JP7155597B2 - Nitrogen-containing polymer films and laminated films - Google Patents

Description

TECHNICAL FIELD The present invention relates to nitrogen-containing polymer films and laminated films, and more particularly to nitrogen-containing polymer films and laminated films that can be suitably used as transparent films for flexible devices such as flexible displays.

In recent years, full-scale development of flexible displays that can be folded or rolled has progressed from the viewpoint of portability and freedom of design. Such displays require a polymer film that can replace glass in order to reduce weight, reduce thickness, and prevent cracking due to bending or impact. In particular, glass substitute films used for front panels of displays are required to have not only excellent optical properties but also high hardness and flex resistance, which are normally contradictory properties.

As a technique for improving film hardness, Patent Documents 1 to 4 propose films in which a hard coat layer is laminated on a substrate such as an acrylic resin film, a polyester resin film, or a triacetylcellulose resin film. However, since the hardness of the base material itself is not sufficient, it is necessary to apply a thick hard coat layer in order to increase the hardness. be. On the other hand, if the thickness of the base material is increased in order to increase the hardness of the base material, breakage or deformation of the base material is likely to occur. It is difficult.

On the other hand, aromatic nitrogen-containing polymers such as aromatic polyamides (aramids), aromatic polyimides, and aromatic polyamide-imides are used as films that have excellent rigidity and mechanical strength and can achieve high levels of hardness and flexibility. Films of this type have been studied, and are disclosed, for example, in Patent Documents 5 to 7. Among these, Patent Literature 6 discloses a film that does not crack or break when subjected to 100,000 cycles of a test of repeated folding at 180°, that is, a dynamic bending endurance test.

JP 2014-65172 A JP 2014-134674 A JP 2014-210412 A JP-A-8-15682 JP 2004-839863 A JP 2017-33033 A JP 2016-138267 A

However, especially in portable flexible displays, it is expected that the film will be stored in a folded state for a long period of time. is required. This is called static bending resistance, as opposed to the dynamic bending resistance described above. At present, no known film is satisfactory in terms of static bending resistance.

The present invention aims to provide a nitrogen-containing polymer film and a laminated film that have both high hardness and flex resistance, which are contradictory properties, and are particularly excellent in both dynamic flex resistance and static flex resistance. With the goal.

The present invention for achieving the above object is characterized by the following.

When the light transmittance at a wavelength of 550 nm is 80 to 100%, the in-plane orientation degree at a position 1 μm in the thickness direction from one surface is Pa, and the in-plane orientation degree at a position 1 μm in the thickness direction from the other surface is Pb. , a nitrogen-containing polymer film satisfying the following formulas (1) to (3).
(1) 3.0≤Pa≤15.0
(2) 3.0≤Pb≤15.0
(3) 0.5≦|Pa−Pb|≦5.0

According to the present invention, it is possible to provide a film that achieves high hardness by having high in-plane orientation and exhibits excellent static bending resistance by highly controlling orientation in the thickness direction. Therefore, the film of the present invention can be suitably used as a transparent film for flexible devices such as flexible displays.

The film of the present invention is composed of a nitrogen-containing polymer. Here, a nitrogen-containing polymer means a polymer having a bond containing a nitrogen atom in its main chain. Examples of such polymers include polyamides, aromatic polyamides (aramids), polyimides, aromatic polyimides, polyamideimides, aromatic polyamideimides, polyetherimides, aromatic polyetherimides, and copolymers thereof. is mentioned. The film of the present invention preferably contains 51 to 100% by mass of the above nitrogen-containing polymer based on the entire film (excluding a cured layer containing a curable resin, which will be described later). More preferably, it is 80 to 100% by mass.

As the nitrogen-containing polymer constituting the film of the present invention, the group consisting of aromatic polyamides, aromatic polyimides and aromatic polyamideimides, since it is easy to achieve both hardness and bending resistance due to high rigidity and high intermolecular force. It is more preferable to contain at least one polymer selected from.

More preferably, the nitrogen-containing polymer constituting the film of the present invention has a structural unit represented by any one of the following chemical formulas (I) to (IV).
Chemical formula (I):

R ¹ and R ² are —H, an aliphatic group having 1 to 5 carbon atoms, —CF ₃ , —CCl ₃ , —OH, —F, —Cl, —Br, —OCH ₃ , a silyl group, or an aromatic ring; is a group containing -CF ₃ , -F, -Cl, or a group containing an aromatic ring are preferred.
Chemical formula (II):

R ³ is a group containing Si, a group containing P, a group containing S, a halogenated hydrocarbon group, a group containing an aromatic ring, or a group containing an ether bond (provided that the structure having these groups in the molecule units may be mixed). A group containing Si, a halogenated hydrocarbon group, a group containing an aromatic ring, or a group containing an ether bond is preferable.
Chemical formula (III):

^R4 is any group. Although not particularly limited, -H, -Cl and -F are preferred.
Chemical formula (IV):

^R5 is any aromatic group, any alicyclic group. Although not particularly limited, phenyl, biphenyl, cyclohexane and decalin are more preferred.

Moreover, among the above, it is particularly preferable to have a structural unit represented by the following chemical formula (V) in terms of achieving excellent optical properties, hardness and flex resistance.
Chemical formula (V):

^R6 is an arbitrary group. Although not particularly limited, -H, -Cl and -F are preferred.

The structural unit represented by the chemical formula (V) is preferably 20 to 100 mol %, more preferably 50 to 100 mol %, of the nitrogen-containing polymer constituting the film of the present invention. In particular, it is more preferably 80 to 100 mol % in terms of exhibiting an excellent effect on dynamic bending resistance at low temperatures (eg, -20°C).

