Methylenedianiline-based polyimide film and graphite sheet manufactured therefrom

Abstract

The present invention provides a polyimide film for a graphite sheet, the polyimide film comprising, as polymeric units, dianhydride monomers and diamine monomers comprising 4,4'-methylenedianiline (MDA), meta-phenylenediamine (MPD), 4,4'-diaminodiphenyl ether (ODA), and para-phenylenediamine (PPD), the foam percentage of the polyimide film being 50% or greater.

Description

Methylenedianiline-based polyimide film and graphite sheet produced therefrom

[0001] The present invention relates to a methylenedianiline-based polyimide film and a graphite sheet produced therefrom. More specifically, it relates to a polyimide film with improved graphitization efficiency and a graphite sheet produced therefrom by introducing methylenedianiline (4,4'-Methylenedianiline, MDA).

[0002] Recent electronic devices are becoming lighter, smaller, thinner, and more highly integrated, resulting in the generation of significant heat. This heat can shorten product lifespan or cause failures and malfunctions. Consequently, thermal management for electronic devices is emerging as a critical issue.

[0003] Graphite sheets are attracting attention as heat dissipation materials for electronic devices because they have a higher thermal conductivity than metal sheets such as copper or aluminum. These graphite sheets can be manufactured in various ways, for example, by carbonizing and graphitizing polymer films. In particular, polyimide films are gaining popularity as polymer films for manufacturing graphite sheets due to their excellent mechanical, thermal, dimensional stability, and chemical stability.

[0004] It is known that the properties of graphite sheets produced from polyimide films are influenced by the properties of the polyimide films. Conventional polyimide films for graphite sheets mainly used 4,4'-diaminodiphenyl ether (ODA) as an aromatic diamine; however, when a large amount of ODA was used, problems arose such as a decrease in mechanical properties like tensile strength, elastic modulus, and heat resistance due to the flexible structure of ODA, or an increase in manufacturing costs due to high costs.

[0005] Therefore, while various polyimide films for graphite sheets are being developed, there is a need to develop polyimide films with improved graphitization efficiency while reducing the ODA content.

[0006] The present invention aims to provide a high-quality polyimide film for graphite sheets and a graphite sheet produced therefrom, which reduces costs by using methylenedianiline (4,4'-Methylenedianiline, MDA) and improves graphitization efficiency by controlling the structure of the polyimide through an optimal monomer combination.

[0007] In addition, the present invention provides a graphite sheet manufactured by carbonizing and graphitizing the polyimide film.

[0008] In addition, the present invention provides a method for manufacturing a polyimide film and a method for manufacturing a graphite sheet.

[0009] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are to be illustrated and described in detail. However, this is not intended to limit the invention to specific embodiments, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0010] The terms used in this application are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0011] Where in this specification, when a quantity, concentration, or other value or parameter is given as an enumeration of a range, a preferred range, a preferred upper limit, and a preferred lower limit, it should be understood that any pair of any upper range limit or preferred value and any lower range limit or preferred value are specifically disclosed, regardless of whether the range is disclosed separately.

[0012] Where a range of numerical values ​​is mentioned in this specification, unless otherwise stated, the range and the scope of the invention within that range are not intended to be limited to the specific value mentioned when defining the range.

[0013] In this specification, "dianhydride" is intended to include its precursor or derivative, and is also referred to as "dianhydride," "dianhydride," or "acid dianhydride." Although these may not technically be dianhydrides, they will nevertheless react with a diamine to form a polyamic acid, which can then be converted into a polyimide.

[0014] In this specification, "diamine" is intended to include its precursors or derivatives, which may not technically be diamines but nevertheless will react with dianhydrides to form polyamic acids, which can then be converted into polyimides.

[0015] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application. Specific details for the implementation of the above invention are described below.

[0016] The present invention relates to a polyimide film for high-quality graphite sheets and a graphite sheet produced therefrom, wherein the graphitization efficiency is improved by introducing methylenedianiline (4,4'-Methylenedianiline, MDA).

[0017] Polyimide film for graphite sheets

[0018] Specifically, the present invention provides a polyimide film for graphite sheets comprising a dianhydride monomer; and a diamine monomer comprising 4,4'-methylenedianiline (MDA), metaphenylenediamine (MPD), 4,4'-diaminodiphenyl ether (ODA), and paraphenylenediamine (PPD) as polymerization units, and having a foaming rate of 50% or more.

