Polyimide-based film having excellent surface flatness and method for producing same

Abstract

The present invention relates to a polyimide-based film and a method for manufacturing the same, and more particularly, to a polyimide-based film having excellent surface flatness and suppressed corrugation due to a low Kc of 1.55 or less, and a method for manufacturing the same.

Description

[0001] This application is a divisional application. The application number of the original application is "202080067256.8", the application date is September 14, 2020, and the invention title is "Polyimide-based film having excellent surface flatness and method for manufacturing the same". Technical Field

[0002] The present disclosure relates to a polyimide-based film having excellent surface flatness, a method for manufacturing the same, and an electronic device, and more particularly to a polyimide-based film having suppressed ripples due to a low Kc, a method for manufacturing the same, and an electronic device. Background Art

[0003] Polyimide (PI)-based resins have properties such as high heat resistance, oxidation resistance, radiation resistance, low temperature resistance, and chemical resistance, and thus are widely used in electronic products, semiconductors, automobiles, airplanes, spacecrafts, etc., and are used as transparent electrode films and cover windows for display devices.

[0004] Recently, research has been conducted to improve the optical properties of polyimide-based resins, and polyimide-based resins having excellent optical properties without significantly reducing their mechanical properties or thermal properties are being developed.

[0005] Polyimide-based films made of polyimide-based resins having excellent mechanical properties, thermal properties, and optical properties are used in various flexible products, and research is being conducted on their use as a glass substitute. For example, research is being conducted on the use of polyimide-based films as cover windows or protective materials for display devices. Summary of the Invention

[0006] [Technical Problem]

[0007] Accordingly, an object of the present disclosure is to provide a polyimide (PI)-based film having excellent surface flatness.

[0008] Another object of the present disclosure is to provide a polyimide (PI)-based film that can suppress the occurrence of ripples due to its low Kc value and has excellent surface flatness.

[0009] Another object of the present disclosure is to provide a method for manufacturing a polyimide (PI)-based film having excellent surface flatness.

[0010] Another object of the present disclosure is to provide a method for manufacturing a polyimide (PI)-based film having a low Kc value by controlling drying conditions.

[0011] Another object of the present disclosure is to provide a method for manufacturing a polyimide (PI)-based film that can suppress the occurrence of ripples.

[0012] Another object of the present disclosure is to provide an electronic device including a polyimide (PI) film having excellent surface flatness due to its low Kc value.

[0013] [Technical Solution]

[0014] To solve the above technical problems, according to one aspect of the present disclosure, a polyimide film having a Kc value of 1.55 or less is provided, wherein the Kc value is a curvature parameter of ripples measured in a wavelength range of 1.0 to 3.0 mm by a phase step deflectometry (PSD).

[0015] The Kc value of the polyimide film may be 1.45 or less.

[0016] The Kc value of the polyimide film may be 1.10 to 1.45.

[0017] The polyimide film may be manufactured from a monomer component containing a dianhydride and a diamine.

[0018] The dianhydride may include at least one selected from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA), pyromellitic dianhydride (PMDA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic anhydride (ODPA), 4,4′-(3,4-bis(dicarboxyphenoxy))-diphenyl sulfide dianhydride (BDSDA), 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (SO2DPA), 4,4'-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (6HBDA), cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA), and dicyclohexyl-3,4,3′,4′-tetracarboxylic dianhydride (HBPDA).

[0019] The diamine may include at least one selected from 3,4-diaminodiphenyl ether (34ODA), 4,4'-diaminodiphenyl ether (4ODA), p-phenylenediamine (pPDA), m-phenylenediamine (mPDA), 4,4'-methylenedianiline (pMDA), 3,3'-methylenedianiline (mMDA), 1,3-bis(3-aminophenoxy)benzene (133APB), 1,3-bis(4-aminophenoxy)benzene (134APB), 2,2'-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (4BDAF), 2,2'-bis(3-aminophenyl)hexafluoropropane (33-6F), 2,2'-bis(4-aminophenyl)hexafluoropropane (44-6F), bis(4-aminophenyl)sulfone (4DDS), bis(3-aminophenyl)sulfone (3DDS), 2,2'-bis(trifluoromethyl)benzidine (TFDB), 1,3-cyclohexanediamine (13CHD), 1,4-cyclohexanediamine (14CHD), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (6HMDA), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (DBOH), bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 9,9-bis(4-aminophenyl)fluorene (FDA), and 9,9-bis(4-amino-3-fluorophenyl)fluorene (F-FDA).

[0020] The monomer component may further contain a dicarbonyl compound.

[0021] The dicarbonyl compound may include at least one of an aromatic dicarbonyl compound and an aliphatic dicarbonyl compound.

[0022] The aromatic dicarbonyl compound may be represented by the following Formula 1:

[0023] [Formula 1]

[0024]

[0025] wherein R1 represents a single bond, *-Ar-*, *-O-Ar-*, *-CAL-*, or *-O-CAL-*, X1 and X2 each independently represent hydrogen, a hydroxyl group (OH), or a halogen element, and X3 represents hydrogen or a halogen element, wherein "Ar" represents a substituted or unsubstituted arylene group, and "CAL" represents an alicyclic group.

[0026] The aromatic dicarbonyl compound may include at least one of the compound represented by the following Formula 3, the compound represented by the following Formula 4, the compound represented by the following Formula 5, the compound represented by the following Formula 6, the compound represented by the following Formula 7, the compound represented by the following Formula 8, and the compound represented by the following Formula 9.

[0027] [Formula 3]

[0028]

[0029] [Formula 4]

[0030]

[0031] [Formula 5]

[0032]

[0033] [Formula 6]

[0034]

[0035] [Formula 7]

[0036]

[0037] [Formula 8]

[0038]

[0039] [Formula 9]

[0040]

[0041] The aliphatic dicarbonyl compound may include at least one of a compound represented by the following formula 10, a compound represented by the following formula 11, a compound represented by the following formula 12, and a compound represented by the following formula 13.

[0042] [Formula 10]

[0043]

[0044] [Formula 11]

[0045]

[0046] [Formula 12]

[0047]

[0048] [Formula 13]

[0049]

[0050] Based on a thickness of 80 μm, the haze of the polyimide film may be 2.0 or less, the average light transmittance at a wavelength of 380 to 780 nm may be 87% or more, and the yellowness index may be 5 or less.

[0051] According to another aspect of the present disclosure, there is provided a method for manufacturing a polyimide-based film, including: preparing a liquid resin composition using a monomer component containing a dianhydride and a diamine, manufacturing a gel-type film using the liquid resin composition, and performing a first drying on the gel-type film at a wind speed of 1.0 m / s or less for 2 to 20 minutes at 50°C to 150°C, wherein in the first drying, when the drying temperature is A°C, the wind speed is B m / s, and the first drying time is T minutes, the drying coefficient conditions according to the following Formula 1 and Formula 2 are satisfied.

[0052] [Formula 1]

[0053] 0.5 ≤ [(A - 40) × B × T] / 100 ≤ 10

[0054] [Formula 2]

[0055] 2 ≤ [(A - 40) × T] / 100 ≤ 10

[0056] The monomer component may further contain a dicarbonyl compound.

[0057] The viscosity of the liquid resin composition may be 1,000 to 250,000 cPs.

[0058] The method for manufacturing the polyimide-based film may further include performing a second drying on the gel-type film at a wind speed of 1.0 to 5.0 m / s at 70°C to 140°C after the first drying.

[0059] The method for manufacturing the polyimide-based film may further include performing a first heat treatment on the gel-type film for 1 minute to 1 hour at a temperature of 100°C to 500°C after the second drying.

[0060] Manufacturing the gel-type film may include casting the liquid resin composition on a carrier.

[0061] Preparing the liquid resin composition may include reacting the monomer component in the presence of a first solvent to prepare a first polymer solution, adding a second solvent to the first polymer solution, followed by filtration and drying to prepare a polymer solid, and dissolving the polymer solid in a third solvent.

[0062] According to another aspect of the present disclosure, there is provided a polyimide-based film manufactured according to the above method.

[0063] According to another aspect of the present disclosure, there is provided an electronic device including the polyimide-based film.

