KR20220065395A - Method for preparing polyimide film for graphite sheet and method for preparing graphite sheet - Google Patents

Abstract

Disclosed is a method for manufacturing a polyimide film for a graphite sheet, including the steps of: allowing a diamine monomer to react with a dianhydride monomer in a solvent to prepare a polyamic acid solution, wherein the polyamic acid solution satisfies Formula 1 and has a weight average molecular weight of 100,000-170,000 g/mol; adding a catalyst composition to the polyamic acid solution to prepare a precursor composition for a polyimide film, wherein the precursor composition satisfies Formula 2; forming the precursor composition into a film, followed by drying, to obtain a gel film; orienting the gel film; and heat treating the oriented gel film to obtain a polyimide film. Also disclosed is a method for manufacturing a graphite sheet using the polyimide film obtained by the above method.

Description

Polyimide film manufacturing method for graphite sheet and graphite sheet manufacturing method

It relates to a method for manufacturing a polyimide film for a graphite sheet and a method for manufacturing a graphite sheet, and more particularly, to a method for manufacturing a polyimide film for a graphite sheet having excellent thermal conductivity and a method for manufacturing a graphite sheet.

Recently, electronic devices are becoming lighter, smaller, thinner, and highly integrated, and as a result, a lot of heat is generated in the electronic devices. Such heat may shorten the life of the product or cause malfunction or malfunction. Accordingly, thermal management of electronic devices is emerging as an important issue.

The graphite sheet has a higher thermal conductivity than a metal sheet such as copper or aluminum, and is attracting attention as a heat dissipation member for electronic devices. Such a graphite sheet may be manufactured by various methods, for example, it may be manufactured by carbonizing and graphitizing a polymer film. In particular, polyimide films are spotlighted as polymer films for graphite sheet production due to their excellent mechanical, thermal, dimensional stability, and chemical stability.

It is known that the physical properties of the graphite sheet prepared from the 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 a polyimide film capable of producing a graphite sheet having higher thermal conductivity.

It is an object of the present invention to provide a method for manufacturing a polyimide film for a graphite sheet and a method for manufacturing a graphite sheet having excellent thermal conductivity.

1. According to one aspect, a method for manufacturing a polyimide film for a graphite sheet is provided. The method is a step of preparing a polyamic acid solution by reacting a diamine monomer and a dianhydride monomer in a solvent, satisfying the following formula 1, and the weight average molecular weight of the polyamic acid is 100,000 g/mol to 170,000 g/mol; Preparing a precursor composition for a polyimide film by adding a catalyst composition to the polyamic acid solution, satisfying Equation 2 below; preparing a gel film by forming and drying the precursor composition; stretching the gel film; and heat-treating the stretched gel film to prepare a polyimide film:

<Equation 1>

In Equation 1, η ₀ is the viscosity (23° C., unit: cps) of the polyamic acid solution, % _(s) is the solid content of the polyamic acid solution, and diamine monomer with respect to the total weight of diamine monomer, dianhydride monomer and solvent and weight percentage (unit: weight %) of the dianhydride monomer, e is a natural constant,

<Equation 2>

In Equation 2, η ₁ is the initial viscosity of the precursor composition (23° C., unit: cps), t(η ₂ ) is the time taken from η ₁ to reach η ₂ (unit: seconds), η ₂ is the final viscosity (23°C, unit: cps) of the precursor composition.

2. In 1 above, in Equation 1, η ₀ may be 50,000cps to 300,000cps, and % _(s) may be 15% to 30% by weight.

3. In 1 or 2, in Equation 2, η ₁ may be 2,500 cps to 30,000 cps, and t(η ₂ ) may be 100 seconds to 400 seconds.

4. In any one of 1 to 3, the diamine monomer is 4,4'-oxydianiline (4,4'-oxydianiline: ODA), p-phenyldiamine (p-phenylene diamine: PPD), or their combinations, wherein the dianhydride monomer may include pyromellitic dianhydride (PMDA).

5. The catalyst composition according to any one of 1 to 4 above, wherein the catalyst composition may include an imidizing agent, a dehydrating agent, a sublimable inorganic filler, and a solvent.

