KR20220032905A - Polyimide-based polymer film, substrate for display device, and optical device using the same - Google Patents

Abstract

The present invention relates to a polyimide-based resin film having a color coordinate b* of 1.5 or more and 2.0 or less at a thickness of 10 μm and a retardation value of 25 nm or less in the thickness direction at a thickness of 10 μm, and a substrate for a display device using the same, and an optical device using the same. According to the present invention, provided are the polyimide-based resin film capable of implementing excellent chemical resistance and low retardation (Rth) in the thickness direction, the substrate for the display device using the same, and the optical device using the same.

Description

A polyimide-based resin film, a substrate for a display device using the same, and an optical device

The present invention relates to a polyimide-based resin film capable of implementing excellent chemical resistance and low retardation (Rth) in the thickness direction, a substrate for a display device using the same, and an optical device.

The display device market is rapidly changing mainly for flat panel displays (FPDs) that have a large area and can be thin and lightweight. Such flat panel displays include a liquid crystal display (LCD), an organic light emitting display (OLED), or an electrophoretic display (EPD).

In particular, in recent years, in order to further expand the applications and uses of the flat panel display, attention has been focused on so-called flexible display devices in which a flexible substrate is applied to the flat panel display. The application of such a flexible display device is being reviewed mainly for mobile devices such as smart phones, and the field of application thereof is gradually expanding.

In general, in manufacturing a flexible display device and a lighting device, a TFT device is manufactured by forming a multilayer inorganic film such as a buffer layer, an active layer, and a gate insulator on a cured polyimide.

However, when light is emitted to the polyimide layer (substrate layer), the emission efficiency may be reduced due to the difference between the refractive index of the upper layer of the inorganic film and the refractive index of the polyimide layer as described above.

In addition, cracks may occur due to various organic solvents used in the process of manufacturing a flexible display device and a lighting device using the polyimide material included in the polyimide layer (substrate layer).

Accordingly, there is a demand for the development of a new polyimide capable of satisfying excellent chemical resistance to organic solvents and excellent optical properties.

The present invention relates to a polyimide-based resin film capable of implementing excellent chemical resistance and low retardation (Rth) in the thickness direction.

Another object of the present invention is to provide a substrate for a display device using the polyimide-based resin film, and an optical device.

In order to solve the above problems, in the present specification, the color coordinate b* at 10 μm thickness is 1.5 or more and 2.0 or less, and the retardation R _th value in the thickness direction at 10 μm thickness is 25 nm or less, a polyimide-based resin film is provided do.

In the present specification, there is also provided a substrate for a display device comprising the polyimide-based resin film.

In the present specification, an optical device including the polyimide-based resin film is also provided.

Hereinafter, a polyimide-based resin film, a substrate for a display device using the same, and an optical device according to specific embodiments of the present invention will be described in more detail.

Unless explicitly stated herein, terminology is for the purpose of referring to specific embodiments only, and is not intended to limit the present invention.

As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite.

As used herein, the meaning of 'comprising' specifies a particular characteristic, region, integer, step, operation, element and/or component, and other specific characteristic, region, integer, step, operation, element, component, and/or group. It does not exclude the existence or addition of

And, in the present specification, terms including ordinal numbers such as 'first' and 'second' are used for the purpose of distinguishing one component from other components, and are not limited by the ordinal number. For example, within the scope of the present invention, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

In the present specification, the (co)polymer is meant to include both polymers or copolymers, the polymer means a homopolymer consisting of a single repeating unit, and the copolymer means a composite polymer containing two or more kinds of repeating units.

In the present specification, examples of the substituent are described below, but is not limited thereto.

In the present specification, the term "substituted" means that other functional groups are bonded instead of hydrogen atoms in the compound, and the position to be substituted is not limited as long as the position at which the hydrogen atom is substituted, that is, the position where the substituent is substituted, is not limited, and when two or more substituted , two or more substituents may be the same as or different from each other.

As used herein, the term "substituted or unsubstituted" refers to deuterium; halogen group; cyano group; nitro group; hydroxyl group; carbonyl group; ester group; imid; amide group; primary amino group; carboxyl group; sulfonic acid group; sulfonamide group; a phosphine oxide group; alkoxy group; aryloxy group; alkyl thiooxy group; arylthioxy group; an alkyl sulfoxy group; arylsulfoxy group; silyl group; boron group; an alkyl group; cycloalkyl group; alkenyl group; aryl group; aralkyl group; aralkenyl group; an alkylaryl group; alkoxysilylalkyl group; an arylphosphine group; Or N, O, and S atom means that it is substituted or unsubstituted with one or more substituents selected from the group consisting of a heterocyclic group containing one or more, or substituted or unsubstituted, two or more of the above-exemplified substituents are linked. . For example, "a substituent in which two or more substituents are connected" may be a biphenyl group. That is, the biphenyl group may be an aryl group or may be interpreted as a substituent in which two phenyl groups are connected.

, 또는

는 다른 치환기에 연결되는 결합을 의미하고, 직접결합은 L 로 표시되는 부분에 별도의 원자가 존재하지 않은 경우를 의미한다. In this specification,

, or

denotes a bond connected to another substituent, and a direct bond denotes a case in which a separate atom does not exist in the portion represented by L .

In the present specification, aromatic is a characteristic that satisfies the Huckels Rule, and a case in which all of the following three conditions are satisfied according to the Huckels Rule may be defined as aromatic.

1) There must be 4n+2 electrons that are completely conjugated by empty p-orbitals, unsaturated bonds, unpaired electron pairs, etc.

2) 4n+2 electrons must form a planar isomer and form a ring structure.

3) All atoms of the ring must be able to participate in conjugation.

In the present specification, the alkyl group is a monovalent functional group derived from an alkane, and may be straight-chain or branched, and the number of carbon atoms in the straight-chain alkyl group is not particularly limited, but is preferably 1 to 20. In addition, the number of carbon atoms of the branched chain alkyl group is 3 to 20. Specific examples of the alkyl group include methyl, ethyl, propyl, n-propyl, isopropyl, butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methyl-butyl, 1-ethyl-butyl, pentyl, n -pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, heptyl , n-heptyl, 1-methylhexyl, octyl, n-octyl, tert-octyl, 1-methylheptyl, 2-ethylhexyl, 2-propylpentyl, n-nonyl, 2,2-dimethylheptyl, 1-ethyl- propyl, 1,1-dimethyl-propyl, isohexyl, 2-methylpentyl, 4-methylhexyl, 5-methylhexyl, 2,6-dimethylheptan-4-yl, and the like. The alkyl group may be substituted or unsubstituted, and when substituted, examples of the substituent are as described above.

