JP6765093B2 - Polyimide - Google Patents

Description

The present invention relates to a polyimide and, more specifically, to a polyimide obtained by using a biphenyltetracarboxylic dianhydride and two kinds of rigid diamine components.

Currently, in various image display devices and solar cells, the current inorganic glass substrate (for example, non-alkali glass substrate, hereinafter simply referred to as glass substrate) is replaced with a plastic substrate for the main purpose of reducing the weight of the device and improving the vulnerability. Consideration is being made to try.
However, the current technology has colorless transparency comparable to that of a glass substrate, excellent low thermal expansion characteristics, extremely high physical heat resistance (glass transition temperature) and chemical heat resistance (thermal oxidation stability), and It is difficult to obtain an ideal plastic substrate with significantly improved mechanical fragility, which is a drawback of glass substrates.

All-aromatic polyimide has the highest level of physical and chemical heat resistance among existing organic polymer materials (resins), so it is applied to electrical insulation members for various purposes, mainly in the electronics field. In addition to being strongly colored by the charge transfer interaction derived from the molecular structure (see, for example, Non-Patent Document 1), the low thermal expansion property is not always sufficient.
Therefore, it is difficult to apply the total aromatic polyimide film as it is to an optical member such as a plastic substrate for an image display device.

On the other hand, by using an alicyclic monomer for either one or both of diamine and tetracarboxylic dianhydride which are raw material monomers of polyimide, the charge transfer interaction observed in all aromatic polyimides is inhibited and colorless and transparent. It is known that a suitable polyimide can be obtained (see, for example, Non-Patent Documents 2 and 3).
However, in this polyimide, since an alicyclic structural unit having inferior heat resistance is introduced into the skeleton, the physical and chemical heat resistance is significantly lowered as compared with the total aromatic polyimide. Moreover, since the introduction of the alicyclic structure also causes a decrease in the linearity of the polyimide main chain, the polyimide into which the alicyclic structure is introduced often does not exhibit low thermal expansion characteristics.
As described above, neither the conventionally known total aromatic polyimide nor the polyimide having an alicyclic structure completely satisfies the characteristics required for the plastic substrate for an image display device.

When manufacturing an organic light emitting diode (OLED) display, a high temperature process (400 to 600) under high vacuum is performed to form a transparent electrode (ITO electrode) or a thin film transistor (for example, a low temperature polycrystalline silicon TFT) on a glass substrate. ℃) is adopted. At this time, since the performance of the polycrystalline silicon TFT improves as the process temperature rises, there is a request from the device side to raise the temperature at the time of manufacturing the TFT as much as possible.

In this high temperature process, the substrate is exposed to a temperature of at least 400-450 ° C., and depending on the required performance of the TFT, it is exposed to a higher temperature. However, in the case of a plastic substrate, volatile organic compounds are formed from the substrate constituent material during this high temperature treatment. A compound (VOC) is generated, and the impurities thereof may contaminate the device, which may cause a significant decrease in device performance, and may also cause thermal deformation when exposed to a high temperature.
In addition, due to the thermal expansion-thermal contraction repeated by the high temperature-room temperature temperature cycle, the element layer is cracked or misaligned due to the hysteresis phenomenon of expansion and contraction in the film surface direction (XY direction) and the irreversibly accumulated residual strain. There is also a risk of serious problems such as.

Therefore, assuming that it is used in the high temperature process as described above, the plastic substrate material should have as high a thermal decomposition temperature (T _d ) as possible in order to ensure thermal stability that can prevent VOC generation, and thermal deformation. It has a glass transition temperature (T _g ) that is sufficiently higher than the maximum process temperature to ensure preventable heat resistance, and is comparable to a glass substrate to prevent thermal expansion and contraction and ensure thermal dimensional stability. It is required to have a low coefficient of linear thermal expansion (CTE).
On top of that, a material that has the same level of colorless transparency as a glass substrate and excellent film forming ability (film toughness) is optimal, but it is extremely difficult to develop such a resin material, and in particular, it is colorless. It is extremely difficult to achieve both transparency and thermal oxidation stability at 400 ° C or higher.

By the way, in the conventional OLED display, the bottom emission method that extracts the light emitted from the light emitting layer to the glass substrate side has been the mainstream, but recently, due to the advantages such as high definition, the light extraction direction is the bottom emission. A top-emission OLED display on the opposite side of the system is also used.
In this method, the light emitted from the light emitting layer is taken out in the direction opposite to that of the substrate, so that the emitted light does not pass through the substrate. Therefore, since coloring of the substrate itself does not pose a serious problem, colorless transparency is not particularly required for this plastic substrate material.
As a substrate for a top-emission OLED display that does not require colorless transparency, all-aromatic polyimide, which is a heat-resistant resin material, is the most promising candidate.

A polyimide resin having a molecular structure represented by the formula [1] as a polyimide resin having the highest thermal oxidation stability and a low coefficient of linear thermal expansion among all aromatic polyimide resins currently produced on a large scale. UPILEX-S manufactured by Ube Industries, Ltd. is known.

