Polyamide-imide film and preparation method thereof

Abstract

The invention discloses a polyamide-imide film and a preparation method thereof, wherein the polyamide-imide film has a specific perforation characteristic, is colorless and transparent, and has excellent mechanical properties and optical properties. The polyamide-imide film comprises a polyamide-imide polymer formed by polymerization of an aromatic diamine compound, an aromatic dianhydride compound, and a dicarbonyl compound, and satisfies the following general formula (1). General formula (1) 4≤X / Y≤12; X: when the film is perforated at a rate of 10mm / min using a 2.5mm spherical tip in UTM compression mode, the maximum diameter (mm) of the perforation including cracks; Y: modulus (GPa) of the film.

Description

[0001] This application is a divisional application of 201880010612.5. The application date of the original application is February 5, 2018, the application number is 201880010612.5, and the invention name is polyamide-imide film and preparation method thereof. Technical Field

[0002] The invention relates to a polyamide-imide film which has specific perforation characteristics, is colorless and transparent, and has excellent mechanical and optical properties, and a preparation method thereof. Background Art

[0003] Since polyamide-imide (PAI) has excellent friction resistance, heat resistance, and chemical resistance, it is used in, for example, primary electrical insulation, coatings, adhesives, extrusion resins, heat-resistant paints, heat-resistant sheets, heat-resistant adhesives, heat-resistant fibers, and heat-resistant films.

[0004] Polyamide-imide is used in various fields. For example, powder made of polyamide-imide is used as a coating for metal wires or magnet wires. It can be mixed with other additives depending on its application. In addition, polyamide-imide is used as a decorative and anti-corrosion coating together with fluoropolymers. It also serves to bond the fluoropolymer to the metal substrate. Further, polyamide-imide is used to coat kitchenware, can be used as a gas separation membrane due to its heat resistance and chemical resistance, and is used in natural gas wells to filter pollutants such as carbon dioxide, hydrogen sulfide, and impurities.

[0005] In recent years, polyamide-imide has been developed in the form of films, which are lower in cost and have excellent optical, mechanical and thermal properties. Summary of the invention

[0006] Technical issues

[0007] The embodiment aims to provide a polyamide-imide film having specific perforation characteristics, being colorless and transparent, and having excellent mechanical and optical properties, and a preparation method thereof.

[0008] Solution to the problem

[0009] According to one embodiment, a polyamide-imide film is provided, which includes a polyamide-imide polymer formed by polymerization of an aromatic diamine compound, an aromatic dianhydride compound, and a dicarbonyl compound, and satisfies the following relationship 1:

[0010] [Relation 1]

[0011] 4≤X / Y≤12

[0012] Where X is the maximum diameter of the perforation including cracks when the membrane is perforated at a rate of 10 mm / min using a 2.5 mm spherical tip in UTM compression mode (mm); and

[0013] Y is the modulus of the film (GPa).

[0014] According to another embodiment, a method for preparing a polyamide-imide film is provided, which includes: polymerizing an aromatic diamine compound, an aromatic dianhydride compound and a dicarbonyl compound to prepare a polyamide-imide polymer solution; adding the polymer solution into a container (tank); extruding and casting the polymer solution in the container, and then drying the cast polymer solution to prepare a gel sheet; and heat-treating the gel sheet, wherein the viscosity of the polymer solution is 100,000 to 300,000 cps, the heat treatment is carried out in a temperature range of 80 to 500°C at a heating rate of 2°C / min to 80°C / min for 5 to 40 minutes, and the maximum temperature of the heat treatment is 300 to 500°C.

[0015] Advantageous Effects of the Invention

[0016] The polyamide-imide film prepared according to the present embodiment has specific perforation characteristics and is colorless and transparent and has excellent mechanical and optical properties.

[0017] According to the method for preparing a polyamide-imide film of the present embodiment, a polyamide-imide film having specific perforation characteristics, being colorless and transparent, and having excellent mechanical and optical properties can be provided.

[0018] Best Mode for Carrying Out the Invention

[0019] The present invention will be described in detail below with reference to the embodiments. The embodiments can be modified into various forms as long as the gist of the present invention is not changed.

[0020] In the present specification, unless otherwise specified, when it is mentioned that a part “includes / comprising” a certain component, it should be understood that the part may also include / comprising other components.

[0021] Furthermore, unless otherwise indicated, all numbers and expressions relating to amounts of components, reaction conditions, and so forth used herein are to be understood as being modified by the word "about."

[0022] The terms "first", "second", etc. used herein are used to describe various components, and these components should not be limited by the terms. These terms are used only to distinguish one component from another.

[0023] [Polyamide-imide film]

[0024] One embodiment provides a polyamide-imide film having specific perforation characteristics, being colorless and transparent, and having excellent mechanical and optical properties.

