JP2023539248A - Polyimide film manufacturing method for graphite sheet and graphite sheet manufacturing method - Google Patents

Abstract

A polyamic acid solution is prepared, and a sublimable inorganic filler solution having a zeta potential of +30 mV to +40 mV or -40 mV to -30 mV is added to the polyamic acid solution to produce a precursor composition for a polyimide film, and the precursor composition Disclosed are a method for producing a polyimide film for a graphite sheet, which includes the step of obtaining a polyimide film from a composition, and a method for producing a graphite sheet using the same. [Selection diagram] None

Description

The present invention relates to a method for producing a polyimide film for a graphite sheet and a method for producing a graphite sheet, and more specifically, it relates to a method for producing a polyimide film for a graphite sheet and a method for producing a graphite sheet with excellent thermal conductivity.

In recent years, electronic devices have become lighter, smaller, thinner, and more highly integrated, and as a result, electronic devices generate a lot of heat. Such heat can shorten the product's lifespan or cause it to malfunction or malfunction. Therefore, thermal management of electronic devices has become an important issue.

Graphite sheets have higher thermal conductivity than metal sheets such as copper and aluminum, and are attracting attention as heat dissipation members for electronic devices. Such graphite sheets can be produced in various ways, for example by carbonizing and graphitizing a polymer film. In particular, polyimide films are attracting attention as polymer films for producing graphite sheets due to their excellent mechanical and thermal dimensional stability and chemical stability.

It is known that the physical properties of a graphite sheet manufactured from a polyimide film are affected by the physical properties of the polyimide film. Therefore, although various polyimide films for graphite sheets have been developed, there is still a need for polyimide films that can produce graphite sheets with higher thermal conductivity.

An object of the present invention is to provide a method for producing a polyimide film for graphite sheets and a method for producing graphite sheets that have excellent thermal conductivity.

1. According to one embodiment, a method for manufacturing a polyimide film for graphite sheets is provided. The method includes preparing a polyamic acid solution, adding a sublimable inorganic filler solution having a zeta potential of +30 mV to +40 mV or -40 mV to -30 mV to the polyamic acid solution to produce a precursor composition for a polyimide film, The method may also include the step of obtaining a polyimide film from the precursor composition.

2. Said 1. The polyamic acid solution is produced by reacting a diamine monomer and a dianhydride monomer in a solvent, and the diamine monomer is 4,4'-oxydianiline (4,4'- oxydianiline), 3,4'-oxydianiline, p-phenylene diamine, m-phenylene diamine, 4,4'-methylene dianiline, 3,3'-methylene dianiline, or a combination thereof The dianhydride monomer includes pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4- Biphenyltetracarboxylic dianhydride, oxydiphthalic anhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, or a combination thereof May include.

3. Said 1. or 2. In this, the average particle size (D ₅₀ ) of the sublimable inorganic filler in the sublimable inorganic filler solution may be 2 μm to 10 μm.

4. Said 1. ~3. In any of these, the sublimable inorganic filler may include dibasic calcium phosphate, barium sulfate, calcium carbonate, or a combination thereof.

5. Said 1. ~4. In any of the above, the sublimable inorganic filler may be added in an amount of 0.1 part by weight to 0.3 part by weight based on 100 parts by weight of the polyamic acid.

6. Said 1. ~5. In any of the above, the precursor composition further includes a dehydrating agent and an imidizing agent, and the step of obtaining a polyimide film from the precursor composition includes forming a film of the precursor composition on a support and drying it. The method may include the step of manufacturing a gel film by using a method of manufacturing a gel film, and heat-treating the gel film.

7. Said 1. ~6. In any of the above, the polyimide film may have a roughness (Ra) of 10 nm to 15 nm as measured based on the ISO 1997 standard.

8. According to another aspect, a method of manufacturing a graphite sheet is provided. The method described in 1. ~7. The method may include producing a polyimide film according to any one of the above, and carbonizing and graphitizing the polyimide film to obtain a graphite sheet.

9. Above 8. In the method, the graphite sheet may have a thickness of 20 μm to 40 μm and a thermal conductivity of 1,400 W/m·K or more.

INDUSTRIAL APPLICATION This invention has the effect of providing the manufacturing method of the polyimide film for graphite sheets with excellent thermal conductivity, and the manufacturing method of a graphite sheet.

