JP7539366B2 - Polyamic acid composition and method for producing same, polyamic acid solution, polyimide, polyimide film, laminate and method for producing same, and flexible device and method for producing same - Google Patents

Description

The present invention relates to a polyamic acid composition, a polyamic acid solution, a polyimide and a polyimide film, and a flexible device using a polyimide film.

There is a demand for thinner, lighter and more flexible displays, such as liquid crystal, organic electroluminescence and electronic paper, as well as devices such as solar cells, touch panels and lighting equipment, and the use of plastic film substrates instead of glass substrates is being considered. In the manufacturing process of electronic devices, electronic elements such as thin-film transistors and transparent electrodes are provided on a substrate. The formation of electronic elements requires high-temperature processes, and plastic film substrates are required to have heat resistance suitable for high-temperature processes, so the use of polyimide as a material for plastic film substrates is being considered.

Manufacturing processes for electronic devices are divided into batch and roll-to-roll types. In a batch process, a resin solution is applied to a glass support and dried to form a laminate of the glass support and film substrate, and after forming elements on it, the film substrate is peeled off from the glass support, making it possible to use current process equipment for glass substrates. When the film substrate is polyimide, a polyamic acid solution acting as a polyimide precursor is applied to the support, and the polyamic acid is heated together with the support to carry out imidization, thereby obtaining a laminate of the support and a polyimide film.

In optical devices such as displays, light emitted from elements is emitted through a film substrate, so the substrate material must be transparent. Polyimides made using monomers with rigid structures or fluorine-based monomers are known to have high transparency and low thermal expansion (Patent Documents 1 and 2). It is known that the use of silicone as a polyimide material reduces the stress at the interface between the glass support and the polyimide film (Patent Documents 3 and 4).

JP 2002-161136 A JP 2012-41530 A JP 2017-226847 A Patent No. 5948545 specification

Polyimides that have a silicone skeleton (polyorganosiloxane structure) introduced to reduce stress at the interface between the support and the polyimide film have a low thermal decomposition temperature, and there are concerns that outgassing from the polyimide film may reduce productivity and contaminate the manufacturing equipment during the formation of electronic devices. The present invention aims to provide a polyimide film that is capable of reducing stress at the interface with the substrate, has excellent heat resistance, and has a high thermal decomposition temperature, and a polyamic acid composition as its precursor.

One embodiment of the present invention is a polyamic acid composition comprising a polyamic acid having a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2), and inorganic fine particles.

It is preferable that the polyamic acid contains a structural unit represented by the following general formula (3) as the structural unit represented by the above general formula (1).

The inorganic microparticles have an average primary particle diameter of 200 nm or less. The inorganic microparticles may be silica microparticles. The inorganic microparticles may be surface-treated.

Polyamic acid can be obtained, for example, by reacting tetracarboxylic dianhydride with diamine in an organic solvent. Tetracarboxylic dianhydride and diamine may be reacted in an organic solvent in which inorganic fine particles are dispersed. By carrying out a polymerization reaction in a dispersion of inorganic fine particles, a polyamic acid composition in which polyamic acid and inorganic fine particles are composited can be obtained.

By using a silicone diamine represented by the following general formula (4) as the diamine, a polyamic acid having a structural unit represented by general formula (2) is obtained.

In general formula (2) and general formula (4), a plurality of ^R2 and ^R3 are each independently an alkyl group having 1 to 3 carbon atoms or an aryl group. A plurality of Y are each independently an alkylene group having 1 to 3 carbon atoms or an arylene group. m is an integer of 1 or more, and is preferably 30 or more and less than 300.

In the general formulas (1) to (3), each of the R ^1s is independently a hydrogen atom, an alkyl group, or an aryl group, and preferably a hydrogen atom. The tetravalent organic group X is a residue of a tetracarboxylic dianhydride. The polyamic acid may contain, for example, the following structure (A), (B), or (C) as the organic group X.

A block copolymer is obtained by reacting a tetracarboxylic dianhydride with a first diamine in an organic solvent to form a polyamic acid segment, and then adding a second diamine. If the first diamine is a diamine that does not contain silicon atoms and the second diamine is a silicone diamine, an ABA-type triblock copolymer is obtained in which a second segment having a polyorganosiloxane structure is bonded to both ends of a first segment that does not contain silicon atoms. The amount (moles) of the tetracarboxylic dianhydride used when forming a polyamic acid segment (first segment) by reacting a tetracarboxylic dianhydride with a first diamine is preferably 1.001 times or more and less than 1.100 times the amount (moles) of the first diamine.

The polyamic acid solution contains the above-mentioned polyamic acid composition and an organic solvent. A polyimide is obtained by dehydrating and cyclizing the polyamic acid. In one embodiment, the polyamic acid solution is applied to a support to form a laminate having a film-like polyamic acid on the support, and the laminate is heated to imidize the polyamic acid, thereby obtaining a polyimide film.

The 1% weight loss temperature of the polyimide film is preferably 450°C or higher. The glass transition temperature of the polyimide film is preferably 300°C or higher. The laminate of the support and the polyimide film preferably has an internal stress of 25 MPa or less at room temperature.

A flexible device can be obtained by forming electronic elements on a polyimide film. Electronic elements can be formed on the polyimide film of a laminate in which a polyimide film is provided on a support, and the polyimide film can be peeled off from the support after the electronic elements are formed.

The above polyimide film has low internal stress when laminated with an inorganic support and has excellent heat resistance, making it suitable as a substrate material for electronic devices.

1 is a graph showing the change in weight upon heating of the polyimide films of Example 2 and Comparative Example 2. 1 is a graph showing the change in weight upon heating of the polyimide films of Example 3 and Comparative Example 3. 1 is a graph showing the change in weight upon heating of the polyimide films of Comparative Example 1B and Comparative Example 1C. 1 is a cross-sectional TEM image of a polyimide film (Comparative Example 2) that does not contain inorganic fine particles. 1 is a cross-sectional TEM image of a polyimide film containing silica particles (Example 2).

The following describes embodiments of the present invention, but the present invention is not limited to these.

[Polyamic acid composition]
One embodiment of the present invention is a polyamic acid composition containing polyamic acid and inorganic fine particles. In the polyamic acid composition, the polyamic acid and the inorganic fine particles may be composited. The polyamic acid is a precursor of polyimide, and polyimide is obtained by a dehydration ring-closing reaction of the polyamic acid.

<Polyamic acid>
The polyamic acid contained in the polyamic acid composition of the present embodiment contains a structural unit represented by the following general formula (1) (hereinafter, may be referred to as "structural unit 1") and a structural unit represented by the following general formula (2) (hereinafter, may be referred to as "structural unit 2").

Structural unit 1 is formed by the reaction of a diamine having a divalent organic group Z that does not contain a silicon atom with a tetracarboxylic dianhydride having a tetravalent organic group X. In general formula (1), Z is a divalent organic group and is a residue of a diamine. For example, when the diamine is 2,2'-bis(trifluoromethyl)benzidine (TFMB), structural unit 1 is represented by the following general formula (3).

Structural unit 2 is formed by reacting a silicone diamine represented by the following general formula (4) with a tetracarboxylic dianhydride having a tetravalent organic group X.

In general formula (1) and general formula (2), X is a tetravalent organic group and is a residue of a tetracarboxylic dianhydride. Each of the multiple R ^1s is independently a hydrogen atom, an alkyl group, or an aryl group. In the polyamic acid obtained by the reaction of a tetracarboxylic dianhydride with a diamine, R ¹ is a hydrogen atom. By esterifying the carboxy group of the polyamic acid, a polyamic acid (polyamic acid ester) in which R ¹ is an alkyl group or an aryl group is obtained. The polyamic acid ester is resistant to hydrolysis and has excellent solution stability.

