KR102210414B1 - Polyimide film, preparation method thereof, and cover window and display device comprising same - Google Patents

Abstract

An embodiment includes a first surface and a second surface opposite to the first surface, and in the first surface, a polyimide-based film having a solvent surface gradient (SC) of 0.03 to 0.2, a method of manufacturing the same, and It relates to a display cover window and a display device using the same.
The polyimide-based film according to the embodiment may improve transparency as well as reduce haze and further improve adhesion, thereby simultaneously improving mechanical properties and optical properties by adjusting the degree of change in the surface of the solvent to the specific range.

Description

Polyimide-based film, a manufacturing method thereof, and a cover window and a display device including the same TECHNICAL FIELD [0001]

The embodiment relates to a polyimide-based film having excellent transparency and high heat resistance and excellent mechanical properties and optical properties, a method for manufacturing the same, and a cover window and a display device including the same.

Polyimide resins such as poly(amide-imide), PAI) have excellent friction, heat, and chemical resistance, and are primary electrical insulation materials, coatings, adhesives, extrusion resins, and heat-resistant paints. , Heat resistant plate, heat resistant adhesive, heat resistant fiber and heat resistant film.

Polyimide is used in various fields. For example, polyimide is made in powder form and used as a coating agent such as metal or magnet wire, and is mixed with other additives depending on the application. In addition, polyimide is used as a paint for decoration and corrosion prevention along with fluoropolymers, and plays a role in bonding fluoropolymers to metal substrates. In addition, polyimide is also used to coat kitchen utensils, and because of its heat resistance and chemical resistance, it is used as a membrane used for gas separation. Used.

In recent years, by forming a film of polyimide, a polyimide-based film having excellent optical, mechanical and thermal properties has been developed inexpensively. These polyimide-based film is an organic light emitting diode (OLED; organic light-emitting diode ) or a liquid crystal display (LCD; liquid -crystal display) can be applied to the display material and the like, in the implementation phase properties antireflection film, a compensation film or a retardation Applicable to film.

When the polyimide-based film is applied to a display device, the transparent cover window included in the display device includes a hard coating layer and a base film. In the process of forming the hard coating layer, haze increases or adhesive strength decreases. A problem of deteriorating physical properties may occur. Accordingly, there is a situation in which research on the development of a film capable of solving the above problems and improving transparency, high heat resistance, and mechanical properties together is continuously required.

Korean Patent Application Publication No. 2014-0122385

The present invention is devised to solve the problem of the prior art.

The technical problem to be solved of the present invention is to provide a polyimide-based film capable of simultaneously improving mechanical properties and optical properties by improving transparency, as well as reducing haze and further improving adhesion.

Another technical problem to be solved of the present invention is to provide a method of manufacturing the polyimide-based film.

Another technical problem to be solved of the present invention is to provide a cover window for a display including the polyimide-based film.

Another technical problem to be solved of the present invention is to provide a display device including the polyimide film.

In order to achieve the above object, one embodiment includes a first surface and a second surface opposite to the first surface, and in the first surface, a soluble agent surface gradient (SC) represented by the following equation 1 is It provides a polyimide-based film of 0.03 to 0.2:

[Equation 1]

In Equation 1 above,

V ₀ is the surface tension before immersing the polyimide-based film in propylene glycol monomethyl ether acetate,

V ₁₀₀₀ is the surface tension after immersing the polyimide-based film in propylene glycol monomethyl ether acetate for 1000 seconds.

In another embodiment, a diamine compound and a dianhydride compound, or a diamine compound, a dianhydride compound, and a dicarbonyl compound are simultaneously or sequentially mixed in an organic solvent, and the mixture is reacted to prepare a polymer solution; Moving the polymer solution to a tank and purging with an inert gas; Casting the polymer solution in the tank on a belt and drying it to prepare a gel-sheet; Preparing a cured film by subjecting the gel-sheet to hot air treatment; Cooling the cured film; And it provides a method of manufacturing a polyimide-based film comprising; winding the cooled cured film.

In addition, another embodiment includes a polyimide-based film, wherein the polyimide-based film includes a first surface and a second surface opposite to the first surface, and the first surface, the second surface, or two In C, when measured with a 3D optical profiler, the peak valley roughness (Spv) represented by Equation 2 below is 0.05 µm to 1.7 µm, and the first surface, the second surface, or both The surface tension (V) is 20 dyne/cm to 45 dyne/cm to provide a cover window for display:

[Equation 2]

In Equation 2 above,

The Spk is the reduced peak height in ISO 25178-2:2012,

Sk is the adjusted core height in ISO 25178-2:2012,

The Svk is the reduced dale height in ISO 25178-2:2012.

In addition, another embodiment is a display unit; And a cover window disposed on the display unit, wherein the cover window includes the polyimide-based film.

Further, another embodiment is a display unit; And the cover window disposed on the display unit.

By controlling the degree of change of the solvent surface (SC) on at least one side of the polyimide-based film according to the embodiment, it is possible to improve transparency, as well as reduce haze and further improve adhesion, thereby simultaneously improving mechanical properties and optical properties.

In addition, the cover window for a display according to the embodiment is controlled by controlling the peak valley roughness (Spv) and surface tension (V) of the polyimide-based film, thereby improving transparency, as well as reducing haze and further improving adhesion, thereby improving mechanical properties and optical properties. Since physical properties can be simultaneously improved, it can be usefully applied to a display device.

1 is a cross-sectional view of a polyimide-based film according to an embodiment.
2 is a cross-sectional view of a display device according to an embodiment.
3 is a schematic flowchart of a method of manufacturing a polyimide-based film according to an embodiment.
4 schematically shows the process equipment of a polyimide-based film according to an embodiment.
5A to 5C are graphs illustrating a method of calculating Sk according to ISO 25178-2:2012 when measuring the peak valley illuminance (Spv) represented by Equation 2 according to an embodiment.

Hereinafter, the invention will be described in detail through embodiments. The implementation is not limited to the content disclosed below, and may be modified in various forms unless the gist of the invention is changed.

In the present specification, in the case where each film, window, panel, or layer is described as being formed "on" or "under" of each film, window, panel, or layer, "On" and "under" include both "directly" or "indirectly" formed. In addition, standards for the top/bottom of each component will be described based on the drawings. The size of each component in the drawings may be exaggerated for the sake of explanation, and does not mean a size that is actually applied.

In the present specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

All numbers and expressions indicating amounts of components, reaction conditions, and the like described herein are to be understood as being modified by the term "about" in all cases unless otherwise specified.

In the present specification, terms such as first and second are used to describe various components, and the components are not limited by the terms. The above terms are used only for the purpose of distinguishing one component into another component.

In addition, "substituted" in the present specification means deuterium, -F, -Cl, -Br, -I, hydroxyl group, cyano group, nitro group, amino group, amidino group, hydrazine group, unless otherwise specified, Hydrazone group, ester group, ketone group, carboxyl group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group, substituted or unsubstituted alkoxy group, substituted or unsubstituted alicyclic oil It means substituted with one or more substituents selected from the group consisting of a device, a substituted or unsubstituted heterocyclic group, a substituted or unsubstituted aryl group, and a substituted or unsubstituted heteroaryl group, and the substituents listed above are connected to each other Can form a ring.

Polyimide film

The polyimide-based film according to an embodiment includes a first surface and a second surface opposite to the first surface to achieve the object, and in the first surface, the surface change of the solvent represented by the following formula 1 Degree (SC) is from 0.03 to 0.2:

[Equation 1]

In Equation 1 above,

V ₀ is the surface tension before immersing the polyimide-based film in propylene glycol monomethyl ether acetate (PGEMA),

V ₁₀₀₀ is the surface tension after immersing the polyimide-based film in propylene glycol monomethyl ether acetate for 1000 seconds.

Polyimide-based films have strong solvent resistance and are hardly soluble in solvents. If it is not well soluble in a solvent, the adhesion of the hard coating layer may be poor, whereas if it is too well soluble in a solvent, the haze may increase. Therefore, in order to improve the adhesion of the hard coating layer of the polyimide-based film and lower the haze, it is necessary to have an appropriate solvent property, and in order to realize such an appropriate solvent property, it should have a degree of change in the surface of the soluble agent in a specific range.