In the present specification, the haloalkyl group refers to a functional group in which a halogen group is substituted with the aforementioned alkyl group, and examples of the halogen group include fluorine, chlorine, bromine or iodine. The haloalkyl group may be substituted or unsubstituted, and when substituted, examples of the substituent are as described above.

In the present specification, a multivalent functional group is a residue in a form in which a plurality of hydrogen atoms bonded to an arbitrary compound are removed, and may include, for example, a divalent functional group, a trivalent functional group, and a tetravalent functional group. For example, the tetravalent functional group derived from cyclobutane refers to a residue in which 4 hydrogen atoms bonded to cyclobutane are removed.

In the present specification, the electron withdrawing group (Electro-withdrawing group) may include at least one selected from the group consisting of a haloalkyl group, a halogen group, a cyano group, a nitro group, a sulfonic acid group, a carbonyl group and a sulfonyl group, preferably For example, it may be a haloalkyl group such as a trifluoromethyl group (-CF ₃ ).

In the present specification, a direct bond or a single bond means that no atom or group of atoms is present at the corresponding position, and thus is connected by a bonding line. Specifically, it refers to a case in which a separate atom does not exist in the portion represented by L ₁ and L ₂ in the formula.

In this specification, the weight average molecular weight means the weight average molecular weight in terms of polystyrene measured by the GPC method. In the process of measuring the polystyrene equivalent weight average molecular weight measured by the GPC method, a commonly known analyzer, a detector such as a differential refraction detector, and a column for analysis may be used, and the temperature at which it is normally applied Conditions, solvents, and flow rates can be applied. As a specific example of the measurement conditions, the evaluation temperature is 160 ° C. using a Waters PL-GPC220 instrument using a Polymer Laboratories PLgel MIX-B 300 mm long column, and 1,2,4-trichlorobenzene is used as a solvent The flow rate was 1 mL/min, and the sample was prepared at a concentration of 10 mg/10 mL, and then supplied in an amount of 200 μL, and the value of Mw can be obtained using a calibration curve formed using a polystyrene standard. The molecular weight of the polystyrene standard was 2,000 / 10,000 / 30,000 / 70,000 / 200,000 / 700,000 / 2,000,000 / 4,000,000 / 10,000,000.

Hereinafter, the present invention will be described in more detail.

1. Polyimide-based resin film

According to an embodiment of the present invention, a polyimide-based resin film having a color coordinate b* of 1.5 or more and 2.0 or less at a thickness of 10 μm and a retardation R _th value of 25 nm or less in a thickness direction at a thickness of 10 μm may be provided.

The inventors have found that, like the polyimide-based resin film of the embodiment, the color coordinate b* at a thickness of 10 μm is 1.5 or more and 2.0 or less, and the retardation R _th value in the thickness direction at a thickness of 10 μm satisfies 25 nm or less, Excellent optical properties of colorless and transparent can be realized through a low degree of yellowing, and at the same time, optical isotropy is increased through a low thickness direction retardation (R _th ) characteristic. Through experimentation, it was confirmed through experimentation that the deterioration of visual sensitivity due to distortion could be prevented, and the invention was completed.

Specifically, the polyimide film according to the present invention can increase the refractive index and can be used as a substrate layer in a flexible display device to reduce the difference in refractive index with each layer constituting the device, and from this, By reducing the amount of light that is extinguished, it is possible to effectively increase the efficiency of the light emission (bottom emission).

Specifically, the polyimide-based resin film of the embodiment may have a color coordinate b* of 1.5 or more and 2.0 or less, or 1.5 or more and 1.8 or less, or 1.5 or more and 1.7 or less, or 1.511 or more and 1.633 or less at a thickness of 10 μm. As such, as the color coordinate b* is lowered, the polyimide-based resin film of the embodiment may have low yellowing properties, thereby implementing excellent optical properties.

In the present invention, "color coordinates" means coordinates in the CIE Lab color space, which is a color value defined by the CIE (Commossion International de l'Eclairage), and any position in the CIE color space is L*, It can be expressed as a*, b* three coordinate values.

Here, the L* value represents brightness. If L*=0, it represents black, and if L*=100, it represents white. In addition, the a* value indicates whether the color having the corresponding color coordinate is biased toward pure red (pure magenta) or pure green (pure green), and the b* value indicates that the color having the corresponding color coordinate is pure yellow and Shows which side of pure blue is biased.

Specifically, the b* value has a range of -b to +b. The maximum value of b* (b* max) represents pure yellow, and the minimum value of b* (b* min) represents pure blue. For example, a negative b* value indicates a color biased toward pure yellow, and a positive number indicates a color biased toward pure blue. When b*=50 and b*=20 are compared, it means that b*=80 is closer to pure yellow than b*=50.

Examples of the method and equipment for measuring color coordinates are not specifically limited, and various methods conventionally used for measuring color coordinates may be applied without limitation. For example, color coordinates (b*) of the polyimide film may be measured using a color meter (Color-Eye 7000A manufactured by GRETAGMACBETH).

When the color coordinate b* at a thickness of 10 μm of the polyimide-based resin film is excessively increased to more than 2, the color coordinate of the polyimide film is misaligned and color distortion occurs, so that it is difficult to apply as a display.

On the other hand, if the color coordinate b* at a thickness of 10 μm of the polyimide-based resin film is excessively reduced to less than 1.5, the chemical resistance of the polyimide film of the polyimide film is rapidly reduced and cracks in an organic solvent such as PGMEA within a short time. This can cause problems that occur.

In addition, the polyimide-based resin film of the embodiment has a retardation value of 25 nm or less, or 0.1 nm or more and 25 nm or less, or 1 nm or more and 25 nm or less, or 10 nm or more and 25 nm or less at a thickness of 10 μm. , or 20 nm or more and 25 nm or less, or 22 nm or more and 25 nm or less. As such, optical isotropy is increased through the retardation (R _th ) characteristic in the low thickness direction, and excellent visibility can be realized by securing a diagonal viewing angle of the display to which the polyimide-based resin film is applied.

This low retardation is a monomer used for preparing a polyimide film, as described below, m-Phenylenediamine (m-PDA), which is a diamine having an asymmetric structure, and 9,9-bis(3), an anhydride with increased steric hindrance by a polycyclic ring. It seems to be achieved by reducing the refractive index difference in the plane direction and the thickness direction using ,4-dicarboxyphenyl)fluorene dianhydride (9,9-Bis(3,4-dicarboxyphenyl)fluorene Dianhydride, BPAF).

