JP2012062344A - Polyimide precursor, polyimide resin, and use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide resin excellent in solubility to an organic solvent, heat resistance, dimensional stability and transparency; a coating resin solution containing the polyimide resin; and TFT substrate, a flexible display substrate and an electronic device material using a coating film formed from the solution.SOLUTION: The polyimide precursor with a specific structure and the polyimide resin can be obtained by copolymerizing a diamine with a specific structure having a trifluoromethyl group, a tetracarboxylic acid dianhydride with a specific structure having a trifluoromethyl group and an aromatic tetracarboxylic acid dianhydride not containing fluorine.

Description

  The present invention relates to a polyimide resin that provides a film having high transparency and excellent heat resistance and dimensional stability. In particular, a polyimide resin that is soluble in an organic solvent and can be suitably used as a material (eg, a glass substitute film for an image display device) that forms a product or member that has high requirements for transparency, heat resistance, and dimensional stability, The present invention relates to a coating resin solution, an optical film comprising the same, and a transparent substrate.

  In recent years, with rapid advances in displays such as liquid crystal, organic EL and electronic paper, and electronics such as solar cells and touch panels, devices are required to be thinner and lighter, and more flexible. Therefore, instead of a glass substrate, a plastic film substrate that can be made thinner, lighter, and flexible has been studied.

  In these devices, various electronic elements such as a thin film transistor and a transparent electrode are formed on a substrate. However, a high temperature process is required to form these electronic elements. However, since plastic films have low heat resistance and low dimensional stability at high temperatures, thermal deformation such as warpage is likely to occur in the manufacturing process, making alignment difficult and possibly destroying electrical elements. .

  Furthermore, when the light emitted from the display element is emitted through the plastic film substrate (for example, bottom emission type organic EL), the plastic film substrate needs to be transparent.

  These device fabrication processes are divided into a batch process and a roll-to-roll process. When using a roll-to-roll fabrication process, new equipment is required and several problems due to rotation and contact must be overcome. On the other hand, the batch process is a process in which a coating resin solution is applied on a glass substrate, dried, a substrate is formed, and then peeled off. For this reason, the glass substrate process and equipment such as the current TFT can be used, which is advantageous in terms of cost.

  From such a background, development of a coating resin solution that can be applied to an existing batch process and that can provide a coating film having high heat resistance, dimensional stability, and high transparency is strongly desired.

  Polyimide has been studied as a material having these requirements. In order to obtain a highly transparent polyimide, an alicyclic monomer or an aromatic monomer containing a fluorine substituent is generally used. However, when an alicyclic monomer is used, a polyimide having high heat resistance and high dimensional stability cannot be obtained although the solubility in an organic solvent is increased. On the other hand, when a monomer containing a fluorine substituent such as 2,2′-bis (trifluoromethyl) benzidine (hereinafter sometimes referred to as TFMB) is used, high heat resistance, dimensional stability, transparency, and organic solvent In many cases, a polyimide having a relatively high solubility is obtained, but a polyimide resin that can sufficiently satisfy all the required characteristics has not been disclosed yet.

  For example, Patent Literature 1 and Patent Literature 2 describe the thermal properties of polyimide using TFMB. However, details of other physical properties are not described.

  Patent Document 3 discloses a soluble polyimide technique using TFMB. Although there is a description of the linear thermal expansion coefficient, it is only a description of the solubility with respect to N-methyl-2-pyrrolidone (NMP), and nothing is described with respect to the solubility in other solvents.

  Patent Document 4 describes a polyimide composed of tetracarboxylic dianhydride represented by the following formula (9) and TFMB.

(In the formula, A ₁ represents an oxygen atom or an NH group.)
The polyester-imide in which A ₁ is oxygen in the formula (9) has solubility in an organic solvent and has relatively high heat resistance and transparency, but has a problem in dimensional stability. Further, in the case of the polyamide-imide in which A ₁ is NH group in the formula (9), although heat resistance and dimensional stability are relatively high, problems remain in transparency.

  As described above, a material having both solubility in an organic solvent that can be suitably used as a coating resin, heat resistance required in practical use, dimensional stability, and transparency has not been disclosed so far.

U.S. Pat. US Pat. No. 5,194,579 Special table flat 8-511812 JP 2010-106225 A

  The present invention relates to a polyimide resin excellent in solubility in an organic solvent, heat resistance, dimensional stability and transparency, a coating resin solution containing the polyimide resin, and a TFT substrate and a flexible display using the coating film formed thereby. It is to provide a substrate and an electronic device material.

  In view of the above problems, as a result of intensive research, the polyimide resin represented by the following formula (8) exhibits excellent characteristics that satisfy the above required characteristics at the same time, and is found to be a useful material in the industrial field. The present invention has been completed.

(In the formula (8), X and Z represent a divalent fluorine-containing aromatic group selected from the following formulas (2) to (4), and X and Z may be the same or different. Represents a tetravalent aromatic group containing no fluorine, R represents a hydrogen atom, a silyl group, or a linear or branched alkyl group having 1 to 12 carbon atoms, M and n represent the molar fraction of each structural unit, and m + n = 1, 0.5 ≦ m ≦ 0.9, and 0.5 ≧ n ≧ 0.1.

