TWI750801B - Polyimide based film having improved surface evenness, method for manufacturing the same and electronic device - Google Patents

Abstract

Disclosed are a polyimide-based film, a method of producing the same and an electronic device, and more particularly, a polyimide-based film having excellent surface evenness and suppressed waviness due to low Kc of 1.55 or less, a method of producing the same and an electronic device.

Description

Polyimide film with improved surface uniformity, manufacture thereof method and electronic device

The present disclosure relates to a polyimide-based film with improved surface uniformity, a method for manufacturing the same, and an electronic device, and more particularly, to a polyimide-based film with suppressed ripple due to low Kc, Its manufacturing method and electronic device.

Polyimide (PI)-based resins have properties such as high heat resistance, oxidation resistance, radiation resistance, low temperature resistance, and chemical resistance, and are therefore widely used in electronic products, semiconductors, automobiles, aircraft, and spacecraft and other similar industries, and is used as a transparent electrode film and a cover window for display devices.

Recently, studies to improve the optical properties of polyimide-based resins have been conducted, and polyimide-based resins with improved optical properties are being developed without major deterioration in mechanical properties or thermal properties.

Polyimide-based films prepared from polyimide-based resins with improved mechanical, thermal, and optical properties are used in various flexible products and are being studied as a replacement for glass. For example, the use of polyimide-based films as cover windows or protective materials for display devices is being studied.

Accordingly, it is an object of the present disclosure to provide polyimide (PI) based films with improved surface uniformity.

Another object of the present disclosure is to provide a polyimide (PI)-based film capable of suppressing the appearance of ripples and having improved surface uniformity due to its low Kc value.

Another object of the present disclosure is to provide a method of fabricating a polyimide (PI)-based film with improved surface uniformity.

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

Another object of the present disclosure is to provide a method of manufacturing a polyimide (PI)-based film capable of suppressing the occurrence of ripples.

Another object of the present disclosure is to provide an electronic device including a polyimide (PI)-based film with improved surface uniformity due to its low Kc value.

According to an aspect of the present disclosure to solve the technical problem, there is provided a polyimide film having a Kc value of 1.55 or less, wherein the Kc value is measured by phase stepped deflectometry (PSD; PSD). ) curvature parameter measured for corrugations in the wavelength range 1.0 mm to 3.0 mm.

The polyimide-based film may have a Kc value of 1.45 or less.

The polyimide-based film may have a Kc value of 1.10 to 1.45.

The polyimide-based film can be produced from monomer components including dianhydride and diamine.

The dianhydride may comprise at least one selected from the group consisting of: 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride; 6FDA ), 3,3',4,4'-biphenyltetracarboxylic dianhydride (3,3',4,4'-biphenyl tetracarboxylic dianhydride; BPDA), 4-(2,5-dioxytetrahydrofuran-3 -yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1, 2-dicarboxylic anhydride; TDA), pyromellitic dianhydride (PMDA), benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic anhydride (4,4'-oxydiphthalic anhydride; ODPA), bisdicarboxyphenoxy diphenyl sulfide dianhydride (BDSDA), 3,3',4,4'-diphenyltetracarboxylic dianhydride (3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride; SO ₂ DPA), 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride) (4, 4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride); 6HBDA), cyclobutane-1,2,3,4-tetracarboxylic dianhydride ; CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride (1,2,3,4-cyclopentane-tetracarboxylic dianhydride; CPDA), 1,2,4,5-cyclohexanetetracarboxylic Acid dianhydride (1,2,4,5-cyclohexanetetracarboxylic dianhydride; CHDA) and dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (dicyclohexyl-3,4,3',4'- tetracarboxylic dianhydride).

The diamine may include at least one selected from the group consisting of: oxydianiline (ODA), p-phenylenediamine (pPDA), m-phenylenediamine (mPDA), 4,4-diaminodiphenylmethane (4,4-methylenedianiline; pMDA), 3,3-diaminodiphenylmethane (3,3-methylenedianiline; mMDA) ), 1,3-bis(3-aminophenoxy)benzene (1,3-bis(3-aminophenoxy)benzene; 133APB), 1,4-bis(4-aminophenoxy)benzene (1 ,3-bis(4-aminophenoxy)benzene; 134APB), bisaminophenoxy phenyl hexafluoropropane (4BDAF), 2,2'-bis(3-aminophenoxy) hexafluoropropane (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), bis(3-aminophenyl)sulfone bistrifluoromethyl benzidine (TFDB), 1,3-cyclohexanediamine (1,3-cyclohexanediamine; 13CHD), 1,4-cyclohexanediamine (1,4-cyclohexanediamine; 14CHD), 2 ,2-bis[4-(4-aminophenoxy)phenyl]propane (2,2-bis[4-(4-aminophenoxy)phenyl]propane; 6HMDA), 2,2-bis(3-amine) 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (DBOH), bis[4-(4-aminophenoxy)phenyl] bis(bis[4-(4-aminophenoxy)phenyl)] [4-(4-aminophenoxy)phenyl]sulfone; DBSDA), bis[4-(3-aminophenoxy)phenyl]sulfone; DBSDA), 9 ,9-bis(4-aminophenyl)fluorene (9,9-bis(4-aminophenyl)fluorene; FDA) and 9,9-bis(4-amino-3-fluorophenyl)fluorene (9, 9-bis(4-amino-3-fluorophenyl )fluorene; F-FDA).

The monomer component may further comprise a dicarbonyl compound.

Dicarbonyl compounds may include aromatic dicarbonyl compounds and aliphatic dicarbonyl compounds at least one of the compounds.

The aromatic dicarbonyl compound can be represented by the following formula 1:

wherein R ₁ represents a single bond, *-Ar-*, *-O-Ar-*, *-CAL-* or *-O-CAL-*, X ₁ and X ₂ each independently represent hydrogen, hydroxyl (OH) or a halogen element, and X ₃ represents hydrogen or a halogen element, wherein "Ar" represents a substituted or unsubstituted aryl group, and "CAL" represents a cycloaliphatic group.

The aromatic dicarbonyl compound may include at least one of: a compound represented by the following formula 3, a compound represented by the following formula 4, a compound represented by the following formula 5, a compound represented by the following formula 6, a compound represented by the following formula 7 The compound represented, the compound represented by the following formula 8, and the compound represented by the following formula 9.

[Formula 9]

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.

Based on a thickness of 80 microns, the polyimide-based film may have a haze of 2.0 or less, an average light transmittance of 87% or more at wavelengths from 380 nm to 780 nm, and an average light transmittance of 5 or less Yellow index.

According to another aspect of the present disclosure, there is provided a method of manufacturing a polyimide film, which includes preparing a liquid resin composition using a monomer component including a dianhydride and a diamine, and using the liquid resin composition to prepare a gel type film, and the first drying of the gel type film at a wind speed of 1.0 m/s or less than 1.0 m/s at 50°C to 150°C for 2 minutes to 20 minutes, wherein in the first drying, when drying When the temperature is A° C., the wind speed is B m/sec, and the first drying period is T minutes, the drying coefficient conditions according to the following Equation 1 and Equation 2 are satisfied.