Therefore, in the polyimide-based film according to an embodiment, when an arbitrary surface of the polyimide-based film is defined as a first surface, and a surface facing it is defined as a second surface, the surface of the soluble agent on the first surface The degree of change may be 0.03 to 0.2, specifically 0.05 to 0.18, and more specifically 0.07 to 0.17.

The degree of change of the surface of the soluble agent is the surface tension (V ₀ ) before immersing the polyimide film in propylene glycol monomethyl ether acetate and the surface after immersing the polyimide film in propylene glycol monomethyl ether acetate for 1000 seconds. It means a value obtained by dividing the difference in tension (V ₁₀₀₀ ) by V ₀ , and is a degree of change in surface tension before and after immersion.

In the polyimide-based film according to the embodiment, the degree of change in the surface of the soluble agent on at least one side is adjusted, thereby improving transparency, as well as reducing haze and further improving adhesion, thereby simultaneously improving mechanical properties and optical properties. In particular, when the degree of change on the surface of the soluble agent of the polyimide film satisfies the above range, the solvent suitability during hard coating is improved, and the adhesion of the hard coating layer is also improved, thereby improving optical properties. If the degree of change in the surface of the soluble agent is less than 0.03, there may be a problem that the adhesion of the coating layer is deteriorated, and when the degree of change in the surface of the soluble agent exceeds 0.2, the optical performance such as transmittance, yellowness, or haze may be lowered. In addition, the adhesion of the coating layer may decrease, and whitening may occur.

In addition, the degree of surface change of the soluble agent on the second side of the polyimide film may be 0.03 to 0.2, specifically 0.05 to 0.18, and more specifically 0.07 to 0.17.

In addition, both the first and second surfaces of the polyimide film may have a degree of change in the surface of the soluble agent from 0.03 to 0.2, specifically 0.05 to 0.18, and more specifically 0.07 to 0.17.

In addition, V ₀ of the first side of the polyimide film is 20 dyne/cm to 45 dyne/cm , specifically 22 dyne/cm to 45 dyne/cm, and more specifically 23 dyne/cm to 43 dyne/cm I can.

In addition, V ₀ of the second side of the polyimide film is 20 dyne/cm to 45 dyne/cm , specifically 22 dyne/cm to 45 dyne/cm, and more specifically 23 dyne/cm to 43 dyne/cm I can.

The polyimide-based film having V ₀ in the above range may implement a low haze value after immersion in a solvent and may improve the adhesion of the hard coating layer. If V ₀ of the first and second surfaces of the polyimide film exceeds 45 dyne/cm, respectively, whitening may occur, resulting in process loss and deterioration of physical properties. In addition, when V ₀ of the first and second surfaces of the polyimide film is less than 20 dyne/cm, respectively, adhesive strength may be reduced.

In addition, in the process of the polyimide-based film, when the solvent is not smoothly penetrated when using a solvent, coating properties may be deteriorated. When the coating property is deteriorated in this way, the wettability is also deteriorated, and the adhesion to the coating film after coating is deteriorated, and peeling may occur. For this reason, the range of the surface tension (V ₁₀₀₀ ) after immersion in a solvent may be important for the polyimide-based film.

Therefore, according to one embodiment, V ₁₀₀₀ of the first side after immersing the polyimide film in propylene glycol monomethyl ether acetate for 1000 seconds is 20 dyne/cm to 50 dyne/cm, specifically 20 dyne/cm to 48 dyne/cm, more specifically 20 dyne/cm to 40 dyne/cm or 20 dyne/cm to 38 dyne/cm.

In addition, V ₁₀₀₀ of the second side of the polyimide film is 20 dyne/cm to 50 dyne/cm, specifically 20 dyne/cm to 48 dyne/cm, more specifically 20 dyne/cm to 40 dyne/cm, or It may be from 20 dyne/cm to 38 dyne/cm.

In addition, the first side and/or the second side of the polyimide film may be further reduced in V ₁₀₀₀ after immersion in propylene glycol monomethyl ether acetate compared to V ₀ before immersion.

In addition, the first side and/or the second side of the polyimide film may be further increased in V ₁₀₀₀ after immersion in propylene glycol monomethyl ether acetate compared to V ₀ before immersion.

On the other hand, the polyimide-based film according to an embodiment of the present invention has a peak valley roughness (Spv) represented by Equation 2 below 0.05 µm when measured by a 3D optical profiler on the first surface. To 1.7 μm:

[Equation 2]

In Equation 2 above,

The Spk is the reduced peak height in ISO 25178-2:2012,

Sk is the adjusted core height in ISO 25178-2:2012,

The Svk is the reduced dale height in ISO 25178-2:2012.

In Equation 2, Spv means peak valley roughness representing the total sum of Spk, Sk and Svk, and may be specifically 0.06 µm to 1.6 µm, more specifically 0.064 µm to 1.6 µm, or 0.1 µm to 1.6 µm.

In Equation 2, Sk is the adjusted core height in ISO 25178-2:2012, as shown in Figs. 5A to 5C, the lowest level and highest level of the central surface. It represents the distance between levels. In (a) to (c) of FIG. 5, X is the area material ratio, Y is the intersection line position, 1 is the secant, and 2 is the smallest inclination value. Secant with smallest gradient, 3 is the equivalent straight line, and Smr1 and Smr2 are the material ratios. The Sk may be, for example, 0.02 µm to 1.2 µm, specifically 0.03 µm to 1.0 µm, and more specifically 0.05 µm to 0.8 µm.

In Equation 2, Spk is the reduced peak height in ISO 25178-2:2012, and means the average height of the peaks protruding from the center surface. The Spk may be, for example, 0.01 µm to 0.7 µm, specifically 0.02 µm to 0.5 µm, and more specifically 0.03 µm to 0.4 µm.

In Equation 2, Svk is the reduced dale height in ISO 25178-2:2012, which means the average height of the concave valley below the central surface. The Svk may be, for example, 0.005 µm to 0.7 µm, specifically 0.01 µm to 0.5 µm, and more specifically 0.01 µm to 0.4 µm.

In addition, Spv of the second side of the polyimide film may have the same value or different values within the same range as the Spv of the first side.

If Spv is within the above range on at least one surface of the polyimide film, the transmittance and yellowness are excellent, a low haze value can be realized after immersion in a solvent, and the adhesion of the hard coating layer can be improved. If the Spv of the polyimide-based film exceeds 1.7 µm, the adhesion of the coating layer may deteriorate and peeling may occur. If it is less than 0.05 µm, there is a problem of blocking each other when winding the polyimide-based film. I can.

In addition, according to an embodiment of the present invention, the polyimide-based film may have a solvent coating index (SCI) of 0.001 µm to 0.2 µm represented by Equation 3 below.

[Equation 3]

In Equation 3 above,

The SC is the degree of surface gradient of the soluble agent,

The Spv is the peak valley roughness.

The SCI represents the product of the soluble agent surface gradient (SC) and the peak valley roughness (Spv), and when it is in the above range, the coating property is excellent, and adhesion may be further improved. The SCI may be specifically 0.001 µm to 0.34 µm, more specifically 0.002 µm to 0.2 µm. The SCI may be 0.003 μm to 0.15 μm. The SCI may be 0.005 µm to 0.1 µm.

In addition, when the polyimide-based film is immersed in a solvent for 1000 seconds, the haze of the first side, the second side or both sides after immersion is less than 2%, specifically 1.5% or less, more specifically 0.01% to 1.0 It can be %. In this case, the solvent may be propylene glycol monomethyl ether acetate.

Meanwhile, the polyimide resin included in the polyimide film may be formed by reacting reactants including a diamine compound and a dianhydride compound simultaneously or sequentially. Specifically, the polyimide resin may include a polyimide polymer formed by polymerization of a diamine compound and a dianhydride compound.