The retardation in the thickness direction may be measured for a wavelength of 532 nm, and examples of the measuring method and equipment are not specifically limited, and various methods used for measuring the retardation in the thickness direction can be applied without limitation.

Specifically, the thickness direction retardation R _th can be calculated through Equation 1 below.

[Equation 1]

R _th (nm) = |[(n _x + n _y ) / 2] - n _z | ×d

(In Equation 1, n _x is the largest refractive index among the in-plane refractive indices of the polyimide resin film measured with light having a wavelength of 532 nm; n _y is the in-plane refractive index of the polyimide resin film measured with light having a wavelength of 532 nm is the refractive index perpendicular to n _x ; n _z is the refractive index in the thickness direction of the polyimide resin film measured with light having a wavelength of 532 nm; d is the thickness of the polyimide film.)

That is, the thickness direction retardation R _th is a value obtained by multiplying the absolute value of the difference between the thickness direction refractive index value (n _z ) and the average value of the plane refractive index values [(n _x +n _y )/2] by the thickness direction, A smaller difference between the refractive index value (n _z ) and the average value [(n _x +n _y )/2] of the plane refractive index values may indicate a lower value.

As the polyimide-based resin film has a thickness direction retardation value of 25 nm or less at a thickness of 10 μm, the average value of the refractive index value in the thickness direction (n _z ) and the plane refractive index value on the display to which the polyimide-based resin film is applied As the difference of [(n _x +n _y )/2] decreases, excellent visibility may be realized.

When the retardation value in the thickness direction of the polyimide-based resin film at a thickness of 10 μm is excessively increased to more than 25 nm, a distortion phenomenon occurs when light is transmitted in a structure in which a polyimide is present on the upper portion when a transparent display is implemented, There is a technical limit in that even a compensation film that compensates up to 45 nm cannot compensate for the refraction of transmitted light.

Meanwhile, the polyimide-based resin film may have a retardation R ₀ value in the plane direction at a thickness of 10 μm of 0.5 nm or less, or 0.01 nm or more and 0.5 nm or less, or 0.01 nm or more and 0.3 nm or less.

The phase difference in the plane direction may be measured with respect to a wavelength of 532 nm, examples of the measurement method and equipment are not specifically limited, and various methods used for measuring the phase difference in the conventional plane direction may be applied without limitation.

Specifically, the in-plane retardation R ₀ may be calculated through Equation 2 below.

[Equation 2]

R ₀ (nm) = ｜ (n _x - n _y ) ｜×d

(In Equation 2, n _x is the largest refractive index among the in-plane refractive indices of the polyimide resin film measured with light having a wavelength of 532 nm; n _y is the in-plane refractive index of the polyimide resin film measured with light having a wavelength of 532 nm n is the refractive index perpendicular to _x ; d is the thickness of the polyimide film.)

That is, the in-plane retardation R ₀ is a value obtained by multiplying the film thickness by the absolute value of the difference value between the plane refractive indices n _x and n _y , and the smaller the difference between the plane refractive indices n _x and n _y , the lower it may be.

As the polyimide-based resin film satisfies the retardation value in the plane direction at 10 μm thickness of 0.5 nm or less, the difference between the plane refractive index n _x and n _y on the display to which the polyimide-based resin film is applied decreases. Visibility may be implemented.

On the other hand, the polyimide-based resin film has at least one glass transition temperature at a temperature of 300 ℃ or more and 400 ℃ or less, or 300 ℃ or more and 350 ℃ or less, or 300 ℃ or more and 330 ℃ or less, or 315 ℃ or more and 330 ℃ or less. can An example of the method for measuring the glass transition temperature is not particularly limited, but, for example, using a thermomechanical analysis device (TMA (Q400 manufactured by TA)), the film pulling force is set to 0.02N, and the temperature is 100 to 200 ℃ After performing the first temperature raising process at a temperature increase rate of 5 °C/min in the range, after cooling at a cooling rate of 4 °C/min in a temperature range of 200 to 100 °C, 5 °C in a temperature range of 80 to 350 °C The inflection point shown in the temperature increase section in the secondary temperature increase process can be obtained as Tg by performing the secondary temperature increase process at a temperature increase rate of /min.

The polyimide-based resin film according to the present invention has a thermal expansion coefficient of 40 ppm/°C or more and 54 ppm/°C or less, or 40 ppm/°C or more and 53 ppm/°C or less, when the temperature is raised in a temperature range of 100°C or more and 200°C or less. , or 45 ppm/℃ or more and 53 ppm/℃ or less, or 46.2 ppm/℃ or more and 53 ppm/℃ or less.

The coefficient of thermal expansion is set to 0.01N or more and 0.1N or less, or 0.01N or more and 0.05N or less for the polyimide-based resin film sample, and is 1 in a temperature range including a temperature range of 100 ℃ to 200 ℃. The pattern of changes in thermal expansion when the temperature is raised at a temperature increase rate of ℃/min or more and 10°C/min or more, or 4°C/min or more and 6°C/min or less is measured by TMA (Q400 manufactured by TA).

As such, as the polyimide-based resin film has a low coefficient of thermal expansion, it is possible to improve heat resistance by alleviating deformation due to heat. It can be prevented from being damaged by the damage and can also suppress the occurrence of warpage in the metal thin film formed on the plastic substrate.

The polyimide-based resin film may have an average refractive index of 1.6985 or more and 1.6999 or less, or 1.6988 or more and 1.6995 or less at a wavelength of 532 nm. As an example of a method of measuring the average refractive index, the refractive indexes in the plane direction (TE) and the thickness direction (TM) were measured at a wavelength of 532 nm using a prism coupler, and the average refractive index was calculated through the following Equation (3).

[Equation 3]

Average refractive index = (n _x + n _y + n _z ) / 3

(In Equation 3, n _x is the largest refractive index among the in-plane refractive indices of the polyimide resin film measured with light having a wavelength of 532 nm; n _y is the in-plane refractive index of the polyimide resin film measured with light having a wavelength of 532 nm. It is the refractive index perpendicular to n _x ; n _z is the refractive index in the thickness direction of the polyimide resin film measured with light having a wavelength of 532 nm.)

The polyimide film may have a yellow index YI of 2.5 or more and 3.0 or less at a thickness of 10 μm. When the yellow index YI at a thickness of 10 μm of the polyimide-based resin film is excessively increased to more than 3, the degree of yellow discoloration of the polyimide film increases, thereby making it difficult to manufacture a colorless and transparent film.

