JP7027867B2 - Surface material for flexible displays - Google Patents

Description

The present invention relates to a polyimide film, a polyimide, a polyimide precursor, a laminate, and a surface material for a display.

While thin flat glass is excellent in hardness, heat resistance, etc., it is difficult to bend, easily breaks when dropped, has problems in workability, and is heavier than plastic products. For this reason, in recent years, resin products such as resin base materials and resin films are being replaced with glass products from the viewpoint of workability and weight reduction, and research on resin products that can be used as glass substitute products has been conducted.

For example, with the rapid progress of displays such as liquid crystals and organic EL and electronics such as touch panels, it has become necessary to make devices thinner, lighter, and more flexible. Conventionally, various electronic elements such as thin transistors and transparent electrodes are formed on a thin plate glass in these devices, but by changing the thin plate glass to a resin film, the impact resistance of the panel itself is enhanced. , Flexible, thinner and lighter.

Generally, the polyimide resin is a highly heat-resistant resin obtained by performing a dehydration ring closure reaction of a polyamic acid obtained by a condensation reaction of an aromatic tetracarboxylic acid anhydride and an aromatic diamine. However, since the polyimide resin is generally colored yellow or brown, it is difficult to use it in fields where transparency is required, such as display applications and optical applications. Therefore, it is being studied to apply a polyimide having improved transparency to a display member. For example, Patent Document 1 describes 1,2,4,5-cyclohexanetetracarboxylic acid and 1,2,4,5-cyclohexanetetracarboxylic acid as polyimide resins having high heat resistance, high transparency and low water absorption. At least one acyl-containing compound selected from the group consisting of anhydrides and reactive derivatives thereof, and at least one selected from compounds having at least one phenylene group and an isopropridene group represented by a specific formula. A polyimide resin obtained by reacting with an imino-forming compound is disclosed, and it is described that it is suitable for a substrate material such as a flat panel display and a mobile phone device.

Further, Patent Document 2 includes a unit structure derived from an aromatic dianhydride and an aromatic diamine, and an additive for improving tear strength, or a functional group selected from the group consisting of a hexafluoro group, a sulfone group and an oxy group. A transparent polyimide film further comprising a unit structure derived from a monomer having is disclosed. Patent Document 3 discloses, as a polyimide film having excellent transparency and heat resistance, a polyimide film in which the highest peak of the peak in the tan δ curve, which is a value obtained by dividing the loss elastic modulus by the storage elastic modulus, is within a specific range. ing.

Further, in Patent Document 4, as a polyimide film used for a substrate of a flexible device, a polyimide film which is colorless and transparent, has a low residual stress generated between it and an inorganic film, and has excellent mechanical and thermal properties can be obtained. For that purpose, a polyimide film in which a polyimide precursor using a specific fluoroaromatic diamine and a silicone compound having a siloxane skeleton having 3 to 200 silicon atoms as a monomer component is disclosed. .. In Patent Document 4, when a polyimide film with an inorganic film (SiN film) was formed using the polyimide precursor, cracks and peeling were not observed after a bending test in which bending was repeated 10 times (○). It is described as observed (Δ).

In the polyimide molded body used for the liquid crystal alignment film (Patent Document 5), 2,2-bis (3,4-dicarboxyphenyl) is used as a raw material for the polyimide resin in order to make the polyimide molded body colorless and transparent. Hexafluoropropanedianhydride is used in combination with a specific aromatic diamine having an amino group at the meta position, and diaminosiloxane is used as a diamine component in order to improve the adhesive strength with an inorganic substrate. Is being done.

Japanese Unexamined Patent Publication No. 2006-199945 Special Table 2014-501301 Publication No. Special Table 2012-503701 International Publication No. 2014/098235 Japanese Unexamined Patent Publication No. 63-170420

Mobile devices with foldable screens should be in the folded state when carried and in the unfolded state when used. Therefore, it is required that the flexible display mounted on the mobile device does not cause display defects even if it is repeatedly bent, and the base material and surface material for the flexible display are resistant to bending when repeatedly bent (hereinafter referred to as "bending resistance"). , Sometimes referred to as dynamic flexion resistance) is required.

In the polyimide film described in Patent Document 4, it is described that the residual stress generated between the polyimide film and the inorganic film is reduced by introducing a silicone component containing three or more silicon atoms. However, a polyimide film into which a silicone component containing three or more silicon atoms has been introduced, as in Comparative Example 1 described later, is easily broken when repeatedly bent, has a low surface hardness, is easily scratched, or has a light emitting panel or a light emitting panel. There is a problem that the shock is transmitted to the circuit and the function as a protective film is insufficient.
From the above, there is a demand for a resin film having both bending resistance and sufficient surface hardness as a protective film.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a resin film in which a decrease in surface hardness is suppressed while improving bending resistance when repeatedly bent.
Further, in the present invention, the polyimide constituting the resin film, the polyimide precursor used for producing the resin film, the laminate having the resin film, and the resin film or the surface material for a display which is the laminate are used. The purpose is to provide.

The surface material for a flexible display of the present invention is a surface material for a flexible display containing a polyimide having a structure represented by the following general formula (1) and containing a polyimide film having a thickness of 27 μm or more and 100 μm or less .

（一般式（１）において、Ｒ^１は芳香族環又は脂肪族環を有するテトラカルボン酸残基である４価の基を表し、Ｒ^２は、ジアミン残基である２価の基を表し、Ｒ^２の総量の２．５モル％以上１０モル％未満が、主鎖にケイ素原子を１個又は２個有するジアミン残基であり、残りのＲ^２が、ケイ素原子を有さず、芳香族環又は脂肪族環を有するジアミン残基であり、前記残りのＲ^２のうちの半分よりも多くが、１，４－シクロヘキサンジアミン残基、ｔｒａｎｓ－１，４－ビスメチレンシクロヘキサンジアミン残基、４，４’－ジアミノジフェニルスルホン残基、３，４’－ジアミノジフェニルスルホン残基、２，２－ビス（４－アミノフェニル）プロパン残基、２，２－ビス（４－アミノフェニル）ヘキサフルオロプロパン残基、及び下記一般式（２）で表される２価の基からなる群から選ばれる少なくとも１種の２価の基である。ｎは繰り返し単位数を表す。）

（一般式（２）において、Ｒ^３及びＲ^４はそれぞれ独立に、水素原子、アルキル基、またはパーフルオロアルキル基を表す。）

(In the 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. 2.5 mol% or more and less than 10 mol% of the total amount of R ² is a diamine residue having one or two silicon atoms in the main chain, and the remaining R ² has no silicon atom and is aromatic. Diamine residues with a ring or aliphatic ring, more than half of the remaining R ² are 1,4-cyclohexanediamine residues, trans-1,4-bismethylenecyclohexanediamine residues, 4 , 4'-diaminodiphenyl sulfone residue, 3,4'-diaminodiphenyl sulfone residue, 2,2-bis (4-aminophenyl) propane residue, 2,2-bis (4-aminophenyl) hexafluoropropane It is at least one divalent group selected from the group consisting of a residue and a divalent group represented by the following general formula (2). N represents the number of repeating units.)

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

In the polyimide film of the present invention, the total light transmittance measured in accordance with JIS K7361-1 is 85% or more.
The yellowness calculated in accordance with JIS K7373-2006 is 20.0 or less.
It has a glass transition temperature in the temperature range of 150 ° C or higher and 400 ° C or lower.
It is preferable that the birefringence index in the thickness direction at a wavelength of 590 nm is 0.040 or less from the viewpoints of light transmission, bending resistance and surface hardness, and reduction of optical strain.
When the birefringence index in the thickness direction at a wavelength of 590 nm is 0.040 or less, the occurrence of rainbow unevenness when the polyimide film is placed on the display surface and the display is viewed with polarized sunglasses is suppressed. Is also preferable. Above all, when the birefringence index in the thickness direction at the wavelength of 590 nm is 0.020 or less, the color reproducibility when the display is viewed from an angle is improved, which is preferable.
Further, above all, when the value obtained by dividing the yellowness calculated according to the JIS K7373-2006 by the film thickness (μm) is 0.04 or less, the yellowish coloring is suppressed and the light transmission is transmitted. Is preferable from the viewpoint of improving.

In the polyimide film of the present invention, the total light transmittance measured in accordance with JIS K7361-1 is 85% or more.
The yellowness calculated in accordance with JIS K7373-2006 is 7.0 or less.
It has a glass transition temperature in the temperature range of 150 ° C or higher and 400 ° C or lower.
It is preferable that the birefringence index in the thickness direction at a wavelength of 590 nm is 0.020 or less from the viewpoints of light transmission, bending resistance and surface hardness, and reduction of optical strain.

In the polyimide film of the present invention, the arithmetic average roughness Ra measured according to JIS B0601 on at least one surface is 100 nm or less to prevent deterioration of transparency, and the polyimide film of the present invention can be used as a surface for a display. It is preferable because it has excellent visibility of the display when used as a material.

In the polyimide film of the present invention, in the polyimide having the structure represented by the general formula (1), R ¹ in the general formula (1) is a cyclohexanetetracarboxylic acid dianhydride residue, cyclopentanetetracarboxylic. Acid dianhydride residue, dicyclohexane-3,4,3', 4'-tetracarboxylic acid dianhydride residue, cyclobutanetetracarboxylic acid dianhydride residue, pyromellitic acid dianhydride residue, 3, 3', 4,4'-biphenyltetracarboxylic acid dianhydride residue, 2,2', 3,3'-biphenyltetracarboxylic acid dianhydride residue, 4,4'-(hexafluoroisopropylidene) diphthal Acid anhydride residues, 3,4'-(hexafluoroisopropyridene) diphthalic acid anhydride residues, 3,3'-(hexafluoroisopropyridene) diphthalic acid anhydride residues, 4,4'-oxydiphthalic acid anhydride At least one tetravalent group selected from the group consisting of substance residues and 3,4'-oxydiphthalic acid anhydride residues is a tetravalent group in terms of light transmission, bending resistance and surface hardness. preferable.

The surface material for a flexible display of the present invention includes a laminate having the polyimide film and a hard coat layer containing at least one polymer of a radically polymerizable compound and a cationically polymerizable compound. You may .

In the surface material for flexible display of the present invention, the radically polymerizable compound is a compound having two or more (meth) acryloyl groups in one molecule, and the cationically polymerizable compound is at least one of an epoxy group and an oxetanyl group. It is preferable that the compound has two or more of the above in one molecule from the viewpoint of adhesion, light transmission and surface hardness.

The surface material for a flexible display of the present invention may be the polyimide film or the laminated body.

According to the present invention, it is possible to provide a resin film in which a decrease in surface hardness is suppressed while improving bending resistance when repeatedly bent.
Further, in the present invention, the polyimide constituting the resin film, the polyimide precursor used for producing the resin film, the laminate having the resin film, and the resin film or the surface material for a display which is the laminate are used. Can be provided.

I. Polyimide film The polyimide film of the present invention is a polyimide film containing a polyimide having a structure represented by the following general formula (1).

（一般式（１）において、Ｒ^１は芳香族環又は脂肪族環を有するテトラカルボン酸残基である４価の基を表し、Ｒ^２は、ジアミン残基である２価の基を表し、Ｒ^２の総量の２．５モル％以上１０モル％未満が、主鎖にケイ素原子を１個又は２個有するジアミン残基であり、残りのＲ^２が、ケイ素原子を有さず、芳香族環又は脂肪族環を有するジアミン残基であり、前記残りのＲ^２のうちの半分よりも多くが、１，４－シクロヘキサンジアミン残基、ｔｒａｎｓ－１，４－ビスメチレンシクロヘキサンジアミン残基、４，４’－ジアミノジフェニルスルホン残基、３，４’－ジアミノジフェニルスルホン残基、２，２－ビス（４－アミノフェニル）プロパン残基、２，２－ビス（４－アミノフェニル）ヘキサフルオロプロパン残基、及び下記一般式（２）で表される２価の基からなる群から選ばれる少なくとも１種の２価の基である。ｎは繰り返し単位数を表す。）

（一般式（２）において、Ｒ^３及びＲ^４はそれぞれ独立に、水素原子、アルキル基、またはパーフルオロアルキル基を表す。）

(In the 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. 2.5 mol% or more and less than 10 mol% of the total amount of R ² is a diamine residue having one or two silicon atoms in the main chain, and the remaining R ² has no silicon atom and is aromatic. Diamine residues with a ring or aliphatic ring, more than half of the remaining R ² are 1,4-cyclohexanediamine residues, trans-1,4-bismethylenecyclohexanediamine residues, 4 , 4'-diaminodiphenyl sulfone residue, 3,4'-diaminodiphenyl sulfone residue, 2,2-bis (4-aminophenyl) propane residue, 2,2-bis (4-aminophenyl) hexafluoropropane It is at least one divalent group selected from the group consisting of a residue and a divalent group represented by the following general formula (2). N represents the number of repeating units.)

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

According to the present invention, the polyimide contained in the polyimide film has a molecular skeleton having an aromatic ring or an aliphatic ring as a tetracarboxylic acid residue, and is 2.5 mol% or more and 10 mol of the total amount of diamine residues. % Is a diamine residue having one or two silicon atoms in the main chain, and the remaining diamine residues are diamine residues having no silicon atom and having an aromatic ring or an aliphatic ring. By having more than half of them are diamine residues having a specific aromatic ring or aliphatic ring, it is possible to provide a resin film having improved dynamic bending resistance and sufficient surface hardness as a protective film. can.
The reason for this is presumed as follows.

The present inventors focused on polyimide among the resins. Polyimide is known to have excellent heat resistance due to its chemical structure. In addition, it is known that the arrangement of molecular chains inside the polyimide film forms a certain ordered structure, and it is thought that thanks to this, it is possible to repeat the folded state and the flat open state at room temperature. Be done. However, it has been confirmed that the bent portion of the film may break due to repeated bending, and in the case of polyimide having a rigid molecular skeleton such as an aromatic ring, the bent portion of the film tends to break easily. rice field. On the other hand, if the flexibility of the polyimide film is increased in order to improve the dynamic bending resistance, the surface hardness tends to decrease, and it is difficult to achieve both the bending resistance and the surface hardness in the resin film. It is thought that the stress generated on the film surface can be relieved by introducing a silicone component, but if the effect of stress relieving is too important and silicone with a large molecular weight is used, the entire film becomes too flexible and bends. If the above steps are repeated, the film tends to be deformed or broken, the surface hardness tends to be insufficient, the film formation becomes difficult, and the film surface tends to have irregularities.
On the other hand, the present inventors have introduced a specific amount of a flexible molecular skeleton having one or two silicon atoms in the main chain and having a small molecular weight between the molecular skeletons containing an aromatic ring or an aliphatic ring. Moreover, when a polyimide having a specific amount of a specific aromatic ring or a molecular skeleton containing an aliphatic ring introduced as a molecular skeleton containing an aromatic ring or an aliphatic ring is used, dynamic bending resistance is maintained while maintaining the surface hardness. It has been found that a polyimide film that improves the above can be obtained. Specifically, in the present invention, the dynamic bending resistance of the polyimide film is improved by introducing a specific amount of a flexible molecular skeleton having a short specific main chain into a rigid molecular skeleton to relieve stress by molecular motion. It is presumed that this makes it possible to appropriately reduce the stress applied to the film during bending.
Further, in the present invention, the surface hardness of the polyimide film is maintained because the main chain of the flexible molecular skeleton to be introduced is short and the film does not become too flexible. Therefore, an aromatic ring or an aliphatic ring is further maintained. It is considered that, by containing the above-mentioned specific amount as the rigid molecular skeleton containing the above, the molecular chains are easily packed together and the molecular chains are likely to be dense. Since the polyimide film described in Patent Document 4 has a glass transition temperature below freezing point due to the introduction of a silicone component containing three or more silicon atoms, bending resistance and surface hardness at room temperature tend to decrease. it is conceivable that. On the other hand, when there are many aromatic diamine residues having an amino group at the meta position or the ortho position, it is difficult to pack the molecular chains together, and as shown in Comparative Example 5 described later, it is considered that the surface hardness tends to decrease. Be done. On the other hand, in the polyimide film of the present invention, among the diamine residues possessed by the polyimide, the remaining diamine residues other than the diamine residue having one or two silicon atoms in the main chain do not have a silicon atom and are aromatic. It is a diamine residue having a group ring or an aliphatic ring, and more than half of them are the above-mentioned specific diamine residues, so that the molecular chains are easily packed together and the molecular chains are likely to be dense. It is presumed that the decrease in surface hardness can be suppressed even when the elastic coefficient is low. Further, in the present invention, the optical characteristics can be improved by containing a specific amount of the above-mentioned specific one as a rigid molecular skeleton containing an aromatic ring or an aliphatic ring.
Further, the thicker the film, the greater the stress applied when the film is bent, so that the film is more likely to break. However, since the polyimide film of the present invention has improved dynamic bending resistance, the film is easily broken. Even if the thickness is increased, breakage when repeatedly bent is suppressed.

