TWI689532B - Polyimide film with voids, manufacturing method thereof, and resin precursor - Google Patents

Abstract

The polyimide film of the present invention is characterized by having voids below 100 nm, and is used for the manufacture of flexible devices.

Description

Polyimide film with voids, manufacturing method thereof, and resin precursor

The present invention relates to a voided polyimide film used in a substrate of a flexible device and a method for manufacturing the same.

The above-mentioned polyimide film preferably has high transparency.

Generally, in applications requiring high heat resistance, a film containing polyimide (PI) is used as the resin film. Normal polyimide is produced by solution polymerization of aromatic tetracarboxylic dianhydride and aromatic diamine to produce a polyimide precursor (polyamide), followed by ring closure at high temperature Thermal imidization of dehydration, or chemical imidization of closed-loop dehydration using a catalyst.

Polyimide is an insoluble and infusible super heat-resistant resin with excellent characteristics such as heat-resistant oxidation, heat resistance, radiation resistance, low temperature resistance, and chemical resistance. Therefore, in addition to being used as an insulating coating agent, an insulating film, etc., polyimide can also be used in a wide range of fields including electronic materials such as semiconductor protective films, TFT-LCD electrode protective films, and the like. Recently, research is also being conducted on the use of polyimide film as a flexible substrate utilizing its transparency, lightness, and flexibility to replace the glass substrate previously used as a substrate for displays.

Regarding the polyimide film as a flexible substrate, for example, research examples like Patent Documents 1 and 2 have been reported.

[Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2011-74384

[Patent Document 2] International Publication No. 2012/118020 Specification

[Non-patent literature]

[Non-Patent Literature 1] J. L. Hendrik et al. Nanoporous Polyimide in Advances in Polymer Science, 141, Progress in Polyimide Chemistry II, PP. 1-43, 1998, Springer

However, for example, as a semiconductor insulating film, a TFT-LCD insulating film, an electrode protective film, an ITO (Indium Tin Oxides) electrode substrate for touch panels, and a heat-resistant substrate for flexible displays, a known transparent polyimide The physical characteristics of imine are insufficient.

For example, when a polyimide film is used as a substrate for a flexible display, the following steps are generally adopted.

First, a polyamic acid, which is a precursor of polyimide, is coated on a glass substrate as a support substrate, and then thermally cured, thereby forming a polyimide film on the support glass. Then, an inorganic film is formed on the upper surface of the polyimide film. Then, after forming a display element on the inorganic film, finally, the polyimide film having a TFT (Thin-Film Transistor, thin film transistor) element and an inorganic film is peeled from the support glass, thereby obtaining a flexible display.

Here, when applying a polyimide film with low transparency to a flexible display, color correction must be performed. Especially when using a film with a significantly lower transparency, correction becomes difficult. Therefore, for films used in flexible displays, the transparency must be high.

As an indicator of the transparency of the film, the yellowness YI is widely used. As a polyimide that reduces the yellowness, for example, there is a report in Patent Document 1. This gazette discloses polyimide with extremely low yellowness. Generally speaking, polyimide with lower yellowness tends to have higher residual stress. Again, yellowness The lower polyimide has no absorption at the wavelength of the laser (308 nm and 355 nm) used in the case of peeling the film from the above support glass. Therefore, if such a polyimide film is applied to a flexible display, the energy required for laser peeling becomes large, or coal tends to be generated during peeling.

Furthermore, Patent Document 2 discloses a technique for reducing residual stress while maintaining the glass transition temperature and Young's modulus of polyimide. The purpose of this patent document is to maintain the adhesion between the polyimide film and the glass substrate and reduce the peeling marks when the polyimide film is mechanically peeled off. Patent Document 2 states that the above object can be achieved by introducing a soft block having a structure derived from a silicon-containing diamine into the polymer chain of polyimide. Paragraphs 55 and 151 of this patent document describe the following purpose: forming a micro-phase separation structure with a uniform structure by polysilicon with a size of about 1 nm to 1 μm, and reducing residual stress. Paragraph 31 records the following main purpose: to confirm the size of the polysilicon region by TEM (Transmission Electron Microscopy) measurement.

The present inventors confirmed that as a result, a polyimide film having a micro-phase separation structure of polysiloxane has a soft skeleton present in the film, so the glass transition temperature tends to decrease. It is also known that the polyimide film of Patent Document 2 has high yellowness, but if laser peeling is applied to it, the polyimide film cannot be peeled from the glass substrate when the laser irradiation energy is small Amine membrane. Here, if the irradiation energy of the laser is increased and peeling is attempted, there is a problem that the polyimide film is burnt and particles are generated.

The present invention was made in view of the problems described above.

That is, the object of the present invention is to provide a polyimide film and a method for manufacturing the same, for the polyimide film, the residual stress generated between the glass substrate and the inorganic film is low; It has excellent adhesion to the glass substrate; and preferably has high transparency; even when the irradiation energy of the laser peeling step is low, good peeling can be performed without causing burnt paste and particles.

In order to solve the above-mentioned problems, the present inventors have repeatedly studied hard. As a result, it was found that the polyimide film with a low YI and a void with a specific structure has a high Tg, and shows a high adhesion between the glass substrate and the inorganic film. The scorch paste or fine particles have excellent releasability, and the present invention has been achieved based on this knowledge. That is, the present invention is as follows.

[1] A polyimide film, which is characterized by having a void of 100 nm or less and is used for the manufacture of flexible devices.

[2] The polyimide film of [1], whose yellowness at a film thickness of 20 μm is 7 or less.

[3] The polyimide film of [1] or [2] has a tensile elongation of 30% or more.

[4] The polyimide film according to any one of [1] to [3], which has a polysiloxane residue.

[5] The polyimide film according to any one of [1] to [4], whose void ratio is in the range of 3% by volume to 15% by volume.

[6] The polyimide film according to any one of [1] to [5], wherein the shape of the void is a flat elliptical sphere with a long axis diameter of 30 nm to 60 nm on average.

[7] The polyimide film according to any one of [1] to [6], wherein the voids exist uniformly in the film thickness direction of the polyimide film.

[8] A resin precursor used in the manufacture of a polyimide film according to any one of [1] to [7], characterized in that it has the following general formula (1) in a resin skeleton Unit 1 represented and Unit 2 represented by the following general formula (2):

{In the above general formula (1) and the above general formula (2), R _{1 is} independently a hydrogen atom, a monovalent aliphatic hydrocarbon having 1 to 20 carbon atoms, or an aromatic group having 6 to 10 carbon atoms; R ₂ And R ₃ are independently a monovalent aliphatic hydrocarbon having 1 to 3 carbon atoms, or an aromatic group having 6 to 10 carbon atoms; X ₁ is a tetravalent organic group having 4 to 32 carbon atoms; and X ₂ is a carbon number 4~32 divalent organic radical}.

[9] The resin precursor according to [8], which is a copolymer of tetracarboxylic dianhydride, diamine, and a compound represented by the following general formula (3),

{In the above general formula (3), there are a plurality of R ₄ which are each independently a single bond or a divalent organic group having 1 to 20 carbon atoms; R ₅ and R ₆ are each independently a monovalent carbon number of 1 to 20 carbon atoms Organic group; R ₇ is a monovalent organic group with a carbon number of 1 to 20 in the presence of a plurality of cases; L ₁ , L ₂ , and L ₃ are independently an amine group, isocyanate group, carboxyl group, and acid anhydride group , Ester group, acyl halide group, hydroxyl group, epoxy group, or mercapto group; j is an integer from 3 to 200; and k is an integer from 0 to 197}.

[10] The resin precursor of [9], wherein the tetracarboxylic dianhydride is selected from pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3, One or more types of tetracarboxylic dianhydride in the group consisting of 3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-biphenylbis(trimellitic acid monoester anhydride).

[11] The resin precursor according to [9] or [10], wherein the mass of the compound represented by the above general formula (3) used in synthesizing the resin precursor is tetracarboxylic dianhydride, diamine, and the above The total amount of the compounds represented by the general formula (3) is 6% by mass to 25% by mass.

[12] A resin composition characterized by containing the resin precursor according to any one of [8] to [11] and a solvent.

[13] The polyimide film according to any one of [1] to [7], which is manufactured by spreading the resin composition as [12] on the surface of a support to form a coating film Next, the support and the coating film are heated under the conditions of an oxygen concentration of 23% by mass or less and a temperature of 250° C. or higher to imidate the resin precursor in the coating film and form in the coating film Void.

[14] The polyimide film of [13], wherein the oxygen concentration during the above heating is 2,000 ppm or less.

[15] A method for manufacturing a polyimide film, characterized by having: A coating film forming step, which spreads the resin composition such as [12] on the surface of the support to form a coating film; a heating step, which applies the support and the coating film to an oxygen concentration of 2,000 ppm or less and a temperature of 250° C. or more Heating under the conditions of the above conditions, the resin precursor in the above coating film is imidized and voids are formed in the above coating film to obtain a voided polyimide film; and a peeling step which converts the voided polyimide film The amine film is peeled from the support.

[16] A flexible display characterized by having a polyimide film according to any one of [1] to [7], an inorganic film, and a TFT.

In addition, as a method of producing a polyimide film with voids, the method described in Non-Patent Document 1 is known.

Non-Patent Document 1 discloses a method of producing a polyimide film with voids by using a polyimide precursor in which polypropylene oxide is introduced into the main chain or side chain. If a coating film of a polyimide precursor having a polypropylene oxide portion is formed, it becomes a film structure of polypropylene oxide microphase separation. If the coating film is heat-treated, it causes simultaneous imidization and thermal decomposition of polypropylene oxide, thereby obtaining a voided polyimide film. However, when polypropylene oxide is introduced into the main chain, the film properties such as transparency are reduced. In addition, in order to introduce polypropylene oxide into the side chain, there is a problem of complexity of synthesis.

