KR102147307B1 - Polyimide film and flexible display panel including the same - Google Patents

Abstract

The present invention relates to a polyimide-based film, a window cover film, and a display panel including the same. More specifically, the present invention relates to a polyimide-based film having improved optical properties such as visibility, a window cover film using the same, and a display device including the same.

Description

Polyimide-based film and a flexible display panel including the same TECHNICAL FIELD

The present invention relates to a polyimide-based film, a window cover film, and a display panel including the same. More specifically, the present invention relates to a polyimide-based film having improved optical properties such as visibility, a window cover film using the same, and a display device including the same.

Display devices are provided with a transparent window cover on the display panel so that the user can see the display from the front of the display panel in order to protect the display panel from scratches or external impact.

Display devices are gradually becoming lighter, thinner, and flexible, and a window cover manufactured from a polymer film having high hardness, high rigidity and flexible properties has been studied in place of tempered glass.

Since such a window cover is formed on the outermost side of the display device, heat resistance, mechanical properties, and optical properties must be satisfied, and in particular, display quality is high, a mura phenomenon, a blackout phenomenon in which the screen looks black at a specific angle, or It is important not to cause distortion due to light, such as the rainbow phenomenon with iridescent spots.

In particular, as the coating layer is laminated on the base layer in order to impart various physical properties, the window cover causes diffuse reflection of light, causes optical stains to deteriorate visibility, and causes eye fatigue when applied to a display.

Therefore, since it replaces tempered glass or a conventional organic material, development of a window cover capable of solving the problem of distortion caused by light, along with mechanical properties, thermal properties, and various optical properties, is still required.

Republic of Korea Patent Publication No. 10-2015-0104282 (2015.09.15)

An object of the present invention is to provide a polyimide-based film with improved appearance quality and excellent visibility, and a window cover film and a display panel using the same.

In addition, the present invention is to provide a polyimide-based film having remarkably improved rainbow or optical staining, a window cover film using the same, and a display panel using the same.

In addition, since the present invention provides a window cover film that replaces tempered glass, etc., it provides a new window cover film that satisfies excellent mechanical properties, thermal properties, and various optical properties, and can solve the distortion problem caused by light. will be.

In one aspect of the present invention, when an interference pattern inspection lamp (FNATECH, FNA-35S) is vertically illuminated on a film having a size of 50 mm in width and 50 mm in length, and when two lines are drawn in the diagonal direction of the film, the two diagonal lines are met. A polyimide-based film having 2 to 20 contour lines divided by the sum of the number of contour lines is provided.

In one aspect of the present invention, the interval between the diagonal lines and the contour lines meeting may be 5 or less when the interval is 2 mm or less.

In one aspect of the present invention, the polyimide-based film may have a modulus of 3 GPa or more according to ASTM E111, and a breaking elongation of 8% or more.

In one aspect of the present invention, the polyimide-based film has a light transmittance of 2% or more, a total light transmittance of 87% or more, a haze of 2.0% or less, and a yellowness of 2% or more, measured at 388 nm according to ASTM D1746. May be 5.0 or less and b* value may be 2.0 or less.

In one aspect of the present invention, the polyimide-based film may have a polyamideimide structure.

In one aspect of the present invention, the polyimide film may include a unit derived from a fluorine-based aromatic diamine, a unit derived from an aromatic dianhydride, and a unit derived from an aromatic diacid dichloride.

In one aspect of the present invention, the polyimide-based film may further include a unit derived from a cycloaliphatic dianhydride.

In one aspect of the present invention, the thickness of the polyimide-based film may be 30 to 110 ㎛.

Another aspect of the present invention is a polyimide-based film according to the above aspect; And

A coating layer formed on one or both surfaces of the polyimide film;

It provides a window cover film comprising a.

In one aspect of the present invention, the coating layer may be any one or more selected from a hard coating layer, an antistatic layer, an anti-fingerprint layer, an antifouling layer, an anti-scratch layer, a low refractive layer, an antireflection layer, and an impact absorbing layer.

Another aspect of the present invention provides a flexible display panel including the polyimide-based film film according to the above aspect.

The polyimide-based film according to the present invention has the advantage of excellent visibility and remarkably improving the rainbow phenomenon.

The window cover film according to the present invention has an advantage of excellent display quality even if a coating layer is formed on the polyimide-based film, it is possible to reduce a rainbow phenomenon in which an iridescent stain is generated on the display, and an appearance quality is improved.

In addition, the polyimide-based film and the window cover film including the same according to the present invention can be applied to various display fields due to excellent optical properties and visibility.

In addition, the window cover film of the present invention satisfies excellent mechanical properties, thermal properties, and various optical properties such as transparency and yellowness, while providing excellent visibility properties so that it can be applied to various displays.

1 is a photograph illustrating a contour line of a polyimide film according to an embodiment of the present invention using an interference fringe inspection lamp.
2 is a photograph illustrating a contour line of a polyimide-based film according to an embodiment of the present invention using an interference fringe inspection lamp.
3 is a photograph illustrating a contour line of a polyimide film according to an embodiment of the present invention using an interference fringe inspection lamp.

Hereinafter, the present invention will be described in more detail through specific examples or examples including the accompanying drawings. However, the following specific examples or examples are only one reference for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

In addition, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. The terms used in the description in the present invention are merely intended to effectively describe specific embodiments and are not intended to limit the present invention.

Throughout the specification describing the present invention, the term “including” a certain element in a certain part means that other elements may be further included rather than excluding other elements unless otherwise specified.

In addition, the singular form used in the specification and the appended claims may be intended to include the plural form unless otherwise indicated in the context.

In the present invention, the polyimide resin is used as a term including polyimide or polyamideimide. The same is true for polyimide-based films.

In the present invention, "polyimide resin solution" is used in the same meaning as "polyimide film-forming composition" and "polyamideimide solution". In addition, a polyimide resin and a solvent may be included to form a polyimide-based film.

In the present invention, the "film" is obtained by applying and drying the "polyimide resin solution" on a support to be peeled, and may be stretched or unstretched.

In the present invention, "one side" refers to any one surface of the polyimide-based film, and the first side may refer to an upper surface and a second surface to refer to a lower surface. More specifically, the first surface may be a surface formed by evaporation of a solvent during production of the film, and may be a surface in contact with air, and the second surface may mean a surface formed by being applied to a support during production of the film.

In the present invention, as shown in Figs. 1 to 3, the "contour line" is visually confirmed when an interference pattern inspection lamp (FUNATECH, FNA-35S) is vertically illuminated on a film having a size of 50 mm in width and 50 mm in length. It means a pattern like a wave that becomes a wave, and in a bright and dark contrast painting, the dark part is defined as a contour line.

The inventors of the present invention have done a lot of research in order to solve the above problems, as a result of the physical properties of the window cover film used in the display, the number of contour lines of the polyimide film under the interference pattern inspection lamp (FUNATECH, FNA-35S) When measured, the present invention was completed by finding that optical stains such as rainbow and mura did not occur in a polyimide-based film having a specific number of contour ranges, and was excellent in visibility and optical properties such as transparency, haze and yellowness. I did.

Specifically, in the range of 20 or less, preferably 15 or less, and more preferably 7 or less of the number of contour lines, the present invention was completed by recognizing that the rainbow phenomenon is more remarkably improved. In addition, it was confirmed that the rainbow phenomenon is more remarkably improved in the range of 5 or less, specifically 4 or less, and specifically 3 or less when the distance between the contour lines meeting the diagonal line is 2 mm or less, thereby completing the present invention.

