partially imidized, but the imidization ratio is preferably 5 mol% or less.

[Preparation of polyamic acid solution]
Hereinafter, the structure of the polyamic acid will be described in more detail with reference to the method for producing the polyamic acid. As described above, polyamic acid is obtained by an addition reaction of tetracarboxylic dianhydride and diamine.

<Tetracarboxylic dianhydride>
Examples of the tetracarboxylic dianhydride include 3,3', 4,4'-biphenyltetracarboxylic dianhydride (hereinafter, may be abbreviated as BPDA), pyromellitic dianhydride, 3,3',. 4,4'-benzophenonetetracarboxylic dianhydride, 2,3,3', 4'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'-diphenylsulfonetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 4, 4'-oxydiphthalic dianhydride, 9,9-bis (3,4-dicarboxyphenyl) fluorene dianhydride, 9,9'-bis [4- (3,4-dicarboxyphenoxy) phenyl] fluorene dianhydride , 3,3', 4,4'-biphenyl ethertetracarboxylic dianhydride, 2,3,5,6-pyridinetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride Anhydride, 4,4'-sulfonyldiphthalic acid dianhydride, paraterphenyl-3,4,3', 4'-tetracarboxylic dianhydride, metaterphenyl-3,3', 4,4' Examples thereof include aromatic ring-type tetracarboxylic dianhydrides such as -tetracarboxylic dianhydride and 3,3', 4,4'-diphenyl ether tetracarboxylic dianhydride. The aromatic ring of the tetracarboxylic dianhydride may have a substituent such as an alkyl group, a halogen, or a halogen-substituted alkyl group.

The tetracarboxylic dianhydride may be an alicyclic tetracarboxylic dianhydride. Examples of the alicyclic tetracarboxylic acid dianhydride include cyclohexanetetracarboxylic acid dianhydride, bicyclo [2.2.2] octane-2,3,5,6-tetracarboxylic acid dianhydride, and 5- (dioxo). Tetrahydrofuryl-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride, 4- (2,5-dioxo tetrahydrofuran-3-yl) -tetraline-1,2-dicarboxylic acid anhydride, tetrahydrofuran -2,3,4,5-Tetracarboxylic acid dianhydride, bicyclo-3,3', 4,4'-tetracarboxylic acid dianhydride, 1,2,3,4-cyclopentanetetracarboxylic acid dianhydride , 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,3-dimethyl-1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, 1,4-dimethyl-1,2, Examples thereof include 3,4-cyclobutanetetracarboxylic acid dianhydride.

Two or more types of tetracarboxylic dianhydride may be used in combination. In order to obtain a polyimide film having a low coefficient of linear expansion, it is preferable that the residue X of the tetracarboxylic dianhydride has a rigid structure. Therefore, it is preferable to use an aromatic ring-type tetracarboxylic dianhydride as a raw material for the polyamic acid, and it is preferable that 95 mol% or more of the tetracarboxylic dianhydride is an aromatic ring type. Among the aromatic ring-type tetracarboxylic dianhydrides, BPDA or pyromellitic dianhydride is preferable, and BPDA is particularly preferable because the rigidity is high and the coefficient of linear thermal expansion of the polyimide film can be lowered. It is preferable that 95 mol% or more of the tetracarboxylic dianhydride is BPDA.

<Diamine>
Examples of the diamine include paraphenylenediamine (hereinafter sometimes abbreviated as PDA), 4,4'-diaminobenzidine, 4,4 "-diaminoparatelphenyl, 4,4'-diaminodiphenyl ether, and 3,4'-diamino. Diphenyl ether, 4,4'-diaminodiphenylsulfone, 1,5-bis (4-aminophenoxy) pentane, 1,3-bis (4-aminophenoxy) -2,2-dimethylpropane, 2,2-bis (4) -Aminophenoxyphenyl) propane, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis (trifluoromethyl) benzidine, 4,4 Aromatic diamines such as'-diaminobenzidine, 9,9'-(4-aminophenyl) fluorene, 9,9'-(4-amino-3-methylphenyl) fluorene; and 1,4-cyclohexanediamine, An alicyclic diamine such as 4,4'-methylenebis (cyclohexaneamine) can be exemplified.

Two or more types of diamines may be used in combination. In order to obtain a polyimide film having a low coefficient of linear expansion, it is preferable that the residue Y of the diamine has a rigid structure. Therefore, it is preferable to use an aromatic ring diamine as a raw material for the polyamic acid, and it is preferable that 95 mol% or more of the diamine is an aromatic diamine. Among the aromatic ring-type diamines, PDA or 4,4 "-diaminoparaterphenyl is preferable, and PDA is particularly preferable because the rigidity is high and the coefficient of linear thermal expansion of the polyimide film can be lowered. 95 mol% or more of the diamine is PDA. Is preferable.

[Method for producing polyamic acid]
As described above, polycarboxylic acid is obtained by reacting tetracarboxylic dianhydride and diamine in an organic solvent. The polyamic acid having the terminal structure (amine terminal) of the general formula (2) is also contained in the general polyamic acid, and is produced by the reaction of tetracarboxylic acid dianhydride and diamine.

The terminal structure (ring-opening acid terminal) of the general formula (1) is formed by the reaction of an amine terminal or diamine of polyamic acid with a single ring-opening body of tetracarboxylic dianhydride, or ring opening of the acid anhydride terminal. Will be done. From the viewpoints of controlling the molecular weight of polyamic acid, controlling the amount of water in the composition, suppressing imidization of polyamic acid, and storing stability of the solution, a monocyclic ring of tetracarboxylic acid dianhydride as a polymerization monomer of polyamic acid. The method using is preferable.

In one embodiment, after hydrocyclic ringing of the tetracarboxylic dianhydride, a mixture of the tetracarboxylic dianhydride and the ring-opened body is reacted with diamine to obtain the terminal structure of the general formula (1). A composition (polyamic acid solution) containing the polyamic acid having the polyamic acid and the polyamic acid having the terminal structure of the general formula (2) can be obtained.

<Hydro-opening of tetracarboxylic dianhydride>
When tetracarboxylic dianhydride is hydrocyclic, only one of the two acid anhydride portions is ring-opened to form a dicarboxylic acid, and the other remains an acid anhydride (single ring compound). .. In the hydrocyclic ring-opening of a tetracarboxylic dianhydride, in addition to the single ring-opened compound, a compound in which both of the two acid anhydride moieties are ring-opened (bicyclic ring-opened compound) is generally produced. The single ring-opened body is represented by the general formula (4), and the double ring-opened body is represented by the general formula (3). X in the general formula (3) and the general formula (4) is a tetracarboxylic dianhydride residue.