When it is necessary to identify the chemical structure and composition ratio of the nitrogen-containing polymer of the present invention, nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR) and mass spectrometry (MS) are combined. analysis can be performed.

The film of the present invention is characterized by having a light transmittance of 80 to 100% at a wavelength of 550 nm. A highly transparent film can be obtained by setting the light transmittance at a wavelength of 550 nm to 80% or more. More preferably, it is 85% or more. When the light transmittance at a wavelength of 550 nm is less than 80%, the film becomes highly turbid, and the visibility may deteriorate when used for displays, transparent substrates, and the like. In order to achieve a light transmittance of 80% or more at a wavelength of 550 nm, it is effective to reduce the amount of metal foreign matter in the raw material and to have a polymer structure that makes it difficult for intramolecular or intermolecular charge transfer to occur. This suppresses absorption of visible light, especially in the low wavelength region. Such polymer structures include the use of polymers containing structural units represented by any of formulas (I) to (IV) above. Moreover, among the above, it is particularly preferable to have a structural unit represented by the following chemical formula (V).

Further, the film of the present invention preferably has a light transmittance of 80 to 100% at a wavelength of 450 nm. By setting the light transmittance at a wavelength of 450 nm to 80% or more, a highly transparent and less colored film can be obtained, which can be suitably used for displays and the like. More preferably, it is 85% or more. When the light transmittance at a wavelength of 450 nm is less than 80%, the film is highly colored, and when used in a display or the like, the screen may have a strong yellow tint, resulting in poor visibility. In order to achieve a light transmittance of 80% or more at a wavelength of 450 nm, it is effective to reduce the amount of metal foreign matter in the raw material and to have a polymer structure in which intramolecular or intermolecular charge transfer is difficult to occur. This suppresses absorption of visible light, especially in the low wavelength region. Such polymer structures include the use of polymers containing structural units represented by any of formulas (I) to (IV) above. Moreover, among the above, it is particularly preferable to have a structural unit represented by the following chemical formula (V).

In the film of the present invention, when the in-plane orientation degree at a position 1 μm in the thickness direction from one surface is Pa and the in-plane orientation degree at a position 1 μm in the thickness direction from the other surface is Pb, the following formulas (1) to ( 3) is characterized by satisfying.
(1) 3.0≤Pa≤15.0
(2) 3.0≤Pb≤15.0
(3) 0.5≦|Pa−Pb|≦5.0
Here, the degree of in-plane orientation is measured by Raman spectroscopy. , I parallel/I perpendicular. The Raman scattering intensity increases as the vibration direction of the polymer molecular chains and the polarization direction of the incident light match. means that

The film of the present invention satisfies the above formulas (1) to (3) at the same time, thereby obtaining high hardness and exhibiting excellent bending resistance. In order to increase the hardness, it is important to suppress distortion when a load is applied in the thickness direction. Therefore, dense packing of polymer chains in the film is effective. On the other hand, with respect to bending resistance, the stress applied to the bent portion of the film when the film is folded 180° is different in the thickness direction with the neutral plane as the boundary, with compression on the inner side of the fold and tension on the outer side of the fold. As a result of intensive investigation, we found that while maintaining the intermolecular force by setting the degree of in-plane orientation to a certain value or higher, we increased the degree of in-plane orientation on the inner side of the fold to increase compression resistance, and suppressed the degree of in-plane orientation on the outer side of the fold. We found that it is effective to give elasticity to the structure. Normally, when there is a difference in the in-plane orientation in the thickness direction, curling tends to occur due to the difference in thermal shrinkage, so the difference in the in-plane orientation in the thickness direction is generally kept small. On the other hand, the present invention is characterized in that the difference in the in-plane orientation degree in the thickness direction is intentionally set to a certain value or more for the reason described above. In addition, curling can be suppressed at the same time by using the nitrogen-containing polymer described above as the polymer and setting the degree of in-plane orientation on both sides to a certain value or more.

If the in-plane orientation degrees Pa and Pb are less than 3.0, the hardness is low, and the film is likely to be scratched or dented when used for the front film of a display. In addition, sufficient dynamic flex resistance is not obtained, and when repeatedly folded, breakage or deformation may occur. Furthermore, when the difference in the in-plane orientation in the thickness direction is set within the range of the present invention, curling may occur in the film. If the in-plane orientation degrees Pa and Pb exceed 15.0, the retardation in the thickness direction increases, and visibility may deteriorate when used for the front film of a display. From the above points, both Pa and Pb are preferably 4.0 to 9.5. In order to keep Pa and Pb within the above ranges, it is preferable to use the aforementioned nitrogen-containing polymer as the polymer. In particular, having a structural unit represented by the above-described chemical formula (V) is more preferable because the colorless transparency and degree of plane orientation of the film can be easily controlled. Moreover, it is preferable to manufacture a film under the conditions described later.

If the in-plane orientation difference |Pa−Pb| etc. may occur. On the other hand, if |Pa−Pb| exceeds 5.0, the film may curl. The range of |Pa-Pb| is more preferably 0.7≦|Pa-Pb|≦5.0, and more preferably 1.0≦|Pa-Pb|≦5.0. In order to make |Pa-Pb| within the above range, it is preferable to use the above nitrogen-containing polymer as the polymer and produce the film under the conditions described below.