6. In the above 5, the catalyst composition comprises 3% to 15% by weight of the imidizing agent based on the total weight of the catalyst composition; 30% to 70% by weight of the dehydrating agent; 0.01% to 0.5% by weight of the sublimable inorganic filler; and the remaining amount of the solvent.

7. In any one of 1 to 6, the catalyst composition may be added in an amount of 30 to 60 parts by weight per 100 parts by weight of the polyamic acid solution.

8. In any one of 1 to 7 above, the drying may be performed at a temperature of 30°C to 200°C for 15 seconds to 30 minutes.

9. In any one of 1 to 8, the gel film may be stretched at a ratio of 1.01 times to 1.5 times in MD (machine direction).

10. In any one of 1 to 9, the heat treatment may be performed at a temperature of 250° C. to 600° C. for 30 seconds to 40 minutes.

11. According to another aspect, a method for manufacturing a graphite sheet is provided. The method comprises the steps of preparing a polyimide film for a graphite sheet by any one of the manufacturing methods of 1 to 10; and carbonizing and graphitizing the polyimide film to obtain a graphite sheet.

12. In the above 11, the graphite sheet may have a thickness of 10 μm to 100 μm, and a thermal conductivity of 1,400 W/m·K or more.

The present invention has the effect of providing a method for manufacturing a polyimide film for a graphite sheet and a method for manufacturing a graphite sheet having excellent thermal conductivity.

In the present specification, the singular expression includes the plural expression unless the context clearly dictates otherwise.

When the positional relationship of two parts is described with ‘on’, ‘on’, ‘on’, ‘beside’, etc., between the two parts unless ‘directly’ or ‘directly’ is used. One or more other parts may be located in

In this specification, terms such as include or have means that the features or components described in the specification exist, and the possibility that one or more other features or components will be added is not excluded in advance.

In interpreting the components, it is construed as including an error range even if there is no separate explicit description.

In the present specification, in "a to b" representing a numerical range, "to" is defined as ≥a and ≤b.

In the present specification, the viscosity may be measured using a HAAKE Mars Rheometer at 23° C. and a shear rate of 1 s ⁻¹ .

The method for producing a polyimide film for a graphite sheet according to an aspect of the present invention is a step of preparing a polyamic acid solution by reacting a diamine monomer and a dianhydride monomer in a solvent, satisfying the following formula 1, and the weight average molecular weight of the polyamic acid is 100,000 g/mol to 170,000 g/mol; Preparing a precursor composition for a polyimide film by adding a catalyst composition to the polyamic acid solution, satisfying Equation 2 below; preparing a gel film by forming and drying the precursor composition; stretching the gel film; and heat-treating the stretched gel film to prepare a polyimide film:

<Equation 1>

In Equation 1, η ₀ is the viscosity (23° C., unit: cps) of the polyamic acid solution, % _(s) is the solid content of the polyamic acid solution, and diamine monomer with respect to the total weight of diamine monomer, dianhydride monomer and solvent and weight percentage (unit: weight %) of the dianhydride monomer, e is a natural constant,

<Equation 2>

In Equation 2, η ₁ is the initial viscosity of the precursor composition (23° C., unit: cps), t(η ₂ ) is the time taken from η ₁ to reach η ₂ (unit: seconds), η ₂ is the final viscosity (23°C, unit: cps) of the precursor composition.

As one of the methods for improving the thermal conductivity of the graphite sheet, there is a method of increasing the orientation of the polyimide film by stretching the gel film. The inventor of the present invention, in manufacturing the polyimide film, the weight average molecular weight of the polyamic acid is 100,000 g / mol to 170,000 g / mol, and when the above formulas 1 and 2 are satisfied, the formation of a gel film suitable for stretching is possible, and as a result, it was found that a polyimide film having excellent orientation can be prepared, and thus the present invention has been completed.

Hereinafter, each step will be described in more detail.

First, a polyamic acid solution may be prepared by reacting a diamine monomer and a dianhydride monomer in a solvent.

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 the aprotic polar solvent include amide solvents such as N,N'-dimethylformamide (DMF) and N,N'-dimethylacetamide (DMAc), and phenolic solvents such as p-chlorophenol and o-chlorophenol. solvent, N-methyl-pyrrolidone (NMP), gamma butyrolactone (GBL), Diglyme, and the like, and these may be used alone or in combination of two or more. In some cases, the solubility of polyamic acid may be controlled by using an auxiliary solvent such as toluene, tetrahydrofuran (THF), acetone, methyl ethyl ketone (MEK), methanol, ethanol, and water.

