Thin film, multilayer electronic device and method for preparing thin film

Abstract

This embodiment proposes a film, a multilayer electronic device including the film, and a method for preparing the film. The film has excellent heat resistance, optical properties, adhesion, etc. due to the inclusion of a polyimide layer, and is therefore suitable for use as a support layer for a foldable display, etc. The film includes a polyimide layer containing an aromatic diamine compound residue and an aromatic dianhydride compound residue. Based on a thickness of 50 μm, the polyimide layer has a ring stiffness value of 3 N / m to 4.5 N / m. This embodiment provides a film that is more conducive to use in a foldable or rollable display, etc. due to its excellent folding resilience. In addition, a film, etc. is provided, which is suitable for use as a support layer for a foldable display, etc. due to its excellent heat resistance, optical properties, adhesion, etc.

Description

Technical Field

[0001] The present embodiment relates to a film, a multilayer electronic device including the film, and a method for preparing the film. The film has excellent heat resistance, optical properties, adhesion, etc. due to its polyimide layer, and is therefore excellent in use as a supporting layer for foldable displays, etc. Background Art

[0002] Since polyimide films have excellent heat resistance and mechanical properties, they are widely used in coatings, composite materials, etc. The above-mentioned polyimide films are usually prepared by coating a composition obtained by solution polymerization of aromatic diamine and aromatic dianhydride into a film, drying at high temperature, and performing ring closure through dehydration.

[0003] Polyimide films are yellow due to their high aromatic ring density, so they have low transmittance in the visible light region and are difficult to use as optical materials. However, in recent years, colorless and transparent polyimide films have been prepared, and various attempts have been made to apply them as optical materials.

[0004] As related prior arts, there are Korean Patent Publication No. 10-2007-0017001, Korean Granted Patent No. 10-1992525, and the like. Summary of the invention

[0005] Technical issues

[0006] The purpose of this embodiment is to provide a film having excellent rigidity, heat resistance and optical properties suitable for foldable or rollable displays, and a multilayer electronic device using the film, etc. Another purpose of this embodiment is to provide a film including a polyimide layer having excellent heat resistance, optical properties, adhesion properties, residual stress properties, etc. Another purpose of this embodiment is to provide a method for preparing the above-mentioned film, etc.

[0007] Solutions to the problem

[0008] To achieve the above object, a film according to an embodiment includes a polyimide layer including an aromatic diamine compound residue and an aromatic dianhydride compound residue, and the polyimide layer has a ring stiffness value of 3 N / m to 4.5 N / m based on a thickness of 50 μm.

[0009] The heat stability index (HS index) of the polyimide layer according to the following first formula can be 5°C 2 / ppm·MPa to 15℃ 2 / ppm·MPa.

[0010] First Form

[0011]

[0012] In the first formula,

[0013] The above HS index is the heat stability index (℃ 2 / ppm·MPa).

[0014] The above-mentioned Tg is the glass transition temperature (°C).

[0015] The above H is the value of the thermal expansion coefficient (ppm / ° C.) of the above polyimide layer.

[0016] The RS is the residual stress (MPa) value of the polyimide layer.

[0017] The adhesion of the polyimide layer may be greater than 200 gf / inch.

[0018] The yellowness of the polyimide layer may be 5.3 or less.

[0019] The comprehensive index of the polyimide layer represented by the following second formula can be 2°C 2 / ppm or above.

[0020] Second Form

[0021]

[0022] In the second formula,

[0023] The above T index is a comprehensive index.

[0024] The above-mentioned Tg is the glass transition temperature (°C).

[0025] The YI is a yellowness value of the polyimide layer at a thickness of 10 μm.

[0026] The above H is the value of the thermal expansion coefficient (ppm / ° C.) of the above polyimide layer.

[0027] The polyimide layer may include 5 to 45 mol of biphenyltetracarboxylic dianhydride residues based on 100 mol of the aromatic dianhydride compound residues as a whole.

[0028] The polyimide layer may contain a biphenyltetracarboxylic dianhydride residue and a pyromellitic dianhydride residue.

[0029] When the total number of moles of the biphenyltetracarboxylic dianhydride residue and the pyromellitic dianhydride residue is taken as a whole, the content of the biphenyltetracarboxylic dianhydride residue may be 15 mol % to 50 mol %.

[0030] When the entire amount of the aromatic dianhydride compound residue is taken as 100 mol %, the content of the pyromellitic dianhydride residue may be less than 60 mol %.

[0031] In order to achieve the above object, a multilayer electronic device according to another embodiment includes: a substrate layer, and a light-emitting functional layer, which is arranged on the substrate layer; the substrate layer includes a thin film, and the thin film is the thin film described above.

[0032] In order to achieve the above-mentioned purpose, according to another embodiment, the method for preparing a film includes: a polymer solution preparation step, by stirring a raw material composition containing an aromatic diamine compound and an aromatic dianhydride compound to prepare a polymer solution having a viscosity of 1000cps to 8000cps measured at 25°C; a sheet preparation step, coating the above-mentioned polymer solution in the form of a sheet and drying it with hot air to prepare the sheet; and a film preparation step, heat treating the above-mentioned sheet at 360°C to 480°C to prepare a polyimide layer.

[0033] The film includes the polyimide layer, the polyimide layer contains the aromatic diamine compound residue and the aromatic dianhydride compound residue, and the polyimide layer has a ring stiffness value of 3 N / m to 4.5 N / m based on a thickness of 50 μm.

[0034] The raw material composition or the polymer solution may further include a leveling stabilizer.

[0035] Effects of the Invention

[0036] The film of this embodiment, the multilayer electronic device including the film, and the method for preparing the film provide a film that is more advantageous for use in foldable or rollable displays, etc., due to excellent folding resilience. In addition, a film is provided, which is suitable for use as a support layer of a foldable display, etc., due to excellent heat resistance, optical properties, adhesion, etc. This embodiment provides a heat-resistant film including a polyimide layer with improved heat resistance and optical properties, etc., so that a thinner, lighter, and improved multilayer electronic device can be provided. In addition, by providing a reliable preparation method, a method for preparing a film with improved workability, etc. can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 and Figure 2 Each of them is a conceptual diagram illustrating a layer structure of a thin film according to an embodiment in cross section.

[0038] Figure 3 and Figure 4 Each of them is a conceptual diagram illustrating a layer structure of a multilayer electronic device according to an embodiment in cross section.

[0039] Figure 5A and Figure 5B A conceptual diagram illustrating the adhesion test process using a cross section.

[0040] Fig. 6A and Figure 6B A conceptual diagram illustrating the ring stiffness test process using a cross section.