The monomer component may further contain a dicarbonyl compound.

The liquid resin composition may have a viscosity of 1,000 centipoise (cP) to 250,000 centipoise.

The method for manufacturing a polyimide-based film may further comprise, after the first drying The gel-type film is dried a second time at 70°C to 140°C with a wind speed of 1.0 m/sec to 5.0 m/sec.

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

Manufacturing the gel-type film may include casting a liquid resin composition on a support.

Preparing the liquid resin composition may include reacting the monomer components 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 solids; and dissolving the polymer solids in a third solvent.

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

According to another aspect of the present disclosure, an electronic device including a polyimide film is provided.

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 of manufacturing the polyimide-based film. The polyimide-based film according to an embodiment of the present disclosure has a low Kc value and can suppress moire generation, and thus can exhibit improved surface uniformity.

The polyimide-based film with low Kc value and improved surface uniformity fabricated according to an embodiment of the present disclosure has glass-like surface properties and thus can be used as a substitute for glass.

10: Light source

20: Light

30: Projection target film

40: flat surface

50: Projected image

λ: wavelength

FIG. 1 is a schematic diagram illustrating a method of projecting an image of a film.

FIG. 2 is an example of a projected image obtained by a method of projecting an image.

3 is a projected image of a film according to an embodiment of the present disclosure.

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

FIG. 5 is a cross-sectional view showing surface roughness, waviness, and shape.

Hereinafter, preferred embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. These embodiments are provided for illustration so that this disclosure will be thorough and complete, and should not be construed as limiting the scope of the disclosure.

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. The same reference numbers refer to the same elements throughout the description of the drawings. When such well-known techniques may not necessarily obscure the subject matter of the present disclosure, detailed descriptions of related well-known techniques may be omitted.

When the terms "comprising," "having," and "consisting of," etc. are used herein, another element may be added unless the expression "only" is used. The singular forms are also intended to include the plural forms unless the context clearly dictates otherwise. Also, even if there is no explicit description thereof, the constituent elements should be construed as containing a range of error.

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

Spatially relative terms such as "below," "beneath," "below," "above," and "below" may be used herein. on" to easily describe the relationship of one element to another element as shown in the figures. It should be understood that the spatially relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures. For example, if the device in one of the figures is turned over, elements described as "below" or "beneath" other elements would then be oriented "above" the other elements. Thus, the exemplary terms "under" or "under" can encompass both an orientation of above and below. Likewise, the exemplary terms "up" or "over" can encompass an up-down orientation.

In the description of a temporal relationship, for example, when using "after", "following", "before", etc. to describe a time series relationship, unless The terms "right" or "directly" are used, which otherwise can also include non-consecutive situations.

It will be understood that, although the terms "first," "second," etc. may be used herein to describe various elements, these elements should not be considered limited by these terms, which are only used to distinguish one element from another. Therefore, the first component mentioned below may be referred to as the second component instead without going beyond the technical idea of the present disclosure.

The term "at least one" should be understood to include all possible combinations of one or more of the associated items. For example, "at least one of the first item, the second item, and the third item" may mean each of the first item, the second item, and the third item, and may A combination of all items derived from two or more of the first item, the second item, and the third item.

The individual features of the various embodiments of the present disclosure may be combined in part or in whole with each other and may be technically interlocked and actuated in various ways, and the individual embodiments may be relative are implemented independently of each other or together in an associated relationship.

The polyimide-based film according to an embodiment of the present disclosure has a Kc value of 1.55 or less, wherein the Kc value is in the wavelength range of 1.0 mm to 3.0 mm by phase step deflection metrology (PSD) The measured curvature parameter. The Kc value represents the waviness of the polyimide-based film according to an embodiment of the present disclosure.

The polyimide-based film according to an embodiment of the present disclosure may be prepared from monomer components including dianhydride and diamine.

In an embodiment of the present disclosure, "monomer components" may refer to all types of monomers used in the manufacture of polyimide-based films. The monomer components may be present in a mixture, or each of the monomers contained in the monomer components may be mixed sequentially.

According to an embodiment of the present disclosure, the dianhydride, for example, includes at least one selected from the group consisting of: 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4-(2,5-dioxytetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2- Dicarboxylic anhydride (TDA), pyromellitic dianhydride (PMDA), benzophenone tetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic anhydride (ODPA), bisdicarboxybenzene Oxydiphenylthiodianhydride (BDSDA), 3,3',4,4'-diphenyltetracarboxylic dianhydride (SO ₂ DPA), 4,4'-(4,4'-isopropylidene Diphenoxy) bis(phthalic anhydride) (6HBDA), cyclobutane-1,2,3,4-tetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetra Carboxylic dianhydride (CPDA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (CHDA) and dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (HBPDA) . As the dianhydride, the above-mentioned compounds may be used alone or as a mixture of two or more compounds.

The diamine may, for example, comprise at least one selected from the group consisting of oxydiphenylamine (ODA), p-phenylenediamine (pPDA), m-phenylenediamine (mPDA), 4,4-diaminodiphenylmethane (pMDA) ), 3,3-diaminodiphenylmethane (mMDA), 1,3-bis(3-aminobenzene) Oxy)benzene (133APB), 1,4-bis(4-aminophenoxy)benzene (134APB), bisaminophenoxyphenylhexafluoropropane (4BDAF), 2,2'-bis(3 -Aminophenyl) hexafluoropropane (33-6F), 2,2'-bis(4-aminophenyl)hexafluoropropane (44-6F), bis(4-aminophenyl) bismuth (4DDS) ), bis(3-aminophenyl) bismuth (3DDS), bistrifluoromethylbenzidine (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]sine, bis[4-(3-aminophenoxy)phenyl]sine, 9,9-bis(4-aminophenyl)fluorene (FDA) and 9,9-bis(4-amino-3-fluorophenyl)fluorene (F-FDA). As diamines, the above-mentioned compounds can be used alone or in a mixture of two or more compounds.

The polyimide film prepared from the monomer including dianhydride and diamine may be a polyimide-based film having repeating units of imine. However, the polyimide-based film according to the present disclosure is not limited thereto.

According to an embodiment of the present disclosure, the monomer component may further include a dicarbonyl compound. When the monomer component further comprises a dicarbonyl compound, in addition to dianhydride and diamine, the polyimide film may have a polyimide-imide copolymer structure, which has repeating units of amide and repeating amides unit.

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

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.

The aromatic dicarbonyl compound according to an embodiment of the present disclosure can be obtained from the following Formula 1 represents.

In Formula 1, R ₁ represents a single bond, *-Ar-*, *-O-Ar-*, *-CAL-* or *-O-CAL-*, and X ₁ and X ₂ each independently represent hydrogen, hydroxyl (OH) or a halogen element, and X ₃ represents hydrogen or a halogen element, wherein "Ar" represents a substituted or unsubstituted aryl group, and "CAL" represents a cycloaliphatic group.

The arylidene group is, for example, a phenylene group represented by the following formula 2.