[0064] [Advantageous Effects]

[0065] According to an embodiment of the present disclosure, a polyimide-based film having a low Kc value can be manufactured by controlling drying conditions in a process for manufacturing a polyimide-based film. The polyimide-based film according to an embodiment of the present disclosure has a low Kc value and can suppress the generation of ripples, thereby exhibiting excellent surface flatness.

[0066] The polyimide-based film having a low Kc value and excellent surface flatness manufactured according to an embodiment of the present disclosure has a glassy surface property and can thus be used as a substitute for glass. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 is a schematic diagram showing a method of projecting a film image.

[0068] Figure 2 is an example of a projected image obtained by the method of projecting an image.

[0069] Figure 3 is a projected image of a film according to an embodiment of the present disclosure.

[0070] Figure 4 is a projected image of a film according to a comparative example.

[0071] Figure 5 is a cross-sectional view showing surface roughness, ripples, and shape. DETAILED DESCRIPTION

[0072] Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the drawings. These embodiments are provided for illustrative purposes so that the present disclosure is thorough and complete, and should not be construed as limiting the scope of the present disclosure.

[0073] The shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for describing the embodiments of the present disclosure are exemplary, and thus the present disclosure is not limited to the items shown in the drawings. Throughout the description of the drawings, the same reference numerals refer to the same elements. When a detailed description of related well-known technologies would unnecessarily obscure the subject matter of the present disclosure, these may be omitted.

[0074] When using terms such as "comprising," "having," and "consisting of" mentioned herein, another element may be added unless the expression "only" is used. The singular form is also intended to include the plural form unless the context clearly indicates otherwise. In addition, even without its explicit description, constituent elements should be understood to include an error range.

[0075] In the description of positional relationships, for example, when using "on", "upper", "lower", and "adjacent" to describe the positional relationship between two elements, there may be at least one other element between these two elements, unless the terms "immediately" or "directly" are used.

[0076] Spatial relative terms such as "below", "beneath", "lower", "above", and "upper" may be used herein to easily describe the relationship of one element to another as shown in the figures. It should be understood that the spatial relative terms are intended to cover different orientations of the device in addition to the orientation depicted in the figures. For example, if the device in a figure is flipped, an element described as "below" or "beneath" another element will be oriented "above" that other element. Thus, the exemplary terms "below" or "beneath" can cover both an upper and a lower orientation. Similarly, the exemplary terms "upward" or "above" can include both an upward and a downward direction.

[0077] In the description of temporal relationships, for example, when using "after", "subsequent to", "before", etc. to describe the chronological relationship, discontinuous cases may also be included, unless the terms "immediately" or "directly" are used.

[0078] It should be understood that although the terms "first", "second", etc. may be used herein to describe various elements, these elements should not be construed as being limited by these terms, which are only used to distinguish one element from another. Thus, without departing from the technical idea of the present disclosure, the first component mentioned below may alternatively be referred to as the second component.

[0079] The term "at least one kind" should be understood to include all possible combinations from one or more related items. For example, "at least one of the first item, the second item, and the third item" may represent each of the first item, the second item, and the third item, and may also represent all combinations of two or more items from the first item, the second item, and the third item.

[0080] The various features of the various embodiments of the present disclosure may be partially or wholly combined with each other, may be technically interlocked and driven in various ways, and the various embodiments may be implemented independently of each other or in an associated relationship together.

[0081] The Kc value of the polyimide-based film according to one embodiment of the present disclosure may be 1.55 or less, where the Kc value is a curvature parameter measured by the phase-step deflectometry (PSD) in the wavelength range of 1.0 to 3.0 mm. The Kc value represents the waviness of the polyimide-based film according to one embodiment of the present disclosure.

[0082] The polyimide film according to an embodiment of the present disclosure can be prepared from a monomer component containing a dianhydride and a diamine.

[0083] In an embodiment of the present disclosure, the "monomer component" may refer to all types of monomers used in manufacturing the polyimide film. The monomer component may exist as a mixture, or each monomer contained in the monomer component may be mixed sequentially.

[0084] According to an embodiment of the present disclosure, the dianhydride includes, for example, at least one selected from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA), pyromellitic dianhydride (PMDA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 4,4′-oxydiphthalic anhydride (ODPA), 4,4′-(3,4-bis(dicarboxyphenoxy))-diphenyl sulfide dianhydride (BDSDA), 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (SO2DPA), 4,4′-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (6HBDA), cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA), and dicyclohexyl-3,4,3′,4′-tetracarboxylic dianhydride (HBPDA). As the dianhydride, the above compounds can be used alone or as a mixture of two or more compounds.

[0085] The diamine may, for example, include at least one selected from 3,4-diaminodiphenyl ether (34ODA), 4,4′-diaminodiphenyl ether (4ODA), p-phenylenediamine (pPDA), m-phenylenediamine (mPDA), 4,4-methylenedianiline (pMDA), 3,3-methylenedianiline (mMDA), 1,3-bis(3-aminophenoxy)benzene (133APB), 1,3-bis(4-aminophenoxy)benzene (134APB), 2,2′-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (4BDAF), 2,2′-bis(3-aminophenyl)hexafluoropropane (33-6F), 2,2′-bis(4-aminophenyl)hexafluoropropane (44-6F), bis(4-aminophenyl)sulfone (4DDS), bis(3-aminophenyl)sulfone (3DDS), 2,2′-bis(trifluoromethyl)benzidine (TFDB), 1,3-cyclohexanediamine (13CHD), 1,4-cyclohexanediamine (14CHD), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (6HMDA), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (DBOH), bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 9,9-bis(4-aminophenyl)fluorene (FDA), and 9,9-bis(4-amino-3-fluorophenyl)fluorene (F-FDA). As the diamine, the above compounds may be used alone or as a mixture of two or more compounds.

[0086] The polyimide film prepared from the monomers containing a dianhydride and a diamine may be a polyimide-based film having imide repeating units. However, the polyimide-based film according to the present disclosure is not limited thereto.

[0087] According to an embodiment of the present disclosure, the monomer component may further include a dicarbonyl compound. When the monomer component includes a dicarbonyl compound in addition to the dianhydride and the diamine, the polyimide-based film may have a polyamide-imide copolymer structure containing imide repeating units and amide repeating units.

[0088] Since the film having a polyamide-imide copolymer structure has imide repeating units, in an embodiment of the present disclosure, the film having a polyamide-imide copolymer structure is also referred to as a "polyimide-based film". Therefore, the polyimide-based film according to an embodiment of the present disclosure may include a polyimide film and a polyamide-imide film.

[0089] According to an embodiment of the present disclosure, the dicarbonyl compound may include at least one of an aromatic dicarbonyl compound and an aliphatic dicarbonyl compound.

[0090] The aromatic dicarbonyl compound according to an embodiment of the present disclosure may be represented by the following Formula 1:

[0091] [Formula 1]

[0092]

[0093] In Formula 1, R1 represents a single bond, *-Ar-*, *-O-Ar-*, *-CAL-* or *-O-CAL-*, X1 and X2 each independently represent hydrogen, a hydroxyl group (OH) or a halogen element, and X3 represents hydrogen or a halogen element, where "Ar" represents a substituted or unsubstituted arylene group, and "CAL" represents an alicyclic group.

[0094] The arylene group is, for example, a phenylene group represented by the following Formula 2.

[0095] [Formula 2]

[0096]

[0097] According to one embodiment of the present disclosure, an example of the unsubstituted arylene group is a phenylene group represented by Formula 2.

[0098] Furthermore, an example of the substituted arylene group is a phenylene group in which the hydrogen (H) of the benzene ring is substituted by a halogen element. More specifically, the substituted arylene group is, for example, a chlorophenylene group in which the hydrogen (H) of the benzene ring is substituted by chlorine (Cl).

[0099] In Formula 1, at least one of X1 and X2 may be a halogen element, and the halogen element may be a chlorine (Cl) atom. In addition, X3 may be hydrogen (H) or chlorine (Cl).

[0100] The aromatic dicarbonyl compound may include at least one of the compounds represented by the following Formula 3, the compounds represented by the following Formula 4, the compounds represented by the following Formula 5, the compounds represented by the following Formula 6, the compounds represented by the following Formula 7, the compounds represented by the following Formula 8, and the compounds represented by the following Formula 9.

