Polyamide film with improved coating adhesion and method for manufacturing the same

Abstract

To provide a polyamide-based film that is used as a cover window of a flexible display device, which has improved coating adhesiveness by primer treatment, and a method for producing the same.SOLUTION: A multilayer film includes a base material layer containing a polyamide-based polymer, and a primer layer formed on the base material layer, wherein the primer layer contains 60-95 wt.% of a polyester-based resin based on the total weight of the primer layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polyamide film with improved coating adhesion and a method for producing the same. [Background technology]

[0002] Display technology continues to develop, supported by the demand accompanying the advancement of IT equipment. In recent years, flexible display devices, which can bend and flexibly deform in response to external forces, have become popular in the mobile device field, where large screens and portability are required simultaneously. In particular, foldable display devices have the major advantage of being able to be folded down to a small size when not in use to increase portability, and then unfolded to provide a large screen when in use.

[0003] Polymer films are preferred as cover windows for these flexible display devices. For example, polyamide-imide (PAI) films are widely used because they are transparent, flexible, and have excellent mechanical properties.

[0004] However, such polyamide films are vulnerable to external scratches, and further improvements are needed in terms of properties required for cover windows, such as fingerprint resistance and antistatic properties.

[0005] For example, Patent Document 1 discloses a cover window film having a hard coat layer and an anti-fingerprint layer formed on a substrate layer made of polyamide-imide (PAI) resin, and a configuration for applying it to a flexible display. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Korean Registered Patent No. 2147367 [Overview of the project]

Problems to be Solved by the Invention

[0007] Currently, polyamide-based films used as cover windows for flexible display devices have difficulty ensuring adhesion to various primer layers such as hard coat layers and optical adhesive layers (OCA) that are coated or adhered to their surfaces, whether used without surface treatment or surface-treated with a normal primer.

[0008] As a result of research by the present inventors, by forming a primer layer with a specific composition containing a polyester-based resin on a polyamide-based substrate layer, the adhesion to functional coating layers such as hard coat layers or OCA layers is improved, and it has been found that the external optical properties and mechanical properties are also improved.

[0009] Therefore, the problem of the implementation example is to provide a polyamide-based film with improved coating adhesion by primer treatment and a method for producing the same.

Means for Solving the Problems

[0010] A multilayer film according to one implementation example includes a substrate layer containing a polyamide-based polymer and a primer layer formed on the substrate layer, and the primer layer contains 60% to 95% by weight of a polyester-based resin based on the total weight of the primer layer.

[0011] The multilayer film according to the implementation example includes a step of preparing a substrate layer containing a polyamide-based polymer and a step of applying and drying a primer layer composition on the substrate layer, and the primer layer composition contains a polymer resin and a solvent, and the polymer resin contains 60% to 95% by weight of a polyester-based resin based on the total weight of the solid content of the primer layer composition.

Effects of the Invention

[0012] The multilayer film according to the above realization example is provided with a primer layer having a specific composition containing a polyester-based resin on a polyamide-based substrate layer, and not only has excellent adhesion to functional layers such as a hard coat layer and an OCA layer coated or adhered to its surface, but also has excellent optical and mechanical properties outside of that.

[0013] Therefore, the multilayer film according to the above realization example can be provided with various functional layers such as a hard coat layer, an anti-fingerprint layer, an anti-static layer, an anti-glare layer, an anti-reflection layer, and an optical adhesive layer for realizing the characteristics required for a cover window of a display device such as a flexible display device.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 shows a cross-sectional view of a multilayer film according to one realization example. [Figure 2] FIG. 2 shows a cross-sectional view of a multilayer film according to another realization example. [Figure 3] FIG. 3 shows a cross-sectional view of a multilayer film according to still another realization example. [Figure 4] FIG. 4 shows the cross-cut test evaluation criteria according to ASTM D3359 Method B. [Figure 5] FIG. 5 shows the 180° peel strength test method according to ASTM D903 standard. [Figure 6] FIG. 6 shows the sessile drop method for calculating the surface energy.

Modes for Carrying Out the Invention

[0017] In this specification, terms used to refer to each component are used to distinguish them from other components and are not intended to limit the scope of the examples provided. Furthermore, in this specification, singular expressions include plural expressions unless the context clearly indicates a different meaning.

[0018] In this specification, the word "includes" is used to specify particular characteristics, areas, stages, processes, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, stages, processes, elements, and / or components unless otherwise stated.

[0019] In this specification, terms such as "first," "second," etc., are used to describe various components, and such components should not be limited by such terms. These terms are used for the purpose of distinguishing one component from another.

[0020] The molecular weights of the compounds or polymers described herein, such as the number-average molecular weight or weight-average molecular weight, are, as is well known, relative masses based on carbon-12 and do not have units listed, but may be understood as equivalent molar masses (g / mol) if necessary.

[0021] In this specification, "substituted" means, unless otherwise specified, deuterium, -F, -Cl, -Br, -I, hydroxyl group, cyano group, nitro group, amino group, amide group, hydrazine group, hydrazone group, ester group, ketone group, carboxyl group, substituted or unsubstituted C1-C 30 Alkyl alkyl groups, substituted or unsubstituted C2-C 30Alkenyl group, substituted or unsubstituted C2-C 30 Alkynyl group, substituted or unsubstituted C1-C 30 Alkoxy group, substituted or unsubstituted C6-C 30 Alicyclic organic group, substituted or unsubstituted C4-C 30 Heterocyclic group, substituted or unsubstituted C6-C 30 Aryl groups, and substituted or unsubstituted C4-C 30 This refers to a molecule substituted with one or more substituents selected from the group consisting of heteroaryl groups, and two adjacent substituents may be linked to form a ring.

[0022] [Multilayer film] Figure 1 shows a cross-sectional view of a multilayer film based on one implementation example. Referring to Figure 1, a multilayer film 11 according to one example includes a base layer 100 containing a polyamide polymer and a primer layer 200 formed on the base layer 100.

[0023] In one implementation example, the primer layer 200 contains 60% to 95% by weight of a polyester resin based on the total weight of the primer layer.

[0024] Furthermore, the primer layer may further contain 5% to 40% by weight of a polyurethane resin based on the total weight of the primer layer.

[0025] The multilayer film according to the above-described example, by having a primer layer with the above-described composition on a polyamide substrate layer, not only exhibits excellent adhesion to functional layers such as hard coat layers and OCA layers coated or bonded to its surface, but can also improve optical and mechanical properties. On the other hand, if the composition of the substrate layer and primer layer falls outside the above range, the surface energy of the primer layer decreases, which can lead to poor adhesion to functional layers such as hard coat layers and OCA layers coated or bonded to its surface, as well as poor optical and mechanical properties.

[0026] A method for manufacturing a multilayer film according to one example includes the steps of preparing a substrate layer containing a polyamide polymer and applying and drying a primer layer composition onto the substrate layer.

[0027] In one example, the primer layer composition comprises a polymer resin and a solvent, wherein the polymer resin contains 60% to 95% by weight of a polyester resin based on the total weight of the solids in the primer layer composition.

[0028] As an example, the solvent may contain more than 75% by weight of water and less than 25% by weight of isopropyl alcohol, based on the total weight of the solvent.

[0029] The primer layer has a certain level of surface energy, which provides excellent adhesion to adjacent layers.

[0030] For example, the surface energy of the primer layer may be 10 dyne or more, 20 dyne or more, 30 dyne or more, 35 dyne or more, 40 dyne or more, or 45 dyne or more, and may also be 100 dyne or less, 90 dyne or less, 80 dyne or less, 70 dyne or less, 60 dyne or less, 55 dyne or less, or 50 dyne or less. As a specific example, the surface energy of the primer layer may be 30 dyne to 70 dyne. As a more specific example, the surface energy of the primer layer may be 35 dyne to 70 dyne, 35 dyne to 65 dyne, 35 dyne to 60 dyne, 35 dyne to 55 dyne, 35 dyne to 50 dyne, or 35 dyne to 45 dyne, but is not limited to these.

[0031] The aforementioned surface energy can be measured by methods known in the art, such as the sessile drop method, but is not particularly limited. Referring to Figure 6, the sessile drop method is a method of calculating the surface energy of a sample by first measuring the contact angle (θ) of the test liquid 3 with respect to the surface of the sample surface 10c, and then using the surface tension of the test liquid, etc., which is known.