[0019] In addition, generally, the thickness of a polyimide film decreases as volatile components escape during the heat treatment process. However, if pores are formed inside the film, the decrease in thickness may be suppressed or the thickness may even increase. In this case, the foaming rate (%) can be calculated as (thickness of graphite sheet / thickness of polyimide film) * 100, and the thicknesses of the graphite sheet and the polyimide film are measured using Mitutoyo R-M6.

[0020] The lower limit of the above foaming rate may be 50% or more, 51% or more, 55% or more, 58% or more, 60% or more, 63% or more, 65% or more, 67% or more, 70% or more, 73% or more, or 75% or more, and the upper limit may not be specifically limited but may be 170% or less, or 150% or less.

[0021] Meanwhile, an unfoamed film refers to a film in which the graphitization of the carbonized film is insufficient to form a graphite sheet. This phenomenon generally occurs when the foaming rate is less than 50%, and because foaming does not occur properly, a prominent gloss appears on the surface of the film. Therefore, an unfoamed film can be identified even with the naked eye.

[0022] In addition, an over-foamed film refers to a film in which foaming has progressed excessively beyond the foaming threshold of the film, and the film cannot maintain its original shape. Even if graphitization has progressed sufficiently, this causes serious defects in appearance and cannot be used as a product.

[0023] The content of 4,4'-methylenedianiline (MDA) in the total diamine monomer of the present invention may be 35 mol% or more and less than 100 mol%, preferably the lower limit may be 36 mol% or more, 37 mol% or more, 38 mol% or more, 39 mol% or more, or 40 mol% or more, and in particular, the content of 4,4'-methylenedianiline is preferably 40 mol% or more. In addition, the upper limit may be 99 mol% or less, 95 mol% or less, 90 mol% or less, 85 mol% or less, 83 mol% or less, 80 mol% or less, 78 mol% or less, 75 mol% or less, 74 mol% or less, 73 mol% or less, 72 mol% or less, 71 mol% or less, or 70 mol% or less.

[0024] By including the above MDA in an amount of 35 mol% or more and less than 100 mol%, manufacturing costs can be reduced compared to the case where 4,4'-oxydianiline (4,4'-diaminodiphenyl ether, ODA) is used alone.

[0025] If the MDA content is less than 35 mol%, it is not desirable because the cost reduction effect is insufficient, and if it is 100 mol%, the elongation decreases, and since the component connecting the rings is carbon (C), the carbon is retained during the carbonization process, which hinders the connection between the rings and thereby weakens graphitization, resulting in non-foaming, which is not desirable.

[0026] In addition, the content of paraphenylenediamine (PPD) among the total diamine monomers may be 5 mol% to 30 mol%, preferably the lower limit may be 6 mol% or more, 7 mol% or more, 8 mol% or more, 9 mol% or more, or 10 mol% or more, and in particular, the content of paraphenylenediamine is preferably 10 mol% or more. The upper limit may be 25 mol% or less, 24 mol% or less, 23 mol% or less, 22 mol% or less, 21 mol% or less, 20 mol% or less, 19 mol% or less, 18 mol% or less, 17 mol% or less, 16 mol% or less, or 15 mol% or less. By including 5 mol% to 30 mol% of the PPD, the all-aromatic structure allows it to withstand high temperatures during the graphitization process and form a structure favorable for graphitization.

[0027] If the above PPD content is less than 5 mol%, the effect of improving strength and foaming is insufficient and is undesirable, and if it exceeds 30 mol%, over-foaming is induced and is undesirable.

[0028] In addition, the content of the metaphenylenediamine (MPD) in the total diamine monomer may be 5 mol% to 30 mol%, preferably the lower limit may be 6 mol% or more, 7 mol% or more, 8 mol% or more, 9 mol% or more, or 10 mol% or more, and the upper limit may be 25 mol% or less, 24 mol% or less, 23 mol% or less, 22 mol% or less, 21 mol% or less, 20 mol% or less, 19 mol% or less, 18 mol% or less, 17 mol% or less, 16 mol% or less, or 15 mol% or less. By including 5 mol% to 30 mol% of the MPD, structural twisting of the polymer chain can be induced to compensate for the reduction in elongation caused by the MDA structure.

[0029] If the above MPD content is less than 5 mol%, the effect of improving elongation is negligible and is undesirable, and if it exceeds 30 mol%, the flexibility of the chain decreases and is undesirable for securing elongation.

