JP2023164496A - Polyimide and polyimide film - Google Patents

Abstract

To provide: a polyimide that can form a film excellent in colorless transparency, heat resistance (physical heat resistance), dimensional stability, thermal stability (chemical heat resistance), mechanical properties and toughness; and a polyimide varnish and a polyimide film that contain the polyimide.SOLUTION: A polyimide has a repeating unit represented by the specified general formula (3), where the divalent organic group Ar is a constitutional unit represented by the specified formula (7).SELECTED DRAWING: None

Description

Application for application of Article 30, Paragraph 2 of the Patent Act (1) Proceedings of the 68th Annual Conference of the Society of Polymer Science and Technology published on May 14, 2019 (2) Published on May 29, 2019 Poster presented at the 68th Annual Meeting of the Society of Polymer Science and Technology

The present invention provides a highly transparent material suitable as a transparent heat-resistant plastic substrate material, that is, an alternative material to the current glass substrate in image display devices such as liquid crystal displays (LCDs), organic light emitting diode displays (OLEDs), and electronic paper (EP). The present invention relates to a polyimide having a high glass transition temperature, a low coefficient of linear thermal expansion, and sufficient film toughness, a heat-resistant film made of the polyimide, and a varnish for forming the polyimide film.

Currently, inorganic glass substrates (for example, alkali-free glass substrates, hereinafter simply referred to as "glass substrates") are used in image display devices such as LCDs, but by using plastic substrates instead of glass substrates, image display BACKGROUND ART Studies are actively being conducted to make devices lighter, thinner, and more flexible.

Polyether sulfone (hereinafter referred to as "PES") has excellent toughness, flame retardancy, and processability in addition to transparency, and has the highest physical heat resistance (i.e., glass transition temperature: T) among the current super engineering plastics. _g = 225°C), but even PES has limited physical heat resistance (also called short-term heat resistance) for various high-temperature processes such as transparent electrode and thin film transistor (TFT) formation in the image display device manufacturing process. In terms of perspective, it is not always sufficient.

In the image display device manufacturing process, there are multiple temperature cycles in which the above-mentioned high-temperature process and cooling to room temperature are repeated, and recently there has been a strong demand for plastic substrate materials to have excellent dimensional stability against temperature cycles. One of the most effective ways to improve dimensional stability is to improve the thermal expansion characteristics of the plastic substrate material in the film plane direction (XY direction), specifically the coefficient of linear thermal expansion in the XY direction below the glass transition temperature (in the glass region). (hereinafter referred to as "CTE") is to be lowered as much as possible. The lower the CTE, the more the reversible thermal expansion-contraction of the film following temperature cycling can be reduced. This can avoid serious problems such as cracks in the element layers, poor adhesion between layers, or misalignment of the elements.

Furthermore, if the reversible dimensional changes due to thermal expansion and contraction are large, there is a high possibility that irreversible dimensional changes will accumulate during repeated thermal expansion and contraction. From these viewpoints, it is preferable to lower the CTE of the transparent plastic substrate as much as possible.

However, most organic polymer films including PES have a high CTE value of 60 to 100 ppm/K, and the reality is that there is no transparent resin material that meets the above requirements for dimensional stability.

On the other hand, wholly aromatic polyimide is currently being used in the electronics field as the most reliable heat-resistant insulating resin material from the viewpoints of physical and chemical heat resistance, electrical insulation, mechanical properties, flame retardance, and ease of manufacturing process. It is widely used in the center. However, "KAPTON-H" (product name) manufactured by DuPont-Toray Co., Ltd., which is expressed by the following formula (14), and "UPILEX-S" (product name), manufactured by Ube Industries, Ltd., which is expressed by the following formula (15), Current fully aromatic polyimide films, represented by (for example, see Non-Patent Document 1), and is not suitable for this purpose.

Under these circumstances, colorless and transparent polyimides are being considered based on molecular designs that interfere with charge transfer interactions. Among wholly aromatic polyimides, the following formula (16):

The polyimide represented by is a limited case among wholly aromatic polyimides that can provide a colorless and transparent film (for example, see Non-Patent Document 2). The transparency of this polyimide film is due to the effect of trifluoromethyl groups (CF ₃ ), which act as electron-withdrawing groups and weaken the cohesive force between polymer chains. It also has solvent solubility, that is, solution processability. However, this polyimide film does not exhibit low thermal expansion characteristics (see, for example, Non-Patent Document 2).

Generally, in order for a polyimide film to exhibit a low CTE, the polyimide main chain needs to have a high degree of molecular orientation in the XY directions (referred to as "in-plane orientation"), and for this purpose, the linearity and rigidity of the polyimide main chain are required. has been reported to be essential (see, for example, Non-Patent Document 3). In the polyimide represented by formula (16), the polyimide main chain has a non-linear structure due to the bent structure at the trifluoroisopropylidene group site, and the in-plane orientation of the main chain has been hindered. This is a factor that does not exhibit expansion characteristics.

An effective method for making polyimide colorless and transparent is to use a non-aromatic, ie, aliphatic, monomer for either or both of the monomer component, tetracarboxylic dianhydride, and the other monomer component, diamine. be. From the viewpoint of heat resistance, cyclic rather than linear aliphatic monomers (referred to as "alicyclic diamines") are usually selected.

For example, the following formula (17):

A general-purpose alicyclic diamine represented by the following formula (18):

The following formula (19) obtained from a general-purpose aromatic tetracarboxylic dianhydride represented by pyromellitic dianhydride (hereinafter referred to as "PMDA"):

The polyimide represented by gives a colorless and transparent film. However, due to the fact that the basicity of aliphatic diamine is much higher than that of aromatic diamine, when performing an equimolar polyaddition reaction (hereinafter simply referred to as "polymerization reaction") using aliphatic diamine, , a salt is formed in the initial stage of the polymerization reaction (see, for example, Non-Patent Document 4). This salt has a crosslinked structure and is difficult to dissolve in an anhydrous polymerization solvent (usually an amide solvent), so the salt may precipitate and the polymerization reaction may not proceed at all. If the formed salt is even slightly soluble in the polymerization solvent, polymerization may proceed gradually by stirring at room temperature after precipitation, and it may take a very long time until the salt is completely dissolved to form a uniform varnish. A polymerization time of hours is required. Furthermore, the reproducibility of the polymerization reaction time required for homogenization and the reproducibility of the molecular weight of the polyimide precursor produced is low.

Further, the polyimide film represented by the above formula (19) does not exhibit low thermal expansion characteristics. This is because the bending of the main chain at the methylene bond site and the mixture of trans-cis isomers at the cyclohexyl group site reduce the linearity of the polyimide main chain and prevent in-plane orientation. .

The following formula (20) is the only alicyclic diamine that is advantageous for reducing thermal expansion of polyimide films:

Trans-1,4-cyclohexanediamine (hereinafter referred to as "t-CHDA") represented by Because it is extremely strong, the precipitated salt does not dissolve at all under any reaction conditions, and a polyimide precursor cannot be obtained (for example, see Non-Patent Document 4).

The above t-CHDA is expressed by the following formula (21):

Because it reacts with the aromatic tetracarboxylic dianhydride represented by 3,3',4,4'-biphenyltetracarboxylic dianhydride (hereinafter referred to as "s-BPDA"), the final homogeneous Although it is possible to obtain a polyimide precursor varnish with high viscosity in . The obtained polyimide precursor is coated on a substrate, dried, and then heated to 300°C or higher to cause a dehydration ring-closing reaction (imidization reaction), resulting in the following formula (22):

A polyimide represented by is obtained, and the film thereof is relatively transparent and exhibits low thermal expansion (see, for example, Non-Patent Document 5). However, this polyimide film does not have practical film toughness. Furthermore, this polyimide is completely insoluble in solvents and has poor solution processability.