Meanwhile, the polyimide-based resin film may take 5 minutes or more to crack after contact with a propylene glycol methyl ether acetate (PGMEA) solvent. Specifically, after dropping PGMEA to an area of 3 cm x 3 cm or more on the surface of the polyimide film, the time it took for cracks to occur using an optical microscope (OLYMPUS BX51, magnification 4X) was longer than 5 minutes, which was excellent Chemical resistance can be realized.

On the other hand, when the time taken for cracks to occur after contacting the polyimide-based resin film with a propylene glycol methyl ether acetate (PGMEA) solvent is reduced to less than 5 minutes, a polyimide material is used to There is a problem in that a crack is generated due to various organic solvents used in the process of manufacturing the flexible display device and the lighting device, and thus the quality is deteriorated.

Meanwhile, the polyimide-based resin film may include a polyimide-based resin. The polyimide-based resin means that it includes all of polyimide, and polyamic acid and polyamic acid ester, which are precursor polymers thereof. That is, the polyimide-based polymer may include at least one selected from the group consisting of a polyamic acid repeating unit, a polyamic acid ester repeating unit, and a polyimide repeating unit. That is, the polyimide-based polymer may include one polyamic acid repeating unit, one polyamic acid ester repeating unit, one polyimide repeating unit, or a copolymer in which two or more repeating units thereof are mixed.

At least one repeating unit selected from the group consisting of the polyamic acid repeating unit, the polyamic acid ester repeating unit, and the polyimide repeating unit may form the main chain of the polyimide-based polymer.

The polyimide-based resin film may include a cured product of the polyimide-based resin. The cured product of the polyimide-based resin means a product obtained through the curing process of the polyimide-based resin.

In particular, the polyimide-based resin may include a polyimide repeating unit represented by Formula 1 below.

[Formula 1]

In Formula 1, X ₁ is an aromatic tetravalent functional group containing multiple rings, and Y ₁ is an aromatic divalent functional group having 10 or less carbon atoms.

In Formula 1, X ₁ is an aromatic tetravalent functional group containing multiple rings, and X ₁ is a functional group derived from a tetracarboxylic dianhydride compound used for synthesizing a polyimide-based resin.

When the aromatic tetravalent functional group containing the polycyclic group is included in X ₁ , an asymmetric structure with increased steric hindrance by the polycyclic ring is introduced into the polyimide chain structure, thereby improving heat resistance by alleviating deformation due to heat. Preferably, the low phase difference can be realized by reducing the difference in refractive index between the plane direction and the thickness direction.

More specifically, the tetravalent functional group of X ₁ may include a tetravalent functional group represented by Formula 2 below.

[Formula 2]

In Formula 2, Ar is a polycyclic aromatic divalent functional group. The polycyclic aromatic divalent functional group is a polycyclic aromatic hydrocarbon compound or a divalent functional group derived from a derivative compound thereof, and may include a fluorenylene group. The derivative compound includes all compounds in which one or more substituents are introduced or carbon atoms are replaced with heteroatoms.

More specifically, in Ar of Formula 2, the polycyclic aromatic divalent functional group may include a fused cyclic divalent functional group containing at least two or more aromatic ring compounds. That is, in the multicyclic aromatic divalent functional group, at least two or more aromatic ring compounds may be contained in the functional group structure, and the functional group may have a fused ring structure.

The aromatic ring compound may include an arene compound containing one or more benzene rings, or a hetero arene compound in which a carbon atom in the arene compound is replaced with a hetero atom.

The aromatic ring compound may be contained in at least two or more of the polycyclic aromatic divalent functional group, and each of the two or more aromatic ring compounds may form a directly fused ring or a fused ring through another ring structure. For example, when two benzene rings are each joined to a cycloalkyl ring structure, it can be defined that two benzene rings form a fused ring through the cycloalkyl ring.

The fused cyclic divalent functional group containing at least two or more aromatic ring compounds is a divalent functional group derived from a fused cyclic compound containing at least two or more aromatic ring compounds or a derivative compound thereof, wherein the derivative compound has one or more substituents introduced therein. or a compound in which a carbon atom is replaced by a hetero atom.

As an example, the tetravalent functional group represented by Formula 2 may include a functional group represented by Formula 2-1 below.

[Formula 2-1]

Meanwhile, in Formula 1, Y ₁ is an aromatic divalent functional group having 10 or less carbon atoms, and Y ₁ may be a functional group derived from a polyamic acid, polyamic acid ester, or a diamine compound used in synthesizing polyimide.

The aromatic divalent functional group having 10 or less carbon atoms may include a phenylene group. More specifically, the aromatic divalent functional group having 10 or less carbon atoms of Y ₁ may include a functional group represented by Formula 3 below.

[Formula 3]

Specific examples of the functional group represented by the following formula (3) include a functional group represented by the following formula (3-1).

[Formula 3-1]

When the functional group represented by Formula 3-1 is included in Y ₁ , an asymmetric structure is introduced into the polyimide chain structure, thereby reducing the difference in refractive index between the plane direction and the thickness direction, thereby realizing a low retardation.

The polyimide-based resin may include a combination of a tetracarboxylic dianhydride represented by the following Chemical Formula 4 and an aromatic diamine having 10 or less carbon atoms.

[Formula 4]

In Formula 4, Ar ' is a polycyclic aromatic divalent functional group. The polycyclic aromatic divalent functional group is a divalent functional group derived from a polycyclic aromatic hydrocarbon compound, and is a divalent functional group derived from a fluorenylene group or a derivative compound thereof, and may include a fluorenylene group. . The derivative compound includes all compounds in which one or more substituents are introduced or carbon atoms are replaced with heteroatoms.

Specific examples of the tetracarboxylic dianhydride represented by Formula 4 include 9,9-bis (3,4-dicarboxyphenyl) fluorene dianhydride (9,9-Bis (3,4-dicarboxyphenyl) fluorene Dianhydride, BPAF). can be heard

The aromatic diamine having 10 or less carbon atoms is a compound in which amino groups (-NH ₂ ) are bonded to both terminals of the aforementioned aromatic divalent functional group having 10 or less carbon atoms, and the description of the aromatic divalent functional group having 10 or less carbon atoms is as described above.

Specific examples of the aromatic diamine having 10 or less carbon atoms include diamines represented by the following formula (a).

[Formula a]

More specifically, the polyimide-based resin is a terminal anhydride group (-OC-O-CO-) of the tetracarboxylic dianhydride represented by Formula 4 and a terminal amino group (-NH ₂ ) of an aromatic diamine having 10 or less carbon atoms. As a result, a bond between the nitrogen atom of the amino group and the carbon atom of the anhydride group may be formed.