That is, the gist of the present invention is as follows.
1. The polyimide precursor containing the repeating unit represented by following formula (1).

(In the formula (1), X and Z represent a divalent fluorine-containing aromatic group selected from the following formulas (2) to (4), and X and Z may be the same or different. Represents a tetravalent aromatic group containing no fluorine, R represents a hydrogen atom, a silyl group, or a linear or branched alkyl group having 1 to 12 carbon atoms, M and n represent the molar fraction of each structural unit, and m + n = 1, 0.5 ≦ m ≦ 0.9, and 0.5 ≧ n ≧ 0.1.

2. In said formula (1), Y is a tetravalent aromatic group chosen from following formula (5)-(7), The polyimide precursor of said 1 characterized by the above-mentioned.

3. Polyimide resin containing the repeating unit represented by following formula (8).

(In the formula (8), X and Z represent a divalent fluorine-containing aromatic group selected from the following formulas (2) to (4), and X and Z may be the same or different. Represents a tetravalent aromatic group containing no fluorine, R represents a hydrogen atom, a silyl group, or a linear or branched alkyl group having 1 to 12 carbon atoms, M and n represent the molar fraction of each structural unit, and m + n = 1, 0.5 ≦ m ≦ 0.9, and 0.5 ≧ n ≧ 0.1.

4). In said formula (8), Y is a tetravalent aromatic group chosen from following formula (5)-(7), The polyimide resin of said 3 characterized by the above-mentioned.

5. 5. The polyimide resin as described in 3 or 4 above, which is chemically imidized.
6). 6. A coating resin solution comprising the polyimide resin according to any one of 3 to 5 above and an organic solvent, wherein the polyimide resin has a solid content concentration of 1% by weight or more.
7). 7. A coating film formed by applying and drying the coating resin solution described in 6 above on a substrate.
8). A TFT substrate comprising the coating film as described in 7 above.
9. 8. A flexible display substrate comprising the coating film as described in 7 above.
10. 8. An electronic device material comprising the coating film as described in 7 above.

  The polyimide resin according to the present invention is soluble in various organic solvents, and the coating film formed using a resin solution containing the polyimide resin has excellent heat resistance, dimensional stability, and transparency. . Therefore, there exists an effect that it can be used suitably for a TFT substrate, a flexible display substrate, and an electronic device material. Moreover, since the coating resin of this invention can utilize the existing process and equipment for glass substrates, it is advantageous in terms of cost.

<Method for producing tetracarboxylic dianhydride>
The manufacturing method of the tetracarboxylic dianhydride used by this invention is not specifically limited, A well-known method is applicable. As an example, a method for producing a tetracarboxylic dianhydride (hereinafter sometimes referred to as TABD) represented by the formula (10) will be described.

  Esters using 4,4′-hydroxy-2,2′-bis (trifluoromethyl) biphenyl (hereinafter sometimes referred to as DHTFMB) represented by the formula (11) and trimellitic anhydride derivative as the raw material Perform the chemical reaction.

  In this case, for example, the DHTFMB hydroxy group and trimellitic anhydride carboxyl group can be directly dehydrated at high temperature, or the DHTFMB diacetate and trimellitic anhydride can be reacted at high temperature. Deaceticating and esterifying (transesterification method), converting the carboxyl group of trimellitic anhydride to a halide, and reacting this with DHTFMB in the presence of an oxygen scavenger (base) (acid) Halide method), a method of activating and carboxylating a carboxyl group in trimellitic anhydride using a tosyl chloride / N, N-dimethylformamide / pyridine mixture, and the like. Among the above-mentioned methods, the acid halide method can be preferably applied in terms of economy and reactivity.

  The production method of TABD used in the present invention by the acid chloride method will be specifically described below. First, trimellitic anhydride chloride (A [mol]) is dissolved in a solvent and sealed with a septum cap. To this solution, DHTFMB (A / 2 [mol]) and an appropriate amount of a base (deoxidizing agent) dissolved in the same solvent are slowly dropped with a syringe or a dropping funnel. After the addition is complete, the reaction mixture is stirred for 24 hours. When the solubility of the target compound in the solvent used in the synthesis is high, first the produced hydrochloride is filtered off from the reaction mixture, and the filtrate is evaporated by an evaporator and dried in a vacuum at 100 to 200 ° C. for 24 hours to form a powder. To obtain a crude product. When the solubility of the target product is low, the mixture of the target product and hydrochloride is filtered off and washed with a large amount of water to dissolve and remove only the hydrochloride. Next, the elementary product that has undergone hydrolysis in the partial washing step is vacuum-dried at 100 to 200 ° C. and subjected to ring-closing treatment. The crude product thus obtained is subjected to recrystallization, washing and heating / vacuum drying steps with an appropriate solvent to obtain high purity TABD.

