KR20210116067A - Polyimide film having excellent moisture resistance and low water absorption - Google Patents

Abstract

The present invention relates to a polyimide film copolymerized by including at least one diamine and at least one acid dianhydride, and more specifically, to a polyimide film that has excellent transparency while securing excellent moisture resistance and moisture absorption characteristics, thereby being used as a cover window of a display.

Description

Polyimide film having moisture absorption and absorption properties {POLYIMIDE FILM HAVING EXCELLENT MOISTURE RESISTANCE AND LOW WATER ABSORPTION}

The present invention relates to a polyimide film, and more particularly, to a polyimide film that can be used as a cover window of a display by having high transparency while simultaneously securing excellent moisture absorption resistance and absorption resistance.

A cover window for protecting a panel is applied to a surface of a display device such as a liquid crystal display (LCD) or an organic light emitting display (OLED). Tempered glass having excellent flatness, heat resistance, chemical resistance and barrier performance against moisture or gas, a small coefficient of linear expansion (CTE), and high light transmittance has been mainly used as a material of a conventional cover window.

Meanwhile, flexible displays such as curved displays or in-folding displays have recently been developed. In order to be applied to such a flexible display, the cover window must also have flexibility, but the conventional glass cover window is generally heavy and fragile, and is not suitable for the flexible display due to poor flexibility.

In order to solve the above problems, recently, cover windows using a plastic material having relatively free formability have been proposed. A cover window using a plastic material has advantages of being light, not easily broken, and implementing various designs. Currently, polycarbonate, polyethylene terephthalate, polymethyl methacrylate, etc. having excellent transparency are mainly used as plastic materials for cover windows. Although these materials have the advantage of excellent transparency, their application is limited due to poor heat resistance with a glass transition temperature (Tg) of 150° C. or less, and poor chemical resistance and mechanical strength. In addition, the cover window is disposed at the outermost portion of the flexible display device. When the above-described materials are applied and continuously exposed to external ultraviolet rays, a yellowing phenomenon occurs, which adversely affects the visibility of the display.

On the other hand, when the cover window is made of a material having a high absorption rate, there is a problem in that internal stress is accumulated in the base film and the adhesive layer. In addition, when moisture introduced into the atmosphere is rapidly released to the outside by heating, a change in dimensions and optical properties of the film constituting the cover window occurs. Accordingly, a decrease in adhesion between materials due to warpage or peeling occurs, as well as problems such as yellowing or whitening, which adversely affects the visibility of the display.

The present invention has been devised to solve the above problems, and it is a novel polyimide film that can be applied as a cover window due to excellent properties such as transparency, flexibility, and mechanical properties while simultaneously securing improved moisture absorption and absorption resistance. intended to provide

In order to achieve the above object, at least one diamine; and at least one acid dianhydride copolymerized, wherein the moisture absorption rate after 72 hours treatment at 85° C. and 85% relative humidity is 1.0% or less, and the water absorption rate after 2 hours treatment at 100° C. is 3.0% or less and a polyimide film having a yellowness change (ΔY.I) of 0.5 or less after moisture absorption treatment or absorption treatment.

In one embodiment of the present invention, the polyimide film has a moisture absorption rate of 0.9% or less, a water absorption rate of 2.5% or less, a change in yellowness after moisture absorption treatment (ΔY.I), and a change in yellowness after absorption treatment (ΔY). .I) may each be 0.5 or less.

In one embodiment of the present invention, the polyimide film may have a light transmittance of 85% or more at a wavelength of 550 nm at a thickness of 30 to 100 μm, and an initial yellowness of 5 or less according to ASTM E313-73 standard.

In one embodiment of the present invention, the diamine may include at least one aromatic diamine, or may include an aromatic diamine and an alicyclic diamine.

In one embodiment of the present invention, the aromatic diamine and the alicyclic diamine may be included in a ratio of 70 to 100: 0 to 30 mol%.

In one embodiment of the present invention, the aromatic diamine is a fluorinated first diamine; It may include at least one selected from the group consisting of a sulfone-based second diamine, a hydroxy-based third diamine, an ether-based fourth diamine, and a non-fluorine-based fifth diamine.

In one embodiment of the present invention, the acid dianhydride may include at least one aromatic acid dianhydride, or may include an aromatic acid dianhydride and an alicyclic acid dianhydride.

In one embodiment of the present invention, the aromatic acid dianhydride and the alicyclic acid dianhydride may be included in a ratio of 70 to 100: 0 to 30 mol%.

In one embodiment of the present invention, the aromatic acid dianhydride may include at least one selected from the group consisting of fluorinated aromatic primary acid dianhydride, non-fluorinated aromatic secondary acid dianhydride, and sulfone-based aromatic tertiary acid dianhydride. have.