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, the diamine monomer may include 4,4'-oxydianiline (ODA), p-phenyldiamine (PPD), or a combination thereof, and in this case, the orientation of the polyimide film may be excellent.

As the dianhydride monomer, various dianhydride 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, the dianhydride monomer may include pyromellitic dianhydride (PMDA), and in this case, the polyimide film may have excellent orientation.

The diamine monomer and the dianhydride monomer are included in the solvent to form a substantially equimolar amount and react, where 'substantially equimolar' means that the dianhydride monomer is contained in an amount of 99.8 to 100.2 mol% based on the total number of moles of the diamine monomer. . Reaction of the diamine monomer and the dianhydride monomer in substantially equimolar amounts includes, for example,

(a) a method in which all of the diamine monomer (or dianhydride monomer) is added in a solvent, and the dianhydride monomer (or diamine monomer) is added and reacted in a substantially equimolar amount;

(b) some of the diamine monomer (or dianhydride monomer) is added in the solvent, and the dianhydride monomer (or diamine monomer) is added in a ratio of 95 to 105 mol% based on the diamine monomer (or dianhydride monomer), A method of reacting by adding a diamine monomer and/or a dianhydride monomer to a substantially equimolar amount;

(c) a part of the diamine monomer (or dianhydride monomer) and a part of the dianhydride monomer (or diamine monomer) in a solvent to form a first composition by adding any one in excess, and in a separate solvent the diamine monomer (or A part of the dianhydride monomer) and a part of the dianhydride monomer (or diamine monomer) are added so that any one is in excess to form a second composition, and the first composition and the second composition are mixed and reacted, wherein the first composition In the case where the diamine monomer (or dianhydride monomer) is in excess, in the second composition, there may be mentioned a method in which the dianhydride monomer (or diamine monomer) is used in excess. In (a) to (c), the diamine monomer and dianhydride monomer may refer to one or more (eg, one or two) diamine monomer and dianhydride monomer.

The weight average molecular weight of the polyamic acid is 100,000 g / mol to 170,000 g / mol (eg, 100,000 g / mol, 110,000 g / mol, 120,000 g / mol, 130,000 g / mol, 140,000 g / mol, 150,000 g / mol , 160,000 g/mol or 170,000 g/mol). In the above range, a gel film suitable for stretching may be formed, and it may be possible to manufacture a polyimide film having a high orientation. For example, the weight average molecular weight of the polyamic acid is 100,000 g / mol to 160,000 g / mol, for example 100,000 g / mol to 150,000 g / mol, for another example 120,000 g / mol to 150,000 g / mol or Another example may be 130,000 g/mol to 150,000 g/mol, but is not limited thereto.

The polyamic acid solution may satisfy Equation 1 below:

<Equation 1>

은 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39 또는 40, 다른 예를 들면 10 내지 39, 또 다른 예를 들면 10 내지 30, 또 다른 예를 들면 15 내지 25일 수 있으나, 이에 한정되는 것은 아니다.In Equation 1, η ₀ is the viscosity (23° C., unit: cps) of the polyamic acid solution, % _(s) is the solid content of the polyamic acid solution, and diamine monomer with respect to the total weight of diamine monomer, dianhydride monomer and solvent and a weight percentage (unit: weight %) of the dianhydride monomer, and e is a natural constant. In the above range, a gel film suitable for stretching may be formed, and it may be possible to manufacture a polyimide film having a high orientation. for example,

is 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34 , 35, 36, 37, 38, 39 or 40, another example of 10 to 39, another example of 10 to 30, another example may be 15 to 25, but is not limited thereto.

According to one embodiment, in Equation 1, η ₀ may be 50,000cps to 300,000cps (eg, 50,000cps, 100,000cps, 150,000cps, 200,000cps, 250,000cps, or 300,000cps). In the above range, a gel film suitable for stretching may be formed, and it may be possible to manufacture a polyimide film having a high orientation. For example, η ₀ may be 70,000cps to 300,000cps, for example, 70,000cps to 250,000cps, for another example, 100,000cps to 150,000cps, but is not limited thereto.