The hydrocyclic ring of the tetracarboxylic dianhydride is preferably carried out in an organic solvent in which water is present. As the organic solvent, a polar solvent having miscibility with water is preferable, and the same organic solvent as the organic solvent used for the polymerization of polyamic acid is preferable. As the organic solvent used for hydrocyclic ring-opening of tetracarboxylic acid and polymerization of polyamic acid, amide-based solvents such as N, N-dimethylformamide, N, N-dimethylacetamide and N-methyl-2-pyrrolidone are preferable. When N-methyl-2-pyrrolidone is used as the organic solvent, the storage stability of the polyamic acid solution tends to be high.

The hydrocyclic ring may be carried out in either a state in which only the tetracarboxylic dianhydride is present or after the tetracarboxylic dianhydride and the diamine are mixed. In the presence of diamine, the addition reaction of tetracarboxylic dianhydride and diamine (polymerization reaction of polyamic acid) and the ring-opening of tetracarboxylic acid competitively occur, but the former tends to be prioritized and the ring-opened body. Tends to be insufficient, and it tends to be difficult to control the amount of ring-opened body produced. Therefore, it is preferable to carry out the hydrocyclic ring-opening of the tetracarboxylic acid before mixing with the diamine.

From the viewpoint of effectively utilizing the water contained in the system to perform hydrocyclic ring while ensuring the solubility (or dispersibility) of tetracarboxylic dianhydride in an organic solvent, tetracarboxylic in the hydrocyclic ring reaction system. The concentration of the acid dianhydride is preferably 3 to 40% by weight, more preferably 5 to 35% by weight, still more preferably 7 to 30% by weight. The concentration of tetracarboxylic dianhydride may be 10% by weight or more, 15% by weight or more, or 17% by weight or more.

The water content in the water-opening reaction system is preferably 200 to 5000 ppm, more preferably 300 to 4000 ppm, further preferably 400 to 3500 ppm, and particularly preferably 500 to 3000 ppm. The water content may be 700 ppm or more or 1000 ppm or more. From the viewpoint of controlling the amount of ring-opened body produced, the amount of water in the hydrocyclic ring-opening reaction system is preferably 1 to 15 mol%, more preferably 2 to 12 mol%, based on the tetracarboxylic dianhydride. It may be 3 to 11 mol%, 5 to 10 mol% or 6 to 9 mol%.

Industrially available organic solvents generally contain tens to hundreds of ppm of water. Water contained in the organic solvent can be used as it is for hydrolysis, but water contained in the organic solvent alone may not sufficiently produce a ring-opened body. Therefore, it is preferable to add water to the organic solvent to adjust the water content within the above range.

The hydrocyclic ring-opening reaction of the tetracarboxylic dianhydride proceeds even at room temperature, but it is preferably carried out under heating from the viewpoint of shortening the reaction time and controlling the amount of ring-opened body produced. The reaction temperature is preferably 50 to 100 ° C., more preferably 60 to 95 ° C., and may be 65 to 90 ° C. or 70 to 85 ° C. From the viewpoint of improving reactivity (ring-opening body formation efficiency), it is preferable that the reaction temperature is high, but when the temperature exceeds 100 ° C. (boiling point of water), the water content of the system sharply decreases and ring-opening body is formed. The amount tends to decrease. The reaction time (heating time) is about 20 minutes to 24 hours, more preferably 1 to 12 hours, still more preferably 2 to 5 hours.

The hydrocyclic ring opens the acid anhydride portion of the tetracarboxylic acid dianhydride, but the residue X of the tetracarboxylic acid dianhydride does not change before and after the reaction. Therefore, the total number of moles x of the tetracarboxylic dianhydride residue X is equal to the amount of the tetracarboxylic dianhydride charged (the total number of moles of the tetracarboxylic dianhydride before the hydrocyclic ring), and the water is added. After the ring-opening reaction, the sum of the number of moles of tetracarboxylic dianhydride (unopened ring) x ₁ , the number of moles of single-opened ring x ₂ , and the number of moles of both ring-opened bodies x ₃ (x ₁ + x _2). Equal to + x ₃ ).

The larger the amount of one-sided ring-opened body produced by water-opening, the smaller the molecular weight of polyamic acid after polymerization tends to be. The total number of moles of tetracarboxylic dian after hydrocyclic ring, that is, the unopened tetracarboxylic dianhydride, the ring-opened tetracarboxylic dianhydride, and the bicyclic dianhydride. The ratio of the number of moles (x ₂ ) of the single-open ring to the total number of moles (x ₁ + x ₂ + x ₃ ) is preferably 0.01 to 0.15 (1 to 15 mol%), and 0.02 to 0.02 to It is more preferably 0.12 (2 to 12 mol%), and may be 0.03 to 0.10 (3 to 10 mol%) or 0.04 to 0.09 (4 to 9 mol%). The ratio of the total number of moles of tetracarboxylic acid _{(x 1 + x 2 + x} 3) the number of moles of both open annulus for _{(x 3): x 3 /} (x 1 + x 2 + x 3) , for example, from 0.0001 to 0 It is about 0.05 (0.01 to 5 mol%), 0.0005 to 0.02 (0.05 to 2 mol%) or 0.001 to 0.1 (0.1 to 1 mol%). You may.

In the reaction between a tetracarboxylic acid (including an unopened dianhydride and a ring-opened body) and a diamine, when a single-opened ring of the tetracarboxylic dianhydride reacts at the amine terminal, it is represented by the general formula (1). A hydrocyclic terminal is produced. In the polymerization reaction, both ring-opened dianhydrides of tetracarboxylic dianhydride hardly react. Therefore, the polyamic acid solution may contain a bicyclic ring of tetracarboxylic dianhydride. Therefore, the number of moles of both ring-opened tetracarboxylic dianhydrides in the polyamic acid solution is substantially equal to the number of moles x ₃ of the tetracarboxylic acid after water ring-opening.

<Polymerization of polyamic acid>
Polyamic acid is obtained by reacting tetracarboxylic dianhydride and diamine in an organic solvent. In this embodiment, a mixture of tetracarboxylic dianhydride obtained by ring-opening and a ring-opening product thereof is reacted with diamine. The reaction between the tetracarboxylic acid and the diamine may be carried out by mixing the tetracarboxylic acid solution after the ring-opening and the diamine. A diamine solution previously dissolved in an organic solvent and a tetracarboxylic acid solution after ring-opening may be mixed. Further, a tetracarboxylic dianhydride that has not undergone a water-opening reaction may be added.

The ratio x / y of the total number of moles of the tetracarboxylic acid (x = x ₁ + x ₂ + x ₃ ) to the total number of moles (y) of the diamine is preferably 0.950 to 1.050, preferably 0.970 to 1.030. Is more preferable, and 0.990 to 1.010 is even more preferable. When x / y is in the above range, the ratio of the terminal structure of the general formula (1) to the terminal structure of the general formula (2) and the molecular weight of the polyamic acid in the polyamic acid are in the appropriate range, and the polyamic acid solution has storage stability. It is easy to obtain a polyimide film having excellent mechanical strength because the molecular weight tends to increase at the time of imidization.