Further, when measuring the in-plane orientation degree Pa and/or Pb of a film laminated with a cured layer containing a curable resin described later, if the interface between the nitrogen-containing polymer film and the cured layer is unclear, the following The interface can be defined in the following way. First, a cross section of the laminated film is continuously subjected to elemental analysis in the thickness direction by combining a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDX). Based on the obtained analysis results, a line analysis diagram is obtained for each detected element, with the vertical axis representing the detected intensity and the horizontal axis representing the measurement position in the thickness direction. The point of intersection when the line analysis diagrams for each element are superimposed is defined as the interface between the nitrogen-containing polymer film and the cured layer. The element species suitable for obtaining the above intersection point is preferably determined according to the composition of the nitrogen-containing polymer film and the cured layer, so it is determined as appropriate from the analysis results. In this case, it is preferable to analyze the nitrogen (N) element on the nitrogen-containing polymer film side and the silicon (Si) element on the hardened layer side. The in-plane orientation degree Pa and/or Pb of the nitrogen-containing polymer film can be obtained by measuring the position 1 μm in the thickness direction from the interface.

The film of the present invention preferably has a glass transition temperature of 150 to 500°C. It is more preferably 200 to 500°C, still more preferably 250 to 500°C. The glass transition temperature is determined from the inflection point of the storage modulus by dynamic viscoelasticity measurement (DMA) according to ASTM E1640-13. If the glass transition temperature is less than 150° C., deformation or cracking may occur when a conductive layer such as ITO, a thin film transistor, a barrier layer, an antireflection layer, or the like is formed on the film. In order to set the glass transition temperature to 150° C. or higher, it is preferable to use the nitrogen-containing polymer described above as the polymer. More preferably, it contains an aromatic polyamide, an aromatic polyimide, or an aromatic polyamideimide.

The film of the present invention preferably has a Young's modulus of 5.0 to 20.0 GPa in at least one direction. More preferably 7.0 to 20.0 GPa, still more preferably 9.0 to 20.0 GPa. If the Young's modulus is less than 5.0 GPa, the hardness is low, and scratches and dents are likely to occur particularly when used for the front film of a display. Moreover, the handleability of the film may deteriorate. In order to keep the Young's modulus in at least one direction within the above range, it is preferable to use the nitrogen-containing polymer described above as the polymer. In particular, having a structural unit represented by the above-described chemical formula (V) is more preferable because the rigidity of the molecular chain is high. In addition, it is preferable to produce the film under the conditions described later, particularly the stretching conditions described later.

The thickness of the film of the present invention is preferably 1-100 μm. If the thickness is less than 1 μm, the handling property is deteriorated, the hardness is lowered, and scratches and dents are likely to occur particularly when used for the front film of a display. On the other hand, when the thickness exceeds 100 μm, the bending resistance may be lowered. From the viewpoint of achieving both hardness and bending resistance, the thickness of the film is more preferably 5 to 80 μm, and even more preferably 10 to 50 μm.

The film of the present invention preferably has a yellowness index (YI) of 0.1 to 5.0. When the yellowness index (YI) exceeds 5.0, the film is highly colored, and when used in a display or the like, the screen may have a strong yellow tint, resulting in deterioration in visibility. The yellowness index (YI) is more preferably 0.1 to 4.0, even more preferably 0.1 to 3.5, because visibility is further improved. In order to achieve a yellowness index (YI) of 0.1 to 5.0, it is effective to reduce the amount of metal foreign matter in the raw material and to use a polymer structure that makes it difficult for charge transfer within or between molecules to occur. is. This suppresses absorption of visible light, especially in the low wavelength region. Such polymer structures include the use of polymers containing structural units represented by any of formulas (I) to (IV) above.

The film of the invention preferably has a haze of 0.1 to 3.0%. If the haze is more than 3.0%, the film becomes highly turbid, and visibility and brightness may be lowered when used for displays, transparent substrates, and the like. The haze is more preferably 0.1 to 2.0%, even more preferably 0.1 to 1.0%. In order to reduce the haze to 0.1 to 3.0%, it is effective to reduce the internal haze by reducing the foreign matter in the film, smooth the film surface, and reduce the irregular reflection (external haze) on the surface. is.

The film of the present invention may be a laminated film in which a curable layer containing a curable resin is laminated on one side or both sides.

Examples of the curable resin contained in the cured layer include thermosetting resins, ultraviolet curable resins, hydrolysis/condensation resins, and the like. More specifically, organic silicone, polyol, melamine, and epoxy , polyfunctional acrylates, urethanes, isocyanates, organic-inorganic hybrids such as alkoxysilane compounds, which are composites of organic and inorganic materials, and silsesquioxane-based resins having curable functional groups. be done. More preferred are epoxy-based, polyfunctional acrylate-based, organic-inorganic hybrid-based, and silsesquioxane-based resins.

Also, the cured layer may contain particles. Here, the particles may be either inorganic particles or organic particles, but it is preferable to contain inorganic particles because high hardness can be easily obtained. Although the inorganic particles are not particularly limited, metal and semimetal oxides, silicides, nitrides, borides, chlorides, carbonates and the like can be mentioned. More specifically, silica (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), zinc oxide (ZnO), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), antimony oxide (Sb ₂ O ₃ ) and Indium tin oxide _{( In2O3} ) etc. are mentioned. Moreover, it is preferable that the particle diameter is 1 nm or more and 300 nm or less. The particles are preferably surface-treated. The term "surface treatment" as used herein means introducing a compound onto the particle surface by chemical bonding (eg, covalent bonding, hydrogen bonding, ionic bonding) or adsorption (eg, physical adsorption, chemical adsorption).