  In this reaction, usable solvents include methyl acetate, ethyl acetate, butyl acetate, tetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, picoline, pyridine, acetone, chloroform, toluene, xylene, dichloromethane, 1 , 2-dichloroethane, N-methyl-2-pyrrolidone, N, N-diethylacetamide, N, N-dimethylacetamide, N, N-dimethylformamide, hexamethylphosphoramide, dimethyl sulfoxide, γ-butyrolactone, 1,3 -Aprotic solvents such as dimethyl-2-imidazolidinone, 1,2-dimethoxyethane-bis (2-methoxyethyl) ether, and phenol, om-cresol, m-cresol, p-cresol, o- Chlorophenol, m-chlorophenol, p Protic solvents such as chloro phenol. These solvents may be used alone or in combination of two or more. Ethyl acetate and tetrahydrofuran are preferably used from the viewpoint of solubility of the reaction reagent and easiness of distillation.

  Although the said esterification reaction is performed at -10-50 degreeC, More preferably, it is performed at 0-30 degreeC. If the reaction temperature is higher than 50 ° C., some side reactions occur, which may reduce the yield, which is not preferable.

  The esterification reaction is performed in a solute concentration range of 5 to 50% by weight. In consideration of control of side reaction and filtration step of precipitation, it is preferably carried out in the range of 10 to 40% by weight.

  The precipitate produced by the esterification reaction contains water-soluble pyridine hydrochloride when pyridine is used as a deoxidizing agent. For example, when tetrahydrofuran is used as a solvent, pyridine hydrochloride hardly dissolves, and the hydrochloride can be separated almost completely only by filtering the reaction solution. Usually, when the solubility of the target product is high, the target product is dissolved in the filtrate, so that the target product with high yield and sufficient purity can be obtained simply by distilling off the solvent from the filtrate and recrystallization from an appropriate solvent. Although it can be obtained, in order to separate and remove trace amounts of chlorine components, the target product is redissolved in chloroform, ethyl acetate, etc., and the organic layer is washed with water using a separatory funnel, or the precipitate is washed thoroughly with water. It is also possible to use a method. The removal of the hydrochloride can be easily judged by the presence or absence of purification of the white precipitate of silver chloride using a 1% silver nitrate aqueous solution as the washing solution. During the washing operation, the ester group-containing tetracarboxylic dianhydride is partially hydrolyzed to be converted into dicarboxylic acid, but is vacuum-dried at 80 to 250 ° C, preferably 120 to 200 ° C. Even if a dicarboxylic acid is produced by partial hydrolysis, it can be easily dehydrated and closed to return to an acid anhydride. A method of treating with an acid anhydride of an organic acid is also applicable. Examples of the acid anhydride of the organic acid that can be used in this case include acetic anhydride, propionic anhydride, maleic anhydride, and phthalic anhydride, and acetic anhydride is preferably used from the viewpoint of easy removal.

<Polymerization of polyimide precursor>
In the polyimide precursor represented by the following formula (1) of the present invention,

  X and Z are selected from the following formulas (2) to (4), and X and Z may be the same or different. If they are the same, control of the manufacturing surface is easier.

  Y in the formula (1) is a tetravalent aromatic group that does not contain fluorine, and is a residue of an aromatic tetracarboxylic dianhydride used in the production. The aromatic tetracarboxylic dianhydride that can be used is not particularly limited except that it does not contain fluorine, but pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyl ether tetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyl sulfone Tetracarboxylic dianhydride, 2,2'-bis (3,4-dicarboxyphenyl) hexafluoropropanoic dianhydride, 2,2'-bis (3,4-dicarboxyphenyl) propanoic dianhydride , Hydroquinone bis (trimellitate anhydride), 1,4,5,8-naphthalene tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride Examples are things. Among them, those having a rigid structure are preferable, and pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride Is particularly preferably used. That is, Y is more preferably a tetravalent aromatic group represented by the following formulas (5) to (7).

  By making the composition of X, Y and Z, the polyimide resin finally obtained has excellent solubility, heat resistance, dimensional stability and transparency.

  R in Formula (1) is any group of a hydrogen atom, a silyl group, and a linear or branched alkyl group having 1 to 12 carbon atoms, and these may be mixed. R does not affect the physical properties of the finally obtained polyimide resin, and is selected from the viewpoint of easy reaction control and ease of separation and purification when imidizing a polyimide precursor to produce a polyimide resin. Usually, all are hydrogen atoms.

  Further, m and n in the formula (1) represent the mole fraction of each structural unit, and satisfy m + n = 1, 0.5 ≦ m ≦ 0.9, 0.5 ≧ n ≧ 0.1. More preferably, 0.6 ≦ m ≦ 0.8 and 0.4 ≧ n ≧ 0.2. If necessary, m and n are copolymerization ratios, which can be adjusted by the charged mole fraction of the two types of tetracarboxylic dianhydrides used in the production. When m is less than 0.5 (n is more than 0.5), the finally obtained polyimide resin has low solubility. When m exceeds 0.9 (n is less than 0.1), the finally obtained polyimide resin has good solubility, but the thermal dimensional stability decreases.