According to one embodiment, in Formula 1, % _(s) is 15% to 30% by weight (eg, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, 20% by weight) , 21% by weight, 22% by weight, 23% by weight, 24% by weight, 25% by weight, 26% by weight, 27% by weight, 28% by weight, 29% by weight or 30% by weight). In the above range, a gel film suitable for stretching may be formed, and it may be possible to manufacture a polyimide film having a high orientation. For example, % _(s) may be 17% to 25% by weight, for example, from 17% to 23% by weight, for example from 20% to 23% by weight, but is not limited thereto. .

Then, a precursor composition for a polyimide film may be prepared by adding the catalyst composition to the polyamic acid solution. Here, the 'catalyst composition' may refer to a composition including an imidizing agent that promotes the ring closure reaction of the polyamic acid and/or a dehydrating agent that promotes the ring closure reaction through the dehydration action of the polyamic acid.

As the imidizing agent, for example, an aliphatic tertiary amine, an aromatic tertiary amine, a heterocyclic tertiary amine, or the like may be used. Among them, a heterocyclic tertiary amine can 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 imidizing agent may be added in an amount of 0.05 mol to 3 mol (eg, 0.2 mol to 2 mol) per 1 mol of the amic acid group in the polyamic acid. However, the present invention is not limited thereto.

Examples of the dehydrating agent include aliphatic acid anhydride, aromatic acid anhydride, N,N'-dialkylcarbodiimide, lower aliphatic halide, halogenated lower aliphatic acid anhydride, arylphosphonic acid dihalide, thionyl halide, and the like. and these may be used alone or in combination of two or more. Among them, aliphatic acid anhydrides such as acetic anhydride, propionic anhydride and lactic acid anhydride can be used from the viewpoints of availability and cost. The dehydrating agent may be added in an amount of 0.5 mol to 5 mol (eg, 1 mol to 4 mol) based on 1 mol of the amic acid group in the polyamic acid. , but is not limited thereto.

According to one embodiment, the catalyst composition may further include a sublimable inorganic filler. Here, the 'sublimable inorganic filler' may mean an inorganic filler that is sublimated by heat during carbonization and/or graphitization processes in manufacturing the graphite sheet. When the polyimide film includes a sublimable inorganic filler, voids are formed in the graphite sheet by the gas generated through sublimation of the sublimable inorganic filler during the manufacture of the graphite sheet, thereby exhausting the sublimation gas generated during the manufacture of the graphite sheet It is possible to obtain a graphite sheet of good quality by being smoothly formed, as well as improve the flexibility of the graphite sheet to ultimately improve the handleability and formability of the graphite sheet. Examples of the sublimable inorganic filler include, but are not limited to, dicalcium phosphate, barium sulfate, calcium carbonate, and the like. The average particle diameter (D ₅₀ ) of the sublimable inorganic filler may be 0.05 μm to 5.0 μm (eg, 0.1 μm to 4.0 μm), and a good quality graphite sheet can be obtained in the above range, but is not limited thereto. The sublimable inorganic filler may be included in an amount of 0.01 parts by weight to 0.5 parts by weight (eg, 0.02 parts by weight to 0.2 parts by weight) based on 100 parts by weight of the polyamic acid, and a good quality graphite sheet can be obtained in the above range, It is not limited.

According to one embodiment, the catalyst composition may further include a solvent. For a description of the solvent that may be included in the catalyst composition, refer to the description of the solvent included in the polyamic acid solution.

According to one embodiment, the catalyst composition may include an imidizing agent, a dehydrating agent, a sublimable inorganic filler and a solvent.

According to one embodiment, the catalyst composition comprises 3% to 15% by weight of the imidizing agent, 30% to 70% by weight of the dehydrating agent, 0.01% to 0.5% by weight of the sublimability, based on the total weight of the catalyst composition. inorganic fillers, and the remainder of a solvent. In this case, a gel film suitable for stretching may be formed, and a polyimide film having a high orientation may be prepared. For example, the catalyst composition may comprise 5% to 10% by weight of the imidizing agent, 40% to 60% by weight of the dehydrating agent, 0.02% to 0.2% by weight of the sublimable inorganic filler, based on the total weight of the catalyst composition. , and a residual amount of a solvent, but is not limited thereto.

