JP7742740B2 - Polyamic acid composition and method for producing same - Google Patents

Description

The present invention relates to a composition containing polyamic acid, an organic solvent, and water, and a method for producing the same.

Polyimide has excellent heat resistance, mechanical properties, and electrical properties, and polyimide films made from this polyimide are widely used in a variety of applications, including as the base material for circuit wiring boards, such as flexible printed wiring boards.

To prepare polyimide, the raw materials tetracarboxylic dianhydride and diamine are typically reacted in an organic solvent to produce the precursor polyamic acid. When the polyamic acid is heat-treated at a high temperature of 200°C or higher, dehydration and ring closure occur within the molecule, yielding polyimide.

Here, the precursor polyamic acid is required to have storage stability. It is often unstable to heat and moisture, but with particular attention to moisture, it is known that polyamic acid hydrolyzes when it contains a large amount of water, and so it is typically stored with low moisture content (see, for example, Patent Documents 1 to 3). That is, based on Patent Documents 1 to 3 and others, the moisture content in polyamic acid has traditionally been limited to a few percent or less, but for the purpose of suppressing hydrolysis, it is desirable for the moisture content to be as low as possible. Typically, polyamic acid is kept stable during storage in such a state with as little moisture content as possible, and is managed using equipment that can maintain this state. In other words, if polyamic acid is stored in an appropriately sealed container, it is understood that the moisture content will not typically change during storage.

Japanese Patent Application Laid-Open No. 2006-124700 Patent No. 5985977 Patent No. 6648195

Yoichi Kodama and Hiroshi Morimine (2009). "New Aromatic Polyimide Adhesives." Recent Advances in Polyimides and Aromatic Polymers 2009 (Proceedings of the 16th Japan Polyimide and Aromatic Polymer Conference), pp. 54-56

However, according to the inventors' research, while polyamic acid should normally have good storage stability if managed and stored properly, as mentioned above, they unexpectedly observed a phenomenon in which, rather than hydrolysis of the polyamic acid, the viscosity of certain polyamic acids gradually increased (thickened) at room temperature. This phenomenon was observed in polyamic acids that reacted with a relatively large amount of the diamine component, leaving amino groups at the molecular ends, and that used components containing ketone groups within the molecule. Therefore, it was speculated that this phenomenon was due to the gradual reaction of these functional groups with each other, even at room temperature, to form imine bonds (see Non-Patent Document 1). In other words, it was speculated that the amino groups at the molecular ends of such polyamic acids reacted with ketone groups intramolecularly or intermolecularly to form imine bonds, which in turn extended the molecular chain into branches and increased the molecular weight, causing the viscosity increase during storage.

To address the problem of viscosity increase during storage in the case of such specific polyamic acids, an immediate countermeasure would be to cool the polyamic acid during storage to suppress the reaction of forming imine bonds. However, this would increase the cost of cooling equipment and would require periodic process management (e.g., pipe blowing) in areas where cooling is difficult (e.g., piping), thereby increasing the process load. Therefore, there is a fundamental need for the development of polyamic acids that do not increase in viscosity.
However, based on previous findings, no method has been predicted for fundamentally solving the problem of gradual viscosity increase at room temperature or the like while suppressing the above-mentioned hydrolysis in such specific polyamic acids.

As a result of intensive research, the present inventors have discovered that, rather than eliminating water as much as possible as in the past, by controlling the water content in polyamic acid within an appropriate range, it is possible to suppress hydrolysis, a concern in the past, while also suppressing problems such as viscosity increase during storage even at room temperature, resulting in polyamic acid with excellent storage stability.

Therefore, an object of the present invention is to provide a polyamic acid composition that is extremely little prone to hydrolysis and thickening during storage.
Another object of the present invention is to provide a method for producing such a polyamic acid composition.

That is, the present invention is as follows.
[1] The following components (a) to (c):
(a) a polyamic acid having an acid anhydride residue derived from a tetracarboxylic dianhydride component and a diamine residue derived from a diamine component;
A polyamic acid composition comprising: (b) an organic solvent; and (c) water,
the component (a) has a ketone group and a primary amino group at a molecular terminal, the ketone group being derived from the tetracarboxylic dianhydride component and/or the diamine component,
a polyamic acid composition, wherein the content of the component (c) is 0.05% by mass or more and 10% by mass or less based on the total of the components (a), (b), and (c);
[2] The polyamic acid composition according to [1], wherein the polyamic acid has a weight average molecular weight (Mw) of 20,000 or more and 2,000,000 or less.
[3] The polyamic acid composition according to [1] or [2], wherein the ketone group in component (a) is contained in an amount of 10 molar parts or more per 100 molar parts of the acid anhydride residue and the diamine residue combined.
[4] The polyamic acid composition according to any one of [1] to [3], wherein the component (b) has a boiling point of 120°C or higher and a water solubility of 10% by mass or higher.
[5] The polyamic acid composition according to any one of [1] to [4], wherein the viscosity of the composition after storage for 30 days under conditions of a temperature of −30° C. to 60° C. and a humidity of 70% or less is 100% to 30% of the initial viscosity.
[6] A method for producing the polyamic acid composition according to any one of [1] to [5], comprising the following steps I and II:
I) a step of reacting a tetracarboxylic dianhydride component with a diamine component in an organic solvent to obtain a polyamic acid solution;
II) a step of adding water to the polyamic acid solution to produce a polyamic acid composition, wherein in step II, water is added so that the water content of the polyamic acid composition is 0.05% by mass or more and 10% by mass or less based on the total mass of the organic solvent, the polyamic acid, and the water.
[7] The method for producing a polyamic acid composition according to [6], characterized in that when adding water in step II, the organic solvent used in step I and water are mixed in advance to prepare a mixed solution containing water in an amount of 1% by mass to 60% by mass based on the total amount of the organic solvent and water, and water is added using the mixed solution in step II.
[8] The method for producing a polyamic acid composition according to [6] or [7], wherein in step I, a solution of polyamic acid is obtained, the polyamic acid having a ketone group in the tetracarboxylic dianhydride component and/or the diamine component and having a weight-average molecular weight (Mw) of 20,000 or more and 2,000,000 or less.