[0101] [Formula 3]

[0102]

[0103] [Formula 4]

[0104]

[0105] [Formula 5]

[0106]

[0107] [Formula 6]

[0108]

[0109] [Formula 7]

[0110]

[0111] [Formula 8]

[0112]

[0113] [Formula 9]

[0114]

[0115] According to an embodiment of the present disclosure, the aromatic dicarbonyl compound may include, for example, at least one of terephthaloyl chloride (TPC) (Formula 3), terephthalic acid (TPA) (Formula 4), isophthaloyl dichloride (IPC) (Formula 5), 1,1'-biphenyl-4,4'-dicarbonyl dichloride (BPDC) (Formula 6), 4,4'-oxybis(benzoyl chloride) (ODBC) (Formula 7), and 2-chloroterephthaloyl dichloride.

[0116] In addition, the aliphatic dicarbonyl compound according to an embodiment of the present disclosure may be an alicyclic dicarbonyl compound. The aliphatic dicarbonyl compound may include at least one of the compounds represented by the following Formula 10, the compounds represented by the following Formula 11, the compounds represented by the following Formula 12, and the compounds represented by the following Formula 13, and the compounds represented by the following Formulas 10 to 13 are also referred to as alicyclic compounds.

[0117] [Formula 10]

[0118]

[0119] [Formula 11]

[0120]

[0121] [Formula 12]

[0122]

[0123] [Formula 13]

[0124]

[0125] According to an embodiment of the present disclosure, as the dicarbonyl compound, the above compounds may be used alone or as a mixture of two or more thereof.

[0126] According to an embodiment of the present disclosure, the Kc value of the polyimide film is 1.55 or less. The Kc value is a curvature parameter of a ripple formed on the polyimide film and having a wavelength range of 1.0 to 3.0 mm, measured by the phase step deflection method (PSD).

[0127] According to an embodiment of the present disclosure, the Kc value refers to the waviness of a ripple formed on the polyimide film and having a wavelength of 1.0 to 3.0 mm.

[0128] The ripple is also referred to as a "waveform" or a "wave-shaped curve".

[0129] Hereinafter, reference will be made to Figure 5 describe the ripple.

[0130] Figure 5 is a cross-sectional view showing surface roughness, ripple, and shape.

[0131] Assume that there is an object having a cross-sectional profile as shown in (A) of Figure 5 , the surface roughness is represented by (B) and is determined by the fine curve at the minimum interval on the surface of (A) of Figure 5 . The ripple is represented by (C) and is a surface curve appearing at an interval greater than the interval of the surface roughness (B), and the shape is represented by (D) and appears at an interval greater than the interval of the ripple (C), which is the appearance of the object.

[0132] Specifically, the surface roughness represented by (B) of Figure 5 is the fine curve drawn around the dotted center line extending straight when a virtual center line is set along the fine curve in the cross-section represented by (A) of Figure 5 and the virtual center line extends straight. In the surface roughness represented by (B) of Figure 5 , the interval between the fine curves can be about several micrometers to several tens of micrometers.

[0133] The ripple represented by (C) of Figure 5 is a surface curve appearing at an interval greater than the interval of the surface roughness (B), and is represented around the dotted line straight. In the ripple represented by (C) of Figure 5 , the interval between the curves can be about several hundred micrometers (μm) to several centimeters (cm).

[0134] According to an embodiment of the present disclosure, the interval between the curves is referred to as the "wavelength (λ)". In the ripple shown in (C) of Figure 5 , the ripple can have a wavelength λ of about several hundred micrometers (μm) to several centimeters (cm).

[0135] According to an embodiment of the present disclosure, the Kc value is a curve parameter for measuring corrugations having a wavelength of 1.0 to 3.0 mm. The Kc value according to an embodiment of the present disclosure is used to evaluate the degree of corrugation within the wavelength (λ) range of 1.0 to 3.0 mm formed on a polyimide-based film.

[0136] Generally, the optimal viewing distance for a person is about 30 to about 40 cm, and the human eye has a high resolution for curves with an interval of 1 to 3 mm at a viewing distance of about 30 to about 40 cm. Therefore, when corrugations with a wavelength (λ) of 1.0 to 3.0 mm, that is, curves with an interval of 1 to 3 mm, are formed on the surface of a display device, such corrugations are very easily perceptible to the human eye. In addition, such corrugations cause screen distortion.

[0137] According to an embodiment of the present disclosure, by adjusting the Kc value of the polyimide-based film to 1.55 or less, the curves visually recognizable by the human eye can be minimized. In addition, by adjusting the Kc value of the polyimide-based film to 1.55 or less, when the polyimide-based film according to an embodiment of the present disclosure is used as a cover window of a display device, the curves visually recognizable by the user's eyes can be minimized, and screen distortion can be minimized.

[0138] According to an embodiment of the present disclosure, Optimap TM PSD (Rhopoint Instruments, UK) is used to measure the Kc value.

[0139] According to an embodiment of the present disclosure, Optimap TM PSD of Rhopoint Instruments (UK) is used to measure the Kc value, and the Kc value is digitized through the program of Optimap TM PSD. According to an embodiment of the present disclosure, the curvature (K) and profile of the surface to be measured are measured by the phase-stepping deflectometry (PSD), and in this case, a periodic sine wave pattern is used.

[0140] It can be interpreted that a low Kc value of the polyimide-based film means a small change in curvature at each point on the surface of the polyimide-based film. A small change in curvature can be interpreted as a small amount of periodic change patterns, such as wavy patterns. Therefore, it is considered that the polyimide-based film is flatter when the Kc value is small than when the Kc value is large.

[0141] According to an embodiment of the present disclosure, the Kc value of the polyimide film is 1.55 or less. When the Kc value of the polyimide film is 1.55 or less, the surface curvature is small like ripples, and excellent flatness is achieved. When such a polyimide film is used as a cover window of a display device, screen distortion does not occur. When a polyimide film with a Kc value of 1.55 or less is used as a cover window of a display device, a user with normal vision may not see the wavy pattern on the display screen.

[0142] When the Kc value of the polyimide film decreases, the flatness of the polyimide film can be improved. For example, according to another embodiment of the present disclosure, the Kc value of the polyimide film may be 1.45 or less. When the Kc value of the polyimide film is 1.45 or less, almost no ripples perceptible to the human eye are generated on the polyimide film.

[0143] Meanwhile, in order to manufacture a polyimide film with a Kc value of 1.10 or less, the drying conditions become more stringent and the productivity of the product will deteriorate.

[0144] Therefore, according to an embodiment of the present disclosure, the Kc value of the polyimide film can be adjusted within the range of 1.10 to 1.55. More specifically, according to an embodiment of the present disclosure, the Kc value of the polyimide film may be 1.10 to 1.45.

[0145] According to an embodiment of the present disclosure, the Kc value can be measured by the following method:

[0146] <Measurement method of Kc value>

[0147] - Measuring device: Optimap from Rhopoint TM (PSD)

[0148] - Optical mode: Extra dull

[0149] - Display mode: Curvature mode (X+Y scan)

[0150] - Curvature mode K: 1.0 to 3.0 mm wavelength range

[0151] - Measuring method: Place a piece of black matte paper on a flat plate in a dark room, place the sample to be measured on it, measure the Kc value 10 times, and use the average value as the Kc value of the sample.

[0152] - Thin film sample: Use a thin film with a thickness of 10 μm or more, more specifically 50 μm or more, and a thickness deviation within ±2%. Outside this thickness deviation, the Kc value will be distorted due to the thickness deviation. In one embodiment of the present disclosure, a polyimide thin film sample with a width of 15 cm × a length of 15 cm × a thickness of 80 μm is used for Kc measurement (thickness deviation ±2%).

[0153] - Others: When measured with a microscope, there are 0.005 foreign substances with a particle size of 50 μm or more per cm 2 or less.

[0154] According to one embodiment of the present disclosure, the polyimide thin film can have various thicknesses. The thickness of the polyimide thin film can be, for example, 10 to 250 μm, and more specifically, the thickness can be 10 to 100 μm.

[0155] In addition, the polyimide thin film of the present disclosure has excellent optical properties. For example, based on a film thickness of 80 μm, the haze of the polyimide thin film according to one embodiment of the present disclosure is 2.0% or less, the light transmittance at a wavelength of 380 to 780 nm is 87% or more, and the yellowness index is 5.0 or less. More specifically, according to one embodiment of the present disclosure, based on a thickness of 80 μm, the haze of the polyimide thin film can be 0.2% to 0.3%.