  The manufacturing method of the polyimide precursor represented by Formula (1) of this invention is not specifically limited, A well-known method is applicable. As an example, the manufacturing method of the polyimide precursor represented by Formula (12) is demonstrated.

  First, TFMB, which is a diamine, is dissolved in a polymerization solvent in a polymerization vessel. To this diamine solution, TABD and 2,3,6,7-naphthalenetetracarboxylic dianhydride (hereinafter sometimes referred to as NTCDA) powder are gradually added, and −20 to 100 using a mechanical stirrer. Stir in the range of ° C, preferably in the range of 20-60 ° C for 1-72 hours. Here, m + n = 1, 0.5 ≦ m ≦ 0.9, and 0.5 ≧ n ≧ 0.1 are satisfied, where m is the TABD molar fraction and n is the NTCDA molar fraction. The number of moles of diamine and the number of moles of tetracarboxylic dianhydride (sum of the number of moles of TABD and NTCDA) are charged at substantially equal moles. The total monomer concentration during the polymerization is 5 to 40% by weight, preferably 10 to 30% by weight. By carrying out polymerization in this monomer concentration range, a polyimide precursor solution having a uniform and high degree of polymerization can be obtained. If the polymerization is performed at a concentration lower than the above monomer concentration range, the degree of polymerization of the polyimide precursor is not sufficiently high, and the finally obtained polyimide resin film may be brittle, which is not preferable.

  The polymerization solvent is not particularly limited, but N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, hexamethylphosphoramide, dimethylsulfoxide, γ- Butyrolactone, 1,3-dimethyl-2-imidazolidinone, 1,2-dimethoxyethane-bis (2-methoxyethyl) ether, terahydrofuran, 1,4-dioxane, picoline, pyridine, acetone, chloroform, toluene, Aprotic solvents such as xylene and protic solvents such as phenol, o-cresol, m-cresol, p-cresol, o-chlorophenol, m-chlorophenol, and p-chlorophenol can be used. These solvents may be used alone or in combination of two or more.

<Production method of polyimide resin>
In the polyimide resin represented by the following formula (8) of the present invention,

  X and Z are selected from the formulas (2) to (4), and X and Z may be the same or different. Y is a tetravalent aromatic group not containing fluorine. Y is more preferably a tetravalent aromatic group represented by formulas (5) to (7).

  By making the composition of X, Y and Z, the solubility, heat resistance, dimensional stability and transparency of the polyimide resin are excellent.

  Furthermore, m and n in Formula (8) represent the mole fraction of each structural unit, and satisfy m + n = 1, 0.5 ≦ m ≦ 0.9, 0.5 ≧ n ≧ 0.1. More preferably, 0.6 ≦ m ≦ 0.8 and 0.4 ≧ n ≧ 0.2. When m is less than 0.5 (n is more than 0.5), the solubility of the polyimide resin is lowered. When m exceeds 0.9 (n is less than 0.1), the solubility of the polyimide resin is good, but the thermal dimensional stability decreases.

  The polyimide resin represented by the formula (8) of the present invention can be produced by a dehydration ring-closing reaction (imidation reaction) of the polyimide precursor obtained by the above method. For the imidation reaction, a known method such as thermal imidization or chemical imidization can be used. Especially, the chemical imidation in which the obtained polyimide resin shows more excellent dimensional stability is more preferable.

  For example, in the case of thermal imidization, the polymerization solution of the polyimide precursor is used as it is or after being appropriately diluted with a solvent, and then the varnish can be easily imidized by heating to 150 to 230 ° C. At this time, toluene, xylene or the like may be added in order to azeotropically distill off water or the like which is a by-product of imidization. Further, a base such as γ-picoline can be added as a catalyst. The obtained varnish can be dropped and deposited in a large amount of poor solvent such as water or methanol, and this can be filtered to isolate the polyimide resin as a powder.

  The chemical imidization can also be performed using a dehydrating cyclization agent (chemical imidization agent) composed of an acid anhydride of an organic acid and an organic tertiary amine. For example, by using the polyimide precursor varnish as it is or after appropriately diluting with a solvent, a dehydration cyclization reagent is added thereto and stirred at 0 to 100 ° C., preferably 20 to 60 ° C. for 0.5 to 48 hours. It can be easily imidized.

  The acid anhydride of the organic acid used in that case is not particularly limited, and acetic anhydride, propionic anhydride, maleic anhydride, phthalic anhydride, etc. can be used, but the cost and ease of post-treatment are not limited. In view of the above, acetic anhydride is preferably used. The organic tertiary amine is not particularly limited, and pyridine, 1,5-dimethylpyridine, β-picoline, γ-picoline, lutidine, isoquinoline, triethylamine, N, N-dimethylaniline and the like can be used.

  In the chemical imidation reaction, the amount of acid anhydride used in the dehydration cyclization reagent is preferably in the range of 1 to 10 times the theoretical dehydration amount of the polyimide precursor, and the basicity in the dehydration cyclization reagent is The amount of catalyst used is preferably in the range of 0.1 to 2 moles relative to the acid anhydride. If the chemical imidization is carried out outside these ranges, the imidation reaction may not be completed, or the imidization may not be completed in the reaction solution and the imidization may be insufficient.

