JP6905227B2 - Diamines and polyimides, and their use - Google Patents

Description

The present invention relates to diamines and polyimides, and their use.

Currently, glass substrates are used in various display devices such as liquid crystal displays and organic EL displays. The glass substrate is an excellent material in that it has high heat resistance, a low coefficient of linear thermal expansion, and high transparency. On the other hand, these displays are required to be lighter and more flexible, and there is a strong demand for a material to replace glass. Various polyimide materials have been studied as materials that satisfy these requirements.

By the way, polyimide has high heat resistance due to its chemical structure. However, most of the polyimides are insoluble in solvents, and it is difficult to form a uniform film by using a polyimide solution coating process. Therefore, a method of uniformly filming polyamic acid, which is a polyimide precursor soluble in a solvent, and converting it into a polyimide film is widely adopted.

However, according to this method, the step of converting polyamic acid to polyimide requires heating at 300 ° C. or higher, and is accompanied by a large reaction shrinkage. Therefore, this method has a problem that not only warpage occurs due to a mismatch in the coefficient of linear thermal expansion between the inorganic material substrate and the polyimide film, but also film defects occur due to water produced as a by-product in some cases.

For the above problems, for example, Patent Documents 1 and 2 disclose a soluble and transparent polyimide.

International Publication No. 2013/121917 Japanese Unexamined Patent Publication No. 2015-214597

However, a polyimide having a structure different from that of the polyimides described in Patent Documents 1 and 2 and having excellent solution processability has been required.

One aspect of the present invention is to provide a polyimide having excellent solution processability.

As a result of diligent research conducted by the present inventor in order to solve the above problems, it was found that a polyimide having excellent solution processability can be prepared by using a diamine having a specific structure, and the present invention has been completed. rice field.

That is, the diamine according to one aspect of the present invention has the following formula (1):

(In the formula (1), the substituent R independently represents an alkyl group or an alkoxy group having 1 to 4 carbon atoms, and n represents the number of substituents R and is an integer of 1 to 4. ).

Further, the polyimide according to one aspect of the present invention has the following formula (3):

It has a repeating unit represented by (in formula (3), the substituent R independently represents an alkyl group or an alkoxy group having 1 to 4 carbon atoms, and n represents the number of substituents R, 1 to 4 X ₁ represents at least one of a tetravalent aliphatic group and an aromatic group).

According to one aspect of the present invention, it is possible to provide a polyimide having excellent solution processability.

It is a figure which shows the infrared absorption spectrum of the polyimide thin film measured in Example 3.

Hereinafter, embodiments of the present invention will be described in detail, but these are aspects of the present invention, and the present invention is not limited to these contents.

In addition, in this specification, "solution processability" means excellent processability because it is excellent in solubility in an organic solvent. For example, when forming a polyimide into a film, a method of dissolving the polyimide in an arbitrary organic solvent, applying the solution to the support, and drying the polyimide is adopted, so that it is very important to have excellent solution processability. It is a characteristic.

<1. Diamine>
The diamine according to the embodiment of the present invention has the following formula (1):

(In the formula (1), the substituent R independently represents an alkyl group or an alkoxy group having 1 to 4 carbon atoms, and n represents the number of substituents R and is an integer of 1 to 4. ).

The diamine has an amide bond in the molecule. Therefore, the polyimide obtained by using the diamine tends to have a linear main chain structure and easily form intermolecular hydrogen bonds. Therefore, it is considered that a film having a low coefficient of linear thermal expansion can be obtained from the polyimide.

In addition, the diamine has a trifluoromethyl group. Since the trifluoromethyl group is sterically bulky, the introduction of the trifluoromethyl group prevents the aggregation and crystallization of the polymer chain. It is considered that this allows solvent molecules to easily penetrate between the molecular chains of the polyimide, and as a result, a polyimide that is soluble in the solvent can be obtained.

Further, as shown in Examples described later, the polyimide obtained by using the diamine has significantly improved solubility in an organic solvent as compared with the polyimide obtained by using a diamine containing no substituent R. Will be done. It is presumed that this is because the dense aggregation of the polymer chains is hindered.

Each substituent R may be the same or different. Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group and a tert-butyl group. Examples of the alkoxy group having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an isobutoxy group, a sec-butoxy group and a tert-butoxy group. Among them, when the substituent R is a methyl group, it is preferable because both solution processability and heat resistance can be achieved at the same time.

The diamine is based on the following formula (2):

It may be represented by. The polyimide obtained by using the diamine can provide a film having more improved transparency due to the bonding position of the trifluoromethyl group. Further, when the substituent R is a methyl group, it is preferable from the viewpoint that both solution processability and heat resistance can be achieved at the same time.

The method for synthesizing the diamine is not limited to this, and examples thereof include a method of obtaining a dinitro compound as a precursor and hydrogen-reducing the dinitro compound in the presence of a catalyst. For example, the diamine represented by the above formula (1) can be obtained by the method represented by the formula (7).

The precursor dinitro compound can be obtained, for example, by reacting 2,2'-bis (trifluoromethyl) benzidine with a chlorinated product of a 4-nitrobenzoic acid derivative having a substituent R. For example, when the diamine of the formula (2) is obtained, 3-methyl-4-nitrobenzoic acid can be used as the 4-nitrobenzoic acid derivative. For the chlorinated product, for example, 3-methyl-4-nitrobenzoic acid is added to thionyl chloride, N, N-dimethylformamide is added as a catalyst to reflux, and then benzene is added to add excess thionyl chloride. It can be obtained by azeotropic distillation.

The reaction of 2,2'-bis (trifluoromethyl) benzidine with a chlorinated product of a 4-nitrobenzoic acid derivative can be carried out, for example, by dissolving them in dehydrated tetrahydrofuran and mixing them. At this time, by coexisting a base such as pyridine or triethylamine as a dehydrochlorination agent, hydrogen chloride generated during the reaction can be removed.

There are various methods for reducing the obtained dinitro compound to diamine, and the method is not particularly limited, but a catalytic reduction method in which hydrogen gas is reacted in the presence of a metal catalyst such as Pd / C or Ni is simple. be. Examples of the solvent used at that time include 1,4-dioxane, ethanol and tetrahydrofuran.

<2. Polyimide>
The polyimide according to one embodiment of the present invention has the following formula (3):

It has a repeating unit represented by (in formula (3), the substituent R independently represents an alkyl group or an alkoxy group having 1 to 4 carbon atoms, and n represents the number of substituents R, 1 to 4 X ₁ represents at least one of a tetravalent aliphatic group and an aromatic group). In other words, X ₁ may be a tetravalent aliphatic group or a tetravalent aromatic group, and may be a structure containing both a tetravalent aliphatic group and an aromatic group (for example, 4). It may be a structure in which a valent aliphatic group and a tetravalent aromatic group are linked).

