Polyimide film, laminate, and surface material for display

Abstract

The invention relates to a polyimide film, a laminate, and a surface material for a display. A method for producing a polyimide film, said method comprising a step in which an acid dianhydride having a molar ratio of 0.5 equivalent of a diamine having one or two silicon atoms in the main chain is introduced into a reaction solution in which a diamine having one or two silicon atoms in the main chain is dissolved, and the resulting mixture is reacted, polyimide precursor having a structure represented by general formula (1 ') by synthesizing amic acid obtained by reacting diamine having one or two silicon atoms in the main chain with both ends of acid dianhydride, adding all or part of the remaining diamine to the amic acid, and adding acid dianhydride.

Description

[0001] This application is a divisional application. The application number of the original application is 201780062133.3, the filing date is August 8, 2017, and the invention title is "Polyimide Film, Laminate, and Surface Material for Display". Technical Field

[0002] Embodiments of the present disclosure relate to a polyimide film, a laminate, and a surface material for a display. Background Art

[0003] Thin flat glass is excellent in hardness, heat resistance, etc. On the other hand, it is difficult to bend, is easily broken when dropped, has problems in processability, and has a disadvantage of being heavier than plastic products. Therefore, in recent years, from the aspects of processability and weight reduction, resin products such as resin substrates and resin films are being replaced with glass products, and research on resin products as glass substitute products is being carried out.

[0004] For example, with the rapid progress of electronics such as liquid crystal, organic EL displays, or touch panels, there is a growing demand for the thinning, lightening, and flexibility of devices. In these devices, various electronic components, such as thin-film transistors or transparent electrodes, have been formed on thin flat glass in the past. By changing the thin flat glass to a resin film, it is possible to enhance the impact resistance, flexibility, thinning, and lightening of the panel itself.

[0005] Generally, polyimide resin is a high heat-resistant resin obtained by subjecting polyamic acid obtained by a condensation reaction of an aromatic tetracarboxylic anhydride and an aromatic diamine to a dehydration ring-closure reaction. However, polyimide resin usually shows yellow or brown coloring, so it is difficult to be used in fields requiring transparency such as display applications and optical applications. Therefore, research has been conducted on the application of polyimide with improved transparency in display components. For example, in Patent Document 1, as a polyimide resin having high heat resistance, high transparency, and low water absorption, a polyimide resin is disclosed which is formed by reacting at least one acyl group-containing compound selected from the group consisting of 1,2,4,5-cyclohexanetetracarboxylic acid, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and their reactive derivatives with at least one imino-forming compound selected from compounds represented by a specific formula having at least one phenylene group and an isopropylidene group, and it is described that it is suitable for substrate materials for flat panel displays, mobile phone devices, etc.

[0006] In addition, a transparent polyimide film is disclosed in Patent Document 2, which contains an aromatic diamine hydride and a unit structure derived from an aromatic diamine, and further contains an additive for improving tear strength, or a unit structure derived from a monomer having a functional group selected from the group consisting of a hexafluoro group, a sulfone group, and an oxygen group. In Patent Document 3, as a polyimide film excellent in transparency and heat resistance, a polyimide film is disclosed in which the peak vertex in the tanδ curve (a value obtained by dividing the loss elastic modulus by the storage elastic modulus) is within a specific range.

[0007] In addition, in Patent Document 4, as a polyimide film for a substrate of a flexible device, a polyimide film is disclosed which is obtained by imidizing a polyimide precursor using a specific fluorine-based aromatic diamine and an organosilicon compound having a siloxane skeleton with 3 to 200 silicon atoms as monomer components in order to obtain a colorless and transparent polyimide film with low residual stress generated between the inorganic film, excellent mechanical properties and thermal properties. It is described in Patent Document 4 that: when a polyimide film with an inorganic film (SiN film) formed using the above polyimide precursor was subjected to a bending test in which bending was repeated 10 times, neither cracks nor peeling (○) were observed, or cracks (△) were observed.

[0008] In addition, in Patent Document 5, as a polyimide having a low refractive index and high fold resistance, it is described that it contains an organosilicon diamine having 2 to 21 silicon atoms in an amount of 10% by weight or more based on the weight of the diamine raw material.

[0009] On the other hand, in a polyimide molded body (Patent Document 6) for a liquid crystal alignment film or the like, in order to improve the adhesion to an inorganic substrate, a diamino siloxane is used as a diamine component that becomes a raw material of the polyimide resin.

[0010] Prior art documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2006-199945

[0013] Patent Document 2: Japanese Patent Application Laid-Open No. 2014-501301

[0014] Patent Document 3: Japanese Patent Application Laid-Open No. 2012-503701

[0015] Patent Document 4: International Publication No. 2014 / 098235

[0016] Patent Document 5: Japanese Patent Application Laid-Open No. 2008-64905

[0017] Patent Document 6: Japanese Unexamined Patent Application Publication No. 63-170420 Summary of the Invention

[0018] Problems to be Solved by the Invention

[0019] Since portable devices with foldable screens are often carried in a folded state, for the flexible displays mounted in such portable devices, it is required that even when they are continuously bent for a long time, they can return to their original state when flattened. For the base materials and surface materials used for flexible displays, resilience after being continuously bent for a long time (hereinafter sometimes referred to as static bending resistance) is also required.

[0020] On the other hand, for the base materials and surface materials used for flexible displays, not only are they required to withstand repeated bending, but also functions to prevent surface damage and breakage of the touch sensors and display panels located below them are required.

[0021] As will be described in detail below, the bending resistance and surface hardness of resin films are considered to be opposite characteristics, and a resin film that balances bending resistance and sufficient surface hardness as a protective film is required.

[0022] The present disclosure has been made in view of the above problems, and its main object is to provide a resin film with improved bending resistance and suppressed reduction in surface hardness.

[0023] In addition, an object of the present disclosure is to provide a laminate having the above resin film and a surface material for a display using the above resin film or the above laminate.

[0024] Means for Solving the Problems

[0025] One embodiment of the present disclosure provides a polyimide film containing a polyimide having a structure represented by the following general formula (1),

[0026] The total light transmittance measured according to JIS K7361-1 is 85% or more,

[0027] The yellowness calculated according to JIS K7373-2006 is 30 or less,

[0028] It has a glass transition temperature in the temperature range of 150°C or higher and 400°C or lower,

[0029] The tensile elastic modulus at 25°C obtained by measuring a 15 mm × 40 mm test piece with a tensile speed of 10 mm / minute and a chuck distance of 20 mm according to JIS K7127 is 1.8 GPa or more.

[0030] [Chemical Formula 1]

[0031]

[0032] (In general formula (1), R 1 represents a tetravalent group, which is a tetracarboxylic acid residue having an aromatic ring or an aliphatic ring, and R 2 represents a divalent group, which is a diamine residue. 10 mol% or more and 50 mol% or less of the total amount of R 2 are diamine residues having one or two silicon atoms in the main chain, and 50 mol% or more and 90 mol% or less are diamine residues having an aromatic ring or an aliphatic ring without silicon atoms. n represents the number of repeating units.)

[0033] In one embodiment of the present disclosure, a polyimide film is provided, wherein the birefringence in the thickness direction at a wavelength of 590 nm is 0.020 or less.

[0034] In one embodiment of the present disclosure, a polyimide film is provided, wherein, when a static bending test is performed according to the following static bending test method, the inner angle measured in this test is 120° or more.

[0035] [Static Bending Test Method]

[0036] A test piece of a polyimide film cut into 15 mm × 40 mm is bent at the midpoint of the long side, and a metal sheet (100 mm × 30 mm × 6 mm) with a thickness of 6 mm is arranged to sandwich the test piece from the upper and lower surfaces at both ends of the long side of the test piece, and the test piece is fixed with tape such that the overlapping portions of both ends of the test piece and the metal sheet on the upper and lower surfaces are each 10 mm. In this state, the test piece is sandwiched from above and below with a glass plate (100 mm × 100 mm × 0.7 mm), and the test piece is fixed in a state of being bent with an inner diameter of 6 mm. At this time, a simulated test piece is inserted into the portion where the test piece does not exist between the metal sheet and the glass plate, and is fixed with tape in parallel with the glass plate. After leaving the test piece fixed in the bent state in an environment of 60 ± 2°C and 93 ± 2% relative humidity (RH) for 24 hours, the glass plate and the fixing tape are removed, and the force applied to the test piece is released. Then, one end of the test piece is fixed, and the inner angle of the test piece 30 minutes after releasing the force applied to the test piece is measured.

[0037] In one embodiment of the present disclosure, a polyimide film is provided, wherein the polyimide having the structure represented by the above general formula (1) contains an aromatic ring and contains at least one selected from the group consisting of (i) a fluorine atom, (ii) an aliphatic ring, and (iii) a structure in which aromatic rings are linked to each other by a sulfonyl group or a fluorine-substituted or unsubstituted alkylene group.

[0038] In one embodiment of the present disclosure, a polyimide film is provided. Among them, in the polyimide having the structure represented by the above general formula (1), R in the above general formula (1) 1 is at least one tetravalent group selected from the group consisting of a cyclohexanetetracarboxylic dianhydride residue, a cyclopentanetetracarboxylic dianhydride residue, a dicyclohexane-3,4,3',4'-tetracarboxylic dianhydride residue, a cyclobutanetetracarboxylic dianhydride residue, a pyromellitic dianhydride residue, a 3,3',4,4'-biphenyltetracarboxylic dianhydride residue, a 2,2',3,3'-biphenyltetracarboxylic dianhydride residue, a 4,4'-(hexafluoroisopropylidene)diphthalic anhydride residue, a 3,4'-(hexafluoroisopropylidene)diphthalic anhydride residue, a 3,3'-(hexafluoroisopropylidene)diphthalic anhydride residue, a 4,4'-oxydiphthalic anhydride residue, and a 3,4'-oxydiphthalic anhydride residue.

[0039] In one embodiment of the present disclosure, a polyimide film is provided. Among them, in the polyimide having the structure represented by the above general formula (1), R in the above general formula (1) 2 The diamine residue that does not have a silicon atom but has an aromatic ring or an aliphatic ring is at least one divalent group selected from the group consisting of a trans-cyclohexanediamine residue, a trans-1,4-bis(methylenecyclohexane)diamine residue, a 4,4'-diaminodiphenyl sulfone residue, a 3,4'-diaminodiphenyl sulfone residue, a 2,2-bis(4-aminophenyl)propane residue, a 2,2-bis(4-aminophenyl)hexafluoropropane residue, and a divalent group represented by the following general formula (2).

[0040] [Chemical formula 2]

[0041]

[0042] (In the general formula (2), R 3 and R 4 each independently represent a hydrogen atom, an alkyl group, or a perfluoroalkyl group.)

[0043] One embodiment of the present disclosure provides a laminate in which the polyimide film of the above one embodiment of the present disclosure and a hard coat are adjacent to each other, and the hard coat contains at least one polymer selected from a radical-polymerizable compound and a cation-polymerizable compound.

[0044] In one embodiment of the present disclosure, a laminate is provided. Among them, the radical-polymerizable compound is a compound having two or more (meth)acryloyl groups in one molecule, and the cation-polymerizable compound is a compound having two or more epoxy groups and oxetanyl groups in one molecule.

[0045] In one embodiment of the present disclosure, there is provided a surface material for a display, which is a polyimide film according to one embodiment of the present disclosure above, or a laminate according to one embodiment of the present disclosure above.

[0046] In one embodiment of the present disclosure, there is provided a surface material for a flexible display, which is a polyimide film according to one embodiment of the present disclosure above, or a laminate according to one embodiment of the present disclosure above.

[0047] Advantages of the Invention

[0048] According to the present disclosure, a resin film with improved bending resistance and suppressed reduction in surface hardness can be provided.

[0049] In addition, the present disclosure can provide a laminate having the above resin film, and a surface material for a display as the above resin film or the above laminate. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a diagram for explaining the maximum stress in the bending of the film.

[0051] Figure 2 It is a diagram for explaining the method of a static bending test. DETAILED DESCRIPTION

[0052] I. Polyimide Film

[0053] The polyimide film according to one embodiment of the present disclosure contains a polyimide having a structure represented by the following general formula (1),

[0054] The total light transmittance measured according to JIS K7361-1 is 85% or more,

[0055] The yellowness calculated according to JIS K7373-2006 is 30 or less,

[0056] It has a glass transition temperature in the temperature range of 150 °C or higher and 400 °C or lower,

[0057] The tensile elastic modulus at 25 °C obtained by measuring a 15 mm × 40 mm test piece with a tensile speed of 10 mm / minute and a chuck distance of 20 mm according to JIS K7127 is 1.8 GPa or more.

[0058] [Chemical Formula 3]

[0059] General formula (1)

[0060]

[0061] (In general formula (1), R 1represents a tetravalent group, which is a tetracarboxylic acid residue having an aromatic ring or an aliphatic ring, R 2 represents a divalent group, which is a diamine residue, R 2 10 mol% or more and 50 mol% or less of the total amount is a diamine residue having 1 or 2 silicon atoms in the main chain, and 50 mol% or more and 90 mol% or less is a diamine residue having an aromatic ring or an aliphatic ring without a silicon atom. n represents the number of repeating units.)

[0062] According to the present disclosure, by making the polyimide contained in the polyimide film have a specific structure (having a tetracarboxylic acid residue containing an aromatic ring or an aliphatic ring, as a diamine residue, containing 10 mol% or more and 50 mol% or less of a diamine residue having 1 or 2 silicon atoms in the main chain, and containing 50 mol% or more and 90 mol% or less of a diamine residue having an aromatic ring or an aliphatic ring without a silicon atom), a polyimide film having the above-mentioned specific total light transmittance, the above-mentioned specific yellowness, the above-mentioned specific glass transition temperature, and the above-mentioned specific tensile elastic modulus is produced. Thus, a resin film with improved bending resistance and sufficient surface hardness as a protective film can be provided.

[0063] Regarding the reason, it is speculated as follows.

[0064] The present inventors focused on the polyimide in the resin. It is known that polyimide has excellent heat resistance due to its chemical structure. In addition, it is known that the arrangement of the molecular chains inside the polyimide film forms a certain ordered structure, and it is considered that for this reason, the resilience when repeating the flat state and the bent state at a certain cycle at room temperature shows good results.

[0065] However, in the case of a resin film using an existing transparent polyimide, even a resin film that shows good results in the test of repeating the flat state and the bent state at a certain cycle, if the bent state is continuously maintained for a long time, it will have a bending tendency and it is difficult to return to flat, and there is a problem of poor static bending resistance. It is speculated that by continuously maintaining the bent state for a long time, due to the continuous application of tensile stress to the outer periphery of the bent part, plastic deformation of the film is caused, and thus it is difficult to recover even when the bending force is released.

[0066] More specifically, it is speculated as follows.

[0067] Bending of the film applies tension to the outer peripheral part of the bend and compressive force to the inner peripheral part of the bend. In the bending of the film as shown in Figure 1 , the maximum stress (σ) at the part where the stress reaches the maximum (stress maximum part) is represented by the following formula (1).

[0068] [Equation 1]

[0069]

[0070] E: Elastic modulus

[0071] y: Maximum value of the distance from the neutral axis (axis serving as the center during bending) ( Figure 1 in the case of, it is half of the film thickness d)

[0072] Curvature (test width)

[0073] d: Film thickness of the film

[0074] As shown in the above formula (1), the above maximum stress (σ) is proportional to the elastic modulus and film thickness of the film, and inversely proportional to the value obtained by subtracting the film thickness from the curvature. Therefore, when the elastic modulus of the film is increased, the stress applied to the film during bending also increases, which becomes a cause of deformation. In a resin film, when the elastic modulus is increased, there is also a tendency for the resilience after bending to deteriorate and the bending resistance to be insufficient. On the other hand, by increasing the elastic modulus of the resin film, there is a tendency to improve the surface hardness. In fact, as shown in Comparative Example 3 described later, although the surface hardness of a polyimide film with a large elastic modulus is improved, the bending resistance deteriorates. Thus, it is considered that the bending resistance and surface hardness of the resin film are opposite characteristics.

[0075] For substrates and surface materials for flexible displays, not only is it required to withstand repeated bending, but also a function of preventing surface damage and preventing breakage of the touch sensor and display panel located below it is required. The higher the elastic modulus of the surface material, such as glass, for example, the more able it is to diffuse the impact from the surface of the display in the plane direction and relieve the local impact, and as a result, the more able it is to prevent breakage of the display panel. The same applies to flexible displays. As a function of protecting the display panel, a surface material with a higher elastic modulus functions more effectively. On the other hand, in the case of a low elastic modulus, although it is sometimes possible to relieve the impact by the deformation of the surface material itself, the depressions and the like generated by the deformation are fixed, and the smoothness of the display surface is greatly reduced, and the appearance is easily damaged.

[0076] In the polyimide film described in Patent Document 4, it is described that: by introducing an organosilicon component containing 3 or more silicon atoms, it has a glass transition temperature below the freezing point, and the residual stress generated with the inorganic film is reduced. However, as shown in Comparative Example 2 described later, since the polyimide film introducing an organosilicon component containing 3 or more silicon atoms has a low glass transition temperature, there are the following problems: the elastic modulus is insufficient at room temperature, the surface hardness is low, and it is easily damaged; or the impact is transmitted to the light-emitting panel or the circuit, and the function as a protective film is insufficient.

[0077] In addition, the polyimide film described in Patent Document 5 is described as having high folding resistance. However, as shown in Comparative Example 4 described later, the polyimide film into which organic silicon diamine (containing about 9 to 10 silicon atoms) is introduced, which corresponds to the example of Patent Document 5, has the following problems: the elastic modulus is insufficient at room temperature, the surface hardness is low, it is easily damaged, and the function as a protective film is insufficient.