[0025] The polyamide-imide film prepared according to the embodiment includes a polyamide-imide polymer formed by polymerizing an aromatic diamine compound, an aromatic dianhydride compound, and a dicarbonyl compound.

[0026] The molar ratio of the aromatic diamine compound to the aromatic dianhydride compound may be 10:2 to 10:4, and specifically 10:2 to 10:3. If the molar ratio range is satisfied, a polyamide-imide film having excellent mechanical and optical properties may be provided.

[0027] The polyamide-imide polymer includes an imide repeating unit formed by polymerizing an aromatic diamine compound and an aromatic dianhydride compound and an amide repeating unit formed by polymerizing an aromatic diamine compound and a dicarbonyl compound.

[0028] The aromatic diamine compound is a compound that forms an imide bond with the aromatic dianhydride compound and an amide bond with the dicarbonyl compound, thereby forming a copolymer.

[0029] In one embodiment, one aromatic diamine may be used as the aromatic diamine compound. If a single aromatic diamine compound is used, the chemical structure of the polyamide-imide polymer may be easily designed and the preparation efficiency may be improved.

[0030] For example, the aromatic diamine compound may include 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFDB) as shown in Formula 1 below, but is not limited thereto.

[0031] [Formula 1]

[0032]

[0033] The aromatic dianhydride compound is a compound that can help improve the optical properties of the polyamide-imide film, such as light transmittance, because it has a low birefringence value.

[0034] In one embodiment, an aromatic dianhydride may be used as the aromatic diamine compound. If a single aromatic diamine compound is used, the chemical structure of the polyamide-imide polymer can be easily designed and the preparation efficiency can be improved.

[0035] The aromatic dianhydride compound may include a compound having a fluorine-containing substituent. Alternatively, the aromatic dianhydride compound may be composed of a compound having a fluorine-containing substituent. In this case, the fluorine-containing substituent may be a fluorinated hydrocarbon group, particularly a trifluoromethyl group. However, it is not limited thereto.

[0036] For example, the aromatic dianhydride compound may include 2,2′-di-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6-FDA) as shown in Formula 2 below, but is not limited thereto.

[0037] [Formula 2]

[0038]

[0039] The aromatic diamine compound and the dianhydride compound may be polymerized to form a polyamic acid.

[0040] Then, the polyamic acid may be converted into a polyimide through a dehydration reaction, the polyimide comprising an imide repeating unit.

[0041] For example, the polyimide may include a compound as shown in Formula 3 below, but is not limited thereto.

[0042] [Formula 3]

[0043]

[0044] In the above formula 3, n is an integer of 1-400.

[0045] The dicarbonyl compound may include at least two dicarbonyl compounds different from each other.

[0046] For example, the dicarbonyl compound may include a first dicarbonyl compound and / or a second dicarbonyl compound.

[0047] The first dicarbonyl compound and the second dicarbonyl compound may be aromatic dicarbonyl compounds, respectively.

[0048] The first dicarbonyl compound and the second dicarbonyl compound may be different compounds from each other.

[0049] For example, the first dicarbonyl compound and the second dicarbonyl compound may be aromatic dicarbonyl compounds different from each other, but are not limited thereto.

[0050] If the first dicarbonyl compound and the second dicarbonyl compound are respectively aromatic dicarbonyl compounds, they contain benzene rings, and thus they can contribute to improving the mechanical properties of the polyamide-imide film prepared therefrom, such as surface hardness and tensile strength.

[0051] In one embodiment, two aromatic dicarbonyl compounds may be used as the dicarbonyl compound. If two aromatic dicarbonyl compounds are used, the chemical structure of the polyamide-imide polymer can be designed to achieve desired properties, and the production efficiency can be improved.

[0052] The dicarbonyl compound may include terephthaloyl chloride (TPC), 1,1′-biphenyl-4,4′-dicarbonyl dichloride (BPDC), or a combination thereof, but is not limited thereto.

[0053] For example, the first dicarbonyl compound may include 1,1′-biphenyl-4,4′-dicarbonyl dichloride (BPDC) as shown in Formula 4 below, but is not limited thereto.

[0054] [Formula 4]

[0055]

[0056] In addition, the second dicarbonyl compound may include terephthaloyl chloride (TPC) as shown in Formula 5 below, but is not limited thereto.

[0057] [Formula 5]

[0058]

[0059] If 1,1'-biphenyl-4,4'-dicarbonyldichloride (BPDC) is used as the first dicarbonyl compound and terephthaloyl chloride (TPC) is used as the second dicarbonyl compound, in an appropriate combination, the polyamide-imide film prepared thereby can have higher oxidation resistance.

[0060] In addition, the aromatic diamine compound and the dicarbonyl compound may be polymerized to form an amide repeating unit as shown in Formula 6 and Formula 7 below.

[0061] [Formula 6]

[0062]

[0063] [Formula 7]

[0064]

[0065] In the above formula 6, x is an integer of 1-400.

