TW202235489A - Polyimide film obtained by copolymerizing at least one diamine and at least one acid dianhydride - Google Patents

Abstract

The present invention provides a polyimide film obtained by copolymerizing at least one diamine and at least one acid dianhydride, which has a yield strength of 50 to 200 MPa measured according to ASTM D882 when the thickness is 30 to 100 μm and a modulus of resilience of 0.5 to 5.0 MPa based on the formula 1, where σ is the yield strength and E is the modulus in formula 1. In more detail, a polyimide film is provided, which can be used as a cover window of a display because of its high modulus of resilience and yield strength to ensure excellent resilience and high flexural properties.

Description

Polyimide membrane

The present invention relates to a polyimide film, and more specifically, to a polyimide film having both excellent resilience and high bending properties due to high modulus of resilience (Modulus of Resilience) and yield strength, which can be used as an exterior of a display Polyimide film covering the window.

On the surface of a display device such as a liquid crystal display (Liquid Crystal Display: LCD) or an organic light emitting display (Organic Light Emitting Display: OLED), a cover window (cover window) is applied to protect the panel. As a material for conventional window coverings, tempered glass with excellent flatness, heat resistance, chemical resistance, moisture and gas barrier performance, small coefficient of linear expansion (CTE) and high light transmittance has been mainly used.

On the other hand, in recent years, flexible displays such as curved displays or in-folding (in-folding) displays have been developed. In order to be applied to such a flexible display, the outer covering window should be flexible. However, the conventional glass outer covering window is usually bulky and fragile, and has low flexibility, so it is not suitable for flexible displays.

In order to solve the above-mentioned problems, in recent years, cladding windows using plastic materials with relatively free formability have been proposed. A cladding window made of a plastic material is light, not easily broken, and has the advantage of being able to present a variety of designs. As plastic materials for window cladding at present, polycarbonate, polyethylene terephthalate, polymethyl methacrylate, etc. which are excellent in transparency are mainly used. Although the above-mentioned materials have the advantage of excellent transparency, their glass transition temperature (Tg) is 150° C. or less, so their heat resistance is poor, and their chemical resistance and mechanical strength are low, so their applications are limited.

In order to solve such a problem, an excessively thick hard coat layer or the like has been introduced into the above-mentioned plastic material, but in this case, the hard coat layer is cracked or the bendability is significantly reduced during molding. In particular, in recent years, displays in a flexible state have been widely used, but there is a limit in improving resilience against physical deformation caused by external force.

The problem to be solved

The present invention was made in order to solve the above-mentioned problems, and its technical task is to provide a novel polyimide film that can be used as an outer window covering simultaneously with excellent resilience and various physical properties such as high bendability, mechanical strength, and transparency. .

Other purposes and advantages of the present invention will be more clearly illustrated by the following specific embodiments of the invention and the scope of the patent application.

Solution to the problem

In order to achieve the above-mentioned technical problems, the present invention provides a polyimide film obtained by copolymerization comprising at least one diamine and at least one acid dianhydride. When the thickness is 30-100 μm, the yield strength measured according to ASTM D882 ( Yield Strength) is 50~200 MPa, and the modulus of resilience (Modulus of Resilience) is 0.5~5.0 MPa.

According to an embodiment of the present invention, based on the above-mentioned film thickness of 30-100 μm, when the above-mentioned polyimide film has a curvature radius of 1-10 mm, the initial recovery height (H _I ) after bending the film for 72 hours is 5 cm Below, the recovery height ( _HF ) after at least one hour has passed is 3 cm or less.

According to an embodiment of the present invention, in the stress-strain curve (Stress-Strain Curve) of the above-mentioned film measured according to ASTM D882, the yield strain (Yield Strain, Y/S) defined by the strain (strain) at the critical point can be 2.0%~5.0%, the slope of the critical point corresponds to at least 80% of the slope of the range of tensile strength 20~40MPa.

According to an embodiment of the present invention, when the film is bent with a curvature radius of 1 to 5 mm, the number of times of bending until breaking may be 100,000 or more.

According to an embodiment of the present invention, the modulus measured according to ASTM D882 may be 3-8 GPa.

According to an embodiment of the present invention, when the thickness is 30-100 μm, the light transmittance at a wavelength of 550 nm can be above 85%, and the yellowness based on the ASTM E313-73 standard can be below 10.

According to an embodiment of the present invention, the above-mentioned at least one diamine may include a fluorinated aromatic first diamine, a fluorinated aromatic second diamine, a hydroxyl-based aromatic third diamine, an ether-based aromatic fourth One or more kinds of diamines, non-fluorine-based aromatic fifth diamines, and alicyclic sixth diamines.

According to an embodiment of the present invention, based on 100 mol% of the total diamines, the contents of the first to sixth diamines may be 10-100 mol%.

According to an embodiment of the present invention, the above-mentioned at least one acid dianhydride may include a fluorinated aromatic first acid dianhydride, a non-fluorinated aromatic second acid dianhydride, a fluorinated aromatic third acid dianhydride, and a fatty acid dianhydride. One or more kinds of the group consisting of cyclic quaternary acid dianhydrides.

According to an embodiment of the present invention, based on 100 mol% of the total acid dianhydride, the contents of the first acid dianhydride to the fourth acid dianhydride may each be 10-100 mol%.