  After the imidization is completed, the reaction solution is dropped into a large amount of poor solvent to precipitate and wash the polyimide resin to remove the reaction solvent and, in the case of chemical imidization, the excess chemical imidizing agent, and then dried under reduced pressure. A polyimide resin powder can be obtained. The poor solvent that can be used is not particularly limited as long as it does not dissolve the polyimide resin, but water, methanol, ethanol, from the viewpoint of affinity with the reaction solvent and chemical imidizing agent and ease of removal by drying, n-propanol, isopropanol and the like are preferably used.

<Coating solution>
The coating resin solution of the present invention contains the polyimide resin obtained by the above method and an organic solvent, and the solid content concentration of the polyimide resin is 1% by weight or more. If it is less than 1% by weight, it is difficult to form a uniform coating film by coating. The preferable range of the solid content concentration varies depending on the film thickness to be formed, the viscosity range required depending on the coating method and the specifications of the coating machine, and the like. Moreover, the solubility to the solvent to be used becomes an upper limit of solid content concentration. For this reason, although the preferable range of solid content concentration cannot be decided unconditionally, 3% by weight to 20% by weight is often preferable.

  The weight average molecular weight of the contained polyimide resin is not particularly limited, but is preferably 5,000 to 2,000,000, and preferably 10,000 to 1,000,000. More preferably, it is 50,000-500,000. If the weight average molecular weight is 5,000 or less, sufficient strength cannot be obtained when a coating film is used, and dimensional stability tends to be reduced, so that sufficient dimensional stability may not be obtained. is there. On the other hand, if it exceeds 2,000,000, the solution viscosity becomes too high and the handling tends to be difficult. In addition, the said weight average molecular weight means the value of polyethyleneglycol conversion by size exclusion chromatography (SEC).

  The organic solvent used in the present invention is not particularly limited as long as it dissolves the polyimide resin of the present invention. For example, amide solvents such as N, N-dimethylformamide and N, N-dimethylacetamide, methyl ethyl ketone, methyl isobutyl Ketone solvents such as ketone, cyclohexanone and cyclopentanone, ether solvents such as 1,3-dioxolane and 1,4-dioxane, pyrrolidone solvents such as N-methyl-2-pyrrolidone, methyl diglyme and ethyl diglyme And glycol ether solvents such as methyltriglyme, ester solvents such as methyl acetate, ethyl acetate and isopropyl acetate, halogen solvents such as chloroform and dichloromethane, and aromatic hydrocarbon solvents such as toluene and xylene. These may be used alone or in combination of two or more. From the viewpoint of solubility, it is preferable to select at least one from an amide solvent, a ketone solvent, an ether solvent, a pyrrolidone solvent, and a glycol ether solvent. In consideration of the ease of solvent removal in drying after coating in addition to solubility, it is preferable to use an amide solvent, a ketone solvent, or an ether solvent alone or in admixture of two or more. Moreover, if it is a range which melt | dissolves a polyimide resin, you may use the poor solvent which cannot melt | dissolve a polyimide resin timely as a mixed solvent.

  In order to impart processing characteristics and various functionalities to the coating resin solution of the present invention as long as the properties of the finally obtained polyimide resin coating film and coating film are not impaired, various other organic or inorganic low You may mix | blend a molecule | numerator or a high molecular compound. Examples include antifoaming agents, leveling agents, surfactants, antistatic agents, dyes, pigments, plasticizers, fine particles, and sensitizers.

  The method for producing a coating film from the coating resin solution of the present invention is not particularly limited, and can be easily produced by a known method. For example, a coating film can be formed by applying and drying the coating resin solution of the present invention on a predetermined substrate. As the substrate to be applied, glass, SUS, silicon wafer, plastic film or the like is used, but is not limited thereto. In particular, when applied as a substrate material for an electronic device, the substrate to be applied is preferably a glass or silicon wafer from the viewpoint that existing equipment can be used.

  As mentioned above, when using the coating film of this invention as an electronic device material instead of glass, it is preferable to apply | coat and dry on a glass substrate, and to manufacture a coating film. The coating film may be peeled off from the glass and used as a coating film for a substrate, or may be peeled off from the glass after forming an electronic device in the form of a glass / coating film laminate. The coating film of the present invention exhibits a low coefficient of linear thermal expansion close to that of glass and has excellent dimensional stability that thermal deformation such as warpage is very small, high heat resistance that can withstand a process temperature of 300 ° C. or higher, and 85% Since it exhibits the above total light transmittance, the transmittance at 400 nm is 65% or less, and it has little transparency, and has high transparency, fields and products in which these characteristics are effective, for example, electronic device materials, It can be suitably used for a TFT substrate and a flexible display substrate. Furthermore, it can be used as an alternative material for the part where glass is used.

  Hereinafter, the present invention will be specifically described by way of examples. The physical property values in the following examples were measured by the following methods.