Hereinafter, each configuration of the present invention will be described in more detail with reference to the drawings. However, this is merely exemplary, and the present invention is not limited to the specific embodiments described by way of example.

1 to 3 are photographs illustrating a contour line of a polyimide-based film according to an embodiment of the present invention using an interference fringe inspection lamp.

Specifically, FIGS. 1 and 2 are photographs of a polyimide-based film according to an embodiment of the present invention, showing a film having a small number of contour lines meeting a diagonal line, specifically 20 or less, and FIG. 3 is a photograph showing a film having a number of contour lines of 20 or less. It is a photograph showing an aspect of a film having more than one. Specifically, in the case of FIG. 1, the number of contour lines from 11 o'clock to 5 o'clock is 13, and the number of diagonal contours from 1 o'clock to 7 o'clock is 16, and the average is 14.5.

As shown in Figs. 1 to 3, when the number of contour lines existing in the film is measured using the interference fringe inspection lamp under the same conditions, it can be seen that the number and spacing of contour lines are formed differently for each film.

The present inventors can provide a film that is very excellent for use as an optical film when the number of contour lines satisfies a specific range, and specifically provides a film that satisfies the visibility and optical properties suitable for use in a flexible display panel. Could It has also been found that a film that satisfies this contour can be achieved by the structure of the base film and the drying and stretching process of the film.

Hereinafter, raw materials and manufacturing means for manufacturing a window cover film satisfying the contour line of the present invention will be described.

<Polyimide film and its manufacturing method>

First, a method of manufacturing a polyimide-based film according to an aspect of the present invention and a film having the characteristics of the present invention will be described.

The polyimide-based film providing the window cover film of the present invention vertically illuminates an interference pattern inspection lamp (FNATECH, FNA-35S) on a film having a size of 50 mm in width and 50 mm in length, and two lines in the diagonal direction of the film When is drawn in an X-shape, the number of contour lines divided by 2 by the sum of the number of contour lines meeting each diagonal line is 2 to 20. Specifically, in the range of 3 to 15, more specifically 4 to 10, the rainbow phenomenon is more remarkably improved, and a window cover film can be provided as an optical film having excellent visibility and optical properties. At this time, for example, if the shape of the contour line meeting the diagonal line is circular, the number of contour lines meeting the diagonal line is assumed to be two.

In addition, it was confirmed that the rainbow phenomenon was more remarkably improved in a range of 5 or less, specifically 4 or less, and specifically 3 or less when the distance between the contour lines meeting the diagonal line is 2 mm or less. Since these properties are obtained by the manufacturing process of the film, this will be described below.

In one aspect of the present invention, the polyimide-based film may have a thickness of 10 to 500 µm, 20 to 250 µm, or 30 to 110 µm.

In addition, in one aspect of the present invention, the polyimide-based film has a modulus of 3 GPa or more, 4 GPa or more, or 5 GPa or more, and an elongation at break of 8% or more, 12% or more, or 15% or more according to ASTM E111, and ASTM The light transmittance measured at 388 nm according to D1746 is 2% or more or 2 to 80%, the total light transmittance measured at 400 to 700 nm is 87% or more, 88% or more, or 89% or more, and the haze is 2.0% or less according to ASTM D1003 , 1.5% or less or 1.0% or less, according to ASTM E313, yellowness is 5.0 or less, 3.0 or less, or 0.4 to 3.0, and b* value may be 2.0 or less, 1.3 or less, or 0.4 to 1.3, It has excellent physical properties that can replace the polyimide film of

In one aspect of the present invention, the polyimide-based film is a polyimide-based resin, and in particular, a polyimide-based resin having a polyamide-imide structure.

Further, more preferably, it may be a polyamide-imide resin containing a fluorine atom and an aliphatic cyclic structure, and accordingly, the number of contour lines satisfies the scope of the present invention, while the appearance quality, mechanical properties, and Dynamic bending properties may have excellent properties.

In one aspect of the present invention, the polyamide-imide resin comprising a fluorine atom and an alicyclic structure is derived from a unit derived from a fluorine-based aromatic diamine, a unit derived from an aromatic dianhydride, and an aromatic diacid dichloride. It may include a derived unit. More preferably, in one aspect of the present invention, the polyamide-imide resin comprising a fluorine atom and an aliphatic cyclic structure is a unit derived from a fluorine-based aromatic diamine, a unit derived from an aromatic dianhydride, a cycloaliphatic The use of a quaternary copolymer comprising a unit derived from a dianhydride and a unit derived from an aromatic diacid dichloride is more suitable for expressing the desired physical properties and may be preferred.

In one aspect of the present invention, an example of a polyamide-imide resin including the fluorine atom and an alicyclic structure is an amine-terminated polyamide oligomer derived from a first fluorine-based aromatic diamine and an aromatic diacid dichloride. And polymerizing the amine-terminated polyamide oligomer and a second fluorine-based aromatic diamine, an aromatic dianhydride, and a cycloaliphatic dianhydride monomer to prepare a polyamide-imily polymer, so it is preferable to achieve the object of the present invention. do. The first fluorine-based aromatic diamine and the second fluorine-based aromatic diamine may be of the same or different types. More specifically, one aspect of the polyamideimide resin may include a block consisting of an amine-terminated polyamide oligomer derived from a first fluorine-based aromatic diamine and an aromatic diacid dichloride, and a polyimide unit at both ends, and the block The content may be 50% or more based on mass.

In one aspect of the present invention, when an amine-terminated oligomer in which an amide structure in a polymer chain is formed by an aromatic diacid dichloride is included as a monomer of a diamine, it is possible to improve not only optical properties but also mechanical strength, especially including modulus. In addition, it is possible to further improve dynamic bending properties.

In one aspect of the present invention, when having a polyamide oligomer block as described above, a diamine monomer containing an amine-terminated polyoligomer and a second fluorine-based aromatic diamine, and a dianhydride containing the aromatic dianhydride and cycloaliphatic dianhydride of the present invention The molar ratio of the water monomer is preferably used in a molar ratio of 1:0.8 to 1.2, and preferably in a molar ratio of 1: 0.9 to 1. In addition, the content of the amine-terminated polyamide oligomer with respect to the whole diamine monomer is not particularly limited, but the content of 30 mol% or more, preferably 50 mol% or more, and more preferably 70 mol% or more, is a contour characteristic of the present invention, mechanical properties, Yellow is also better for satisfying optical properties. In addition, the composition ratio of the aromatic dianhydride and the cycloaliphatic dianhydride is not particularly limited, but when considering the achievement of transparency, yellowness, mechanical properties, etc. in addition to the contour characteristics of the present invention, the ratio of 30 to 80 mol%: 70 to 20 mol% It is recommended to use as, but is not limited thereto.

In one aspect of the present invention, the polyamide-imide resin is derived from a unit derived from a fluorine-based aromatic diamine, a unit derived from an aromatic dianhydride, a unit derived from a cycloaliphatic dianhydride, and an aromatic diacid dichloride. The use of a quaternary copolymer containing all of the units is preferred because it can satisfy the desired contour characteristics, appearance quality, and optical characteristics.