[0078] In summary, a resin film that has both bending resistance and sufficient surface hardness as a protective film is required. However, as mentioned above, the bending resistance and surface hardness of the resin film are considered to be contradictory properties, and it is difficult to maintain the surface hardness while improving the bending resistance. The stress generated on the film surface can be relaxed by introducing an organic silicon component, but if too much emphasis is placed on the stress relaxation effect and an organic silicon with a large molecular weight is used, the entire film becomes too soft and it is difficult to achieve both surface hardness and stability.

[0079] In this regard, the inventors have found that when a polyimide obtained by introducing a specific amount of a soft molecular skeleton with a small molecular weight having 1 or 2 silicon atoms in the main chain between molecular skeletons containing aromatic rings or aliphatic rings is used, a polyimide film can be manufactured that can adjust the glass transition temperature while maintaining the elastic modulus derived from the molecular skeleton containing aromatic rings or aliphatic rings. The polyimide film disclosed in the present invention can maintain sufficient surface hardness as a protective film by introducing a specific amount of a soft molecular skeleton having 1 or 2 silicon atoms in the main chain between molecular skeletons containing aromatic rings or aliphatic rings, while improving bending resistance. As shown in the results of the dynamic bending test and the static bending test in the examples described later, not only the recovery of the film after repeated bending, that is, the dynamic bending resistance, is improved, but also the recovery of the film after being bent for a long time, that is, the static bending resistance, is improved. In the present disclosure, it is speculated that the improvement in bending resistance is because stress relaxation caused by molecular motion can be achieved by introducing a specific amount of the above-mentioned specific short main chain soft molecular skeleton into the rigid molecular skeleton, thereby reducing the stress applied to the film during bending. In addition, it is believed that by limiting the diamine residue to have 1 or 2 silicon atoms to shorten the soft part of the main chain and introducing a specific amount of the short main chain soft molecular skeleton into the rigid molecular skeleton, the polyimide film of the present disclosure can suppress the decrease in elastic modulus at room temperature and can also maintain sufficient surface hardness as a protective film at room temperature.

[0080] Hereinafter, the polyimide film of the present disclosure will be described in detail.

[0081] The polyimide film of the present disclosure contains a polyimide having a structure represented by the above general formula (1) and has the above-mentioned specific characteristics. Unless the effects of the present disclosure are impaired, the polyimide film may further contain other components and may have other configurations.

[0082] 1. Polyimide

[0083] The polyimide is obtained by reacting a tetracarboxylic acid component with a diamine component. Preferably, a polyamic acid is obtained by polymerizing a tetracarboxylic acid component with a diamine component and imidized. The imidization can be carried out by thermal imidization or by chemical imidization. In addition, it can also be manufactured by a method of combining thermal imidization and chemical imidization.

[0084] The polyimide used in the present disclosure contains a polyimide having a structure represented by the following general formula (1).

[0085] [Chemical formula 4]

[0086] General formula (1)

[0087]

[0088] (In general formula (1), R 1 represents a tetravalent group, which is a tetracarboxylic acid residue having an aromatic ring or an aliphatic ring, R 2 represents a divalent group, which is a diamine residue, and 10 mol% or more and 50 mol% or less of the total amount of R 2 is a diamine residue having one or two silicon atoms in the main chain, and 50 mol% or more and 90 mol% or less is a diamine residue having an aromatic ring or an aliphatic ring without a silicon atom. n represents the number of repeating units.)

[0089] Here, the tetracarboxylic acid residue refers to the residue obtained by removing 4 carboxyl groups from the tetracarboxylic acid, and represents the same structure as the residue obtained by removing the acid anhydride structure from the tetracarboxylic dianhydride.

[0090] In addition, the diamine residue refers to the residue obtained by removing 2 amino groups from the diamine.

[0091] The tetracarboxylic acid residue in R 1 of the above general formula (1) can be the residue obtained by removing the acid anhydride structure from a tetracarboxylic dianhydride having an aromatic ring or the residue obtained by removing the acid anhydride structure from a tetracarboxylic dianhydride having an aliphatic ring.

[0092] As the tetracarboxylic dianhydride having an aromatic ring, examples thereof include pyromellitic dianhydride, 3,3’,4,4’-benzophenone tetracarboxylic dianhydride, 2,2’,3,3’-benzophenone tetracarboxylic dianhydride, 3,3’,4,4’-biphenyltetracarboxylic dianhydride, 2,2’,3,3’-biphenyltetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 1,3-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride, 1,4-bis[(3,4-dicarboxy)benzoyl]benzene dianhydride, 2,2-bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride, 2,2-bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}propane dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, 4,4’-bis[4-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, 4,4’-bis[3-(1,2-dicarboxy)phenoxy]biphenyl dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}ketone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfone dianhydride, bis{4-[4-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, bis{4-[3-(1,2-dicarboxy)phenoxy]phenyl}sulfide dianhydride, 4,4’-(hexafluoroisopropylidene)diphthalic anhydride, 3,4’-(hexafluoroisopropylidene)diphthalic anhydride, 3,3’-(hexafluoroisopropylidene)diphthalic anhydride, 4,4’-oxydiphthalic anhydride, 3,4’-oxydiphthalic anhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,4,9,10-pyrenetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 1,2,7,8-phenanthrenetetracarboxylic dianhydride, etc.

[0093] As the tetracarboxylic dianhydride having an aliphatic ring, examples thereof include cyclohexanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, dicyclohexane-3,4,3’,4’-tetracarboxylic dianhydride, cyclobutanetetracarboxylic dianhydride, etc.

[0094] These tetracarboxylic dianhydrides can be used alone or in combination of two or more kinds.

[0095] The diamine residue having one or two silicon atoms in the main chain in the above general formula (1) 2 can be a residue obtained by removing two amino groups from a diamine having one or two silicon atoms in the main chain. The polyimide film of the present disclosure can not only improve the balance between bending resistance and surface hardness as described above, but also easily suppress the orientation by introducing a specific amount of a flexible molecular skeleton having one or two silicon atoms in the main chain between the molecular skeletons containing an aromatic ring or an aliphatic ring as the main component, and can easily become a polyimide film with a reduced birefringence as described above.

[0096] As the diamine having one silicon atom in the main chain, for example, a diamine represented by the following general formula (A) can be cited. In addition, as the diamine having two silicon atoms in the main chain, for example, a diamine represented by the following general formula (B) can be cited.

[0097] [Chemical formula 5]

[0098] General formula (A)

[0099]

[0100] General formula (B)

[0101]

[0102] (In general formula (A) and general formula (B), L is each independently a direct bond or an -O- bond, and R 10 each independently represents a monovalent hydrocarbon group having 1 to 20 carbon atoms with or without substituents and containing or not containing an oxygen atom or a nitrogen atom. R 11 each independently represents a divalent hydrocarbon group having 1 to 20 carbon atoms with or without substituents and containing or not containing an oxygen atom or a nitrogen atom.)

[0103] As the monovalent hydrocarbon group represented by R 10 examples thereof include an alkyl group, an aryl group, and a combination thereof having 1 to 20 carbon atoms. The alkyl group can be any of linear, branched, and cyclic, or a combination of linear or branched and cyclic.

[0104] As the alkyl group having 1 to 20 carbon atoms, an alkyl group having 1 to 10 carbon atoms is preferred. Specifically, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, etc. can be cited. As the above-mentioned cyclic alkyl group, a cycloalkyl group having 3 to 10 carbon atoms is preferred. Specifically, cyclopentyl, cyclohexyl, etc. can be cited. As the above-mentioned aryl group, an aryl group having 6 to 12 carbon atoms is preferred. Specifically, phenyl, tolyl, naphthyl, etc. can be cited. In addition, as R 10 The monovalent hydrocarbon group represented can be an aralkyl group. For example, benzyl, phenethyl, phenylpropyl, etc. can be cited.

[0105] As the hydrocarbon group containing or not containing an oxygen atom or a nitrogen atom, for example, a group formed by bonding a divalent hydrocarbon group described later to the above monovalent hydrocarbon group using at least one of an ether bond, a carbonyl bond, an ester bond, an amide bond, and an imide bond (-NH-) can be cited.

[0106] As R 10 The substituents that the monovalent hydrocarbon group represented can have are not particularly limited as long as the effects of the present disclosure are not impaired. For example, halogen atoms such as fluorine atoms and chlorine atoms, hydroxyl groups, etc. can be cited.

[0107] As R 10 The monovalent hydrocarbon group represented is preferably an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 10 carbon atoms from the viewpoint of achieving both improved bending resistance and surface hardness. As the alkyl group having 1 to 3 carbon atoms, methyl is more preferred. As the aryl group having 6 to 10 carbon atoms, phenyl is more preferred.

[0108] As R 11 The divalent hydrocarbon group represented can be an alkylene group having 1 to 20 carbon atoms, an arylene group, or a group formed by a combination thereof. The alkylene group can be any of linear, branched, and cyclic, or a combination of linear or branched and cyclic.

[0109] As the alkylene group having 1 to 20 carbon atoms, an alkylene group having 1 to 10 carbon atoms is preferred. For example, a group formed by a combination of linear or branched alkylene groups such as methylene, ethylene, various propylene groups, various butylene groups, and cyclohexylene, and cyclic alkylene groups can be cited.

[0110] As the above-mentioned arylene group, an arylene group having 6 to 12 carbon atoms is preferred. As the arylene group, phenylene, biphenylene, naphthylene, etc. can be cited, and it can further have substituents for the aromatic ring described later.

[0111] Examples of the divalent hydrocarbon group containing or not containing an oxygen atom or a nitrogen atom include a group formed by bonding the above divalent hydrocarbon groups to each other using at least one of an ether bond, a carbonyl bond, an ester bond, an amide bond, and an imide bond (-NH-).

[0112] As the divalent hydrocarbon group represented by R 11 The substituents that the divalent hydrocarbon group may have can be the same as the substituents that the monovalent hydrocarbon group represented by the above R 10 may have.

[0113] As the divalent hydrocarbon group represented by R 11 From the aspect of balancing the improvement of bending resistance and surface hardness, an alkylene group having 1 to 6 carbon atoms or an arylene group having 6 to 10 carbon atoms is preferred, and an alkylene group having 2 to 4 carbon atoms is more preferably used.

[0114] From the aspect of balancing the improvement of bending resistance and surface hardness, the molecular weight of the diamine residue having one or two silicon atoms in the main chain is preferably 1000 or less, more preferably 800 or less, still more preferably 500 or less, and particularly preferably 300 or less.

[0115] The diamine residue having one or two silicon atoms in the main chain can be used alone or in combination of two or more.

[0116] The diamine residue in the above general formula (1) represented by R 2 and having an aromatic ring without a silicon atom can be a residue obtained by removing two amino groups from a diamine having an aromatic ring without a silicon atom.

[0117] As the diamine having an aromatic ring described above, for example, p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzanilide, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 2-(3-aminophenyl)-2-(4-aminophenyl)propane, 2,2-bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2,2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2-(3-aminophenyl)-2-(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 1,1-bis(3-aminophenyl)-1-phenylethane, 1,1-bis(4-aminophenyl)-1-phenylethane, 1-(3-aminophenyl)-1-(4-aminophenyl)-1-phenylethane, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(3-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminobenzoyl)benzene, 1,3-bis(4-aminobenzoyl)benzene, 1,4-bis(3-aminobenzoyl)benzene, 1,4-bis(4-aminobenzoyl)benzene, 1,3-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(4-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(3-amino-α,α-dimethylbenzyl)benzene, 1,4-bis(4-amino-α,α-dimethylbenzyl)benzene, 1,3-bis(3-amino-α,α-bis(trifluoromethyl)benzyl)benzene, 1,3-bis(4-amino-α,α-bis(trifluoromethyl)benzyl)benzene, 1,4-bis(3-amino-α,α-bis(trifluoromethyl)benzyl)benzene, 1,4-bis(4-amino-α,α-bis(trifluoromethyl)benzyl)benzene, 2,6-bis(3-aminophenoxy)benzonitrile, 2,6-bis(3-aminophenoxy)pyridine, N,N'-bis(4-aminophenyl)terephthalamide, 9,9-bis(4-aminophenyl)fluorene, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-dichloro-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, bis[4-(3-aminophenoxy)phenyl]ketone, bis[4-(4-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl]ether, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 1,3-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(3-aminophenoxy)benzoyl]benzene, 1,4-bis[4-(4-aminophenoxy)benzoyl]benzene, 1,3-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,3-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(3-aminophenoxy)-α,α-dimethylbenzyl]benzene, 1,4-bis[4-(4-aminophenoxy)-α,α-dimethylbenzyl]benzene, 4,4'-bis[4-(4-aminophenoxy)benzoyl]diphenyl ether, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]benzophenone, 4,4'-bis[4-(4-amino-α,α-dimethylbenzyl)phenoxy]diphenyl sulfone, 4,4'-bis[4-(4-aminophenoxy)phenoxy]diphenyl sulfone, 3,3'-diamino-4,4'-diphenoxybenzophenone, 3,3'-diamino-4,4'-dibiphenoxybenzophenone, 3,3'-diamino-4-phenoxybenzophenone, 3,3'-diamino-4-biphenoxybenzophenone, 6,6'-bis(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane, 6,6'-bis(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirobiindane, etc., and diamines obtained by substituting a part or all of the hydrogen atoms on the aromatic ring of the above diamines with substituents selected from a fluoro group, a methyl group, a methoxy group, a trifluoromethyl group, or a trifluoromethoxy group can all be used.,

[0118] These diamines can be used alone or in combination of two or more kinds.,

[0119] In the above general formula (1), the R 2 The diamine residue that does not have a silicon atom but has an aliphatic ring can be a residue obtained by removing two amino groups from a diamine having an aliphatic ring.,

[0120] As the diamine having an aliphatic ring as described above, for example, trans - cyclohexanediamine, trans - 1,4 - bis(methylenecyclohexane)diamine, 2,6 - bis(aminomethyl)bicyclo[2,2,1]heptane, 2,5 - bis(aminomethyl)bicyclo[2,2,1]heptane, etc. can be cited.

[0121] These diamines can be used alone or in combination of two or more.

[0122] The polyimide film of the present disclosure is obtained by making R in the above general formula (1) 2 wherein R 2 10 mol% or more and 50 mol% or less of the total amount is a diamine residue having one or two silicon atoms in the main chain, and 50 mol% or more and 90 mol% or less of the total amount of R 2 is a diamine residue having an aromatic ring or an aliphatic ring without a silicon atom. The bending resistance is improved, and sufficient surface hardness as a protective film can be obtained. In R of the above general formula (1) 2 , from the aspect of improving the adhesion to an organic film when laminating with an organic film such as a hard coat described later, the diamine residue having one or two silicon atoms in the main chain is preferably 15 mol% or more of the total amount of R 2 , and more preferably 20 mol% or more. On the other hand, in R of the above general formula (1) 2 , from the aspect of improving surface hardness and light transmittance, the diamine residue having one or two silicon atoms in the main chain is preferably 45 mol% or less of the total amount of R 2 , and more preferably 40 mol% or less.

[0123] It should be noted that as long as 10 mol% or more and 50 mol% or less of the total amount of R 2 is a diamine residue having one or two silicon atoms in the main chain, and 50 mol% or more and 90 mol% or less of the total amount of R 2 is a diamine residue having an aromatic ring or an aliphatic ring without a silicon atom, other diamine residues different from the diamine residue having one or two silicon atoms in the main chain and the diamine residue having an aromatic ring or an aliphatic ring without a silicon atom may be included in R of the above general formula (1) 2 . This other diamine residue is preferably 10 mol% or less of the total amount of R 2 , more preferably 5 mol% or less, still more preferably 3 mol% or less, and particularly preferably 1 mol% or less. As this other diamine residue, for example, a diamine residue having no silicon atom and no aromatic ring or aliphatic ring can be cited. From the aspect of improving the tensile elastic modulus and surface hardness, a diamine residue having three or more silicon atoms in the main chain is preferably not included.

[0124] Among them, preferably: R 2 More than 10 mol% and less than 50 mol% of the total amount is a diamine residue having 1 or 2 silicon atoms in the main chain, and R 2 In the total amount (100 mol%) of, more than 50 mol% and less than 99 mol% of the balance (100% - x%) of the mol% (x mol%) of the diamine residue having 1 or 2 silicon atoms in the main chain is a diamine residue having an aromatic ring or an aliphatic ring without a silicon atom.

[0125] As the polyimide having the structure represented by the above general formula (1), from the viewpoints of improving light transmittance and surface hardness, the following polyimide is preferably used: containing an aromatic ring and containing at least one selected from the group consisting of (i) a fluorine atom, (ii) an aliphatic ring, and (iii) a structure in which aromatic rings are linked to each other by a sulfonyl group or a fluorine-substituted or unsubstituted alkylene group. The polyimide having the structure represented by the above general formula (1) contains at least one selected from a tetracarboxylic acid residue having an aromatic ring and a diamine residue having an aromatic ring, so that the molecular skeleton becomes rigid, the orientation is improved, and the surface hardness is improved. However, the rigid aromatic ring skeleton has a tendency for the absorption wavelength to extend to a longer wavelength, and the transmittance in the visible light region tends to decrease.

[0126] When the polyimide contains (i) a fluorine atom, it is difficult for the charge migration to occur in the electronic state in the polyimide skeleton, so the light transmittance is improved.

[0127] When the polyimide contains (ii) an aliphatic ring, the charge migration in the skeleton can be suppressed by cutting off the conjugation of the π electrons in the polyimide skeleton, so the light transmittance is improved.

[0128] When the polyimide contains (iii) a structure in which aromatic rings are linked to each other by a sulfonyl group or a fluorine-substituted or unsubstituted alkylene group, the charge migration in the skeleton can be suppressed by cutting off the conjugation of the π electrons in the polyimide skeleton, so the light transmittance is improved.