The thickness of the cured layer is preferably 0.2 to 30.0 μm, more preferably 0.2 to 15.0 μm per side. If the thickness is less than 0.2 μm, the effect of improving hardness may not be sufficiently obtained. On the other hand, when the thickness exceeds 30.0 μm, the bending resistance is lowered, and cracks may occur in the cured layer when the laminated film is bent. Here, when the interface between the nitrogen-containing polymer film and the cured layer of the laminated film is unclear, the interface can be defined and the thickness of the cured layer can be determined in the same manner as in the in-plane orientation measurement described above. can.

Moreover, the hardened layer may be two or more layers with different structures on one side.

The method for producing the film and laminated film of the present invention will be described below using aromatic polyamide and aromatic polyimide as examples, but the present invention is not limited thereto.

Various known methods can be used to obtain an aromatic polyamide. For example, when using a low-temperature solution polymerization method using an acid dichloride and a diamine as raw materials, N-methylpyrrolidone, N,N-dimethylacetamide, A method of synthesizing by solution polymerization in an aprotic organic polar solvent such as dimethylformamide or dimethylsulfoxide, or a method of synthesizing by interfacial polymerization using an aqueous medium can be employed. Solution polymerization in an aprotic organic polar solvent is preferred because the molecular weight of the polymer can be easily controlled. When acid dichloride and diamine are used as raw materials, hydrogen chloride is produced as a by-product as the polymerization reaction progresses. Alternatively, organic neutralizing agents such as ethylene oxide, propylene oxide, ammonia, triethylamine, triethanolamine and diethanolamine may be used.

Various known methods can be used for obtaining the aromatic polyimide or its precursor polyamic acid. A method of synthesis by solution polymerization in an aprotic organic polar solvent such as methyl-2-pyrrolidone, N,N-dimethylacetamide, dimethylformamide and dimethylsulfoxide can be employed. As a method of ring-closing the synthesized aromatic polyamic acid to obtain an aromatic polyimide, a thermal ring-closing method, a chemical ring-closing method, or a combination thereof is used. The thermal ring-closing method is generally a method of heat-treating polyamic acid at about 100 to 500° C. to close the ring. On the other hand, the chemical ring closure method uses aliphatic tertiary amines such as trimethylamine and triethylamine, and heterocyclic tertiary amines such as isoquinoline, pyridine, and beta-picoline as catalysts, and aliphatic groups such as acetic anhydride, propionic anhydride, and butyric anhydride. This is a method of ring closure using a dehydrating agent such as a carboxylic anhydride or an aromatic acid anhydride such as benzoic anhydride.

In addition to the above-mentioned polymer, the film-forming stock solution of the present invention may contain an additive made of an inorganic material, an organic material, or an organic-inorganic hybrid material for the purpose of surface formation, hardness improvement, refractive index control, and the like. Although the additive is not particularly limited, examples thereof include inorganic substances such as SiO ₂ , TiO ₂ , Al ₂ O ₃ , CaSO ₄ , BaSO ₄ , CaCO ₃ , carbon black, carbon nanotubes, fullerene, zeolite, and other fine metal powders. be done. Examples of the organic material include particles made of organic polymers such as crosslinked polyvinylbenzene, crosslinked acryl, crosslinked polystyrene, polyester particles, polyimide particles, polyamide particles, and fluororesin particles, or surfaces coated with the above organic polymers. Inorganic particles subjected to the treatment of Moreover, an alkoxysilane compound etc. are mentioned as an organic inorganic hybrid material.

The film-forming stock solution prepared as described above is formed into a film by a so-called solution film-forming method. The solution film forming method includes, for example, a dry-wet method in which heat treatment is performed sequentially through a drying step and a water washing step in a wet bath, a dry method in which heat treatment is performed after the drying step, or after introduction into a wet bath without a drying step. , a wet method in which heat treatment is performed, and the like. As a method for making the difference in the in-plane orientation degree in the thickness direction within the scope of the present invention, in the dry-wet method and the dry method, the solvent evaporation rate difference in the thickness direction is increased, and the polymer concentration is increased when peeling from the support. For example, it may be made small and tension may be applied in the longitudinal direction to separate it. In any film-forming method, a method such as increasing the temperature difference of hot air introduced to both surfaces during heat treatment can be used. Here, the dry-wet method will be described as an example.

When a film is formed by a dry-wet method, a film-forming stock solution is extruded from a die onto a support such as a drum, an endless belt, or a support film, and then dried until the film-like material has self-retaining properties. be. At this time, the solvent in the film-like material extruded onto the support evaporates mainly from the surface side. Therefore, in order to obtain uniform drying conditions in the thickness direction of the film-like material, a method such as heating the support is used to promote solvent convection from the support side. On the other hand, in the present invention, by controlling the support temperature Tb (°C) when extruding the membrane-forming stock solution and the hot air temperature Ta (°C) introduced to the surface of the membrane, solvent drying on the support side and the surface side is controlled. It is preferable to control the in-plane orientation difference in the thickness direction by intentionally creating a speed difference. Specifically, Ta and Tb are preferably controlled within the following ranges.

80≦Tb<Ta≦180
20≤Ta-Tb
If Tb is less than 80° C., the solvent convection from the side of the support is reduced, and peeling from the support may be difficult. On the other hand, when Ta exceeds 180° C., rapid evaporation of the solvent from the surface may roughen the surface of the film or form a skin, making it difficult to peel the film from the support. If Ta-Tb is less than 20°C, the difference in solvent drying rate between the support side and the surface side is not sufficient, and the difference |Pa-Pb| in the in-plane orientation in the thickness direction may be less than 0.5. .

After the drying process, the film-like material is peeled off from the support and introduced into a wet process, where desalting, solvent removal, and the like are performed. Here, it is possible to further improve the in-plane orientation difference in the thickness direction by stretching in the longitudinal direction by applying tension when peeling from the support.