[0041] Description of Reference Numerals

[0042] 100: Base material layer

[0043] 300: Light-emitting functional layer

[0044] 500: Overlay

[0045] 800: Multilayer Electronic Devices

[0046] 50: Polyimide layer

[0047] 60: Adhesive layer

[0048] G: Amorphous silicon (Si) based glass plate

[0049] T:Tape

[0050] LS-T1: Fixed part

[0051] LS-T2: Pressurizing part DETAILED DESCRIPTION

[0052] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in a variety of different embodiments and is not limited to the embodiments described in this specification. Throughout the specification, the same or similar components are given the same reference numerals.

[0053] In the present specification, when a component is described as “including” a component, unless there is a special description to the contrary, it means that other components are also included rather than excluded.

[0054] In this specification, when it is described that one component is “connected” to another component, it includes not only the case of being “directly connected” but also the case of being “connected with other component interposed therebetween”.

[0055] In the present specification, B being located on A means that B is located on A in direct contact or with another structure therebetween, and should not be limited to the meaning that B is located on the surface of A in contact.

[0056] In the present specification, the term "combination of..." included in the Markush-type description refers to a mixture or combination of one or more constituent elements selected from the group consisting of the constituent elements of the Markush-type description, thereby meaning that the present invention includes one or more constituent elements selected from the group consisting of the above constituent elements.

[0057] Throughout the present specification, descriptions in the form of "A and / or B" mean "A or B, or A and B".

[0058] Throughout the present specification, unless otherwise specified, terms such as "first", "second" or "A", "B" etc. are used to distinguish the same terms from each other.

[0059] Unless otherwise specified, the expression of a single type in the present specification is interpreted as including the meaning of the single type or plural types explained in the context.

[0060] In this specification, relative sizes, thicknesses, etc. of components shown in the drawings may be exaggerated for convenience of explanation.

[0061] In this specification, the yellowness (YI) is based on a value calculated according to ASTM E-313 standard using the CIE colorimetric system using a spectrophotometer (UltraScan PRO from Hunter Associates Laboratory).

[0062] In the present specification, the viscosity mentioned without mentioning a specific temperature refers to the viscosity measured at room temperature, illustratively, refers to the viscosity measured at 25°C.

[0063] Hereinafter, this embodiment will be described in more detail.

[0064] Polyimide films have characteristics of a brown colored film if they are excellent in heat resistance, but have characteristics of poor heat resistance if they are transparent films. That is, there is a trade-off relationship between heat resistance and transparency.

[0065] Based on the insulating properties of polyimide films, polyimide films are used as insulating layers of electronic products. In addition, based on the foldability or flexibility of the plastic film itself and the insulating properties of polyimide films, attempts to apply polyimide films to flexible displays or foldable displays continue.

[0066] Films used as support layers for displays must be able to withstand harsh environments such as repeated exposure to high temperatures during the display manufacturing process. In addition, residual stress must be controlled to ensure stable physical properties of other layers stacked on the support layer, and thermal expansion characteristics, etc., also need to be controlled.

[0067] In addition, in order to apply the polyimide layer to a foldable or rollable display, not only the ability to fold flexibly but also the ability to recover with appropriate elasticity is required. The present inventors prepared a film having a polyimide layer, confirmed its characteristics, and proposed the present embodiment, wherein the polyimide layer can satisfy various opposite characteristics required when used as a support layer of a display or the like at an appropriate level or more.

[0068] Figure 1 and Figure 2 Each of them is a conceptual diagram illustrating a layer structure of a thin film according to an embodiment in cross section, Figure 3 and Figure 4 Each of them is a conceptual diagram illustrating a layer structure of a multilayer electronic device according to an embodiment in cross section, Figure 5A and Figure 5B This is a conceptual diagram illustrating the adhesion test process in cross section. Fig. 6A and Figure 6B A conceptual diagram illustrating the ring stiffness test process using a cross section.

[0069] In the following, reference will be made to Figures 1 to 6B The thin films and the like applied to the multilayer electronic device 800 and the base material layer 100 are described in detail.

[0070] film

[0071] The film according to one embodiment includes a polyimide layer 50 (see Figure 1 ).

[0072] The polyimide layer 50 contains an aromatic diamine compound residue and an aromatic dianhydride compound residue.

[0073] The polyimide layer 50 may have excellent loop stiffness characteristics.

[0074] The polyimide layer 50 having a thickness of 50 μm may have a ring stiffness value of 3 N / m to 4.5 N / m. The polyimide layer 50 having a thickness of 50 μm may have a ring stiffness value of 3.1 N / m to 4.2 N / m. The polyimide layer 50 having a thickness of 50 μm may have a ring stiffness value of 3.2 N / m to 4.1 N / m.

[0075] In this case, since the polyimide layer has excellent bending resilience, when applied to a bendable or rollable multilayer electronic device, it can have better folding resilience.

[0076] The loop stiffness can be measured using a loop stiffness tester (LOOP STIFFNESS TESTER, TOYOSEIKI). The two ends of a polyimide film sample having a thickness of 50 μm are fixed to a fixed portion so that the width is 15 mm and the length is 120 mm, and the sample is pressurized at a pressurization speed of 3.3 mm / s using a pressurization portion until the final separation distance L between the pressurization portion and the fixed portion is 20 mm, and then the loop stiffness of the sample can be measured with a sensor. In the case of this embodiment, the value measured in the MD direction of the film as the length direction is used as a reference (refer to FIG. 6).

[0077] The heat stability index (HS index) of the polyimide layer 50 according to the following first formula can be 5°C 2 / ppm·MPa to 15℃ 2 / ppm·MPa.

[0078] First Form

[0079]

[0080] In the first formula,

[0081] The above HS index is the heat stability index (℃ 2 / ppm·MPa).

[0082] The above-mentioned Tg is the glass transition temperature (°C).

[0083] The above H is the value of the thermal expansion coefficient (ppm / ° C.) of the above polyimide layer.

[0084] The RS is the residual stress (MPa) value of the polyimide layer.

[0085] The heat stability index of the polyimide layer can be 5°C 2 / ppm·MPa or more. The above heat stability index can be 6℃ 2 / ppm·MPa or more. The above heat stability index can be 7℃ 2 / ppm·MPa or more. The above heat resistance stability index can be 7.3℃ 2 / ppm·MPa or more. The heat resistance stability index of the polyimide layer can be 15°C 2 / ppm·MPa or less. The above heat stability index can be 13℃ 2 / ppm·MPa or less.

[0086] When the polyimide layer has the above-mentioned heat resistance stability index, the polyimide layer has a higher glass transition temperature, a lower thermal expansion coefficient and a lower residual stress, and thus is very suitable for being used as a support layer of a multilayer electronic device.