In addition, another example of a polyamide-imide resin containing the fluorine atom and an alicyclic structure in the present invention is a mixture of a fluorine-based aromatic diamine, an aromatic dianhydride, a cycloaliphatic dianhydride, and an aromatic diacid dichloride. It may be a polymerized and imidized polyamide-imide resin. These resins have a random copolymer structure, and based on 100 moles of diamine, 40 moles or more, preferably 50 to 80 moles of aromatic diacid dichloride may be used, and the content of aromatic dianhydride may be 10 to 50 moles, and The content of the aliphatic dianhydride may be 10 to 60 moles, and the sum of diacid dichloride and dihydrate may be polymerized in a ratio of 1:0.8 to 1.1 moles with respect to the diimine monomer. Polymerization is preferably carried out in a molar ratio of 1: 0.9 to 1, more preferably in a molar ratio of 1:1. The random polyamideimide of the present invention is slightly different in optical properties and mechanical properties such as contour characteristics and transparency compared to the block-type polyamideimide resin, but may still fall within the scope of the present invention.

In one aspect of the present invention, the fluorine-based aromatic diamine component may be used in combination with 2,2'-bis(trifluoromethyl)-benzidine and other known aromatic diamine components, but 2,2'-bis (trifluoromethyl) Methyl)-benzidine may be used alone. By using such a fluorine-based aromatic diamine, as a polyamideimide-based film, excellent optical properties can be improved and yellowness can be improved based on the mechanical properties required by the present invention. In addition, by improving the tensile modulus of the polyamide-imide-based film, the mechanical strength of the hard coat film can be improved, and the dynamic bending properties can be further improved.

Aromatic dianhydrides include 4,4'-hexafluoroisopropylidene diphthalic anhydride (6FDA) and biphenyltetracarboxylic dianhydride (BPDA), oxydiphthalic dianhydride (ODPA), and sulfonyl dip. Talyanhydride (SO2DPA), (isopropylidenediphenoxy) bis (phthalic anhydride) (6HDBA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2, 3,4-tetrahydronaphthalene-1,2-dicarboxylic dianhydride (TDA), 1,2,4,5-benzene tetracarboxylic dianhydride (PMDA), benzophenone tetracarboxylic dian Hydride (BTDA), bis (carboxyphenyl) dimethyl silane dianhydride (SiDA), bis (dicarboxyphenoxy) diphenyl sulfide dianhydride (BDSDA) at least one, but the present invention is not limited thereto. .

Cycloaliphatic dianhydride is, for example, 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 5-(2,5-dioxotetrahydrofuryl)-3-methylcyclohexene-1 ,2-dicarboxylic dianhydride (DOCDA), bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BTA), bicyclooctene- 2,3,5,6-tetracarboxylic dianhydride (BODA), 1,2,3,4-cyclopentane tetracarboxylic dianhydride (CPDA), 1,2,4,5-cyclohexane Tetracarboxylic dianhydride (CHDA), 1,2,4-tricarboxy-3-methylcarboxycyclopentane dianhydride (TMDA), 1,2,3,4-tetracarboxycyclopentane dianhydride (TCDA ) And any one or a mixture of two or more selected from the group consisting of derivatives thereof.

In one aspect of the present invention, when the amide structure in the polymer chain is formed by the aromatic diacid dichloride, not only optical properties but also mechanical strength including modulus can be greatly improved, and dynamic bending properties Can be further improved.

Aromatic diacid dichloride is isophthaloyl dichloride (IPC), terephthaloyl dichloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloride ([1 ,1'-Biphenyl]-4,4'-dicarbonyl dichloride, BPC), 1,4-naphthalene dicarboxylic dichloride (NPC), 2,6-naphthalene dicarboxylic dichloride Dichloride (2,6-naphthalene dicarboxylic dichloride, NTC), 1,5-naphthalene dicarboxylic dichloride (1,5-naphthalene dicarboxylic dichloride, NEC) and a mixture of two or more selected from the group consisting of derivatives thereof It can be used, but is not limited thereto.

Hereinafter, a method for producing a polyimide-based film is illustrated.

In one aspect of the present invention, the polyimide-based film may be prepared by applying a "polyimide-based resin solution" including a polyimide-based resin and a solvent on a substrate, followed by drying or drying and stretching. That is, the polyimide-based film may be prepared by a solution casting method.

For example, the polyimide film is a step of preparing an oligomer by reacting a fluorine-based aromatic diamine with an aromatic diacid dichloride, and a polyamic acid solution is prepared by reacting the prepared oligomer with a fluorine-based aromatic diamine, an aromatic dianhydride and a cycloaliphatic dianhydride. It may be prepared by imidizing the polyamic acid solution to prepare a polyamideimide resin, and applying a polyamideimide solution in which the polyamideimide resin is dissolved in an organic solvent to form a film.

Hereinafter, each step will be described in more detail by taking the case of manufacturing a block-type polyamideimide film as an example.

The step of preparing the oligomer may include reacting a fluorine-based aromatic diamine with an aromatic diacid dichloride in a reactor, and purifying and drying the obtained oligomer. In this case, the fluorine-based aromatic diamine may be added in a molar ratio of 1.01 to 2 compared to the aromatic diacid dichloride, and an amine-terminated polyamide oligomer monomer may be prepared. Although the molecular weight of the oligomer monomer is not particularly limited, for example, when the weight average molecular weight is in the range of 1000 to 3000 g/mol, more excellent physical properties can be obtained.

In addition, in order to introduce the amide structure, it is preferable to use an aromatic carbonyl halide monomer such as terephthaloyl chloride or isophthaloyl chloride, not terephthalic acid ester or terephthalic acid itself. This is not clear, but the chlorine element affects the physical properties of the film. Seems to be crazy.

Next, the step of preparing the polyamic acid solution may be performed through a solution polymerization reaction of reacting the prepared oligomer with a fluorine-based aromatic diamine, an aromatic dianhydride and a cycloaliphatic dianhydride in an organic solvent. At this time, the organic solvent used for the polymerization reaction is, for example, dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylformsulfoxide (DMSO), ethyl It may be any one or two or more polar solvents selected from cellosolve, methylcellosolve, acetone, diethylacetate, m-cresol, and the like.

More specifically, after reacting a fluorine-based aromatic diamine and an aromatic diacid dichloride to prepare an intermediate in the form of an oligomer including an amide unit, the oligomer and the fluorine-based aromatic diamine, an aromatic dianhydride, and a cycloaliphatic dianhydride are reacted to prepare a polyamic acid solution. By preparing and imidizing, a polyamide-imide-based film in which polyamide blocks are uniformly distributed can be prepared. As such, the polyamide-imide film having amide blocks has excellent mechanical properties over the entire area, excellent optical properties, and further improves the coating properties and coating uniformity of the coating composition used in post-coating processes such as hard coating layers. As a result, the optical properties of the final window cover film are further improved, thereby providing a film having excellent optical properties in which optical stains such as rainbow and mura do not occur.

The imidation from the polyamic acid may be performed through chemical imidation, and more preferably, the polyamic acid solution is chemically imidized using pyridine and acetic anhydride. Subsequently, imidization may be performed using an imidization catalyst and a dehydrating agent at a low temperature of 150°C or less, preferably 100°C or less, and specifically 50 to 150°C.

Through such a method, it is possible to impart uniform mechanical properties to the entire film compared to the case of a reaction of imidization by heat at high temperature.