The concentration of polyamic acid in the polyamic acid solution (total concentration of diamine and tetracarboxylic acid) is preferably 5 to 45% by weight, more preferably 10 to 35% by weight, further preferably 13 to 30% by weight, and 15% by weight. % Or more or 17% by weight or more. By setting the charging concentration within the above range, the polymerization reaction is likely to proceed, and gelation due to abnormal polymerization of the undissolved raw material is suppressed. In the present embodiment, since the reaction system contains a single ring-opened dianhydride of tetracarboxylic dianhydride, an excessive increase in molecular weight of the polyamic acid is suppressed, and an excessive viscosity of the reaction solution viscosity is suppressed even when the charged concentration is high. It can suppress the rise and gelation.

From the viewpoint of increasing the polymerization reaction rate and suppressing the depolymerization reaction, the reaction temperature (solution temperature) is preferably 0 ° C. to 70 ° C., more preferably 20 ° C. to 65 ° C., and may be 30 to 60 ° C. .. When the reaction temperature is excessively high, in addition to the decrease in molecular weight due to the depolymerization of the polyamic acid, dehydration cyclization (imidization) of the polyamic acid is likely to occur, and the water content increases accordingly, so that the polyamic acid solution Storage stability may decrease. Therefore, it is preferable to control the temperature at the time of polymerization to around 50 ° C. to suppress an increase in the water content due to imidization of the polyamic acid. For the purpose of adjusting the molecular weight of the polyamic acid, the obtained polyamic acid solution may be held at about 70 to 100 ° C. to carry out hydrolysis (depolymerization) of the polyamic acid. However, from the viewpoint of suppressing an increase in the water content due to imidization, the time for heating to 70 ° C. or higher is preferably 3 hours or less, more preferably 1 hour or less.

In the reaction of tetracarboxylic dianhydride and its mixture of hemicyclic and bicyclics with diamine, mainly tetracarboxylic dianhydride and the acid dianhydride moiety of hemicyclic and diamine Reacts with the amino groups of diamines, and the ring-opening dicarboxylic acids of the single-ring and bi-rings hardly react with the amino groups of diamine. When the amino group of the diamine reacts with the acid dianhydride portion of the single ring-opening body, a polyamic acid having a hydrocyclic ring end of the general formula (1) is produced, and polymerization does not proceed any further. Therefore, a low molecular weight polyamic acid can be obtained by using a single ring-opened dianhydride tetracarboxylic dianhydride. The larger the ratio of single ring-opened bodies (x ₂ / x), the smaller the molecular weight of polyamic acid tends to be. Since both ring-opened bodies hardly react with diamine, a polyamic acid solution containing both ring-opened bodies can be obtained.

<Introduction of alkoxysilane terminal>
The polyamic acid of the embodiment of the present invention may contain other terminal structures in addition to the terminal structures of the general formulas (1) and (2). In one embodiment, the polyamic acid composition may have a terminal structure (alkoxysilane terminal) represented by the general formula (5) in addition to the terminal structures of the general formulas (1) to (3). ..

R ¹ in the general formula (5) is a divalent organic group, preferably a phenylene group or an alkylene group having 1 to 5 carbon atoms. R ² is an alkyl group, X is a residue of tetracarboxylic dianhydride, and Y is a residue of diamine.

The polyamic acid having the terminal structure represented by the general formula (5) can be obtained by reacting an alkoxysilane compound containing an amino group with the polyamic acid in a solution. The terminal may be modified by adding an alkoxysilane compound containing an amino group to the polyamic acid composition having the terminal structures represented by the general formulas (1) and (2).

When an alkoxysilane compound having an amino group is added to the polyamic acid, the viscosity of the polyamic acid solution tends to decrease. The reaction temperature for modification with the alkoxysilane compound containing an amino group is preferably 0 to 80 ° C, more preferably 20 to 60 ° C.

The alkoxysilane compound containing an amino group is represented by the following general formula (6). R ¹ and R ² in the general formula (6) are the same as those in the general formula (5).

R ¹ may be a divalent organic group, but a phenylene group or an alkylene group having 1 to 5 carbon atoms is preferable because of its high reactivity with the acid anhydride group of the polyamic acid, and among them, 1 to 1 to 5 carbon atoms. An alkylene group of 5 is preferred. R ² may be an alkyl group having 1 to 5 carbon atoms, but is preferably a methyl group or an ethyl group, and a methyl group is preferable from the viewpoint of improving the adhesion between the polyamic acid and the glass.

Specific examples of the alkoxysilane compound having an amino group include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, and 3-aminopropyl. Examples thereof include methyldimethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane, 3-phenylaminopropyltrimethoxysilane, 2-aminophenyltrimethoxysilane, and 3-aminophenyltrimethoxysilane.

The ratio α / x of the total number of moles α of the alkoxysilane compound having an amino group to the total number of moles of the tetracarboxylic dian x is preferably 0.0001 to 0.0050, more preferably 0.0005 to 0.0050, and 0. More preferably, it is 0010 to 0.0030. When α / x is 0.0001 or more, the adhesion between the inorganic substrate such as glass and the polyimide film is improved, and there is an effect that natural peeling is suppressed. When α / x is 0.0100 or less, the molecular weight of polyamic acid can be maintained, so that the storage stability of the polyamic acid solution is excellent and the mechanical strength of the polyimide film can be secured.

<Additives>
The polyamic acid solution may contain various additives. For example, the polyamic acid solution may contain a surface conditioner for the purpose of defoaming the solution and improving the smoothness of the surface of the polyimide film. As the surface conditioner, one that exhibits appropriate compatibility with polyamic acid and polyimide and has antifoaming property may be selected. Acrylic compounds, silicon compounds and the like are preferable because harmful substances are less likely to be generated during high-temperature heating, and acrylic compounds are particularly preferable because they are excellent in recoatability.

Specific examples of the surface conditioner composed of an acrylic compound include DISPARLON LF-1980, LF-1983, LF-1985 (manufactured by Kusumoto Kasei Co., Ltd.), BYK-3440, BYK-3441, BYK-350, BYK- 361N, (manufactured by Big Chemie Japan Co., Ltd.) and the like.

The amount of the surface conditioner added is preferably 0.0001 to 0.1 parts by weight, more preferably 0.001 to 0.1 parts by weight, based on 100 parts by weight of the polyamic acid. When the amount added is 0.0001 parts by weight or more, a sufficient effect can be exerted on improving the smoothness of the surface of the polyimide film. When the addition amount is 0.1 part by weight or less, the polyimide film is less likely to become turbid. The surface conditioner may be added to the polyamic acid solution as it is, or may be diluted with a solvent before being added. The timing of adding the surface conditioner is not particularly limited, and may be added at the time of polymerization or terminal modification of the polyamic acid. When performing alkoxysilane modification, a surface conditioner may be added after the alkoxysilane modification.

The polyamic acid solution may contain inorganic fine particles and the like. Examples of the inorganic fine particles include fine particle silicon dioxide (silica) powder, inorganic oxide powder such as aluminum oxide powder, fine particle calcium carbonate powder, and inorganic salt powder such as calcium phosphate powder. The presence of coarse particles in which the fine particles are agglomerated can cause defects in the polyimide film, so it is preferable that the inorganic fine particles are uniformly dispersed in the solution.