The polyamic acid composition of the present invention suppresses hydrolysis, a conventional concern, while also suppressing the problem of viscosity increase during storage even at room temperature, resulting in excellent storage stability. Furthermore, it can be produced without the need for cooling equipment or process management to prevent viscosity increase, resulting in excellent cost performance. Furthermore, because the polyamic acid composition of the present invention does not undergo structural changes due to iminization before imidization, polyimides with little quality variation between lots can be obtained.

The following describes an embodiment of the present invention.

[Polyamic acid composition]
As described above, the polyamic acid composition of the present invention contains (a) polyamic acid, (b) organic solvent, and (c) water. Components (a) to (c) will be described in detail below.

<(a) Polyamic Acid>
The polyamic acid (a) used in the present invention is composed of an acid anhydride residue, which is a tetravalent group derived from a tetracarboxylic dianhydride (hereinafter sometimes simply referred to as "acid anhydride") component, and a diamine residue, which is a divalent group derived from a diamine compound (hereinafter sometimes simply referred to as "diamine") component, and when the combination of these components is considered as one repeating unit, it is composed of a polymer of this repeating unit. The polyamic acid (a) component can be represented, for example, by the following formula (1):

(In the above formula, X2 is a tetravalent acid anhydride residue derived from a tetracarboxylic dianhydride component, Y2 is a divalent diamine residue derived from a diamine component, and n represents a repeating unit.)

Here, as shown in the above formula (1), the polyamic acid of component (a) has a primary amino group (-NH ₂ ) (hereinafter, this may be simply referred to as an "amino group") at the molecular end. The presence of an amino group at the molecular end can be controlled by adjusting the amounts (molar ratio) of the acid anhydride component and the diamine component charged, as will be described later in the production method.

The polyamic acid of component (a) is also characterized by containing a predetermined amount of ketone groups in its molecular skeleton. The ketone group content is 10 molar parts or more relative to 100 molar parts of the total of the acid anhydride residue (X2 in Formula (1)) and diamine residue (Y2 in Formula (1)). Containing such a quantity of ketone groups increases the number of reaction sites with the amino groups at the molecular terminals, which tends to result in a more pronounced increase in viscosity during storage, as described above. Therefore, polyamic acids having such a quantity of ketone groups are the subject of the present invention. While there are no particular restrictions on the ketone group content, it is preferably 15 molar parts or more, more preferably 25 molar parts or more, as this facilitates the realization of the effects of the present invention.

It is sufficient that either X2 or Y2 in the polyamic acid has a ketone group; it is not necessary that all structural units of all polyamic acids contain a ketone group. In other words, as long as the above-mentioned range of ketone groups is met, the ketone group may be contained in either the acid anhydride residue or the diamine residue, or in both. Furthermore, as long as the molecule as a whole satisfies the above-mentioned numerical range, it may contain structural units that do not contain a ketone group.

Here, the tetracarboxylic acid dianhydride containing a ketone group is not particularly limited, but examples include 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, 2,3',3,4'-benzophenonetetracarboxylic acid dianhydride, 2,2',3,3'-benzophenonetetracarboxylic acid dianhydride, 4,4'-(paraphenylenedicarbonyl)diphthalic anhydride, and 4,4'-(metaphenylenedicarbonyl)diphthalic anhydride.

The acid anhydride residue may be derived from a tetracarboxylic acid dianhydride that does not contain a ketone group, and any known tetracarboxylic acid dianhydride commonly used in polyimides may be used without limitation. Aromatic tetracarboxylic acid dianhydrides are preferred as such tetracarboxylic acid dianhydrides. Alicyclic tetracarboxylic acid anhydrides may also be used, such as 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, fluorenylidenebisphthalic anhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride, and cyclopentanonebisspironorbornanetetracarboxylic acid dianhydride.