The polyimide having the molecular structure represented by the above formula [1] has a considerably low coefficient of linear thermal expansion (thickness, type of cast solvent, thermal imidization temperature and other film production conditions, but is about 9 to 19 ppm / Although it has a range of K), it does not reach the value (4 to 5 ppm / K) of the glass substrate (non-alkali glass), and there is room for improvement in terms of the coefficient of linear thermal expansion (for example, non-alkali glass). See Patent Document 4).
In order to reduce the coefficient of linear thermal expansion of polyimide, it is necessary to make its main chain structure as straight and rigid as possible. From this point of view, the polyimide having the molecular structure represented by the formula [2] has a structure advantageous for low thermal expansion.
In fact, it is known that the coefficient of linear thermal expansion of this polyimide is lower than the value of the glass substrate and exhibits a coefficient of linear thermal expansion comparable to that of a silicon wafer (see, for example, Non-Patent Document 5).

However, in the polyimide represented by the above formula [2], since the polymer chains are hardly entangled with each other, not only a serious problem that the polyimide film is remarkably weakened arises, but also (see, for example, Non-Patent Document 5). Since the thermal decomposition temperature is lower than that of the polyimide represented by the formula [1], it is not suitable as a substrate for a top emission type OLED display.

Further, the copolymer of the polyimide of the formula [1] and the polyimide of the formula [2] exhibits a lower coefficient of linear thermal expansion than the polyimide film represented by the formula [1], but has thermal oxidation stability and flexibility of the film. There is a problem that the sex is reduced.

Since the general-purpose polyimide represented by the formula [3] (KAPTON (registered trademark) -H, manufactured by Toray DuPont Co., Ltd.) has an ether bond which is a flexible linking group in the main chain, the formula [3] The brittleness of the polyimide film of 2] is eliminated to give an extremely tough film, while the linearity of the main chain is lost and the low thermal expansion characteristics are deteriorated (see, for example, Non-Patent Document 6).
The ether group contained in the polyimide of the formula [3] has the best thermal stability among various linking groups, but enhances the thermal oxidation stability in air and the VOC suppression ability under high vacuum to the utmost limit. From this point of view, it is desirable to eliminate the linking group as much as possible even if it is an ether group.

Since total aromatic polyimide is insoluble in a solvent by itself, a varnish of polyamic acid, which is a precursor, is applied onto a glass substrate and dried, and then in an inert gas atmosphere such as nitrogen or in a vacuum at 300 ° C. or higher. The thermal dehydration cyclization reaction (thermal imidization reaction) can be completed by heat treatment at a high temperature of the above, and an extremely homogeneous and smooth film can be produced.

For example, as shown in the scheme below, in the case of the polyimide represented by the formula [1], the tetracarboxylic acid dianhydride represented by the formula [4] (3,3', 4,4'-biphenyltetracarboxylic) Acid dianhydride: s-BPDA (hereinafter referred to as s-BPDA) and diamine represented by the formula [5] (p-phenylenediamine: hereinafter referred to as PDA), such as N-methyl-2-pyrrolidone (hereinafter referred to as NMP), etc. A polyimide film can be obtained by subjecting it to an equimolar addition reaction in an amide solvent to obtain a varnish containing a polyamic acid represented by the formula [6], and then thermally imidizing this as described above.

The polyimide film represented by the formula [2] is obtained from pyromellitic dianhydride (hereinafter referred to as PMDA) represented by the formula [7] and a PDA.

Further, in the polyimide copolymer of the formulas [1] and [2], s-BPDA of the formula [4] and PMDA of the formula [7] are used in combination as a tetracarboxylic dianhydride, and these tetracarboxylic acids are used. (Ii) It is easily obtained by reacting the total amount of anhydride with a PDA represented by a substantially equimolar formula [5], and the characteristics of the polyimide film are controlled by changing the molar ratio of s-BPDA and PMDA. Is also possible.

When manufacturing an OLED display using a plastic substrate, it is desirable to divert the current manufacturing equipment and manufacturing technology as much as possible in order to avoid the introduction of new manufacturing equipment.
In response to such a request, a current glass substrate is used as a substrate (hereinafter referred to as a glass substrate), a heat-resistant resin film such as a polyimide film is formed on the glass substrate, and then an ITO transparent electrode, a TFT, or the like is vacuumed on the film. After forming and sealing in the process, a manufacturing process of finally peeling and removing the glass substrate is taken.
At that time, since the initial step of forming the polyimide film on the glass substrate is performed by a continuous process instead of the batch method, it is desirable to form the polyimide film at a high temperature as much as possible and in an air atmosphere from the viewpoint of process simplification.

The thermal imidization reaction in the production of the polyimide film can be performed in an air atmosphere if the temperature is not too high, but the thermal imidization reaction is carried out at a high temperature exceeding 400 ° C. as used in the high temperature process described above. Attempt, oxygen in the air causes a partial thermal oxidative decomposition (deterioration) reaction of the polyimide, which may cause problems such as poor adhesion of the film and impaired toughness of the film and smoothness of the film surface. .. In such a case, depending on the state of the film, it may not be usable in the subsequent OLED device assembly process.

Since the polyimide whose low thermal expansion characteristics have been improved by the above-mentioned copolymerization method is not always suitable for the thermal imidization process in air, new equipment is required to form the polyimide film in nitrogen or vacuum, which is expensive. Cost increase is inevitable.
Moreover, even if it is a high-quality polyimide film obtained by thermal imidization in nitrogen or vacuum, the polyimide has a low line comparable to that of a glass substrate, which is required for a substrate for a top emission OLED display. It is difficult to satisfy all the performances of the coefficient of thermal expansion, the thermal decomposition temperature exceeding UPILEX-S, the glass transition temperature of 400 ° C. or higher, and sufficient film toughness.
If this problem can be solved, it can be an extremely useful material that has not been conventionally used as a substrate material for the above-mentioned top emission OLED in the technical field, but such a material is not known.