Since the polyimide has a structure derived from the diamine represented by the formula (1) as described above, it is excellent in solution processability and has a low coefficient of linear thermal expansion when formed into a film. In addition, the polyimide exhibits high heat resistance due to its chemical structure.

The polyimide has the following formula (4):

It may have a repeating unit represented by (in formula (4), X ₁ represents at least one of a tetravalent aliphatic group and an aromatic group).

The tetravalent aliphatic group can be, for example, a structure derived from the following alicyclic tetracarboxylic dianhydride: (1S, 2R, 4S, 5R) -cyclohexanetetracarboxylic dianhydride (cis, cis). , Sis-1,2,4,5-cyclohexanetetracarboxylic dianhydride), (1S, 2S, 4R, 5R) -cyclohexanetetracarboxylic dianhydride, (1R, 2S, 4S, 5R) -cyclohexanetetra Vicarboxylic dianhydride, bicyclo [2.2.2] octane-2,3,5,6-tetracarboxylic dianhydride, bicyclo [2.2.2] octo-7-ene-2,3,5 , 6-Tetetracarboxylic dianhydride, 5- (dioxotetrahydrofuryl-3-methyl) -3-cyclohexene-1,2-dicarboxylic dianhydride, 4- (2,5-dioxotetraxethylene-3-yl) )-Tetraline-1,2-dicarboxylic dianhydride, tetrahydrofuran-2,3,4,5-tetracarboxylic dianhydride, bicyclo-3,3', 4,4'-tetracarboxylic dianhydride, 1 , 2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,3-dimethyl-1,2-2,3,4-cyclobutanetetracarboxylic acid Dihydride or 1,4-dimethyl-1,2-2,3,4-cyclobutanetetracarboxylic dianhydride and the like. That is, the tetravalent aliphatic group can be derived from the structure sandwiched between the acid anhydride groups of these alicyclic tetracarboxylic dianhydrides.

The cause of the polyimide coloring yellow or brown is the intramolecular and / or intermolecular charge transfer interaction of the polyimide. In order to obtain a transparent polyimide, it is necessary to suppress these charge transfer interactions. As a means therefor, in the formula (4), as X _1, it is effective to select a tetravalent aliphatic group.

Above all, from the viewpoint that the main chain of polyimide can have a more rigid structure, X ₁ is expressed by the following equation (5):

It is preferably a tetravalent aliphatic group represented by. The structure represented by the formula (5) can be introduced into polyimide by using 1,2,3,4-cyclobutanetetracarboxylic dianhydride.

The tetravalent aromatic group can be, for example, a structure derived from the following aromatic tetracarboxylic dianhydrides: 4,4'-(hexafluoroisopropyridene) diphthalic acid dianhydride or 1,4-bis. (Fluoromethyl-2,3,5,6-benzenetetracarboxylic dianhydride) and the like. That is, the tetravalent aromatic group can be derived from the structure sandwiched between the acid anhydride groups of these aromatic tetracarboxylic dianhydrides. Examples of the tetravalent aromatic group include those containing an aromatic ring and at least one selected from the group consisting of a hexafluoroisopropylidene group, a sulfonyl group, an ether bond and an ester bond. When the polyimide contains a tetravalent aromatic group, the solution processability can be improved.

Above all, from the viewpoint that the solution processability can be further improved without impairing the heat resistance, X ₁ is expressed by the following formula (6):

It is preferably a tetravalent aromatic group represented by. The structure represented by the formula (6) can be introduced into the polyimide by using 4,4'-(hexafluoroisopropyridene) diphthalic acid dianhydride.

In the polyimide, when the total repeating unit is 100 mol%, the content of the repeating unit represented by the formula (3) is preferably 70 mol% or more, more preferably 80 mol% or more. It is more preferably 90 mol% or more, and particularly preferably 100 mol% (the polyimide is composed of a repeating unit represented by the formula (3)). When the content of the repeating unit represented by the formula (3) is 70 mol% or more, it is possible to provide a polyimide having more excellent solution processability, transparency, high heat resistance, and a low coefficient of linear thermal expansion.

The polyimide is a repeating unit represented by the above formula (3), and a repeating unit in which X ₁ is a tetravalent aliphatic group represented by the formula (5) (hereinafter, also referred to as a repeating unit (a)). ) And a repeating unit represented by the above formula (3), wherein X ₁ is a tetravalent aromatic group represented by the formula (6) (hereinafter, also referred to as a repeating unit (b)). It may contain at least two kinds of repeating units of. In this case, the transparency can be improved based on the tetravalent aliphatic group of the repeating unit (a), and the solution processability can be improved based on the tetravalent aromatic group of the repeating unit (b). It is preferable because it can be used.

When the total number of moles of the repeating unit (a) and the repeating unit (b) is 100 mol%, the composition ratio (molar ratio) of the repeating unit (a) and the repeating unit (b), that is, [(a)). ] / [(B)] is preferably 95/5 to 5/95, more preferably 90/10 to 10/90, and even more preferably 80/20 to 20/80. It is particularly preferably 70/30 to 50/50. With the above composition ratio, the improvement in transparency due to the tetravalent aliphatic group of the repeating unit (a) and the improvement in solution processability due to the tetravalent aromatic group of the repeating unit (b). Good balance. Further, for example, when giving priority to improving transparency, [(a)] / [(b)] is preferably 95/5 to 55/45, and is 90/10 to 60/40. Is more preferable, and 85/15 to 65/35 is even more preferable. On the other hand, when giving priority to improving the solution processability, [(a)] / [(b)] is preferably 5/95 to 50/50, and preferably 10/90 to 40/60. More preferably, it is 15/85 to 35/65.