[0087] The adhesion of the polyimide layer 50 may be 200 gf / inch or more. The adhesion may be 220 gf / inch or more. The adhesion may be 230 gf / inch or more. The adhesion of the polyimide layer 50 may be 350 gf / inch or less. The adhesion may be 330 gf / inch or less. The adhesion may be 300 gf / inch or less. The adhesion may be 280 gf / inch or less. When the polyimide layer has an adhesion within the above range, the polyimide layer as a supporting layer has an appropriate level of adhesion that is not excessive or sufficient with the composition of the light-emitting functional layer, etc., and therefore may have excellent properties as a substrate for a multilayer electronic device.

[0088] Adhesion force can be measured by a method for testing the adhesion of a polyimide layer. For example, the adhesion force can be measured by forming (curing) a polyimide layer on an amorphous silicon (Amorphous Si)-based glass substrate and then performing a peeling test using a UTM universal tester. Specifically, a portion of the polyimide layer can be lifted using a tape or the like, and a 180° peeling test can be performed, and the adhesion force can be measured using a UTM universal tester. As more specific conditions, the conditions proposed in the embodiments described below can be applied (refer to Figure 5A and Figure 5B ).

[0089] The comprehensive index of the polyimide layer 50 represented by the following second formula can be 2°C 2 / ppm or above.

[0090] Second Form

[0091]

[0092] In the second formula,

[0093] The above T index is a comprehensive index.

[0094] The above-mentioned Tg is the glass transition temperature (°C).

[0095] The YI is a yellowness value of the polyimide layer at a thickness of 10 μm.

[0096] The above H is the value of the thermal expansion coefficient (ppm / ° C.) of the above polyimide layer.

[0097] The comprehensive index of the polyimide layer 50 can be 2°C 2 / ppm or more. The above comprehensive index can be 2.2℃ 2 / ppm or more. The comprehensive index of the polyimide layer 50 can be 15°C 2 / ppm or less. The above comprehensive index can be 10℃ 2 / ppm or less. The above comprehensive index can be 7℃ 2 / ppm or less.

[0098] The thermal expansion coefficient of the polyimide layer 50 may be 35 ppm / °C or less. The thermal expansion coefficient may be 30 ppm / °C or less. The thermal expansion coefficient of the polyimide layer 50 may be 27 ppm / °C or less. The thermal expansion coefficient may be 25 ppm / °C or less. In addition, the thermal expansion coefficient of the polyimide layer 50 may be 10 ppm / °C or more. The thermal expansion coefficient may be 15 ppm / °C or more. In the case of having the above thermal expansion coefficient values, since the volume change caused by high thermal changes is small, it is suitable for use as a substrate for a multilayer electronic device.

[0099] As for the measurement of residual stress, the residual stress measurement method of polyimide film can be applied. Specifically, the residual stress can be measured using the 500TC (FSM 128) equipment of Frontier Semiconductor. Specifically, a polyimide layer is formed on a 6-inch silicon wafer whose bending amount has been measured in advance, and the residual stress is measured by comparing the difference in bending amount. A more specific method is based on the method described in the embodiment described below.

[0100] The residual stress of the polyimide layer 50 may be 25 MPa or less. The residual stress may be 22 MPa or less. The residual stress may be 20 MPa or less. The residual stress of the polyimide layer 50 may be 18 MPa or less. The residual stress may be 16 MPa or less. The residual stress of the polyimide layer 50 may be 10 MPa or more. When having the above-mentioned residual stress characteristics, the polyimide layer is highly useful as a support layer for multilayer electronic devices.

[0101] When stacking devices with a multilayer structure, stress due to physical mismatch may occur at the interface adjacent to the surface of the polyimide layer. This may cause problems such as cracks, inversion or interlayer peeling in the stack. This will not only cause serious problems in the manufacturing process of multilayer electronic devices, but also cause serious problems in the reliability of the product itself. Therefore, in order to apply the polyimide layer as a polyimide film as a support layer, it must have stable characteristics even in the process of repeated exposure to 350°C to 400°C temperature. As one of the several criteria that can be evaluated, residual stress can be applied. The residual stress is believed to be caused by the following factors: high heat applied during the preparation of the polyimide film (polyimide layer); difference in thermal expansion coefficient between the supporting substrate; and the rigidity of the polymer chain itself. This embodiment reduces the generation of residual stress while maintaining other characteristics above a certain level by applying the method described below.

[0102] The polyimide layer 50 may have a thickness of 2 μm to 100 μm, 2 μm to 55 μm, or greater than 2 μm and less than 40 μm.

[0103] The polyimide layer 50 has a constant thickness as a whole. Specifically, in the polyimide layer 50, when the polyimide layer 50 is divided into 40 regions having substantially equal areas, each thickness measured at 40 points in each region is within a range of -5% to +5% compared to the average value of the thickness measured at the 40 points in each region, and the thickness uniformity is excellent.

[0104] The polyimide layer 50 has excellent heat resistance characteristics.

[0105] The glass transition temperature of the polyimide layer 50 may be above 365°C. The glass transition temperature may be above 370°C. The glass transition temperature may be above 375°C. The glass transition temperature of the polyimide layer 50 may be below 390°C. The glass transition temperature is based on the result of measurement using a DMA measuring device. For example, the DMA measuring device adopts the DMA Q800 model of Texas Instruments, and the tension mode can be applied as the measurement mode. Specifically, the temperature is measured from 25°C to 450°C at a heating rate of 3°C / min, the frequency is 1Hz, and the amplitude is 20μm. The Tg value can be obtained under the above conditions.

[0106] The polyimide layer 50 has excellent optical characteristics.

[0107] The yellow index is based on a value calculated according to ASTM E-313 using the CIE colorimetric system using a spectrophotometer (UltraScan PRO from Hunter Associates Laboratory).

[0108] The yellowness of the polyimide layer 50 may be 5.3 or less. The yellowness may be 4.3 or less. The yellowness may be 4.1 or less. The yellowness of the polyimide layer 50 may be greater than 1. The yellowness of the polyimide layer is measured based on a value measured on a film having a thickness of 10 μm.

[0109] The in-plane phase difference value was measured at room temperature using the Alpha / Theta mode of the Rotate Analyzer Method using the RETS-100 model of OTSUKA Electronics Co., Ltd., and the in-plane phase difference Re value at 550 nm was used as the reference. The in-plane phase difference measurement of the polyimide layer was based on the value measured on a film having a thickness of 10 μm.

