JP2020117615A - Polyimide acid composition, method for producing polyimide acid composition and method for producing polyimide - Google Patents

Abstract

To provide a polyimide acid composition capable of obtaining a polyimide film layer useful as a backplane substrate of a flexible display required for forming a fine TFT.SOLUTION: There is provided a high-quality polyimide film layer obtained by a step of applying and drying a polyamic acid composition which comprises at least a polyamic acid obtained from an aromatic tetracarboxylic acid and a diamine and an organic solvent, in which the content of one or more compounds selected from a fatty acid having 8 to 30 carbon atoms, a fatty acid salt having 8 to 30 carbon atoms, a fatty acid amide having 8 to 30 carbon atoms and a fatty acid derivative having 8 to 30 carbon atoms is 0.05 mass% or less with respect to the polyamide acid, onto a glass substrate, followed by performing heat treatment at 350°C or more and 550°C or less, wherein the number of fine defects which can be observed only with a differential interference microscope is 2 pieces/square cm or less.SELECTED DRAWING: None

Description

The present invention has few defects and relates to a polyamic acid composition for obtaining a polyimide film having a smooth surface suitable for forming a fine thin film element, and further, a polyamide preferably used for producing a flexible electronic device substrate. The present invention relates to an acid composition and a method for producing a polyimide.

The present inventors have earnestly studied to provide a polyimide film that can be suitably used as a substrate for a flexible electronic device, and as shown in Patent Documents 1 to 4, for example, have a novel chemical structure having a benzoxazole skeleton. We have developed a polyimide film that has Such a polyimide film exhibits an extremely low coefficient of linear expansion, high heat resistance, and low heat shrinkage, and can be suitably used as a substrate for fine semiconductor devices and the like. For example, as shown in Patent Documents 5 to 7, it can be applied as a substrate for a semiconductor device or a substrate for a display element. Furthermore, as shown in Patent Document 8, the present inventors have developed a process of temporarily supporting a polyimide film by bonding it to an inorganic substrate such as glass, forming a fine device on the film surface, and then peeling it from the inorganic substrate. It was

Japanese Patent No. 3858892 Japanese Patent No. 3937235 Japanese Patent No. 3953057 Japanese Patent No. 3956940 Japanese Patent No. 3761030 Japanese Patent No. 3738870 Japanese Patent No. 4131412 Japanese Patent No. 5796292

In the process of promoting the above-mentioned development, the present inventors have encountered a phenomenon in which unevenness defects having a very slight and gentle curvature occur on the film surface. This kind of defect is difficult to find in the enlarged observation of the outermost surface with a normal optical microscope because the unevenness is gentle, and can be observed with a differential interference microscope capable of obtaining a strong contrast. As a result of observing the inside of the film at the defective portion whose position is specified with a differential interference microscope in detail, the present inventors have found that micro bubbles are generated inside the film. The present inventors tried to analyze the micro-bubble portion generated inside the polyimide film, and its periphery in detail, but it is not possible to find a trace that is likely to be the source of the micro-bubbles, and the occurrence of such defects is extremely high. It was incomprehensible.

As a result of intensive investigations by the inventors to solve the above problems, a polyamic acid composition which is a precursor for producing a polyimide film, and a raw material monomer and a solvent for producing the polyamic acid composition , Found out the cause of micro bubbles and found a method to eliminate the cause.

That is, the present invention has the following configurations.
[1] A composition containing at least a polyamic acid obtained from an aromatic tetracarboxylic acid and a diamine and an organic solvent, wherein the polyamic acid has a fatty acid having 8 to 30 carbon atoms, a fatty acid salt having 8 to 30 carbon atoms, and carbon. A polyamic acid composition, characterized in that the sum of fatty acid amides having 8 to 30 carbon atoms and fatty acid derivatives having 8 to 30 carbon atoms is 0.05% by mass or less.
[2] At least a part of the inner wall is housed in a container made of a polymer material having a glass transition temperature of 40° C. or lower,
log ₁₀ (day)≦2300×(1/T)−5.3
(Here, day is the storage time (unit: day) and T is the storage temperature (unit: K).)
The method for producing a polyamic acid composition according to [1], characterized in that an aromatic tetracarboxylic acid after storage at a storage temperature and storage time satisfying the following relational expression is used as a polymerization raw material.
[3] At least a part of the inner wall is housed in a container made of a polymer material having a glass transition temperature of 40° C. or lower,
log ₁₀ (day)≦2300×(1/T)−5.3
(Here, day is the storage time (unit: day) and T is the storage temperature (unit: K).)
The method for producing a polyamic acid composition according to [1], wherein the diamine after being stored within the range of storage temperature and storage time satisfying the following relational expression is used as a polymerization raw material.
[4] At least a part of the inner wall is housed in a container made of a polymer material having a glass transition temperature of 40° C. or lower,
log ₁₀ (day)≦2300×(1/T)−5.3
(Here, day is the storage time (unit: day) and T is the storage temperature (unit: K).)
The method for producing a polyamic acid composition according to [1], characterized in that an organic solvent after storage at a storage temperature and storage time satisfying the following relational expression is used as a polymerization solvent.
[5] At least a part of the inner wall is housed in a container made of a polymer material having a glass transition temperature of 40° C. or lower,
log ₁₀ (day)≦2300×(1/T)−5.3
(Here, day is the storage time (unit: day) and T is the storage temperature (unit: K).)
The method for producing a polyamic acid composition according to [1], characterized in that a solvent dispersion of inorganic particles after storage at a storage temperature and storage time satisfying the relation ..
[6] The polymer material forming a part of the inner wall of the container is a fatty acid having 8 to 30 carbon atoms, a fatty acid salt having 8 to 30 carbon atoms, a fatty acid amide having 8 to 30 carbon atoms, and 8 to 30 carbon atoms. 0.05% to 5% by mass of at least one compound selected from the fatty acid derivatives described in [2] to [5]. Method.
[7] A method for producing a polyimide, which comprises heat-treating the polyamic acid composition according to the above [1] at a temperature of at least 350°C to 550°C.

