KR102286059B1 - Graphite sheet and manufacturing method for the same - Google Patents

Abstract

The present invention relates to a polyimide film for a graphite sheet formed from a composition for forming a polyimide film comprising a polyamic acid and an imidization catalyst, and a method for manufacturing the polyimide film for a graphite sheet. Through this, the present invention provides a polyimide film having low brittleness when applied to a graphite sheet and having excellent surface quality and securing high thickness at the same time, a manufacturing method thereof, and a graphite sheet manufacturing method using the same.

Description

High-thickness graphite sheet and manufacturing method thereof

The present invention relates to a polyimide film for a high-thickness graphite sheet, a method for manufacturing the polyimide film for a graphite sheet, and a method for manufacturing a graphite sheet using the same.

Graphite is a material with very good thermal conductivity and has been in the spotlight as a means of heat dissipation. In particular, artificial graphite manufactured in the form of a thin sheet has excellent thermal conductivity of about 2 to about 7 times compared to copper or aluminum, and thus is preferably used as a heat dissipation means applied to electronic devices.

Recent electronic devices have a tendency to increase in the amount of heat generated per unit volume as their structures become lighter, smaller, thinner and more highly integrated. In this case, the performance of the electronic device may be directly adversely affected, such as a decrease in the operation speed of the semiconductor due to a thermal load and a shortened lifespan due to deterioration of the battery.

As one of the methods for solving this problem, a method of applying a graphite sheet having a relatively thick thickness to an electronic device has been proposed. Since the high-thickness graphite sheet is advantageous in terms of heat capacity compared to a conventional thin graphite sheet, for example, a graphite sheet having a thickness of 30 μm or less, heat can be efficiently dissipated even if the amount of heat generated by electronic devices increases. There is an advantage.

In general, the artificial graphite sheet is manufactured by carbonizing and graphitizing a polyimide film, which is a precursor. In the manufacture of the high-thickness graphite sheet, a high-thickness polyimide film, for example, a polyimide film having a thickness of 100 µm or more, may be used according to a desired thickness level.

However, even when a graphite sheet is manufactured using a high-thickness polyimide film, it is difficult to obtain a high-quality graphite sheet having a smooth surface and an internal graphite structure not damaged during the heat treatment process, so there is a problem of low yield.

This is because, assuming that carbonization and graphitization proceed almost simultaneously in the surface layer and the inside of the polyimide film, in the case of a high-thickness polyimide film, the amount of sublimation gas generated from the inside is large, and the graphite structure formed on the surface layer or during the formation is damaged. It is presumed to be due to the increased probability of being destroyed. In addition, the pressure is greatly increased by a relatively large amount of sublimation gas not only on the surface, but also on the center of the film and the inner side adjacent thereto, and the graphite structure formed or formed is destroyed as one cause.

Therefore, there is a high need for a technology capable of manufacturing a high-quality graphite sheet with an intact surface quality and a graphite structure while having a high thickness.

One object of the present invention is to provide a polyimide film capable of securing a high thickness while having low brittleness and excellent surface quality when applied to a graphite sheet, and a method for manufacturing the same.

Another object of the present invention is to provide a method for manufacturing a graphite sheet that is excellent in surface quality and thermal conductivity, and can secure high thickness while having low brittleness.

All of the above and other objects of the present invention can be achieved by the present invention described below.

One embodiment of the present invention is polyamic acid; and an imidization catalyst; A polyimide film for a graphite sheet formed from a composition for forming a polyimide film comprising it's about

<Equation 1>

First surface damage rate (%) = { ( A ₁ / A ₀ ) × 100 }

In Equation 1, A ₀ is a polyimide film specimen having a size of 200 mm × 25 mm after heat treatment at 15° C. to 1,200° C. at a temperature increase rate of 1° C./min to 5° C./min to carbonize, and then 1.5° C./min. Primary graphitization by heat treatment from 1,200 °C to 2,200 °C at a temperature increase rate of 5 °C/min to 2,200 °C, and secondary graphitization by heat treatment from 2,200 °C to 2,500 °C at a temperature increase rate of 0.4 °C/min to 1.3 °C/min, and 8.5 ℃ / min to 20 ℃ / a heating rate of min from 2,500 ℃ by heating up to 2,800 ℃ area was measured by taking pictures in ten magnification the graphite sheet specimens obtained graphitized 3rd (mm ^2), a ₁ is the ^{It is the area of the damaged area (mm 2} ) measured by taking a picture at a magnification of 10 for the graphite sheet specimen.