In addition, the polyimide-based resin may further include a polyimide repeating unit represented by the following Chemical Formula 5 in addition to the polyimide repeating unit represented by Chemical Formula 1 above.

[Formula 5]

In Formula 5, X ₂ is a tetravalent functional group different from that of X ₁ , and Y ₂ is an aromatic divalent functional group having 10 or less carbon atoms.

X ₂ may be one of the tetravalent functional groups represented by Formula 6 below.

[Formula 6]

In Formula 6, R ₁ to R ₆ are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and L ₃ is a single bond, -O-, -CO-, -COO-, -S-, -SO-, -SO ₂ -, -CR ₇ R ₈ -, -(CH ₂ ) _t -, -O(CH ₂ ) _t O-, -COO(CH ₂ ) _t OCO-, -CONH-, phenylene, or their Any one selected from the group consisting of combinations, wherein R ₇ and R ₈ are each independently hydrogen, an alkyl group having 1 to 10 carbon atoms, or a halo alkyl group having 1 to 10 carbon atoms, and t is an integer from 1 to 10 .

Specific examples of the functional group represented by the formula (6) include a functional group represented by the following formula (6-1).

[Formula 6-1]

When the functional group represented by Formula 6-1 is included in X ₂ , the ether functional group having an electron withdrawing effect and two benzene rings are introduced into the polyimide chain structure in a bent form, thereby maintaining the arrangement in the thickness direction. In addition, chemical resistance can also be significantly improved.

That is, the polyimide-based polymer may include a first repeating unit containing a repeating unit represented by Chemical Formula 1, wherein the repeating unit derived from tetracarboxylic acid dianhydride is a functional group represented by Chemical Formula 2; and a second repeating unit containing a repeating unit represented by Formula 5, wherein the repeating unit derived from tetracarboxylic dianhydride is a functional group represented by Formula 6 above. The first repeating unit and the second repeating unit are randomly arranged in the polyimide-based polymer to form a random copolymer, or a block between the first repeating units and a block between the second repeating units to form a block copolymer can

The polyimide-based polymer including the repeating unit represented by Chemical Formula 1 and the repeating unit represented by Chemical Formula 5 may be prepared by reacting two or more different tetracarboxylic dianhydride compounds with a diamine compound. A random copolymer may be synthesized by simultaneously adding tetracarboxylic dianhydride, or a block copolymer may be synthesized by sequential addition.

The polyimide-based resin may include 50 mol% or more and 60 mol% or less of the polyimide repeating unit represented by Chemical Formula 1. In addition, the polyimide-based resin may include 40 mol% or more and 50 mol% or less of the polyimide repeating unit represented by Chemical Formula 5. The polyimide-based resin film synthesized from the polyimide-based resin within the above numerical range has a color coordinate b* of 1.5 or more and 2.0 or less at a thickness of 10 μm, and a retardation R _th value in the thickness direction at a thickness of 10 μm is 25 nm The following can be simultaneously satisfied.

Accordingly, excellent optical properties of colorless and transparent can be realized through a low degree of yellowing, and at the same time, optical isotropy is increased through a low thickness direction retardation (Rth) characteristic, thereby securing a display diagonal viewing angle to which the polyimide-based resin film is applied. , it is possible to prevent deterioration of visibility due to light distortion.

On the other hand, when the polyimide-based resin contains an excessively small amount of less than 50 mol% of the polyimide repeating unit represented by Formula 1 in the polyimide-based resin, the thickness direction retardation R _th value increases to more than 25 nm and distortion of light due to the increase in retardation As a result, visibility is deteriorated, and the color coordinate b* increases to more than 2, and thus there is a problem in that the degree of yellow discoloration increases.

In addition, when the polyimide repeating unit represented by Chemical Formula 1 in the polyimide-based resin is excessively contained in excess of 60 mol%, the color coordinate b* decreases to less than 1.5 and the chemical resistance of the polyimide film rapidly decreases, resulting in a decrease in PGMEA and Cracks may occur within a short time in the same organic solvent.

The polyimide repeating unit represented by Formula 1 and the polyimide repeating unit represented by Formula 5 are 70 mol% or more, or 80 mol% or more, or 90 mol% or more, based on the total repeating units contained in the polyimide-based resin, or 70 mol% or more and 100 mol% or less, 80 mol% or more and 100 mol% or less, 70 mol% or more and 90 mol% or less, 70 mol% or more and 99 mol% or less, 80 mol% or more and 99 mol% or less, 90 mol% or more 99 It may be contained in mol% or less.

That is, the polyimide-based resin is composed of only the polyimide repeating unit represented by the formula (1) and the polyimide repeating unit represented by the formula (5), or most of the polyimide repeating unit represented by the formula (1) and the polyimide repeating unit represented by the formula (5) It may be formed of a polyimide repeating unit.

More specifically, in the polyimide-based resin, other diamines other than the diamine capable of inducing an aromatic divalent functional group having 10 or less carbon atoms may not be mixed, or may be mixed in a fraction of less than 1 mol%.

The weight average molecular weight (GPC measurement) of the polyimide-based resin is not particularly limited, but may be, for example, 1000 g/mol or more and 200000 g/mol or less, or 10000 g/mol or more and 200000 g/mol or less.

The polyimide-based resin according to the present invention can exhibit excellent colorless and transparent properties while maintaining properties such as heat resistance and mechanical strength due to a rigid structure, and can be used for device substrates, display cover substrates, and optical films. , IC (integrated circuit) package, electrodeposition film, multi-layer flexible printed circuit (FRC), tape, touch panel, protective film for optical disk, etc. there is.

More specifically, examples of the method for synthesizing the polyimide-based resin film are not particularly limited, for example, forming a coating film by applying a resin composition containing the polyimide-based resin to a substrate (step 1); drying the coating film (step 2); A method for producing a film, including the step of curing the dried coating film by heat treatment (step 3), may be used.

Step 1 is a step of forming a coating film by applying the resin composition containing the above-described polyimide-based resin to a substrate. A method of applying the resin composition containing the polyimide-based resin to the substrate is not particularly limited, and for example, a method such as screen printing, offset printing, flexographic printing, and inkjet printing may be used.

In addition, the resin composition containing the polyimide-based resin may be dissolved or dispersed in an organic solvent. When having such a form, for example, when polyimide-type resin is synthesize|combined in an organic solvent, the reaction solution itself obtained may be sufficient as the solution, and what diluted this reaction solution with another solvent may be sufficient. Moreover, when polyimide-type resin is obtained as powder, what was made to melt|dissolve this in an organic solvent and was made into a solution may be sufficient.