In general formula (2) and general formula (4), a plurality of ^R2 and ^R3 are each independently an alkyl group having 1 to 3 carbon atoms or an aryl group. A plurality of Y are each independently an alkylene group having 1 to 3 carbon atoms or an arylene group. m is an integer of 1 or more.

The inclusion of structural unit 2 tends to reduce the internal stress of the polyimide film obtained by imidizing polyamic acid. The content of the structural unit represented by general formula (2) in the polyamic acid is preferably 0.3 to 7 mol%, more preferably 0.5 to 5 mol%, and even more preferably 0.7 to 4 mol%.

The weight average molecular weight of the polyamic acid is, for example, 10,000 to 1,000,000, preferably 30,000 to 500,000, and more preferably 40,000 to 100,000. If the weight average molecular weight is 10,000 or more, the mechanical strength of the polyimide film can be ensured. If the weight average molecular weight is 1,000,000 or less, the polyamic acid exhibits sufficient solubility in the solvent, and a coating film or film with a smooth surface and uniform thickness can be obtained. The molecular weight is a value calculated as polyethylene oxide by gel permeation chromatography (GPC).

<Tetracarboxylic acid dianhydride>
In the general formulas (1) to (3), the organic group X is a residue of a tetracarboxylic dianhydride, and is a tetravalent organic group derived from the tetracarboxylic dianhydride used in the polymerization of the polyamic acid.

Specific examples of tetracarboxylic dianhydrides include pyromellitic dianhydride, 3,3'4,4'-biphenyltetracarboxylic acid, 1,4-phenylenebis(trimellitate dianhydride), 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 9,9-bis(3, Examples of such tetracarboxylic dianhydrides include 4-dicarboxyphenyl)fluorene dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, dicyclohexyl-3,3',4,4'-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, and 2'-oxodispiro[2.2.1]heptane-2,1"-cycloheptane-3,2"-bicyclo[2.2.1]heptane-5,5'-6,6'-tetracarboxylic dianhydride. When a plurality of tetracarboxylic dianhydrides are used, a polyamic acid having a plurality of types of organic groups X can be obtained.

Among the exemplified tetracarboxylic dianhydrides, pyromellitic dianhydride (PMDA) and 3,3'4,4'-biphenyltetracarboxylic dianhydride (BPDA) are preferred from the viewpoint of improving the heat resistance and mechanical strength of the polyimide film. From the viewpoint of improving the transparency (reducing yellowness) of the polyimide film, it is preferred to use tetracarboxylic dianhydrides having a bent structure such as 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), and 4,4'-oxyphthalic dianhydride (OPDA). Among these, BPAF is preferred because it can reduce the birefringence of the polyimide film.

From the viewpoint of obtaining a polyimide film having excellent heat resistance and low birefringence, it is preferable to use PMDA and/or BPDA, and BPAF as the tetracarboxylic dianhydride. The residue of PMDA is a tetravalent organic group represented by formula (A), the residue of BPDA is a tetravalent organic group represented by formula (B), and the residue of BPAF is a tetravalent organic group represented by formula (C).

That is, the polyamic acid preferably contains, as a tetracarboxylic dianhydride-derived structure (organic group X in general formulas (1) to (3)), one or more selected from the group consisting of tetravalent organic groups represented by formula (A) and tetravalent organic groups represented by formula (B), as well as a tetravalent organic group represented by formula (C). Preferred combinations of tetracarboxylic dianhydrides are a combination of PMDA and BPAF, a combination of BPDA and BPAF, and a combination of PMDA, BPDA and BPAF.

From the viewpoint of improving the transparency and heat resistance of the polyimide film and reducing birefringence and internal stress, the total of PMDA, BPDA and BPAF is preferably 60 mol% or more, more preferably 70 mol%, and even more preferably 80 mol% or more, based on 100 mol% of the total amount of the tetracarboxylic dianhydride components of the polyamic acid. The total of PMDA, BPDA and BPAF may be 90 mol% or more, or may be 100 mol%.

From the viewpoint of obtaining a polyimide film with low birefringence, the amount of BPAF relative to 100 mol% of the total amount of the tetracarboxylic dianhydride components of the polyamic acid is preferably 30 mol% or more, more preferably 35 mol% or more, and even more preferably 40 mol% or more. From the viewpoint of obtaining a polyimide film with excellent heat resistance, the total amount of PMDA and BPDA relative to 100 mol% of the total amount of the tetracarboxylic dianhydride components of the polyamic acid is preferably 10 mol% or more, more preferably 20 mol% or more, and even more preferably 30 mol% or more.

When the tetracarboxylic dianhydride is a combination of PMDA and BPAF, from the viewpoint of obtaining a polyimide film with high transparency and low birefringence, the amount of BPAF relative to the total of PMDA and BPAF is preferably 30 to 90 mol%, more preferably 35 to 70 mol%, and even more preferably 40 to 60 mol%. From the viewpoint of obtaining a polyimide film with excellent alkali resistance, the tetracarboxylic dianhydride is preferably a combination of BPDA and BPAF, and the amount of BPAF relative to the total of BPDA and BPAF is preferably 30 to 90 mol%, more preferably 35 to 70 mol%, and even more preferably 40 to 60 mol%.

<Diamine>
As the diamine, a diamine not containing a silicon atom and a silicone diamine are used. By using a diamine not containing a silicon atom, a structural unit 1 having a divalent residue Z is formed.

By using a silicone diamine represented by the general formula (4) as the diamine, a structural unit 2 having a polyorganosiloxane structure is formed. The silicone diamine represented by the general formula (4) is a diamine derived from a silicone compound (both terminal amino-modified silicone). Specific examples of Y in the general formulas (2) and (4) include an ethylene group, a propylene group, and a phenylene group, of which a propylene group is preferred. Examples of ^R2 and ^R3 include a methyl group, an ethyl group, a propyl group, and a phenyl group. From the viewpoint of suppressing the decrease in heat resistance of the polyimide, it is preferable that at least one of ^R2 and ^R3 is an alkyl group, of which a methyl group is preferred.

The number of repeating units m of the siloxane structure is preferably 30 or more, more preferably 40 or more, and even more preferably 51 or more. When the structural unit 2 contains a polyorganosiloxane structure with a repeating unit number m of 30 or more, microdomains are easily formed, and the internal stress of the polyimide film tends to be reduced due to the stress relaxation effect. On the other hand, if the number of repeating units m is excessively large, the compatibility between the structural unit 1 and the structural unit 2 may be excessively reduced, and the haze of the polyimide film may become large. Therefore, the number of repeating units m is preferably less than 300, more preferably less than 250, and even more preferably less than 200. m may be less than 160, less than 100, or less than 80.

Specific examples of silicone diamines include methylphenyl silicone modified at both ends with amino (e.g., Shin-Etsu Chemical's "X22-1660B-3" (number average molecular weight 4,400) and "X22-9409" (number average molecular weight 1,300)), dimethyl silicone modified at both ends with amino (e.g., Shin-Etsu Chemical's "X22-161A" (number average molecular weight 1,600), "X22-161B" (number average molecular weight 3,000), "KF-8010" (number average molecular weight 860), "KF-8012" (number average molecular weight 4,400), and "KF-8008" (number average molecular weight 11,400); Dow's "BY16-835U" (number average molecular weight 900); and Chisso's "Silaplane FM-3321" (number average molecular weight 5,000)). From the viewpoint of reducing internal stress in the laminate of the polyimide film and the inorganic support, dimethyl silicone modified with amino groups at both ends is preferred.