On the other hand, in the case of a combination of an alicyclic tetracarboxylic dianhydride and an aromatic diamine, the above-mentioned salt formation does not occur, and a polyimide precursor varnish can be obtained by a normal method. By selecting monomers used in the polymerization reaction, namely alicyclic tetracarboxylic dianhydride and aromatic diamine, that have a linear, planar, and rigid structure, it is possible to obtain a transparent polyimide with low thermal expansion. It is. There are very limited available alicyclic tetracarboxylic dianhydrides that have a linear, planar, and rigid structure; for example, the following formula (23):

Only alicyclic tetracarboxylic dianhydride with a rigid structure represented by 1,2,3,4-cyclobutanetetracarboxylic dianhydride (hereinafter referred to as "CBDA") is known. In addition to this, for example, the following formula (24):

A high molecular weight polyimide precursor can be easily produced by a polymerization reaction with an aromatic diamine having a rigid and linear structure represented by 2,2'-bis(trifluoromethyl)benzidine (hereinafter referred to as "TFMB"). is obtained, which is cast into a film and thermally imidized to obtain the following formula (25):

The polyimide film represented by is transparent and uncolored and exhibits a low CTE (for example, see Non-Patent Document 5). However, although this polyimide film is a self-supporting film, it does not have sufficient flexibility, and polyimide itself does not have solution processability (see, for example, Non-Patent Document 6).

CBDA is produced by a photodimerization reaction of maleic anhydride using an ultraviolet irradiation device (see, for example, Non-Patent Document 7). For this reason, it is not possible to apply a large-scale production method using a large heated reaction vessel, and it is not easy to reduce costs.

On the other hand, the following formula (26):

(In formula (26), the central cyclohexane moiety has a boat-shaped structure.)
cis, cis, cis-1,2,4,5-cyclohexanetetracarboxylic dianhydride (hereinafter referred to as "H-PMDA" or "(1S,2R,4S,5R)-cyclohexanetetracarboxylic dianhydride") It is obtained by catalytic reduction of inexpensive PMDA and can be produced on a large scale, making it the lowest cost and most practical of the currently available alicyclic tetracarboxylic dianhydrides. .

When H-PMDA is polymerized at room temperature with an aromatic diamine containing an ether bond, which is a flexible linking group, to obtain a polyimide precursor, the degree of polymerization estimated from its intrinsic viscosity is not necessarily high, but it is transparent. It is known to provide a polyimide film having excellent toughness (see, for example, Non-Patent Document 8). For example, the following formulas (27) and (28):

Polyimide represented by is a typical example, but these polyimide films do not exhibit low thermal expansion characteristics because the in-plane orientation of the main chain is hindered due to the non-linear structure of the main chain.

On the other hand, when a diamine with a rigid and highly linear structure is used, such as TFMB represented by formula (24), in hopes of achieving low thermal expansion, in addition to the low degree of polymerization, the rigidity is disadvantageous to the entanglement of polymer chains. Due to the influence of the main chain structure, polyimide films become extremely fragile and difficult to form (for example, see Non-Patent Document 8).

If a diamine component that has an extremely rigid and highly linear structure that is advantageous for lowering CTE and has extremely high reactivity becomes available, it would be possible to combine it with H-PMDA to create a low-cost, practical, low-heat component. Expandable transparent polyimides may be obtained, but such diamines are not known.

In order to increase the polymerization reactivity between H-PMDA and diamine, it is often effective to carry out the polymerization reaction at a high temperature (sometimes referred to as "one-pot polymerization"). In this polymerization method, the imidization reaction proceeds simultaneously without stopping at the polyimide precursor, and polyimide is produced in the solution. If a stable polyimide varnish can be obtained by one-pot polymerization, a polyimide film can be produced by simply applying the varnish to a substrate and drying it (i.e., without a higher temperature thermal imidization reaction), thereby shortening the process. There are great benefits from this point of view.

However, when one-pot polymerization is performed using a rigid and linear diamine that is advantageous for lowering CTE, the resulting polyimide loses its solubility, and the reaction solution often becomes nonuniform, such as gelation or precipitation. It is no longer possible to produce a high-quality film through the steps of isolation, redissolution, and film formation of polyimide. Therefore, the diamine suitable for this purpose must have a rigid and linear structure in order to lower the CTE of the polyimide film as much as possible, and at the same time must not deteriorate the solubility of the produced polyimide in the polymerization solvent. Therefore, it is not easy to solve these problems with current technology.

Prog. Polym. Sci., 26, 259-335 (2001). Eur. Polym. J., 49, 3657-3672 (2013). Macromolecules, 29, 7897-7909 (1996). High Performance. Polym., 19, 175-193 (2007). High Performance. Polym., 15, 47-64 (2003). Polymer, 74, 1-15 (2015). J. Polym. Sci., Part A, 38, 108-116 (2000). J. Polym. Sci., Part A, 51, 575-592 (2013).

An object of the present invention is to provide a transparent heat-resistant resin material that can contribute to reducing the weight and improving the fragility of image display devices.
That is, the problem to be solved by the present invention is to form a film that is colorless and transparent, has excellent heat resistance (physical heat resistance), dimensional stability, thermal stability (chemical heat resistance), mechanical properties, and toughness. An object of the present invention is to provide a polyimide capable of producing polyimide, as well as a polyimide varnish and a polyimide film containing the polyimide.

As a result of intensive studies to achieve the above object, the present inventors discovered that H-PMDA represented by the above formula (26) and a novel diamine containing an alicyclic structure and an amide group or an imide group The resulting polyimide has excellent properties that make it suitable for use as a plastic substrate material for image display devices, including excellent solution processability, high transparency, very high glass transition temperature, relatively low coefficient of linear thermal expansion, and sufficient The present inventors have discovered that the film also has excellent film toughness, and have completed the present invention.

That is, the present invention is as shown below.
<1> Below formula (1):

Or the following formula (2):

Diamine represented by.
<2> General formula (3) below:

A polyimide having a repeating unit represented by the formula (3), in which the divalent organic group Ar is a structural unit represented by any one of the following formulas (4) to (7).




<3> A varnish obtained by dissolving the polyimide described in <2> above in an organic solvent.
<4> A heat-resistant film containing the polyimide according to <2> above.
<5> The heat-resistant film according to <4> above, which has a glass transition temperature of 320° C. or higher, a linear thermal expansion coefficient of 40 ppm/K or lower, and a light transmittance of 70% or higher at a wavelength of 400 nm.
<6> A plastic substrate for an image display device, comprising the heat-resistant film according to <4> or <5> above.

According to the present invention, it is possible to form a film that is excellent in colorless transparency, heat resistance (physical heat resistance), dimensional stability, thermal stability (chemical heat resistance), mechanical properties, and toughness.
The diamine of the present invention has unprecedentedly high polymerization reactivity with tetracarboxylic dianhydride and has a bulky substituent, so even when reacted with H-PMDA, the reaction solution does not gel. Polyimide having a sufficiently high molecular weight can be obtained while suppressing precipitation and precipitation. In addition, since the polyimide of the present invention is compatible with existing film-forming processes, high-quality polyimide can be easily produced, and the resulting polyimide film has excellent properties, such as high transparency and high glass transition temperature. , has a low coefficient of thermal expansion and sufficient flexibility, making it possible to apply the polyimide of the present invention as a plastic substrate material instead of the glass substrate used in current image display devices. It is possible to provide a material useful for making devices lighter and more flexible.

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

Or the following formula (2):

It is a diamine represented by Hereinafter, the diamine represented by formula (1) may be referred to as "AMB-mTOL", and the diamine represented by formula (2) may be referred to as "AB-MP-HPMDI".
An amidation reaction will be described below as an example of the method for producing a diamine of the present invention, but the present invention is not limited thereto.

(Production of diamine “AMB-mTOL” represented by formula (1))
Dissolve m-tolidine in a solvent, seal it with a septum cap, and use it as Solution A. Next, 3-methyl-4-nitrobenzoyl chloride (hereinafter referred to as "3M4NBC") is dissolved in the same solvent, an appropriate amount of base (deoxidizing agent) is added thereto, and the solution is sealed similarly to obtain Solution B. Solution A is cooled in an ice bath, and while stirring with a stirrer, solution B is slowly added dropwise to solution A using a syringe, allowed to react for several hours, and then stirred at room temperature for 12 hours. After the reaction, the precipitate precipitated was separated by filtration, washed with a small amount of reaction solvent, then washed with water to remove water-soluble hydrochloride as a by-product, and heated in a temperature range of 50 to 120°C for 5 to 50 minutes. The dinitro compound is obtained by vacuum drying for 12 hours. This can be purified by recrystallization from an appropriate solvent and then used in the next hydrogen reduction step, but the purification step is omitted because the dinitro compound of high purity can be obtained with just the washing and drying steps described above. It's okay.
The reduction reaction of the terminal nitro group of the obtained dinitro compound can be carried out as follows, for example. First, the dinitro compound is dissolved in a solvent, and an appropriate amount of palladium/carbon (Pd/C) catalyst is added thereto. This reaction solution is reacted at a temperature below the boiling point of the solvent used, that is, in a hydrogen atmosphere, for 2 to 24 hours while being heated to a constant temperature in the range of room temperature to 150°C. The end point of the reaction can be confirmed by thin layer chromatography by the complete disappearance of the dinitro compound and the appearance of only one new spot. After the reaction is complete, the catalyst residue is removed by filtration. The filtrate may be concentrated using an evaporator as appropriate. If a precipitate is deposited by concentration, it is filtered, washed well with a small amount of reaction solvent, then water and methanol, and finally dried under vacuum for 5 to 12 hours at a temperature below the melting point of the product, that is, in the temperature range of 50 to 120°C. In this way, a diamine represented by formula (1) can be obtained. This may be used as it is in the next polymerization step, or may be further purified by recrystallization from an appropriate solvent.