If a material with extremely high thermal oxidation stability that is compatible with the high-temperature thermal imidization process in air is obtained, it is a common technology not only for OLED displays but also for various image display devices such as liquid crystal displays. After completion, the material can also be applied to a useful, heat-resistant, easily peelable layer material in the final step of peeling and removing the glass substrate from the plastic substrate.
The polyimide layer formed on the glass substrate is often too adhesive and may make it difficult to peel off or remove the glass substrate in the final step. On the other hand, the polyimide / polyimide interface is often inferior in adhesion to the glass / polyimide interface.
Based on this finding, by using the material to form an extremely smooth release layer on the glass substrate and forming the plastic substrate material on it, the release step in the final process is significantly improved. Become.

Prog. Polym. Sci., 26, 259-335 (2001). J. Polym. Sci., Part A, 38, 108-116 (2000). Polymer, 55, 4693-4708 (2014). Macromolecules, 32, 387-396 (1999). High Perform. Polym., 21, 709-728 (2009). Polym. J., 39, 610-621 (2007).

The present invention has been made in view of the above circumstances, and is a polyimide that can be suitably used as a substrate material for electronic devices such as top emission type OLED displays and can contribute to weight reduction and vulnerability improvement of devices. The purpose is to provide.

As a result of diligent studies to achieve the above object, the present inventors have found that a polyimide copolymer containing a repeating unit represented by the formulas (1) and (2) has an extremely high VOC suppressing ability and is excellent. They have found that they have low thermal expansion characteristics, high glass transition temperature, and sufficient film-forming ability, and are suitable for substrate materials for top-emission OLED displays, etc., and have completed the present invention.

２． 前記式（２）で表される繰り返し単位の含有率が１〜５０ｍｏｌ％である１のポリイミド。
３． 式（３）及び（４）で表される繰り返し単位を含むポリイミド前駆体。

４． 前記式（４）で表される繰り返し単位の含有率が１〜５０ｍｏｌ％である３のポリイミド前駆体。
５． ３又は４のポリイミド前駆体を含むワニス。
６． １又は２のポリイミドからなり、２０ｐｐｍ／Ｋ以下の線熱膨張係数、４００℃以上のガラス転移温度又は動的粘弾性測定により４００℃まで明瞭なガラス転移が検出されないこと、及び５％重量減少温度が空気雰囲気中で５６０℃以上であり、更に２０％以上の最大破断伸びを有するポリイミドフィルム。
７． １又は２のポリイミドからなるトップ・エミッション方式有機発光ダイオードディスプレイ用基板。
８． １又は２のポリイミドからなるトップ・エミッション方式有機発光ダイオードディスプレイ用のガラス基板剥離層。
９． ５のワニスを基体上に塗布し、乾燥後、熱イミド化反応させるポリイミドフィルムの製造方法。
１０． 式（５）

で表されるｐ−フェニレンジアミンと、式（６）

で表されるナフタレンビスイミド基含有ジアミンとを、式（７）

で表されるテトラカルボン酸二無水物と重付加反応させることを特徴とする、式（３）及び（４）で表される繰り返し単位を含むポリイミド前駆体の製造方法。

That is, the present invention provides the following polyimides and polyimide precursors.
1. 1. A polyimide containing a repeating unit represented by the formulas (1) and (2).

2. 1 Polyimide having a content of 1 to 50 mol% of the repeating unit represented by the formula (2).
3. 3. A polyimide precursor containing a repeating unit represented by the formulas (3) and (4).

4. The polyimide precursor of 3 having a content of 1 to 50 mol% of the repeating unit represented by the formula (4).
5. Varnish containing 3 or 4 polyimide precursors.
6. Consisting of 1 or 2 polyimides, no clear glass transition up to 400 ° C detected by linear thermal expansion coefficient of 20 ppm / K or less, glass transition temperature of 400 ° C or higher or dynamic viscoelasticity measurement, and 5% weight loss temperature Is a polyimide film having a maximum breaking elongation of 20% or more at 560 ° C. or higher in an air atmosphere.
7. Top emission organic light emitting diode display substrate made of 1 or 2 polyimides.
8. A glass substrate release layer for a top emission organic light emitting diode display made of 1 or 2 polyimides.
9. A method for producing a polyimide film in which the varnish of No. 5 is applied onto a substrate, dried, and then subjected to a thermal imidization reaction.
10. Equation (5)

P-phenylenediamine represented by and formula (6)

The naphthalene bisimide group-containing diamine represented by the formula (7)

A method for producing a polyimide precursor containing a repeating unit represented by the formulas (3) and (4), which comprises a polyaddition reaction with a tetracarboxylic dianhydride represented by.

The polyimide of the present invention not only has a very low coefficient of linear thermal expansion required to achieve high thermal stability and high dimensional stability, but also has a high glass transition temperature and sufficient film toughness. Combined.
The polyimide of the present invention having such characteristics is suitable as a substrate material for a photoelectric conversion element such as a solar cell, a substrate material for an electronic device such as an image display device such as an OLED, and particularly as a substrate material for a top emission type OLED display. It can be used for device weight reduction and vulnerability improvement.
Further, the film obtained by applying the material on the glass substrate is useful as a heat-resistant easily peelable layer, and can provide an important technique for replacing the current glass substrate with a plastic substrate.