In one embodiment of the present invention, the ratio (a/b) of the number of moles of the diamine (a) and the acid dianhydride (b) may be in the range of 0.7 to 1.3.

In one embodiment of the present invention, the polyimide film may be used as a cover window of a display device.

According to one embodiment of the present invention, it is possible to secure excellent moisture absorption resistance and absorption resistance characteristics through the adoption of predetermined components constituting the polyimide film and control of its content, and warpage through such moisture absorption and absorption characteristics Prevents delamination and minimizes yellowing.

In addition, the present invention exhibits high light transmittance, low yellowness, and excellent moisture absorption and absorption resistance, thereby improving workability and reliability of the final product.

Accordingly, the polyimide film of the present invention can be usefully applied as a cover window for display devices and flexible displays in the art, including flat panel display panels, and other IT products, electronic products, home appliances, etc. known in the art. is also applicable.

The effect according to the present invention is not limited by the contents exemplified above, and more various effects are included in the present specification.

Hereinafter, the present invention will be described in detail. Examples of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art, and the following examples may be modified in various other forms, and the scope of the present invention is not limited to the following examples It is not limited to an example. In this case, like reference numerals refer to like structures throughout this specification.

Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used with the meaning commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, terms defined in a commonly used dictionary are not to be interpreted ideally or excessively unless clearly specifically defined.

In addition, throughout the specification, when a part "includes" a certain component, this means that other components may be further included, rather than excluding other components, unless otherwise stated. In addition, throughout the specification, "on" or "on" means that it includes not only the case where it is located above or below the target part, but also the case where there is another part in the middle, and the direction of gravity must be It does not mean that it is positioned above the reference. And, in the present specification, terms such as “first” and “second” do not indicate any order or importance, but are used to distinguish components from each other.

<Polyimide film>

The polyimide resin film according to an embodiment of the present invention is a transparent film that can be provided in a display device, and more specifically, can be used as a cover window of a flexible display.

Here, the cover window refers to a film disposed at the outermost portion of the flexible display device to protect the display device. The cover window may be a window film alone or a film in which an adhesive layer and a window coating layer are formed on a separate substrate film made of an optically transparent resin.

On the other hand, the cover window of the display exposed to the outside must have processing characteristics such as flexibility and excellent optical characteristics in daily life, and also must support excellent adhesion to other substrates. When the conventional plastic window has high water absorption and moisture absorption, the dimensional change of the film itself occurs due to the inflow of moisture present in the atmosphere, as well as reduced adhesion to other adjacent substrates, and/or yellowing, etc. of the optical properties is deteriorated. Accordingly, it is difficult to be applied as a cover window of a foldable display.

In contrast, the polyimide film according to the present invention has excellent moisture absorption and absorption resistance compared to conventionally known plastic films, and the amount of yellowness change (ΔY.I) according to the moisture absorption/absorption treatment is below a specific range. characterized in that it is minimized. Accordingly, the polyimide film can be applied without limitation to display devices known in the art, and in particular, when applied as a cover window of an in-folding or out-folding type foldable mobile phone, It can continuously exhibit high optical properties and excellent adhesion through excellent moisture absorption/absorption properties.

In one embodiment of the present invention, the polyimide film may include at least one diamine; and at least one acid dianhydride as a copolymer, wherein the moisture absorption rate is 1.0% or less, the water absorption rate is 3.0% or less, and the amount of yellowness change (ΔY) according to the moisture absorption / absorption treatment .I) may be 0.5 or less.

In the present specification, 'moisture absorption' refers to the amount of change (percentage) between the weight and the initial dry weight after moisture absorption treatment of the polyimide film under predetermined conditions (eg, 85° C. and 85% relative humidity for 72 hours). it means. In addition, 'water absorption' refers to the amount of change (percentage) between the weight and the initial dry weight after absorption treatment of the polyimide film under predetermined conditions (eg, immersed in distilled water and left at 100°C for 2 hours). In addition, in the present specification, 'yellowness change amount (ΔY.I)' refers to a change value between yellowness and initial yellowness after at least one of the above-described moisture absorption treatment and absorption treatment is performed.

Here, the above-described moisture absorption rate, water absorption rate, and yellowness change value (ΔY.I) may be affected by the thickness of the film. The values of the moisture absorption rate, water absorption rate, and yellowness change value (ΔY.I) may be measured based on the thickness of the polyimide film 10 to 100 μm, specifically 20 to 90 μm, more specifically 80±5 μm. Also, in the present invention, the change in yellowness (eg, ΔY.I) means a value measured based on a predetermined thickness of the polyimide film, but is not particularly limited thereto, and the yellowness according to the change in thickness of the polyimide film It is also within the scope of the present invention to express the change value (eg, ΔY.I) as a ratio.