(Production of diamine “AB-MP-HPMDI” represented by formula (2))
In the production of the above AMB-mTOL, 4-nitrobenzoyl chloride (hereinafter referred to as "4-NBC") which does not contain a methyl substituent is used in place of 3M4NBC, and this and the 4-nitrobenzoyl chloride represented by the following formula (8) are used. A dinitro compound is obtained by amidation reaction with a diamine in the same manner as above, and then catalytic reduction is performed in the same manner as above to reduce the nitro group, which is represented by formula (2). diamine can be obtained.

The diamine represented by the above formula (8) can be synthesized as follows, for example. 2-Methoxy-4-nitroaniline (hereinafter referred to as "2MeO-4NA", X mmol) is dissolved in N,N-dimethylacetamide (DMAc). H-PMDA powder (0.5 mmol) is added to this solution, and the solution is refluxed at 150 to 180° C. for 1 to 12 hours in a nitrogen atmosphere. After the reaction, the reaction solution is concentrated using an evaporator or a precipitant (poor solvent) that is miscible with DMAc is added to precipitate the precipitate, and the precipitate is filtered and washed. Vacuum drying for ~12 hours yields the dinitro form. Although the dinitro compound can be purified by recrystallization and then used in the next hydrogen reduction step, the purification step may be omitted since the dinitro compound can be obtained with a sufficiently high purity by only the washing and drying steps described above. The nitro group of the dinitro compound can be reduced by the same method as above.

In the above amidation reaction, the amount (mol) of acid chloride (3M4NBC or 4-NBC) to be charged is twice the amount (mol) of the diamine (m-tolidine or the compound represented by formula (8)) ( (equivalent), but in some cases it may be increased 2 to 5 times in order to increase the yield.

Solvents that can be used in the amidation reaction are not particularly limited as long as they can dissolve the reaction raw materials, but include ether solvents such as tetrahydrofuran (THF), 1,4-dioxane, diglyme, and triglyme, and γ-butyrolactone. , ester solvents such as ethyl acetate, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, hexa Amide solvents such as methylphosphoramide, ketone solvents such as acetone, cyclopentanone, and cyclohexanone, sulfone solvents such as dimethyl sulfoxide and sulfolane, chlorine solvents such as dichloromethane, chloroform, and 1,2-dichloroethane, toluene , xylene, etc. Further, these solvents may be used alone or in combination of two or more. From the viewpoint of solubility of the reaction raw material and ease of removal, at least one selected from THF, DMF, and DMAc is preferably used.

The reaction temperature of the amidation reaction is preferably -10 to 50°C, more preferably 0 to 30°C. When the reaction temperature is 50° C. or lower, side reactions are unlikely to occur and there is no risk that the yield will decrease.

The amidation reaction is carried out at a solute concentration of preferably 5 to 50% by mass, more preferably 10 to 40% by mass, taking into account the control of side reactions and the step of filtering precipitation.

The deoxidizing agent used in the amidation reaction is not particularly limited, and organic tertiary amines such as pyridine, triethylamine, and N,N-dimethylaniline, and inorganic bases such as potassium carbonate and sodium hydroxide can be used. From the viewpoint of ease of removal of hydrochloride, pyridine is preferably used.

The precipitate generated by the amidation reaction contains not only the dinitro compound but also water-soluble pyridine hydrochloride when pyridine is used as a deoxidizing agent. Since the dinitro form is insoluble in water, the hydrochloride salt can be removed simply by thoroughly washing the precipitate with water. Completion of hydrochloride removal can be easily confirmed from the presence or absence of white precipitate of silver chloride using a 1% aqueous silver nitrate solution as a washing liquid.

A known method can be applied to the amidation reaction, and methods other than the reaction of a dicarboxylic acid dichloride and an amine in the presence of a base (acid acceptor) described above can be applied. For example, from trans-1,4-cyclohexanedicarboxylic acid (hereinafter referred to as "t-CHDCA") and 2MeO-4NA, N,N'-dicyclohexylcarbodiimide (hereinafter referred to as "DCC"), triphenyl phosphite/pyridine , diphenyl (2,3-dihydro-2-thioxo-3-benzoxazolyl) phosphonate/triethylamine, 1-hydroxybenzotriazole/DCC, 1-hydroxy-7-azabenzotriazole, N-hydroxysuccinimide/DCC, etc. It can also be carried out using a condensing agent.

The method for the reduction reaction of the nitro group to the amino group is not particularly limited, and any known method can be applied. In addition to the above-mentioned method using hydrogen and Pd/C, catalytic reduction methods using metal powders such as tin, zinc, iron, etc. in acidic hydrochloric acid, and methods using an ethanol solution of tin chloride dihydrate can also be applied. be. Solvents that can be used in the above catalytic reduction reaction carried out in a hydrogen atmosphere using Pd/C as a catalyst are not particularly limited as long as the dinitro form is dissolved, but N,N-dimethylformamide (DMF), N,N - Amide solvents such as dimethylacetamide (DMAc), N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, and hexamethylphosphoramide, alcohol solvents such as methanol, ethanol, and propanol, and tetrahydrofuran. , ether solvents such as 1,4-dioxane, diglyme, and triglyme, ester solvents such as γ-butyrolactone and ethyl acetate, toluene, and xylene. Further, these solvents may be used alone or in combination of two or more. DMF and DMAc are preferably used from the viewpoint of solubility of reaction raw materials and ease of removal. Further, it is preferable that the solvent has high solubility for the product diamine. If the solubility is extremely poor, a portion of the monoamine may precipitate at the stage, which may prevent the reduction reaction from proceeding completely.

<Polyimide>
The polyimide of the present invention has the following general formula (3):

It is a polyimide having a repeating unit represented by the formula (3), in which the divalent organic group Ar is a structural unit represented by any one of the following formulas (4) to (7). That is, the polyimide of the present invention has a structural unit derived from H-PMDA and has a structural unit represented by any one of the following formulas (4) to (7).

The polyimide of the present invention is obtained by a polymerization reaction between a tetracarboxylic dianhydride and a diamine.

(Tetracarboxylic dianhydride)
H-PMDA is used as the tetracarboxylic dianhydride.
During the above polymerization reaction, an alicyclic tetracarboxylic dianhydride other than H-PMDA is used as a copolymerization component together with H-PMDA within a range that does not impair the polymerization reactivity with the diamine and the required properties of the polyimide. I can do it.
The alicyclic tetracarboxylic dianhydride that can be used in this case is not particularly limited, but for example, (1S,2S,4R,5R)-cyclohexanetetracarboxylic dianhydride (hereinafter referred to as "H'-PMDA") (1R,2S,4S,5R)-cyclohexanetetracarboxylic dianhydride (hereinafter referred to as “H”-PMDA), bicyclo[2.2.2]oct-7-ene-2,3 , 5,6-tetracarboxylic dianhydride (hereinafter referred to as "BTA"), bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic dianhydride, bicyclo[2.2] .2] Heptanetetracarboxylic dianhydride, 5-(dioxotetrahydrofuryl-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 4-(2,5-dioxotetrahydrofuran-3-yl) )-tetralin-1,2-dicarboxylic anhydride, tetrahydrofuran-2,3,4,5-tetracarboxylic dianhydride, bicyclo-3,3',4,4'-tetracarboxylic dianhydride, 3c -Carboxymethylcyclopentane-1r,2c,4c-tricarboxylic acid 1,4:2,3-dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4- Examples include cyclopentanetetracarboxylic dianhydride, etc. These may be used alone, or two or more types may be used in combination.
When these alicyclic tetracarboxylic dianhydrides are used as copolymerization components, the amount used is preferably 1 to 70 mol% of the total amount of alicyclic tetracarboxylic dianhydrides including H-PMDA. , more preferably in the range of 10 to 50 mol%.