Hereinafter, the polyimide film according to the present invention will be described in detail.
The polyimide film according to the present invention contains a polyimide having a structure represented by the general formula (1). As long as the effect of the present invention is not impaired, other components may be further contained, or other components may be contained.

1. 1. Polyimide Polyimide is obtained by reacting a tetracarboxylic acid component with a diamine component. It is preferable to obtain polyamic acid by polymerization of a tetracarboxylic acid component and a diamine component and imidize it. The imidization may be performed by thermal imidization or chemical imidization. It can also be produced by a method in which thermal imidization and chemical imidization are used in combination.
The polyimide film according to the present invention contains a polyimide having a structure represented by the general formula (1).
Further, the polyimide according to the present invention has a structure represented by the general formula (1).

Here, the tetracarboxylic acid residue means a residue obtained by removing four carboxyl groups from the tetracarboxylic acid, and represents the same structure as the residue obtained by removing the acid dianhydride structure from the tetracarboxylic dianhydride. ..
Further, the diamine residue means a residue obtained by removing two amino groups from the diamine.

The tetracarboxylic acid residue in R ¹ of the general formula (1) is a residue obtained by removing the acid dianhydride structure from the tetracarboxylic acid dianhydride having an aromatic ring, or a tetracarboxylic acid having an aliphatic ring. It can be a residue obtained by removing the acid dianhydride structure from the dianhydride.
Examples of the tetracarboxylic acid dianhydride having an aromatic ring include pyromellitic acid dianhydride, 3,3', 4,4'-benzophenone tetracarboxylic acid dianhydride, 2,2', 3,3'. -Benzophenone tetracarboxylic acid dianhydride, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride, 2,2', 3,3'-biphenyltetracarboxylic acid 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) 3,4-Dicarboxyphenyl) sulfonate 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-hexafluoropropanedianhydride, 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 Thing, 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} sulfonate dianhydride, bis {4- [3- (1,2-dicarboxy) phenoxy] phenyl} sulfonate dianhydride, bis {4- [4- (1,2-dicarboxy) phenoxy] phenyl} sulfide dianhydride, bis {4- [3 -(1,2-dicarboxy) phenoxy] phenyl} sulf Ido dianhydride, 4,4'-(hexafluoroisopropyridene) diphthalic acid anhydride, 3,4'-(hexafluoroisopropyridene) diphthalic acid anhydride, 3,3'-(hexafluoroisopropyridene) diphthalate Acid anhydride, 4,4'-oxydiphthalic acid anhydride, 3,4'-oxydiphthalic acid anhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetra Carboxy acid dianhydride, 1,2,5,6-naphthalenetetracarboxylic acid dianhydride, 1,2,3,4-benzenetetracarboxylic acid dianhydride, 3,4,9,10-perylenetetracarboxylic Examples thereof include acid dianhydride, 2,3,6,7-anthracenetetracarboxylic acid dianhydride, 1,2,7,8-phenanthrentetracarboxylic acid dianhydride and the like.
Examples of the tetracarboxylic acid dianhydride having an aliphatic ring include cyclohexanetetracarboxylic acid dianhydride, cyclopentanetetracarboxylic acid dianhydride, and dicyclohexane-3,4,3', 4'-tetracarboxylic acid dianhydride. Anhydrides, cyclobutanetetracarboxylic acid dianhydrides and the like can be mentioned.
These can be used alone or in combination of two or more.

In the polyimide having the structure represented by the general formula (1), R ¹ in the general formula (1) is cyclohexanetetracarboxylic acid dian, among others, from the viewpoint of light transmission, bending resistance and surface hardness. Anhydrous residue, cyclopentanetetracarboxylic acid dianhydride residue, dicyclohexane-3,4,3', 4'-tetracarboxylic acid dianhydride residue, cyclobutanetetracarboxylic acid dianhydride residue, pyromerit Acid dianhydride residue, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride residue, 2,2', 3,3'-biphenyltetracarboxylic acid dianhydride residue, 4,4 '-(Hexafluoroisopropyridene) diphthalic acid anhydride residue, 3,4'-(hexafluoroisopropyridene) diphthalic acid anhydride residue, 3,3'-(hexafluoroisopropyridene) diphthalic acid anhydride residue , 4,4'-Oxydiphthalic acid anhydride residue, and at least one tetravalent group selected from the group consisting of 3,4'-oxydiphthalic acid anhydride residue is preferable.
In R ¹ , the total content of these suitable residues is preferably 50 mol% or more, more preferably 70 mol% or more, still more preferably 90 mol% or more.
In particular, R ¹ in the general formula (1) is a 4,4'-(hexafluoroisopropylidene) diphthalic acid anhydride residue, 3,4'-(, from the viewpoint of a good balance between light transmission and surface hardness. Hexafluoroisopropylidene) diphthalic acid anhydride residue, 3,3'-(hexafluoroisopropyridene) diphthalic acid anhydride residue, 4,4'-oxydiphthalic acid anhydride residue, and 3,4'-oxydiphthalate residue. It is more preferably a tetravalent group of at least one selected from the group consisting of acid anhydride residues, 4,4'-(hexafluoroisopropylidene) diphthalic acid anhydride residues, and 4,4'-. It is even more preferred that it is at least one tetravalent group selected from oxydiphthalic acid anhydride residues.

^R1 of the general formula (1) includes pyromellitic acid dianhydride residue, 3,3', 4,4'-biphenyltetracarboxylic acid dianhydride residue, and 2,2', 3, A group of tetracarboxylic acid residues (Group A) suitable for improving rigidity, such as at least one selected from the group consisting of 3'-biphenyltetracarboxylic acid dianhydride residues, and cyclohexanetetracarboxylic acid dianhydride. Anhydride residue, cyclopentanetetracarboxylic acid dianhydride residue, dicyclohexane-3,4,3', 4'-tetracarboxylic acid dianhydride residue, cyclobutanetetracarboxylic acid dianhydride residue, 4, 4'-(Hexafluoroisopropylidene) diphthalic acid anhydride residue, 3,4'-(hexafluoroisopropyridene) diphthalic acid anhydride residue, 3,3'-(hexafluoroisopropyridene) diphthalic acid anhydride residue Tetra suitable for improving light transmission, such as at least one selected from the group consisting of groups, 4,4'-oxydiphthalic acid anhydride residues, and 3,4'-oxydiphthalic acid anhydride residues. It is also preferable to use it in combination with the carboxylic acid residue group (Group B). In this case, the content ratio of the tetracarboxylic acid residue group (group A) suitable for improving the rigidity and the tetracarboxylic acid residue group (group B) suitable for improving the light transmission is For 1 mol of the tetracarboxylic acid residue group (group B) suitable for improving light transmission, the tetracarboxylic acid residue group (group A) suitable for improving the rigidity was 0. It is preferably 05 mol or more and 9 mol or less, more preferably 0.1 mol or more and 5 mol or less, and further preferably 0.3 mol or more and 4 mol or less.
Among them, the group B includes 4,4'-(hexafluoroisopropyridene) diphthalic acid anhydride residues and 3,4'-(hexafluoroisopropyridene) diphthalic acid anhydride residues containing a fluorine atom. It is preferable to use at least one from the viewpoint of improving surface hardness and light transmission.

The content ratio of the diamine residue having one or two silicon atoms in the main chain in R ² of the general formula (1) is 2.5 mol% or more and less than 10 mol% of the total amount of R ² , and is active. From the viewpoint of bending resistance and surface hardness, it is preferably 3 mol% or more and 8 mol% or less, and more preferably 4 mol% or more and 7 mol% or less.
In the polyimide film of the present invention, a specific amount of a flexible molecular skeleton having one or two silicon atoms in the main chain is introduced between the molecular skeletons containing an aromatic ring or an aliphatic ring as a main component. As described above, not only the dynamic bending resistance is improved and the decrease in surface hardness is suppressed, but also the orientation is easily suppressed and the double refractive index is likely to be reduced.

In R ² of the general formula (1), the diamine residue having one or two silicon atoms in the main chain is the residue obtained by removing two amino groups from the diamine having one or two silicon atoms in the main chain. Can be the basis.
Examples of the diamine having one silicon atom in the main chain include a diamine represented by the following general formula (A). Examples of the diamine having two silicon atoms in the main chain include diamines represented by the following general formula (B).

（一般式（Ａ）及び一般式（Ｂ）において、Ｌはそれぞれ独立して、直接結合又は－Ｏ－結合であり、Ｒ^１０はそれぞれ独立して、置換基を有していても良く、酸素原子又は窒素原子を含んでいても良い炭素数１以上２０以下の１価の炭化水素基を表す。Ｒ^１１はそれぞれ独立して、置換基を有していても良く、酸素原子又は窒素原子を含んでいても良い炭素数１以上２０以下の２価の炭化水素基を表す。）

(In the general formula (A) and the general formula (B), L may be an independent direct bond or an —O— bond, and R ¹⁰ may be independent and have a substituent, and oxygen may be used. It represents a monovalent hydrocarbon group having 1 or more and 20 or less carbon atoms which may contain an atom or a nitrogen atom. R ¹¹ may independently have a substituent and may contain an oxygen atom or a nitrogen atom. It represents a divalent hydrocarbon group having 1 or more and 20 or less carbon atoms which may be contained.)

Examples of the monovalent hydrocarbon group represented by R ¹⁰ include an alkyl group having 1 to 20 carbon atoms, an aryl group, and a combination thereof. The alkyl group may be linear, branched or cyclic, and may be linear or a combination of branched and cyclic.
The alkyl group having 1 or more and 20 or less carbon atoms is preferably an alkyl group having 1 or more and 10 or less carbon atoms, and specifically, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and the like. Examples thereof include a t-butyl group, a pentyl group and a hexyl group. The cyclic alkyl group is preferably a cycloalkyl group having 3 to 10 carbon atoms, and specific examples thereof include a cyclopentyl group and a cyclohexyl group. The aryl group is preferably an aryl group having 6 to 12 carbon atoms, and specific examples thereof include a phenyl group, a tolyl group, and a naphthyl group. Further, the monovalent hydrocarbon group represented by R ¹⁰ may be an aralkyl group, and examples thereof include a benzyl group, a phenylethyl group and a phenylpropyl group.
Examples of the hydrocarbon group which may contain an oxygen atom or a nitrogen atom include an ether bond, a carbonyl bond, an ester bond, an amide bond, and imino, which are a divalent hydrocarbon group described later and the monovalent hydrocarbon group. Examples include groups bonded by at least one of the bonds (-NH-).
The substituent that the monovalent hydrocarbon group represented by ^R10 may have is not particularly limited as long as the effect of the present invention is not impaired, and for example, a halogen atom such as a fluorine atom or a chlorine atom. , Hydrocarbons and the like.

The monovalent hydrocarbon group represented by R ¹⁰ is an alkyl group having 1 or more and 3 or less carbon atoms or an aryl group having 6 or more carbon atoms and 10 or less carbon atoms from the viewpoint of improving bending resistance and compatibility with surface hardness. It is preferable to have. The alkyl group having 1 or more and 3 or less carbon atoms is more preferably a methyl group, and the aryl group having 6 or more and 10 or less carbon atoms is more preferably a phenyl group.

Examples of the divalent hydrocarbon group represented by R ¹¹ include an alkylene group having 1 to 20 carbon atoms, an arylene group, and a group in combination thereof. The alkylene group may be linear, branched or cyclic, and may be linear or a combination of branched and cyclic.
The alkylene group having 1 or more and 20 or less carbon atoms is preferably an alkylene group having 1 or more and 10 or less carbon atoms. Examples thereof include a group obtained by combining a cyclic or branched alkylene group with a cyclic alkylene group.
The arylene group is preferably an arylene group having 6 to 12 carbon atoms, and examples of the arylene group include a phenylene group, a biphenylene group, a naphthylene group and the like, and further have a substituent for an aromatic ring described later. You may be.
As the divalent hydrocarbon group which may contain an oxygen atom or a nitrogen atom, the divalent hydrocarbon groups are ether-bonded, carbonyl-bonded, ester-bonded, amide-bonded, and imino-bonded (-NH-). Examples include at least one bonded group.
The substituent that the divalent hydrocarbon group represented by R ¹¹ may have is the same as the substituent that the monovalent hydrocarbon group represented by R ¹⁰ may have. Good.

The divalent hydrocarbon group represented by R ¹¹ is an alkylene group having 1 or more and 6 or less carbon atoms or an arylene group having 6 or more and 10 or less carbon atoms from the viewpoint of improving bending resistance and achieving both surface hardness. It is preferably present, and more preferably it is an alkylene group having 2 or more and 4 or less carbon atoms.

From the viewpoint of improving bending resistance and achieving both 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. It is more preferably 500 or less, and particularly preferably 300 or less.
The diamine residue having one or two silicon atoms in the main chain may be used alone or in combination of two or more.

Further, in the polyimide having the structure represented by the general formula (1), the diamine residue having one or two silicon atoms in the main chain in ^R2 in the general formula (1) has two silicon atoms. Individual diamine residues are preferable from the viewpoint of light transmission, bending resistance and surface hardness, and further, 1,3-bis (3-aminopropyl) tetramethyldisiloxane residues, 1,3. -Bis (4-aminobutyl) tetramethyldisiloxane, 1,3-bis (5-aminopentyl) tetramethyldisiloxane and the like are preferable from the viewpoint of easy availability, light transmission and surface hardness.

In R 2 of the general formula (1), the remaining R ² of the total amount of R ² excluding the diamine residue having one or ^two silicon atoms in the main chain does not have a silicon atom. Diamine residues with an aromatic or aliphatic ring, more than half of the remaining R ² are 1,4-cyclohexanediamine residues, trans-1,4-bismethylenecyclohexanediamine residues. (Trans-1,4-bis (aminomethyl) cyclohexane residue), 4,4'-diaminodiphenyl sulfone residue, 3,4'-diaminodiphenyl sulfone residue, 2,2-bis (4-aminophenyl) At least one divalent group selected from the group consisting of a propane residue, a 2,2-bis (4-aminophenyl) hexafluoropropane residue, and a divalent group represented by the general formula (2). (Hereinafter, it may be referred to as "at least one divalent group selected from the above group").
That is, if the diamine residue having one or two silicon atoms in the main chain in the total amount of R ² (100 mol%) is x mol% (2.5 ≦ x <10), then (2.5 ≦ x <10) of R ² More than 90 mol%, which is 100-x) mol%, and 97.5 mol% or less are diamine residues having no silicon atom and having an aromatic ring or an aliphatic ring, and {(100-x) of R ² ) / 2} mol% excess is the basis for at least one divalent agent selected from the group. Among them, the ratio of at least one divalent group selected from the group among the remaining ^R2 , that is, the total amount of diamine residues having no silicon atom and having an aromatic ring or an aliphatic ring. The ratio of at least one divalent group selected from the above group when 100 mol% is preferably 70 mol% or more, preferably 85 mol% or more, from the viewpoint of surface hardness and light transmission. It is more preferably present, and even more preferably 95 mol% or more. It should be noted that R ² may contain another diamine residue having no silicon atom and having an aromatic ring or an aliphatic ring, which is different from at least one divalent group selected from the above group. good.
Here, the diamine residue having no silicon atom and having an aromatic ring can be a residue obtained by removing two amino groups from the diamine having no silicon atom and having an aromatic ring, and the silicon atom can be used. The diamine residue having an aliphatic ring without a silicon atom can be a residue obtained by removing two amino groups from a diamine having an aliphatic ring without a silicon atom.

Among at least one divalent group selected from the above group, trans-1,4-bismethylenecyclohexanediamine residue and 4,4'-diaminodiphenylsulfone residue are selected from the viewpoint of surface hardness and light transmission. Group, 3,4'-diaminodiphenyl sulfone residue, 2,2-bis (4-aminophenyl) propane residue, 2,2-bis (4-aminophenyl) hexafluoropropane residue, and the above general formula ( It is preferably at least one divalent group selected from the group consisting of the divalent group represented by 2). As the divalent group represented by the general formula (2), it is more preferable that R ³ and R ⁴ are perfluoroalkyl groups, and among them, a perfluoroalkyl group having 1 or more and 3 or less carbon atoms is preferable. It is more preferably a trifluoromethyl group or a perfluoroethyl group. Further, as the alkyl group in R ³ and R ⁴ in the general formula (2), an alkyl group having 1 or more carbon atoms and 3 or less carbon atoms is preferable, and a methyl group or an ethyl group is more preferable.