According to one embodiment, the catalyst composition may be added in an amount of 30 to 60 parts by weight per 100 parts by weight of the polyamic acid solution. In the above range, a gel film suitable for stretching may be formed, and it may be possible to manufacture a polyimide film having a high orientation. For example, the catalyst composition may be added in an amount of 35 parts by weight to 55 parts by weight, for example, 37 parts by weight to 52 parts by weight per 100 parts by weight of the polyamic acid solution, but is not limited thereto.

The precursor composition may satisfy the following formula 2:

<Equation 2>

이 25 미만인 경우에는 지나치게 느린 부분 이미드화로 인해 이후 겔 필름이 형성되지 않는 문제가 있을 수 있다. 한편,

이 75 초과인 경우에는 지나치게 빠른 부분 이미드화로 인해 이후 딱딱한 겔 필름이 얻어지고, 그 결과 겔 필름을 연신할 수 없게 되는 문제가 있을 수 있다. 따라서, 식 2를 만족해야만 연신에 적합한 겔 필름이 형성될 수 있고, 고배향성의 폴리이미드 필름의 제조가 가능할 수 있다. 예를 들어,

는 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74 또는 75, 다른 예를 들면 30 내지 75, 또 다른 예를 들면 30 내지 74일 수 있으나, 이에 한정되는 것은 아니다.In Equation 2, η ₁ is the initial viscosity of the precursor composition (23° C., unit: cps), t(η ₂ ) is the time taken from η ₁ to reach η ₂ (unit: seconds), η ₂ is the final viscosity (23°C, unit: cps) of the precursor composition. More specifically, η ₁ is the viscosity immediately after adding the catalyst composition to the polyamic acid solution, and η ₂ is the point at which the viscosity no longer increases when the viscosity is continuously measured after adding the catalyst composition to the polyamic acid solution is the viscosity, that is, the maximum viscosity. When the catalyst composition is added to the polyamic acid solution, partial imidization of the amic acid group proceeds,

If it is less than 25, there may be a problem in that a gel film is not formed thereafter due to excessively slow partial imidization. Meanwhile,

If the value exceeds 75, there may be a problem in that a hard gel film is subsequently obtained due to excessively rapid partial imidization, and as a result, the gel film cannot be stretched. Therefore, only when Equation 2 is satisfied, a gel film suitable for stretching may be formed, and a polyimide film having a high orientation may be manufactured. for example,

is 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 , 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74 Or 75, for another example, 30 to 75, another example may be 30 to 74, but is not limited thereto.

According to one embodiment, in Equation 2, η ₁ is 2,500cps to 30,000cps (eg, 2,500cps, 5,000cps, 7,500cps, 10,000cps, 12,500cps, 15,000cps, 17,500cps, 20,000cps, 22,500cps, 25,000 cps, 27,500 cps or 30,000 cps). In the above range, a gel film suitable for stretching may be formed, and it may be possible to manufacture a polyimide film having a high orientation. For example, η ₁ may be 5,000cps to 25,000cps, for example, 7,500cps to 15,000cps, but is not limited thereto.

According to one embodiment, in Equation 2, t(η ₂ ) may be 100 seconds to 400 seconds (eg, 100 seconds, 150 seconds, 200 seconds, 250 seconds, 300 seconds, 350 seconds, or 400 seconds). . In the above range, a gel film suitable for stretching may be formed, and it may be possible to manufacture a polyimide film having a high orientation. For example, t(η ₂ ) may be 100 seconds to 390 seconds, and for another example, t(η ₂ ) may be 100 seconds to 380 seconds, but is not limited thereto.

Then, the precursor composition may be formed into a film and dried to prepare a gel film.

Here, the 'gel film' is in the intermediate stage of curing from polyamic acid to polyimide, and may have self-supporting properties. The gel film of the present invention may have a weight average molecular weight of 100,000 g/mol to 170,000 g/mol of polyamic acid, and may have a state suitable for stretching by satisfying Formulas 1 and 2 above.

According to one embodiment, the precursor composition may be cast on a support and dried to prepare a gel film, and as the support, a glass plate, an aluminum foil, an endless stainless belt, a stainless drum, or the like may be used.