As the imidation catalyst, any one or two or more selected from pyridine, isoquinoline, and β-quinoline may be used. In addition, as the dehydrating agent, any one or two or more selected from acetic anhydride, phthalic anhydride, and maleic anhydride may be used, but is not limited thereto.

In addition, additives such as flame retardants, adhesion enhancers, inorganic particles, antioxidants, UV inhibitors, and plasticizers may be mixed with the polyamic acid solution to prepare a polyamideimide resin.

Further, after imidation, the resin is purified using a solvent to obtain a solid content, which is dissolved in a solvent to obtain a polyamideimide solution. The solvent may include, for example, N,N-dimethylacetamide (DMAc), but is not limited thereto.

The step of forming a film of the polyamideimide solution is carried out by applying the polyamideimide solution to a substrate and then drying in a drying step partitioned into a drying region. Further, if necessary, stretching may be performed after drying or before drying, or a heat treatment step may be further provided after the drying or stretching step. As the substrate, for example, glass, stainless steel, or film may be used, but is not limited thereto. Application may be performed by die coater, air knife, reverse roll, spray, blade, casting, gravure, spin coating, or the like.

Hereinafter, a method for producing a polyimide-based film having a small number of contour lines by forming a film of a polyamideimide solution will be described.

Specifically, the polyamideimide solution is cast on a carrier film such as a polyethylene terephthalate film or a polyimide film or a stainless steel belt (SUS belt), and then prepared through primary drying, peeling, secondary drying and stretching, and tertiary drying. Can be.

An example of the film manufacturing process for satisfying the number of contour lines of the present invention will be described as an example of a step of slowly drying with a solvent content of 10 to 30% by weight in a primary drying having a plurality of heating steps, and after peeling, the first The secondary drying step of controlling the content of the solvent to 1 to 10% by weight by simultaneously performing stretching and drying at a temperature higher than the drying temperature and the solvent content is 1% by weight or less, preferably 0.3% by weight or less, within 5 minutes, preferably By adopting the third drying step of drying at high temperature within 1 to 5 minutes, the film of the present invention can be prepared. The stretching is more preferably crystallized when stretching, or a degree of not showing white turbidity due to surface damage, and very preferably by shrinking stretching after stretching, the elongation is more preferably adjusted to 0.95 to 1.1.

Hereinafter, an example is taken for each drying step.

As a preferred example of the drying step of the present invention, the number of contour lines can be further reduced by performing drying while gradually increasing the temperature by dividing into four steps during the first drying, and at this time, the last step, that is, after passing through the fourth step, the film By performing the peeling in the range of 10 to 30% by weight of, it is preferred because it is combined with the following drying step and stretching step to further reduce the number of contour lines.

In the first drying step, the drying temperature of the first step is set to 70°C to 120°C, and the drying temperature of the next step is 5 to 70°C or less, and more preferably 15 to 50°C. ℃ is preferred because it can produce a film with fewer contour lines, and the drying temperature in the last step is dried at 200°C or less, preferably 120 to 180°C, and the content of the solvent is adjusted to 10 to 30% by weight. The drying temperature in the first step is 70 to 120°C, the drying temperature in the second step is 90°C to 140°C, the drying temperature in the third step is 110°C to 160°C, and the drying temperature in the fourth step is 120°C. It may be to 180 ℃, as long as the difference between the drying temperature in each step is not particularly limited.

During the primary drying, heating may be performed using hot air, infrared rays or NIR, but is not limited thereto. Since the degree of evaporation of the solvent may vary depending on the heating method, the primary drying temperature may also vary depending on the heating method. In the polyimide-based film that has been first dried, the residual solvent amount is 10 to 30% by weight, and when the residual solvent amount is less than 10% by weight, it is difficult to peel the polyimide-based film from the support member in the subsequent process, and the number of contour lines is also achieved. It is not good because it may be difficult to do, and if it is larger than 30% by weight, not only it is difficult to maintain the shape of the polyimide-based film, but also optical properties or rainbow phenomenon may further occur, and the number of contour lines may increase.

Next, the primary dried polyimide-based film is peeled from the support member. The peeled polyimide film can be moved by a roll or the like.

Subsequently, the peeled polyimide film is subjected to secondary drying and stretching at the same time.

In the secondary drying, the residual solvent remaining in the polyimide-based film after the primary drying is further evaporated. The temperature at the time of secondary drying is set higher than the maximum temperature at the time of the primary drying to prevent defects such as tearing of the film due to stretching, and to reduce the number of contour lines. The secondary drying temperature is not particularly limited above the maximum temperature of the primary drying temperature, but may be, for example, 150 ℃ to 300 ℃. In the second drying, as in the first drying, it can be heated using hot air, infrared or NIR, and the drying temperature may vary depending on the heating method.

Next, a drawing process will be described. In the drawing of the present invention, drying is performed simultaneously with drawing.

In order to minimize the number of contour lines, stretching is preferably within a range in which no cloudiness occurs during stretching. Most preferably, it is preferred to draw the draw ratio of 0.95 to 1.1 times. The draw ratio is the same even in the case of stretching in the machine direction, the width direction, or the machine direction and the width direction. When maintaining at the above draw ratio, a film having the number of contour lines of the present invention can be obtained. Even if it is out of the above range, when excessive whitening occurs due to stretching, it is difficult to satisfy the contour line of the present invention because it is excessively crystallized or due to physical damage to the film, and it is difficult to satisfy some physical properties such as haze or transparency. It is good to keep the draw ratio.

In the present invention, when achieving the above draw ratio, it is more preferable to reduce the stretching after stretching to impart structural rearrangement of the film. For example, compared to the case of stretching and heat treatment, the number of contour lines can be reduced by 10% or more in the case of shrinking stretching after stretching, which is better.

In the present invention, maintaining the residual solvent amount of the polyimide film after secondary drying and stretching is 15% by weight or less, for example, 1 to 10% by weight or less, preferably 2 to 10% by weight, to reduce the number of contour lines. It is even better.

In the present invention, stretching may be performed in various ways, but stretching may be performed using a tenter, but is not limited thereto.

As mentioned above, the maximum temperature during stretching is higher than the temperature during primary drying, and it can be successively stretched in stages. For example, the first step may be 150°C to 200°C, the second step may be 200°C to 250°C, and the third step may be 250°C to 300°C.

In the case of stretching, as in the case of primary drying, heating may be performed using hot air or infrared rays, and the stretching temperature may vary depending on the heating method.

Subsequently, the second drying and third drying of the stretched polyimide-based film is performed to evaporate the solvent as much as possible. The third drying temperature is higher than the temperature at the time of the first drying, the second drying and stretching, and may be 200 ℃ to 500 ℃. The third drying may be heated using hot air or infrared rays, and drying may be performed in a nitrogen environment as needed. It is preferable to evaporate the residual solvent quickly during the third drying, and more preferably, dry so that the residual solvent amount is 5% by weight or less, preferably 1% by weight or less, more preferably 0.3% by weight or less, and the drying temperature is within 5 minutes It is better to carry out, preferably for 1 to 5 minutes to achieve the object of the present invention.

<Window cover film with a coating layer formed thereon and its manufacturing method>

Another aspect of the present invention is the polyimide-based film described above; It provides a window cover film comprising; and a coating layer formed on the polyimide-based film.

When the coating layer is laminated on the polyimide-based film having a specific range of surface hardness change rate, visibility is remarkably improved, and the number of contour lines is also inferior, and a window cover film can be provided.