[0032] As a result, in the multilayer film according to the above-mentioned example, the adhesion between the primer layer and the substrate layer can be extremely excellent.

[0033] For example, the result of a cross-cut test on the surface of the primer layer according to the ASTM D3359 standard may be 3B or higher. More specifically, the result of a cross-cut test on the surface of the primer layer according to the ASTM D3359 standard may be 4B or higher. More specifically, the result of a cross-cut test on the surface of the primer layer according to the ASTM D3359 standard may be 5B or higher.

[0034] The aforementioned cross-cut test involves cutting the sample surface into a grid pattern at regular intervals, applying and removing adhesive tape, and then measuring the number of grid units that did not produce flakes. According to the ASTM D3359 standard (Method B), the sample is evaluated into five grades (from 0B to 5B) based on the percentage of grid units that did not produce flakes relative to the total number of grid units. A higher grade number indicates better interlayer adhesion (see Figure 4).

[0035] Figure 2 shows a cross-sectional view of a multilayer film from another implementation example. Referring to Figure 2, the multilayer film 12 may further include a functional layer 300.

[0036] In the multilayer film 12, the primer layer 200 may be interposed between the substrate layer 100 and the functional layer 300.

[0037] The functional layer may be a hard coat layer, an optical adhesive layer, a printed coating layer, a fingerprint-resistant layer, an antistatic layer, an anti-glare layer, an anti-reflective layer, and is not particularly limited.

[0038] For example, the functional layer may be one or more selected from the group consisting of a hard coat layer, an optical adhesive layer, and a printed coating layer.

[0039] As a specific example, the multilayer film may have a structure consisting of a hard coat layer, a primer layer, and a substrate layer.

[0040] As another specific example, the multilayer film may have a print coating layer / primer layer / substrate layer structure.

[0041] As another specific example, the multilayer film may have a structure of a substrate layer / primer layer / optical adhesive layer.

[0042] Figure 3 shows a cross-sectional view of a multilayer film from another implementation example. Referring to Figure 3, the multilayer film 13 may include two or more functional layers 310, 320. In the multilayer film 13, a first primer layer 210 is interposed between the base layer 100 and the first functional layer 310, and a second primer layer 220 is interposed between the base layer 100 and the second functional layer 320.

[0043] As a specific example, the multilayer film may have a structure consisting of a hard coat layer, a first primer layer, a substrate layer, a second primer layer, and an optical adhesive layer.

[0044] As another specific example, the multilayer film may have a structure of print coating layer / first primer layer / substrate layer / second primer layer / optical adhesive layer.

[0045] As another specific example, the multilayer film may have a structure of hard coat layer / first primer layer / substrate layer / second primer layer / print coat layer.

[0046] The first primer layer and the second primer layer may have the same composition and properties.

[0047] On the other hand, the first primer layer and the second primer layer may differ in terms of composition and / or properties.

[0048] For example, the first primer layer may contain a polyester resin, and the second primer layer may contain a polyurethane resin. Furthermore, the first primer layer may have a thickness of, for example, 0.03 μm to 1.0 μm, and the second primer layer may have a thickness of, for example, 0.03 μm to 0.3 μm.

[0049] As a specific example, the first functional layer may be a hard coat layer, and the second functional layer may be an optical adhesive layer or a printed coating layer, but is not limited to these.

[0050] In the aforementioned multilayer film, the primer layer can improve the adhesion between the functional layer and the substrate layer.

[0051] As an example, the hard coat layer or printed coat layer formed on the primer layer may have improved adhesion to the substrate layer via the primer layer. Specifically, the surface of the hard coat layer or printed coat layer may have a cross-cut test result of 3B or higher, 4B or higher, or more specifically, 5B or higher, according to the ASTM D3359 standard (see Figure 4).

[0052] As another example, an optical adhesive layer formed by laminating an optical adhesive (OCA) sheet onto the primer layer may have improved adhesion to the substrate layer via the primer layer. Specifically, the 180° peel strength of the optical adhesive layer to the substrate layer according to ASTM D903 may be 0.8 kgf / inch or more. More specifically, the peel strength may be 0.9 kgf / inch or more, 1.0 kgf / inch or more, or 1.1 kgf / inch or more. The upper limit of the peel strength is not particularly limited, but for example, it may be 10 kgf / inch or less, 5 kgf / inch or less, 3 kgf / inch or less, or 2 kgf / inch or less. The peel strength is obtained by measuring the load applied while peeling the two layers whose adhesion strength is to be measured 180° at a constant speed. The peel strength can be measured using a peel tester or a universal tester.

[0053] Figure 5 shows the 180° peel strength test method according to the ASTM D903 standard. Referring to Figure 5, the base material layer 10a of the sample is attached to the alignment plate 21 and fixed with the upper jig 22a, and then the functional layer 10b of the sample to be measured for peel strength is fixed to the lower jig 22b. Then, the upper jig 22a is raised at a constant speed, and the peel strength can be obtained by measuring the load applied while peeling the functional layer 10b from the base material layer 10a of the sample by 180°.

[0054] The multilayer film according to the above-described example has excellent optical properties and is advantageous for application to the cover window of a display device.

[0055] The multilayer film according to the above-mentioned example has a light transmittance, for example, an average visible light transmittance, that is above a certain level, specifically 70% or more, 75% or more, 80% or more, 82% or more, 83% or more, 85% or more, 88% or more, 89% or more, or 90% or more. On the other hand, the upper limit of the light transmittance range of the film is not particularly limited, but could be, for example, 100% or less, 95% or less, or 92% or less. Such transmittance can be measured, for example, using a haze meter NDH-5000W from Nippon Denshoku Industries Co., Ltd., in accordance with the JIS K7136 standard.

[0056] Furthermore, the multilayer film according to the above-mentioned example has a haze level below a specific level, which may be, for example, 5% or less, 4% or less, 3.5% or less, 3% or less, 2% or less, 1.5% or less, 1.2% or less, or 1% or less. On the other hand, the lower limit of the haze range of the film is not particularly limited, but may be, for example, 0% or more, or 0.5% or more. Such haze can be measured, for example, using the NDH-5000W haze meter from Nippon Denshoku Industries Co., Ltd., in accordance with the JIS K7136 standard.

[0057] Furthermore, the yellowness index (YI) of the substrate is 5 or less, and may be, for example, 4.5 or less, 4 or less, 3.8 or less, 3.5 or less, 3 or less, 2.8 or less, 2.5 or less, or 2.3 or less, but is not limited to these values.

[0058] As a specific example, the multilayer film may have a haze of 3% or less, a light transmittance of 85% or more, and a yellowness index (YI) of 5 or less.

[0059] The following will provide a detailed explanation of each constituent layer of the multilayer film based on the above-mentioned implementation example.

[0060] [Primer layer] The primer layer is formed on the substrate layer. The primer layer contains a polymer resin, and may include, for example, a curable resin, specifically a thermosetting resin or a UV-curable resin. The polymer resin can form a solid phase structure of the primer layer upon curing.

[0061] The primer layer may further contain one or more polymer resins selected from polyester resins, polyurethane resins, acrylic resins, silicone resins, and epoxy resins.

[0062] According to one example, the primer layer contains a polyester resin. The polyester resin content in the primer layer may be 60% to 95% by weight based on the total weight of the primer layer. For example, the polyester resin content in the primer layer may be 60% or more by weight, 65% or more by weight, 70% or more by weight, or 75% or more by weight, and may also be 95% or less by weight, 90% or less by weight, 85% or less by weight, or 80% or less by weight. Specifically, the primer layer may be, but is not limited to, 65% to 95% by weight, 70% to 95% by weight, or 70% to 90% by weight based on the total weight of the primer layer.

[0063] The polyester resin may be a monopolymer resin or copolymer resin obtained by polycondensation of a dicarboxylic acid and a diol. Alternatively, the polyester resin may be a blended resin obtained by mixing the monopolymer resin or copolymer resin.

[0064] Examples of the aforementioned dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, 2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid, diphenylsulfoncarboxylic acid, anthracenedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, malonic acid, dimethylmalonic acid, succinic acid, 3,3-diethylsuccinic acid, glutaric acid, 2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid, trimethyladipic acid, pimelic acid, azelaic acid, sebacic acid, suberic acid, and dodecadicarboxylic acid.