Further, from the viewpoint of improving the surface hardness and light transmission of the polyimide film of the present invention, at least one divalent group selected from the above group is 70 mol% or more of the total amount of ^R2 . It is preferably 80 mol% or more, more preferably 90 mol% or more, and particularly preferably a diamine having one or two silicon atoms in the main chain in the total amount of R ² . It is preferable that all the remaining ^R2 except the residue is at least one divalent group selected from the above group.

Used for a diamine residue having no silicon atom and having an aromatic ring, which may be contained in R ² of the general formula (1), which is different from at least one divalent group selected from the above group. Examples of the diamine to be obtained include p-phenylenediamine, o-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl sulfide, and 4,4'-diaminodiphenyl sulfide. , 4,4'-diaminobenzophenone, 3,4'-diaminobenzophenone, 4,4'-diaminobenzanilide, 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 2- (3-aminophenyl) -2- (4-Aminophenyl) Propane, 2- (3-Aminophenyl) -2- (4-Aminophenyl) -1,1,1,3,3,3-Hexafluoropropane, 1,1-di (4-Aminophenyl) -1-phenylethane, 1- (3-aminophenyl) -1- (4-aminophenyl) -1-phenylethane, 1,3-bis (4-aminophenoxy) benzene, 1, 4-Bis (4-aminophenoxy) benzene, 1,3-bis (4-aminobenzoyl) benzene, 1,4-bis (4-aminobenzoyl) benzene, 1,3-bis (4-amino-α, α) -Dimethylbenzyl) benzene, 1,4-bis (4-amino-α, α-dimethylbenzyl) benzene, 1,3-bis (4-amino-α, α-ditrifluoromethylbenzyl) benzene, 1,4- Bis (4-amino-α, α-ditrifluoromethylbenzyl) benzene, N, N'-bis (4-aminophenyl) terephthalamide, 9,9-bis (4-aminophenyl) fluorene, 3,3'- Dichloro-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminobiphenyl, 4,4'-bis (4-amino) Phenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) phenyl] ether, 2,2- Bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1,1,3,3,3-hexafluoropropane, 1,3 -Bis [4- (4-aminophenoxy) benzoyl] Ben Zen, 1,4-bis [4- (4-aminophenoxy) benzoyl] benzene, 1,3-bis [4- (4-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- (4- (4- (4-) 4-) Aminophenoxy) Phenoxy] diphenyl sulfone, 6,6'-bis (4-aminophenoxy) -3,3,3', 3'-tetramethyl-1,1'-spirobiindan, etc., and the aromatic ring of the diamine. A diamine in which a part or all of the upper hydrogen atom is substituted with a substituent selected from a fluoro group, a methyl group, a methoxy group, a trifluoromethyl group, or a trifluoromethoxy group can be used. Among them, p-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylsulfide, 4,4'-diaminobenzophenone, 4,4'-diaminobenzanilide, 4,4'-diaminodiphenylmethane, 1 , 1-di (4-aminophenyl) -1-phenylethane, 1,4-bis (4-aminophenoxy) benzene, 1,4-bis (4-aminobenzoyl) benzene, 1,4-bis (4-) Amino-α, α-dimethylbenzyl) benzene, 1,4-bis (4-amino-α, α-ditrifluoromethylbenzyl) benzene, N, N'-bis (4-aminophenyl) terephthalamide, 9,9 -Bis (4-aminophenyl) fluorene, 3,3'-dichloro-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4 '-Diaminobiphenyl, 4,4'-bis (4-aminophenoxy) biphenyl, bis [4- (4-aminophenoxy) phenyl] ketone, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4 -(4-Aminophenoxy) phenyl] ether, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] -1,1, 1,3,3,3-hexafluoropropane, 1,4-bis [4- (4-aminophenoxy) benzoyl] benzene, 1,4-bis [4- (4-aminophenoxy) -α, α-dimethyl Benzene] benzene, 4,4'-bis [4- (4-aminophenoxy) benzoyl] diphenyl ether, 4,4'-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] benzophenone, 4, At least selected from the group consisting of 4'-bis [4- (4-amino-α, α-dimethylbenzyl) phenoxy] diphenyl sulfone and 4,4'-bis [4- (4-aminophenoxy) phenoxy] diphenyl sulfone. It is preferably one kind.
These can be used alone or in combination of two or more.

Used for diamine residues having no silicon atom and having an aliphatic ring, which may be contained in R ² of the general formula (1), which is different from at least one divalent group selected from the above group. Examples of the diamine to be obtained include 2,6-bis (aminomethyl) bicyclo [2,2,1] heptane, 2,5-bis (aminomethyl) bicyclo [2,2,1] heptane and the like.
These can be used alone or in combination of two or more.

R ² of the general formula (1) contains a diamine residue having no silicon atom and having an aromatic ring or an aliphatic ring, which is different from at least one divalent group selected from the above group. In this case, the content ratio is not particularly limited, but is preferably 30 mol% or less, preferably 20 mol% or less, of the total amount of R ² (100 mol%) from the viewpoint of surface hardness and light transmission. It is more preferably present, and even more preferably 10 mol% or less.

Further, the polyimide having the structure represented by the general formula (1) contains an aromatic ring and (i) fluorine from the viewpoint of improving the light transmittance and the surface hardness. A polyimide comprising at least one selected from the group consisting of an atom, (iii) an aliphatic ring, and (iii) a structure in which aromatic rings are linked to each other with a sulfonyl group or an alkylene group which may be substituted with fluorine. It is preferable to have. The polyimide having the structure represented by the general formula (1) has a rigid molecular skeleton by containing at least one selected from a tetracarboxylic acid residue having an aromatic ring and a diamine residue having an aromatic ring. The orientation is increased and the surface hardness is improved, but the rigid aromatic ring skeleton tends to have an absorption wavelength extending to a long wavelength, and the transmittance in the visible light region tends to decrease.
When (i) a fluorine atom is contained in the polyimide, the charge transfer in the electronic state in the polyimide skeleton can be made difficult, and the light transparency is improved.
When the polyimide contains (ii) an aliphatic ring, the light transmission is improved in that the transfer of charges in the skeleton can be inhibited by breaking the conjugation of π electrons in the polyimide skeleton.
When the polyimide contains a structure in which (iii) aromatic rings are linked to each other with an alkylene group which may be substituted with a sulfonyl group or fluorine, the transfer of charge in the skeleton is performed by breaking the conjugation of π electrons in the polyimide skeleton. Light transmission is improved in that it can be inhibited.

As the polyimide having the structure represented by the general formula (1), among them, the polyimide containing a fluorine atom is preferably used from the viewpoint of improving the light transmittance and the surface hardness.
As for the content ratio of fluorine atoms, the ratio (F / C) of the number of fluorine atoms (F) to the number of carbon atoms (C) measured on the polyimide surface by X-ray photoelectron spectroscopy is preferably 0.01 or more. Further, it is preferably 0.05 or more. On the other hand, if the content ratio of fluorine atoms is too high, the heat resistance inherent in polyimide may deteriorate. Therefore, the ratio (F / C) of the number of fluorine atoms (F) to the number of carbon atoms (C) is 1 or less. It is preferably 0.8 or less, and more preferably 0.8 or less.
Here, the above ratio measured by X-ray photoelectron spectroscopy (XPS) can be obtained from the value of atomic% of each atom measured using an X-ray photoelectron spectrometer (for example, Theta Probe of Thermo Scientific). ..

Further, the polyimide having the structure represented by the general formula (1) is aromatic when the total of R ¹ and R ² in the general formula (1) is 100 mol% from the viewpoint of improving the surface hardness. The total of the tetracarboxylic acid residue having a group ring and the diamine residue having an aromatic ring is preferably 50 mol% or more, more preferably 60 mol% or more, and more preferably 75 mol% or more. Even more preferable.

Further, the polyimide having the structure represented by the general formula (1) does not have a tetracarboxylic acid residue of R ¹ and a silicon atom of R ² and is aromatic because the surface hardness and light transmittance are improved. It is preferable that at least one of the diamine residues having a group ring or an aliphatic ring contains an aromatic ring and a fluorine atom, and further, it does not have a tetracarboxylic acid residue of R ¹ and a silicon atom of R ² . It is preferable that both the diamine residue having an aromatic ring or an aliphatic ring contains an aromatic ring and a fluorine atom.
The polyimide having the structure represented by the general formula (1) has an improved surface hardness and light transmittance, and when the total of R ¹ and R ² in the general formula (1) is 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. Even more preferably, it is 75 mol% or more.

Further, the polyimide having the structure represented by the general formula (1) is a polyimide in which 50% or more of hydrogen atoms bonded to carbon atoms contained in the polyimide are hydrogen atoms directly bonded to an aromatic ring. However, it is preferably used from the viewpoints of improving light transmission and surface hardness, and dynamic bending resistance. The ratio of the hydrogen atoms (number) directly bonded to the aromatic ring to the total hydrogen atoms (number) bonded to the carbon atoms contained in the polyimide is further preferably 60% or more, preferably 70% or more. Is more preferable.
When 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide are polyimides, which are hydrogen atoms directly bonded to the aromatic ring, the polyimide is stretched at, for example, 200 ° C. or higher even after being heated in the atmosphere. However, it is preferable from the viewpoint that the optical characteristics, particularly the change in the total light transmittance and the yellowness YI value is small, and the decrease in the dynamic bending resistance are suppressed. When 50% or more of the hydrogen atoms bonded to the carbon atoms contained in the polyimide are polyimides, which are hydrogen atoms directly bonded to the aromatic ring, the reactivity with oxygen is low, so that the chemical structure of the polyimide changes. It is difficult to do so, and it is presumed that deterioration of the polyimide film due to oxidation is suppressed. Polyimide film is often used for devices that require a processing process that involves heating due to its high heat resistance, but 50% or more of the hydrogen atoms bonded to carbon atoms contained in polyimide are in the aromatic ring. In the case of polyimide, which is a hydrogen atom to be directly bonded, it is not necessary to carry out these subsequent steps in an inert atmosphere in order to maintain transparency, so there is an advantage that equipment costs and costs for atmosphere control can be suppressed. There is.
Here, the ratio of the hydrogen atoms (number) directly bonded to the aromatic ring to the total hydrogen atoms (number) bonded to the carbon atoms contained in the polyimide is the mass of the decomposition product of polyimide by high performance liquid chromatography or gas chromatograph. It can be determined using an analyzer and NMR. For example, the sample is decomposed with an alkaline aqueous solution or supercritical methanol, the obtained decomposition product is separated by high performance liquid chromatography, and the qualitative analysis of each separated peak is performed by a gas chromatograph mass spectrometer, NMR, etc. The ratio of hydrogen atoms (number) directly bonded to the aromatic ring can be determined from the total hydrogen atoms (number) contained in the polyimide by performing the test using high performance liquid chromatography and quantifying the amount.

In the structure represented by the general formula (1), n represents the number of repeating units and is 1 or more.
The number of repeating units n in the polyimide may be appropriately selected depending on the structure so as to indicate a preferable glass transition temperature described later, and is not particularly limited.
The average number of repeating units is usually 10 to 2000, and more preferably 15 to 1000.

The polyimide used in the present invention may contain one or more types of polyimide having a structure represented by the general formula (1).
Further, the polyimide used in the present invention may have a structure different from the structure represented by the general formula (1) in a part thereof as long as the effect of the present invention is not impaired. In the polyimide used in the present invention, the structure represented by the general formula (1) is preferably 95% or more, more preferably 98% or more, and 100% of the total number of repeating units of the polyimide. It is even more preferable to have.
Examples of the structure different from the structure represented by the general formula (1) include a case where a tetracarboxylic acid residue having no aromatic ring or an aliphatic ring is contained, and a polyamide structure.
Examples of the polyamide structure that may be contained include a polyamide-imide structure containing a tricarboxylic acid residue such as trimellitic acid anhydride and a polyamide structure containing a dicarboxylic acid residue such as terephthalic acid.

The polyimide used in the polyimide film of the present invention and the polyimide of the present invention preferably have a weight average molecular weight of 35,000 or more from the viewpoint of dynamic bending resistance of the polyimide film, and more preferably 40,000 or more. , 50,000 or more is even more preferable, and 80,000 or more is particularly preferable. If the weight average molecular weight of the polyimide is less than the lower limit, the strength of the polyimide film may decrease, and the polyimide film may be easily deformed or broken due to repeated bending. The upper limit of the weight average molecular weight of the polyimide used in the polyimide film of the present invention is not particularly limited, but is usually 10000000 or less.
The weight average molecular weight of the polyimide can be measured by gel permeation chromatography (GPC) using a polyimide film or a solution in which polyimide is dissolved. Specifically, the polyimide film of the present invention or a test piece obtained by collecting 13 to 15 mg of the polyimide of the present invention is immersed in 6 mL of N-methylpyrrolidone (NMP) and heated to 60 ° C. in a water bath while heating the stirrer. The NMP solution in which the polyimide is dissolved is obtained by stirring at a rotation speed of 200 rpm for 3 to 60 hours until the dissolution is visually confirmed. The weight average molecular weight is measured by GPC using the obtained NMP solution. In GPC, a 10 mmol% LiBr-NMP solution having a water content of 500 ppm or less was used as the developing solvent, and a Tosoh GPC device (HLC-8120, column used: GPC LF-804 manufactured by SHODEX) was used, the sample injection amount was 50 μL, and the solvent flow rate. The measurement is performed under the conditions of 0.5 mL / min and 40 ° C. The weight average molecular weight is determined based on a polystyrene standard sample having the same concentration as the sample.
As the polyimide used in the polyimide film of the present invention, a polyimide that does not dissolve in NMP is also preferable from the viewpoint of dynamic bending resistance. That is, the polyimide used in the polyimide film of the present invention is one or more selected from the group consisting of polyimides that are soluble in NMP and have a weight average molecular weight of the lower limit or more, and polyimides that are insoluble in NMP. This is preferable from the viewpoint of dynamic bending resistance. Here, whether it is soluble or insoluble in NMP can be determined by dissolving a polyimide film or polyimide in NMP by the same method as the method for preparing an NMP solution in the above-mentioned GPC measuring method. A polyimide that does not dissolve in a solvent can suppress a decrease in the strength of the polyimide film, and therefore tends to make it difficult for the film to be deformed or broken due to repeated bending.

Further, the polyimide used in the present invention preferably has a glass transition temperature in a temperature range of 150 ° C. or higher and 400 ° C. or lower. When the glass transition temperature is 150 ° C. or higher, the heat resistance is excellent, more preferably 200 ° C. or higher, and even more preferably 250 ° C. or higher. Further, when the glass transition temperature is 400 ° C. or lower, the baking temperature can be reduced, and more preferably 380 ° C. or lower.
Further, the polyimide used in the present invention preferably does not have a peak of the tan δ curve in a temperature region of −150 ° C. or higher and 0 ° C. or lower, whereby the surface hardness of the polyimide film at room temperature can be improved. Further, the polyimide used in the present invention may further have a peak of the tan δ curve in a temperature region exceeding 0 ° C. and lower than 150 ° C.
The glass transition temperature of the polyimide used in the present invention is obtained from the peak temperature of the temperature-tan δ (tan δ = loss elastic modulus (E ″) / storage elastic modulus (E ′)) curve obtained by dynamic viscoelasticity measurement. It is a thing. The glass transition temperature of polyimide means the temperature of the peak at which the maximum value of the peak is the maximum when there are a plurality of peaks of the tan δ curve. As the dynamic viscoelasticity measurement, for example, the dynamic viscoelasticity measuring device RSA III (TA Instrument Japan Co., Ltd.) sets the measurement range to -150 ° C to 400 ° C, and raises the temperature at a frequency of 1 Hz. It can be performed at a speed of 5 ° C./min. Further, the sample width can be measured as 5 mm and the distance between chucks as 20 mm.
In the present invention, the peak of the tan δ curve has an inflection point which is a maximum value, and the peak width between the valleys of the peak is 3 ° C. or more, which is derived from the measurement of noise and the like. Small vertical fluctuations are not interpreted as the peak.