The amount of silicone diamine represented by general formula (4) relative to the total amount of diamine components of polyamic acid (100 mol%) is preferably 0.3 to 7 mol%, more preferably 0.5 to 5 mol%, and even more preferably 0.7 to 4 mol%. The copolymerization ratio of silicone diamine is preferably in the range of 2 to 30 mass% relative to the mass of polyamic acid (total amount of tetracarboxylic dianhydride and diamine charged), more preferably 5 to 25 mass%, and even more preferably 10 to 20 mass%. If the amount of silicone diamine is in the above range, the internal stress of the laminate of the polyimide film obtained by imidization of polyamic acid and an inorganic substrate such as glass tends to be small.

By including structural unit 1, it is possible to control the properties of the polyimide film obtained by imidizing polyamic acid, such as transparency, heat resistance, and mechanical strength. From the viewpoint of obtaining a polyimide with little coloration and high transparency, the divalent organic group Z in structural unit 1 is preferably a fluorine-containing aromatic group. An example of a diamine having a fluorine-containing aromatic group is fluoroalkyl-substituted benzidine.

Fluoroalkyl-substituted benzidines have a fluoroalkyl group on one or both benzene rings of benzidine (4,4'diaminobiphenyl). The fluoroalkyl group is preferably a trifluoromethyl group. Among fluoroalkyl-substituted benzidines, trifluoromethyl-substituted benzidines having one or more trifluoromethyl groups on each of the two benzene rings are preferred, and among them, 2,2'-bis(trifluoromethyl)benzidine (TFMB) is particularly preferred because it gives a highly transparent polyimide. As described above, polyamic acid using TFMB as the diamine has a structure represented by general formula (3) as structural unit 1.

The amount of TFMB relative to 100 mol% of the total amount of diamine components in the polyamic acid is preferably 60 to 99.7 mol%, more preferably 70 to 99.5 mol%, and even more preferably 80 to 99.3 mol%. The content of the structural unit represented by general formula (3) in the polyamic acid is preferably 60 to 99.7 mol%, more preferably 70 to 99.5 mol%, and even more preferably 80 to 99.3 mol%.

The polyamic acid may contain a structure other than that of general formula (3) as structural unit 1. That is, a diamine other than TFMB that does not contain silicon atoms may be used as the diamine component of the polyamic acid. Examples of diamines not containing silicon atoms include 1,4-diaminocyclohexane, 1,4-phenylenediamine, 1,3-phenylenediamine, 4,4'-oxydianiline, 3,4'-oxydianiline, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 4,4'-diaminobenzanilide, 4'-aminophenyl-4-aminobenzene, N,N'-bis(4-aminophenyl)terephthalamide, 4,4'-diaminodiphenylsulfone, m-tolidine, o-tolidine, 4,4'-bis(aminophenoxy)biphenyl, 2-(4-aminophenyl)-6-aminobenzoxazole, 3,5-diaminobenzoic acid, 4,4'-diamino-3,3'dihydroxybiphenyl, and 4,4'-methylenebis(cyclohexaneamine).

<Polyamic acid sequence>
The arrangement of the structural unit 1 and the structural unit 2 in the polyamic acid may be random or block. The polyamic acid may be a block copolymer having a first segment containing the structural unit 1 and not containing the structural unit 2, and a second segment containing the structural unit 2. The arrangement of the blocks in the block copolymer may be an AB type in which the second segment is bonded to one end of the first segment, an ABA type in which the second segment is bonded to both ends of the first segment, or an (AB) _n type in which the first segment and the second segment are alternately arranged. Since the polymerization of the polyamic acid is easy and a block structure is easily formed, the block copolymer is preferably an ABA triblock structure.

The first segment is a segment consisting of repeating structural unit 1. When only TFMB and silicone diamine are used as the diamine components of the polyamic acid, the first segment is a segment consisting of repeating units of general formula (3). When a diamine other than TFMB and silicone diamine is used as the diamine component, the proportion of the structure of general formula (3) in the first segment is preferably 60 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more.

The second segment may consist of only structural unit 2, or may contain structural unit 1 and structural unit 2. When the silicone diamine has a high molecular weight (e.g., m in general formula (4) is 30 or more), even if structural unit 2 is not continuous in the polymer sequence, it can form a microdomain similar to the block structure.

When a polyamic acid containing a polysiloxane structure as structural unit 2 is imidized on an inorganic support such as glass to form a polyimide film, the internal stress in the laminate of the inorganic support and the polyimide film tends to be small. Although the detailed mechanism is not clear, it is thought that when a domain derived from silicone (polyorganosiloxane) is present in the polyimide film, when stress is generated in the polyimide film, the silicone-derived domain undergoes microscopic plastic deformation to relieve the stress, thereby reducing the internal stress of the entire polyimide film.

In particular, when the polyamic acid and polyimide are block copolymers, contain a domain (second segment) and a continuous phase (first segment), and have a difference in elastic modulus between the domain and the continuous phase, it is believed that stress is concentrated in the domain formed by the second segment, and stress is effectively relieved. When the compatibility between the components constituting the domain and the components constituting the continuous phase is high, a clear interface is not formed, and stress concentration in the domain is difficult due to partial compatibility, and the stress relief effect tends to be reduced. In addition, since silicone has a low glass transition temperature, when the domain of the second segment is partially compatible with the continuous phase, the glass transition temperature (Tg) tends to shift to the low temperature side. Therefore, it is preferable that the domain (second segment) derived from silicone has low compatibility with the continuous phase of the polyamic acid and polyimide. As described above, if the polyamic acid is a block copolymer having a first segment that does not contain structural unit 2, the compatibility between the first segment and the second segment is low, and a phase separation structure due to microdomains is easily formed, and stress relief is promoted.

[Inorganic fine particles]
As described above, by introducing the structural unit 2 derived from silicone diamine into polyamic acid, the internal stress in the laminate of the polyimide film and the substrate tends to be reduced. On the other hand, by introducing the polysiloxane structure, the heat resistance of the polyimide tends to decrease and the thermal decomposition temperature tends to be lowered. In this embodiment, a polyamic acid composition having a polyamic acid having a structural unit 1 derived from a diamine that does not contain silicon atoms and a structural unit 2 derived from silicone diamine and inorganic fine particles having an average primary particle diameter of 200 nm or less is prepared, and the polyamic acid in the composition is imidized, thereby improving the heat resistance of the polyimide having a polyorganosiloxane structure.

As the material for the inorganic fine particles, insulating materials such as silica, zirconia, titania, alumina, magnesium oxide, barium titanate, silicon nitride, etc. are preferred. The inorganic fine particles may be montmorillonite, bentonite, layered silicate, etc. Among them, silica is preferred as the material for the inorganic fine particles because of its high transparency and excellent effect of improving heat resistance due to interaction with polyamic acid having a polyorganosiloxane structure.

From the viewpoint of maintaining the transparency of the polyimide, the average particle diameter of the inorganic fine particles is preferably 200 nm or less, more preferably 100 nm or less, even more preferably 50 nm or less, and may be 30 nm or less. On the other hand, from the viewpoint of ensuring dispersibility, the average primary particle diameter of the inorganic fine particles is preferably 5 nm or more, more preferably 10 nm or more.