According to an embodiment of the present invention, the molar ratio (a/b) of the above-mentioned diamine (a) to the above-mentioned acid dianhydride (b) may be in the range of 0.7˜1.3.

According to an embodiment of the present invention, the above-mentioned polyimide film can be used as a cover window of a display device.

Invention effect

According to an embodiment of the present invention, the polyimide film can ensure a high modulus of resilience and yield strength and exhibit excellent resilience against physical deformation through the selection of predetermined components constituting the polyimide film and its content adjustment. In addition, by adjusting the slope of the tensile elastic region, high yield strain and high bending properties can be achieved.

In addition, in the present invention, high light transmittance, low yellowness, excellent modulus and surface hardness are exhibited, so that the handleability and reliability of the final product can be improved.

Therefore, the polyimide film of the present invention can be effectively used as the cover window of the display device of this field represented by flat panel display panel, flexible display, etc. Products, home appliances, etc.

The effects of the present invention are not limited to the contents exemplified above, and various effects are included in this specification.

Hereinafter, the present invention will be described in detail. The embodiments of the present invention are provided for more complete description to those skilled in the art. The following embodiments can be modified into various other forms, and the scope of the present invention is not limited by the following embodiments. At this time, the same reference symbols refer to the same structures throughout the specification.

Unless otherwise defined, all terms (including technical and scientific terms) used in this specification can be used according to the meaning commonly understood by those skilled in the art to which this invention belongs. In addition, terms defined in commonly used dictionaries should not be ideally or excessively interpreted unless clearly defined otherwise.

In addition, throughout the specification, when it is stated that a certain part "includes" a certain component, unless there is a particularly contrary statement, it means that other components may be further included, not excluded. In addition, throughout the specification, the meaning of "on" includes not only the case of being located above or below the object part, but also the case of other parts in between, and it is not located on the basis of the direction of gravity. In addition, in the specification of the present application, terms such as "first" and "second" do not indicate any order or degree of importance, and are used to distinguish a plurality of constituent elements from one another.

＜Polyimide film＞

The polyimide resin film according to an embodiment of the present invention is a transparent film that can be provided on a display device, and more specifically, can be used as a cover window of a flexible display.

Here, the cover window refers to a film arranged on the outermost side of the flexible display device to protect the display device. Such a cover window may be a single window film, or may be a film in which a window coating layer is formed on a separate substrate film made of an optically transparent resin.

On the other hand, the cover window of a display exposed to the outside should not only have processing characteristics such as flexibility and excellent optical characteristics in daily life, but also need to have predetermined resilience against physical deformation caused by external loads. In particular, when cladding windows are folded, if the stress-induced deformation exceeds the yield strain, then permanent deformation occurs without recovery and cannot be restored.

In the present invention, it is intended to select specific physical properties related to resilience among the original physical properties of the membrane material, such as modulus of resilience (modulus of Resilience) and yield strength (Yield Strength), and to control these physical properties in a ratio Conventional plastic materials and/or polyimide films are used to improve resilience. Therefore, when the above-mentioned polyimide film is used as an outer cover window of a foldable display device, the film resilience before and after static folding is excellent, and high reliability can be provided. Such a display device can be applied without limitation to display devices known in the art, especially in-folding and out-folding foldable displays.

According to a specific example of the present invention, the above-mentioned polyimide film comprises at least one diamine and at least one acid dianhydride and is obtained by copolymerization. When the thickness is 30-10 μm, the yield strength (Yield Strength) measured according to ASTM D882 can be 50~200 MPa, the modulus of resilience (Modulus of Resilience, R) can be 0.5~5.0 MPa.

(上述式中，σ為屈服強度，E為模數) Here, the modulus of resilience can be defined by the following [Formula 1]. [Formula 1]

(In the above formula, σ is the yield strength and E is the modulus)

Specifically, the modulus of resilience (R), as one of the rheological properties of the material, means the energy per unit volume that the material can absorb without permanent deformation. For example, when a predetermined material is deformed, although the strain is elastic at a small amount of deformation, once it changes from elastic deformation to plastic deformation under certain conditions, a permanent deformation will occur that can no longer be recovered. That is, the modulus of resilience is the maximum energy that can be stored in the single volume of the material within the elastic limit, which means the elastic recovery force. The physical properties such as elastic modulus (R), yield strength (Yield Strength), and yield strain (Yield Strain) to be controlled in the present invention can be understood from the stress-strain curve (Stress-Strain Curve, S-S curve). Such a stress-strain curve (S-S curve) represents the relationship between the stress (stress) applied to the polymer material by the tensile test of the polymer material and the strain (strain) of the polymer material corresponding to the stress. The curve on the graph of the relationship can be called a curve representing the change of the required stress as the strain of the polymer material increases. As shown in FIG. 1 below, in general, the horizontal axis (eg, x-axis) represents tensile strain (Strain), and the vertical axis (eg, y-axis) represents stress (tensile strength, Stress).

In the present invention, the parameters of the above-mentioned modulus of resilience (Modulus of Resilience) and yield strength (Yield Strength) and their values may be affected by the thickness of the above-mentioned polyimide film. The values of such elastic modulus and yield strength can be measured based on the thickness of the above-mentioned polyimide film of 30-100 μm, specifically 30-90 μm, more specifically 80±5 μm.

