Liquid crystal-containing powder low-dielectric polyamide acid, polyimide film and method for producing the same

Abstract

This invention relates to low-dielectric polyamic acid and polyimide films containing liquid crystal polymer powder and methods for manufacturing the same. It provides a polyamic acid solution containing 10-40% by weight of liquid crystal polymer powder and comprising an acid dianhydride component and a diamine component. The acid dianhydride component comprises benzophenone tetracarboxylic dianhydride (BTDA), biphenyl tetracarboxylic dianhydride (BPDA), and pyromellitic tetracarboxylic dianhydride (PMDA). The diamine component is composed of m-tolidine and p-phenylenediamine (PPD).

Description

Technical Field

[0001] This invention relates to polyamic acid and polyimide films containing liquid crystal powder with low dielectric properties, and methods for manufacturing the same. Background Technology

[0002] Polyimide (PI) is a polymer material with the highest level of heat resistance, reagent resistance, electrical insulation, chemical resistance and weather resistance among organic materials, based on the imide ring with excellent chemical stability and rigid aromatic backbone.

[0003] In particular, due to its excellent insulation properties, namely its excellent electrical properties such as low dielectric constant, it has attracted much attention as a high-functionality polymer material in the fields of electrical, electronic and optical engineering.

[0004] In recent years, as electronic products have become lighter and smaller, thin circuit boards with high integration and flexibility have been actively developed.

[0005] Such thin circuit boards are mostly used in structures where circuits containing metal foil are formed on polyimide films that have excellent heat resistance, low temperature resistance and insulation properties and are easy to bend.

[0006] As such thin circuit boards, flexible metal foil laminates are mainly used, such as flexible copper foil laminates (FCCLs) that use thin copper plates as metal foils. In addition, polyimide is also used as a protective film, insulating film, etc. for thin circuit boards.

[0007] On the other hand, as various functions have been integrated into electronic devices in recent years, these electronic devices are required to have fast computing and communication speeds. In order to meet this requirement, thin circuit boards capable of high-speed communication at high frequencies are being developed.

[0008] To achieve high-frequency, high-speed communication, insulators with high impedance are required that can maintain electrical insulation even at high frequencies. Impedance is inversely proportional to the frequency at which the insulator is formed and its dielectric constant (Dk). Therefore, to maintain insulation at high frequencies, the dielectric constant should be as low as possible.

[0009] However, in reality, the dielectric properties of typical polyimides are not yet good enough to maintain adequate insulation in high-frequency communications.

[0010] In addition, it is well known that the lower the dielectric properties of an insulator, the more it can reduce the generation of unwanted parasitic capacitance and noise in thin circuit boards, thereby greatly solving the problem of communication delay.

[0011] Therefore, in practice, polyimide with low dielectric properties is considered the most important factor affecting the performance of thin circuit boards.

[0012] In particular, in the case of high-frequency communication, dielectric dissipation is inevitable through polyimide. The dielectric dissipation factor (Df) refers to the degree of energy waste in thin circuit boards and is closely related to the signal transmission delay that determines the communication speed. Therefore, keeping the dielectric dissipation factor of polyimide as low as possible is also considered an important factor affecting the performance of thin circuit boards.

[0013] Furthermore, the more moisture a polyimide film contains, the higher its dielectric constant and the greater its dielectric loss factor. While polyimide films are suitable as materials for thin circuit boards due to their excellent inherent properties, their relatively high susceptibility to moisture due to the polar imide groups can potentially reduce their insulating properties.

[0014] Therefore, in practice, there is a need to develop polyimide films that maintain the unique mechanical properties of polyimide at a certain level while having low dielectric properties, especially low dielectric loss factor.

[0015] [Existing Technical Documents]

[0016] [Patent Literature]

[0017] (Patent Document 1) Korean Patent Publication No. 10-2015-0069318 Summary of the Invention

[0018] Technical issues

[0019] Therefore, in order to solve the problems mentioned above, polyamic acid and polyimide films with both low dielectric and mechanical properties are provided, as well as methods for manufacturing the same.

[0020] Therefore, the actual object of the present invention is to provide specific embodiments thereof.