[0066] In the above formula 7, y is an integer of 1-400.

[0067] According to another embodiment, the polyamide-imide film may include a polyamide-imide polymer formed by polymerization of an aromatic diamine compound, an aromatic dianhydride compound and a dicarbonyl compound, wherein the aromatic diamine compound may include one aromatic diamine compound, the aromatic dianhydride compound may include one aromatic dianhydride compound, and the dicarbonyl compound may include two aromatic dicarbonyl compounds.

[0068] For example, the aromatic diamine compound may include 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB), the aromatic dianhydride compound may include 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6-FDA), and the dicarbonyl compound may include terephthaloyl chloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloride (BPDC), or a combination thereof, but is not limited thereto.

[0069] Alternatively, the aromatic diamine compound may consist of one diamine compound, the aromatic dianhydride compound may consist of one aromatic dianhydride compound, and the dicarbonyl compound may consist of two dicarbonyl compounds.

[0070] For example, the aromatic diamine compound may consist of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB), the aromatic dianhydride compound may consist of 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6-FDA), and the dicarbonyl compound may consist of terephthaloyl chloride (TPC) and 1,1'-biphenyl-4,4'-dicarbonyl dichloride (BPDC).

[0071] The present embodiment is characterized in that it is possible to provide a polyamide-imide film whose optical characteristics, mechanical properties and flexibility are improved in a balanced manner by appropriately controlling the contents of imide repeating units and amide repeating units without requiring a complicated process.

[0072] Furthermore, it is possible to provide a polyamide-imide film having well-balanced improvements in optical characteristics, mechanical properties, and flexibility without requiring the steps of precipitation, filtration, drying, and redissolution employed in the prior art.

[0073] The content of the imide repeating unit and the amide repeating unit may be controlled by the amount of the aromatic dianhydride compound and the dicarbonyl compound.

[0074] In the polyamide-imide polymer included in the polyamide-imide film, a molar ratio of the imide repeating unit to the amide repeating unit may be 50:50 to 20:80, but is not limited thereto.

[0075] If the molar ratio of the imide repeating unit to the amide repeating unit is within the above range, the polyamide-imide film has excellent optical properties such as light transmittance and haze.

[0076] The polyamide-imide film satisfies the following relationship 1:

[0077] [Relation 1]

[0078] 4≤X / Y≤12

[0079] Where X is the maximum diameter of the perforation including cracks when the film is perforated at a rate of 10 mm / min using a 2.5 mm spherical tip in UTM compression mode (mm); and Y is the modulus of the film (GPa).

[0080] The polyamide-imide film may have a compressive strength of 0.4 kgf / μm or more based on a thickness of 50 μm, and in particular, the compressive strength may be 0.45 kgf / μm or more, or 0.46 kgf / μm or more, but is not limited thereto.

[0081] The polyamide-imide film is based on a thickness of 50 μm, and the maximum diameter (X) of the perforation may be 60 mm or less. In particular, the maximum diameter of the perforation may be 5 to 60 mm, 10 to 60 mm, 15 to 60 mm, 20 to 60 mm, 25 to 60 mm, or 25 to 58 mm, but it is not limited thereto.

[0082] The polyamide-imide film may have a modulus of 5.0 GPa or more based on a thickness of 50 μm, and in particular, the modulus may be 5.1 GPa or more, but is not limited thereto.

[0083] The polyamide-imide film may have a surface hardness of HB or higher. Specifically, the surface hardness may be H or higher, or 2H or higher, but is not limited thereto.

[0084] The polyamide-imide film may have a yellowness index (YI) of 5 or less based on a thickness of 50 μm. Specifically, the yellowness index may be 4.5 or less, but is not limited thereto. More specifically, the yellowness index may be 4 or less, 3.8 or less, or 3.6 or less, but is not limited thereto.

[0085] The polyamide-imide film may have a haze of 2% or less based on a thickness of 50 μm. Specifically, the haze may be 1.8% or less, or 1.5% or less, but it is not limited thereto. More specifically, the haze may be 1.0% or less, or 0.9% or less, but it is not limited thereto.

[0086] The polyamide-imide film may have a light transmittance of 85% or more measured at 550 nm based on a thickness of 50 μm. In particular, the light transmittance measured at 550 nm based on a thickness of 50 μm may be 86% or more, 87% or more, or 88% or more, but is not limited thereto.

[0087] The polyamide-imide film can have a thickness of 15 kgf / mm based on a thickness of 50 μm. 2In particular, the tensile strength may be 18 kgf / mm 2 or greater, but it is not limited thereto.

[0088] The polyamide-imide film may have an elongation of 15% or more based on a thickness of 50 μm, and in particular, the elongation may be 16% or more, but is not limited thereto.

[0089] The various properties of the polyamide-imide films described above can be combined.