[0129] As the polyimide having the structure represented by the above general formula (1), from the viewpoints of improving light transmittance and surface hardness, a polyimide containing a fluorine atom is preferably used.

[0130] Regarding the content ratio of fluorine atoms, the ratio (F / C) of the number of fluorine atoms (F) to the number of carbon atoms (C), which is obtained by measuring the polyimide surface using X-ray photoelectron spectroscopy, is preferably 0.01 or more, and more preferably 0.05 or more. On the other hand, when the content ratio of fluorine atoms is too high, the original heat resistance of the polyimide may decrease. Therefore, the ratio (F / C) of the number of fluorine atoms (F) to the number of carbon atoms (C) is preferably 1 or less, and more preferably 0.8 or less.

[0131] Here, the above ratio obtained by measuring using X-ray photoelectron spectroscopy (XPS) can be obtained from the atomic% values of each atom measured using an X-ray photoelectron spectroscopy apparatus (for example, Theta Probe manufactured by Thermo Scientific).

[0132] In addition, in the polyimide having the structure represented by the above general formula (1), from the aspect of improving the surface hardness, when the total of R 1 and R 2 in the above general formula (1) is set to 100 mol%, the total of the tetracarboxylic acid residue having an aromatic ring and the diamine residue having an aromatic ring is preferably 50 mol% or more, more preferably 60 mol% or more, and even more preferably 75 mol% or more.

[0133] In addition, in the polyimide having the structure represented by the above general formula (1), from the aspects of improving the surface hardness and light transmittance, it is preferable that at least one of the tetracarboxylic acid residue of R 1 and the diamine residue of R 2 that does not have a silicon atom and has an aromatic ring or an aliphatic ring contains an aromatic ring and a fluorine atom. More preferably, both the tetracarboxylic acid residue of R 1 and the diamine residue of R 2 that does not have a silicon atom and has an aromatic ring or an aliphatic ring contain an aromatic ring and a fluorine atom.

[0134] In the polyimide having the structure represented by the above general formula (1), from the aspects of improving the surface hardness and light transmittance, when the total of R 1 and R 2 in the above general formula (1) is set to 100 mol%, the total of the tetracarboxylic acid residue having an aromatic ring and a fluorine atom and the diamine residue having an aromatic ring and a fluorine atom is preferably 50 mol% or more, more preferably 60 mol% or more, and even more preferably 75 mol% or more.

[0135] In addition, in the polyimide having the structure represented by the above general formula (1), from the viewpoints of improving light transmittance and surface hardness, a polyimide in which 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide are hydrogen atoms directly bonded to an aromatic ring is preferably used. The ratio of the number of hydrogen atoms directly bonded to an aromatic ring to the total number of hydrogen atoms (number) bonded to the carbon atoms contained in the polyimide is more preferably 60% or more, and even more preferably 70% or more.

[0136] In the case of a polyimide in which 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide are hydrogen atoms directly bonded to an aromatic ring, even after a heating process in the atmosphere, for example, even when stretching is performed at 200 °C or higher, the change in optical properties, particularly the total light transmittance and the yellowness index YI value, is small, and thus it is preferable. In the case of a polyimide in which 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide are hydrogen atoms directly bonded to an aromatic ring, the reactivity with oxygen is low, and thus it can be speculated that the chemical structure of the polyimide is not easily changed. Polyimide films are mostly used for devices that require processing steps accompanied by heating due to their high heat resistance. In the case of a polyimide in which 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide are hydrogen atoms directly bonded to an aromatic ring, it is not necessary to perform these subsequent steps in an inert atmosphere in order to maintain transparency, and thus it has the advantage of being able to suppress the equipment cost and the cost for atmosphere control.

[0137] Here, the ratio of the number of hydrogen atoms directly bonded to an aromatic ring to the total number of hydrogen atoms (number) bonded to the carbon atoms contained in the polyimide can be determined by using high performance liquid chromatography, gas chromatography-mass spectrometry, and NMR for the decomposition products of the polyimide. For example, the sample is decomposed using an alkaline aqueous solution or supercritical methanol, the resulting decomposition products are separated by high performance liquid chromatography, qualitative analysis of each peak obtained by this separation is performed using gas chromatography-mass spectrometry and NMR, etc., and quantification is performed using high performance liquid chromatography, whereby the ratio of the number of hydrogen atoms directly bonded to an aromatic ring to the total number of hydrogen atoms (number) contained in the polyimide can be determined.

[0138] In addition, in the polyimide having the structure represented by the above general formula (1), from the viewpoints of bending resistance and surface hardness, the content ratio (mass%) of silicon atoms in the polyimide is preferably 0.7 mass% or more and 6.5 mass% or less, more preferably 0.7 mass% or more and 5.5 mass% or less, and even more preferably 0.7 mass% or more and 4.2 mass% or less.

[0139] Herein, the content ratio (mass %) of silicon atoms in the polyimide can be determined from the molecular weight of the feedstock used in the production of the polyimide. Additionally, the content ratio (mass %) of silicon atoms in the polyimide can be determined in the same manner as described above by using high performance liquid chromatography, gas chromatography - mass spectrometry analyzer, NMR, elemental analysis, XPS / ESCA, and TOF - SIMS for the decomposition products of the obtained polyimide.

[0140] In the polyimide having the structure represented by the above general formula (1), from the aspects of light transmittance, bending resistance, and surface hardness, where R in the above general formula (1) 1 is preferably at least one tetravalent group selected from the group consisting of cyclohexanetetracarboxylic dianhydride residue, cyclopentanetetracarboxylic dianhydride residue, dicyclohexane - 3,4,3’,4’ - tetracarboxylic dianhydride residue, cyclobutanetetracarboxylic dianhydride residue, pyromellitic dianhydride residue, 3,3’,4,4’ - biphenyltetracarboxylic dianhydride residue, 2,2’,3,3’ - biphenyltetracarboxylic dianhydride residue, 4,4’ - (hexafluoroisopropylidene) diphthalic anhydride residue, 3,4’ - (hexafluoroisopropylidene) diphthalic anhydride residue, 3,3’ - (hexafluoroisopropylidene) diphthalic anhydride residue, 4,4’ - oxydiphthalic anhydride residue, and 3,4’ - oxydiphthalic anhydride residue.

[0141] The above R 1 preferably contains 50 mol% or more, more preferably 70 mol% or more, and even more preferably 90 mol% or more in total of these preferred residues.

[0142] Especially from the aspect of good balance between light transmittance and surface hardness, R in the above general formula (1) 1 is more preferably at least one tetravalent group selected from the group consisting of 4,4’ - (hexafluoroisopropylidene) diphthalic anhydride residue, 3,4’ - (hexafluoroisopropylidene) diphthalic anhydride residue, 3,3’ - (hexafluoroisopropylidene) diphthalic anhydride residue, 4,4’ - oxydiphthalic anhydride residue, and 3,4’ - oxydiphthalic anhydride residue.

[0143] As R of the above general formula (1) 1, it is also preferred to use the following Group A and Group B in combination: Group A is a group of tetracarboxylic acid residues suitable for improving rigidity, selected from at least one of the group consisting of pyromellitic dianhydride residues, 3,3',4,4'-biphenyltetracarboxylic dianhydride residues, and 2,2',3,3'-biphenyltetracarboxylic dianhydride residues; Group B is a group of tetracarboxylic acid residues suitable for improving light transmittance, selected from at least one of the group consisting of cyclohexanetetracarboxylic dianhydride residues, cyclopentanetetracarboxylic dianhydride residues, dicyclohexane-3,4,3',4'-tetracarboxylic dianhydride residues, cyclobutanetetracarboxylic dianhydride residues, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride residues, 3,4'-(hexafluoroisopropylidene)diphthalic anhydride residues, 3,3'-(hexafluoroisopropylidene)diphthalic anhydride residues, 4,4'-oxydiphthalic anhydride residues, and 3,4'-oxydiphthalic anhydride residues. In this case, regarding the content ratio of the above-mentioned tetracarboxylic acid residue group suitable for improving rigidity (Group A) to the tetracarboxylic acid residue group suitable for improving light transmittance (Group B), per 1 mole of the tetracarboxylic acid residue group suitable for improving light transmittance (Group B), the above-mentioned tetracarboxylic acid residue group suitable for improving rigidity (Group A) is preferably 0.05 mole or more and 9 moles or less, more preferably 0.1 mole or more and 5 moles or less, and even more preferably 0.3 mole or more and 4 moles or less.

[0144] Among them, as the above-mentioned Group B, from the aspects of improving surface hardness and light transmittance, it is preferred to use at least one of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride residues and 3,4'-(hexafluoroisopropylidene)diphthalic anhydride residues containing fluorine atoms.

[0145] In the polyimide having the structure represented by the above general formula (1), from the aspects of light transmittance, flexural resistance, and surface hardness, R in the above general formula (1) 2 Among the above-mentioned diamine residues having no silicon atom but having an aromatic ring or an aliphatic ring, it is preferably at least one divalent group selected from the group consisting of trans-cyclohexanediamine residues, trans-1,4-bis(methylenecyclohexane)diamine residues, 4,4'-diaminodiphenyl sulfone residues, 3,4'-diaminodiphenyl sulfone residues, 2,2-bis(4-aminophenyl)propane, 2,2-bis(4-aminophenyl)hexafluoropropane residues, and divalent groups represented by the following general formula (2). In particular, from the aspect of balancing light transmittance and surface hardness, it is more preferably at least one divalent group selected from the group consisting of 4,4'-diaminodiphenyl sulfone residues, 3,4'-diaminodiphenyl sulfone residues, 2,2-bis(4-aminophenyl)propane, 2,2-bis(4-aminophenyl)hexafluoropropane residues, and divalent groups represented by the following general formula (2). As the divalent group represented by the following general formula (2), it is more preferably that R 3 and R 4 are perfluoroalkyl groups.

[0146] [Chemical Formula 6]

[0147] General formula (2)

[0148]

[0149] (In general formula (2), R 3 and R 4 each independently represents a hydrogen atom, an alkyl group, or a perfluoroalkyl group.)

[0150] In addition, in the polyimide having the structure represented by the above general formula (1), from the viewpoints of light transmittance, bending resistance, and surface hardness, the diamine residue having one or two silicon atoms in the main chain in R 2 in the above general formula (1) is preferably a diamine residue having two silicon atoms, and further preferably 1,3-bis(3-aminopropyl)tetramethyldisiloxane residue, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, 1,3-bis(5-aminopentyl)tetramethyldisiloxane, etc. from the viewpoints of availability and achieving both light transmittance and surface hardness.)

[0151] In the structure represented by the above general formula (1), n represents the number of repeating units and is 1 or more.)

[0152] The number of repeating units n in the polyimide can be appropriately selected according to the structure so that it exhibits the preferred glass transition temperature described below, and there is no particular limitation.)

[0153] The average number of repeating units is usually 10 to 2000, and more preferably 15 to 1000.)

[0154] The polyimide used in the present disclosure may contain one or two or more polyimides having the structure represented by the above general formula (1).)

[0155] In addition, in the polyimide used in the present disclosure, as long as the effects of the present disclosure are not impaired, it may also have a structure different from the structure represented by the above general formula (1) in a part thereof. In the polyimide used in the present disclosure, the structure represented by the above general formula (1) is preferably 95% or more, more preferably 98% or more, and even more preferably 100% of the total number of repeating units of the polyimide.)

[0156] As a structure different from the structure represented by the above general formula (1), for example, cases including a tetracarboxylic acid residue having no aromatic ring or aliphatic ring, or a polyamide structure can be cited.)

[0157] As polyamide structures that can be included, for example, a polyamideimide structure containing a tricarboxylic acid residue such as trimellitic anhydride and a polyamide structure containing a dicarboxylic acid residue such as terephthalic acid can be cited.

[0158] The polyimide used in the present disclosure has a glass transition temperature in the temperature range of 150 °C or higher and 400 °C or lower. By making the above glass transition temperature 150 °C or higher, the heat resistance is excellent, and it is further preferably 200 °C or higher. In addition, by making the glass transition temperature 400 °C or lower, the baking temperature can be reduced, and it is further preferably 380 °C or lower.

[0159] In addition, the polyimide used in the present disclosure preferably does not have a peak in the tanδ curve in the temperature range of -150 °C or higher and 0 °C or lower. Thus, the surface hardness of the polyimide film at room temperature can be improved. In addition, the polyimide used in the present disclosure may further have a peak in the tanδ curve in the temperature range higher than 0 °C and lower than 150 °C.

[0160] The glass transition temperature of the polyimide used in the present disclosure can be measured in the same manner as the glass transition temperature of the polyimide film described later.

[0161] 2. Additives

[0162] In the polyimide film of the present disclosure, in addition to the above polyimide, additives can be further contained as needed. As the above additives, for example, inorganic particles for reducing the optical distortion of the polyimide film, silica fillers for smooth winding, surfactants for improving film-forming properties and defoaming properties, etc. can be cited.

[0163] 3. Characteristics of the polyimide film

[0164] The polyimide film of the present disclosure has the above-mentioned specific total light transmittance, yellowness, glass transition temperature, and tensile elastic modulus. The polyimide film of the present disclosure preferably further has the characteristics described later.

[0165] The total light transmittance of the polyimide film of the present disclosure measured according to JIS K7361-1 is 85% or more. Thus, due to the high transmittance, the transparency is good, and it can be a glass substitute material. The total light transmittance of the polyimide film of the present disclosure measured according to JIS K7361-1 is further preferably 88% or more, more preferably 89% or more, and particularly preferably 90% or more.

[0166] When the thickness of the polyimide film of the present disclosure is 5 μm or more and 100 μm or less, the total light transmittance measured according to JIS K7361-1 is preferably 85% or more, further preferably 88% or more, more preferably 89% or more, and particularly preferably 90% or more.

[0167] In addition, when the thickness of the polyimide film of the present disclosure is 50 μm ± 5 μm, the total light transmittance measured according to JIS K7361-1 is preferably 85% or more, more preferably 88% or more, still more preferably 89% or more, and particularly preferably 90% or more.

[0168] The total light transmittance measured according to JIS K7361-1 can be measured using, for example, a haze meter (e.g., HM150 manufactured by Murakami Color Research Institute). It should be noted that for the total light transmittance at different thicknesses, the conversion value can be obtained from the measured value of the total light transmittance at a certain thickness using the Lambert-Beer law, and this conversion value can be used.

[0169] In addition, in the polyimide film of the present disclosure, the yellowness (YI value) calculated according to JIS K7373-2006 is 30 or less. Thus, due to the low yellowness, coloring of the yellow tone can be suppressed, the light transmittance is improved, and it can be a substitute material for glass. The yellowness (YI value) calculated according to JIS K7373-2006 is preferably 20 or less, more preferably 15 or less, and still more preferably 10 or less.

[0170] When the thickness of the polyimide film of the present disclosure is 5 μm or more and 100 μm or less, the yellowness (YI value) calculated according to JIS K7373-2006 is preferably 30 or less, more preferably 20 or less, still more preferably 15 or less, and preferably 10 or less.

[0171] In addition, when the thickness of the polyimide film of the present disclosure is 50 μm ± 5 μm, the yellowness (YI value) calculated according to JIS K7373-2006 is preferably 10 or less, more preferably 7 or less, and still more preferably 5 or less.

[0172] It should be noted that the yellowness (YI value) can be measured according to the above JIS K7373-2006 using an ultraviolet-visible-near-infrared spectrophotometer (e.g., V-7100 manufactured by JASCO Corporation), and the transmittance is measured using the spectroscopic colorimetric method specified in JIS Z8722, and the yellowness is calculated based on the measured transmittance.

[0173] It should be noted that for the yellowness at different thicknesses, for a sample with a specific film thickness, the transmittances at each wavelength measured at 5 nm intervals between 380 nm and 780 nm can be used to obtain the conversion values of the transmittances at each wavelength at different thicknesses in the same way as the above total light transmittance using the Lambert-Beer law, and the yellowness at different thicknesses can be calculated from the measured value of the yellowness at a certain thickness based on this conversion value and used.

[0174] In addition, the polyimide film of the present disclosure has a glass transition temperature in the temperature range of above 150°C and below 400°C. Regarding the temperature range having the above-mentioned glass transition temperature, from the aspect of excellent heat resistance, it is preferably 200°C or higher, and from the aspect of being able to reduce the baking temperature, it is preferably 380°C or lower.

[0175] It should be noted that the above-mentioned glass transition temperature is obtained from the peak temperature of the temperature - tanδ (tanδ = loss elastic modulus (E”) / storage elastic modulus (E’)) curve obtained by dynamic viscoelasticity measurement. When there are two or more peaks in the tanδ curve, the glass transition temperature of the polyimide film refers to the temperature of the peak with the largest maximum value of the peak.

[0176] As the dynamic viscoelasticity measurement, for example, a dynamic viscoelasticity measurement device RSA III (TA Instruments Japan Inc.) can be used, the measurement range is set to -150°C to 400°C, and the measurement is carried out under the conditions of a frequency of 1 Hz and a heating rate of 5°C / minute. In addition, the sample width can be 5 mm and the chuck spacing can be 20 mm for the measurement.

[0177] In the present disclosure, the peak of the tanδ curve refers to a peak having an inflection point as the maximum value and a peak width between the valleys of the peak of 3°C or more. For the fine up and down fluctuations due to measurement such as interference, they are not interpreted as the above-mentioned peak.

[0178] In addition, the polyimide film of the present disclosure preferably does not have a peak of the tanδ curve in the temperature range of above -150°C and below 0°C. In the case of containing a diamine residue having a long siloxane bond in the main chain, there is a peak of the tanδ curve in such a low temperature range, but the polyimide film of the present disclosure usually does not have a peak of the tanδ curve in such a low temperature range because it has a short bond with one or two silicon atoms. Compared with a polyimide film containing a diamine residue having a long siloxane bond in the main chain and having a peak of the tanδ curve in the temperature range of above -150°C and below 0°C, a decrease in the tensile elastic modulus at room temperature can be suppressed, and sufficient surface hardness as a protective film can be maintained.