Specifically, the polyimide film according to the present invention may have a moisture absorption rate of 1.0% or less, more specifically 0.9% or less, after 72 hours of treatment at 85° C. and 85% relative humidity. In addition, the polyimide film may have a water absorption rate of 3.0% or less after treatment at 100° C. for 2 hours, and specifically 2.5% or less. In this case, the lower limit of the moisture absorption treatment and the absorption treatment is not particularly limited, and may be, for example, more than 0%.

In addition, in the polyimide film according to the present invention, the change value (ΔY.I) between the yellowness and the initial yellowness after being treated under at least one of a predetermined moisture absorption condition and an absorption condition may be 0.5 or less. Specifically, the amount of change in yellowness and initial yellowness after moisture absorption (ΔY.I); And the amount of change (ΔY.I) of the yellowness and the initial yellowness after the absorption treatment is 0.5 or less, and more specifically, it may be more than 0 and 0.5 or less.

In the case of the polyimide film of the present invention having the above-mentioned moisture absorption rate, water absorption rate, yellowness change (ΔY.I) parameters and corresponding values, it has high resistance to moisture even under a harsh environment, so that it maintains high optical properties and excellent adhesion. can be maintained as

In order for the polyimide film according to the present invention to be used as a cover window for a mobile communication terminal or a tablet PC, it must have excellent optical properties such as high transparency and light transmittance in order to increase the visibility of the display screen.

For another embodiment of the present invention, the polyimide film may have a light transmittance of 85% or more at a wavelength of 550 nm at a thickness of 30 to 100 μm, specifically 89% or more, and more specifically 90% to 99%. have. In addition, the yellowness (Y.I.) according to the ASTM E313 standard may be 5 or less, specifically 4 or less, and more specifically 3.5 or less. The aforementioned yellowness may mean an initial yellowness value before moisture absorption and absorption treatment is performed.

The polyimide film according to the present invention is not particularly limited, as long as it satisfies the above-described moisture absorption resistance, water absorption resistance and low yellowness characteristics, components constituting the polyimide resin and/or its composition.

For example, the polyimide film may include at least one at least one diamine; and at least one acid dianhydride. Specifically, the polyamic acid composition including the aforementioned diamine, acid dianhydride, and, if necessary, a solvent may be imidized and heat-treated at a high temperature.

In general, polyimide (PI) resin refers to a high heat-resistant resin manufactured by preparing a polyamic acid derivative by solution polymerization of an aromatic acid dianhydride and an aromatic diamine or aromatic diisocyanate, and then imidizing it by ring-closing dehydration at a high temperature. The polyimide resin is a polymer material containing an imide ring, and has excellent heat resistance, chemical resistance, abrasion resistance and electrical properties based on the chemical stability of the imide ring. The polyimide resin may be in the form of a random copolymer or a block copolymer.

The diamine (a) component constituting the polyimide film of the present invention is not limited as long as it is a compound having an intramolecular diamine structure, and common diamine compounds known in the art may be used without limitation. For example, an aromatic, alicyclic, or aliphatic compound having a diamine structure, or a combination thereof may be used.

In particular, in the present invention, the excellent moisture absorption resistance and water absorption resistance of the polyimide film; Considering optical properties such as high light transmittance, low YI, and low haze, at least one aromatic diamine may be used, or the aromatic diamine and the alicyclic diamine may be mixed. .

Specific examples of the aforementioned aromatic diamine include fluorine-based, sulfone-based, hydroxy-based, ether-based, and non-fluorine-based diamines having a fluorinated substituent, either alone or in appropriate combination. The above can be mixed. Accordingly, in the present invention, as the diamine compound, fluorinated aromatic first diamine, sulfone-based aromatic second diamine, hydroxy-based aromatic third diamine, ether-based aromatic fourth diamine, and non-fluorine-based aromatic fifth diamine are used as diamine compounds. Each of them may be used alone, or two or more thereof may be used as a mixture.

Non-limiting examples of diamine monomers (a) that can be used include oxydianiline (ODA), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (2,2'-TFDB) ), 2,2'-bis (trifluoromethyl) -4,3'-diaminobiphenyl (2,2'-Bis (trifluoromethyl) -4,3'-Diaminobiphenyl), 2,2'-bis ( Trifluoromethyl)-5,5'-diaminobiphenyl (2,2'-Bis(trifluoromethyl) -5,5'-Diaminobiphenyl), 2,2'-bis(trifluoromethyl)-4,4 '-diaminophenyl ether (2,2'-Bis(trifluoromethyl)-4,4'-diaminodiphenyl ether, 6-FODA), bisaminohydroxyphenyl hexafluoropropane (DBOH), bisaminophenoxyphenyl hexafluoro Ropropane (4BDAF), bisaminophenoxyphenylpropane (6HMDA), bisaminophenoxydiphenylsulfone (DBSDA), bis(4-aminophenyl)sulfone (4,4'-DDS), bis(3-aminophenyl) ) sulfone (3,3'-DDS), sulfonyldiphthalic anhydride (SO2DPA), 4,4'-oxydianiline (4,4'-ODA), or one or a mixture of two or more thereof form, etc., can be applied.