Another embodiment of the present invention is polyamic acid; and an imidization catalyst; After gelling a composition for forming a polyimide film comprising A method for producing a polyimide film for a graphite sheet, comprising filming to a thickness, wherein the polyimide film has a first surface damage rate of 0% or 0.001% to 0.004% of the polyimide film represented by Formula 1 above It relates to a method for producing a mid film.

Another embodiment of the present invention comprises the steps of preparing a carbonized sheet by heat-treating the above-described polyimide film from 15 °C to 1,200 °C; and graphitizing the carbonized sheet while changing the temperature increase rate step by step from 1,200° C. to 2,800° C. to prepare a graphite sheet having a thickness of 50 μm to 100 μm; Including, wherein the graphite sheet has a second surface damage rate of 0% or 0.001% to 0.004%, which is represented by the following Equation 2:

<Equation 2>

Second surface damage rate (%) = { ( B ₁ / B ₀ ) × 100 }

In Equation 2, B ₀ ^{is the area (mm 2} ) measured by photographing the graphite sheet specimen at 10 magnification, and B ₁ is the area of the damaged area measured by photographing the graphite sheet specimen at 10 magnification (mm). ² ) is.

The manufacturing of the carbonized sheet may include thermally decomposing the polyimide film while raising the temperature at a rate of 1° C./min to 5° C./min.

The graphitization is the primary graphitization of the carbonized sheet while raising the temperature from 1,200 ° C to 2,200 ° C, then secondary graphitization while raising the temperature from 2,200 ° C to 2,500 ° C, and then tertiary graphitization from 2,500 ° C to 2,800 ° C it could be

The temperature increase rate of the primary graphitization is 1.5° C./min to 5° C./min, the temperature increase rate of the secondary graphitization is 0.4° C./min to 1.3° C./min, and the temperature increase rate of the tertiary graphitization is 8.5 It may be ℃/min to 20℃/min.

In the above embodiments, the molar ratio of the amic acid group of the polyamic acid to the imidization catalyst in the composition for forming a polyimide film may be 1:0.15 to 1:0.20.

In the above embodiments, the composition for forming a polyimide film includes 100 parts by weight of polyamic acid; and 17 parts by weight to 36 parts by weight of the imidization catalyst.

In the above embodiments, the composition for forming a polyimide film further comprises 1,500 ppm to 2,500 ppm of an inorganic filler based on 100 parts by weight of the polyamic acid, wherein the inorganic filler is calcium carbonate, dibasic calcium phosphate, hydrogen phosphate It may include one or more of calcium, barium sulfate, silica, titanium oxide, alumina, silicon nitride, and boron nitride.

The present invention relates to a polyimide film with low brittleness when applied to a graphite sheet and having excellent surface quality and securing high thickness at the same time, a manufacturing method thereof, and excellent surface quality and thermal conductivity using the same, low brittleness and high thickness It provides a graphite sheet manufacturing method that can secure the degree.

1 shows the surface quality evaluation results of Example 1 of the present invention.
2 shows the surface quality evaluation results of Comparative Example 7 of the present invention.
3 shows the surface quality evaluation results of Comparative Example 5 of the present invention.
4 exemplarily shows a method of measuring an area when measuring a first surface damage rate of the present invention.

polyimide film

One embodiment of the present invention relates to a polyimide film for a graphite sheet. The polyimide film for the graphite sheet of the present invention is polyamic acid; and an imidization catalyst; It is formed from a composition for forming a polyimide film comprising a, and is a gelled and imidized product of the composition for forming a polyimide film.

The polyimide film for a graphite sheet of the present invention has a thickness of 100 μm to 200 μm, which is thicker than the conventional one, and provides a graphite sheet having a thickness of 50 μm to 100 μm even after carbonization and graphitization.

In addition, the polyimide film for a graphite sheet of the present invention has a thickness of 50 μm to 100 μm when applied as a graphite sheet of high thickness, and at the same time the first surface damage rate represented by the following formula 1 is 0% or 0.001% to 0.004% It achieves excellent surface quality.