Specific examples of the organic solvent include toluene, N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-methylcaprolactam, 2-pyrrolidone, N-ethyl Pyrrolidone, N-vinylpyrrolidone, dimethylsulfoxide, tetramethylurea, pyridine, dimethylsulfone, hexamethylsulfoxide, gamma-butyrolactone, 3-methoxy-N,N-dimethylpropanamide, 3- Ethoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, 1,3-dimethyl-imidazolidinone, ethyl amyl ketone, methyl nonyl ketone, methyl ethyl ketone, methyl isoa Milk ketone, methyl isopropyl ketone, cyclohexanone, ethylene carbonate, propylene carbonate, diglyme, 4-hydroxy-4-methyl-2-pentanone, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol monopropyl ether, ethylene glycol monopropyl ether acetate, ethylene glycol monoisopropyl ether, ethylene glycol monoisopropyl ether acetate, ethylene glycol monobutyl ether, ethylene glycol monobutyl ether Acetate etc. are mentioned. These may be used alone or may be used in combination.

The resin composition containing the polyimide-based resin may contain a solid content in an amount to have an appropriate viscosity in consideration of fairness such as applicability during the film forming process. For example, the content of the composition may be adjusted so that the content of the total resin is 5 wt% or more and 25 wt% or less, or 5 wt% or more and 20 wt% or less, or 5 wt% or more and 15 wt% or less .

In addition, the resin composition containing the polyimide-based resin may further include other components in addition to the organic solvent. As a non-limiting example, when the resin composition containing the polyimide-based resin is applied, the film thickness uniformity or surface smoothness is improved, the adhesion to the substrate is improved, or the dielectric constant or the conductivity is changed. Or, an additive capable of increasing the compactness may be additionally included. Such additives may be exemplified by a surfactant, a silane-based compound, a dielectric or a crosslinking compound, and the like.

Step 2 is a step of drying the coating film formed by applying the resin composition containing the polyimide-based resin to the substrate.

The drying step of the coating film may be carried out by a heating means such as a hot plate, a hot air circulation furnace, an infrared furnace, and may be performed at a temperature of 50 °C or more and 150 °C or less, or 50 °C or more and 100 °C or less.

Step 3 is a step of curing the dried coating film by heat treatment. In this case, the heat treatment may be performed by a heating means such as a hot plate, a hot air circulation furnace, an infrared furnace, and may be performed at a temperature of 200 °C or higher, or 200 °C or higher and 300 °C or lower.

The thickness of the polyimide-based resin film is not particularly limited, but can be freely adjusted within, for example, 0.01 µm or more and 1000 µm or less. When the thickness of the polyimide-based resin film increases or decreases by a specific value, physical properties measured in the polyimide-based resin film may also change by a specific value.

2. Substrate for display device

Meanwhile, according to another embodiment of the present invention, a substrate for a display device including the polyimide-based resin film of the other embodiment may be provided. The content regarding the polyimide-based resin film may include all of the content described above in the embodiment.

A display device including the substrate may be a liquid crystal display device (LCD), an organic light emitting diode (OLED), a flexible display, or a rollable display or foldable display. ) and the like, but is not limited thereto.

The display device may have various structures depending on the field of application and specific form, for example, a structure including a cover plastic window, a touch panel, a polarizing plate, a barrier film, a light emitting device (OLED device, etc.), a transparent substrate, etc. there is.

The polyimide-based resin film of another embodiment described above may be used for various purposes such as a substrate, an external protective film, or a cover window in these various display devices, and more specifically, it may be applied as a substrate.

For example, the substrate for the display device may have a structure in which a device protection layer, a transparent electrode layer, a silicon oxide layer, a polyimide-based resin film, a silicon oxide layer, and a hard coating layer are sequentially stacked.

The transparent polyimide substrate may include a silicon oxide layer formed between the transparent polyimide-based resin film and the cured layer in terms of improving solvent resistance to moisture permeability and optical properties, and the silicon oxide layer is poly It may be produced by curing silazane.

Specifically, the silicon oxide layer is formed by curing the coated polysilazane after coating and drying a solution containing polysilazane before the step of forming a coating layer on at least one surface of the transparent polyimide-based resin film. it could be

The substrate for a display device according to the present invention can provide a transparent polyimide cover substrate having excellent warpage characteristics and impact resistance, and solvent resistance, optical characteristics, moisture permeability and scratch resistance by including the device protection layer described above. there is.

3. Optics

Meanwhile, according to another embodiment of the present invention, an optical device including the polyimide-based resin film of the other embodiment may be provided. The content regarding the polyimide-based resin film may include all of the content described above in the embodiment.

The optical device may include all kinds of devices using properties realized by light, for example, a display device. Specific examples of the display device include a liquid crystal display device (LCD), an organic light emitting diode (OLED), a flexible display, or a rollable display or foldable display. and the like, but is not limited thereto.

The optical device may have various structures depending on the field of application and specific form, and for example, a structure including a cover plastic window, a touch panel, a polarizing plate, a barrier film, a light emitting device (OLED device, etc.), a transparent substrate, etc. there is.

The polyimide-based resin film of the other embodiments described above may be used for various purposes such as a substrate, an external protective film, or a cover window in these various optical devices, and more specifically, may be applied to a substrate.

According to the present invention, a polyimide-based resin film capable of implementing excellent chemical resistance and low retardation (Rth) in the thickness direction, a substrate for a display device using the same, and an optical device can be provided.

The invention is described in more detail in the following examples. However, the following examples only illustrate the present invention, and the content of the present invention is not limited by the following examples.

<Examples and Comparative Examples: Preparation of polyimide precursor composition and polyimide film>

Example 1

(1) Preparation of polyimide precursor composition

After the organic solvent DEAc was filled in a stirrer through which a nitrogen stream flows, m-phenylenediamine (m-PDA) was added and dissolved at the same temperature while the temperature of the reactor was maintained at 25 °C. 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (9, 9-Bis(3,4-dicarboxyphenyl)fluorene Dianhydride, BPAF) and 4,4'-Oxydiphthalic Anhydride (ODPA) were added at the same temperature and stirred for 24 hours to form a polyimide precursor A composition was obtained. At this time, the molar ratios of the added m-PDA, BPAF, and OPDA are as shown in Table 1 below.