[0021] Methods for solving problems

[0022] An embodiment of the present invention for achieving the objectives described above provides a polyamic acid solution comprising an acid dianhydride component and a diamine component, and comprising 10 to 40% by weight of liquid crystal polymer powder. The acid dianhydride component comprises 3,3',4,4'-Benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-Biphenyltetracarboxylic dianhydride (BPDA), and Pyromellitic dianhydride (PMDA). The diamine component comprises m-tolidine and p-Phenylenediamine (PPD).

[0023] Based on the total content of the above-mentioned diamine components of 100 mol%, the content of meta-toluidine can be more than 20 mol% and less than 40 mol%, and the content of p-phenylenediamine can be more than 60 mol% and less than 80 mol%.

[0024] In addition, based on the total content of the above-mentioned dianhydride components of 100 mol%, the content of benzophenone tetracarboxylic dianhydride can be more than 30 mol% and less than 50 mol%, the content of biphenyl tetracarboxylic dianhydride can be more than 25 mol% and less than 45 mol%, and the content of pyromellitic tetracarboxylic dianhydride can be more than 15 mol% and less than 35 mol%.

[0025] In addition, the liquid crystal polymer of the above-mentioned liquid crystal polymer powder can be polyester, with a melting point of 300-330°C and a D50 of 3-7 μm.

[0026] Another embodiment of the present invention provides a varnish comprising the above-described polyamic acid solution.

[0027] Another embodiment of the present invention provides a polyimide film obtained by subjecting the above-mentioned polyamic acid solution to an imidization reaction.

[0028] The dielectric constant of the above-mentioned polyimide film can be below 3.5, the dielectric loss factor can be below 0.0035, and the tensile strength can be above 200 MPa.

[0029] Another embodiment of the present invention provides a method for manufacturing a polyimide film, comprising: (a) polymerizing an acid dianhydride component comprising benzophenone tetracarboxylic dianhydride (BTDA), biphenyl tetracarboxylic dianhydride (BPDA) and pyromellitic tetracarboxylic dianhydride (PMDA) and a diamine component comprising m-tolidine and p-phenylenediamine (PPD) in an organic solvent to produce polyamic acid; (b) adding liquid crystal polymer powder to the polyamic acid and mixing it; and (c) imidizing the polyamic acid comprising the liquid crystal polymer powder.

[0030] Another embodiment of the present invention provides a multilayer film comprising the above-described polyimide film, a flexible metal foil laminate comprising the above-described polyimide film and a conductive metal foil, and an electronic component comprising the above-described flexible metal foil laminate.

[0031] Invention Effects

[0032] As described above, the present invention provides a polyimide film with both low dielectric and mechanical properties by forming a polyamic acid and polyimide film with specific components and specific composition ratios and the method thereof, thereby enabling it to be effectively applied in a variety of fields that require these properties, especially electronic components such as flexible metal foil laminates. Detailed Implementation

[0033] Best practice

[0034] Hereinafter, embodiments of the present invention will be described in more detail in the order of "polyimide film" and "method for manufacturing polyimide film".

[0035] Prior to this, the terms or vocabulary used in this specification and the scope of the claims should not be interpreted as having their usual or dictionary meanings, but should be interpreted based on the principle that the inventor can appropriately define the concepts of the terms to best illustrate the invention, and in accordance with the meanings and concepts consistent with the technical ideas of the invention.

[0036] Therefore, the embodiments described in this specification are only one of the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. It should be understood that at the time of filing this application, there may be many equivalents and modifications that can replace these embodiments.

[0037] In this specification, unless the context clearly specifies otherwise, singular expressions include plural expressions. It should be understood in this specification that terms such as “comprising,” “possessing,” or “having” are intended to specify the presence of the implemented features, numbers, steps, constituent elements, or combinations thereof, and do not presuppose the presence or additional possibilities of more than one other feature, number, step, constituent element, or combination thereof.

[0038] In this specification, when quantities, concentrations, or other values ​​or parameters are given as a range, a preferred range, or a preferred upper limit and a preferred lower limit, it should be understood that any pair of ranges formed by any upper limit or preferred value and any lower limit or preferred value is specifically disclosed, regardless of whether the range is disclosed individually.