Specifically, the yield strength (Yield Strength) of the polyimide film of the present invention can be 50~195 MPa, and the rebound modulus (Modulus of Resilience, R) can be 0.5~4.0 MPa, more specifically, yield The strength (Yield Strength) can be 100~190 MPa, and the rebound modulus (Modulus of Resilience, R) can be 2.0~3.5 MPa. In the case of the polyimide film of the present invention that satisfies the above-mentioned parameters of resilience modulus and yield strength (Yield Strength), high elasticity can be ensured without permanent deformation and excellent recovery characteristics can be exhibited.

In order to be used as an outer covering window of a mobile communication terminal or a tablet PC, etc., the polyimide film of the present invention preferably possesses excellent properties such as excellent flexibility, high transparency, and light transmittance together with the above-mentioned resilience modulus and yield strength characteristics. Optical properties, high mechanical properties.

In particular, compared with conventional plastic materials and/or polyimide films, the polyimide film of the present invention is characterized by having both high yield strain and high bending properties. When such a polyimide film is used as an outer cover window of an in-folding type foldable mobile phone, it can exhibit an excellent effect of folding endurance due to its high flexibility and high strength. .

As a specific example, in the stress-strain curve (Stress-Strain Curve) of the above-mentioned film measured according to ASTM D882, the yield strain (Yield Strain, Y/ S) may be 2.0%-5.0%, and the slope of the critical point corresponds to at least 80% of the slope of the range of tensile strength 20-40 MPa.

In this specification, the strain at yield is defined by the stress- The x-intercept value of the predetermined critical point (threshold slope (threshold slope), X ₂ ≥ X ₁ × 0.8) of at least 80% of the strain slope (Stress-Strain slope, X ₁ ), that is, the tensile strain (Tensile strain) To define (see Figure 1 below). Such a yield strain is newly defined in the present invention, and is a property inherent to a specific composition of a polyimide film, and is a feature different from conventional polyimide films.

Specifically, in a stress-strain curve (S-S curve) obtained by a tensile test performed at 25° C., the yield strain (Y/S) of the polyimide film may be 2.0%˜4.8%. From the perspective of improving bending resistance, the yield strain (Y/S) may preferably be 2.0% to 4.0%, more preferably 2.0 to 3.8%. In the case of a polyimide film that satisfies such a yield strain (Y/S) parameter, it exhibits excellent flexibility and can suppress the occurrence of cracks in repeated bending fatigue, and exhibits excellent bendability.

As another specific example, based on a film thickness of 30-100 μm, when the above-mentioned polyimide film has a radius of curvature of 1-10 mm, the initial recovery height (H _I ) after bending the film for 72 hours can be 5 cm or less , the recovery height ( _HF ) after 1 hour can be 3 cm or less. Specifically, the initial recovery height (H _I ) may be 3 cm or less, and the recovery height ( _HF ) after 1 hour may be 0.5 cm or less. At this time, the lower limit of the restored height of the film at the beginning or after 1 hour is not particularly limited, and may be, for example, 0 cm or more.

As yet another specific example, when the above-mentioned polyimide film is bent with a radius of curvature of 1 mm to 5 mm, the number of times of bending until breaking may be 100,000 or more. In particular, when bending with a bending radius of 1 mm, the number of times of bending until breaking may be 100,000 or more, specifically 200,000 or more, preferably millions (1,000,000) or more. At this time, the upper limit of the deformation of the number of times of bending until fracture is not particularly limited, for example, may be 3,000,000 or less, specifically 2,500,000 or less.

In consideration of scratch resistance, reliability, etc. of a display, the polyimide film of the present invention preferably has excellent mechanical properties of high modulus.

As a specific example, the polyimide film may have a modulus of 3 to 8 GPa, and may be 3.5 to 7 GPa from the viewpoint of simultaneously exhibiting mechanical hardness and excellent flexibility. Here, the modulus means a value measured in accordance with ASTM D882. When the above-mentioned modulus is smaller than the above-mentioned numerical value, it is difficult to exhibit sufficient hardness, and when it is larger than the above-mentioned numerical value, flexibility may decrease and foldability may decrease.

In order to improve the visibility of a display screen, the polyimide film of the present invention preferably has excellent optical properties such as high transparency and light transmittance.

As a specific example, when the above-mentioned polyimide film has a thickness of 30-100 μm, the light transmittance at a wavelength of 550 nm can be more than 85%, specifically more than 89%, more specifically 90%-99% . In addition, the yellowness (Y.I.) based on the ASTM E313-73 standard may be 10 or less, specifically 7 or less, more specifically 5 or less.

In this specification, unless otherwise mentioned, the above-mentioned physical properties of the polyimide film are based on the above-mentioned film thickness of 10-100 μm, specifically 30-80 μm. However, it is not limited to the above-mentioned thickness range, and can be appropriately adjusted within a normal thickness range known in the art.

As long as the polyimide film of the present invention satisfies the above-mentioned resilience modulus and yield strength characteristics, the components constituting the polyimide resin and/or its composition are not particularly limited.

As an example, the above-mentioned polyimide film is obtained by copolymerization containing at least one kind of diamine and at least one kind of acid dianhydride. Specifically, polyamic acid containing diamine, acid dianhydride, and if necessary, a solvent can be combined. The product is produced by imidization and heat treatment at high temperature.