In addition, the polyimide resin includes an imide repeating unit derived from polymerization of a diamine compound and a dianhydride compound, and an amide repeating unit derived from polymerization of the diamine compound and dicarbonyl compound. Polyamide-imide polymers.

Since the polyamide-imide polymer includes an imide repeating unit, it may correspond to a polyimide-based resin in a broad sense.

The diamine compound is an imide bonded to the dianhydride compound and an amide bonded to the dicarbonyl compound to form a copolymer.

The diamine compound is not particularly limited, but may be, for example, an aromatic diamine compound having an aromatic structure. For example, the diamine compound may be a compound of Formula 1 below.

<Formula 1>

In Formula 1,

E is a substituted or unsubstituted divalent C ₆ -C ₃₀ aliphatic cyclic group, a substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaliphatic cyclic group, a substituted or unsubstituted divalent C ₆ -C ₃₀ aromatic cyclic group , A substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaromatic ring group, a substituted or unsubstituted C ₁ -C ₃₀ alkylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkenylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkynylene group, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si(CH ₃ ) ₂ -, -C(CH ₃ ) _2- And -C(CF ₃ ) ₂ -.

e is selected from an integer of 1 to 5, and when e is 2 or more, E may be the same or different from each other.

(E) _e of Formula 1 may be selected from the group represented by Formulas 1-1a to 1-14a.

Specifically, (E) _e of Formula 1 may be selected from the group represented by Formulas 1-1b to 1-13b, but is not limited thereto:

More specifically, (E) _e of Formula 1 may be a group represented by Formula 1-6b.

In one embodiment, the diamine compound may include a compound having a fluorine-containing substituent. Alternatively, the diamine compound may be formed of a compound having a fluorine-containing substituent. In this case, the fluorine-containing substituent may be a fluorinated hydrocarbon group, and specifically, a trifluoromethyl group, but is not limited thereto. When the content of fluorine contained in the polyimide resin increases, the surface tension may increase.

In another embodiment, the diamine compound may be one diamine compound, or two or more diamine compounds. Specifically, the diamine compound may be composed of a single component, for example, the diamine compound is 2,2'-bis (trifluoromethyl) benzidine (2,2'-Bis (trifluoromethyl) having a structure as follows) benzidine, TFMB).

In addition, when two or more diamine compounds are included, 2,2'-bis(trifluoromethyl)benzidine having a fluorine-containing substituent is included as the first diamine compound, and 4,4'- as the second diamine compound. Oxydianiline (4,4'-oxydianiline, ODA) may be included.

Since the dianhydride compound has a low birefringence value, it is a compound that can contribute to the improvement of optical properties such as transmittance of the polyimide film.

The dianhydride compound is not particularly limited, but may be, for example, an aromatic dianhydride compound having an aromatic structure. For example, the aromatic dianhydride compound may be a compound of Formula 2 below.

<Formula 2>

In Formula 2,

G is a substituted or unsubstituted tetravalent C ₆ -C ₃₀ aliphatic cyclic group, a substituted or unsubstituted tetravalent C ₄ -C ₃₀ heteroaliphatic cyclic group, a substituted or unsubstituted tetravalent C ₆ -C ₃₀ aromatic cyclic group , A substituted or unsubstituted tetravalent C ₄ -C ₃₀ heteroaromatic cyclic group, and the aliphatic cyclic group, the hetero aliphatic cyclic group, the aromatic cyclic group or the heteroaromatic cyclic group is present alone or condensed with each other Or a substituted or unsubstituted C ₁ -C ₃₀ alkylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkenylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkynylene group, -O-,- S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si(CH ₃ ) ₂ -, -C(CH ₃ ) ₂ -and -C(CF ₃ ) It is connected by a connector selected from ₂ -.

G in Formula 2 may be selected from the group represented by Formulas 2-1a to 2-9a, but is not limited thereto.

For example, G in Formula 2 may be a group represented by Formula 2-8a.

In one embodiment, the dianhydride compound may include a compound having a fluorine-containing substituent. Alternatively, the dianhydride compound may be formed of a compound having a fluorine-containing substituent. In this case, the fluorine-containing substituent may be a fluorinated hydrocarbon group, and specifically, a trifluoromethyl group, but is not limited thereto.

In another embodiment, the dianhydride compound may be composed of one single component or a mixture of two components.

For example, the dianhydride compound is 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (2,2'-bis-(3,4) having the following structure. -dicarboxyphenyl) hexafluoropropane dianhydride, 6-FDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (3,3',4,4'-biphenyltetracarboxylic dianhydride, BPDA) or mixtures thereof It may include.

The diamine compound and the dianhydride compound may be polymerized to produce polyamic acid.

Subsequently, the polyamic acid may be converted to polyimide through a dehydration reaction, and the polyimide includes an imide repeating unit.

The polyimide may form a repeating unit represented by Formula A below.

<Formula A>

In Formula A, descriptions of E, G and e are as described above.

For example, the polyimide may include a repeating unit represented by Formula A-1 below, but is not limited thereto.

<Formula A-1>

In Formula A-1, n is an integer of 1 to 400.

The dicarbonyl compound is not particularly limited, but may be, for example, a compound represented by the following formula (3).

<Formula 3>

In Chemical Formula 3,

J is a substituted or unsubstituted divalent C ₆ -C ₃₀ aliphatic cyclic group, a substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaliphatic cyclic group, a substituted or unsubstituted divalent C ₆ -C ₃₀ aromatic cyclic group , A substituted or unsubstituted divalent C ₄ -C ₃₀ heteroaromatic ring group, a substituted or unsubstituted C ₁ -C ₃₀ alkylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkenylene group, a substituted or unsubstituted C ₂ -C ₃₀ alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O) ₂ -, -Si(CH ₃ ) ₂ -, It may be selected from -C(CH ₃ ) ₂ -and -C(CF ₃ ) ₂ -.

j is selected from an integer of 1 to 5, and when j is 2 or more, J may be the same or different from each other.

X is a halogen atom. Specifically, X may be F, Cl, Br, I, or the like. More specifically, X may be Cl, but is not limited thereto.

(J) _j of Formula 3 may be selected from the group represented by Formulas 3-1a to 3-14a, but is not limited thereto.

Specifically, (J) _j of Formula 3 may be selected from the group represented by Formulas 3-1b to 3-8b, but is not limited thereto:

More specifically, (J) _j of Formula 3 may be a group represented by Formula 3-2b or a group represented by 3-3b.

In one embodiment, the dicarbonyl compound may be one or more dicarbonyl compounds.

The dicarbonyl compound may be an aromatic dicarbonyl compound including an aromatic structure, and specifically, terephthaloyl chloride (TPC), 1,1′-biphenyl-4, having the following structure 4'-dicarbonyl dichloride (1,1'-biphenyl-4,4'-dicarbonyl dichloride, BPDC) or a combination thereof may be included, but is not limited thereto.

The diamine compound and the dicarbonyl compound may be polymerized to form a repeating unit represented by Formula B below.

<Formula B>

In Formula B, descriptions of E, J, e and j are as described above.

For example, the diamine compound and the dicarbonyl compound may be polymerized to form an amide repeating unit represented by Formulas B-1 and B-2.

<Formula B-1>

In Formula B-1, x is an integer of 1 to 400.

<Formula B-2>

Y in Formula B-2 is an integer of 1 to 400.

According to one embodiment, the polyimide-based film may further include a filler.

The filler may be at least one selected from the group consisting of barium sulfate, silica, or calcium carbonate. When the polyimide-based film includes the filler, it is possible to improve surface roughness and windability, as well as improve the effect of improving running scratches during film production.

In addition, the particle diameter of the filler may be 0.01 or more to less than 1.0 ㎛. For example, the particle diameter of the filler may be 0.05 to 0.9 μm or 0.1 to 0.8 μm.

The polyimide-based film may contain the filler in an amount of 0.01 to 3% by weight. For example, the polyimide-based film may contain the filler in an amount of 0.05 to 2.5% by weight, 0.1 to 2% by weight, or 0.2 to 1.7% by weight.