2. 2. Additives The polyimide film of the present invention may further contain additives, if necessary, in addition to the polyimide. Examples of the additive include inorganic particles, a silica filler for facilitating winding, a surfactant for improving film forming property and defoaming property, and the like.

3. 3. Characteristics of Polyimide Film The polyimide film of the present invention preferably has a total light transmittance of 85% or more as measured in accordance with JIS K7361-1. When the transmittance is high, the transparency becomes good, and it can be suitably used as a glass substitute material. The total light transmittance of the polyimide film of the present invention measured in accordance with JIS K7361-1 is preferably 88% or more, more preferably 89% or more, and particularly 90% or more. Is preferable.
The polyimide film of the present invention has a thickness of 5 μm or more and 100 μm or less, and the total light transmittance measured in accordance with JIS K7361-1 is preferably 85% or more, more preferably 88% or more. Further, it is preferably 89% or more, and particularly preferably 90% or more.
Further, the polyimide film of the present invention has a thickness of 55 μm ± 5 μm, and the total light transmittance measured according to the JIS K7361-1 is preferably 85% or more, more preferably 88% or more. , More preferably 89% or more, and particularly preferably 90% or more.
The total light transmittance measured according to JIS K7361-1 can be measured by, for example, a haze meter (for example, HM150 manufactured by Murakami Color Technology Laboratory). From the measured value of the total light transmittance of a certain thickness, the converted value of the total light transmittance of different thickness can be obtained by Lambertbert's law, and it can be used.

Further, the polyimide film of the present invention preferably has a yellowness (YI value) of 20.0 or less calculated in accordance with the JIS K7373-2006. When the degree of yellowness is low, yellowish coloring is suppressed, light transmission is improved, and it can be suitably used as a glass substitute material. The yellowness (YI value) calculated in accordance with JIS K7373-2006 is preferably 11.0 or less, more preferably 7.0 or less, and preferably 5.0 or less. More preferably, it is more preferably 4.0 or less, and particularly preferably 3.0 or less.
The polyimide film of the present invention preferably has a thickness of 5 μm or more and 100 μm or less and a yellowness (YI value) of 20.0 or less, which is calculated in accordance with JIS K7373-2006, preferably 11.0 or less. Is more preferably 7.0 or less, further preferably 5.0 or less, particularly preferably 4.0 or less, and most preferably 3.0 or less.
Further, the polyimide film of the present invention has a thickness of 55 μm ± 5 μm, and the yellowness (YI value) calculated in accordance with the JIS K7373-2006 is preferably 20.0 or less, preferably 11.0 or less. It is more preferably 7.0 or less, further preferably 5.0 or less, particularly preferably 4.0 or less, and most preferably 3.0 or less. ..
The yellowness (YI value) is measured by a spectrophotometer specified in JIS Z8722 using an ultraviolet-visible near-infrared spectrophotometer (for example, JASCO Corporation V-7100) in accordance with JIS K7373-2006. It can be calculated based on the transmittance measured by the color method.
From the measured value of the yellowness of a certain thickness, the yellowness of a different thickness is the above-mentioned total for each transmittance at each wavelength measured at 5 nm intervals between 380 nm and 780 nm of a sample of a specific film thickness. Similar to the light transmittance, the converted value of each transmittance at each wavelength having a different thickness can be obtained by Lambertvale's law, and can be calculated and used based on the converted value.

Further, the polyimide film of the present invention suppresses yellowish coloring, improves light transmission, and can be suitably used as a glass substitute material. Therefore, the yellow color calculated in accordance with JIS K7373-2006. The value (YI value / film thickness (μm)) obtained by dividing the degree (YI value) by the film thickness (μm) is preferably 0.04 or less, and more preferably 0.03 or less.
In the present invention, the value (YI value / film thickness (μm)) obtained by dividing the yellowness (YI value) by the film thickness (μm) is placed in the second decimal place in accordance with Rule B of JIS Z8401: 1999. Rounded value.

Further, the polyimide film of the present invention preferably has a glass transition temperature in a temperature range of 150 ° C. or higher and 400 ° C. or lower. The temperature region having the glass transition temperature is more preferably 200 ° C. or higher, further preferably 250 ° C. or higher, and 380 from the viewpoint of being able to reduce the baking temperature, from the viewpoint of excellent heat resistance. More preferably, it is below ° C.
Further, it is preferable that the polyimide film of the present invention does not have a peak of the tan δ curve in a temperature region of −150 ° C. or higher and 0 ° C. or lower. When the main chain has a diamine residue having a long siloxane bond, it may have a peak of the tanδ curve in such a low temperature region, but the silicon atom-containing diamine residue used in the present invention contains a silicon atom. Since it is a short bond with one or two, it usually does not have a peak of the tanδ curve in such a low temperature region. Maintaining sufficient surface hardness as a protective film as compared with a polyimide film having a diamine residue having a long siloxane bond in the main chain, which has a peak of the tanδ curve in the temperature range of −150 ° C. or higher and 0 ° C. or lower. Can be done.
The glass transition temperature can be measured in the same manner as the glass transition temperature of the polyimide described above.

Further, the polyimide film of the present invention has a tensile elastic modulus of 0.8 GPa or more at 25 ° C., which is measured by measuring a 15 mm × 40 mm test piece in accordance with JIS K7127 with a tensile speed of 8 mm / min and a distance between chucks of 20 mm. It is preferably .2 GPa or less from the viewpoint of dynamic bending resistance and surface hardness, more preferably 1.3 GPa or more and 5.0 GPa or less, and more preferably 1.8 GPa or more and 4.5 GPa or less. , 2.0 GPa or more and 4.0 GPa or less is more preferable. When the polyimide film of the present invention has a low tensile modulus because the molecular chains are packed together by containing a specific amount of at least one divalent group selected from the above group as a diamine residue in the polyimide. Even so, it is presumed that the decrease in surface hardness can be suppressed.
The tensile elastic modulus was determined by cutting a test piece having a width of 15 mm and a length of 40 mm from a polyimide film using a tensile tester (for example, manufactured by Shimadzu Corporation: Autograph AG-X 1N, load cell: SBL-1KN) and at 25 ° C. The tensile speed can be measured as 8 mm / min, and the distance between chucks can be measured as 20 mm. The thickness of the polyimide film used to determine the tensile elastic modulus is preferably 55 μm ± 5 μm.

Further, in the polyimide film of the present invention, the birefringence in the thickness direction at a wavelength of 590 nm is preferably 0.040 or less, more preferably 0.020 or less, and further preferably 0.020 or less, from the viewpoint of reducing optical distortion. It is preferably 0.015 or less, more preferably 0.010 or less, and even more preferably less than 0.008. If the polyimide film of the present invention has reduced optical distortion, it is possible to suppress deterioration of the display quality of the display when the polyimide film of the present invention is used as a surface material for a display. Further, when a film having a birefringence index of more than 0.040 in the thickness direction at a wavelength of 590 nm is placed on the display surface and the display is viewed with polarized sunglasses, rainbow unevenness may occur and the visibility may be deteriorated. be. On the other hand, when the birefringence in the thickness direction of the film installed on the surface of the display is 0.040 or less, the occurrence of rainbow unevenness when the display is viewed with polarized sunglasses is suppressed. Further, when the birefringence in the thickness direction of the film installed on the display surface is 0.020 or less, the color reproducibility when the display is viewed from an angle is improved.
The birefringence in the thickness direction of the polyimide film of the present invention at a wavelength of 590 nm can be determined as follows.
First, the thickness direction retardation value (Rth) of the polyimide film is measured with light at 25 ° C. and a wavelength of 590 nm using a phase difference measuring device (for example, manufactured by Oji Measuring Instruments Co., Ltd., product name “KOBRA-WR”). do. For the thickness direction retardation value (Rth), the phase difference value incident at 0 degrees and the phase difference value incident at an angle of 40 degrees are measured, and the thickness direction retardation value Rth is calculated from these phase difference values. The retardation value of the oblique 40-degree incident is measured by injecting light having a wavelength of 590 nm onto the retardation film from a direction inclined by 40 degrees from the normal of the retardation film.
The birefringence in the thickness direction of the polyimide film can be obtained by substituting it into the formula: Rth / d. The d represents the film thickness (nm) of the polyimide film.
The thickness direction retardation value is nx for the refractive index in the slow-phase axial direction (the direction in which the refractive index is maximized in the in-plane direction of the film) in the in-plane direction of the film, and the phase-advancing axial direction (the film surface) in the film surface. When the refractive index in the inward direction (the direction in which the refractive index is minimized) is ny and the refractive index in the thickness direction of the film is nz, it is expressed as Rth [nm] = {(nx + ny) /2-nz} × d. be able to.

Further, in the polyimide film of the present invention, the arithmetic average roughness Ra measured according to JIS B0601 on at least one surface is preferably 100 nm or less, more preferably 90 nm or less, and more preferably 80 nm or less. Is even more preferable. When the arithmetic average roughness Ra is not more than the upper limit value, it is possible to prevent a decrease in the transparency of the film, and when the polyimide film of the present invention is used as a surface material for a display, the arithmetic average roughness The visibility of the display can be improved by arranging the surface whose Ra is equal to or less than the upper limit value so as to be on the side to be visually recognized. It is particularly preferable that the arithmetic average roughness Ra on at least one surface of the polyimide film of the present invention is 2.0 or less from the viewpoint of improving the visibility of the display.

In the polyimide film of the present invention, the pencil hardness is preferably 2B or more, more preferably B or more, and even more preferably HB or more.
The pencil hardness of the polyimide film is determined by adjusting the humidity of the measurement sample for 2 hours under the conditions of a temperature of 25 ° C. and a relative humidity of 60%, and then using a test pencil specified by JIS-S-6006, JIS K5600-5-4. It can be performed by performing a pencil hardness test (0.98 N load) specified in (1999) on the film surface and evaluating the highest pencil hardness that does not damage the film. As the testing machine, for example, a pencil scratch coating film hardness testing machine manufactured by Toyo Seiki Co., Ltd. can be used.

The haze value of the polyimide film of the present invention is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.0 or less from the viewpoint of light transmission. It is preferable that the haze value can be achieved when the thickness of the polyimide film is 5 μm or more and 100 μm or less.
The haze value can be measured by a method according to JIS K-7105, and can be measured by, for example, a haze meter HM150 manufactured by Murakami Color Technology Laboratory.

Further, in the polyimide film of the present invention, the number of times until the polyimide film breaks exceeds 100,000 times when the dynamic bending test is performed according to the following dynamic bending test method because of its excellent dynamic bending resistance. It is preferably 150,000 times or more, more preferably 180,000 times or more, and particularly preferably 200,000 times or more.
[Dynamic bending test method]
The test piece of the polyimide film cut out to a size of 20 mm × 100 mm is fixed to the endurance test system in a constant temperature and humidity chamber (manufactured by Yuasa System Equipment, planar body no-load U-shaped expansion and contraction test jig DMX-FS) with tape. .. Further, the test piece is folded at the position of half of the long side, and the distance between both ends of the long side of the folded test piece is 6 mm, and the bent portion of the test piece is folded so that the radius of curvature is 3 mm. Set the state. After that, in an environment of 60 ± 2 ° C. and 93 ± 2% relative humidity (RH), changing from a flat open state to the folded state is regarded as one bending, and the number of bendings is 90 times per minute. Bending is repeated until it breaks, and the number of bendings until the test piece breaks is measured.

Further, the atomic% of the silicon atom (Si) on the surface of the film measured by X-ray photoelectron spectroscopy of the polyimide film is preferably 0.1 or more and 10 or less, and more preferably 0.2 or more and 5 or less.
Here, the above ratio measured by X-ray photoelectron spectroscopy (XPS) can be obtained from the value of atomic% of each atom measured using an X-ray photoelectron spectrometer (for example, Theta Probe of Thermo Scientific). ..

In a preferred embodiment, the ratio (F / C) of the number of fluorine atoms (F) to the number of carbon atoms (C) on the surface of the film measured by X-ray photoelectron spectroscopy of the polyimide film is 0.01 or more and 1 or less. It is preferably 0.05 or more and 0.8 or less.
Further, the ratio (F / N) of the number of fluorine atoms (F) to the number of nitrogen atoms (N) on the film surface measured by X-ray photoelectron spectroscopy of the polyimide film is preferably 0.1 or more and 20 or less. Further, it is preferably 0.5 or more and 15 or less.
Further, the ratio (F / Si) of the number of fluorine atoms (F) to the number of silicon atoms (Si) on the surface of the film as measured by X-ray photoelectron spectroscopy of the polyimide film is preferably 1 or more and 50 or less, and more preferably. It is preferably 3 or more and 30 or less. Within these ranges, the adhesion when forming the functional layer on the surface of the polyimide film or polyimide of the present invention is improved.

4. Structure of Polyimide Film The thickness of the polyimide film of the present invention may be appropriately selected depending on the intended use, but from the viewpoint of strength, it is preferably 1 μm or more, more preferably 5 μm or more, still more preferably 10 μm or more. Is preferable. On the other hand, from the viewpoint of bending resistance, the thickness of the polyimide film is preferably 200 μm or less, more preferably 150 μm or less, and further preferably 100 μm or less. If the film is thick, the difference between the inner diameter and the outer diameter at the time of bending becomes large, and the load on the film becomes large, so that the bending resistance tends to decrease. However, the polyimide film of the present invention has a large thickness. It is possible to improve the dynamic bending resistance, and in particular, when the thickness is 30 μm or more and 100 μm or less, the effect of improving the dynamic bending resistance is high.

Further, the polyimide film of the present invention may be subjected to surface treatment such as saponification treatment, glow discharge treatment, corona discharge treatment, ultraviolet treatment, and flame treatment.

5. Method for manufacturing polyimide film As the method for manufacturing the polyimide film of the present invention, for example, as the first manufacturing method,
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 a polyimide precursor resin composition preparation step).
A step of applying the polyimide precursor resin composition to a support to form a polyimide precursor resin coating film (hereinafter referred to as a polyimide precursor resin coating film forming step).
Examples of the method for producing a polyimide film include a step of imidizing the polyimide precursor by heating (hereinafter referred to as an imidization step).

（一般式（１’）において、Ｒ^１、Ｒ^２及びｎは、前記一般式（１）と同様である。）

(In the general formula (1'), R ¹ , R ² and n are the same as those in the general formula (1).)

In the first manufacturing method, a step of further stretching at least one of the polyimide precursor resin coating film and the imidized coating film obtained by imidizing the polyimide precursor resin coating film (hereinafter referred to as a stretching step). ) May have.
Hereinafter, each step will be described in detail.

(1) Polyimide precursor resin composition preparation step The polyimide precursor resin composition prepared in the first production method includes a polyimide precursor having a structure represented by the general formula (1') and an organic solvent. May be contained, and if necessary, an additive or the like may be contained.

<Polyimide precursor>
The polyimide precursor of the present invention suitable for producing the polyimide film to the polyimide of the present invention is a polyimide precursor having a structure represented by the general formula (1').
The polyimide precursor having the structure represented by the general formula (1') has a tetracarboxylic acid component which is a tetracarboxylic acid residue in ^R1 of the general formula (1') and the general formula (1'). It is a polyamic acid obtained by polymerization with a diamine component which becomes a diamine residue in ^R2 .
Here, as ^R1 , ^R2 , and n of the general formula (1'), the same ones as ^R1 , ^R2 , and n of the general formula (1) described in the polyimide can be used.

The polyimide precursor having the structure represented by the general formula (1') preferably has a number average molecular weight of 10,000 or more, preferably 20,000 or more, from the viewpoint of strength and dynamic bending resistance when formed into a film. It is more preferably 30,000 or more, further preferably 50,000 or more, and particularly preferably 50,000 or more. On the other hand, if the number average molecular weight is too large, the viscosity becomes high and workability such as filtration may be deteriorated. Therefore, it is preferably 10,000,000 or less, and more preferably 500,000 or less.
The number average molecular weight of the polyimide precursor can be determined by NMR (for example, manufactured by BRUKER, AVANCE III). For example, a polyimide precursor solution is applied to a glass plate and dried at 100 ° C. for 5 minutes, then 10 mg of solid content is dissolved in 7.5 ml of a dimethyl sulfoxide-d6 solvent, NMR measurement is performed, and the mixture is bonded to an aromatic ring. The number average molecular weight can be calculated from the peak intensity ratio of hydrogen atoms.