References to the singular term herein include the plural term unless the context clearly dictates otherwise.

When the positional relationship of two parts is described with words such as "on top", "on top", "bottom on", "on the side", etc., unless "directly" or "directly" is used, One or more other parts may be located between the parts.

The use of terms such as "comprising" or "having" herein refers to the presence of a feature or component described in the specification, and one or more additional features or components. This does not exclude the possibility that this may occur.

When interpreting the constituent elements, they shall be interpreted to include a margin of error even if there is no separate explicit statement.

In this specification, "a to b" indicating a numerical range is defined as ≧a and ≦b.

According to one aspect of the present invention, a method for producing a polyimide film for a graphite sheet (hereinafter referred to as a "method for producing a polyimide film") is provided. The method includes preparing a polyamic acid solution, adding a sublimable inorganic filler solution having a zeta potential of +30 mV to +40 mV or -40 mV to -30 mV to the polyamic acid solution to produce a precursor composition for a polyimide film, The method may also include the step of obtaining a polyimide film from the precursor composition.

Each step will be explained in more detail below.

First, a polyamic acid solution is prepared.

Polyamic acid solutions can be prepared using conventional methods known in the art. For example, a polyamic acid solution can be produced by reacting a diamine monomer and a dianhydride monomer in a solvent. The type and number are not particularly limited.

The solvent is not particularly limited as long as it can dissolve the polyamic acid. For example, the solvent may include an aprotic polar solvent. Examples of aprotic polar solvents include amide solvents such as N,N'-dimethylformamide (DMF) and N,N'-dimethylacetamide (DMAc), and phenolic solvents such as p-chlorophenol and o-chlorophenol. Solvents include N-methyl-pyrrolidone (NMP), γ-butyrolactone (GBL), Diglyme, and the like, and these may be used alone or in combination of two or more. Optionally, auxiliary solvents such as toluene, tetrahydrofuran (THF), acetone, methyl ethyl ketone (MEK), methanol, ethanol, water, etc. may be used to adjust the solubility of the polyamic acid.

As the diamine monomer, various diamine monomers known in the art may be used without limitation within a range that does not impair the purpose of the present invention. For example, diamine monomers include 4,4'-oxydianiline (ODA), 3,4'-oxydianiline, p-phenylene diamine (PPD), m - may include phenylene diamine, 4,4'-methylene dianiline, 3,3'-methylene dianiline, or a combination thereof, in which case the formation of a polyimide film that favors molecular orientation is possible; A graphite sheet with excellent thermal conductivity can be formed during carbonization and graphitization.

As the dianhydride monomer, various dianhydride monomers known in the art may be used without restriction within a range that does not impair the purpose of the present invention. For example, dianhydride monomers include pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4- Biphenyltetracarboxylic dianhydride, oxydiphthalic anhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, or a combination thereof In such a case, it is possible to form a polyimide film that is advantageous for molecular orientation, and it is possible to form a graphite sheet having excellent thermal conductivity upon carbonization and graphitization.

The diamine monomer and the dianhydride monomer are contained in the solvent in substantially equimolar amounts; here, "substantially equimolar" refers to the number of moles of the entire diamine monomer. This means that the dianhydride monomer is contained in an amount of 99.8 mol % to 100.2 mol % based on . Reacting the diamine monomer and the dianhydride monomer in substantially equimolar amounts can, for example,
(a) Adding the entire diamine monomer (or dianhydride monomer) to a solvent, and adding dianhydride monomer (or diamine monomer) in a substantially equimolar amount; how to react,
(b) A portion of the diamine monomer (or dianhydride monomer) is added to the solvent, and 95 mol % to 105 mol % based on the diamine monomer (or dianhydride monomer) is added. After adding dianhydride monomer (or diamine monomer) at a ratio of %, diamine monomer and/or dianhydride monomer are added in substantially equimolar amounts. how to react,
(c) Either part of the diamine monomer (or dianhydride monomer) or part of the dianhydride monomer (or diamine monomer) is in excess amount in the solvent. a portion of the diamine monomer (or dianhydride monomer) and a portion of the dianhydride monomer (or diamine monomer) in another solvent to form a first composition. The first composition and the second composition are mixed and reacted, but at this time, the diamine When the monomer (or dianhydride monomer) is in an excessive amount, a method of using an excessive amount of the dianhydride monomer (or diamine monomer) in the second composition can be mentioned. In (a) to (c) above, the diamine monomer and dianhydride monomer mean one or more (for example, one or two) diamine monomer and dianhydride monomer. .