Examples of aromatic tetracarboxylic dianhydrides that do not have a ketone group include pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4,4'-oxydiphthalic dianhydride (ODPA), bis(2,3-dicarboxyphenyl)ether dianhydride, 5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxydiphenyl ether dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}diphenyl ether dianhydride, and bis{3,5-di(trifluoromethyl)diphenyl ether dianhydride}. bis(dicarboxyphenoxy)bis(trifluoromethyl)benzene dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}pyromellitic dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}, bis(dicarboxyphenoxy)trifluoromethylbenzene dianhydride, bis(dicarboxyphenoxy)bis(trifluoromethyl)benzene dianhydride, bis(dicarboxyphenoxy)tetrakis(trifluoromethyl)benzene dianhydride, 2,2-bis{(4-(3,4-dicarboxyphenoxy)phenyl}hexafluoropropane dianhydride, bis {(trifluoromethyl)dicarboxyphenoxy}biphenyl dianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}bis(trifluoromethyl)biphenyl dianhydride, bis(dicarboxyphenoxy)bis(trifluoromethyl)biphenyl dianhydride, 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, naphthalene-2,3,6,7-tetracarboxylic dianhydride, naphthalene-1,2,5,6-tetracarboxylic dianhydride, naphthalene-1,2,6,7-tetracarboxylic dianhydride, naphthalene Naphthalene-1,2,4,5-tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 1,4,5,8-tetrachloronaphthalene-2,3,6,7-tetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyl phenyltetracarboxylic acid dianhydride, 3,3",4,4"-p-terphenyltetracarboxylic acid dianhydride, 2,2",3,3"-p-terphenyltetracarboxylic acid dianhydride, 2,3,3",4"-p-terphenyltetracarboxylic acid dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)methane dianhydride 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 2,2',3,3'-diphenylsulfonetetracarboxylic dianhydride, 2,3,3',4'-diphenylsulfonetetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, perylene-2,3,8,9-tetracarboxylic dianhydride, perylene-3,4,9,10-tetracarboxylic dianhydride, perylene-4,5,10,11-tetracarboxylic dianhydride dicarboxylic acid dianhydride, perylene-5,6,11,12-tetracarboxylic acid dianhydride, phenanthrene-1,2,7,8-tetracarboxylic acid dianhydride, phenanthrene-1,2,6,7-tetracarboxylic acid dianhydride, phenanthrene-1,2,9,10-tetracarboxylic acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic acid dianhydride, (trifluoromethyl)pyromellitic acid dianhydride, di(trifluoromethyl)pyromellitic acid dianhydride, di(heptafluoropropyl)pyromellitic acid dianhydride Examples include methyltrifluoromethylpyromellitic dianhydride, pentafluoroethylpyromellitic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, 5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxybiphenyl dianhydride, 2,2',5,5'-tetrakis(trifluoromethyl)-3,3',4,4'-tetracarboxybiphenyl dianhydride, 5,5'-bis(trifluoromethyl)-3,3',4,4'-tetracarboxybenzophenone dianhydride, and trifluoromethylbenzene dianhydride.

On the other hand, diamines containing a ketone group include, but are not limited to, 3,3'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis(4-aminophenoxy)benzophenone, 4,4'-bis(3-aminophenoxy)benzophenone (BABP), 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene (BABB), 1,4-bis(4-aminobenzoyl)benzene, 1,3-bis(4-aminobenzoyl)benzene, and the like.

The diamine residue may also be derived from a diamine that does not contain a ketone group, and any known diamine compound commonly used in polyimides may be used without restriction. Aromatic diamine compounds are preferred as such diamines. Also, alicyclic diamine compounds may be used, as described above.

For example, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, 3,7-diamino-2,8-dimethylbenzothiophenesulfone, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), 2,2'-difluoro 4,4'-diaminobiphenyl, 3,3'-difluoro-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl ether (4,4'-DAPE), 3,3-diaminodiphenyl ether, bis(p-β-amino-t-butylphenyl)ether, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis(3-aminophenoxy)benzene (APB), 1,3-bis(4-aminophenoxy)benzene (TPE-R), or 1,4-bis(4-aminophenoxy)benzene. More preferably, 4,4'-diaminodiphenyl ether (4,4'-DAPE), 1,3-bis(3-aminophenoxy)benzene (APB), 1,3-bis(4-aminophenoxy)benzene (TPE-R), or 1,4-bis(4-aminophenoxy)benzene, 2,2'-dimethyl-4,4'-diaminobiphenyl (m-TB), 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,6-dimethyl-m-phenylenediamine, 2,5- dimethyl-p-phenylenediamine, 2,4-diaminomesitylene, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 2,4-toluenediamine, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 4,4'-diaminobiphenyl, 3,3'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 4,4'-diamino-p-terphenyl, 3,3'-diamino-p-terphenyl, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino- t-butyl)toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, 2,6-diaminopyridine, 2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, piperazine, 9,9-bis(4-aminophenyl)fluorene, 4,4'-diaminobenzanilide, 5-amino-2-(4-aminophenyl)benzimidazole, 5-amino-2-(4-aminophenyl)benzoxazole, etc.

The polyamic acid component (a) preferably has a weight-average molecular weight in the range of 20,000 to 2,000,000. A more preferred lower limit is 40,000, and an even more preferred lower limit is 60,000. A more preferred upper limit is 1,500,000, and an even more preferred upper limit is 1,000,000. Having a weight-average molecular weight equal to or greater than the above-mentioned lower limit makes the film after imidization stronger, while having a weight-average molecular weight equal to or less than the above-mentioned upper limit makes it easier to adjust the viscosity of the polyamic acid solution.