When producing the above-mentioned polyimide, other diamines may be used in addition to the diamine represented by the formula (1). Examples of other diamines include p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3. '-Diaminodiphenylsulfide, 3,4'-diaminodiphenylsulfide, 4,4'-diaminodiphenylsulfide, 3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone , 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2 , 2-di (3-aminophenyl) propane, 2,2-di (4-aminophenyl) propane, 2- (3-aminophenyl) -2- (4-aminophenyl) propane, 1,1-di ( 3-Aminophenyl) -1-phenylethane, 1,1-di (4-aminophenyl) -1-phenylethane, 1- (3-aminophenyl) -1- (4-aminophenyl) -1-phenylethane , 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,4-bis (3-aminophenoxy) benzene, 1,4-bis (4-aminophenoxy) ) Benzene, 1,3-bis (3-aminobenzoyl) benzene, 1,3-bis (4-aminobenzoyl) benzene, 1,4-bis (3-aminobenzoyl) benzene, 1,4-bis (4-) Aminobenzoyl) benzene, 1,3-bis (3-amino-α, α-dimethylbenzyl) benzene, 1,3-bis (4-amino-α, α-dimethylbenzyl) benzene, 1,4-bis (3) -Amino-α, α-dimethylbenzyl) benzene, 1,4-bis (4-amino-α, α-dimethylbenzyl) benzene, 2,6-bis (3-aminophenoxy) benzonitrile, 2,6-bis (3-Aminophenoxy) pyridine, 4,4'-bis (3-aminophenoxy) biphenyl, 4,4'-bis (4-aminophenoxy) biphenyl, bis [4- (3-aminophenoxy) phenyl] ketone, Bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (3-aminophenoxy) phenyl] sulfide, bis [4- (4-aminophenoki) Si) phenyl] sulfide, bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] ether, bis [ 4- (4-Aminophenoxy) phenyl] ether, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 1, 3-Bis [4- (3-aminophenoxy) benzoyl] benzene, 1,3-bis [4- (4-aminophenoxy) benzoyl] benzene, 1,4-bis [4- (3-aminophenoxy) benzoyl] Benzene, 1,4-bis [4- (4-aminophenoxy) benzoyl] benzene, 1,3-bis [4- (3-aminophenoxy) -α, α-dimethylbenzyl] benzene, 1,3-bis [ 4- (4-Aminophenoxy) -α, α-dimethylbenzyl] benzene, 1,4-bis [4- (3-aminophenoxy) -α, α-dimethylbenzyl] benzene, 1,4-bis [4- (4-Aminophenoxy) -α, α-dimethylbenzyl] benzene, 4,4'-bis [4- (4-aminophenoxy) benzoyl] diphenyl ether, 4,4'-bis [4- (4-amino-α) , Α-dimethylbenzyl) phenoxy] benzophenone, 4,4'-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] diphenylsulfone, 4,4'-bis [4- (4-aminophenoxy) ) Phenoxy] diphenylsulfone, 3,3'-diamino-4,4'-diphenyloxybenzophenone, 3,3'-diamino-4,4'-dibiphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-biphenyloxybenzophenone, 6,6'-bis (3-aminophenoxy) -3,3,3', 3'-tetramethyl-1,1'-spirobiindane, 6,6' -Bis (4-aminophenoxy) -3,3,3', 3'-tetramethyl-1,1'-spirobiindan, 1,3-bis (3-aminopropyl) tetramethyldisiloxane, 1,3-bis (4-Aminobutyl) tetramethyldisiloxane, α, ω-bis (3-aminopropyl) polydimethylsiloxane, α, ω-bis (3-aminobutyl) polydimethylsiloxane, bis (aminomethyl) ether, bis ( 2-aminoethyl) ether, bis ( 3-Aminopropyl) ether, bis [(2-aminomethoxy) ethyl] ether, bis [2- (2-aminoethoxy) ethyl] ether, bis [2- (3-aminopropoxy) ethyl] ether, 1, 2 -Bis (aminomethoxy) ethane, 1,2-bis (2-aminoethoxy) ethane, 1,2-bis [2- (aminomethoxy) ethoxy] ethane, 1,2-bis [2- (2-aminoethoxy) ethane ) Ethane] ethane, ethylene glycol bis (3-aminopropyl) ether, diethylene glycol bis (3-aminopropyl) ether, triethylene glycol bis (3-aminopropyl) ether, ethylenediamine, 1,3-diaminopropane, 1,4 -Diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diamino Benzene, 1,12-diaminododecane, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, trans-1,4-diaminocyclohexane, 1,2-di (2-aminoethyl) Cyclohexane, 1,3-di (2-aminoethyl) cyclohexane, 1,4-di (2-aminoethyl) cyclohexane, bis (4-aminocyclohexyl) methane, 2,6-bis (aminomethyl) bicyclo [ 2.2.1] Heptane, 2,5-bis (aminomethyl) bicyclo [2.2.1] Heptane, 1,4-diamino-2-fluorobenzene, 1,4-diamino-2,3-difluorobenzene , 1,4-diamino-2,5-difluorobenzene, 1,4-diamino-2,6-difluorobenzene, 1,4-diamino-2,3,5-trifluorobenzene, 1,4-diamino-2 , 3,5,6-Tetrafluorobenzene, 1,4-diamino-2- (trifluoromethyl) benzene, 1,4-diamino-2,3-bis (trifluoromethyl) benzene, 1,4-diamino- 2,5-bis (trifluoromethyl) benzene, 1,4-diamino-2,6-bis (trifluoromethyl) benzene, 1,4-diamino-2,3,5-tris (trifluoromethyl) benzene, 1,4-Diamino-2,3,5,6-tetrakis (trifluoromethyl) benzene, 2-fluorobenzidine, 3-fluorobenzidine, 2,3-difluorobenze Zin, 2,5-difluorobenzidine, 2,6-difluorobenzidine, 2,3,5-trifluorobenzidine, 2,3,6-trifluorobenzidine, 2,3,5,6-tetrafluorobenzidine, 2, 2'-difluorobenzidine, 3,3'-difluorobenzidine, 2,3'-difluorobenzidine, 2,2', 3-trifluorobenzidine, 2,3,3'-trifluorobenzidine, 2,2', 5 -Trifluorobenzidine, 2,2', 6-trifluorobenzidine, 2,3', 5-trifluorobenzidine, 2,3', 6,-trifluorobenzidine, 2,2', 3,3'-tetra Fluorobenzidine, 2,2', 5,5'-tetrafluorobenzidine, 2,2', 6,6'-tetrafluorobenzidine, 2,2', 3,3', 6,6'-hexafluorobenzidine, 2,2', 3,3', 5,5', 6,6'-octafluorobenzidine, 2- (trifluoromethyl) benzidine, 3- (trifluoromethyl) benzidine, 2,3-bis (trifluoro) Methyl) benzidine, 2,5-bis (trifluoromethyl) benzidine, 2,6-bis (trifluoromethyl) benzidine, 2,3,5-tris (trifluoromethyl) benzidine, 2,3,6-tris ( Trifluoromethyl) benzidine, 2,3,5,6-tetrakis (trifluoromethyl) benzidine, 2,3'-bis (trifluoromethyl) benzidine, 2,2', 3-bis (trifluoromethyl) benzidine, 2,3,3'-tris (trifluoromethyl) benzidine, 2,2', 5-tris (trifluoromethyl) benzidine, 2,2', 6-tris (trifluoromethyl) benzidine, 2,3', 5-tris (trifluoromethyl) benzidine, 2,3', 6-tris (trifluoromethyl) benzidine, 2,2', 3,3'-tetrakis (trifluoromethyl) benzidine, 2,2', 5, Examples include, but are not limited to, 5'-tetrakis (trifluoromethyl) benzidine and 2,2', 6,6'-tetrakis (trifluoromethyl) benzidine.