Generally speaking, polyimide (polyimide, PI) resin refers to the solution polymerization of aromatic acid dianhydride and aromatic diamine or aromatic diisocyanate to produce polyamic acid derivatives, and then make them under high temperature. High heat-resistant resin produced by ring-closing dehydration and imidization. Such a polyimide resin is a polymer substance containing an imide ring, and is excellent in heat resistance, chemical resistance, abrasion resistance, and electrical properties due to the chemical stability of the imide ring. The aforementioned polyimide resin may be in the form of a random copolymer or a block copolymer.

The diamine (a) component constituting the polyimide film of the present invention is not limited as long as it has a diamine structure in its molecule, and ordinary diamine compounds known in the art can be used without limitation. For example, there are aromatic, alicyclic, and aliphatic compounds having a diamine structure, or combinations thereof.

Especially, in the present invention, when considering the mechanical properties such as high modulus of resilience and yield strength, high flexibility, modulus (Modulus) of polyimide film; High Transmittance (High Transmittance), low Y.I, low When improving optical properties such as haze, at least one aromatic diamine can be used or a mixture of the above-mentioned aromatic diamine and alicyclic diamine can be used.

Specific examples of the above-mentioned aromatic diamine include fluorine-based, sulfone-based, hydroxyl-based (Hydroxyl), ether (Ether)-based, and non-fluorine-based diamines having a fluorinated substituent. Therefore, in the present invention, as the diamine compound, a fluorinated aromatic first diamine introduced with a fluorine substituent, a fluorine-based aromatic second diamine, a hydroxyl-based aromatic third diamine, an ether-based aromatic The fourth diamine and the fifth non-fluorine-based aromatic diamine are used alone or in a state of mixing two or more of them appropriately.

As non-limiting examples of diamine monomers (a) that can be used, oxydiphenylamine (ODA), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (2 ,2'-TFDB), 2,2'-bis(trifluoromethyl)-4,3'-diaminobiphenyl (2,2'-Bis(trifluoromethyl)-4,3'-Diaminobiphenyl), 2, 2'-bis(trifluoromethyl)-5,5'-diaminobiphenyl (2,2'-Bis(trifluoromethyl)-5,5'-Diaminobiphenyl), 2,2'-bis(trifluoromethyl) )-4,4'-diaminophenyl ether (2,2'-Bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 6-FODA), bisaminohydroxyphenyl hexafluoropropane (DBOH), bisamino Phenoxyphenylhexafluoropropane (4BDAF), bisaminophenoxyphenylpropane (6HMDA), bisaminophenoxydiphenyldrone (DBSDA), bis(4-aminophenyl)drone (4,4 '-DDS), bis (3-aminophenyl) diphenylamine (3,3'-DDS), sulfonyl diphthalic anhydride (SO2DPA), 4,4'-oxydiphenylamine (4,4'- ODA), or a mixture of one or more of them, etc.

When considering the high transparency, high glass transition temperature and low yellowness of the polyimide film, the fluorinated first diamine can use 2,2'-bis(trifluoroform) which can induce linear macromolecularization base)-4,4'-diaminobiphenyl (2,2'-TFDB), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (1,4-Bis(4 -amino-2-trifluoromethylphenoxy)benzene, 6-FAPB). In addition, bis(4-aminophenyl)pyridine (4,4'-DDS) or 3,3'-DDS can be used as the second diamine of the phenylene system. In addition, the third hydroxyl-based diamine can use 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (2,2-Bis(3-amino-4-hydroxyphenyl)-hexafluoro propane, BIS -AP-AF). In addition, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenylether (6-FODA) or oxydiphenylamine (ODA) can be used as the ether-based fourth diamine. In addition, 2,2-bis(3-amino-4-methylphenyl)-hexafluoropropane (2,2-Bis(3-amino-4-methylphenyl)- hexafluoropropane, BIS-AT-AF), m-tolidine or p-phenylenediamine (p-PDA).

In the diamine monomer (a) of the present invention, the above-mentioned fluorinated aromatic first diamine, fluorinated aromatic second diamine, hydroxyl-based aromatic third diamine, ether-based aromatic fourth diamine, non- The content of the fluorine-based aromatic fifth diamine is not particularly limited, each based on 100 mol% of the overall diamine, may be 0-100 mol%, specifically 10-90 mol%, more specifically may be 20~80 mole%. Wherein, the content of at least one of the above-mentioned first diamine to fifth diamine is contained in such a manner as to satisfy 100 mol% of the whole diamine.

According to a specific example of the present invention, as the diamine monomer (a), a fluorinated first diamine and an ether-based fourth diamine can be used in combination. At this time, their usage ratio is not particularly limited, for example, it may be 50-90:10-50 mol % ratio.

According to another specific example of the present invention, as the diamine monomer (a), at least one fluorinated first diamine can be used in combination. At this time, their usage ratio may be 50~90:10~50 mole % ratio, which is not particularly limited.

The alicyclic diamine is not particularly limited as long as it contains at least one alicyclic ring in the molecular structure. As a non-limiting example of cycloaliphatic diamines that can be used, 2,2-bis(3-amino-4-hydroxycyclohexyl)hexafluoropropane [2,2-bis(3-amino-4-hydroxycyclohexyl )hexafluoropropane], 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane (MACM), 4,4'-methylenebiscyclohexylamine (PACM), 1,3-bis(amino Methyl)cyclohexane (1,3-BAC), 1,4-bis(aminomethyl)cyclohexane (1,4-BAC), cis-1,2-cyclohexanedimethylamine, trans Formula - 1,2-cyclohexanedimethylamine, 1,4-cyclohexyldiamine (1,4-cyclohexyldiamine, CHDA), bis(4-aminocyclohexyl) ether or mixtures thereof, etc.