In addition, for reasons such as film-forming properties during coating, the polyamic acid (component (a)) in the polyamic acid composition of the present invention is dissolved in a concentration of preferably 5 to 30% by mass, more preferably 8 to 20% by mass.

<(b) Organic Solvent>
The organic solvent of component (b) used in the present invention is not limited as long as it can be used in the polymerization reaction of the tetracarboxylic dianhydride and diamine, which are the raw materials for the polyamic acid, and can adequately dissolve the polyamic acid prepared therefrom, and examples thereof include N,N-dimethylformamide, N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone, 2-butanone, dimethyl sulfoxide, dimethyl sulfate, cyclohexanone, dioxane, tetrahydrofuran, diglyme, triglyme, γ-butyrolactone, etc. Two or more of these organic solvents can also be used in combination.

Of these, taking into consideration miscibility with water (component (c)) (solubility in water) and non-reactivity, those with a water solubility of 10% by mass or more relative to 100% by mass of the organic solvent are more preferred.

Furthermore, it is preferable that the organic solvent of component (b) has a boiling point higher than that of water, and more preferably a boiling point (at normal pressure) of 120°C or higher. Organic solvents with such high boiling points are preferred because they can prevent problems such as the organic solvent volatilizing before water and causing precipitation of polyamic acid when the polyamic acid composition is used to form a film.

From this perspective, N,N-dimethylformamide, N,N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone are particularly preferred as (b) organic solvents.

<(c) Water>
As described above, the present invention has discovered that by incorporating an appropriate amount of water into a polyamic acid composition, a polyamic acid composition with excellent storage stability can be obtained without affecting the polymerization reaction. The content of water (component (c)) in the polyamic acid composition is 0.05% by mass to 10% by mass. The preferred lower limit is 0.08% by mass, and more preferably 0.10% by mass. The preferred upper limit is 7% by mass, and more preferably 5% by mass. By having the water content at or above the lower limit, it is possible to significantly suppress thickening of the polyamic acid composition during storage. Furthermore, by having the water content at or below the upper limit, it is possible to suppress occurrence of precipitation due to decreased solubility of the polyamic acid (component (a)), and occurrence of viscosity decrease due to hydrolysis.

The water component (c) may be added by any method or route of incorporation, provided that it is adjusted to fall within the aforementioned range in the polyamic acid composition. It may be derived from the acid anhydride or diamine raw material, or may be intentionally added (added water). Furthermore, it may contain trace amounts of water that are inevitably mixed in during reactions such as polymerization or during storage, and is not limited thereto.

<Other ingredients>
The polyamic acid composition of the present invention may contain, as necessary, fillers such as silicon dioxide, aluminum oxide, boron nitride, magnesium oxide, beryllium oxide, aluminum nitride, silicon nitride, aluminum fluoride, calcium fluoride, and metal salts of organic phosphinic acids, as well as other components, as long as the purpose of the present invention is not impaired. These components are typically used in an amount of 10% by mass or less in the polyamic acid composition. Furthermore, these components may be used alone or in combination of two or more.

<Characteristics of Polyamic Acid Composition>
The polyamic acid composition of the present invention may contain a polyamic acid other than the polyamic acid of component (a), for example, as represented by formula (1). The other polyamic acid may be a polyamic acid synthesized in an equimolar ratio using a tetracarboxylic dianhydride and a diamine compound, which are generally used in the preparation of polyimides (polyamic acids). In this case, the other polyamic acid is preferably present in an amount of 50% by mass or less, based on 100% by mass of the total of the polyamic acid and the polyamic acid of component (a).

Furthermore, the polyamic acid composition of the present invention preferably has a solids content of approximately 5 to 30% by mass.

The polyamic acid composition of the present invention preferably exhibits minimal increase in viscosity over time during storage. During storage, it is preferable that the water content of component (c) be maintained within the range, and the composition is typically stored in a sealed state. Storage temperatures are preferably compatible with a wide range, from frozen storage (approximately -30°C) to outdoor storage (maximum of approximately 60°C), but are more preferably between 0°C and room temperature (typically approximately 25°C), even more preferably between 0°C and 15°C, and particularly preferably between 0°C and 10°C. Furthermore, it is preferable that the humidity during storage be 70% or less. For such polyamic acid compositions of the present invention, the viscosity after 30 days of storage under the above temperature and humidity conditions is preferably between 100% and 30%, more preferably between 100% and 50%, of the initial viscosity.

The viscosity of the polyamic acid composition of the present invention can be selected appropriately depending on the solid content and application, but a viscosity of 700 to 70,000 mPa·s is preferably used.

[Method of producing polyamic acid composition]
Next, a method for producing the polyamic acid composition will be described.
The polyamic acid composition of the present invention is preferably produced as follows: That is, the following steps I and II:
I) a step of reacting a tetracarboxylic dianhydride component with a diamine component in an organic solvent to obtain a polyamic acid solution;
II) adding water to the polyamic acid solution obtained in step I to produce a polyamic acid composition containing 0.05% by mass or more and 10% by mass or less of water (the preferred range is as described above).