When imidizing a polyamic acid by chemical imidization, the polyamic acid solution may contain an imidization catalyst. As the imidization catalyst, a tertiary amine is preferable, and a heterocyclic tertiary amine is particularly preferable. Preferred specific examples of the heterocyclic tertiary amine include pyridine, 2,5-diethylpyridine, picoline, quinoline, isoquinoline and the like. From the viewpoint of catalytic effect and cost, the amount of the imidization catalyst used is about 0.01 to 2.00 equivalents with respect to the amide group of the polyamic acid which is the polyimide precursor, and 0.02 to 1.20 equivalents. It is preferable to have. From the viewpoint of enhancing the storage stability of the solution, an imidization catalyst may be added to the polyamic acid solution immediately before the use of the polyamic acid solution (coating on the substrate).

[Characteristics of polyamic acid solution]
<Abundance ratio of hydrocyclic ring-opened terminal structure of polyamic acid>
Since the terminal structure of the polyamic acid is controlled, the polyamic acid solution is excellent in storage stability and handleability, and the high molecular weight is increased during imidization, so that the polyimide film has excellent mechanical strength.

As described above, the amount of the tetracarboxylic dianhydride residue X in the polycarboxylic acid is the total number of moles of the tetracarboxylic acid x (single-open ring of the tetracarboxylic acid anhydride and the tetracarboxylic dianhydride and the tetracarboxylic acid. Equal to the sum of the dianhydride and the bicyclic ring). Further, the amount of diamine residue Y is equal to the total number of moles y of diamine.

By the polymerization of polyamic acid, almost all of the single ring-opening bodies contribute to the formation of the terminal structure represented by the general formula (1). Therefore, the number of moles z of the terminal structure represented by the general formula (1) in the polyamic acid is substantially equal to the number of moles x ₂ of the single ring-opened ring body. The ratio z / x of the number of moles z of the terminal structure represented by the general formula (1) in the polyamic acid to the total number of moles x of the tetracarboxylic dianhydride residue X is 0.01 to 0.15. Preferably, 0.02 to 0.12 is more preferable, and it may be 0.03 to 0.10 or 0.04 to 0.09. As described above, since a z ≒ x _2, z / x is substantially equal to the production rate x _{2 /} x pieces open annulus in the tetracarboxylic acid after hydrolysis ring opening. When z / x is in this range, the viscosity of the polyamic acid solution can be kept low, and the molecular weight is sufficiently increased during imidization, so that a polyimide film having excellent mechanical strength can be obtained. In other words, by adjusting the ratio of the one-sided ring-opened body produced by water ring-opening before polymerization of the polyamic acid, it is possible to produce a polyimide film having a low viscosity of the polyamic acid solution and excellent mechanical strength. It will be possible.

<Molecular weight of polyamic acid>
The weight average molecular weight of the polyamic acid in the polyamic acid solution is preferably 5000 to 45000, more preferably 10000 to 40,000, further preferably 15000 to 32000, and may be 20000 to 30000. When the weight average molecular weight is 5000 or more, the characteristics of the polyimide film obtained by imidization of the polyamic acid tend to be improved. When the weight average molecular weight is 45,000 or less, the solution viscosity can be kept low even when the solid content concentration is high, and the change in molecular weight when the polyamic acid solution is stored for a long period of time tends to be suppressed. The number average molecular weight of the polyamic acid is preferably 3000 to 25000, more preferably 5000 to 22000, and even more preferably 10000 to 20000.

<Concentration and viscosity of solution>
The solid content concentration of the polyamic acid composition is preferably 10% by weight or more, more preferably 13% by weight or more, still more preferably 15% by weight or more. The higher the solid content concentration of the polyamic acid solution, the smaller the amount of solvent used, which can contribute to improvement of production efficiency, reduction of environmental load, cost reduction and the like. The upper limit of the solid content concentration is not particularly limited, but the solid content concentration of the solution is preferably 40% by weight or less, more preferably 35% by weight or less in order to obtain a viscosity suitable for coating on a substrate. After the polymerization of the polyamic acid, the solid content concentration may be adjusted by adding or volatilizing a solvent.

From the viewpoint of coatability on the substrate, the viscosity of the polyamic acid solution at a temperature of 23 ° C. is preferably 1 to 150 poise, more preferably 3 to 100 poise. The viscosity of the solution tends to increase exponentially as the solid content concentration increases, but as described above, the solid content concentration of the solution is 15% by weight or more or 20% by weight due to the low molecular weight of polyamic acid. Even if it is%, the viscosity can be adjusted within the above range. In the polyamic acid solution, the ratio logη / D of the log η of the viscosity η at a temperature of 23 ° C. and the solid content concentration D of the polyamic acid is preferably 0.12 or less, more preferably 0.11 or less, and 0.10 or less. Is even more preferable. The unit of viscosity η is poise, and the unit of solid content concentration D is% by weight.

<Imidization rate of polyamic acid>
The imidization ratio of the polyamic acid in the polyamic acid solution is preferably 5 mol% or less, more preferably 4 mol% or less. Due to the low imidization rate, the viscosity of the solution is kept low, and the change in viscosity during storage of the polyamic acid solution tends to be suppressed. In addition, since the water content in the polyamic acid solution is small due to the low imidization rate, the change in viscosity due to hydrolysis of the polyamic acid during long-term storage (storage) of the polyamic acid solution is suppressed and stored. Increased stability.

As described above, by lowering the polymerization temperature of the polyamic acid (for example, about 50 ° C.), the imidization of the polyamic acid can be suppressed. As a method for lowering the molecular weight of the polyamic acid, it is generally performed to hydrolyze (depolymerize) the polyamic acid by raising the polymerization temperature or raising the temperature after the polymerization (for example, 70 ° C. or higher). .. However, since imidization also proceeds by heating for hydrolysis, it may cause an increase in the viscosity of the solution and a decrease in storage stability. On the other hand, in the embodiment of the present invention, by including the single ring-opened dianhydride of tetracarboxylic dianhydride in the reaction system, the hydroopened ring terminal represented by the general formula (1) is produced, so that the molecular weight is increased. It does not rise excessively and does not require high temperature heating for depolymerization. Therefore, imidization due to heating is suppressed, and the storage stability of the polyamic acid solution tends to be improved.

<Moisture content of polyamic acid solution>
The water content of the polyamic acid solution is preferably 1500 ppm or less. The water content of the polyamic acid solution may be 1300 ppm or less, 1200 ppm or less, or 1100 ppm or less. The smaller the water content in the polyamic acid solution, the better the storage stability tends to be.

The main sources of water in the polyamic acid solution are (A) water contained in the raw material, (B) water produced by dehydration cyclization (imidization) of polyamic acid, and (C) water mixed from the environment. By reducing these water content, a polyamic acid solution having a low water content can be obtained.