1 is a cross-sectional view of a polyimide-based film according to an embodiment. Specifically, a polyimide-based film 100 including a first surface 101 and a second surface 102 opposite to the first surface 101 is illustrated in FIG. 1.

The first surface may be a surface that does not directly contact the casting body 110 for casting the polyimide-based resin during the process of manufacturing the polyimide-based film. That is, the first surface may be an air surface in contact with air when the polyimide resin is cast.

The second surface may be a surface in direct contact with the casting body 110 in the process of manufacturing the polyimide-based film. That is, the second surface may be a belt surface in contact with the casting body, for example, a belt or the like in the casting process.

The polyimide-based film according to the embodiment may prevent a problem of lowering adhesion, and improve mechanical and optical properties such as haze and yellowness by controlling the degree of change of the surface of the soluble agent on at least one side.

According to one embodiment, the yellow index of the polyimide-based film may be 5 or less. For example, the yellowness may be 4 or less, 3.5 or less, 2.8 or less, 2.5 or less, 2.3 or less, or 2.1 or less.

According to one embodiment, the transmittance of the polyimide-based film may be 80% or more. For example, the transmittance may be 85% or more, 88% or more, 89% or more, 80% to 99%, 80% to 99%, or 85% to 99%.

The compressive strength of the polyimide-based film is 0.4 kgf/µm or more. Specifically, the compressive strength may be 0.45 kgf/µm or more or 0.46 kgf/µm or more, but is not limited thereto.

The polyimide film has a surface hardness of HB or higher. Specifically, the surface hardness may be H or more or 2H or more, but is not limited thereto.

The polyimide-based film has a tensile strength of 15 kgf/mm ² or more. Specifically, the tensile strength may be 18 kgf/mm ² or more, 20 kgf/mm ² or more, 21 kgf/mm ² or more, or 22 kgf/mm ^{2 or} more, but is not limited thereto.

The polyimide-based film has an elongation of 15% or more. Specifically, the elongation may be 16% or more, 17% or more, or 17.5% or more, but is not limited thereto.

The polyimide-based film according to an embodiment may secure excellent optical properties such as low haze and low yellowness (YI) as well as excellent adhesion. Further, it is possible to implement long-term stable mechanical properties for a substrate requiring flexibility in terms of modulus, elongation, tensile properties and elastic resilience.

Manufacturing method of polyimide film

The method for preparing a polyimide-based film according to an embodiment is a diamine compound and a dianhydride compound, or a diamine compound, a dianhydride compound, and a dicarbonyl compound are simultaneously or sequentially mixed in an organic solvent, and the mixture is reacted. Preparing a polymer solution; Moving the polymer solution to a tank and purging with an inert gas; Casting the polymer solution in the tank on a belt and drying it to prepare a gel-sheet; Preparing a cured film by subjecting the gel-sheet to hot air treatment; Cooling the cured film; And winding the cooled cured film.

3 is a schematic flowchart of a method of manufacturing a polyimide-based film according to an embodiment.

3, the method of manufacturing the polyimide film is a mixture of a diamine compound and a dianhydride compound, or a diamine compound, a dianhydride compound, and a dicarbonyl compound simultaneously or sequentially in an organic solvent in a polymerization facility. And reacting the mixture to prepare a polymer solution (S100); Moving the polymer solution to a tank (S200); Purging using an inert gas (S300); Casting the polymer solution in the tank on a belt and drying it to prepare a gel-sheet (S400); Manufacturing a cured film by hot air treatment while moving the gel-sheet (S500); Cooling while moving the cured film (S600); And winding the cooled cured film using a winder (S700).

In the method for producing the polyimide film, the polymer solution is a diamine compound and a dianhydride compound, or a diamine compound, a dianhydride compound, and a dicarbonyl compound simultaneously or sequentially mixed in an organic solvent in a polymerization facility. And, it may be prepared by reacting the mixture (S100).

The diamine compound, the dianhydride compound, or both may include a compound having a fluorine-containing substituent, and the compound having a fluorine-containing substituent is 10 mol% to 90 mol% based on the total mol of the mixture, specifically It may be 20 mol% to 90 mol%, more specifically 20 mol% to 85 mol%, 30 mol% to 90 mol%, or 30 mol% to 85 mol%. When the content of fluorine is too high in the mixture, the surface tension may increase, and when the content of fluorine is too small, it may be difficult to achieve the degree of surface change and the range of surface tension of the soluble agent of the present invention.

remind The types of the diamine compound, the dianhydride compound and the dicarbonyl compound are as described above.

In one embodiment, the polymer solution may be prepared by simultaneously adding the diamine compound and the dianhydride compound to an organic solvent, or simultaneously adding the diamine compound, the dianhydride compound and the dicarbonyl compound to react. have.

In another embodiment, the preparing of the polymer solution may include preparing a polyamic acid (PAA) solution by first mixing and reacting the diamine compound and the dianhydride compound in a solvent; And forming an amide bond and an imide bond at the same time by secondary mixing and reacting the dicarbonyl compound with the polyamic acid (PAA) solution. The polyamic acid solution is a solution containing polyamic acid.

In another embodiment, the step of preparing the polymer solution may include preparing a polyamic acid solution by first mixing and reacting the diamine compound and the dianhydride compound in a solvent; Dehydrating the polyamic acid solution to prepare a polyimide (PI) solution; And secondary mixing and reacting the dicarbonyl compound to the polyimide (PI) solution to further form an amide bond. The polyimide solution is a solution containing a polymer having an imide repeating unit.

In another embodiment, the step of preparing the polymer solution may include preparing a polyamide (PA) solution by first mixing and reacting the diamine compound and the dicarbonyl compound in a solvent; And secondary mixing and reacting the dianhydride compound to the polyamide (PA) solution to further form an imide bond. The polyamide solution is a solution containing a polymer having an amide repeating unit.

The polymer solution prepared as described above may be a solution containing a polymer containing at least one selected from the group consisting of polyamic acid (PAA) repeat units, polyamide (PA) repeat units, and polyimide (PI) repeat units. .

Alternatively, the polymer contained in the polymer solution includes an imide repeating unit derived from polymerization of the diamine compound and the dianhydride compound, and an amide repeating unit derived from polymerization of the diamine compound and the dicarbonyl compound. ) Includes repeating units.

In one embodiment, the step of preparing the polymer solution may further include adding a catalyst.

The catalyst may include, for example, beta picoline or acetic anhydride, but is not limited thereto. When the catalyst is added, the reaction rate may be improved, and chemical bonding between or within the repeating unit structure may be improved.

In one embodiment, the step of preparing the polymer solution may further include adjusting the viscosity of the polymer solution.

Specifically, the step of preparing the polymer solution includes: (a) mixing and reacting a diamine compound and a dianhydride compound, or a diamine compound, a dianhydride compound, and a dicarbonyl compound simultaneously or sequentially in an organic solvent to obtain a first Preparing a polymer solution; (b) measuring the viscosity of the first polymer solution to evaluate whether a target viscosity is reached; And (c) preparing a second polymer solution having a target viscosity by adding the dicarbonyl compound when the viscosity of the first polymer solution does not reach the target viscosity.

The target viscosity may be 100,000 cps to 500,000 cps at room temperature. Specifically, the target viscosity may be 100,000 cps to 400,000 cps, 100,000 cps to 350,000 cps, 100,000 cps to 300,000 cps, 150,000 cps to 300,000 cps, or 150,000 cps to 250,000 cps at room temperature. However, it is not limited thereto.

In another embodiment, the content of the solid content contained in the polymer solution may be 10% by weight to 20% by weight. Specifically, the content of the solid content contained in the second polymer solution may be 12% to 18% by weight, but is not limited thereto.

When the content of the solid content in the polymer solution is within the above range, a polyimide) film can be effectively produced in an extrusion and casting process. In addition, the prepared polyimide-based film may have mechanical properties such as improved modulus and optical properties such as low yellowness.