In step I, before adding water, the specified tetracarboxylic dianhydride component and diamine component are reacted in an organic solvent and typically stirred at a temperature ranging from 0 to 100°C for 30 minutes to 24 hours to cause a polymerization reaction, producing the polyamic acid component (a). During the reaction, the reaction components are dissolved in the organic solvent so that the resulting polyamic acid component (a) is in the range of 5 to 30% by mass, preferably 10 to 20% by mass. As mentioned above, the polyamic acid composition may contain polyamic acids other than the polyamic acid component (a).

When adding the tetracarboxylic dianhydride component and the diamine component, polymerization begins as soon as the two come into contact. Therefore, it is preferable to prepare one of the raw materials by mixing it with an organic solvent in advance, and then add the other raw material to that mixture to carry out the reaction. More preferably, for reasons such as preventing inactivation of the tetracarboxylic dianhydride due to the solubility of the monomers and moisture in the solvent, it is more preferable to add the tetracarboxylic dianhydride to a solution in which the diamine and organic solvent have been mixed in advance.

Here, the amounts (molar ratio) of the tetracarboxylic dianhydride component and diamine component used as raw materials when reacting them are preferably adjusted so that the ratio of tetracarboxylic dianhydride to diamine is less than 1 mole. This theoretically allows the terminals of the prepared polyamic acid (component (a)) to be primary amino groups (—NH ₂ ). The presence and amount of primary amino groups can be confirmed using known methods. If the ratio of tetracarboxylic dianhydride to diamine is too low, the polyamic acid (component (a)) tends not to be sufficiently polymerized. Therefore, the ratio of tetracarboxylic dianhydride to diamine is preferably within the range of 0.970 to 0.998 moles, more preferably 0.980 to 0.995 moles.

In addition, in step I, as described above, a tetracarboxylic dianhydride component and/or a diamine component containing a ketone group is used. It is preferable to adjust the blending of raw materials appropriately so that the entire molecule contains a predetermined amount of (a) polyamic acid having the above-described ketone group content.

In addition, in Step I, the weight-average molecular weight of the resulting polyamic acid is adjusted to be 20,000 or more and 2,000,000 or less. If water is added in an amount greater than a specified amount before the polymerization reaction, the tetracarboxylic dianhydride will be deactivated (hydrolyzed), making it difficult to obtain polyamic acid with the desired molecular weight. Therefore, it is preferable to polymerize in Step I to the weight-average molecular weight range described above.

In Step II, water can be added directly to the polyamic acid solution prepared in Step I to adjust the water content to a predetermined level. However, to prevent precipitation of the polyamic acid, it is preferable to first prepare an aqueous solution by mixing water with the same organic solvent as used in Step I, and then add this to the polyamic acid solution. This aqueous solution is preferably prepared so that the water content is 1% by mass to 60% by mass, and more preferably 5% by mass to 30% by mass, based on the total amount of the organic solvent and water. Preparing the aqueous solution within this water content range makes it possible to adjust the water content by small amounts while preventing the precipitation of the polyamic acid. This is also advantageous in that it allows water to be mixed uniformly and quickly into the polyamic acid solution.

[Uses of polyamic acid braids]
The polyamic acid composition of the present invention easily gives a tough film because an imine reaction also occurs during imidization, and is therefore particularly suitable for use as an electrical insulating material, a film, a protective film, a coating agent, etc. The polyamic acid composition of the present invention can be imidized by heating under known methods and conditions to form a polyimide.

The following examples are provided to more specifically explain the features of the present invention. However, the scope of the present invention is not limited to these examples. In the following examples, various measurements and evaluations were performed as follows, unless otherwise noted.

[Viscosity measurement]
The viscosity was measured at 25°C using an E-type viscometer (manufactured by Brookfield, trade name: DV-II+Pro). The rotation speed was set so that the torque was 10% to 90%, and the value was read when the viscosity stabilized 2 minutes after the start of measurement.

[Measurement of weight average molecular weight]
The weight average molecular weight (Mw) was measured by gel permeation chromatography (manufactured by Tosoh Corporation, trade name: HLC-8420GPC) using polystyrene as a standard substance and N,N-dimethylacetamide as an eluent.

The abbreviations used in the Examples and Reference Examples represent the following compounds.
BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride PMDA: pyromellitic dianhydride BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride m-TB: 2,2'-dimethyl-4,4'-diaminobiphenyl TPE-R: 1,3-bis(4-aminophenoxy)benzene 4,4'-DAPE: 4,4'-diaminodiphenyl ether DMAc: N,N-dimethylacetamide In the following examples, DMAc with a water content of less than 200 ppm is used.