[0039] Where a range of values ​​is mentioned in this specification, unless otherwise stated, the range is intended to include the endpoints and all integers and fractions within that range. The scope of this invention is not intended to be limited to the specific values ​​mentioned when defining the range.

[0040] In this specification, “acid dianhydride” is intended to include its precursors or derivatives, which, although technically not acid dianhydrides, can still react with diamines to form polyamic acid, which can then be converted back into polyimide.

[0041] In this specification, "diamine" is intended to include its precursors or derivatives, which, although technically they may not be diamines, can still react with dianhydrides to form polyamic acid, which can then be converted back into polyimide.

[0042] The polyamic acid of the present invention may contain an acid dianhydride component comprising benzophenone tetracarboxylic dianhydride (BTDA), biphenyl tetracarboxylic dianhydride (BPDA) and pyromellitic tetracarboxylic dianhydride (PMDA) and a diamine component composed of m-tolidine and p-phenylenediamine (PPD), and may contain 10 to 40% by weight of liquid crystal polymer powder.

[0043] Based on the total content of the above-mentioned diamine components of 100 mol%, the content of meta-toluidine can be more than 20 mol% and less than 40 mol%, and the content of p-phenylenediamine can be more than 60 mol% and less than 80 mol%.

[0044] In particular, meta-toluidine has a hydrophobic methyl group, which contributes to the low moisture absorption properties of polyimide films.

[0045] Based on a total content of 100 mol% of the above-mentioned dianhydride components, the content of benzophenone tetracarboxylic dianhydride can be 30 mol% or more but less than 50 mol%, the content of biphenyl tetracarboxylic dianhydride can be 25 mol% or more but less than 45 mol%, and the content of pyromellitic tetracarboxylic dianhydride can be 15 mol% or more but less than 35 mol%.

[0046] The polyimide chain derived from biphenyl dianhydride of the present invention has a structure known as a charge transfer complex (CTC), which is a regular linear structure in which the electron donor and electron acceptor are close to each other, thus enhancing the intermolecular interaction.

[0047] In addition, benzophenone tetracarboxylic dianhydride, which has a carbonyl group, also contributes to the expression of CTC, just like biphenyl tetracarboxylic dianhydride.

[0048] This structure prevents the formation of hydrogen bonds with moisture, thus maximizing the reduction of the hygroscopicity of the polyimide film.

[0049] In one specific example, the aforementioned dianhydride component may further include pyromellitic dianhydride. Pyromellitic dianhydride, as an acid dianhydride component with a relatively rigid structure, can impart moderate elasticity to the polyimide film, and is therefore preferred.

[0050] To ensure that the polyimide film simultaneously achieves adequate elasticity and moisture absorption, the ratio of dianhydride content is particularly important. For example, the lower the ratio of biphenyltetracarboxylic dianhydride, the less likely it is to be expected to achieve the low moisture absorption resulting from the aforementioned CTC structure.

[0051] In addition, biphenyl dianhydride and benzophenone dianhydride contain two benzene rings corresponding to the aromatic moiety, while pyromellitic dianhydride contains one benzene ring corresponding to the aromatic moiety.

[0052] In the dianhydride component, when the molecular weight is the same, the increase in the content of pyromellitic dianhydride can be understood as an increase in intramolecular imide groups. This can be understood as the ratio of imide groups derived from the aforementioned pyromellitic dianhydride in the polyimide polymer chain being relatively increased compared to the ratio of imide groups derived from biphenyl dianhydride and benzophenone tetracarboxylic dianhydride.

[0053] That is, the increase in the content of pyromellitic dianhydride can also be regarded as a relative increase in the number of imide groups relative to the overall polyimide film, so it is difficult to expect a low moisture absorption rate.

[0054] Conversely, if the content of pyromellitic dianhydride is reduced, the rigid structure is relatively reduced, and the elasticity of the polyimide film may decrease below the desired level.