In one embodiment, the preparing of the polymer solution may further include adjusting the pH of the polymer solution. In this step, the pH of the polymer solution may be adjusted to 4 to 7 or 4.5 to 7.

The pH of the polymer solution can be adjusted by adding a pH adjusting agent. The pH adjusting agent is not particularly limited, but may include, for example, amine-based compounds such as alkoxyamine, alkylamine, and alkanolamine.

By adjusting the pH of the polymer solution to the above range, it is possible to prevent damage to the equipment in the subsequent process, to prevent the occurrence of defects in the film prepared from the polymer solution, and to target optical properties in terms of yellowness and modulus. And mechanical properties.

The pH adjuster may be added in an amount of 0.1 mol% to 10 mol% based on the total number of moles of monomers in the polymer solution.

The step of preparing the polymer solution may further include purging using an inert gas. By removing moisture and reducing impurities through the inert gas purging step, the reaction yield can be increased, and the surface appearance and mechanical properties of the final film can be excellently implemented.

In this case, the inert gas may be at least one selected from the group consisting of nitrogen, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn), It is not limited. Specifically, the inert gas may be nitrogen.

The polyimide resin used to prepare the polymer solution may have a molar ratio of imide repeating units: amide repeating units of 10:90 to 90:10, for example, 20:80 to 50:50. . In this case, the imide repeating unit may be a repeating unit represented by Formula A, and the amide repeating unit may be a repeating unit represented by Formula B.

When the molar ratio of the polyimide-based resin satisfies the above range, it is easy to adjust the viscosity of the polymer solution using the above-described monomers for preparing it, whereby the gel-sheet and the cured film have no defects on the surface. It is easy to produce a uniform film.

By appropriately controlling the content of the imide repeating unit and the amide repeating unit, a polyimide-based film having improved optical properties, mechanical properties, and flexibility in a balanced manner can be obtained without a complicated process. In addition, it is possible to obtain a polyimide-based film with improved optical properties, mechanical properties, and flexibility in a balanced manner without going through processes such as precipitation, filtration, drying, and re-dissolution as in the prior art. The content of each of the imide repeating unit and the amide repeating unit may be adjusted by the amount of the aromatic dianhydride compound and the dicarbonyl compound added.

4 schematically shows a process equipment of a polyimide-based film according to an embodiment.

Specifically, the polymer solution described above is prepared in the polymerization facility 10, and the polymer solution prepared in this way may be moved and stored in the tank 20 (S200).

Accordingly, the manufacturing method according to an embodiment minimizes the content of impurities at a source in the manufacturing process of the polymer solution, or even if predetermined impurities are present, they are appropriately controlled in a subsequent process so as not to deteriorate the physical properties of the final film. To prepare a film. The tank 20 is a place to store the polymer solution before filming it, and the internal temperature thereof may be -20 °C to 20 °C.

Specifically, the internal temperature may be -20°C to 15°C, -20°C to 10°C, -20°C to 5°C, or -20°C to 0°C, but is not limited thereto.

By adjusting the temperature of the tank 20 to the above range, it is possible to prevent the polymer solution from being deteriorated during storage, and to reduce the moisture content to prevent defects in the film produced therefrom.

The method of manufacturing the polyimide film may further include performing vacuum degassing on the polymer solution transferred to the tank 20.

The vacuum defoaming may be performed for 30 minutes to 3 hours after reducing the internal pressure of the tank to 0.1 bar to 0.7 bar. By performing vacuum defoaming under such conditions, air bubbles inside the polymer solution can be reduced, and as a result, surface defects of the film produced therefrom can be prevented, and optical properties such as haze can be excellently implemented.

In addition, the method of manufacturing the polyimide-based film may include purging the polymer solution moved to the tank 20 using an inert gas (S300).

Specifically, the purging is performed by purging the internal pressure of the tank to 1 to 2 atmospheres using an inert gas. By performing nitrogen purging under such conditions, moisture in the polymer solution is removed and impurities are reduced, so that the reaction yield can be increased, and optical properties such as haze and mechanical properties can be excellently implemented.

The vacuum defoaming step and the step of purging the tank with nitrogen gas are performed as separate processes.

For example, the vacuum defoaming step may be performed, and thereafter, the step of purging the tank with nitrogen gas may be performed, but the present invention is not limited thereto.

By performing the step of vacuum degassing and/or the step of purging the tank with nitrogen gas, physical properties of the surface of the prepared polyimide film may be improved.

Thereafter, storing the polymer solution in the tank 20 for 12 to 360 hours; may further include. At this time, the internal temperature of the tank may be continuously maintained at -20 ℃ to 20 ℃.

The manufacturing method of the polyimide film may include a step of producing a gel-sheet by casting the polymer solution in the tank 20 and drying it (S400).

The polymer solution may be cast on a casting body such as a casting roll or a casting belt.

Referring to FIG. 4, in one embodiment, the polymer solution is applied on the casting belt 30 as a casting body, dried while moving, and manufactured as a gel-like sheet.

When the polymer solution is injected onto the belt 30, the injection amount may be 300 g/min to 700 g/min. When the injection amount of the polymer solution satisfies the above range, the gel-sheet may be uniformly formed with an appropriate thickness.

In addition, the casting thickness of the polymer solution may be 200 to 700 ㎛. When the polymer solution is cast in such a thickness range, and then dried and heat treated to form a final film, appropriate thickness and thickness uniformity can be ensured.

After casting the polymer solution, the gel-sheet may be prepared by drying at a temperature of 60° C. to 150° C. for a period of 5 minutes to 60 minutes. During the drying, a part or all of the solvent of the polymer solution is volatilized to prepare the gel-sheet.

As described above, the polymer solution may be 100,000 cps to 500,000 cps at room temperature, for example, 100,000 cps to 400,000 cps, for example, 100,000 cps to 350,000 cps. There may be, for example, 150,000 cps to 350,000 cps. By satisfying this viscosity range, the polymer solution can be cast to a uniform thickness without defects when cast on a belt.

The manufacturing method of the polyimide-based film may include the step of preparing a cured film by hot air treatment while moving the gel-sheet (S500).

4, the hot air treatment of the gel-sheet may be performed by passing through the thermosetting machine 40. When heat treatment by hot air is performed, the amount of heat may be evenly applied. If the amount of heat is not evenly distributed, satisfactory surface roughness cannot be achieved, and in this case, the surface tension may increase or decrease too much.

The hot air treatment of the gel-sheet may have a starting temperature of 80°C or higher, specifically 80°C to 180°C, and more specifically 100°C to 180°C. In addition, the maximum temperature during the hot air treatment may be 300 ℃ to 500 ℃. For example, the maximum temperature during the hot air treatment may be 300°C to 400°C, 310°C to 380°C, 320°C to 370°C, or 330°C to 370°C.

According to one embodiment, the hot air treatment of the gel-sheet may be performed in three steps, and 1 minute to 10 minutes at a hot air temperature of 100° C. to 180° C., 10 minutes to 30 minutes at 200° C. to 300° C., 300° C. To 400 ℃ can be carried out for 5 minutes to 20 minutes.

More specifically, the hot air treatment of the gel-sheet is performed at a hot air temperature of 100°C to 170°C for 1 minute to 10 minutes, 200°C to 270°C for 10 minutes to 30 minutes, and 320°C to 370°C for 5 minutes to 15 minutes Can be. In particular, the hot air temperature may be the starting temperature is important, and the starting temperature may be carried out for 1 minute to 4 minutes, specifically 2 minutes to 3 minutes in the range of 100 ℃ to 170 ℃, more specifically 120 ℃ to 170 ℃. have.

That is, referring to FIG. 4, an inlet temperature of the thermosetting machine 40 may be a hot air treatment start temperature, and a temperature of a predetermined region inside the thermosetting machine 40 may be a maximum temperature during hot air treatment.

By controlling the hot air temperature and the hot air time in the above range, the surface tension of both sides of the polyimide-based film can be controlled. In addition, when treated in the above range, the gel-sheet can be cured to have an appropriate surface hardness and modulus, and the cured film can simultaneously secure high light transmittance and low haze.