[0030] In addition, the content of the 4,4'-diaminodiphenyl ether (ODA) among the total diamine monomers may be 5 mol% to 50 mol%, preferably the lower limit may be 6 mol% or more, 7 mol% or more, 8 mol% or more, 9 mol% or more, or 10 mol% or more, or 15 mol% or more, and the upper limit may be 49 mol% or less, 48 ​​mol% or less, 47 mol% or less, 46 mol% or less, 45 mol% or less, 44 mol% or less, 43 mol% or less, 42 mol% or less, 41 mol% or less, or 40 mol% or less. By including 5 mol% to 50 mol% of the ODA, the reduction in elongation due to the PPD structure is compensated for, and foaming can be controlled to maintain the quality of the product.

[0031] If the above ODA content is less than 5 mol%, it is undesirable because high-quality graphite sheets cannot be obtained due to over-foaming, and if it exceeds 50 mol%, it is undesirable because the cost reduction effect is negligible and physical properties such as tensile strength decrease.

[0032] In one embodiment, based on a total content of 100 mol% of the total diamine monomer, the content of 4,4'-methylenedianiline (MDA) may be 35 to 75 mol%; the content of metaphenylenediamine (MPD) may be 5 to 15 mol%; the content of paraphenylenediamine (PPD) may be 5 to 20 mol%; and the content of 4,4'-diaminodiphenyl ether (ODA) may be 5 to 45 mol%. In particular, the content of 4,4'-methylenedianiline is preferably 40 to 70 mol%, and the content of paraphenylenediamine is preferably 10 to 15 mol%.

[0033] The 4,4'-methylenedianiline (MDA) applied to the polyimide film for graphite sheets of the present invention is an aromatic diamine having a structure similar to 4,4'-diaminodiphenyl ether (ODA) and is the most accessible diamine monomer in terms of cost. However, due to differences in structural flexibility, the elongation of the polyimide film is reduced, and the graphitization process is not easily carried out during the manufacturing process of graphite sheets (G / S), which limits its use as a graphite sheet. Accordingly, the present invention improves elongation and increases graphitization efficiency by controlling the PI structure through the use of diamine monomers including MDA, MPD, ODA, and PPD in appropriate amounts, thereby ensuring the compatibility of the polyimide film for graphite sheets.

[0034] The above dianhydric monomers are pyromellitic dianhydride (PMDA), biphenyl tetracarboxylic dianhydride (BPDA), benzophenone tetracarboxylic dianhydride (BTDA), oxydiphthalic dianhydride (ODPA), diphenylsulfone-3,4,3',4'-tetracarboxylic dianhydride (DSDA), bis(3,4-dicarboxyphenyl)sulfide dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, p-phenylenebis(trimellitic monoester acid anhydride), p-biphenylenebis(trimelytic monoester acid anhydride), m-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, p-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), 2,3,6,7-naphthalene tetracarboxylic acid dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride and It may include one or more selected from the group consisting of 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride.

[0035] Preferably, the dianhydride monomer may include one or more selected from the group consisting of pyromellitic dianhydride (PMDA), biphenyl tetracarboxylic dianhydride (BPDA), and benzophenone tetracarboxylic dianhydride (BTDA), and more preferably, may include pyromellitic dianhydride (PMDA).

[0036] In one embodiment, the polyimide film for a graphite sheet may comprise a dianhydride monomer comprising pyromellitic dianhydride (PMDA); and a diamine monomer comprising 4,4'-methylenedianiline (MDA), metaphenylenediamine (MPD), 4,4'-diaminodiphenyl ether (ODA), and paraphenylenediamine (PPD) as a polymerization unit.

[0037] The thickness of the polyimide film for the graphite sheet above can be appropriately selected considering the application, usage environment, and physical properties of the polyimide film. For example, the thickness of the polyimide film for the graphite sheet may be 20 to 150 μm, but is not limited thereto.

[0038] In addition, the polyimide film for the graphite sheet may contain 90 to 110 mol% of the dianhydride monomer, preferably 95 to 105 mol%, more preferably 98 to 102 mol%, and even more preferably 100 mol%.

[0039] In addition, the polyimide film for the graphite sheet may contain 90 to 110 mol% of the diamine monomer, preferably 95 to 105 mol%, more preferably 98 to 102 mol%, and even more preferably 100 mol%.

[0040] The molar ratio of the above dianhydride monomer to the above diamine monomer may be 1:2 to 2:1, and preferably 1:1.