<Equation 1>

First surface damage rate (%) = { ( A ₁ / A ₀ ) × 100 }

In Equation 1, A ₀ is a polyimide film specimen having a size of 200 mm × 25 mm after heat treatment at 15° C. to 1,200° C. at a temperature increase rate of 1° C./min to 5° C./min to carbonize, and then 1.5° C./min. Primary graphitization by heat treatment from 1,200 °C to 2,200 °C at a temperature increase rate of 5 °C/min to 2,200 °C, and secondary graphitization by heat treatment from 2,200 °C to 2,500 °C at a temperature increase rate of 0.4 °C/min to 1.3 °C/min, and 8.5 ℃ / min to 20 ℃ / a heating rate of min from 2,500 ℃ by heating up to 2,800 ℃ area was measured by taking pictures in ten magnification the graphite sheet specimens obtained graphitized 3rd (mm ^2), a ₁ is the ^{It is the area of the damaged area (mm 2} ) measured by taking a picture at a magnification of 10 for the graphite sheet specimen.

Specifically, the first surface damage rate is 200 mm × 25 mm in size, and a polyimide specimen having any one of 50 μm to 100 μm in thickness from 15° C. at a temperature increase rate of 1° C./min to 5° C./min. After carbonization by heat treatment to 1,200° C., primary graphitization is performed by heat treatment from 1,200° C. to 2,200° C. at a temperature increase rate of any one of 1.5° C./min to 5° C./min, and any one of 0.4° C./min to 1.3° C./min. Secondary graphitization by heat treatment from 2,200° C. to 2,500° C. at one temperature increase rate, and tertiary graphitization by heat treatment from 2,500° C. to 2,800° C. at any one temperature increase rate of 8.5° C./min to 20° C./min. When prepared as a specimen, it means a surface damage rate occurring in the graphite sheet.

More specifically, the first surface damage rate is a size of 200 mm × 25 mm, a polyimide specimen having a thickness of 125 μm is heat-treated from 15° C. to 1,200° C. at a temperature increase rate of 1° C./min. Primary graphitization by heat treatment from 1,200 °C to 2,200 °C at a temperature increase rate of °C/min, secondary graphitization by heat treatment from 2,200 °C to 2,500 °C at a temperature increase rate of 0.4 °C/min, and a temperature increase rate of 8.5 °C/min When the graphite sheet specimen is prepared by tertiary graphitization by heat treatment from 2,500° C. to 2,800° C. with a furnace, it refers to the surface damage rate occurring in the graphite sheet.

In the first surface damage rate, A ₀ ^{is the area in mm 2} measured after photographing the graphite sheet specimen at 10 magnification using a digital camera, and A ₁ is the graphite sheet specimen using a digital camera. It is the area of the damaged area ^{in mm 2} measured after taking a picture at 10 magnification.

At this time, each area is measured by applying a filter with a grid drawn at intervals of 1 mm horizontally and 1 mm vertically to a digital image photograph taken at 10 magnification, and then visually confirming the number of ^{squares (mm 2 ) included in the area.} It can be performed in a way that counts and measures.

4 illustrates a method of measuring an area when measuring the first surface damage rate expressed by Equation 1 above. 4, when measuring the first surface damage rate represented by Equation 1, prepare a digital image photograph taken at 10 magnification for the graphite sheet prepared as in (a), 1 mm horizontal and 1 mm vertical Apply a filter with a grid drawn at intervals of . At this time, the area of one cell formed by the grid is 1 mm ² . In the first surface damage rate, A ₀ is measured by counting the case where the graphite sheet occupies 50% or more of the area of one cell formed by the lattice as in (b). _{A 0} measured in (b) of FIG. 4 is a portion marked in blue and there are a total of 200, so it may be measured as ^{200 mm 2 .} In the first surface damage rate, A ₁ is measured by counting the case where the damage visible to the naked eye occupies 50% or more of the area occupied by the graphite sheet in the area of one cell formed by the grid as in (c). _{A 1} measured in (c) of FIG. 4 is a portion indicated in yellow and there are 159 in total, so it may be measured as ^{159 mm 2 .} If the A ₀ value and A ₁ in this example are substituted into the surface damage rate of Equation 1, the damage rate in the graphite specimen of 20 mm × 10 mm size in FIG. 4 is 79.5%.