The polymer concentration when peeling the film-like material from the support is preferably 30 to 70% by mass, more preferably 40 to 60% by mass. If the polymer concentration at the time of peeling is less than 30% by mass, the self-holding property is not sufficient, and peeling from the support may be difficult, or two-layer peeling may occur, leaving a film-like substance on the support. . If the polymer concentration at the time of peeling exceeds 70% by mass, the film will devitrify and the haze of the final film will exceed 3.0%. The difference in the degree of in-plane orientation in the thickness direction may fall outside the scope of the present invention.

The solvent in the wet process is generally aqueous, but may contain a small amount of inorganic or organic solvent or inorganic salt in addition to water. The solvent temperature is usually 5 to 90°C.

Furthermore, it is preferable to stretch the film in the longitudinal direction when peeling the film from the support and/or during the wet process. The draw ratio in the longitudinal direction is preferably 1.05 to 1.40 times, more preferably 1.10 to 1.30 times. If the draw ratio in the longitudinal direction is less than 1.05 times, the orientation of the polymer chains does not proceed sufficiently, and the difference in the degree of in-plane orientation or the degree of in-plane orientation in the thickness direction may fall outside the scope of the present invention. . The stretch ratio in the longitudinal direction is defined as a value obtained by dividing the length of the film after stretching by the length of the film before peeling from the support.

The film that has undergone the wet process is then introduced into a tenter or the like, and subjected to heat treatment and stretching in the width direction of the film. The atmosphere of the heat treatment step may be an air atmosphere, but an inert atmosphere such as nitrogen or argon is most preferable because the yellowness index (YI) can be suppressed to a lower level.

Here, the heat treatment temperature during stretching in the width direction is important for controlling the orientation of polymer chains, and in order to suppress stretching unevenness in the film, it is common to control the heat treatment temperature to be uniform. On the other hand, in the present invention, of the two surfaces of the film, by controlling the temperature of the side with a high degree of in-plane orientation to be lower than the temperature of the side with a low degree of in-plane orientation, the difference in the degree of in-plane orientation in the thickness direction is reduced. Further improvement is preferable. The heat treatment temperature difference between both surfaces of the film is more preferably 5 to 50.degree. C., more preferably 10 to 40.degree. In order to control the heat treatment temperature difference between both surfaces of the film within the above range, the temperature of the hot air introduced into the tenter (or the set temperature when using a radiation heater) is separately controlled for the upper and lower surfaces. be done. The heat treatment temperature difference between both surfaces of the film can be easily measured by attaching a seal-type thermolabel to both surfaces of the film before introducing the tenter. The heat treatment temperature is preferably within the range of 200 to 400° C. for both surfaces of the film from the viewpoint of film stretchability, mechanical properties, optical properties, and the like. If the heat treatment temperature is less than 200° C., the film is likely to be torn, making it difficult to sufficiently stretch the film, and the difference in the degree of in-plane orientation or the degree of in-plane orientation in the thickness direction may fall outside the scope of the present invention. Also, Young's modulus and hardness may decrease. On the other hand, if the heat treatment temperature exceeds 400° C., the orientation of the molecular chains is relaxed even if the film is stretched. be. In addition, a decrease in Young's modulus and hardness and an increase in yellowness index (YI) may occur. As described above, it is preferable to appropriately adjust the stretch ratio in the width direction according to the stretching temperature, but 1.1 to 1.1. It is preferably within the range of 7 times, more preferably 1.2 to 1.6 times. If the draw ratio in the width direction is less than 1.1 times, the orientation of the polymer chains does not proceed sufficiently, and the difference in the degree of in-plane orientation or the degree of in-plane orientation in the thickness direction may fall outside the scope of the present invention. . If the stretch ratio in the width direction exceeds 1.7 times, the toughness of the film may be reduced, or the in-plane retardation may be increased, resulting in reduced visibility when used as a front film for a display. The stretch ratio in the width direction is defined as a value obtained by dividing the film width after stretching by the film width before stretching.

The present invention may be a laminated film in which a curable layer containing a curable resin is laminated on one side or both sides of the film produced by the above method.

As a method for laminating the cured layer, there is a method in which a coating agent made of a curable resin is coated on a film, dried and cured in this order. In addition, when laminating two or more cured layers with a different structure, one layer at a time may be coated, dried, and cured in that order, or multiple coating agents may be coated simultaneously using a multi-layer slit die or the like. , dried and cured.

Examples of coating methods include a dip coating method, a roller coating method, a wire bar coating method, a gravure coating method and a die coating method. The drying method includes heat transfer drying, hot air drying, drying by infrared irradiation, drying by microwave irradiation, and the like, and is not particularly limited, but drying by hot air irradiation is preferable.

Curing methods include heat curing and curing by irradiation with active energy rays such as electron beams and ultraviolet rays. In the case of heat curing, it is preferably cured at a temperature of 40 to 200°C, more preferably 80 to 200°C. When curing by irradiation with ultraviolet rays or electron beams, the oxygen concentration in the atmosphere is preferably low, and curing is more preferably performed in an atmosphere of an inert gas such as nitrogen or argon. If the oxygen concentration is high, curing may be insufficient. The types of ultraviolet lamps used for irradiating ultraviolet rays include, for example, a discharge lamp system, a flash system, a laser system, and an electrodeless lamp system. When ultraviolet curing is performed using a discharge lamp type high-pressure mercury lamp, the ultraviolet illuminance is preferably 100 to 3,000 mW/cm ² , more preferably 200 to 2,000 mW/cm ² .