[Example 1]
262.8 parts by weight of DMAc, 10.54 parts by weight of TPE-R (36.06 mol parts), and 7.66 parts by weight of m-TB (36.06 mol parts) were added to an airtight polymerization kettle and stirred at room temperature for 30 minutes or more to completely dissolve. After cooling the polymerization kettle to 20 ° C, 6.90 parts by weight of BTDA (21.42 mol parts) was added and stirred for 10 minutes, followed by 10.90 parts by weight of PMDA (49.98 mol parts) and stirring at room temperature for 4 hours [acid anhydride/diamine (molar ratio): 0.990, ketone group content: 15 mol parts]. Thereafter, a mixture of 1.2 parts by weight of DMAc and 0.3 parts by weight of pure water was added and stirred at room temperature for 2 hours to obtain a polyamide solution (polyamic acid composition) A with a viscosity of 3,490 cP (moisture content: 0.1% by weight). This polyamic acid solution A was stored for a certain period of time under a reduced pressure of 0.03 MPa, and the change in viscosity over time was evaluated. The results are shown in Table 1.

[Example 2]
234.0 parts by weight of DMAc, 10.54 parts by weight of TPE-R (36.06 mol parts), and 7.66 parts by weight of m-TB (36.06 mol parts) were added to an airtight polymerization kettle and stirred at room temperature for 30 minutes or more to completely dissolve. After cooling the polymerization kettle to 20 ° C, 6.90 parts by weight of BTDA (21.42 mol parts) was added and stirred for 10 minutes, followed by 10.90 parts by weight of PMDA (49.98 mol parts) and stirring at room temperature for 4 hours [acid anhydride/diamine (molar ratio): 0.990, ketone group content: 15 mol parts]. Then, a mixture of 21.0 parts by weight of DMAc and 9.0 parts by weight of pure water was added and stirred at room temperature for 2 hours to obtain a polyamide solution B with a viscosity of 3,350 cP (water content: 3% by weight). This polyamic acid solution B was stored for a certain period of time under a reduced pressure of 0.03 MPa, and the change in viscosity over time was evaluated. The results are shown in Table 1.

[Comparative Example 1]
264.0 parts by weight of DMAc, 10.54 parts by weight of TPE-R (36.06 mol parts), and 7.66 parts by weight of m-TB (36.06 mol parts) were added to an airtight polymerization kettle and stirred at room temperature for at least 30 minutes to completely dissolve. After cooling the polymerization kettle to 20°C, 6.90 parts by weight of BTDA (21.42 mol parts) were added and stirred for 10 minutes, followed by 10.90 parts by weight of PMDA (49.98 mol parts) and stirring at room temperature for 4 hours to obtain a polyamide solution C with a viscosity of 3,710 cP [acid anhydride/diamine (molar ratio): 0.990, ketone group content as specified above: 15 mol parts] (moisture content: 0% by weight). This polyamic acid solution C was stored for a certain period of time under a reduced pressure of 0.03 MPa, and the change in viscosity over time was evaluated. The results are shown in Table 1.

[Example 3]
234.0 parts by weight of DMAc, 10.56 parts by weight of TPE-R (36.13 mol parts), and 7.67 parts by weight of m-TB (36.13 mol parts) were added to an airtight polymerization kettle and stirred at room temperature for 30 minutes or more to completely dissolve. After cooling the polymerization kettle to 20 ° C, 6.88 parts by weight of BTDA (21.38 mol parts) was added and stirred for 10 minutes, followed by 10.87 parts by weight of PMDA (49.88 mol parts) and stirring at room temperature for 4 hours [acid anhydride / diamine (molar ratio): 0.986, ketone group content: 15 mol parts]. Then, a mixture of 24.0 parts by weight of DMAc and 6.0 parts by weight of pure water was added and stirred at room temperature for 2 hours to obtain a polyamide solution D with a viscosity of 2,030 cP (water content: 2% by weight). This polyamic acid solution D was stored for a certain period of time under a reduced pressure of 0.03 MPa, and the change in viscosity over time was evaluated. The results are shown in Table 1.

[Comparative Example 2]
234.0 parts by weight of DMAc, 10.56 parts by weight of TPE-R (36.13 mol parts), and 7.67 parts by weight of m-TB (36.13 mol parts) were added to an airtight polymerization kettle and stirred at room temperature for at least 30 minutes to completely dissolve. After cooling the polymerization kettle to 20°C, 6.88 parts by weight of BTDA (21.38 mol parts) were added and stirred for 10 minutes, followed by 10.87 parts by weight of PMDA (49.88 mol parts) and stirring at room temperature for 4 hours to obtain a polyamide solution E with a viscosity of 2,110 cP [acid anhydride/diamine (molar ratio): 0.986, ketone group content as specified above: 15 mol parts] (moisture content: 0% by weight). This polyamic acid solution E was stored for a certain period of time under a reduced pressure of 0.03 MPa, and the change in viscosity over time was evaluated. The results are shown in Table 1.

[Example 4]
234.0 parts by weight of DMAc and 13.81 parts by weight of 4,4'-DAPE (68.99 mol parts) were added to an airtight polymerization kettle and stirred at room temperature for at least 30 minutes to achieve complete dissolution. After cooling the kettle to 20°C, 22.19 parts by weight of BTDA (68.85 mol parts) was added and stirred at room temperature for 4 hours (acid anhydride/diamine (molar ratio): 0.998, ketone group content as specified above: 50 mol parts). A mixture of 24.0 parts by weight of DMAc and 6.0 parts by weight of pure water was then added and stirred at room temperature for 2 hours to obtain polyamic acid solution F with a viscosity of 3,550 cP (water content: 2% by weight). This polyamic acid solution F was stored for a certain period of time under a reduced pressure of 0.03 MPa, and the change in viscosity over time was evaluated. The results are shown in Table 1.