In the present invention, an aromatic diamine and an alicyclic diamine can be used in combination as the diamine monomer (a), and in this case, their mixing ratio can be appropriately adjusted in consideration of the physical properties of the polyimide film. For example, based on 100 mol% of the overall diamine, the mixing ratio of aromatic diamine and alicyclic diamine can be 0~100 : 100~0 mol%, specifically 10~90 : 90~10 Mole % ratio.

As the acid dianhydride (b) monomer constituting the polyimide film of the present invention, ordinary compounds known in the art having an acid dianhydride structure in the molecule can be used without limitation. For example, aromatic, alicyclic, and aliphatic compounds having a dianhydride structure, or combinations thereof, etc. can be used, specifically, at least one alicyclic dianhydride can be used, or at least one aromatic compound can be used. an aromatic acid dianhydride, or a mixture of the above-mentioned aromatic acid dianhydrides and alicyclic acid dianhydrides.

Specific examples of the above-mentioned aromatic acid dianhydrides include fluorinated aromatic first acid dianhydrides, non-fluorinated aromatic second acid dianhydrides, and pyrene-based aromatic third acid dianhydrides. Therefore, in the present invention, as the acid dianhydride compound, a fluorinated aromatic first acid dianhydride, a non-fluorinated aromatic second acid dianhydride, and a fluorine-based aromatic third acid dianhydride can be used as the acid dianhydride compound. They are used alone or in combination of two or more of them appropriately.

The above-mentioned fluorinated first acid dianhydride monomer is not particularly limited as long as it is an aromatic acid dianhydride having a fluorine substituent introduced therein. As a non-limiting example of a fluorinated first acid dianhydride that can be used, there is 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (2,2-bis(3,4-dicarboxyphenyl ) hexafluoropropane dianhydride, 6-FDA), 4-(trifluoromethyl) pyromellitic dianhydride (4-(trifluoromethyl) pyromellitic dianhydride, 4-TFPMDA) and the like. These may be used alone or in combination of two or more. Among the fluorinated acid dianhydrides, 6-FDA is a compound that is very suitable for transparency due to its obvious property of restricting the formation of charge transfer complexes (CTC: Change transfer complex) between molecular chains and within molecular chains.

In addition, the non-fluorinated second acid dianhydride monomer is not particularly limited as long as it is a non-fluorinated aromatic acid dianhydride that does not introduce a fluorine substituent. As non-limiting examples of non-fluorinated second acid dianhydride monomers that can be used, there are pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (3,3',4,4'-Biphenyl tetracarboxylic acid dianhydride, BPDA), benzophenone tetracarboxylic dianhydride (BTDA), oxygen diphthalic dianhydride (ODPA), 4,4-(4, 4-isopropylidenediphenoxy)bis(phthalic anhydride)(4,4-(4,4-Isopropylidenediphenoxy)bis(phthalic anhydride), BPADA), bis(carboxyphenyl)dimethylsilane Dianhydride (Bis (3,4dicarboxyphenyl) dimethylsilane dianhydride, SiDA) and so on. These may be used alone or in combination of two or more.

In addition, the third acid dianhydride monomer of the phosphonium system is not particularly limited as long as it is an acid dianhydride having a phosphine group introduced therein. 3',4,4'-diphenylsulfonetetracarboxylic dianhydride, DSDA).

In the acid dianhydride monomer (b) of the present invention, the contents of the above-mentioned fluorinated aromatic first acid dianhydride, non-fluorinated aromatic second acid dianhydride, and fluorinated aromatic third acid dianhydride are not particularly limited. . For example, based on 100 mol% of the whole acid dianhydride, their content can be in the range of 0-100 mol%, specifically 10-90 mol%, more specifically 20-80 mol%. Wherein, the content of at least one of the first acid dianhydride to the third acid dianhydride is contained in such a manner as to satisfy 100 mol% of the whole acid dianhydride.

The alicyclic (alicyclic) acid dianhydride is not particularly limited as long as it has an alicyclic ring instead of an aromatic ring in the compound and has an acid dianhydride structure. As non-limiting examples of usable cycloaliphatic dianhydrides, there are cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), bicyclo[2 ,2,2]-7-octene-2,3,5,6-tetracarboxylic dianhydride (BCDA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4 -Tetralin-1,2-dicarboxylic anhydride (TDA), 1,1'-bicyclohexane-3,3',4,4'-tetracarboxylic dianhydride (H-BPDA), 1,2,4 ,5-cyclohexane-tetracarboxylic dianhydride (H-PMDA), cyclopentanone bis-spironorbornane (cyclopentanone bis-spironorbornane, cpODA), bicyclo[2.2.2]octane-2,3,5, 6-tetracarboxylic acid 2,3:5,6-dianhydride (Bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic2,3:5,6-dianhydride (7CI,8CI)) or one of them mixtures of the above, etc.