[0041] The polyimide film for the graphite sheet may contain 10 to 30 wt% of polyamic acid solids, preferably 13 to 25 wt%, and more preferably 17 to 20 wt%. By controlling the polyamic acid solid content of the polyimide film for the graphite sheet, the increase in viscosity can be controlled and the process time during the curing process can be shortened.

[0042] The polyimide film for the graphite sheet described above may additionally include a filler. Here, the filler may refer to an inorganic filler that is sublimated by heat during the carbonization and / or graphitization process when manufacturing the graphite sheet. When the polyimide film includes the filler, foamy pores are formed in the graphite sheet by the gas generated through the sublimation of the filler during the manufacturing of the graphite sheet, thereby improving the flexibility of the graphite sheet and ultimately improving the handling and moldability of the graphite sheet.

[0043] The above filler may include one or more selected from the group consisting of calcium carbonate, disodium phosphate, calcium hydrogen phosphate, barium sulfate, silica, titanium oxide, alumina, and silicon nitride, and preferably may include one or more selected from the group consisting of calcium carbonate, disodium phosphate, and calcium hydrogen phosphate. The above filler has excellent dispersibility and does not appear on the surface of the polyimide film, thereby reducing surface defects, and may have the effect of inducing an appropriate foaming phenomenon during carbonization and / or graphitization to obtain a high-quality graphite sheet.

[0044] graphite sheet

[0045] In another aspect of the present invention, a graphite sheet is provided by carbonizing and graphitizing the polyimide film for the graphite sheet.

[0046] The thickness of the graphite sheet may be 10 to 150 μm, but is not limited thereto.

[0047] The polyimide film for graphite sheets described above can be manufactured using various methods commonly used in the relevant technical field.

[0048] Method for manufacturing a polyimide film and a graphite sheet

[0049] In another aspect of the present invention, a method for manufacturing a polyimide film for a graphite sheet is provided, comprising: (a) a step of manufacturing a polyamic acid comprising a dianhydride monomer; and a diamine monomer comprising 4,4'-methylenedianiline (MDA), metaphenylenediamine (MPD), 4,4'-diaminodiphenyl ether (ODA) and paraphenylenediamine (PPD) as a polymerization unit; and (b) a step of manufacturing a polyimide film for a graphite sheet by imidizing the polyamic acid, wherein the foaming rate is 50% or more.

[0050] Polyamic acid, dianhydride, diamine, etc. are applied in the same way as the polyimide film for graphite sheets described above.

[0051] The above polyamic acid can be prepared in the presence of a solvent. That is, the above polyamic acid may additionally contain a solvent.

[0052] The above solvent may include one or more selected from the group consisting of N,N'-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), N,N'-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), diethylacetamide (DEAc), N-ethyl-2-pyrrolidone (NEP), N,N'-diethylformamide (DEF), dimethylpropanamide (DMPA), and gamma-butyrolactone (GBL), and preferably N,N'-dimethylformamide (DMF) may be used.

[0053] The above polyamic acid is at a temperature of 23℃ and 1s -1The viscosity measured under shear rate conditions may be in the range of 5,000 to 500,000 cP. Specifically, the lower limit of the viscosity of the polyamic acid solution may be 8,000 cP or more, 10,000 cP or more, 20,000 cP or more, 50,000 cP or more, 60,000 cP or more, 70,000 cP or more, 80,000 cP or more, 90,000 cP or more, or 95,000 cP or more, and the upper limit may be 450,000 cP or less, 400,000 cP or less, 350,000 cP or less, 300,000 cP or less, or 280,000 cP or less. By controlling the viscosity range of the above polyamic acid solution, a polyimide film with excellent processability and desired physical properties can be manufactured.

[0054] In step (b), the method for producing a polyimide film for a graphite sheet by imidizing a polyamic acid may use, for example, a thermal imidization method, a chemical imidization method, or a combined imidization method using both thermal imidization and chemical imidization methods.

[0055] The thermal imidation method is a method of carrying out an imidation reaction solely by heating without applying a dehydrating ring-closing agent, etc., and is a method of obtaining a polyimide film in which the polyamic acid is imidized by forming a film on a support and then gradually increasing the temperature in a variable temperature range of 100 to 600 ℃ and heat treating for 1 to 8 hours.