[0055] For this reason, when the content of biphenyl dianhydride and benzophenone dianhydride is higher than the above range or the content of pyromellitic dianhydride is lower than the above range, the mechanical properties of the polyimide film are reduced, and the heat resistance level suitable for manufacturing flexible metal foil laminates cannot be guaranteed.

[0056] Conversely, when the contents of biphenyltetracarboxylic dianhydride and benzophenonetetracarboxylic dianhydride are below the above range or the contents of pyromellitic dianhydride are above the above range, it is difficult to achieve appropriate levels of dielectric constant, dielectric loss factor and moisture absorption rate, and therefore the results are unsatisfactory.

[0057] On the other hand, the liquid crystal polymer of the above-mentioned liquid crystal polymer powder can be polyester, with a melting point of 300-330°C and a D50 of 3-7 μm.

[0058] The liquid crystal polymer powder exhibits excellent dispersibility and low hygroscopicity when mixed in the polyamic acid of the present invention, thus achieving the following effects: further enhancing the low dielectric properties of the varnish containing the polyamic acid solution and the polyimide film obtained by imidizing the polyamic acid solution, while minimizing the decrease in mechanical properties.

[0059] The aforementioned varnish can also be used as a low-dielectric thermoplastic polyimide coated on flexible metal foils (e.g., copper foil).

[0060] The dielectric constant of the above-mentioned polyimide film can be below 3.5, the dielectric loss factor can be below 0.0035, and the tensile strength can be above 200 MPa.

[0061] In this regard, when the polyimide film satisfies all the requirements of dielectric constant (Dk), dielectric loss factor (Df) and tensile strength, it can be used as an insulating film for flexible metal foil laminates. Moreover, even when the manufactured flexible metal foil laminate is used in electrical signal transmission circuits that transmit signals at high frequencies of 10 GHz or higher, its insulation stability can be ensured and the signal transmission delay can be minimized.

[0062] The polyimide film that meets all the above conditions is a novel polyimide film that has not been known to date. The dielectric loss factor (Df) will be described in detail below.

[0063] <Dielectric loss factor>

[0064] The term "dielectric loss factor" refers to the force dissipated by a dielectric (or insulator) when molecular friction hinders molecular motion caused by an alternating electric field.

[0065] The dielectric loss factor is typically used as an index to represent the ease with which charge dissipates (dielectric loss). A higher dielectric loss factor means that the charge dissipates more easily, while a lower dielectric loss factor means that the charge dissipates less easily. In other words, the dielectric loss factor is a standard for measuring power loss. As the dielectric loss factor decreases, signal transmission delay caused by power loss can be reduced, while maintaining fast communication speeds.

[0066] This is a highly demanded aspect of the polyimide film used as an insulating film, and the polyimide film of the present invention can have a dielectric loss factor of less than 0.0035 at a very high frequency of 10 GHz.

[0067] In this invention, polyamic acid can be manufactured by the following methods:

[0068] (1) A method of polymerization in which all diamine components are added to a solvent and then acid dianhydride components are added in a manner that is substantially equal in molar to the diamine components;

[0069] (2) A method of polymerization in which all the acid dianhydride components are added to the solvent, and then the diamine components are added in a manner that is substantially equal in molar to the acid dianhydride components;

[0070] (3) After adding a portion of the diamine component to the solvent, a portion of the acid dianhydride component is mixed relative to the reaction component at a ratio of about 95 to 105 mol%, and then the remaining diamine component is added, followed by the remaining acid dianhydride component, so that the diamine component and the acid dianhydride component are polymerized in a substantially equimolar manner.

[0071] (4) After adding the acid dianhydride component to the solvent, a portion of the diamine compound is mixed relative to the reaction component at a ratio of about 95 to 105 mol%, then other acid dianhydride components are added, followed by the addition of the remaining diamine component, so that the diamine component and the acid dianhydride component are polymerized in a substantially equimolar manner.