Unlike the conventional polyimide film, which has a high surface damage rate when applied as a high-thickness graphite sheet in the range of 50 μm to 100 μm, making it difficult to achieve both thickness and surface quality, the polyimide film of the present invention is brittle when applied to a graphite sheet. It is low, excellent in surface quality, and at the same time high thickness can be secured.

The composition for forming a polyimide film includes the following polyamic acid and an imidization catalyst.

(polyamic acid)

In the composition for forming a polyimide film, polyamic acid serves as a precursor to be converted into polyimide by an imidization catalyst. The polyamic acid is not particularly limited as long as it is obtained by polymerizing a dianhydride monomer and a diamine-based monomer.

For example, the dianhydride monomer that can be used as a raw material of the polyamic acid is pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3',4, 4'-biphenyltetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 3,4,9,10-perylene tetra Carboxylic dianhydride, bis (3,4-dicarboxyphenyl) propane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4 -dicarboxyphenyl) ethane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, bis (3,4-dicarboxyphenyl) ethane dianhydride, oxydiphthalic anhydride, bis (3) ,4-dicarboxyphenyl) sulfone dianhydride, p-phenylenebis(trimellitic monoester acid anhydride), ethylenebis(trimellitic monoester acid anhydride), bisphenol Abis(trimellitic) monoester acid anhydride) and derivatives thereof. When the dianhydride monomer of the above example is used, it is possible to obtain a polyamic acid having excellent imidization efficiency and improved uniformity. In addition, the dianhydride monomer of the above example may be used alone or in mixture of two or more.

For example, the diamine that can be used as a raw material of the polyamic acid is 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane, benzidine, 3,3'-dichlorobenzidine, 4 , 4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether (4,4'-ox Cydianiline), 3,3'-diaminodiphenyl ether (3,3'-oxydianiline), 3,4'-diaminodiphenyl ether (3,4'-oxydianiline), 1,5- Diaminonaphthalene, 4,4'-di

Aminodiphenyl diethyl silane, 4,4'-diaminodiphenyl silane, 4,4'-diaminodiphenyl ethylphosphine oxide, 4,4'-diaminodiphenyl N-methylamine, 4,4' - may be at least one of diaminodiphenyl N-phenyl amine, 1,4-diaminobenzene (p-phenylenediamine), 1,3-diaminobenzene, 1,2-diaminobenzene, and derivatives thereof . When the diamine monomer of the above example is used, it is possible to obtain a polyamic acid having excellent imidization efficiency and improved uniformity. In addition, the monomers of the above examples may be used alone or in mixture of two or more.

For example, a dianhydride monomer and a diamine monomer that can be used as a raw material of the polyamic acid may be used for polymerization of the polyamic acid in a molar ratio of 1:0.9 to 1:1.1. Within the above range, it is possible to obtain a polyamic acid having excellent imidization efficiency and improved uniformity.

The weight average molecular weight of the polyamic acid is not particularly limited, but 150,000 g/mole or more to 1,000,000 g/mole or less, specifically 170,000 g/mole or more to 700,000 g/mole or less, more specifically 190,000 g/mole or more to 500,000 g It can be less than /mole. Within the above range, the polyamic acid may further improve the heat resistance and mechanical properties of the polyimide film of the present invention.

The viscosity of the polyamic acid is not particularly limited, but may be 90,000 cP or more to 500,000 cP or less, specifically 150,000 cP or more to 400,000 cP, and more specifically 180,000 cP or more to 300,000 cP. Within the above range, the polyamic acid may further improve the heat resistance and mechanical properties of the polyimide film of the present invention.

The polyamic acid may be dissolved in an organic solvent and used as a polyamic acid solution. In this case, the polyamic acid solution may further improve processability and workability during the manufacture of the polyimide film.

The organic solvent is not particularly limited as long as it is a solvent in which the polyamic acid can be dissolved, and specifically, it may be an aprotic polar solvent.

For example, the aprotic polar solvent includes an amide solvent such as N,N'-dimethylformamide (DMF) and N,N'-dimethylacetamide (DMAc), p-chlorophenol, and o-chlorophenol. phenolic solvents such as N-methyl-pyrrolidone (NMP), gamma butyrolactone (GBL) and Diglyme.