[0110] The in-plane phase difference value Re of the polyimide layer 50 may be 3.0 or less. The in-plane phase difference value Re may be 2.0 or less. The in-plane phase difference value Re may be 1.5 or less. The in-plane phase difference value Re may be 1.0 or less. The in-plane phase difference value Re of the polyimide layer 50 may be 0.1 or more. The polyimide layer having the in-plane phase difference value within the above range has excellent optical properties suitable for use in displays.

[0111] The light transmittance of the polyimide layer 50 may be 85% or more. The light transmittance may be 88% or more. The light transmittance may be 99% or less. The light transmittance is based on the visible light transmittance measured on a film having a thickness of 10 μm.

[0112] The haze of the polyimide layer 50 may be 1% or less. The haze may be 0.6% or less. The haze may be 0.52% or less. The haze may be 0.45% or less. The haze of the polyimide layer 50 may be 0.001% or more. The polyimide layer having the haze characteristic has optical properties that appear clear to the naked eye, and is therefore very suitable for use as a substrate film such as a display. The haze is based on a value measured on a film having a thickness of 10 μm.

[0113] The polyimide layer 50 includes a polymer obtained by polymerizing an aromatic diamine compound and an aromatic dianhydride compound. In other words, the polyimide layer includes an aromatic diamine compound residue and an aromatic dianhydride compound residue.

[0114] The aromatic diamine compound may include 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane (HFBAPP), 4,4'-diamino-2,2'-bis(trifluoromethyl)diphenyl ether (BTFDPE), 2,2-bis(4-(4-amino-2-(trifluoromethyl)phenoxy)phenyl)hexafluoropropane (HFFAPP) or 3,5-diaminobenzotrifluoride (DATF).

[0115] Specifically, the aromatic diamine compound may be a compound represented by the following Chemical Formula 1-1.

[0116] Chemical formula 1-1

[0117]

[0118] As the above-mentioned aromatic dianhydride compound, two or more selected from the group consisting of 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6-FDA), 4,4'-oxydiphthalic anhydride (ODPA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA) and combinations thereof can be used. Preferably, three kinds can be used.

[0119] Specifically, as the aromatic dianhydride compound, compounds represented by the following Chemical Formulas 2-1 to 2-3 may be used together.

[0120] Chemical formula 2-1

[0121]

[0122] Chemical formula 2-2

[0123]

[0124] Chemical formula 2-3

[0125]

[0126] The polymer may be formed by reacting the aromatic diamine compound and the aromatic dianhydride compound at a molar ratio of 1:0.95 to 1.05.

[0127] The polyimide layer 50 may contain the biphenyltetracarboxylic acid dianhydride residue of Chemical Formula 2-3 at a ratio of 5 to 45 mols when the above-mentioned dianhydride residue is taken as 100 mols as a whole. The polyimide layer 50 may contain the biphenyltetracarboxylic acid dianhydride residue of Chemical Formula 2-3 at a ratio of 8 to 30 mols when the dianhydride residue is taken as 100 mols as a whole. The polyimide layer having the compound residue of Chemical Formula 2-3 within the above range may further improve heat resistance, workability, etc.

[0128] The polyimide layer 50 includes biphenyltetracarboxylic acid dianhydride residues and pyromellitic acid dianhydride residues, and when the total number of moles of the biphenyltetracarboxylic acid dianhydride residues and the pyromellitic acid dianhydride residues is taken as a whole, the content of the biphenyltetracarboxylic acid dianhydride residues can be 15 mol% to 50 mol%. The polyimide layer 50 includes biphenyltetracarboxylic acid dianhydride residues and pyromellitic acid dianhydride residues, and when the total number of moles of the biphenyltetracarboxylic acid dianhydride residues and the pyromellitic acid dianhydride residues is taken as a whole, the content of the biphenyltetracarboxylic acid dianhydride residues can be 18 mol% to 45 mol%. When the above residues within the above range are included, the viscosity can be controlled with excellent workability during the preparation process, while improving the heat resistance and optical properties as trade-off properties.

[0129] In the polyimide layer 50, when the above-mentioned aromatic dianhydride residues are taken as 100 mol%, the content of the above-mentioned pyromellitic dianhydride residues may be less than 60 mol%. In the polyimide layer 50, when the above-mentioned aromatic dianhydride residues are taken as 100 mol%, the content of the above-mentioned pyromellitic dianhydride residues may be less than 55 mol%. When the above-mentioned pyromellitic dianhydride residues are included in the above-mentioned content range, it is relatively advantageous for viscosity control, etc., so that a polyimide layer having appropriate workability and further improved heat resistance can be obtained.

[0130] The polyimide layer may include 25 to 55 molar ratios of the residue of Chemical Formula 2-1, 35 to 55 molar ratios of the residue of Chemical Formula 2-2, and 5 to 25 molar ratios of the residue of Chemical Formula 2-3 based on 100 moles of the aromatic diamine compound residue.

[0131] The polyimide layer including the above-mentioned residues in the above-mentioned molar ratio may have excellent heat resistance and excellent optical characteristics.

[0132] The polyimide layer 50 may contain a compound having a hydroxyl group. This can be detected by the residue of a compound used as a leveling stabilizer in the preparation process described below. The leveling stabilizer helps to form a more uniform film in the preparation process of the polyimide layer, which can help to improve the heat resistance of the film, improve the residual stress characteristics, and improve the adhesion.

[0133] The leveling stabilizer may be any one selected from the group consisting of methanol, ethanol, butanol, propanol and a combination thereof, or may be methanol or isopropanol. When the above compound is used as a leveling stabilizer, while maintaining optical properties and heat resistance properties, effects such as more stable film formation and improved residual stress can be obtained.

[0134] The film may further include an adhesive layer 60 on one surface of the polyimide layer (see Figure 2 ).

[0135] The adhesive layer 60 may be an optical adhesive layer having excellent light transmittance and / or transparency, for example, a laminate including an optically clear adhesive (OCA), a pressure sensitive adhesive (PSA), or a combination thereof may be used.

[0136] The film may further include a release film or a reinforcement film on the other surface of the polyimide layer. The release film or the reinforcement film may be a polyethylene terephthalate film (PET film), etc., but is not limited thereto.

[0137] The above-mentioned film includes the polyimide layer described above, satisfies the heat resistance and optical properties at the same time, and also plays the role of a supporting layer, so it is excellent in use as a substrate layer. In addition, when the above-mentioned film is used as a substrate layer, not only the upper surface of the light-emitting functional layer corresponding to the front surface of the multilayer electronic device can be transparently prepared, but also the substrate layer corresponding to the back thereof can be transparently prepared. Thus, it is possible to provide a film that is excellent in use in foldable, flexible, and bendable devices and is reliable in terms of heat resistance, thickness, insulation, and support.