The present invention provides a polyimide film which achieves the above object by a simple method without reducing the film physical properties and a method for manufacturing the same.

According to the present invention, a polyimide film can be formed, which has a low residual stress generated between a glass substrate or an inorganic film, is excellent in adhesion with a glass substrate, and preferably has a high transparency, and even It can also be stripped when the irradiation energy is low in the laser stripping step, without causing concentration The generation of burnt paste or fine particles of amide imine film.

FIG. 1 is a STEM image (left) and an SEM image (right) of Example 1. FIG.

FIG. 2 is an ATR (Attenuated Total Reflectance) spectrum of the films obtained in Examples 1, 2 and Reference Examples.

Figure 3 is an SEM image of Example 7.

Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "embodiment") will be described in detail. Furthermore, the present invention is not limited to the following embodiments, and can be implemented with various modifications within the scope of the gist thereof.

The polyimide film with voids in this embodiment is a film containing polyimide with a void structure having a size of 100 nm or less. The shape of the void may be a spherical structure, a flat elliptical sphere, etc., preferably a flat elliptical sphere.

When the void is a flat elliptical sphere, the maximum major axis diameter is preferably 100 nm or less, further preferably 80 nm or less, more preferably in the range of 10 to 70 nm, and most preferably in the range of 30 nm to 60 nm. If the void has a size exceeding 100 nm, the polyimide film produces haze. If it is 1 nm or less, sufficient peelability cannot be ensured during laser peeling, and the polyimide film is burnt by laser irradiation, resulting in generation of fine particles.

The porosity of the voided polyimide film of the present embodiment is preferably in the range of 3% by volume to 15% by volume, and more preferably in the range of 6% by volume to 12% by volume. If the void ratio is 3% by volume or more, the ease of peeling during laser peeling is improved, and the scorching of the polyimide film is suppressed, and the generation of fine particles is suppressed. If it is 15% by volume or less, the film tends to exhibit excellent physical properties.

The porosity can be scanned by scanning electron microscope (STEM) or scanning electron microscope (SEM) Observed image analysis and calculation.

The voids of the polyimide film preferably exist uniformly in the entire film. A polyimide film in which voids are uniformly distributed tends to have a high tensile elongation and a low birefringence (Rth), which is preferable. It is especially preferred that the voids are uniform in the thickness direction of the polyimide film.

The uniformity in the film thickness direction of the void can be known by image analysis of the cross-sectional observation of the polyimide film using STEM or SEM. The details are as follows: the obtained electro-imaging is divided into 2 μm regions in the film thickness direction, and the porosity is determined for each region. Find the difference between the maximum value and the minimum value for these void ratios. In addition, when the difference between the maximum value and the minimum value (△void ratio (%)=maximum void ratio (%)-minimum void ratio (%)) is 5% or less, it can be evaluated as the void The uniformity in the film thickness direction is high, which is preferable. This value is more preferably 3% or less, further preferably 1% or less, and particularly preferably 0.5% or less.

In terms of excellent adhesion and adhesion between the glass substrate and the inorganic film, the polyimide film of the present invention preferably contains a polysilicon structure partially. Examples of the inorganic film include CVD (Chemical Vapor Deposition) films and sputtering films such as silicon nitride and silicon oxide.

The content (mass ratio) of polysiloxane residues contained in the polyimide film is preferably in the range of 3 to 15% by mass, and more preferably 6 to 12% by mass. If the content of polysiloxane residue exceeds 15% by mass, sufficient peelability cannot be ensured during laser peeling, and the polyimide film is burnt by laser irradiation, resulting in the generation of particles. On the other hand, when the value is 3% by mass or less, the adhesion to the glass substrate cannot be sufficiently ensured.

The following specifically describes a method for producing a polyimide film having a void structure according to this embodiment.

Specifically, the resin skeleton contains the unit 1 represented by the following general formula (1) and the unit 2 represented by the following general formula (2):

{In the above general formula (1) and the above general formula (2), R _{1 is} independently a hydrogen atom, a monovalent aliphatic hydrocarbon having 1 to 20 carbon atoms, or an aromatic group having 6 to 10 carbon atoms; R ₂ And R ₃ are independently a monovalent aliphatic hydrocarbon having 1 to 3 carbon atoms, or an aromatic group having 6 to 10 carbon atoms; X ₁ is a tetravalent organic group having 4 to 32 carbon atoms; and X ₂ is a carbon number 4~32 divalent organic radical}

The resin composition of the resin precursor (polyamide) and the solvent is spread on the substrate to form a coating film, and secondly, the support and the coating film are heated by controlling the oxygen concentration and the heating temperature to form a coating film. Polyimide film with voids of structure as described above.

Regarding the aforementioned resin precursor, the unit structure 1 represented by the general formula (1) is a structure obtained by reacting tetracarboxylic dianhydride and diamine. X _{1 is} derived from tetracarboxylic dianhydride, and X _{2 is} derived from diamine.

The unit structure 2 represented by the general formula (2) is a structure derived from polysiloxane monomer.

Regarding the resin precursor of this embodiment, X ₂ in the general formula (1) is preferably derived from 2,2′-bis(trifluoromethyl)benzidine, 4,4-(diaminodiphenyl) The residue of 碸, 3,3-(diaminodiphenyl) 碸.

Preferably, part of R ₂ and R ₃ in the general formula (2) is phenyl.

In the resin precursor of the present invention, the total mass of the resin structure including the unit 1 and the unit 2 is preferably 30% by mass or more with respect to all resin precursors.

<tetracarboxylic dianhydride>

Next, the tetravalent organic group X ₁ of the tetracarboxylic dianhydride deriving unit 1 contained in it will be described.

As the tetracarboxylic dianhydride, specifically, it is preferably selected from an aromatic tetracarboxylic dianhydride having 8 to 36 carbon atoms, an aliphatic tetracarboxylic dianhydride having 6 to 50 carbon atoms, and a carbon number It is a compound in 6-36 alicyclic tetracarboxylic dianhydride. The so-called carbon number here also includes the number of carbons contained in the carboxyl group.

環[3,2,1]辛烷-2,4-二酮-6-螺-3'-(四氫呋喃-2',5'-二酮)、4-(2,5-二側氧四氫呋喃-3-基)-1,2,3,4-四氫萘-1,2-二羧酸酐、乙二醇-雙-(3,4-二羧酸酐苯基)醚、4,4'-聯苯雙(偏苯三甲酸單酯酸酐)(以下亦記為TAHQ)等。 More specifically, examples of the aromatic tetracarboxylic dianhydride having 8 to 36 carbon atoms include: 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (hereinafter also referred to as 6FDA ), 5-(2,5-dioxytetrahydro-3-furanyl)-3-methyl-cyclohexene-1,2 dicarboxylic anhydride, pyromellitic dianhydride (hereinafter also referred to as PMDA) , 1, 2, 3, 4-benzenetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (hereinafter also referred to as BTDA), 2,2',3, 3'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (hereinafter also referred to as BPDA), 3,3',4,4'-diphenyl Benzene tetracarboxylic dianhydride (hereinafter also referred to as DSDA), 2,2',3,3'-biphenyltetracarboxylic dianhydride, methylene-4,4'-diphthalic dianhydride, 1,1-ethylene-4,4'-diphthalic dianhydride, 2,2-propylene-4,4'-diphthalic dianhydride, 1,2-ethylidene- 4,4'-diphthalic dianhydride, 1,3-trimethylene-4,4'-diphthalic dianhydride. 1,4-tetramethylene-4,4'-diphthalic dianhydride, 1,5-pentamethylene-4,4'-diphthalic dianhydride, 4,4'-oxygen Diphthalic dianhydride (hereinafter also referred to as ODPA), thio-4,4'-diphthalic dianhydride, sulfonyl-4,4'-diphthalic dianhydride, 1 ,3-bis(3,4-dicarboxyphenyl)phthalic anhydride, 1,3-bis(3,4-dicarboxyphenoxy)phthalic anhydride, 1,4-bis(3,4-dicarboxy Phenoxy)phthalic anhydride, 1,3-bis[2-(3,4-dicarboxyphenyl)-2-propyl]phthalic anhydride, 1,4-bis[2-(3,4-bis Carboxyphenyl)-2-propyl]phthalic anhydride, bis[3-(3,4-dicarboxyphenoxy)phenyl]methanedianhydride, bis[4-(3,4-dicarboxyphenoxy )Phenyl]methane dianhydride, 2,2-bis[3-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 2,2-bis[4-(3,4-dicarboxybenzene Oxy)phenyl]propane dianhydride (hereinafter also referred to as BPADA), bis (3,4-dicarboxyphenoxy) dimethyl silane dianhydride, 1,3-bis (3,4-dicarboxyphenyl )-1,1,3,3-tetramethyldisilazane dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-Naphthalene tetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 2,3,6,7-anthracene tetracarboxylic dianhydride, 1,2,7 , 8-phenanthrenetetracarboxylic dianhydride, etc. As the aliphatic tetracarboxylic dianhydride having 6 to 50 carbon atoms, for example, ethyltetracarboxylic dianhydride, 1,2,3,4-butane Tetracarboxylic dianhydride, etc. As the alicyclic tetracarboxylic dianhydride having 6 to 36 carbon atoms, for example, 1,2,3,4-cyclobutane tetracarboxylic dianhydride (hereinafter also referred to as CBDA) ), cyclopentane tetracarboxylic dianhydride, cyclohexane-1,2,3,4-tetracarboxylic dianhydride, cyclohexane-1,2,4,5-tetracarboxylic dianhydride (hereinafter referred to as CHDA), 3,3',4,4'-biscyclohexyltetracarboxylic dianhydride, carbonyl-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, methylene-4 ,4,-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, 1,2-ethylidene-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride , 1,1-ethylene-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, 2,2-propylene-4,4'-bis(cyclohexane- 1,2-dicarboxylic acid) dianhydride, oxy-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, thio-4,4'-bis(cyclohexane- 1,2-dicarboxylic acid) dianhydride, sulfonyl-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, bicyclo[2,2,2]oct-7-ene -2,3,5,6-tetracarboxylic dianhydride, rel-[1S,5R,6R]-3-oxabis

Cyclo[3,2,1]octane-2,4-dione-6-spiro-3'-(tetrahydrofuran-2',5'-dione), 4-(2,5-bilateral oxygen tetrahydrofuran- 3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, ethylene glycol-bis-(3,4-dicarboxylic anhydride phenyl) ether, 4,4'-linked Benzobis (trimellitic acid monoester anhydride) (hereinafter also referred to as TAHQ), etc.