The weight average molecular weight of the polyimide is preferably in the range of 20,000 to 500,000, more preferably in the range of 30,000 to 300,000, and more preferably in the range of 40,000 to 300,000, although it depends on the intended use. It is more preferably in the range of 200,000. When the weight average molecular weight is 20,000 or more, a film having sufficient strength can be obtained. On the other hand, when the weight average molecular weight is 500,000 or less, good solution processability can be maintained without significant deterioration in handling during coating due to an increase in solution viscosity, so that the surface is smooth and the film thickness is high. A uniform film can be obtained. In the present specification, the weight average molecular weight molecular weight means a value in terms of polyethylene glycol by gel permeation chromatography (GPC). When the polyimide is insoluble in the solvent used for GPC measurement, the molecular weight of polyamic acid, which is a precursor thereof, can be used instead of the molecular weight of the polyimide itself.

The intrinsic viscosity of the polyimide is preferably 0.3 to 10 dL / g, more preferably 0.5 to 10 dL / g. When the intrinsic viscosity is 0.3 dL / g or more, it has a sufficient molecular weight, so that a film having sufficient strength can be obtained. On the other hand, when the intrinsic viscosity is 10 dL / g or less, good solution processability can be maintained without significant deterioration in handling during coating due to an increase in solution viscosity, so that the surface is smooth and the film thickness is uniform. Film can be obtained. The intrinsic viscosity can be measured by the method described in Examples described later.

The method for producing the polyimide is not particularly limited, and can be obtained by using a known method. For example, the tetracarboxylic dianhydride represented by the formula (8) and the diamine represented by the formula (1) are stirred and polymerized in a solvent to obtain a polyamic acid as a precursor, which is further imidized. By doing so, the above-mentioned polyimide can be obtained.

Examples of the tetracarboxylic dianhydride represented by the formula (8) include the above-mentioned alicyclic tetracarboxylic dianhydride and / or aromatic tetracarboxylic dianhydride.

When the diamine represented by the formula (1) is used in combination with another diamine (that is, copolymerization), the content of the diamine represented by the formula (1) is when the total amount of the diamine is 100 mol%. The higher the content, the more preferable, in the order of 10 mol% or more, 50 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, 95 mol% or more, and 100 mol%.

The solvent at the time of polymerization may be any one as long as the polyamic acid and the polyimide can be uniformly dissolved, and is not limited as long as it does not inhibit the reaction. Examples of the solvent include amide-based solvents and cyclic ester-based solvents. Examples of the amide solvent include N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide and hexamethylphosphoramide. Examples of the cyclic ester solvent include γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone and α-methyl-γ-butyrolactone.

The imidization method is not particularly limited, and known methods (chemical imidization method and thermal imidization method) can be applied.

First, a method for producing polyimide by chemical imidization will be described. The polyimide precursor varnish obtained by polymerization or the polyimide precursor varnish appropriately diluted with the same solvent as the solvent used at the time of polymerization is composed of an organic acid anhydride and a tertiary amine as a catalyst under stirring. The chemical imidizing agent is added dropwise. Then, the imidization reaction can be easily completed by stirring the varnish at 0 to 100 ° C., preferably 20 to 50 ° C. for 0.5 to 48 hours.

The organic acid anhydride is not particularly limited, and examples thereof include acetic anhydride, propionic anhydride, maleic anhydride, and phthalic anhydride. Of these, acetic anhydride is preferably used from the viewpoint of cost and ease of post-treatment (removal). The tertiary amine is not particularly limited, and examples thereof include pyridine, triethylamine, N, N-dimethylaniline and the like. Of these, pyridine is preferably used from the viewpoint of safety.

The amount of the organic acid anhydride in the chemical imidizing agent to be added is not particularly limited, but is in the range of 1 to 10 times the molar amount of the theoretical dehydration of the polyimide precursor, and is 2 from the viewpoint of reaction completion, reaction rate and post-treatment. It is preferably in the range of ~ 5 times the molar amount. The amount of the tertiary amine used as a catalyst is not particularly limited, but is 0.1 to 1 times the molar amount of the organic acid anhydride from the viewpoint of reaction completion, reaction rate and post-treatment (easiness of removal). It is preferably in the range of.

The polyimide can also be obtained by imidization (thermal imidization) by a thermal method. Imidization by a thermal method may be carried out by heating a polyamic acid solution. Alternatively, a polyamic acid solution may be cast or applied to a support such as a glass plate, a metal plate or PET (polyethylene terephthalate), and then heat treatment may be performed in the range of 80 ° C. to 500 ° C. Further, the polyamic acid can be dehydrated and ring-closed by putting the polyamic acid solution directly into a container that has been subjected to a mold release treatment such as coating with a fluororesin and heating and drying under reduced pressure. A polyimide resin can be obtained by dehydrating and ring-closing the polyamic acid by such a thermal method. The heating time of each of the above treatments varies depending on the treatment amount and the heating temperature of the polyamic acid solution for dehydration and ring closure, but is generally performed in the range of 1 minute to 5 hours after the treatment temperature reaches the maximum temperature. Is preferable.

When the azeotropic method using an azeotropic solvent is used, water produced by dehydration ring closure by adding a solvent azeotropically with water such as toluene or xylene to the polyamic acid solution and raising the temperature to 170 to 200 ° C. It may be allowed to react for about 1 hour to 5 hours while actively removing the water from the system. After completion of the reaction, the reaction solution is added dropwise to a poor solvent such as alcohol to precipitate the polyimide, and if necessary, the polyimide is washed with alcohol or the like and then dried to obtain a polyimide resin.

The poor solvent used in the above-mentioned precipitation-precipitation operation is not particularly limited as long as it does not dissolve the polyimide. As the poor solvent, for example, water, methanol, ethanol, n-propanol or isopropanol or the like, or a mixed solvent thereof is preferable from the viewpoint of miscibility with the reaction solvent and the chemical imidizing agent and ease of removal by drying. Used.

When a polyimide solution containing polyimide, a chemical imidizing agent or an azeotropic agent is dropped into a poor solvent, the solid content concentration of the polyimide solution is not particularly limited as long as it has a viscous structure that allows stirring, but the particle size is reduced. It is preferable that the concentration is dilute from the viewpoint of However, if the concentration is too dilute, a large amount of poor solvent is used to precipitate the polyimide, which is not preferable. From these viewpoints, it is preferable to dilute the polyimide solution so that the solid content concentration is 15% by weight or less, preferably 10% by weight or less, and then add a poor solvent to the polyimide solution. The amount of the poor solvent to be used is preferably equal to or more than the amount of the polyimide solution, and more preferably 2 to 3 times the amount. Since the polyimide obtained here contains a small amount of a chemical imidizing agent and / or an azeotropic agent, it is preferable to wash it several times with the above-mentioned poor solvent.