It is an infrared absorption spectrum of the polyimide precursor thin film produced in Example 1. It is an infrared absorption spectrum of the polyimide thin film produced in Example 1.

Hereinafter, the present invention will be described in more detail.
The polyimide according to the present invention is a copolymer of polyimide using at least two kinds of diamines containing the repeating units represented by the formulas (1) and (2).

As can be seen from the formula (2), the polyimide of the present invention contains 1,4,5,8-naphthalbisimide structural units.
In this structural unit, since the imide group is composed of a 6-membered ring having no bond angle distortion, it is more thermally than a normal polyimide composed of a 5-membered ring imide group (for example, the above formulas [1] to [3]). Since it is stable, the polyimide obtained by introducing this structural unit has improved thermal stability.

Further, as can be seen from the above formulas (1) and (2), the polyimide of the present invention has a rigid main chain structure with high linearity and does not contain any substituents, so that it has low linear thermal expansion characteristics. Excellent and has extremely high thermal oxidation stability.
Since the polyimide of the present invention having such a structure is insoluble in a solvent, in order to form the above-mentioned polyimide film, a solution (varnish) of a polyimide precursor (polyamic acid) soluble in an amide solvent is used. After coating and drying on the substrate, it is necessary to heat to 300 ° C. or higher to imidize.

At that time, when the polyamic acid is polymerized by a usual method, the tetracarboxylic acid dianhydride (s-BPDA) represented by the formula (7) and 1,4,5,8- represented by the formula (8) are used. PDA represented by the following formula (5) in which the total amount of naphthalene tetracarboxylic acid dianhydride (hereinafter referred to as 1,4,5,8-NTDA) and these tetracarboxylic acid dianhydrides is substantially equal to the molar amount. Is subjected to a double addition reaction at room temperature in an amide-based solvent.

However, 1,4,5,8-NTDA represented by the above formula (8) is completely insoluble in any solvent at room temperature, and the stability of the 6-membered ring acid anhydride group is too high. It shows almost no polymerization reactivity with diamine. Therefore, it is impossible to obtain a uniform polyamic acid varnish using 1,4,5,8-NTDA.
As described above, 1,4,5,8-NTDA has poor polymerization reactivity at room temperature, but the reactivity can be improved by refluxing the reaction solution at the boiling point of the amide solvent.
However, such a heating operation of the reaction solution causes imidization to proceed at the same time as the formation of the polyamic acid, and the solubility of the product often drops sharply.
Therefore, in the case of a rigid structure like the polyimide of the present invention, a precipitate is precipitated at the initial stage of the reaction and a uniform varnish cannot be obtained, and subsequent film formation cannot be performed.

In order to avoid precipitation of precipitates, tetracarboxylic acid dianhydrides copolymerizing with 1,4,5,8-NTDA, diamines, bent structures, bulky substituents, or fluorine-containing substituents that weaken the intermolecular force are used. Although it must be introduced, the introduction of these substituents often impairs low linear thermal expansion properties and thermal oxidative stability.
Thus, in the conventional method, 1,4,5,8-NTDA can be used to introduce 1,4,5,8-naphthalbisimide groups into the main chain of polyimide, even if only partially. It was difficult.

As a means for solving the above problems, in the present invention, a naphthalene bisimide group-containing diamine represented by the following formula (6) is adopted as a diamine component.
That is, in the present invention, the PDA represented by the formula (5) and the naphthalene bisimide group-containing diamine represented by the formula (6) that can be synthesized by the method described later are represented by the formula (7) in a solvent. By subjecting it to a double addition reaction with s-BPDA, a uniform varnish of a polyimide precursor (polyamic acid) containing the repeating units represented by the formulas (3) and (4) can be obtained, which is commonly used. The polyimide film of the present invention can be produced by casting and performing a heat-dehydration cyclization reaction (thermal imidization).

The method for producing the polyimide precursor is not particularly limited, and a known method can be applied. More specifically, for example, a PDA represented by the formula (5) and a naphthalene bisimide group-containing diamine represented by the formula (6) are dissolved in a solvent and represented by the formula (7) with stirring. Examples thereof include a method in which powder of s-BPDA is gradually added and stirred at 0 to 100 ° C., preferably 20 to 60 ° C. for 0.5 to 100 hours, preferably 5 to 72 hours.
At this time, the substance amount (mol) ratio of the diamine components of the formulas (5) and (6) to the tetracarboxylic dianhydride represented by the formula (7) is usually 0, with respect to the total amount of diamine 1. It is about 8 to 1.1, preferably 0.9 to 1.1, and more preferably 0.95 to 1.05.

In the above reaction, the ratio of the PDA represented by the formula (5) to the naphthalene bisimide group-containing diamine represented by the formula (6) is not particularly limited, but the formulas (5) and ( Of the total amount (100 mol%) of each diamine represented by 6), it is preferable to use 1 to 50 mol% of the naphthalene bisimide group-containing diamine represented by the formula (6), and more preferably 5 to 25 mol%. It is even more preferable to use 8 to 23 mol%.

The total monomer concentration in the reaction solution is preferably 5 to 50% by mass, more preferably 10 to 40% by mass. By carrying out the polymerization in this range, the solubility of the monomer and the polyimide precursor can be sufficiently ensured, and a uniform and highly polymerizable polyimide precursor solution can be obtained.
If the degree of polymerization of the polyimide precursor increases too much and it becomes difficult to stir the polymerization solution, it may be appropriately diluted with the same solvent.