According to one embodiment, the polyamic acid may be included in an amount of 5 parts by weight to 35 parts by weight based on 100 parts by weight of the polyamic acid solution. Within the above range, the polyamic acid solution may have a molecular weight and viscosity suitable for forming a film. For example, the polyamic acid may be contained in an amount of 5 parts by weight to 30 parts by weight, based on 100 parts by weight of the polyamic acid solution, and as another example, 15 parts by weight to 20 parts by weight, but the content is not limited thereto. isn't it.

According to one embodiment, the polyamic acid solution may have a viscosity of 100,000 cP to 500,000 cP at 23° C. and a shear rate of 1 s ^-1 . Within the above range, the polyamic acid has a predetermined molecular weight while providing excellent processability when forming a polyimide film. Here, "viscosity" may be measured using a HAAKE Mars Rheometer. For example, the viscosity of a polyamic acid solution is 150,000 cP to 450,000 cP at 23° C. and a shear rate of 1 s ^-1 , another example is 200,000 cP to 400,000 cP, and still another example is 250,000 cP to 450,000 cP. It may be 350,000 cP, but is not limited to this.

According to one embodiment, the polyamic acid may have a weight average molecular weight of 100,000 g/mol to 500,000 g/mol. This range is advantageous for producing graphite sheets with better thermal conductivity. Here, the "weight average molecular weight" may be measured using gel chromatography (GPC) using polystyrene as a standard sample. For example, the weight average molecular weight of polyamic acid may be 150,000 g/mol to 500,000 g/mol, and as another example, it may be 100,000 g/mol to 400,000 g/mol, but is not limited thereto. It's not a thing.

Next, a sublimable inorganic filler solution having a zeta potential of +30 mV to +40 mV or -40 mV to -30 mV is added to the polyamic acid solution to prepare a polyimide film precursor composition.

"Sublimable inorganic filler" means an inorganic filler that sublimes by heat during the carbonization and/or graphitization process during the production of graphite sheets. When the polyimide film includes a sublimable inorganic filler, voids may be formed in the graphite sheet due to gas generated through sublimation of the sublimable inorganic filler during manufacture of the graphite sheet. This not only makes it possible to smoothly exhaust the sublimation gas generated during graphite sheet manufacturing to obtain a high-quality graphite sheet, but also improves the flexibility of the graphite sheet, ultimately improving the handling properties of the graphite sheet. Moldability can be improved. Examples of sublimable inorganic fillers include dibasic calcium phosphate, barium sulfate, calcium carbonate, etc., but are not limited thereto.

The inventor of the present invention controlled the zeta potential of the sublimable inorganic filler solution to +30 mV to +40 mV or -40 mV to -30 mV and added it to the polyamic acid solution. They found that they can be uniformly dispersed in a polyimide film with an appropriate size and uniform particle size distribution, and as a result, it is possible to produce a graphite sheet with excellent thermal conductivity, and have developed the present invention. completed. Here, "zeta potential" can be measured using a zeta potential measuring device based on ISO 13099-2 (colloidal systems-methods for zeta-potential determination-part 2: optical methods). Good. According to one embodiment, the zeta potential of the sublimable inorganic filler solution may be between +32 mV and +40 mV or between -40 mV and -32 mV. According to other embodiments, the zeta potential of the sublimable inorganic filler solution may be between +35 mV and +40 mV or between -35 mV and -40 mV, but is not limited thereto.

The zeta potential control method is not particularly limited, and various methods known to those skilled in the art may be used. For example, the zeta potential of a sublimable inorganic filler solution can be determined by adding a surfactant or a charged polymer to the sublimable inorganic filler-containing solution, or by changing the pH of the sublimable inorganic filler-containing solution. It can be controlled by adjusting or other methods.

The sublimable inorganic filler solution may include a solvent and a sublimable inorganic filler. For the explanation regarding the solvent contained in the sublimable inorganic filler solution, refer to the explanation regarding the solvent contained in the polyamic acid solution.