[0156] As described above, the Kc value of the polyimide thin film according to one embodiment of the present disclosure is 1.55 or less, and thus has excellent surface characteristics and excellent optical characteristics. Therefore, the polyimide thin film according to the present disclosure can be used as a cover window, a transparent protective film, a light diffusing plate, or a liquid crystal alignment layer of a display device, a base film of a hard coating film, or a substrate of a flexible display.

[0157] In addition, the polyimide thin film according to one embodiment of the present disclosure can be used as a substitute for glass, for example.

[0158] In order for the polyimide thin film to replace glass, the polyimide thin film needs to have excellent optical properties and excellent surface properties. Conditions for excellent surface properties include, for example, uniform thickness, surface flatness, and low surface roughness. Here, surface flatness includes cases where there are no or very few wrinkles or curves on the surface.

[0159] When the surface properties of the polyimide thin film, especially the surface uniformity, are poor, the light passing through the polyimide thin film will be distorted. As a result, distortion will appear on the screen viewed through the polyimide thin film.

[0160] As Figure 1As shown, when light propagates through a polyimide-based film in a dark environment, the distortion on the screen observed through the polyimide-based film can be confirmed by an image projected onto a flat surface.

[0161] Specifically, Figure 1 is a schematic diagram showing a method of projecting a film image, Figure 2 is an example of a projection image 50 obtained by the image projection method.

[0162] Referring to Figure 1 , the light 20 emitted by the light source 10 passes through the projection target film 30 and is incident on the flat surface 40 to form a projection image 50.

[0163] The projection image 50 projected onto the flat surface 50 being clear and having no shadow difference in the image means that the projection target film 30 is flat and there are no ripples, etc. At the same time, as Figure 2 shown, the occurrence of a shadow difference in the projection image means that the projection target film 30 is not flat and image distortion occurs.

[0164] When the polyimide-based film has large ripples, image distortion occurs on the screen displayed through the polyimide-based film.

[0165] Such ripples occur when manufacturing the polyimide-based film by casting.

[0166] When a liquid resin composition formed of a polyimide-based resin is cast on a flat substrate and then dried to manufacture a polyimide-based film, the flatness of the polyimide-based film decreases during the drying process for solvent volatilization, resulting in ripples. For example, during the process of drying the polyimide-based film using hot air, depending on the intensity of the hot air and the application time of the hot air, ripples can appear in the polyimide-based film, thereby reducing the flatness of the polyimide-based film.

[0167] When the wind speed of the hot air applied to the gel-type polyimide-based film formed by casting to dry the gel-type polyimide-based film is strong, traces can be formed on the gel-type polyimide-based film by the hot air. In addition, when the temperature of the hot air is too high, uneven portions are formed on the surface due to the rapid volatilization of the solvent.

[0168] According to an embodiment of the present disclosure, a polyimide-based film having a Kc value of 1.55 or less can be manufactured by optimizing the drying conditions of the polyimide-based film.

[0169] Hereinafter, a method of manufacturing a polyimide-based film according to an embodiment of the present disclosure will be described in detail.

[0170] A method for manufacturing a polyimide-based film according to an embodiment of the present disclosure includes preparing a liquid resin composition using a monomer component including a dianhydride and a diamine, manufacturing a gel-type film using the liquid resin composition, and first drying the gel-type film at a wind speed of 1.0 m / s or less for 2 to 20 minutes at 50°C to 150°C.

[0171] According to an embodiment of the present disclosure, first, a liquid resin composition is prepared using a monomer component including a dianhydride and a diamine. The monomer component may further include a dicarbonyl compound.

[0172] The dianhydride, diamine, and dicarbonyl compound have been described, and thus their detailed descriptions are omitted to avoid redundancy.

[0173] A first solvent may be used for solution polymerization of the monomer component. Specifically, the monomer component may react in the presence of the first solvent to prepare a first polymer solution. An organic solvent may be used as the first solvent for solution polymerization.

[0174] There is no particular limitation on the type of the first solvent. The first solvent may include, for example, at least one selected from m-cresol, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), dimethylformamide (DMF), diethylformamide (DEF), dimethylacetamide (DMAc), diethylacetamide (DEAc), acetone, ethyl acetate, propylene glycol monomethyl ether (PGME), and propylene glycol monomethyl ether acetate (PGMEA). In addition, a low-boiling solvent such as tetrahydrofuran (THF) or chloroform or a weakly absorbent solvent such as γ-butyrolactone may be used as the first solvent. The first solvent may be used alone or in combination of two or more according to the purpose.

[0175] There is no particular limitation on the content of the first solvent. Based on the total weight of the first polymer solution, the content of the first solvent may be 50 wt% to 95 wt%. More specifically, based on the total weight of the first polymer solution, the content of the first solvent may be 70 wt% to 90 wt%.

[0176] When the monomer component does not include a dicarbonyl compound, the molar amounts of the dianhydride and the diamine may be adjusted to be equal to each other.

[0177] When the monomer component includes a dicarbonyl compound, the molar amount of the mixture of the dianhydride and the dicarbonyl compound may be adjusted to be equal to the molar amount of the diamine.

[0178] There is no particular limitation on the method applied for preparing the liquid resin composition using the monomer component. Here, the liquid resin composition may be referred to as a liquid polyimide-based resin composition.

[0179] According to an embodiment of the present disclosure, the preparation of the liquid resin composition includes reacting a monomer component in the presence of a first solvent to prepare a first polymer solution, adding a second solvent to the first polymer solution, followed by filtration and drying to prepare a polymer solid, and dissolving the polymer solid in a third solvent.

[0180] However, the embodiments of the present disclosure are not limited thereto, and polyimide resin compositions can also be prepared by using a monomer component containing a dianhydride and a diamine to prepare a polyamic acid and then performing thermal curing. In addition, after adding a chemical curing agent to a polyimide polymer solution containing a polyamic acid, a polyimide film can be immediately formed in the form of a film without filtration using a second solvent.

[0181] To prepare the liquid resin composition, first, the monomer component is polymerized to prepare a first polymer solution. The first polymer solution may include a polyamic acid solution. At this time, there are no special restrictions on the reaction conditions. The reaction temperature can be adjusted, for example, in the range of -10°C to 80°C, and the reaction time can be adjusted to 2 to 48 hours. The preparation of the first polymer solution can be carried out in an inert gas atmosphere such as argon or nitrogen.

[0182] Next, the first polymer solution can be imidized. At this time, the polyamic acid contained in the first polymer solution can be imidized.

[0183] For imidization, thermal imidization, chemical imidization, or a combination of thermal imidization and chemical imidization can be used.

[0184] According to an embodiment of the present disclosure, chemical imidization can be used. Chemical imidization is a method of applying a dehydrating agent such as acetic anhydride and an imidization catalyst such as isoquinoline, β-methylpyridine, pyridine, or a tertiary amine to the first polymer solution.

[0185] Thermal imidization can be used in combination with chemical imidization.

[0186] When thermal imidization is used in combination with chemical imidization, a dehydrating agent and an imidization catalyst are added to the first polymer solution and then heated at 20°C to 180°C for 1 to 12 hours so that imidization can be carried out.

[0187] Next, a second solvent is added to the first polymer solution, followed by filtration and drying to prepare a polymer solid.

[0188] According to an embodiment of the present disclosure, a second solvent is used to obtain a solid of the polyimide resin. Therefore, a solvent that does not dissolve the polyamic acid contained in the first polymer solution can be used as the second solvent, and the polyimide polymer solid can precipitate due to the difference in solubility.

[0189] A solvent having a lower polarity than the first solvent can be used as the second solvent. The second solvent may include, for example, at least one selected from water, alcohols, ethers, and ketones.

[0190] There is no particular limitation on the content of the second solvent. The amount of the second solvent used may be 5 to 20 times the weight of the polyamic acid contained in the first polymer solution.

[0191] The drying conditions after filtering the obtained polymer solid are determined in consideration of the boiling points of the second solvent and the first solvent remaining in the polymer solid. For example, the polymer solid can be dried at a temperature of 50°C to 150°C for 2 to 24 hours.

[0192] Next, the polymer solid is dissolved in a third solvent to prepare a liquid resin composition. The liquid resin composition may also be referred to as a polyimide resin composition.