[0065] Examples of the aforementioned diols include ethylene glycol, propylene glycol, hexamethylene glycol, neopentyl glycol, 1,2-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone.

[0066] As a specific example, the polyester resin may contain a monomer composition of terephthalic acid and ethylene glycol. As another specific example, the polyester resin may contain a monomer composition of terephthalic acid and neopentyl glycol. The weight-average molecular weight (Mw) of the polyester resin may be, for example, 10,000 to 100,000, or 10,000 to 50,000. The polyester resin may have a hydroxyl group or a carboxyl group as a functional group.

[0067] In other realizations, the primer layer may further contain a polyurethane resin. For example, the content of the polyurethane resin in the primer layer may be 5% by weight or more, 10% by weight or more, 15% by weight or more, or 20% by weight or more, and may also be 40% by weight or less, 35% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, or 15% by weight or less. Specifically, the primer layer may further contain, but is not limited to, 5% to 35% by weight or 10% to 30% by weight of polyurethane resin based on the total weight of the primer layer.

[0068] The polyurethane resin may be formed by the reaction of a diisocyanate compound and a polyol. The diisocyanate compound and the polyol may contain at least one of linear, branched, alicyclic, and aromatic compounds. Specifically, the diisocyanate compound may contain at least one of a linear, branched, or alicyclic diisocyanate compound having 4 to 12 carbon atoms, and an aromatic diisocyanate compound having 6 to 20 carbon atoms. The polyol may contain two or more, for example, two to four hydroxyl groups (-OH). Specifically, the polyol may be a linear, branched, or cyclic aliphatic polyol compound having 4 to 12 carbon atoms, or an aromatic polyol compound having 6 to 20 carbon atoms.

[0069] The polyurethane resin may include, but is not limited to, a urethane acrylate compound. Examples of the urethane acrylate compound include, but are not limited to, a bifunctional urethane acrylate oligomer with a weight-average molecular weight of 1400 to 25000, a trifunctional urethane acrylate oligomer with a weight-average molecular weight of 1700 to 16000, a tetrafunctional urethane acrylate oligomer with a weight-average molecular weight of 500 to 2000, a hexafunctional urethane acrylate oligomer with a weight-average molecular weight of 818 to 2600, a nnahfunctional urethane acrylate oligomer with a weight-average molecular weight of 2500 to 5500, a decahfunctional urethane acrylate oligomer with a weight-average molecular weight of 3200 to 3900, and a decahfunctional urethane acrylate oligomer with a weight-average molecular weight of 2300 to 20000.

[0070] The glass transition temperature (Tg) of the urethane acrylate compound may be -80°C to 100°C, -80°C to 90°C, -80°C to 80°C, -80°C to 70°C, -80°C to 60°C, -70°C to 100°C, -70°C to 90°C, -70°C to 80°C, -70°C to 70°C, -70°C to 60°C, -60°C to 100°C, -60°C to 90°C, -60°C to 80°C, -60°C to 70°C, -60°C to 60°C, -50°C to 100°C, -50°C to 90°C, -50°C to 80°C, -50°C to 70°C, or -50°C to 60°C.

[0071] The primer layer may further contain a photoinitiator. Examples of the aforementioned photoinitiators include, but are not limited to, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone, methylbenzoyl formate, α,α-dimethoxy-α-phenylacetophenone, 2-benzoyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone, 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, or bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide. Other commercially available products include Irgacure® 184, Irgacure 500, Irgacure 651, Irgacure 369, Irgacure 907, Darocur® 1173, Darocur MBF, Irgacure 819, Darocur TPO, Irgacure 907, and Esacure® KIP 100F. The photoinitiators can be used alone or in mixtures of two or more different types.

[0072] The photoinitiator may be included in the primer layer in an amount of 1 to 10 parts by weight, or 3 to 7 parts by weight, per 100 parts by weight of the total weight of the polymer resin.

[0073] The primer layer is formed by applying and drying a primer composition onto the substrate layer.

[0074] The primer layer composition comprises a polymer resin and a solvent. In one example, the polymer resin contains 60% to 95% by weight of a polyester resin based on the total solid content weight of the primer layer composition. Specifically, the polymer resin may be, but is not limited to, 65% to 95% by weight, 70% to 95% by weight, or 70% to 90% by weight based on the total solid content weight of the primer layer composition.

[0075] Furthermore, the polymer resin may further contain 5% to 30% by weight of polyurethane resin based on the total solid weight of the primer layer composition. Specifically, the polymer resin may further contain 10% to 30% by weight of polyurethane resin based on the total solid weight of the primer layer composition, but is not limited thereto.

[0076] The content of the solvent is not particularly limited, as it can be adjusted in various ways within a range that does not degrade the physical properties of the primer layer composition. For example, the content of the solvent may be such that the solid content in the primer layer composition is 1% to 50% by weight, specifically 1% to 30% by weight, or more specifically 1% to 10% by weight.

[0077] The aforementioned solvents may include water; alcoholic solvents such as methanol, ethanol, isopropyl alcohol, and butanol; alkoxy alcoholic solvents such as 2-methoxyethanol, 2-ethoxyethanol, and 1-methoxy-2-propanol; ketoneic solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, methyl propyl ketone, and cyclohexanone; etheric solvents such as propylene glycol monopropyl ether, propylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethyl glycol monoethyl ether, diethyl glycol monopropyl ether, diethyl glycol monobutyl ether, and diethylene glycol-2-ethylhexyl ether; and aromatic solvents such as benzene, toluene, and xylene; which may be used alone or in combination.

[0078] For example, the solvent contains water, and specifically the water content based on the total weight of the solvent is 50% by weight or more, 60% by weight or more, 70% by weight or more, 75% by weight or more, more than 75% by weight, 80% by weight or more, or 85% by weight or more, and may also be 100% by weight or less, less than 100% by weight, 99% by weight or less, 95% by weight or less, 90% by weight or less, or 85% by weight or less. More specifically, the water content based on the total weight of the solvent may be more than 75% by weight to 100% by weight or less, more than 75% by weight to less than 100% by weight, or 80% by weight to 95% by weight, but is not limited thereto.

[0079] As another example, the solvent contains isopropyl alcohol, and specifically, the isopropyl alcohol content based on the total weight of the solvent is less than 50% by weight, 40% by weight or less, 30% by weight or less, 25% by weight or less, less than 25% by weight, 20% by weight or less, or 15% by weight or less, and may also be greater than 0% by weight, 1% by weight or more, 5% by weight or more, 10% by weight or more, 15% by weight or more, or 20% by weight or more. More specifically, the isopropyl alcohol content based on the total weight of the solvent may be between 0% by weight and less than 25% by weight, greater than 0% by weight and less than 25% by weight, or 5% by weight and 20% by weight, but is not limited thereto.

[0080] As a specific example, the solvent may contain more than 75% by weight of water and less than 25% by weight of isopropyl alcohol, based on the total weight of the solvent. In addition, the primer layer composition may further contain additives such as photoinitiators.

[0081] The surface energy of the primer layer composition may be 25 dyne to 40 dyne, or 30 dyne to 40 dyne, but is not limited thereto. The method described above or other known methods can be used to measure the surface energy.

[0082] The primer layer composition can be applied to a substrate layer by methods such as bar coating, knife coating, roll coating, blade coating, die coating, microgravure coating, comma coating, slot die coating, lip coating, or solvent casting, and then dried and cured to form a primer layer.

[0083] The drying step can remove the solvent contained in the primer layer composition. The drying temperature is 70°C or higher, 90°C or higher, or 110°C or higher, and may be, for example, 70°C to 200°C or 90°C to 150°C. The drying time is, for example, 1 to 20 minutes, and may be, specifically, 1 to 10 minutes or 3 to 7 minutes, but is not limited thereto.

[0084] The primer layer may be cured by light and / or heat. For example, the primer layer can be UV cured, with a light intensity of 100 mJ or more, 200 mJ or more, or 300 mJ or more, such as 100 mJ to 1000 mJ or 300 mJ to 700 mJ. The curing may be partial or complete.