Considering the high transparency, high glass transition temperature, and low yellowness of the polyimide film, fluorinated primary diamine can induce linear polymerization of 2,2'-bis(trifluoromethyl)-4,4 '-diaminobiphenyl (2,2'-TFDB), 1,4-Bis(4-amino-2-trifluoromethylphenoxy)benzene (6-FAPB) may be used. In addition, as the sulfone-based second diamine, bis(4-aminophenyl)sulfone (4,4'-DDS) or 3,3'-DDS may be used. In addition, the hydroxy tertiary diamine is 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (2,2-bis (3-amino-4-hydroxyphenyl) -hexafluoropropane, BIS-AP -AF) can be used. In addition, as the ether-based quaternary diamine, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6-FODA) or oxydianiline (ODA) may be used. In addition, as the non-fluorine-based fifth diamine, 2,2-bis (3-amino-4-methylphenyl)-hexafluoropropane (2,2-Bis (3-amino-4-methylphenyl)-hexafluoropropane, BIS-AT-AF ), m-tolidine, or p-phenylenediamine (p-PDA) may be used.

In the diamine monomer (a) of the present invention, the content of the fluorinated aromatic first diamine, sulfone-based aromatic second diamine, hydroxy-type aromatic third diamine, ether-based aromatic fourth diamine, non-fluorine-based aromatic fifth diamine, etc. is particularly Although not limited, each may be 0 to 100 mol% based on 100 mol% of the total diamine, specifically 10 to 90 mol%, more specifically 20 to 80 mol%. However, the content of at least one of the first to fifth diamines is included to satisfy 100 mol% of the total diamine.

Non-limiting examples of alicyclic diamines compatible with the aforementioned aromatic diamines include 2,2-bis(3-amino-4-hydroxycyclohexyl)hexafluoropropane [2,2-bis(3) -amino-4-hydroxy cyclohexyl)hexafluoropropane], 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane (MACM), 4,4'-methylenebicyclohexylamine (PACM), 1,3 -Bis(aminomethyl)cyclohexane (1,3-BAC), 1,4-bis(aminomethyl)cyclohexane (1,4-BAC), cis-1,2-cyclohexanedimethanamine, trans-1 ,2-cyclohexanedimethanamine, bis(4-aminocyclohexyl) ether, N-(4-aminocyclohexyl)-1,4-cyclohexanediamine, or a mixture thereof may be used.

In the diamine monomer (a) of the present invention, the mixing ratio of the aromatic diamine and the alicyclic diamine may be 70 to 100: 0 to 30 mol% based on 100 mol% of the total diamine, and specifically 80 to 100: 0 to 20 It may be a mole % ratio.

If a preferred example of the present invention is given, as the diamine (a), the first fluorinated aromatic diamine and the fourth etheric aromatic diamine may be mixed. At this time, their use ratio is not particularly limited, and may be, for example, a ratio of 60 to 95: 40 to 5 mol%.

In another preferred example of the present invention, at least one fluorinated aromatic primary diamine may be mixed as the acid dianhydride (b). At this time, their ratio may be 50 to 80: 20 to 50 mol%, but is not particularly limited thereto.

As the acid dianhydride (b) monomer constituting the polyimide film of the present invention, conventional compounds known in the art having an intramolecular acid dianhydride structure may be used without limitation. For example, an aromatic, alicyclic, or aliphatic compound having an acid dianhydride structure, or a combination thereof, may be used, and specifically, at least one aromatic acid dianhydride is used, or the aromatic acid dianhydride and the alicyclic compound are used. Group acid dianhydride can be mixed (混用).

Specific examples of the above-mentioned aromatic acid dianhydride include fluorinated aromatic primary acid dianhydride, non-fluorinated aromatic secondary acid dianhydride, and sulfone-based aromatic tertiary acid dianhydride used alone or in a combination form in which at least two or more thereof are mixed. have.

The fluorinated first acid dianhydride monomer is not particularly limited as long as it is an aromatic acid dianhydride into which a fluorine substituent is introduced. Non-limiting examples of the fluorinated first acid dianhydride that can be used include 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride (2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 6-FDA), and 4-(trifluoromethyl)pyromellitic dianhydride (4-(trifluoromethyl)pyromellitic dianhydride, 4-TFPMDA). These may be used alone or in combination of two or more. Among fluorinated acid dianhydrides, 6-FDA is a very suitable compound for transparency because it has a very high property of limiting the formation of a change transfer complex (CTC) between and within molecular chains.