Among them, from the viewpoint of lowering CTE, improving chemical resistance, increasing glass transition temperature (Tg), and improving mechanical elongation, it is preferable to use 1 selected from the group consisting of BTDA, PMDA, BPDA, and TAHQ More than one species. In addition, in the case of obtaining a film with higher transparency, from the viewpoint of reduction in yellowness, reduction in birefringence, and improvement in mechanical elongation, it is preferably Use one or more selected from the group consisting of 6FDA, ODPA and BPADA. In addition, from the viewpoints of reduction in residual stress, reduction in yellowness, reduction in birefringence, improvement in chemical resistance, improvement in Tg, and improvement in mechanical elongation, BPDA is preferred. In addition, from the viewpoint of reduction in residual stress and reduction in yellowness, CHDA is preferable. Among these, from the viewpoint of high chemical resistance, reduction of residual stress, reduction of yellowness, reduction of birefringence, and improvement of total light transmittance, it is preferable to exhibit high chemical resistance and high Tg And at least one of the rigid structures of low CTE selected from the group consisting of PMDA and BPDA, and one or more selected from the group consisting of 6FDA, ODPA and CHDA with lower yellowness and birefringence. use.

In the resin precursor of the present invention, it is preferable that the component derived from biphenyltetracarboxylic acid (BPDA) contains 20 mol% or more of all components derived from the tetracarboxylic dianhydride of the resin precursor.

Regarding the resin precursor of this embodiment, a dicarboxylic acid may be used in addition to the above-mentioned tetracarboxylic dianhydride within a range that does not impair its performance, thereby preparing a polyamidoamide imide precursor. By using such a precursor, the obtained film can adjust various properties such as an increase in mechanical elongation, an increase in glass transition temperature, and a decrease in yellowness. Examples of such dicarboxylic acids include dicarboxylic acids having an aromatic ring and alicyclic dicarboxylic acids. Particularly preferred is at least one compound selected from the group consisting of aromatic dicarboxylic acids having 8 to 36 carbon atoms and alicyclic dicarboxylic acids having 6 to 34 carbon atoms. The number of carbons mentioned here also includes the number of carbons contained in the carboxyl group.

Among these, dicarboxylic acids having aromatic rings are preferred.

Specifically, for example, isophthalic acid, terephthalic acid, 4,4'-biphenyl dicarboxylic acid, 3,4'-biphenyl dicarboxylic acid, 3,3'-biphenyl dicarboxylic acid , 1,4-naphthalene dicarboxylic acid, 2,3-naphthalene dicarboxylic acid, 1,5-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-sulfonyl dibenzoic acid, 3 ,4'-sulfonylbisbenzoic acid, 3,3'-sulfonylbisbenzoic acid, 4,4'-oxybisbenzoic acid, 3,4'-oxybisbenzoic acid, 3,3'- Oxybisbenzoic acid, 2,2-bis(4-carboxyphenyl)propane, 2,2-bis(3-carboxyphenyl)propane, 2,2'- Dimethyl-4,4'-biphenyldicarboxylic acid, 3,3'-dimethyl-4,4'-biphenyldicarboxylic acid, 2,2'-dimethyl-3,3'-bi Phthalic acid, 9,9-bis(4-(4-carboxyphenoxy)phenyl) stilbene, 9,9-bis(4-(3-carboxyphenoxy)phenyl) stilbene, 4,4 '-Bis(4-carboxyphenoxy)biphenyl, 4,4'-bis(3-carboxyphenoxy)biphenyl, 3,4'-bis(4-carboxyphenoxy)biphenyl, 3, 4'-bis(3-carboxyphenoxy)biphenyl, 3,3'-bis(4-carboxyphenoxy)biphenyl, 3,3'-bis(3-carboxyphenoxy)biphenyl, 4 ,4'-bis(4-carboxyphenoxy)-p-terphenyl, 4,4'-bis(4-carboxyphenoxy)-m-terphenyl, 3,4'-bis(4-carboxyphenoxy) Radical)-p-terphenyl, 3,3'-bis(4-carboxyphenoxy)-p-terphenyl, 3,4'-bis(4-carboxyphenoxy)-m-terphenyl, 3,3' -Bis(4-carboxyphenoxy)-triphenylbenzene, 4,4'-bis(3-carboxyphenoxy)-p-terphenyl, 4,4'-bis(3-carboxyphenoxy)- M-terphenyl, 3,4'-bis(3-carboxyphenoxy)-p-terphenyl, 3,3'-bis(3-carboxyphenoxy)-p-terphenyl, 3,4'-bis( 3-Carboxyphenoxy)-metatriphenyl, 3,3'-bis(3-carboxyphenoxy)-metatriphenyl, 1,1-cyclobutanedicarboxylic acid, 1,4-cyclohexyl Alkanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4,4'-benzophenonedicarboxylic acid, 1,3-phenylene diacetic acid, 1,4-phenylene diacetic acid, etc.; And 5-aminoisophthalic acid derivatives described in International Publication No. 2005/068535. In the case where the dicarboxylic acid and the polymer are actually copolymerized, it can also be used in the form of acetyl chloride, active ester, etc. derived from sulfenyl chloride and the like.

Among these, terephthalic acid is particularly preferred from the viewpoint of lowering the YI value and increasing Tg. In the case where dicarboxylic acid and tetracarboxylic dianhydride are used together, from the viewpoint of the chemical resistance of the film obtained, it is preferably relative to the sum of dicarboxylic acid and tetracarboxylic dianhydride The overall mole number, dicarboxylic acid is less than 50 mole%.

<diamine>

In the resin precursor of the present embodiment, as the diamine of X ₂ in the derivation unit 1, specifically, for example, 4,4-(diaminodiphenyl) benzene (hereinafter also referred to as 4,4) -DAS), 3,4-(diaminodiphenyl) ash and 3,3-(diaminodiphenyl) ash (hereinafter also referred to as 3,3-DAS), 2,2'-bis( Trifluoromethyl) benzidine (hereinafter also referred to as TFMB), 2,2'-dimethyl 4,4'-diaminobiphenyl (hereinafter also referred to as m-TB), 1,4-diamine Benzene (hereinafter also referred to as p-PD), 1,3-diaminobenzene (hereinafter also referred to as m-PD), 4-aminophenyl 4'-aminobenzoate (hereinafter also referred to as APAB) ), 4,4'-diaminobenzoate (hereinafter also referred to as DABA), 4,4'- (or 3,4'-, 3,3'-, 2,4'-) diamino Diphenyl ether, 4,4'-(or 3,3'-) diaminodiphenyl sulfone, 4,4'-(or 3,3'-) diaminodiphenyl sulfide, 4,4' -Benzophenone diamine, 3,3'-benzophenone diamine, 4,4'-bis(4-aminophenoxy) phenylbenzene, 4,4'-bis(3-amino Phenoxy) phenylbenzene, 4,4'-bis(4-aminophenoxy)biphenyl, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4- Aminophenoxy)benzene, 2,2-bis{4-(4-aminophenoxy)phenyl}propane, 3,3',5,5'-tetramethyl-4,4'-di Aminodiphenylmethane, 2,2'-bis(4-aminophenyl)propane, 2,2',6,6'-tetramethyl-4,4'-diaminobiphenyl, 2, 2',6,6'-tetratrifluoromethyl-4,4'-diaminobiphenyl, bis{(4-aminophenyl)-2-propyl}1,4-benzene, 9,9 -Bis(4-aminophenyl) stilbene, 9,9-bis(4-aminophenoxyphenyl) stilbene, 3,3'-dimethylbenzidine, 3,3'-dimethoxy Benzidine and 3,5-diaminobenzoic acid, 2,6-diaminopyridine, 2,4-diaminopyridine, bis(4-aminophenyl-2-propyl)-1,4- Benzene, 3,3'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (3,3'-TFDB), 2,2'-bis[3(3-aminophenoxy )Phenyl] hexafluoropropane (3-BDAF), 2,2'-bis[4(4-aminophenoxy)phenyl] hexafluoropropane (4-BDAF), 2,2'-bis(3 -Aromatic diamines such as aminophenyl) hexafluoropropane (3,3'-6F), 2,2'-bis(4-aminophenyl) hexafluoropropane (4,4'-6F). Among these, from the viewpoint of reduction in yellowness, reduction in CTE, and higher Tg, it is preferable to use a member selected from the group consisting of 4,4-DAS, 3,3-DAS, 1,4-cyclohexanediamine, and TFMB , And one or more of the groups formed by APAB.