The manufacturing method of the polyimide-based film may include cooling while moving the cured film (S600).

4, the cured film is performed after passing through the thermosetting machine 40, and may be performed using a separate cooling chamber (not shown), and an appropriate temperature atmosphere without a separate cooling chamber It can also be carried out by composition.

The step of cooling while moving the cured film may include: a first temperature reduction step of reducing temperature at a rate of 5°C/min to 10°C/min; And a second temperature reduction step of reducing temperature at a rate of 10° C./min to 20° C./min.

In this case, specifically, the second temperature reduction step is performed after the first temperature reduction step, and the temperature reduction speed of the first temperature reduction step may be faster than the temperature reduction speed of the second temperature reduction step.

For example, a maximum speed during the first temperature reduction step is faster than a maximum speed during the second temperature reduction step. Alternatively, the lowest speed during the first temperature reduction step is faster than the lowest speed during the second temperature reduction step.

By performing the cooling step of the cured film in multiple steps as described above, the physical properties of the cured film can be more stabilized, and the optical properties and mechanical properties of the film established in the curing process can be more stably maintained for a long period of time.

The moving speed of the gel-sheet and the cured film may be the same.

The method of manufacturing the polyimide-based film may include winding the cooled cured film using a winder (S700).

4, the winding of the cooled cured film may use a roll-type winder 50.

At this time, the ratio of the moving speed of the gel-sheet on the belt during drying: the moving speed of the cured film upon winding is 1:0.95 to 1:1.40. Specifically, the ratio of the moving speed may be 1:0.99 to 1:1.20, 1:0.99 to 1:1.10, or 1:1.10 to 1:1.05, but is not limited thereto.

When the ratio of the moving speed is out of the above range, there is a concern that mechanical properties of the cured film may be damaged, and flexibility and elastic properties may be deteriorated.

Specifically, the moving speed of the gel-sheet on the belt during drying may be 0.1 m/min to 15 m/min, for example, 0.5 m/min to 10 m/min.

The physical properties of the polyimide-based film described above are based on a thickness of 40 μm to 60 μm. For example, the physical properties of the polyimide-based film are based on a thickness of 50 μm. In addition, the'MD direction' refers to a direction in which the belt moves during the manufacturing process of the film, and the'TD direction' refers to a direction perpendicular to the MD direction.

The polyimide-based film may exhibit excellent optical and mechanical properties by being manufactured according to the above-described manufacturing method. The polyimide-based film may be applicable to various applications requiring flexibility and transparency. For example, the polyimide film may be applied to solar cells, displays, semiconductor devices, sensors, and the like.

Cover window for display

The cover window for a display according to an embodiment of the present invention includes a polyimide-based film, the polyimide-based film includes a first surface and a second surface opposite to the first surface, and the first surface, On the second surface or both, when measured with a 3D optical profiler, the peak valley roughness (Spv) represented by Equation 2 below is 0.05 µm to 1.7 µm, and the first polyimide film Surface tension (V) of the surface, the second surface, or both may be 20 dyne/cm to 45 dyne/cm:

[Equation 2]

In Equation 2 above,

The Spk, the Sk and the Svk are as described above.

In addition, in the cover window for the display, the polyimide film satisfies Equation 2, and the soluble agent surface gradient (SC) represented by Equation 1 below may be 0.03 to 0.2:

[Equation 1]

In Equation 1 above,

The V ₀ and V ₁₀₀₀ are as described above.

In addition, in the cover window for a display, the polyimide-based film may have a solvent coating index (SCI) of 0.001 µm to 0.2 µm represented by Equation 3 below:

[Equation 3]

In Equation 3 above,

The SC and the Spv are as described above.

In addition, when the polyimide film is immersed in propylene glycol monomethyl ether acetate for 1000 seconds, the haze of the polyimide film after immersion may be less than 2%.

Such a cover window for a display can be usefully applied to a display device.

Display device

A display device according to an embodiment includes a display unit; And a cover window disposed on the display unit, wherein the cover window includes the polyimide film.

A display device according to another embodiment includes a display unit; And the cover window disposed on the display unit.

2 is a cross-sectional view of a display device according to an embodiment. Specifically, FIG. 2 includes a display unit 400 and a polyimide-based film 100 and a functional layer 200 having a first surface 101 and a second surface 102 on the display unit 400 A display device in which the cover window 300 is disposed and the adhesive layer 500 is disposed between the display unit 400 and the cover window 300 is illustrated.

The display unit may display an image and may have a flexible characteristic.

The display unit may be a display panel for displaying an image, for example, a liquid crystal display panel or an organic light emitting display panel. The organic light emitting display panel may include a front polarizing plate and an organic EL panel.

The front polarizing plate may be disposed on the front surface of the organic EL panel. Specifically, the front polarizing plate may be adhered to a surface on which an image is displayed in the organic EL panel.

The organic EL panel displays an image by self-emission in units of pixels. The organic EL panel may include an organic EL substrate and a driving substrate. The organic EL substrate may include a plurality of organic electroluminescent units each corresponding to a pixel. Specifically, each may include a cathode, an electron transport layer, a light emitting layer, a hole transport layer, and an anode. The driving substrate may be driveably coupled to the organic EL substrate. That is, the driving substrate is coupled so as to apply a driving signal such as a driving current to the organic EL substrate, so that current is applied to each of the organic electroluminescent units to drive the organic EL substrate.

In addition, an adhesive layer may be included between the display unit and the cover window. The adhesive layer may be an optically transparent adhesive layer, and is not particularly limited.

The cover window is disposed on the display unit. The cover window may be positioned at the outermost side of the display device according to the embodiment to protect the display unit.

The cover window may include a polyimide-based film and a functional layer. The functional layer may be at least one selected from the group consisting of a hard coating, a reflectance reducing layer, an antifouling layer, and an anti-glare layer. The functional layer may be coated on at least one surface of the polyimide-based film.

The above will be described in more detail by the following examples. However, the following examples are for illustrative purposes only, and the scope of the examples is not limited thereto.

<Example 1>

After filling 250 kg of dimethylacetamide (DMAc), an organic solvent, into a 1,000L glass reactor with a temperature controllable double jacket under a nitrogen atmosphere at 20 ℃, 2,2'-bis (trifluoromethyl) as the first aromatic diamine ) Benzidine (TFMB) 1 mol was slowly added and dissolved.

Then, 0.5 mol of 2,2'-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6-FDA) as the first aromatic dianhydride was slowly added and stirred for 1 hour.

Then, 0.2 mol of 3,4,3′,4′′-biphenyltetracarboxylic dianhydride (BPDA) as a second aromatic dianhydride was added to the mixture, followed by stirring for 1 hour, and After adding 0.3 mol of terephthaloyl chloride (TPC) as a lebonyl compound, it was stirred for 1 hour to prepare a first polymer solution.

After measuring the viscosity of the prepared first polymer solution, when the measured viscosity does not reach the target viscosity, a 10% by weight TPC solution was prepared in the DMAc organic solvent and 1 mL was added until the viscosity reached 200,000 cps. Thereafter, the stirring process was repeated for 30 minutes to prepare a second polymer solution.

The second polymer solution was transferred to a tank at -10 °C and stored, and degassed for 1.5 hours so that the pressure in the tank became 0.3 bar, and then the internal pressure of the tank was purged to 1.5 atmospheres using nitrogen gas. After purging, the second polymer solution was stored in a tank for 30 hours.

Subsequently, the second polymer solution was cast and dried to prepare a gel-sheet. Then, while moving the gel-sheet, hot air treatment was performed at about 150° C. for about 3 minutes, 250° C. for 20 minutes, and then at 350° C. for about 10 minutes. It was wound up using a winder. At this time, the movement speed of the gel-sheet on the belt during drying is 1 m/s, and the ratio of the movement speed of the gel-sheet on the belt during drying: the movement speed of the film during winding is in the range of 1:1.01 to 1:1.10. The speed of the winder was adjusted.