[Comparative Example 3]
264.0 parts by weight of DMAc and 13.81 parts by weight of 4,4'-DAPE (68.99 mol parts) were added to an airtight polymerization kettle and stirred at room temperature for at least 30 minutes to completely dissolve. After cooling the kettle to 20°C, 22.19 parts by weight of BTDA (68.85 mol parts) was added and stirred at room temperature for 4 hours to obtain polyamic acid solution G with a viscosity of 3,750 cP (acid anhydride/diamine (molar ratio): 0.998, ketone group content as specified above: 50 mol parts) (water content: 0% by weight). This polyamic acid solution G was stored for a certain period of time under a reduced pressure of 0.03 MPa, and the change in viscosity over time was evaluated. The results are shown in Table 1.

Comparative Examples 1 to 3 do not contain water, so the moisture content is low and it is believed that the viscosity increases due to iminization.

In Examples 1 to 4, the addition of water appears to have suppressed thickening due to iminization. Furthermore, even after 30 days or more, the viscosity remained between 100% and 30% of the initial viscosity, demonstrating good storage stability.

[Reference example 1]
The decrease in polyamic acid solubility due to the addition of water was evaluated as follows. First, 150 parts by mass of polyamic acid solution C from Comparative Example 1 before aging was weighed into a flask equipped with a stirring blade. Next, 4 parts by mass of water was gradually added to this polyamic acid solution C while stirring, and the mixture was stirred at room temperature for 1 hour. Immediately after the addition of water, the polyamic acid precipitated, but after 1 hour of stirring, it was completely dissolved. In the same manner, another 4 parts by mass of water was added and the mixture was stirred for 1 hour, and this procedure was repeated until the precipitated polyamic acid no longer dissolved. The results are shown in Table 2.

The results in Table 2 show that as the water content in the polyamic acid solution increases, it takes longer for the precipitated polyamic acid to dissolve, and when the water content exceeds 11% by mass, it no longer dissolves within one hour. Therefore, it was confirmed that it is preferable to keep the water content of the polyamic acid solution (composition) at 10% by mass or less.

[Reference example 2]
Polyamic acid solution A (35 days old) from Example 1, polyamic acid solution B (before aging) from Example 2, and polyamic acid solution C (before aging) from Comparative Example 1 were each applied to copper foil and then heated and dried at 140°C or less to remove the solvent. Further, stepwise heat treatment from 150°C to 360°C was performed to complete imidization. The copper foil was etched away from the resulting metal-clad laminate to obtain a 20 μm-thick polyimide film. Dynamic mechanical analysis (DMA) was performed on the resulting polyimide film, and the glass transition temperature was determined from the peak temperature of the loss modulus. Furthermore, tear propagation resistance was measured using a light-load tear tester. The results are shown in Table 3.

The results in Table 3 show that there was no difference in the physical properties of the polyimide film depending on whether or not water was added.

[Reference example 3]
The effect of premixing an organic solvent with water before adding water to a polyamic acid solution was evaluated as follows. First, 50 g of the polyamic acid solution C from Comparative Example 1 before aging was weighed into a 100 ml cup. Next, 2 g of a mixture of water and organic solvent (DMAc) at different ratios was added to completely cover the surface of the polyamic acid solution, and it was observed whether precipitation of polyamic acid occurred at the interface. The results are shown in Table 4.

In the mixed solution of water:organic solvent=20:80, no precipitation of polyamic acid was observed.
In the mixed solution of water:organic solvent=30:70, a small amount of polyamic acid was precipitated, but this was dissolved by gently shaking the container.
In the mixed solution of water:organic solvent=50:50, precipitation of polyamic acid was observed, but the precipitated polyamic acid was dissolved by stirring the whole.
When the water content was 100 wt %, a large amount of polyamic acid was precipitated, and the polyamic acid did not dissolve for a long time even when the entire solution was stirred.

The above results suggest that when adding water to a polyamic acid solution (composition), mixing it with an organic solvent beforehand to form a mixed solution can prevent precipitation of the polyamic acid, or, if precipitation does occur, can be quickly dissolved, making it easier to add water.

[Reference example 4]
264.0 parts by weight of DMAc, 10.39 parts by weight of TPE-R (35.53 mol parts), and 7.54 parts by weight of m-TB (35.53 mol parts) were added to an airtight polymerization kettle and stirred at room temperature for 30 minutes or more to completely dissolve. After cooling the polymerization kettle to 20 ° C, 7.01 parts by weight of BTDA (21.74 mol parts) was added and stirred for 10 minutes, and then 11.07 parts by weight of PMDA (50.73 mol parts) was added and stirred at room temperature for 4 hours to obtain a polyamide solution H with a viscosity of 3,580 cP [acid anhydride/diamine (molar ratio): 1.020, ketone group content: 15 mol parts].
This polyamic acid solution H was stored for a certain period of time under a reduced pressure of 0.03 MPa, and the change in viscosity over time was evaluated. The results are shown in Table 5.