[0085] The thickness of the primer layer may be between 0.03 μm and 1.0 μm. For example, the thickness of the primer layer may be 0.03 μm or more, 0.05 μm or more, 0.07 μm or more, 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, 0.4 μm or more, or 0.5 μm or more, and may also be 1.0 μm or less, 0.9 μm or less, 0.8 μm or less, 0.7 μm or less, 0.6 μm or less, 0.5 μm or less, 0.4 μm or less, 0.3 μm or less, 0.2 μm or less, or 0.1 μm or less. As a specific example, the thickness of the primer layer may be between 0.03 μm and 0.1 μm or between 0.1 μm and 0.5 μm.

[0086] [Base material layer] The substrate layer provides mechanical properties to the multilayer film while serving as the base layer for the primer layer.

[0087] In one embodiment, the substrate layer comprises a polyamide polymer. Specifically, the substrate layer may be a transparent polyamide film. The polyamide polymer comprises amide repeating units. The amide repeating units may be formed by the polymerization of a diamine compound and a dicarbonyl compound. That is, the polyamide polymer may be formed by the simultaneous or sequential reaction of reactants containing a diamine compound and a dicarbonyl compound.

[0088] In some embodiments, the polyamide polymer may further contain imide repeating units. Specifically, the polyamide polymer may be a copolymer containing amide repeating units and imide repeating units, that is, a polyamide-imide polymer. The imide repeating units can be formed by the polymerization of a diamine compound and a dianhydride compound. That is, the polyamide-imide polymer can be formed by the simultaneous or sequential reaction of reactants containing a diamine compound, a dianhydride compound, and a dicarbonyl compound.

[0089] [[ID=③]] The diamine compound can form an imide bond with the dianhydride compound and an amide bond with the dicarbonyl compound to form a polymer.

[0090] The diamine compound is not particularly limited, and for example, it can be an aromatic diamine compound containing an aromatic structure. For example, the diamine compound can be a compound of Chemical Formula 1 below.

[0091] [Chemical Formula 1] JPEG0007893767000001.jpg538In Chemical Formula 1, E is a substituted or unsubstituted divalent C6-C 30 alicyclic group, a substituted or unsubstituted divalent C4-C 30 heteroalicyclic group, a substituted or unsubstituted divalent C6-C 30 aromatic ring group, a substituted or unsubstituted divalent C4-C 30 aromatic heterocyclic group, a substituted or unsubstituted C1-C 30 alkylene group, a substituted or unsubstituted C2-C 30 alkenylene group, a substituted or unsubstituted C2-C 30 alkynylene group, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2-, and -C(CF3)2-, and e is selected from integers from 1 to 5. When e is 2 or more, E can be the same as or different from each other.

[0092] (E) of Chemical Formula 1 eThe group can be selected from, but is not limited to, the groups represented by the following chemical formulas 1-1a to 1-14a. JPEG0007893767000002.jpg95150

[0093] Specifically, (E) of the above chemical formula 1 e The group can be selected from, but is not limited to, the groups represented by the following chemical formulas 1-1b to 1-13b. JPEG0007893767000003.jpg102151

[0094] More specifically, (E) of the above chemical formula 1 e This may be a group represented by chemical formula 1-6b or a group represented by chemical formula 1-9b.

[0095] In one example, the diamine compound may include a compound having a fluorine-containing substituent or a compound having an ether group (-O-).

[0096] The diamine compound may consist of a compound having a fluorine-containing substituent. In this case, the fluorine-containing substituent is a fluorinated hydrocarbon group, and may specifically be a trifluoromethyl group, but is not limited to this.

[0097] In some implementations, one type of diamine compound may be used as the diamine compound. That is, the diamine compound may consist of a single component.

[0098] For example, the diamine compound may include, but is not limited to, 2,2'-Bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB), which has the structure shown below. JPEG0007893767000004.jpg4778

[0099] Because the dianhydride compound has a low birefringence value, it can contribute to improving optical properties such as the transmittance of the film containing the imide repeating units.

[0100] The aforementioned dianhydride compound is not particularly limited, but may, for example, be an aromatic dianhydride compound containing an aromatic structure. Specifically, the aromatic dianhydride compound may be the compound of the following chemical formula 2. [C2] JPEG0007893767000005.jpg3247

[0101] In the above chemical formula 2, G is a substituted or unsubstituted tetravalent C6-C 30 Alicyclic group, substituted or unsubstituted tetravalent C4-C 30 Heteroalicyclic groups, substituted or unsubstituted tetravalent C6-C 30 Aromatic ring group, substituted or unsubstituted tetravalent C4-C 30 Aromatic heterocyclic groups, wherein the alicyclic group, the heteroalicyclic group, the aromatic ring group, or the aromatic heterocyclic group exist individually, are bonded to each other to form a fused ring, or are substituted or unsubstituted C1-C 30 Alkylene group, substituted or unsubstituted C2-C 30 Alkenylene group, substituted or unsubstituted C2-C 30 The molecules are linked by an alkynylene group and a linking group selected from -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2-, and -C(CF3)2-.

[0102] In the aforementioned chemical formula 2, G can be selected from, but is not limited to, the groups represented by the following chemical formulas 2-1a to 2-9a. JPEG0007893767000006.jpg88149

[0103] For example, G in chemical formula 2 may be the group represented by chemical formula 2-2a, the group represented by chemical formula 2-8a, or the group represented by chemical formula 2-9a.

[0104] In one example, the dianhydride compound may include a compound having a fluorine-containing substituent, a compound having a biphenyl group, or a compound having a ketone group.

[0105] The fluorine-containing substituent is a fluorinated hydrocarbon group, and may specifically be a trifluoromethyl group, but is not limited to this.

[0106] In other realizations, the dianhydride compound may consist of one single component or a mixture of two components.

[0107] For example, the dianhydride compound may include, but is not limited to, one or more compounds selected from the group consisting of 2,2'-Bis-(3,4-Dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), which have the structures shown below. JPEG0007893767000007.jpg39138

[0108] The diamine compound and the dianhydride compound can polymerize to produce a polyamic acid.

[0109] Next, the polyamic acid can be formed into an imide-based repeating unit by a dehydration reaction. The imide-based repeating unit can be represented by the following chemical formula A. [Chemical A] JPEG0007893767000008.jpg4074 In the above chemical formula A, the explanations for E, G, and e are as described above.

[0110] For example, the imide-based repeating unit may include, but is not limited to, the repeating unit represented by the following chemical formula A-1. [Chemical A-1] JPEG0007893767000009.jpg37128 In the above chemical formula A-1, n is an integer from 1 to 400.

[0111] The dicarbonyl compound is not particularly limited, but for example, it may be a compound of the following chemical formula 3. [C3] JPEG0007893767000010.jpg1837

[0112] In the above chemical formula 3, J is a substituted or unsubstituted divalent C6-C 30 Alicyclic group, substituted or unsubstituted divalent C4-C 30 Heteroalicyclic groups, substituted or unsubstituted divalent C6-C 30 Aromatic ring group, substituted or unsubstituted divalent C4-C 30 Aromatic heterocyclic groups, substituted or unsubstituted C1-C 30 Alkylene group, substituted or unsubstituted C2-C 30 Alkenylene group, substituted or unsubstituted C2-C 30 The group is selected from alkynylene, -O-, -S-, -C(=O)-, -CH(OH)-, -S(=O)2-, -Si(CH3)2-, -C(CH3)2-, and -C(CF3)2-, j is selected from an integer between 1 and 5, and if j is 2 or greater, J are the same or different from each other, and X is a halogen atom. Specifically, X can be F, Cl, Br, I, etc. More specifically, X can be Cl, but is not limited to this.

[0113] (J) of the aforementioned chemical formula 3 j The group can be selected from, but is not limited to, the groups represented by the following chemical formulas 3-1a to 3-14a. JPEG0007893767000011.jpg109164

[0114] Specifically, (J) of the above chemical formula 3 j The group can be selected from, but is not limited to, the groups represented by the following chemical formulas 3-1b to 3-8b. JPEG0007893767000012.jpg74150

[0115] More specifically, (J) of the above chemical formula 3 j This can be the group represented by chemical formula 3-1b, the group represented by chemical formula 3-2b, the group represented by 3-3b, or the group represented by 3-8b.