[0138] Multilayer electronic devices

[0139] In order to achieve the above-mentioned purpose, a multilayer electronic device 800 according to an embodiment of the present embodiment includes: a substrate layer 100; and a light-emitting functional layer 300, which is disposed on the substrate layer (see Figure 3 The multilayer electronic device 800 may further include a cover layer 500 disposed on the light emitting functional layer 300 (see Figure 4 ).

[0140] The base layer 100 includes the film described above.

[0141] The multilayer electronic device 800 may be a display device.

[0142] The multilayer electronic device 800 may be, for example, a large-area display device, a foldable display device, a bendable display device, or a flexible display device.

[0143] The multilayer electronic device 800 may be, for example, a bendable mobile communication device (eg, a mobile phone) or a bendable laptop computer.

[0144] The light-emitting functional layer 300 includes a color development layer (not shown in the figure), which has an element that emits light according to a signal. Exemplarily, the light-emitting functional layer includes: a signal transmission layer (not shown in the figure), which transmits an external electrical signal to the color development layer; a color development layer (not shown in the figure), which is arranged on the above-mentioned signal transmission layer and develops color according to a given signal; and an encapsulation layer (not shown in the figure) for protecting the above-mentioned color development layer. The signal transmission layer (not shown in the figure) may include a thin film transistor (TFT), for example, LTPS, a-SiTFT or oxide TFT may be applied, but not limited thereto. As an encapsulation layer (not shown in the figure), a thin film encapsulation (Thin Film Encapsulation, TFE) may be applied, but not limited thereto.

[0145] The color-developing layer may be a self-luminous color-developing layer. For example, quantum dot light-emitting diodes (QLED), organic light-emitting diodes (OLED), etc. may be used as the color-developing layer, but it is not limited thereto.

[0146] The light-emitting functional layer 300 may include a sensor layer (not shown in the figure). For example, a touch sensor may be applied. The sensor layer may be disposed above or below the color development layer.

[0147] The light-emitting functional layer 300 may further include a polarizing layer (not shown in the figure). The polarizing layer may be disposed above or below the color-developing layer.

[0148] The light-emitting functional layer 300 may further include a color filter layer (not shown in the figure). The color filter layer may be disposed above or below the color development layer.

[0149] The light emitting functional layer 300 may be disposed on the substrate layer 100 .

[0150] The cover layer 500 may be disposed on the light emitting functional layer 300 .

[0151] As the cover layer 500 , a plastic film, glass, or the like used as a cover layer of a display device can be used.

[0152] An adhesive layer (not shown) may be further applied between the light-emitting functional layer 300 and the cover layer 500 .

[0153] According to the type of light-emitting device applied to the above-mentioned light-emitting functional layer, the above-mentioned covering layer 500 may also include an electrode layer (not shown in the figure). The above-mentioned electrode layer is arranged on one surface of the above-mentioned light-emitting functional layer, and the optical bonding layer may or may not be arranged between the above-mentioned electrode layer and the above-mentioned light-emitting functional layer. The above-mentioned electrode layer may be a transparent metal layer, and preferably a transparent metal layer with a sealing function is applied. The above-mentioned electrode layer may induce the driving of the light-emitting layer of the light-emitting functional layer while allowing the light emitted from the light-emitting functional layer to pass through. Exemplarily, the above-mentioned electrode layer may be used as the cathode of the above-mentioned light-emitting functional layer. As described above, the structure including a signal transmission layer at the lower part of the other surface of the light-emitting layer and an electrode layer on one surface of the above-mentioned light-emitting layer at the same time is conducive to the application of light-emitting functional layers such as OLED.

[0154] The base layer 100 includes the film described above.

[0155] The base material layer 100 includes a polyimide layer 50 .

[0156] The base material layer 100 may include a polyimide layer 50 and an adhesive layer 60 located on the polyimide layer.

[0157] The adhesive layer 60 may be an optical adhesive layer having excellent light transmittance and / or transparency. For example, as the adhesive layer, a laminate including an optically clear adhesive (OCA), a pressure sensitive adhesive (PSA), or a combination thereof may be used.

[0158] Since the specific description about the above-mentioned film and the above-mentioned polyimide layer overlaps with the above-mentioned description, the description thereof will be omitted.

[0159] As required, the multilayer electronic device may further include an additional boundary layer (not shown in the figure) below the substrate layer, or may be further connected to a support unit (or driving unit) of a rollable or bendable display.

[0160] As required, the multi-layer electronic device may be further connected to an additional drive unit (or support unit) of a rollable or bendable display on the cover layer.

[0161] As the driving unit or the supporting unit, any unit generally applicable to a rollable or bendable display may be used without limitation.

[0162] The light transmittance of the multilayer electronic device 800 may be 85% or more. The light transmittance may be 90% or more. The light transmittance may be 99% or less. The light transmittance may be measured in a manner similar to the light transmittance measurement of the polyimide layer.

[0163] Film preparation method

[0164] A method for preparing a thin film according to an embodiment includes: a polymer solution preparing step; a sheet preparing step; and a thin film preparing step.

[0165] The polymer solution preparation step is a step of preparing a polymer solution by stirring a raw material composition containing diamine and dianhydride. The polymer solution preparation step may include a reaction process and an aging process.

[0166] The diamine mentioned above may be an aromatic diamine compound.

[0167] The above-mentioned diamine may include one or more aromatic diamine compounds.

[0168] The dianhydride may be an aromatic dianhydride compound.

[0169] The above-mentioned dianhydride may include three or more kinds of aromatic dianhydride compounds.

[0170] The raw material composition for preparing the polymer solution may include the aromatic diamine compound and the aromatic dianhydride compound in a molar ratio of 1:0.95 to 1.05.

[0171] When the dianhydride compound as a whole is taken as 100 moles, the above raw material composition may contain the biphenyltetracarboxylic dianhydride compound of Chemical Formula 2-3 in a ratio of 5 to 45 moles. When the dianhydride compound as a whole is taken as 100 moles, the above raw material composition may contain the biphenyltetracarboxylic dianhydride compound of Chemical Formula 2-3 in a ratio of 8 to 30 moles. When a polyimide layer containing the compound of Chemical Formula 2-3 is prepared in the above range, the heat resistance, workability, etc. of the polyimide layer can be further improved.