<Infrared absorption spectrum>
Using a Fourier transform infrared spectrophotometer (FT-IR5300 manufactured by JASCO Corporation), an infrared absorption (FT-IR) spectrum of tetracarboxylic dianhydride was measured by the KBr method. In order to confirm the completion of imidization, infrared absorption spectra of the polyimide resin powder and the thin film (about 5 μm thick) were measured.

^<1 H-NMR spectrum>
A ¹ H-NMR spectrum of tetracarboxylic dianhydride was measured in deuterated dimethyl sulfoxide using a JEOL NMR spectrophotometer (ECP400).

<Differential scanning calorimetry (melting point and melting curve)>
The melting point and melting curve of tetracarboxylic dianhydride were measured using a differential scanning calorimeter (DSC3100) manufactured by Bruker Ax in a nitrogen atmosphere at a heating rate of 5 ° C./min.

<Intrinsic viscosity>
A 0.5 wt% solution of the polyimide precursor and polyimide resin was measured at 30 ° C. using an Ostwald viscometer.

<Linear thermal expansion coefficient: CTE>
Using a thermomechanical analyzer (TMA4000) manufactured by Bruker AXS, a constant load (0.5 g per 1 μm of film thickness) was applied to the test piece by thermomechanical analysis, and the test piece at a heating rate of 5 ° C./min. From the elongation value, the linear thermal expansion coefficient of the polyimide film was determined as an average value in the range of 100 to 200 ° C.

<Glass transition temperature: Tg>
By thermomechanical analysis using a Bruker AXS thermomechanical analyzer (TMA4000), a constant load (0.5 g per 1 μm of film thickness) was applied to the test piece, and the elongation of the test piece at a heating rate of 5 ° C./min. The value was measured as a function of temperature, and in the elongation-temperature curve (TMA curve), the temperature at which the test piece started to grow rapidly was determined from the intersection of the two tangents, and the glass transition temperature (Tg) of the polyimide film was determined.

<5% weight loss temperature: T _d ⁵ >
When the initial weight of the polyimide film is reduced by 5% in a temperature rising process at a heating rate of 10 ° C./min in nitrogen or air using a thermogravimetric analyzer (TG-DTA2000) manufactured by Bruker AXS The temperature of was measured.

<Cutoff wavelength (transparency)>
Using a UV-visible spectrophotometer (V-530) manufactured by JASCO Corporation, the visible / ultraviolet transmittance from 200 nm to 900 nm was measured. The wavelength (cutoff wavelength) at which the transmittance was 0.5% or less was used as an index of the transparency of the film.

<Light transmittance (transparency)>
The light transmittance at 400 nm was measured using an ultraviolet-visible spectrophotometer (V-530) manufactured by JASCO Corporation.

<Birefringence: Δn and its wavelength dispersion>
Using an Abbe refractometer with a polarizer (Abbe 4T) manufactured by Atago Co., Ltd., the refractive index at a certain wavelength in the direction parallel to the polyimide film (n _in ) and the direction perpendicular to the polyimide film (n _out ) (the wavelength 589 nm of the sodium lamp) The birefringence (Δn = n _in −n _out ) was determined from the difference between these refractive indexes.

<Elastic modulus, elongation at break, strength at break>
Using an A & D tensile tester (Tensilon UTM-II), a tensile test (stretching speed: 8 mm / min) was performed on a polyimide test piece (3 mm × 30 mm × 20 μm thickness), and the elastic modulus and fracture Elongation and breaking strength were determined.

<Synthesis of tetracarboxylic dianhydride>
Tetracarboxylic dianhydride (TABD) represented by the following formula (10) is

  It was synthesized from a diol (DHTFMB) represented by the formula (11) and trimellitic anhydride chloride.

First, DHTFMB was synthesized as follows. 2.20 g (10 mmol) of 2,2′-bis (trifluoromethyl) benzidine (TFMB) was placed in a 500 mL eggplant-shaped flask, and 100 mL of water was added and stirred to suspend. To this, 24 mL (100 mmol) of concentrated hydrochloric acid was added and stirred to give A solution. A 50 mL eggplant-shaped flask was charged with 1.38 g (30 mmol) of sodium nitrite, and 8 mL of water was added to dissolve it to prepare a solution B. The solution B was quickly added to the solution A cooled in an ice bath with a syringe while stirring. After stirring for 2 hours, 0.1 g of urea was added to decompose unreacted sodium nitrite, and the mixture was further stirred for 30 minutes to obtain solution C. Next, 7 mL of phosphoric acid and 600 mL of water were placed in a 1 L three-necked flask, and a reflux tube was attached and heated to 120 ° C. in a nitrogen atmosphere. The solution C was slowly added to this aqueous solution, and hydrolyzed by refluxing at 120 ° C. for 1 hour. After cooling to room temperature, the product was extracted with diethyl ether, and the solvent was distilled off with an evaporator to obtain an orange oily product. Water and activated carbon were added thereto for decolorization, followed by hot filtration, and water was removed by an evaporator to obtain a pale yellow solid. Finally, recrystallization and vacuum drying were performed with cyclohexane to obtain white crystals with a yield of 43%. The product obtained from the FT-IR spectrum and the ¹ H-NMR spectrum was confirmed to be the target diol represented by the formula (2). The analysis results are shown below.