In the present invention, as the acid dianhydride monomer (b), an aromatic acid dianhydride and an alicyclic acid dianhydride can be used in combination, and in this case, their mixing ratio can be appropriately adjusted in consideration of the physical properties of the polyimide film. For example, based on 100 mol% of the overall acid dianhydride, the mixing ratio of aromatic acid dianhydride and alicyclic acid dianhydride can be 0~100: 100~0 mol% ratio, specifically 10~90: 90~10 mol% ratio.

According to a specific example of the present invention, as the acid dianhydride (b), a fluorinated aromatic first acid dianhydride and an alicyclic acid dianhydride, or a fluorinated aromatic first acid dianhydride and a non-fluorinated Mixed use of aromatic second acid dianhydrides. At this time, their usage ratio is not particularly limited, for example, it may be 10~90: 90~10 mol% ratio, specifically, it may be 30~80: 70~20 mol% ratio.

According to another specific example of the present invention, as the acid dianhydride (b), an alicyclic acid dianhydride and a non-fluorinated aromatic second acid dianhydride may be used in combination. At this time, their usage ratio may be 30~80:20~70 mol% ratio, but not particularly limited thereto.

As another preferable example of the present invention, at least one kind of non-fluorinated aromatic second acid dianhydride can be used in combination as the acid dianhydride (b). At this time, their usage ratio may be 50~80:20~50 mol% ratio, but not particularly limited thereto.

In the polyamic acid composition constituting the polyimide film of the present invention, the ratio (a/b) of the number of moles of the diamine component (a) to the number of moles of the acid dianhydride component (b) may be 0.7~1.3, preferably 0.8~1.2, more preferably 0.9~1.1.

The polyamic acid composition of the present invention can use organic solvents known in the art without limitation as solvents for the solution polymerization of the above-mentioned monomers. As an example of a usable solvent, one selected from m-cresol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl One or more polar solvents selected from oxone (DMSO), acetone, diethyl acetate, and dimethyl phthalate (DMP). In addition, tetrahydrofuran (THF), a low-boiling solution such as chloroform, or a solvent such as γ-butyrolactone can be used. At this time, the content of the solvent (the first solvent for polymerization) is not particularly limited, but in order to obtain a suitable molecular weight and viscosity of the polyamic acid composition (polyamic acid solution), based on the weight of the overall polyamic acid composition , the content thereof may preferably be 50 to 95% by weight, more preferably 70 to 90% by weight.

The above-mentioned polyamic acid composition can be produced by reacting at least one acid dianhydride and at least one diamine into an organic solvent. For example, in order to improve the physical properties of polyimide, diamine (a) and The acid dianhydride (b) is adjusted to an equivalent ratio of approximately 1:1. The composition of such a polyamic acid composition is not particularly limited. For example, based on 100% by weight of the overall weight of the polyamic acid composition, it may contain 2.5 to 25.0% by weight of acid dianhydride, 2.5 to 25.0% by weight of diamine and It is composed of an organic solvent that satisfies the balance of 100% by weight of the composition. Wherein, the content of the organic solvent may be 70 to 90% by weight. In addition, the above-mentioned polyamic acid composition may include 30 to 70% by weight of acid dianhydride and 30 to 70% by weight of diamine based on 100% by weight of the corresponding solid content, and there is no particular limitation thereto.

The polyamic acid composition constituted as above may have a viscosity in the range of about 1,000~200,000 cps, preferably about 5,000~50,000 cps. When the viscosity of the polyamic acid composition is in the above-mentioned range, it is easy to adjust the thickness when coating the polyamic acid composition, and the coating surface can be uniformly formed.

According to needs, the above-mentioned polyamic acid composition may contain at least one of plasticizer, antioxidant, flame retardant, dispersant, viscosity modifier, leveling agent, etc. additive.

The polyimide resin film of the present invention can be manufactured according to a common method known in the art, for example, by coating (casting) the above-mentioned polyimide composition on a substrate, such as a glass substrate Then, while slowly increasing the temperature in the range of 30-350 °C, it is produced by inducing the imide ring closure reaction (imidazation) for 0.5-8 hours.

At this time, the coating method can be used without limitation by a common method known in the art, for example, can be selected from spin coating (Spin coating), dip coating (Dip coating), solvent casting (Solvent casting), slot At least any one method in the group consisting of die coating (Slot die coating) and spray coating. The polyamic acid composition can be coated at least once or more so that the colorless and transparent polyimide resin layer has a thickness of several hundred nm to several tens of μm.

In the method for producing a polyimide film of the present invention, as the imidization method applied in the step of imidizing the polymerized polyamic acid by casting it on a support, thermal imidization can be applied. Chemical imidization method, chemical imidization method, or combined use of thermal imidization method and chemical imidization method.

The thermal imidization method is to obtain a polyamide by casting a polyamide acid composition (polyamide acid solution) on a support and heating it slowly in the temperature range of 30~400°C for 1~10 hours. imine membrane method.

In addition, the chemical imidization method is to add a dehydrating agent represented by acid anhydrides such as acetic anhydride and acyl imidate represented by amines such as isoquinoline, β-picoline, and pyridine into the polyamide acid composition. Method for Aminating Catalysts. When the thermal imidization method is used in combination with such a chemical imidization method, the heating conditions of the polyamic acid composition can be adjusted according to the type of the polyamic acid composition and the properties of the polyimide film to be produced. thickness etc. to change.