[0072] (5) A method in which a portion of a diamine component and a portion of an acid dianhydride component are reacted in a solvent in excess of either component to form a first composition, and a portion of a diamine component and a portion of an acid dianhydride component are reacted in another solvent in excess of either component to form a second composition, and the first and second compositions are then mixed and polymerization is completed, wherein if the diamine component is in excess when forming the first composition, the acid dianhydride component is in excess in the second composition, and if the acid dianhydride component is in excess in the first composition, the diamine component is in excess in the second composition, thereby mixing the first and second compositions to polymerize the total diamine component and acid dianhydride component used in their reaction in a substantially equimolar manner; etc.

[0073] However, the polymerization methods described above are not limited to the examples above, and the polyamic acid described above can certainly be manufactured using any known method.

[0074] In one specific example, the method for manufacturing the polyimide film of the present invention may include:

[0075] (a) The step of manufacturing polyamic acid by carrying out the production of an acid dianhydride component comprising benzophenone tetracarboxylic dianhydride (BTDA), biphenyl tetracarboxylic dianhydride (BPDA) and pyromellitic tetracarboxylic dianhydride (PMDA) and a diamine component consisting of m-tolidine and p-phenylenediamine (PPD) in an organic solvent.

[0076] (b) the step of adding liquid crystal polymer powder to the above-mentioned polyamic acid and mixing it; and

[0077] (c) The step of imidizing the polyamic acid containing the liquid crystal polymer powder.

[0078] Based on a total content of 100 mol% for the above-mentioned diamine components, the content of meta-toluidine can be between 20 mol% and 40 mol%, and the content of p-phenylenediamine can be between 60 mol% and 80 mol%. Based on a total content of 100 mol% for the above-mentioned dianhydrides, the content of benzophenone tetracarboxylic dianhydride can be between 30 mol% and 50 mol%, the content of biphenyl tetracarboxylic dianhydride can be between 25 mol% and 45 mol%, and the content of pyromellitic tetracarboxylic dianhydride can be between 15 mol% and 35 mol%.

[0079] In this invention, the polymerization method of polyamic acid as described above can be defined by random polymerization. From the perspective of maximizing the effect of the invention in reducing the dielectric loss factor (Df), polyimide films made from the polyamic acid of the invention manufactured by the process described above can be preferentially used.

[0080] However, the above-described polymerization method results in shorter repeating units within the polymer chain, which may limit the utilization of the various excellent properties of the polyimide chain derived from the dianhydride component. Therefore, block polymerization is a particularly preferred polymerization method for polyamic acid in this invention.

[0081] On the other hand, there are no particular limitations on the solvent used to synthesize polyamic acid; any solvent can be used as long as it dissolves polyamic acid, with amide-based solvents being preferred.

[0082] Specifically, the solvent mentioned above can be an organic polar solvent, more specifically, it can be an aprotic polar solvent, for example, it can be one or more selected from the group consisting of N,N-dimethylformamide (DMF), N,N-dimethylacetamide, N-methylpyrrolidone (NMP), γ-butyrolactone (GBL), and diethylene glycol dimethyl ether (Diglyme), but is not limited thereto, and can be used alone or in combination as needed.

[0083] In one example, the solvents described above may particularly preferably be N,N-dimethylformamide and N,N-dimethylacetamide.

[0084] In addition, fillers can be added during the polyamic acid manufacturing process to improve various film properties such as lubricity, thermal conductivity, corona resistance, and loop hardness. There are no particular limitations on the fillers added; preferred examples include silica, titanium dioxide, alumina, silicon nitride, boron nitride, dicalcium phosphate, calcium phosphate, and mica.

[0085] The particle size of the filler is not particularly limited, but can be determined according to the desired membrane characteristics and the type of filler added. Generally, the average particle size is 0.05 to 100 μm, preferably 0.1 to 75 μm, more preferably 0.1 to 50 μm, and particularly preferably 0.1 to 25 μm.

[0086] If the particle size is below the above range, it is not easy to show the modification effect; if it is above the above range, it may sometimes cause significant damage to the surface properties or a significant decrease in mechanical properties.

[0087] Furthermore, there is no particular limitation on the amount of filler added; it can be determined based on the desired membrane characteristics or filler particle size. Generally, the amount of filler added is 0.01 to 100 parts by weight relative to 100 parts by weight of polyimide, preferably 0.01 to 90 parts by weight, and more preferably 0.02 to 80 parts by weight.