Furthermore, the present invention preferably has the following configurations.
[8] The polyimide film obtained by the manufacturing method of [7], wherein the number of defects having a diameter of 2 μm or more observed by a differential interference microscope is 2/cm 2 or less.
[9] The defect portion having a diameter of 2 μm or more observed by the differential interference microscope is a convex defect derived from a cavity having an outer diameter size in the film plane direction of 0.5 μm or more and 5 μm or less existing inside the film at the same plane coordinate position. The polyimide film according to [8], which is
[10] The polyimide film according to [8] or [9], which has an outer diameter size of 0.1 μm or more and 3 μm or less as observed by observing the cross section of the cavity in the film thickness direction.
[11] A composition containing at least a polyamic acid obtained from an aromatic tetracarboxylic acid and a diamine, and an organic solvent, wherein the polyamic acid has a fatty acid having 8 to 30 carbon atoms, a fatty acid salt having 8 to 30 carbon atoms, and carbon. A polyamic acid composition in which the content of at least one compound selected from fatty acid amides having 8 to 30 carbon atoms and fatty acid derivatives having 8 to 30 carbon atoms is 0.05% by mass or less,
A step of forming into a film shape,
The method for producing a polyimide film according to any one of [8] to [11], which includes at least a step of performing heat treatment at a temperature of 350° C. or higher and 550° C. or lower.

The polyamic acid composition of the present invention is a polyimide precursor and is used as an intermediate material for producing a polyimide film. Furthermore, the polyamic acid composition of the present invention is applied to a smooth substrate such as a glass substrate, dried and then heat-treated to obtain a polyimide layer (finally peeling from the substrate to form a polyimide film). Used as a so-called "varnish". A laminate of glass and a polyimide layer obtained through such steps is used to form a flexible device by peeling from a substrate after forming an electronic device such as a finely processed TFT on the polyimide layer. Used. A typical flexible device is the backplane of a flexible display.
First, the drawback handled by the present invention is a drawback found when the surface of a polyimide film is observed with a differential interference microscope. A differential interference microscope is a type of phase-contrast microscope that superimposes observation lights with different phase differences and uses the interference of light caused by the difference in the refractive index of an object to be observed and fine unevenness to observe. .. By using a differential interference microscope, it is possible to observe a transparent internal structure of an object to be observed, an extremely gentle step or unevenness with high contrast.
As described above, the inventors of the present invention have confirmed that extremely small microbubbles are present inside the film at the location corresponding to the drawback handled by the present application, and the microbubbles inside the film are extremely gentle on the film surface. It is believed that the formation of unevenness having a step causes defects.

The present inventors have selected, in the polyamic acid composition, at least a fatty acid having 8 to 30 carbon atoms, a fatty acid salt having 8 to 30 carbon atoms, a fatty acid amide having 8 to 30 carbon atoms, and a fatty acid derivative having 8 to 30 carbon atoms. One or more compounds (hereinafter referred to as causative compounds) according to the present invention have been found to generate micro bubbles when detected.
Furthermore, as a result of investigating the origin of the causative compound that causes the microbubbles, tetracarboxylic acid anhydride, which is a raw material of the polyamic acid composition, a diamine, a material that is mainly used for the inner wall of the container that contains the solvent and the like. It became clear that it was caused by. That is, the causative compound is the material of the plastic container, the inner layer material of the metal can, or the material inside the storage bag, that is, the solid lubricant or modifier added to the sealant resin, the plasticizer, the stabilizer, etc. It was an additive or an oligomer component. The material of the inner wall of the container and the sealant resin are polymer materials having a relatively low glass transition temperature. For such a relatively low molecular weight polymer material, the additives as described above are used for stably supplying the product. Further, if the oligomer component is a polymer material, it is difficult to stochastically reduce it to zero.
However, as a result of intensive studies, the present inventors have found that when the polymer material used for the inner wall of the container has a glass transition temperature of 40° C. or lower, the safety temperature can be properly controlled even when the polymer material is stored in such a container. It was found that, if this is the case, the contamination of the causative compound can be kept to the minimum necessary.
That is, a polyamic acid composition that is a precursor of a polyimide film, a monomer that is a raw material thereof, a solvent, or the like is stored in a container whose inner wall is coated with a polymer material having a glass transition temperature of 40°C or less, and 40°C or less. It is possible to suppress the amount of the causative compound mixed into the polyamic acid to the amount below that the microbubbles become visible by storing at the temperature of

The unevenness of the surface, which is difficult to find without such a differential interference microscope, has not been a particular problem in general flexible printed circuit boards, COF, TAB, and the like. However, in the case of TFT processing, which requires a very fine pattern processing by a photolithography method, as represented by a backplane of a flexible display, the accuracy of pattern formation by exposure is reduced even if there is a submicron order step. Therefore, it is very important to reduce such defects.