According to an embodiment, drying may be performed at a temperature of 30° C. to 200° C. (eg, 80° C. to 180° C.) for 15 seconds to 30 minutes (eg, 2 minutes to 10 minutes). In the above range, a gel film suitable for stretching may be formed, and a polyimide film having a high orientation may be manufactured, but is not limited thereto.

Then, the gel film can be stretched.

The stretching may be performed in at least one of a machine direction (MD) and a transverse direction (TD).

According to one embodiment, the stretch is 1.01 times to 1.5 times MD (eg, 1.01 times, 1.05 times, 1.1 times, 1.15 times, 1.2 times, 1.25 times, 1.3 times, 1.35 times, 1.4 times, 1.45 times or 1.5 times). In the above range, it may be possible to manufacture a polyimide film having a high orientation, and as a result, the thermal conductivity of the graphite sheet may be excellent. For example, the stretching may be performed at a ratio of 1.03 times to 1.5 times in MD, for example 1.05 times to 1.4 times, and for another example, 1.1 times to 1.4 times, but is not limited thereto.

Then, the stretched gel film may be heat-treated to prepare a polyimide film.

The solvent and the like remaining in the stretched gel film are removed by heat treatment of the stretched gel film, and most of the remaining amic acid groups are imidized to obtain a polyimide film.

According to an embodiment, the heat treatment is performed at a temperature of 250° C. to 600° C. (eg, 260° C. to 550° C., for example, 270° C. to 500° C.) for 30 seconds to 40 minutes (eg, 2 minutes to 15 minutes). Sufficient imidization may be achieved in the above range, but the present invention is not limited thereto.

The polyimide film prepared by the above-described manufacturing method has excellent orientation, and as a result, the graphite sheet prepared therefrom may have excellent thermal conductivity.

According to another aspect, there is provided a method for manufacturing a graphite sheet from the above-described polyimide film. The method comprises the steps of preparing a polyimide film according to 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 chain of a polyimide film to form a preliminary graphite sheet including an amorphous carbon body, an amorphous carbon body and/or an amorphous carbon body. For example, the polyimide film is heated under reduced pressure or in an inert gas atmosphere. It may be carried out by increasing the temperature from room temperature to a temperature in the range of 1,000° C. to 1,500° C., which is the highest temperature, over 0.3° C./min to 10° C./min, and maintaining the temperature for 10 minutes to 180 minutes, but is not limited thereto. Optionally, pressure may be applied to the polyimide film using a hot press or the like during carbonization for high carbon orientation, and the pressure at this time is, for example, 5 kg/cm ² or more, for example, 15 kg/cm ² or more. , Another example may be 25kg/cm ² or more, but is not limited thereto.

'Graphitization' is a process of rearranging carbon in an amorphous carbon body, an amorphous carbon body and/or an amorphous carbon body to form a graphite sheet, for example, a preliminary graphite sheet, optionally from room temperature to the highest temperature in an inert gas atmosphere Phosphorus may be carried out by raising the temperature over 0.5 °C/min to 20 °C/min to a temperature in the range of 2,500 °C to 3,000 °C, and holding for 10 minutes to 300 minutes, but is not limited thereto. Optionally, pressure may be applied to the preliminary graphite sheet using a hot press during graphitization for high orientation of carbon, and the pressure at this time is, for example, 100 kg/cm ² or more, for example, 200 kg/cm ² Above, another example may be 300kg/cm ² or more, but is not limited thereto.

According to one embodiment, the graphite sheet has a thickness of 10 μm to 100 μm (eg, 15 μm to 90 μm), and a thermal conductivity of 1,400 W/m·K or more (eg, 1,400 W/m·K) to 1,500 W/m·K). The graphite sheet according to an embodiment of the present invention may have excellent thermal conductivity because it is manufactured using a polyimide film with high orientation prepared from a gel film suitable for stretching.

Hereinafter, the present invention will be described in more detail by way of examples. However, this is presented as a preferred example of the present invention, and it cannot be construed as limiting the present invention in any sense.

Example

Examples 1 to 5 and Comparative Examples 1 to 4

341.5 g of dimethylformamide as a solvent was added to the reactor, and the temperature was adjusted to 20°C. 51.5 g of 4,4'-oxydianiline (ODA) was added thereto, followed by the addition of 55.5 g of pyromellitic dianhydride (PMDA). After raising the temperature to 40 ℃, pyromellitic dianhydride was added little by little to prepare a polyamic acid solution having the value of Equation 1 in Table 1 and the weight average molecular weight (Mw).