[0172] The raw material composition includes biphenyltetracarboxylic acid dianhydride compound and pyromellitic acid dianhydride compound. In the raw material composition, when the molar sum of the biphenyltetracarboxylic acid dianhydride compound and the pyromellitic acid dianhydride compound is taken as a whole, the content of the biphenyltetracarboxylic acid dianhydride compound can be 15 mol % to 50 mol %, in the raw material composition, when the molar sum of the biphenyltetracarboxylic acid dianhydride compound and the pyromellitic acid dianhydride compound is taken as a whole, the content of the biphenyltetracarboxylic acid dianhydride compound can be 18 mol % to 45 mol %, when the above-mentioned compound within the above-mentioned range is included, the viscosity can be controlled with excellent workability during the preparation process, while improving the heat resistance and optical properties as a tradeoff characteristic.

[0173] In the raw material composition, when the above-mentioned aromatic dianhydride compound is taken as 100 mol%, the content of the above-mentioned pyromellitic dianhydride compound can be less than 60 mol%. In the raw material composition, when the above-mentioned aromatic dianhydride compound is taken as 100 mol%, the content of the above-mentioned pyromellitic dianhydride compound can be less than 55 mol%. When the above-mentioned raw material composition contains the above-mentioned pyromellitic dianhydride compound in the above-mentioned content range, it is relatively beneficial to control the viscosity of the raw material composition, so that a polyimide layer with further improved heat resistance while having appropriate workability can be obtained.

[0174] The raw material composition may include 25 to 55 molar ratios of the compound of Chemical Formula 2-1, 35 to 55 molar ratios of the compound of Chemical Formula 2-2, and 5 to 25 molar ratios of the compound of Chemical Formula 2-3 based on 100 moles of the aromatic diamine compound.

[0175] The above molar ratios are based on solid content.

[0176] The above reaction process is a process of stirring the above raw material composition in an organic solvent and initiating an imidization reaction. For convenience, the product in the above reaction process is referred to as a reaction solution.

[0177] The solid content of the raw material composition in the organic solvent may be 10% to 40% by weight, 15% to 30% by weight, or 18% to 25% by weight. When the solid content is as described above, the workability is more excellent.

[0178] The stirring of the raw material composition can be divided into primary stirring, secondary stirring and tertiary stirring.

[0179] The above-mentioned primary stirring is a step of initiating a reaction while stirring an aromatic diamine compound containing a halogen element in its molecule (eg, the compound of Chemical Formula 1) and an aromatic dianhydride compound containing a halogen element in its molecule (eg, the compound of Chemical Formula 2-1) in an organic solvent.

[0180] The aromatic diamine compound may be a compound that is soluble in an organic solvent (eg, N-methyl-2-pyrrolidone (NMP)) at 20° C. to 45° C. in an inert atmosphere.

[0181] The aromatic dianhydride compound may be added to the aromatic diamine compound to be stirred once, and the reaction may be performed at a reaction temperature of 5° C. to 15° C. for a reaction time of 1 hour to 7 hours.

[0182] The secondary stirring is a step of initiating a reaction while stirring the reaction product of the primary stirring and the aromatic dianhydride compound (e.g., the compound of Chemical Formula 2-3) that does not contain a halogen element in the molecule. The secondary stirring can be carried out at a reaction temperature of 30° C. to 70° C. for a reaction time of 30 minutes to 10 hours.

[0183] The three stirrings are steps of initiating the reaction while stirring the reaction product of the two stirrings and the aromatic dianhydride compound (e.g., the compound of Chemical Formula 2-2) that does not contain a halogen element in the molecule. The three stirrings can be carried out at a reaction temperature of 30° C. to 70° C. for a reaction time of 30 minutes to 10 hours.

[0184] Through the above-mentioned process, a reaction solution can be prepared.

[0185] The reaction solution can prepare a polymer solution having a viscosity of 1000 cps to 8000 cps at 25° C. when measuring the viscosity.

[0186] The above polymer solution may further contain a leveling stabilizer.

[0187] The functions and types of the above-mentioned leveling stabilizers are as described above.

[0188] Based on 100 parts by weight of the polymer solution, the content of the leveling stabilizer may be 0.01 parts by weight to 5 parts by weight, 0.1 parts by weight to 3 parts by weight, or 0.2 parts by weight to 2 parts by weight.

[0189] The aging process is a process of forming the reaction solution into a polymer solution with a certain viscosity and fully dispersing the leveling stabilizer. The aging process may be a process of stirring at 10° C. to 35° C. for 2 to 6 hours.

[0190] Whether the preparation of the polymer solution is completed can be confirmed by measuring the viscosity of the polymer solution. The above-mentioned polymer solution is a precursor of the polyimide layer, should be easy to coat, etc. and suitable for forming a layer with a constant thickness, and should have excellent optical properties. Therefore, preferably, considering workability and physical properties, the reaction is induced so that the polymer solution has a viscosity of 1000cps to 8000cps based on the value measured at 25°C. Preferably, a polymer solution having a viscosity of 2000cps or more and less than 5000cps is prepared. More preferably, the above-mentioned viscosity is 3000cps or more and less than 4,500cps. When the above-mentioned viscosity is too low, less than 1000cps, it may be difficult to manufacture the prepared polyimide layer to have a certain thickness or an expected thickness, and the heat resistance may be insufficient. When the above-mentioned viscosity is greater than 8000cps, gelation may occur, so it may be substantially difficult to form a film.

[0191] Additional additives, process stabilizers, etc. may be added to the polymer solution as needed. As the additives, process stabilizers, etc., any additives, process stabilizers, etc., may be used without limitation as long as they are used in polyimide polymerization.

[0192] The sheet preparation step is a step of preparing a dry sheet by applying the polymer solution in the form of a sheet and then drying it.

[0193] The polymer solution is coated on a substrate such as a glass plate, and dried by applying a drying temperature and a drying time. For example, the drying temperature may be 100° C. to 180° C. The drying time may be 3 minutes to 60 minutes. In order to control the optical properties of the polyimide layer, the drying may be performed in an inert atmosphere or a vacuum oven.

[0194] The film preparation step is a step of preparing a polyimide film by heat-treating the above-mentioned sheet.

[0195] The above-mentioned heat treatment can be performed by adopting a heat treatment temperature and a heat treatment temperature rising rate.

[0196] The above-mentioned heat treatment temperature may be 150°C to 450°C. The above-mentioned heat treatment temperature may be 300°C to 430°C. The above-mentioned heat treatment temperature may be 360°C to 400°C. The heating rate to the above-mentioned heat treatment temperature may be 3°C / minute to 25°C / minute. The above-mentioned heating rate may be 10°C / minute to 20°C / minute. The above-mentioned heating rate may be 13°C / minute to 17°C / minute. When the above-mentioned heat treatment temperature and heating rate are applied, the degree of polymerization and the like may be controlled so that the prepared film has the expected physical properties and can be subjected to more stable heat treatment.