According to one embodiment, the average particle size (D ₅₀ ) of the sublimable inorganic filler in the sublimable inorganic filler solution may be between 2 μm and 10 μm. Within the above range, the sublimable inorganic filler can be uniformly dispersed within the polyimide film with an appropriate size and uniform particle size distribution, and as a result, it is possible to manufacture a graphite sheet with excellent thermal conductivity. be. Here, the "average particle size (D ₅₀ )" is calculated using a particle size analyzer (SALD-2201, Shimadzu) after ultrasonic dispersing the sublimable inorganic filler solution at 25°C for 5 minutes. It may be measured using For example, the average particle size (D ₅₀ ) of the sublimable inorganic filler in the sublimable inorganic filler solution may be 3 μm to 8 μm, and as another example, may be 4 μm to 7 μm, but is not limited thereto. It's not a thing.

According to one embodiment, the sublimable inorganic filler may be added in an amount of 0.05 parts by weight to 0.3 parts by weight based on 100 parts by weight of polyamic acid. Within the above range, the sublimable inorganic filler can be uniformly dispersed within the polyimide film with an appropriate size and uniform particle size distribution, and as a result, it is possible to manufacture a graphite sheet with excellent thermal conductivity. be. For example, the sublimable inorganic filler may be added in an amount of 0.10 parts by weight to 0.28 parts by weight, based on 100 parts by weight of polyamic acid, and as another example, 0.12 parts by weight to 0.26 parts by weight. However, it is not limited to this.

Thereafter, a polyimide film is obtained from the precursor composition.

The method for obtaining the polyimide film from the precursor composition is not particularly limited, and various methods known to those skilled in the art may be used. For example, the polyimide film may be obtained using a thermal imidization method, a chemical imidization method, or a composite imidization method using a combination of a thermal imidization method and a chemical imidization method.

The thermal imidization method is a method in which the imidization reaction proceeds only by heating without using a dehydrating agent or an imidizing agent. For example, after coating a precursor composition on a support, the temperature is heated at 40°C to 400°C. In this method, the temperature is gradually raised in a temperature range of 40° C. to 300° C., and a polyimide film is obtained by heat treatment for 1 hour to 8 hours.

The chemical imidization method is a method of applying a dehydrating agent and/or an imidizing agent to a precursor composition to promote imidization of polyamic acid.

In the composite imidization method, a dehydrating agent and an imidizing agent are added to a precursor composition, coated on a support, and then heated at 80°C to 200°C (for example, 100°C to 180°C) to remove the dehydrating agent and the imidizing agent. This is a method of obtaining a polyimide film by activating the imidizing agent, partially curing it, and then heating it at 200° C. to 400° C. for 5 seconds to 400 seconds.

According to one embodiment, the precursor composition further includes a dehydrating agent and an imidizing agent, and the step of obtaining a polyimide film from the precursor composition includes coating the precursor composition on a support (e.g., The method may include the steps of: casting) and drying to produce a gel film, and heat treating the gel film. The order of addition of the sublimable inorganic filler solution, dehydrating agent, and imidizing agent is not particularly limited, and the sublimable inorganic filler solution, dehydrating agent, and imidizing agent are added to the polyamic acid solution at the same time, or A dehydrating agent and an imidizing agent may be added after adding the sublimable inorganic filler solution.

A "dehydrating agent" is an agent that promotes the ring-closing reaction through a dehydrating action on polyamic acid. Examples of dehydrating agents include aliphatic acid anhydrides, aromatic acid anhydrides, N,N'-dialkylcarbodiimides, lower aliphatic halides, halogenated lower aliphatic acid anhydrides, arylphosphonic acid dihalides, and thionyl halides. These compounds may be used alone or in combination of two or more. Among these, aliphatic acid anhydrides such as acetic anhydride, propionic anhydride, and lactic anhydride may be used from the viewpoint of availability and cost.

The "imidizing agent" is one that promotes the ring-closing reaction of polyamic acid. Examples of imidizing agents include aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines. Among them, heterocyclic tertiary amines may be used from the viewpoint of reactivity as a catalyst. Examples of the heterocyclic tertiary amine include quinoline, isoquinoline, β-picoline, and pyridine, and these may be used alone or in combination of two or more.