Examples 2 and 3

As shown in Table 1 below, a film was prepared in the same manner as in Example 1, except that the content of each reactant, the content of the compound having a fluorine-containing substituent, the hot air temperature and the hot air time were different.

Examples 4 and 5

As shown in Table 1 below, content of each reactant using TFMB as the first aromatic diamine, oxydianiline (ODA) as the second aromatic diamine, 6FDA as the first aromatic dianhydride, and BPDA as the second aromatic dianhydride , A film was prepared in the same manner as in Example 1, except that the content of the compound having a fluorine-containing substituent, the hot air temperature, and the hot air time were different.

Comparative Examples 1, 2, 4 and 5

As shown in Table 1 below, a film was prepared in the same manner as in Example 1, except that the content of each reactant, the content of the compound having a fluorine-containing substituent, the hot air temperature and the hot air time were different.

Comparative Example 3

As shown in Table 1 below, a film was prepared in the same manner as in Example 4, except that the content of each reactant, the content of the compound having a fluorine-containing substituent, the hot air temperature and the hot air time were different.

<Evaluation example>

For the films prepared in Examples 1 to 5 and Comparative Examples 1 to 5, the following physical properties were measured and evaluated.

<Evaluation Example 1: Measurement of surface tension>

Surface tension measurement before immersion in solvent (PGMEA)

It was measured according to the German industrial standard (DIN 55660) using the Mobile Surface Analyzer of Germany Kruss. Specifically, the contact angle of the standard solution of diiodomethane and distilled water was measured with a camera, and the contact angle was substituted into the Owens-Wendt-Rabel-Kaelble (OWRK) equation of Equation 4 below. Surface tension was calculated:

<Equation 4>

In Equation 4 above,

D: dispersion

P: polar

σ _sl : interfacial tension between phases

σ _l : liquid surface tension

σ _s : solid surface tension

Surface tension measurement after immersion in PGMEA

0.1 g of the polyimide-based films of Examples and Comparative Examples were immersed in 10 mL of propylene glycol monomethyl ether acetate (PGMEA) for 1000 seconds. After immersion, using the film, the contact angle of diiodomethane and distilled water was measured with a camera, and the contact angle was calculated using the OWRK equation of Equation 4 above.

<Evaluation Example 2: Measurement of transmittance>

The light transmittance at 550 nm was measured using a haze meter NDH-5000W manufactured by Denshoku High School in Japan.

<Evaluation Example 3: Measurement of yellowness (YI)>

Yellow Index (YI) was measured using a CIE colorimeter by a spectrophotometer (UltraScan PRO, Hunter Associates Laboratory).

The results of Evaluation Examples 1 to 3 are shown in Table 2 below.

As can be seen from Table 2, the polyimide-based films of Examples 1 to 5 all satisfy the range of 0.03 to 0.2, wherein the degree of change of the surface of the soluble agent (SC) on the first and second surfaces is within the range of 0.03 to 0.2. It was confirmed that both transmittance and yellowness were excellent compared to the polyimide-based films of Comparative Examples 1 to 5, which did not satisfy.

Specifically, it can be seen that the polyimide-based films of Examples 1 to 5 satisfies the degree of change in the surface of the soluble agent in the above range, so that the transmittance is all 85% or more, and the yellowness is in the range of 1 to 3.5.

On the other hand, as in Comparative Examples 1 to 5, when the degree of change in the surface of the soluble agent exceeded 0.2, the yellowness or transmittance was poor. In addition, in the case of Comparative Examples 1 and 2, the surface tension of at least one side was as low as less than 20 dyne/cm.

On the other hand, it can be seen that the degree of surface change and surface tension of the soluble agent of the polyimide film vary depending on the content of the compound having a fluorine-containing substituent, the hot air temperature, and the hot air time. In particular, as in Comparative Example 2, when the hot air temperature increases, the imidation reaction is accelerated, so that the surface tension of one side of the film is too low, and in this case, it can be predicted that wettability may deteriorate.

In addition, it can be seen that the surface tension may decrease as the content of the compound having a fluorine-containing substituent in the mixture increases when preparing the polymer solution. In particular, as in Comparative Example 3, when the content of the compound having a fluorine-containing substituent was 27.5 mol%, which was lower than that of the other examples, the surface tension was significantly increased to more than 50 dyne/cm.

In particular, as in Comparative Example 3, when the surface tension of the solvent before immersion was too large, the transmittance was significantly reduced to 80%, and the yellowness of the polyimide-based films of Examples 1 to 5 was also 4.5. It can be seen that the increase of about 1.5 to 2 times or more compared to the yellowness.

On the other hand, in the case of Comparative Examples 4 and 5, the surface tension of both the first and second surfaces before PGMEA immersion was lower than 20 dyne/cm, and the surface tension of at least one surface was lowered even after immersion.

In addition, the polyimide film of Comparative Example 5 is the same as Comparative Example 4, but when the hot air temperature and time are adjusted, the yellowness is 3.7, which is very high compared to Comparative Examples 4 and 1 to 3.

<Evaluation Example 4: Measurement of surface peak valley roughness (Spv)>

The peak valley roughness of the surface of the polyimide-based films of Examples and Comparative Examples was measured, and the results are shown in Table 3 below.

The peak valley roughness was measured using a 3D optical profiler (Optical Profiler Contour GT) manufactured by BRUKER. At the positions of the three arbitrary points of Examples and Comparative Examples, the peak valley roughness of the surface was measured, and each value represented an average value. At each location, an image was taken by the 3D optical profiler in an area of 220 μm X 220 μm, and peak valley roughness (Spv) was measured based on this.

When measuring peak valley roughness, Spk, Sk, and Svk are all adjusted values according to ISO 25178-2:2012.

In Table 3 below, Spk is the reduced peak height in ISO 25178-2:2012, Sk is the adjusted core height in ISO 25178-2:2012, and Svk is the This is the reduced dale height in ISO 25178-2:2012.

As shown in Table 3, in the case of the polyimide-based films of Examples 1 to 5, the peak valley roughness (Spv) of the first and second surfaces of the polyimide-based film is both within the range of 0.05 µm to 1.7 µm. there was.

On the other hand, in Comparative Examples 1 and 5, the peak valley roughness of the first or second surface was remarkably high. In particular, in the case of Comparative Example 1, it was confirmed that both the peak valley roughness of the first side or the second side was increased.

<Evaluation Example 5: Haze Measurement>

Haze was measured using a haze meter NDH-5000W manufactured by Denshoku High School in Japan. Specifically, 0.1 g of the polyimide-based films of Examples and Comparative Examples were immersed in 10 mL of propylene glycol monomethyl ether acetate (PGMEA) for 1000 seconds, and then the haze was measured. The measurement was repeated three times, and their average value was taken as the haze value.

<Evaluation Example 6: Adhesion Test>

Hard coating adhesion was measured with the polyimide-based films of Examples and Comparative Examples.

The prepared polyimide-based film was cut to a width of 2 mm, and was cross-cut in each of 3 spaces horizontally and vertically, and the tape was attached thereto and then removed. Thereafter, the adhesion was measured based on the remaining amount:

Adhesion A: 8 or more remaining out of total 9

Adhesion B: remaining 6 to less than 8 out of total 9

Adhesion C: 4 to less than 6 remaining amount out of 9

Adhesion D: 3 or less out of total 9

The results of Evaluation Examples 5 and 6 are shown in Table 4 below.

As shown in Table 4, it can be seen that the polyimide-based film of the Example is superior to the polyimide-based film of Comparative Example after immersion in a solvent (PGMEA) for 1000 seconds, and the adhesion of haze and hard coating.

Specifically, the polyimide films of Examples 1 and 4 had a haze of 0.65% or 0.89% after immersion in a solvent, whereas the polyimide films of Comparative Examples 1, 3 and 4 were 1.8% to 3.5%. Haze increased, and in particular, in the case of Comparative Example 3, it can be seen that the haze was increased by 5 times or more compared to Example 1 to 3.5%.