According to an embodiment of the present disclosure, as an example of an unsubstituted propynyl group, there is a phenylene group represented by Formula 2.

Further, as an example of the substituted arylidene group, there is a phenylene group in which hydrogen (H) of a benzene ring is substituted with a halogen element. More specifically, a substituted arylidene group is, for example, a chlorophenylene group in which the hydrogen (H) of the benzene ring is replaced with chlorine (Cl).

In Formula 1, _{at least one of X 1} and X ₂ may be a halogen element, and the halogen element may be a chlorine (Cl) atom. Additionally, X ₃ may be hydrogen (H) or chlorine (Cl).

The aromatic dicarbonyl compound may include at least one of: a compound represented by the following formula 3, a compound represented by the following formula 4, a compound represented by the following formula 5, A compound represented by the following formula 6, a compound represented by the following formula 7, a compound represented by the following formula 8, and a compound represented by the following formula 9.

[Formula 7]

According to an embodiment of the present disclosure, the aromatic dicarbonyl compound may, for example, comprise at least one of the following: terephthalic acid chloride (TPC) (formula 3), terephthalic acid (TPA) (formula 4), isophthalide Acrylic dichloride (IPC) (formula 5), 1,1'-biphenyl-4,4'-dicarbonyl dichloride (BPDC) (formula 6), 4,4'-oxybisbenzyl chloride (ODBC) (Formula 7) and 2-chloroterephthalamide dichloride.

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 following: 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, and the compound represented by the following formula 10 to The compound represented by the following formula 13 may also be referred to as an alicyclic compound.

[Formula 13]

According to an embodiment of the present disclosure, as the dicarbonyl compound, the above-mentioned compounds may be used alone or in the form of a mixture of two or more thereof.

According to an embodiment of the present disclosure, the polyimide-based film has a Kc value of 1.55 or less. The Kc value is a curvature parameter measured by phase step deflection metrology (PSD) for ripples in the wavelength range of 1.0 mm to 3.0 mm formed on the polyimide-based film.

According to an embodiment of the present disclosure, the Kc value means the waviness formed on the polyimide film with a wavelength of 1.0 mm to 3.0 mm.

Ripple is also known as "wave shape" or "wave pattern curve".

Hereinafter, the moiré will be described with reference to FIG. 5 .

FIG. 5 is a cross-sectional view showing surface roughness, waviness, and shape.

Assuming that there is an object having a cross-sectional profile as shown in (A) of FIG. 5 , the surface roughness is represented by (B) and determined by a fine curve appearing at the smallest interval on the surface of (A) of FIG. 5 , the corrugations are represented by (C) and are surface curves that appear at intervals greater than the surface roughness (B) intervals, and the shapes are represented by (D) and appear at intervals greater than the intervals of the corrugations (C), the corrugations of the object Exterior.

Specifically, the surface roughness shown by (B) of FIG. 5 is The fine curve in the cross section indicated by (A) of 5 is a fine curve drawn around the virtual center line extending in a straight line when a virtual center line is set and the virtual center line extends in a straight line. In the surface roughness represented by (B) of FIG. 5 , the interval between fine curves may be about several micrometers to several tens of micrometers.

The waviness represented by (C) of FIG. 5 is a surface curve which appears at intervals larger than the surface roughness (B) interval, and is represented by a virtual straight line. In the corrugations represented by (C) of FIG. 5 , the interval between the curves may be about several hundreds of micrometers (μm) to several centimeters (cm).

According to an embodiment of the present disclosure, the interval between the curves is called "wavelength (λ)". The corrugations shown in (C) of FIG. 5 may have a wavelength λ of about several hundreds of micrometers (μm) to several centimeters (cm).

According to an embodiment of the present disclosure, the Kc value is a curve parameter measured for ripples with a wavelength of 1.0 mm to 3.0 mm. The Kc value according to one embodiment of the present disclosure is used to evaluate the waviness in the wavelength (λ) range of 1.0 mm to 3.0 mm formed on the polyimide-based film.

In general, the optimum viewing distance for humans is about 30 cm to about 40 cm, and the human eye has high resolution for curves spaced 1 mm to 3 mm apart at viewing distances of about 30 cm to about 40 cm. Therefore, when a ripple having a wavelength (λ) of 1.0 mm to 3.0 mm (ie, a curve having an interval of 1 mm to 3 mm) is formed on the surface of the display device, such ripple is extremely easy to be perceived by the human eye. In addition, this ripple causes screen distortion.

According to an embodiment of the present disclosure, by adjusting the Kc value of the polyimide-based film to 1.55 or less, it is possible to minimize the curve visually recognized by the human eye. 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, a curve visually recognized by a user's eyes can be minimized and screen distortion can be minimized.

According to an embodiment of the present disclosure ^{, Kc values were measured using an Optimap™} PSD (Rhopoint Instruments, UK).

According to an embodiment of the present disclosure, an Optimap ^™ PSD from Rhopoint Instruments (UK) was used to measure the Kc value, and the Kc value was digitized by the program of the ^{Optimap™ PSD.} According to one embodiment of the present disclosure, the curvature (K) and profile of the surface to be measured are measured by phase step deflection metrology (PSD), and in this case, a periodic sine wave pattern is used.

It can be explained that the low Kc value of the polyimide-based film means a small change in curvature at various points on the surface of the polyimide-based film. Small changes in curvature can be interpreted as a few periodically changing patterns, such as moiré patterns. Therefore, the polyimide-based film is considered to be flatter when the Kc value is small than when the Kc value is large.

According to an embodiment of the present disclosure, the polyimide-based film has a Kc value of 1.55 or less. When the polyimide-based film has a Kc value of 1.55 or less, surface curvature such as corrugations is small and improved uniformity is achieved. When such a polyimide film is used as a cover window for a display device, screen distortion does not occur. When a polyimide-based film having a Kc value of 1.55 or less is used as a cover window of a display device, the moiré pattern on the display screen may not be visible to a user with normal vision.

As the Kc value of the polyimide-based film decreases, the uniformity of the polyimide-based film can be improved. For example, according to another embodiment of the present disclosure, the polyimide-based film may have a Kc value of 1.45 or less. When the Kc value of the polyimide film is When the value is 1.45 or less, the polyimide-based film hardly generates ripples detectable by the human eye.

Meanwhile, drying conditions become harsher than necessary in order to manufacture a polyimide-based film having a Kc value of 1.10 or less, and productivity of products may be lowered.

Therefore, according to an embodiment of the present disclosure, the Kc value of the polyimide film can be adjusted in the range of 1.10 to 1.55. More specifically, according to an embodiment of the present disclosure, the polyimide-based film may have a Kc value of 1.10 to 1.45.

According to an embodiment of the present disclosure, the Kc value can be measured by the following methods:

<Measurement method of Kc value>

- Measuring device: Optimap ^TM (PSD) from Rhopoint

- Light Mode: Ultra Dark

- Display mode: Curvature mode (X+Y scan)

- Curvature mode K: 1.0mm to 3.0mm wavelength range

- Measurement method: A piece of black suede paper is placed on a surface plate in a dark room, a sample to be measured is placed on it, the Kc value is measured 10 times, and the average value is used as the Kc value of the sample .