The inorganic fine particles may be surface-treated for the purpose of improving dispersibility and increasing the interaction with polyamic acid and polyimide. Various known treatments can be applied as the surface treatment. For example, nanosilica particles can be surface-treated with a silane coupling agent. As the silane coupling agent used for the surface treatment of nanosilica, an alkoxysilane compound having an amino group or a glycidyl group as a functional group is preferably used, and among them, from the viewpoint of enhancing the interaction with polyamic acid and polyimide, an amino group-containing alkoxysilane is preferable. Examples of amino group-containing alkoxysilane include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-(2-aminoethyl)aminopropyltrimethoxysilane, 3-phenylaminopropyltrimethoxysilane, 2-aminophenyltrimethoxysilane, and 3-aminophenyltrimethoxysilane. Among them, 3-aminopropyltriethoxysilane is preferable from the viewpoint of the stability of the raw material. For example, the surface treatment can be carried out by adding a silane coupling agent to a dispersion liquid (organosilica sol) of amorphous nanosilica and stirring for about 1 to 10 hours at 20 to 80° C. A catalyst may be used for the purpose of promoting the reaction, etc.

The content of inorganic fine particles in the polyamic acid composition is preferably 1 to 30 parts by weight, more preferably 3 to 20 parts by weight, per 100 parts by weight of polyamic acid. If the content of inorganic fine particles is 1 part by weight or more, it can contribute to improving heat resistance. If the content of inorganic fine particles is 30 parts by weight or less, it can suppress adverse effects on the mechanical properties and transparency of the polyimide film.

A polyamic acid composition containing polyamic acid and inorganic fine particles can be prepared, for example, by adding inorganic fine particles to a polyamic acid solution. A diamine and a tetracarboxylic dianhydride may be added to a dispersion in which inorganic fine particles are dispersed in an organic solvent, and the polyamic acid may be polymerized in the dispersion. By carrying out polymerization in a dispersion of inorganic fine particles, a polyamic acid composition in which polyamic acid and inorganic fine particles are composited can be prepared. By using a composition in which polyamic acid and inorganic fine particles are composited, the heat resistance of the polyimide obtained by dehydrating the polyimide tends to be improved.

[Polymerization of polyamic acid]
A polyamic acid can be obtained by reacting a diamine with a tetracarboxylic dianhydride in an organic solvent. For example, a diamine is dissolved or dispersed in a slurry state in an organic solvent to prepare a diamine solution, and a tetracarboxylic dianhydride is added to the diamine solution in the form of a solution or solid in which the tetracarboxylic dianhydride is dissolved or dispersed in a slurry state in an organic solvent. A diamine may be added to a tetracarboxylic dianhydride solution.

There are no particular limitations on the organic solvent used in the polymerization of polyamic acid. The organic solvent is preferably one that can dissolve the tetracarboxylic dianhydride and diamine used, and can also dissolve the polyamic acid produced by polymerization. Specific examples of organic solvents used in the polymerization of polyamic acid include urea-based solvents such as tetramethylurea and N,N-dimethylethylurea; sulfoxide or sulfone-based solvents such as dimethylsulfoxide, diphenylsulfone, and tetramethylsulfone; ester-based solvents such as N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), N,N'-diethylacetamide, N-methyl-2-pyrrolidone (NMP), and γ-butyrolactone; amide-based solvents such as hexamethylphosphoric triamide; halogenated alkyl solvents such as chloroform and methylene chloride; aromatic hydrocarbon-based solvents such as benzene and toluene; phenol-based solvents such as phenol and cresol; ketone-based solvents such as cyclopentanone; and ether-based solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, and p-cresol methyl ether. Usually, these solvents are used alone, but two or more of them may be appropriately combined as necessary. In order to increase the solubility and reactivity of the polyamic acid, the organic solvent used in the polymerization of the polyamic acid is preferably selected from amide solvents, ketone solvents, ester solvents and ether solvents, and in particular, amide solvents such as DMF, DMAC, NMP, etc. In order to increase the stability of the solution, an ether solvent such as diethylene glycol or tetrahydrofuran may be added.

As described above, polyamic acid may be synthesized by reacting tetracarboxylic dianhydride with diamine in a dispersion liquid in which inorganic fine particles are dispersed in an organic solvent. In this case, it is preferable to select an organic solvent that is capable of dissolving tetracarboxylic dianhydride and diamine and has excellent dispersibility of inorganic fine particles.

When preparing polyamic acid by polymerization of diamine and tetracarboxylic dianhydride, a polyamic acid copolymer having a plurality of structural units can be obtained by using a diamine that does not contain silicon atoms, such as TFMB, and a silicone diamine as the diamine, and adjusting the amount of the diamine. For example, a polyamic acid having structural unit 1 and structural unit 2 can be obtained by using a diamine that does not contain silicon atoms, such as TFMB, and a silicone diamine as the diamine. By changing the ratio of the diamine, the ratio of structural unit 1 and structural unit 2 in the polyamic acid can be adjusted arbitrarily. Similarly, a polyamic acid having a plurality of organic groups X can be obtained by using a plurality of tetracarboxylic dianhydrides. For example, a polyamic acid having structures (A) and (C) as the tetravalent organic group X can be obtained by using PMDA and BPAF as the tetracarboxylic dianhydrides, and a polyamic acid having structures (B) and (C) as the tetravalent organic group X can be obtained by using BPDA and BPAF. Two or more polyamic acids can also be blended to obtain a polyamic acid containing a plurality of tetracarboxylic dianhydrides and diamines.

The dissolution and reaction of the diamine and tetracarboxylic dianhydride is preferably carried out in an inert gas atmosphere such as argon or nitrogen. The temperature conditions for the reaction of the diamine and tetracarboxylic dianhydride are not particularly limited, but are, for example, 25°C to 150°C. From the viewpoint of sufficiently promoting the reaction of the silicone diamine and suppressing the decomposition of the polyamic acid, 40°C to 150°C is preferable, and 60°C to 120°C is more preferable. The reaction time may be set arbitrarily, for example, within the range of 10 minutes to 30 hours. As the reaction proceeds, the molecular weight of the polyamic acid increases, and the viscosity of the reaction solution increases.

Fluorine-containing diamines such as TFMB have a slower reaction rate than fluorine-free aromatic diamines. The reaction rate can be increased by increasing the concentration of tetracarboxylic dianhydride and diamine in the reaction solution. The concentration of the raw materials (diamine and tetracarboxylic dianhydride) in the reaction solution is preferably 15 to 30% by weight.

A polyamic acid having a first segment with an acid anhydride group at the end is prepared, and a silicone diamine is added to obtain an ABA triblock copolymer in which a second segment is bonded to both ends of the first segment. First, a tetracarboxylic dianhydride is reacted with a first diamine in an organic solvent to form a first segment. The first diamine is a component other than silicone diamine among the diamines constituting the polyamic acid, and is a diamine that does not contain silicon atoms. The first diamine is, for example, TFMB. The first diamine may contain a diamine other than TFMB.

The amount (total number of moles) of tetracarboxylic dianhydrides added when forming the first segment is preferably greater than the amount (total number of moles) of the first diamine. By adding a large amount of tetracarboxylic dianhydride, a polyamic acid (first segment) having an acid anhydride group at the end is formed. On the other hand, if the amount of tetracarboxylic dianhydride added is excessively large, the molecular weight of the first segment may not increase sufficiently. In forming the first segment, the total number of moles of tetracarboxylic dianhydride is preferably 1.001 times or more and less than 1.100 times the total number of moles of the first diamine, more preferably 1.01 to 1.09 times, and even more preferably 1.03 to 1.08 times.