The amount of the dehydrating agent and imidizing agent to be added is not particularly limited, but the amount of the dehydrating agent to be added is 0.5 mol to 7 mol (as another example, 1 mol to 1 mol of the amic acid group in the polyamic acid). The imidizing agent may be used in a proportion of 0.05 mol to 3 mol (as another example, 0.2 mol to 3 mol) per 1 mol of amic acid groups in the polyamic acid. 2 mol). Within the above range, imidization is sufficient and it is easy to cast into a film.

Supports used in the gel film manufacturing step include glass plates, aluminum foils, endless stainless steel belts, stainless steel drums, etc., and the drying temperature is 40°C to 300°C (for example, 80°C to 200°C), The drying time may be 1 minute to 10 minutes (eg, 3 minutes to 7 minutes), but is not limited thereto. Here, the gel film is in the intermediate stage of curing from polyamic acid to polyimide and has self-supporting properties.

In some cases, the gel film may further include a step of stretching the gel film in order to adjust the thickness and size of the polyimide film finally obtained and improve the orientation, and the stretching may be performed using MD (machine direction). and TD (transverse direction).

The heat treatment temperature of the gel film may be, for example, 50°C to 700°C, another example is 150°C to 600°C, another example is 200°C to 600°C, and the heat treatment time is, for example, The duration may be 1 minute to 10 minutes (for example, 3 minutes to 7 minutes), but is not limited thereto. The solvent remaining in the gel film may be removed by heat treatment of the gel film, and most of the remaining amic acid groups may be imidized to obtain a polyimide film.

In some cases, the polyimide film thus obtained may be heat-finished at a temperature of 400° C. to 650° C. for 5 seconds to 400 seconds to further cure the polyimide film. Heat finishing may be performed under a predetermined tension to relieve internal stresses that may remain in the material.

According to one embodiment, the polyimide film may have a roughness (Ra) of 10 nm to 15 nm as measured based on the ISO 1997 standard. Within the above range, there may be an effect of increasing the thermal conductivity when manufacturing a graphite sheet from a polyimide film, but it is not limited thereto.

In the polyimide film manufactured by the above-mentioned polyimide film manufacturing method, the sublimable inorganic filler can be uniformly dispersed in the polyimide film with an appropriate size and uniform particle size distribution, resulting in a high thermal conductivity. It is possible to produce graphite sheets with excellent quality.

According to another aspect, a method of manufacturing graphite sheets from the aforementioned polyimide films is provided. The method may include manufacturing a polyimide film by the method described above, and carbonizing and graphitizing the polyimide film to obtain a graphite sheet.

"Carbonization" is a process of thermally decomposing the polymer chains of a polyimide film to form an amorphous carbon body, an amorphous carbon body, and/or a pre-graphite sheet containing an amorphous carbon body. The film may be heated and held under reduced pressure or an inert gas atmosphere from room temperature to a maximum temperature in the range of 1,000°C to 1,500°C for 10 to 20 hours, It is not limited to this. Optionally, pressure may be applied to the polyimide film using a hot press or the like during carbonization to ensure high orientation of carbon, and the pressure at this time may be, for example, 5 kg/cm ² or more, or as another example, It may be 15 kg/cm ² or more, and as another example, it may be 25 kg/cm ² or more, but is not limited to this.

Graphitization is a process in which the carbon of an amorphous carbon body, an amorphous carbon body, and/or an amorphous carbon body is rearranged to form a graphite sheet. For example, a preliminary graphite sheet is selectively exposed to an inert gas atmosphere. The method may include, but is not limited to, raising and holding the temperature from room temperature to a maximum temperature in the range of 2,500° C. to 3,000° C. for 20 to 30 hours. Optionally, pressure may be applied to the preliminary graphite sheet using a hot press or the like during graphitization to obtain a high degree of orientation of carbon, and the pressure at this time may be, for example, 100 kg/cm ² or more, as another example. may be 200 kg/cm ² or more, and as another example, 300 kg/cm ² or more, but is not limited to this.