In one aspect of the present invention, the window cover film having the hard coating layer has a light transmittance of 3% or more, measured at 388nm according to ASTM D1746, and a total light transmittance of 87% or more, 88% or more, or 89 % Or more, haze of 1.5% or less, 1.2% or less or 1.0% or less according to ASTM D1003, and yellowness of 4.0 or less, 3.0 or less or 2.0 or less, and b value of 2.0 or less, 1.5 or less or 1.2 or less according to ASTM E313 All can be satisfied.

According to an aspect of the present invention, the present invention can provide a window cover film in which various coating layers are formed for imparting the functionality of the window cover film in addition to the hard coating layer or in addition to the hard coating layer.

For a specific example, the coating layer may include any one or more layers selected from a hard coating layer, a restoration layer, an impact diffusion layer, a self-cleaning layer, an anti-fingerprint layer, an anti-scratch layer, a low refractive index layer, and an impact absorbing layer, but is limited thereto. no.

Even if the various coating layers as described above are formed on the polyimide-based film having contour characteristics of the present invention, it is possible to provide a window cover film having excellent display quality, high optical characteristics, and in particular, remarkably reducing the rainbow phenomenon.

In one aspect of the present invention, specifically, the coating layer may be formed on one side or both sides of the polyimide-based film. For example, it may be disposed on the upper surface of the polyimide-based film, and may be disposed on the upper and lower surfaces of the polyimide-based film, respectively. The coating layer may protect a polyimide-based film having excellent optical and mechanical properties from external physical or chemical damage.

In one aspect of the present invention, the coating layer may have a solid content of 0.01 to 200 g/m 2 based on the total area of the polyimide film. Preferably, based on the total area of the polyimide-based film, the solid content may be 20 to 200 g/m 2. By providing the above-described basis weight, while maintaining the functionality, surprisingly excellent rainbow phenomenon does not occur, it is possible to implement excellent visibility.

In one aspect of the present invention, specifically, the coating layer may be formed by applying a composition for forming a coating layer including a coating solvent on a polyimide-based film.

The coating solvent is not particularly limited, but may preferably be a polar solvent. For example, the polar solvent may be any one or more solvents selected from an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, an amide-based solvent, a sulfoxide-based solvent, and an aromatic hydrocarbon-based solvent. Specifically, the polar solvent is dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylformsulfoxide (DMSO), acetone, diethylacetate, propylene Glycol methyl ether, m-cresol, methanol, ethanol, isopropanol, butanol, 2-methoxyethanol, methylcellusob, ethylcellosorb, methylethylketone, methylbutylketone, methylisobutylketone, methylphenylketone, diethyl It may be any one or more solvents selected from ketone, dipropyl ketone, cyclohexanone, hexane, heptane, octane, benzene, toluene and xylene.

In one aspect of the present invention, as a method of forming a coating layer by applying a coating layer forming composition on the polyimide-based film for the coating layer, for example, a spin coating method, an immersion method, a spray method, a die coating method, Select from bar coat method, roll coater method, meniscus coat method, flexo printing method, screen printing method, bead coat method, air knife coat method, reverse roll coat method, blade coat method, casting coat method, gravure coat method, etc. Any one or more of the methods may be used, but are not limited thereto.

Preferably, in one aspect of the present invention, the coating layer may be a hard coating layer. The hard coating layer may include any one or more selected from organic materials and inorganic materials. For example, the organic material includes carbon, and may include any one or more selected from non-metal elements such as hydrogen, oxygen, and nitrogen based on carbon. The inorganic material refers to a material other than an organic material, and may include any one or more selected from metal elements such as alkaline earth metal, alkali metal, transition metal, post-transition metal and metalloid. For example, the inorganic material may include carbon dioxide, carbon monoxide, diamond, carbonate, etc. as exceptions.

In one aspect of the present invention, the hard coating layer may be an organic material layer or an inorganic material layer alone, or may be a mixed layer of organic and inorganic materials, and is not particularly limited, but preferably 10 to 90% by weight of organic material and 10 to 90% by weight of inorganic material % Can be included. Preferably, it may contain 40 to 80% by weight of an organic material and 20 to 60% by weight of an inorganic material. Even if the hard coating layer including organic materials and inorganic materials is formed as described above, it has excellent bonding with the polyimide-based film, and distortion of light does not occur. In particular, the effect of improving the rainbow phenomenon is excellent.

In one aspect of the present invention, the hard coating layer is not particularly limited, but may be a layer including any one or more polymers selected from acrylic polymers, silicone polymers, epoxy polymers, and urethane polymers.

Specifically, the hard coating layer may be formed from a composition for forming a coating layer including an epoxysilane resin to prevent deterioration of optical properties when formed on a polyimide-based film and improve surface hardness. Specifically, the epoxy siloxane resin may be a siloxane (Siloxane) resin containing an epoxy group. The epoxy group may be a cyclic epoxy group, an aliphatic epoxy group, an aromatic epoxy group, or a mixture thereof. The siloxane resin may be a polymer compound in which a silicon atom and an oxygen atom form a covalent bond.

Preferably, for example, the epoxysiloxane resin may be a silsesquioxane resin. Specifically, it may be a compound in which an epoxy group is directly substituted on a silicon atom of the silsesquioxane compound at all times, or an epoxy group is substituted by a substituent substituted on the silicon atom. As a non-limiting example, a 2-(3,4-epoxycyclohexyl) group or a 3-glycidoxy group may be substituted silsesquioxane resin.

The epoxysiloxane resin may be prepared by hydrolysis and condensation reaction between an alkoxysilane having an epoxy group alone or an alkoxysilane having an epoxy group and a heterogeneous alkoxysilane in the presence of water. In addition, the epoxysilane resin may be formed by polymerization of a silane compound containing an epoxycyclohexyl group.

For example, the alkoxysilane compound having an epoxy group is 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, and 3-glycylate. It may be any one or more selected from doxypropyltrimethoxysilane and the like.

In one aspect of the present invention, the epoxysiloxane resin may have a weight average molecular weight of 1,000 to 20,000 g/mol, but is not limited thereto. When it has a weight average molecular weight in the above range, by having an appropriate viscosity, it is possible to improve the flowability, coatability, curing reactivity, etc. of the composition for forming a coating layer, and it is possible to improve the surface hardness of the hard coating layer.

In one aspect of the present invention, the epoxysiloxane resin may contain 20 to 65% by weight, preferably 20 to 60% by weight, based on the total weight of the composition for forming a coating layer. When included in the above range, it is possible to improve the surface hardness of the hard coating layer, and to induce uniform curing to prevent physical defects such as cracks due to partial over-curing.

In one aspect of the present invention, the composition for forming the coating layer may further include a crosslinking agent and an initiator.