The organic solvent may further adjust the solubility of the polyamic acid by using an auxiliary solvent if necessary. The auxiliary solvent may be, for example, toluene, tetrahydrofuran, acetone, methyl ethyl ketone, methanol, ethanol, water, or the like.

When the polyamic acid is dissolved in an organic solvent and used as a polyamic acid solution, the polyamic acid solution contains the polyamic acid solid content in an amount of 15 wt% to 20 wt%, and the organic solvent is 80 wt% to 85 wt% may include Within the above range, it is advantageous to control the weight average molecular weight and viscosity of the entire polyamic acid solution, and may be more advantageous for the film forming process.

(Imidization catalyst)

The imidization catalyst in the composition for forming a polyimide film serves to promote conversion of polyamic acid to polyimide.

The imidization catalyst may be an imine-based component such as an aliphatic tertiary amine, an aromatic tertiary amine, and a heterocyclic tertiary amine. Among these, a heterocyclic tertiary amine may be preferable from the viewpoint of reactivity as a catalyst. Non-limiting examples of heterocyclic tertiary amines include quinoline, isoquinoline, β-picoline (BP), pyridine, and the like, and these may be used alone or in combination of two or more.

In one embodiment, the content of the imidization catalyst in the precursor composition for a polyimide film is 0.15 mol to 0.2 mol, for example, 0.15 mol, 0.16 mol, 0.17 mol, based on 1 mol of the amic acid functional group of the aforementioned polyamic acid; 0.18 moles, 0.19 moles, 0.20 moles. Within the above range, the imidization catalyst can further improve crystallinity while arranging the matrix structure of the polyimide film of the present invention more regularly than before.

In another embodiment, the content of the imidization catalyst in the precursor composition for the polyimide film may be 17 parts by weight to 36 parts by weight based on 100 parts by weight of the amic acid of the polyamic acid. Within the above range, the imidization catalyst can further improve crystallinity while arranging the matrix structure of the polyimide film of the present invention more regularly than before.

(Inorganic filler)

The composition for forming a polyimide film may further include an inorganic filler in addition to the above-described components. Among the composition for forming a polyimide film, the inorganic filler may be present in a dispersed state in a matrix in the polyimide film and sublimate upon carbonization and/or graphitization to induce a predetermined foaming phenomenon. In this case, the polyimide film may form a polyimide gap with high regularity due to a structure in which the inorganic filler is uniformly dispersed in the polyimide matrix. Predetermined pores formed by such foaming can improve the bending resistance of the graphite sheet, and when carbonization and/or graphitization, the inorganic filler is sublimated and the polyimide is converted into graphite, thereby providing excellent regularity and alignment of the graphite sheet. can be manufactured. In addition, as the inorganic filler is sublimated, it can also serve as a passage for gas release by itself, thereby preventing surface defects and damage due to foaming.

The inorganic filler is not particularly limited as long as it has sublimability at a temperature of 1,000° C. or higher, but specifically, one of calcium carbonate, dibasic calcium phosphate, calcium hydrogen phosphate, barium sulfate, silica, titanium oxide, alumina, silicon nitride, and boron nitride. It may include more than one species. When the inorganic filler of the above example is used, the polyimide film can obtain a high-thickness graphite sheet with further improved bending resistance and structural uniformity. In addition, the inorganic filler of the above example may be used alone or in mixture of two or more.

The content of the inorganic filler in the precursor composition for the polyimide film may be 1,500 ppm to 2,500 ppm, specifically 1,250 ppm to 2,250 ppm, and more specifically 1,500 ppm to 2,000 ppm, based on 100 parts by weight of the polyamic acid. Within the above range, when the polyimide film is carbonized and/or graphitized, the sublimation gas generated inside the film is smoothly discharged to the outside of the film, further improving the surface quality, and converting the polyimide structure to the artificial graphite structure efficiency can be further improved.

The average particle diameter of the inorganic filler is not particularly limited, but may be 1.5 μm to 4.5 μm. Within the above range, the inorganic filler can further reduce the formation of bright spots due to excessive foaming while preventing the surface roughness of the polyimide film from being excessively lowered, thereby further improving the surface quality.

(additive)

The composition for forming a polyimide film may further include an additive including a dehydrating agent in addition to the above-described components.