The non-fluorinated secondary acid dianhydride monomer is not particularly limited as long as it is a non-fluorinated aromatic acid dianhydride into which a fluorine substituent is not introduced. Non-limiting examples of non-fluorinated tertiary acid dianhydride monomers that can be used include Pyromellitic Dianhydride (PMDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (3 ,3′,4,4′-Biphenyl tetracarboxylic acid dianhydride, BPDA), benzophenone tetracarboxylic dianhydride (BTDA), oxydiphthalic dianhydride (ODPA), 4,4-(4,4-Isopropylidenediphenoxy) )bis(phthalic anhydride) (BPADA), bis(carboxyphenyl)dimethylsilane dianhydride (Bis(3,4dicarboxyphenyl)dimethylsilanedianhydride, SiDA), and the like. These may be used alone, or two or more thereof may be used in combination.

In addition, the sulfone-based tertiary acid dianhydride monomer is not particularly limited as long as it is an acid dianhydride introduced with a sulfone group. For example, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride (3,3', 4,4'-DIPHENYLSULFONETETRACARBOXYLIC DIANHYDRIDE (DSDA).

In the acid dianhydride monomer (b) of the present invention, the content of the fluorinated aromatic primary acid dianhydride, the non-fluorinated aromatic secondary acid dianhydride, and the sulfonic aromatic tertiary acid dianhydride is not particularly limited. For example, they may be included in the range of 0 to 100 mol%, specifically 10 to 90 mol%, and more specifically 20 to 80 mol%, based on 100 mol% of the total acid dianhydride. However, the content of at least one of the first acid dianhydride to the third acid dianhydride is included to satisfy 100 mol% of the total acid dianhydride.

The alicyclic acid dianhydride is not particularly limited as long as it is a compound having an acid dianhydride structure while having an alicyclic ring rather than an aromatic ring in the compound. Non-limiting examples of alicyclic acid dianhydrides compatible with the aforementioned aromatic acid dianhydride include cyclobutane tetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentane tetracarboxylic Dianhydride (CPDA), bicyclo[2,2,2]-7-octene-2,3,5,6-tetracarboxylic acid dianhydride (BCDA), 4-(2,5-dioxotetra) Hydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (TDA), 1,1'-bicyclohexane-3,3',4 ,4'-tetracarboxylic dianhydride (H-BPDA), 1,2,4,5-cyclohexane-tetracarboxylic dianhydride (H-PMDA), Bicyclo[2.2.2]octane-2 ,3,5,6-tetracarboxylic2,3:5,6-dianhydride (7CI,8CI) or a mixture of one or more thereof.

In the acid dianhydride monomer (b) of the present invention, the mixing ratio of the aromatic acid dianhydride and the alicyclic acid dianhydride may be 70 to 100: 0 to 30 mol% based on 100 mol% of the total acid dianhydride, and specifically 80 to 100 : It may be in a ratio of 0 to 20 mol%.

In a preferred example of the present invention, as the acid dianhydride (b), a fluorinated primary acid dianhydride and a non-fluorinated secondary acid dianhydride may be mixed. At this time, their use ratio is not particularly limited, and may be, for example, a ratio of 10 to 80: 90 to 20 mol%.

In another preferred example of the present invention, at least one non-fluorinated tertiary acid dianhydride may be mixed as the acid dianhydride (b). At this time, their ratio may be 50 to 80: 20 to 50 mol%, but is not particularly limited thereto.

In another preferred example of the present invention, as the acid dianhydride (b), an alicyclic acid dianhydride and a non-fluorinated second acid dianhydride may be mixed. At this time, their ratio may be 5 to 30: 95 to 70 mol%, but is not particularly limited thereto.

In the polyamic acid composition constituting the polyimide film of the present invention, the ratio (a/b) of the number of moles of the diamine component (a) to the number of moles of the acid dianhydride component (b) may be 0.7 to 1.3, preferably 0.8 to 1.2, and more preferably 0.9 to 1.1.

The polyimide film of the present invention constituted as described above includes a repeating unit obtained from at least one aromatic diamine and at least one aromatic acid dianhydride. When a repeating unit composed of such an aromatic diamine and an aromatic acid dianhydride is included, excellent moisture absorption and absorption resistance properties are exhibited, and yellowing phenomenon can be minimized after moisture absorption/absorption treatment. In addition, it contains the main chain of a polyimide composed of an aromatic diamine and an aromatic acid dianhydride, and even if a predetermined alicyclic component (eg, diamine, acid dianhydride) is included, it exhibits excellent moisture absorption resistance and absorption resistance, and yellowing according to it The phenomenon can be minimized.