[Reference example 5]
264.0 parts by weight of DMAc, 10.74 parts by weight of TPE-R (36.73 mol parts), and 7.80 parts by weight of m-TB (36.73 mol parts) were added to an airtight polymerization kettle and stirred at room temperature for 30 minutes or more to completely dissolve. After cooling the polymerization kettle to 20 ° C, 6.40 parts by weight of BPDA (21.75 mol parts) was added and stirred for 10 minutes, and then 11.07 parts by weight of PMDA (50.75 mol parts) was added and stirred at room temperature for 4 hours to obtain a polyamide solution I with a viscosity of 3,060 cP [acid anhydride/diamine (molar ratio): 0.987, ketone group content: 0 mol parts].
This polyamic acid solution I was stored for a certain period of time under a reduced pressure of 0.03 MPa, and the change in viscosity over time was evaluated. The results are shown in Table 5.

As shown in Reference Example 4, it was confirmed that thickening did not occur under conditions where there was more than 1 mole of tetracarboxylic dianhydride per mole of diamine, or under conditions where there was no ketone, as shown in Reference Example 5.

[Reference example 6]
255.0 parts by mass of DMAc and 22.42 parts by mass of m-TB (105.62 parts by mole) were added to an airtight polymerization kettle and stirred at room temperature for 30 minutes or more to completely dissolve them. After cooling the polymerization kettle to 20°C, 22.58 parts by mass of PMDA (103.51 parts by mole) was added and stirred at room temperature for 4 hours to obtain a polyamide solution J with a viscosity of 22,500 cP.

[Reference example 7]
255.0 parts by mass of DMAc, 0.18 parts by mass of water, and 22.42 parts by mass of m-TB (105.62 parts by mole) were added to an airtight polymerization kettle and stirred at room temperature for 30 minutes or more to completely dissolve. After cooling the polymerization kettle to 20°C, 22.58 parts by mass of PMDA (103.51 parts by mole) was added and stirred at room temperature for 4 hours to obtain a polyamide solution K with a viscosity of 800 cP.

Reference Examples 6 and 7 show that adding water before polymerization does not increase the viscosity and inhibits the polymerization reaction.

Claims (9)

The following components (a) to (c):
(a) a polyamic acid having an acid anhydride residue derived from a tetracarboxylic dianhydride component and a diamine residue derived from a diamine component;
A polyamic acid composition comprising: (b) an organic solvent; and (c) water,
The component (a) is represented by the following formula (1), and has a ketone group and a primary amino group at a molecular terminal, the ketone group being derived from the tetracarboxylic dianhydride component and/or the diamine component:
a polyamic acid composition, wherein the content of the component (c) is 0.05% by mass or more and 10% by mass or less based on the total of the components (a), (b), and (c);
(In the above formula (1), X2 is a tetravalent acid anhydride residue derived from a tetracarboxylic dianhydride component, Y2 is a divalent diamine residue derived from a diamine component, and n represents a repeating unit.) The polyamic acid composition according to claim 1, characterized in that the polyamic acid has a weight average molecular weight (Mw) of 20,000 or more and 2,000,000 or less. 3. The polyamic acid composition according to claim 1, wherein the ketone groups in component (a) are derived from 3,3',4,4'-benzophenonetetracarboxylic dianhydride as the tetracarboxylic dianhydride component, and are contained in an amount of 10 parts by mole or more per 100 parts by mole of the total of the acid anhydride residues and the diamine residues. The polyamic acid composition according to any one of claims 1 to 3, characterized in that component (b) has a boiling point of 120°C or higher and a water solubility of 10% by mass or higher. The polyamic acid composition according to any one of claims 1 to 4, characterized in that the viscosity of the composition after 30 days of storage at a temperature of -30°C to 60°C and a humidity of 70% or less is 100% to 30% of the initial viscosity. 6. The polyamic acid composition according to claim 1, wherein the composition has a viscosity in the range of 700 to 70,000 mPa·s. A method for producing the polyamic acid composition according to any one of claims 1 to 6 , comprising the following steps I and II:
I) a step of reacting a tetracarboxylic dianhydride component with a diamine component in an organic solvent to obtain a polyamic acid solution;
II) a step of adding water to the polyamic acid solution to produce a polyamic acid composition, wherein in step II, water is added so that the water content of the polyamic acid composition is 0.05% by mass or more and 10% by mass or less based on the total mass of the organic solvent, the polyamic acid, and the water. 8. The method for producing a polyamic acid composition according to claim 7, wherein, when adding water in step II, the organic solvent used in step I and water are mixed in advance to prepare a mixed solution containing water in an amount of 1% by mass to 60 % by mass based on the total amount of the organic solvent and water, and water is added using the mixed solution in step II. 9. The method for producing a polyamic acid composition according to claim 7 or 8, wherein step I produces a solution of a polyamic acid having a ketone group in the tetracarboxylic dianhydride component and/or the diamine component and having a weight average molecular weight (Mw) of 20,000 or more and 2,000,000 or less.