FIG. 1 is a graph showing the results of the storage experiment of the present invention.

The polyimide of the present invention is a multimer having an imide bond. Generally, polyimide is obtained as a condensate of tetracarboxylic dianhydride and diamine. As a general method for producing a polyimide, an organic solvent solution of polyamic acid (polyimide precursor) obtained by reacting tetracarboxylic dianhydride and diamine in a solvent (also referred to as polyamic acid composition) is used as a support. There is known a method in which a precursor film is formed by coating and drying it on a substrate, and is further converted into a polyimide by causing an imidization reaction by heating or the action of a catalyst. When forming a film of a polyimide, a method of peeling the precursor film from the support and imidizing is generally used. In addition, a method of imidizing without peeling is also known for the purpose of coating the support. The method of applying a precursor solution on a support such as a glass substrate and drying it, and imidizing it on the support is being studied for practical use in applications where a polyimide film is used as a substrate of a flexible device.

As the tetracarboxylic dianhydride of the present invention, preferably, an aromatic tetracarboxylic dianhydride and an alicyclic tetracarboxylic dianhydride can be used. Aromatic tetracarboxylic dianhydrides are preferable from the viewpoint of heat resistance, and alicyclic tetracarboxylic dianhydrides are preferable from the viewpoint of light transmittance. The tetracarboxylic dianhydrides may be used alone or in combination of two or more.

Examples of the aromatic tetracarboxylic acid of the present invention include pyromellitic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 4,4′-oxydiphthalic acid dianhydride, 3,3 ',4,4'-Benzophenonetetracarboxylic acid dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic acid dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy) ) Phenyl]propanoic anhydride and the like. The use of pyromellitic dianhydride is preferred in the present invention.

Examples of the alicyclic tetracarboxylic acids of the present invention include cyclobutanetetracarboxylic acid, 1,2,4,5-cyclohexanetetracarboxylic acid, 3,3′,4,4′-bicyclohexyltetracarboxylic acid and the like. Included are cyclic tetracarboxylic acids and their acid anhydrides. Among these, a dianhydride having two anhydride structures (for example, cyclobutanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 3,3′,4,4 '-Bicyclohexyl tetracarboxylic acid dianhydride and the like) are preferable. The alicyclic tetracarboxylic acids may be used alone or in combination of two or more.
When importance is attached to transparency, the alicyclic tetracarboxylic acids are, for example, preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more of the total tetracarboxylic acids.

The diamines of the present invention are not particularly limited, and aromatic diamines, aliphatic diamines, alicyclic diamines and the like usually used in polyimide synthesis can be used. From the viewpoint of heat resistance, aromatic diamines are preferable, and among the aromatic diamines, aromatic diamines having a benzoxazole structure can be used. The use of aromatic diamines having a benzoxazole structure makes it possible to exhibit high heat resistance, high elastic modulus, low heat shrinkability, and low linear expansion coefficient. The diamines may be used alone or in combination of two or more.