[0116] In one embodiment, the dicarbonyl compound may be used as a single dicarbonyl compound or as a mixture of at least two different dicarbonyl compounds. When two or more dicarbonyl compounds are used, the dicarbonyl compound is (J) in the chemical formula 3. j Two or more groups selected from the groups represented by the chemical formulas 3-1b to 3-8b may be used.

[0117] In other realizations, the dicarbonyl compound may be an aromatic dicarbonyl compound containing an aromatic structure.

[0118] For example, the dicarbonyl compound may include a first dicarbonyl compound and / or a second dicarbonyl compound different from the first dicarbonyl compound.

[0119] The first dicarbonyl compound and the second dicarbonyl compound may each be an aromatic dicarbonyl compound.

[0120] The first dicarbonyl compound and the second dicarbonyl compound may be, but are not limited to, different aromatic dicarbonyl compounds.

[0121] If the first dicarbonyl compound and the second dicarbonyl compound are both aromatic dicarbonyl compounds, they contain a benzene ring, which can contribute to improving the mechanical properties of the manufactured polyamide resin film, such as surface hardness and tensile strength.

[0122] The dicarbonyl compound may include, but is not limited to, terephthaloyl chloride (TPC), isophthaloyl chloride (IPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloride (BPDC), or a combination thereof, having the following structures. JPEG0007893767000013.jpg30147

[0123] For example, the first dicarbonyl compound may include BPDC, and the second dicarbonyl compound may include TPC, but is not limited thereto.

[0124] Specifically, when BPDC is used as the first dicarbonyl compound and TPC as the second dicarbonyl compound in an appropriate combination, the resulting film containing the polyamide resin can have high oxidation resistance.

[0125] Alternatively, the first dicarbonyl compound may include IPC, and the second dicarbonyl compound may include TPC, but is not limited thereto.

[0126] Specifically, by appropriately combining IPC as the first dicarbonyl compound and TPC as the second dicarbonyl compound, the resulting polyamide resin-containing film can have high oxidation resistance, thereby reducing manufacturing costs.

[0127] The diamine compound and the dicarbonyl compound can polymerize to form a repeating unit represented by the following chemical formula B. [Case B] JPEG0007893767000014.jpg3167 In the above chemical formula B, the explanations for E, J, e, and j are as described above.

[0128] For example, the diamine compound and the dicarbonyl compound can polymerize to form amide repeating units represented by chemical formulas B-1 and B-2.

[0129] Alternatively, the diamine compound and the dicarbonyl compound may polymerize to form amide repeating units represented by chemical formulas B-2 and B-3.

[0130] [Case B-1] JPEG0007893767000015.jpg34128 In the above chemical formula B-1, x is an integer between 1 and 400.

[0131] [Case B-2] JPEG0007893767000016.jpg37128 In the above chemical formula B-2, y is an integer from 1 to 400.

[0132] [Case B-3] JPEG0007893767000017.jpg38128 In the above chemical formula B-3, y is an integer from 1 to 400.

[0133] According to one example, the polyamide polymer may contain repeating units represented by the following chemical formula A and repeating units represented by the following chemical formula B. [Chemical A] JPEG0007893767000018.jpg4380 In the above chemical formula A, the explanations for E, G, and e are as described above.

[0134] [Case B] JPEG0007893767000019.jpg2860 In the above chemical formula B, the explanations for E, J, e, and j are as described above.

[0135] The polyamide polymer may contain imide repeating units and amide repeating units in a molar ratio of 0:100 to 75:25. For example, the molar ratio of imide repeating units to amide repeating units in the polyamide polymer may be, but is not limited to, 2:98 to 70:30, 0:100 to 60:40, 2:98 to 60:40, 5:95 to 60:40, 0:100 to 55:45, 5:95 to 55:45, 0:100 to 50:50, or 5:95 to 50:50.

[0136] Specifically, in the polyamide polymer, the molar ratio of the repeating unit represented by chemical formula A to the repeating unit represented by chemical formula B may be 2:98 to 75:25. Specifically, the molar ratio of the repeating unit represented by chemical formula A to the repeating unit represented by chemical formula B may be, but are not limited to, 2:98 to 70:30, 2:98 to 60:40, 5:95 to 60:40, 5:95 to 55:45, or 5:95 to 50:50.

[0137] The substrate layer may further contain one or more additives selected from the group consisting of fillers, pigments, and UV absorbers.

[0138] One example of a method for producing a polyamide film includes the steps of preparing a polyamide polymer solution (S100), casting the solution and then drying it to produce a gel sheet (S200), and heat-treating the gel sheet (S300).

[0139] First, a polyamide polymer solution is prepared (S100). The polyamide polymer solution can be obtained by polymerizing a diamine compound, a dicarbonyl compound, and selectively a dianhydride compound in an organic solvent.

[0140] Specifically, the polyamide polymer solution can be prepared by simultaneously or sequentially mixing a diamine compound, a dicarbonyl compound, and selectively a dianhydride compound in an organic solvent in a reactor and reacting the mixture.

[0141] As an example, the polymer solution can be prepared by simultaneously adding a diamine compound and a dicarbonyl compound to an organic solvent and allowing them to react.

[0142] As another example, the step of preparing the polymer solution can be carried out by simultaneously adding a diamine compound, a dianhydride compound, and a dicarbonyl compound to an organic solvent and allowing them to react.

[0143] As another example, the step of preparing the polymer solution may include the steps of: first mixing and reacting the diamine compound and the dianhydride compound in a solvent to prepare a polyamic acid (PAA) solution; and second mixing and reacting the dicarbonyl compound with the polyamic acid (PAA) solution to form amide and imide bonds. The polyamic acid solution is a solution containing a polymer having polyamic acid repeating units.

[0144] Alternatively, the step of preparing the polymer solution may include the steps of: preparing a polyamic acid solution by primary mixing and reacting the diamine compound and the dianhydride compound in a solvent; preparing a polyimide (PI) solution by dehydrating the polyamic acid solution; and forming additional amide bonds by secondary mixing and reacting the dicarbonyl compound with the polyimide (PI) solution. The polyimide solution is a solution containing a polymer having imide repeating units.

[0145] As another example, the step of preparing the polymer solution may include the steps of: preparing a polyamide (PA) solution by primary mixing and reacting the diamine compound and the dicarbonyl compound in a solvent; and secondary mixing and reacting the dianhydride compound with the polyamide (PA) solution to form additional imide bonds. The polyamide solution is a solution containing a polymer having amide repeating units.

[0146] The descriptions of the diamine compounds, dianhydride compounds, and dicarbonyl compounds are as stated above.

[0147] The solid content in the polymer solution may be 10% to 30% by weight. Alternatively, the solid content in the polymer solution may be 15% to 25% by weight, but is not limited to these values.

[0148] Next, the polymer solution is cast to produce a gel sheet (S200). For example, the polymer solution can be applied to a support, extruded, and / or dried to form a gel sheet.

[0149] Furthermore, the casting thickness of the polymer solution can be 200 μm to 700 μm. By casting the polymer solution within this thickness range, appropriate thickness and thickness uniformity can be ensured when the final film is manufactured after drying and heat treatment.

[0150] The viscosity of the polymer solution can be 80,000 cps to 500,000 cps at room temperature. By satisfying this viscosity range, the polymer solution can be cast to a uniform thickness without defects when cast, and a polyamide film of substantially uniform thickness can be formed without local / partial thickness changes during the drying process.

[0151] After casting the polymer solution, a gel sheet can be produced by drying it at a temperature of 60°C to 150°C, 70°C to 150°C, or 80°C to 150°C for 5 to 60 minutes. Specifically, a gel sheet can be produced by drying the polymer solution at a temperature of 70°C to 140°C for 15 to 40 minutes.

[0152] During the drying process, some or all of the solvent in the polymer solution may evaporate, thereby producing the gel sheet.

[0153] Subsequently, the dried gel sheet is heat-treated to form a polyamide film (S300).

[0154] The step of heat-treating the gel sheet includes a step of heat-treating it with at least one heater. The step of heat-treating the gel sheet may further include a step of heat-treating it with hot air.