When a second diamine is added after forming a first segment by reaction of a tetracarboxylic dianhydride with a first diamine, the acid anhydride group at the end of the first segment reacts with the second diamine, resulting in a polyamic acid having residues of the second diamine at both ends. If a portion of the tetracarboxylic dianhydride remains unreacted when the first segment is formed, the second segment extends at both ends of the first segment due to the reaction between the unreacted tetracarboxylic dianhydride and the second diamine. After the first segment is formed, additional tetracarboxylic dianhydride may be added in addition to the second diamine.

If the second diamine contains a silicone diamine, a block copolymer is obtained in which a second segment containing structural unit 2 is bonded to both ends of a first segment not containing structural unit 2. The second diamine may be only a silicone diamine, or may contain a diamine other than silicone diamine. In addition to the polysiloxane structure derived from the silicone diamine, the second segment may contain a structure derived from the first diamine that remained unreacted when the first segment was formed.

[Polyamic acid solution]
The polyamic acid solution used for preparing the inorganic fine particle-containing polyimide contains the above polyamic acid composition (polyamic acid and inorganic fine particles) and a solvent. The solution obtained by reacting diamine with tetracarboxylic dianhydride in a dispersion of inorganic fine particles can be used as it is as the inorganic fine particle-containing polyamic acid solution. Inorganic fine particles may be added to the polyamic acid solution. The concentration of polyamic acid and the viscosity of the solution may be adjusted by removing a part of the solvent from the polymerization solution or adding a solvent. The solvent to be added may be different from the solvent used for the polymerization of polyamic acid. In addition, the polyamic acid solution may be prepared by dissolving the solid polyamic acid resin obtained by removing the solvent from the polymerization solution in a solvent. As the organic solvent for the polyamic acid solution, amide-based solvents, ketone-based solvents, ester-based solvents and ether-based solvents are preferred, and among them, amide-based solvents such as DMF, DMAC, and NMP are preferred.

For the purpose of improving processing characteristics and imparting various functions, an organic or inorganic low-molecular-weight or high-molecular-weight compound may be blended into the polyamic acid solution. Examples of additives include dyes, pigments, surfactants, leveling agents, plasticizers, silicones, silane coupling agents, sensitizers, and fillers. In addition to polyamic acid, the polyamic acid solution may contain resin components such as photocurable components, thermosetting components, and non-polymerizable resins.

In order to promote the imidization reaction, an imidization agent and/or a dehydrating agent may be added to the polyamic acid solution. The imidization agent is not particularly limited, but it is preferable to use a tertiary amine, and among them, a heterocyclic tertiary amine is preferable. Examples of heterocyclic tertiary amines include pyridine, picoline, quinoline, and isoquinoline. Examples of dehydration catalysts include acetic anhydride, propionic anhydride, n-butyric anhydride, benzoic anhydride, and trifluoroacetic anhydride.

Imidazoles may be added to the polyamic acid solution. Imidazoles are compounds containing a 1,3-diazole ring structure, such as 1H-imidazole, 2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-phenylimidazole. Among these, 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole, and 1-benzyl-2-phenylimidazole are preferred, and 1,2-dimethylimidazole and 1-benzyl-2-methylimidazole are particularly preferred.

The amount of imidazole added is preferably about 0.005 to 0.1 moles per mole of amide group in polyamic acid, more preferably 0.01 to 0.08 moles, and even more preferably 0.015 to 0.050 moles. "Amide group in polyamic acid" refers to an amide group generated by a polyaddition reaction of diamine and tetracarboxylic dianhydride. If the amount of imidazole added is within the above range, in addition to improving the storage stability of the polyamic acid solution, it is expected to improve the heat resistance of the polyimide film and reduce the internal stress of the laminate of the inorganic support and the polyimide film.

When adding imidazoles, it is preferable to add them after the polymerization of polyamic acid. The imidazoles may be added directly to the polyamic acid solution, or may be added to the polyamic acid solution as an imidazole solution.

[Polyimide and polyimide film]
Polyimide is obtained by dehydration ring closure of polyamic acid. Dehydration ring closure can be performed by an azeotropic method using an azeotropic solvent, a thermal method, or a chemical method. Imidization of polyamic acid to polyimide can be at any ratio between 1 and 100%, and partially imidized polyamic acid may be synthesized.

To obtain a polyimide film, a method is preferred in which a polyamic acid solution is applied in the form of a film to a support such as a glass plate, a metal plate, or a PET (polyethylene terephthalate) film, and the polyamic acid is dehydrated and ring-closed by heating. As described above, an imidizing agent and/or a dehydration catalyst may be added to the polyamic acid solution to shorten the heating time and to express characteristics. To adapt to a batch-type device manufacturing process, it is preferable to use a glass substrate as the support, and alkali-free glass is preferably used.

In forming a polyimide film on a support, first, a polyamic acid solution containing inorganic fine particles is applied to the support to form a coating film, and then the laminate of the support and the polyamic acid coating film is heated at a temperature of 40 to 200°C for 3 to 120 minutes to remove the solvent. For example, drying may be performed at two or more temperatures, such as 30 minutes at 50°C and then 30 minutes at 100°C.

By heating the laminate of the support and the polyamic acid at a temperature of 200 to 400°C for 3 to 300 minutes, the polyamic acid undergoes dehydration and ring closure, resulting in a laminate in which a polyimide film containing fine particles is provided on the support. At this time, it is preferable to gradually increase the temperature from a low temperature to a maximum temperature. The rate of temperature increase is preferably 2 to 10°C/min, more preferably 4 to 10°C/min. The maximum temperature is preferably 250 to 400°C. If the maximum temperature is 250°C or higher, the imidization proceeds sufficiently, and if the maximum temperature is 400°C or lower, thermal deterioration and coloration of the polyimide can be suppressed. In the heating for imidization, any temperature may be maintained for any time until the maximum temperature is reached.

The heating atmosphere may be in air, under reduced pressure, or in an inert gas such as nitrogen. To achieve higher transparency, heating under reduced pressure or in an inert gas is preferred. Examples of heating devices include hot air ovens, infrared ovens, vacuum ovens, inert ovens, and hot plates.

[Characteristics and uses of polyimide]
The polyimide may be directly subjected to a coating or molding process for producing a product or a member. As described above, the polyimide may be formed into a polyimide film in a film shape. On the surface of the polyimide film, various inorganic thin films such as metal oxides and transparent electrodes may be formed. The method for forming these inorganic thin films is not particularly limited, and examples thereof include PVD methods such as CVD, sputtering, vacuum deposition, and ion plating.

The polyimide film of this embodiment has heat resistance and transparency, and can be used as an alternative material to glass, and can be applied to printed matter, color filters, flexible displays, optical films, liquid crystal displays, image display devices such as organic electroluminescence and electronic paper, 3D displays, touch panels, transparent conductive film substrates, solar cells, etc. In these applications, the thickness of the polyimide film is, for example, about 1 to 200 μm, and preferably about 5 to 100 μm.

Because the polyimide film of this embodiment has a small internal stress when laminated with the glass support, a batch-type device fabrication process can be applied in which a polyamic acid solution is applied to the support, heated to imidize, electronic elements, etc. are formed on the polyimide film of the laminate, and then the polyimide film is peeled off from the support.