[0056] Chemical imidation is a method of promoting imidation by applying a dehydrating agent and / or a catalyst (imidizing agent) to a precursor composition. The dehydrating agent is not particularly limited as long as it can promote a ring-closing reaction through dehydration action on the polyamic acid, and examples of the dehydrating agent include acetic anhydride. The catalyst is not particularly limited as long as it can promote a ring-closing reaction on the polyamic acid, and examples of the catalyst include tertiary amines, such as quinoline, isoquinoline (IQ), β-picoline (BP), etc.

[0057] The graphite sheet described above can be manufactured using various methods commonly used in the field of graphite sheet manufacturing. For example, the graphite sheet can be manufactured by carbonizing and graphitizing a polyimide film.

[0058] In addition, in another aspect of the present invention, a method for manufacturing a graphite sheet is provided, comprising: (a') a step of manufacturing a polyimide film for the graphite sheet; and (b') a step of carbonizing and graphitizing the polyimide film to manufacture a graphite sheet.

[0059] Specifically, step (a') can produce a polyimide film according to the method for producing a polyimide film for a graphite sheet.

[0060] The carbonization described above may be performed, for example, at a temperature of 1,000 to 1,500 ℃ for 1 to 15 hours, but is not limited thereto. Through the carbonization process, the polymer chains of the polyimide film are thermally decomposed to oxidize all atoms except carbon, thereby forming a preliminary graphite sheet comprising an amorphous carbon body, amorphous carbon body, and / or amorphous carbon body.

[0061] The graphitization described above may be performed, for example, at a temperature of 2,000 to 3,000 °C for 1 to 20 hours, but is not limited thereto. Through the graphitization process, carbon in an amorphous carbon body, amorphous carbon body, and / or amorphous carbon body is rearranged to form a graphite layer, and a graphite sheet may be formed. At this time, a foaming phenomenon may occur.

[0062] The polyimide film for graphite sheets according to the present invention and the graphite sheet produced therefrom have the effect of reducing costs by introducing methylenedianiline (4,4'-Methylenedianiline, MDA), improving graphitization efficiency by controlling the structure of the polyimide by deriving an optimal monomer combination, and obtaining high-quality graphite sheets.

[0063] In addition, the polyimide film according to the present invention, by including MDA, has the effect of relatively higher price competitiveness and excellent productivity and process efficiency.

[0064] In addition, the polyimide film for graphite sheets according to the present invention and the graphite sheet produced therefrom have the effect of obtaining a graphite sheet with an excellent appearance.

[0065] Examples are provided to aid in understanding the present invention. The following examples are provided merely to facilitate a better understanding of the invention, and the scope of the invention is not limited by these examples.

[0066] <Example>

[0067] [Manufacture of Polyimide Film]

[0068] Example 1-1

[0069] A polyamic acid solution was prepared by adding the solvent dimethylformamide (DMF) to a 500 ml reactor equipped with a stirrer and a nitrogen inlet / outlet pipe, adding a diamine monomer comprising 40 mol% 4,4'-methylenedianiline (MDA), 10 mol% metaphenylenediamine (MPD), 40 mol% 4,4'-diaminodiphenyl ether (ODA), and 10 mol% paraphenylenediamine (PPD), and a dianhydride monomer comprising 100 mol% pyromellitic dianhydride (PMDA), and reacting at 25°C for 4 hours (solid content 18.5 wt%, viscosity at 23°C 200,000 cP).

[0070] 50g of the above polyamic acid solution was mixed with 2g of catalyst (BP, β-picoline) and 12g of dehydrating agent (AA, acetic anhydride) to prepare a mixed solution, and the mixed solution was cast onto a SUS (or glass plate) substrate using a doctor blade and dried at 110°C for 4 to 12 minutes to produce a gel film. Afterward, the gel film was separated from the substrate and heat-treated at 250 to 400°C for 8 to 24 minutes to produce a polyimide film having a thickness of 50㎛.

[0071] Examples 1-2

[0072] A polyimide film was prepared in the same manner as in Example 1-1, except that instead of using a diamine monomer comprising 4,4'-methylenedianiline (MDA) 40 mol%, metaphenylenediamine (MPD) 10 mol%, 4,4'-diaminodiphenyl ether (ODA) 40 mol%, and paraphenylenediamine (PPD) 10 mol% in Example 1-1, a diamine monomer comprising 4,4'-methylenedianiline (MDA) 50 mol%, metaphenylenediamine (MPD) 10 mol%, 4,4'-diaminodiphenyl ether (ODA) 30 mol%, and paraphenylenediamine (PPD) 10 mol% was used.