Further, an aromatic tetracarboxylic dianhydride can be used as a copolymerization component together with H-PMDA within a range that does not impair the polymerization reactivity with the diamine and the required properties of the polyimide.
The aromatic tetracarboxylic dianhydride that can be used in this case is not particularly limited, but includes, for example, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2, 3,3',4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride, 3,4'- Oxydiphthalic anhydride, 3,3'-oxydiphthalic anhydride, hydroquinone-diphthalic anhydride, 4,4'-biphenol-diphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic acid Examples include dianhydride, 4,4'-(hexafluoroisopropylidene) diphthalic anhydride, and the like. These may be used alone or in combination of two or more.
When these aromatic tetracarboxylic dianhydrides are used as a copolymerization component, the amount used is preferably 1 to 30 mol%, more preferably 1 to 30 mol% of the total amount of tetracarboxylic dianhydrides including H-PMDA. It is in the range of 1 to 20 mol%.

(diamine)
As the diamine, a compound that provides a structural unit represented by any one of the above formulas (4) to (7) is used.
The compound that provides the structural unit represented by the above formula (4) is AMB-mTOL (diamine represented by the above formula (1)).
The compound that provides the structural unit represented by the above formula (5) is AB-MP-HPMDI (diamine represented by the above formula (2)).
The compound giving the structural unit represented by the above formula (6) is the following formula (9):

It is a diamine represented by (hereinafter referred to as "AB-mTOL"). Although the method for producing AB-mTOL is not particularly limited, it can be obtained, for example, by the method of Synthesis Example 1 described below.
The compound providing the structural unit represented by the above formula (7) is represented by the following formula (10):

It is a diamine represented by (hereinafter referred to as "AB-44ODA"). The method for producing AB-44ODA is not particularly limited, but it can be obtained, for example, by the method of Synthesis Example 2 described below.

An aliphatic diamine together with a compound that provides a structural unit represented by any one of the above formulas (4) to (7) within a range that does not impair the polymerization reactivity with the tetracarboxylic dianhydride and the required properties of the polyimide. can be used as a copolymerization component.
The aliphatic diamine that can be used in this case is not particularly limited, but for example, 4,4'-methylenebis(cyclohexylamine), 4,4'-methylenebis(3-methylcyclohexylamine), 4,4'-methylenebis( 3-ethylcyclohexylamine), 4,4'-methylenebis(3,5-dimethylcyclohexylamine), 4,4'-methylenebis(3,5-diethylcyclohexylamine), isophoronediamine, trans-1,4-cyclohexanediamine , cis-1,4-cyclohexanediamine, 1,4-cyclohexanebis(methylamine), 2,5-bis(aminomethyl)bicyclo[2.2.1]heptane, 2,6-bis(aminomethyl)bicyclo [2.2.1] Heptane, 3,8-bis(aminomethyl)tricyclo[5.2.1.0]decane, 1,3-diaminoadamantane, 2,2-bis(4-aminocyclohexyl)propane, 2,2-bis(4-aminocyclohexyl)hexafluoropropane, 1,3-propanediamine, 1,4-tetramethylenediamine, 1,5-pentamethylenediamine, 1,6-hexamethylenediamine, 1,7- Heptamethylene diamine, 1,8-octamethylene diamine, 1,9-nonamethylene diamine), and the like. These may be used alone or in combination of two or more.
When using these aliphatic diamines as copolymerization components, the amount used is the total amount of diamines including the compound providing the structural unit represented by any one of the above formulas (4) to (7). The range is preferably 1 to 50 mol%, more preferably 5 to 30 mol%.

In addition, the above-mentioned compound can be used together with a compound that provides a structural unit represented by any one of the above formulas (4) to (7), within a range that does not impair the polymerization reactivity with the tetracarboxylic dianhydride and the required properties of the polyimide. Aromatic diamines other than the compound providing the structural unit represented by any one of formulas (4) to (7) can be used as a copolymerization component.
Aromatic diamines that can be used in this case are not particularly limited, but include, for example, p-phenylenediamine, m-phenylenediamine, 2,4-diaminotoluene, 2,5-diaminotoluene, 2,4-diaminoxylene, , 4-diaminodurene, 4,4'-methylene dianiline, 4,4'-methylenebis(3-methylaniline), 4,4'-methylenebis(3-ethylaniline), 4,4'-methylenebis(2- methylaniline), 4,4'-methylenebis(2-ethylaniline), 4,4'-methylenebis(3,5-dimethylaniline), 4,4'-methylenebis(3,5-diethylaniline), 4,4 '-Methylenebis(2,6-dimethylaniline), 4,4'-methylenebis(2,6-diethylaniline), 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether , 2,4'-diaminodiphenyl ether, 2,2'-diaminodiphenyl ether, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 4,4'-diaminobenzophenone, 3,3'-diaminobenzophenone , 4,4'-diaminobenzanilide, benzidine, 3,3'-dihydroxybenzidine, 3,3'-dimethoxybenzidine, o-tolidine, m-tolidine, 1,4-bis(4-aminophenoxy)benzene, 1 , 4-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 4,4'-bis(4-aminophenoxy) biphenyl, bis(4-(3-aminophenoxy)phenyl)sulfone, bis(4-(4-aminophenoxy)phenyl)sulfone, 2,2-bis(4-(4-aminophenoxy)phenyl)propane, p- Terphenylenediamine, 2,2'-bis(trifluoromethyl)benzidine, 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane, 2,2-bis(4-aminophenyl)hexafluoro Propane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 2,4'-diaminodiphenyl ether, 2,2'-diaminodiphenyl ether, 1,4-bis(4- aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 4,4'-bis (4-aminophenoxy)biphenyl, bis(4-(3-aminophenoxy)phenyl)sulfone, bis(4-(4-aminophenoxy)phenyl)sulfone, 2,2-bis(4-(4-aminophenoxy)) phenyl)propane, 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 2,2-bis(4- aminophenyl) hexafluoropropane, 4,4'-methylene dianiline, 4,4'-methylenebis(3-methylaniline), 4,4'-methylenebis(3-ethylaniline), 4,4'-methylenebis(2 -methylaniline), 4,4'-methylenebis(2-ethylaniline), 4,4'-methylenebis(3,5-dimethylaniline), 4,4'-methylenebis(3,5-diethylaniline), 4, Examples include 4'-methylenebis(2,6-dimethylaniline) and 4,4'-methylenebis(2,6-diethylaniline). These may be used alone or in combination of two or more.
When these aromatic diamines are used as a copolymerization component, the amount used is preferably in the range of 1 to 50 mol%, more preferably 5 to 30 mol%, based on the total amount of diamines.

There is no particular restriction on the method of reacting the tetracarboxylic dianhydride and the diamine, and any known method can be used.
For example, in a reaction vessel equipped with a nitrogen inlet tube, a stirring device, a Dean-Stark trap, and a condenser, a diamine, an azeotropic agent, and an imidization catalyst are dissolved in a polymerization solvent at room temperature, and while stirring, a tetracarboxylic dianhydride is dissolved. A polyimide varnish is obtained by adding the powder and refluxing at 150 to 250°C for 0.5 to 12 hours. From the viewpoint of suppressing coloring of the varnish, the polymerization reaction is preferably carried out in an atmosphere of an inert gas such as nitrogen, but the introduction of an inert gas can also be omitted.

During the above polymerization reaction, the charging ratio (mole ratio) of diamine and tetracarboxylic dianhydride can be 0.8 to 1.1, but preferably 0.9 to 1 of the total amount of diamine. -1.1, more preferably 0.95-1.05. From the viewpoint of obtaining as high a molecular weight as possible, the monomers are charged in substantially equimolar amounts.

The initial monomer (solute) concentration during the above polymerization reaction is preferably 5 to 60% by mass, more preferably 10 to 50% by mass. If polymerization is started at a monomer concentration within this range, the molecular weight of the polyimide can be sufficiently increased, and the solubility of the monomer and the polyimide to be produced can be sufficiently ensured. Non-uniformity can be suppressed. Note that if the molecular weight of the polyimide increases too much and the reaction solution becomes difficult to stir, it can be diluted with an appropriate amount of the same solvent.