More specifically, the above-mentioned situation of using the thermal imidization method and the chemical imidization method together can be put into a dehydrating agent and an imidization catalyst in the polyamic acid composition, and after casting on the support body, at 80 ~300°C, preferably at 150~250°C, to activate the dehydrating agent and imidization catalyst, thereby partially curing and drying to obtain a polyimide film.

The thickness of the polyimide film thus formed is not particularly limited, and can be appropriately adjusted according to the field of application. For example, it may be in the range of 10 to 150 μm, preferably in the range of 30 to 100 μm.

The polyimide film of the present invention produced as described above and its modified examples can be effectively used in various fields requiring high resilience, high bending properties, and excellent optical properties. In particular, it can be used as a cover window of a display device to prevent surface scratches and impart excellent flexibility and visibility to flexible display devices.

In the present invention, a display device refers to a flexible display device or a non-flexible display device that displays images, including not only a flat panel display device (FPD: Flat Panel Display Device), but also a curved display device (Curved Display Device), a foldable display device (Foldable Display Device), flexible display device (Flexible Display Device), foldable mobile phone, smart phone, mobile communication terminal or tablet PC, etc. Specifically, the above-mentioned display device may be a liquid crystal display device (Liquid Crystal Display), an electrophoretic display device (Electrophoretic Display), an organic light emitting display device (Organic Light Emitting Display), an inorganic EL display device (Inorganic Light Emitting Display), a field emission Field Emission Display, Surface-conduction Electron-emitter Display, Plasma Display, Cathode Ray Display, Electronic Paper, etc. As a specific example, it may be a flat display panel such as LCD, PDP, OLED, or the like. Not limited to the above application, the polyimide film of the present invention can be applied to common display devices known in the art, and can also be used as a substrate for a flexible display or a protective film.

As a specific example of a display device having the above-mentioned polyimide film, it may include a display unit, a polarizer, a touch panel, a cover window, and a protective film, and the above-mentioned cover window may include the polyimide film according to an embodiment of the present invention. imide film. Here, the components constituting the display device are not particularly limited, and may include common components known in the art.

Hereinafter, the present invention will be described in more detail by specific examples. The following examples are merely illustrations for helping the understanding of the present invention, and the scope of the present invention is not limited thereto.

[ Example 1~4. Polyimide Membrane Manufacturing ]

The polyamic acid composition was produced using the composition containing the diamine and acid dianhydride shown in Table 1 below.

After coating the above-mentioned polyamic acid composition on glass for LCD with a bar coater (Bar Coater), it was carried out in a convection oven in a nitrogen atmosphere at 80°C for 30 minutes, at 150°C for 30 minutes, and at 200°C. Drying and imide ring-closing reaction (Imidazation) were carried out while gradually raising the temperature step by step for 1 hour and then at 300° C. for 1 hour. Thus, a polyimide film having a film thickness of 80 μm with an imidization rate of 85% or more was produced. Afterwards, the polyimide membrane was separated from the glass and obtained.

[Table 1] Diamine (mole%) Acid dianhydride (mole%) first monomer second monomer first monomer second monomer Example 1 TFDB (100) - BPADA (70) BPDA (30) Example 2 TFDB (100) - BPDA (80) 6FDA (20) Example 3 TFDB (70) 6FODA (30) CBDA (20) BPDA (80) Example 4 TFDB (70) 6FAPB (30) BPADA (60) CBDA (40) Comparative example 1 p-PDA (100) - BTDA (70) DSDA (30) Comparative example 2 m-Tol (100) - OPDA (50) PMDA (50) Comparative example 3 BIS-AT-AF (70) p-PDA (30) CpODA (30) BTDA (70) Comparative example 4 m-Tol (80) 4,4-DABAN (20) CpODA (70) OPDA (30)

[ comparative example 1~4. Polyimide Membrane Manufacturing ]

Except having used the composition described in said Table 1, it carried out similarly to said Examples 1-4, and produced the polyimide film of Comparative Examples 1-4, respectively.

[ Experimental example . Physical property evaluation ]

The physical properties of the polyimide resin films produced in Examples 1 to 4 and Comparative Examples 1 to 4 were evaluated as follows, and the results are shown in Table 2 below. At this time, the physical properties in Table 2 below are based on a thickness of 50 μm.

＜Physical property evaluation method＞

1) Transmittance measurement

Measurements were performed at a wavelength of 550 nm using a UV-Vis NIR Spectrophotometer (UV-Vis NIR Spectrophotometer, Shimadzu, model name: UV-3150).

2) Determination of yellowness

The yellowness at 550 nm was measured using a spectrophotometer (Konica Minolta, CM-3600A) according to ASTM E313-73 standard.

3) Thickness measurement

The thickness of the film was measured with a thickness meter (Mitutoyo, model name: 547-401).

4) Modulus determination

UTM (Instron, model name: 5942) was used to measure tensile strength (MPa) and elastic modulus (GPa) according to ASTM D882 standard.

5) Determination of Yield Strain

UTM (Instron, model name: 5942) is used to measure the slope of the stress-strain curve (Stress-Strain slope threshold, X1) in the range of 20~40 MPa in accordance with the ASTM D882 standard and meet the critical value of more than 80%. (X2 ≥ X1×0.8) corresponds to the strain (Strain, x value).