[0179] In addition, in the polyimide film of the present disclosure, the tensile elastic modulus at 25°C, which is obtained by measuring a test piece of 15 mm × 40 mm at a tensile speed of 10 mm / minute and a chuck distance of 20 mm in accordance with JIS K7127, is 1.8 GPa or more. Thus, due to the high tensile elastic modulus at 25°C (room temperature), sufficient surface hardness as a protective film can be maintained at room temperature, and it can be used as a surface material. The above tensile elastic modulus is preferably 2.0 GPa or more, and more preferably 2.4 GPa or more. On the other hand, from the aspect of improving bending resistance, the above tensile elastic modulus is preferably 5.2 GPa or less. From the aspect of improving bending resistance, the above tensile elastic modulus can be 4.0 GPa or less, or can be 3.5 GPa or less.

[0180] The above tensile elastic modulus can be measured using a tensile testing machine (for example, manufactured by Shimadzu Corporation: Aotograph AG-X1N, load cell: SBL-1KN). A test piece with a width of 15 mm × a length of 40 mm is cut out from the polyimide film, and the tensile speed is set to 10 mm / minute and the chuck distance is set to 20 mm at 25°C for measurement. The polyimide film for obtaining the above tensile elastic modulus preferably has a thickness of 50 μm ± 5 μm.

[0181] In addition, in the polyimide film of the present disclosure, from the aspect of reducing optical distortion, the birefringence in the thickness direction at a wavelength of 590 nm is preferably 0.020 or less. When having such birefringence, when using the polyimide film of the present disclosure as a surface material for a display, a decrease in the display quality of the display can be suppressed. The birefringence in the thickness direction at a wavelength of 590 nm is preferably smaller, preferably 0.015 or less, more preferably 0.010 or less, and even more preferably less than 0.008.

[0182] It should be noted that the birefringence in the thickness direction at a wavelength of 590 nm of the polyimide film of the present disclosure can be obtained as follows.

[0183] First, using a retardation measuring device (for example, manufactured by Oji Scientific Instruments Co., Ltd., product name "KOBRA-WR"), the retardation value (Rth) in the thickness direction of the polyimide film is measured at 25°C using light with a wavelength of 590 nm. Regarding the retardation value (Rth) in the thickness direction, the retardation value at 0-degree incidence and the retardation value at 40-degree incidence are measured, and the retardation value Rth in the thickness direction is calculated from these retardation values. Regarding the retardation value at 40-degree incidence, light with a wavelength of 590 nm is incident on the retardation film from a direction inclined 40 degrees from the normal line of the retardation film for measurement.

[0184] The birefringence in the thickness direction of the polyimide film can be obtained by substituting it into the formula: Rth / d. Here, d represents the film thickness (nm) of the polyimide film.

[0185] It should be noted that when the refractive index in the slow axis direction in the plane of the film (the direction with the maximum refractive index in the film plane) is set as nx, the refractive index in the fast axis direction in the film plane (the direction with the minimum refractive index in the film plane) is set as ny, and the refractive index in the thickness direction of the film is set as nz, the phase difference in the thickness direction can be expressed as Rth [nm] = {(nx + ny) / 2 - nz} × d.

[0186] In the polyimide film of the present disclosure, the pencil hardness is preferably 2B or more, more preferably B or more, and still more preferably HB or more.

[0187] The pencil hardness of the above polyimide film can be evaluated as follows: After conditioning the test sample at a temperature of 25°C and a relative humidity of 60% for 2 hours, using a test pencil specified in JIS-S-6006, a pencil hardness test (0.98N load) specified in JIS K5600-5-4 (1999) is carried out on the film surface, and the highest pencil hardness without damage is evaluated. For example, a pencil scratch coating hardness tester manufactured by Toyo Seiki Co., Ltd. can be used.

[0188] From the aspect of light transmittance, the haze value of the polyimide film of the present disclosure is preferably 10 or less, more preferably 8 or less, and still more preferably 5 or less. This haze value is preferably achievable when the thickness of the polyimide film is 5 μm or more and 100 μm or less.

[0189] The above haze value can be measured by the method according to JIS K-7105. For example, it can be measured using a haze meter HM150 manufactured by Murakami Color Technology Research Institute.

[0190] In the polyimide film of the present disclosure, from the aspect of excellent bending resistance, when a static bending test is carried out according to the following static bending test method, the inner angle measured in this test is preferably 120° or more, more preferably 125° or more.

[0191] [Static Bending Test Method]

[0192] A test piece of a polyimide film cut into 15 mm × 40 mm is bent at the midpoint of its long side, and metal sheets (100 mm × 30 mm × 6 mm) with a thickness of 6 mm are arranged to sandwich the test piece from the upper and lower surfaces at both ends of the long side of the test piece. The test piece is fixed with tape such that the overlapping portions of the two ends of the test piece and the metal sheets on the upper and lower surfaces are each 10 mm. In this state, the test piece is clamped from above and below with a glass plate (100 mm × 100 mm × 0.7 mm), and the test piece is fixed in a state of being bent with an inner diameter of 6 mm. At this time, a simulated test piece is inserted into the portion where the test piece does not exist between the metal sheet and the glass plate, and the test piece is fixed with tape in a manner parallel to the glass plate. After leaving the test piece fixed in the bent state in an environment of 60 ± 2°C and 93 ± 2% relative humidity (RH) for 24 hours, the glass plate and the fixing tape are removed, and the force applied to the test piece is released. Then, one end of the test piece is fixed, and the inner angle of the test piece 30 minutes after releasing the force applied to the test piece is measured.

[0193] In addition, in the polyimide film of the present disclosure, from the aspect of excellent bending resistance, when a dynamic bending test is performed according to the following dynamic bending test method, the inner angle of the test piece is preferably 155° or more, and more preferably 160° or more.

[0194] [Dynamic Bending Test Method]

[0195] A test piece of a polyimide film cut into a size of 20 mm × 100 mm is fixed with tape in a durability test system (DMX-FS, a surface body unloaded U-shaped expansion test fixture manufactured by YUASA SYSTEM Co., Ltd.) inside a thermo-hygrostat. The test piece is set in the same bending state as the above-mentioned static bending test, that is, set such that the distance between both ends of the long side of the test piece in the bent state is 6 mm (fixed in a state of being bent with an inner diameter of 6 mm), and then the test piece is repeatedly bent 200,000 times at a bending frequency of 90 times per minute in an environment of 60 ± 2°C and 93 ± 2% relative humidity (RH).

[0196] Then, the test piece is removed, one end of the obtained test piece is fixed, and the inner angle of the test piece 30 minutes after repeating 200,000 times is measured.

[0197] In addition, in the polyimide film of the present disclosure, from the aspect of excellent surface hardness, the Young's modulus measured by the following measurement method is preferably 2.3 GPa or more, and more preferably 2.4 GPa or more.

[0198] The Young's modulus is measured at a temperature of 25 °C using nanoindentation in accordance with ISO 14577. Specifically, the measuring device uses PICODENTOR HM500 manufactured by Fischer Instruments Co., Ltd., and a Vickers indenter is used as the measuring indenter. Measurements are taken at arbitrary points on the surfaces of eight locations of the polyimide film, and the value obtained by numerical averaging is taken as the Young's modulus. It should be noted that the measurement conditions are set as follows: maximum indentation depth: 1000 nm, load time: 20 seconds, creep time: 5 seconds.

[0199] In addition, the atomic percentage of silicon atoms (Si) on the film surface of the polyimide film measured by X-ray photoelectron spectroscopy is preferably 0.1 or more and 10 or less, and more preferably 0.2 or more and 5 or less.

[0200] Here, the above ratio obtained by measurement using X-ray photoelectron spectroscopy (XPS) can be obtained from the values of the atomic percentages of each atom measured using an X-ray photoelectron spectrometer (for example, Theta Probe manufactured by Thermo Scientific).

[0201] In addition, as a preferred embodiment, the ratio (F / C) of the number of fluorine atoms (F) to the number of carbon atoms (C) on the film surface of the polyimide film measured by X-ray photoelectron spectroscopy is preferably 0.01 or more and 1 or less, and more preferably 0.05 or more and 0.8 or less.

[0202] In addition, the ratio (F / N) of the number of fluorine atoms (F) to the number of nitrogen atoms (N) on the film surface of the polyimide film measured by X-ray photoelectron spectroscopy is preferably 0.1 or more and 20 or less, and more preferably 0.5 or more and 15 or less.

[0203] In addition, the ratio (F / Si) of the number of fluorine atoms (F) to the number of silicon atoms (Si) on the film surface of the polyimide film measured by X-ray photoelectron spectroscopy is preferably 1 or more and 50 or less, and more preferably 3 or more and 30 or less.

[0204] In addition, in the polyimide film of the present disclosure, from the aspect of the adhesion between the polyimide film and the hard coat and from the aspect of the surface hardness of the laminate formed by laminating the hard coat adjacent to the polyimide film, it is preferable that no peeling of the coating film occurs when the adhesion test is performed according to the following adhesion test method.

[0205] [Adhesion Test Method]

[0206] A resin composition for evaluating adhesion was prepared by adding 10 parts by mass of 1-hydroxycyclohexyl phenyl ketone to a 40% by mass solution of pentaerythritol triacrylate in methyl isobutyl ketone. The composition was coated onto a test piece of polyimide film cut into 10 cm × 10 cm, and irradiated with ultraviolet rays at an exposure of 200 mJ / cm 2 to cure it, thereby forming a cured film with a film thickness of 10 μm. For this cured film, a cross-cut test was carried out according to JIS K 5600-5-6, and after repeatedly performing 5 peeling operations with tape, the presence or absence of peeling of the coating film was observed.

[0207] 4. Structure of the polyimide film

[0208] The thickness of the polyimide film of the present disclosure can be appropriately selected according to the use, preferably 1 μm or more, more preferably 5 μm or more, and still more preferably 10 μm or more. On the other hand, it is preferably 200 μm or less, more preferably 150 μm or less, and still more preferably 100 μm or less.

[0209] When the thickness is thin, the strength decreases and it is easy to break; when the thickness is thick, the difference between the inner diameter and the outer diameter during bending becomes large, the load on the film increases, and thus the bending resistance may decrease.

[0210] In addition, surface treatments such as saponification treatment, glow discharge treatment, corona discharge treatment, ultraviolet treatment, and flame treatment can be performed on the polyimide film of the present disclosure.

[0211] 5. Manufacturing method of the polyimide film

[0212] As a manufacturing method of the polyimide film of the present disclosure, for example, the following manufacturing method of the polyimide film as the first manufacturing method can be cited. This manufacturing method includes:

[0213] A step of preparing a polyimide precursor resin composition containing a polyimide precursor having a structure represented by the following general formula (1') and an organic solvent (hereinafter referred to as the polyimide precursor resin composition preparation step);

[0214] A step of coating the above polyimide precursor resin composition onto a support to form a polyimide precursor resin coating film (hereinafter referred to as the polyimide precursor resin coating film formation step); and

[0215] A step of imidizing the above polyimide precursor by heating (hereinafter referred to as the imidization step).

[0216] [Chemical formula 7]

[0217] General formula (1')[[]]

[0218]

[0219] (In the general formula (1’), R 1 , R 2 and n are the same as those in the above general formula (1).)

[0220] In the above first manufacturing method, a step of stretching at least one of the polyimide precursor resin coating film and the post-imide coating film obtained by imidizing the polyimide precursor resin coating film (hereinafter referred to as the stretching step) may be further included.

[0221] Hereinafter, each step will be described in detail.

[0222] (1) Polyimide Precursor Resin Composition Preparation Step

[0223] The polyimide precursor resin composition prepared in the above first manufacturing method contains the polyimide precursor represented by the above general formula (1’) and an organic solvent, and may contain additives and the like as needed. The polyimide precursor represented by the above general formula (1’) is a polyamic acid obtained by polymerization of a tetracarboxylic acid component that is a tetracarboxylic acid residue in R 1 in the above general formula (1’) and a diamine component that is a diamine residue in R 2 in the above general formula (1’).

[0224] Here, R 1 , R 2 and n in the above general formula (1’) may use the same groups or numbers as R 1 , R 2 and n in the above general formula (1) described in the above polyimide.

[0225] From the aspect of the strength when forming a film, at least one of the number average molecular weight and the weight average molecular weight of the polyimide precursor represented by the above general formula (1’) is preferably 10,000 or more, more preferably 20,000 or more. On the other hand, when the average molecular weight is too large, the viscosity becomes high, and the workability such as filtration may be reduced. From this aspect, it is preferably 10,000,000 or less, more preferably 500,000 or less.

[0226] The number average molecular weight of the polyimide precursor can be determined by NMR (for example, BRUKER, AVANCEIII). For example, the polyimide precursor solution can be coated on a glass plate, dried at 100 °C for 5 minutes, then 10 mg of the solid component can be dissolved in 7.5 ml of dimethyl sulfoxide-d6 solvent, and NMR measurement can be performed, and the number average molecular weight can be calculated from the peak intensity ratio of the hydrogen atoms bonded to the aromatic ring.

[0227] The weight-average molecular weight of the polyimide precursor can be measured using gel permeation chromatography (GPC).

[0228] The polyimide precursor is made into a 0.5 wt% concentration solution in N-methylpyrrolidone (NMP). As the eluent, a 10 mmol% LiBr-NMP solution with a water content of 500 ppm or less is used. Using a GPC device (HLC-8120) manufactured by Tosoh Corporation (the column used: GPC LF-804 manufactured by SHODEX), the measurement is carried out under the conditions of a sample injection volume of 50 μL, a solvent flow rate of 0.5 mL / minute, and 40 °C. The weight-average molecular weight is determined based on a polystyrene standard sample with the same concentration as the sample.

[0229] The above polyimide precursor solution is obtained by reacting the above tetracarboxylic dianhydride with the above diamine in a solvent. As the solvent used for the synthesis of the polyimide precursor (polyamic acid), there is no particular limitation as long as it can dissolve the above tetracarboxylic dianhydride and diamine. For example, aprotic polar solvents or water-soluble alcohol solvents can be used. In the present disclosure, preferably, organic solvents containing nitrogen atoms such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, 1,3-dimethyl-2-imidazolidinone, etc.; γ-butyrolactone, etc. are used. Among them, when directly using the above polyimide precursor solution (polyamic acid solution) for preparing the polyimide precursor resin composition, when the polyimide precursor resin composition contains inorganic particles described later, from the aspect of suppressing the dissolution of inorganic particles, organic solvents containing nitrogen atoms are preferably used, and among them, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, or a combination thereof is preferably used. It should be noted that an organic solvent refers to a solvent containing carbon atoms.

[0230] In addition, the above polyimide precursor solution is prepared by combining at least two kinds of diamines. Polyamic acid can be synthesized by adding acid dianhydride to a mixed solution of at least two kinds of diamines, or at least two kinds of diamine components can be added stepwise to the reaction solution in an appropriate molar ratio to control to some extent the order in which each raw material is incorporated into the polymer chain.

[0231] For example, 0.5 equivalents of the molar ratio of acid dianhydride of the diamine having one or two silicon atoms in the main chain can be added to and reacted with a reaction solution in which the diamine having one or two silicon atoms in the main chain is dissolved, thereby synthesizing an amide acid in which the diamine having one or two silicon atoms in the main chain reacts with both ends of the acid dianhydride. All or part of the remaining diamine is added thereto, and acid dianhydride is added to carry out the polymerization of polyamic acid. When polymerizing by this method, the diamine having one or two silicon atoms in the main chain is introduced into the polyamic acid in a form linked via one acid dianhydride.

[0232] From the aspect of determining to some extent the positional relationship of the amic acid having 1 or 2 silicon atoms in the main chain and easily obtaining a film with excellent flexibility while maintaining surface hardness, it is preferable to polymerize the polyamic acid by such a method.

[0233] When the number of moles of the diamine in the above polyimide precursor solution (polyamic acid solution) is set to X and the number of moles of the tetracarboxylic dianhydride is set to Y, it is preferably such that Y / X is 0.9 or more and 1.1 or less, more preferably 0.95 or more and 1.05 or less, further preferably 0.97 or more and 1.03 or less, and particularly preferably 0.99 or more and 1.01 or less. By setting it within such a range, the molecular weight (degree of polymerization) of the obtained polyamic acid can be moderately adjusted.

[0234] The step of the polymerization reaction can be appropriately selected from known methods and is not particularly limited.

[0235] In addition, the polyimide precursor solution obtained by the synthesis reaction can be directly used, and other components can be mixed therein as needed; or the solvent of the polyimide precursor solution can be dried and dissolved in other solvents for use.

[0236] From the aspect of forming a uniform coating film and polyimide film, the viscosity of the above polyimide precursor solution at 25 °C is preferably 500 cps or more and 200000 cps or less.

[0237] The viscosity of the polyimide precursor solution can be measured at 25 °C using a viscometer (such as TVE-22HT, Toki Sangyo Co., Ltd.).

[0238] The above polyimide precursor resin composition can contain additives as needed. As the above additives, for example, inorganic particles for reducing the optical deformation of the polyimide film, silica fillers for smooth winding, surfactants for improving film-forming properties or defoaming properties, etc. can be cited, and the same additives as those described in the above polyimide film can be used.

[0239] The organic solvent used in the above polyimide precursor resin composition is not particularly limited as long as it can dissolve the above polyimide precursor. For example, nitrogen atom-containing organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, 1,3-dimethyl-2-imidazolidinone can be used; γ-butyrolactone, etc. Among them, for the above reasons, nitrogen atom-containing organic solvents are preferably used.