The solvent used when polymerizing polyimide is not particularly limited as long as it can sufficiently dissolve the raw material monomer and the polyimide to be produced and has a boiling point of 150° C. or higher from the viewpoint of completing the imidization reaction. For example, amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, hexamethylphosphoramide, and γ-butyrolactone. , cyclic ester solvents such as γ-valerolactone, δ-valerolactone, and γ-caprolactone, sulfonic solvents such as dimethyl sulfoxide and sulfolane, ether solvents such as diglyme and triglyme, m-cresol, p-cresol, and 3-chloro. Phenol solvents such as phenol and 4-chlorophenol, and ketone solvents such as cyclopentanone and cyclohexanone can be used. These solvents may be used alone or in combination of two or more. From the viewpoint of solubility and boiling point of the reaction raw materials, N,N-dimethylacetamide, N-methyl-2-pyrrolidone and γ-butyrolactone are preferably used.
It is preferable that the solvent used has low hygroscopicity in some cases. By using a low hygroscopic solvent, the risk of partial precipitation of polyimide due to moisture absorption during coating and whitening of the coating film is reduced, and costs are reduced by eliminating the need for humidity control during coating. It is also advantageous. From this point of view, γ-butyrolactone, cyclopentanone, cyclohexanone, diglyme, triglyme, etc. are suitable as the solvent to be used.

Examples of the entraining agent used to remove water generated during the imidization reaction include toluene, xylene, benzene, cumene, cyclohexane, ethyl acetate, and pyridine. Toluene and xylene are preferably used from the viewpoint of boiling point and ease of removal.

In the above polymerization reaction, an imidization catalyst can be used as appropriate. Examples of organic bases that can be used include 1-ethylpiperidine, pyridine, bipyridine, picoline, pyrimidine, pyrazine, pyridazine, triazine, quinoline, quinoxaline, acridine, phenazine, benzimidazole, benzoxazole, and isomers and derivatives thereof. Other examples include organic acids such as benzoic acid and its analogs. These basic catalysts and acidic catalysts may be used alone or in combination. The amount of these catalysts added is not particularly limited, but is preferably in a molar ratio of 0.1 to 10 times the theoretical dehydration amount of 1. However, since the above-mentioned imidization catalyst may color the polyimide varnish and deteriorate the transparency of the polyimide film as a result, it is preferable to use it while paying attention to coloring.

The completion of the imidization reaction of the polyimide obtained by the polymerization reaction is determined by dissolving the polyimide isolated as a powder in a deuterated solvent and measuring the ¹ H-NMR spectrum. This can be confirmed by the complete disappearance of protons. In addition, by preparing a polyimide thin film with a thickness of 4 to 5 μm or by measuring the FT-IR spectrum using the KBr method using polyimide powder, for example, the complete disappearance of the amide C=O stretching vibration band derived from the polyimide precursor and the imide Completion of imidization can also be confirmed from the appearance of characteristic absorption bands.

(Physical properties of polyimide)
The intrinsic viscosity of the polyimide of the present invention is preferably in the range of 0.2 to 5 dL/g, more preferably in the range of 0.5 to 2 dL/g. If the intrinsic viscosity is 0.2 dL/g or more, the molecular weight of the polyimide is sufficiently high, so that the entanglement of the polymer chains is sufficient, and it is possible to suppress the occurrence of cracks and the like during film formation. On the other hand, if the intrinsic viscosity is 5 dL/g or less, the varnish has an appropriate viscosity, does not require a long time for defoaming, and has good handling during coating.

By using the polyimide of the present invention, it is possible to form a film that is colorless and transparent, has excellent heat resistance (physical heat resistance), dimensional stability, thermal stability (chemical heat resistance), mechanical properties, and toughness. The preferred physical properties of the film are as follows.

The light transmittance (T ₄₀₀ ) at a wavelength of 400 nm is preferably 70% or more, more preferably 75% or more, and even more preferably 80% or more when the film has a thickness of about 20 μm. Within this range, transparency is excellent.
The total light transmittance (T _tot ) is preferably 85% or more, more preferably 86% or more, still more preferably 87% or more when the film has a thickness of about 20 μm. Within this range, transparency is excellent.
The yellowness index (YI) is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less when the film has a thickness of about 20 μm. Within this range, colorless transparency is excellent.
The haze is preferably 2.0 or less, more preferably 1.8 or less, even more preferably 1.5 or less when the film is about 20 μm thick. Within this range, transparency is excellent.

The glass transition temperature (Tg) is preferably 320°C or higher, more preferably 340°C or higher, even more preferably 360°C or higher. Within this range, the polyimide substrate has heat resistance (physical heat resistance) suitable for manufacturing image display devices such as liquid crystal displays and OLED displays.

The coefficient of linear thermal expansion (CTE) is preferably 40 ppm/K or less, more preferably 35 ppm/K or less, even more preferably 30 ppm/K or less when the film has a thickness of about 20 μm. Within this range, dimensional stability is excellent.

The 5% mass loss temperature (T _d ⁵ ) is the temperature at which the mass of a polyimide film (20 μm thick) decreases by 5% of its initial mass during a temperature increase process in nitrogen at a temperature increase rate of 10 °C/min. The temperature is preferably 400°C or higher, more preferably 420°C or higher, even more preferably 440°C or higher. Further, in the temperature raising process at a heating rate of 10°C/min in air, the temperature at which the mass of the polyimide film (20 μm thick) decreases by 5% of the initial mass is preferably 400°C or higher, more preferably 410°C or higher. ℃ or higher, more preferably 420℃ or higher. Within this range, thermal stability (chemical heat resistance) is excellent.

The tensile modulus (E) is preferably 2.7 GPa or more, more preferably 3.0 GPa or more, even more preferably 3.2 GPa or more.
The breaking strength (σ _b ) is preferably 0.08 GPa or more, more preferably 0.10 GPa or more, still more preferably 0.12 GPa or more.
The elongation at break (ε _b ) has an average value (av) of preferably 5% or more, more preferably 7% or more, even more preferably 10% or more, and a maximum value (max) of preferably 10% or more. More preferably, it is 12% or more, and still more preferably 15% or more.
Within these ranges, the film has excellent mechanical properties, particularly excellent toughness.

Pencil hardness is preferably 4H or higher, more preferably 5H or higher. Within this range, the hardness is excellent.

In addition, the above-mentioned physical property values in the present invention can be specifically measured by the method described in the Examples.

<Polyimide varnish>
Since the polyimide of the present invention has sufficiently high solvent solubility, it can be made into a varnish with a high solid content that is stable at room temperature. The polyimide varnish of the present invention is obtained by dissolving the polyimide of the present invention in an organic solvent. That is, the polyimide varnish of the present invention contains the polyimide of the present invention and an organic solvent, and the polyimide is dissolved in the organic solvent. The organic solvent is not particularly limited as long as it dissolves the polyimide, but it is preferable to use the above-mentioned compounds alone or in a mixture of two or more types as a reaction solvent used in the production of polyimide.
The polyimide varnish of the present invention may be a polyimide solution itself in which polyimide obtained by a polymerization method is dissolved in a reaction solvent, or may be a polyimide solution to which a diluting solvent is further added.

The method for producing polyimide varnish is not particularly limited, and known methods can be applied.
The polyimide varnish obtained in one step as described above can be used as it is, or it can be suitably diluted with the same solvent and then slowly dropped into a large amount of poor solvent to precipitate, filtered, washed and dried to form a polyimide varnish. Can be isolated as a powder. The poor solvent that can be used in this case is not particularly limited as long as it is a solvent that mixes well with the polymerization solvent and does not dissolve the polyimide, but water, methanol, ethanol, propanol, etc. are used, for example. Two or more of these may be used in combination. The obtained polyimide powder may be redissolved in a solvent at a solid content concentration of 5 to 40% by mass to form a polyimide varnish. As the solvent that can be used in this case, the same solvent as the above-mentioned solvent that can be used in the polymerization reaction of polyimide can be used. When redissolving the polyimide powder in a solvent, it may be heated at 40 to 200°C for 1 minute to 24 hours as long as the varnish does not become noticeably colored.