[0088] If the filler content is below the above range, the modification effect brought about by the filler will not be easily observed; if it is above the above range, the mechanical properties of the membrane may be significantly damaged. There are no particular limitations on the method of adding the filler; any known method can be used.

[0089] In the manufacturing method of the present invention, the polyimide film can be manufactured by thermal imidization and chemical imidization.

[0090] Alternatively, it can be manufactured by a combined imidization method that combines thermal imidization and chemical imidization.

[0091] The aforementioned thermal imidization method is a method that eliminates chemical catalysts and uses heat sources such as hot air or infrared dryers to induce the imidization reaction.

[0092] In the above-described thermal imidization method, the gel membrane can be heat-treated at a variable temperature ranging from 100 to 600°C to imidize the amyl acid groups present in the gel membrane. More specifically, the heat treatment can be performed at 200 to 500°C, and more specifically, at 300 to 500°C to imidize the amyl acid groups present in the gel membrane.

[0093] However, a portion of the amic acid (about 0.1 mol% to 10 mol%) may also undergo imidization during the formation of the gel film. For this purpose, the polyamic acid composition can be dried at a variable temperature ranging from 50°C to 200°C, which also falls under the category of the above-mentioned thermal imidization method.

[0094] In the case of chemical imidization, polyimide films can be manufactured using dehydrating agents and imidizing agents in accordance with methods known in the art.

[0095] As an example of the composite imidization method, a dehydrating agent and an imidizing agent can be added to a polyamic acid solution, and then partially cured and dried by heating at 80 to 200°C, preferably at 100 to 180°C, and then heated at 200 to 400°C for 5 to 400 seconds, thereby producing a polyimide film.

[0096] The polyimide film of the present invention manufactured according to the manufacturing method described above can have a dielectric constant of 3.5 or less, a dielectric loss factor of 0.0035 or less, and a tensile strength of 200 MPa or more.

[0097] The present invention provides a multilayer film comprising the above-described polyimide film and a flexible metal foil laminate comprising the above-described polyimide film and a conductive metal foil.

[0098] The metal foil used is not particularly limited. When the flexible metal foil laminate of the present invention is used in electronic or electrical equipment applications, it may be, for example, a metal foil containing copper or copper alloy, stainless steel or its alloy, nickel or nickel alloy (including 42 alloy), aluminum or aluminum alloy.

[0099] In conventional flexible metal foil laminates, rolled copper foil or electrolytic copper foil is commonly used, and these types of copper foil are also preferred in this invention. Furthermore, the surface of these metal foils may be coated with an anti-rust layer, a heat-resistant layer, or an adhesive layer.

[0100] In this invention, the thickness of the metal foil is not particularly limited, as long as it is thick enough to fully perform its function according to its intended use.

[0101] The flexible metal foil laminate of the present invention can be a structure in which a metal foil is laminated on one side of the polyimide film, or a structure in which an adhesive layer containing thermoplastic polyimide is attached to one side of the polyimide film and the metal foil is laminated in the state of being attached to the adhesive layer.

[0102] The present invention also provides an electronic component comprising the above-described flexible metal foil laminate as an electrical signal transmission circuit. The above-described electrical signal transmission circuit can be an electronic component that transmits signals at a high frequency of at least 2 GHz, specifically at a high frequency of at least 5 GHz, and more specifically at a high frequency of at least 10 GHz.

[0103] The aforementioned electronic components may be, for example, communication circuits for portable terminals, communication circuits for computers, or communication circuits for spacecraft, but are not limited thereto.

[0104] Implementation

[0105] The following detailed description of the invention's function and effects will be provided through specific embodiments. However, these embodiments are merely illustrative and the scope of the claims is not limited thereto.

[0106] <Manufacturing Example>

[0107] In a 500ml reactor equipped with a stirrer and nitrogen injection / exhaust pipe, DMF was added while nitrogen was being injected. After setting the reactor temperature to below 30°C, meta-toluidine and p-phenylenediamine, which are diamine components, and benzophenone tetracarboxylic dianhydride, biphenyl tetracarboxylic dianhydride, and pyromellitic tetracarboxylic dianhydride, which are acid dianhydrides, were added and confirmed to be completely dissolved.