Further, the polyimide precursor having the structure represented by the general formula (1') preferably has a weight average molecular weight of 20,000 or more, preferably 30,000, from the viewpoint of strength and dynamic bending resistance when formed into a film. The above is more preferable, 40,000 or more is further preferable, and 80,000 or more is particularly preferable. On the other hand, if the weight average molecular weight is too large, the viscosity becomes high and the workability such as filtration may be deteriorated. Therefore, it is preferably 10,000,000 or less, and more preferably 500,000 or less.
The weight average molecular weight of the polyimide precursor can be measured by gel permeation chromatography (GPC). Specifically, the polyimide precursor is a N-methylpyrrolidone (NMP) solution having a concentration of 0.5% by weight, and the developing solvent is a 10 mmol% LiBr-NMP solution having a water content of 500 ppm or less. Using HLC-8120, column used: GPC LF-804 manufactured by SHODEX, measurement is performed under the conditions of a sample injection amount of 50 μL, a solvent flow rate of 0.5 mL / min, and 40 ° C. The weight average molecular weight is determined based on a polystyrene standard sample having the same concentration as the sample.

The polyimide precursor solution is obtained by reacting the above-mentioned tetracarboxylic dianhydride with the above-mentioned diamine in a solvent. The solvent used for synthesizing the polyimide precursor (polyamic acid) is not particularly limited as long as the above-mentioned tetracarboxylic acid dianhydride and diamine can be dissolved, and for example, an aprotonic polar solvent or a water-soluble alcohol-based solvent can be used. Can be used. In the present invention, among others, N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, 1,3-dimethyl-2-imidazolidinone, etc. It is preferable to use an organic solvent containing a nitrogen atom; γ-butyrolactone or the like. Above all, when the polyimide precursor solution (polyamide acid solution) is used as it is for the preparation of the polyimide precursor resin composition, it is preferable to use an organic solvent containing a nitrogen atom, and above all, N, N-dimethylacetamide, N- It is preferable to use methyl-2-pyrrolidone or a combination thereof. The organic solvent is a solvent containing a carbon atom.

Further, the polyimide precursor solution is prepared by combining at least two kinds of diamines, but acid dianhydride may be added to a mixed solution of at least two kinds of diamines to synthesize polyamic acid, or at least. The two diamine components may be added stepwise to the reaction solution at an appropriate molar ratio to control the sequence in which each raw material is incorporated into the polymer chain to some extent.
For example, an acid dianhydride having a molar ratio of 0.5 equal to that of a diamine having one or two silicon atoms in the main chain in a reaction solution in which a diamine having one or two silicon atoms in the main chain is dissolved. Is added and reacted to synthesize an amic acid reacted with a diamine having one or two silicon atoms in the main chain at both ends of the acid dianhydride, and all or part of the remaining diamine is added thereto. Then, acid dianhydride may be added to polymerize the polyamic acid. When polymerized by this method, a diamine having one or two silicon atoms in the main chain is introduced into the polyamic acid in a linked form via one acid dianhydride.
By polymerizing the polyamic acid by such a method, the positional relationship of the amic acid having one or two silicon atoms in the main chain is specified to some extent, and it is easy to obtain a film having excellent bending resistance while maintaining the surface hardness. It is preferable from the point of view.

When the number of moles of diamine in the polyimide precursor solution (polyamide acid solution) is X and the number of moles of tetracarboxylic acid dianhydride is Y, Y / X may be 0.9 or more and 1.1 or less. It is 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. Within such a range, the molecular weight (degree of polymerization) of the polyamic acid obtained can be appropriately adjusted.
The procedure of the polymerization reaction can be appropriately selected and used by a known method, and is not particularly limited.
Further, the polyimide precursor solution obtained by the synthesis reaction may be used as it is, and other components may be mixed therewith, if necessary, or the solvent of the polyimide precursor solution is dried and dissolved in another solvent. You may use it.

The viscosity of the polyimide precursor solution at 25 ° C. is preferably 500 cps or more and 200,000 cps or less from the viewpoint of forming a uniform coating film and a polyimide film.
The viscosity of the polyimide precursor solution can be measured at 25 ° C. using a viscometer (for example, TVE-22HT, Toki Sangyo Co., Ltd.).

<Polyimide precursor resin composition>
As the polyimide precursor resin composition, the polyimide precursor solution may be used, or an additive may be contained if necessary. Examples of the additive include inorganic particles, a silica filler for facilitating winding, a surfactant for improving film forming property and defoaming property, and the like as described in the above-mentioned polyimide film. Similar ones can be used.

The organic solvent used in the polyimide precursor resin composition is not particularly limited as long as the polyimide precursor can be dissolved. For example, it contains nitrogen atoms such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, 1,3-dimethyl-2-imidazolidinone. Organic solvent; γ-butyrolactone and the like can be used, but among them, it is preferable to use an organic solvent containing a nitrogen atom for the above-mentioned reason.

The content of the polyimide precursor in the polyimide precursor resin composition is 50% by mass or more in the solid content of the resin composition from the viewpoint of forming a polyimide film having a uniform coating film and handleable strength. It is preferably 60% by mass or more, and the upper limit may be appropriately adjusted depending on the contained components.
The organic solvent in the polyimide precursor resin composition is preferably 40% by mass or more, and more preferably 50% by mass or more in the resin composition from the viewpoint of forming a uniform coating film and a polyimide film. It is preferable, and it is preferably 99% by mass or less.

Further, it is preferable that the water content of the polyimide precursor resin composition is 1000 ppm or less because the storage stability of the polyimide precursor resin composition is improved and the productivity can be improved. If the polyimide precursor resin composition contains a large amount of water, the polyimide precursor may be easily decomposed.
The water content of the polyimide precursor resin composition can be determined using a Karl Fischer Moisture Meter (for example, Mitsubishi Chemical Corporation, trace moisture measuring device CA-200 type).
As described above, in order to reduce the water content to 1000 ppm or less, it is preferable to dehydrate the organic solvent to be used, use a solvent having a controlled water content, and handle the solvent in an environment with a humidity of 5% or less.

The viscosity of the polyimide precursor resin composition at 25 ° C. is preferably 500 cps or more and 200,000 cps or less from the viewpoint of forming a uniform coating film and a polyimide film.
The viscosity of the polyimide precursor resin composition can be measured using a viscometer (for example, TVE-22HT, Toki Sangyo Co., Ltd.) at 25 ° C. with a sample volume of 0.8 ml.

(2) Polyimide precursor resin coating film forming step As a support used in the step of applying the polyimide precursor resin composition to a support to form a polyimide precursor resin coating film, the surface is smooth and heat resistant. There is no particular limitation as long as it is a material having properties and solvent resistance. For example, an inorganic material such as a glass plate, a metal plate whose surface is mirror-treated, and the like can be mentioned. The shape of the support is selected by the coating method, and may be, for example, a plate shape, a drum shape, a belt shape, a sheet shape that can be wound on a roll, or the like.

The coating means is not particularly limited as long as it can be coated with a desired film thickness, and for example, known ones such as a die coater, a comma coater, a roll coater, a gravure coater, a curtain coater, a spray coater, and a lip coater can be used. ..
The coating may be performed by a single-wafer coating device or a roll-to-roll coating device.

After applying the polyimide precursor resin composition to the support, the solvent in the coating film is dried at a temperature of 150 ° C. or lower, preferably 30 ° C. or higher and 120 ° C. or lower, until the coating film becomes tack-free. By setting the drying temperature of the solvent to 150 ° C. or lower, the imidization of the polyamic acid can be suppressed.

The drying time may be appropriately adjusted according to the film thickness of the polyimide precursor resin coating film, the type of solvent, the drying temperature, etc., but is usually 30 seconds to 240 minutes, preferably 1 minute to 180 minutes, more preferably. Is preferably 90 seconds to 120 minutes. If it exceeds the upper limit, it is not preferable from the viewpoint of the production efficiency of the polyimide film. On the other hand, if it is below the lower limit, the appearance of the obtained polyimide film may be affected by the rapid drying of the solvent.

The method for drying the solvent is not particularly limited as long as the solvent can be dried at the above temperature, and for example, an oven, a drying oven, a hot plate, infrared heating, or the like can be used.
When a high degree of control of optical properties is required, the atmosphere of the solvent when it is dried is preferably an inert gas atmosphere. The inert gas atmosphere is preferably a nitrogen atmosphere, preferably an oxygen concentration of 500 ppm or less, more preferably 100 ppm or less, and most preferably 50 ppm or less. Heat treatment in the atmosphere can oxidize the film, causing it to color or reduce its performance.

(3) Imidization Step In the first production method, the polyimide precursor is imidized by heating.
When the production method has a stretching step, the imidization step may be performed on the polyimide precursor in the polyimide precursor resin coating film before the stretching step, or the polyimide precursor resin after the stretching step. This may be performed on the polyimide precursor in the coating film, or on both the polyimide precursor in the polyimide precursor resin coating film before the stretching step and the polyimide precursor existing in the film after the stretching step. You may go.

The imidization temperature may be appropriately selected according to the structure of the polyimide precursor.
Usually, the temperature rise start temperature is preferably 30 ° C. or higher, and more preferably 100 ° C. or higher. On the other hand, the temperature rise end temperature is preferably 250 ° C. or higher.

The temperature rising rate is preferably appropriately selected depending on the film thickness of the obtained polyimide film, and when the film thickness of the polyimide film is thick, it is preferable to slow down the temperature rising rate.
From the viewpoint of the production efficiency of the polyimide film, the temperature is preferably 5 ° C./min or more, and more preferably 10 ° C./min or more. On the other hand, the upper limit of the temperature rising rate is usually 50 ° C./min, preferably 40 ° C./min or less, and more preferably 30 ° C./min or less. It is preferable to set the temperature rise rate from the viewpoints of suppressing poor appearance and decrease in strength of the film, controlling whitening due to the imidization reaction, and improving light transmission.

The temperature rise may be continuous or stepwise, but it is preferable to raise the temperature continuously from the viewpoints of suppressing poor appearance and strength deterioration of the film and controlling whitening associated with the imidization reaction. Further, the temperature rising rate may be constant or may be changed in the middle of the above-mentioned entire temperature range.

The atmosphere at the time of temperature rise of imidization is preferably an inert gas atmosphere. The inert gas atmosphere is preferably a nitrogen atmosphere, preferably an oxygen concentration of 500 ppm or less, more preferably 200 ppm or less, and even more preferably 100 ppm or less. Heat treatment in the atmosphere can oxidize the film, causing it to color or reduce its performance.
However, when 50% or more 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 an inert gas atmosphere is not used. A polyimide having high light transmittance can be obtained.

The heating method for imidization is not particularly limited as long as the temperature can be raised at the above temperature, and for example, an oven, a heating furnace, infrared heating, electromagnetic induction heating or the like can be used.

Above all, it is more preferable to set the imidization ratio of the polyimide precursor to 50% or more before the stretching step. By setting the imidization ratio to 50% or more before the stretching step, even when stretching is performed after the step and then heating is performed at a higher temperature for a certain period of time to perform imidization, the appearance of the film may be poor. Whitening is suppressed. Above all, from the viewpoint of improving the surface hardness of the polyimide film, it is preferable to set the imidization ratio to 80% or more, further to 90% or more, and further to 100% in the imidization step before the stretching step. Is preferable. It is presumed that the surface hardness is improved by stretching after imidization because the rigid polymer chains are easily oriented.
The imidization rate can be measured by analyzing the spectrum by infrared measurement (IR) or the like.

In order to obtain the final polyimide film, it is preferable to proceed the reaction to 90% or more, further 95% or more, and further 100% of imidization.
In order to allow the reaction to proceed to 90% or more and even 100% of imidization, it is preferable to keep the temperature at the end temperature for a certain period of time, and the holding time is usually 1 minute to 180 minutes, further 5 minutes to 150 minutes. It is preferably a minute.

(4) Stretching Step The first manufacturing method includes a stretching step of stretching at least one of the polyimide precursor resin coating film and the imidized coating film obtained by imidizing the polyimide precursor resin coating film. May be. When the stretching step is provided, it is particularly preferable to include a step of stretching the coating film after imidization from the viewpoint of improving the surface hardness of the polyimide film.

In the first production method, it is preferable to carry out the step of stretching 101% or more and 10000% or less when the initial dimension before carrying out stretching is 100%, while heating at 80 ° C. or higher.
The heating temperature during stretching is preferably in the range of the glass transition temperature of the polyimide or the polyimide precursor ± 50 ° C., and preferably in the range of the glass transition temperature ± 40 ° C. If the stretching temperature is too low, the film may not be deformed and sufficient orientation may not be induced. On the other hand, if the stretching temperature is too high, the orientation obtained by stretching may be relaxed by the temperature, and sufficient orientation may not be obtained.
The stretching step may be performed at the same time as the imidization step. Stretching the imidized coating film after imidization of 80% or more, further 90% or more, further 95% or more, particularly substantially 100% imidization improves the surface hardness of the polyimide film. It is preferable from the point of view.

The draw ratio of the polyimide film is preferably 101% or more and 10000% or less, and more preferably 101% or more and 500% or less. By stretching in the above range, the surface hardness of the obtained polyimide film can be further improved.

The method for fixing the polyimide film at the time of stretching is not particularly limited, and is selected according to the type of stretching device and the like. Further, the stretching method is not particularly limited, and it is possible to stretch while passing through a heating furnace by using a stretching device having a transporting device such as a tenter. The polyimide film may be stretched in only one direction (longitudinal stretching or transverse stretching), or may be stretched in two directions by simultaneous biaxial stretching, sequential biaxial stretching, diagonal stretching, or the like.

The first manufacturing method is preferable because it is easy to reduce the birefringence of the polyimide film. According to the first manufacturing method, a polyimide film having a birefringence in the thickness direction at a wavelength of 590 nm of 0.020 or less can be suitably formed. Further, according to the first manufacturing method, the total light transmittance measured according to JIS K7361-1 is 85% or more, and the yellowness calculated according to JIS K7373-2006 is 20. It is possible to suitably form a polyimide film having a glass transition temperature in a temperature region of 1.0 or less, 150 ° C. or more and 400 ° C. or less, and a birefringence in the thickness direction at a wavelength of 590 nm of 0.020 or less.

Further, as a method for producing the polyimide film of the present invention, as a second production method,
A step of preparing a polyimide resin composition containing a polyimide having a structure represented by the general formula (1) and an organic solvent (hereinafter referred to as a polyimide resin composition preparation step).
Examples thereof include a method for producing a polyimide film, which comprises a step of applying the polyimide resin composition to a support and drying a solvent to form a polyimide resin coating film (hereinafter referred to as a polyimide resin coating film forming step).

When the polyimide having the structure represented by the general formula (1) is satisfactorily dissolved in an organic solvent, the polyimide is dissolved in the organic solvent instead of the polyimide precursor resin composition, and an additive is required. A polyimide resin composition containing the above can also be preferably used.
When the polyimide having the structure represented by the general formula (1) has a solvent solubility such that it dissolves in an organic solvent at 25 ° C. in an amount of 5% by mass or more, the production method can be preferably used.

In the polyimide resin composition preparation step, as the polyimide having the structure represented by the general formula (1), the polyimide having the above-mentioned solvent solubility is selected from the same polyimides as described in the polyimide film. Can be used. As a method for imidization, chemical imidization performed by using a chemical imidizing agent is used instead of heat dehydration for the dehydration ring closure reaction of the polyimide precursor having the structure represented by the general formula (1'). Is preferable. When performing chemical imidization, known compounds such as amines such as pyridine and β-picolinic acid, carbodiimides such as dicyclohexylcarbodiimide, and acid anhydrides such as acetic anhydride may be used as the dehydration catalyst. The acid anhydride is not limited to acetic anhydride, and examples thereof include propionic acid anhydride, n-butyric acid anhydride, benzoic acid anhydride, and trifluoroacetic anhydride, but the acid anhydride is not particularly limited. At that time, a tertiary amine such as pyridine or β-picolinic acid may be used in combination. However, since these amines deteriorate the optical properties, especially the yellowness (YI value) when they remain in the film, the reaction solution reacted from the precursor to the polyimide is not cast as it is to form a film. It is preferable to purify by reprecipitation or the like to remove components other than polyimide to 100 ppm or less of the total weight of the polyimide before forming a film.