[Formula a]

(2) Preparation of polyimide film

The polyimide precursor composition was spin-coated on a glass substrate. The glass substrate coated with the polyimide precursor composition was placed in an oven and heated at a rate of 5 °C/min, and the curing process was carried out by maintaining at 80 °C for 5 to 30 minutes and at 260 °C for 60 minutes. Hardening

After completion of the process, the glass substrate was immersed in water to remove the film formed on the glass substrate and dried in an oven at 100° C. to prepare a polyimide film having a thickness of 10 μm.

Example 2-3, Comparative Example 1-6

A polyimide precursor composition and a polyimide film were prepared in the same manner as in Example 1, except that the molar ratios of m-PDA, BPAF, and OPDA were changed as shown in Table 1 below.

<Experimental Example: Measurement of physical properties of polyimide precursor composition and polyimide film obtained in Examples and Comparative Examples>

The physical properties of the polyimide precursor composition and the polyimide film obtained in Examples and Comparative Examples were measured in the following manner, and the results are shown in Table 1.

1. Viscosity

The viscosity of the polyimide precursor composition prepared in Examples and Comparative Examples was measured and shown in Table 1 below. Specifically, the viscosity was measured using a plate rheometer (model name: LVDV-1II Ultra, manufactured by Brookfield), put 5 ml of the polyimide precursor composition in a container, lower the spindle, and adjust the rpm. After waiting for a minute, the viscosity value was measured when there was no change in torque. The spindle used at this time was 52Z and the temperature was set to 25 ℃.

2. Yellow index (YI), color coordinates (b*)

For the polyimide films prepared in Examples and Comparative Examples, the yellow index and color coordinates (b*) were measured using a color meter (GRETAGMACBETH's Color-Eye 7000A), and are shown in Table 1 below.

3. Thickness direction retardation (R _th ), in-plane phase difference (R ₀ )

Using the trade name "AxoScan" manufactured by AXOMETRICS as a measuring device, the value of the refractive index with respect to light at 532 nm of the polyimide films prepared in Examples and Comparative Examples was inputted, then temperature: 25 ° C., humidity: After measuring the retardation in the thickness direction and in the plane direction using light with a wavelength of 532 nm under the conditions of 40%, the retardation measurement value in the thickness direction (measured value measured by automatic measurement of a measuring device) was used to measure the film, was calculated by converting it into a retardation value per 10 μm in thickness, and is shown in Table 1 below.

Specifically, the thickness direction retardation R _th was calculated through Equation 1 below.

[Equation 1]

R _th (nm) = |[(n _x + n _y ) / 2] - n _z | ×d

(In Equation 1, n _x is the largest refractive index among the in-plane refractive indices of the polyimide resin film measured with light having a wavelength of 532 nm; n _y is the in-plane refractive index of the polyimide resin film measured with light having a wavelength of 532 nm is the refractive index perpendicular to n _x ; n _z is the refractive index in the thickness direction of the polyimide resin film measured with light having a wavelength of 532 nm; d is the thickness of the polyimide film.)

In addition, the in-plane retardation R ₀ was calculated through Equation 2 below.

[Equation 2]

R ₀ (nm) = ｜ (n _x - n _y ) ｜×d

(In Equation 2, n _x is the largest refractive index among the in-plane refractive indices of the polyimide resin film measured with light having a wavelength of 532 nm; n _y is the in-plane refractive index of the polyimide resin film measured with light having a wavelength of 532 nm n is the refractive index perpendicular to _x ; d is the thickness of the polyimide film.)

4. refractive index

For the polyimide films prepared in Examples and Comparative Examples, refractive indices in the plane direction (TE) and thickness direction (TM) were measured at a wavelength of 532 nm using a prism coupler, and the average refractive index was calculated through the following Equation (3).

[Equation 3]

Average refractive index = (n _x + n _y + n _z ) / 3

(In Equation 3, n _x is the largest refractive index among the in-plane refractive indices of the polyimide resin film measured with light having a wavelength of 532 nm; n _y is the in-plane refractive index of the polyimide resin film measured with light having a wavelength of 532 nm. It is the refractive index perpendicular to n _x ; n _z is the refractive index in the thickness direction of the polyimide resin film measured with light having a wavelength of 532 nm.)

5. Coefficient of Thermal Expansion (CTE) and Glass Transition Temperature (Tg)

After preparing the polyimide films prepared in Examples and Comparative Examples in a size of 5 mm x 20 mm, the sample was loaded using an accessory. The length of the film actually measured was the same as 16 mm. Set the film pulling force to 0.02N and heat it to a temperature of 260 ℃ at a temperature increase rate of 5 ℃/min. Q400) of the company.

After cooling the film after the first temperature raising process to 80 °C at a cooling rate of 4 °C/min, heating the cooled sample to 350 °C at a temperature increase rate of 5 °C/min 100 °C to 200 °C and The change in thermal expansion of the sample at 200 °C to 250 °C was measured by TMA.

In addition, after the primary cooling, a second temperature increase process was performed at a temperature increase rate of 5 °C/min in a temperature range of 80 °C to 350 °C again, and when an inflection point was seen in the temperature increase section, this was designated as Tg.

6. Chemical resistance

For the polyimide films prepared in Examples and Comparative Examples, in order to evaluate the chemical resistance to PGMEA (propylene glycol methyl ether acetate), PGMEA was dropped onto a polyimide film coated on glass in an area of 3 cm x 3 cm or more ( dropping), using an optical microscope (OLYMPUS BX51, magnification 4X) to measure the time it took for cracks to occur, and are shown in Table 1 below.

Experimental Example Measurement Results of Examples and Comparative Examples division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Monomer molar ratio (ODPA/BPAF/m-PDA) 0.5/0.5/0.99
0.45/0.55/0.99 0.4/0.6/0.99 1/0/0.99 0.8/0.2/0.99 0.35/0.65/0.99 0.3/0.7/0.99 0.2/0.8/0.99 0/1/0.99 Solid content (%) 18.4 20.4 20.5 20.6 20.4 20.3 20.3 20.0 20.0 Viscosity (cP) 3697 3512 3666 3500 3300 2890 3083 3200 3900 b* 1.633 1.511 1.546 2.372 2.140 1.428 1.367 1.079 1.099 YI 2.953 2.747 2.814 4.1 3.737 2.62 2.499 2.026 1.8 R _th (nm) 22 25 24 35 31 22 20 21 19 R ₀ (nm) 0.136 0.285 0.037 0.129 0.765 0.178 0.125 0.075 0.123 Average refractive index @532nm 1.6988 1.6991 1.6995 1.7054 1.7046 1.6956 1.6971 1.6983 1.6989 CTE(ppm/℃)1st heating @ 100~200 ℃ 46.2 49.0 53.0 55.7 57.0 58.9 54.7 - 46.1 CTE(ppm/℃)2nd heating @ 100~200 ℃ 61.0 63.0 57.3 60.6 55.9 57.2 62.7 - 57.0 CTE(ppm/℃)2nd heating @ 200~250 ℃ 83.6 89.1 84.0 97.6 80.2 75.1 82.9 - 60.2 Tg (℃) 327.2 319.0 324.5 340.0 338.2 338.1 336.8 - ND(not detected) Chemical resistance (min) 5 5 5 >5 5 4 3 One 0