<Introduction of Silicon Compound>

The structure represented by the above general formula (2) is derived from polysiloxane monomers. The amount of polysiloxane monomer used when synthesizing the resin precursor is based on the mass of the resin precursor, and is preferably 6% by mass to 25% by mass. The effect of reducing the stress generated between the obtained polyimide film and the inorganic film is fully obtained From the viewpoint of the effect of reducing yellowness and yellowness, it is advantageous to use the polysiloxane monomer in an amount of 6% by mass or more. This value is more preferably 8% by mass or more, and further preferably 10% by mass or more. On the other hand, when the amount of the polysiloxane monomer used is 25% by mass or less, the obtained polyimide film does not generate white turbidity, the transparency is improved, and good heat resistance is obtained, which is advantageous from this viewpoint. This value is more preferably 22% by mass or less, and further preferably 20% by mass or less. From the viewpoints of chemical resistance, total light transmittance, residual stress, adhesion to glass substrates, and ease of laser peeling, the use amount of polysiloxane monomer is particularly preferably 10% by mass or more and 20 Mass% or less. As described below, it can be considered that when the coating film of the resin precursor is thermally cured under the control of the oxygen concentration, part of the polysiloxane introduced into the resin precursor is cyclic trimer, cyclic tetramer, etc. The form is sparse. It is preferable to adjust the introduction of the polysiloxane monomer when the resin precursor is adjusted in such a manner that the mass ratio of the polysilicone residue after dispersion becomes a range of 4 to 18 mass% relative to the mass of the total polyimide film. the amount.

As the monovalent aliphatic hydrocarbon group having 1 to 20 carbon atoms in the general formula (2), for example, an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, etc.; and one having 6 to 10 carbon atoms Examples of aromatic groups include aryl groups and the like. The alkyl group having 1 to 20 carbon atoms is preferably an alkyl group having 1 to 10 carbon atoms from the viewpoint of heat resistance and residual stress. Specific examples include methyl, ethyl, and propyl groups. , Isopropyl, butyl, isobutyl, tertiary butyl, pentyl, hexyl, etc. The cycloalkyl group having 3 to 20 carbon atoms is preferably a cycloalkyl group having 3 to 10 carbon atoms from the above viewpoint, and specific examples thereof include cyclopentyl group and cyclohexyl group. As the aryl group having 6 to 10 carbon atoms, from the above viewpoint, specifically, for example, phenyl, tolyl, naphthyl and the like can be mentioned.

As the polysiloxane monomer derived from the unit 2 described above, for example, a polysiloxane compound represented by the following general formula (3) is preferably used.

[Chemical 4]

{In the above general formula (3), there are a plurality of R ₄ which are each independently a single bond or a divalent organic group having 1 to 20 carbon atoms; R ₅ and R ₆ are each independently a monovalent carbon number of 1 to 20 carbon atoms Organic group; R ₇ is a monovalent organic group with a carbon number of 1 to 20 in the presence of a plurality of cases; L ₁ , L ₂ and L ₃ are independently an amine group, isocyanate group, carboxyl group, acid anhydride group, Ester group, halo group, hydroxyl group, epoxy group, or mercapto group; j is an integer of 3~200, and k is an integer of 0~197}

Examples of the divalent organic group having 1 to 20 carbon atoms for R ₄ include methylene, alkylene having 2 to 20 carbon atoms, cycloalkyl having 3 to 20 carbon atoms, and 6 to 20 carbon atoms. Extend aryl and so on. The alkylene group having 2 to 20 carbon atoms is preferably an alkylene group having 2 to 10 carbon atoms from the viewpoint of heat resistance, residual stress and cost, and specific examples include dimethylene , Trimethylene, tetramethylene, pentamethylene, hexamethylene, etc. The cycloalkyl group having 3 to 20 carbon atoms is preferably a cycloalkyl group having 3 to 10 carbon atoms from the above viewpoint. Specifically, for example, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, etc. may be mentioned. Among these, from the above viewpoint, a divalent aliphatic hydrocarbon having 3 to 20 carbon atoms is preferred. The arylene group having 6 to 20 carbon atoms is preferably an aromatic group having 3 to 20 carbon atoms from the above viewpoint, and specific examples thereof include phenylene and naphthyl groups.

In the general formula (3), R ₅ and R ₆ are synonymous with R ₂ and R ₃ in the general formula (2), and the preferred aspect is the same as described above with respect to the general formula (2). Also, the preferred aspect of R _{7 is} the same as R ₂ and R ₃ .

In the general formula (3), j is an integer of 3 to 200, preferably an integer of 10 to 200, more preferably an integer of 20 to 150, further preferably an integer of 30 to 100, particularly preferably 35 to 80 Integer. In the general formula (3), k is an integer of 0 to 197, preferably 0 to 100, more preferably 0 to 50, and particularly preferably 0 to 25. If k exceeds 197, when preparing a resin composition containing a resin precursor and a solvent, there may be problems such as white turbidity of the composition. When k is 0, it is preferable from the viewpoint of increasing the molecular weight of the resin precursor, and from the viewpoint of the heat resistance of the obtained polyimide. When k is 0, from the viewpoint of increasing the molecular weight of the resin precursor, and from the viewpoint of the heat resistance of the obtained polyimide, j is preferably 3 to 200.

In the general formula (3), L ₁ , L ₂ and L ₃ are each independently an amine group, an isocyanate group, a carboxyl group, an acid anhydride group, an acid ester group, an acyl halide group, a hydroxyl group, an epoxy group, or a mercapto group.

The amine group can also be substituted. Examples of substituted amine groups include bis(trialkylsilyl)amine groups. In the general formula (3), specific examples of compounds in which L ₁ , L ₂ , and L ₃ are amine groups include amine-modified methylphenyl polysiloxanes at both ends (for example, X22 manufactured by Shin-Etsu Chemical Co., Ltd.) -1660B-3 (number-average molecular weight 4,400) and X22-9409 (number-average molecular weight 1,300)); amine-modified dimethyl polysiloxane at both ends (such as X22-161A manufactured by Shin-Etsu Chemical Co., Ltd. (number-average molecular weight 1,600) , X22-161B (number average molecular weight 3,000) and KF8012 (number average molecular weight 4,400); BY16-835U (number average molecular weight 900) manufactured by Dow Corning Toray; and Silaplane FM3311 (number average molecular weight 1000) manufactured by Chisso Corporation, etc.

Specific examples of the compounds in which L ₁ , L ₂ , and L ₃ are isocyanate groups include isocyanate-modified polysiloxanes obtained by reacting the above-mentioned two-terminal amine-modified polysiloxane and carbamide compounds.

Specific examples of compounds in which L ₁ , L ₂ , and L ₃ are carboxyl groups include, for example, X22-162C (number average molecular weight 4,600) of Shin-Etsu Chemical Co., Ltd., and BY16-880 (number average molecular weight 6,600) manufactured by Dow Corning Toray. .

Examples of the case where L ₁ , L ₂ , and L ₃ are acid anhydride groups include, for example, groups having the following formula

Acetyl compounds of at least one of the groups represented by each.

Specific examples of compounds in which L ₁ , L ₂ , and L ₃ are acid anhydride groups include, for example, X22-168AS (manufactured by Shin-Etsu Chemical, number average molecular weight 1,000), X22-168A (manufactured by Shin-Etsu Chemical, number average molecular weight 2,000) , X22-168B (manufactured by Shin-Etsu Chemical Co., Ltd., number-average molecular weight 3,200), X22-168-P5-8 (manufactured by Shin-Etsu Chemical Co., Ltd., number-average molecular weight 4,200), DMS-Z21 (manufactured by Gelest Corporation, number-average molecular weight 600-800), etc.

Specific examples of the compounds in which L ₁ , L ₂ , and L ₃ are acid ester groups include compounds obtained by reacting the above compounds in which L ₁ , L ₂ , and L ₃ are carboxyl groups or acid anhydride groups with alcohol.

Examples of the case where L ₁ , L ₂ , and L ₃ are an amide halide group include, for example, carboxylic acid chloride, carboxylic acid fluoride, carboxylic acid bromide, and carboxylic acid iodide.

Specific examples of compounds in which L ₁ , L ₂ , and L ₃ are hydroxyl groups include, for example, KF-6000 (manufactured by Shin-Etsu Chemicals, number average molecular weight 900), KF-6001 (manufactured by Shin-Etsu Chemicals, number average molecular weight 1,800), KF -6002 (manufactured by Shin-Etsu Chemical, number average molecular weight 3,200), KF-6003 (manufactured by Shin-Etsu Chemical, number average molecular weight 5,000), etc. It can be considered that a compound having a hydroxyl group reacts with a compound having a carboxyl group or an acid anhydride group.

Specific examples of compounds in which L ₁ , L ₂ , and L ₃ are epoxy groups include X22-163 (manufactured by Shin-Etsu Chemical Co., Ltd., number-average molecular weight of 400), KF-105 (Shinyoshi Chemical Co., Ltd.) Manufacturing, number average molecular weight 980), X22-163A (manufactured by Shin-Etsu Chemical, number average molecular weight 2,000), X22-163B (manufactured by Shin-Etsu Chemical, number average molecular weight 3,500), X22-163C (manufactured by Shin-Etsu Chemical, number average molecular weight 5,400); X22-169AS (manufactured by Shin-Etsu Chemicals, number average molecular weight 1,000), X22-169B (manufactured by Shin-Etsu Chemicals, number average molecular weight 3,400) as two-terminal alicyclic epoxy type; X22-9002 as epoxy type of both-terminal side chain (Manufactured by Shin-Etsu Chemical Co., functional group equivalent of 5,000 g/mol), etc. It can be considered that a compound having an epoxy group reacts with a diamine.