[0073] Examples 1-3

[0074] A polyimide film was prepared in the same manner as in Example 1-1, except that instead of using a diamine monomer comprising 4,4'-methylenedianiline (MDA) 40 mol%, metaphenylenediamine (MPD) 10 mol%, 4,4'-diaminodiphenyl ether (ODA) 40 mol%, and paraphenylenediamine (PPD) 10 mol% in Example 1-1, a diamine monomer comprising 4,4'-methylenedianiline (MDA) 60 mol%, metaphenylenediamine (MPD) 10 mol%, 4,4'-diaminodiphenyl ether (ODA) 15 mol%, and paraphenylenediamine (PPD) 15 mol% was used.

[0075] Examples 1-4

[0076] A polyimide film was prepared in the same manner as in Example 1-1, except that instead of using a diamine monomer comprising 4,4'-methylenedianiline (MDA) 40 mol%, metaphenylenediamine (MPD) 10 mol%, 4,4'-diaminodiphenyl ether (ODA) 40 mol%, and paraphenylenediamine (PPD) 10 mol% in Example 1-1, a diamine monomer comprising 4,4'-methylenedianiline (MDA) 70 mol%, metaphenylenediamine (MPD) 10 mol%, 4,4'-diaminodiphenyl ether (ODA) 10 mol%, and paraphenylenediamine (PPD) 10 mol% was used.

[0077] Comparative Example 1-1

[0078] A polyimide film was prepared in the same manner as in Example 1-1, except that a diamine monomer containing 100 mol% of 4,4'-methylenedianiline (MDA) was used instead of a diamine monomer containing 40 mol% of 4,4'-methylenedianiline (MDA), 10 mol% of metaphenylenediamine (MPD), 40 mol% of 4,4'-diaminodiphenyl ether (ODA), and 10 mol% of paraphenylenediamine (PPD) in Example 1-1.

[0079] Comparative Example 1-2

[0080] A polyimide film was prepared in the same manner as in Example 1-1, except that instead of using a diamine monomer containing 4,4'-methylenedianiline (MDA) 40 mol%, metaphenylenediamine (MPD) 10 mol%, 4,4'-diaminodiphenyl ether (ODA) 40 mol%, and paraphenylenediamine (PPD) 10 mol% in Example 1-1, a diamine monomer containing 4,4'-methylenedianiline (MDA) 70 mol% and 4,4'-diaminodiphenyl ether (ODA) 30 mol% was used.

[0081] Comparative Examples 1-3

[0082] A polyimide film was prepared in the same manner as in Example 1-1, except that instead of using a diamine monomer containing 4,4'-methylenedianiline (MDA) 40 mol%, metaphenylenediamine (MPD) 10 mol%, 4,4'-diaminodiphenyl ether (ODA) 40 mol%, and paraphenylenediamine (PPD) 10 mol% in Example 1-1, a diamine monomer containing 4,4'-methylenedianiline (MDA) 70 mol% and metaphenylenediamine (MPD) 30 mol% was used.

[0083] Comparative Examples 1-4

[0084] A polyimide film was prepared in the same manner as in Example 1-1, except that instead of using a diamine monomer containing 4,4'-methylenedianiline (MDA) 40 mol%, metaphenylenediamine (MPD) 10 mol%, 4,4'-diaminodiphenyl ether (ODA) 40 mol%, and paraphenylenediamine (PPD) 10 mol% in Example 1-1, a diamine monomer containing 4,4'-methylenedianiline (MDA) 70 mol% and paraphenylenediamine (PPD) 30 mol% was used.

[0085] Comparative Examples 1-5

[0086] A polyimide film was prepared in the same manner as in Example 1-1, except that instead of using a diamine monomer containing 4,4'-methylenedianiline (MDA) 40 mol%, metaphenylenediamine (MPD) 10 mol%, 4,4'-diaminodiphenyl ether (ODA) 40 mol%, and paraphenylenediamine (PPD) 10 mol% in Example 1-1, a diamine monomer containing 4,4'-methylenedianiline (MDA) 70 mol%, metaphenylenediamine (MPD) 10 mol%, and paraphenylenediamine (PPD) 20 mol% was used.