[0240] Regarding the content of the above-mentioned polyimide precursor in the above-mentioned polyimide precursor resin composition, from the viewpoints of forming a uniform coating film and a polyimide film having operable strength, it is preferably 50% by mass or more, more preferably 60% by mass or more, in the solid content of the resin composition, and the upper limit can be appropriately adjusted according to the components contained.

[0241] When the above-mentioned polyimide precursor resin composition contains the above-mentioned inorganic particles, the content of the above-mentioned inorganic particles is appropriately set according to the required optical properties. From the viewpoint of controlling optical properties, it is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, in the solid content of the resin composition, and preferably 50% by mass or less, preferably 40% by mass or less.

[0242] From the viewpoints of forming a uniform coating film and a polyimide film, the organic solvent in the above-mentioned polyimide precursor resin composition is preferably 40% by mass or more, more preferably 50% by mass or more, in the resin composition, and preferably 99% by mass or less.

[0243] In addition, in the above-mentioned polyimide precursor resin composition, from the viewpoints of good storage stability of the polyimide precursor resin composition and improved productivity, it preferably contains 1000 ppm or less of water content. When the polyimide precursor resin composition contains a large amount of water, the polyimide precursor is liable to decompose. In addition, when the polyimide precursor resin composition contains the above-mentioned inorganic particles, the above-mentioned inorganic particles may dissolve and no longer function as a refractive index adjusting component.

[0244] It should be noted that the water content of the polyimide precursor resin composition can be determined using a Karl Fischer moisture meter (for example, manufactured by Mitsubishi Chemical Corporation, trace moisture measuring device CA-200 type).

[0245] The method for preparing the above-mentioned polyimide precursor resin composition is not particularly limited. When the polyimide precursor resin composition contains the above-mentioned inorganic particles, for example, 1) a method of dispersing the above-mentioned inorganic particles into a polyimide precursor solution and homogenizing it; 2) a method of mixing a polyimide precursor solution with an organic solvent in which the above-mentioned inorganic particles are dispersed and homogenizing it; 3) a method of dissolving a polyimide precursor into an organic solvent in which the above-mentioned inorganic particles are dispersed and homogenizing it; and the like.

[0246] In order to make the water content 1000 ppm or less as described above, it is preferable to previously dry the inorganic particles before use or use an organic solvent in which the water content has been controlled by dehydrating the organic solvent to be used, and perform the treatment in an environment with a humidity of 5% or less.

[0247] As a method for dispersing the above inorganic particles in an organic solvent, known methods such as stirring and ultrasonic irradiation can be used. Among them, from the aspect of preventing moisture from mixing in, a dispersion method that does not use a medium such as inorganic microbeads is preferably used, and a dispersion method by ultrasonic irradiation or vibration is preferably used.

[0248] From the aspect of forming a uniform coating film and a polyimide film, the viscosity of the above polyimide precursor resin composition with a solid content of 15% by weight is preferably 500 cps or more and 100,000 cps or less at 25°C.

[0249] The viscosity of the polyimide precursor resin composition can be measured at 25°C with a sample volume of 0.8 ml using a viscometer (for example, TVE-22HT, Toki Sangyo Co., Ltd.).

[0250] (2) Polyimide Precursor Resin Coating Film Formation Step

[0251] In the step of coating the above polyimide precursor resin composition onto a support to form a polyimide precursor resin coating film, the support used is not particularly limited as long as it is a material with a smooth surface and heat resistance and solvent resistance. For example, inorganic materials such as glass plates and metal plates with a mirror-finished surface can be cited. In addition, the shape of the support is selected according to the coating method. For example, it can be plate-shaped, and it can also be cylindrical, belt-shaped, or a sheet that can be wound into a roll.

[0252] The above coating means is not particularly limited as long as it is a method capable of coating with a target film thickness. For example, known coating machines such as a die coater, a comma coater, a roll coater, an intaglio coater, a curtain coater, a spray coater, and a die lip coater can be used.

[0253] Coating can be carried out using a sheet-fed coating device or a roll-to-roll coating device.

[0254] After coating the polyimide precursor resin composition onto the support, the solvent in the above coating film is dried at a temperature of 150°C or lower, preferably at 30°C or higher and 120°C or lower, until the coating film is non-tacky. By setting the drying temperature of the solvent to 150°C or lower, the imidization of polyamic acid can be suppressed.

[0255] The drying time can be appropriately adjusted according to the film thickness of the polyimide precursor resin coating film, the type of solvent, the drying temperature, etc. It is preferably set to usually 1 minute to 60 minutes, preferably 2 minutes to 30 minutes. If it exceeds the upper limit value, it is not preferred from the aspect of the production efficiency of the polyimide film. On the other hand, if it is lower than the lower limit value, since the solvent dries rapidly, it may affect the appearance of the obtained polyimide film.

[0256] The drying method of the solvent is not particularly limited as long as the solvent can be dried at the above temperature. For example, an oven, a drying furnace, a heating plate, infrared heating, etc. can be used.

[0257] In the case where high-precision control of optical properties is required, the atmosphere during solvent drying is preferably an inert gas atmosphere. As the inert gas atmosphere, a nitrogen atmosphere is preferred, and the oxygen concentration is preferably 100 ppm or less, more preferably 50 ppm or less. When heat treatment is carried out in the atmosphere, the film may be oxidized, resulting in coloring or performance degradation.

[0258] (3) Imidization process

[0259] In the above first manufacturing method, imidization of the above polyimide precursor is carried out by heating.

[0260] In this manufacturing method, in the case where there is a stretching process, the imidization process can be carried out on the polyimide precursor in the above polyimide precursor resin coating film before the stretching process, can be carried out on the polyimide precursor in the above polyimide precursor resin coating film after the stretching process, or can be carried out on both the polyimide precursor in the above polyimide precursor resin coating film before the stretching process and the polyimide precursor present in the film after the stretching process.

[0261] The imidization temperature can be appropriately selected according to the structure of the polyimide precursor.

[0262] Generally, it is preferable to set the starting temperature of the temperature increase to 30 °C or higher, more preferably 100 °C or higher. On the other hand, the ending temperature of the temperature increase is preferably set to 250 °C or higher.

[0263] The heating rate is preferably appropriately selected according to the film thickness of the obtained polyimide film. In the case where the film thickness of the polyimide film is relatively thick, it is preferable to make the heating rate slow.

[0264] From the aspect of the manufacturing efficiency of the polyimide film, it is preferably set to 5 °C / minute or higher, more preferably 10 °C / minute or higher. On the other hand, the upper limit of the heating rate is usually set to 50 °C / minute, preferably 40 °C / minute or less, more preferably 30 °C / minute or less. From the aspect of suppressing appearance defects or strength reduction of the film, being able to control the whitening accompanying the imidization reaction, and improving light transmittance, it is preferably set to the above heating rate.

[0265] The temperature increase can be continuous or stepwise. From the aspect of suppressing appearance defects or strength reduction of the film and controlling the whitening accompanying the imidization reaction, it is preferably set to be continuous. In addition, within the above entire temperature range, the heating rate can be fixed, or it can also change midway.

[0266] When imidizing, the atmosphere during heating is preferably an inert gas atmosphere. As the inert gas atmosphere, a nitrogen atmosphere is preferred, and the oxygen concentration is preferably 500 ppm or less, more preferably 200 ppm or less, and even more preferably 100 ppm or less. When performing heat treatment in the air, the film may be oxidized, resulting in coloring or performance degradation.

[0267] Among them, when more than 50% of the hydrogen atoms bonded to the carbon atoms contained in the polyimide are hydrogen atoms directly bonded to the aromatic ring, the influence of oxygen on the optical properties is small, and a polyimide with high light transmittance can be obtained even without using an inert gas atmosphere.

[0268] The heating method for imidization is not particularly limited as long as the temperature can be raised as described above. For example, an oven, a heating furnace, infrared heating, electromagnetic induction heating, etc. can be used.

[0269] Among them, it is more preferable that the imidization rate of the polyimide precursor is 50% or more before the stretching step. By making the imidization rate 50% or more before the stretching step, even when stretching is performed after this step and then heating is further performed at a high temperature for a certain period of time for imidization, poor appearance and whitening of the film can be suppressed. Among them, from the aspect of improving the surface hardness of the polyimide film, it is preferable that the imidization rate is 80% or more in this imidization step before the stretching step, and it is preferable to make the reaction proceed to an imidization rate of 90% or more, and further 100%. By stretching after imidization, the rigid polymer chains are more likely to be oriented, so it is speculated that the surface hardness is improved.

[0270] It should be noted that the measurement of the imidization rate can be carried out by analysis of the spectrum based on infrared measurement (IR), etc.

[0271] In order to obtain the final polyimide film, it is preferable to make the reaction proceed to an imidization rate of 90% or more, further 95% or more, and further 100%.

[0272] In order to make the reaction proceed to an imidization rate of 90% or more, and further 100%, it is preferable to hold at the end temperature of the temperature rise for a certain period of time. This holding time is preferably set to usually 1 minute to 180 minutes, and further 5 minutes to 150 minutes.

[0273] (4) Stretching step

[0274] The above-described first manufacturing method may include a stretching step of stretching at least one of the above-described polyimide precursor resin coating film and the imidized coating film obtained by imidizing the polyimide precursor resin coating film. In the case of having this stretching step, from the viewpoint of improving the surface hardness of the polyimide film, a step of stretching the imidized coating film is preferably included.

[0275] In the above-described first manufacturing method, when the initial size before stretching is set to 100%, a step of stretching 101% or more and 10,000% or less while heating at 80°C or higher is preferably performed.

[0276] The heating temperature during stretching is preferably in the range of ±50°C of the glass transition temperature of the polyimide and the polyimide precursor, and more preferably in the range of ±40°C of the glass transition temperature. When the stretching temperature is too low, the film may not deform and sufficient orientation may not be induced. On the other hand, when the stretching temperature is too high, the orientation obtained by stretching is relaxed due to the temperature, and sufficient orientation may not be obtained.

[0277] The stretching step may be performed simultaneously with the imidization step. From the viewpoint of improving the surface hardness of the polyimide film, it is preferable to stretch the imidized coating film after imidization at an imidization rate of 80% or more, further 90% or more, still more preferably 95% or more, and particularly substantially 100%.

[0278] The stretching ratio of the polyimide film is preferably 101% or more and 10,000% or less, and more preferably 101% or more and 500% or less. By stretching within the above range, the surface hardness of the obtained polyimide film can be further improved.

[0279] The method of fixing the polyimide film during stretching is not particularly limited and is selected according to the type of stretching device and the like. In addition, the stretching method is not particularly limited. For example, a stretching device having a conveying device such as a tenter can be used to perform stretching while passing through a heating furnace. The polyimide film can be stretched in only one direction (longitudinal stretching or transverse stretching), or can be stretched in two directions by synchronous biaxial stretching, sequential biaxial stretching, diagonal stretching, or the like.

[0280] In addition, as the manufacturing method of the polyimide film of the present disclosure, the following manufacturing method of the polyimide film as the second manufacturing method can be cited. This manufacturing method includes:

[0281] A step of preparing a polyimide resin composition containing a polyimide having the structure represented by the above general formula (1) and an organic solvent (hereinafter referred to as the polyimide resin composition preparation step); and

[0282] A step of coating the above polyimide resin composition onto a support and drying the solvent to form a polyimide resin coating film (hereinafter referred to as the polyimide resin coating film forming step).

[0283] When the polyimide having the structure represented by the above general formula (1) is well dissolved in an organic solvent, it is also possible to preferably use a polyimide resin composition in which the above polyimide rather than the polyimide precursor resin composition is dissolved in an organic solvent and contains additives as needed.

[0284] When the polyimide having the structure represented by the above general formula (1) has a solvent solubility of dissolving 5% by mass or more in an organic solvent at 25°C, this manufacturing method can be preferably used.

[0285] In the polyimide resin composition preparation step, the polyimide having the structure represented by the above general formula (1) can be selected from the same polyimides as those described in the above polyimide film and used as the polyimide having the above solvent solubility. As a method of imidization, chemical imidization is preferably used, in which a chemical imidization agent is used instead of heating dehydration to carry out the dehydration ring-closure reaction of the polyimide precursor. In the case of carrying out chemical imidization, as the dehydration catalyst, known compounds such as amines such as pyridine and β-pyridinecarboxylic acid, carbodiimides such as dicyclohexylcarbodiimide, and acid anhydrides such as acetic anhydride can be used. As the acid anhydride, acetic anhydride is not limited, and propionic anhydride, n-butyric anhydride, benzoic anhydride, trifluoroacetic anhydride, etc. can be cited, and there is no particular limitation. In addition, tertiary amines such as pyridine and β-pyridinecarboxylic acid can also be used in combination at this time. However, when these amines remain in the film, the optical properties, especially the yellowness index (YI value), will be reduced. Therefore, it is preferred not to directly cast and form a film from the reaction solution that has reacted from the precursor to the polyimide, but to purify it by reprecipitation or the like, and remove components other than polyimide to less than 100 ppm of the total weight of the polyimide before forming the film.

[0286] As the organic solvent used in the polyimide resin composition preparation step, the same organic solvents as those described in the above polyimide precursor resin composition preparation step in the above first manufacturing method can be used.

[0287] The above polyimide resin composition can contain additives as needed. As the above additives, the same additives as those described in the above polyimide precursor resin composition preparation step in the above first manufacturing method can be used.

[0288] In addition, in the above-described second method, as a method for making the water content of the above polyimide resin composition 1000 ppm or less and a method for dispersing the above inorganic particles in an organic solvent, the same methods as those described in the polyimide precursor resin composition preparation step in the above-described first production method can be used.

[0289] In addition, in the polyimide resin film formation step in the above-described second production method, the support and coating method can be the same support and coating method as the support and coating method described in the polyimide precursor resin film formation step in the above-described first production method.

[0290] In the polyimide resin film formation step in the above-described second production method, as the drying temperature, it is preferably set at 80°C or higher and 150°C or lower under normal pressure. Under reduced pressure, it is preferably set in the range of 10°C or higher and 100°C or lower.

[0291] In addition, the above-described second production method may have a stretching step of stretching the polyimide resin film after the polyimide resin film formation step. This stretching step can be the same as the stretching step in the above-described first production method.

[0292] 6. Use of the polyimide film

[0293] The use of the polyimide film of the present disclosure is not particularly limited, and it can be used as components such as a base material and a surface material of glass products such as thin flat glass used in the past. The polyimide film of the present disclosure has improved bending resistance, sufficient surface hardness as a protective film, and reduced optical distortion. Therefore, it can preferably be used as a surface material for a display that can cope with a curved surface.

[0294] Specifically, the polyimide film of the present disclosure can be preferably used, for example, in thin and curved flexible organic EL displays, portable terminals such as smartphones or watch-type terminals, display devices inside automobiles, flexible panels used in watches, etc. In addition, the polyimide film of the present disclosure can also be applied to components for image display devices such as liquid crystal display devices and organic EL display devices, components for touch panels, flexible printed circuit boards, components for solar cell panels such as surface protective films or substrate materials, components for optical waveguides, and other semiconductor-related components.

[0295] II. Laminate

[0296] A laminate according to an embodiment of the present disclosure is a laminate in which the polyimide film according to an embodiment of the present disclosure and a hard coat are adjacent to each other, and the hard coat contains at least one polymer selected from radical polymerizable compounds and cationic polymerizable compounds.

[0297] Since the laminate of the present disclosure uses the polyimide film of the present disclosure, its bending resistance is improved. In addition, since it has a hard coat and the adhesion between the polyimide film and the hard coat is excellent, its surface hardness is further improved. In the laminate of the present disclosure, it is presumed that the reason for the excellent adhesion between the polyimide film and the hard coat is that the polyimide having the structure represented by the above general formula (1) contained in the polyimide film has excellent miscibility with the above specific hard coat by containing a specific amount of diamine residues having one or two silicon atoms in the main chain.

[0298] In addition, since the laminate of the present disclosure uses the polyimide film of the present disclosure, its optical distortion is reduced. Therefore, when the laminate of the present disclosure is used as a surface material for a display, a reduction in the display quality of the display can be suppressed.

[0299] 1. Polyimide film

[0300] As the polyimide film used in the laminate of the present disclosure, the polyimide film of the present disclosure described above can be used, and thus the description thereof is omitted here.

[0301] 2. Hard coat

[0302] The hard coat used in the laminate of the present disclosure contains at least one polymer selected from a radical polymerizable compound and a cationic polymerizable compound.

[0303] (1) Radical polymerizable compound

[0304] A radical polymerizable compound refers to a compound having a radical polymerizable group. As the radical polymerizable group possessed by the above radical polymerizable compound, any functional group capable of undergoing a radical polymerization reaction may be used, and there is no particular limitation. For example, a group containing a carbon-carbon unsaturated double bond can be cited. Specifically, vinyl, (meth)acryloyl, etc. can be cited. It should be noted that when the above radical polymerizable compound has two or more radical polymerizable groups, these radical polymerizable groups may be the same or different from each other.

[0305] From the aspect of improving the hardness of the hard coat, the number of radical polymerizable groups possessed by the above radical polymerizable compound in one molecule is preferably two or more, and more preferably three or more.

[0306] As the above-mentioned radically polymerizable compound, from the viewpoint of high reactivity, a compound having a (meth)acryloyl group is preferred. A compound called a polyfunctional acrylate monomer having 2 to 6 (meth)acryloyl groups in one molecule, or an oligomer having several (meth)acryloyl groups in the molecule and a molecular weight of several hundred to several thousand, called urethane (meth)acrylate, polyester (meth)acrylate, or epoxy (meth)acrylate, can be preferably used.

[0307] It should be noted that in this specification, (meth)acryloyl represents acryloyl and methacryloyl, and (meth)acrylate represents acrylate and methacrylate.