Specific examples of compounds in which L ₁ , L ₂ , and L ₃ are mercapto groups include, for example, X22-167B (manufactured by Shin-Etsu Chemicals, number average molecular weight 3,400), X22-167C (manufactured by Shin-Etsu Chemicals, number average molecular weight 4,600), and the like. It can be considered that a compound having a mercapto group reacts with a compound having a carboxyl group or an acid anhydride group.

From the viewpoint of increasing the molecular weight of the resin precursor or the viewpoint of the heat resistance of the obtained polyimide, it is preferred that L ₁ , L ₂ , and L ₃ are each independently an amine group or an acid anhydride group, and then From the viewpoint of avoiding the cloudiness of the resin composition containing the resin precursor and the solvent, and from the viewpoint of cost, it is preferable that any one of L ₁ , L ₂ , and L ₃ is an amine group; or L ₁ and L ₂ are independent of each other The ground is an amine group or an anhydride group, and k is 0. In the latter case, it is more preferable that both L ₁ and L ₂ are amine groups.

The number average molecular weight of the resin precursor of this embodiment is preferably 3,000 to 1,000,000, more preferably 5,000 to 500,000, further preferably 7,000 to 300,000, and particularly preferably 10,000 to 250,000. From the viewpoint of obtaining good heat resistance and strength (for example, strong elongation), it is preferable that the molecular weight is 3,000 or more, and the concept of solubility in solvents is obtained well. It is preferable that it is 1,000,000 or less from the viewpoint that it can be applied without any penetration at a required film thickness during processing such as coating. From the viewpoint of obtaining higher mechanical elongation, the molecular weight is preferably 50,000 or more. In the present disclosure, the aforementioned number average molecular weight is a value calculated by standard polystyrene conversion using gel permeation chromatography.

Regarding the resin precursor of this embodiment, a part of it may be imidate. The amidation of the resin precursor can be carried out by the well-known chemical amidation or thermal amidation. Among these, thermoimidation is preferred. As a specific method, it is preferable to heat the solution at 130 to 200° C. for 5 minutes to 2 hours after preparing the resin composition by the following method. By this method, part of the polymer can be dehydrated and imidized without causing precipitation of the resin precursor. Here, by controlling the heating temperature and the heating time, it is possible to control the rate of amidation. The partial imidization can improve the viscosity stability of the resin composition when stored at room temperature. The range of the imidate ratio is preferably 5% to 70% from the viewpoint of the solubility and storage stability of the solution.

Alternatively, N,N-dimethylformamide dimethyl acetal, N,N-dimethylformamide diethyl acetal, etc. may be added to the resin precursor to heat the carboxylic acid Part or all of the esterification. By doing so, the viscosity stability of the resin composition when stored at room temperature can be improved.

<resin composition>

The resin precursor of the present embodiment as described above is preferably used in the form of a resin composition (varnish) dissolved in a solvent.

With this configuration, a transparent polyimide film can be manufactured without a special combination of solvents.

In a more preferred aspect, the resin composition of this embodiment can react tetracarboxylic dianhydride, diamine, and polysiloxane monomer in a solvent, such as an organic solvent, as a precursor of the resin. Manufactured in the form of polyamic acid solution containing polyamic acid and solvent. Here, the conditions during the reaction are not particularly limited. For example, the reaction temperature may be -20 to 150°C, and the reaction time may be 2 to 48. Conditions of hours. In order to allow the reaction with the polysiloxane monomer to proceed sufficiently, it is preferable to perform heating at a temperature of 120° C. or higher for about 30 minutes or more in the synthesis reaction. In addition, the reaction is preferably carried out in an inert environment such as argon or nitrogen.

The solvent is not particularly limited as long as it dissolves the polyamic acid. As a well-known reaction solvent, for example, it is selected from dimethylene glycol dimethyl ether (DMDG), m-cresol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), Dimethyl acetamide (DMAc), dimethyl sulfoxide (DMSO), acetone, diethyl acetate, Equamide M100 (trade name: manufactured by Idemitsu Kosei), and Equamide B100 (trade name: Idemitsu Kosei) One or more polar solvents are more useful. Among them, one or more selected from NMP, DMAc, Equation M100, and Equation B100 are preferred. In addition, a low-boiling-point solution such as tetrahydrofuran (THF), chloroform, or a low-absorption solvent such as γ-butyrolactone may be used together with or instead of the above-mentioned solvent.

The resin composition of this embodiment may contain an alkoxysilane compound in an amount of 0.01 to 2% by mass relative to 100% by mass of the resin precursor in order to impart sufficient adhesion to the support of the obtained polyimide film. .

When the content of the alkoxysilane compound is 0.01% by mass or more relative to 100% by mass of the resin precursor, good adhesion to the support can be obtained, and from the viewpoint of storage stability of the resin composition, the alkyl The content of the oxysilane compound is preferably 2% by mass or less. The content of the alkoxysilane compound relative to the resin precursor is more preferably 0.02 to 2% by mass, further preferably 0.05 to 1% by mass, particularly preferably 0.05 to 0.5% by mass, and particularly preferably 0.1 to 0.5% by mass.

Examples of alkoxysilane compounds include 3-acetylureidopropyltriethoxysilane, bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, and 3-glycidoxy Propyltrimethoxysilane, phenyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane Silane, γ-aminopropyltripropoxysilane, γ-aminopropyltributoxysilane, γ-aminoethyltriethoxysilane, γ-aminoethyltrimethoxysilane, γ-aminoethyltripropoxysilane, γ-aminoethyltributoxysilane, γ-aminobutyltriethoxysilane, γ-aminobutyltrimethoxysilane, γ-amine Butyltripropyloxysilane, γ-aminobutyltributoxysilane, etc. These can also be used in combination of 2 or more types.

<Production of Polyimide Film with Void>

The polyimide resin film having a void structure of this embodiment can be produced by the following method: spreading the resin composition on the surface of the support to form a coating film, and then, applying the support and the coating film to oxygen Heat at a concentration of 23% by mass or less and a temperature of 250°C or more.

In this manual, the unit "mass%" of the oxygen concentration is a volume-based percentage, and the unit "ppm" of the oxygen concentration described later is a volume-based percentage.

Here, as the support, for example, an inorganic substrate like a glass substrate such as an alkali-free glass substrate is not particularly limited.

Examples of the method for spreading the polyimide precursor on the substrate include known coating methods such as spin coating, slit coating, and blade coating.

Then, by using a hot plate, an oven, or the like to heat to 80° C. to 200° C., the solvent is evaporated to prepare a coating film (pre-baked film). At this time, the polysiloxane portion and the polyimide portion that become the resin precursor form a film with a micro-phase separation structure.

Then, by putting the support and the coating film into an oven having an oxygen concentration of 23% by mass or less and heating to 250° C. or higher, the resin precursor is dehydrated and imidized, and the micro-phase-separated polysiloxane Part of the part is decomposed and removed to form voids, whereby the polyimide film of this embodiment can be made. It can be considered that by heating above 250°C, the polysiloxane in the resin precursor is partially heated Decomposition occurs, and cyclic trimers and/or cyclic tetramers are generated and evaporated to be removed. Instead of making a pre-baked film, the coated support can be directly put into an oven with controlled oxygen concentration and heated to above 250°C.

The size and porosity of the voids can be controlled by, for example, setting the polysilicon content, curing temperature, curing time, oxygen concentration, etc. in the polymer to an appropriate range.

Specifically, for example, if the introduction amount of the polysiloxane portion represented by the general formula (2) in the resin precursor is increased, the size of the polysiloxane area in the pre-baked film becomes larger. The size of the polysilicon area structure becomes one of the factors for controlling the void structure. If the polysilicon part is completely thermally decomposed, the size of the area of the pre-baked film becomes the maximum size of the gap of the obtained polyimide film. Therefore, by controlling the size of the polysilicon area of the prebaked film, the void size (average long axis diameter) of the obtained polyimide film can be controlled. In order to control the size of the polysilicon region of the prebaked film to 100 nm or less, as long as the mass ratio of the polysilicone portion represented by the general formula (2) of the resin precursor is set to 25% by mass of the total resin precursor Just follow. Here, by controlling one or more factors among curing temperature, curing time, and oxygen concentration during curing, the size of the voids of the polyimide film and the polysiloxane of the pre-baked film can be adjusted to any degree The size relationship of the area size.

The oxygen concentration during heating in this embodiment is preferably 2,000 ppm or less. When the oxygen concentration during heating is within this range, there is a tendency to produce uniform voids in the film. Therefore, the film tends to have a higher tensile elongation and a lower birefringence (Rth), which is preferable. On the other hand, if it is heated at an oxygen concentration of more than 2,000 ppm and 23% by mass or less, the uniformity in the film thickness direction of the voids tends to be slightly impaired.

It can be speculated that this phenomenon is caused by the thermal decomposition reaction of the polysilicon portion of the resin precursor when the oxygen concentration is 2,000 ppm or more. The reason is unknown, but the inventors speculate that the reason is that, in the presence of a significant amount of oxygen, the organic gene on the silicon atom of polysilicon Oxygen is oxidized to produce formaldehyde, formic acid, hydrogen, carbon dioxide, etc., which is converted into a highly crosslinked gel-like heat-resistant polymer.

However, by controlling the oxygen concentration to 2,000 ppm or less, a void structure starts to be uniformly generated in the polyimide film. When comparing at the same heating temperature, it was confirmed that the lower the oxygen concentration, the larger the size of the void.

In addition, when the oxygen concentration is 2,000 ppm or less, as long as the oxygen concentration is the same, the higher the heating temperature, the larger the size of the voids of the polyimide film.