[0090] For example, the polyamide-imide film may include a polyamide-imide polymer formed by polymerizing an aromatic diamine compound, an aromatic dianhydride compound, and a dicarbonyl compound, and may satisfy the above-mentioned Relationship 1.

[0091] As another example, the polyamide-imide film can satisfy the above-mentioned relationship 1 and, based on a thickness of 50 μm, can have a compressive strength of 0.4 kgf / μm or greater, a maximum diameter of a perforation of 60 mm or less, a modulus of 5.0 GPa or greater, a surface hardness of HB or greater, a yellowness index of 5 or less, a haze of 2% or less, and a light transmittance of 85% or greater measured at 550 nm.

[0092] As another example, the polyamide-imide film may include a polyamide-imide polymer formed by polymerization of an aromatic diamine compound, an aromatic dianhydride compound, and a dicarbonyl compound, wherein the aromatic diamine compound may include 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB), the aromatic dianhydride compound may include 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6-FDA), and the dicarbonyl compound may include terephthaloyl chloride (TPC), 1,1'-biphenyl-4,4'-dicarbonyl dichloride (BPDC), or a combination thereof.

[0093] [Method for preparing polyamide-imide film]

[0094] According to one embodiment, a method for preparing a polyamide-imide film may include polymerizing an aromatic diamine compound, an aromatic dianhydride compound, and a dicarbonyl compound to prepare a polyamide-imide polymer solution; adding the polymer solution into a tank; extruding and casting the polymer solution in the tank, and then drying the cast polymer solution to prepare a gel sheet; and heat-treating the gel sheet, wherein the viscosity of the polymer solution is 100,000 to 300,000 cps.

[0095] In addition, the dicarbonyl compound may include a first dicarbonyl compound and a second dicarbonyl compound. In this case, the step of preparing the polymer solution may include polymerizing an aromatic diamine compound, an aromatic dianhydride compound, a first dicarbonyl compound, and a second dicarbonyl compound in an organic solvent to obtain a first polymer solution; and further adding the second dicarbonyl compound to the first polymer solution to obtain a second polymer solution, but is not limited thereto.

[0096] In particular, the preparation method of the polyamide-imide film includes polymerizing an aromatic diamine compound, an aromatic dianhydride compound, a first dicarbonyl compound and a second dicarbonyl compound in an organic solvent to obtain a first polymer solution; further adding the second dicarbonyl compound to the first polymer solution to obtain a second polymer solution with a viscosity of 100,000-300,000 cps; adding the second polymer solution into a container; extruding and casting the second polymer solution in the container, and then drying the cast second polymer solution to prepare a gel sheet; and heat-treating the gel sheet.

[0097] The organic solvent used in the polymerization reaction may be at least one of dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), meta-cresol, tetrahydrofuran (THF) and chloroform, but is not limited thereto. In particular, the organic solvent used in the polymerization reaction may be dimethylacetamide (DMAc), but is not limited thereto.

[0098] The step of obtaining the first polymer solution may include polymerizing the aromatic diamine compound, the aromatic dianhydride compound, the first dicarbonyl compound, and the second dicarbonyl compound simultaneously or sequentially.

[0099] In particular, in one embodiment, the step of obtaining the first polymer solution may include simultaneously polymerizing the aromatic diamine compound, the aromatic dianhydride compound, the first dicarbonyl compound, and the second dicarbonyl compound.

[0100] In another embodiment, the step of obtaining the first polymer solution may include polymerizing the aromatic diamine compound and the aromatic dianhydride compound to obtain a polyamic acid solution; and, adding the first dicarbonyl compound and the second dicarbonyl compound to the polyamic acid solution for polymerization. The polyamic acid solution is a solution containing polyamic acid.

[0101] In another embodiment, the step of obtaining the first polymer solution may include polymerizing the aromatic diamine compound and the aromatic dianhydride compound to obtain a polyamic acid solution; dehydrating the polyamic acid solution to obtain a polyimide solution; and adding the first dicarbonyl compound and the second dicarbonyl compound to the polyimide solution for polymerization. The polyimide solution is a solution containing a polymer having an imide repeating unit.

[0102] In another embodiment, the step of obtaining the first polymer solution may include polymerizing the aromatic diamine compound, the first dicarbonyl compound and the second dicarbonyl compound to obtain an amide polymer solution; and, adding the aromatic dianhydride compound to the amide polymer solution for polymerization. The amide polymer solution is a solution containing a polymer having an amide repeating unit.

[0103] The copolymer contained in the first polymer solution includes an imide repeating unit obtained by polymerizing the aromatic diamine compound and the aromatic dianhydride compound, and an amide repeating unit obtained by polymerizing the aromatic diamine compound and the dicarbonyl compound.

[0104] In the step of obtaining the first polymer solution, in the step of obtaining the second polymer, or after the step of obtaining the second polymer, a catalyst may be further added.

[0105] Examples of the catalyst include, but are not limited to, β-picoline, acetic anhydride, and the like.