Further, in the present invention, the intrinsic viscosity of the polyimide precursor of the present invention is in the range of 0.3 to 5.0 dL / g from the viewpoint of the toughness of the polyimide film and the handleability of the varnish containing the precursor thereof. preferable.

The tetracarboxylic dianhydride used in producing the polyimide precursor of the present invention is s-BPDA as described above, but as long as the required properties of the obtained polyimide (film) are not impaired, s- Tetracarboxylic dianhydride other than BPDA can be partially used.
Specific examples of the tetracarboxylic dianhydride that can be used in combination include pyromellitic dianhydride, 2,3,3', 4'-biphenyltetracarboxylic dianhydride, 2,2', 3,3'-. Biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 3,4'-oxydiphthalic dianhydride, 3,3'-oxydiphthalic dianhydride, hydroquinone-diphthalic dianhydride, 4, Examples thereof include 4'-biphenol-diphthalic dianhydride, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride, and 4,4'-(hexafluoroisopropyridene) diphthalic acid anhydride. May be used alone or in combination of two or more. When these tetracarboxylic dianhydrides are used, the content thereof is preferably 30 mol% or less, more preferably 10 mol% or less, but not used, based on the total amount of tetracarboxylic dianhydrides including s-BPDA. Is the best.

On the other hand, there are two types of diamine components, PDA and naphthalene bisimide group-containing diamine as described above, but also in this case, as long as the required characteristics of the obtained polyimide (film) are not impaired, they can be used as copolymerization components. Rigid diamines such as rigid diamines, benzidines, 4,4 "-p-terphenylenediamines and diamines represented by the formula (9) may be used alone or in combination of two or more. The amount is preferably 50 mol% or less, more preferably 30 mol% or less, still more preferably 10 mol% or less, based on the total amount of diamine, but it is optimal not to use it.

Further, a diamine having a bent structure may be partially used as long as the required characteristics of the obtained polyimide are not impaired.
Specific examples of such diamines include m-phenylenediamine, o-phenylenediamine, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, and 2,4'-diamino. Diphenyl ether, 2,2'-diaminodiphenyl ether, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, and Examples thereof include 4,4'-bis (4-aminophenoxy) biphenyl, which may be used alone or in combination of two or more. The content of these diamines is preferably 30 mol% or less, more preferably 10 mol% or less, still more preferably 5 mol% or less, and most preferably not used, based on the total amount of diamines.
Considering that the polyimide film of the present invention is imparted with high thermal oxidation stability, the monomers used in the production of the polyimide precursor are aromatic tetracarboxylic acid dianhydrides containing no substituents or linking groups. Aromatic diamines are preferred.

Considering the diamine component and the tetracarboxylic dianhydride component described above, the content of the repeating unit represented by the formulas (3) and (4) in the polyimide precursor of the present invention is preferably 50 mol% or more. 70 mol% or more is more preferable, 80 mol% or more is further preferable, 90 mol% or more is further preferable, and 100 mol% is optimal.
Further, in particular, the content of the repeating unit represented by the formula (4) is preferably 1 to 50 mol%, more preferably 5 to 25 mol%, and even more preferably 8 to 23 mol%.
Similarly, in the polyimide of the present invention, the content of the repeating unit represented by the formulas (1) and (2) is preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 80 mol% or more, and 90 mol. % Or more is more preferable, and 100 mol% is optimal.
Further, in particular, the content of the repeating unit represented by the formula (2) is preferably 1 to 50 mol%, more preferably 5 to 25 mol%, and even more preferably 8 to 23 mol%.

The solvent used for producing the polyimide precursor of the present invention is not limited in its structure as long as the raw material monomer and the produced polyimide precursor are dissolved. For example, N, N-dimethylformamide, N, N-dimethylacetamide. , N-Methyl-2-pyrrolidone, 3-methoxyN, N-dimethylpropanamide, 3-n-butoxy N, N-dimethylpropanamide, 3-sec-butoxy N, N-dimethylpropanamide, 3-t- Amide solvents such as butoxy N, N-dimethylpropanamide, 1,3-dimethyl-2-imidazolidinone; γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, α- Cyclic ester solvent such as methyl-γ-butyrolactone; carbonate solvent such as ethylene carbonate and propylene carbonate; glycol solvent such as triethylene glycol; phenol such as m-cresol, p-cresol, 3-chlorophenol and 4-chlorophenol. System solvent: An aproton solvent such as acetophenone, sulfolane, dimethylsulfoxide and the like can be mentioned.
Further, phenol, o-cresol, butyl acetate, ethyl acetate, isobutyl acetate, propylene glycol methyl acetate, tetrahydrofuran, diethylene glycol dimethyl ether, methyl isobutyl ketone, diisobutyl ketone, as long as the solubility of the raw material monomer and the produced polyimide precursor is not hindered. , Cyclohexanone, methyl ethyl ketone, acetone, butanol, ethanol, xylene, toluene and common solvents such as chlorobenzene may be used in combination.

The polymerization solution (varnish) of the polyimide precursor obtained by the above production method may be used as it is for producing the polyimide (film), or the polymerization solution is mixed with a large amount of water or a poor solvent such as methanol. A solution (crocodile) in which the precipitated solid is filtered, dried, isolated as a powder, and dissolved in a solvent again may be used for producing the polyimide (film) of the present invention.