The inventors confirmed that, from the viewpoint of controlling the size of the void, it is preferable to suppress the oxygen concentration during the heat treatment to 1,000 ppm or less. From the viewpoint of controlling the size of the void, the heating temperature is preferably in the range of 250°C to 480°C, and further preferably in the range of 280°C to 450°C.

It is particularly preferable to control the oxygen concentration to 100 ppm or less, and the heating temperature to the range of 280°C to 450°C.

Examples of the inert gas used when controlling the oxygen concentration include nitrogen gas and Ar gas. From the economic viewpoint, nitrogen gas is preferred. In addition, in order to control the oxygen concentration, a vacuum oven or the like may be used for heating under reduced pressure.

The thickness of the polyimide film of the present embodiment is not particularly limited, but it is preferably in the range of 1 to 200 μm, and more preferably 5 to 50 μm.

Furthermore, in the polyimide film of the present embodiment, the residual stress of the film thickness of 10 μm is preferably 25 MPa or less.

The polyimide film of this embodiment preferably has a yellowness (YI) of 7 or less at a thickness of 20 μm. The polyimide film having a YI value within this range can be used without color correction when it is applied to a substrate for a flexible display. The YI value of the 20 μm film thickness of the polyimide film is more preferably 6 or less, Particularly preferred is 5 or less.

In addition, when the thickness of the resin film is not 20 μm, the yellowness of the thickness of 20 μm can be known by converting the measured value of the film to the thickness.

<Laminate>

The present invention also provides a laminate including a support and a polyimide film formed on the support. The laminate can be obtained by spreading the resin composition on the surface of the support to form a coating film, and then, the support and the coating film are at an oxygen concentration of 23% by mass or less and a temperature of 250° C. or more Under heating conditions.

This laminate is used, for example, in the manufacture of flexible devices.

More specifically, a semiconductor device can be formed on a polyimide film having a laminate, and then the support can be peeled off to obtain a soft device including the polyimide film and the semiconductor device formed thereon.

As described above, the polyimide film of the present embodiment has a specific void structure, whereby the residual stress generated between the glass substrate or the inorganic film is low, the adhesion to the glass substrate is excellent, and even in laser In the peeling step, when the irradiation energy is low, it can be peeled well without causing burnt paste and particles. Therefore, the polyimide film of this embodiment is very suitable as a substrate for flexible displays.

Hereinafter, a more preferable aspect of the case where the polyimide film of the present embodiment is used as a substrate for a flexible display will be described.

In the case of forming a flexible display, a glass substrate is used as a support, a polyimide film as a flexible substrate is formed thereon, and then a TFT or the like is formed thereon. Typically, the step of forming a TFT is performed at a temperature in a wide range of 150-650°C. In order to show real The required performance in the world is mainly to form TFT-IGZO (InGaZnO) oxide semiconductor or TFT (a-Si-TFT, LTPS-TFT) around 250℃~450℃.

At this time, if the residual stress generated between the flexible substrate and the polyimide film is high, after expansion in the high-temperature TFT formation step and shrinkage at room temperature cooling, warpage and damage of the glass substrate may occur. Problems such as peeling of the flexible substrate from the glass substrate. Generally, the thermal expansion coefficient of the glass substrate is smaller than that of the resin, so residual stress is generated between the flexible substrate and the resin film. In consideration of this aspect, the polyimide film of the present embodiment is preferably based on the film thickness of 10 μm, and the residual stress generated between the glass and the glass is 25 MPa or less.

In addition, regarding the polyimide film of the present embodiment, from the viewpoint of excellent fracture strength when processed as a flexible substrate to improve the yield, it is preferred that the tensile elongation is based on the film thickness of 20 μm. More than 30%. In particular, if the tensile elongation is 33% or more, when the inorganic film on the polyimide film is arranged, there is a tendency that peeling or cracking of the film is unlikely to occur. Among them, particularly good is more than 40%.

The polyimide film of the present embodiment preferably has at least one glass transition temperature in the range of -150°C to 0°C and the range of 150°C to 380°C, respectively, and is greater than 0°C and less than 150°C There is no glass transition temperature in the area.

In addition, regarding the polyimide film of the present embodiment, in order not to cause softening at the TFT element formation temperature, the glass transition temperature in the high-temperature region is preferably present at 250°C or higher.

Furthermore, the polyimide film of the present embodiment is preferably provided with chemical resistance that can withstand the photoresist stripping liquid in the photolithography step used when manufacturing the TFT element.

Among the light extraction methods of the flexible display, there are known a top emission method for extracting light from the front side of the TFT element and a bottom emission method for extracting light from the back side. The characteristic of the top emission method is that the TFT element does not become an obstacle, so it is easy to increase the aperture ratio. On the other hand, the bottom glow side The characteristics of the formula are: easy alignment and easy manufacturing. If the TFT element is transparent, the aperture ratio can also be increased in the bottom-emission method, so as a large-scale organic EL flexible display, it is expected to adopt a bottom-emission method that is easy to manufacture. When a resin substrate is used for the colorless transparent resin substrate of the bottom-emission method, the resin substrate is arranged on the visible side. Therefore, as a resin substrate, from the viewpoint of improving image quality, it is particularly required that the yellowness (YI value) is low and the total light transmittance is high.

The polyimide film and laminate of this embodiment can be used as a substrate, for example, in the manufacture of semiconductor insulating films, TFT-LCD insulating films, electrode protective films, flexible devices, and the like. Here, the flexible device is, for example, a flexible display, a flexible solar cell, a substrate for a flexible touch panel electrode, a flexible lighting, a flexible battery, or the like. The polyimide film of this embodiment that satisfies the above-mentioned physical properties can be used particularly in applications where the existing polyimide film is limited in use due to the yellow color it has, especially in the use of colorless transparent substrates for flexible displays.

In addition to this, the polyimide film of this embodiment can also be used, for example, as a protective film, a diffuser sheet and a coating film in a TFT-LCD, etc. (for example, an intermediate layer of a TFT-LCD, a gate insulating film, a liquid crystal alignment film, etc.) , ITO substrate for touch panel, cover glass for smartphone instead of resin substrate, etc. where colorless transparency and low birefringence are required. If the polyimide of this embodiment is used as a liquid crystal alignment film, it contributes to the increase in the aperture ratio, and a high contrast ratio TFT-LCD can be manufactured.

[Example]

Hereinafter, the present invention will be described in further detail based on examples. However, these are described for explanation, and the scope of the present invention is not limited to the following examples.

Various evaluations of Examples and Comparative Examples were carried out as follows.

(Determination of number average molecular weight)

The number average molecular weight (Mn) was measured using gel permeation chromatography (GPC) under the following conditions.

Solvent: For N,N-dimethylformamide (manufactured by Wako Pure Chemical Industries, for high performance liquid chromatography), add 24.8 mmol/L of lithium bromide monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) immediately before the measurement , Purity 99.5%), and 63.2mmol/L phosphoric acid (manufactured by Wako Pure Chemical Industries, for high-performance liquid chromatography)

Calibration curve: made using standard polystyrene (manufactured by Tosoh Corporation)

Column: Shodex KD-806M (manufactured by Showa Denko)

Flow rate: 1.0mL/min

Column temperature: 40℃

Pump: PU-2080Plus (made by JASCO)

Detector: RI-2031Plus (RI: differential refractometer, manufactured by JASCO) and UV-2075Plus (UV-VIS: ultraviolet-visible absorbance meter, manufactured by JASCO)

(Production of laminate and single-release film)

Using a bar coater, apply the resin precursor composition obtained in each synthesis example to an alkali-free glass substrate (thickness 0.7 mm), perform leveling at room temperature for 5 to 10 minutes, and use a vertical curing oven (Manufactured by Koyo Lindberg, type name VF-2000B) heated at 140 ℃ for 60 minutes (pre-baked), and then heated in a hot air oven under a nitrogen atmosphere for 60 minutes, thereby making a film with a thickness of 20 μm on a glass substrate A laminate of polyimide film.

Here, the oxygen concentration and curing temperature in the hot air oven are set as described in Table 1. The oxygen concentration meter uses a zirconia LC-750L manufactured by TORAY ENGINEERING. The cured laminate was immersed in water, and after standing for 24 hours, the polyimide film was peeled off from the glass and used for the following evaluations. Among them, the evaluation of the laser peelability and the measurement of the adhesive strength are provided in a state where they are not peeled off from the glass substrate, and the evaluation of the residual stress and the infrared measurement separately form the polyimide film.

(Evaluation of tensile elongation)

The cured polyimide film was cut to a size of 5 mm×50 mm, and stretched at a speed of 100 mm/min using a tensile tester (manufactured by A&D Co., Ltd.: RTG-1210) to measure the tensile elongation.

(Evaluation of glass transition temperature and linear expansion coefficient)

The glass transition temperature and the coefficient of linear expansion (CTE) of the area above room temperature are measured by cutting the cured polyimide film to a size of 5 mm × 50 mm as a test piece, which is analyzed by thermomechanical analysis get on. Using a thermomechanical analyzer (TMA-50) manufactured by Shimadzu Corporation as the measuring device, the temperature range is 50 to 450°C under the conditions of a load of 5 g, a heating rate of 10°C/min, and a nitrogen flow (flow rate of 20 ml/min). Determination of the elongation of the test piece. The inflexion point of the obtained graph is obtained as the glass transition temperature, and the CTE of the polyimide film at 100 to 250°C is obtained.

(Evaluation of laser peelability)

Nd: The third harmonic of the Yag laser (355 nm) was used to gradually increase the irradiation energy from the glass substrate side of the laminate obtained above, and the polyimide was peeled off.