[0106] Further adding the catalyst can accelerate the reaction rate and produce an effect of increasing the binding force between or within the repeating unit structures.

[0107] In addition, in the step of adding a catalyst, drying and re-dissolving the polymer solution, or in the step of adding a solvent in the extrusion step, the viscosity of the polymer solution may be appropriately adjusted.

[0108] In another embodiment, the step of obtaining the first polymer solution may include adding the aromatic dianhydride compound, the first dicarbonyl compound, and the second dicarbonyl compound to an excess amount of the aromatic diamine compound.

[0109] Particularly, the aromatic dianhydride compound may be used in an amount of 20 mol % to 50 mol % based on the total moles of the aromatic dianhydride compound, the first dicarbonyl compound, and the second dicarbonyl compound, but is not limited thereto.

[0110] If the content of the aromatic dianhydride compound is within the above range, the polyamide-imide film has excellent mechanical properties in terms of modulus, tensile strength, elongation, surface hardness, and the like.

[0111] In addition, the first dicarbonyl compound and the second dicarbonyl compound may be used in an amount of 50 mol % to 80 mol % based on the total moles of the aromatic dianhydride compound, the first dicarbonyl compound, and the second dicarbonyl compound, but is not limited thereto.

[0112] If the content of the dicarbonyl compound is within the above range, the polyamide-imide film has excellent optical properties in terms of light transmittance, haze, and the like.

[0113] In another embodiment, in the step of obtaining the first polymer solution, the first dicarbonyl compound may be used in an amount of 50 mol % to 70 mol % based on the total moles of the first dicarbonyl compound and the second dicarbonyl compound, but is not limited thereto.

[0114] The first dicarbonyl compound may be 1,1′-biphenyl-4,4′-dicarbonyl dichloride (BPDC), and the second dicarbonyl compound may be terephthaloyl dichloride (TPC).

[0115] If the content of the first dicarbonyl compound is less than 50 mol%, the physical properties of the polyamide-imide film, such as tensile strength and modulus, may be reduced. If the content of the first dicarbonyl compound exceeds 70 mol%, the optical properties, such as haze, may be reduced.

[0116] Preferably, in the step of obtaining the first polymer solution, (I) an excess of the aromatic diamine compound, at least the same molar amount as the other reactants, (II) 20 mol % to 50 mol % of the aromatic dianhydride compound based on the total molar number of the aromatic dianhydride compound, the first dicarbonyl compound and the second dicarbonyl compound, and (III) 50 mol % to 80 mol % of the first dicarbonyl compound and the second dicarbonyl compound based on the total molar number of the aromatic dianhydride compound, the first dicarbonyl compound and the second dicarbonyl compound can be used.

[0117] Specifically, 50 mol % to 70 mol % of the first dicarbonyl compound (e.g., 1,1'-biphenyl-4,4'-dicarbonyldichloride, BPDC) based on the total moles of the first dicarbonyl compound and the second dicarbonyl compound, and 30 mol % to 50 mol % of the second dicarbonyl compound (e.g., terephthaloyl chloride, TPC) based on the total moles of the first dicarbonyl compound and the second dicarbonyl compound can be used.

[0118] By properly controlling the contents of imide repeating units and amide repeating units, a polyamide-imide film can be provided whose optical characteristics, mechanical properties and flexibility are improved in a balanced manner without requiring the steps of precipitation, filtration, drying and redissolution used in the prior art.

[0119] After the step of obtaining the first polymer solution, a second dicarbonyl compound may be further added to the first polymer solution to obtain a second polymer solution having a viscosity of 100,000 to 300,000 cps.

[0120] A weight ratio of the second dicarbonyl compound added in the step of obtaining the first polymer solution to the second dicarbonyl compound added in the step of obtaining the second polymer solution may be 90:10 to 99:1, but is not limited thereto.

[0121] In addition, the second dicarbonyl compound added in the step of obtaining the second polymer solution may be in the form of a solution in which the second dicarbonyl compound is dissolved in an organic solvent at a concentration of 5 to 20 wt %, but is not limited thereto.

[0122] This facilitates achieving exactly the desired viscosity.

[0123] The viscosity of the second polymer solution may be 100,000 to 300,000 cps, but is not limited thereto.

[0124] If the viscosity of the second polymer solution is within the above range, the polyamide-imide film can be efficiently prepared in the extrusion and casting steps. In addition, the polyamide-imide film prepared thereby can have improved mechanical properties such as modulus.

[0125] According to one embodiment, the second polymer solution may include a solid content of 10 wt % to 20 wt %. Specifically, the second polymer solution may include a solid content of 12 wt % to 18 wt %, but is not limited thereto.

[0126] If the second polymer solution contains a solid content within the above range, the polyamide-imide film can be efficiently prepared in the extrusion and casting steps. In addition, the polyamide-imide film prepared thereby can have improved mechanical properties such as modulus and optical properties such as low yellowness index.