Specifically, the crosslinking agent is not particularly limited as long as it can form a crosslinking bond with an epoxysiloxane resin to solidify the composition for forming a coating layer and improve the hardness of the hard coating layer, but the crosslinking agent is, for example, the crosslinking agent (3 ,4-epoxycyclohexyl)methyl-3',4'-epoxycyclohexanecarboxylate, diglycidyl 1,2-cyclohexanedicarboxylate, 2-(3,4-epoxycyclohexyl-5, 5-spiro-3,4-epoxy)cyclohexane-meta-dioxane, bis (3,4-epoxycyclohexylmethyl) adipate), bis (3,4-epoxy-6-methylcyclohexyl) adipate, 3,4-epoxy-6-methylcyclohexylmethyl-3',4'-epoxy-6'-methylcyclohexanecarboxylate, 1,4-cyclohexanedimethanol bis(3,4-epoxycyclohexanecarboxyl Rate), ethylenebis(3,4-epoxycyclohexanecarboxylate), 3,4-epoxycyclohexylmethyl(meth)acrylate, bis(3,4-epoxycyclohexylmethyl) adipate, 4-vinylcyclo Hexenedioxide, vinylcyclohexene monooxide, 1,4-cyclohexanedimethanol diglycidyl ether and 2,2'-((1-methylethylidene)bis(cyclohexane-4,1-diyloxy It may be any one or more selected from methylene)) bisoxirane. Preferably, (3,4-epoxycyclohexyl) methyl-3',4'-epoxycyclohexane carboxylate and bis(3,4-epoxycyclohexyl) containing a compound to which two 3,4-epoxycyclohexyl groups are linked Hexylmethyl) adipate) may be any one or more selected from.

In one aspect of the present invention, the content of the crosslinking agent is not particularly limited, and may include, for example, 5 to 150 parts by weight based on 100 parts by weight of the epoxysiloxane resin. In addition, according to an aspect of the present invention, the crosslinking agent may contain 3 to 30% by weight, and preferably 5 to 20% by weight, based on the total weight of the composition for forming a coating layer. In the case of the above range, it is possible to improve the coating properties and curing reactivity of the composition for forming a coating layer.

In one aspect of the present invention, the initiator may be a photoinitiator or a thermal initiator. Preferably, it is a photoinitiator, and for example, the photoinitiator may include a photo-cationic initiator. The photo-cationic initiator may initiate polymerization of the epoxysiloxane resin and the epoxy-based monomer.

Specifically, the photocationic initiator may be any one or more selected from an onium salt and an organometallic salt, but is not limited thereto. For example, it may be one or more selected from diaryliodonium salt, triarylsulfonium salt, aryldiazonium salt, and iron-arene complex, but is not limited thereto.

In one aspect of the present invention, the content of the photoinitiator is not particularly limited, and may include, for example, 1 to 15 parts by weight based on 100 parts by weight of the epoxy siloxane resin. In addition, according to an aspect of the present invention, the crosslinking agent may contain 0.1 to 10% by weight, preferably 0.3 to 5% by weight, based on the total weight of the composition for forming a coating layer. When the content of the photoinitiator is included in the above range, the hard coating layer has excellent curing efficiency, and property degradation due to residual components after curing can be prevented.

In one aspect of the present invention, the composition for forming the coating layer is a filler, a lubricant, a light stabilizer, a thermal polymerization inhibitor, a leveling agent, a lubricant, an antifouling agent, a thickener, a surfactant, an antifoaming agent, an antistatic agent, a dispersing agent, an initiator, a coupling agent. , Antioxidants, UV stabilizers, colorants, etc. may further include any one or more additives selected from, but is not limited thereto.

The hard coating layer may further include inorganic particles to impart hardness. The inorganic particles may preferably be silica, more preferably surface-treated silica, but are not limited thereto. In this case, the surface treatment may include a functional group capable of reacting with the crosslinking agent described above.

According to one aspect, the inorganic particles may have an average diameter of 1 to 500 nm, preferably 10 to 300 nm, but are not limited thereto.

When forming the hard coating layer as described above on a conventional polyimide-based film, the rainbow phenomenon could not be escaped due to distortion of light. However, in the polyimide-based film according to the present invention, even if the hard coating layer as described above is formed, a rainbow phenomenon hardly occurs, and excellent visibility can be implemented.

In one aspect of the present invention, the window cover film may further include a base layer. The base layer may be formed on the other surface of the polyimide-based film on which the coating layer is not formed.

In one aspect of the present invention, the polyimide-based film may be prepared as a film and then laminated on the base layer, and may be laminated after applying and coating a polyamic acid resin composition that is a precursor of the polyimide-based film. However, it is not particularly limited as long as it can form the above-described stacked configuration.

In one aspect of the present invention, the base layer is not particularly limited as long as it is a base film of a commonly used window cover film, but, for example, any selected from ester polymer, carbonate polymer, styrene polymer and acrylic polymer, etc. It may contain more than one. Specifically, for example, it may include any one or more selected from polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, polycarbonate, polystyrene and polymethyl methacrylate, but is limited thereto. It is not.

In one aspect of the present invention, the base layer may be a single layer, or a multilayer in which two or more are stacked. Specifically, the base layer may be laminated including an optical adhesive layer at the interface of two or more base films.

In one aspect of the present invention, the base layer may have a thickness of 50 to 300 μm. Preferably it may be 100 to 300㎛, and more preferably may be 150 to 250㎛. By having the above thickness, not only the mechanical properties are satisfied, but also when the polyimide-based film is laminated, the distortion of light can be significantly reduced.

In one aspect of the present invention, for a specific example, the optical adhesive layer is selected from an optical transparent adhesive (OCA, Optical clear adhesive), an optical transparent resin (OCR, Optical clear resin) and a pressure sensitive adhesive (PSA, Pressure sensitive adhesive), etc. It may include any one or more, but is not limited thereto.

In one aspect of the present invention, the window cover film may further include a second optical adhesive layer at the interface between the base layer and the polyimide film.

Specifically, the second optical adhesive layer formed at the interface between the base layer and the polyimide film may be the same as or different from the optical adhesive layer in the above-described gaseous layer, and may be formed to a thickness of, for example, 20 to 120 μm. have. Preferably it may be formed of 20 to 80㎛. When formed with a thickness within the above range, the window cover film may implement excellent optical properties and light distortion improvement effects as a whole.

In one aspect of the present invention, the window cover film is excellent as a window substrate on the outermost surface of a flexible display panel because it has high surface hardness and excellent flexibility, is lighter than tempered glass, and has excellent durability against deformation.

Another aspect of the present invention provides a display device including a display panel and the above-described window cover film formed on the display panel.

In one aspect of the present invention, the display device is not particularly limited as long as it is a field requiring excellent optical properties, and a display panel suitable therefor may be selected and provided. Preferably, the window cover film may be applied to a flexible display device, and specific examples include any one or more selected from various image display devices such as a liquid crystal display device, an electroluminescent display device, a plasma display device, and a field emission display device. It may be included in the image display device and applied, but is not limited thereto.

In the display device including the window cover film of the present invention described above, not only the display quality is excellent, but also the distortion caused by light is significantly reduced, so that the rainbow phenomenon in which iridescent spots are generated is remarkably improved, and excellent visibility. It can minimize the user's eyestrain.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples. However, the following Examples and Comparative Examples are only one example for describing the present invention in more detail, and the present invention is not limited by the following Examples and Comparative Examples.

The following physical properties were measured as follows.

1) Pencil hardness

For the film, according to JISK5400, a line of 20 mm was drawn at a rate of 50 mm/sec using a load of 750 g, and the pencil hardness was measured based on a case where a scratch occurred no more than once by repeating it 5 or more times.

2) Modulus/Elongation at break

In accordance with ASTM E111, a polyamideimide film having a thickness of 50 µm, a length of 50 mm, and a width of 10 mm was measured using UTM 3365 of Instron under the conditions of pulling at 50 mm/min at 25°C. The unit of modulus is GPa, and the unit of elongation at break is %.