The organic solvent used in the reaction solution for chemically imidizing the polyimide precursor in the polyimide resin composition preparation step is, for example, the one described in the polyimide precursor resin composition preparation step in the first production method. Similar ones can be used. Examples of the organic solvent used for redissolving the polyimide purified from the reaction solution in the polyimide resin composition preparation step include ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, and ethylene glycol mono-normal-butyl ether. Ethylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, ortho-dichlorobenzene, xylene, cresol, chlorbenzene, isobutyl acetate, isopentyl acetate, normal-butyl acetate, normal-propyl acetate, normal-pentyl acetate, cyclohexanol, cyclohexanone, Examples thereof include 1.4-dioxane, tetrachloroethylene, toluene, methylisobutylketone, methylcyclohexanol, methylcyclohexanone, methyl-normal-butylketone, dichloromethane, dichloroethane and mixed solvents thereof, among which dichloromethane and normal-butyl acetate. , At least one selected from the group consisting of propylene glycol monomethyl ether acetate and a mixed solvent thereof can be preferably used.

The polyimide resin composition may contain an additive, if necessary. As the additive, the same additive as described in the polyimide precursor resin composition preparation step in the first production method can be used.
Further, in the second method, the method for setting the water content of the polyimide resin composition to 1000 ppm or less is the same as the method described in the polyimide precursor resin composition preparation step in the first production method. Can be used.

Further, in the polyimide resin coating film forming step of the second manufacturing method, the support and the coating method used are the same as those described in the polyimide precursor resin coating film forming step of the first manufacturing method. be able to.
In the polyimide resin coating film forming step in the second production method, the drying temperature is preferably 80 ° C. or higher and 150 ° C. or lower under normal pressure. Under reduced pressure, the temperature is preferably in the range of 10 ° C. or higher and 100 ° C. or lower.

Further, the second manufacturing method may include a stretching step of stretching the polyimide resin coating film after the polyimide resin coating film forming step. The stretching step can be the same as the stretching step in the first manufacturing method.

The second manufacturing method is preferable because it is easy to reduce the yellowness (YI value) of the polyimide film and it is easy to reduce the arithmetic average roughness Ra of at least one surface of the polyimide film. According to the second manufacturing method, it is possible to suitably form a polyimide film in which the value obtained by dividing the yellowness calculated according to JIS K7373-2006 by the film thickness (μm) is 0.04 or less. be. Further, according to the second manufacturing method, the total light transmittance measured according to JIS K7361-1 is 85% or more, and the yellowness calculated according to JIS K7373-2006 is determined by the film. The value divided by the thickness (μm) is 0.04 or less, the glass transition temperature is in the temperature region of 150 ° C. or higher and 400 ° C. or lower, and the double refractive index in the thickness direction at a wavelength of 590 nm is 0.040 or less. A polyimide film can be suitably formed.

6. Uses of Polyimide Film The use of the polyimide film of the present invention is not particularly limited, and it can be used as a member such as a base material or a surface material in which glass products such as thin flat glass have been conventionally used. Since the polyimide film of the present invention has improved dynamic bending resistance and has sufficient surface hardness as a protective film, it can be suitably used as a surface material for displays, and in particular, a surface for flexible displays. It can be suitably used as a material, and can also be suitably used as a surface material for a foldable display.
Further, specifically, the polyimide film of the present invention is a flexible panel used for, for example, a thin and bendable flexible type organic EL display, a mobile terminal such as a smartphone or a wristwatch type terminal, a display device inside an automobile, or a wristwatch. Etc., it can be suitably used. Further, the polyimide film of the present invention is a member for an image display device such as a liquid crystal display device or an organic EL display device, a member for a touch panel, a flexible printed substrate, a member for a solar cell panel such as a surface protective film or a substrate material, and an optical waveguide. It can also be applied to members and other semiconductor-related members.

II. Laminates The laminate of the present invention is a laminate having the above-mentioned polyimide film of the present invention and a hard coat layer containing at least one polymer of a radically polymerizable compound and a cationically polymerizable compound.
Since the laminate of the present invention uses the polyimide film of the present invention described above, it has improved dynamic bending resistance, and further has a hard coat layer, so that the surface hardness is further improved. ..

1. 1. Polyimide film As the polyimide film used for the laminate of the present invention, the above-mentioned polyimide film of the present invention can be used, and thus the description thereof is omitted here.

2. 2. Hard Coat Layer The hard coat layer used in the laminate of the present invention contains at least one polymer of a radically polymerizable compound and a cationically polymerizable compound.

(1) Radical polymerizable compound The radically polymerizable compound is a compound having a radically polymerizable group. The radically polymerizable group contained in the radically polymerizable compound may be any functional group capable of causing a radical polymerization reaction, and is not particularly limited, and examples thereof include a group containing a carbon-carbon unsaturated double bond. Specific examples thereof include a vinyl group and a (meth) acryloyl group. When the radically polymerizable compound has two or more radically polymerizable groups, these radically polymerizable groups may be the same or different from each other.

The number of radically polymerizable groups contained in one molecule of the radically polymerizable compound is preferably two or more, and more preferably three or more, from the viewpoint of improving the hardness of the hard coat layer.
As the radically polymerizable compound, a compound having a (meth) acryloyl group is preferable from the viewpoint of high reactivity, and further, (meth) acryloyl is preferable from the viewpoint of adhesion, light transmission and surface hardness. Compounds having two or more groups in one molecule are preferable. For example, a compound called a polyfunctional acrylate monomer having 2 to 6 (meth) acryloyl groups in one molecule, or a molecule called urethane (meth) acrylate, polyester (meth) acrylate, or epoxy (meth) acrylate. Monomers having a number of (meth) acryloyl groups within and having a molecular weight of several hundred to several thousand can be preferably used.
In addition, in this specification, (meth) acryloyl represents each of acryloyl and methacryloyl, and (meth) acrylate represents each of acrylate and methacrylate.

Specific examples of the radically polymerizable compound include vinyl compounds such as divinylbenzene; ethylene glycol di (meth) acrylate, bisphenol A epoxy di (meth) acrylate, and 9,9-bis [4- (2-(2-(. Meta) acryloyloxyethoxy) phenyl] fluorene, alkylene oxide-modified bisphenol A di (meth) acrylate (for example, ethoxylated (ethylene oxide modified) bisphenol A di (meth) acrylate), trimethyl propantri (meth) acrylate, tri Methylol ethanetri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate , Polyacrylate polyacrylates such as dipentaerythritol hexa (meth) acrylates, diacrylates such as bisphenol A diglycidyl ether diacrylates, epoxy acrylates such as hexanediol diglycidyl ether diacrylates, hydroxyl groups such as polyisocinates and hydroxyethyl acrylates. Examples thereof include urethane acrylate obtained by the reaction of the contained acrylate.

(2) Cationicly polymerizable compound The cationically polymerizable compound is a compound having a cationically polymerizable group. The cationically polymerizable group contained in the cationically polymerizable compound may be any functional group capable of causing a cationically polymerizable reaction, and is not particularly limited, and examples thereof include an epoxy group, an oxetanyl group, and a vinyl ether group. When the cationically polymerizable compound has two or more cationically polymerizable groups, these cationically polymerizable groups may be the same or different from each other.

The number of cationically polymerizable groups contained in one molecule of the cationically polymerizable compound is preferably two or more, and more preferably three or more, from the viewpoint of improving the hardness of the hard coat layer.
Further, as the cationically polymerizable compound, a compound having at least one of an epoxy group and an oxetanyl group as the cationically polymerizable group is preferable, and the epoxy group and the epoxy group and the surface hardness are considered from the viewpoint of adhesion, light transmission and surface hardness. A compound having at least one oxetanyl group at least two in one molecule is more preferable. A cyclic ether group such as an epoxy group or an oxetanyl group is preferable because the shrinkage associated with the polymerization reaction is small. Further, among the cyclic ether groups, compounds having an epoxy group are easily available, compounds having various structures are easily available, the durability of the obtained hard coat layer is not adversely affected, and compatibility with radically polymerizable compounds is easily controlled. There is an advantage. Of the cyclic ether groups, the oxetanyl group has a higher degree of polymerization than the epoxy group and has low toxicity, and when the obtained hard coat layer is combined with a compound having an epoxy group, the cation in the coating film There are advantages such as accelerating the network formation rate obtained from the polymerizable compound and forming an independent network without leaving an unreacted monomer in the film even in a region mixed with the radically polymerizable compound.

Examples of the cationically polymerizable compound having an epoxy group include polyglycidyl ether of a polyhydric alcohol having an alicyclic ring, or a cyclohexene ring or cyclopentene ring-containing compound with an appropriate oxidizing agent such as hydrogen peroxide or peracid. Alicyclic epoxy resin obtained by epoxidation; polyglycidyl ether of aliphatic polyhydric alcohol or its alkylene oxide adduct, polyglycidyl ester of aliphatic long chain polybasic acid, homopolymer of glycidyl (meth) acrylate, An aliphatic epoxy resin such as a copolymer; a glycidyl ether produced by reacting bisphenols such as bisphenol A, bisphenol F and hydrogenated bisphenol A, or derivatives such as alkylene oxide adducts and caprolactone adducts thereof with epichlorohydrin. And novolak epoxy resin and the like, and examples thereof include glycidyl ether type epoxy resin derived from bisphenols.

Examples of the alicyclic epoxy resin include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate (UVR-6105, UVR-6107, UVR-6110) and bis-3,4-epoxycyclohexylmethyl adipate. (UVR-6128) (The above is the trade name in parentheses and is manufactured by Dow Chemical Co., Ltd.).

Examples of the glycidyl ether type epoxy resin include sorbitol polyglycidyl ether (Denacol EX-611, Denacol EX-612, Denacol EX-614, Denacol EX-614B, Denacol EX-622) and polyglycerol polyglycidyl ether (Denacol EX). -512, Denacol EX-521), Pentaeryth Little Polyglycidyl Ether (Denacol EX-411), Diglycerol Polyglycidyl Ether (Denacol EX-421), Gglycerol Polyglycidyl Ether (Denacol EX-313, Denacol EX-314), Trimethylol Propanepolyglycidyl Ether (Denacol EX-321), Resoltinol Diglycidyl Ether (Denacol EX-201), Neopentyl Glycol Diglycidyl Ether (Denacol EX-211), 1,6 Hexanodiol Diglycidyl Ether (Denacol EX-) 212), Hydrodibisphenol 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), phenylglycidyl ether (Denacol EX-141), phenol glycidyl ether (Denacol EX-145), butylphenyl glycidyl ether (Denacol EX-146), diglycidyl phthalate (Denacol EX-721), hydroquinone diglycidyl ether (Denacol EX-203), Diglycidyl terephthalate (Denacol EX-711), Glycidyl phthalimide (Denacol EX-731), Dibromophenyl glycidyl ether (Denacol EX-147), Dibromoneopentyl glycol diglycidyl ether (Denacol EX-221) (The above is the product name in parentheses and is made by Nagase Chemtex.)

Other commercially available epoxy resins include Epicoat 825, Epicoat 827, Epicoat 828, Epicoat 828EL, Epicoat 828XA, Epicoat 834, Epicoat 801 and Epicoat 801P, Epicoat 802, Epicoat 815, Epicoat 815XA, and Epicoat 816A. Epicoat 819, Epicoat 834X90, Epicoat 1001B80, Epicoat 1001X70, Epicoat 1001X75, Epicoat 1001T75, Epicoat 806, Epicoat 806P, Epicoat 807, Epicoat 152, Epicoat 154, Epicoat 871, Epicoat 191P, Epicoat YX310, Epicoat DX255, Epicoat YX8000 Etc. (The above product name is made by Japan Epoxy Resin).

Examples of the cationically polymerizable compound having an oxetanyl group include 3-ethyl-3-hydroxymethyloxetane (OXT-101) and 1,4-bis-3-ethyloxetane-3-ylmethoxymethylbenzene (OXT-121). , Bis-1-ethyl-3-oxetanylmethyl ether (OXT-221), 3-ethyl-3--2-ethylhexyloxymethyloxetane (OXT-212), 3-ethyl-3-phenoxymethyloxetane (OXT-) 211) (The product name in parentheses is the product name of Toa Synthetic), and the product names include Ethanacole EHO, Ethanacole OXBP, Ethanacole OXTP, and Ethanacole OXMA (trade name, manufactured by Ube Kosan).

(3) Polymerization Initiator The polymer of at least one of the radically polymerizable compound and the cationically polymerizable compound contained in the hard coat layer used in the present invention is, for example, the radically polymerizable compound and the cationically polymerizable compound. It can be obtained by adding a polymerization initiator to at least one kind, if necessary, and carrying out a polymerization reaction by a known method.

As the polymerization initiator, a radical polymerization initiator, a cationic polymerization initiator, a radical, a cationic polymerization initiator and the like 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 promote radical polymerization and cation polymerization.

The radical polymerization initiator may be any kind as long as it can release a substance that initiates radical polymerization by at least one of light irradiation and heating. For example, examples of the photoradical polymerization initiator include imidazole derivatives, bisimidazole derivatives, N-arylglycine derivatives, organic azide compounds, titanocenes, aluminate complexes, organic peroxides, N-alkoxypyridinium salts, thioxanthone derivatives and the like. More specifically, 1,3-di (tert-butyldioxycarbonyl) benzophenone, 3,3', 4,4'-tetrakis (tert-butyldioxycarbonyl) benzophenone, 3-phenyl-5-. Isooxazolone, 2-mercaptobenzimidazole, bis (2,4,5-triphenyl) imidazole, 2,2-dimethoxy-1,2-diphenylethan-1-one (trade name: Irgacure 651, Ciba Japan Co., Ltd.) , 1-Hydroxy-cyclohexyl-phenyl-ketone (trade name: Irgacure 184, manufactured by Ciba Japan Co., Ltd.), 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butane-1- On (trade name: Irgacure 369, manufactured by Ciba Japan Co., Ltd.), bis (η5-2,4-cyclopentadiene-1-yl) -bis (2,6-difluoro-3- (1H-pyrrole-1-yl) ) -Phenyl) Titanium) (trade name: Irgacure 784, manufactured by Ciba Japan Co., Ltd.), etc., but is not limited thereto.

In addition to the above, commercially available products can be used, specifically, Irgacure 907, Irgacure 379, Irgacure 819, Irgacure 127, Irgacure 500, Irgacure 754, Irgacure 250, Irgacure 1800, Irgacure 1870 manufactured by Ciba Japan Co., Ltd. , Irgacure OXE01, DAROCUR TPO, DAROCUR1173, Japan Siber Hegner Co., Ltd. of SpeedcureMBB, SpeedcurePBZ, SpeedcureITX, SpeedcureCTX, SpeedcureEDB, Esacure ONE, Esacure KIP150, Esacure KTO46, manufactured by Nippon Kayaku Co., of (stock) KAYACURE DETX-S, KAYACURE CTX , KAYACURE BMS, KAYACURE DMBI and the like.

Further, the cationic polymerization initiator may be any material as long as it 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 ester, imide sulfonate, dialkyl-4-hydroxysulfonium salt, aryl sulfonic acid-p-nitrobenzyl ester, silanol-aluminum complex, (η ⁶ -benzene) (η ⁵ -cyclopentadi). Enyl) iron (II) and the like are exemplified, and more specific examples thereof include, but are not limited to, benzointosilate, 2,5-dinitrobenzyltosylate, N-tosiphthalateimide and the like.

Examples of the agent used as both the radical polymerization initiator and the cationic polymerization initiator include aromatic iodonium salts, aromatic sulfonium salts, aromatic diazonium salts, aromatic phosphonium salts, triazine compounds, iron arene complexes and the like. More specifically, chloride, bromide, borofluoride salt, hexafluorophosphate salt, hexafluoro of iodonium such as diphenyliodonium, ditriliodonium, bis (p-tert-butylphenyl) iodonium, and bis (p-chlorophenyl) iodonium. Iodonium salt such as antimonate salt, chloride, bromide, borofluoride salt, hexafluorophosphate salt, hexafluoroantimonate of sulfonium such as triphenylsulfonium, 4-tert-butyltriphenylsulfonium, tris (4-methylphenyl) sulfonium. Sulfonium salts such as salts, 2,4,6-tris (trichloromethyl) -1,3,5-triazine, 2-phenyl-4,6-bis (trichloromethyl) -1,3,5-triazine, 2- Examples thereof include, but are not limited to, 2,4,6-substituted-1,3,5-triazine compounds such as methyl-4,6-bis (trichloromethyl) -1,3,5-triazine. ..

(4) Additive The hard coat layer used in the present invention includes, if necessary, an antistatic agent, an antiglare agent, an antifouling agent, and inorganic or organic fine particles for improving hardness, in addition to the polymer. It may contain additives such as a leveling agent and various sensitizers.