FT-IR: 3316 cm ⁻¹ (phenolic OH group), 1593 cm ⁻¹ (biphenylene group)
¹ H-NMR: δ 10.2 ppm (OH, 2H), δ 7.0 to 7.1 ppm (C _arom H on biphenylene group, 6H)
DSC: melting point 151.0 ° C.
Next, tetracarboxylic dianhydride (TABD) represented by the formula (10) was synthesized from trimellitic anhydride chloride and DHTFMB obtained as described above as follows. First, 4.21 g (20 mmol) of trimellitic chloride was placed in an eggplant-shaped flask, and 18.9 mL of dehydrated tetrahydrofuran (THF) was added and dissolved, followed by septum sealing to prepare Solution A. Further, in another flask, 3.22 g (10 mmol) of DHTFMB was dissolved in 14.5 mL of THF, 2.42 mL (30 mmol) of pyridine was added thereto and dissolved, and a septum was sealed to prepare Solution B.

  Solution B was added dropwise with stirring to solution A cooled in an ice bath, and the mixture was stirred for 3 hours, and then stirred at room temperature for 12 hours. Precipitated white pyridine hydrochloride was filtered off, the solvent was distilled off from the filtrate with an evaporator, and the precipitate was washed repeatedly with water to remove pyridine. The product was vacuum-dried at 80 ° C. for 12 hours, an appropriate amount of acetic anhydride was further added, and the mixture was heated at 120 ° C. for 3 hours to completely close the partially opened acid anhydride group. Toluene was added thereto to remove acetic anhydride azeotropically, and the resulting white solid was vacuum dried at 120 ° C. for 24 hours to obtain a crude product in a yield of 42%. Finally, it was recrystallized with toluene (recrystallization yield: 92%) and dried in vacuo at 120 ° C. for 24 hours to obtain white crystals. The product obtained from the FT-IR spectrum is the target tetracarboxylic dianhydride represented by the formula (10), and the endothermic peak of melting by differential thermal analysis was very sharp. High purity was confirmed. The analysis results are shown below.

FT-IR: 1856 cm ⁻¹ , 1784 cm ⁻¹ (acid anhydride group C═O stretching vibration), 1750 cm ⁻¹ (ester group C═O stretching vibration)
DSC: melting point 245.3 ° C.

Example 1
<Polymerization of polyimide precursor, imidization and evaluation of polyimide film characteristics>
N, N-dimethylacetamide (hereinafter sometimes referred to as DMAc) in which 10 mmol of 2,2′-bis (trifluoromethyl) benzidine (TFMB) was placed in a well-dried closed reaction vessel equipped with a stirrer and sufficiently dehydrated with molecular sieves 4A. In this solution, 7 mmol of tetracarboxylic dianhydride powder (TABD) represented by the formula (10) and 2,3,6,7-naphthalene tetracarboxylic dianhydride (NTCDA, JFE Chemical) 3 mmol) (solute concentration: 30% by weight). When stirring was continued at room temperature, the solution viscosity increased and it became difficult to stir. Therefore, the solution was appropriately diluted with the same solvent to 23% by weight and stirred for a total of 74 hours to obtain a uniform and viscous polyimide precursor solution. This polyimide precursor solution did not precipitate or gel at all even when allowed to stand at room temperature and −20 ° C. for one month, and showed high solution storage stability. The intrinsic viscosity of the polyimide precursor measured with an Ostwald viscometer in DMAc at a concentration of 0.5% by weight at 30 ° C. was 1.62 dL / g, which was a high polymer.

  An excess amount of acetic anhydride / pyridine (volume ratio 7/3) was added dropwise to the polyimide precursor solution while stirring, and the mixture was stirred at room temperature for 24 hours for chemical imidization. At this time, no non-uniformity such as gelation of the reaction solution and precipitation of the precipitate was observed. After the chemical imidization was completed, the reaction solution was dropped into a large amount of methanol to precipitate and filter the polyimide resin, washed thoroughly with methanol, and then vacuum dried at 100 ° C. to obtain a polyimide resin powder. When the infrared absorption spectrum was measured, it was confirmed that the chemical imidization was almost completed. The intrinsic viscosity of the obtained polyimide resin was 2.42 dL / g. The chemical structure of the obtained polyimide resin is shown in Formula (13). In formula (13), m is 0.7 and n is 0.3.

  The polyimide resin powder was dissolved in DMAc to obtain a uniform varnish of 11.6% by weight. This was coated on a glass substrate and vacuum dried at 150 ° C. for 2 hours and then at 180 ° C. for 1 hour to prepare a polyimide film. The obtained polyimide film having a film thickness of 14 μm usually maintained high transparency despite the combined use of NTCDA, which is disadvantageous in transparency, and was hardly visually colored. Furthermore, this system had a very low coefficient of linear thermal expansion (13.1 ppm / K). Other physical properties are also shown in Table 1.