- Film samples: Films having a thickness of 10 microns or more, more specifically 50 microns or more, and thickness deviations within ±2% were used. Outside of thickness deviations, the Kc value can be distorted by thickness deviations. In an embodiment of the present disclosure, a polyimide-based film sample having a width of 15 cm x 15 cm length x 80 microns thickness was used for Kc measurement (thickness deviation ±2%).

- Other: Foreign substances having a particle size of 50 microns or more ^{are present in an amount of 0.005 per square centimeter (ea/cm 2} ) or less than 0.005 per square centimeter when measured with a microscope.

According to an embodiment of the present disclosure, the polyimide-based films may have different thicknesses. The polyimide-based film may have a thickness of, for example, 10 to 250 micrometers, and more specifically, may have a thickness of 10 to 100 micrometers.

In addition, the polyimide-based films of the present disclosure have improved optical properties. For example, based on a film thickness of 80 microns, a polyimide-based film according to an embodiment of the present disclosure has a haze of 2.0% or less, 87% at wavelengths of 380 nm to 780 nm or greater than 87% light transmittance and a yellow index of 5.0 or less. More specifically, according to an embodiment of the present disclosure, the polyimide-based film may have a haze of 0.2% to 0.3% based on a thickness of 80 microns.

As described above, the polyimide-based film according to an embodiment of the present disclosure has a Kc value of 1.55 or less, and thus has improved surface features and improved optical properties. Therefore, the polyimide-based 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 coat film, or a base film of a flexible display. substrate.

In addition, the polyimide-based film according to an embodiment of the present disclosure can be used, for example, as a substitute for glass.

In order for a polyimide-based film to replace glass, the polyimide-based film requires improved optical properties as well as improved surface properties. Conditions for improved surface properties include, for example, uniform thickness, surface uniformity, and low surface roughness. Here, surface uniformity includes the case where there are no or very few wrinkles or curves on the surface.

When the surface characteristics (specifically, the uniformity of the surface) of the polyimide-based film are not excellent, light passing through the polyimide-based film may be distorted. Therefore, through the Distortion may appear on the screen observed with imide films.

As shown in FIG. 1, when light is transmitted through the 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 on a flat surface.

Specifically, FIG. 1 is a schematic diagram illustrating a method of projecting an image of a film, and FIG. 2 is a diagram illustrating an example of a projected image 50 obtained by the image projection method.

Referring to FIG. 1 , light 20 emitted from a light source 10 passes through a projection target film 30 and is incident on a flat surface 40 to form a projection image 50 .

The case where the projected image 50 projected on the flat surface 50 is clear and there is no shadow difference in the image means that the projection target film 30 is flat and free of ripples or the like. Meanwhile, as shown in FIG. 2 , the case in which a difference in shadows occurs in the projected image means that the projection target film 30 is not flat and image distortion occurs.

When the polyimide film has large ripples, image distortion may appear on the screen displayed through the polyimide film.

Such waviness may occur when a polyimide-based film is fabricated by casting.

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 uniformity of the polyimide-based film decreases due to solvent volatilization in the drying process, resulting in ripples. For example, in the process of using hot air to dry the polyimide film, depending on the intensity of the hot air and the application time of the hot air, ripples may appear in the polyimide film, thereby causing polyimide Deterioration of the uniformity of the amine film.

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, the Marks are formed on the membrane. In addition, when the temperature of the hot air is too high, due to The rapid evaporation of the solvent can form a non-uniform part on the surface.

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

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

A method of 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 The gel-type film is first dried at 50°C to 150°C for 2 minutes to 20 minutes at a wind speed of 1.0 m/sec or less.

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

Dianhydrides, diamines, and dicarbonyl compounds have been described, and thus detailed explanations thereof are omitted to avoid redundancy.

The first solvent can be used for solution polymerization of the monomer components. Specifically, the monomer components can be reacted in the presence of a first solvent to prepare a first polymer solution. An organic solvent can be used as the first solvent for solution polymerization.

There is no specific limitation on the type of the first solvent. The first solvent may, for example, comprise at least one selected from the group consisting of m-cresol, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), dimethyl Formaldehyde (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 point solvent such as tetrahydrofuran (THF) or chloroform, or a weakly absorbing solvent such as γ-butyrolactone can be used as the first solvent. Depending on the purpose, the first solvent may be used alone or in combination of two or more.

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

When the monomer component does not contain a dicarbonyl compound, the molar amount of the dianhydride and the molar amount of the diamine may be adjusted to be equal to each other.

When the monomer component contains the dicarbonyl compound, the molar amount of the mixture of the dianhydride and the dicarbonyl compound can be adjusted to be equal to the molar amount of the diamine.

There is no particular limitation on the method suitable for preparing the liquid resin composition using the monomer components. Here, the liquid resin composition may be referred to as a liquid polyimide-based resin composition.

According to an embodiment of the present disclosure, preparing a liquid resin composition includes reacting monomer components in the presence of a first solvent to prepare a first polymer solution, and adding a second solvent to the first polymer solution , followed by filtration and drying to prepare polymer solids, and dissolving the polymer solids in a third solvent.

However, the embodiments of the present disclosure are not limited thereto, and the polyimide-based resin composition may also be prepared by preparing polyimide using monomer components including dianhydride and diamine and then thermally curing. In addition, after adding the chemical curing agent to the polyimide-based polymer solution containing the polyamic acid, a polyimide-based film in the form of a film can be formed immediately without filtration using a second solvent.

In order to prepare the liquid resin composition, the monomer components are first polymerized to prepare first polymer solution. The first polymer solution may comprise a polyamic acid solution. At this time, the reaction conditions are not particularly limited. 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 hours to 48 hours. The preparation of the first polymer solution can be carried out under an inert gas atmosphere such as argon or nitrogen.

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

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

According to one embodiment of the present disclosure, chemical imidization may be used. Chemical imidization is a method of applying a dehydrating agent such as acetic anhydride and an imidization catalyst such as isoquinoline, beta-picoline, pyridine or tertiary amines to the first polymer solution.

Thermal imidization can be used in combination with chemical imidization.

When thermal imidization and chemical imidization are used in combination, the dehydrating agent and the imidization catalyst are added to the first polymer solution, and then heated at 20°C to 180°C for 1 hour to 12 hours, This allows the imidization to proceed.

Next, a second solvent was added to the first polymer solution, followed by filtration and drying to prepare polymer solids.

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

A solvent less polar than the first solvent can be used as the second solvent. The second solvent may, for example, comprise at least one selected from the group consisting of water, alcohols, ethers, and ketones.

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

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

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.

According to an embodiment of the present disclosure, the third solvent may be the same as the first solvent. Thus, the third solvent may, for example, comprise at least one selected from the group consisting of m-cresol, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), di- Methylformamide (DMF), Diethylformamide (DEF), Dimethylacetamide (DMAc), Diethylacetamide (DEAc), Acetone, Ethyl Acetate, Propylene Glycol Monomethyl Ether ( PGME) and propylene glycol monomethyl ether acetate (PGMEA).