[0197] The advantage of the heat treatment is that it can be performed not only in an inert atmosphere but also in an air atmosphere. This embodiment also has the following characteristics: even if the heat treatment is performed in an air atmosphere, it has excellent optical properties, thereby further improving process workability.

[0198] The film produced by the above production method includes the above polyimide film. The above polyimide film has the same properties as the polyimide layer included in the film described above.

[0199] The following is a more detailed description through specific examples. The following examples are only examples to help understand the present invention, and the scope of the present invention is not limited thereto.

[0200] Example: Preparation of polyimide layer

[0201] Example 1

[0202] In a temperature-controllable double-jacketed 1L glass reactor at 40°C, 458 g of N-methyl-2-pyrrolidone (NMP) as an organic solvent was charged, and then 0.170 mol (100 mol parts) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFDB) as an aromatic diamine was slowly added and dissolved. Next, 0.051 mol (30 mol parts) of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6-FDA) was slowly added, and the mixture was stirred at 10°C for 3 hours (one stirring).

[0203] 0.034 mol (20 mol parts) of 3,3',4,4'-biphenyltetracarboxylic anhydride (BPDA) was added to the first stirring solution and stirred at 50 degrees Celsius for 4 hours to prepare a second stirring solution.

[0204] After adding 0.085 mol (50 mol parts) of pyromellitic dianhydride (PMDA) to the secondary stirring solution, the mixture was stirred at 50° C. for 4 hours to prepare a tertiary stirring solution.

[0205] Based on 100 parts by weight of the solution stirred three times, 2 parts by weight of isopropyl alcohol was added as a leveling stabilizer, and the mixture was stirred for another 4 hours.

[0206] After measuring the viscosity, additives and process stabilizers were further added and stirred for 4 hours to obtain a polymer solution. After the above polymer solution was coated on a glass plate, it was dried in a vacuum oven at 150°C for 10 minutes. Thereafter, heat treatment was performed. Specifically, the temperature was raised from 150°C to 400°C at a rate of 15°C / min and cured, and finally a polyimide film with a thickness of 10 μm was obtained, which was applied as the polyimide layer of Example 1.

[0207] Examples 2, 3 and Comparative Examples 1 to 4

[0208] The polyimide layers of Examples 2 and 3 and Comparative Example 1 were prepared in the same manner as above, except that the molar ratio of the monomers was changed as shown in Table 1 below.

[0209] For Comparative Examples 2 to 4, the monomer molar ratios shown in Table 1 below were also applied, but the heat treatment temperature was raised to 350° C. and cured in Comparative Example 3, and raised to 500° C. and cured in Comparative Example 4.

[0210] Table 1

[0211]

[0212] TFMB: 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl

[0213] 6FDA: 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride

[0214] PMDA: pyromellitic dianhydride

[0215] BPDA: 2,3,3',4'-biphenyltetracarboxylic dianhydride

[0216] *Indicates to the second decimal place.

[0217] ** In the film formation evaluation, in the process of preparing a polyimide layer from a polymer solution in the same manner, the case where a thin film polyimide layer can be prepared is indicated by ○, and the case where the workability is poor due to too low viscosity is indicated by △.

[0218] For Examples 1 to 3 and Comparative Example 2, the viscosity # measured at room temperature (about 25° C.) was about 5000 CPS to about 5500 CPS, showing good processability. For Comparative Example 1, the viscosity measured at room temperature (about 25° C.) was too low, about 2000 CPS, and for Comparative Example 3, the viscosity was about 1500 CPS, showing poor workability.

[0219] #For viscosity measurement, the temperature of the polymer solution (varnish) was maintained at 25°C, and a BH-II model viscometer from TOKISANGYO was used. The RPM was set to 4, and a No. 4 rotor was used to confirm whether the target viscosity was achieved.

[0220] Hereinafter, physical properties of the samples of Examples 1 to 3 and Comparative Examples 1 to 3 were measured.

[0221] Example: Physical property evaluation of polyimide layer (polyimide film) A

[0222] 1. For thickness measurement, a digital micrometer 547-401 from Mitsutoyo Co., Ltd. of Japan was used to measure the thickness at five points at any position, and the average value thereof was taken as the thickness.

[0223] 2. The light transmittance (%) and haze (%) were measured using a haze meter NDH-5000W manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS K 7105.

[0224] 3. Yellowness (YI) was measured using the CIE colorimetric system using a spectrophotometer (UltraScan PRO from Hunter Associates Laboratory). YI was calculated according to ASTM E-313 specifications.

[0225] 4. To measure the coefficient of thermal expansion (CTE), a thermal expansion coefficient measuring instrument, specifically, Seiko Exstar 6000 (TMA6100) model of SEICO INST. (JAPAN) was used for measurement. The measurement method is as follows: the change in the range of 50 to 250 based on the second heating is defined as the CTE value.

[0226] -First heating: Start at 30℃ → Heat to 360℃ (10℃ / min↑) → 30℃

[0227] - Second heating: 30℃→360℃ heating (5℃ / min↑)

[0228] 5. To measure the glass transition temperature (Tg), a DMA Q800 model from Texas Instruments was used in the tensile mode. The temperature was increased from 25°C to 450°C at a rate of 3°C / min, with a frequency of 1 Hz and an amplitude of 20 μm, and the Tg value was taken at tangent delta.

[0229] 6. To measure the adhesion force, a polyimide layer was solidified on an amorphous silicon-based glass substrate, the glass substrate and a portion of the polyimide film were separated by a laser lift off (LLO) process, and then a tape was fixed on the separated polyimide film. Figure 5A and Figure 5B The polyimide layer is peeled off using the UTM universal tester equipment for measurement. As the measurement mode, a 180° peeling test (see Figure 5A and Figure 5B ), and the result unit is expressed in gf / inch. Specifically, the pre-test and test speeds are 0.83 mm / sec, the post-test speed is 10 mm / sec, the distance to the target mode in the pre-test is 10 mm, and the trigger force is 0.001 N.

[0230] 7. Residual stress was measured using 500TC (FSM 128) equipment from Frontier Semiconductor. PIVarnish was applied to a 6-inch silicon wafer whose warpage was measured in advance using a coater, pre-baked at 80°C for 30 minutes, and then heat-cured at 350°C for 60 minutes using a high-temperature oven (manufactured by Koyo Lindbergh, model: VF-2000B) with the oxygen concentration in the oven adjusted to 10 mass ppm, thereby preparing a silicon wafer with a polyimide resin film having a thickness of 15 μm. At this time, the residual stress was measured by comparing the degree of warpage caused by the difference in thermal expansion between the silicon wafer and the PI film.