[0155] The aforementioned heat treatment with hot air may be carried out at a temperature in the range of 60°C to 500°C for 5 minutes to 200 minutes. Specifically, the heat treatment of the gel sheet may be carried out at a rate of 2°C / min to 80°C / min in the range of 80°C to 350°C for 10 minutes to 150 minutes. In this case, the starting temperature of the heat treatment of the gel sheet may be 60°C or higher. Specifically, the starting temperature of the heat treatment of the gel sheet may be 80°C to 180°C. Furthermore, the maximum temperature during the heat treatment may be 200°C to 500°C.

[0156] The aforementioned at least one heater may include an IR heater. However, the type of the at least one heater can be varied and is not limited to the examples given above. The heat treatment with the at least one heater may be carried out in a temperature range of 300°C or higher. Specifically, the heat treatment with the at least one heater may be carried out in a temperature range of 300°C to 500°C for 1 to 30 minutes.

[0157] The thickness of the substrate layer is 20 μm or more, 30 μm or more, 40 μm or more, 50 μm or more, or 100 μm or more, and may also be 500 μm or less, 400 μm or less, 300 μm or less, or 200 μm or less. As a specific example, the thickness of the substrate layer may be 20 μm to 500 μm, and more specifically, 40 μm to 200 μm or 50 μm to 200 μm.

[0158] [Functional Layer] The multilayer film may further include a functional layer. The functional layer is formed on the primer layer, thereby allowing the primer layer to be interposed between the functional layer and the substrate layer.

[0159] The functional layer may be a hard coat layer, an optical adhesive layer, a printed coating layer, a fingerprint-resistant layer, an antistatic layer, an anti-glare layer, an anti-reflective layer, and is not particularly limited.

[0160] For example, the functional layer may be one or more selected from the group consisting of a hard coat layer, an optical adhesive layer, and a printed coating layer.

[0161] According to one example, the multilayer film may further include a hard coat layer formed on the primer layer. The hard coat layer can improve the mechanical and / or optical properties of the multilayer film.

[0162] The hard coat layer may contain at least one of organic components, inorganic components, and inorganic composite components as a hard coat agent. For example, the hard coat layer may contain an organic resin. Specifically, the organic resin may be a curable resin. Thus, the hard coat layer may be a curable coat layer.

[0163] Specifically, the hard coat layer may contain one or more compounds selected from the group consisting of urethane acrylate compounds, acrylic ester compounds, and epoxy acrylate compounds. More specifically, the hard coat layer may contain urethane acrylate compounds and acrylic ester compounds.

[0164] The content of the organic resin may be 30% to 100% by weight based on the total weight of the hard coat layer. Specifically, the content of the organic resin may be 40% to 90% or 50% to 80% by weight based on the total weight of the hard coat layer.

[0165] The hard coat layer may further selectively contain fillers. The fillers may be, for example, inorganic particles. Examples of fillers include silica, barium sulfate, zinc oxide, or alumina. The particle size of the fillers may be 1 nm to 1000 nm. The filler content may be 25% by weight or more, 30% by weight or more, or 35% by weight or more, and may also be 50% by weight or less, 45% by weight or less, or 40% by weight or less, based on the total weight of the hard coat layer.

[0166] The hard coat layer may further contain a photoinitiator. The photoinitiator may be used alone or in a mixture of two or more different types.

[0167] In addition, the hard coat layer may further contain additives such as antifouling agents, antistatic agents, surfactants, UV absorbers, UV stabilizers, anti-yellowing agents, leveling agents, or dyes for improving color values. The content of these additives is varied within a range that does not degrade the physical properties of the hard coat layer, and may be, for example, 0.01% to 10% by weight based on the total weight of the hard coat layer, but is not limited thereto.

[0168] The thickness of the hard coat layer is 2 μm or more, 3 μm or more, 5 μm or more, or 10 μm, and may also be 50 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less. For example, the thickness of the hard coat layer may be 2 μm to 20 μm. Specifically, the thickness of the hard coat layer may be 5 μm to 20 μm.

[0169] According to other realizations, the multilayer film may further include a printed coating layer formed on the primer layer.

[0170] The aforementioned printed coating layer contains a binder resin, which may include, for example, ester compounds, urethane compounds, epoxy compounds, or mixtures thereof.

[0171] Specifically, the ester compound comprises at least one selected from the group consisting of phthalic acid resins, isophthalic acid resins, and terephthalic acid resins; the urethane compound comprises a resin obtained by polymerizing an isocyanate compound such as diphenylmethane diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate with a polyol; and the epoxy compound may comprise one or more selected from the group consisting of bisphenol A type epoxy resins, bromide bisphenol A type epoxy resins, novolac resins, and glycidylamine resins.

[0172] Furthermore, the print coating layer may contain pigments or dyes. The pigments may be inorganic pigments such as carbon black, barium sulfate, calcium carbonate, titanium dioxide, yellow iron oxide, black iron, chrome yellow, chrome vermilion, cadmium yellow, cadmium red, Prussian blue, and ultramarine, or organic pigments such as insoluble azo, soluble azo, phthalocyanine, quinacridone, polyazo, or mixtures thereof.

[0173] The printable coating layer can be formed by coating the primer layer with a printable coating layer composition, and the coating may be performed using screen printing or heat transfer.

[0174] As an example, the print coating layer composition may be a thermosetting resin composition. The thermosetting resin composition may include a binder resin, a pigment, and a solvent. Specifically, the thermosetting resin composition may contain 10% to 50% by weight of the binder resin, 1% to 20% by weight of the pigment, and 40% to 80% by weight of the solvent, based on the total weight of the thermosetting resin composition.

[0175] The solvent may be a ketone or an alcohol. Specifically, the solvent may be ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, 2-heptanone, and 3-heptanone; alcohols such as ethanol, propanol, butanol, hexanol, cyclohexanol, ethylene glycol, diethylene glycol, and glycerin; or a mixture thereof.

[0176] According to one example, the thermosetting resin composition may further contain additives. Specifically, the additive may be one or more selected from the group consisting of leveling agents, dispersants, and thickeners. According to one example, the content of the additive may be 1% to 10% by weight based on the total weight of the thermosetting resin composition.

[0177] The thickness of the printed coating layer may be 1 μm to 50 μm. For example, the thickness of the printed coating layer may be 3 μm to 50 μm, 3 μm to 20 μm, 10 μm to 50 μm, 15 μm to 40 μm, 20 μm to 50 μm, 15 μm to 20 μm, 10 μm to 15 μm, 2 μm to 10 μm, 5 μm to 10 μm, or 2 μm to 7 μm.

[0178] In another example, the multilayer film may further include an optical adhesive layer formed on the primer layer.

[0179] The optical adhesive layer may include, but is not particularly limited to, acrylic resins, epoxy resins, urethane resins, etc.

[0180] As an example, the optical adhesive layer may contain an acrylic resin and be formed by the reaction of one or more acrylic compounds. The acrylic compound may be one or more selected from, for example, 2-ethylhexyl acrylate, 4-hydroxybutyl acrylate, methyl acrylate, acrylic acid, etc. The reaction of the acrylic compound is carried out in a solvent, and examples of the solvent include ethyl acetate, butyl acetate, toluene, or a mixture thereof.

[0181] The optical adhesive layer may further contain a photoinitiator. For example, 2,2'-azobis(isobutyronitrile) (AIBN), benzoyl peroxide (BPO), etc., may be used as the photoinitiator.

[0182] The optical adhesive layer may further contain a crosslinking agent. For example, glycidyl crosslinking agents, isocyanate crosslinking agents, epoxy crosslinking agents, and mixtures thereof may be used as the crosslinking agent. The content of the crosslinking agent may be 0.2 to 0.6 parts by weight per 100 parts by weight of the resin used to prepare the optical adhesive layer.

[0183] The optical adhesive layer may further contain organic or inorganic particles. For example, the organic particles may include particles containing at least one of polybutyl acrylate (PBA) and polymethyl methacrylate (PMMA). The content of the organic or inorganic particles may be 1 to 10 parts by weight per 100 parts by weight of the resin used to prepare the optical adhesive layer.

[0184] As an example, the optical adhesive layer may be formed by coating an optical adhesive layer composition onto the primer of the multilayer film. As another example, the optical adhesive layer may be manufactured in advance in sheet form and then attached to the primer layer of the multilayer film.