[0087] Comparative Examples 1-6

[0088] A polyimide film was prepared in the same manner as in Example 1-1, except that instead of using a diamine monomer containing 4,4'-methylenedianiline (MDA) 40 mol%, metaphenylenediamine (MPD) 10 mol%, 4,4'-diaminodiphenyl ether (ODA) 40 mol%, and paraphenylenediamine (PPD) 10 mol% in Example 1-1, a diamine monomer containing 4,4'-methylenedianiline (MDA) 70 mol%, 4,4'-diaminodiphenyl ether (ODA) 20 mol%, and metaphenylenediamine (MPD) 10 mol% was used.

[0089] Comparative Examples 1-7

[0090] A polyimide film was prepared in the same manner as in Example 1-1, except that instead of using a diamine monomer containing 4,4'-methylenedianiline (MDA) 40 mol%, metaphenylenediamine (MPD) 10 mol%, 4,4'-diaminodiphenyl ether (ODA) 40 mol%, and paraphenylenediamine (PPD) 10 mol% in Example 1-1, a diamine monomer containing 4,4'-methylenedianiline (MDA) 60 mol%, 4,4'-diaminodiphenyl ether (ODA) 30 mol%, and metaphenylenediamine (MPD) 10 mol% was used.

[0091]

[0092] Table 1 below lists the composition and content of the dianhydride monomer and diamine monomer used when preparing the polyimide films according to Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-7.

[0093] Classification Anhydride Monomer (mol%) Diamine Monomer (mol%) PM D AM D A D O M P P PD Example 1-1 100 40 40 10 10 Example 1-2 100 50 30 10 10 Example 1-3 100 60 15 10 15 Example 1-4 100 70 10 10 10 Comparative Example 1-1 100 10 0--- Comparative Example 1-2 100 70 30-- Comparative Example 1-3 100 70 30- Comparative Example 1-4 100 70--30 Comparative Example 1-5 100 70 10 20 Comparative Example 1-6 100 70 20 10- Comparative Example 1-7 100 60 30 10-

[0094] [Manufacture of Graphite Sheets]

[0095] Example 2-1

[0096] The polyimide film prepared according to Example 1-1 was heated to 1,300 ℃ under vacuum conditions using an electric furnace and then carbonized by maintaining the temperature for 10 to 15 hours. Afterwards, the film was heated to 2,300 ℃ under argon gas and then graphitized by maintaining the temperature for 10 to 20 hours to produce a graphite sheet.

[0097] Examples 2-2 to 2-4

[0098] A graphite sheet was prepared in the same manner as in Example 2-1, except that instead of using the polyimide film prepared according to Example 1-1 in Example 2-1, each of the polyimide films prepared according to Examples 1-2 to 1-4 was used.

[0099] Comparative Examples 2-1 to 2-7

[0100] A graphite sheet was prepared in the same manner as in Example 2-1, except that instead of using the polyimide film prepared according to Example 1-1 in Example 2-1, each of the polyimide films prepared according to Comparative Examples 1-1 to 1-7 was used.

[0101] <Experimental Example>

[0102] Experimental Example 1: Comparison of Foaming Rates of Graphite Sheets

[0103] The foaming thickness of graphite sheets prepared according to Examples 2-1 to 2-4 and Comparative Examples 2-1 to 2-7 using polyimide films prepared according to Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-7 was measured to compare the foaming rates. The foaming thickness was measured using a Mitutoyo R-M6. The results are listed in Table 2 below. Non-foaming is distinguished by a foaming rate of less than 50% or by appearance (surface gloss), while over-foaming is based on whether the film maintains its shape.

[0104] Polyimide Film Graphite Sheet Foaming Rate (%) Example 1-1 Example 2-1 75% Example 1-2 Example 2-2 67% Example 1-3 Example 2-3 58% Example 1-4 Example 2-4 51% Comparative Example 1-1 Comparative Example 2-1 Unfoamed Comparative Example 1-2 Comparative Example 2-2 Unfoamed Comparative Example 1-3 Comparative Example 2-3 Unfoamed Comparative Example 1-4 Comparative Example 2-4 Overfoamed Comparative Example 1-5 Comparative Example 2-5 Overfoamed Comparative Example 1-6 Comparative Example 2-6 Unfoamed Comparative Example 1-7 Comparative Example 2-7 45%

[0105] According to Table 2, the graphite sheets according to Examples 2-1 to 2-4, prepared using a film containing at least a certain amount of each monomer of MDA, MPD, ODA, and PPD, were found to have a foaming rate of 50% or more, and due to the appropriate foaming rate, the exhaust of sublimation gas generated during carbonization and / or graphitization was facilitated, allowing for the acquisition of high-quality graphite sheets.