[0308] As the above-mentioned radically polymerizable compound, specifically, for example, vinyl compounds such as divinylbenzene can be cited; ethylene glycol di(meth)acrylate, bisphenol A epoxy di(meth)acrylate, 9,9-bis[4-(2-(meth)acryloyloxyethoxy)phenyl]fluorene, epoxy alkane-modified bisphenol A di(meth)acrylate (such as ethoxylated (ethylene oxide-modified) bisphenol A di(meth)acrylate, etc.), trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate and other polyol polyacrylates, epoxy acrylates such as diacrylate of bisphenol A diglycidyl ether and diacrylate of hexanediol diglycidyl ether, urethane acrylate obtained by the reaction of polyisocyanate with a hydroxy group-containing acrylate such as hydroxyethyl acrylate, etc.

[0309] (2) Cationically polymerizable compound

[0310] A cationically polymerizable compound refers to a compound having a cationically polymerizable group. As the cationically polymerizable group possessed by the above-mentioned cationically polymerizable compound, any functional group capable of undergoing a cationic polymerization reaction may be used, and there is no particular limitation. For example, an epoxy group, an oxetanyl group, a vinyl ether group, etc. can be cited. It should be noted that when the above-mentioned cationically polymerizable compound has two or more cationically polymerizable groups, these cationically polymerizable groups may be the same or different from each other.

[0311] From the viewpoint of improving the hardness of the hard coat, the number of cationically polymerizable groups possessed by the above-mentioned cationically polymerizable compound in one molecule is preferably two or more, and more preferably three or more.

[0312] In addition, as the above-mentioned cationically polymerizable compound, a compound having at least one of an epoxy group and an oxetanyl group as a cationically polymerizable group is preferred. From the aspect of small shrinkage accompanying the polymerization reaction, cyclic ether groups such as an epoxy group and an oxetanyl group are preferred. In addition, a compound having an epoxy group in the cyclic ether group has the following advantages: compounds with diverse structures are easily obtained, it does not have an adverse effect on the durability of the resulting hard coat, and the compatibility with the radically polymerizable compound is also easily controlled. In addition, the oxetanyl group in the cyclic ether group has the following advantages: it has a higher degree of polymerization and lower toxicity compared to the epoxy group. When the resulting hard coat is combined with a compound having an epoxy group, the formation rate of the network structure obtained from the cationically polymerizable compound in the coating film can be accelerated. Even in the region where it is mixed with the radically polymerizable compound, unreacted monomers do not remain in the film, and an independent network structure can be formed.

[0313] Examples of the cationically polymerizable compound having an epoxy group include polyglycidyl ethers of polyhydric alcohols having an alicyclic ring, or alicyclic epoxy resins obtained by epoxidizing compounds containing a cyclohexene ring or a cyclopentene ring using an appropriate oxidizing agent such as hydrogen peroxide or peroxyacid; polyglycidyl ethers of aliphatic polyhydric alcohols or their alkylene oxide adducts, polyglycidyl esters of aliphatic long-chain polyacids, homopolymers and copolymers of glycidyl (meth)acrylate, etc., aliphatic epoxy resins; glycidyl ethers produced by the reaction of bisphenols such as bisphenol A, bisphenol F, hydrogenated bisphenol A, or their derivatives such as alkylene oxide adducts and caprolactone adducts with epichlorohydrin, and glycidyl ether type epoxy resins derived from bisphenols such as novolac epoxy resins.

[0314] Examples of the above-mentioned alicyclic epoxy resins include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (UVR-6105, UVR-6107, UVR-6110), bis-3,4-epoxycyclohexylmethyl adipate (UVR-6128) (in the parentheses above are trade names, manufactured by Dow Chemical).

[0315] In addition, examples of the above-mentioned glycidyl ether type epoxy resins include sorbitol polyglycidyl ether (Denacol EX-611, Denacol EX-612, Denacol EX-614, Denacol EX-614B, Denacol EX-622), polyglycerol polyglycidyl ether (Denacol EX-512, Denacol EX-521), pentaerythritol polyglycidyl ether (Denacol EX-411), diglycerol polyglycidyl ether (Denacol EX-421), glycerol polyglycidyl ether (Denacol EX-313, Denacol EX-314), trimethylolpropane polyglycidyl ether (Denacol EX-321), resorcinol diglycidyl ether (Denacol EX-201), neopentyl glycol diglycidyl ether (Denacol EX-211), 1,6-hexanediol diglycidyl ether (Denacol EX-212), hydrogenated bisphenol A diglycidyl ether (Denacol EX-252), ethylene glycol diglycidyl ether (Denacol EX-810, Denacol EX-811), polyethylene glycol diglycidyl ether (Denacol EX-850, Denacol EX-851, Denacol EX-821), propylene glycol glycidyl ether (Denacol EX-911), polypropylene glycol glycidyl ether (Denacol EX-941, Denacol EX-920), allyl glycidyl ether (Denacol EX-111), 2-ethylhexyl glycidyl ether (Denacol EX-121), phenyl glycidyl ether (Denacol EX-141), phenol glycidyl ether (Denacol EX-145), butylphenyl glycidyl ether (Denacol EX-146), phthalic acid diglycidyl ester (Denacol EX-721), hydroquinone diglycidyl ether (Denacol EX-203), terephthalic acid diglycidyl ester (Denacol EX-711), glycidyl phthalimide (Denacol EX-731), dibromophenyl glycidyl ether (Denacol EX-147), dibromoneopentyl glycol diglycidyl ether (Denacol EX-221) (the above, the content in parentheses is the trade name, manufactured by Nagase ChemteX).

[0316] In addition, as epoxy resins of other commercially available products, examples include those with trade names Epikote 825, Epikote 827, Epikote 828, Epikote 828EL, Epikote 828XA, Epikote 834, Epikote 801, Epikote 801P, Epikote 802, Epikote 815, Epikote 815XA, Epikote 816A, Epikote 819, Epikote834X90, Epikote 1001B80, Epikote 1001X70, Epikote 1001X75, Epikote 1001T75, Epikote 806, Epikote 806P, Epikote 807, Epikote 152, Epikote 154, Epikote 871, Epikote 191P, Epikote YX310, Epikote DX255, Epikote YX8000, Epikote YX8034, etc. (The above are trade names, manufactured by Japan Epoxy Resin).

[0317] As cationically polymerizable compounds having an oxetanyl group, for example, 3-ethyl-3-hydroxymethyloxetane (OXT-101), 1,4-bis(3-ethyloxetane-3-ylmethoxymethyl)benzene (OXT-121), bis(1-ethyl-3-oxetanylmethyl)ether (OXT-221), 3-ethyl-3-(2-ethylhexyloxymethyl)oxetane (OXT-212), 3-ethyl-3-phenoxymethyloxetane (OXT-211) (the above, the content in parentheses is the trade name, manufactured by Toagosei Co., Ltd.), and trade names ETERNACOLL EHO, ETERNACOLL OXBP, ETERNACOLL OXTP, ETERNACOLL OXMA (the above are trade names, manufactured by Ube Industries, Ltd.).

[0318] Among them, from the aspects of the adhesion between the polyimide film and the hard coat, as well as the light transmittance and surface hardness, it is preferable that the above radical polymerizable compound is a compound having two or more (meth)acryloyl groups in one molecule, and the above cationically polymerizable compound is a compound having at least one of two or more epoxy groups and oxetanyl groups in one molecule.

[0319] (3) Polymerization initiator

[0320] At least one polymer of the radical polymerizable compound and the cationic polymerizable compound contained in the hard coat used in the present disclosure can be obtained, for example, by adding a polymerization initiator as needed to at least one of the radical polymerizable compound and the cationic polymerizable compound and performing a polymerization reaction using a known method.

[0321] As the above polymerization initiator, a radical polymerization initiator, a cationic polymerization initiator, a radical and cationic polymerization initiator, etc. can be appropriately selected and used. These polymerization initiators are decomposed by at least one of light irradiation and heating to generate radicals or cations to carry out radical polymerization and cationic polymerization.

[0322] The radical polymerization initiator only needs to be able to release a substance that initiates radical polymerization by at least any one of light irradiation and heating. For example, as a photo radical polymerization initiator, imidazole derivatives, bisimidazole derivatives, N-aryl glycine derivatives, organic azides, titanocene compounds, aluminate complexes, organic peroxides, N-alkoxypyridinium salts, thioxanthone derivatives, etc. can be cited. Further, 1,3-bis(tert-butyldioxycarbonyl)benzophenone, 3,3',4,4'-tetrakis(tert-butyldioxycarbonyl)benzophenone, 3-phenyl-5-isoxazolone, 2-mercaptobenzimidazole, bis(2,4,5-triphenyl)imidazole, 2,2-dimethoxy-1,2-diphenylethane-1-one (trade name Irgacure 651, manufactured by CHIBA JAPAN Co., Ltd.), 1-hydroxycyclohexyl phenyl ketone (trade name Irgacure184, manufactured by CHIBA JAPAN Co., Ltd.), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one (trade name Irgacure 369, manufactured by CHIBA JAPAN Co., Ltd.), bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium) (trade name Irgacure 784, manufactured by CHIBA JAPAN Co., Ltd.), etc. can be specifically cited, but are not limited to these.

[0323] In addition to the above, commercially available products can also be used. Specifically, examples include Irgacure 907, Irgacure 379, Irgacure 819, Irgacure 127, Irgacure 500, Irgacure 754, Irgacure 250, Irgacure 1800, Irgacure 1870, Irgacure OXE01, DAROCUR TPO, DAROCUR 1173 manufactured by CHIBA JAPAN Co., Ltd.; Speedcure MBB, Speedcure PBZ, Speedcure ITX, Speedcure CTX, Speedcure EDB, Esacure ONE, Esacure KIP150, Esacure KTO46 manufactured by Nippon Siber Hegner Co., Ltd.; KAYACURE DETX-S, KAYACURE CTX, KAYACURE BMS, KAYACURE DMBI manufactured by Nippon Kayaku Co., Ltd., etc.

[0324] In addition, the cationic polymerization initiator only needs to be a substance that can release a substance that initiates cationic polymerization by at least one of light irradiation and heating. Examples of the cationic polymerization initiator include sulfonic acid esters, imide sulfonic acid esters, dialkyl-4-hydroxy sulfonium salts, p-nitrobenzyl aryl sulfonates, silanol-aluminum complexes, (η 6 -benzene)(η 5 -cyclopentadienyl)iron(II), etc. Further specific examples include benzoin p-toluenesulfonate, 2,5-dinitrobenzyl p-toluenesulfonate, N-p-toluenesulfonyl phthalimide, etc., but are not limited to these.

[0325] Examples of the polymerization initiator that can be used as both a radical polymerization initiator and a cationic polymerization initiator include aromatic iodonium salts, aromatic sulfonium salts, aromatic diazonium salts, aromatic phosphonium salts, triazine compounds, iron-arene complexes, etc. Further specific examples include chlorides, bromides, fluoroborate salts, hexafluorophosphate salts, hexafluoroantimonate salts, etc. of iodonium salts such as diphenyliodonium salt, xylyliodonium salt, bis(p-tert-butylphenyl)iodonium salt, bis(p-chlorophenyl)iodonium salt; chlorides, bromides, fluoroborate salts, hexafluorophosphate salts, hexafluoroantimonate salts, etc. of sulfonium salts such as triphenylsulfonium, 4-tert-butyltriphenylsulfonium, tris(4-methylphenyl)sulfonium; 2,4,6-substituted-1,3,5-triazine compounds such as 2,4,6-tris(trichloromethyl)-1,3,5-triazine, 2-phenyl-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-methyl-4,6-bis(trichloromethyl)-1,3,5-triazine, etc., but are not limited to these.

[0326] (4) Additives

[0327] In the hard coating used in the present disclosure, in addition to the above polymers, additives such as antistatic agents, antiglare agents, antifouling agents, inorganic or organic fine particles for improving hardness, leveling agents, and various sensitizers can be contained as needed.

[0328] 3. Structure of the laminate

[0329] The laminate of the present disclosure is not particularly limited as long as the above polyimide film and the above hard coating are adjacent to each other. It can be a laminate in which the above hard coating is laminated adjacent to one surface of the above polyimide film, or a laminate in which the above hard coating is laminated adjacent to both surfaces of the above polyimide film. In addition, in addition to the above polyimide film and the above hard coating, the laminate of the present disclosure can further be laminated with other layers such as gels containing urethane, acrylic resins, etc. within the range that does not impair the effects of the present disclosure.

[0330] The overall thickness of the laminate of the present disclosure can be appropriately selected according to the use. From the aspect of strength, it is preferably 10 μm or more, more preferably 40 μm or more. On the other hand, from the aspect of bending resistance, it is preferably 300 μm or less, more preferably 250 μm or less.

[0331] In addition, in the laminate of the present disclosure, the thickness of each hard coating can be appropriately selected according to the use, preferably 2 μm or more and 80 μm or less, more preferably 3 μm or more and 50 μm or less. In addition, from the aspect of preventing warping, hard coatings can be formed on both surfaces of the polyimide film.

[0332] 4. Characteristics of the laminate

[0333] The pencil hardness of the hard coating side surface of the laminate of the present disclosure is preferably H or more, more preferably 2H or more, and even more preferably 3H or more.

[0334] The pencil hardness of the laminate of the present disclosure can be measured in the same manner as the pencil hardness of the above polyimide film.

[0335] The total light transmittance of the laminate of the present disclosure measured according to JIS K7361-1 is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. Thus, due to the high transmittance, the transparency is good, and it can be a glass substitute material.

[0336] The above total light transmittance of the laminate of the present disclosure can be measured in the same manner as the total light transmittance of the above polyimide film measured according to JIS K7361-1.

[0337] The yellowness index (YI value) of the laminate of the present disclosure calculated according to JIS K7373-2006 is preferably 30 or less, more preferably 20 or less, still more preferably 15 or less, and particularly preferably 10 or less.

[0338] The above-mentioned yellowness index (YI value) of the laminate of the present disclosure can be measured in the same manner as the yellowness index (YI value) of the above-mentioned polyimide film calculated according to JIS K7373-2006.

[0339] From the aspect of light transmittance, the haze value of the laminate of the present disclosure is preferably 10 or less, more preferably 8 or less, still more preferably 5 or less.

[0340] The haze value of the laminate of the present disclosure can be measured in the same manner as the haze value of the above-mentioned polyimide film.

[0341] The birefringence in the thickness direction of the laminate of the present disclosure at a wavelength of 590 nm is preferably 0.020 or less, preferably 0.015 or less, more preferably 0.010 or less, and still more preferably less than 0.008.

[0342] The above-mentioned birefringence of the laminate of the present disclosure can be measured in the same manner as the birefringence in the thickness direction of the above-mentioned polyimide film at a wavelength of 590 nm.

[0343] 5. Use of the laminate

[0344] The use of the laminate of the present disclosure is not particularly limited. For example, it can be used for the same uses as the above-mentioned polyimide film of the present disclosure.

[0345] 6. Manufacturing method of the laminate

[0346] As a manufacturing method of the laminate of the present disclosure, for example, the following manufacturing method can be cited, which includes:

[0347] A step of forming a coating film of a hard coat-forming composition containing at least one of a radically polymerizable compound and a cationically polymerizable compound on at least one surface of the above-mentioned polyimide film of the present disclosure; and

[0348] A step of curing the above-mentioned coating film.

[0349] The above-mentioned hard coat-forming composition contains at least one of a radically polymerizable compound and a cationically polymerizable compound, and may further contain a polymerization initiator, a solvent, an additive, etc. as needed.

[0350] Here, as the radical polymerizable compound, cationic polymerizable compound, polymerization initiator, and additive contained in the above-described composition for forming a hard coat, the same substances as those described in the above hard coat can be used, and the solvent can be appropriately selected from known solvents and used.

[0351] As a method for forming a coating film of the above-described composition for forming a hard coat on at least one surface of the polyimide film, for example, a method of coating the above-described composition for forming a hard coat on at least one surface of the polyimide film by using a known coating means can be cited.

[0352] The above coating means is not particularly limited as long as it is a method capable of coating with a target film thickness. For example, the same means as those for coating the above-described polyimide precursor resin composition onto a support can be cited.

[0353] The coating film of the above-described curable resin composition for a hard coat is dried as needed to remove the solvent. As a drying method, for example, reduced-pressure drying, heat drying, and a method of further combining these dryings can be cited. In addition, when drying is performed at normal pressure, it is preferably performed at 30°C or higher and 110°C or lower.

[0354] For the coating film coated with the above-described curable resin composition for a hard coat and dried as needed, corresponding to the polymerizable groups of the radical polymerizable compound and cationic polymerizable compound contained in the curable resin composition, the coating film is cured by at least any one of light irradiation and heating, whereby a hard coat containing at least one polymer of the radical polymerizable compound and cationic polymerizable compound can be formed on at least one surface of the polyimide film.

[0355] Light irradiation mainly uses ultraviolet rays, visible light, electron rays, ionizing radiation, etc. In the case of ultraviolet curing, ultraviolet rays emitted from the light of a super-high-pressure mercury lamp, high-pressure mercury lamp, low-pressure mercury lamp, carbon arc lamp, xenon arc lamp, metal halide lamp, etc. are used. The irradiation amount of the energy ray source is 50 to 5000 mJ / cm 2 or so in terms of the cumulative exposure amount at a ultraviolet wavelength of 365 nm.

[0356] When heating is performed, it is usually performed at a temperature of 40°C or higher and 120°C or lower. In addition, the reaction can also be carried out by leaving it at room temperature (25°C) for 24 hours or more.

[0357] III. Surface material for display

[0358] The surface material for a display according to one embodiment of the present disclosure is the polyimide film according to one embodiment of the present disclosure or the laminate according to one embodiment of the present disclosure.

[0359] The surface material for a display according to the present disclosure is configured and used in a manner that it is located on the surface of various displays. The surface material for a display according to the present disclosure has improved bending resistance like the polyimide film and the laminate according to the present disclosure, and has sufficient surface hardness as a protective film. Therefore, it can be particularly preferably used for flexible display applications. In addition, the surface material for a display according to the present disclosure has reduced optical distortion like the polyimide film and the laminate according to the present disclosure, and thus can suppress the reduction of the display quality of the display.