An inorganic filler, an adhesion promoter, a release agent, a flame retardant, an ultraviolet stabilizer, a surfactant, a leveling agent, and an antifoaming agent are added to the polyimide varnish obtained as described above to the extent that the required properties of the polyimide film are not impaired. , a fluorescent brightener, a crosslinking agent, a polymerization initiator, a photosensitizer, and other various additives may be added.

<Heat-resistant film>
The heat-resistant film of the present invention contains the polyimide of the present invention. Therefore, the polyimide film of the present invention has excellent colorless transparency, heat resistance (physical heat resistance), dimensional stability, thermal stability (chemical heat resistance), mechanical properties, and toughness. The preferred physical properties of the film of the present invention are as described above.
There are no particular limitations on the method for producing the polyimide film of the present invention, and known methods can be used. For example, the heat-resistant film of the present invention can be obtained by applying the polyimide varnish obtained by the above method onto a substrate and drying it. Further, heat treatment may be performed at a higher temperature if necessary.
Specifically, a polyimide varnish is applied onto a substrate made of glass, copper, aluminum, stainless steel, silicon, etc., and the temperature is preferably 40 to 220°C, more preferably 60 to 200°C, and preferably 10 minutes to 4 hours. More preferably, drying is performed for 0.5 to 2 hours. Subsequently, the temperature is further increased, and heat treatment is performed preferably at 200 to 350°C, more preferably 250 to 330°C, preferably for 10 minutes to 2 hours, more preferably 0.5 to 1 hour, to obtain a polyimide film. From the viewpoint of suppressing coloration of the polyimide film, the heat treatment temperature is preferably 350° C. or lower, and it is further preferable to perform the heat treatment in vacuum or in an inert gas such as nitrogen. In addition, from the viewpoint of smoothness and low thermal expansion characteristics of the polyimide film surface, it is preferable that the drying and heat treatment steps are performed in as many stages as possible so that the temperature is gradually increased, and furthermore, the drying and heat treatment steps at temperatures exceeding 200°C are It is preferable to carry out in vacuum or in an inert gas such as nitrogen.

The polyimide film of the present invention is suitably used as a film for various members such as color filters, flexible displays, semiconductor parts, and optical members. The polyimide film of the present invention is particularly suitably used as a substrate for image display devices such as liquid crystal displays and OLED displays.

The thickness of the polyimide film of the present invention is not particularly limited, and can be adjusted as appropriate depending on the intended use. When used as a plastic substrate material to replace glass substrates in image display devices such as LCDs, OLEDs, and EPs, the film thickness is preferably in the range of 20 to 100 μm, and when used as a flexible circuit board, it is preferably 30 to 200 μm. range.

[Evaluation of physical properties]
EXAMPLES Hereinafter, the present invention will be explained in detail with reference to examples, but it is not limited to these examples. In addition, the physical property values in the following examples were measured by the following method.

<Infrared absorption (FT-IR) spectrum>
The infrared absorption spectrum of the diamine was measured by the KBr plate method using a Fourier transform infrared spectrophotometer "FT/IR-4100" (manufactured by JASCO Corporation).

< ^1H -NMR spectrum>
^{The 1} H-NMR spectrum of the diamine was 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 temperature increase rate of 5° C./min.

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

<Transparency: light transmittance, cutoff wavelength, yellowness, haze>
The transparency of the polyimide film was evaluated from the following optical properties. The light transmittance curve of a polyimide film (about 20 μm thick) was measured in the wavelength range of 200 to 800 nm using an ultraviolet-visible spectrophotometer "V-530" (manufactured by JASCO Corporation), and the light transmittance at a wavelength of 400 nm was determined. (T ₄₀₀ ) and the wavelength at which the light transmittance becomes virtually zero (cutoff wavelength, λ _cut ) were determined. Further, based on this spectrum, the yellowness index (YI) was determined using a color calculation program (manufactured by JASCO Corporation) based on the ASTM E313 standard. Furthermore, total light transmittance (T _tot ) and turbidity (haze) were determined using a haze meter "NDH4000" (manufactured by Nippon Denshoku Kogyo Co., Ltd.) based on JIS K7361-1 and JIS K7136 standards.

<Glass transition temperature (T _g )>
The glass transition temperature (T _g ) of a polyimide film (approximately 20 μm thick) was measured using a thermomechanical analyzer "TMA4000" (manufactured by Netch Japan Co., Ltd.), and the loss energy was measured at a frequency of 0.1 Hz and a heating rate of 5 °C/min. was determined from the peak temperature of the curve. The higher the T _g , the higher the physical heat resistance.

<Coefficient of linear thermal expansion (CTE)>
The CTE of a polyimide film (approximately 20 μm thick) was measured using a thermomechanical analyzer “TMA4000” (manufactured by Netch Japan Co., Ltd.) at a temperature increase rate of 5°C/min under a load of 0.5 g/film thickness of 1 μm. The elongation was determined as an average value in the range of 100 to 200°C. The closer the CTE value is to 0, the better the dimensional stability is.

<Tensile modulus, elongation at break, strength at break>
The mechanical properties of the polyimide film (about 20 μm thick) were evaluated using a tensile tester "Tensilon UTM-2" (manufactured by A&D Co., Ltd.). A test piece (30 mm length x 3 mm width x approximately 20 μm thickness) was prepared, and a tensile test (stretching speed: 8 mm/min) was performed to determine the tensile modulus (E) and fracture from the initial initial slope of the stress-strain curve. Breaking strength (σ _b ) was determined from the point stress, and elongation at break (ε _b ) was determined from the elongation rate at the time of judgment. The higher the elongation at break, the higher the toughness of the film.

<5% mass reduction temperature (T _d ⁵ )>
The 5% mass loss temperature (T _d ⁵ ) of a polyimide film (approximately 20 μm thick) was determined using a thermogravimetric analyzer "TG-DTA2000" (manufactured by Netch Japan Co., Ltd.) in nitrogen and air, and the temperature increase rate. It was determined from the temperature at which the mass of the polyimide film (20 μm thick) decreased by 5% of its initial mass during a temperature raising process at 10° C./min. The higher the T _d ⁵ value, the higher the chemical heat resistance (thermal stability).

<Pencil hardness>
The surface hardness of the polyimide film was measured using a pencil hardness tester "BEVS 1301/750" (manufactured by BEVS, pencil tip load: 750 g) for a polyimide film formed on a glass substrate according to the ASTM D3363 standard. A pencil scratch test (Mitsubishi Pencil Uni, pencil hardness range: 6B to 6H) was conducted, and evaluation was made based on the presence or absence of scratches on the film surface.

[Synthesis of diamine]
The method for producing diamine of the present invention will be specifically shown below, but the method is not limited to these Examples.

Example 1
<Synthesis of AMB-mTOL>
The diamine (AMB-mTOL) of the present invention represented by the above formula (1) was synthesized as follows.
First, in a reaction vessel, m-tolidine (25 mmol) was dissolved in well-dehydrated DMAc (20 mL), 6.0 mL of pyridine was added as a deoxidizing agent, and the mixture was sealed with a septum cap to obtain Solution A. Next, in a separate container, 3-methyl-4-nitrobenzoyl chloride (3M4NBC, 60 mmol) was dissolved in dehydrated DMAc (10 mL) and sealed in the same manner as Solution B. While cooling and stirring Solution B in an ice bath, Solution A was gradually added dropwise with a syringe, and after stirring for several hours, stirring was continued for an additional 24 hours at room temperature. The precipitated yellow precipitate was separated by filtration, washed with toluene to remove excess 3M4NBC, then thoroughly washed with water to remove the by-product pyridine hydrochloride, and vacuum-dried at 120°C for 12 hours. A yellow powder was obtained with a yield of 85%. The analysis results of this product are shown below.
Melting point (DSC): 251°C.
FT-IR spectrum (KBr plate method, cm ^-1 ): 3274 (amide group, N-H stretching vibration), 3103/3033 (aromatic C-H stretching vibration), 2984/2929/2857 (aliphatic C-H Stretching vibration), 1651/1588 (amide group, C═O stretching vibration), 1523/1343 (nitro group, N—O stretching vibration).
¹ H-NMR spectrum (400 MHz, DMSO-d ₆ , δ, ppm): 10.48 [s, 2H (actually measured integrated intensity: 2.00) NHCO], 8.13 [d, 2H (1.98H), J = 8.4Hz, 6,6'-proton of terminal nitrobenzene (NB)), 8.06 [sd, 2H (2.00H), J = 1.4Hz, 3,3'-proton of NB], 7 .99 [dd, 2H (1.95H), J = 8.4, 1.6Hz, 5,5'-proton of NB], 7.73 [sd, 2H (2.05H), J = 1.8Hz , 3,3'-proton of central biphenyl (BP)], 7.68 [dd, 2H (2.02H), J=8.3, 2.0Hz, 5,5'-proton of BP], 7. 09 [d, 2H (2.06H), J = 8.2Hz, 6,6'-proton of BP], 2.61 [s, 6H (5.97H), 2,2'-CH ₃ of NB] . 2.05 [s, 6H (6.01H), 2,2'-CH ₃ of BP].