The method for drying the polyimide thus obtained by the chemical imidization method or the thermal imidization method may be vacuum drying or hot air drying. Vacuum drying is desirable in order to completely dry the solvent contained in the resin. The drying temperature is preferably in the range of 80 to 200 ° C. from the viewpoint of preventing decomposition of the residual solvent and deterioration of the resin due to the residual solvent. The drying time is arbitrary as long as the solvent contained in the resin can be completely dried, but it is preferably 15 hours or less from the viewpoint of manufacturing process cost, and 8 hours from the viewpoint of sufficiently drying the residual solvent. The above is preferable.

<3. Varnish>
The varnish according to the embodiment of the present invention contains the polyimide according to the embodiment of the present invention in a solid content concentration of 5% by weight or more. When the solid content concentration is 5% by weight or more, the smoothness of the film obtained by coating the varnish can be ensured. The solid content concentration is preferably 5 to 40% by weight, more preferably 10 to 25% by weight.

The varnish can be obtained by uniformly dissolving the above-mentioned polyimide in an organic solvent. The organic solvent is not particularly limited, and examples thereof include amide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, dimethyl sulfoxide, symmetric glycol diethers, and ethers. Moreover, these organic solvents may be used in mixture.

Examples of the amide solvent include N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone and cyclohexanone. Examples of the ether solvent include tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane and the like. Examples of the ester solvent include methyl acetate, ethyl acetate, butyl acetate, γ-butyrolactone, α-acetolactone, β-propiolactone and δ-valerolactone. Symmetrical glycol diethers include methyl monoglime (1,2-dimethoxyethane), methyl diglime (bis (2-methoxyethyl) ether), and methyl triglime (1,2-bis (2-methoxyethoxy) ethane). ), Methyltetraglime (bis [2- (2-methoxyethoxyethyl)] ether), ethyl monoglime (1,2-diethoxyethane), ethyl diglime (bis (2-ethoxyethyl) ether) and butyl jig Examples thereof include lime (bis (2-butoxyethyl) ether). Examples of ethers include dipropylene glycol methyl ether, tripropylene glycol methyl ether, propylene glycol n-propyl ether, dipropylene glycol n-propyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, and tripylene glycol n-. Examples thereof include propyl ether, propylene glycol phenyl ether, dipropylene glycol dimethyl ether, 1,3-dioxolane, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether and ethylene glycol monoethyl ether.

It is preferable that at least one organic solvent is selected from these. Furthermore, it is particularly preferable that the polyimide is dissolved in all of the amide solvent, the ketone solvent and the ether solvent, because the solvent suitable for the substrate to be coated can be selected each time. Among these, as organic solvents, amide-based solvents and ketones are used from the viewpoint of preventing problems such as whitening, non-uniformity and solidification due to moisture absorption of the coating film during coating and drying. A mixed solvent with a system solvent or an ether solvent is preferable, and further, it is more preferable to use a ketone solvent or an ether solvent alone, or a mixed solvent thereof. Among them, particularly preferable amide-based solvents include dimethylformamide, dimethylacetamide and N-methylpyrrolidone. Particularly preferred ketone solvents include methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone and cyclohexanone. Particularly preferred ether solvents are methyl monoglime (1,2-dimethoxyethane), methyl diglime (bis (2-methoxyethyl) ether) and methyl triglime (1,2-bis (2-methoxyethoxy) ethane). And so on.

The viscosity of the varnish is selected at any time according to the coating thickness and the coating environment, but is preferably 0.1 to 50 Pa · s, and more preferably 0.5 to 30 Pa · s. When the viscosity of the varnish is 0.1 Pa · s or more, a sufficient viscosity can be secured, and as a result, a sufficient film thickness accuracy can be ensured. Further, if the viscosity of the varnish is 50 Pa · s or less, the film thickness accuracy can be ensured, and the occurrence of appearance defects such as gel defects due to the occurrence of a portion that dries immediately after coating can be more reliably prevented. can. The above viscosity is a kinematic viscosity at 23 ° C. measured using an E-type viscometer.

The varnish may further contain a photocurable component or a thermosetting component, a non-polymerizable binder resin other than polyimide, or other components.

Various organic or inorganic low molecular weight compounds or high molecular weight compounds may be blended in order to impart processing characteristics or various functionalities to the varnish. For example, dyes, surfactants, leveling agents, plasticizers, fine particles, sensitizers and the like can be used. The fine particles include organic fine particles such as polystyrene and polytetrafluoroethylene, and inorganic fine particles such as colloidal silica, carbon and layered silicate. They may be porous or hollow. Further, as a function of the low molecular weight or high molecular weight compound, a pigment or a filler can be mentioned. The form of the low molecular weight or high molecular weight compound may be a fiber.

<4. Film>
The film (polyimide film) according to the embodiment of the present invention is obtained by drying the varnish (polyimide varnish) according to the embodiment of the present invention. The film can be produced by applying a varnish on a substrate and drying the film. A film can also be obtained by applying a polyamic acid, which is a polyimide precursor, to a substrate and heating the obtained film to imidize and dry it. From the viewpoint of thermal expansion characteristics and dimensional stability of the obtained film, the method of applying the above-mentioned polyimide varnish and drying it is more preferable.

As the substrate to which the varnish is applied, a glass substrate; a metal substrate such as SUS or a metal belt; a plastic film such as polyethylene terephthalate, polycarbonate, polyacrylate, polyethylene naphthalate and triacetyl cellulose is used. It is not limited. In order to adapt to the current batch type device manufacturing process, it is preferable to use a glass substrate.

The drying temperature during film production can be selected according to the process, and is not particularly limited as long as it does not affect the characteristics.

Various inorganic thin films such as metal oxides and transparent electrodes may be formed on the surface of the film. The method for forming these inorganic thin films is not particularly limited, and examples thereof include a CVD method and a PVD method such as a sputtering method, a vacuum deposition method, and an ion plating method.

<5. Use of polyimide>
The polyimide according to one embodiment of the present invention exhibits extremely useful properties such as low linear thermal expansion coefficient and excellent solution processability and transparency, in addition to the original properties of polyimide such as heat resistance and insulation.

Therefore, the polyimide according to one embodiment of the present invention may be used in fields and products in which these characteristics are effective, for example, substrates, color filters, printed matter, optical materials, electronic devices, image display devices, and the like. It is preferable, and even more preferably, it is used as a substitute material for the portion where glass or a transparent material is currently used. This makes it possible to provide a substrate, an image display device, an optical material, and an electronic device, which are lightweight and flexible, which glass does not have, and have the characteristics of high definition.