3) light transmittance

According to ASTM D1746 standard, the total light transmittance and UV/Vis (Shimadzu, UV3600) measured over the entire 400 to 700 nm wavelength range using a Spectrophotometer (Nippon Denshoku, COH-400) were used for a 50 μm thick film. Thus, the single wavelength light transmittance measured at 388 nm was measured. The unit is %.

4) haze

It was measured using a Spectrophotometer (Nippon Denshoku, COH-400) based on a film having a thickness of 50 μm according to ASTM D1003 standard. The unit is %.

5) Yellowness (YI) and b* value

It was measured using a Colorimeter (HunterLab, ColorQuest XE) based on a film having a thickness of 50 μm in accordance with ASTM E313 standard.

6) Weight average molecular weight (Mw) and polydispersity index (PDI)

The weight average molecular weight and polydispersity index of the prepared film were measured using GPC (Waters GPC system, Waters 1515 isocratic HPLC Pump, Waters 2414 Reflective Index detector) by dissolving the film sample in DMAc eluent containing 0.05M LiBr. In the measurement, the GPC column was connected to Olexis, Polypore and mixed D columns, the solvent was DMAc solution, the standard was polymethyl methacrylate (PMMA STD), 35 ℃, flow of 1mL / min It was analyzed by rate.

7) Rainbow observation

After blackening one side of the film, it was observed whether rainbow occurred with the naked eye under a three-wavelength lamp in a dark room.

Top: Rainbow is not visible, and uniform color is shown

Medium: The rainbow phenomenon is light, and the color is uniform.

Bottom: The rainbow looks strong and the color is strong

8) Number of contour lines

Three films were prepared by randomly selecting three regions of 50 mm width and 50 mm length on the film. Using an interference fringe inspection lamp (FNATECH, FNA-35S), a sodium light source that emits a wavelength range between 550 and 600 nm is used, and in a bright and dark contrast picture that can be seen with the naked eye when vertically illuminated on three films. The dark part is defined as a contour line. If the dark side is a circle with a filled center, the entire circle is considered as a single contour line. The number of contour lines was evaluated by evaluating the number of contour lines meeting the diagonal lines when a line was drawn in the diagonal direction. When the shape of the contour line meeting the diagonal line is circular, the number of contour lines meeting the diagonal line is assumed to be two. In addition, the spacing of the contour lines is the spacing of the contour lines obtained from the diagonal line in which the number of contour lines is large among the two diagonal lines.

The method of calculating the contour line is defined as drawing two diagonal lines in a 50 mm horizontal and 50 mm vertical area, and dividing the sum of the number of contour lines obtained by two diagonal lines by 2. For example, in FIG. 1, the number of contour lines is 13 on a diagonal line from 11 o'clock to 5 o'clock, and 16 on a diagonal line from 1 o'clock to 7 o'clock, so it is assumed that (13+16)/2=14.5.

In addition, two diagonal lines were drawn for each of the three films, the number of contour lines meeting each diagonal line was measured, and the average of all three regions was calculated as the number of contour lines.

For example, if the average value of the contour lines meeting two diagonal lines in the first area is 5, and the average value of the contour lines existing on the two diagonal lines in each of the second area and the third area is 8, the number of contour lines is (5+8) +8)/3=7.

[Example 1]

Terephthaloyl dichloride (TPC) and 2,2'-bis(trifluoromethyl)-benzidine (TFMB) were added to a mixed solution of dichloromethane and pyridine in a reactor, and stirred at 25° C. for 2 hours under a nitrogen atmosphere. At this time, the molar ratio of TPC:TFMB was set to 300:400, and the solid content was adjusted to be 10% by weight. Thereafter, the reactant was precipitated in an excess of methanol, and the solid content obtained by filtration was vacuum-dried at 50° C. for 6 hours or longer to obtain an oligomer, and the FW (Formula Weight) of the prepared oligomer was 1670 g/mol.

N,N-dimethylacetamide (DMAc), 100 moles of the oligomer and 28.6 moles of 2,2'-bis(trifluoromethyl)-benzidine (TFMB) were added to the reactor as a solvent and stirred sufficiently. After confirming that the solid raw material has been completely dissolved, fumed silica (surface area 95 m 2 /g, <1 μm) is added to DMAc in an amount of 1000 ppm relative to the solid content, and then dispersed using ultrasonic waves. 64.1 mol of cyclobutanetetracarboxylic dianhydride (CBDA) and 64.1 mol of 4,4'-hexafluoroisopropylidene diphthalic anhydride (6FDA) were sequentially added and sufficiently stirred, and then at 40°C. Polymerized for 10 hours. At this time, the content of the solid content was 20% by weight. Then, pyridine (Pyridine) and acetic anhydride (Acetic Anhydride) were sequentially added to the solution in an amount of 2.5 times the total dianhydride content, and stirred at 60° C. for 12 hours.

After the polymerization was completed, the polymerization solution was precipitated in an excess of methanol, and then the solid content obtained by filtration was vacuum-dried at 50° C. for 6 hours or more to obtain a polyamideimide powder. The powder was diluted and dissolved in DMAc at 20% by weight to prepare a polyimide resin solution.

The polyimide resin solution was continuously coated on a glass support at room temperature using a slot die, and dried in a drying area designed with four drying areas. The first drying area was dried at 90℃ for 2 minutes, the second drying area was dried at 125℃ for 2 minutes, the third drying area was dried at 130℃ for 2 minutes, and the fourth drying area was dried at 150℃ for 2 minutes. I did. The solvent content of the film passed through the drying area was 21% by weight.

Subsequently, the dried film was peeled off from the support, and stretching and drying were performed using a pin tenter. The stretching area was divided into three areas, the first stretching area was non-stretched at 160°C, the second stretching area was set to 210°C, and 1.02 times the film width of the first stretching area was stretched, and the third The stretching area was set to 260° C., and the stretching width of the second stretching area was maintained as it is. The solvent content of the film passing through the stretched region was adjusted to 9% by weight.

Next, the stretched film was quickly dried at 300° C. for 3 minutes to prepare a film having a residual solvent amount of 1%.

The prepared polyamideimide film has a thickness of 50 μm, a total light transmittance of 89.73%, a haze of 0.4, a yellowness (YI) of 1.9, a b* value of 1.0, a modulus of 6.5 GPa, an elongation at break of 21.2%, and a weight average. The molecular weight was 310,000 g/mol, the polydispersity index (PDI) was 2.11, and the pencil hardness was HB. In addition, as a result of measuring the number of contour lines, it was confirmed that there were 9, and the case where the distance between the contour lines meeting the diagonal line was 2 mm or less was 2 on average, and the distance between the contour lines was also distant, so optical characteristics were excellent. In addition, it was confirmed that the visibility was excellent because no rainbow was observed.

[Example 2]

The same polyimide resin solution as in Example 1 was continuously coated on a glass support at room temperature using a slot die, and dried in a drying zone designed with four drying zones. The first drying area was dried at 70℃ for 2 minutes, the second drying area was dried at 130℃ for 2 minutes, the third drying area was dried at 145℃ for 2 minutes, and the fourth drying area was dried at 160℃ for 2 minutes. I did. The solvent content of the film passed through the drying area was 18% by weight.

Except for, it carried out similarly to Example 1, and produced the film.