The polyamic acid composition of the present invention may use, without limitation, an organic solvent known in the art as a solvent for the solution polymerization of the above-mentioned monomers. Examples of usable solvents include m-cresol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), acetone, diethyl At least one polar solvent selected from acetate and dimethyl phthalate (DMP) may be used. In addition, a low-boiling solution such as tetrahydrofuran (THF), chloroform, or a solvent such as γ-butyrolactone may be used. At this time, the content of the solvent (the first solvent for polymerization) is not particularly limited, but is preferably 50 to 95% by weight based on the total weight of the polyamic acid composition in order to obtain an appropriate molecular weight and viscosity of the polyamic acid composition (polyamic acid solution). , More preferably, it may be included in the range of 70 to 90% by weight.

The polyamic acid composition described above can be prepared by adding at least one kind of acid dianhydride and at least one kind of diamine to an organic solvent and then reacting, for example, diamine (a) and acid dianhydride (b) to improve the physical properties of polyimide. ) can be adjusted to an equivalence ratio of approximately 1:1. The composition of the polyamic acid composition is not particularly limited, and for example, based on 100% by weight of the total weight of the polyamic acid composition, 2.5 to 25.0% by weight of acid dianhydride, 2.5 to 25.0% by weight of diamine, and the remaining amount satisfying 100% by weight of the composition It may be composed of an organic solvent. Here, the content of the organic solvent may be 70 to 90% by weight. In addition, the polyamic acid composition may be included in the range of 30 to 70 wt% of acid dianhydride, and 30 to 70 wt% of diamine, based on 100 wt% of the solid content, but is not particularly limited thereto.

The polyamic acid composition constituted as described above may have a viscosity in the range of about 1,000 to 200,000 cps, preferably about 5,000 to 50,000 cps. When the viscosity of the polyamic acid composition falls within the above-mentioned range, thickness control during coating of the polyamic acid composition is easy, and the coating surface can be uniformly exhibited.

If necessary, the polyamic acid composition may contain a small amount of at least one additive such as a plasticizer, an antioxidant, a flame retardant, a dispersant, a viscosity modifier, a leveling agent, etc. within a range that does not significantly impair the purpose and effect of the present invention. can

The polyimide resin film according to the present invention may be prepared according to a conventional method known in the art, for example, 30 to 350 after coating (casting) the above-described polyamic acid composition on a substrate, for example, a glass substrate. It can be prepared by inducing the imide ring closure reaction (Imidazation) for 0.5 to 8 hours while gradually increasing the temperature in the range of °C.

At this time, the coating method can be used without limitation a conventional method known in the art, for example, spin coating (Spin coating), dip coating (Dip coating), solvent casting (Solvent casting), slot die coating (Slot die coating) and It may be made by at least one method selected from the group consisting of spray coating. The polyamic acid composition may be coated at least once or more so that the colorless and transparent polyimide resin layer has a thickness of several hundred nm to several tens of μm.

In the polyimide film manufacturing method according to the present invention, the imidization method applied to the imidization step by casting the polymerized polyamic acid to a support is thermal imidization method, chemical imidization method, or thermal imidization method and chemical It can be applied in combination with the imidization method.

The thermal imidization method is a method of obtaining a polyimide film by casting a polyamic acid composition (polyamic acid solution) on a support and heating it for 1 to 10 hours while gradually increasing the temperature in a temperature range of 30 to 400°C.

In addition, the chemical imidization method is a method of adding a dehydrating agent represented by an acid anhydride such as acetic anhydride and an imidization catalyst represented by amines such as isoquinoline, β-picoline, and pyridine to the polyamic acid composition. When the thermal imidization method or the thermal imidization method is used in combination with the chemical imidization method, the heating conditions of the polyamic acid composition may vary depending on the type of the polyamic acid composition, the thickness of the polyimide film to be prepared, and the like.

More specifically, when the thermal imidization method and the chemical imidization method are used in combination, a dehydrating agent and an imidization catalyst are added to the polyamic acid composition and cast on a support, then 80 to 300° C., preferably 150 to 250 After partial curing and drying by heating at °C to activate the dehydrating agent and imidization catalyst, a polyimide film can be obtained.

The thickness of the polyimide film thus formed is not particularly limited and may be appropriately adjusted according to the field to which it is applied. For example, it may be in the range of 10 to 150 μm, preferably in the range of 30 to 100 μm.

The polyimide film and modifications thereof of the present invention prepared as described above can be usefully used in various fields requiring excellent moisture absorption/absorption properties and excellent optical properties. In particular, it is applied as a cover window of the display device to prevent surface abrasion and to provide excellent flexibility and visibility to the flexible display device.