[0106] Meanwhile, in the case of Comparative Examples 2-1 to 2-7, which were prepared using films containing only some of the four types of diamines or not containing a certain amount, they were found to be unfoamed (Comparative Examples 2-1 to 2-3 and 2-6), overfoamed (Comparative Examples 2-4 and 2-5), or had a foaming rate of less than 50% (Comparative Example 2-7).

[0107] Therefore, by using monomers including MDA, MPD, ODA, and PPD, the present invention overcomes the limitation of low graphitization efficiency of conventional MDA-based PI and enables the economical production of high-quality graphite sheets by efficiently inducing graphitization through monomer structure control. In addition, it is possible to secure the compatibility of MDA-based polyimide as a graphite sheet.

[0108]

[0109] The specification omits detailed descriptions of matters that can be sufficiently recognized and inferred by those skilled in the art of the present invention, and various modifications are possible within the scope of not altering the technical concept or essential configurations of the present invention, in addition to the specific examples described in this specification. Accordingly, the present invention may be implemented in a manner different from that specifically described and exemplified in this specification, and this is a matter that can be understood by those skilled in the art.

Claims

1. Anhydrous monomer; and Diamine monomers comprising 4,4'-methylenedianiline (MDA), metaphenylenediamine (MPD), 4,4'-diaminodiphenyl ether (ODA), and paraphenylenediamine (PPD) as polymerization units, Polyimide film for graphite sheets with a foaming rate of 50% or more.

2. In Paragraph 1, A polyimide film for graphite sheets having a 4,4'-methylenedianiline (MDA) content of 35 mol% or more and less than 100 mol% among the total diamine monomers.

3. In Paragraph 1, A polyimide film for graphite sheets having a paraphenylenediamine (PPD) content of 5 mol% to 30 mol% among the total diamine monomers.

4. In Paragraph 1, A polyimide film for graphite sheets having a metaphenylenediamine (MPD) content of 5 mol% to 30 mol% among the total diamine monomers.

5. In Paragraph 1, A polyimide film for graphite sheets having a content of 4,4'-diaminodiphenyl ether (ODA) of 5 mol% to 50 mol% among the total diamine monomers.

6. In Paragraph 1, The above dianhydric monomers are pyromellitic dianhydride (PMDA), biphenyl tetracarboxylic dianhydride (BPDA), benzophenone tetracarboxylic dianhydride (BTDA), oxydiphthalic dianhydride (ODPA), diphenylsulfone-3,4,3',4'-tetracarboxylic dianhydride (DSDA), bis(3,4-dicarboxyphenyl)sulfide dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, p-phenylenebis(trimellitic monoester acid anhydride), p-biphenylenebis(trimelytic monoester acid anhydride), m-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, p-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), 2,3,6,7-naphthalene tetracarboxylic acid dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride and A polyimide film for graphite sheets comprising one or more selected from the group consisting of 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride.

7. In Paragraph 1, A polyimide film for graphite sheets in which the above dianhydric monomer comprises pyromellitic dianhydride (PMDA).

8. In Paragraph 1, A polyimide film for a graphite sheet, wherein the thickness of the polyimide film is 20 to 150 μm.

9. A graphite sheet manufactured using a polyimide film according to any one of claims 1 to 8.

10. In Paragraph 9, A graphite sheet having a thickness of 10 to 150 μm.

11. (a) a step of preparing a polyamic acid comprising, as polymerization units; a dianhydride monomer; and a diamine monomer comprising 4,4'-methylenedianiline (MDA), metaphenylenediamine (MPD), 4,4'-diaminodiphenyl ether (ODA) and paraphenylenediamine (PPD); and (b) a step of preparing a polyimide film by imidizing the above polyamic acid; comprising, A method for manufacturing a polyimide film for graphite sheets having a foaming rate of 50% or more.

12. (a') A step of manufacturing a polyimide film for a graphite sheet according to claim 1; and (b') a step of carbonizing and graphitizing the polyimide film to produce a graphite sheet; a method for manufacturing a graphite sheet comprising.

13. In Paragraph 12, A method for manufacturing a graphite sheet, wherein the carbonization is performed at a temperature of 1,000 to 1,500 ℃ for 1 to 15 hours.

14. In Paragraph 12, A method for manufacturing a graphite sheet, wherein the graphitization is performed at a temperature of 2,000 to 3,000 ℃ for 1 to 20 hours.