[0193] According to an embodiment of the present disclosure, the third solvent may be the same as the first solvent. Thus, the third solvent may include, for example, at least one selected from m-cresol, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), dimethylformamide (DMF), diethylformamide (DEF), dimethylacetamide (DMAc), diethylacetamide (DEAc), acetone, ethyl acetate, propylene glycol monomethyl ether (PGME), and propylene glycol monomethyl ether acetate (PGMEA).

[0194] The viscosity of the liquid resin composition prepared as described above may be 100 to 300,000 cPs. When the viscosity of the liquid resin composition is less than 100 cPs, it may be difficult to form a film by casting the liquid resin composition, and it may be difficult to peel off the film formed by casting from the casting substrate due to low molecular weight. On the other hand, when the viscosity of the liquid resin composition exceeds 300,000 cPs, the pressure applied during the casting process increases due to the high viscosity, which is disadvantageous in terms of processing.

[0195] More specifically, the viscosity of the liquid resin composition may be 1,000 to 250,000 cPs. When the viscosity of the liquid resin composition is 1,000 to 250,000 cPs, it is easy to form a film by casting the liquid resin composition, and it is also easy to dry it. For example, when the viscosity of the liquid resin composition is 1,000 cPs or more, it is not difficult to form a film by casting the liquid resin composition, and the film formed by casting can be peeled off from the casting substrate without difficulty. In addition, when the viscosity of the liquid resin composition is 250,000 cPs or less, the casting process can be carried out without increasing the pressure for casting the liquid resin composition beyond what is required.

[0196] According to an embodiment of the present disclosure, the viscosity of the liquid resin composition may be from 1000 to 30,000 cPs.

[0197] According to an embodiment of the present disclosure, based on the total weight of the liquid resin composition, the solid content contained in the liquid resin composition may be adjusted within the range of 5 wt% to 30 wt%.

[0198] Next, a gel-like film is manufactured from the liquid resin composition. The film in the gel state may be referred to as an uncured gel-like polyimide film.

[0199] A casting method may be used to manufacture the gel-type film.

[0200] Specifically, according to an embodiment of the present disclosure, the preparation of the gel-like film includes casting the liquid resin composition on a carrier.

[0201] There is no particular limitation on the casting method, and a casting method known in the art may be employed. The gel-like film is manufactured by casting.

[0202] A glass plate, an aluminum substrate, a circulating stainless steel belt, a stainless steel drum, or a heat-resistant polymer film may be used as the carrier.

[0203] According to an embodiment of the present disclosure, the gel-type film is an uncured polyimide film, and its curing is not complete. In an embodiment of the present disclosure, even if the film is partially cured, when the curing is not complete, it is still referred to as a gel-type film or an uncured polyimide film.

[0204] Next, the gel-type film is first dried at a wind speed of 1.0 m / s or less at 50°C to 150°C for 2 to 20 minutes.

[0205] More specifically, the gel-type film manufactured by casting may be first dried at a temperature of 70°C to 150°C and a wind speed of 1.0 m / s or less for 2 to 20 minutes.

[0206] When the first drying time exceeds 20 minutes, the process efficiency deteriorates, and when hot air is applied for a long time, ripples are formed on the polyimide film.

[0207] In addition, when the first drying time is less than 2 minutes, the solvent contained in the gel-type film cannot be completely dried, and thus ripples appear in the film.

[0208] According to an embodiment of the present disclosure, when the wind speed used for the first drying is increased, the drying time can be shortened, and when the wind speed is decreased, the drying time can be extended. At this time, the wind speed is adjusted within a range such that the Kc value of the polyimide film does not exceed 1.55.

[0209] For example, in the first drying, the wind speed can be adjusted within the range of 0.2 m / s to 1.0 m / s.

[0210] Specifically, in the first drying, when the drying temperature is A °C, the wind speed is B m / s, and the first drying time is T minutes, the drying coefficient conditions according to the following Formula 1 and Formula 2 are satisfied:

[0211] [Formula 1]

[0212] 0.5 ≤ [(A - 40) × B × T] / 100 ≤ 10

[0213] [Formula 2]

[0214] 2 ≤ [(A - 40) × T] / 100 ≤ 10

[0215] When the value of "[(A - 40) × B × T] / 100" in Formula 1 is less than 0.5 or when the value of "[(A - 40) × T] / 100" in Formula 2 is less than 2, the first drying may not be complete. When the drying in the first drying is incomplete, most of the solvent will be removed in the subsequent second drying or the like. However, since the second drying is usually carried out at a wind speed higher than that of the first drying, unevenness will occur in the polyimide-based film during the process of evaporating a large amount of solvent at a strong wind speed during the second drying.

[0216] On the other hand, when the value of "[(A - 40) × B × T] / 100" in Formula 1 exceeds 10 or the value of "[(A - 40) × T] / 100" in Formula 2 exceeds 10, high-temperature hot air may be applied, or hot air with a high wind speed may be applied. When high-temperature hot air or hot air with a high wind speed is applied, unevenness such as ripples will occur in the polyimide-based film.

[0217] According to an embodiment of the present disclosure, drying is performed to remove the solvent contained in the gel-type film, and the Kc value of the polyimide-based film can be adjusted by optimizing the wind speed during the drying process.

[0218] Generally, since a solvent with a high boiling point is used in the process of preparing the liquid resin composition, it can be inferred that strong wind speed should be applied to the cast gel-like film to effectively remove the solvent.

[0219] However, when a strong wind speed is applied to the gel-type film during the first drying in which the solvent is not completely removed, a wavy pattern or a similar pattern is formed on the gel-type film by the wind, and the wavy pattern is retained in the resulting polyimide. As a result, the Kc value of the polyimide-based film increases. To prevent this increase in Kc, according to one embodiment of the present disclosure, the solvent is removed by applying wind to the gel-type film at a temperature, wind speed, and time suitable for the drying coefficient conditions according to Formula 1 and Formula 2.

[0220] In particular, when wind is applied to the gel-type film for a long time, a wavy pattern or a similar pattern is formed on the surface of the polyimide-based film by the wind, thereby making the polyimide-based film non-uniform and imparting a high Kc value to the polyimide-based film.

[0221] Therefore, according to one embodiment of the present disclosure, the wind speed in the first drying is determined in consideration of the drying time and temperature. The wind speed is measured as follows.

[0222] <Method for Measuring Wind Speed>

[0223] Measuring device: TSI 5725 anemometer

[0224] Measuring method: The anemometer is installed at a height of about 1 cm above the carrier, and the wind speed is measured when the measurement inlet direction of the anemometer is parallel to the surface of the carrier. When the wind speed in the first drying exceeds 1.0 m / s, ripples appear in the polyimide-based film and the ripples increase. Therefore, according to one embodiment of the present disclosure, the wind speed in the first drying can be maintained below 1.0 m / s, and depending on the temperature of the wind, the wind speed can be 0.8 m / s or less, or 0.5 m / s or less.

[0225] However, when the wind speed is less than 0.2 m / s, the wind speed is affected by the pressure or convection change of the surrounding air. For this reason, it is difficult to maintain a wind speed below 0.2 m / s and it is not easy to control the wind speed. As a result, there are limitations in obtaining a product with uniform quality. Therefore, according to one embodiment of the present disclosure, the wind speed can be adjusted to 0.2 m / s or more in the first drying.

[0226] In addition, the temperature in the first drying can be maintained at 50°C to 150°C, or, as needed, in the range of 70°C to 150°C.

[0227] Generally, the drying efficiency increases with an increase in temperature. On the other hand, when the temperature in the first drying process is increased such that the drying temperature approaches the boiling point of the solvent, bubbles are formed on the surface of the polyimide-based film and bending occurs due to the rapid volatilization of the solvent, so the surface uniformity of the polyimide-based film deteriorates.

[0228] Therefore, the first drying is carried out at a temperature above 50°C to ensure the drying efficiency and at a temperature below 150°C to prevent the rapid volatilization of the solvent. To improve the drying efficiency, the first drying can be carried out in the temperature range of 70°C to 150°C.

[0229] According to an embodiment of the present disclosure, after the first drying, the proportion of the residual solvent content of the uncured polyimide-based film (gel-type film) can be adjusted to 50 wt% or less. More specifically, the proportion of the residual solvent content of the uncured polyimide-based film after the first drying can be adjusted to 40 wt% or less.