In the present invention, a display device refers to a flexible display device or a non-flexible display device that displays an image, and includes a flat panel display device (FPD) as well as a curved display device. , a foldable display device, a flexible display device, a foldable mobile phone, a smart phone, a mobile communication terminal, or a tablet PC. Specifically, the display device includes a liquid crystal display, an electrophoretic display, an organic light emitting display, an inorganic EL display, and a field emission display. It may be a field emission display device, a surface-conduction electron-emitter display device, a plasma display device, a cathode ray tube display device, or electronic paper. For example, it may be a flat panel display panel such as LCD, PDP, or OLED. Not limited to the above-mentioned use, the polyimide film of the present invention may be applied to a conventional display device known in the art, and may be utilized as a substrate or a protective film for other flexible displays.

A specific example of the display device provided with the above-described polyimide film includes a display unit, a polarizing plate, a touch screen panel, a cover window, and a protective film, wherein the cover window is a polyimide according to an embodiment of the present invention. It may include a film. Here, each component constituting the display device is not particularly limited, and may include conventional components known in the art.

Hereinafter, the present invention will be described in more detail through specific examples. The following examples are merely examples to help the understanding of the present invention, and the scope of the present invention is not limited thereto.

[Examples 1-5. polyimide film production]

A polyamic acid composition was prepared using a composition including diamine and acid dianhydride shown in Table 1 below.

After coating the polyamic acid composition on a glass plate for LCD using a bar coater, in a nitrogen atmosphere convection oven at 80° C. for 30 minutes, 150° C. for 30 minutes, 200° C. for 1 hour, at 300° C. 1 While gradually raising the temperature step by step with time, drying and imide ring closure reaction (Imidazation) were carried out. Thus, a polyimide film having a film thickness of 80 µm having an imidization ratio of 85% or more was produced. Thereafter, the polyimide film was separated from the glass plate and taken.

Diamine (mol%) Acid dianhydride (mol%) first monomer second monomer first monomer second monomer Example 1 TFDB(100) - BPADA(70) BPDA(30) Example 2 TFDB(100) - BPDA(80) 6FDA(20) Example 3 BIS-AT-AF(100) - 6FDA(60) BPADA(40) Example 4 TFDB(80) 6FODA(20) BPDA(90) CBDA(10) Example 5 TFDB(80) 6FAPB(20) BPADA(80) CBDA(20) Comparative Example 1 TFDB(100) - CBDA(70) BPDA(30) Comparative Example 2 TFDB(100) - CBDA(80) 6FDA(20) Comparative Example 3 BIS-AT-AF(100) - 6FDA(60) CpODA(40) Comparative Example 4 TFDB(80) 6FODA(20) BPDA(60) CPDA(40) Comparative Example 5 TFDB(80) 6FAPB(20) BPADA(60) CHDA(40)

[Comparative Examples 1 to 5. polyimide film production]

Except for using the composition shown in Table 1 above, in the same manner as in Examples 1 to 5, polyimide films of Comparative Examples 1 to 5 were prepared, respectively.

[Experimental example. Physical property evaluation]

The physical properties of the polyimide resin films prepared in Examples 1 to 5 and Comparative Examples 1 to 5 were evaluated in the following manner, and the results are shown in Table 2 below. At this time, each physical property in Table 2 is based on a thickness of 80 μm.

<Method for evaluating physical properties>

1) Measurement of light transmittance

At 400nm and 550nm wavelengths, using a UV-Vis NIR Spectrophotometer, measurements were made at a C light source and a viewing angle of 2 degrees, which is the standard of ASTM E313-73.

2) Yellowness measurement

The yellowness at 550 nm was measured according to ASTM E313 standard using a UV spectrometer (Cotica Minolta CM-3700d).

3) thickness measurement

After coating a transparent polyamic acid resin with a film thickness of 20 μm or less on a silicon wafer, drying and imide ring closure reaction were carried out. did.

4) Measurement of moisture absorption

The prepared polyimide resin film was cut into a square having a size of 5 cm × 5 cm. After drying the cut specimen at 110° C. for 1 hour, the weight was measured and this was used as the initial weight (W1). The specimen, whose initial weight was measured, was placed in a thermo-hygrostat at 85° C./relative humidity of 85% and subjected to moisture absorption treatment for 72 hours. The moisture absorption was calculated by substituting the measured values into the following [Equation 1].

[Equation 1]

Moisture absorption (%) = [(W2-W1)/W1] X 100

5) Absorption rate measurement

The prepared polyimide resin film was cut into a square having a size of 5 cm × 5 cm. After drying the cut specimen at 110° C. for 1 hour, the weight was measured and this was used as the initial weight (W1). After measuring the initial weight, the specimen was immersed in distilled water at 100° C. for 2 hours, and the weight thereof was measured to be the weight (W3) after absorption treatment. The absorption rate was calculated by substituting the measured values into the following [Equation 2].