The nitrogen-containing polymer film and laminated film of the present invention can be used as display materials, display material substrates, circuit substrates, optical waveguide substrates, semiconductor mounting substrates, transparent conductive films, retardation films, touch panels, capacitors, printer ribbons, acoustic diaphragms, It is preferably used in various applications such as solar cells, optical recording media, base films for magnetic recording media, packaging materials, pressure-sensitive adhesive tapes, adhesive tapes, and decorative materials. Among them, it can be used particularly suitably as a transparent film for flexible devices such as flexible displays because it has high transparency and has both contradictory properties of high hardness and bending resistance.

EXAMPLES The present invention will be described more specifically with reference to examples below.

The methods for measuring physical properties and evaluating effects in the present invention were carried out according to the following methods.

(1) Light transmittance at wavelengths of 550 nm and 450 nm Measurement was performed using the following equipment, and the light transmittance at each wavelength was obtained from the following formula.

Apparatus: UV measuring instrument U-3410 (manufactured by Hitachi Instrument Co., Ltd.)
Wavelength range: 300nm to 800nm
Measurement speed: 120 nm/min Measurement mode: Transmission Light transmittance (%) = (Tr1/Tr0) x 100
However, Tr1 is the intensity of light that has passed through the sample, and Tr0 is the intensity of light that has passed through air at the same distance except that it does not pass through the sample.

(2) In-plane orientation Pa, Pb
Raman scattering intensity was measured at a position of 1 μm in the thickness direction from one surface and a position of 1 μm in the thickness direction from the other surface of the cross section of the sample using the following apparatus, and the degree of in-plane orientation was obtained from the following formula.

Apparatus: Near-infrared Raman spectrometer (manufactured by Photon Design)
Measurement mode: Microscopic Raman Objective lens: 100x Beam diameter: 1 μm (align the center to the position of 1 μm in the thickness direction)
Cross slit: 1mm
Light source: YAG laser/1064 nm
Laser power: 400mW
Diffraction grating: Single300gr/mm
Slit: 100 μm
Detector: InGaAs (manufactured by Nippon Roper Co., Ltd.)
Degree of in-plane orientation = I parallel/I perpendicular, where I parallel is the Raman scattering intensity with a polarized light arrangement that matches the in-plane direction of the sample, and I vertical is the Raman scattering intensity with a polarized light arrangement that matches the thickness direction of the sample. . For the Raman scattering intensity of aromatic polyamide and aromatic polyimide, the Raman band at 1610 to 1620 cm ⁻¹ attributed to the C═C stretching mode of aromatic rings was used. The degree of in-plane orientation was the average value obtained for each of the cross section in the longitudinal direction of the sample and the cross section in the width direction orthogonal thereto.

(3) Glass transition temperature Determined from the inflection point of the storage modulus (E') by dynamic viscoelasticity measurement (DMA) according to ASTM E1640-13. DMA was performed using the following equipment and conditions.

Device: Viscoelasticity measuring device DMS6100 (manufactured by Seiko Instruments Inc.)
Measurement mode: Tensile mode Measurement frequency: 1Hz
Heating rate: 5°C/min Temperature range: 25°C to 400°C
Holding time: 2 minutes (4) Young's modulus A sample cut to a width of 10 mm and a length of 150 mm in the measurement direction was measured using a robot Tensilon AMF/RTA-100 (manufactured by Orientec) with a chuck distance of 50 mm and a tensile speed of 300 mm/ A tensile test was performed under the conditions of minutes, temperature of 23° C. and relative humidity of 65%, and the load-elongation curve was obtained.

(5) Thickness The thickness was calculated by observing the cross section of the sample using the following device.

Section preparation: Electronic sample freezing device MODEL: RM and rotary microtome MODEL: RM (manufactured by Japan Microtome Research Institute)
Observation device: Scanning electron microscope (FE-SEM) JSM-6700F type (manufactured by JEOL Ltd.)
Observation magnification: 3,000 times Observation mode: LEI mode Acceleration voltage: 3 kV
(6) yellowness index (YI)
Measurement was performed at a temperature of 23° C. and a humidity of 65% RH using a spectral colorimeter (manufactured by Nippon Denshoku Industries Co., Ltd.). Sample dimensions were 40 mm x 50 mm and were measured in transmission mode.

(7) Haze Measured using the following equipment.

Apparatus: Turbidity meter NDH5000 (manufactured by Nippon Denshoku Industries Co., Ltd.)
Light source: White LED 5V3W (rated)
Light receiving element: Si photodiode with V(λ) filter Measurement light flux: φ14 mm (incidence aperture φ25 mm)
Optical conditions: conforming to JIS-K7136 (2000) (8) Static bending resistance A sample was prepared and placed under the following conditions at a temperature of 23°C and a humidity of 65% RH.

Sample size: width 25 mm, length 20 mm
Sample preparation: Leave unloaded for 24 hours in an atmosphere with a temperature of 23°C and a humidity of 65% RH. Folded 180 degrees in the longitudinal direction and installed After leaving it for 24 hours under the above conditions, remove the load, fix one end face to the horizontal surface with tape, and measure the distance from the horizontal surface to the other end face to measure the warp. Height (mm) was evaluated. In addition, the value after the decimal point of the measured value was discarded and used as the warpage height value.

(9) Dynamic flex resistance Using a mandrel conforming to JIS-K5600-5-1 (1999), measurements were made at temperatures of 23°C and -20°C under the following conditions.

Sample size: short side 50 mm x long side 100 mm
Sample installation: Installed so that the position of 50 mm in the long side direction is the folding line (cylinder contact part) Cylinder size: 2 mm in diameter
Folding times: 1 million times Folding speed: 1Hz
Judgment criteria: A case where no discoloration, cracks, tears, or breakage was confirmed after the specified number of tests was judged to be O, and a case where it was confirmed was judged to be X.