[0360] The surface material for a display according to the present disclosure can be used for various known displays without particular limitation. For example, it can be used for the displays described in the applications of the polyimide film according to the present disclosure.

[0361] It should be noted that when the surface material for a display according to the present disclosure is the laminate according to the present disclosure, the surface that becomes the outermost surface after the laminate is disposed on the surface of the display can be the surface on the polyimide film side or the surface on the hard coat side. Among them, it is preferable to configure the surface material for a display according to the present disclosure such that the surface on the hard coat side becomes the outermost surface. In addition, the surface material for a display according to the present disclosure can have a layer for preventing fingerprint adhesion on the outermost surface.

[0362] In addition, as a method for disposing the surface material for a display according to the present disclosure on the surface of the display, there is no particular limitation. For example, a method using an adhesive layer can be cited. As the above-mentioned adhesive layer, an existing well-known adhesive layer that can be used for adhering the surface material for a display can be used.

[0363] Examples

[0364] [Evaluation method]

[0365] <Weight-average molecular weight of polyimide precursor>

[0366] Regarding the weight-average molecular weight of the polyimide precursor, a 0.5 wt% concentration N-methylpyrrolidone (NMP) solution of the polyimide precursor is prepared. As the eluent, a 10 mmol% LiBr-NMP solution with a water content of 500 ppm or less is used. Using a GPC device (manufactured by Tosoh, HLC-8120, column used: SHODEX GPC LF-804), the measurement is carried out under the conditions of a sample injection volume of 50 μL, a solvent flow rate of 0.4 mL / minute, and 40 °C. The weight-average molecular weight of the polyimide precursor is determined based on a polystyrene standard sample with the same concentration as the sample.

[0367] <Viscosity of polyimide precursor solution>

[0368] The viscosity of the polyimide precursor solution was measured at 25 °C with a sample volume of 0.8 ml using a viscometer (e.g., TVE-22HT, Toki Sangyo Co., Ltd.).

[0369] <Weight-average molecular weight of polyimide>

[0370] Regarding the weight-average molecular weight of polyimide, a 0.2 wt% concentration solution of polyimide in N-methylpyrrolidone (NMP) was prepared as the developing agent. A 30 mmol% LiBr-NMP solution with a water content of 500 ppm or less was used, and measurements were carried out using a GPC device (manufactured by Tosoh, HLC-8120, column used: SHODEX GPC LF-804) under the conditions of a sample injection volume of 50 μL, a solvent flow rate of 0.4 mL / min, and a temperature of 40 °C. The weight-average molecular weight of polyimide was determined based on a polystyrene standard sample with the same concentration as the sample.

[0371] <Viscosity of polyimide solution>

[0372] The viscosity of the polyimide solution was measured at 25 °C with a sample volume of 0.8 ml using a viscometer (e.g., TVE-22HT, Toki Sangyo Co., Ltd.).

[0373] <Silicon atom content ratio (mass%) of polyimide>

[0374] The silicon atom content ratio (mass%) of polyimide was calculated from the molecular weights of the starting materials.

[0375] For example, in the case of the polyimide in Example 1 where 0.9 mol of 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB) and 0.1 mol of 1,3-bis(3-aminopropyl)tetramethyldisiloxane (AprTMOS) were used per 1 mol of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) as the dianhydride component, the calculation can be as follows.

[0376] From 6FDA: (C)12.01×19+(F)19.00×6+(O)16.00×4+(H)1.01×6 = 412.25

[0377] From TFMB: {(C)12.01×14+(F)19.00×6+(N)14.01×2+(H)1.01×6}×0.9 = 284.60

[0378] From AprTMOS: {(C)12.01×10+(O)16.00×1+(N)14.01×2+(Si)28.09×2+(H)1.01×24}×0.1 = 24.45,

[0379] The molecular weight of 1 mole of the polyimide repeating unit was calculated to be 412.25 + 284.60 + 24.45 = 721.30.

[0380] The content ratio (mass%) of silicon atoms in 1 mole of the polyimide repeating unit was determined to be

[0381] (28.09×2×0.1) / 721.30×100 = 0.8 (mass%).

[0382] It should be noted that for the two-terminal amine-modified diphenyl silicone oil of Comparative Example 3 (manufactured by Shin-Etsu Chemical Co., Ltd.: X22-1660B-3, side-chain phenyl type, number-average molecular weight 4400), assuming that the amino group is bonded to the silicone through -(CH 2 ) 3 -, the number of repeating units of diphenylsiloxane was calculated to be 19.7 on average from the number-average molecular weight of 4400, and it was calculated that an average of 21.7 silicon atoms were contained in 1 molecule.

[0383] In addition, for the silicone diamine of Comparative Example 4 (manufactured by Shin-Etsu Silicone Co., Ltd.: KF-8010, number-average molecular weight 860), assuming that the amino group is bonded to the silicone through -(CH 2 ) 3 -, the number of repeating units of dimethylsiloxane was calculated to be 8.2 on average from the number-average molecular weight of 860, and it was calculated that an average of 10.2 silicon atoms were contained in 1 molecule.

[0384] <Total light transmittance>

[0385] The measurement was carried out in accordance with JIS K7361-1 using a haze meter (HM150 manufactured by Murakami Color Technology Research Institute).

[0386] In addition, for example, the total light transmittance at a thickness of 100 μm can be converted using the Lambert-Beer law.

[0387] Specifically, according to the Lambert-Beer law, the transmittance T is expressed by the following formula:

[0388] Log 10 (1 / T) = kcb

[0389] (k = a constant inherent to the substance, c = concentration, b = optical path).

[0390] In the case of the transmittance of the film, assuming that the density is constant even when the film thickness changes, c becomes a constant, so the above formula can be expressed using a constant f as:

[0391] Log 10 (1 / T) = fb

[0392] (f = kc)

[0393] Here, if the transmittance at a certain film thickness is known, the inherent constant f of each substance can be obtained. Therefore, if the formula T = 1 / 10 f·b is used, substituting the inherent constant into f and the target film thickness into b, the transmittance at the desired film thickness can be obtained.

[0394] <YI value (yellowness degree)>

[0395] Regarding the YI value, in accordance with JIS K7373 - 2006, using an ultraviolet - visible - near - infrared spectrophotometer (JASCO Corporation V - 7100), the transmittance is measured by the spectrophotometric colorimetry method specified in JIS Z8720, and the YI value is calculated based on this transmittance.

[0396] In addition, for example, regarding the YI value at a thickness of 100 μm, for a sample with a certain specific film thickness, the transmittances at each wavelength measured at 5 - nm intervals between 380 nm and 780 nm can be used to obtain the conversion values of the transmittances at each wavelength for different thicknesses in the same way as the above total light transmittance using the Lambert - Beer law, and the YI value at a thickness of 100 μm is calculated based on this conversion value for use.

[0397] <Haze value>

[0398] The measurement is carried out in accordance with JIS K - 7105 using a haze meter (HM150 manufactured by Murakami Color Technology Research Institute).

[0399] <Birefringence>

[0400] Using a phase - difference measuring device (manufactured by Oji Scientific Instruments Co., Ltd., product name "KOBRA - WR"), the phase - difference value in the thickness direction (Rth) of the polyimide film is measured at 25 °C using light with a wavelength of 590 nm. Regarding the phase - difference value in the thickness direction (Rth), the phase - difference value for 0 - degree incidence and the phase - difference value for 40 - degree inclined incidence are measured, and the thickness - direction phase - difference value Rth is calculated from these phase - difference values. Regarding the phase - difference value for 40 - degree inclined incidence, light with a wavelength of 590 nm is incident on the phase - difference film from a direction inclined 40 degrees from the normal of the phase - difference film for measurement.

[0401] The birefringence of the polyimide film is obtained by substituting it into the formula: Rth / d (film thickness of the polyimide film (nm)).

[0402] <Glass transition temperature>

[0403] Using a dynamic viscoelasticity measuring device RSA III (TA Instruments Japan Inc.), the measurement range was set from -150°C to 400°C, and dynamic viscoelasticity measurement was carried out with a frequency of 1 Hz, a heating rate of 5°C / minute, a sample width of 5 mm, and a chuck distance of 20 mm. The glass transition temperature (Tg) was determined from the peak temperature of tanδ (tanδ = loss elastic modulus (E”) / storage elastic modulus (E’)).

[0404] <Tensile elastic modulus>

[0405] After conditioning a test piece of a polyimide film cut into 15 mm × 40 mm for 2 hours at a temperature of 25°C and a relative humidity of 60%, the tensile elastic modulus at 25°C was measured in accordance with JIS K7127 with a tensile speed of 10 mm / minute and a chuck distance of 20 mm. The tensile testing machine used was (manufactured by Shimadzu Corporation: Aotograph AG-X 1N, load cell: SBL-1KN).

[0406] <Young's modulus>

[0407] At a temperature of 25°C, the Young's modulus of the surface of a test piece of a polyimide film cut into 15 mm × 15 mm was measured using nanoindentation in accordance with ISO14577. Specifically, the measuring device used was PICODENTOR HM500 manufactured by Fischer Instruments Co., Ltd., and a Vickers indenter was used as the measuring indenter. For the surface of the test piece, arbitrary points at 8 locations were measured, and the value obtained by numerical averaging was taken as the Young's modulus. It should be noted that the measurement conditions were set as follows: maximum indentation depth: 1000 nm, load time: 20 seconds, creep time: 5 seconds.

[0408] <Static bending test>

[0409] Hereinafter, refer to Figure 2 The method of the static bending test will be described.

[0410] A test piece 1 of a polyimide film cut into 15 mm × 40 mm is bent at the midpoint of its long side, and metal sheets 2 (100 mm × 30 mm × 6 mm) with a thickness of 6 mm are arranged to sandwich the test piece 1 from the upper and lower surfaces at both ends of the long side of the test piece 1, and are fixed with tape such that the overlapping portions of both ends of the test piece 1 and the metal sheets 2 on the upper and lower surfaces are each 10 mm. The metal sheet 2 with the test piece 1 fixed is clamped from above and below by glass plates (100 mm × 100 mm × 0.7 mm) 3a and 3b, and the test piece 1 is fixed in a state of being bent with an inner diameter of 6 mm. At this time, simulation test pieces 4a and 4b are inserted into the portions of the metal sheet 2 where the test piece 1 is not present, and are fixed with tape such that the glass plates 3a and 3b are parallel.

[0411] After allowing the test piece fixed in such a bent state to stand in an environment of 60 ± 2°C and 93 ± 2% relative humidity (RH) for 24 hours, the glass plates and the tape for fixing the test piece are removed, and the force applied to the test piece is released. Then, one end of the test piece is fixed, and the inner angle of the test piece is measured 30 minutes after the force applied to the test piece is released.

[0412] It should be noted that when the film is not affected by this static bending test and is completely restored, the above inner angle is 180°.

[0413] <Dynamic Bending Test>

[0414] A test piece of a polyimide film cut into a size of 20 mm × 100 mm is fixed with tape in a durability test system (manufactured by YUASA SYSTEM Co., Ltd., surface body unloaded U-shaped expansion test fixture DMX-FS) in a thermo-hygrostat. The test piece is set in the same folded state as in the above static bending test, that is, it is set such that the distance between both ends of the long side of the folded test piece is 6 mm, and then it is repeatedly bent 200,000 times at a bending frequency of 90 times per minute in an environment of 60 ± 2°C and 93 ± 2% relative humidity (RH), or 25°C ± 2°C and 50 ± 10% relative humidity (RH).

[0415] Then, 30 minutes after the test piece is removed, one end of the obtained test piece is fixed, and the inner angle of the test piece is measured.

[0416] It should be noted that when the film is not affected by this dynamic bending test and is completely restored, the above inner angle is 180°.

[0417] <Pencil Hardness>

[0418] The pencil hardness is evaluated as follows: After conditioning the test sample for 2 hours at a temperature of 25°C and a relative humidity of 60%, a test pencil specified in JIS-S-6006 is used, and a pencil scratch coating hardness tester manufactured by Toyo Seiki Co., Ltd. is used to conduct a pencil hardness test (0.98N load) specified in JIS K5600-5-4 (1999) on the film surface, and the highest pencil hardness without causing damage is evaluated.

[0419] <Adhesion evaluation>

[0420] To 40 mass% methyl isobutyl ketone solution of pentaerythritol triacrylate, 10 mass parts of 1-hydroxycyclohexyl phenyl ketone (manufactured by BASF, Irgacure 184) relative to 100 mass parts of pentaerythritol triacrylate was added to prepare a resin composition for a hard coat for adhesion evaluation.

[0421] The above resin composition for a hard coat was coated on a test piece of a polyimide film cut into 10 cm × 10 cm, and irradiated with ultraviolet rays at an exposure of 200 mJ / cm 2 to cure it, forming a cured film with a film thickness of 10 μm, and a laminate was manufactured. For this cured film, a cross-cut test based on JIS K 5600-5-6 was conducted. After repeatedly performing 5 peeling operations with tape, the presence or absence of peeling of the coating film was observed, and evaluation was carried out according to the following evaluation criteria.

[0422] A: Even after repeatedly performing 5 peeling operations with tape, no peeling of the coating film occurred.

[0423] B: No peeling of the coating film occurred after performing 1 peeling operation with tape, but peeling of the coating film occurred before repeatedly performing 5 peeling operations with tape.

[0424] C: After performing 1 peeling operation with tape, the coating film peeled off entirely along the cut edge.

[0425] (Synthesis Example 1)

[0426] In a 500 ml detachable flask, a solution prepared by dissolving 302.0 g of dehydrated dimethylacetamide and 2.49 g (10 mmol) of 1,3-bis(3-aminopropyl)tetramethyldisiloxane (AprTMOS) was controlled at a liquid temperature of 30°C. 2.22 g (5 mmol) of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) was slowly added in such a way that the temperature rise was 2°C or less, and the mixture was stirred with a mechanical stirrer for 4 hours. 28.8 g (90 mmol) of 2,2'-bis(trifluoromethyl)benzidine (TFMB) was added thereto. After confirming complete dissolution, 42.0 g (94.5 mmol) of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) was slowly added in several portions in such a way that the temperature rise was 2°C or less, and a polyimide precursor solution 1 (solid content: 20% by weight) in which a polyimide precursor 1 was dissolved was synthesized. The molar ratio of TFMB to AprTMOS used in the polyimide precursor 1 was 90:10. The viscosity of the polyimide precursor solution 1 (solid content: 20% by weight) at 25°C was 40150 cps, and the weight-average molecular weight of the polyimide precursor 1 measured by GPC was 253000.

[0427] (Synthesis Examples 2 - 6)

[0428] The reaction was carried out according to the procedure of Synthesis Example 1 above using the raw materials and solid content concentrations described in Table 1 to prepare polyimide precursor solutions 2 - 6.

[0429] (Comparative Synthesis Example 1)

[0430] In a 500 ml detachable flask, a solution prepared by dissolving 345.3 g of dehydrated dimethylacetamide and 49.7 g (200 mmol) of 1,3-bis(3-aminopropyl)tetramethyldisiloxane (AprTMOS) was controlled at a liquid temperature of 30°C. 88.4 g (199 mmol) of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) was slowly added in such a way that the temperature rise was 2°C or less, and a comparative polyimide precursor solution 1 (solid content: 40% by weight) in which a comparative polyimide precursor 1 was dissolved was synthesized. The viscosity of the comparative polyimide precursor solution 1 (solid content: 40% by weight) at 25°C was 3900 cps, and the weight-average molecular weight of the comparative polyimide precursor 1 measured by GPC was 42000.

[0431] Hereinafter, the abbreviations in the table are as described below.

[0432] TFMB: 2,2'-bis(trifluoromethyl)benzidine

[0433] AprTMOS: 1,3-bis(3-aminopropyl)tetramethyldisiloxane

[0434] BAPS-M: Bis[4-(3-aminophenoxy)phenyl]sulfone

[0435] 6FDA: 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride

[0436] PMDA: Pyromellitic dianhydride

[0437] sBPDA: 3,3',3,4'-Biphenyltetracarboxylic dianhydride

[0438] [Table 1]

[0439] Table 1

[0440]

[0441] (Examples 1 - 6, Comparative Example 1)

[0442] Using polyimide precursor solutions 1 - 6 and comparative polyimide precursor solution 1, perform the following steps (1) - (3) to separately produce polyimide films with a thickness of 50 μm ± 5 μm.

[0443] (1) Coat each polyimide precursor solution onto glass and dry it in a circulating oven at 120°C for 10 minutes.

[0444] (2) Under a nitrogen flow (oxygen concentration below 100 ppm), heat it at a rate of 10°C / minute to 350°C, hold it at 300°C for 1 hour, and then cool it to room temperature.

[0445] (3) Peel it off from the glass to obtain each polyimide film.

[0446] For each of the obtained polyimide films, evaluate them using the above evaluation method. The evaluation results are shown in Table 2.

[0447] [Table 2]

[0448] Table 2

[0449]

[0450] (Synthesis Example 7)

[0451] In Synthesis Example 1, instead of 2,2'-bis(trifluoromethyl)benzidine (TFMB), use an equimolar amount of bis[4-(3-aminophenoxy)phenyl]sulfone (BAPS-M), and make the solid content concentration 30 wt%, and otherwise synthesize polyimide precursor solution 7 using the same method as in Synthesis Example 1. The viscosity of the obtained polyimide precursor solution at 25°C and the weight average molecular weight of the polyimide precursor are shown in Table 3.