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

More specifically, the liquid resin composition may have a viscosity of 1,000 centipoise to 250,000 centipoise. When the liquid resin composition has a viscosity of 1,000 centipoise to 250,000 centipoise, it is easy to form a film by casting the liquid resin composition, and it is also easy to to dry the film. For example, when the viscosity of the liquid resin composition is 1,000 centipoise or more, it is not difficult to form a film by casting the liquid resin composition, and it is possible to peel off the cast substrate without difficulty by cast film. In addition, when the viscosity of the liquid resin composition is 250,000 cps or less, the casting process can be performed without increasing the pressure for casting the liquid resin composition more than necessary.

According to an embodiment of the present disclosure, the liquid resin composition may have a viscosity of 1000 cps to 30,000 cps.

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 can be adjusted within a range of 5 wt % to 30 wt %.

Next, the gelatinous film is produced from the liquid resin composition. The film in a gel state may be referred to as an uncured polyimide-based film in a gel state.

The casting method may be suitable for the manufacture of gel-type membranes.

Specifically, according to an embodiment of the present disclosure, preparing the gel-like film includes casting a liquid resin composition on a support.

There is no specific limitation on the casting method, and casting methods known in the art can be applied. Gel-like membranes are produced by casting.

Glass plates, aluminum substrates, endless stainless steel belts, stainless steel tubs, or heat-resistant polymer films can be used as supports.

According to an embodiment of the present disclosure, the gel-type film is an uncured polyimide-based film that has not been cured yet. In one embodiment of the present disclosure, although the film is partially cured, when curing is not complete, it is referred to as a gel-type film or an uncured polyimide-based film.

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

More specifically, the gel-type film fabricated by casting can be first dried for 2 minutes to 20 minutes at a temperature of 70° C. to 150° C. and a wind speed of 1.0 m/sec or less.

When the first drying period exceeds 20 minutes, processing efficiency may decrease, and when hot air is applied for a long time, ripples may be formed on the polyimide-based film.

In addition, when the first drying period is less than 2 minutes, the solvent contained in the gel-type film may not be completely dried and thus ripples may occur in the film.

According to an embodiment of the present disclosure, as the wind speed applied to the first drying increases, the drying period may decrease, and as the wind speed decreases, the drying period may increase. At this time, the wind speed was adjusted within a range where the Kc value of the polyimide-based film did not exceed 1.55.

For example, in the first drying, the wind speed can be adjusted in the range of 0.2 m/sec to 1.0 m/sec.

Specifically, in the first drying, when the drying temperature is A° C., the wind speed is B m/sec, and the first drying period is T minutes, the drying coefficient conditions according to the following Equation 1 and Equation 2 are satisfied :

When the value of “[(A-40)×B×T]/100” in Equation 1 is less than 0.5 or when “[(A-40)×T]/100” in Equation 2 is less than 2, The first drying may not be completed. When drying is not completed in the first drying, most of the solvent will be Removed in secondary drying, etc. However, since the second drying is usually performed at a higher wind speed than the first drying, inhomogeneity may occur in the polyimide-based film during the evaporation of a large amount of solvent at a strong wind speed during the second drying.

On the other hand, when the value of “[(A-40)×B×T]/100” in Equation 1 exceeds 10 or the value of “[(A-40)×T]/100” in Equation 2 When more than 10, high temperature hot air may be applied, or hot air with high wind speed may be applied. When hot air at a high temperature is applied or hot air with a high wind speed is applied, unevenness such as moire may occur in the polyimide-based film.

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-type film can be adjusted by optimizing the wind speed during drying.

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

However, when a strong wind speed is applied to the gel-type film in the first drying in which the solvent is not completely removed, a corrugated pattern or the like is formed on the gel-type film by the wind, and this corrugated pattern remains In finished polyimide. Therefore, the Kc value of the polyimide-based film may increase. To prevent this increase in Kc, according to one embodiment of the present disclosure, by applying wind to the gel-type film at a temperature, wind speed, and time suitable for the drying factor conditions according to Equation 1 and Equation 2 Remove the solvent.

Specifically, when wind is applied to the gel-type film for a long time, a corrugated pattern or the like is formed on the surface of the polyimide-type film by the wind, thereby making the polyimide-type film uneven and imparting Polyimide films have high Kc values.

Therefore, according to an embodiment of the present disclosure, considering the drying period and Temperature to judge the wind speed of the first drying. The wind speed is measured as follows.

<How to measure wind speed>

Measuring equipment: TSI 5725 anemometer

Measurement method: Install the anemometer at a height of about 1 cm above the support, and measure the wind speed when the measurement inlet direction of the anemometer is parallel to the surface of the support. When the wind speed exceeds 1.0 m/sec in the first drying, waviness may occur in the polyimide-based film and the waviness may increase. Therefore, according to an embodiment of the present disclosure, depending on the temperature of the wind, the wind speed in the primary drying may be kept at 1.0 m/s or less, and the wind speed may be 0.8 m/s or less than 0.8 m/s, or 0.5 m/s or less than 0.5 m/s.

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

In addition, the temperature in the primary drying may be maintained within a range of 50°C to 150°C, or, if necessary, within a range of 70°C to 150°C.

In general, drying efficiency increases with increasing temperature. On the other hand, when the temperature is increased during the first drying so that the drying temperature is close to the boiling point of the solvent, air bubbles may be formed on the surface of the polyimide-based film, and may be bent due to the rapid volatilization of the solvent, so polyimide The surface uniformity of the imine-based film deteriorates.

Therefore, the first drying is performed at a temperature of 50°C or higher in order to ensure drying efficiency, and the first drying is performed at a temperature of 150°C or lower In order to prevent the rapid evaporation of the solvent. In order to improve the drying efficiency, the first drying can be carried out in the temperature range of 70°C to 150°C.

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

According to an embodiment of the present disclosure, after the first drying, the gel-type film may be subjected to a second drying at 70° C. to 140° C. with a wind speed of 1.0 m/sec to 5.0 m/sec. When the wind speed of the second drying is less than 1.0 m/s or the temperature is lower than 70°C, the speed of the second drying may be excessively reduced. When the speed of the second drying is excessively reduced, the efficiency of the process may decrease, and the physical properties of the polyimide-based film may be changed due to the increase of the drying time.

Since the gel-like film is dried and hardened to some extent by the first drying, there is little possibility that the surface properties of the gel-like film are changed by the wind applied in the second drying. However, when the wind speed of the second drying exceeds 5.0 m/sec or the temperature exceeds 140° C., wrinkles or bending may occur in the polyimide-based film due to high temperature and strong wind. When wrinkling or bending occurs in the polyimide-based film, the waviness of the polyimide-based film increases and the curvature parameter Kc may exceed 1.55. Meanwhile, the wind speed in the second drying may be adjusted in the range of, for example, 1.5 m/sec to 5.0 m/sec, and more specifically, the wind speed in the second drying may be in the range of 1.6 m/sec to 3.0 m/sec Adjustable within the range of meters per second. In addition, in the second drying, the temperature may be adjusted in the range of 100°C to 140°C.