According to one embodiment, the graphite sheet may have a thickness of 20 μm to 40 μm (eg, 22 μm to 32 μm) and a thermal conductivity of 1,400 W/m·K or more. The graphite sheet according to an embodiment of the present invention is manufactured using a polyimide film in which the sublimable inorganic filler is uniformly dispersed with an appropriate size and uniform particle size distribution, so it has excellent thermal conductivity. can have a degree. For example, the thermal conductivity of a graphite sheet is 1,500 W/m・K or more, another example is 1,600 W/m・K or more, another example is 1,700 W/m・K or more, and yet another example is 1,600 W/m・K or more. For example, it may be 1,800 W/m·K or more, but is not limited to this.

Hereinafter, the present invention will be explained in more detail with reference to Examples. However, this is presented as a preferred example of the present invention, and should not be construed as limiting the present invention in any way.

Example 1
15 g of pyromellitic dianhydride as a dianhydride monomer, 15 g of 4,4'-oxydianiline as a diamine monomer, and 100 g of dimethylformamide as a solvent were mixed and reacted, and the viscosity was 300,000 cP. A polyamic acid solution was prepared.

The polyamic acid solution has a zeta potential controlled to +40 mV, and a sublimable inorganic filler solution containing 10 g of dibasic calcium phosphate (average particle size ( _D50 : 5 μm)) as a sublimable inorganic filler and 200 g of dimethylformamide as a solvent. After adding acetic anhydride as a dehydrating agent and β-picoline as an imidizing agent at a 5 molar ratio and a 1 molar ratio, respectively, to 1 mol of amic acid groups of the polyamic acid, the precursor composition was prepared. Manufactured. At this time, the amount of sublimable inorganic filler per 100 parts by weight of polyamic acid in the precursor composition was 0.14 parts by weight. Here, the zeta potential is measured using a zeta potential measurement device (Zeta-potential & Particle size Analyzer ELSZ-2000ZS, Photo OTSUKA ELECTRONICS) according to ISO 13099-2 (Col. loidal systems-Methods for zeta-potential determination-Part 2: Optical It was measured based on the following methods.

The precursor composition was cast to a thickness of 80 μm on a SUS plate (100SA, Sandvik) using a doctor blade, and dried at 100° C. for 5 minutes to prepare a gel film. After separating the gel film from the SUS plate, the gel film was heat-treated at 300° C. for 5 minutes to produce a polyimide film having a thickness of 60 μm.

Examples 2 to 8 and Comparative Examples 1 to 4
A polyimide film was manufactured using the same method as in Example 1, except that a sublimable inorganic filler solution having a zeta potential listed in Table 1 below was used.

Evaluation example 1
The roughness (Ra) (unit: nm) of the polyimide films produced in Examples and Comparative Examples was measured based on ISO 1997 using a surface roughness measuring device (SE600, Kosaka laboratory Ltd.), and the results are as follows: are shown in Table 1 below.

From Table 1, it can be seen that the roughness of the polyimide films of Examples 1 to 8 produced using the sublimable inorganic filler solution having a zeta potential of the present invention is lower than that of Comparative Examples 1 to 4. Based on this, it can be predicted that the sublimable inorganic filler is more uniformly dispersed in the polyimide films of Examples 1 to 8.

Evaluation example 2
The surfaces of the polyimide films produced in Examples 1 and 2 and Comparative Example 2 were etched using a plasma surface etching method to prepare specimens. Etching was performed using K1050X RF Plasma Etcher (EMITECH) equipment at 100 W for 30 minutes, and the gas used for etching was air. Then, using a scanning electron microscope (SEM), the surface of the specimen was photographed at 1,000x magnification at 10 non-overlapping positions, and the sublimable inorganic filler particles photographed at the 10 positions. All particle sizes were measured.

As a result of the measurement, in the case of Example 1, of all the sublimable inorganic fillers measured, inorganic fillers with a particle size of 2 μm or less accounted for 54%, and inorganic fillers with a particle size of 5 μm or more accounted for 8%.

In the case of Example 2, of all the sublimable inorganic fillers measured, inorganic fillers with a particle size of 2 μm or less accounted for 45%, and inorganic fillers with a particle size of 5 μm or more accounted for 16%.

In the case of Comparative Example 2, of all the sublimable inorganic fillers measured, inorganic fillers with a particle size of 2 μm or less accounted for 33%, and inorganic fillers with a particle size of 5 μm or more accounted for 52%.

Based on this, the example polyimide film produced using the sublimable inorganic filler solution having a zeta potential of the present invention has a more uniform sublimable inorganic filler distribution than the comparative example polyimide film which does not have this. I understand.