6) Rebound modulus

(上述式中，σ為屈服強度，E為模數) Using the above-mentioned modulus and yield strength (Yield Strength), the rebound modulus was calculated according to the following formula 1. At this time, the yield strength was calculated as the yield strength at the yield point by the same method as the above-mentioned yield strain. [Formula 1]

(In the above formula, σ is the yield strength and E is the modulus)

7) Determination of bending characteristics (Dynamic Folding cycle (number of dynamic folding cycles))

Bending characteristics were measured using a planar body unloaded U-folding test equipment (DLDMLS-FS, YUASA), and the radius of curvature was adjusted to 1 mm to 5 mm to measure the number of folding cycles (Folding Cycle).

8) Determination of resilience

The restoring force was confirmed by measuring the height of the film when the sample was taken out after 72 hours were fixed on a static folding holder (Static Folding Holder, radius of curvature 1-10 nm) with the lapse of predetermined time. [Table 2]

the yield strain (Yield Strain, %) Yield Strength (Yield Strength, MPa) rebound Modulus (MPa) Resilience (cm) dynamic fold Cycles (@1R) modulus (Gpa) Transmittance (%T, @550nm) yellowness (Y.I) initial high Height after 1 hour Height after 3 hours Example 1 3.2 172 3.08 < 0.1 0 0 2000K 4.8 89.5 3.4 Example 2 3.1 160 3.05 1.0 0.1 < 0.1 1800K 4.2 89.8 2.5 Example 3 2.8 180 2.89 1.8 0.8 0.2 1400K 5.6 89.1 3.0 Example 4 3.0 168 2.88 0.5 < 0.1 < 0.1 1700K 4.9 90.0 2.7 Comparative example 1 1.3 80 0.46 6.9 6.1 5.5 60K 6.9 82.1 17.1 Comparative example 2 1.5 83 0.49 7.3 5.7 4.8 90K 7.1 84.1 14.7 Comparative example 3 1.5 72 0.42 6.2 5.3 4.3 80K 6.1 84.7 15.4 Comparative example 4 1.4 66 0.38 6.3 5.5 4.4 80K 5.8 83.4 16.8

As shown in the above Table 2, it can be seen that the polyimide film of the present invention not only exhibits high resilience modulus, yield strength and yield strain characteristics compared with the comparative examples, but also exhibits excellent resilience and high flexibility at the same time . In addition, it was found that it has excellent transparency, mechanical properties, and thermal expansion coefficient.

Therefore, it was confirmed that the polyimide film of the present invention can be effectively used as a cover window of a display device.

none.

Fig. 1 is a stress-strain curve (Stress) defined by yield strength (Yield Strength), yield strain (Yield Strain) and modulus of resilience (Modulus of Resilience) in the tensile test utilizing polyimide film of the present invention -Strain Curve) graph.

Claims (12)

A polyimide film obtained by copolymerization comprising at least one diamine and at least one acid dianhydride, when the thickness is 30-100 μm, the yield strength measured according to ASTM D882 is 50-200 MPa, based on the following formula 1 The rebound modulus is 0.5~5.0 MPa, Formula 1

In the above formula 1, σ is the yield strength, and E is the modulus. For the polyimide film of claim 1, based on the film thickness of 30-100 μm, when the radius of curvature is 1-10 mm, the initial recovery height H _I of the film after bending for 72 hours is 5 cm or less, after at least The restored height H _F after 1 hour was 3 cm or less. For the polyimide film of claim 1, in the stress-strain curve of the film measured according to ASTM D882, the yield strain Y/S defined by the strain at the critical point is 2.0% to 5.0%, and the critical point is The slope corresponds to at least 80% of the slope in the interval of tensile strength 20 to 40 MPa. For the polyimide film of claim 1, when the film is bent with a curvature radius of 1 to 5 mm, the number of times of bending until it breaks is more than 100,000 times. Such as the polyimide film of claim 1, the modulus measured according to ASTM D882 is 3 ~ 8 GPa. For example, the polyimide film of claim 1, when the thickness is 30-100 μm, the light transmittance at a wavelength of 550 nm is above 85%, and the yellowness based on ASTM E313-73 standard is below 10. Such as the polyimide film of claim 1, the at least one diamine includes a first diamine selected from fluorinated aromatics, a second aromatic diamine of a fluoride system, a third aromatic diamine of a hydroxyl group, and an aromatic aromatic diamine of an ether system. One or more of the group consisting of the fourth diamine of the fluorine-free aromatic group and the sixth diamine of the alicyclic group. For example, in the polyimide film of claim 7, based on 100 mol% of the whole diamine, the contents of the first diamine to the sixth diamine are each 10-100 mol%. As the polyimide film of claim 1, the at least one acid dianhydride comprises a fluorinated aromatic first acid dianhydride, a non-fluorinated aromatic second acid dianhydride, and a fluorinated aromatic third acid dianhydride. Anhydrides and alicyclic fourth acid dianhydrides are composed of one or more types. For example, in the polyimide film of claim 9, based on 100 mol% of the whole acid dianhydride, the contents of the first acid dianhydride to the fourth acid dianhydride are respectively 10-100 mol%. For the polyimide film of claim 1, the molar ratio a/b of the diamine a to the acid dianhydride b is in the range of 0.7 to 1.3. The polyimide film as claimed in claim 1, which is used as a cover window of a display device.

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