Here, the surface of the polyimide peeled with the minimum irradiatable energy that can be peeled is observed with an optical microscope, and the presence or absence of burnt paste and fine particles on the surface of the polyimide is studied. Consider the situation that occurs on substantially the entire surface of the film as peelable "bad", consider the situation that occurs on only a small part of the film as peelable "possible", and there will be no such occurrence Evaluation is regarded as "good" in peelability.

(Evaluation of residual stress)

Using a residual stress measuring device (manufactured by Tencor, model name FLX-2320), the "warpage amount" of a 6-inch silicon wafer with a thickness of 625 μm ± 25 μm was measured. The resin precursor composition obtained in each synthesis example was coated on the silicon wafer by a bar coater, and pre-baked at 140°C for 60 minutes After the clock, heat treatment was carried out in a vertical curing furnace (manufactured by Koyo Lindberg, model name VF-2000B) at the oxygen concentration and curing temperature described in Table 1 to produce silicon with a polyimide film with a film thickness of 10 μm Wafer.

Using the above-mentioned residual stress measuring device to measure the warpage of the polyimide-attached wafer, the residual stress generated between the silicon wafer and the resin film was evaluated by comparing with the warpage of the above-mentioned silicon wafer .

(Observation of gaps using electron microscope)

An ultrathin section prepared by embedding a polyimide film in an epoxy resin and using a microtome (LEICA EM UC6) was used as a specimen for inspection. The transmission electron microscope (manufactured by Hitachi, Ltd.: S-5500) was used to observe the cross-sectional direction of the film in the SEM and STEM modes at an acceleration voltage of 30 kV.

According to the state of the void structure observed by the STEM image, the average value of the void ratio and the maximum major axis length were separately obtained using image processing software.

Furthermore, the uniformity in the film thickness direction of the voids of the polyimide film was determined as follows. The electro-imaging of each polyimide film was divided into 2 μm regions in the film thickness direction, and after performing image processing on each region, the porosity was determined. Next, the difference between the maximum value and the minimum value is obtained for the void ratio (△void ratio (%)=maximum void ratio (%)-minimum void ratio (%)). In addition, the value of the △ porosity is used as an index of uniformity in the film thickness direction of the void.

In the case where the value is 5% or less, it can be evaluated that the uniformity of the voids in the film thickness direction is high. This value is more preferably 3% or less, further preferably 1% or less, and particularly preferably 0.5% or less.

(Measurement of inter-region distance and electron density of void structure using small-angle X-ray scattering measurement (SAXS))

Perform small angle X-ray scattering (SAXS) measurement under the following conditions to estimate the area of the void structure The distance between domains and the electron density of the island structure.

Device: NanoViewer manufactured by Rigaku

、第二縫隙：0.2mm

、保護縫隙：0.8mm

) Optical system: Point Collimation (first gap: 0.4mm

、Second gap: 0.2mm

、Protection gap: 0.8mm

)

Incident X-ray wavelength λ: 0.154nm

X-ray incidence direction: perpendicular to the film surface (though view)

Detector: PILATUS100K

Camera length: 842mm

Measurement time: 900 seconds

Sample: 10 pieces of each film are overlapped and measured

Regarding the electron density, calculate the invariant Q from the following equation (1), estimate the electron density difference △ρ, and determine whether the island-like area of the island structure is polysilicone or void based on the electron density difference from polyimide .

為相分離結構之島部分之體積分率} {In equation (1) above, Q is the invariant; Q is the scattered wave vector; I(q) is the scattering intensity; V is the irradiation volume; ρ is the electron density; and

Is the volume fraction of the island part of the phase separation structure}

=0.1。又，計算出Q/2π²=13,580(0.1<2θ<2.7°)。 Here, the scattered wave vector q is calculated within the range of 0.1<q<2.0(nm ^-1 ). The scattering intensity I(q) is corrected for absolute intensity, so the volume V is not considered. Regarding the volume fraction, assume

=0.1. Furthermore, Q/2π ² =13,580 (0.1<2θ<2.7°) was calculated.

(Estimation of polysiloxane content in polyimide film by infrared absorption spectroscopy (ATR))

Using a bar coater, apply the resin precursor composition to an alkali-free glass substrate (thickness 0.7 mm), perform leveling at room temperature for 5 to 10 minutes, and then use a vertical curing oven (manufactured by Koyo Lindberg) , Model name VF-2000B) heated at 95°C for 60 minutes (pre-bake). An ATR spectrum was obtained for this prebaked film, the peak area of 1,500 cm ^{-1 which} is the absorption of the benzene ring was normalized to 1, and the absorbance of 1,100 cm ^{-1 which was} the absorption of the SiO bond was determined.

The polyimide film heated at the oxygen concentration and curing temperature described in Table 1 was also subjected to the same measurement as described above, and the absorbance of 1,100 cm ^-1 as the absorption of SiO bond was obtained.

By comparing the value of the prebaked film with the value of the cured polyimide film for the absorbance of 1,100 cm ^-1 , the residual rate of polysiloxane residues was estimated. Furthermore, based on the amount of polysiloxane monomer added when synthesizing the polyimide precursor, and the residual rate of polysiloxane residues in the polyimide film after curing, the polyimide film obtained is calculated Silicone content.

As a measuring device for ATR, "Nicolet Continium" manufactured by Thermo Fisher Scientific was used.

Fig. 2 shows the ATR spectra of the films obtained in Examples 1, 2 and Reference Examples. The graph of FIG. 2 is the spectrum of the films obtained in Reference Example 1, Example 2 and Example 1 in order from top to bottom.

(Adhesion strength with glass substrate)

For the polyimide film included in the laminate obtained above, using a cutting knife, two slits with a width of 10 mm and a length of 100 mm were carved, and the ends were peeled off and clamped on the chuck at a stretching speed of 100 mm/min. Determination of 180° peel strength.

As a tensile testing machine, RTG-1210 manufactured by A&D Co., Ltd. was used.

(Determination of Birefringence (Rth))

A polyimide film with a film thickness of 15 μm was used as a sample, and the measurement was performed using a phase difference birefringence measuring device (manufactured by Oji Scientific Instruments Co., Ltd., KOBRA-WR). The wavelength of the measurement light is set to 589 nm.

(Measurement method of yellowness (YI))

A polyimide film with a film thickness of 20 μm was used as a sample, and measurement was carried out using Spectrophotometer (SE600) manufactured by Nippon Denshoku Industries Co., Ltd. The light source uses D65 light source.

<Preparation and evaluation of resin precursor composition>

[Synthesis Example 1]

For a 3L separable flask with a stir bar equipped with an oil bath, NMP 1,000g was added while introducing nitrogen, and 4,4-(diaminodiphenyl) sulfone as a diamine was added while stirring 239.6g (0.965 Mol), and then, 3,3',4,4'-biphenyltetracarboxylic dianhydride 294.22g (1.0 mol) as tetracarboxylic dianhydride was added, and it stirred at room temperature for 30 minutes. The temperature was raised to 50°C and stirred for 12 hours. Thereafter, amine-modified methylphenyl polysiloxane oil (manufactured by Shin-Etsu Chemical Co., Ltd.: X22-1660B-3 (number-average molecular weight 4,400)) of both ends as polysiloxane monomers was added dropwise from the dropping funnel 109.3 g (17% by mass relative to the total resin precursor) is a polysiloxane monomer solution obtained by dissolving in NMP 298g. Then, the reaction system was heated to 80° C., and after stirring for 1 hour, the oil bath was removed and returned to room temperature, thereby obtaining a transparent NMP solution (resin precursor composition) of a resin precursor (polyamide). The number average molecular weight (Mn) of the polyamide obtained here is about 33,000.

[Synthesis Examples 2 to 6 and 9]

Regarding the above Synthesis Example 1, the type and amount of diamine and tetracarboxylic dianhydride, and the content of the polysiloxane monomer solution were changed as described in Table 1, except for the same method as Synthesis Example 1. The NMP solution (resin precursor composition) of the transparent resin precursor (polyamide) was obtained by the formula.

Table 1 summarizes the number average molecular weight (Mn) of the obtained polyamides.

[Synthesis Example 7]

For a 10L separable flask with a stir bar equipped with an oil bath, 5,502g of NMP was added while introducing nitrogen, and 2,8.8'-bis(trifluoromethyl)benzidine as a diamine was added while stirring, and 308.8g( 0.96 mol), then, pyromellitic dianhydride 185.4g (0.85 mol) as tetracarboxylic dianhydride and 4,4'-(hexafluoroisopropylidene) diphthalic anhydride 66.64 g (0.15 mol). Furthermore, while stirring it, 113.64 g of polysiloxane monomer X22-1660B-3 (17% by mass relative to the total resin precursor) was dissolved in NMP 568g while being added dropwise from the dropping funnel Silicone monomer solution. After the dropwise addition, after stirring at room temperature for 1 hour, the temperature was raised to 80°C, and after stirring for 4 hours, the oil bath was removed and returned to room temperature, thereby obtaining a transparent NMP solution containing polyamic acid with an average molecular weight of 62,000 (Resin precursor composition).

[Synthesis Example 8]

The addition amount of TFMB was set to 317.02g (0.99 mol), except that the polysiloxane monomer solution was not added, and the same operation as in Synthesis Example 7 was carried out, thereby obtaining a polyamic acid containing a number average molecular weight of 58,000 The transparent NMP solution (resin precursor composition).

The abbreviations of the ingredients in Table 1 have the following meanings.