In the batch-type device manufacturing process, the polyamic acid solution is applied to the support and imidized by heating using the above method, forming a laminate in which a polyimide film is tightly laminated on the support. Electronic elements such as TFTs are formed on the polyimide film of this laminate. In the formation of TFT elements, oxide semiconductors, amorphous silicon, etc. are generally formed at high temperatures of 300°C or higher.

If the thermal decomposition temperature of the polyimide film is low, outgassing may occur from the polyimide film due to heating during element formation, which may cause performance degradation or peeling of the element formed on the polyimide film. Therefore, the 1% weight loss temperature Td1 of the polyimide film is preferably 450°C or higher. Td1 may be 460°C or higher, 465°C or higher, 470°C or higher, or 475°C or higher.

If the glass transition temperature of the polyimide film is lower than the process temperature during the formation of the electronic device, dimensional changes during and after device formation during cooling can cause stress at the interface between the support and the polyimide film, which can lead to warping or breakage. Therefore, the Tg of the polyimide film is preferably 300°C or higher, more preferably 350°C or higher, and even more preferably 380°C or higher. The Tg may be 390°C or higher, 395°C or higher, or 400°C or higher.

As described above, polyimides having a polyorganosiloxane structure derived from silicone diamine generally tend to have lower heat resistance than polyimides that do not contain a polyorganosiloxane structure, and as shown in the heating weight changes in Figure 1 (Comparative Example 2) and Figure 2 (Comparative Example 3), weight loss is observed from around 200 to 300°C.

Figure 4 is a transmission electron microscope (TEM) image of a cross section of a polyimide film that does not contain inorganic particles (Comparative Example 2 described below), which shows the formation of silicone domains (white island regions). When a polyimide having a polyorganosiloxane structure is heated, cyclic siloxanes are likely to be produced by condensation between adjacent siloxane bonds, and this is thought to be one of the factors behind the thermal decomposition (thermal weight loss) at around 200 to 300°C.

Figure 5 is a cross-sectional TEM image of a polyimide film containing silica microparticles (Example 2 described below), in which black regions can be seen in addition to the white island regions similar to those in Figure 4. These black regions are silica particles, and it can be seen that the silica particles are dispersed so as to penetrate between the silicone domains. In this way, it is presumed that the dispersion of inorganic microparticles between the silicone domains prevents adjacent domains from approaching each other, suppressing the generation of cyclic siloxanes due to heating, thereby increasing the thermal decomposition temperature.

As described above, polyimide films having polyorganosiloxane domains tend to disperse stress and reduce internal stress. In this embodiment, polyimide having a polyorganosiloxane structure is composited with inorganic fine particles, so that the stress relaxation effect of the polyorganosiloxane domains is maintained while thermal decomposition caused by siloxane condensation ring reaction and the like is suppressed, and it is believed that the polyimide film has small internal stress and excellent heat resistance.

Generally, the thermal expansion coefficient of glass is smaller than that of resin, so heating during electronic device formation and subsequent temperature changes during cooling cause stress to occur at the interface of the laminate between the support and the polyimide film. If stress remains at the interface between the support and the polyimide film formed on the support, and the polyimide film shrinks when cooled to room temperature after being heated to a high temperature during the electronic device formation process, problems such as warping of the laminate, damage to the glass support, and peeling of the flexible substrate (polyimide film) from the glass support may occur.

As described above, the polyimide film produced using the inorganic fine particle-containing polyamic acid solution of this embodiment has heat resistance, transparency, and low thermal expansion, and can reduce internal stress in the laminate with the glass support. The internal stress of the laminate of the support and the polyimide film is preferably 30 MPa or less, more preferably 25 MPa or less, and even more preferably 20 MPa or less.

In a batch-type device manufacturing process, in order to accurately form or mount electronic elements and the like on the polyimide film, it is preferable that the adhesion between the support and the polyimide film is high. The 90°C peel strength from the support of the polyimide film tightly laminated on the support is preferably 0.05 N/cm or more, and more preferably 0.1 N/cm or more. On the other hand, from the viewpoint of workability when peeling the polyimide film from the support after mounting, the peel strength is preferably 0.25 N/cm or less.

The method for peeling the polyimide film from the support is not particularly limited. For example, it may be peeled off by hand, or a peeling device such as a drive roll or a robot may be used. Peeling may be performed by reducing the adhesion between the support and the polyimide film. For example, a polyimide film may be formed on a support provided with a peeling layer. A silicon oxide film may be formed on a substrate having a large number of grooves, and peeling may be promoted by infiltrating an etching solution. Peeling may also be performed by irradiation with laser light.

When peeling a polyimide film from a support by laser irradiation, it is necessary to have the polyimide film absorb the laser light, so the cutoff wavelength of the polyimide film (the wavelength at which the transmittance is 0.1% or less) is required to be longer than the wavelength of the laser light used for peeling. Since a XeCl excimer laser with a wavelength of 308 nm is often used for laser peeling, the cutoff wavelength of the polyimide film is preferably 320 nm or more, and more preferably 330 nm or more. On the other hand, if the cutoff wavelength is long, the polyimide film tends to be colored yellow, so the cutoff wavelength is preferably 390 nm or less. From the viewpoint of achieving both transparency (low yellowness) and processability for laser peeling, the cutoff wavelength of the polyimide film is preferably 320 to 390 nm, and more preferably 330 to 380 nm.

The transparency of the polyimide film can be evaluated by the total light transmittance and haze according to JIS K7105-1981. The total light transmittance of the polyimide film is preferably 80% or more, more preferably 85% or more. The haze of the polyimide film is preferably 1.5% or less, more preferably 1.2% or less, and even more preferably 1.0% or less. For applications such as displays, high transmittance is required over the entire wavelength range of visible light. The yellowness index (YI) of the polyimide film is preferably 15 or less, more preferably 10 or less. YI can be measured according to JIS K7373-2006. Such highly transparent polyimide films can be used as transparent substrates for glass replacement applications, etc.

Organic EL displays and organic EL lighting are examples of flexible devices that use polyimide film as a substrate. There are two types of organic EL devices: bottom emission, in which light is extracted from the substrate side, and top emission, in which light is extracted from the opposite side of the substrate. Transparent polyimide films, which have high visible light transmittance and a small YI, are also suitable as substrate materials for bottom emission organic EL devices.

In bottom emission type organic EL devices, light is emitted through the substrate, so in addition to transparency, the substrate material may be required to have optical isotropy and a small retardation (Rth) in the thickness direction due to birefringence from the viewpoint of improving visibility. Similarly, a small Rth may be required for a touch panel substrate. Specifically, based on a polyimide film thickness of 10 μm, Rth is preferably 300 nm or less, more preferably 200 nm or less, even more preferably 100 nm or less, and particularly preferably 50 nm or less. Rth is the product of the birefringence in the thickness direction (the difference between the average refractive index in the plane and the refractive index in the thickness direction) and the thickness. That is, the birefringence in the thickness direction of the polyimide film is preferably 0.03 or less, more preferably 0.02 or less, even more preferably 0.01 or less, and particularly preferably 0.005 or less.

The following provides specific examples, but these are provided for illustrative purposes only and the present invention is not limited to the examples below.

[Evaluation method]
<Yellowness>
The light transmittance of the polyimide film in the range of 200 to 800 nm was measured using an ultraviolet-visible-near infrared spectrophotometer ("V-650" manufactured by JASCO Corporation), and the yellowness index (YI) was calculated according to the formula described in JIS K7373.

<HAZE>
The measurement was performed using an integrating sphere haze meter ("HM-150N" manufactured by Murakami Color Research Laboratory) according to the method described in JIS K7136.