[0127] After obtaining the second polymer solution, the pH of the second polymer solution may be adjusted by adding a neutralizing agent.

[0128] Examples of the neutralizing agent include, but are not limited to, amine-based neutralizing agents such as alkoxyamines, alkylamines, alkanolamines, and the like.

[0129] The neutralizing agent may be used in an amount of about 0.1 mol % to about 10 mol % based on the total moles of monomers in the polyamide-imide polymer solution.

[0130] The pH of the second polymer solution adjusted by the neutralizer may be about 4 to about 7. In particular, the pH of the second polymer solution may be about 4.5 to about 7 after being adjusted.

[0131] If the pH of the second polymer solution is within the above range, damage to the equipment in the subsequent extrusion and casting steps can be prevented. In addition, the polyamide-imide film thus prepared can have improved optical properties due to reduced yellow index or prevention of increase in yellow index, and improved mechanical properties in terms of modulus, etc.

[0132] After the step of obtaining the polymer solution or after the step of obtaining the second polymer solution, the polymer solution may be added to a tank.

[0133] Here, once the polymer solution is obtained, the step of transferring the polymer solution to the container is performed, and no additional steps are required. In particular, the polymer solution prepared in the polymerization device is transferred and stored in the container without any separate precipitation and redissolution to remove impurities. In the conventional method, in order to remove impurities generated during the preparation of the polymer solution, such as hydrochloric acid (HCl), the prepared polymer solution needs to be purified by a separate step to remove impurities, and then the purified polymer solution is redissolved in a solvent. However, in this case, there is an increase in the loss of active ingredients in the step of removing impurities, resulting in a problem of reduced yield.

[0134] Therefore, the preparation method according to the present embodiment ultimately minimizes the amount of impurities generated in the step of preparing the polymer solution or appropriately controls the impurities in the subsequent steps, and even if a certain amount of impurities exist, it will not cause the physical properties of the final film to deteriorate. Therefore, the method has the advantage of not requiring a separate precipitation or redissolution step when preparing the film.

[0135] Here, the temperature in the container is preferably -20 to 0° C. This is to prevent degradation of the added polymer solution and reduce the water content therein.

[0136] After the step of adding the prepared polymer solution into the container, the method may further include vacuum degassing for 1 to 2 hours until the pressure in the container is reduced to 0.2 to 0.4 bar.

[0137] Alternatively, after the step of adding the prepared polymer solution into the container, the method may further include purging the container with nitrogen at a pressure of 1 to 2 atmospheres.

[0138] The vacuum degassing step and the step of purging the container with nitrogen are performed in separate processes.

[0139] For example, the vacuum degassing step may be performed first, and then the nitrogen purging step may be performed, but it is not limited thereto.

[0140] The step of vacuum degassing and / or the step of purging the container with nitrogen may improve physical properties of the surface of the polyamide-imide film obtained thereby.

[0141] Then, the polymer solution in the container is extruded and cast, and the cast polymer solution is then dried to prepare a gel sheet.

[0142] In the above-mentioned extrusion and casting steps, the above-mentioned organic solvents may be used.

[0143] The polymer solution is extruded and cast onto a casting body such as a casting roll, a casting belt, etc. In this case, the polymer solution is cast onto the casting body at a rate of about 0.5 m / min to about 15 m / min and a thickness of 200 to 700 μm. If the extrusion and casting rates are within the above ranges, the polyamide-imide film prepared by the preparation method of the present embodiment can have improved optical properties and mechanical properties.

[0144] That is, if the viscosity of the polymer solution is within the above range, extrusion and casting at the above extrusion rate may be advantageous in improving its optical and mechanical properties.

[0145] After the polymer solution is cast on the casting body, the solvent contained in the polymer solution may be removed through a drying step, thereby forming a gel sheet on the casting body.

[0146] The drying step may be performed at a temperature of about 60° C. to about 150° C. for about 5 minutes to about 60 minutes.

[0147] Thereafter, the gel sheet is heat-treated, thereby manufacturing the polyamide-imide film according to the present embodiment.

[0148] The heat treatment may be performed at a temperature range of 80 to 500° C., at a heating rate of 2° C. / min to 80° C. / min, for 5 to 40 minutes or 5 to 30 minutes. In particular, the heat treatment may be performed at a temperature range of 80 to 470° C., at a heating rate of 10° C. / min to 80° C. / min, for 5 to 30 minutes or 5 to 20 minutes.

[0149] The maximum temperature of the heat treatment may be 300-500° C. or 320-500° C. More specifically, the maximum temperature in the heat treatment may be 350-500° C., 380-500° C., 400-500° C., 410-480° C., 410-470° C. or 410-450° C., but is not limited thereto.