[0230] According to an embodiment of the present disclosure, after the first drying, the gel-type film can be secondarily dried at a wind speed of 1.0 to 5.0 m / s at 70°C to 140°C. When the wind speed of the secondary drying is less than 1.0 m / s or its temperature is less than 70°C, the speed of the secondary drying will be excessively reduced. When the speed of the secondary drying is excessively reduced, the efficiency of the process will be reduced, and the physical properties of the polyimide-based film will change due to the extended drying time.

[0231] Since the gel-like film is dried and hardened to some extent by the first drying, it is almost impossible to change the surface properties of the gel-type film by the wind applied during the secondary drying. However, when the wind speed of the secondary drying exceeds 5.0 m / s or its temperature exceeds 140°C, wrinkles or bends will appear in the polyimide-based film due to the high-temperature strong wind. When wrinkles or bends appear in the polyimide-based film, the corrugation of the polyimide-based film increases, and the curvature parameter Kc will exceed 1.55. At the same time, the wind speed during the secondary drying can be adjusted in the range of, for example, 1.5 to 5.0 m / s, and more specifically, the wind speed during the secondary drying can be adjusted in the range of 1.6 to 3.0 m / s. In addition, during the secondary drying, the temperature can be adjusted in the range of 100°C to 140°C.

[0232] According to an embodiment of the present disclosure, after the secondary drying, the gel-type film can be subjected to a first heat treatment.

[0233] In the first heat treatment, a known thermal curing process can be employed. For example, the gel-type film can be heat-treated at a temperature of 100°C to 500°C for 1 minute to 1 hour. Through such heat treatment, the gel-type film is thermally cured to complete the polyimide-based film. The first heat treatment is also referred to as thermal curing.

[0234] The first heat treatment can be carried out on a carrier or a separately heat-treated carrier. For example, after the secondary drying, the gel-type film can be separated from the carrier, fixed to a support for the first heat treatment, and then the first heat treatment can be carried out. A pin-type frame or a clip-type frame can be used to support the gel-type film.

[0235] According to an embodiment of the present disclosure, the content of volatile components remaining in the polyimide-based film after the first heat treatment can be adjusted within a range of 5 wt% or less.

[0236] According to an embodiment of the present disclosure, the second heat treatment can be performed while applying a predetermined tension to the polyimide-based film that has been subjected to the first heat treatment. The residual stress inside the polyimide-based film can be removed by the second heat treatment.

[0237] When the second heat treatment is performed, the coefficient of thermal expansion of the polyimide-based film can be reduced. For example, the second heat treatment causes residual stress, which causes the polyimide-based film to shrink, thereby reducing thermal expansion and reducing the hysteresis of the coefficient of thermal expansion in the polyimide-based film.

[0238] The tension and temperature applied to the second heat treatment are related. Therefore, the tension can vary according to the temperature applied to the second heat treatment.

[0239] The second heat treatment can be performed at a temperature of 100°C to 500°C for 1 minute to 1 hour, and can be performed at a temperature of 250°C to 350°C for 2 to 15 minutes.

[0240] Another embodiment of the present disclosure provides a polyimide-based film manufactured according to the above manufacturing method.

[0241] Hereinafter, the present disclosure will be described in more detail with reference to specific preparation examples and examples. These examples should not be construed as limiting the scope of the present disclosure.

[0242] <Preparation Example 1>

[0243] 419.1 g of N,N-dimethylacetamide (DMAc) as the first solvent was charged into a 1 L reactor equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a cooler. While nitrogen was passed through the reactor, the temperature of the reactor was adjusted to 25°C, 32.023 g (0.10 mol) of TFDB as the diamine was dissolved therein, and the solution was maintained at 25°C. 8.885 g (0.02 mol) of 6FDA as the dianhydride was added to the solution and dissolved, and the reaction was carried out while stirring. At this time, the temperature of the reactor was lowered to 10°C, the temperature of the solution was maintained at 8°C, 16.24 g (0.08 mol) of TPC as the dicarbonyl compound was added to the solution, and the reaction was carried out at 25°C for 12 hours to obtain a first polymer solution with a solid content of 12 wt%. The first polymer solution may contain polyamic acid. Therefore, the first polymer solution is also referred to as a polyamic acid solution.

[0244] 1.58 g of pyridine and 2.02 g of acetic anhydride were added to the obtained first polymer solution. The resulting solution was stirred for 30 minutes and then stirred at 80 °C for 0.5 hour. After cooling to room temperature, 10 L of methanol as the second solvent was added to precipitate the solid. The precipitated solid was filtered, crushed, washed again with 2 L of methanol, and dried in vacuo at 100 °C for 6 hours to obtain a powdery polyimide-based polymer solid. The obtained polyimide-based polymer solid was dissolved again in DMAc as the third solvent to prepare a liquid resin composition having a solid content of 12% by weight. This liquid resin composition is also referred to as a polyimide-based resin composition. Here, the polyimide-based resin composition is a polyamide-imide resin composition.

[0245] <Preparation Example 2>

[0246] 432.4 g of N,N-dimethylacetamide (DMAc) as the first solvent was charged into a 1 L reactor equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a cooler. While nitrogen was passed through the reactor, the temperature of the reactor was adjusted to 25 °C. 32.023 g (0.10 mol) of TFDB as the diamine was dissolved therein, and the solution was maintained at 25 °C. 5.884 g (0.02 mol) of BPDA as the dianhydride was added to the solution, and then stirred for 2 hours. Subsequently, 8.885 g (0.02 mol) of 6FDA as the dianhydride was added and dissolved, and the reaction was carried out for a predetermined period while stirring. At this time, the temperature of the reactor was lowered to 10 °C, the temperature of the solution was maintained at 8 °C, 12.18 g (0.06 mol) of TPC as the dicarbonyl compound was added to the solution, and the reaction was carried out at 25 °C for 12 hours to obtain a first polymer solution having a solid content of 12% by weight.

[0247] 3.16 g of pyridine and 4.04 g of acetic anhydride were added to the obtained first polymer solution. The resulting solution was stirred for 30 minutes and then stirred at 80 °C for 0.5 hour. After cooling to room temperature, 10 L of methanol as the second solvent was added to precipitate the solid. The precipitated solid was filtered, crushed, washed again with 2 L of methanol, and dried in vacuo at 100 °C for 6 hours to obtain a powdery polyimide-based polymer solid. The obtained polyimide-based polymer solid was dissolved again in DMAc as the third solvent to prepare a liquid resin composition having a solid content of 12% by weight. This liquid resin composition is also referred to as a polyimide-based resin composition. Here, the polyimide-based resin composition is a polyamide-imide resin composition.

[0248] <Preparation Example 3>

[0249] In a 1 L reactor equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a cooler, 400.9 g of N,N-dimethylacetamide (DMAc) as the first solvent was charged. While nitrogen was passed through the reactor, the temperature of the reactor was adjusted to 25°C, and 32.023 g (0.10 mol) of TFDB as the diamine was dissolved therein, and the solution was maintained at 25°C. 1.961 g (0.01 mol) of CBDA as the dianhydride was added to this solution, and then it was stirred for 2 hours. Subsequently, 4.443 g (0.01 mol) of 6FDA as the dianhydride was added and dissolved, and it was reacted for a predetermined period while stirring. At this time, the temperature of the reactor was lowered to 10°C, the temperature of the solution was maintained at 8°C, 16.24 g (0.08 mol) of TPC as the dicarbonyl compound was added to this solution, and the reaction was carried out at 25°C for 12 hours to obtain a first polymer solution with a solid content of 12% by weight.

[0250] 1.58 g of pyridine and 2.02 g of acetic anhydride were added to the obtained first polymer solution, and the resulting solution was stirred for 30 minutes and then stirred at 80°C for 0.5 hour, cooled to room temperature, and 10 L of methanol as the second solvent was added to precipitate the solid. The precipitated solid was filtered, crushed, washed again with 2 L of methanol, and dried in vacuo at 100°C for 6 hours to obtain a powdery polyimide-based polymer solid. The obtained polyimide-based polymer solid was dissolved again in DMAc as the third solvent to prepare a liquid resin composition with a solid content of 12% by weight. This liquid resin composition is also referred to as a polyimide-based resin composition. Here, the polyimide-based resin composition is a polyamide-imide resin composition.