<Internal stress>
The polyamic acid solutions prepared in the Examples and Comparative Examples were applied by a spin coater onto Corning alkali-free glass (thickness 0.7 mm, 100 mm x 100 mm) whose warpage had been measured in advance, and heated at 80°C in air for 30 minutes and at 380°C in a nitrogen atmosphere for 60 minutes to obtain a laminate having a polyimide film with a thickness of 10 μm on the glass substrate. In order to eliminate the influence of water absorption by the polyimide film, the laminate was dried at 120°C for 10 minutes, and then the warpage of the laminate at 25°C in a nitrogen atmosphere was measured using a thin film stress measurement device (Tencor "FLX-2320-S") to evaluate the internal stress between the glass substrate and the polyimide film.

<Retardation (Rth)>
The retardation in the thickness direction Rth for light having a wavelength of 590 nm was measured using a phase difference meter "OPTIPRO" manufactured by Shintech Co., Ltd., and the retardation in the thickness direction Rth(10) at a thickness of 10 μm was calculated from the film thickness D (μm) of the sample based on the following formula.
Rth(10)=Rth×10/D

<Glass transition temperature (Tg)>
Using a thermomechanical analyzer (Hitachi High-Tech Science's "TMA/SS7100"), a load of 98.0 mN was applied to a sample with a width of 3 mm and a length of 10 mm, and the sample was heated from 20°C to 450°C at a rate of 10°C/min, and the temperature and strain (elongation) were plotted (TMA curve). The intersection point extrapolated from the tangents of the TMA curve before and after the change in slope was determined as the glass transition temperature.

<1% weight loss temperature (Td1)>
Using a TG/DTA/7200 manufactured by SII Nano Technology, the temperature was raised from 25° C. to 500° C. (550° C. for Comparative Example 1B and Comparative Example 1C) at a rate of 20° C./min in a nitrogen atmosphere, and the weight was 1 The temperature at which the capacitance decreased by % was defined as Td1 of the polyimide film.

[Abbreviations of compounds and reagents]
In the following, compounds and reagents are described by the following abbreviations.
<Solvent>
NMP: 1-methyl-2-pyrrolidone DGDE: diethylene glycol diethyl ether <tetracarboxylic acid dianhydride>
PMDA: Pyromellitic dianhydride BPAF: 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride BPDA: 3,3'4,4'-biphenyltetracarboxylic dianhydride (diamine)
TFMB: 2,2'-bis(trifluoromethyl)benzidine (silicone diamine: both end-modified silicones manufactured by Shin-Etsu Chemical Co., Ltd.)
X-22-1660B-3: A compound represented by the general formula (4) in which R ² is a methyl group, R ³ is a phenyl group, the proportion of phenyl is 25 mol%, and m is 40; Mw=4400
KF-8012: A compound represented by the general formula (4) in which R ² and R ³ are methyl and m is 57 to 65; Mw=4,400 to 5,000
＜Other＞
APS: 3-aminopropyltriethoxysilane

[Example 1]
<Preparation of polyamic acid solution>
(Nanosilica surface treatment)
In a 300 mL glass separable flask equipped with a stirrer equipped with a stainless steel stirring rod and a nitrogen inlet tube, 4.6 g of organosilica sol (Nissan Chemical's "NMP-ST-R2", average primary particle size of nanosilica: 10 to 15 nm, NMP dispersion with nanosilica content of 30 wt%) and 37.1 g of NMP were charged and stirred. Thereafter, 4.2 g of a 3 wt% NMP solution of APS was added and stirred at 25°C for 1 hour to perform surface treatment of the nanosilica.

(Polyamic Acid Polymerization)
7.012 g of TFMB was added to the NMP solution of the surface-treated nanosilica particles and stirred. 3.244 g of PMDA was added to this solution, and after stirring for 10 minutes or more, 3.764 g of BPAF was added and stirred at room temperature for 12 hours. NMP was added to this solution to dilute the polyamic acid concentration to 15% by weight, and after heating in an oil bath at 80°C for 5 minutes, 2.0 g of a 10% DGDE solution of KF-8012 was slowly dropped. After dropping, the mixture was stirred at 80°C for 30 minutes and quenched with ice water to obtain a uniform and transparent polyamic acid solution. This polyamic acid solution contained 10 parts by weight of nanosilica with respect to a total of 100 parts by weight of the charged amount of tetracarboxylic dianhydride (PMDA and BPAF) and diamine (TFMB).

[Comparative Example 1A]
A separable flask was charged with 56.0 g of NMP as a solvent, and neither organosilica sol nor APS was added. Otherwise, the same procedure as in Example 1 was repeated to prepare a polyamic acid solution not containing inorganic fine particles.

[Comparative Example 1B]
The surface treatment of nanosilica was carried out in the same manner as in Example 1, and TFMB, PMDA and BPAF were added in that order to the NMP solution of the surface-treated nanosilica particles, and the mixture was stirred at room temperature for 12 hours, and then diluted with NMP to prepare a polyamic acid solution with a concentration of 15 wt %. No reaction with silicone diamine was carried out.

[Comparative Example 1C]
Without adding organosilica sol and APS, TFMB, PMDA and BPAF were added in this order to 56.0 g of NMP, stirred at room temperature for 12 hours, and then diluted with NMP to prepare a polyamic acid solution not containing inorganic fine particles. No reaction with silicone diamine was carried out.

[Examples 2, 3 and 4C]
A polyamic acid solution containing nanosilica was prepared in the same manner as in Example 1, except that the type and amount of tetracarboxylic dianhydride used in the polymerization of polyamic acid and the type of silicone diamine were changed as shown in Table 1.

[Examples 4A, 4B and 4D]
The amount of organosilica sol added in the surface treatment of nanosilica was changed so that the amount of nanosilica was 3 parts by weight, 5 parts by weight, and 20 parts by weight per 100 parts by weight of the total of tetracarboxylic dianhydride and diamine, and the amount of APS added was changed accordingly.Other than that, a polyamic acid solution containing nanosilica was prepared in the same manner as in Example 4C.

[Comparative Examples 2 to 4]
A polyamic acid solution not containing inorganic fine particles was prepared in the same manner as in Comparative Example 1A, except that the type and amount of tetracarboxylic dianhydride used in the polymerization of polyamic acid and the type of silicone diamine were changed as shown in Table 1.

[Preparation of polyimide film]
The polyamic acid solutions of the above Examples and Comparative Examples were applied onto a glass plate using a spin coater, and heated in air at 80° C. for 30 minutes and in a nitrogen atmosphere at 380° C. for 1 hour to obtain polyimide films having thicknesses of 10 to 15 μm.

The compositions of the polyamic acids in the Examples and Comparative Examples, and the evaluation results of the properties of the polyimide films are shown in Table 1. TG-DTA charts of the polyimide films of Example 2 and Comparative Example 2 are shown in Figure 1, TG-DTA charts of the polyimide films of Example 3 and Comparative Example 3 are shown in Figure 2, TG-DTA charts of the polyimide films of Comparative Examples 1B and 1C are shown in Figure 3, and cross-sectional TEM images of the polyimide films of Comparative Example 2 and Example 2 are shown in Figures 4 and 5.

The amount of tetracarboxylic dianhydride (mol%) in Table 1 is the value relative to 100 mol% of the total diamine, and the amount of silicone diamine and nanosilica (phr) is the value relative to 100 parts by weight of the total amount of diamine and tetracarboxylic dianhydride charged. The haze of the polyimide films of all the examples and comparative examples was less than 1%, and the YI was 10 or less.