The dehydrating agent promotes a ring closure reaction through a dehydration action on polyamic acid, and specifically, aliphatic acid anhydride, aromatic acid anhydride, N,N'-dialkylcarbodiimide, halogenated lower aliphatic, halogenated lower fatty acid anhydride, arylphos phonic acid dihalide, thionyl halide, or a mixture of two or more thereof.

Among the above examples, when an aliphatic acid anhydride such as acetic anhydride, propionic anhydride, and lactic acid anhydride, or a mixture of two or more thereof is used, the effect of easiness of raw material acquisition and cost reduction can be realized.

The amount of the dehydrating agent added in the composition for forming a polyimide film may be 0.5 to 5 moles based on 1 mole of the amic acid group in the polyamic acid. Within the above range, the imidization efficiency of the composition for forming a polyimide film by a dehydration action may be further improved.

Another embodiment of the present invention is polyamic acid; and an imidization catalyst; After gelling a composition for forming a polyimide film comprising It relates to a method for producing a polyimide film for a graphite sheet, comprising filming to a thickness. Through this, the present invention provides the effect of more economically and efficiently manufacturing a polyimide film capable of securing a high thickness while having low brittleness when applied to a graphite sheet.

In addition, the polyimide film prepared by the method of manufacturing the polyimide film for the graphite sheet has a surface damage rate of 0% or 0.001% to 0.004% represented by the above-mentioned Formula 1. The description of Equation 1 is the same as described above.

In addition, the composition for forming the polyimide film and each component included therein, specific examples, and descriptions of the content are the same as described above.

Specifically, the molar ratio of the amic acid group of the polyamic acid to the imidization catalyst in the composition for forming a polyimide film may be 1:0.15 to 1:0.20.

Specifically, the composition for forming a polyimide film includes 100 parts by weight of polyamic acid; and 17 parts by weight to 36 parts by weight of the imidization catalyst.

Specifically, the composition for forming a polyimide film further comprises 1,500 ppm to 2,500 ppm of an inorganic filler based on 100 parts by weight of polyamic acid, and the inorganic filler is calcium carbonate, dibasic calcium phosphate, calcium hydrogen phosphate, sulfuric acid. It may include one or more of barium, silica, titanium oxide, alumina, silicon nitride, and boron nitride.

In the method for producing a polyimide film of the present invention, a step of preparing a polyamic acid may be additionally performed prior to gelling the composition for forming a polyimide film. The step of preparing the polyamic acid is not particularly limited, and an appropriate method may be employed among methods such as emulsion polymerization, solution polymerization, bulk polymerization, and suspension polymerization.

In the method for producing the polyimide film, when the gelation temperature is less than 110° C., it is difficult to film the composition for forming a polyimide film into a polyimide film. On the other hand, when the gelation temperature is higher than 200° C., there is a problem in that when the polyimide film obtained due to excessive gelation is applied as a high-thickness graphite sheet, brittleness occurs.

Specifically, in the gelation process, the composition for forming a polyimide film may be prepared as a solution, applied to a support, and dried to prepare a sheet-shaped gel. The support may be a glass plate, an aluminum foil, an endless stainless belt, or a stainless drum, but is not limited thereto. The coating method is not particularly limited, and may be, for example, a casting method. In this case, the sheet-shaped gel may be dried and gelled for 10 to 20 minutes in the range of the gelation temperature to prepare a sheet-shaped gel having self-supporting properties.

The sheet-shaped gel produced and gelled in the sheet shape is then peeled from the support and then subjected to primary imidization at 200° C. to 400° C. and secondary imidization at 300° C. to 500° C. to form a film. In the case of performing primary and secondary imidization as described above, amic acid remaining unreacted may be additionally imidized, and the quality of the polyimide film may be more homogeneously improved. In addition, within the above temperature range, the conversion efficiency of polyamic acid to polyimide may be further improved.

The polyimide film filmed as described above has a thickness of 100 μm to 200 μm. When the thickness of the polyimide film is less than 100 μm, it is difficult to apply it as a graphite sheet having a high thickness. On the other hand, when the thickness of the polyimide film exceeds 200 μm, brittleness becomes excessively high.

graphite sheet

Another embodiment of the present invention relates to a method for manufacturing a high-thickness graphite sheet having a second surface damage rate of 0% or 0.001% to 0.004% represented by the following formula (2).