[0185] The thickness of the optical adhesive layer may be, for example, 30 μm or more, 40 μm or more, or 50 μm or more, and may also be 200 μm or less, 150 μm or less, or 100 μm or less.

[0186] [Effects and Uses] The multilayer film according to the above-mentioned example has a primer layer of a specific composition containing a polyester resin on a polyamide substrate layer, which provides excellent adhesion to the hard coat layer and OCA layer coated or bonded to its surface, as well as excellent optical and mechanical properties.

[0187] Therefore, the multilayer film according to the above-mentioned example may be equipped with various functional layers such as a hard coat layer, an anti-fingerprint layer, an anti-static layer, an anti-glare layer, an anti-reflective layer, and an optical adhesive layer to achieve the characteristics required for the cover window of a display device such as a flexible display device.

[0188] The multilayer film according to the above-described embodiment can be applied to a display device. For example, the multilayer film according to the above-described embodiment can be applied to the cover window of a display device. The display device is a flexible display device, and one example is a foldable display device.

[0189] A display device according to one embodiment includes a display panel and a cover window disposed on the viewing surface of the display panel, wherein the multilayer film having the above configuration is applied to the cover window.

[0190] An adhesive layer is formed between the cover window and the display panel, and for example, the adhesive layer may contain an optically transparent adhesive.

[0191] The display panel 20 may be a liquid crystal display (LCD) panel. Alternatively, the display panel 20 may be a light-emitting diode (LED) display panel.

[0192] (Examples) The examples described below are for illustrative purposes only and do not limit the feasible scope.

[0193] (Manufacturing Example 1A: Substrate Layer Film) In a 1 L glass reactor with a temperature-controllable double jacket, dimethylacetamide (DMAc) was filled under a nitrogen atmosphere at 20°C. Then, the diamine compound 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl (TFDB) was gradually added and dissolved. Subsequently, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropanedianhydride (6-FDA) was gradually added as the dianhydride compound and stirred for 1 hour. Finally, terephthaloyl chloride (TPC) and isophthaloyl chloride (IPC) were added as dicarbonyl compounds and stirred for 1 hour to prepare the polymer solution. The types and molar ratios of monomers for the preparation of the polymer solution were adjusted as shown in Table 1 below.

[0194] The obtained polymer solution was applied to a glass plate, dried with hot air at 80°C for 30 minutes, then peeled off the glass plate and fixed to a pin frame. The temperature was then increased at a rate of 2°C / min in the temperature range of 80°C to 300°C to obtain a transparent polyamide film with a thickness of 50 μm.

[0195] (Manufacturing Examples 1B-1D: Substrate Layer Film) The procedure of Production Example 1A was repeated, but the type and molar ratio of monomers used to prepare the polymer solution were changed as shown in Table 1 below to produce the films of Production Examples 1B to 1D.

[0196] [Table 1]

[0197] (Manufacturing example 2: Optical adhesive (OCA)) 100 parts by weight of a 2-ethylhexyl acrylate / 4-hydroxybutyl acrylate mixture (80:20, w / w), 4 parts by weight of organic particles (core-shell structure, core: polybutyl acrylate (PBA), shell: polymethacrylate (PMMA), particle size 130 nm, refractive index 1.48), and 0.005 parts by weight of a photopolymerization initiator (Irgacure 651) were mixed in a glass container. The dissolved oxygen in the glass container was replaced with nitrogen gas, and the polymerization reaction was carried out by irradiating with ultraviolet light using a low-pressure lamp (BL Lamp, Sankyo Electric Co., Ltd., Japan) for several minutes. As a result, a (meth)acrylic copolymer containing organic particles was obtained with a viscosity of approximately 1000 cps and a refractive index of 1.47-1.48. To this, 0.35 parts by weight of a photopolymerization initiator (Irgacure 184) was added to prepare an adhesive composition. The adhesive composition was coated onto a polyester film (release film, PET, 50 μm thick) to form an adhesive film with a thickness of 100 μm. The upper surface of the adhesive film was covered with a 75 μm thick release film, and then both sides were irradiated with a low-pressure lamp (BL Lamp, Sankyo Electric Co., Ltd.) for approximately 6 minutes to obtain an optical adhesive (OCA) sheet.

[0198] (Manufacturing Example 3: Hard Coat Layer Composition) A hard coat layer composition was prepared by adding 54.32 parts by weight of urethane acrylate oligomer (PU2050, Miwon Specialty Chemicals), 23.28 parts by weight of polyfunctional acrylate monomer (M300, Miwon Specialty Chemicals), 19.4 parts by weight of silica sol (MA-ST, Nissan Chemicals) in which silica fine particles with a particle size of 10 nm to 15 nm were dispersed in methanol at a concentration of 30% by weight, and 3 parts by weight of photoinitiator (I-184, BASF).

[0199] (Manufacturing Example 4: Printed Coating Layer Composition) A mixture of 50% by weight of a colored pigment (carbon black), 2% by weight of a polymer dispersant (BYK-P104S), 35% by weight of an acrylic resin (based on solid content), and 13% by weight of ethyl acetate was prepared and pre-mixed for 30 minutes. Then, it was milled (6-8 passes) with a Dyno Mill (registered trademark) to prepare a particle size distribution of 10 μm or less. The mill base prepared as described above (20% by weight), 60% by weight of ethyl acetate, 18.6% by weight of an acrylic resin (based on solid content), and 1.4% by weight of a silane compound (γ-glycidoxypropyltrimethoxysilane, trade name Silquest (registered trademark) A-187, Momentive Performance Materials) were mixed and stirred to prepare a printable coating layer composition.

[0200] (Example 1: Manufacturing of multilayer film) Step 1) Preparation of the primer layer composition A primer layer composition was prepared by mixing a polyester resin (PLASCOAT 446, GOO Chemical, Japan) and a polyurethane resin (solids content 28% by weight, H-15, Daiichi Kogyo Seiyaku Co., Ltd., Japan) in a weight ratio of 7:3 (by weight of solids content), adding a solution of water (H2O) and isopropyl alcohol (IPA) in a ratio of 85:15 by weight, and then stirring at room temperature for 30 minutes.

[0201] Step 2) Formation of the primer layer The primer layer composition obtained in the previous step was applied to one surface of the substrate layer obtained in Manufacturing Example 1 using a bar coater, and then dried to form a primer layer. The amount applied was adjusted by the size of the bar, and after drying, the thickness of the primer layer was measured using an optical thickness measuring instrument (Film metrics F-20) and is shown in Table 2 below. As a result, a multilayer film was obtained in which a primer layer was formed on a substrate layer.

[0202] (Examples 2-12) The same procedure as in Example 1 was repeated, but the film used in the substrate layer, the components and content of the primer layer composition, and the thickness of the primer layer were adjusted as shown in Table 2 below to produce a multilayer film.

[0203] (Comparative Examples 1-3) The same procedure as in Example 1 was repeated, but without adding polyester resin during the production of the primer layer composition. Instead, polyurethane resin (28% by weight solids, H-15, Daiichi Kogyo Seiyaku Co., Ltd.) and acrylic resin (55% by weight solids, PRIMAL AC-26, Dow Chemical Co., Ltd.) were blended in the weight ratios (by weight of solids) shown in Table 2 below. In addition, the composition of the solvent in the primer layer composition and the thickness of the primer layer were adjusted as shown in Table 2 below to produce a multilayer film.

[0204] (Comparative Example 4) The same procedure as in Example 1 was repeated, but the polyimide (PI) film of Production Example 1D was used as the base layer, and the components and content of the primer layer composition were adjusted as shown in Table 2 below to produce a multilayer film.

[0205] (Comparative Example 5) The polyamide-imide film obtained in the above-mentioned production example 1A was used as the base layer, and was used as is without forming a primer layer.

[0206] [Table 2]

[0207] (Test Example 1: Adhesion strength between primer layer and substrate layer (cross-cut test)) The adhesion between the primer layer and the substrate layer of the film sample was evaluated by a cross-cut test. The surface of the primer layer was cut into a grid pattern at regular intervals according to ASTM D3359 (Method B) standard, and then tape (Knit Tape 50B, Nitto Denko Corporation) was applied and peeled off to check the degree to which thin flakes of the grid unit were generated on the surface. Grades from 0B to 5B were assigned according to the following criteria, with 5B being the best evaluation (see Figure 4).