(10) Hardness Measured according to JIS-K5600-5-4 (1999) at a temperature of 23° C. and a humidity of 65% RH using the following equipment.

Apparatus: Surface measuring machine HEIDON-14DR (manufactured by Shinto Kagaku Co., Ltd.)
Weight: 750gf
Angle: 45°
Movement speed: 30mm/min
Movement distance: 10mm
Sample fixation: Tape the sample on the glass plate Pencil used: Hi-Uni (manufactured by Mitsubishi Pencil Co., Ltd.), 10B, 9B, 8B, 7B, 6B, 5B, 4B, 3B, 2B in order from the softest (lowest hardness) , B, HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, 9H, 10H
Determination of hardness: The test was performed 5 times, and if there were no scratches or dents in the 3rd to 5th times, it was determined to have the hardness.

In the present invention, a coating agent comprising a film-forming stock solution and a curable resin was prepared according to the following method.

(11) Preparation of membrane-forming stock solution Polymer A: Dehydrated N-methyl-2-pyrrolidone (NMP, manufactured by Mitsubishi Chemical Corporation) was added with 2,2'-ditrifluoromethyl-4,4'-diaminobiphenyl (TFMB) as a diamine. , manufactured by Toray Fine Chemicals Co., Ltd.) was dissolved under a nitrogen stream, and the liquid temperature was cooled to 8°C in an ice water bath. To this, 2-chloroterephthaloyl chloride (CTPC, manufactured by Nippon Light Metal Co., Ltd.) corresponding to 99 mol% of the total amount of diamine was added over 30 minutes while the system was kept in an ice water bath under a nitrogen stream. After adding the total amount, stirring was performed for about 2 hours to polymerize the aromatic polyamide (polymer A). The resulting polymerization solution was neutralized with 97 mol% lithium carbonate (manufactured by Honjo Chemical Co., Ltd.) and 6 mol% diethanolamine (manufactured by Tokyo Kasei Co., Ltd.) with respect to the total amount of acid chloride to obtain a polymer having a polymer concentration of 10% by mass. A film-forming stock solution of A was obtained.

Polymer B: As raw material monomers, diamine is TFMB corresponding to 90 mol% and 4,4'-diaminodiphenyl ether (DPE, manufactured by Tokyo Kasei Kogyo Co., Ltd.) corresponding to 10 mol% with respect to the total amount of diamine, and acid chloride is diamine. Terephthaloyl chloride (TPC, manufactured by Tokyo Chemical Industry Co., Ltd.) corresponding to 60 mol% of the total amount and isophthaloyl chloride (IPC, manufactured by Tokyo Chemical Industry Co., Ltd.) corresponding to 39 mol% Polymer A In the same manner as above, a film-forming stock solution of polymer B was obtained.

Polymer C: As raw material monomers, diamine is TFMB corresponding to 100 mol% of the total amount of diamine, and acid chloride is IPC corresponding to 60 mol% and TPC corresponding to 39 mol% of the total amount of diamine. A film-forming stock solution of polymer C was obtained in the same manner as for polymer A.

Polymer D: TFMB was dissolved as a diamine in dehydrated NMP at room temperature. Then, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA, manufactured by Tokyo Chemical Industry Co., Ltd.) corresponding to 70 mol% of the total amount of diamine and 1,2,3 corresponding to 29 mol% ,4-cyclopentanetetracarboxylic dianhydride (CPDA, manufactured by Tokyo Kasei Kogyo Co., Ltd.) was added over 30 minutes and stirred for 2 hours. Next, pyridine and acetic anhydride (both manufactured by Tokyo Kasei Kogyo Co., Ltd.) corresponding to 200 mol % of the total amount of diamine were added, and the mixture was stirred at 70°C for 1 hour to obtain a polymer D film-forming stock solution.

Polymer E: TFMB was dissolved as a diamine in dehydrated NMP at room temperature. 6FDA corresponding to 20 mol % and CPDA corresponding to 20 mol % with respect to the total amount of diamine were added thereto over 15 minutes and stirred for 1 hour. Next, TPC corresponding to 59 mol % with respect to the total amount of diamine was added over 15 minutes and stirred for 1 hour. Finally, pyridine and acetic anhydride corresponding to 80 mol % of the total amount of diamine were added, and the mixture was stirred at 70°C for 1 hour to obtain a polymer E film-forming stock solution.

Polymer F: As raw material monomers, 2-chloro-1,4-phenylenediamine (CPA, manufactured by Nippon Kayaku Co., Ltd.) corresponding to 80 mol% of diamine and DPE corresponding to 20 mol% with respect to the total amount of diamine, and acid A membrane-forming stock solution of polymer F was obtained in the same manner as for polymer A, except that the chloride was CTPC corresponding to 99 mol % of the total amount of diamine.

(12) Preparation of Coating Agent Containing Curable Resin Silica particle organosilica sol MEK-AC-5140Z (manufactured by Nissan Chemical Industries, Ltd.) is used as the particles, and polyfunctional acrylate KAYARAD PET30 (manufactured by Nippon Kayaku Co., Ltd.) is used as the resin, A coating agent having a solid concentration of 50% by mass was prepared by diluting with toluene.