(A) Most of the water derived from the raw material is the water contained in the organic solvent. By carrying out hydrocyclic ringing of the tetracarboxylic dianhydride before the polymerization of the polyamic acid, the water in the organic solvent is consumed, so that the amount of water derived from the raw material (A) in the polyamic acid solution is reduced. Further, since imidization is suppressed by lowering the polymerization temperature of the polyamic acid, the increase in water content due to (B) imidization can be suppressed. In particular, the suppression of imidization greatly contributes to the decrease in water content.

The water content of the polyamic acid solution can be reduced by drying the raw material or treating it under reduced pressure. However, in the present embodiment, the water content of the polyamic acid can be reduced even if these treatments are not performed, and the cost is low. It is possible to prepare a polyamic acid solution having a small water content and excellent storage stability.

[Polyimide film]
By applying the polyamic acid solution on the substrate and imidizing it, a laminate in which the polyimide film is closely laminated on the substrate can be obtained. An inorganic substrate is preferable as the substrate. Examples of the inorganic substrate include a glass substrate and various metal substrates. When the polyimide film is a substrate for a flexible device, a glass substrate is preferable because the conventional device manufacturing equipment can be used as it is. Examples of the glass substrate include soda lime glass, borosilicate glass, non-alkali glass and the like. In particular, non-alkali glass generally used in the manufacturing process of thin film transistors is preferable. The thickness of the inorganic substrate is preferably about 0.4 to 5.0 mm from the viewpoint of substrate handleability, heat capacity, and the like.

As a solution coating method, known coating methods such as gravure coating method, spin coating method, silk screen method, dip coating method, bar coating method, knife coating method, roll coating method, and die coating method can be applied.

The imidization may be either chemical imidization using a dehydration ring closure agent (imidization catalyst) or thermal imidization in which the imidization reaction proceeds only by heating without the action of the dehydration ring closure agent or the like. Thermal imidization is preferable because impurities such as a dehydration ring closure agent are less likely to remain. The heating temperature and heating time in thermal imidization can be appropriately determined, and may be, for example, as follows.

First, in order to volatilize the solvent, it is heated at a temperature of 100 to 200 ° C. for 3 to 120 minutes. The heating can be performed under air, under reduced pressure, or in an inert gas such as nitrogen. As the heating device, a hot air oven, an infrared oven, a vacuum oven, a hot plate or the like may be used. After volatilizing the solvent, it is heated at a temperature of 200 to 500 ° C. for 3 to 300 minutes in order to further imidize. The heating temperature is preferably from low temperature to gradually high temperature, and the maximum temperature is preferably in the range of 300 to 500 ° C. When the maximum temperature is 300 ° C. or higher, thermal imidization tends to proceed, and the mechanical strength of the obtained polyimide film tends to improve. When the maximum temperature is 500 ° C. or lower, thermal deterioration of polyimide can be suppressed.

The thickness of the polyimide film is preferably 3 to 50 μm. When the thickness of the polyimide film is 3 μm or more, the mechanical strength required for the substrate film can be secured. When the thickness of the polyimide film is 50 μm or less, the natural peeling of the polyimide film from the inorganic substrate tends to be suppressed.

Since the polyamic acid composition having the terminal structures of the above general formulas (1) and (2) tends to have a high molecular weight due to thermal imidization, a polyimide film having high mechanical strength even when the molecular weight of the polyamic acid is small. Is obtained. The water-opened ring terminal of the general formula (1) hardly reacts with the amine terminal of the general formula (2) in the storage environment of the polyamic acid solution. Therefore, the polyamic acid solution is excellent in storage stability.

The hydrous ring terminal of the general formula (1) is dehydrated and ring-closed by heating at the time of thermal imide to become an acid anhydride group, reacts with the amine terminal of the general formula (2) to form an amide bond, and is dehydrated and cyclized. An imide bond is formed. That is, at the time of thermal imidization, the polyamic acid having the terminal structure of the general formula (1) reacts with the polyamic acid having the terminal structure of the general formula (2) to increase the molecular weight. Therefore, even when the molecular weight of polyamic acid is low, a polyimide film having excellent mechanical strength can be obtained by increasing the molecular weight during thermal imidization. The double ring-opened body represented by the general formula (3) also dehydrates and closes the ring during thermal imidization and reacts with the amine terminal of the general formula (2), so that it can contribute to the increase in molecular weight during thermal imidization. ..

A polyimide film can be obtained by peeling the polyimide film from a laminate of a substrate such as glass and a polyimide film. From the viewpoint of suppressing deformation of the polyimide film and the elements formed on the polyimide film due to the tension at the time of peeling, the peel strength when the polyimide film is peeled from the laminate of the glass substrate and the polyimide film is 1, 1 N / cm or less is preferable, 0.5 N / cm or less is more preferable, and 0.3 N / cm or less is further preferable. On the other hand, from the viewpoint of suppressing the natural peeling of the polyimide film from the glass substrate, the peel strength is preferably 0.01 N / cm or more, more preferably 0.3 N / cm or more, still more preferably 0.5 N / cm or more.

The breaking strength of the polyimide film is preferably 350 MPa or more, more preferably 400 MPa or more, and even more preferably 450 MPa or more. When the breaking strength is within the above range, even if the film thickness is small, it is possible to prevent the polyimide film from breaking in a process such as transportation or peeling from an inorganic substrate. From the same viewpoint, the elongation at the breaking point of the polyimide film is preferably 15% or more, more preferably 20% or more, still more preferably 25% or more. The break point elongation may be 30% or more. The upper limit of the breaking strength and the breaking point elongation of the polyimide film is not particularly limited. The breaking strength may be 700 MPa or less. The break point elongation may be 80% or less or 60% or less.

The coefficient of linear thermal expansion of the polyimide film is preferably 10 ppm / ° C or less. When the coefficient of linear thermal expansion is 10 ppm / ° C. or less, it can be suitably used as a substrate for a flexible device in which an element is formed at a high temperature. The coefficient of linear thermal expansion of the polyimide film may be 9 ppm / ° C. or lower, or 8 ppm / ° C. or lower. The coefficient of linear thermal expansion of the polyimide film may be 1 ppm / ° C. or higher.

[Formation of electronic devices on polyimide film]
When a polyimide film is used as a substrate for a flexible device or the like, an electronic element is formed on the polyimide film. An electronic element may be formed on the polyimide film before the polyimide film is peeled from an inorganic substrate such as glass. That is, it is flexible by forming an electronic element on a laminated polyimide film in which a polyimide film is closely laminated on an inorganic substrate such as glass, and then peeling the polyimide film on which the electronic element is formed from the inorganic substrate. You get the device. This process has the advantage that the production equipment using the existing inorganic substrate can be used as it is, is useful for manufacturing electronic devices such as flat panel displays and electronic paper, and is also suitable for mass production.