The substrate is a plastic substrate for an image display device (for example, a flexible display substrate), a TFT substrate, a transparent conductive film substrate, or the like. The image display device is a flexible display, a liquid crystal display device, an organic EL, an electronic paper, a 3-D display, or the like. The optical material is an optical film or the like. Electronic devices include touch panels and solar cells. For example, the plastic substrate for an image display device according to an embodiment of the present invention may include a film according to an embodiment of the present invention, or is composed of a film according to an embodiment of the present invention. You may.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention.

The present invention can also be configured as follows.

<1> The following formula (1):

Diamine represented by (in the formula (1), the substituent R independently represents an alkyl group or an alkoxy group having 1 to 4 carbon atoms, n represents the number of substituents R, and is an integer of 1 to 4 be).

<2> The following formula (2):

The diamine according to <1> represented by.

<3> The following formula (3):

In a polyimide having a repeating unit represented by (3), the substituent R independently represents an alkyl group or an alkoxy group having 1 to 4 carbon atoms, and n represents the number of substituents R, 1 to 1. It is an integer of 4 and X ₁ represents at least one of a tetravalent aliphatic group and an aromatic group).

<4> The following formula (4):

The polyimide according to <3> having a repeating unit represented by (X ₁ represents at least one of a tetravalent aliphatic group and an aromatic group in the formula (4)).

<5> X ₁ is the following formula (5):

The polyimide according to <3> or <4>, which is a tetravalent aliphatic group represented by.

<6> X ₁ is the following formula (6):

The polyimide according to <3> or <4>, which is a tetravalent aromatic group represented by.

<7> A varnish containing the polyimide according to any one of <3> to <6> at a solid content concentration of 5% by weight or more.

<8> A film obtained by drying the varnish according to <7>.

<9> A plastic substrate for an image display device including the film according to <8>.

[Evaluation of physical properties]
Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The physical property values in the following examples were measured by the following methods.

<Infrared absorption (FT-IR) spectrum>
The infrared absorption spectrum of diamine was measured by the KBr method using a Fourier transform infrared spectrophotometer (FT-IR4100, manufactured by JASCO Corporation). The infrared absorption spectra of the polyimide precursor and the polyimide were separately prepared as a thin film having a thickness of about 4 to 5 μm and measured by a transmission method.

< ^{1 1} H-NMR spectrum>
^{The 1} H-NMR spectra of the diamine and the polyimide powder were measured using an NMR spectrophotometer (ECP400, manufactured by JEOL Ltd.) using deuterated dimethyl sulfoxide (DMSO-d _{6) as a solvent.}

<Differential scanning calorimetry (melting point and melting curve)>
The melting point and melting curve of the diamine were measured using a differential scanning calorimeter (DSC3100, manufactured by Netch Japan Co., Ltd.) in a nitrogen atmosphere at a heating rate of 5 ° C./min.

<Intrinsic viscosity (η _inh )>
The reduced viscosities of the polyimide precursor (PAA) and the polyimide (PI) were measured using an Ostwald viscometer at a solid content concentration of 0.5% by weight and 30 ° C. This value can be regarded as the intrinsic viscosity, and the higher this value, the higher the molecular weight.

<Glass transition temperature (T _g )>
_{The glass transition temperature (T g} ) of the polyimide film (about 20 μm thick) was determined by using a thermomechanical analyzer (TMA4000, manufactured by Netch Japan Co., Ltd.) with a frequency of 0.1 Hz and a heating rate of 5 ° C./min. Obtained from the peak temperature. The _{higher the T g} , the higher the physical heat resistance.

<Coefficient of linear thermal expansion (CTE)>
For the CTE of the polyimide film (about 20 μm thickness), a thermomechanical analyzer (TMA4000, manufactured by Netch Japan Co., Ltd.) was used, and the elongation of the test piece at a heating rate of 5 ° C./min per load of 0.5 g / film thickness of 1 μm was obtained. , As an average value in the range of 100 to 200 ° C. The closer the CTE value is to 0, the better the thermal dimensional stability.

<5% weight loss temperature (T _d ⁵ )>
The 5% weight loss temperature (T _d ⁵ _{) of the polyimide film (about 20 μm thickness) was set in nitrogen (N 2} ) and in air (air) using a thermogravimetric analyzer (TG-DTA2000) manufactured by Netch Japan Co., Ltd. In the heating process at a heating rate of 10 ° C./min, the weight of the polyimide film (20 μm thickness) was determined from the temperature when the initial weight was reduced by 5%. The _{higher the T d} ⁵ value, the higher the chemical heat resistance (thermal stability).

<Tension modulus, elongation at break, strength at break>
The mechanical properties of the polyimide film (thickness of about 20 μm) were evaluated using a tensile tester (Tensilon UTM-II) manufactured by A & D Co., Ltd. A test piece (30 mm length x 3 mm width x about 20 μm thickness) was prepared, and a tensile test (stretching speed: 8 mm / min) was performed. From the initial gradient of the stress-strain curve, the tensile elastic modulus (E) and the breaking point stress from breaking strength (σ _b), it was determined breaking elongation (epsilon _b) from elongation at break. The higher the elongation at break, the higher the toughness of the film. The elongation at break showed an average value (ave) and a maximum value (max).

<Transparency of polyimide film: light transmittance, cut-off wavelength, yellowness index, haze>
The transparency of the polyimide film was evaluated from the following optical characteristics. The light transmittance curve of the polyimide film (about 20 μm thickness) was measured in the wavelength range of 200 to 800 nm using an ultraviolet-visible spectrophotometer (V-530) manufactured by Nippon Kogaku Co., Ltd., and the light transmittance (T _{400) at a wavelength of 400 nm was measured.} ), And the wavelength (cut-off wavelength (λ _cut )) at which the light transmittance is practically zero was determined. Based on this spectrum, a color calculation program (JASCO Corporation) was used to determine the yellowness index (YI value) based on the ASTM E313 standard. Further, using a haze meter (NDH4000, manufactured by Nippon Denshoku Industries Co., Ltd.), the total light transmittance (T _tot ) and turbidity (haze) were determined based on JIS K7361-1 and JIS K7136 standards.

<Thickness direction birefringence (Δn _th)>
Using an Abbe refractometer 4T (manufactured by ATAGO) with a polarizing plate and an eyepiece, a NaD line (589.3 nm) was used as the light source, and a methylene iodide solution saturated with sulfur was used as the intermediate solution (n ^D = 1.72-1). Using the .80) and the test piece (n ^D = 1.72), the _in- plane refractive index n in and the out-of-plane refractive index n _{out of} the polyimide film were measured, and the birefringence Δn _th (= n) in the thickness direction was measured. _in −n _out ) was obtained.

<Solution processability>
Solution processability was evaluated based on solubility in solvents. The polyimide powder was added to a solvent having a weight of 99 times, and the mixture was stirred for 5 minutes using a test tube mixer to visually confirm the dissolved state. Here, when the polyimide powder was uniformly dissolved in the solvent, it was evaluated as "exhibiting excellent solubility".