Example 9
The polyimide film produced in Example 1 was heated to 1,500° C. at a rate of 2.0° C./min using an electric furnace under argon gas, and then maintained at the temperature for 1 hour to carbonize. Thereafter, the temperature of the carbonized polyimide film was increased to 2,900°C at a rate of 2.5°C/min under argon gas, and the temperature was maintained at the same temperature for 1 hour to graphitize it to form a graphite sheet with a thickness of 30 μm. Manufactured.

Examples 10 to 16 and Comparative Examples 5 to 8
A graphite sheet was manufactured using the same method as in Example 9, except that the polyimide film listed in Table 2 below was used.

Evaluation example 3
The thermal diffusivity of the graphite sheets manufactured in Examples and Comparative Examples in the planar direction was measured using a laser flash method using a thermal diffusivity measuring device (LFA 467, Netsch), and the density was added to the thermal diffusivity measurement value. (weight/volume) and specific heat (specific heat measurement value using DSC) to calculate the thermal conductivity, and the results are shown in Table 2 below.

From Table 2 above, the graphite sheets of Examples 9 to 16 manufactured from polyimide films manufactured using the manufacturing method of the present invention had superior thermal conductivity compared to Comparative Examples 5 to 8, which did not. I understand.

Up to now, the present invention has been discussed focusing on Examples. Those skilled in the art to which the present invention pertains will understand that the present invention may be embodied in various forms without departing from the essential characteristics thereof. Accordingly, the disclosed embodiments are to be considered in an illustrative rather than a restrictive light. The scope of the invention is indicated in the claims rather than the foregoing description, and all differences within the scope of equivalents are to be construed as included in the invention.

INDUSTRIAL APPLICATION This invention has the effect of providing the manufacturing method of the polyimide film for graphite sheets with excellent thermal conductivity, and the manufacturing method of a graphite sheet.

Claims (9)

Prepare a polyamic acid solution,
A sublimable inorganic filler solution having a zeta potential of +30 mV to +40 mV or -40 mV to -30 mV is added to the polyamic acid solution to produce a precursor composition for a polyimide film, and a polyimide film is obtained from the precursor composition. including steps,
Method for producing polyimide film for graphite sheets. The polyamic acid solution is produced by reacting a diamine monomer and a dianhydride monomer in a solvent,
The diamine monomers include 4,4'-oxydianiline, 3,4'-oxydianiline, p-phenylene diamine, m-phenylene diamine, and 4,4'-oxydianiline. , 4'-methylene dianiline, 3,3'-methylene dianiline, or a combination thereof;
The dianhydride monomer includes pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and 2,3,3',4-biphenyltetracarboxylic dianhydride. comprising acid dianhydride, oxydiphthalic anhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, or combinations thereof; The method for producing a polyimide film for graphite sheets according to claim 1. The method for producing a polyimide film for a graphite sheet according to claim 1, wherein the sublimable inorganic filler in the sublimable inorganic filler solution has an average particle size (D ₅₀ ) of 2 μm to 10 μm. The method for producing a polyimide film for a graphite sheet according to claim 1, wherein the sublimable inorganic filler includes dibasic calcium phosphate, barium sulfate, calcium carbonate, or a combination thereof. The method for producing a polyimide film for a graphite sheet according to claim 1, wherein the sublimable inorganic filler is added in an amount of 0.1 part by weight to 0.3 part by weight based on 100 parts by weight of the polyamic acid. The precursor composition further includes a dehydrating agent and an imidizing agent,
2. Obtaining a polyimide film from the precursor composition comprises casting the precursor composition on a support and drying to produce a gel film, and heat treating the gel film. A method for producing polyimide film for graphite sheets. The method of manufacturing a polyimide film for a graphite sheet according to claim 1, wherein the polyimide film has a roughness (Ra) of 10 nm to 15 nm as measured based on the ISO 1997 standard. A method for producing a graphite sheet, comprising the steps of producing the polyimide film according to any one of claims 1 to 7, and carbonizing and graphitizing the polyimide film to obtain a graphite sheet. The method for producing a graphite sheet according to claim 8, wherein the graphite sheet has a thickness of 20 μm to 40 μm and a thermal conductivity of 1,400 W/m·K or more.