3. 3. Structure of Laminate The laminate of the present invention is not particularly limited as long as it has the polyimide film and the hard coat layer, and the hard coat layer is laminated on one surface side of the polyimide film. It may be one in which the hard coat layer is laminated on both sides of the polyimide film. Further, the laminate of the present invention is used to improve the adhesion between the polyimide film and the hard coat layer, for example, in addition to the polyimide film and the hard coat layer, as long as the effects of the present invention are not impaired. It may have another layer such as a primer layer. Further, in the laminate of the present invention, the polyimide film and the hard coat layer may be located adjacent to each other.

The overall thickness of the laminate of the present invention may be appropriately selected depending on the intended use, but is preferably 10 μm or more, and more preferably 40 μm or more from the viewpoint of strength. On the other hand, from the viewpoint of bending resistance, it is preferably 300 μm or less, and more preferably 250 μm or less.
Further, in the laminated body of the present invention, the thickness of each hardcoat layer may be appropriately selected depending on the intended use, but is preferably 2 μm or more and 80 μm or less, and more preferably 3 μm or more and 50 μm or less. Further, from the viewpoint of curl prevention, a hard coat layer may be formed on both sides of the polyimide film.

4. Characteristics of Laminate The laminate of the present invention preferably has a pencil hardness of H or more, more preferably 2H or more, and even more preferably 3H or more on the surface on the hard coat layer side.
The pencil hardness of the laminate of the present invention can be measured in the same manner as the pencil hardness of the polyimide film.

The laminated body of the present invention preferably has a total light transmittance of 85% or more, more preferably 88% or more, and further more than 90%, as measured in accordance with JIS K7361-1. Is preferable. Since the transmittance is high as described above, the transparency is improved and the material can be used as a substitute for glass.
The total light transmittance of the laminate of the present invention can be measured in the same manner as the total light transmittance measured in accordance with JIS K7361-1 of the polyimide film.

In the laminated body of the present invention, the yellowness (YI value) calculated in accordance with JIS K7373-2006 is preferably 30 or less, more preferably 20 or less, and more preferably 15 or less. It is more preferably 10 or less, and particularly preferably 10 or less.
The yellowness (YI value) of the laminate of the present invention can be measured in the same manner as the yellowness (YI value) calculated in accordance with JIS K7373-2006 of the polyimide film.

The haze value of the laminate of the present invention is preferably 10 or less, more preferably 8 or less, still more preferably 5 or less, from the viewpoint of light transmission.
The haze value of the laminate of the present invention can be measured in the same manner as the haze value of the polyimide film.

The birefringence in the thickness direction of the laminate of the present invention at a wavelength of 590 nm is preferably 0.020 or less, preferably 0.015 or less, more preferably 0.010 or less, and even more. It is preferably less than 0.008.
The birefringence of the laminate of the present invention can be measured in the same manner as the birefringence in the thickness direction of the polyimide film at a wavelength of 590 nm.

5. Use of Laminate The use of the laminate of the present invention is not particularly limited, and for example, it can be used in the same manner as the above-mentioned use of the polyimide film of the present invention.

6. Method for manufacturing a laminated body As a method for manufacturing a laminated body of the present invention, for example,
A step of forming a coating film of a composition for forming a hard coat layer containing at least one of a radically polymerizable compound and a cationically polymerizable compound on at least one surface of the polyimide film of the present invention.
Examples thereof include a manufacturing method including a step of curing the coating film.

The composition for forming a hard coat layer 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 and the like, if necessary.
Here, as the radically polymerizable compound, the cationically polymerizable compound, the polymerization initiator and the additive contained in the composition for forming the hard coat layer, the same ones as described in the above hard coat layer can be used. , The solvent can be appropriately selected from known solvents and used.

As a method for forming the coating film of the hard coat layer forming composition on at least one surface of the polyimide film, for example, the hard coat layer forming composition is known on at least one surface of the polyimide film. Examples thereof include a method of coating by a coating means.
The coating means is not particularly limited as long as it can be applied with a desired film thickness, and examples thereof include the same means as those for applying the polyimide precursor resin composition to the support.

The coating film of the curable resin composition for the hard coat layer is dried as necessary to remove the solvent. Examples of the drying method include vacuum drying, heat drying, and a method of combining these drying methods. When drying at normal pressure, it is preferable to dry at 30 ° C. or higher and 110 ° C. or lower.

Depending on the polymerizable group of the radically polymerizable compound and the cationically polymerizable compound contained in the curable resin composition, the curable resin composition for the hard coat layer is applied to the coating film and dried as necessary. By curing the coating film by at least one of light irradiation and heating, a hard coat layer containing at least one polymer of a radically polymerizable compound and a cationically polymerizable compound is formed on at least one surface of the polyimide film. Can be formed.

Ultraviolet rays, visible light, electron beams, ionizing radiation and the like are mainly used for light irradiation. In the case of ultraviolet curing, ultraviolet rays emitted from light rays such as ultra-high pressure mercury lamps, high pressure mercury lamps, low pressure mercury lamps, carbon arcs, xenon arcs, and metal halide lamps are used. The irradiation amount of the energy radiation source is about 50 to 5000 mJ / cm ² as the integrated exposure amount at the ultraviolet wavelength of 365 nm.
When heating, it is usually treated at a temperature of 40 ° C. or higher and 120 ° C. or lower. Further, the reaction may be carried out by leaving it at room temperature (25 ° C.) for 24 hours or more.

III. Surface material for display The surface material for display of the present invention is the above-mentioned polyimide film of the present invention or the laminate of the present invention.

The surface material for a display of the present invention is arranged and used so as to be located on the surface of various displays. The surface material for a display of the present invention is particularly suitable for a flexible display because it has improved bending resistance and sufficient surface hardness as a protective film, like the polyimide film of the present invention and the laminate of the present invention described above. Can be used.

The surface material for a display of the present invention can be used for various known displays, and is not particularly limited, but can be used, for example, for the display described in the application of the polyimide film of the present invention.

When the surface material for a display of the present invention is the laminate of the present invention, the outermost surface after being arranged on the surface of the display may be the surface on the polyimide film side or the hard coat layer. It may be a side surface. Above all, it is preferable to arrange the surface material for a display of the present invention so that the surface on the hard coat layer side becomes the surface on the front side. Further, the surface material for a display of the present invention may have a fingerprint adhesion prevention layer on the outermost surface.

The method for arranging the display surface material of the present invention on the surface of the display is not particularly limited, and examples thereof include a method via an adhesive layer. As the adhesive layer, a conventionally known adhesive layer that can be used for adhering a surface material for a display can be used.

Hereinafter, unless otherwise specified, measurements or evaluations were performed at 25 ° C.
[Evaluation methods]
<Weight average molecular weight of polyimide precursor>
For the weight average molecular weight of the polyimide precursor, the polyimide precursor is prepared as a solution of N-methylpyrrolidone (NMP) having a concentration of 0.5% by weight, and the solution is filtered through a syringe filter (pore size: 0.45 μm) to develop the solution. As a solvent, a 10 mmol% LiBr-NMP solution having a water content of 500 ppm or less was used, and a GPC device (HLC-8120 manufactured by Tosoh Co., Ltd., column used: GPC LF-804 manufactured by SHODEX) was used, the sample injection amount was 50 μL, and the solvent flow rate was 0.5 mL. The measurement was carried out under the condition of / min and 40 ° C. The weight average molecular weight of the polyimide precursor is a polystyrene standard sample having the same concentration as the sample (weight average molecular weight: 364,700, 204,000, 103,500, 44,360,27,500, 13,030,6,300, It was used as a conversion value for standard polystyrene measured based on 3,070). The elution time was compared with the calibration curve to determine the weight average molecular weight.
<Viscosity of polyimide precursor solution>
The viscosity of the polyimide precursor solution was measured using a viscometer (for example, TVE-22HT, Toki Sangyo Co., Ltd.) at 25 ° C. with a sample volume of 0.8 ml.

<Weight average molecular weight of polyimide>
Regarding the polyimide film shown in Table 2, a test piece obtained by cutting the polyimide film to a weight of 13 to 15 mg was immersed in 6 mL of N-methylpyrrolidone (NMP) and heated to 60 ° C. in a water bath while heating. The NMP solution in which the test piece was dissolved was obtained by stirring with a stirrer at a rotation speed of 200 rpm for 3 to 60 hours until the dissolution was visually confirmed. The solution is filtered through a syringe filter (pore size: 0.45 μm), and a 30 mmol% LiBr-NMP solution having a water content of 500 ppm or less is used as a developing solvent. Measurement was performed using GPC LF-804) manufactured by GPC, with a sample injection amount of 50 μL, a solvent flow rate of 0.5 mL / min, and a temperature of 40 ° C. The weight average molecular weight of the polyimide is a polystyrene standard sample having the same concentration as the sample (weight average molecular weight: 364,700, 204,000, 103,500, 44,360,27,500, 13,030, 6,300, 3, It was used as a conversion value with respect to standard polystyrene measured based on 070). The elution time was compared with the calibration curve to determine the weight average molecular weight. If the test piece did not dissolve, it was judged as "not measurable".
Regarding the polyimide powder in Table 6, 15 mg of the polyimide powder was immersed in 15,000 mg of N-methylpyrrolidone (NMP), and the mixture was visually heated at a rotation speed of 200 rpm using a stirrer while heating at 60 ° C. in a water bath. By stirring for 3 to 60 hours until dissolution was confirmed in, an NMP solution having a concentration of 0.1% by weight was obtained. The solution is filtered through a syringe filter (pore size: 0.45 μm), and a 30 mmol% LiBr-NMP solution having a water content of 500 ppm or less is used as a developing solvent, and a GPC device (manufactured by Tosoh, HLC-8120, detector: differential) is used. Refractometer (RID) detector, column used: SHODEX GPC LF-804 connected in series), sample injection amount 50 μL, solvent flow rate 0.4 mL / min, column temperature 37 ° C, detector temperature 37 ° C The measurement was performed under the conditions of. The weight average molecular weight of the polyimide is a polystyrene standard sample having the same concentration as the sample (weight average molecular weight: 364,700, 204,000, 103,500, 44,360,27,500, 13,030, 6,300, 3, It was used as a conversion value with respect to standard polystyrene measured based on 070). The elution time was compared with the calibration curve to determine the weight average molecular weight.
<Viscosity of polyimide solution>
The viscosity of the polyimide solution was measured using a viscometer (for example, TVE-22HT, Toki Sangyo Co., Ltd.) at 25 ° C. with a sample volume of 0.8 ml.

<Film thickness measurement method>
A total of 5 film thicknesses at the four corners and the center of the polyimide film test piece cut into a size of 10 cm x 10 cm were measured using a digital linear gauge (manufactured by Ozaki Seisakusho Co., Ltd., model PDN12 digital gauge), and the measured values were measured. Was taken as the film thickness of the polyimide film.

<Total light transmittance>
It was measured by a haze meter (HM150 manufactured by Murakami Color Technology Research Institute) in accordance with JIS K7361-1.
Further, for example, the total light transmittance at a thickness of 100 μm can be converted according to Lambert Veil's law.
Specifically, according to Lambert-Beer's law, the transmittance T is
Log ₁₀ (1 / T) = kcb
It is represented by (k = substance-specific constant, c = concentration, b = optical path length).
In the case of film transmittance, c is also a constant assuming that the density is constant even if the film thickness changes. Therefore, in the above equation, Log ₁₀ (1 / T) = fb using the constant f.
It can be expressed as (f = kc). Here, if the transmittance at a certain film thickness is known, the unique constant f of each substance can be obtained. Therefore, by substituting a constant unique to f and a target film thickness into b using the equation of T = 1/10 ^{f · b} , the transmittance at a desired film thickness can be obtained.

<YI value (yellowness)>
The YI value also includes the transmittance measured by the spectrophotometric method specified in JIS Z8720 using an ultraviolet-visible near-infrared spectrophotometer (JASCO Corporation V-7100) in accordance with JIS K7373-2006. It was calculated to.
Further, for example, the YI value at a thickness of 100 μm is the same as the total light transmittance for each wavelength measured at 5 nm intervals between 380 nm and 780 nm or less of a sample of a specific film thickness. According to Beer's law, the converted value of each transmittance at each wavelength of different thickness can be obtained, and it can be calculated and used based on it.

<Haze value>
It was measured by a haze meter (HM150 manufactured by Murakami Color Technology Research Institute) in accordance with JIS K-7105.

<Birerefringence>
The thickness direction retardation value (Rth) of the polyimide film was measured with light at 25 ° C. and a wavelength of 590 nm using a phase difference measuring device (manufactured by Oji Measuring Instruments Co., Ltd., product name “KOBRA-WR”). For the thickness direction retardation value (Rth), the phase difference value incident at 0 degrees and the phase difference value incident at an angle of 40 degrees were measured, and the thickness direction retardation value Rth was calculated from these phase difference values. The retardation value of the oblique 40-degree incident was measured by injecting light having a wavelength of 590 nm onto the retardation film from a direction inclined by 40 degrees from the normal of the retardation film.
The birefringence of the polyimide film was obtained by substituting it into the formula: Rth / d (film thickness (nm) of the polyimide film).

<Glass transition temperature>
A polyimide film that has been left to stand in an environment of 23 ° C ± 2 ° C RH 30 to 50% for 24 hours is sampled to a size of 10 cm square or more. It was cut into a width of 5 mm and a length of 50 mm (so that the sample length was 20 mm at the time of chucking). The width was measured using a caliper, and the average value measured three times at different positions was recorded. At this time, if a part of the width measurement had a fluctuation range of 3% or more of the average value, the sample was not used. As the thickness of the film, the value measured by the film thickness measuring method was used. For the samples that can be used, a dynamic viscoelastic modulus measuring device RSA III (TA Instruments Japan Co., Ltd.) is used, the measurement range is -150 ° C to 400 ° C, the frequency is 1 Hz, and the heating rate is 5 ° C. Dynamic viscoelastic measurement was performed with / min, sample width of 5 mm, and chuck distance of 20 mm, and the glass transition from the peak temperature of tan δ (tan δ = loss elastic modulus (E'') / storage elastic modulus (E')). The temperature (Tg) was determined. At the time of analysis of peaks and inflection points, the data was quantified and analyzed from the numerical values without visual evaluation.

<Tension modulus>
A polyimide film test piece cut into a size of 15 mm × 40 mm was conditioned for 2 hours under the conditions of a temperature of 25 ° C. and a relative humidity of 60%. , The tensile modulus at 25 ° C. was measured. A tensile tester (manufactured by Shimadzu Corporation: Autograph AG-X 1N, load cell: SBL-1KN) was used.

<Dynamic bending test>
A test piece of a polyimide film cut out to a size of 20 mm × 100 mm was fixed to a constant temperature and humidity chamber durability test system (manufactured by Yuasa System Equipment, a planar non-load U-shaped expansion and contraction test jig DMX-FS) with tape. .. Further, the test piece is folded at the position of half of the long side, and the distance between both ends of the long side of the folded test piece is 6 mm, and the bent portion of the test piece is folded so that the radius of curvature is 3 mm. The state was set. After that, in an environment of 60 ± 2 ° C. and 93 ± 2% relative humidity (RH), changing from a flat open state to the folded state is regarded as one bending, and the number of bendings is 90 times per minute. Bending was repeated until it broke, and the number of times the test piece was bent until it broke was measured.

<Pencil hardness>
To determine the hardness of the pencil, use a test pencil specified by JIS-S-6006 after adjusting the humidity of the measurement sample for 2 hours under the conditions of a temperature of 25 ° C and a relative humidity of 60%. Using a tester, a pencil hardness test (0.98 N load) specified in JIS K5600-5-4 (1999) was performed on the film surface to evaluate the highest pencil hardness that does not damage the film.

<Arithmetic Mean Roughness Ra>
Surface observation was performed in tapping mode using an atomic force microscope (AFM) (Made by Bruker, MultiMode 8 HR) on the surface of the polyimide film that was not in contact with the substrate (glass plate) during film production, and JIS B0601: The arithmetic average roughness Ra was obtained in accordance with 2013. The arithmetic average roughness Ra was obtained by performing four 10 μm square field observations, and the average value thereof was taken as the arithmetic average roughness Ra of the polyimide film. ..