[0208] -5B: The cross-section is clean, and the grid squares are not separated (0% of the grid area) -4B: Small pieces of the coating are separated at the intersections (less than 5% of the grid area). -3B: Small pieces of coating are separated along the corners and at the intersections of the cut sections (5% to 15% of the grid area). -2B: The edges of the coating's cut surface and a portion of the square are separated (15% to 35% of the grid area). -1B: The coating peels off significantly along the edges of the cut surface, separating the squares (35% to 65% of the grid area). -0B: The coating peels off and the separation of the squares becomes more severe (more than 65% of the grid area).

[0209] (Test Example 2: Adhesion between hard coat layer and substrate layer (cross-cut test)) A hard coat layer was formed on the primer layer of the film sample, and the adhesion between the hard coat layer and the substrate layer was evaluated by a cross-cut test.

[0210] First, the hard coat layer composition obtained in Production Example 3 was applied to the primer layer of the film sample by die coating (or, if there was no primer layer, it was applied directly to the substrate layer). After drying the solvent at 80°C for about 1 minute, high-pressure mercury lamp ultraviolet light was applied at 1000 mJ / cm². 2 The film was cured by irradiation with light intensity. As a result, a film was obtained having a 5 μm thick hard coat layer on the substrate layer and primer layer.

[0211] Subsequently, a cross-cut test was performed on the surface of the hard coat layer according to ASTM D3359 (Method B) standard, as in Test Example 1.

[0212] (Test Example 3: Adhesion between the printed coating layer and the substrate layer (cross-cut test)) A printed coating layer was formed on the primer layer of the film sample, and the adhesion between the printed coating layer and the substrate layer was evaluated by a cross-cut test.

[0213] First, the printable coating layer composition obtained in Production Example 4 was applied to the primer layer of the film sample by silkscreen coating (or, if there was no primer layer, it was applied directly to the substrate layer). Solvent drying and heat curing were performed at 80°C for about 30 minutes. As a result, a film was obtained having a printable coating layer with a thickness of 3.0 μm on the substrate layer and primer layer.

[0214] Subsequently, a cross-cut test was performed on the surface of the printed coating layer in accordance with ASTM D 3359 (Method B) standard, similar to the test example 1.

[0215] (Test Example 4: Adhesion strength between optical adhesive layer and substrate layer (180° peel strength)) An optical adhesive layer (OCA layer) was formed on the primer layer of the film sample, and the adhesion strength between the optical adhesive layer and the substrate layer was evaluated by a 180° peel test.

[0216] First, the OCA sheet obtained in Production Example 2 was attached to the primer layer of the film sample by moving a rubber-coated roller back and forth once at a load of 2 kg and a speed of 5 mm / s (or, if there was no primer layer, it was attached directly to the substrate layer). As a result, a film having an OCA layer on the substrate layer and primer layer was obtained.

[0217] For the aforementioned OCA layer, the 180° peel strength was measured using a universal testing machine (UTM) at a speed of 300 mm / min according to the ASTM D903 standard (see Figure 5).

[0218] (Test Example 5: Surface Energy) The surface energy was calculated using the Cecil Drop method by measuring the contact angle of the test solution (deionized water, diiodomethane) on the surface of the primer layer (or substrate layer if there is no primer layer) of the film sample using KRUSS's MSA (Mobile Surface Analyzer) product (see Figure 6).

[0219] First, deionized water with a known surface tension was dropped onto a surface, and the process of determining the contact angle was repeated five times to obtain the average of the five resulting contact angle values. Similarly, diiodomethane with a known surface tension was dropped onto a surface, and the process of determining the contact angle was repeated five times to obtain the average of the five contact angle values. Then, using the average contact angles for deionized water and diiodomethane, the surface energy was calculated based on Young's equation shown below.

[0220] JPEG0007893767000022.jpg636 Note that θ is the contact angle of the liquid with respect to the film, σ l σ is the surface tension of the liquid, s σ is the surface energy of the film, sl This is the interfacial tension between the film and the liquid.

[0221] The interfacial tension between the film and the liquid can be obtained by the known WORK (Owens-Wendt-Rabel-Kaelble) method, and a more specific method can be found in known literature (e.g., Supplementary Information - Surface energy and wettability of van der Waals structures, Nanoscale, Issue 10, 2016).

[0222] (Test Example 6: Measurement of Light Transmittance and Haze) Using the NDH-5000W haze meter from Nippon Denshoku Industries Co., Ltd., total transmittance and haze were measured according to the JIS K7136 standard.

[0223] (Test example 7: Measurement of yellowness) Yellowness (YI) was measured using a spectrophotometer (UltraScan PRO, Hunter Associates Laboratory) under conditions of D65 and 10°, in accordance with the ASTM-E313 standard. The results of the aforementioned test example are summarized in the table below.

[0224] [Table 3]

[0225] As shown in the table above, multilayer films using polyamide films (PAI or PA) as the base film, as in Examples 1 to 12, with a primer layer containing polyester resin, generally exhibited high surface energy, excellent cross-cut test results for the hard coat layer and printed coat layer, and high peel strength for the adhesive layer.

[0226] On the other hand, as in Comparative Examples 1-3, when the primer layer did not contain an ester-based polymer, the surface energy of the multilayer film was low, resulting in poor cross-cut test results for the hard coat layer and low measured adhesive peel strength. Furthermore, when a polyimide (PI) film was used, as in Comparative Example 4, or when no primer layer was formed, as in Comparative Example 5, the cross-cut test results for the hard coat layer were poor, and low measured adhesive peel strength. [Explanation of symbols]

[0227] 3: Test solution 10a: Sample (substrate layer) 10b: Sample (Functional Layer) 10c: Sample (surface) 11: Multilayer film based on one implementation example 12: Multilayer film as an alternative implementation example 13: Multilayer films as another implementation example 21: Alignment Plate 22a: Upper jig 22b: Lower jig 100: Base material layer 200: Primer layer 210: First primer layer 220: Second primer layer 300: Functional Layer 310: 1st functional layer 320: 2nd functional layer

Claims

1. It is a multilayer film, A substrate layer containing a polyamide polymer, The substrate layer includes a primer layer formed on the substrate layer, The aforementioned polyamide polymer is a copolymer containing amide repeating units and imide repeating units. The molar ratio of the imide-based repeating unit to the amide-based repeating unit is 2:98 to 70:

30. The primer layer comprises 60% to 95% by weight of polyester resin and 5% to 40% by weight of polyurethane resin, based on the total weight of the primer layer. The thickness of the primer layer is 0.03 μm to 1.0 μm. The surface of the primer layer was subjected to a cross-cut test based on the ASTM D3359 standard, and the result was 4B or higher. The multilayer film further includes a functional layer, The primer layer is interposed between the substrate layer and the functional layer. The functional layer is one or more selected from the group consisting of a hard coat layer, an optical adhesive layer, and a printed coating layer. The result of a cross-cut test on the surface of the hard coat layer or the printed coat layer according to the ASTM D3359 standard is 5B or higher. A multilayer film having an optical adhesive layer with respect to the substrate layer having a 180° peel strength of 0.8 kgf / inch or more according to the ASTM D903 standard.

2. The multilayer film according to claim 1, wherein the surface energy of the primer layer is 30 dyne to 70 dyne.

3. Haze is 3% or less, The light transmittance is 85% or more. The multilayer film according to claim 1, wherein the yellowness index (YI) is 5 or less.

4. The steps include preparing a substrate layer containing a polyamide polymer, The steps include applying the primer layer composition onto the substrate layer and drying it, The aforementioned polyamide polymer is a copolymer containing amide repeating units and imide repeating units. The molar ratio of the imide-based repeating unit to the amide-based repeating unit is 2:98 to 70:

30. The primer layer composition comprises a polymer resin and a solvent. The method for producing a multilayer film according to claim 1, wherein the polymer resin comprises 60% to 95% by weight of polyester resin and 5% to 40% by weight of polyurethane resin based on the total weight of solids in the primer layer composition, and the solvent comprises more than 75% by weight of water and less than 25% by weight of isopropyl alcohol based on the total weight of the solvent.

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