Among the diamines of the present invention, examples of aromatic diamines include 2,2′-dimethyl-4,4′-diaminobiphenyl and 1,4-bis[2-(4-aminophenyl)-2-propyl. ] Benzene (bisaniline), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene, 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl, 4,4'-bis(4 -Aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[ 4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]-1,1 , 1,3,3,3-hexafluoropropane, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, m-aminobenzylamine, p-aminobenzylamine, 3,3′-diaminodiphenyl ether, 3, 4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfoxide, 3,4'-diaminodiphenyl sulfoxide, 4,4'-diaminodiphenyl sulfoxide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzophenone , 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, bis[4-(4-aminophenoxy)phenyl]methane, 1,1-bis[4-(4- Aminophenoxy)phenyl]ethane, 1,2-bis[4-(4-aminophenoxy)phenyl]ethane, 1,1-bis[4-(4-aminophenoxy)phenyl]propane, 1,2-bis[4 -(4-aminophenoxy)phenyl]propane, 1,3-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,1 -Bis[4-(4-aminophenoxy)phenyl]butane, 1,3-bis[4-(4-aminophenoxy)phenyl Phenyl]butane, 1,4-bis[4-(4-aminophenoxy)phenyl]butane, 2,2-bis[4-(4-aminophenoxy)phenyl]butane, 2,3-bis[4-(4 -Aminophenoxy)phenyl]butane, 2-[4-(4-aminophenoxy)phenyl]-2-[4-(4-aminophenoxy)-3-methylphenyl]propane, 2,2-bis[4-( 4-aminophenoxy)-3-methylphenyl]propane, 2-[4-(4-aminophenoxy)phenyl]-2-[4-(4-aminophenoxy)-3,5-dimethylphenyl]propane, 2, 2-bis[4-(4-aminophenoxy)-3,5-dimethylphenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3 -Hexafluoropropane, 1,4-bis(3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 4,4'-bis (4-aminophenoxy)biphenyl, bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfoxide, Bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 1,3-bis[4- (4-Aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(3-aminophenoxy)benzoyl]benzene, 4,4′ -Bis[(3-aminophenoxy)benzoyl]benzene, 1,1-bis[4-(3-aminophenoxy)phenyl]propane, 1,3-bis[4-(3-aminophenoxy)phenyl]propane, 3 ,4'-diaminodiphenyl sulfide, 2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, bis[4-(3-aminophenoxy) )Phenyl]methane, 1,1-bis[4-(3-aminophenoxy)phenyl]ethane, 1,2-bis[4-(3-aminophenoxy)phenyl]ethane, bis[4-(3-aminophenoxy) )Phenyl]sulfoxide, 4,4'-bis[3-(4-aminophenoxy)benzoi Di]phenyl ether, 4,4′-bis[3-(3-aminophenoxy)benzoyl]diphenyl ether, 4,4′-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4, 4′-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenyl sulfone, bis[4-{4-(4-aminophenoxy)phenoxy}phenyl] sulfone, 1,4-bis[4 -(4-Aminophenoxy)phenoxy-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)phenoxy-α,α-dimethylbenzyl]benzene, 1,3-bis[4 -(4-Amino-6-trifluoromethylphenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-fluorophenoxy)-α,α-dimethylbenzyl]benzene 1,3-bis[4-(4-amino-6-methylphenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-amino-6-cyanophenoxy)-α, α-Dimethylbenzyl]benzene, 3,3′-diamino-4,4′-diphenoxybenzophenone, 4,4′-diamino-5,5′-phenoxybenzophenone, 3,4′-diamino-4,5′- Diphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 4,4'-diamino-5-phenoxybenzophenone, 3,4'-diamino-4-phenoxybenzophenone, 3,4'-diamino-5'- Phenoxybenzophenone, 3,3'-diamino-4,4'-dibiphenoxybenzophenone, 4,4'-diamino-5,5'-dibiphenoxybenzophenone, 3,4'-diamino-4,5'-dibiphenoxybenzophenone 3,3′-diamino-4-biphenoxybenzophenone, 4,4′-diamino-5-biphenoxybenzophenone, 3,4′-diamino-4-biphenoxybenzophenone, 3,4′-diamino-5′- Biphenoxybenzophenone, 1,3-bis(3-amino-4-phenoxybenzoyl)benzene, 1,4-bis(3-amino-4-phenoxybenzoyl)benzene, 1,3-bis(4-amino-5-) Phenoxybenzoyl)benzene, 1,4-bis(4-amino-5-phenoxybenzoyl)benzene, 1,3-bis(3-amino-4-biphenoxybenzoyl)benzene, 1,4-bi Sus(3-amino-4-biphenoxybenzoyl)benzene, 1,3-bis(4-amino-5-biphenoxybenzoyl)benzene, 1,4-bis(4-amino-5-biphenoxybenzoyl)benzene, 2,6-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzonitrile, and some or all of the hydrogen atoms on the aromatic ring of the above aromatic diamine are halogen atoms or 1 carbon atoms. ~3 alkyl group or alkoxyl group, cyano group, or part or all of hydrogen atoms of the alkyl group or alkoxyl group is substituted with a halogenated alkyl group having 1 to 3 carbon atoms or alkoxyl group Examples include aromatic diamines.

Examples of the aliphatic diamines of the present invention include 1,2-diaminoethane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane and 1,8-diaminooctane. ..
Examples of the alicyclic diamines of the present invention include 1,4-diaminocyclohexane and 4,4′-methylenebis(2,6-dimethylcyclohexylamine).

Examples of the diamines having a benzoxazole structure of the present invention include 5-amino-2-(p-aminophenyl)benzoxazole, 6-amino-2-(p-aminophenyl)benzoxazole and 5-amino-2. -(M-aminophenyl)benzoxazole, 6-amino-2-(m-aminophenyl)benzoxazole, 2,2'-p-phenylene bis(5-aminobenzoxazole), 2,2'-p-phenylene Bis(6-aminobenzoxazole), 1-(5-aminobenzoxazolo)-4-(6-aminobenzoxazolo)benzene, 2,6-(4,4'-diaminodiphenyl)benzo[1,2 -D:5,4-d']bisoxazole, 2,6-(4,4'-diaminodiphenyl)benzo[1,2-d:4,5-d']bisoxazole, 2,6-(3 ,4'-Diaminodiphenyl)benzo[1,2-d:5,4-d']bisoxazole, 2,6-(3,4'-diaminodiphenyl)benzo[1,2-d:4,5- d′]bisoxazole, 2,6-(3,3′-diaminodiphenyl)benzo[1,2-d:5,4-d′]bisoxazole, 2,6-(3,3′-diaminodiphenyl) Examples thereof include benzo[1,2-d:4,5-d']bisoxazole.

In the present invention, the polyimide preferably used is preferably a film comprising a condensation product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, and further,
(A) a film of a condensate of an aromatic tetracarboxylic dianhydride and a diamine containing at least a diamine having a benzoxazole skeleton,
(B) A film of a condensate of an aromatic tetracarboxylic dianhydride and a diamine containing at least a diamine having an ether bond in the molecule,
(C) a film of a condensate of an aromatic tetracarboxylic dianhydride and a diamine containing at least phenylenediamine,
(D) a film of a condensate of biphenyltetracarboxylic dianhydride and an aromatic diamine,
It is preferably made of at least one polyimide film selected from

The film thickness of the polyimide of the present invention is not particularly limited, but is preferably 0.5 μm to 200 μm, more preferably 3 μm to 50 μm. When the thickness is 0.5 μm or less, it is difficult to control the film thickness, and there is a possibility that a part of polyimide will be missing. Therefore, it may be difficult to peel off the second polyimide layer. On the other hand, when the thickness is 200 μm or more, it takes time to manufacture, and it may be difficult to control the unevenness of the film thickness. The thickness variation of the polyimide layer is essential to be 5% or less, preferably 4% or less, and more preferably 3% or less.