[0231] 8. Loop Stiffness Tester (TOYOSEIKI) was used to measure the loop stiffness. The two ends of a polyimide film with a width of 15 mm, a length of 120 mm, and a thickness of 50 μm were fixed to the fixing part of the tester, and the polyimide film was pressed at a pressing speed of 3.3 mm / s using a pressing part until the final separation distance between the pressing part and the fixing part ( Figure 6B The ring stiffness of the polyimide film was measured by using a sensor until the L of the film was 20 mm. The measurement was performed at room temperature with the mechanical direction of the film as the length direction.

[0232] The above measurement results are shown in Table 2 below.

[0233] Table 2

[0234]

[0235]

[0236] *The heat resistance stability index is a value evaluated according to the above-mentioned first formula.

[0237] *The comprehensive index is the value evaluated by the above second formula.

[0238] Referring to Table 1 and Table 2, Examples 1 to 3 have a ring stiffness within an appropriate range, have flexibility, and have an appropriate resilience when folded, and therefore can be confirmed to be suitable for use as a support layer for foldable or rollable displays. At the same time, relatively low thermal expansion coefficients and small residual stresses were confirmed, and it was also confirmed that not only optical properties and heat resistance properties, but also optical properties such as yellowness, adhesion, and residual stress, which are required for use as a support, and comprehensive properties related to processability and reliability are excellent.

[0239] The preferred embodiments of the present invention are described in detail above, but the scope of the present invention is not limited thereto. Various modifications and improvements by ordinary technicians in the technical field of the present invention using the basic concepts of the present invention defined in the scope of protection of the attached invention claims also fall within the scope of the present invention.

Claims

1. A film, characterized in that: comprising a polyimide layer containing an aromatic diamine compound residue and an aromatic dianhydride compound residue, Based on a thickness of 50 μm, the polyimide layer has a ring stiffness value of 3 N / m to 4.5 N / m. The above aromatic diamine compound residue includes a 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl residue, The above aromatic dianhydride compound residues include 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, biphenyltetracarboxylic dianhydride residues and pyromellitic dianhydride residues. The thermal expansion coefficient of the polyimide layer is 10 ppm / °C or more and 35 ppm / °C or less. The heat stability index of the polyimide layer according to the following first formula, that is, the HS index, is 5°C 2 / ppm·MPa to 15℃ 2 / ppm·MPa: First Form In the first formula, The above HS index is the heat stability index, and its unit is ℃ 2 / ppm·MPa, The above Tg is the glass transition temperature, and its unit is °C. The above H is the thermal expansion coefficient of the above polyimide layer, and its unit is ppm / °C. The RS is the residual stress value of the polyimide layer, and its unit is MPa; The comprehensive index of the polyimide layer represented by the following second formula is 2°C 2 / ppm or above: Second Form In the second formula, The above T index is a comprehensive index. The above Tg is the glass transition temperature, and its unit is °C. The above YI is the yellowness value of the above polyimide layer at a thickness of 10 μm. The H is the thermal expansion coefficient of the polyimide layer, and its unit is ppm / °C.

2. The film according to claim 1, characterized in that The adhesion of the polyimide layer is 200 gf / inch or more. To measure the adhesion, a polyimide layer was cured on an amorphous silicon-based glass substrate, a laser lift-off process was applied to separate the glass substrate and a portion of the polyimide film, and then a tape was fixed on the separated polyimide film and the polyimide layer was peeled off using a UTM universal tester device for measurement. As a measurement mode, a 180° peel test was applied, and the result unit was expressed by gf / inch. Specifically, the pre-test speed and the test speed were 0.83 mm / sec, and the post-test speed was 10 mm / sec. In the pre-test, the distance to the target pattern was 10 mm, and the trigger force was 0.001 N.

3. The film according to claim 1, characterized in that The polyimide layer has a yellowness index of 5.3 or less.

4. The film according to claim 1, characterized in that The polyimide layer includes 5 to 45 mol of biphenyltetracarboxylic dianhydride residues based on 100 mol of the total aromatic dianhydride compound residues.

5. The film according to claim 1, characterized in that The polyimide layer contains biphenyltetracarboxylic dianhydride residues and pyromellitic dianhydride residues. The content of the biphenyltetracarboxylic dianhydride residue is 15 mol % to 50 mol % based on the total molar number of the biphenyltetracarboxylic dianhydride residue and the pyromellitic dianhydride residue as a whole. The content of the pyromellitic dianhydride residue is less than 60 mol % when the entire aromatic dianhydride compound residue is taken as 100 mol %.

6. A multi-layer electronic device, characterized in that: include: a substrate layer, and A light-emitting functional layer is disposed on the substrate layer; The substrate layer comprises a film, The above-mentioned film is the film according to claim 1.

7. A method for preparing a thin film, characterized in that: include: a polymer solution preparation step of preparing a polymer solution having a viscosity of 1000 cps to 8000 cps measured at 25° C. by stirring a raw material composition comprising an aromatic diamine compound and an aromatic dianhydride compound, a sheet preparation step of applying the polymer solution in the form of a sheet and drying it with hot air to prepare the sheet, and a film preparation step of heat-treating the sheet at 360° C. to 480° C. to prepare a polyimide layer; The film comprises the polyimide layer. The polyimide layer contains the aromatic diamine compound residue and the aromatic dianhydride compound residue. Based on a thickness of 50 μm, the polyimide layer has a ring stiffness value of 3 N / m to 4.5 N / m. The above aromatic diamine compound residue includes a 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl residue, The above aromatic dianhydride compound residues include 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, biphenyltetracarboxylic dianhydride residues and pyromellitic dianhydride residues. The thermal expansion coefficient of the polyimide layer is 10 ppm / °C or more and 35 ppm / °C or less. The raw material composition or the polymer solution further comprises a leveling stabilizer, The heat stability index of the polyimide layer according to the following first formula, that is, the HS index, is 5°C 2 / ppm·MPa to 15℃ 2 / ppm·MPa: First Form In the first formula, The above HS index is the heat stability index, and its unit is ℃ 2 / ppm·MPa, The above Tg is the glass transition temperature, and its unit is °C. The above H is the thermal expansion coefficient of the above polyimide layer, and its unit is ppm / °C. The RS is the residual stress value of the polyimide layer, and its unit is MPa; the comprehensive index of the polyimide layer represented by the following second formula is 2°C 2 / ppm or above: Second Form In the second formula, The above T index is a comprehensive index. The above Tg is the glass transition temperature, and its unit is °C. The above YI is the yellowness value of the above polyimide layer at a thickness of 10 μm. The H is the thermal expansion coefficient of the polyimide layer, and its unit is ppm / °C.

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