The method of peeling the polyimide film from the inorganic substrate is not particularly limited. For example, it may be peeled off by hand, or it may be peeled off using a mechanical device such as a drive roll or a robot. A release layer may be provided between the inorganic substrate and the polyimide film, and before the release, a treatment for reducing the adhesion between the inorganic substrate and the polyimide film is performed by contact with a liquid or irradiation with laser light. May be good. Specific examples of the method of reducing the adhesion are a method of forming a silicon oxide film on an inorganic substrate having a large number of grooves and peeling it off by infiltrating an etching solution; and an amorphous silicon layer on the inorganic substrate. A method of separating by a provided laser beam can be mentioned.

Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited to these examples.

[Evaluation methods]
<Moisture content>
Volumetric titration A Karl Fischer titer (“890 Tightland” manufactured by Metrohm Japan) was used to measure the water content in the solution according to the volumetric titration method of JIS K0068. However, when the resin was precipitated in the titration solvent, a 1: 4 mixed solution of Aquamicron GEX (manufactured by Mitsubishi Chemical Corporation) and N-methylpyrrolidone was used as the titration solvent.

<Viscosity>
The viscosity was measured according to JIS K7117-2: 1999 using a viscometer (“RE-215 / U” manufactured by Toki Sangyo Co., Ltd.). The attached constant temperature bath was set to 23 ° C., and the measurement temperature was always constant.

<Molecular weight>
The molecular weight was measured by gel permeation chromatography (GPC). A GPC system equipped with CO-8020, SD-8022, DP-8020, AS-8020 and RI-8020 (all manufactured by Toso) was used, and two Shoudex: GPC KD-806M (8 mmΦ x 30 cm) columns were used. As a guard column, one GPC KD-G (4.6 mmΦ × 1 cm) was used. RI was used as the detector. As the eluent, a solution in which 30 mM LiBr and 30 mM phosphoric acid were dissolved in DMF was used. Measurement was performed under the conditions of a solution concentration of 0.4% by weight, an injection volume of 30 μL, an injection pressure of about 1.3 to 1.7 MPa, a flow rate of 0.6 mL / min, and a column temperature of 40 ° C., and a calibration curve prepared using polyethylene oxide as a standard sample. Based on the line, the weight average molecular weight (Mw) and the number average molecular weight (Mn) were calculated.

<Amount of ring-opened body produced>
The NMP solution of tetracarboxylic acid after the hydrocyclic ring treatment was diluted with methanol so that the tetracarboxylic acid concentration was 0.1% by weight, stirred at 60 ° C. for 1 hour or more, and the carboxylic acid produced by the hydrocyclic ring opening. Acid methyl esterification was performed. This solution was analyzed by high-speed liquid chromatography (manufactured by Shimadzu Corporation) under the following conditions, and the amount of acid dianhydride, single-ring-opened diester, and double-ring-opened tetraester detected was added to the ring-opened ring. The abundance ratios of unopened acid dianhydride, single ring-opened body and double ring-opened body in the tetracarboxylic acid solution after the reaction (amount of ring-opened ring produced) were calculated.
Column: DAISOPAK SP-200-5-ODS-BP (4.6 mmφ x 250 mm)
Column temperature: 40 ° C
Mobile phase: Methanol / water = 45/55 (containing 0.1 wt% tetrafluoroacetic acid)
Flow velocity: 0.8 mL / min Detection wavelength: 275 nm

<Imidization rate>
40 mg of the polyamic acid solution was diluted with heavy DMSO, and the imidization ratio was calculated from the ratio of the proton peak area of the phenyl group to the proton peak area of the amide group measured by ¹ H-NMR.

<Storage stability of polyamic acid solution>
The polyamic acid solution was placed in a 50 mL screw bottle, sealed, and stored in an environment of 23 ° C. and 55% RH for 1 week. Those with an initial and post-storage change of 5% or less were OK, and the viscosity change exceeded 5%. The thing was NG.

<Breaking strength and breaking point elongation>
A polyimide film was cut into a width of 15 mm and a length of 150 mm to prepare a test piece, and two parallel marking lines 50 mm apart were attached to the center of the test piece. Using a tensile tester (“UBFA-1 AGS-J” manufactured by Shimadzu Corporation), a tensile test was conducted at a tensile speed of 10 mm / min according to JIS K7127: 1999, and the stress (breaking strength) when the test piece broke. And elongation (breaking point elongation) was determined.

<Coefficient of thermal expansion>
A polyimide film is cut into a width of 3 mm and a length of 10 mm to prepare a test piece, and a thermomechanical analyzer (“TMA / SS120CU” manufactured by SII Nanotechnology) is used to load a sample with a load of 29.4 mN on the long side. Was added, and thermomechanical analysis was performed by the tensile load method. First, the temperature was raised from 20 ° C. to 500 ° C. at 100 ° C./min (first temperature rise), cooled to 20 ° C., and then raised to 500 ° C. at 10 ° C./min (second temperature rise). The amount of change in the strain of the sample per unit temperature in the range of 100 to 300 ° C. at the time of the second temperature rise was defined as the coefficient of linear thermal expansion.

[Example 1]
<Hydro-opening of tetracarboxylic dianhydride>
425 g of N-methyl-2-pyrrolidone (NMP) was placed in a glass separable flask equipped with a stirrer with a seal stopper made of polytetrafluoroethylene, a stirring blade and a nitrogen introduction tube. The water content in NMP was 300 ppm. To this, 0.342 g of water and 109.5 g of 3,3', 4,4'-biphenyltetracarboxylic dianhydride (BPDA) were added, and the mixture was stirred under a nitrogen atmosphere for 150 minutes while heating at 80 ° C. A part of BPDA was hydrocyclic. After the reaction, the solution was cooled to 50 ° C.

In this reaction system, the amount of water contained in NMP is 1.9% in molar ratio with respect to BPDA, and the amount of water added is 5.1% in molar ratio with respect to BPDA. The total amount of water in the water was 7.0% in molar ratio with respect to BPDA. The resulting solution contained unring-opened BPDA, a single ring-opened body of BPDA, and a bi-ring-opened body of BPDA in a molar ratio of 94.53: 5.19: 0.28.

<Polymerization of polyamic acid>
To the partially ring-opened BPDA solution obtained above, 425.0 g of NMP was added to dilute it, 39.9 g of paraphenylenediamine (PDA), and 0 of 4,4'-diaminodiphenyl ether (ODA). After adding .62 g and stirring the solution in a nitrogen atmosphere for 60 minutes while heating at 50 ° C., the solution was rapidly cooled in a water bath to obtain a polyamic acid solution. The total concentration of diamine and tetracarboxylic acid in this reaction solution was 15% by weight, and the molar ratio x / y of tetracarboxylic acid / diamine was 1.000.

<Modification with alkoxysilane compound>
The above polyamic acid solution is heated to 50 ° C., 7.48 g of a 1% NMP solution of 3-aminopropyltriethoxysilane (γ-APS) is added, and the mixture is stirred for 3 hours to have a viscosity of 5.8 poisons at 23 ° C. A solution of alkoxysilane-modified polyamic acid was obtained. The ratio α / x of the total number of moles (α) of the alkoxysilane compound to the total number of moles (x) of the tetracarboxylic dian was 0.001.