As shown in Table 1, the polyimide film obtained in Examples satisfies the thickness direction retardation R _th value of 22 nm or more and 25 nm or less, and at the same time the color coordinate b* is 1.511 or more and 1.633 or less, and about 5 minutes for PGMEA. It was confirmed that excellent chemical resistance could be realized as cracks occurred only after passing through. On the other hand, in Comparative Examples 1 and 2, the thickness direction retardation R _th value increased to 31 nm or more and 35 nm or less, compared to the Example, so that a visual sensation suitable for display It is difficult to express sexiness, and there is a limitation in that color distortion occurs because the color coordinate b* is higher than 2.14 and less than 2.372.

In addition, in the case of Comparative Examples 3 to 6, the color coordinate b* was 1.099 or more and 1.428 or less, which was lower than the Example, and cracks occurred within 4 minutes for PGMEA in the chemical resistance evaluation, confirming that it was inferior to the Example.

And, in the case of Comparative Examples 1, 2, 3, and 4, the CTE (ppm/℃, 1st heating @ 100~200 ℃) was as high as 54.7 ppm/℃ or more and 58.9 ppm/℃ or less, and 46.2 ppm/℃ or more and 53 ppm. It was confirmed that the heat resistance was poorer than that of the Examples having /℃ or less.

Claims (20)

The color coordinate b* at a thickness of 10 μm is 1.5 or more and 2.0 or less,
A polyimide-based resin film, wherein the retardation R _th value in the thickness direction at a thickness of 10 μm is 25 nm or less.
According to claim 1,
The polyimide-based resin film is a polyimide-based resin film having a retardation R ₀ value of 0.5 nm or less in the plane direction in a thickness of 10 μm.
According to claim 1,
The polyimide-based resin film has at least one glass transition temperature at a temperature of 300°C or higher and 400°C or lower.
According to claim 1,
The polyimide-based resin film has a thermal expansion coefficient of 40 ppm/°C or more and 54 ppm/°C or less, measured by raising the temperature in a temperature range of 100°C or more and 200°C or less.
According to claim 1,
The polyimide-based resin film has an average refractive index of 1.6985 or more and 1.6999 or less at a wavelength of 532 nm, a polyimide-based resin film.
According to claim 1,
The polyimide film has a yellow index YI of 2.5 or more and 3.0 or less in a thickness of 10 μm, a polyimide-based resin film.
The method of claim 1,
The polyimide-based resin film is a polyimide-based resin film that takes 5 minutes or more from the time the polyimide-based resin film is contacted with the propylene glycol methyl ether acetate solvent to the occurrence of cracks.
The method of claim 1,
The polyimide-based resin film is a polyimide-based resin film comprising a polyimide-based resin including a polyimide repeating unit represented by the following formula (1):
[Formula 1]

In Formula 1,
X ₁ is an aromatic tetravalent functional group containing multiple rings,
Y ₁ is an aromatic divalent functional group having 10 or less carbon atoms.
9. The method of claim 8,
Wherein X ₁ is a tetravalent functional group comprising a tetravalent functional group represented by the following formula (2), polyimide-based resin film:
[Formula 2]

In Formula 2, Ar is a polycyclic aromatic divalent functional group.
10. The method of claim 9,
In Ar of Formula 2, the polycyclic aromatic divalent functional group is
A polyimide-based resin film comprising a fused cyclic divalent functional group containing at least two or more aromatic ring compounds.
10. The method of claim 9,
In Ar of Formula 2, the polycyclic aromatic divalent functional group includes a fluorenylene group, a polyimide-based resin film.
10. The method of claim 9,
The tetravalent functional group represented by Formula 2 includes a functional group represented by the following Formula 2-1, a polyimide-based resin film:
[Formula 2-1]

.
9. The method of claim 8,
The aromatic divalent functional group having 10 or less carbon atoms of Y ₁ includes a functional group represented by the following Chemical Formula 3, a polyimide-based resin film:
[Formula 3]

.
14. The method of claim 13,
The functional group represented by Chemical Formula 3 includes a functional group represented by the following Chemical Formula 3-1, a polyimide-based resin film:
[Formula 3-1]

.
9. The method of claim 8,
The polyimide-based resin is a polyimide-based resin film comprising a combination of a tetracarboxylic dianhydride represented by the following Chemical Formula 4 and an aromatic diamine having 10 or less carbon atoms:
[Formula 4]

In Formula 4, Ar ' is a polycyclic aromatic divalent functional group.
9. The method of claim 8,
The polyimide-based resin is
In addition to the polyimide repeating unit represented by Chemical Formula 1, the polyimide-based resin film further comprising a polyimide repeating unit represented by the following Chemical Formula 5:
[Formula 5]

In Formula 5,
X ₂ is a tetravalent functional group different from that of X ₁ ,
Y ₂ is an aromatic divalent functional group having 10 or less carbon atoms.
17. The method of claim 16,
Wherein X ₂ is one of the tetravalent functional groups represented by the following formula (6), a polyimide-based resin film:
[Formula 6]

In Formula 6, R ₁ to R ₆ are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and L ₃ is a single bond, -O-, -CO-, -COO-, -S-, -SO-, -SO ₂ -, -CR ₇ R ₈ -, -(CH ₂ ) _t -, -O(CH ₂ ) _t O-, -COO(CH ₂ ) _t OCO-, -CONH-, phenylene or a combination thereof It is any one selected from the group consisting of, wherein R ₇ and R ₈ are each independently one of hydrogen, an alkyl group having 1 to 10 carbon atoms, or a halo alkyl group having 1 to 10 carbon atoms, and t is an integer of 1 to 10.
17. The method of claim 16,
The polyimide-based resin is a polyimide-based resin film comprising 50 mol% or more and 60 mol% or less of the polyimide repeating unit represented by Formula 1.
A substrate for a display device comprising the polyimide-based resin film of claim 1 .
An optical device comprising the polyimide-based resin film of claim 1 .