According to an embodiment of the present disclosure, after the second drying, the The gel-type film is subjected to the first heat treatment.

In the first heat treatment, known thermal curing processes can be applied. For example, the gel-type film may 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-type film. The first heat treatment is also called thermal curing.

The first heat treatment can be performed on the support or on a separate heat treated support. For example, after the second drying, the gel-type membrane can be separated from the support, can be fixed to the support for the first heat treatment, and then can be subjected to the first heat treatment. A latch frame or clip frame can be used to support gel-type membranes.

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

According to an embodiment of the present disclosure, the second heat treatment may be performed when a predetermined tensile force is applied to the polyimide-based film subjected to the first heat treatment. The residual stress inside the polyimide film can be removed by the second heat treatment.

When the second heat treatment is performed, the thermal expansion coefficient of the polyimide-based film can be lowered. For example, the second heat treatment creates residual stress that causes the polyimide-based film to shrink, thereby reducing thermal expansion and reducing hysteresis in the coefficient of thermal expansion in the polyimide-based film.

The tension and temperature applied to the second heat treatment are related. Therefore, the tensile force may vary depending on the temperature applied to the second heat treatment.

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

Another embodiment of the present disclosure provides a manufacturing method according to the above-mentioned manufacturing method. Manufactured polyimide film.

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.

<Preparation Example 1>

419.1 grams of N,N-dimethylacetamide (DMAc) as the first solvent was charged into a 1 liter reactor equipped with a stirrer, nitrogen sparger, dropping funnel, temperature controller and cooler while Nitrogen gas was passed through the reactor, the temperature of the reactor was adjusted to 25°C, 32.023 grams (0.10 moles) of TFDB as a diamine was dissolved therein, and the solution was maintained at 25°C. 8.885 grams (0.02 moles) of 6FDA as a dianhydride was added to the solution and dissolved and allowed to react while stirring. At this point, the temperature of the reactor was lowered to 10°C, the temperature of the solution was kept at 8°C, 16.24 g (0.08 moles) of TPC as a dicarbonyl compound was added to the solution, and the reaction was continued at 25°C for 12 hours To obtain a first polymer solution with a solids content of 12% by weight. The first polymer solution may contain polyamic acid. Therefore, the first polymer solution is also referred to as a polyamic acid solution.

1.58 g of pyridine and 2.02 g of acetic anhydride were added to obtain a first polymer solution, and the resulting solution was stirred for 30 minutes and then stirred at 80° C. for 0.5 hour and cooled to room temperature, and 10 liters of methanol as a second solvent was added to Precipitated solid. The precipitated solid was filtered, pulverized, washed again with 2 liters of methanol, and dried under vacuum 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 12% by weight. The liquid resin composition is also called a polyimide resin composition. Here, the polyimide resin composition is a polyimide-imide resin composition.

<Preparation Example 2>

432.4 grams of N,N-dimethylacetamide (DMAc) as the first solvent was charged into a 1 liter reactor equipped with a stirrer, nitrogen sparger, dropping funnel, temperature controller and cooler, while nitrogen Through the reactor, the temperature of the reactor was adjusted to 25°C, 32.023 grams (0.10 moles) of TFDB as a diamine was dissolved therein, and the solution was kept at 25°C. 5.884 grams (0.02 moles) of BPDA as dianhydride was added to the solution, followed by stirring for 2 hours. Next, 8.885 grams (0.02 moles) of 6FDA as a dianhydride was added thereto and dissolved and allowed to react under stirring for a predetermined period of time. At this point, the temperature of the reactor was lowered to 10°C, the temperature of the solution was kept at 8°C, 12.18 g (0.06 moles) of TPC as a dicarbonyl compound was added to the solution, and the reaction was continued at 25°C for 12 hours To obtain a first polymer solution with a solids content of 12% by weight.

3.16 grams of pyridine and 4.04 grams of acetic anhydride were added to obtain a first polymer solution, and the resulting solution was stirred for 30 minutes and then stirred at 80° C. for 0.5 hours and cooled to room temperature, and 10 liters of methanol as a second solvent was added to Precipitated solid. The precipitated solid was filtered, pulverized, washed again with 2 liters of methanol and dried under vacuum at 100° C. for 6 hours to obtain a powdered 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 12% by weight. The liquid resin composition is also called a polyimide resin composition. Here, the polyimide resin composition is a polyimide-imide resin composition.

<Preparation Example 3>

400.9 grams of N,N-dimethylacetamide (DMAc) as the first solvent was charged into a device equipped with a stirrer, nitrogen sparger, dropping funnel, temperature control The temperature of the reactor was adjusted to 25°C in a 1-liter reactor of the cooler and cooler, while nitrogen gas was passed through the reactor, and 32.023 grams (0.10 moles) of TFDB as a diamine was dissolved therein, and the solution was kept at 25 °C. 1.961 grams (0.01 moles) of CBDA as a dianhydride was added to the solution, followed by stirring for 2 hours. Next, 4.443 grams (0.01 moles) of 6FDA as a dianhydride was added and dissolved and allowed to react under stirring for a predetermined period of time. At this point, the temperature of the reactor was lowered to 10°C, the temperature of the solution was kept at 8°C, 16.24 g (0.08 moles) of TPC as a dicarbonyl compound was added to the solution, and the reaction was continued at 25°C for 12 hours To obtain a first polymer solution with a solids content of 12% by weight.

1.58 g of pyridine and 2.02 g of acetic anhydride were added to obtain a first polymer solution, and the resulting solution was stirred for 30 minutes and then stirred at 80° C. for 0.5 hour and cooled to room temperature, and 10 liters of methanol as a second solvent was added to Precipitated solid. The precipitated solid was filtered, pulverized, washed again with 2 liters of methanol and dried under vacuum at 100° C. for 6 hours to obtain a powdered 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 12% by weight. The liquid resin composition is also called a polyimide resin composition. Here, the polyimide resin composition is a polyimide-imide resin composition.

<Preparation Example 4>

587.5 grams of N,N-dimethylacetamide (DMAc) as the first solvent was charged into a 1 liter reactor equipped with a stirrer, nitrogen sparger, dropping funnel, temperature controller and cooler while Nitrogen gas was passed through the reactor, the temperature of the reactor was adjusted to 25°C, 640.046 grams (0.20 moles) of TFDB as a diamine was dissolved therein, and the solution was maintained at 25°C. 11.77 grams (0.04 Molar) BPDA as a dianhydride was added to the solution, followed by stirring for 2 hours. Next, 71.8 grams (0.16 moles) of 6FDA as a dianhydride was added and dissolved and allowed to react under stirring for a predetermined period of time. The reaction was continued at 25°C for 12 hours to obtain a first polymer solution with a solids content of 20% by weight.

6.328 grams of pyridine and 8.08 grams of acetic anhydride were added to obtain a first polymer solution, and the resulting solution was stirred for 30 minutes and then stirred at 80°C for 1 hour and cooled to room temperature, and 10 liters of methanol as a second solvent was added to Precipitated solid. The precipitated solid was filtered, pulverized, washed again with 2 liters of methanol and dried under vacuum at 100° C. for 6 hours to obtain a powdered 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. The liquid resin composition is also called a polyimide resin composition. Here, the polyimide resin composition is a polyimide resin composition.