In addition, in the case of hard coating adhesion, the polyimide-based films of Examples 1 and 4 had a residual amount of 8 or more out of 9, whereas the polyimide-based films of Comparative Examples 1 and 4 had a residual amount of 3 or less. And most showed peeling. In the case of Comparative Example 3, in the case of the hard coating adhesion, the remaining amount was 6 or more and less than 8, but after immersion in a solvent, the haze was high, and a whitening phenomenon was observed.

On the other hand, it can be seen that the haze of the polyimide-based film of Comparative Example 5 is 3.7%, which increases the haze by 5 to 6 times or more compared to Examples 1 and 4 of the present application. Furthermore, the remaining amount of hard coating adhesive strength of the polyimide-based film of Comparative Example 5 was 3 or less, and most were peeled off.

Therefore, it was confirmed that, as in Comparative Examples 1 and 4, when the surface variation of the soluble agent of the polyimide-based film was high and the surface tension was low, the hard coating adhesion was significantly reduced, and as in Comparative Example 3, the surface tension of the polyimide-based film was high. In this case, it was confirmed that whitening phenomenon occurred. In addition, as in Comparative Example 5, when the peak valley roughness on at least one side was high and both the surface tension were low, it was confirmed that the haze during film formation increased (haze during film formation: 2.5%) and the haze increased even after immersion in the solvent.

10 polymerization equipment 20 tank
30: belt 40: thermosetting machine
50: winder
100: polyimide film
101: page 1 102: page 2
110: casting body 200: functional layer
300: cover window 400: display unit
500: adhesive layer

Claims (18)

Including a polyimide polymer formed by polymerization of an aromatic diamine compound and an aromatic dianhydride compound,
Comprising a first surface and a second surface opposite to the first surface,
In the first aspect, the degree of surface gradient (SC) of the solvent represented by the following equation 1 is 0.03 to 0.2,
In the second side, the degree of surface change of the soluble agent is 0.03 to 0.2,
In the first surface, when measured with a 3D optical profiler, the peak valley roughness (Spv) represented by Equation 2 below is 0.05 µm to 1.7 µm,
In the second surface, the peak valley roughness (Spv) is 0.05 ㎛ to 1.7 ㎛,
Polyimide film:
[Equation 1]

[Equation 2]

In Equation 1 above,
V ₀ is the surface tension before immersing the polyimide-based film in propylene glycol monomethyl ether acetate,
V ₁₀₀₀ is the surface tension after immersing the polyimide-based film in propylene glycol monomethyl ether acetate for 1000 seconds,
In Equation 2 above,
The Spk is the reduced peak height in ISO 25178-2:2012,
Sk is the adjusted core height in ISO 25178-2:2012,
The Svk is the reduced dale height in ISO 25178-2:2012. delete delete delete The method of claim 1,
V ₀ of the first surface is 20 dyne/cm to 45 dyne/cm polyimide-based film. The method of claim 1,
V ₀ of the second surface is 20 dyne/cm to 45 dyne/cm, a polyimide film. The method of claim 5,
V ₁₀₀₀ of the first surface is 20 dyne/cm to 50 dyne/cm, a polyimide-based film. The method of claim 6,
V ₁₀₀₀ of the second side is 20 dyne/cm to 50 dyne/cm, a polyimide film. The method of claim 1,
The polyimide-based film has a solvent coating index (SCI) of 0.001 µm to 0.2 µm represented by the following formula 3, a polyimide-based film.
[Equation 3]

In Equation 3 above,
The SC is the degree of surface gradient of the soluble agent,
The Spv is the peak valley roughness. A polyimide-based film comprising a polyimide polymer formed by polymerization of an aromatic diamine compound and an aromatic dianhydride compound,
The polyimide-based film includes a first surface and a second surface opposite to the first surface,
In the first aspect, the degree of surface gradient (SC) of the solvent represented by the following equation 1 is 0.03 to 0.2,
In the second side, the degree of change in the surface of the soluble agent is 0.03 to 0.2,
On the first surface, when measured with a 3D optical profiler, the peak valley roughness (Spv) represented by Equation 2 below is 0.05 µm to 1.7 µm,
In the second surface, the peak valley roughness (Spv) is 0.05 ㎛ to 1.7 ㎛,
The first surface, the second surface, or both have a surface tension (V) of 20 dyne/cm to 45 dyne/cm, a cover window for a display:
[Equation 1]

[Equation 2]

In Equation 1 above,
V ₀ is the surface tension before immersing the polyimide-based film in propylene glycol monomethyl ether acetate,
V ₁₀₀₀ is the surface tension after immersing the polyimide-based film in propylene glycol monomethyl ether acetate for 1000 seconds,
In Equation 2 above,
The Spk is the reduced peak height in ISO 25178-2:2012,
The Sk is the adjusted core height in ISO 25178-2:2012,
The Svk is the reduced dale height in ISO 25178-2:2012. The method of claim 10,
The polyimide film has a surface gradient (SC) of 0.03 to 0.2 represented by the following formula 1 in terms of satisfying the formula 2, a cover window for a display:
[Equation 1]

In Equation 1 above,
V ₀ is the surface tension before immersing the polyimide-based film in propylene glycol monomethyl ether acetate,
V ₁₀₀₀ is the surface tension after immersing the polyimide-based film in propylene glycol monomethyl ether acetate for 1000 seconds. The method of claim 11,
The polyimide-based film has a solvent coating index (SCI) of 0.001 µm to 0.2 µm represented by the following formula 3, a cover window for a display:
[Equation 3]

In Equation 3 above,
The SC is the degree of surface gradient of the soluble agent,
The Spv is the peak valley roughness. The method of claim 12,
When the polyimide-based film is immersed in propylene glycol monomethyl ether acetate for 1000 seconds, the haze of the polyimide-based film after immersion is less than 2%, a cover window for a display. A display unit; And
Includes; a cover window disposed on the display unit,
The display device, wherein the cover window includes the polyimide-based film of claim 1. A display unit; And
A display apparatus comprising: the display cover window of claim 10 disposed on the display unit. As a method for producing a polyimide film,
Simultaneously or sequentially mixing an aromatic diamine compound and an aromatic dianhydride compound, or an aromatic diamine compound, an aromatic dianhydride compound, and an aromatic dicarbonyl compound in an organic solvent, and reacting the mixture to prepare a polymer solution;
Moving the polymer solution to a tank and purging with an inert gas;
Casting the polymer solution in the tank on a belt and drying it to prepare a gel-sheet;
Preparing a cured film by subjecting the gel-sheet to hot air treatment;
Cooling the cured film; And
Including; winding the cooled cured film
The hot air treatment is performed at a hot air temperature of 100°C to 180°C for 1 minute to 10 minutes, 200°C to 300°C for 10 minutes to 30 minutes, and 300°C to 400°C for 5 minutes to 20 minutes,
The polyimide-based film includes a first surface and a second surface opposite to the first surface,
In the first aspect, the degree of surface gradient (SC) of the solvent represented by the following equation 1 is 0.03 to 0.2,
In the second side, the degree of surface change of the soluble agent is 0.03 to 0.2,
In the first surface, when measured with a 3D optical profiler, the peak valley roughness (Spv) represented by Equation 2 below is 0.05 µm to 1.7 µm,
In the second surface, the peak valley roughness (Spv) is 0.05 ㎛ to 1.7 ㎛,
Method for producing a polyimide film:
[Equation 1]

[Equation 2]

In Equation 1 above,
V ₀ is the surface tension before immersing the polyimide-based film in propylene glycol monomethyl ether acetate,
V ₁₀₀₀ is the surface tension after immersing the polyimide-based film in propylene glycol monomethyl ether acetate for 1000 seconds,
In Equation 2 above,
The Spk is the reduced peak height in ISO 25178-2:2012,
Sk is the adjusted core height in ISO 25178-2:2012,
The Svk is the reduced dale height in ISO 25178-2:2012. The method of claim 16,
The diamine compound, the dianhydride compound, or both include a compound having a fluorine-containing substituent,
The method for producing a polyimide film, wherein the compound having the fluorine-containing substituent is 10 to 90 mol% based on the total mol of the mixture. delete

Images