[0108] Based on a total content of 100 mol% for the above-mentioned diamine components, the content of meta-toluidine is 30 mol%, the content of p-phenylenediamine is 70 mol%, and based on a total content of 100 mol% for the above-mentioned dianhydrides, the content of benzophenone tetracarboxylic dianhydride is 40 mol%, the content of biphenyl tetracarboxylic dianhydride is 35 mol%, and the content of pyromellitic tetracarboxylic dianhydride is 25 mol%.

[0109] Then, under a nitrogen atmosphere, the reactor temperature was raised to 40°C while stirring continuously for 120 minutes to produce polyamic acid.

[0110] Polyester-based liquid crystal polymer powder with a D50 of about 5 μm is added to the polyamic acid thus manufactured, and then stirred.

[0111] A catalyst and dehydrating agent are added to the final polyamic acid produced in this way. After removing air bubbles by high-speed rotation at speeds of 1,500 rpm or higher, it is then coated onto a glass substrate using a spin coater.

[0112] Subsequently, a gel film was prepared by drying at 120°C for 30 minutes under a nitrogen atmosphere. The gel film was then heated to 450°C at a rate of 2°C / min and heat-treated at 450°C for 60 minutes. Finally, it was cooled to 30°C at a rate of 2°C / min to obtain the final polyimide film, which was then peeled off from the glass substrate by dipping it in distilled water.

[0113] The thickness of the manufactured polyimide film is 15 μm. The thickness of the manufactured polyimide film was measured using an Electric Film Thickness Tester from Anritsu Corporation.

[0114] <Examples 1 to 4 and Comparative Examples 1 to 3>

[0115] The manufacturing process was carried out according to the manufacturing example described above, and the content of the liquid crystal polymer powder was adjusted as shown in Table 1.

[0116] [Table 1]

[0117] Example 1 10.0 3.45 0.00334 274 Example 2 20.0 3.44 0.00315 251 Example 3 30.0 3.41 0.00288 226 Example 4 40.0 3.39 0.00235 201 Comparative Example 1 0 3.52 0.00370 315 Comparative Example 2 5 3.49 0.00358 288 Comparative Example 3 50 3.35 0.00226 149

[0118] <Experimental Example> Evaluation of Dielectric Constant, Dielectric Loss Factor, and Tensile Strength

[0119] As shown in Table 1 above, the dielectric constant, dielectric loss factor and tensile strength of the polyimide films manufactured in Examples 1 to 4 and Comparative Examples 1 to 3 were measured.

[0120] (1) Dielectric constant determination

[0121] The dielectric constant (Dk) was measured at 10 GHz using a Keysight SPDR measuring instrument.

[0122] (2) Dielectric loss factor measurement

[0123] The dielectric loss factor (Df) was determined using an Agilent 4294A resistance meter after the flexible metal foil laminate was left to stand for 72 hours.

[0124] (3) Tensile strength test

[0125] The polyimide film was cut into pieces 10 mm wide and 40 mm long, and the tensile strength was determined using an Instron 5564 UTM instrument from Instron according to the ASTM D-882 method. The crosshead speed was measured at 5 mm / min.

[0126] As shown in Table 1, the polyimide film manufactured according to the embodiments of the present invention satisfies all the conditions of a dielectric constant of 3.5 or less, a dielectric loss factor of 0.0035 or less, and a tensile strength of 200 MPa or more.

[0127] Comparative Examples 1 and 2, which contain no liquid crystal polymer powder or only a small amount (5% by weight) of it, exhibited excellent tensile strength characteristics compared to the Examples, but also showed high dielectric constant and dielectric loss factor, resulting in reduced dielectric properties compared to the Examples.

[0128] In addition, compared with the examples, Comparative Example 3, which contained an excess (50% by weight) of liquid crystal polymer powder, showed excellent dielectric properties, but the tensile strength properties were reduced.