The film of the condensate of tetracarboxylic dianhydride and diamine of the present invention, that is, the polyimide film can be obtained by a solution film forming method. The solution forming method of polyimide is a stainless steel roll or an endless belt, or a polymer film such as PET is used as a long or endless support, and a precursor solution of a polyimide resin is applied onto the support, After drying, the polyimide precursor film is peeled off from the support, and preferably both ends of the film are gripped by clips or pins, and while being transported, further heat treatment is performed to chemically react the polyimide precursor into polyimide to form a polyimide. It is a method of obtaining a film. The polyimide film obtained using such a method has a thickness variation of 5% or less, preferably 3.6% or less, more preferably 2.4% or less, and a tensile breaking strength of 90 MPa or more, preferably 180 MPa or more, The polyimide film is more preferably 350 MPa or more, still more preferably 450 MPa or more.

In the present invention, in order to adjust the properties of the polyimide layer, it is possible to add an inorganic substance to the polyimide, but this should be kept to the necessary minimum. Generally, when a polymer is formed into a film, a small amount of inorganic particles called a lubricant is added to positively generate minute projections on the film surface, and when the film and the film or the film and the smooth surface overlap with each other, The slipperiness of the film is developed by incorporating the air layer. In the present invention, the silicon oxide component contained in the polyimide layer is preferably 6000 ppm or less, preferably 4500 ppm or less, more preferably 1800 ppm or less, still more preferably 900 ppm or less. The addition of an excessive amount of lubricant may increase the roughness of the film surface and may hinder the peelability of the second polyimide layer.
Such inorganic particles are often passed on to the polyamic acid composition while being dispersed in an organic solvent or the like.

In the present invention, the defect or the outer diameter size of the micro bubbles is the diameter in the case of a circular shape or a spherical shape, and the diameter of the circumscribed circle is called the outer diameter size in the case of a distorted shape or an irregular shape. If there is a clear image, the diameter of the circumscribed circle can be determined relatively easily by image processing or the like.

The polyamic acid composition of the present invention includes a polyamic acid solution in an organic solvent and a polyamic acid film (also referred to as GF: gel film or green film) obtained by drying the polyamic acid organic solvent. It should be noted that although referred to as a polyamic acid film for convenience, when the polyamic acid solution is actually applied to a support and dried, imidization due to a dehydration condensation reaction proceeds with a part of the polyamic acid at the same time as the drying. The acid, the polyimide, and the organic solvent coexist.
In the present invention, at least one selected from fatty acids having 8 to 30 carbon atoms, fatty acid salts having 8 to 30 carbon atoms, fatty acid amides having 8 to 30 carbon atoms, and fatty acid derivatives having 8 to 30 carbon atoms with respect to the polyamic acid composition. Although the content of the above compound (hereinafter referred to as fatty acid compound) is specified, the abundance of the polyamic acid varies depending on the process of the polyimidization as described above, and therefore, in the present invention, “with respect to the mass of the polyamic acid”. The term "" means the total amount of the tetracarboxylic acid and the diamine which are the raw materials of the polyamic acid.

In the present invention, a fatty acid having 8 to 30 carbon atoms, a fatty acid salt having 8 to 30 carbon atoms, a fatty acid amide having 8 to 30 carbon atoms, and a fatty acid amide having 8 to 30 carbon atoms, which are contained in a polyamic acid composition which is a precursor of polyimide. The polyimide is obtained by using a polyamic acid composition in which the content of at least one compound selected from fatty acid derivatives is 0.1% by mass or less based on the mass of the polyamic acid.

The fatty acid having 8 to 30 carbon atoms of the present invention may be either saturated fatty acid or unsaturated fatty acid, for example, octanoic acid, caprylic acid, nonanoic acid, pelargonic acid, dodecanoic acid, lauric acid, tetradecanoic acid, myristic acid, pentadecane. Acid, pentadecylic acid, hexadecanoic acid, palmitic acid, 9-hexadecenoic acid, palmitoleic acid, heptadecanoic acid, margaric acid, octadecanoic acid, stearic acid, cis-9-octadecenoic acid, oleic acid, 11-octadecenoic acid, vaccenic acid, cis , Cis-9,12-octadecadienoic acid, linoleic acid, 9,12,15-octadecantrienoic acid, (9,12,15)-linolenic acid, 6,9,12-octadecatrienoic acid, (6, 9,12)-Linolenic acid, 9,11,13-octadecatrienoic acid, eleostearic acid, eicosanoic acid, arachidic acid, 8,11-eicosadienoic acid, 5,8,11-eicosatrienoic acid, mead acid , 5,8,11-eicosatetraenoic acid, arachidonic acid, docosanoic acid, behenic acid, tetracosanoic acid, lignoceric acid, cis-15-tetracosanoic acid, nervonic acid, hexacosanoic acid, cerotic acid, octacosanoic acid, montanic acid, Examples thereof include triacontanoic acid, melissic acid, erucic acid, nervonic acid, arachidonic acid, eicosatetraenoic acid, docosapentaenoic acid and docosahexaenoic acid.