From the above analysis results, this product has the desired formula (11):

It was identified as a dinitro form represented by

The above dinitro compound was reduced as follows. First, this dinitro compound (11.283 g) was dissolved in DMAc (30 mL), Pd/C (1.204 g) was added as a catalyst, and the mixture was refluxed at 80°C for 6 hours in a hydrogen atmosphere. The completion of the reduction reaction was determined by thin layer chromatography. After cooling the reaction solution to room temperature, the Pd/C residue was separated and removed by filtration.The filtrate was dropped into a large amount of saturated brine to precipitate, and the precipitate was filtered to remove water and a small amount. The product was washed with methanol and vacuum dried at 120° C. for 12 hours to obtain a white powder with a yield of 87%.The analysis results of this product are shown below.
Melting point (DSC): 210°C.
FT-IR spectrum (KBr plate method, cm ^-1 ): 3442 (amino group, N-H stretching vibration), 3350/3291 (amino group + amide group, N-H stretching vibration), 3026 (aromatic C-H stretching vibration), 2917/2859 (aliphatic C-H stretching vibration), 1625/1578 (amide group, C=O stretching vibration), 1500 (1,4-phenylene group).
¹ H-NMR spectrum (400 MHz, DMSO-d ₆ , δ, ppm): 9.76 [s, 2H (2.00H), NHCO], 7.70-7.62 [m, 8H (8.07H) , 3,3',5,5'-proton of terminal aniline (AN) + 3,3',5,5'-proton of central BP], 7.01 [d, 2H (1.99H), J= 8.3Hz, 6,6'-proton of BP], 6.66[d, 2H (1.98H), J = 8.3Hz, 6,6'-proton of AN], 5.53[s, 4H (3.99H), NH ₂ ], 2.13[s, 6H (6.07H), 2,2'-CH ₃ of BP]. 2.02 [s, 6H (5.89H), 2,2'-CH ₃ of AN].
Elemental analysis (molecular weight 478.59): Estimated value (%) C; 75.29, H; 6.32, N; 11.71, analytical value C; 74.67, H; 6.46, N; 11. 55.

From the above analysis results, this product was identified as the desired diamine (AMB-mTOL) of the present invention represented by the above formula (1).

Example 2
<Synthesis of AB-MP-HPMDI>
The diamine (AB-MP-HPMDI) of the present invention represented by the above formula (2) was synthesized as follows.
First, as a starting material, the following formula (12):

The dinitro compound represented by was synthesized as follows. In a three-necked flask, 11.271 g (67 mmol) of 2-methoxy-4-nitroaniline (2MeO-4NA) was dissolved in DMAc (30 mL), 6.763 g (30 mmol) of H-PMDA powder was added to this solution, and the mixture was placed in a nitrogen atmosphere. The mixture was refluxed at 180° C. for 5 hours. After the reaction, the reaction solution was cooled to room temperature and concentrated using an evaporator, and then ethanol (200 mL) was added to precipitate. The precipitate was filtered, washed with ethanol, and then vacuum dried at 120° C. for 12 hours to obtain a pale yellow powder with a yield of 53%.
FT-IR spectrum (KBr plate method, cm ^-1 ): 3088/3006 (aromatic C-H stretching vibration), 2953/2879 (aliphatic C-H stretching vibration), 1777/1718 (imide group, C=O Stretching vibration), 1527/1350 (nitro group, N-O stretching vibration), 1390 (imide group, N-Ar stretching vibration), 1255/1194 (ether group, C-O stretching vibration).

The above dinitro compound was reduced in the same manner as described in Example 1 in DMAc in the presence of Pd/C under reflux at 80° C. for 3.5 hours in a hydrogen atmosphere. Completion of the reduction reaction was confirmed by thin layer chromatography. A white powder was obtained with a yield of 92%.
FT-IR spectrum (KBr plate method, cm ^-1 ): 3463/3370/3234 (amino group, N-H stretching vibration), 2943/2874 (aliphatic C-H stretching vibration), 1774/1709 (imide group, C=O stretching vibration), 1398 (imide group, N-Ar stretching vibration), 1254/1193 (ether group, C-O stretching vibration).

The following formula (8) obtained as above:

From the diamine represented by and 4-NBC, an amidation reaction was carried out in DMF in the same manner as described in Example 1, and the following formula (13) was obtained with a yield of 69%:

A pale yellow powder product was obtained.
FT-IR spectrum (KBr plate method, cm ^-1 ): 3344 (amide group, N-H stretching vibration), 3111/3078 (aromatic C-H stretching vibration), 2942/2867 (aliphatic C-H stretching vibration) ), 1775/1718 (imide group, C=O stretching vibration), 1685 (amide group, C=O stretching vibration), 1516/1347 (nitro group, N-O stretching vibration), 1389 (imide group, N-Ar stretching vibration), 1200 (ether group, CO stretching vibration).

The above dinitro compound was reduced in the same manner as described in Example 1 in DMAc in the presence of Pd/C under reflux at 80° C. for 3.5 hours in a hydrogen atmosphere. Completion of the reduction reaction was confirmed by thin layer chromatography. A white powder was obtained with a yield of 76%. The analysis results of this product are shown below.
FT-IR spectrum (KBr plate method, cm ^-1 ): 3451 (amino group, N-H stretching vibration), 3358/3227 (amino group + amide group, N-H stretching vibration), 3137/3033 (aromatic C -H stretching vibration), 2938/2875 (aliphatic C-H stretching vibration), 1775/1711 (imide group, C=O stretching vibration), 1656 (amide group, C=O stretching vibration), 1390 (imide group, N-Ar stretching vibration), 1254/1202 (ether group, C-O stretching vibration).
¹ H-NMR spectrum (400 MHz, DMSO-d ₆ , δ, ppm): 9.91 [s, 2H (2.00H), NHCO], 7.75-7.64 [m, 6H (6.03H) , 3,3',5,5'-proton of terminal AN + N-(6,6'-proton of 2-methoxyphenyl group), 7.48-7.40 [m, 2H (1.98H), N -(3,3'-proton of 2-methoxyphenyl group], 7.24-7.01 [m, 2H (1.99H), N-(5,5'-proton of 2-methoxyphenyl group), 6.62 [d, 4H (4.01H), J = 10.8Hz, 2,2',6,6'-proton of terminal AN], 5.80 [s, 4H (3.95H), NH ₂ ], 3.74 [s, 6H (5.84H), CH ₃ ], 3.40-1.80 [m, 8H, central cyclohexyl group].

From the above analysis results, this product was identified as the desired diamine (AB-MP-HPMDI) of the present invention represented by formula (2).

Synthesis example 1
<Synthesis of AB-mTOL>
The diamine (AB-mTOL) represented by the above formula (9) was obtained by an amidation reaction of m-tolidine and 4-NBC, followed by a reduction reaction of the nitro group in the same manner as described in Example 1. It was synthesized by The analysis results of this product are shown below.
Melting point (DSC): 295°C.
FT-IR spectrum (KBr plate method, cm ^-1 ): 3458 (amino group, N-H stretching vibration), 3376/3305 (amino group + amide group, N-H stretching vibration), 3037 (aromatic C-H Stretching vibration), 2917 (aliphatic C-H stretching vibration), 1650/1530 (amide group, C=O stretching vibration), 1508 (1,4-phenylene group).
¹ H-NMR spectrum (400 MHz, DMSO-d ₆ , δ, ppm): 9.75 [s, 2H (2.00H), NHCO], 7.74 [d, 4H (4.03H), J = 8 .6Hz, 3,3',5,5'-proton of terminal AN], 7.69 [sd, 2H (1.93H), J = 1.9Hz, 3,3'-proton of central BP], 7 .61 [dd, 2H (1.99H), J = 8.3, 2.0Hz, 5,5'-proton of central BP], 7.00 [d, 2H (1.96H), J = 8. 2Hz, 6,6'-proton of BP], 6.61 [d, 4H (4.02H), J = 8.6Hz, 2,2',6,6'-proton of terminal AN], 5.75 [s, 4H (4.10H), NH ₂ ], 2.01 [s, 6H (6.03H), CH ₃ ].
Elemental analysis (molecular weight 450.54): Estimated value (%) C; 74.65, H; 5.82, N; 12.44, analytical value C; 74.44, H; 5.99, N; 12. 38.