(Synthesis Example 1)
In a 500 ml separable flask, add 466.1 g of dehydrated dimethylacetamide and 1.23 g (5 mmol) of 1,3-bis (3-aminopropyl) tetramethyldisiloxane (AprTMOS) to dissolve AprTMOS. Place 1.23 g (3 mmol) of 4,4'-(hexafluoroisopropyridene) diphthalic acid anhydride (6FDA) in a place where the temperature of the solution is controlled to 30 ° C. so that the temperature rise becomes 2 ° C or less. The mixture was gradually added to the mixture and stirred with a mechanical stirrer for 30 minutes. 62.4 g (195 mmol) of 2,2'-bis (trifluoromethyl) benzidine (TFMB) was added thereto, and after confirming that the solution was completely dissolved, 4,4'-(hexafluoroisopropyridene) diphthalic acid was added. 91.6 g (206 mmol) of anhydride (6FDA) was gradually added in several portions so that the temperature rise was 2 ° C. or lower, and a polyimide precursor solution (solid content 25% by weight) in which the polyimide precursor was dissolved was added. Synthesized. The molar ratio of TFMB used for polyimide precursor 1 to AprTMOS was 97.5: 2.5. The viscosity of the polyimide precursor solution (solid content 25% by weight) at 25 ° C. was 48900 cps, and the weight average molecular weight of the polyimide precursor 1 measured by GPC was 156400.

(Synthesis Examples 2-4)
In the procedure of Synthesis Example 1, the reaction was carried out so as to have the raw material and solid content concentrations shown in Table 1 to prepare polyimide precursor solutions 2 to 4.

In the following, the abbreviations in the table are as follows.
TFMB: 2,2'-bis (trifluoromethyl) benzidine AprTMOS: 1,3-bis (3-aminopropyl) tetramethyldisiloxane 6FDA: 4,4'-(hexafluoroisopropyridene) diphthalic acid anhydride

(Comparative synthesis example 1)
12.25 g of both-terminal amine-modified diphenyl silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd .: X22-1660B-3 (number average molecular weight 4400)) while introducing nitrogen gas into a 3 L separable flask equipped with an oil bath with a stirring rod. 3432 g of N-methyl-2-pyrrolidone (NMP) was added, followed by 6FDA 222.12 g (0.5 mol), and the mixture was stirred at room temperature for 30 minutes. Then, after confirming that 152.99 g (0.478 mol) of 2,2'-bis (trifluoromethyl) benzidine (TFMB) was added and dissolved, the mixture was stirred at room temperature for 3 hours and then heated to 80 ° C. After stirring for 4 hours, the oil bath was removed and the temperature was returned to room temperature to obtain a comparative polyimide precursor solution 1. The solid content concentration of the comparative polyimide precursor solution 1 was 10% by weight, the viscosity at 25 ° C. was 89 cps, and the weight average molecular weight of the comparative polyimide precursor 1 measured by GPC was 66900.

(Examples 1 to 4, Comparative Example 1)
Using the polyimide precursor solutions 1 to 4 and the comparative polyimide precursor solution 1, the following procedures (1) to (3) were carried out to prepare polyimide films having the thickness shown in Table 2, respectively.
(1) Each polyimide precursor solution was applied onto a glass plate and dried in a circulation oven at 120 ° C. for 10 minutes.
(2) The temperature was raised to 350 ° C. at a heating rate of 10 ° C./min under a nitrogen stream (oxygen concentration of 100 ppm or less), held for 1 hour, and then cooled to room temperature.
(3) Each polyimide film was obtained by peeling from a glass plate.

The polyimide films of Examples 1 to 4 and Comparative Example 1 were evaluated using the above evaluation method. The evaluation results are shown in Table 2. The polyimide film obtained in Comparative Example 1 had a lot of unevenness, so that the arithmetic mean roughness Ra could not be measured.

(Comparative synthesis example 2)
In a 500 ml separable flask, 3081 g of dehydrated dimethylacetamide and 322 g (1.00 mol) of 2,2'-bis (trifluoromethyl) benzidine (TFMB) were placed, and the temperature of the solution in which TFMB was dissolved was adjusted. To the place controlled to 30 ° C, 443 g (1.00 mol) of 4,4'-(hexafluoroisopropyridene) diphthalic acid anhydride (6FDA) was gradually divided into several times so that the temperature rise was 2 ° C or less. A polyimide precursor solution 2 (solid content 20% by weight) in which the polyimide precursor 2 was dissolved was synthesized. The viscosity of the polyimide precursor solution 2 (solid content 20% by weight) at 25 ° C. was 34920 cps, and the weight average molecular weight of the polyimide precursor 2 measured by GPC was 408500.

(Comparative Synthesis Examples 3 and 4)
In the procedure of Synthesis Example 1, the reaction was carried out so that the raw materials and solid content concentrations shown in Table 3 were obtained, and the comparative polyimide precursor solutions 3 and 4 were obtained.

(Examples 5 to 8, Comparative Examples 2 to 4)
Using the polyimide precursor solutions 1 to 4 and the comparative polyimide precursor solutions 2 to 4, a polyimide film having a thickness of 80 μm ± 5 μm was prepared by the same procedure as in Example 1. For each polyimide film, the dynamic bending test and the evaluation of the pencil hardness were performed. The evaluation results are shown in Table 4.

The polyimide films shown in Table 4 were further evaluated using the above evaluation method. The evaluation results are shown in Table 5.

From Tables 2 and 4, it was shown that the polyimide films of Examples 1 to 8 corresponding to the polyimide films of the present invention were resin films having improved dynamic bending resistance and suppressed a decrease in surface hardness. Further, from Tables 2 and 4, it was shown that the polyimide films of Examples 1 to 8 corresponding to the polyimide film of the present invention are resin films having improved dynamic bending resistance regardless of the thickness of the film. .. Further, from Tables 2 and 5, it was shown that the polyimide film of the present invention is a resin film having high transparency and excellent optical properties.
On the other hand, the polyimide film of Comparative Example 1 was inferior in dynamic bending resistance and significantly inferior in pencil hardness. Since the comparative polyimide precursor 1 of Comparative Example 1 had poor film forming property, it is presumed that the surface condition of the film also affected the result of the pencil hardness. Further, the polyimide films of Comparative Examples 2 to 4 were inferior in dynamic bending resistance.

(Example 9)
To a 40% by mass methyl isobutyl ketone solution of pentaerythritol triacrylate, 10 parts by mass of 1-hydroxy-cyclohexyl-phenyl-ketone (BASF, Irgacure 184) was added to 100 parts by mass of pentaerythritol triacrylate to harden it. A resin composition for a coat layer was prepared.
The polyimide film of Example 2 was cut into a size of 10 cm × 10 cm, the resin composition for a hard coat layer was applied to the surface on the side not in contact with the substrate (glass plate) at the time of film production, and ultraviolet rays were emitted at 200 mJ / cm under a nitrogen stream. It was irradiated with an exposure amount of ² and cured to form a hard coat layer which is a cured film having a thickness of 10 μm, and a laminated body was prepared.

(Example 10)
(1) Preparation of polyimide (chemical imidization)
A solution in which dehydrated dimethylacetamide (466 g) and 1,3-bis (3-aminopropyl) tetramethyldisiloxane (AprTMOS) (1.31 g) are dissolved is placed in a 1 L separable flask. 4,4'-(hexafluoroisopropyridene) diphthalic acid anhydride (6FDA) (1.17 g) was gradually added to a place where the temperature was controlled to 30 ° C. so that the temperature rise was 2 ° C. or less. The mixture was stirred with a mechanical stirrer for 30 minutes. 2,2'-Bis (trifluoromethyl) benzidine (TFMB) (65.9 g) was added thereto, and after confirming that the solution was completely dissolved, 4,4'-(hexafluoroisopropyridene) diphthalic acid anhydride was added. The substance (6FDA) (91.7 g) was gradually added in several portions so that the temperature rise was 2 ° C. or lower, and the polyimide precursor solution 5 (solid content 25% by mass) in which the polyimide precursor 5 was dissolved was added. Synthesized.
The above-mentioned polyimide precursor solution 5 (400 g) cooled to room temperature was added to a 5 L separable flask under a nitrogen atmosphere. Dehydrated dimethylacetamide (109 g) was added thereto, and the mixture was stirred until uniform. Next, the catalyst pyridine (41.4 g) and acetic anhydride (53.4 g) were added and stirred at room temperature for 24 hours to synthesize a polyimide solution. Butyl acetate (406 g) was added to the obtained polyimide solution and stirred until uniform, and then methanol (902 g) was gradually added to obtain a solution in which slight turbidity was observed. Methanol (2105 g) was added to the turbid solution at once to obtain a white slurry. The slurry was filtered and washed with methanol 5 times to obtain polyimide 5 (91 g). The weight average molecular weight of the polyimide measured by GPC was 201269.

(2) Production of Polyimide Film Polyimide 5 was dissolved in a solvent (dichloromethane) to prepare a polyimide solution 5 having a solid content of 14% by mass. The viscosity of the polyimide solution 5 (solid content 14% by mass) at 25 ° C. was 4290 cps.
Using the polyimide solution 5 obtained as described above, the following steps (i) to (iii) were carried out to prepare a polyimide film having a thickness of 50 μm ± 5 μm.
(I) The polyimide solution 5 was applied onto a glass plate and dried in a circulation oven at 120 ° C. for 10 minutes.
(Ii) The temperature was raised to 250 ° C. at a heating rate of 10 ° C./min under a nitrogen stream (oxygen concentration of 100 ppm or less), maintained at 250 ° C. for 1 hour, and then cooled to room temperature.
(Iii) A polyimide film was obtained by peeling from a glass plate.

(Examples 11, 12, 13)
(1) Preparation of polyimide (chemical imidization)
In the procedure for synthesizing the polyimide 5 of Example 10, the reaction was carried out after adjusting the diamine ratio as shown in Table 6 to obtain polyimides 6, 7 and 8. Table 6 shows the weight average molecular weights of polyimides 6, 7, and 8 measured by GPC.
(2) Production of Polyimide Film In Example 10, polyimides 6, 7 and 8 were used instead of polyimide 5, respectively, and the solid content concentration was adjusted to 15% by mass in the same manner as in Example 10. The polyimide solutions 6, 7, and 8 shown in Table 6 were obtained. Table 6 shows the viscosities of the polyimide solutions 6, 7, and 8 (solid content 15% by mass) at 25 ° C.
Polyimide films of Examples 11, 12, and 13 were obtained in the same manner as in Example 10 except that the polyimide solutions 6, 7, and 8 were used instead of the polyimide solution 5 in Example 10.
The polyimide films of Examples 10 to 13 were evaluated using the above evaluation method. The evaluation results are shown in Table 7.

From Table 7, it was shown that the polyimide films of Examples 10 to 13 corresponding to the polyimide film of the present invention were resin films having improved dynamic bending resistance and suppressed a decrease in surface hardness. As a result, in the polyimide film of the present invention, even when the polyimide synthesized by chemical imidization is used as the polyimide having the structure represented by the general formula (1), it is synthesized by thermal imidization. It was clarified that the dynamic bending resistance was improved and the decrease in surface hardness was suppressed as in the case of using polyimide. Further, from Table 7, the polyimide films of Examples 10 to 13 corresponding to the polyimide film of the present invention are resin films having particularly reduced YI values and surface roughness, and having high transparency and excellent optical characteristics. Shown.

(Examples 14 to 19, Comparative Example 5)
In the procedure of Synthesis Example 1, the reaction was carried out so that the raw materials and solid content concentrations shown in Table 8 were obtained, and the polyimide precursor solutions 9 to 14 and the polyimide precursor solution 5 of Comparative Example were obtained.
The thicknesses shown in Table 9 are the same as in Example 1 except that the polyimide precursor solutions 9 to 14 and the comparative example polyimide precursor solution 5 are used instead of the polyimide precursor solution 1. The polyimide films of the above were prepared respectively.
The polyimide films of Examples 14 to 19 and Comparative Example 5 were evaluated using the above evaluation method. The evaluation results are shown in Table 9.

From Table 9, the polyimide films of Examples 14 to 19 corresponding to the polyimide film of the present invention are excellent in dynamic bending resistance, and the 2,2'-bis (4- (3-amino) described in Patent Document 5 is exhibited. It was shown that the resin film was suppressed in the decrease in surface hardness as compared with Comparative Example 5 in which phenoxy) phenyl) hexafluoropropane was used as a diamine having no silicon atom. Further, from Table 9, it was shown that the polyimide films of Examples 14 to 19 corresponding to the polyimide film of the present invention are resin films having high transparency and excellent optical properties.

Claims (12)

A surface material for a flexible display containing a polyimide having a structure represented by the following general formula (1) and containing a polyimide film having a thickness of 27 μm or more and 100 μm or less .

(In the 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. 2.5 mol% or more and less than 10 mol% of the total amount of R ² is a diamine residue having one or two silicon atoms in the main chain, and the remaining R ² has no silicon atom and is aromatic. Diamine residues with a ring or aliphatic ring, more than half of the remaining R ² are 1,4-cyclohexanediamine residues, trans-1,4-bismethylenecyclohexanediamine residues, 4 , 4'-diaminodiphenyl sulfone residue, 3,4'-diaminodiphenyl sulfone residue, 2,2-bis (4-aminophenyl) propane residue, 2,2-bis (4-aminophenyl) hexafluoropropane It is at least one divalent group selected from the group consisting of a residue and a divalent group represented by the following general formula (2). N represents the number of repeating units.)

(In the general formula (2), R ³ and R ⁴ independently represent a hydrogen atom, an alkyl group, or a perfluoroalkyl group.) The polyimide film is
The total light transmittance measured according to JIS K7361-1 is 85% or more.
The yellowness calculated in accordance with JIS K7373-2006 is 20.0 or less.
It has a glass transition temperature in the temperature range of 150 ° C or higher and 400 ° C or lower.
The birefringence in the thickness direction at a wavelength of 590 nm is 0.040 or less.
The surface material for a flexible display according to claim 1. The surface material for a flexible display according to claim 2, wherein the polyimide film has a birefringence of 0.020 or less in the thickness direction at a wavelength of 590 nm. The surface material for a flexible display according to claim 2, wherein the polyimide film has a yellowness calculated in accordance with JIS K7373-2006 divided by a film thickness (μm) of 0.04 or less. .. The polyimide film is
The total light transmittance measured according to JIS K7361-1 is 85% or more.
The yellowness calculated in accordance with JIS K7373-2006 is 7.0 or less.
It has a glass transition temperature in the temperature range of 150 ° C or higher and 400 ° C or lower.
The birefringence in the thickness direction at a wavelength of 590 nm is 0.020 or less.
The surface material for a flexible display according to claim 1. The surface material for a flexible display according to any one of claims 1 to 5, wherein the polyimide film has an arithmetic average roughness Ra of 100 nm or less measured in accordance with JIS B0601 on at least one surface. In the polyimide having the structure represented by the general formula (1), R ¹ in the general formula (1) is a cyclohexanetetracarboxylic acid dianhydride residue, a cyclopentanetetracarboxylic acid dianhydride residue, or a dihydride. Cyclohexane-3,4,3', 4'-tetracarboxylic acid dianhydride residue, cyclobutanetetracarboxylic acid dianhydride residue, pyromellitic acid dianhydride residue, 3,3', 4,4'- Biphenyltetracarboxylic acid dianhydride residue, 2,2', 3,3'-biphenyltetracarboxylic acid dianhydride residue, 4,4'-(hexafluoroisopropylidene) diphthalic acid anhydride residue, 3, 4'-(Hexafluoroisopropylidene) diphthalic acid anhydride residue, 3,3'-(hexafluoroisopropyridene) diphthalic acid anhydride residue, 4,4'-oxydiphthalic acid anhydride residue, and 3, The surface material for a flexible display according to any one of claims 1 to 6, which is a tetravalent group of at least one selected from the group consisting of 4'-oxydiphthalic acid anhydride residues. The surface material for a flexible display according to any one of claims 1 to 7, wherein the polyimide film has a thickness of 80 μm or more and 100 μm or less. The invention according to any one of claims 1 to 8, further comprising a laminate having the polyimide film and a hard coat layer containing at least one polymer of a radically polymerizable compound and a cationically polymerizable compound. Surface material for flexible displays . The radically polymerizable compound is a compound having two or more (meth) acryloyl groups in one molecule, and the cationically polymerizable compound is a compound having at least one of an epoxy group and an oxetanyl group in one molecule. The surface material for a flexible display according to claim 9 . The surface material for a flexible display according to any one of claims 1 to 8, which is the polyimide film. The surface material for a flexible display according to claim 9 or 10, which is the laminated body.