In the polyimide film (heat resistant film) of the present invention, a varnish containing a polyimide precursor obtained by the above method is cast on a substrate such as glass, copper, aluminum, stainless steel, silicon, etc., and in an oven, 40 to 40 to The polyimide precursor film obtained by heating and drying at 180 ° C., preferably 50 to 150 ° C., together with the substrate, in vacuum, in an inert gas such as nitrogen, or in air, 200 to 450 ° C., preferably 250 to 250 to It can be obtained by heating at 430 ° C.
At this time, the heating temperature is preferably 200 ° C. or higher from the viewpoint of completing the imidization reaction, and preferably 450 ° C. or lower from the viewpoint of suppressing thermal decomposition of the produced polyimide film. If the imidization temperature is 400 ° C. or lower, it may be carried out in air.

Further, instead of the above heat treatment, the imidization reaction can be carried out by immersing the polyimide precursor film in a solution containing a dehydration cyclization reagent such as acetic anhydride in the presence of a tertiary amine such as pyridine or triethylamine. ..
Further, the dehydration cyclization reagent is previously put into a polyimide precursor varnish at room temperature, stirred, and then cast and dried on the substrate to prepare a partially imidized polyimide precursor film. It can also be made into a polyimide film by further heat-treating it under the above conditions.

A laminate of a metal layer and a polyimide resin layer can be obtained by applying and drying the varnish of the polyimide precursor of the present invention on a metal foil, for example, a copper foil, and then imidizing it under the above conditions. Further, an adhesive-free flexible printed circuit board can be manufactured by etching the metal layer into a desired circuit shape using an etching solution such as an aqueous solution of ferric chloride.

The thickness of the polyimide film of the present invention is not particularly limited, and can be appropriately set according to the purpose of use.
For example, when it is used as a substrate for a photoelectric conversion device such as a solar cell, a plastic substrate for an image display device such as an OLED display or a liquid crystal display, a glass substrate peeling layer, or a flexible circuit board, it is preferably about 1 to 100 μm.

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 the naphthalene bisimide group-containing diamine was measured by the KBr plate method using a Fourier transform infrared spectrophotometer (FT-IR4100, manufactured by JASCO Corporation). Moreover, the infrared absorption spectrum of the polyimide precursor and the polyimide thin film (thickness of about 5 μm) was measured by the transmission method.
< ^{1 1} H-NMR spectrum>
A ¹ H-NMR spectrum of a naphthalene bisimide group-containing diamine was measured in deuterated dimethyl sulfoxide using an NMR spectrometer (ECP400, manufactured by JEOL Ltd.).
<Differential scanning calorimetry (melting point and melting curve)>
The melting point and melting curve of the naphthalene bisimide group-containing diamine were measured at a heating rate of 5 ° C./min in a nitrogen atmosphere using a differential scanning calorimeter (DSC3100, manufactured by Netch Japan Co., Ltd.).
<Intrinsic viscosity>
A 0.5 mass% polyimide precursor solution was measured at 30 ° C. using an Ostwald viscometer.
<Glass transition temperature (T _g )>
Using a dynamic viscoelasticity measuring device (TA, Instrument Japan Co., Ltd., Q800), a polyimide film (20 μm thickness) was used from the peak temperature of the loss elastic modulus curve at a frequency of 0.1 Hz and a heating rate of 5 ° C./min. ) Was determined. The higher the T _g , the more the rapid softening is suppressed up to the higher temperature range, and the higher the physical heat resistance. In addition, even when T _g is not very clear or very broad in this measurement, the film does not substantially soften within the measurement temperature range, and it has excellent physical heat resistance. Represents.
<Coefficient of linear thermal expansion: CTE>
Thermomechanical analysis using a thermomechanical analyzer (TMA4000, manufactured by Netch Japan Co., Ltd.) shows that 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 is 100 to 100. The CTE of the polyimide film (film thickness of about 20 μm) was determined as an average value in the range of 200 ° C. The closer the CTE value is to 0, the better the dimensional stability with respect to the thermal process.
<5% weight loss temperature (T _d ⁵ )>
Using a thermogravimetric analyzer (TG-DTA2000, manufactured by Netch Japan Co., Ltd.), the weight of the polyimide film (20 μm thickness) was increased in the heating process in nitrogen and air at a heating rate of 10 ° C./min. The temperature was measured when the weight was reduced by 5% from the initial weight. The higher these values are, the higher the chemical heat resistance (thermal stability) is, and it means that the generation of VOC is suppressed up to a higher temperature.
<Mechanical properties: Tensile modulus, elongation at break, strength at break>
A tensile test (stretching speed: 8 mm / min) was performed on a polyimide test piece (30 mm length x 3 mm width x 20 μm thickness) using a tensile tester (A & D Co., Ltd., Tensilon UTM-2). The elastic modulus was obtained from the initial gradient of the stress-strain curve, and the elongation at break (%) was obtained from the elongation at break of the film. The higher the elongation at break, the higher the toughness of the film.