[0150] After the heat treatment step, a step of cooling the heat-treated plate may be further performed. The cooling step may include a first cooling step with a cooling rate of 100°C / min to 1000°C / min and a second cooling step with a cooling rate of 40°C / min to 400°C / min.

[0151] In particular, the second temperature reduction step may be performed after the first temperature reduction step.

[0152] In addition, the temperature reduction rate of the first temperature reduction step may be faster than the temperature reduction rate of the second temperature reduction step.

[0153] For example, the maximum rate of the first temperature reduction step is faster than the maximum rate of the second temperature reduction step. Alternatively, the minimum rate of the first temperature reduction step is faster than the minimum rate of the second temperature reduction step.

[0154] Since the polyamide-imide polymer has high oxidation resistance, it is hardly affected by oxygen contained in the atmosphere during the heat treatment step. Therefore, the polyamide-imide film prepared according to the present embodiment can have improved optical characteristics.

[0155] Furthermore, when a polyimide film is formed in a conventional method, nitrogen purging is required to prevent the film from yellowing and ensure the transparency of the film. However, according to the present embodiment, a polyamide-imide film having excellent optical characteristics can be produced without nitrogen purging.

[0156] For details of the polyamide-imide film obtained by the method for producing the polyamide-imide film, reference may be made to the description in the above-mentioned [Polyamide-imide film] section.

[0157] For example, the polyamide-imide film produced by the above-mentioned production method can satisfy the above-mentioned relationship 1.

[0158] Invention

[0159] The present invention is described in detail below with reference to examples. However, the following examples are intended to further illustrate the present invention, and the scope of the present invention is not limited thereto.

[0160] Examples 1-7

[0161] Dimethylacetamide (DMAc) as an organic solvent was charged into a 1 L glass reactor equipped with a temperature-controllable double jacket under a nitrogen atmosphere at 20° C. Then, 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFDB) as an aromatic diamine was slowly added thereto to dissolve it.

[0162] Subsequently, 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6-FDA) as an aromatic dianhydride was slowly added thereto while the mixture was stirred for 1 hour.

[0163] Then, 1,1'-biphenyl-4,4'-dicarbonyldichloride (BPDC) was added as the first dicarbonyl compound and stirred for 1 hour, and terephthaloyl dichloride (TPC) was added as the second dicarbonyl compound and stirred for 1 hour to prepare a first polymer solution.

[0164] The viscosity of the first polymer solution thus prepared was measured. If the measured viscosity did not reach the target viscosity, a TPC solution having a mass concentration of 10% in a DMAc organic solvent was prepared, and 1 mL of the TPC solution was added to the aforementioned first polymer solution, followed by stirring for 30 minutes. This process was repeated until the viscosity fell within the range of 100,000 cps to 300,000 cps, thereby preparing a second polymer solution.

[0165] The second polymer solution was coated on a glass plate and then dried for 30 minutes under hot air at 80° C. The dried polyamide-imide polymer was peeled off the glass plate, fixed on a pin plate holder, and heat-treated at a temperature range of 80° C. to 500° C. at a heating rate of 2° C. / min to 80° C. / min for 30 minutes to obtain a polyamide-imide film with a thickness of 50 μm.

[0166] According to the above embodiment, the yield reaches about 100% just before the film forming step (ie before coating). The "yield" here refers to the ratio of the molar number of the residual material in the coating solution to the molar number of the added material.

[0167] According to the conventional preparation method, the yield immediately before the film-forming step is about 60% due to the inevitable loss of materials in the polyimidization, precipitation, filtration and drying steps.

[0168] In Examples 1 to 7, each polyamide-imide membrane was prepared by the same method as above, except that the molar ratios of TFDB, 6-FDA, TPC and BPDC were as shown in Table 1 below.

[0169] [Table 1]

[0170]

[0171] Comparative Examples 1-3

[0172] In Comparative Example 1, a colored PI film of the GF series provided by SKC Kolon PI was used.

[0173] In Comparative Example 2, an acrylic film produced in-house by SKC was used.

[0174] In Comparative Example 3, a PET film produced by SKC under the trade name SG65C was used.

[0175] [Evaluation Example]

[0176] The following properties of the films of Examples 1 to 7 and Comparative Examples 1 to 3 were measured and evaluated.

[0177] Evaluation Example 1: Measurement of film thickness

[0178] The thickness was measured at five points in the width direction using a digital micrometer (Digital Micrometer) 547-401 manufactured by Mitsutoyo Co., Ltd. of Japan, and the average value was taken as the thickness.

[0179] Evaluation Example 2: Measurement of compressive strength

[0180] The compressive strength of the film was measured using Instron's universal testing machine UTM 5566A. A sample was cut 10 cm in a direction perpendicular to the main shrinkage direction of the film and 10 cm in the main shrinkage direction. The tensile strength was measured when the sample was punctured when compressed at a rate of 10 mm / min using a 2.5 mm spherical tip in the UTM compression mode.