The fatty acid salt having 8 to 30 carbon atoms of the present invention includes the above-exemplified fatty acid alkali metal salts, ammonium salts, divalent metal salts, trivalent metal salts, tetravalent metal salts and the like.

A typical example of the C8-C30 fatty acid amide of the present invention is a compound obtained by a dehydration condensation reaction of the above-exemplified fatty acid and ammonia, and is sometimes called an aliphatic amide. Examples of the fatty acid amide include stearic acid amide, oleic acid amide, erucic acid amide, methylenebisstearic acid amide, and ethylenebisstearic acid amide.

The fatty acid derivative having 8 to 30 carbon atoms of the present invention is an ester of the above-exemplified fatty acid, a halogen-substituted product, a polymer derived from an unsaturated bond, or the like.
In the present invention, at least one compound (fatty acid) selected from at least these fatty acids having 8 to 30 carbon atoms, fatty acid salts having 8 to 30 carbon atoms, fatty acid amides having 8 to 30 carbon atoms and fatty acid derivatives having 8 to 30 carbon atoms (fatty acid The content of the (system compound) is 0.1% by mass or less, preferably 0.01% by mass, and more preferably 0.003% by mass based on the mass of the polyamic acid in the polyamic acid composition. The lower limit is below the detection lower limit, so it is not specified.

These fatty acid compounds are present in a state of being dissolved in the solvent of the polyamic acid composition if the amount is extremely small, but since the solvent of the polyamic acid composition is originally poor in compatibility, the amount of the solvent is increased by drying. When it decreases, it reaches a concentration higher than the solubility and precipitates to form fine particles or micelles in the composition. That is, the fine particles or micelles are formed in the polyamic acid film, and are further decomposed or sublimated during the heat treatment for dehydrating and condensing the polyamic acid to generate fine bubbles. When the amount of these fatty acid compounds is within the predetermined range, the temperature is sufficiently high when the concentration at which fine particles or micelles are formed is reached, and the compounds are decomposed or sublimated before being precipitated in the form of fine particles or micelles. Therefore, micro bubbles do not occur.

As a result of investigating the origin of these fatty acid compounds, the present inventors have found that they originate from the container for storing the raw material of these polyamic acids and the polyamic acid solution. That is, these fatty acid compounds are accumulated by shifting from the material used for the inner wall of the container to the raw material or the polyamic acid solution during storage. Since these fatty acid compounds have relatively high chemical stability, they do not directly hinder the polymerization reaction of polyamic acid or the dehydration reaction when converting polyamic acid to polyimide, and are therefore easily overlooked.

An example of the container for storing the polyamic acid raw material, the solvent, the polyamic acid composition, and the like used in the present invention is a canister or a small metal can. A polyethylene film, a propylene film, a polyolefin film, a vinyl fluoride film, a polyester film, or the like is laminated on the inner wall of these metal containers to prevent direct contact between the contents and the metal. Also for the lid, similar relatively flexible resin is often used as a sealer.
As another example of the container for storing the polyamic acid raw material, the solvent, the polyamic acid composition and the like used in the present invention, a so-called poly container can be exemplified. The plastic container is made of a relatively flexible polymer material having high chemical stability such as polyethylene, polypropylene, polyolefin and polyvinyl chloride.
In the present invention, when the polyamic acid raw material is a solid lump or powder, a bag made of a polymer material such as polyester or nylon, a so-called poly bag, or a paper bag having a polymer film arranged inside is used. There are cases. In the case of such a bag-shaped container, since the innermost layer of the container is a sealant for heat sealing, the contents come into direct contact with the sealant layer.

The fatty acid compound of the present invention is widely used as an additive to polyethylene, polypropylene, polyolefin and the like used for the inner wall of containers and sealants. If a container whose inner wall is covered with a material that does not use any of these can be used, the mixing of these fatty acid compounds can be eliminated, but in reality it is difficult to arrange such a container.

In the present invention, even when a container whose inner wall is covered with a material containing a fatty acid compound as an additive as described above is used, if the container is stored under a specific condition, the amount of the aliphatic compound mixed in the microbubbles is reduced. Can be suppressed to an amount equal to or less than that.
That is,
log ₁₀ (day)≦2300×(1/T)−5.3
(Here, day is the storage time (unit: day) and T is the storage temperature (unit: K).)
If the storage temperature and storage time satisfy the following relational expression, the amount of the fatty acid compound mixed can be kept below the microbubble generation limit, and as a result, a defect of diameter 2 μm or more observed by a differential interference microscope. It is possible to obtain a polyimide film having a number of not more than 2 pieces/square cm, preferably 1 piece/square cm, more preferably 1 piece/10 cm 2, still more preferably 1 piece/100 cm 2. The storage temperature and storage time that satisfy the relational expression are, for example, 1 month (30 days) at 60° C., 3 months (90 days) at 40° C., and 8 months (240 days) at 25° C. ..