(Example 2)
3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (hereinafter sometimes referred to as s-BPDA) is used instead of NTCDA, and the copolymer composition is changed to TABD: s-BPDA = 60: 40 Except for the above, the polyimide precursor was polymerized in the same manner as described in Example 1, and chemical film formation was performed by chemical imidization and film formation. In this system, high transparency was maintained even though s-BPDA, which is a general-purpose tetracarboxylic dianhydride which is disadvantageous in transparency, was used in combination. It also had a relatively low coefficient of linear thermal expansion. The physical property values are shown in Table 1.

(Comparative Example 1)
Among the tetracarboxylic dianhydride components, NTCDA and s-BPDA were not used as the copolymerization component, and the polyimide precursor was polymerized and chemically imidized according to the method described in Example 1 except that TABD was used alone. did. The obtained polyimide resin powder was dissolved in cyclopentanone to obtain a uniform varnish of 15% by weight. This was cast into a film according to the method described in Example 1, and the film physical properties were evaluated. The obtained polyimide film showed high transparency, but low thermal expansion characteristics were not obtained. Table 1 shows the film properties.

(Comparative Example 2)
The polyimide precursor was polymerized according to the method described in Example 1 except that NTBDA was used alone, without using TABD as a copolymerization component of the tetracarboxylic dianhydride component, and an intrinsic viscosity of 2.15 dL / g. A uniform varnish (15% by weight) was obtained. When chemical imidization was performed, a mixed solution of acetic anhydride and pyridine was added thereto. As a result, the solution became non-uniform and it was difficult to obtain a uniform polyimide varnish. This is because the solvent solubility of this polyimide resin is low. Therefore, instead of chemical imidization, a polyimide precursor varnish was applied on a glass substrate according to a conventional method, dried in a hot air dryer at 60 ° C. for 2 hours, vacuumed at 200 ° C. for 1 hour, and then vacuumed at 330 ° C. for 1 hour. Thermal imidization was performed to produce a polyimide film. In this system, the polyimide resin powder and film showed almost no solvent solubility, but a very low coefficient of linear thermal expansion. On the other hand, the light transmittance at 400 nm was considerably lower than the results of Examples 1 and 2, and the transparency was poor. Table 1 shows the film properties.

(Comparative Example 3)
Among the tetracarboxylic dianhydride components, the polyimide precursor was polymerized according to the method described in Example 1 except that TABD was not used as a copolymerization component and s-BPDA was used alone, and an intrinsic viscosity of 1. A uniform varnish (15% by weight) of 74 dL / g was obtained. Since the polyimide resin powder obtained by chemical imidization did not exhibit sufficient solubility in general-purpose organic solvents, it was difficult to obtain a uniform and stable polyimide varnish. Therefore, as described in Comparative Example 2, the polyimide precursor varnish was applied to a glass substrate and dried, and then heat imidized in vacuum at 250 ° C. for 1 hour and then at 300 ° C. for 1 hour to prepare a polyimide film. This system did not exhibit low thermal expansion characteristics, and the light transmittance at 400 nm was considerably lower than the results of Examples 1 and 2, and the transparency was poor. Table 1 shows the film properties.

Claims (10)

The polyimide precursor containing the repeating unit represented by following formula (1).

(In the formula (1), X and Z represent a divalent fluorine-containing aromatic group selected from the following formulas (2) to (4), and X and Z may be the same or different. Represents a tetravalent aromatic group containing no fluorine, R represents a hydrogen atom, a silyl group, or a linear or branched alkyl group having 1 to 12 carbon atoms, M and n represent the molar fraction of each structural unit, and m + n = 1, 0.5 ≦ m ≦ 0.9, and 0.5 ≧ n ≧ 0.1.

2. The polyimide precursor according to claim 1, wherein Y in the formula (1) is a tetravalent aromatic group selected from the following formulas (5) to (7).

Polyimide resin containing the repeating unit represented by following formula (8).

(In the formula (8), X and Z represent a divalent fluorine-containing aromatic group selected from the following formulas (2) to (4), and X and Z may be the same or different. Represents a tetravalent aromatic group containing no fluorine, R represents a hydrogen atom, a silyl group, or a linear or branched alkyl group having 1 to 12 carbon atoms, M and n represent the molar fraction of each structural unit, and m + n = 1, 0.5 ≦ m ≦ 0.9, and 0.5 ≧ n ≧ 0.1.

In said Formula (8), Y is a tetravalent aromatic group chosen from following formula (5)-(7), The polyimide resin of Claim 3 characterized by the above-mentioned.

5. The polyimide resin according to claim 3, wherein the polyimide resin is chemically imidized. A coating resin solution comprising the polyimide resin according to any one of claims 3 to 5 and an organic solvent, wherein the polyimide resin has a solid content concentration of 1% by weight or more. A coating film formed by applying and drying the coating resin solution according to claim 6 on a substrate. A TFT substrate comprising the coating film according to claim 7. A flexible display substrate comprising the coating film according to claim 7. An electronic device material comprising the coating film according to claim 7.