The polyimide film of Comparative Example 1C, which did not contain silicone diamine, had a Td1 of 500°C or more and showed excellent heat resistance, but the internal stress of the laminate exceeded 50 MPa. In Comparative Example 1A, in which a polyorganosiloxane structure was introduced by reaction with silicone diamine, the internal stress was reduced to less than half of that of Comparative Example 1A, and the birefringence of the polyimide film was also reduced accordingly. However, in Comparative Example 1A, Td1 was significantly lower than in Comparative Example 1C. From these results, it can be seen that the polyimide film prepared using polyamic acid in which a polysiloxane structure was introduced by reaction with silicone diamine can reduce the internal stress in the laminate with the substrate, but the introduction of the polysiloxane structure tends to reduce heat resistance.

In Example 1, in which polyamic acid of the same composition as Comparative Example 1A was synthesized in a nanosilica dispersion, the same low internal stress as Comparative Example 1A was maintained, and Td1 was increased by 20°C compared to Comparative Example 1A. Comparisons between Comparative Example 2 and Example 2, Comparative Example 3 and Example 3, and Comparative Example 4 and Examples 4A to 4D also show that by combining with inorganic fine particles, heat resistance is improved while maintaining low internal stress. Furthermore, in Examples 4A to 4D, a tendency was observed for Td1 and Tg to increase as the amount of inorganic fine particles added increased.

These results show that polyimide films made using polyamic acid composited with inorganic microparticles, in which a polysiloxane structure has been introduced by reacting with silicone diamine, have low internal stress in the laminate with the substrate and have excellent heat resistance.

In FIG. 1, in Comparative Example 2, weight loss was observed at 210°C to 300°C, whereas in Example 2, which contains inorganic fine particles, weight loss in this temperature range was suppressed. In FIG. 2, in Comparative Example 3, weight loss occurred from around 270°C, whereas in Example 3, which contains inorganic fine particles, weight loss was hardly observed until around 400°C, and the 1% weight loss temperature Td1 was higher than in Comparative Example 3. From these results, it can be seen that by including inorganic fine particles, thermal decomposition at low temperatures is suppressed and the 1% weight loss temperature Td1 is raised. It can also be seen that in Examples 2 and 3, weight loss (thermal decomposition) is suppressed even in the high temperature range of 400°C or higher, compared to Comparative Examples 2 and 3.

In a comparison of Comparative Example 1B and Comparative Example 1C, in which polyimides not containing a polysiloxane structure were compared between those containing inorganic fine particles and those not containing inorganic fine particles, Comparative Example 1B had a slightly higher Td1 than Comparative Example 1C, but Figure 3 shows no clear difference in the weight loss tendency between the two, and even in Comparative Example 1C, which does not contain inorganic fine particles, no thermal weight loss was observed around 200 to 300°C, as in Comparative Example 2 (Figure 1) and Comparative Example 3 (Figure 2). From these results, it can be said that the improvement in heat resistance due to the use of inorganic fine particles is an effect specific to polyimides having a polysiloxane structure.

From the comparison between Comparative Example 1A and Comparative Example 1C (difference in heat resistance with and without silicone diamine) and the graphs of weight loss shown in Figures 1 to 3, it is believed that the decrease in heat resistance around 200 to 300°C in polyimide that does not contain inorganic fine particles, and the associated decrease in Td1, are due to the introduction of a polysiloxane structure. As shown in the comparison between each example and comparative example, by combining a polyimide with a polysiloxane structure and inorganic fine particles, thermal decomposition caused by the polysiloxane structure is suppressed, and it is believed that the combination of a polyimide having a polysiloxane structure and inorganic fine particles specifically improves heat resistance.

In FIG. 4 (a cross-sectional TEM image of the polyimide film of Comparative Example 2), white island regions were observed. These are thought to be domains of silicone (polysiloxane structure), and while these domains have an effect of reducing internal stress, they are presumed to be the cause of the weight loss at around 200 to 300° C. In FIG. 5 (a cross-sectional TEM image of the polyimide film of Example 2), in addition to the white domains, black regions were observed. These black regions are thought to be silica particles. These black regions (silicone particles) are dispersed so as to penetrate between the white domains (silicone domains), and it is thought that the silica particles have an effect of inhibiting or suppressing interactions between domains (for example, the generation of cyclic siloxanes due to a reaction between siloxanes caused by heating), which contributes to the improvement of heat resistance.

Claims (14)

A polyamic acid containing a structural unit represented by the following general formula (1) and a structural unit represented by the following general formula (2); and silica particles having an average primary particle size of 5 to 200 nm,

The polyamic acid contains a structural unit represented by the following general formula (3) as the structural unit represented by the general formula (1),

The content of the structural unit represented by general formula (3) in the polyamic acid is 60 to 99.7 mol %.
Polyamic acid composition:
Each of the R ^1s independently represents a hydrogen atom, an alkyl group, or an aryl group;
Each of the plurality of R ² and R ³ is independently an alkyl group having 1 to 3 carbon atoms or an aryl group;
X is a tetravalent organic group;
Z is a divalent organic group not containing a silicon atom,
each of the multiple Y's independently represents an alkylene group having 1 to 3 carbon atoms or an arylene group;
m is an integer of 1 or more and less than 300 . The polyamic acid composition according to claim 1, wherein the content of the structural unit represented by general formula (2) in the polyamic acid is 0.3 to 7 mol %. 3. The polyamic acid composition according to claim 1, wherein in the general formula (1) and the general formula (2), X comprises one or more selected from the group consisting of tetravalent organic groups represented by the following formulas (A), (B) and (C):

4. The polyamic acid composition according to claim 1, comprising 1 to 30 parts by weight of said silica particles based on 100 parts by weight of said polyamic acid. A method for producing the polyamic acid composition according to any one of claims 1 to 4 , comprising the steps of:
A method for producing a polyamic acid, comprising reacting a tetracarboxylic dianhydride with a diamine in an organic solvent in which the silica particles are dispersed. A tetracarboxylic dianhydride is reacted with a first diamine in an organic solvent to form a polyamic acid segment, and then a second diamine is added,
The method for producing a polyamic acid composition according to claim 5 , wherein the first diamine comprises 2,2'-bis(trifluoromethyl)benzidine, and the second diamine is a silicone diamine represented by the following general formula (4):

However, R ² , R ³ , Y, and m in the general formula (4) are the same as R ² , R ³ , Y, and m in the general formula (2) above. 7. The method for producing a polyamic acid composition according to claim 6 , wherein the total number of moles of the tetracarboxylic dianhydride is 1.001 times or more and less than 1.100 times the total number of moles of the primary diamine. A polyamic acid solution comprising the polyamic acid composition according to any one of claims 1 to 4 and an organic solvent. 5. A silica particle-containing polyimide obtained by cyclodehydrating the polyamic acid in the polyamic acid composition according to claim 1 . A polyimide film comprising the silica particle-containing polyimide according to claim 9 . A laminate comprising the polyimide film according to claim 10 provided on a support. A method for producing a laminate, comprising applying the polyamic acid solution according to claim 8 onto a support to form a film of polyamic acid on the support, and imidizing the polyamic acid by heating to form a polyimide film on the support. A flexible device comprising the polyimide film according to claim 10 and an electronic element formed on the polyimide film. A method for producing a flexible device, comprising forming a laminate by the method according to claim 12 , forming an electronic element on the polyimide film of the laminate, and then peeling the polyimide film from the support.

Images