Hereinafter, the present invention will be specifically described with reference to examples.
<Experimental Example 1>
1.5 g each of 5-amino-2-(4-aminophenyl)benzoxazole and pyromellitic dianhydride immediately after purification were weighed, sealed in a sample bottle with 12 ml of chloroform, and extracted for 2 hours while ultrasonically dispersing. did. The extract was filtered, the filtrate was concentrated to dryness at room temperature under a nitrogen atmosphere, dissolved in deuterated chloroform, and then subjected to ¹ H-NMR measurement (400 MHz). For quantification, 50 μg of dimethylisophthalate was added as an internal standard. As a result, at least 0.001 mass% or more of C8-30 fatty acids, C8-30 fatty acid salts, C8-30 fatty acid amides and C8-30 fatty acid derivatives were detected in both raw materials. Was not done.

<Polymeric acid polymerization example>
Polyamic acid was polymerized using this raw material.
After nitrogen-substituting the inside of a reaction vessel equipped with a nitrogen introduction tube, a thermometer, and a stirring rod, 100 parts by mass of 5-amino-2-(4-aminophenyl)benzoxazole was distilled and purified to obtain N,N-dimethylacetamide 1400. A dispersion of 96 parts by mass of pyromellitic acid dianhydride and 100 parts by mass of pyromellitic dianhydride, and colloidal silica as a lubricant dispersed in dimethylacetamide (“Snowtex (registered trademark of Nissan Chemical Industries)”) )DMAC-ST30" (product delivered within one week from the manufacturing date) so that silica (lubricant) is 0.12% by mass based on the total polymer solid content in the polyamic acid solution), When stirred at the reaction temperature for 18 hours, a brown viscous polyamic acid solution A (polyamic acid composition A) was obtained.
10 g of this polyamic acid solution was reprecipitated in a large amount of chloroform, and the supernatant was concentrated to dryness at room temperature under a nitrogen atmosphere, dissolved in deuterated chloroform, and then subjected to ¹ H-NMR measurement (400 MHz). For quantification, 50 μg of dimethylisophthalate was added as an internal standard. As a result, at least 0.001% by mass or more of a C8-30 fatty acid, a C8-30 fatty acid salt, and a C8-30 fatty acid derivative were not detected. The reduced viscosity of this polyamic acid was 3.6 dl/g.

<Production example of polyimide film>
The polyamic acid solution A was coated on a G3 size (370 mm×470 mm glass substrate for a display substrate (support)) using a precision coater with 5 mm on each side as a blank, and dried at 110° C. for 5 minutes to obtain a glass substrate. To obtain a polyamic acid film layer A. The residual solvent amount in the film measured by TGA was 35% by mass.
A part of this polyamic acid film layer A was peeled off from the glass substrate, 5 g was weighed, and the sample bottle was tightly stoppered with 50 ml of chloroform and extracted for 2 hours while ultrasonically dispersing. The extract was filtered, the filtrate was concentrated to dryness under a nitrogen atmosphere, dissolved in deuterated chloroform, and then subjected to ¹ H-NMR measurement (400 MHz). For quantification, 50 μg of dimethylisophthalate was added as an internal standard. As a result, even in the polyamic acid film, at least 0.001% by mass or more of a fatty acid having 8 to 30 carbon atoms, a fatty acid salt having 8 to 30 carbon atoms, a fatty acid amide having 8 to 30 carbon atoms, and a fatty acid derivative having 8 to 30 carbon atoms Was not detected.
The polyamic acid film layer A supported on the glass substrate obtained in the same manner was dried in a vacuum dryer at 150° C. for 20 minutes, and further heat-treated at 450° C. for 15 minutes in an inert oven to give a glass substrate. A supported 25 μm thick polyimide film layer A was obtained.

<Measurement of the number of defects>
5 mm on the four sides (10 mm from the glass edge) of the obtained polyimide film layer A was regarded as a blank space, and 5 squares of 50 mm×50 mm were randomly extracted from the area inside thereof to make an observation area. The surface of the observation area was observed with a 100× differential interference microscope (field of view: approximately 1.5 mmφ), and the number was counted together with the mapping, with a defect of 2 μm or more where the color unevenness is remarkable as a defect. When the number of defects exceeded 75 (corresponding to 3.0 defects/square cm), it was judged as "a large number of defects" and the coefficient was canceled. The number of defects of 2 μm or more was 0.0/cm 2.

<Comparative Experimental Example 1>
<Storage of polyamic acid raw material>
Immediately after purification, 5-amino-2-(4-aminophenyl)benzoxazole and pyromellitic dianhydride were stored in a plastic bag having an inner surface of a polyolefin sealant and stored at 40° C. for 60 days. Both are powder raw materials.
The N,N-dimethylacetamide purified by distillation was placed in a metal can whose inner surface was coated with polyethylene, tightly sealed, and publicly stored at 40° C. for 60 days.
A metal can whose inner surface was similarly polyethylene coated with a dispersion (“Snowtex (registered trademark) DMAC-ST30” manufactured by Nissan Kagaku Kogyo Co., Ltd.) in which colloidal silica delivered within one week of production was dispersed in dimethylacetamide. It was stored in a container, securely sealed, and stored at 40° C. for 60 days.

Using the raw material stored at 40° C. for 60 days, a polymerization operation was performed in the same manner as in Experimental Example 1 to obtain a polyamic acid solution B. 10 g of this polyamic acid solution B was reprecipitated in a large amount of chloroform, and the supernatant was concentrated to dryness at room temperature under a nitrogen atmosphere, dissolved in deuterated chloroform, and then subjected to ¹ H-NMR measurement (400 MHz). For quantification, 50 μg of dimethylisophthalate was added as an internal standard. As a result, 0.12% by mass of erucic acid amide was detected with respect to the polyamic acid.