[0452] [Table 3]

[0453] Table 3

[0454]

[0455] (Synthesis Example 8)

[0456] In Synthesis Example 6, instead of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), an equimolar amount of the acid dianhydride component shown in Table 4 was used, and a polyimide precursor solution 8 was synthesized in the same manner as in Synthesis Example 6. The viscosity of the obtained polyimide precursor solution 8 (solid content: 30% by weight) at 25°C and the weight-average molecular weight of polyimide precursor 8 are shown in Table 4.

[0457] (Synthesis Example 9)

[0458] In a 500-ml detachable flask, a solution prepared by dissolving 169.5 g of dehydrated dimethylacetamide, 12.4 g (50 mmol) of 1,3-bis(3-aminopropyl)tetramethyldisiloxane (AprTMOS), and 16.0 g (50 mmol) of 2,2'-bis(trifluoromethyl)benzidine (TFMB) was controlled at a liquid temperature of 30°C, and 44.2 g (99.5 mmol) of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) was slowly added in several portions so that the temperature rise was 2°C or less, thereby synthesizing a polyimide precursor solution 9 (solid content: 30% by weight) in which polyimide precursor 9 was dissolved. The molar ratio of TFMB to AprTMOS used in polyimide precursor 9 was 50:50. The viscosity of polyimide precursor solution 9 at 25°C was 5380 cps, and the weight-average molecular weight of polyimide precursor 9 measured by GPC was 62,000.

[0459] [Table 4]

[0460] Table 4

[0461]

[0462] (Examples 7 to 9)

[0463] Using polyimide precursor solutions 7 to 9, polyimide films were produced in the same manner as in Example 1, and each of the obtained polyimide films was evaluated using the above evaluation method. The evaluation results are shown in Table 5. For the polyimide film of Example 8, in the glass transition temperature measurement, there was also a small peak of tanδ at around 250°C.

[0464] [Table 5]

[0465] Table 5

[0466]

[0467] (Comparative Synthesis Example 2)

[0468] In a 3 L detachable flask equipped with an oil bath and a stir bar, while introducing nitrogen, 12.25 g of a diphenyl silicone oil modified with diamine at both ends (manufactured by Shin-Etsu Chemical Co., Ltd.: X22-1660B-3 (number average molecular weight 4400)) and 3432 g of N-methyl-2-pyrrolidone (NMP) were added. Then, 222.12 g (0.5 mol) of 6FDA was added, and the mixture was stirred at room temperature for 30 minutes. Then, 152.99 g (0.478 mol) of 2,2'-bis(trifluoromethyl)benzidine (TFMB) was added. After confirming dissolution, the mixture was stirred at room temperature for 3 hours, then heated to 80 °C and stirred for 4 hours. Then, the oil bath was removed and the temperature was returned to room temperature to obtain Comparative Polyimide Precursor Solution 2. The solid content concentration of Comparative Polyimide Precursor Solution 2, the viscosity at 25 °C, and the weight average molecular weight of Comparative Polyimide Precursor 2 measured by GPC are shown in Table 6 respectively.

[0469] (Comparative Synthesis Example 3)

[0470] In a 500 ml detachable flask, a solution prepared by dissolving 169.5 g of dehydrated dimethylacetamide and 32.0 g (100 mmol) of 2,2'-bis(trifluoromethyl)benzidine (TFMB) was controlled at a liquid temperature of 30 °C, and 21.7 g (99.5 mmol) of pyromellitic dianhydride (PMDA) was slowly added in several portions such that the temperature rise was 2 °C or less, to synthesize Comparative Polyimide Precursor Solution 3 (solid component 20 wt%) in which Comparative Polyimide Precursor 3 was dissolved. The viscosity of Comparative Polyimide Precursor Solution 3 at 25 °C was 23400 cps, and the weight average molecular weight of Comparative Polyimide Precursor 3 measured by GPC was 82800.

[0471] [Table 6]

[0472] Table 6

[0473]

[0474] (Comparative Examples 2 - 3)

[0475] Using Comparative Polyimide Precursor Solutions 2 - 3, polyimide films were produced in the same manner as in Example 1, and for each of the obtained polyimide films, evaluation was performed using the above evaluation method. The evaluation results are shown in Table 7.

[0476] [Table 7]

[0477] Table 7

[0478]

[0479] As shown in Table 2, Table 5, and Table 7, the polyimide films of Examples 1 to 9 equivalent to the polyimide film of the present disclosure are resin films that have improved bending resistance, particularly static bending resistance, while suppressing a decrease in surface hardness. The polyimide films of Examples 1 to 9 also have excellent adhesion to the hard coat.

[0480] In contrast, the result of the static bending test of the polyimide film of Comparative Example 1 was 0 degrees, and the bending resistance was so poor that the crease of the static bending test remained on the film and could not be restored at all, and the pencil hardness deteriorated significantly. In addition, the static bending resistance of the polyimide film of Comparative Example 2 was poor, the pencil hardness deteriorated significantly, and in addition, the adhesion to the hard coat was poor. Further, the polyimide film of Comparative Example 3 had a large elastic modulus and good surface hardness, but poor bending resistance and poor adhesion to the hard coat.

[0481] (Example 10)

[0482] (1) Preparation of Polyimide (Chemical Imidization)

[0483] In a 500 mL detachable flask, a solution prepared by dissolving dehydrated dimethylacetamide (300.0 g) and 1,3-bis(3-aminopropyl)tetramethyldisiloxane (AprTMOS) (3.83 g, 15 mmol) was controlled at a liquid temperature of 30 °C, and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) (3.42 g, 7.7 mmol) was slowly added in such a manner that the temperature rise was 2 °C or less, and the mixture was stirred with a mechanical stirrer for 1 hour. 2,2'-Bis(trifluoromethyl)benzidine (TFMB) (44.4 g, 139 mmol) was added thereto, and after confirming complete dissolution, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) (64.7 g, 146 mmol) was slowly added in several portions in such a manner that the temperature rise was 2 °C or less, and a polyimide precursor solution 1' (solid content: 28% by weight) in which polyimide precursor 1' was dissolved was synthesized.

[0484] The above solution was cooled to room temperature, dehydrated dimethylacetamide (165.3 g) was added and stirred until homogeneous. Subsequently, pyridine (48.5 g, 613 mmol) and acetic anhydride (62.6 g, 613 mmol) as catalysts were added, and the mixture was stirred at room temperature for 24 hours to synthesize a polyimide solution. The obtained polyimide solution (346.4 g) was transferred to a 5-L detachable flask, butyl acetate (235.3 g) was added and stirred until homogeneous. Subsequently, methanol (523.5 g) was slowly added to obtain a slightly turbid solution. Methanol (1.221 kg) was added all at once to the turbid solution to obtain a white slurry. The above slurry was filtered and washed with methanol 5 times to obtain polyimide 1 (65.8 g). The weight-average molecular weight of the polyimide measured by GPC was 125,000.

[0485] (2) Manufacture of polyimide film

[0486] Polyimide 1 was dissolved in a mixed solvent of butyl acetate and PGMEA (8:2, volume ratio) to prepare a polyimide solution 1 with a solid content of 25% by mass. The viscosity of polyimide solution 1 (solid content 25% by weight) at 25 °C was 21,630 cps.

[0487] Using the polyimide solution 1 obtained above, the following steps (i) to (iii) were carried out to produce a polyimide film with a thickness of 50 μm ± 5 μm.

[0488] (i) Polyimide solution 1 was coated on glass and dried in a circulating oven at 120 °C for 10 minutes.

[0489] (ii) Under a nitrogen stream (oxygen concentration 100 ppm or less), the temperature was raised to 250 °C at a rate of 10 °C / minute, held at 250 °C for 1 hour, and then cooled to room temperature.

[0490] (iii) It was peeled off from the glass to obtain a polyimide film.

[0491] (Examples 11 - 12)

[0492] (1) Preparation of polyimide (chemical imidization)

[0493] Using the steps for synthesizing polyimide in Example 10 above, the reaction was carried out by adjusting to achieve the diamine ratios recorded in Table 8 to obtain polyimides 2 - 3.

[0494] (2) Manufacture of polyimide film

[0495] In Example 10, instead of polyimide 1, polyimide 2 or polyimide 3 was used and adjusted to achieve the solid content concentration described in Table 8. Otherwise, polyimide solutions 2 to 3 shown in Table 8 were obtained in the same manner as in Example 10.

[0496] In Example 10, polyimide solutions 2 to 3 were used instead of polyimide solution 1, and polyimide films of Examples 11 to 12 were obtained in the same manner as in Example 10.

[0497] (Comparative Example 4)

[0498] (1) Preparation of Comparative Polyimide 1 (Chemical Imidization)

[0499] Dehydrated dimethylformamide (144.0 g) and 2,2-bis-[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane (HFBAPP) (31.2 g, 60 mmol) were added to a 500 ml detachable flask and stirred until completely dissolved. The solution was cooled to 0°C, and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) (39.9 g, 90 mmol) was slowly added and stirred until dissolved. Then, silicone diamine KF-8010 (trade name, manufactured by Shin-Etsu Silicone, molecular weight 860) (24.9 g, 30 mmol) was added and stirred for 4 hours to obtain a polyamic acid solution. Next, β-methylpyridine (8.4 g, 90 mmol) and acetic anhydride (55.2 g, 540 mmol) as catalysts were added to the above solution, and the mixture was stirred in an oil bath at 100°C for 1 hour to obtain a polyimide solution. The obtained polyimide solution was dropped into a large amount of isopropyl alcohol (IPA) to precipitate polyimide. The polyimide obtained by filtration was stirred and washed in IPA, and after filtration again, the polyimide was thoroughly dried at 80°C under reduced pressure to obtain Comparative Polyimide 1. The weight-average molecular weight of Comparative Polyimide 1 measured by GPC was 199,000.

[0500] (2) Manufacture of Comparative Polyimide Film

[0501] Comparative Polyimide 1 was dissolved in dimethylformamide (DMF) to prepare Comparative Polyimide Solution 1 with a solid content of 30% by mass. The viscosity of Comparative Polyimide Solution 1 (solid content 30% by weight) at 25°C was 48,630 cps. Chemical imidization solution 4 was mixed in such a way that the solid content was 33.3% by weight, and the following steps (iv) to (v) were carried out to produce a polyimide film with a thickness of 50 μm ± 5 μm.

[0502] (iv) The comparative polyimide solution 1 was coated on glass, dried in a circulating oven at 80 °C for 15 minutes, and then dried at 250 °C for 5 minutes.

[0503] (v) It was peeled off from the glass to obtain a polyimide film.

[0504] [Table 8]

[0505] Table 8

[0506]

[0507] For each of the obtained polyimide films, the above evaluation method was used for evaluation. The evaluation results are shown in Table 9.

[0508] [Table 9]

[0509] Table 9

[0510]

[0511] As shown in Table 9, the polyimide films of Examples 10 to 12 corresponding to the polyimide film of the present disclosure are resin films that suppress a decrease in surface hardness while improving bending resistance.

[0512] In contrast, the polyimide film of Comparative Example 4 has good bending resistance, but poor pencil hardness and is prone to surface damage.

Claims

1. A method for manufacturing a polyimide film, which comprises the following steps: adding an acid dianhydride in a molar ratio of 0.5 equivalents of a diamine having one or two silicon atoms in the main chain to the reaction solution in which the diamine having one or two silicon atoms in the main chain is dissolved and reacting them, thereby synthesizing an amic acid formed by the reaction of the diamine having one or two silicon atoms in the main chain with both ends of the acid dianhydride, adding all or part of the remaining diamine thereto, adding an acid dianhydride and polymerizing a polyimide precursor having a structure represented by the following general formula (1’), This manufacturing method comprises: (i) a step of preparing a polyimide precursor resin composition containing the polyimide precursor and an organic solvent; a step of coating the polyimide precursor resin composition on a support to form a polyimide precursor resin coating film; and a step of imidizing the polyimide precursor by heating, or, comprises: (ii) a step of chemically imidizing the polyimide precursor to manufacture a polyimide having a structure represented by the following general formula (1); a step of preparing a polyimide resin composition containing the polyimide having the structure represented by the general formula (1) and an organic solvent; and a step of coating the polyimide resin composition on a support and drying the solvent to form a polyimide resin coating film, The polyimide film contains a polyimide having a structure represented by the following general formula (1), and the total light transmittance measured according to JIS K7361-1 is 85% or more, the yellowness calculated according to JIS K7373-2006 is 30 or less, it has a glass transition temperature in the temperature range of 150 °C or higher and 400 °C or lower, the tensile elastic modulus at 25 °C obtained by measuring a 15 mm × 40 mm test piece with a tensile speed of 10 mm / minute and a chuck distance of 20 mm according to JIS K7127 is 1.8 GPa or more, [Chemical formula 1] General formula (1) In general formula (1), R 1 represents a tetravalent group, which is a tetracarboxylic acid residue having an aromatic ring or an aliphatic ring, R 2 represents a divalent group, which is a diamine residue, and 10 mol% or more and 50 mol% or less of the total amount of R 2 is a diamine residue having one or two silicon atoms in the main chain, and 50 mol% or more and 90 mol% or less is a diamine residue having an aromatic ring or an aliphatic ring without a silicon atom. n represents the number of repeating units, [Chemical formula 2] General formula (1’) In general formula (1’), R 1 , R 2 and n are the same as those in the general formula (1).

2. The method for manufacturing a polyimide film according to claim 1, wherein, the birefringence in the thickness direction of the polyimide film at a wavelength of 590 nm is 0.020 or less.

3. The method for manufacturing a polyimide film according to claim 1 or 2, wherein, when the polyimide film is subjected to a static bending test according to the following static bending test method, the inner angle measured in this test is 120° or more, The static bending test method is as follows: A test piece of a polyimide film cut into 15 mm × 40 mm is bent at the midpoint of the long side, and a metal sheet (100 mm × 30 mm × 6 mm) with a thickness of 6 mm is arranged to sandwich the test piece from the upper and lower surfaces at both ends of the long side of the test piece. The overlapping parts of both ends of the test piece and the metal sheet on the upper and lower surfaces are each 10 mm and fixed with tape. In this state, it is clamped from the upper and lower with a glass plate (100 mm × 100 mm × 0.7 mm), and the test piece is fixed in a state of being bent with an inner diameter of 6 mm. At this time, a simulated test piece is inserted into the part where the test piece does not exist between the metal sheet and the glass plate, and fixed with tape in a manner parallel to the glass plate. After leaving the test piece fixed in a bent state in an environment of 60 ± 2 °C and 93 ± 2% relative humidity (RH) for 24 hours, the glass plate and the fixing tape are removed, the force applied to the test piece is released, and then one end of the test piece is fixed, and the inner angle of the test piece 30 minutes after releasing the force applied to the test piece is measured.

4. The method for manufacturing a polyimide film according to claim 1 or 2, wherein, the pencil hardness of the polyimide film in the pencil hardness test (0.98 N load) specified in JIS K5600-5-4 (1999) is HB or higher.

5. The method for manufacturing a polyimide film according to claim 1 or 2, wherein, the polyimide having the structure represented by the general formula (1) contains an aromatic ring and contains at least one selected from the group consisting of (i) a fluorine atom, (ii) an aliphatic ring, and (iii) a structure in which aromatic rings are linked to each other by a sulfonyl group or a fluorine-substituted or unsubstituted alkylene group.

6. The method for manufacturing a polyimide film according to claim 1 or 2, wherein, In the polyimide having the structure represented by the general formula (1), R in the general formula (1) 1 is at least one tetravalent group selected from the group consisting of a cyclohexanetetracarboxylic dianhydride residue, a cyclopentanetetracarboxylic dianhydride residue, a dicyclohexane-3,4,3',4'-tetracarboxylic dianhydride residue, a cyclobutanetetracarboxylic dianhydride residue, a pyromellitic dianhydride residue, a 3,3',4,4'-biphenyltetracarboxylic dianhydride residue, a 2,2',3,3'-biphenyltetracarboxylic dianhydride residue, a 4,4'-(hexafluoroisopropylidene)diphthalic anhydride residue, a 3,4'-(hexafluoroisopropylidene)diphthalic anhydride residue, a 3,3'-(hexafluoroisopropylidene)diphthalic anhydride residue, a 4,4'-oxydiphthalic anhydride residue, and a 3,4'-oxydiphthalic anhydride residue.

7. The method for manufacturing a polyimide film according to claim 1 or 2, wherein, In the polyimide having the structure represented by the general formula (1), R in the general formula (1) 2 The diamine residue having no silicon atom but having an aromatic ring or an aliphatic ring is at least one divalent group selected from the group consisting of a trans-cyclohexanediamine residue, a trans-1,4-bis(methylene)cyclohexanediamine residue, a 4,4'-diaminodiphenylsulfone residue, a 3,4'-diaminodiphenylsulfone residue, a 2,2-bis(4-aminophenyl)propane residue, a 2,2-bis(4-aminophenyl)hexafluoropropane residue, and a divalent group represented by the following general formula (2). [Chemical formula 3] General formula (2) In general formula (2), R 3 and R 4 each independently represents a hydrogen atom, an alkyl group or a perfluoroalkyl group.

8. A laminate, in which a polyimide film manufactured by the method for manufacturing a polyimide film according to claim 1 or 2 and a hard coat are adjacent to each other, and the hard coat contains at least one polymer selected from a radical polymerizable compound and a cationic polymerizable compound.

9. The laminate according to claim 8, wherein, the radical polymerizable compound is a compound having two or more (meth)acryloyl groups in one molecule, and the cationic polymerizable compound is a compound having at least one group selected from two or more epoxy groups and oxetanyl groups in one molecule.

10. A surface material for a display, which is a polyimide film manufactured by the method for manufacturing a polyimide film according to claim 1 or 2, or a laminate in which the polyimide film and a hard coat containing at least one polymer selected from a radical polymerizable compound and a cationic polymerizable compound are adjacent to each other.

11. The surface material for a display according to claim 10, wherein, the surface material for a display is used for a flexible display.

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