[0129] Therefore, it can be confirmed that the dielectric constant, dielectric loss factor, and tensile strength are at the desired levels only within the range of the liquid crystal polymer powder content in the embodiment.

[0130] This result is achieved due to the specific components and composition ratios in this application, indicating that the content of each component plays a decisive role.

[0131] On the other hand, the polyimide films of Comparative Examples 1 to 3, which have different compositions from those of the Examples, are expected to be difficult to use in electronic components that transmit signals at gigabit-level high frequencies, in terms of dielectric constant, dielectric loss factor, and tensile strength, compared to the polyimide films of the Examples.

[0132] The above description refers to embodiments of the present invention. However, those skilled in the art should be able to make various applications and modifications within the scope of the present invention based on the above description.

[0133] Industrial availability

[0134] This invention provides polyimide films with both low dielectric and mechanical properties by forming polyamic acid and polyimide films with specific components and specific composition ratios and by the manufacturing method thereof. This enables them to be effectively applied in a variety of fields that require these properties, especially electronic components such as flexible metal foil laminates.

Claims

1. A polyamic acid solution comprising an acid dianhydride component and a diamine component, and containing 10-30% by weight of liquid crystal polymer powder. The dianhydride components include benzophenone tetracarboxylic dianhydride (BTDA), biphenyl tetracarboxylic dianhydride (BPDA), and pyromellitic tetracarboxylic dianhydride (PMDA). The diamine component consists of meta-toluidine and p-phenylenediamine (PPD). Based on a total content of 100 mol% of the aforementioned dianhydride components, The content of benzophenone tetracarboxylic dianhydride is between 30 mol% and 50 mol%. The content of biphenyltetracarboxylic dianhydride is between 25 mol% and 45 mol%. The content of pyromellitic dianhydride is between 15 mol% and 35 mol%. The polyimide film obtained by imidizing the polyamic acid solution has a dielectric constant of 3.5 or less, a dielectric loss factor of 0.0035 or less, and a tensile strength of 200 MPa or more.

2. The polyamic acid solution according to claim 1, wherein, based on a total diamine content of 100 mol%, the content of meta-toluidine is 20 mol% to 40 mol%, and the content of p-phenylenediamine is 60 mol% to 80 mol%.

3. The polyamic acid solution according to claim 1, wherein the liquid crystal polymer powder is a polyester with a melting point of 300~330℃ and a D50 of 3~7μm.

4. A varnish comprising a polyamic acid solution according to any one of claims 1 to 3.

5. A polyimide film obtained by imidizing a polyamic acid solution according to any one of claims 1 to 3.

6. A method for manufacturing a polyimide film, comprising: (a) A step of producing polyamic acid by polymerizing an acid dianhydride component comprising benzophenone tetracarboxylic dianhydride (BTDA), biphenyl tetracarboxylic dianhydride (BPDA) and pyromellitic tetracarboxylic dianhydride (PMDA) and a diamine component consisting of meta-toluidine and p-phenylenediamine (PPD) in an organic solvent. (b) The step of adding 10-30% by weight of liquid crystal polymer powder to the polyamic acid and mixing it; and (c) The step of imidizing the polyamic acid containing the liquid crystal polymer powder. Based on a total dianhydride content of 100 mol%, the content of benzophenone tetracarboxylic dianhydride is 30 mol% to 50 mol%, the content of biphenyl tetracarboxylic dianhydride is 25 mol% to 45 mol%, and the content of pyromellitic tetracarboxylic dianhydride is 15 mol% to 35 mol%. The polyimide film has a dielectric constant of less than 3.5, a dielectric loss factor of less than 0.0035, and a tensile strength of more than 200 MPa.

7. The method for manufacturing the polyimide film according to claim 6, wherein, based on a total diamine content of 100 mol%, the content of meta-toluidine is 20 mol% to 40 mol%, and the content of p-phenylenediamine is 60 mol% to 80 mol%.

8. A multilayer film comprising the polyimide film of claim 5.

9. A flexible metal foil laminate comprising the polyimide film of claim 5 and a conductive metal foil.

10. An electronic component comprising the flexible metal foil laminate of claim 9.