(Example 1)
A film-forming undiluted solution composed of polymer A was cast into a film form from a spinneret onto a stainless steel endless belt controlled to a surface temperature (Tb) of 100°C. Next, the cast film-like material was introduced into an oven chamber with a hot air temperature (Ta) of 130° C. to evaporate the solvent until the polymer concentration reached 50 mass %. Next, the film-like material was peeled off from the endless belt and introduced into a water tank in which pure water at 40° C. was flowing for desalting and solvent removal. Here, the film was stretched 1.15 times in the longitudinal direction (MD) in the process from casting to leaving the water bath. Finally, the film taken out of the water tank was introduced into a tenter and subjected to heat treatment and stretched 1.35 times in the width direction (TD). Here, the temperature of the hot air in the tenter was controlled so that the surface side which was not in contact with the support during casting was 280°C, and the surface side which was in contact with the support was 300°C. Table 1 shows the film-forming conditions described above, and Table 2 shows the physical properties of the film made of polymer A obtained.

Further, a coating agent comprising a curable resin was applied onto the obtained film comprising polymer A using a bar coater and dried in an oven at 80° C. for 2 minutes. Next, in a nitrogen atmosphere, UV lamp system LightHammer 10 Mark II (manufactured by Heraeus) was used to irradiate ultraviolet rays with an output of 120 W/cm and an integrated light amount of 400 mJ/cm ² to cure the coating film, thereby forming a cured layer having a thickness of 5 μm. Laminated. Similarly, a cured layer having a thickness of 5 μm was laminated on the other surface to obtain a laminated film having a total thickness of 35 μm. Table 2 shows the physical properties of the obtained laminated film.

(Examples 2-4)
A film was obtained in the same manner as in Example 1 except that the film-forming stock solution and film-forming conditions were changed as shown in Table 1. Table 2 shows the physical properties of the obtained film.

(Example 5)
A film made of polymer E was obtained in the same manner as in Example 1, except that the film-forming stock solution and film-forming conditions were changed as shown in Table 1. Table 2 shows the physical properties of the obtained film.

Further, on the obtained film made of Polymer E, cured layers each having a thickness of 5 μm on each side were laminated on both sides in the same manner as in Example 1 to obtain a laminate film having a total thickness of 35 μm. Table 2 shows the physical properties of the obtained laminated film.

(Examples 6-9)
A film was obtained in the same manner as in Example 1 except that the film-forming stock solution and film-forming conditions were changed as shown in Table 1. Table 2 shows the physical properties of the obtained film.

(Example 10)
A film composed of polymer A was obtained in the same manner as in Example 1, except that the amount of the casting stock solution was adjusted to control the final thickness to 15 μm. Table 2 shows the physical properties of the obtained film.

Further, on the obtained film made of polymer A, cured layers each having a thickness of 3 μm on each side were laminated on both sides in the same manner as in Example 1 to obtain a laminate film having a total thickness of 21 μm. Table 2 shows the physical properties of the obtained laminated film.

(Example 11)
A film composed of polymer A was obtained in the same manner as in Example 1, except that the amount of the film-forming stock solution to be cast was adjusted to control the final thickness to 40 μm. Table 2 shows the physical properties of the obtained film.

(Comparative example 1)
A film-forming undiluted solution composed of Polymer F was cast in a film form from a spinneret onto a stainless steel endless belt whose surface temperature (Tb) was controlled to 100°C. Then, the cast film-like material was introduced into an oven chamber with a hot air temperature (Ta) of 130° C. to evaporate the solvent. Attempts were made to peel the resulting film, but the drying progressed on the surface side and formed a skin, while the drying was insufficient on the support side, resulting in two-layer delamination in which the film remained, resulting in peeling. I couldn't do it.

(Comparative Examples 2-5)
A film was obtained in the same manner as in Example 1 except that the film-forming stock solution and film-forming conditions were changed as shown in Table 1. Table 2 shows the physical properties of the obtained film.

Claims (6)

Contains at least one polymer selected from the group consisting of aromatic polyamides, aromatic polyimides and aromatic polyamideimides, has a light transmittance of 80 to 100% at a wavelength of 550 nm, and is positioned 1 μm in the thickness direction from one surface. The nitrogen-containing polymer film satisfies the following formulas (1) to (3), where Pa is the degree of in-plane orientation at a position 1 μm in the thickness direction from the other surface, and Pb is the degree of in-plane orientation at a position 1 μm in the thickness direction from the other surface.
(1) 3.0≤Pa≤15.0
(2) 3.0≤Pb≤15.0
(3) 0.5≦|Pa−Pb|≦5.0 The nitrogen-containing polymer film according to claim 1, which has a glass transition temperature of 150 to 500°C. 3. The nitrogen-containing polymer film according to claim 1, which has a Young's modulus of 5.0 to 20.0 GPa in at least one direction. 4. The nitrogen-containing polymer film according to any one of claims 1 to 3, comprising a polymer having a structural unit represented by any one of the following chemical formulas (I) to (IV).
Chemical formula (I):

R ¹ and R ² are —H, an aliphatic group having 1 to 5 carbon atoms, —CF ₃ , —CCl ₃ , —OH, —F, —Cl, —Br, —OCH ₃ , a silyl group, or an aromatic ring; is a group containing
Chemical formula (II):

R ³ is a group containing Si, a group containing P, a group containing S, a halogenated hydrocarbon group, a group containing an aromatic ring, or a group containing an ether bond (provided that the structure having these groups in the molecule units may be mixed).
Chemical formula (III):

^R4 is any group.
Chemical formula (IV):

^R5 is any aromatic group, any alicyclic group. 5. The nitrogen-containing polymer film according to any one of claims 1 to 4, which contains a polymer having a structural unit represented by the following chemical formula (V).
Chemical formula (V):

^R6 is an arbitrary group. A laminated film obtained by laminating a curable layer containing a curable resin on one or both sides of the nitrogen-containing polymer film according to any one of claims 1 to 5.