From the above analysis results, this product was identified as the desired diamine (AB-mTOL) represented by formula (9).

Synthesis example 2
<Synthesis of AB-44ODA>
The diamine (AB-44ODA) represented by the above formula (10) was prepared by an amidation reaction between 4,4'-oxydianiline and 4-NBC, followed by a nitro group reaction in the same manner as described in Example 1. It was synthesized by performing a reduction reaction. The analysis results of this product are shown below.
Melting point (DSC): 282°C.
FT-IR spectrum (KBr plate method, cm ^-1 ): 3409 (amino group, N-H stretching vibration), 3375/3322/3221 (amino group + amide group, N-H stretching vibration), 3036 (aromatic C -H stretching vibration), 1658/1572 (amide group, C=O stretching vibration), 1509 (1,4-phenylene group), 1257 (ether group, C-O stretching vibration).
¹ H-NMR spectrum (400 MHz, DMSO-d ₆ , δ, ppm): 9.78 [s, 2H (2.00H), NHCO], 7.76-7.71 [m, 8H (8.04H) , 3,3',5,5'-proton of terminal AN + 3,3',5,5'-proton of central biphenyl ether (BE) group], 6.97 [d, 4H (3.92H), J = 9.1 Hz, 2,2',6,6'-proton of central BE], 6.61 [d, 4H (4.08H), J = 8.6 Hz, 2,2',6 of terminal AN , 6'-proton], 5.75 [s, 4H (4.02H), NH ₂ ].
Elemental analysis (molecular weight 438.49): estimated value (%) C; 71.22, H; 5.06, N; 12.78, analytical value C; 71.21, H; 5.16, N; 12. 64.

From the above analysis results, this product was identified as the desired diamine (AB-44ODA) represented by formula (10).

<Polymerization, film formation, and property evaluation of polyimide film>
Example 3
The diamine of the present invention represented by the formula (1) obtained in Example 1 (5 mmol) was placed in a separable flask, and γ-butyrolactone (GBL) sufficiently dehydrated with molecular sieves 4A was added and dissolved. At this time, the solvent was calculated and added so that the total solute concentration was 40% by mass. To this diamine solution, 1-ethylpiperidine (1-EPD, 10 mmol) and benzoic acid (10 mmol) were added as a catalyst, and then H-PMDA (manufactured by Mitsubishi Gas Chemical Co., Ltd.) powder (5 mmol) was added. The temperature was raised to .degree. C. and stirred for 4 hours in a nitrogen atmosphere to obtain a uniform and viscous polyimide varnish (solution). After moderately diluting this polyimide varnish with the same solvent, it was slowly dropped into a large amount of poor solvent (methanol) to precipitate white, fibrous polyimide. After filtering and washing, it was vacuum dried at 120°C for 12 hours. A polyimide powder was obtained. This was redissolved in pure GBL to obtain a uniform polyimide varnish with a solid content concentration of 10% by mass. The reduced viscosity of the polyimide measured using an Ostwald viscometer in GBL at 30° C. and a concentration of 0.5% by mass was 3.82 dL/g.
This polyimide varnish was applied to a glass substrate, dried in a hot air dryer at 80°C for 2 hours, and then heated stepwise in vacuum at 150°C for 30 minutes, 200°C for 30 minutes, and 250°C for 1 hour. In order to remove residual stress, this film was peeled off from the substrate and further heat treated in vacuum at 3250° C. for 1 hour to obtain a transparent and flexible polyimide film with a thickness of about 20 μm.

Table 1 shows the film properties. Dynamic viscoelasticity measurements showed that this polyimide film had a very high T _g of 367°C. Furthermore, the linear thermal expansion coefficient was 24.3 ppm/K, and it also exhibited low thermal expansion characteristics. This is due to the use of the diamine of the invention described in Example 1. Further, the 5% mass loss temperature (T _d ⁵ ) was 448° C. in nitrogen and 428° C. in air, and the thermal stability was also good. Further, the light transmittance at a wavelength of 400 nm was 80.3%, the degree of yellow was 2.8, and the haze was 1.79%, indicating high transparency. Furthermore, when the mechanical properties were evaluated, the tensile modulus was as high as 5.46 GPa, and the elongation at break was 13% at maximum, indicating flexibility. It also had high pencil hardness. Other properties are also shown in Table 1.

Example 4
The diamine of the present invention represented by the above formula (2) obtained in Example 2 was used instead of the diamine represented by the above formula (1), and 1-EPD was used alone as a catalyst. Polymerization was carried out in the same manner as described in Example 3, film formation was performed, and physical properties were evaluated. Table 1 shows the film properties. This polyimide film exhibited a relatively low CTE and also retained high transparency and heat resistance. This is due to the use of the diamine of the invention described in Example 2.

Example 5
Except that the diamine represented by the above formula (9) obtained in Synthesis Example 1 (AB-mTOL) was used instead of the diamine represented by the above formula (1), and 1-EPD was used alone as a catalyst. was polymerized in the same manner as described in Example 3, a film was formed, and the physical properties were evaluated. Table 1 shows the film properties. This polyimide film exhibited a relatively low CTE and also retained high transparency and heat resistance. This is the first effect expressed by combining H-PMDA and AB-mTOL.

Example 6
Except that the diamine (AB-44ODA) represented by the above formula (10) obtained in Synthesis Example 2 was used instead of the diamine represented by the above formula (1), and 1-EPD was used alone as a catalyst. was polymerized in the same manner as described in Example 3, a film was formed, and the physical properties were evaluated. Table 1 shows the film properties. This polyimide film exhibited a relatively low CTE and also retained high transparency and heat resistance. This is the first effect expressed by combining H-PMDA and AB-44ODA.

Comparative example 1
Example 3 except that 4,4'-oxydianiline (4,4'-ODA) was used instead of the diamine represented by formula (1) above, and 1-EPD was used alone as the catalyst. Polymerization was performed in the same manner as described above, film formation was performed, and physical properties were evaluated. Table 1 shows the film properties. The CTE of this polyimide film was 46.6 ppm/K, and it did not exhibit low thermal expansion characteristics. This is because the molecular structure of diamine does not contain precisely designed structural units.

Comparative example 2
Polymerization was carried out in the same manner as described in Example 3, except that m-tolidine was used instead of the diamine represented by the above formula (1) and 1-EPD was used alone as a catalyst, and the film was formed. The physical properties were evaluated. Table 1 shows the film properties. Although this polyimide film had a very high Tg, the CTE was 57.5 ppm/K and did not exhibit low thermal expansion properties. This is because the molecular structure of m-tolidine does not contain precisely designed structural units.

Comparative example 3
The same method as described in Example 3 except that 4,4'-diaminobenzanilide (DABA) was used instead of the diamine represented by formula (1) above, and 1-EPD was used alone as a catalyst. Polymerization was carried out using However, precipitates were generated during the polymerization reaction, and a uniform varnish could not be obtained. This is because the molecular structure of DABA does not contain precisely designed structural units, and the resulting polyimide has insufficient solubility.

Claims (5)

General formula (3) below:

A polyimide having a repeating unit represented by the following formula (3), in which the divalent organic group Ar is a structural unit represented by the following formula (7).
A varnish obtained by dissolving the polyimide according to claim 1 in an organic solvent. A heat-resistant film comprising the polyimide according to claim 1. The heat-resistant film according to claim 3, having a glass transition temperature of 320°C or higher, a linear thermal expansion coefficient of 40 ppm/K or lower, and a light transmittance of 70% or higher at a wavelength of 400 nm. A plastic substrate for an image display device, comprising the heat-resistant film according to claim 3 or 4.