To the obtained solution, 0.02 part by weight of an acrylic surface conditioner (“BYK-361N” manufactured by Big Chemie Japan) was added to 100 parts by weight of the solid content of the alkoxysilane-modified polyamic acid, and the mixture was uniformly dispersed. To obtain an alkoxysilane-modified polyamic acid solution containing a surface conditioner.

[Example 2 and Example 3]
Ring-opening of BPDA was carried out in the same manner as in Example 1 except that the amounts of NMP, BPDA and water charged were changed as shown in Table 1. After that, polymerization of polyamic acid and terminal modification by γ-APS were carried out in the same manner as in Example 1 except that the amounts of PDA, ODA and NMP charged and the amount of γ-APS charged were changed as shown in Table 2. To obtain an alkoxysilane-modified polyamic acid solution containing a surface conditioner.

[Comparative Example 1]
<Polymerization of polyamic acid>
170.0 g of NMP was placed in a glass separable flask equipped with a stirrer with a seal stopper made of polytetrafluoroethylene, a stirring blade and a nitrogen introduction tube. 8.0 g of PDA and 0.19 g of ODA were added thereto, and the solution was stirred under a nitrogen atmosphere for 30 minutes while heating at 50 ° C. After confirming that the diamine was uniformly dissolved, 21.8 g of BPDA was added, and the mixture was stirred under a nitrogen atmosphere for 60 minutes and then quickly cooled in a water bath to obtain a polyamic acid solution. In this reaction system, no water was added except for the water contained in NMP (2.7% by molar ratio with respect to BPDA). The charged concentration of diamine and tetracarboxylic dianhydride was 15% by weight, and the molar ratio of BPDA / diamine was 0.989.

<Modification with alkoxysilane compound>
The temperature of the above polyamic acid solution was adjusted to about 50 ° C. Next, 1.30 g of a 1% NMP solution of γ-APS was added, and the mixture was stirred for 3 hours to obtain a solution of alkoxysilane-modified polyamic acid having a viscosity of 170 poise at 23 ° C. NMP was added to this solution to dilute it so that the solid content concentration was 10% by weight. The viscosity of the diluted solution at 23 ° C. was 40 poise. To this solution, 0.02 parts by weight of an acrylic surface conditioner was added to 100 parts by weight of the solid content of polyamic acid to obtain an alkoxysilane-modified polyamic acid solution containing the surface conditioner.

[Comparative Example 2 and Comparative Example 3]
<Polymerization of polyamic acid>
The charged amounts of NMP, BPDA, PDA and ODA were changed as shown in Table 2, the temperature was raised to 80 ° C. after the addition of BPDA, and the reaction was carried out in a nitrogen atmosphere. In Comparative Example 2, the reaction time was 10 hours, and in Comparative Example 3, the reaction time was 9 hours. Except for these changes, polyamic acid was polymerized in the same manner as in Comparative Example 1.

<Modification with alkoxysilane compound>
Alkoxysilane modification was performed in the same manner as in Comparative Example 1 except that the amount of γ-APS added was changed as shown in Table 2, and NMP was added and diluted so as to have the solid content concentration shown in Table 2. After that, an acrylic surface conditioner was added and uniformly dispersed.

[Comparative Example 4]
In the same manner as in Comparative Example 2, NMP, PDA and ODA were charged, the temperature was raised to 80 ° C. after adding BPDA, and the mixture was stirred under a nitrogen atmosphere. After the solution became uniform, 0.064 g of water (3.2% by molar ratio to BPDA) was added, and the mixture was stirred for 9 hours. Then, alkoxysilane modification was performed in the same manner as in Comparative Example 2, NMP was added to dilute the solid content concentration as shown in Table 2, and then an acrylic surface conditioner was added to uniformly disperse the mixture.

[Preparation of polyimide film]
A polyamic acid solution is applied on a square non-alkali glass plate for FPD (“Eagle XG” manufactured by Corning Inc.) with a thickness of 0.7 mm and a side of 150 mm after drying with a spin coater so that the thickness becomes about 10 μm. Then, it was dried in a hot air oven at 120 ° C. for 30 minutes. Then, in a nitrogen atmosphere, the temperature was raised from 20 ° C. to 120 ° C. at 7 ° C./min, the temperature was raised from 120 ° C. to 450 ° C. at 7 ° C./min, and heated at 450 ° C. for 10 minutes. A laminate of plates was obtained. In any of Examples 1 to 3 and Comparative Examples 1 to 4, the polyimide film has an appropriate peeling strength with respect to the non-alkali glass plate, does not peel off naturally during heating, and It was possible to peel off the polyimide film from the glass plate.

[Summary of manufacturing conditions and evaluation results]
Table 1 shows the conditions for hydro-opening of the tetracarboxylic dianhydride in Examples 1 to 3 and the amounts of single-opened ring and bi-opened ring-formed bodies produced.

Amount of raw material charged in the synthesis of polyamic acid of Examples and Comparative Examples, ratio of raw material charged (ratio x / y of total molar x of tetracarboxylic acid to total molar y of diamine) and a piece of tetracarboxylic acid dianhydride Table 2 shows the ratio of ring-opened bodies x ₂ / x), the temperature of the polymerization reaction, the solid content concentration D of the polyamic acid solution after the polymerization reaction and the polyamic acid solution after the alkoxysilane modification, and the solution viscosity η. Table 3 shows the evaluation results of the molecular weight of the polyamic acid in the polyamic acid solution after the alkoxysilane modification, the water content of the solution and the storage stability, and the evaluation results of the polyimide film.

In Examples 1 to 3 in which a part of BPDA was hydroopened and then mixed with diamine to polymerize the polyamic acid, even if the molecular weight of the polyamic acid was 30,000 or less and the solid content concentration D of the solution was 15% by weight or more. It was possible to use it for producing a film without diluting it as it was. The imidization ratio of the polyamic acid in the polyamic acid solution of Example 2 was 3 mol%.

In Comparative Example 1 in which BPDA was reacted with diamine without hydro-opening, the molecular weight of polyamic acid was significantly increased and the solution viscosity was high as compared with Examples 1 to 3, so that when a film was produced, , It was necessary to dilute with NMP to reduce the solid content concentration. In Comparative Examples 2 and 3 in which the polymerization temperature of the polyamic acid was raised to 80 ° C., the molecular weight of the polyamic acid was lower than that of Comparative Example 1, but the molecular weight was higher and the solid content concentration was higher than that of Examples 1 to 3. Was less than 15%, and the solution viscosity had to be adjusted. In Comparative Example 4 in which water was added to the polyamic acid solution for hydrolysis, the molecular weight of the polyamic acid was further lower than that of Comparative Example 2, but the molecular weight of the polyamic acid was higher than that of Examples 1 to 3. it was high.