The prepared polyamideimide film has a thickness of 50 μm, a total light transmittance of 89.73%, a haze of 0.4, a yellowness (YI) of 1.9, a b* value of 1.0, a modulus of 6.5 GPa, an elongation at break of 21.2%, and a weight average. The molecular weight was 310,000 g/mol, the polydispersity index (PDI) was 2.11, and the pencil hardness was HB. In addition, as a result of measuring the number of contour lines, it was confirmed that there were 19, and an average of 3 cases where the distance between the contour lines meeting the diagonal line was 2 mm or less. In addition, it was confirmed that the visibility was excellent because no rainbow was observed.

[Example 3]

The same polyimide resin solution as in Example 1 was continuously coated on a glass support at room temperature using a slot die, and dried in a drying zone designed with four drying zones. Subsequently, the dried film was peeled off from the support, and stretching and drying were performed using a pin tenter. The stretching area was divided into three areas, the first stretching area was non-stretched at 160°C, the second stretching area was set to 210°C, and the film width of the first stretching area was stretched 1.05 times, and the third The stretching area was set at 260° C. and relaxed to reduce the stretching ratio to 1.02 times the stretching ratio. The solvent content of the film passing through the stretched region was adjusted to 7% by weight. Next, the stretched film was dried at 200° C. for 1 minute to prepare a film having a residual solvent amount of 0.8%.

The prepared polyamideimide film has a thickness of 50 μm, a total light transmittance of 89.73%, a haze of 0.4, a yellowness (YI) of 1.9, a b* value of 1.0, a modulus of 6.5 GPa, an elongation at break of 21.2%, and a weight average. The molecular weight was 310,000 g/mol, the polydispersity index (PDI) was 2.11, and the pencil hardness was HB. In addition, as a result of measuring the number of contour lines, it was confirmed that there were 5, and the average of 3 cases where the distance between the diagonal lines and the contour lines meeting was 2 mm or less. In addition, since no rainbow was observed, it was confirmed that the visibility was more excellent.

[Example 4]

In Example 1, the same was carried out except that the draw ratio was stretched 1.8 times in the machine direction. There was no cloudiness during stretching, and as a result of measuring the number of contour lines of the prepared film, it was 19, and the average of 5 cases where the distance between the contour lines meeting the diagonal line was 2 mm or less. In addition, it was confirmed that no rainbow was observed.

[Comparative Example 1]

The same polyimide resin solution as in Example 1 was continuously coated on a glass support at room temperature using a slot die, dried at 80° C. for 30 minutes, 100° C. for 1 hour, and cooled at room temperature. The film was prepared. At this time, the solvent content of the film was 35% by weight. Thereafter, the film was peeled off, and stretching was performed 1.05 times while drying at 150°C. Then, a stepwise heat treatment was performed at 250 to 300° C. for 2 hours at a heating rate of 20° C./min. At this time, the solvent content of the film was 3% by weight.

The prepared polyamideimide film has a thickness of 50 μm, a total light transmittance of 87.5%, a haze of 0.6, a yellowness (YI) of 1.9, a b* value of 1.0, a modulus of 6.5 GPa, an elongation at break of 21.2%, and a weight average. The molecular weight was 310,000 g/mol, the polydispersity index (PDI) was 2.11, and the pencil hardness was HB. In addition, as a result of measuring the number of contour lines, it was confirmed that it was 30, and the average of 10 cases where the distance between the contour lines meeting the diagonal line was 2 mm or less. In addition, it was confirmed that the rainbow phenomenon appeared soft.

[Comparative Example 2]

Add 100 parts by weight of N,N-dimethylacetamide (DMAc) and 2,2'-bis(trifluoromethyl)-benzidine (TFMB) to the reactor under a nitrogen atmosphere, and stir sufficiently, and then 4,4'-hexafluoroiso 30 parts by weight of propylidene diphthalic anhydride (6FDA) was added and sufficiently stirred until dissolved. Thereafter, 30 parts by weight of 3,3', 4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and sufficiently stirred until dissolved. Thereafter, 40 parts by weight of terephthaloyl dichloride (TPC) was added and stirred for 6 hours to dissolve and react to prepare a polyamic acid resin composition. Each monomer was adjusted to be 6.5% by weight of solid content. To the composition, pyridine (Pyridine) and acetic anhydride (Acetic Anhydride) were sequentially added to 2.5 times the number of moles of the total dianhydride, and stirred at 60° C. for 1 hour. Thereafter, the solution was precipitated in an excess of methanol, and then the solid content obtained by filtration was vacuum-dried at 50° C. for 6 hours or more to obtain polyamideimide powder. The powder was diluted and dissolved in DMAc at 20% by weight to prepare a composition for forming a base layer.

The composition for forming the base layer was prepared under the same conditions as in Comparative Example 1. The thickness of the film was 50 μm.

As a result of measuring the physical properties of the prepared film, the total light transmittance was 87.03%, the haze was 0.67%, the yellowness (YI) was 2.6, and the b* value was 1.55.

In addition, as a result of measuring the number of contour lines of the prepared film, it was confirmed that it was 47, and an average of 20 cases where the distance between the contour lines meeting the diagonal line was 2 mm or less. In addition, it was confirmed that rainbow was observed.

Although the present invention has been described through the above-specified matters and limited embodiments, this is only provided to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments, to which the present invention pertains. Those of ordinary skill in the field can make various modifications and variations from these descriptions.

Therefore, the spirit of the present invention is limited to the described embodiments and should not be defined, and all those having equivalent or equivalent modifications to the claims as well as the claims to be described later fall within the scope of the present invention. .

Claims (11)

When the interference pattern inspection lamp (FUNATECH, FNA-35S) is vertically illuminated on a film of 50 mm in width and 50 mm in length, and two lines are drawn in the diagonal direction of the film, the sum of the number of contour lines that meet the two diagonal lines is 2 A polyimide-based film in which the number of contour lines divided by 2 to 20 and the interval between the contour lines meeting the diagonal line is 2 mm or less is 5 or less. delete The method of claim 1,
The polyimide-based film is a polyimide-based film having a modulus of 3 GPa or more and an elongation at break of 8% or more according to ASTM E111. The method of claim 1,
The polyimide-based film has a light transmittance of 2% or more measured at 388 nm according to ASTM D1746, a total light transmittance of 87% or more, a haze of 2.0% or less, a yellowness of 5.0 or less, and a b* value measured at 400 to 700 nm. This polyimide film is 2.0 or less. The method of claim 1,
The polyimide-based film is a polyimide-based film having a polyamide-imide structure. The method of claim 1,
The polyimide film is a polyimide film comprising a unit derived from a fluorine-based aromatic diamine, a unit derived from an aromatic dianhydride, and a unit derived from an aromatic diacid dichloride. The method of claim 6,
The polyimide-based film further comprises a unit derived from a cycloaliphatic dianhydride. The method of claim 1,
The polyimide-based film has a thickness of 30 to 110 µm. The polyimide film of any one of claims 1 and 3 to 8; And
A coating layer formed on one or both surfaces of the polyimide film;
Window cover film comprising a. The method of claim 9,
The coating layer is any one or more selected from a hard coating layer, an antistatic layer, an anti-fingerprint layer, an antifouling layer, an anti-scratch layer, a low refractive layer, an antireflection layer, and an impact absorbing layer. A flexible display panel comprising the polyimide-based film of any one of claims 1, 3 to 8.

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