[Abbreviation]
3-Methyl-4-nitrobenzoic acid = 3M4NB
3M4NB chlorinated body = 3M4NBC
N, N-dimethylformamide = DMF
Tetrahydrofuran = THF
2,2'-bis (trifluoromethyl) benzidine = TFMB
N, N-dimethylacetamide = DMAc
1,2,3,4-Cyclobutanetetracarboxylic dianhydride = CBDA
N-methyl-2-pyrrolidone = NMP
Dimethyl sulfoxide = DMSO
4,4'-(Hexafluoroisopropylidene) diphthalic anhydride = 6FDA
γ-Butyrolactone = GBL.

[Example 1]
<Synthesis of diamine>
The diamine (hereinafter referred to as M-ABMB) according to the embodiment of the present invention represented by the above formula (2) synthesizes a dinitro compound (hereinafter referred to as M-NBMB) which is a precursor of M-ABMB. Then, it was synthesized by reducing the nitro group. Specifically, the procedure was as follows.

First, M-NBMB was synthesized as follows. 10.86 g (60 mmol) of 3M4NB (manufactured by Tokyo Kasei) and 50 mL of thionyl chloride were placed in a three-necked flask. Three drops of DMF as a catalyst were further added to the flask, and the mixture was refluxed at 80 ° C. for 3 hours. Benzene was added to this solution, excess thionyl chloride was azeotropically distilled off under reduced pressure, and the mixture was further vacuum dried at room temperature for 12 hours to obtain yellow 3M4NBC (melting point 32 ° C.).

Next, in an eggplant flask, 5.15 g (27 mmol) of the above 3M4NBC was dissolved in dehydrated THF and sealed with a septum cap to prepare Liquid A. Next, in another eggplant flask, 3.20 g (10 mmol) of TFMB was dissolved in dehydrated THF (15 mL), 2.5 mL (31 mmol) of pyridine was further added as a dehydrochlorination agent, and the mixture was sealed with a septum cap to prepare solution B. While cooling the liquid B in an ice bath, the liquid A was slowly added to the liquid B with a syringe. The obtained mixture of solution A and solution B was further stirred at room temperature for 12 hours. Then, a large amount of water was poured into the obtained reaction solution to precipitate a blackish yellow precipitate. This was separated by filtration, washed with water, and vacuum dried at 120 ° C. for 12 hours to obtain a crude product. In order to remove the black residue, this crude product was dissolved in ethyl acetate and passed through a silica gel column to obtain an eluate. This eluate was concentrated with an evaporator to precipitate a precipitate. The precipitate was filtered off, washed with ethyl acetate and dried at 120 ° C. for 12 hours to give a pale yellow product in 76% yield (melting point: 236 ° C.). From the FT-IR and ¹ H-NMR spectra, it was confirmed that the obtained product was the target dinitro compound (M-NBMB).

Next, M-NBMB was reduced as follows. In a three-necked flask, 4.69 g (7.25 mmol) of M-NBMB was dissolved in 1,4-dioxane, Pd / C (0.475 g) was added as a catalyst, and reflux was performed at 80 ° C. for 10 hours in a hydrogen atmosphere. did. The completion of the reduction reaction was confirmed by thin layer chromatography. After completion of the reaction, the reaction mixture was hot-filtered to remove the catalyst, and the filtrate was added dropwise to a large amount of ion-exchanged water to precipitate a precipitate. The precipitate was separated by filtration and vacuum dried at 120 ° C. for 12 hours to obtain a white product with a reduction reaction yield of 85%.

The analysis results of this white product are as follows. FT-IR (KBr, cm ^-1 ): 3368/3226 (amine, NH), 3111/3050 (aromatic CH), 2959 (CH ₃ , CH), 1627/1525 (amide, C) = O), 1500 (1,4-phenylene), 1320/1255 (CF ₃ , CF). ^{1 1} H-NMR (400 MHz, DMSO-d ₆ , δ, ppm): 10.15 (s, 2H, NHCO), 8.52 (dd, 2H, J = 8.4, 2.0 Hz, central biphenyl group 5,5'-proton), 8.33 (sd, 2H, J = 2.1Hz, central biphenyl group 3,3'-proton), 7.68-7.64 (m, 4H, terminal anilino group) 3,3'-proton + 5,5'-proton), 7.32 (d, 2H, J = 8.5Hz, central biphenyl group 6,6'-proton), 6.68 (d, 2H, J = 8.5 Hz, 6,6'-proton of terminal anilino group), 5.62 (s, 4H, NH ₂ ), 2.14 (s, 6H, CH ₃ ). Elemental analysis (C ₃₀ H ₂₄ O ₂ N ₄ F ₆ , molecular weight 586.54): Estimated value C; 61.43%, H; 4.12%, N; 9.55%, Analytical value C; 61.35 %, H; 4.26%, N; 9.53%. From these analysis results, it was confirmed that this product was the diamine (M-ABMB) represented by the target formula (1).

[Example 2]
<Polyimide precursor polymerization, chemical imidization, film formation and film physical characteristics>
In the reaction vessel, 1.1731 g (2 mmol) of the diamine (M-ABMB) described in Example 1 was dissolved in dehydrated DMAc. 0.3922 g (2 mmol) of CBDA powder was added little by little to the obtained solution, and the mixture was sealed. The solid content concentration at the beginning of the reaction was 30% by weight. When stirring was continued at room temperature, the polymerization reaction proceeded, the viscosity of the solution increased, and it became difficult to sufficiently stir. Therefore, DMAc was gradually added to the reaction vessel, and after stirring for 72 hours, the solution was diluted until the solid content concentration reached 18% by weight. After stirring for 72 hours, a viscous and uniform polyimide precursor solution was obtained. The intrinsic viscosity of the obtained polyimide precursor was 1.75 dL / g.

The polyimide precursor solution was appropriately diluted with DMAc (in this case, diluted to 6.0% by weight). While stirring this diluted polyimide precursor solution, a mixed solution of acetic anhydride (20 mmol) and pyridine (volume ratio of acetic anhydride to pyridine: 7/3) was slowly added dropwise at room temperature as a chemical imidizing agent. After the dropping was completed, the mixture was further stirred in a closed container for 24 hours. This reaction solution was appropriately diluted with DMAc and then added dropwise to a large amount of water to precipitate a white precipitate. The white precipitate was filtered off, washed thoroughly with water and methanol, and vacuum dried at 100 ° C. for 12 hours. The obtained powder was dissolved in deuterated DMSO and ¹ H-NMR spectrum was measured. As a result, both the NHCO proton and COOH proton signals derived from the polyimide precursor were completely eliminated, confirming the completion of chemical imidization.