In Comparative Examples 1 to 4, in order to suppress the increase in the molecular weight, the charging ratio x / y of the tetracarboxylic dianhydride and the diamine was set to 0.99, and the ratio was intentionally shifted from the equimolar. It can be seen that the molecular weight is higher and the solution viscosity is higher than in Examples 1 to 3. From these results, it can be seen that a polyamic acid solution having a low molecular weight and a high solid content concentration and a low viscosity can be obtained by ring-opening a part of the tetracarboxylic dianhydride and then reacting with the diamine.

In Comparative Examples 2 to 4 in which the polymerization reaction was carried out at 80 ° C., the water content of the polyamic acid solution was increased and the storage stability was lowered. The imidization ratio of the polyamic acid in the polyamic acid solution of Comparative Example 2 was 17 mol%. From these results, in Comparative Examples 2 to 4, although the polyamic acid was depolymerized by heating at 80 ° C. and the molecular weight decreased, imidization by dehydration ring closure proceeded in parallel with this, and the water content in the solution. It is considered that the storage stability of the solution decreased due to the increase in.

In Examples 1 to 3, although the molecular weight of the polyamic acid was lower than that in Comparative Examples 1 to 4, the obtained polyimide film exhibited the same mechanical strength as in Comparative Examples 1 to 4 and had low thermal expansion. The coefficients are shown. It is considered that this is because the hydrocyclic ring-opening terminal represented by the general formula (1) reacted at the time of imidization and became high molecular weight. In Examples 1 to 3, since the production rate x ₂ / x of the single ring-opened body by water ring-opening is about 0.05, the total number of moles of the tetracarboxylic dianhydride residue X in the polyamic acid x It is estimated that the ratio z / x of the number of moles z at the ring-opening terminal to water is also about 0.05 (5%).

From these results, the polyamic acid solution obtained by hydroopening the tetracarboxylic dianhydride and then reacting with the diamine has a low molecular weight, a low viscosity even at a high solid content concentration, and excellent storage stability. I understand. Further, it can be seen that the polyimide film produced by using the polyamic acid exhibits excellent mechanical strength similar to that in the case of using a high molecular weight polyamic acid solution.

Claims (23)

1. Polyamic acid solution containing a polyamic acid having a terminal structure represented by the general formula (1) and a polyamic acid having a terminal structure represented by the general formula (2):
   

   

   X is a tetravalent organic group which is a tetracarboxylic dianhydride residue, and Y is a divalent organic group which is a diamine residue.
2. The polyamic acid solution according to claim 1, wherein the polyamic acid has a weight average molecular weight of 5000 or more and 45000 or less.
3. The ratio z / x of the number of moles z of the terminal structure represented by the general formula (1) to the total number of moles x of the tetracarboxylic dianhydride residue X is 0.01 to 0.15. , The polyamic acid solution according to claim 1 or 2.
4. The polyamic acid solution according to any one of claims 1 to 3, which has a water content of 1500 ppm or less.
5. The polyamic acid solution according to any one of claims 1 to 4, further comprising a compound represented by the general formula (3).
   

   
6. The ratio x ₃ / x of the number of moles x ₃ of the compound represented by the general formula (3) to the total number of moles x of the tetracarboxylic dianhydride residue X in the composition is 0.001 to The polyamic acid solution according to claim 5, which is 0.05.
7. The polyamic acid solution according to any one of claims 1 to 6, further comprising a polyamic acid having a terminal structure represented by the general formula (5):
   

   

   R ¹ is a divalent organic group, and R ² is an alkyl group having 1 to 5 carbon atoms.
8. The polyamic acid solution according to any one of claims 1 to 7, wherein the imidization ratio of the polyamic acid is 5 mol% or less.
9. The polyamic acid solution according to any one of claims 1 to 8, wherein the solid content concentration of the polyamic acid is 10% by weight or more.
10. The polyamic acid solution according to any one of claims 1 to 9, wherein the log η / D of the logarithmic log η of the viscosity η at a temperature of 23 ° C. and the solid content concentration D of the polyamic acid is 0.12 or less.
    However, the unit of viscosity η is poise, and the unit of solid content concentration D is% by weight.
11. A method for producing a polyamic acid solution.
    A water ring-opening step in which a tetracarboxylic dianhydride is hydroopened to form a ring-opened body; and a mixture of the tetracarboxylic dianhydride and the ring-opened body thereof is reacted with a diamine to polymerize a polyamic acid. Polymerization process,
    Including
    By the water ring-opening step, a single ring-opened body represented by the general formula (4) is produced.
    

    

    The polyamic acid solution contains a polyamic acid having a terminal structure represented by the general formula (1) and a polyamic acid having a terminal structure represented by the general formula (2).
    

    

    X is a tetravalent organic group which is a tetracarboxylic dianhydride residue, and Y is a divalent organic group which is a diamine residue.
12. The method for producing a polyamic acid solution according to claim 11, wherein the water ring-opening is carried out in a solution containing 1 to 15 mol% of water with respect to the total amount of the tetracarboxylic dianhydride.
13. The method for producing a polyamic acid solution according to claim 11 or 12, wherein the water ring opening is carried out at a temperature of 50 to 100 ° C.
14. The method for producing a polyamic acid solution according to any one of claims 11 to 13, wherein the weight average molecular weight of the polyamic acid is 5000 or more and 45000 or less.
15. The method for producing a polyamic acid solution according to any one of claims 11 to 14, wherein the water content of the composition after the polymerization step is 1500 ppm or less.
16. The method for producing a polyamic acid solution according to any one of claims 11 to 15, wherein the imidization ratio in the composition after the polymerization step is 5 mol% or less.
17. The polyamide according to any one of claims 11 to 16, wherein the amount of the single ring-opened tetracarboxylic dianhydride after the water-opening is 1 to 15 mol% with respect to the total amount of the tetracarboxylic acid. Method for producing an acid solution.
18. The method for producing a polyamic acid solution according to any one of claims 11 to 17, further comprising a step of reacting an alkoxysilane compound with a polyamic acid to modify the terminal of the polyamic acid with an alkoxysilane.
19. A polyimide film containing a polyimide which is a dehydrated cyclized product of the polyamic acid contained in the polyamic acid solution according to any one of claims 1 to 10.
20. A laminate in which the polyimide film according to claim 19 is closely laminated on a substrate.
21. A method for manufacturing a laminate in which a polyimide film is closely laminated on a substrate.
    A method for producing a laminate, wherein the polyamic acid solution according to any one of claims 1 to 10 is applied onto a substrate, and the polyamic acid is dehydrated and cyclized by heating to be imidized.
22. A method for manufacturing a laminate in which a polyimide film is closely laminated on a substrate.
    A polyamic acid solution is prepared by the method according to any one of claims 11 to 18.
    A method for producing a laminate, in which the polyamic acid solution is applied onto a substrate, and the polyamic acid is dehydrated and cyclized by heating to be imidized.
23. A flexible device in which an electronic element is provided on the polyimide film according to claim 20.