In the prepared polyamic acid solution, based on the total weight of the catalyst composition, 57.7 wt% of acetic anhydride as a dehydrating agent, 7.1 wt% of β-picoline as an imidizing agent, and dicalcium phosphate (average particle diameter (D ₅₀ ): 2.0 μm) A catalyst composition in which 0.1% by weight and the remaining amount of dimethylformamide were mixed was added. At this time, the amount of the catalyst composition added was adjusted so that the precursor composition for a polyimide film had the value of Equation 2 in Table 1.

The prepared precursor composition was cast on a SUS plate (100SA, Sandvik) to a thickness of 250 μm using a doctor blade to form a film, and dried at 130° C. for 4 minutes to prepare a gel film.

After separating the prepared gel film from the SUS plate, the gel film was stretched in MD at the draw ratio of Table 1.

The stretched gel film was heat-treated at 420° C. for 5 minutes to prepare a polyimide film having a thickness of 50 μm.

evaluation example

(1) Viscosity: Using a viscosity measuring device (Rheostress 600, Haake), the polyamic acid solution and the precursor composition according to time (unit: seconds) under the conditions of a shear rate of 1/s, a temperature of 23° C., and a 1 mm plate gap. Viscosity (unit: cps) was measured.

(2) Weight average molecular weight (Mw): The weight average molecular weight (unit: g/mol) of polyamic acid in terms of polystyrene was obtained using molecular weight measuring equipment (Sykam GPC SYSTEM, Razerchrom).

(3) Thermal conductivity (unit: W/m·K): After heating the polyimide films prepared in Examples and Comparative Examples to 1,200°C at a rate of 1°C/min under nitrogen gas using an electric furnace, the temperature It was kept for 2 hours to carbonize. Thereafter, the temperature was raised to 2,800° C. at a rate of 10° C./min under argon gas, and graphitized by maintaining at the temperature for 2 hours, thereby preparing a graphite sheet having a thickness of 25 μm.

The thus-prepared graphite sheet was cut into a circular shape with a diameter of 25.4 mm to prepare a specimen, and the thermal diffusivity of the specimen was measured by a laser flash method using a thermal diffusivity measuring device (LFA 467, Netsch Co.). Thermal conductivity was obtained by multiplying the measured value of the thermal diffusivity by density and specific heat (theoretical value: 0.85 kJ/kg·K).

η ₀ % _(s) Equation 1 Mw η ₁ t(η ₂ ) Equation 2 gel film
formed or not draw ratio thermal conductivity Example 1 289,340 25 10 118,611 9,580 175 55 ○ 1.1 times 1,428 Example 2 139,940 22 17 136,534 11,027 198 56 ○ 1.3 times 1,493 Example 3 52,500 18 39 153,878 12,474 267 47 ○ 1.5 times 1,409 Example 4 140,335 22 17 130,025 10,809 366 30 ○ 1.4 times 1,434 Example 5 142,960 22 17 133,579 7,556 102 74 ○ 1.1 times 1,438 Comparative Example 1 90,490 24 5 93,349 7,543 162 47 ○ Cannot be stretched 1,310 Comparative Example 2 144,339 18 88 183,058 14,808 276 54 ○ Cannot be stretched 1,227 Comparative Example 3 135,162 22 16 134,775 14,918 651 23 × - - Comparative Example 4 137,025 22 16 137,746 5,156 57 90 ○ Cannot be stretched 1,284

As can be seen from Table 1, in the case of Examples 1 to 5 satisfying the ranges of Formula 1, Mw, and Formula 2 of the present invention, a gel film suitable for stretching was formed, and the polyimide film having excellent orientation by stretching It was possible to manufacture, and as a result, the graphite sheet prepared therefrom had excellent thermal conductivity. On the other hand, in the case of Comparative Example 1, in which Formula 1 does not fall within the scope of the present invention, the strength of the gel film is weak and there is a problem of tearing during stretching, and in Comparative Example 2 where Formula 1 exceeds the scope of the present invention, the strength of the gel film There was a problem of not being able to stretch because it was strong. In addition, in the case of Comparative Example 3 in which Formula 2 does not fall within the scope of the present invention, there is a problem in that the gel film is not formed due to less drying, and in Comparative Example 4 in which Formula 2 exceeds the scope of the present invention, imidization is excessive There was a problem that the extension was not possible. As a result, the graphite sheets prepared from the polyimide films of Comparative Examples 1, 2, and 4 showed lower thermal conductivity than in Examples.