[Equation 2]

Absorption rate (%) = [(W3-W1)/W1] X 100

6) Measurement of yellowness change (ΔY.I) after moisture absorption and absorption treatment

After the moisture absorption treatment and the absorption treatment were respectively performed, the yellowness was measured, and the amount of change in the yellowness was expressed according to the following [Equation 3].

[Equation 3]

ΔY.I = Y.I measured after standing in a moisture absorption condition (or absorption condition) - Initial Y.I

thickness
(μm) Moisture absorption (%)
[85℃, 85%, 72h] Absorption rate (%)
[100℃, 2h] %T.
(@550nm) Early Y.I. ΔY.I
(after moisture absorption) ΔY.I
(after absorption) Example 1 80 0.6 2.1 89.6 2.9 0.1 0.2 Example 2 0.7 2.2 89.9 2.7 0.2 0.3 Example 3 0.8 2.2 89.5 3.0 0.2 0.3 Example 4 0.9 2.3 89.3 2.8 0.3 0.4 Example 5 0.9 2.4 89.9 2.6 0.4 0.5 Comparative Example 1 80 2.1 4.9 88.8 2.5 2.3 3.5 Comparative Example 2 2.4 5.2 89.1 2.1 2.8 4.2 Comparative Example 3 2.3 4.3 89.3 3.0 1.9 3.1 Comparative Example 4 2.8 4.4 89.2 3.3 1.7 3.0 Comparative Example 5 2.9 4.5 89.1 3.8 2.1 3.4

As shown in Table 2, the polyimide film according to the present invention not only has more improved properties in terms of moisture absorption and absorption rate, but also minimizes the yellowness change value due to moisture absorption and absorption treatment to continuously maintain high optical properties. was able to confirm that

Specifically, when it is composed of an aromatic diamine and an aromatic acid dianhydride, it can be seen that it has excellent moisture absorption and absorption resistance and low yellowness change, and when the alicyclic diamine and/or the alicyclic acid dianhydride is included in a predetermined range or less There was no significant change in the moisture absorption rate, water absorption rate and yellowing properties of the film. On the other hand, in the case of Comparative Example in which an alicyclic component is included in a certain amount or more, it can be seen that the moisture absorption rate and water absorption rate characteristics of the polyimide film are rapidly decreased, and thus it can be seen that yellowing is necessarily caused.

Accordingly, it was confirmed that the polyimide film of the present invention can be usefully applied as a cover window of a display device as it has excellent moisture absorption and absorption resistance and high optical properties.

Claims (11)

at least one diamine; And a polyimide film copolymerized including at least one acid dianhydride,
The moisture absorption rate is 1.0% or less after 72 hours of treatment at 85°C and 85% relative humidity.
The water absorption rate after 2 hours treatment at 100 ° C is 3.0% or less,
The polyimide film whose yellowness change amount (ΔY.I) after moisture absorption treatment or absorption treatment is 0.5 or less. According to claim 1,
Moisture absorption is less than 0.9%,
Absorption rate is less than 2.5%,
The polyimide film, wherein the amount of change in yellowness (ΔY.I) after the moisture absorption treatment and the amount of change in yellowness (ΔY.I) after the absorption treatment are 0.5 or less, respectively. According to claim 1,
At a thickness of 30 to 100 μm, the light transmittance at a wavelength of 550 nm is 85% or more,
A polyimide film having a yellowness of 5 or less according to ASTM E313-73 standard. According to claim 1,
The diamine comprises at least one aromatic diamine, or a polyimide film comprising an aromatic diamine and an alicyclic diamine. 5. The method of claim 4,
The aromatic diamine and the cycloaliphatic diamine are included in a ratio of 70 to 100: 0 to 30 mol%, a polyimide film. 5. The method of claim 4,
The aromatic diamine is a fluorinated first diamine; A polyimide film comprising at least one selected from the group consisting of a sulfone-based second diamine, a hydroxy-based third diamine, an ether-based fourth diamine, and a non-fluorine-based fifth diamine. According to claim 1,
The acid dianhydride is a polyimide film comprising at least one aromatic acid dianhydride, or an aromatic acid dianhydride and an alicyclic acid dianhydride. 8. The method of claim 7,
The aromatic acid dianhydride and the alicyclic acid dianhydride are 70 to 100: 0 to 30 mol% ratio, the polyimide film. 8. The method of claim 7,
The aromatic acid dianhydride is a polyimide film comprising at least one selected from the group consisting of a fluorinated aromatic primary acid dianhydride, a non-fluorinated aromatic secondary acid dianhydride, and a sulfone-based aromatic tertiary acid dianhydride. According to claim 1,
A ratio (a/b) of the number of moles of the diamine (a) and the acid dianhydride (b) is in the range of 0.7 to 1.3. According to claim 1,
A polyimide film used as a cover window for display devices.