[0251] <Preparation Example 4>

[0252] In a 1 L reactor equipped with a stirrer, a nitrogen injector, a dropping funnel, a temperature controller, and a cooler, 587.5 g of N,N-dimethylacetamide (DMAc) as the first solvent was charged. While nitrogen was passed through the reactor, the temperature of the reactor was adjusted to 25°C, and 640.046 g (0.20 mol) of TFDB as the diamine was dissolved therein, and the solution was maintained at 25°C. 11.77 g (0.04 mol) of BPDA as the dianhydride was added to this solution, and then it was stirred for 2 hours. Subsequently, 71.8 g (0.16 mol) of 6FDA as the dianhydride was added and dissolved, and it was reacted for a predetermined period while stirring. The reaction was carried out at 25°C for 12 hours to obtain a first polymer solution with a solid content of 20% by weight.

[0253] 6.328 g of pyridine and 8.08 g of acetic anhydride were added to the obtained first polymer solution, and the resulting solution was stirred for 30 minutes and then stirred at 80 °C for 1 hour, cooled to room temperature, and 10 L of methanol as a second solvent was added to precipitate the solid. The precipitated solid was filtered, crushed, washed again with 2 L of methanol, and dried in vacuo at 100 °C for 6 hours to obtain a powdery polyimide-based polymer solid. The obtained polyimide-based polymer solid was dissolved again in DMAc as a third solvent to prepare a liquid resin composition having a solid content of 20% by weight. This liquid resin composition is also referred to as a polyimide-based resin composition. Here, the polyimide-based resin composition is a polyimide resin composition.

[0254] <Example 1>

[0255] The polyimide-based resin composition, i.e., the liquid resin composition prepared in Preparation Example 1, was cast on a substrate to produce a gel-type film (an uncured polyimide-based film in a gel state), and the gel-type film was first dried at 80 °C for 20 minutes at a wind speed of 0.2 m / s and then second dried at 140 °C for 10 minutes at an increased wind speed of 1.6 m / s.

[0256] The gel-type film was mounted on a pin-type tenter and heat-treated for 1 hour while raising the temperature from 120 °C to 280 °C. The gel-like film was cured by the first heat treatment to produce a polyimide-based film. The produced polyimide-based film is a polyamide-imide film.

[0257] The polyimide-based film produced by the first heat treatment was removed from the tenter frame and then second heat-treated at 280 °C for 5 minutes to remove the residual stress in the film.

[0258] <Examples 2 to 8>

[0259] Except for the first drying conditions as shown in Table 1 below, polyimide-based films were produced in the same manner as in Example 1, and these polyimide-based films refer to Examples 2 to 8.

[0260] <Example 9>

[0261] The polyimide-based resin composition, i.e., the liquid resin composition prepared in Preparation Example 2, was cast on a substrate to produce a gel-type film, and the gel-type film was first dried at 80 °C for 20 minutes at a wind speed of 0.2 m / s and then second dried at 140 °C for 10 minutes at an increased wind speed of 1.6 m / s.

[0262] The gel-type film is mounted on a pin tenter and heat-treated for 1 hour while raising the temperature from 120 °C to 280 °C. The gel-like film is cured by the first heat treatment to produce a polyimide-based film. The produced polyimide-based film is a polyamide-imide film.

[0263] The heat-treated film is removed from the tenter frame and then further heat-treated at 280 °C for 5 minutes to remove the residual stress in the film.

[0264] The polyimide-based film produced by the first heat treatment is removed from the tenter frame and then heat-treated at 280 °C for 5 minutes in the second heat treatment to remove the residual stress in the film.

[0265] <Examples 10 to 16>

[0266] Except for the first drying conditions as shown in Table 1 below, polyimide-based films are produced in the same manner as in Example 9, and these polyimide-based films refer to Examples 10 to 16.

[0267] <Example 17>

[0268] A polyimide-based resin composition is poured onto a substrate, that is, the liquid resin composition prepared in Example 3 is used to produce a gel-type film (an uncured polyimide-based film in a gel state). The gel-type film is first dried at 80 °C for 20 minutes with a wind speed of 0.2 m / s and then second dried at 140 °C for 10 minutes with an increased wind speed of 1.6 m / s.

[0269] The gel-type film is mounted on a pin tenter and heat-treated for 1 hour while raising the temperature from 120 °C to 250 °C. The gel-like film is cured by the first heat treatment to produce a polyimide-based film. The produced polyimide-based film is a polyamide-imide film.

[0270] The heat-treated film is removed from the tenter frame and then heat-treated at 250 °C for 5 minutes in the second heat treatment to remove the residual stress in the film.

[0271] <Examples 18 to 24>

[0272] Except for the first drying conditions as shown in Table 1 below, polyimide-based films are produced in the same manner as in Example 17, and these polyimide-based films refer to Examples 18 to 24.

[0273] <Example 25>

[0274] A polyimide-based resin composition was cast on a substrate, i.e., the liquid resin composition prepared in Preparation Example 4, to produce a gel-type film (an uncured polyimide-based film in a gel state), and the gel-type film was first dried at 80°C for 20 minutes at a wind speed of 0.2 m / s and then second dried at 140°C for 10 minutes at an increased wind speed of 1.6 m / s.

[0275] The gel-type film was mounted on a pin-type tenter and first heat-treated for 1 hour while raising the temperature from 120°C to 280°C. The gel-like film was cured by the first heat treatment to produce a polyimide-based film. The produced polyimide-based film was a polyamide-imide film.

[0276] The heat-treated film was removed from the tenter frame and then second heat-treated at 280°C for 5 minutes to remove the residual stress in the film.

[0277] <Examples 26 to 32>

[0278] Except for the first drying conditions as shown in Table 1 below, polyimide-based films were produced in the same manner as in Example 25, and these polyimide-based films refer to Examples 26 to 32.

[0279] <Comparative Examples 1 to 5>

[0280] Except for the first drying conditions as shown in Table 1 below, polyimide-based films were produced in the same manner as in Example 1, and these polyimide-based films refer to Comparative Examples 1 to 5.

[0281] <Comparative Examples 6 to 10>

[0282] Except for the first drying conditions as shown in Table 1 below, polyimide-based films were produced in the same manner as in Example 9, and these polyimide-based films refer to Comparative Examples 6 to 10.

[0283] <Comparative Examples 11 to 15>

[0284] Except for the first drying conditions as shown in Table 1 below, polyimide-based films were produced in the same manner as in Example 17, and these polyimide-based films refer to Comparative Examples 11 to 15.

[0285] <Comparative Examples 16 to 20>

[0286] Except for the first drying conditions as shown in Table 1 below, polyimide-based films were produced in the same manner as in Example 25, and these polyimide-based films refer to Comparative Examples 16 to 20.

[0287] Based on the “[(A - 40)×B×T] / 100” in the first drying condition calculation formula 1 and “[(A - 40)×T] / 100” in formula 2 of Examples 1 to 32 and Comparative Examples 1 to 20, and they are shown in Table 1.

[0288] [Table 1]

[0289]

[0290]

[0291]

[0292] <Method for Measuring Physical Properties>

[0293] The physical properties of the polyimide films manufactured in Examples 1 to 32 and Comparative Examples 1 to 20 were measured by the following method, and the results are shown in Table 2.

[0294] (1) Measurement of Film Thickness

[0295] The thickness of the polyimide films manufactured in the Examples and Comparative Examples was measured using an Anritsu electronic micrometer. The thickness deviation caused by this instrument is below ±0.5%.

[0296] (2) Light Transmittance

[0297] The average light transmittance of the polyimide films manufactured in the Examples and Comparative Examples was measured using a UV spectrometer (Cotica Minolta CM - 3700d) in the wavelength range of 380 to 780 nm. The thickness of the polyimide films is shown in Table 1.

[0298] (3) Yellowness Index (YI):

[0299] The yellowness index of the polyimide films manufactured in the Examples and Comparative Examples was measured according to ASTM E313 using a UV spectrophotometer (CM - 3700D, Konica Minolta Inc.).

[0300] (4) Haze

[0301] The haze of the polyimide films manufactured in the Examples and Comparative Examples was measured using a haze meter HM - 150.