[1] Synthesis of diamine [Synthesis example 1] Synthesis of naphthalene bisimide group-containing diamine N-methyl-2-pyrrolidone (NMP) obtained by thoroughly dehydrating 1,4,5,8-NTDA (10 mmol) in a three-necked flask. ) Dispersed in 45 mL, and this was used as A dispersion. Next, PDA (100 mmol) was dissolved in 20 mL of NMP, and this was used as solution B. The dispersion A was gradually added to the solution B with stirring, and stirring was continued at room temperature for 12 hours to obtain a uniform reaction solution. Subsequently, the mixture was refluxed at 200 ° C. for 7 hours, cooled to room temperature, and the precipitated precipitate was washed thoroughly with NMP and then with methanol to completely remove the excess amount of PDA, and finally at 200 ° C. for 12 Vacuum drying for hours gave a red powder with a yield of 87% and a melting point of 497 ° C. The analysis results shown below were obtained for this product. From these analysis results, it was confirmed that this product was the target naphthalene bisimide group-containing diamine represented by the above formula (6).

FT-IR spectrum (KBr, cm ^-1 ): 3411, 3320, 3221 (NH expansion and contraction), 3068 (aromatic CH expansion and contraction), 1704, 1657 (6-membered ring imide group C = O expansion and contraction), 1515 (1,4-phenylene group)
^{1 1} H-NMR spectrum (400 MHz, DMSO-d ₆ , δ, ppm): 8.68 (s, 4H, proton on naphthalene group), 7.02 (d, 4H, J = 8.6 Hz, terminal aniline) 3,5-proton), 6.67 (d, 4H, J = 8.6Hz, 2,6-proton of terminal aniline), 5.31 (s, 4H, amine)
Elemental analysis (molecular weight 448.44): Estimated value C; 69.64%, H; 3.60%, N; 12.49%, Analytical value C; 69.18%, H; 3.98%, N; 12.44%.

[2] Production of polyimide precursor, imidization and characterization of polyimide film [Example 1]
2.7 mmol of p-phenylenediamine (PDA) and 0.3 mmol of the naphthalene bisimide group-containing diamine obtained in Synthesis Example 1 were placed in a well-dried reaction vessel, and NMP (5.) was sufficiently dehydrated with Molecular Sieves 4A. 1 mL) was added and stirred. According to this diamine charging ratio, a copolymer having a naphthalene bisimide group-containing diamine content of 10 mol% with respect to the total amount of diamine is obtained. This diamine solution is warmed on a hot plate to dissolve the undissolved naphthalene bisimide group-containing diamine and the temperature is returned to room temperature, and then 3,3', 4,4'-biphenyltetracarboxylic dianhydride is added to this solution. 3 mmol of (s-BPDA) powder was added slowly. Polymerization is started from a solute concentration of 20% by mass, a solvent is gradually added, and finally the solute concentration is diluted to 12.3% by mass, and the mixture is stirred at room temperature for 72 hours to obtain a uniform and viscous polyimide precursor solution ( I got a varnish).
The reduced viscosity of the polyimide precursor measured with an Ostwald viscometer at a concentration of 0.5% by mass at 30 ° C. in NMP was 2.23 dL / g. FIG. 1 shows the infrared absorption spectrum of the thin film of the polyimide precursor obtained. 2623 cm ^-1 with broad absorption band (hydrogen-bonding COOH group O-H expansion and contraction), 1712 cm ^-1 with hydrogen-bonding COOH group C = O expansion and contraction vibration band, 1659 cm ^-1 with amide group C = O expansion and contraction vibration band, 1515 cm ^A 1,4-phenylene group expansion and contraction vibration band was observed in ^-1, and an amino group NH expansion and contraction vibration band derived from the monomer and an acid anhydride group C = O expansion and contraction vibration band of tetracarboxylic acid dianhydride were not observed. From this, it was confirmed that the desired polyimide precursor was produced.

This polyimide precursor solution was applied to a glass substrate and dried in a hot air dryer at 80 ° C. for 3 hours to prepare a polyimide precursor film. This was thermally imidized together with the glass substrate at 250 ° C. for 1 hour in vacuum and then at 350 ° C. for 1 hour, then peeled off from the substrate and further heat-treated at 400 ° C. for 1 hour in vacuum to remove residual stress. A flexible polyimide film having a thickness of about 20 μm was obtained. FIG. 2 shows an infrared absorption spectrum of a polyimide thin film (about 5 μm thick) separately prepared under the same conditions. 3070 cm ^-1 is aromatic CH telescopic vibration band, 1773, 1715 cm ^-1 is imide group C = O telescopic vibration band, 1515 cm ^-1 is 1,4-phenylene group telescopic vibration band, 1357 cm ^-1 is imide group N- The imidization reaction is complete because an imide ring-angled vibration zone is observed in the C (aromatic) expansion and contraction vibration zone, 738 cm ^-1 , and no absorption band based on the COOH group or amide group derived from the polyimide precursor is observed. It was confirmed that the desired polyimide was produced.

When the obtained polyimide film was subjected to dynamic viscoelasticity measurement (room temperature to 500 ° C.), a very broad loss elastic modulus peak was observed at 316 ° C., but it was difficult to determine the glass transition temperature from this. Met. Further, the coefficient of linear thermal expansion was very low at 12.8 ppm / K, and it was confirmed that the obtained film had excellent low thermal expansion characteristics. This is because the main chain structure of the polyimide of the present invention is extremely rigid and highly linear, and the polyimide main chain is remarkably oriented in the direction parallel to the film surface in the thermal imidization step. it is conceivable that. The 5% weight loss temperature (T _d ⁵ ) was 592 ° C. in nitrogen and 571 ° C. in air, confirming that it had extremely high thermal stability. In particular, T _d ^{5 in} air is an unprecedentedly high value, and this result indicates that the polyimide of the present invention has outstanding thermal oxidation stability. Further, as a result of evaluating the mechanical properties of the obtained film, the average tensile elastic modulus (Young's modulus) was 6.95 GPa, the average breaking elongation was 19.9%, and the maximum breaking elongation was 41.4%, and sufficient film toughness was also obtained. It was confirmed that it was retained.