The obtained fibrous polyimide powder was redissolved in DMAc at a solid content concentration of 10% by weight to obtain a uniform solution. This was cast on a glass substrate and dried at 60 ° C. for 2 hours in a hot air dryer. Further, it was dried in vacuum at 200 ° C. for 1 hour and then at 300 ° C. for 1 hour. After that, the obtained film was peeled off from the substrate and heat-treated in vacuum at 330 ° C. for 1 hour to obtain a flexible and cloudy polyimide film. When the physical properties of this film were evaluated, it showed an extremely low CTE value (3.6 ppm / K) and high heat resistance (T _g = 325 ° C.). Other physical property values are shown in Table 1. The chemically imidized polyimide powder showed excellent solubility in NMP and DMAc at room temperature. Example 2 corresponds to an example in which 100 mol% of CBDA was used as the tetracarboxylic dianhydride.

[Example 3]
The polyimide precursor was polymerized in the same manner as in Example 2 except that 95 mol% of CBDA and 5 mol% of 6FDA were used as the tetracarboxylic dianhydride, and the polyimide was chemically imidized and cast film-formed. I got a film. FIG. 1 shows an infrared absorption spectrum of a polyimide thin film prepared separately. The infrared absorption spectrum was measured using a Fourier transform infrared spectrophotometer FT / IR-4100 type A (manufactured by JASCO Corporation). Table 1 shows the physical property values. This film (thickness of about 20 μm) shows a higher T ₄₀₀ value, a lower YI value, and a lower haze value than the film of Example 2, indicating that the transparency is improved. It is considered that this is a result of improving the solvent solubility by copolymerizing 6 FDA by 5 mol% and preventing the aggregation of the main chain in the solvent evaporation process during film formation. Moreover, in addition to a low CTE value (16.9 ppm / K), it _{showed high heat resistance (T g} = 348 ° C.). The chemically imidized polyimide powder shows excellent solubility in a mixed solvent of DMAc, DMAc / GBL (volume ratio 1/1) and a mixed solvent of DMAc / CPN (volume ratio 1/1), and has a solid content concentration of about about 1/1. It was possible to obtain 10% by weight varnish.

[Example 4]
The polyimide precursor was polymerized in the same manner as in Example 2 except that 70 mol% of CBDA and 30 mol% of 6FDA were used as the tetracarboxylic dianhydride, and the polyimide was chemically imidized and cast film-formed. I got a film. Table 1 shows the physical property values. This film had _{excellent transparency, as shown by the high T 400} value, low YI value and low haze value. Moreover, in addition to a low CTE value (17.9 ppm / K), it _{showed high heat resistance (T g} = 334 ° C.). The chemically imidized polyimide powder showed excellent solubility in NMP, DMAc and DMF at room temperature.

[Example 5]
The polyimide precursor was polymerized in the same manner as in Example 2 except that 50 mol% of CBDA and 50 mol% of 6FDA were used as the tetracarboxylic dianhydride, and the polyimide was chemically imidized and cast film-formed. I got a film. Table 1 shows the physical property values. This film had _{better transparency than a high T 400} value, a low YI value and a low haze value. Moreover, in addition to a relatively low CTE value (23.6 ppm / K), it _{showed high heat resistance (T g} = 349 ° C.). The chemically imidized polyimide powder showed excellent solubility in NMP, DMAc, DMF and DMSO at room temperature.

[Example 6]
A polyimide precursor was polymerized in the same manner as in Example 2 except that 6FDA was used as the tetracarboxylic dianhydride, and chemical imidization and cast film formation were performed to obtain a polyimide film. rice field. Table 1 shows the physical property values. This film had _{better transparency than a high T 400} value, a low YI value and a low haze value. In addition, the chemically imidized polyimide powder showed excellent solubility in NMP, DMAc, DMF, DMSO, GBL, triglime, cyclopentanone, acetone and THF at room temperature. A stable varnish was obtained at a solid content concentration of 15% by weight using GBL as a solvent. When the molecular weight was measured by gel permeation chromatography using THF as an elution solvent, it was found that the number average molecular weight (M _n ) = 2.3 × 10 ⁴ and the weight average molecular weight (M _w ) = 5.7 × 10 ⁴ .

[Comparative Example 1]
In order to investigate the effect of the methyl substituent on the diamine according to the embodiment of the present invention, a diamine without a methyl substituent (ABMB) was used and subjected to a double addition reaction with CBDA by the method described in Example 2 to carry out a polyimide precursor. I got a body. ABMB is represented by the following formula (9).

When the chemical imidizing agent was added dropwise to the solution of the polyimide precursor in the same manner as in Example 2, it was difficult to carry out chemical imidization because the reaction solution gelled. This is because the solvent solubility of the polyimide obtained from CBDA and ABMB is insufficient. This result is in contrast to the result of using the diamine according to the embodiment of the present invention (Example 2), and the presence of the methyl substituent in the diamine according to the embodiment of the present invention determines the solubility of the polyimide. It suggests that it contributes significantly.

[Comparative Example 2]
The polyimide precursor was polymerized in the same manner as in Example 2 except that TFMB was used instead of M-ABMB as the diamine. When a chemical imidizing agent was added dropwise to the solution in the same manner as in Example 2, it was difficult to carry out chemical imidization because the reaction solution gelled. This is because the solvent solubility of the polyimide obtained from CBDA and TFMB is insufficient.

The polyimide according to one embodiment of the present invention is suitably used as a film, for example, in a substrate, a color filter, a printed matter, an optical material, an electronic device, an image display device, or the like. Therefore, it can be widely used in these industrial fields.

Claims (9)

The following formula (1):

Diamine represented by (in the formula (1), the substituent R independently represents an alkyl group or an alkoxy group having 1 to 4 carbon atoms, n represents the number of substituents R, and is an integer of 1 to 4 be). The following formula (2):

The diamine according to claim 1. The following formula (3):

In a polyimide having a repeating unit represented by (3), the substituent R independently represents an alkyl group or an alkoxy group having 1 to 4 carbon atoms, and n represents the number of substituents R, 1 to 1. It is an integer of 4 and X ₁ represents at least one of a tetravalent aliphatic group and an aromatic group). The following formula (4):

The polyimide according to claim 3 having a repeating unit represented by (in formula (4), X ₁ represents at least one of a tetravalent aliphatic group and an aromatic group). X ₁ is the following formula (5):

The polyimide according to claim 3 or 4, wherein the polyimide is a tetravalent aliphatic group represented by. X ₁ is the following formula (6):

The polyimide according to claim 3 or 4, wherein the polyimide is a tetravalent aromatic group represented by. A varnish containing the polyimide according to any one of claims 3 to 6 at a solid content concentration of 5% by weight or more. A film obtained by drying the varnish according to claim 7. A plastic substrate for an image display device including the film according to claim 8.

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