(Diamine)

4,4-DAS: 4,4-(diaminodiphenyl) ash

TFMB: 2,2'-bis(trifluoromethyl) benzidine

(Tetracarboxylic dianhydride)

BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride

PMDA: pyromellitic dianhydride

6FDA: 4,4'-(hexafluoroisopropylidene) diphthalic anhydride

(Polysiloxane monomer)

1660B: Made by Shin-Etsu Chemical Co., Ltd., product name "X22-1660B-3" amine-modified methyl phenyl polysiloxane oil at both ends, number average molecular weight 4,400

FM3311: Made by Chisso Corporation, product name "Silaplane FM3311": Amine modified dimethyl polysiloxane oil at both ends, average molecular weight of 1,000

[Examples 1 to 18 and Comparative Examples 1 to 3]

Using the resin precursor composition synthesized in the above synthesis example, a polyimide film was produced under the conditions of the oxygen concentration and curing temperature described in Table 1 according to the above method, and various evaluations were performed.

The evaluation results are shown in Tables 2 and 3.

Figure 1 shows the STEM image (left) and SEM image (right) of the polyimide film obtained in Example 1; Figure 3 shows the SEM image of the polyimide film obtained in Example 7 Like.

Reference Example 1

This reference example is to verify that when the curing temperature is lowered, all the silicone components remain It is carried out without forming voids in the film.

Using the resin precursor composition obtained in the above Synthesis Example 1, the curing conditions were set to an oxygen concentration of 50 ppm and a curing temperature of 95° C. Other than that, a film was formed by the above method, and ATR measurement and electron microscope observation were performed.

The results are shown in Table 2.

Regarding the difference in electron density between the regional structures of the island-in-sea structure obtained by SAXS observation, in the examples, it was close to the difference between the electron density of polyimide and air, so it was confirmed that voids were formed in the film; another In the comparative example of the aspect, since it becomes a value close to the difference in electron density between polyimide and polysiloxane, it is confirmed that no void is formed.

Also, referring to the cross-sectional STEM image in the film thickness direction of Example 1, it can be confirmed that the island portion is white. From this, it can also be determined that the island portion is a void. According to the SEM image, it is also possible to confirm that the island portion is depressed, so it can be determined that the portion is a void.

As shown in Table 2, it was confirmed that Examples 1 to 18 simultaneously satisfy the following conditions in terms of film physical properties.

(1) Residual stress is 25 MPa or less, (2) Polyimide film does not scorch after laser peeling, (3) No particles after laser peeling, (4) Glass transition temperature and polysilicon are introduced The oxygen polymer is not lower than that of the polymer, (5) the tensile elongation is 30% or more, and (6) is excellent in adhesion with the glass substrate.

According to the results in Table 3, for Examples 1, 4, 5, and 6 in which the oxygen concentration at the time of curing is 2,000 ppm or less, the uniformity in the film thickness direction of the formed voids is extremely high, and the birefringence The value of (Rth) is extremely small.

Therefore, the polyimide films obtained in these examples satisfy the performance for application to substrates for flexible displays.

In contrast, when the polyimide films obtained in Comparative Examples 1 to 3 were peeled by laser, the polyimide was burnt and colored, and as a result, fine particles were generated.

Based on the above results, it was confirmed that the polyimide film obtained from the resin precursor of the present invention has low residual stress generated between the glass substrate and the inorganic film, and is excellent in adhesion with the glass substrate even in the laser peeling step It can also be peeled off well when the irradiation energy is low, and it does not cause scorch or particles of the polyimide film during peeling.

Furthermore, the present invention is not limited to the above-mentioned embodiment, and various modifications can be made.

[Industry availability]

The polyimide film of the present invention can be suitably used for, for example, semiconductor insulating films, TFT-LCD insulating films, electrode protective films, substrates for flexible displays, substrates for ITO electrodes of touch panels, and the like. Especially useful as various substrates.

Claims (22)

A flexible display is characterized by having a polyimide film, and the interior of the polyimide film has a void of 100 nm or less. A flexible display is characterized by having a polyimide film having a void of 100 nm or less inside, and the polyimide film is peeled off from a support and used. The flexible display according to claim 1 or 2, wherein the polyimide film is provided with an inorganic film. The flexible display according to claim 1 or 2, wherein the polyimide film has a TFT. A flexible display according to claim 1 or 2, wherein the yellowness of the 20 μm film thickness of the above polyimide film is 7 or less. The flexible display according to claim 1 or 2, wherein the above-mentioned polyimide film has a tensile elongation of 30% or more. The flexible display according to claim 1 or 2, wherein the polyimide film has polysilicon residues. The flexible display according to claim 1 or 2, wherein the porosity of the polyimide film is in the range of 3% by volume to 15% by volume. The flexible display according to claim 1 or 2, wherein the shape of the voids of the polyimide film is a flat elliptical sphere with an average long axis diameter of 30 nm to 60 nm. The flexible display according to claim 1 or 2, wherein the voids of the polyimide film exist uniformly in the film thickness direction of the polyimide film. The flexible display according to claim 1 or 2, wherein the polyimide film has a source derived from an aromatic tetracarboxylic dianhydride selected from carbon numbers 8 to 36, and an aliphatic tetracarboxylic dianhydride selected from carbon numbers 6 to 50, And the structure of alicyclic tetracarboxylic dianhydride compound with 6 to 36 carbon atoms. A resin precursor characterized in that it is used to manufacture a polyimide film having a void of 100 nm or less and used as a substrate of a flexible device. The resin precursor has the following general formula (1) in the resin skeleton ) Represents the unit 1, and the unit 2 represented by the following general formula (2), and based on the mass of the resin precursor, contains 6 to 25% by mass of the aforementioned unit 2:

{In the above general formula (1) and the above general formula (2), R _{1 is} independently a hydrogen atom, a monovalent aliphatic hydrocarbon having 1 to 20 carbon atoms, or an aromatic group having 6 to 10 carbon atoms; R ₂ And R ₃ are independently a monovalent aliphatic hydrocarbon having 1 to 3 carbon atoms, or an aromatic group having 6 to 10 carbon atoms; X ₁ is a tetravalent organic group having 4 to 32 carbon atoms; and X ₂ is a carbon number 4~32 divalent organic radical}. A resin precursor characterized in that it is used to produce a polyimide film having a void of 100 nm or less and peeled off from a support. The resin precursor has the following general formula (1) in the resin skeleton ) Represents the unit 1, and the unit 2 represented by the following general formula (2), and based on the mass of the resin precursor, contains 6 to 25% by mass of the aforementioned unit 2:

{In the above general formula (1) and the above general formula (2), R _{1 is} independently a hydrogen atom, a monovalent aliphatic hydrocarbon having 1 to 20 carbon atoms, or an aromatic group having 6 to 10 carbon atoms; R ₂ And R ₃ are independently a monovalent aliphatic hydrocarbon having 1 to 3 carbon atoms, or an aromatic group having 6 to 10 carbon atoms; X ₁ is a tetravalent organic group having 4 to 32 carbon atoms; and X ₂ is a carbon number 4~32 divalent organic radical}. The resin precursor according to claim 12 or 13, which is a copolymer of tetracarboxylic dianhydride, diamine, and a compound represented by the following general formula (3),

{In the above general formula (3), there are a plurality of R ₄ which are each independently a single bond or a divalent organic group having 1 to 20 carbon atoms; R ₅ and R ₆ are each independently a monovalent carbon number of 1 to 20 carbon atoms Organic group; R ₇ is a monovalent organic group with a carbon number of 1 to 20 in the presence of a plurality of cases; L ₁ , L ₂ , and L ₃ are independently an amine group, isocyanate group, carboxyl group, and acid anhydride group , Ester group, acyl halide group, hydroxyl group, epoxy group, or mercapto group; j is an integer from 3 to 200; and k is an integer from 0 to 197}. The resin precursor according to claim 14, wherein the tetracarboxylic dianhydride is selected from pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3' , 4,4'-biphenyltetracarboxylic dianhydride, and 4,4'-biphenylbis(trimellitic acid monoester anhydride), one or more than one kind of tetracarboxylic dianhydride. The resin precursor according to claim 14, wherein the mass of the compound represented by the general formula (3) used in synthesizing the resin precursor is tetracarboxylic dianhydride, diamine, and the general formula (3) The total of the compound is 6% by mass to 25% by mass. The resin precursor according to claim 12 or 13, which has a source derived from an aromatic tetracarboxylic dianhydride selected from carbon numbers 8 to 36, an aliphatic tetracarboxylic dianhydride from carbon numbers 6 to 50, and a carbon number from 6 to The structure of 36 alicyclic tetracarboxylic dianhydride compounds. A method for manufacturing a polyimide film, comprising the following steps: a polyimide film forming step, which forms a polyimide film having a void of less than 100 nm on a support; and a peeling step, which is from the above support The above polyimide film was peeled off. The method for manufacturing the polyimide film of claim 18, wherein the peeling step includes a laser peeling step of peeling the polyimide film from the support by laser irradiation. The method for manufacturing a polyimide film according to claim 18 or 19, wherein the step of forming the polyimide film includes forming a coating film of the resin precursor on the surface of the support, followed by a heating step, the resin The precursor has a unit 1 represented by the following general formula (1) and a unit 2 represented by the following general formula (2) in the resin skeleton:

{In the above general formula (1) and the above general formula (2), R _{1 is} independently a hydrogen atom, a monovalent aliphatic hydrocarbon having 1 to 20 carbon atoms, or an aromatic group having 6 to 10 carbon atoms; R ₂ And R ₃ are independently a monovalent aliphatic hydrocarbon having 1 to 3 carbon atoms, or an aromatic group having 6 to 10 carbon atoms; X ₁ is a tetravalent organic group having 4 to 32 carbon atoms; and X ₂ is a carbon number 4~32 divalent organic radical}. A laminate comprising a support and a polyimide film. The polyimide film is formed on the support, and the polyimide film has a void of 100 nm or less inside. A substrate for flexible touch panel electrodes is characterized by having a polyimide film, and the polyimide film has a void of 100 nm or less inside.

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