[Example 2]
According to the method described in Example 1, except that the diamine charging ratio was changed to 2.4 mmol of PDA and 0.6 mmol of naphthalene bisimide group-containing diamine obtained in Synthesis Example 1 (naphthalene bisimide group-containing diamine content 20 mol%). Polymerization was carried out to obtain a uniform and viscous polyimide precursor solution (varnish). The reduced viscosity of this polyimide precursor was 1.73 dL / g. This varnish was film-formed and thermally imidized according to the conditions described in Example 1 to obtain a polyimide film. In the dynamic viscoelasticity measurement, a very broad loss elastic modulus peak was observed at 321 ° C., but it was difficult to determine the glass transition temperature from this. The CTE was 16.4 ppm / K, and low thermal expansion characteristics were confirmed. T _d ⁵ was 589 ° C. in nitrogen and 561 ° C. in air, and maintained extremely high thermal stability. The average tensile modulus was 6.29 GPa, the average breaking elongation was 26.1%, and the maximum breaking elongation was 46.3%.
From the above, since the polyimide film of Example 2 has further improved film toughness as compared with the polyimide film of Example 1, an increase in the content of the naphthalene bisimide group-containing diamine improves the film toughness of the polyimide film. It was found to contribute to.

[Comparative Example 1]
Using pyromellitic dianhydride (PMDA) as the tetracarboxylic dianhydride component and PDA as the diamine component, the polyimide film is polymerized, film-formed, and thermally imidized according to the method and production conditions described in Example 1. It was prepared and its physical properties were evaluated. Although this polyimide film showed extremely low CTE (2.8 ppm / K), it was very fragile and the elongation at break was substantially 0%. In addition, this film was easily broken when folded with a goby. This is because it is derived from this polyimide-based rod-shaped main chain structure, and there is almost no entanglement between the polymer chains. Further, T _d ⁵ was 576 ° C. in nitrogen and 551 ° C. in air, and although it can be said that the thermal stability was high, it was inferior to the polyimide films of Examples 1 and 2. This is because this polyimide film uses PMDA as a tetracarboxylic dianhydride.

[Comparative Example 2]
Using PMDA as the tetracarboxylic dianhydride component and 4,4'-oxydianiline (ODA) as the diamine component, the polyimide was polymerized, formed into a film, and thermally imidized according to the method and production conditions described in Example 1. A film was prepared and its physical properties were evaluated. This polyimide film showed an extremely high glass transition temperature (409 ° C.) and had excellent toughness with a maximum elongation at break of 85%, but had a CTE of 42.8 ppm / K and did not exhibit low thermal expansion characteristics. Further, T _d ⁵ is 567 ° C. in nitrogen, 552 ° C. in air, thermal stability can be said to be high, and clearly inferior to the polyimide films of Examples 1 and 2, T _d in nitrogen The value of ⁵ was inferior to that of the polyimide described in Comparative Example 1. This is because this polyimide film uses PMDA as a tetracarboxylic dianhydride and ODA containing an ether bond (linking group) as a diamine.

[Comparative Example 3]
Using BPDA as the tetracarboxylic dianhydride component and PDA as the diamine component, a polyimide film was prepared by polymerization, film formation, and thermal imidization according to the method and production conditions described in Example 1, and the physical properties were evaluated. In the dynamic viscoelasticity measurement, a very broad loss elastic modulus peak was observed at 309 ° C., but it was difficult to determine the glass transition temperature from this. The CTE of this polyimide film was 19.4 ppm / K, which was a low thermal expansion characteristic, but was inferior to the values of the polyimide films described in Examples 1 and 2. Further, T _d ⁵ was 589 ° C. in nitrogen, which was equivalent to the value of the polyimide film described in Examples 1 and 2. However, since T _d ⁵ in the air, which reflects the thermal oxidation stability, is 551 ° C., this polyimide film is slightly inferior in thermal oxidation stability to the values of the polyimide films of Examples 1 and 2. It was.

Claims (7)

A polyimide precursor containing a repeating unit represented by the formulas (3) and (4).

The polyimide precursor according to claim 1, wherein the content of the repeating unit represented by the formula (4) is 1 to 50 mol%. A varnish containing the polyimide precursor according to claim 1 or 2. A substrate for a top emission organic light emitting diode display made of a polyimide obtained from the polyimide precursor according to claim 1 or 2. A glass substrate release layer for a top emission organic light emitting diode display made of polyimide obtained from the polyimide precursor according to claim 1 or 2. A method for producing a polyimide film, wherein the varnish according to claim 3 is applied onto a substrate, dried, and then subjected to a thermal imidization reaction. Equation (5)

P-phenylenediamine represented by and formula (6)

The naphthalene bisimide group-containing diamine represented by the formula (7)

A method for producing a polyimide precursor containing a repeating unit represented by the formulas (3) and (4), which comprises a polyaddition reaction with a tetracarboxylic dianhydride represented by.

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