[0181] Evaluation Example 3: Measurement of the maximum diameter of perforations

[0182] The perforated sample was placed on a flat glass plate and the diameter was measured using a Tajima length measuring tape (GL19-55BL) as the longest distance from the center of the perforation to the periphery.

[0183] Evaluation Example 4: Measurement of modulus

[0184] The compressive strength of the film was measured using the universal testing machine UTM 5566A of Instron. A sample was cut at least 5 cm in the direction perpendicular to the main shrinkage direction of the film and 10 cm in the main shrinkage direction. The sample was fixed in the machine with clips set at intervals of 5 cm. At room temperature, the sample was stretched at a rate of 5 mm / min until it broke, and a stress-strain curve was obtained. In the stress-strain curve, the slope of the load relative to the initial strain was used as the modulus (GPa).

[0185] Evaluation Example 5: Measurement of surface hardness

[0186] The surface hardness was measured using a pencil hardness tester (CT-PC1, CORE TECH, Korea) with a pencil hardness measuring pen at an angle of 45°, a pencil speed of 300 mm / min, and a constant load (750 g). The pencils used were Mitsubishi pencils with strengths ranging from H to 9H, F, HB, and B to 6B.

[0187] Evaluation Example 6: Measurement of Yellowness Index (YI)

[0188] The yellowness index (YI) was measured using a spectrophotometer (UltraScan PRO, Hunter Associates Laboratory) using the CIE colorimetric system.

[0189] Evaluation Example 7: Measurement of light transmittance and haze (HZ)

[0190] The light transmittance and haze at 550 nm were measured using a haze meter NDH-5000W manufactured by Nippon Denshoku Kogyo.

[0191] [Table 2]

[0192]

[0193] As shown in Table 2 above, it can be seen that, unlike Comparative Examples 1-3, the polyamide-imide films in Examples 1-7 are colorless and transparent, and are excellent in mechanical and optical properties because they have a specific range of perforation characteristics (X / Y).

Claims

1. A polyamide-imide film comprising a polyamide-imide polymer formed by polymerization of an aromatic diamine compound, an aromatic dianhydride compound and a dicarbonyl compound, and satisfying the following relationship 1: [Relation 1] 4≤X / Y≤12 Where X is the maximum diameter of the perforation including cracks when the membrane is perforated at a rate of 10 mm / min using a 2.5 mm spherical tip in UTM compression mode; and Y is the modulus of the film, GPa; The polyamide-imide film has a compressive strength of 0.4 kgf / μm or more based on a thickness of 50 μm; The polyamide-imide film has a modulus of 5.0 GPa or more based on a thickness of 50 μm; The aromatic diamine compound is composed of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl; The aromatic dianhydride compound includes 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride; The dicarbonyl compound includes terephthaloyl chloride, 1,1′-biphenyl-4,4′-dicarbonyl dichloride or a combination thereof. 2 . The polyamide-imide film according to claim 1 , having a maximum diameter X of perforations of 60 mm or less based on a thickness of 50 μm.

3. The polyamide-imide film according to claim 1, having a surface hardness of HB or more, a yellowness index of 5 or less, a haze of 2% or less, and a light transmittance measured at 550 nm of 85% or more based on a thickness of 50 μm.

4. A method for preparing a polyamide-imide film according to claim 1, comprising: polymerizing an aromatic diamine compound, an aromatic dianhydride compound, and a dicarbonyl compound to prepare a polyamide-imide polymer solution; adding the polymer solution into a container; Extruding and casting the polymer solution in the container, and then drying the cast polymer solution to prepare a gel sheet; and subjecting the gel sheet to a heat treatment, wherein the viscosity of the polymer solution is 100,000 to 300,000 cps, the heat treatment is performed at a temperature range of 80 to 500° C. at a heating rate of 2° C. / min to 80° C. / min for 5 to 40 minutes, and the maximum temperature of the heat treatment is 400 to 500° C.; After the step of adding the prepared polymer solution into the container, the process further comprises vacuum degassing for 1 to 2 hours until the pressure in the container drops to 0.2 to 0.4 bar; and the temperature in the container is -20°C to 0°C.

5. The method for preparing a polyamide-imide film according to claim 4, characterized in that: After the step of adding the prepared polymer solution into the container, the method further comprises purging the container with nitrogen at a pressure of 1 to 2 atmospheres; and the drying is performed at a temperature of 60 to 150° C. for 5 to 60 minutes.

6. The method for preparing a polyamide-imide film according to claim 4, characterized in that: After the heat treatment step, the heat-treated plate is further subjected to a cooling treatment. Wherein, the cooling step includes a first cooling step with a cooling rate of 100°C / min to 1000°C / min and a second cooling step with a cooling rate of 40°C / min to 400°C / min; The second temperature reduction step is performed after the first temperature reduction step; and The cooling rate of the first cooling step is faster than the cooling rate of the second cooling step.

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