[0302] (5) Measurement of Kc Value

[0303] - Measuring device: Optimap of Rhopoint TM (PSD)

[0304] - Optical mode: Extra dull

[0305] - Display mode: Curvature mode (X+Y scan)

[0306] - Curvature mode K: Set wavelength range (Kc) from 1.0 to 3.0 mm

[0307] - Measurement method: Place a black matte paper on a flat plate in a dark room, place the sample to be measured on it, measure the Kc value 10 times, and use the average value as the Kc value of the sample.

[0308] - Film sample: Polyimide films with a width of 15 cm × length of 15 cm × thickness of 80 μm (Examples 1 to 32 and Comparative Examples 1 to 20) are used for Kc measurement (thickness deviation ±2%).

[0309] - Others: When measured with a microscope, there are 0.005 foreign substances with a particle size of 50 μm or more per cm 2 as follows.

[0310] [Table 2]

[0311]

[0312]

[0313]

[0314] As can be seen from Table 2, the Kc values of the polyimide films according to Examples 1 to 32 of the present disclosure are 1.55 or less. The Kc value of the polyimide film is affected by the temperature, wind speed, and drying time in the first drying.

[0315] As can be seen from Table 1 and Table 2, when the polyimide film is first dried at a relatively low temperature below 100 °C, the first drying should be carried out for a relatively long period of time at various wind speeds within the range that satisfies the drying coefficient conditions according to Formula 1 and Formula 2 to obtain a low Kc value. In addition, when the polyimide film is first dried at a relatively high temperature above 100 °C, the first drying should be carried out for a relatively short period of time at various wind speeds within the range that satisfies the drying coefficient conditions according to Formula 1 and Formula 2 to obtain a low Kc value.

[0316] On the other hand, it can be seen that when the polyimide film is first dried at a relatively low temperature below 100°C, in the case of short-time drying, there will be a problem that the first drying is not fully carried out and a large amount of solvent volatilizes during the second drying process. Therefore, the Kc value of the polyimide film increases and the flatness decreases. In addition, it can be seen that when the polyimide film is first dried at a relatively high temperature above 100°C, in the case of long-time drying, excessive solvent volatilization will occur, and a wavy pattern will be formed on the polyimide film by high-temperature hot air. Therefore, the Kc value increases and the flatness decreases.

[0317] Figure 3 is the projection image of the film according to Example 1 of the present disclosure, Figure 4 is the projection image of the film according to Comparative Example 15. From Figure 3 and Figure 4 it can be seen that compared with the polyimide film manufactured according to the comparative example, the polyimide film with a low Kc value of 1.55 or less manufactured according to the embodiment of the present disclosure has better surface flatness and hardly has or does not have unevenness such as a wavy pattern.

[0318] The polyimide film according to the embodiment of the present disclosure can be used in various electronic devices. Therefore, another embodiment of the present disclosure provides an electronic device including the polyimide film according to the present disclosure. The polyimide film according to the present disclosure can be used as, for example, a cover window of an electronic device.

[0319] [Description of Reference Numerals]

[0320] 10: Light source

[0321] 20: Light

[0322] 30: Film to be projected

[0323] 40: Flat surface

[0324] 50: Projection image.

Claims

1. A polyimide film, the Kc value of the polyimide film is 1.45 or less, Among them, The Kc value is the curvature parameter of the ripple with a wavelength range of 1.0 to 3.0 mm measured by the phase step deflection method PSD, wherein the polyimide film is manufactured from a monomer component containing dianhydride, diamine and dicarbonyl compound, The dianhydride includes at least one selected from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA), pyromellitic dianhydride (PMDA), 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic anhydride (ODPA), 4,4′-(3,4-bis(dicarboxyphenoxy))-diphenyl sulfide dianhydride (BDSDA), 3,3′,4,4′-diphenylsulfone tetracarboxylic dianhydride (SO2DPA), 4,4'-(4,4′-isopropylidenediphenoxy)bis(phthalic anhydride) (6HBDA), cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA) and dicyclohexyl-3,4,3′,4′-tetracarboxylic dianhydride (HBPDA), The diamine includes at least one selected from 3,4-diaminodiphenyl ether (34ODA), 4,4'-diaminodiphenyl ether (4ODA), p-phenylenediamine (pPDA), m-phenylenediamine (mPDA), 4,4-methylenedianiline (pMDA), 3,3-methylenedianiline (mMDA), 1,3-bis(3-aminophenoxy)benzene (133APB), 1,3-bis(4-aminophenoxy)benzene (134APB), 2,2'-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (4BDAF), 2,2'-bis(3-aminophenyl)hexafluoropropane (33-6F), 2,2'-bis(4-aminophenyl)hexafluoropropane (44-6F), bis(4-aminophenyl)sulfone (4DDS), bis(3-aminophenyl)sulfone (3DDS), 2,2'-bis(trifluoromethyl)benzidine (TFDB), 1,3-cyclohexanediamine (13CHD), 1,4-cyclohexanediamine (14CHD), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (6HMDA), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (DBOH), bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 9,9-bis(4-aminophenyl)fluorene (FDA) and 9,9-bis(4-amino-3-fluorophenyl)fluorene (F-FDA), and The dicarbonyl compound includes at least one of aromatic dicarbonyl compound and aliphatic dicarbonyl compound.

2. The polyimide film according to claim 1, wherein The Kc value of the polyimide-based film is from 1.10 to 1.

45.

3. The polyimide film according to claim 1, wherein, The aromatic dicarbonyl compound is represented by the following formula 1: [Formula 1] wherein, R1 represents a single bond, *-Ar-*, *-O-Ar-*, *-CAL-* or *-O-CAL-*; X1 and X2 each independently represent hydrogen, a hydroxyl group (OH) or a halogen element; and X3 represents hydrogen or a halogen element, wherein, "Ar” represents a substituted or unsubstituted arylene group, and "CAL” represents a divalent alicyclic group.

4. The polyimide film according to claim 1, wherein, The aromatic dicarbonyl compound includes at least one of the compound represented by the following formula 3, the compound represented by the following formula 4, the compound represented by the following formula 5, the compound represented by the following formula 6, the compound represented by the following formula 7, the compound represented by the following formula 8, and the compound represented by the following formula 9: [Formula 3] [Formula 4] [Formula 5] [Formula 6] [Formula 7] [Formula 8] [Formula 9] 5. The polyimide film according to claim 1, wherein The aliphatic dicarbonyl compound includes at least one of the compound represented by the following formula 10, the compound represented by the following formula 11, the compound represented by the following formula 12, and the compound represented by the following formula 13: [Formula 10] [Formula 11] [Formula 12] [Formula 13] 6. The polyimide film according to claim 1, wherein, Based on a thickness of 80 μm, the haze of the polyimide-based film is 2.0 or less, the average light transmittance at a wavelength of 380 to 780 nm is 87% or more, and the yellowness index is 5 or less.

7. A method for manufacturing a polyimide-based film, comprising: Preparing a liquid resin composition using a monomer component containing a dianhydride, a diamine, and a dicarbonyl compound; Manufacturing a gel-type film using the liquid resin composition; And First drying the gel-type film at a temperature of 50°C to 150°C with a wind speed of 1.0 m / s or less for a drying time of 2 to 20 minutes, wherein, in the first drying, when the temperature is A°C, the wind speed is B m / s, and the drying time is T minutes, the drying coefficient conditions according to the following formula 1 and formula 2 are satisfied: [Formula 1] 0.5 ≤ [(A - 40) × B × T] / 100 ≤ 10 [Formula 2] 2 ≤ [(A - 40) × T] / 100 ≤ 10.

8. The method according to claim 7, wherein, The viscosity of the liquid resin composition is 1,000 to 250,000 cPs.

9. The method according to claim 7, wherein In the first drying, the wind speed is 0.2 m / s or more.

10. The method according to claim 7, further comprising, after the first drying, second drying the gel-type film at 70°C to 140°C with a wind speed of 1.0 to 5.0 m / s.

11. The method according to claim 10, further comprising, after the second drying, first heat-treating the gel-type film at a temperature of 100°C to 500°C for 1 minute to 1 hour.

12. The method according to claim 7, wherein Manufacturing the gel-type film includes casting the liquid resin composition on a carrier.

13. The method according to claim 7, wherein Preparing the liquid resin composition includes: Reacting the monomer component in the presence of a first solvent to prepare a first polymer solution; Adding a second solvent to the first polymer solution, followed by filtration and drying to prepare a polymer solid; and Dissolve the polymer solid in a third solvent.

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