<Example 1>

The polyimide-based resin composition, which is the liquid resin composition prepared in Preparation Example 1, was cast on a substrate to manufacture a gel-type film (uncured polyimide-based film in a gel state), And the gel-type film was first dried at 80°C with a wind speed of 0.2 m/sec for 20 minutes and secondly dried at 140°C with an elevated wind speed of 1.6 m/sec for 10 minutes.

The gel-type film was mounted on a pin-type tenter and the first heat treatment was performed for 1 hour while the temperature was raised from 120°C to 280°C. The gel-like film is cured by the first heat treatment to manufacture a polyimide-based film. The manufactured polyimide film is a polyimide-imide film.

The polyimide-based film produced by the first heat treatment is self-tenter frame) and then a second heat treatment at 280°C for 5 minutes to remove residual stress in the film.

<Example 2 to Example 8>

Polyimide-based films were produced in the same manner as in Example 1 except that the first drying conditions were shown in Table 1 below, and these polyimide-based films were referred to as Examples 2 to 8.

<Example 9>

The polyimide-based resin composition, which is the liquid resin composition prepared in Preparation Example 2, was cast on the substrate to manufacture a gel-type film, and the gel-type film was heated at 80° C. at 0.2 m/sec. The first drying was carried out at a wind speed of 1.6 m/s for 20 minutes and the second drying was carried out at 140 °C for 10 minutes with an increasing wind speed of 1.6 m/s.

The gel-type film was mounted on a pin tenter and subjected to a first heat treatment for 1 hour while the temperature was raised from 120°C to 280°C. The gel-like film is cured by the first heat treatment to manufacture a polyimide-based film. The manufactured polyimide film is a polyimide-imide film.

The heat treated film was removed from the tenter and then further heat treated at 280°C for 5 minutes to remove residual stress in the film.

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

<Example 10 to Example 16>

Polyimide-based films were produced in the same manner as in Example 9 except that the first drying conditions were shown in Table 1 below, and these polyimide-based films were referred to as Examples 10 to 16.

<Example 17>

The polyimide-based resin composition, which is the liquid resin composition prepared in Preparation Example 3, was cast on a substrate to prepare a gel-type film (uncured polyimide-based film in a gel state), And the gel-type film was first dried at 80°C with a wind speed of 0.2 m/sec for 20 minutes and secondly dried at 140°C with an elevated wind speed of 1.6 m/sec for 10 minutes.

The gel-type film was mounted on a pin tenter and subjected to a first heat treatment for 1 hour while the temperature was raised from 120°C to 250°C. The gel-like film is cured by the first heat treatment to manufacture a polyimide-based film. The manufactured polyimide film is a polyimide-imide film.

The heat treated film was removed from the tenter and then a second heat treatment was performed at 250°C for 5 minutes to remove residual stress in the film.

<Example 18 to Example 24>

Polyimide-based films were produced in the same manner as in Example 17 except that the first drying conditions were shown in Table 1 below, and these polyimide-based films were referred to as Examples 18 to 24.

<Example 25>

The polyimide-based resin composition, which is the liquid resin composition prepared in Preparation Example 4, was cast on a substrate to prepare a gel-type film (uncured polyimide-based film in a gel state), And the gel-type film was first dried at 80°C with a wind speed of 0.2 m/sec for 20 minutes and secondly dried at 140°C with an elevated wind speed of 1.6 m/sec for 10 minutes.

The gel-type film was mounted on a pin tenter and subjected to a first heat treatment for 1 hour while the temperature was raised from 120°C to 280°C. The gel-like film is cured by the first heat treatment to manufacture a polyimide-based film. The manufactured polyimide film is polyimide- imide film.

The heat treated film was removed from the tenter and then a second heat treatment was performed at 280°C for 5 minutes to remove residual stress in the film.

<Example 26 to Example 32>

Polyimide-based films were produced in the same manner as in Example 25 except that the first drying conditions were shown in Table 1 below, and these polyimide-based films were referred to as Examples 26 to 32.

<Comparative Example 1 to Comparative Example 5>

Polyimide-based films were produced in the same manner as in Example 1 except that the first drying conditions were shown in Table 1 below, and these polyimide-based films were referred to as Comparative Example 1 to Comparative Example 5.

<Comparative Example 6 to Comparative Example 10>

Polyimide-based films were produced in the same manner as in Example 9 except that the first drying conditions were shown in Table 1 below, and these polyimide-based films were referred to as Comparative Example 6 to Comparative Example 10.

<Comparative Example 11 to Comparative Example 15>

Polyimide-based films were produced in the same manner as in Example 17 except that the first drying conditions were shown in Table 1 below, and these polyimide-based films were referred to as Comparative Example 11 to Comparative Example 15.

<Comparative Example 16 to Comparative Example 20>

Polyimide-based films were produced in the same manner as in Example 25 except that the first drying conditions were shown in Table 1 below, and these polyimide-based films were referred to as Comparative Example 16 to Comparative Example 20.

Based on Example 1 to Example 32 and Comparative Example 1 to Comparative Example 20 Primary drying conditions, "[(A-40)×B×T]/100" in Equation 1 and "[(A-40)×T]/100" in Equation 2 were calculated and shown in Table 1 middle.

<Method of Measuring Physical Properties>

The physical properties of the polyimide-based films produced in Examples 1 to 32 and Comparative Examples 1 to 20 were measured by the following methods and the results are shown in Table 2.

(1) Film thickness measurement

An Anritsu electronic micrometer was used to measure the thickness of the polyimide-based films produced in the Examples and Comparative Examples. The thickness deviation caused by the device is ±0.5% or less.

(2) Light transmittance

The average light transmittances of the polyimide-based films produced in Examples and Comparative Examples were measured in a wavelength range of 380 nm to 780 nm using a UV spectrometer (Cotica Minolta CM-3700d). The thicknesses of the polyimide-based films are shown in Table 1.

(3) Yellowness Index (YI): The polyimides produced in Examples and Comparative Examples were measured using a UV spectrophotometer (CM-3700D, Konica Minolta Inc.) according to ASTM E313 Yellowness index of the film.

(4) Haze

The haze of the polyimide-based films produced in Examples and Comparative Examples was measured using a haze meter HM-150.

(5) Measure Kc value

- Measuring device: Optimap ^TM (PSD) from Rhopoint

- Light Mode: Ultra Dark

- Display mode: Curvature mode (X+Y scan)

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

- Measurement method: place a piece of black suede paper on the surface plate in the dark room, The sample to be measured is placed thereon, the Kc value is measured 10 times, and the average value is used as the Kc value of the sample.

- Film samples: Polyimide-based films with 15 cm width x 15 cm length x 80 microns thickness (Example 1 to Example 32 and Comparative Example 1 to Comparative Example 20) for Kc measurement (thickness deviation ±2%) .

- Others: Foreign substances having a particle size of 50 microns or more are present in an amount of 0.005 particles/cm 2 or less when measured with a microscope.