Up to now, the present invention has been mainly examined in the examples. Those of ordinary skill in the art to which the present invention pertains will understand that the present invention can be implemented in modified forms without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments are to be considered in an illustrative rather than a restrictive sense. The scope of the present invention is indicated in the claims rather than the foregoing description, and all differences within the scope equivalent thereto should be construed as being included in the present invention.

Claims (12)

A step of preparing a polyamic acid solution by reacting a diamine monomer and a dianhydride monomer in a solvent, wherein the following formula 1 is satisfied, and the weight average molecular weight of the polyamic acid is 100,000 g/mol to 170,000 g/mol;
Preparing a precursor composition for a polyimide film by adding a catalyst composition to the polyamic acid solution, satisfying Equation 2 below;
preparing a gel film by forming and drying the precursor composition;
stretching the gel film; and
Including the step of heat-treating the stretched gel film to prepare a polyimide film,
Method for producing polyimide film for graphite sheet:
<Equation 1>

In Equation 1, η ₀ is the viscosity (23° C., unit: cps) of the polyamic acid solution, % _(s) is the solid content of the polyamic acid solution, and diamine monomer with respect to the total weight of diamine monomer, dianhydride monomer and solvent and weight percentage (unit: weight %) of the dianhydride monomer, e is a natural constant,
<Equation 2>

In Equation 2, η ₁ is the initial viscosity of the precursor composition (23° C., unit: cps), t(η ₂ ) is the time taken from η ₁ to reach η ₂ (unit: seconds), η ₂ is the final viscosity (23°C, unit: cps) of the precursor composition.
The method of claim 1,
In Formula 1, η ₀ is 50,000cps to 300,000cps, % _(s) is 15% to 30% by weight, a method for producing a polyimide film for a graphite sheet.
According to claim 1,
In Formula 2, η ₁ is 2,500 cps to 30,000 cps, and t (η ₂ ) is 100 seconds to 400 seconds, a method for producing a polyimide film for a graphite sheet.
According to claim 1,
The diamine monomer comprises 4,4'-oxydianiline (4,4'-oxydianiline), p-phenyldiamine (p-phenylene diamine), or a combination thereof,
The dianhydride monomer is pyromellitic dianhydride (pyromellitic dianhydride), the method for producing a polyimide film for a graphite sheet.
According to claim 1,
The catalyst composition comprises an imidizing agent, a dehydrating agent, a sublimable inorganic filler and a solvent, a method for producing a polyimide film for a graphite sheet.
6. The method of claim 5,
The catalyst composition is
3% to 15% by weight of the imidizing agent;
30% to 70% by weight of the dehydrating agent;
0.01% to 0.5% by weight of the sublimable inorganic filler; and
A method for producing a polyimide film for a graphite sheet, comprising the remaining amount of the solvent.
According to claim 1,
The catalyst composition is added in an amount of 30 to 60 parts by weight per 100 parts by weight of the polyamic acid solution, a method for producing a polyimide film for a graphite sheet.
According to claim 1,
The drying is performed for 15 seconds to 30 minutes at a temperature of 30 ℃ to 200 ℃, a method for producing a polyimide film for a graphite sheet.
According to claim 1,
The method for producing a polyimide film for a graphite sheet, wherein the gel film is stretched at a ratio of 1.01 to 1.5 times in MD (machine direction).
The method of claim 1,
The heat treatment is carried out for 30 seconds to 40 minutes at a temperature of 250 ℃ to 600 ℃, a method for producing a polyimide film for a graphite sheet.
The method of any one of claims 1 to 10, comprising: preparing a polyimide film for a graphite sheet; and
A method for producing a graphite sheet, comprising the step of carbonizing and graphitizing the polyimide film to obtain a graphite sheet.
12. The method of claim 11,
The graphite sheet has a thickness of 10 μm to 100 μm, and a thermal conductivity of 1,400 W/m · K or more, a method of manufacturing a graphite sheet.