When the polyolefin sheet on the inner surface of the polybag used for storing the polyamic acid powder raw material was analyzed, 1.5% by mass of erucic acid amide was detected. Similarly, when the polymer film on the inner surface of the metal can storing the liquid raw material was analyzed, 0.01 mass% of stearic acid was detected. It can be concluded that at least the erucic acid amide contained in the polyamic acid solution B is derived from the storage container.

Using the obtained polyamic acid solution B, the same operation as in Experimental Example 1 was carried out to obtain a polyimide film layer B supported on a glass substrate. When the surface of the obtained polyimide film layer B was observed with a differential interference microscope, it was detected that there were 3 defects/square cm of 2 μm or more on the air surface side. Further, when the cross section of the defect portion of the film was observed, fine bubbles having an outer diameter of 1.0 μm to 1.8 μm were observed in the range of 1 to 5 μm from the air surface of the film.

<Storage experiment>
The 5-amino-2-(4-aminophenyl)benzoxazole and pyromellitic dianhydride immediately after purification used in the comparative experiment example were stored in a poly bag whose inner surface used in the comparative experiment example was a polyolefin sealant, The film was stored for the storage temperature and storage time shown in Table 1, and then a polyimide film layer supported on a glass substrate was prepared by the same operation as in Experimental Example 1, and a defect was observed with a differential interference microscope. The results are shown in Table 1. Here, when the number of defects is 1.0 or less/square cm, it is ◯, it exceeds 1.0/square cm, and when it is 2.0 or less/square cm, it is Δ, and it exceeds 2.0/square cm. The case was marked as x.

The result of the storage experiment is plotted in FIG. 1 by plotting the logarithm of the storage time on the vertical axis and the reciprocal of the storage temperature on the horizontal axis. The diagonal line drawn by the broken line in the graph in Fig. 1 is
log ₁₀ (day)=2300×(1/T)−5.3
Therefore, it can be seen that the polyimide film layer having a low number of defects can be obtained in the portion below the oblique line.

As described above, if the raw material is stored and managed under the conditions shown by the present invention, a high-quality polyimide film layer with few defects can be obtained. The polyimide film layer obtained in the present invention can be suitably used for forming a high-quality fine pattern, and is most suitable for manufacturing a backplane of a flexible display, which requires particularly fine TFT formation.

Claims (7)

A composition containing at least a polyamic acid obtained from an aromatic tetracarboxylic acid and a diamine and an organic solvent, wherein the polyamic acid has a fatty acid having 8 to 30 carbon atoms, a fatty acid salt having 8 to 30 carbon atoms, and 8 to 8 carbon atoms. A polyamic acid composition characterized in that the total amount of 30 fatty acid amides and C8-30 fatty acid derivatives is 0.05% by mass or less. At least a part of the inner wall is stored in a container made of a polymer material having a glass transition temperature of 40° C. or lower,
log ₁₀ (day)≦2300×(1/T)−5.3
(Here, day is the storage time (unit: day) and T is the storage temperature (unit: K).)
The method for producing a polyamic acid composition according to claim 1, wherein the aromatic tetracarboxylic acid after storage within a storage temperature and a storage time satisfying the following relational expression is used as a polymerization raw material. At least a part of the inner wall is stored in a container made of a polymer material having a glass transition temperature of 40° C. or lower,
log ₁₀ (day)≦2300×(1/T)−5.3
(Here, day is the storage time (unit: day) and T is the storage temperature (unit: K).)
The method for producing a polyamic acid composition according to claim 1, wherein the diamine after being stored at a storage temperature and a storage time satisfying the following relational expression is used as a polymerization raw material. At least a part of the inner wall is stored in a container made of a polymer material having a glass transition temperature of 40° C. or lower,
log ₁₀ (day)≦2300×(1/T)−5.3
(Here, day is the storage time (unit: day) and T is the storage temperature (unit: K).)
The method for producing a polyamic acid composition according to claim 1, wherein the organic solvent after storage within a storage temperature and a storage time satisfying the following relational expression is used as a polymerization solvent. At least a part of the inner wall is stored in a container made of a polymer material having a glass transition temperature of 40° C. or lower,
log ₁₀ (day)≦2300×(1/T)−5.3
(Here, day is the storage time (unit: day) and T is the storage temperature (unit: K).)
The method for producing a polyamic acid composition according to claim 1, wherein a solvent dispersion of inorganic particles after storage within a storage temperature and storage time range satisfying the following relational expression is added to a polymerization raw material. .. The polymer material forming part of the inner wall of the container is a fatty acid having 8 to 30 carbon atoms, a fatty acid salt having 8 to 30 carbon atoms, a fatty acid amide having 8 to 30 carbon atoms, and a fatty acid derivative having 8 to 30 carbon atoms. The method for producing a polyamic acid composition according to any one of claims 2 to 5, which comprises 0.05 to 5 mass% of at least one compound selected from the above. A method for producing a polyimide, comprising heat-treating the polyamic acid composition according to claim 4 at a temperature of at least 350°C and not more than 550°C.