As can be seen from Table 2, the polyimide-based films according to Examples 1 to 32 according to the present disclosure have Kc values of 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.

As can be seen from Table 1 and Table 2, when the polyimide film is first dried at a relatively low temperature of 100°C or lower, the first drying should The drying factor conditions of Equation 1 and Equation 2 were carried out for relatively long times at different wind speeds in order to obtain low Kc values. In addition, when the polyimide-based film is first dried at a relatively high temperature exceeding 100° C., the first drying should be at different wind speeds within a range that satisfies the drying coefficient conditions according to Equation 1 and Equation 2 for a relatively short time in order to obtain low Kc values.

On the other hand, it can be seen that when the polyimide-based film is first dried at a relatively low temperature of 100° C. or lower, in the case of drying for a short time, there may be no effect of the first drying. The problem is that a lot of solvent volatilizes during the second drying. Therefore, the Kc value of the polyimide-based film increases and the uniformity decreases. In addition, it can be seen that when the polyimide film is first dried at a relatively high temperature exceeding 100°C, in the case of drying for a long time, excessive solvent volatilization may occur and can be removed by high temperature hot air A corrugated pattern is formed on the polyimide-based film, so the Kc value increases and the uniformity decreases.

3 is a projected image of a film according to Example 1 of the present disclosure, and FIG. 4 is a projected image of a film according to Comparative Example 15. As can be seen from FIGS. 3 and 4 , the polyimide-based films produced according to the examples of the present disclosure have low Kc values of 1.55 or less, compared to the polyimide-based films produced according to the comparative examples. The films have better surface uniformity and little or no unevenness, such as moiré patterns.

The polyimide-based films according to the embodiments of the present disclosure can be applied to various electronic devices. Accordingly, another embodiment of the present disclosure provides an electronic device including the polyimide-based film according to the present disclosure. The polyimide-based film according to the present disclosure can be applied to, for example, a cover window of an electronic device.

Claims (19)

A polyimide-based film having a Kc value of 1.55 or less, wherein the Kc value is measured by phase stepped deflectometry (PSD) for corrugations in a wavelength range of 1.0 mm to 3.0 mm The measured curvature parameter, wherein the polyimide-based film is prepared from a monomer component comprising a dianhydride and a diamine, wherein the dianhydride comprises at least one selected from the group consisting of: 2,2-bis (3,4-Dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 4-(2,5-di-oxygen Tetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA), pyromellitic dianhydride (PMDA), benzophenone tetracarboxylic dianhydride (BTDA) ), 4,4'-oxydiphthalic anhydride (ODPA), bisdicarboxyphenoxydiphenylthiodianhydride (BDSDA), 3,3',4,4'-diphenyltetracarboxylic acid Dianhydride (SO ₂ DPA), 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), wherein the diamine comprises at least one selected from the group consisting of oxydiphenylamine (ODA), p-phenylenediamine Amine (pPDA), m-phenylenediamine (mPDA), 4,4-diaminodiphenylmethane (pMDA), 3,3-diaminodiphenylmethane (mMDA), 1,3-bis(3-amine) phenylphenoxy)benzene (133APB), 1,4-bis(4-aminophenoxy)benzene (134APB), bisaminophenoxyphenyl hexafluoropropane (4BDAF), 2,2'-bis (3-Aminophenyl) hexafluoropropane (33-6F), 2,2'-bis(4-aminophenyl)hexafluoropropane (44-6F), bis(4-aminophenyl) bismuth (4DDS), bis(3-aminophenyl) bis(3DDS), bistrifluoromethylbenzidine (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] bis[4-(3-aminophenoxy)phenyl] bis[4-(3-aminophenoxy)phenyl] bis(4-aminophenoxy), 9,9-bis(4-aminophenyl) ) fluorene (FDA) and 9,9-bis(4-amino-3-fluorophenyl)fluorene (F-FDA). The polyimide-based film of claim 1, wherein the polyimide-based film has a Kc value of 1.45 or less. The polyimide-based film of claim 1, wherein the polyimide-based film has a Kc value of 1.10 to 1.45. The polyimide film according to claim 1, wherein the monomer component further comprises a dicarbonyl compound. The polyimide-based film of claim 4, wherein the dicarbonyl compound includes at least one of an aromatic dicarbonyl compound and an aliphatic dicarbonyl compound. The polyimide-based film according to claim 5, wherein the aromatic dicarbonyl compound is represented by the following formula 1:

wherein R ₁ represents a single bond, *-Ar-*, *-O-Ar-*, *-CAL-* or *-O-CAL-*; X ₁ and X ₂ each independently represent hydrogen, hydroxyl (OH) or a halogen element; and X ₃ represents hydrogen or a halogen element, wherein "Ar" represents a substituted or unsubstituted aryl group, and "CAL" represents a divalent cycloaliphatic group. The polyimide-based film according to claim 5, wherein the aromatic dicarbonyl compound includes at least one of the following: a compound represented by the following formula 3, a compound represented by the following formula 4, a 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 6]

The polyimide-based film according to claim 5, wherein the aliphatic dicarbonyl compound includes at least one of the following: a compound represented by the following formula 10, a compound represented by the following formula 11, a compound represented by the following formula 12 The compound represented and the compound represented by the following formula 13: [Formula 10]

The polyimide-based film of claim 1, wherein the polyimide-based film has a haze of 2.0 or less, based on a thickness of 80 microns, at a wavelength of 380 nm to 780 nm 87 % or more of an average light transmittance of 87% and a yellowness index of 5 or less. A method of manufacturing a polyimide-based film, comprising: preparing a liquid resin composition using a monomer component comprising a dianhydride and a diamine; using the liquid resin composition to manufacture a gel-type film; drying the gel-type film for the first time at a temperature of ℃ with a wind speed of 1.0 m/s or less than 1.0 m/s for a drying period of 2 minutes to 20 minutes, wherein in the first drying, When the temperature is A°C, the wind speed is B m/s, and the drying period is T minutes, the drying factor conditions according to the following equations 1 and 2 are satisfied:

The method for producing a polyimide film according to claim 10, wherein the monomer component further comprises a dicarbonyl compound. The method for producing a polyimide-based film according to claim 10, wherein the liquid resin composition has a viscosity of 1,000 cps to 250,000 cps. The method for producing a polyimide-based film according to claim 10, wherein the wind speed in the first drying is 0.2 m/sec or more. The method for manufacturing a polyimide film according to claim 10, further comprising, after the first drying, at 70° C. to 140° C. at a wind speed of 1.0 m/s to 5.0 m/s for the first time. The gel-type film is secondary dried. The method for manufacturing a polyimide-based film according to claim 14, 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. The method for producing a polyimide-based film as claimed in claim 10, wherein producing the gel-type film includes casting the liquid resin composition on a support. The method for producing a polyimide-based film according to claim 10, wherein preparing the liquid resin composition comprises: reacting the monomer components 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. A polyimide-based film manufactured using the method described in any one of claim 10 to claim 17. An electronic device, comprising the polyimide film according to any one of claim 1 to claim 9.

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