The high-thickness graphite sheet manufacturing method comprises the steps of: heat-treating a polyimide film from 15° C. to 1,200° C. to prepare a carbonized sheet; and graphitizing the carbonized sheet while changing the temperature increase rate step by step from 1,200° C. to 2,800° C. to prepare a graphite sheet having a thickness of 50 μm to 100 μm; includes

<Equation 2>

Second surface damage rate (%) = { ( B ₁ / B ₀ ) × 100 }

In Equation 2, B ₀ ^{is the area (mm 2} ) measured by photographing the graphite sheet specimen at 10 magnification, and B ₁ is the area of the damaged area measured by photographing the graphite sheet specimen at 10 magnification (mm). ² ) is.

In this case, the specific method of measuring the second surface damage rate (%) is the same as the measuring method of the first surface damage rate expressed by Equation 1 above.

The polyimide film is the above-mentioned polyimide film, polyamic acid; and an imidization catalyst; It is formed from a composition for forming a polyimide film containing may be

In the method for manufacturing the high-thickness graphite sheet of the present invention, the polyimide film is the same as the above-described polyimide film of the present invention, and since it is manufactured by the above-described polyimide film of the present invention, a description thereof will be omitted.

(carbonization step)

In the method for manufacturing a high-thickness graphite sheet of the present invention, the step of preparing the carbonized sheet is performed by applying the above-described polyimide film of the present invention from 15° C. to 1,200° C., specifically from 20° C. to 1,200° C., more specifically 50° C. It is carbonized by heat treatment at an elevated temperature from 1200°C. Within the above temperature range, the polymer chain of the polyimide film is sufficiently thermally decomposed, thereby preparing a carbonized sheet in which an amorphous carbon body is formed, which can be used for graphitization for the production of a graphite sheet.

Specifically, in the carbonization method, the polyimide film is put into a high-temperature furnace facility such as an electric furnace, and then pyrolyzed while heating the polyimide film from 15°C to the highest temperature of 1,200°C in a nitrogen/argon atmosphere for about 12 to 14 hours. , converting the polyimide film into a carbonized sheet.

In the step of preparing the carbonized sheet, the rate of temperature increase during carbonization may be 1° C./min to 5° C./min. Within the temperature increase rate range, the polymer chain of the polyimide film is sufficiently thermally decomposed, thereby preparing a carbonized sheet in which an amorphous carbon body is formed, which can be used for graphitization for the production of a graphite sheet.

(graphitization step)

In the method of manufacturing a high-thickness graphite sheet of the present invention, the step of preparing the graphite sheet is graphitized while changing the temperature increase rate stepwise in a temperature range of 1,200 ° C to 2,800 ° C. It is prepared from a graphite sheet of ㎛ to 100 ㎛. Through this graphitization process, a graphite sheet formed by rearranging carbon in the amorphous carbon body in the carbonized sheet is prepared.

Specifically, the graphitization method is not particularly limited, but after the carbonized sheet is put into a high-temperature furnace facility such as an electric furnace, in a mixed gas atmosphere containing nitrogen, argon and a small amount of helium, from 1,200°C to 2,800°C for about 10 hours It can be prepared by gradually increasing the temperature and maintaining it over 14 hours.

More specifically, in the step of preparing the graphite sheet, the carbonized sheet is first graphitized while the temperature is raised from 1,200 ° C. to 2,200 ° C., and then secondary graphitized while the temperature is raised from 2,200 ° C. to 2,500 ° C., and then from 2,500 ° C. It may include tertiary graphitization to 2,800°C. In this case, the carbon rearrangement efficiency of the amorphous carbon body in the carbonized sheet is further improved, the brittleness is low even in the high thickness range, and the surface quality can be excellent.

More specifically, the temperature increase rate of the primary graphitization is 1.5 ℃ / min to 5 ℃ / min, the temperature increase rate of the secondary graphitization is 0.4 ℃ / min to 1.3 ℃ / min, the tertiary graphitization The temperature increase rate may be 8.5 °C/min to 20 °C/min. In this case, the carbon rearrangement efficiency of the amorphous carbon body in the carbonized sheet is further improved, the brittleness is low even in the high thickness range, and the surface quality can be excellent.

In addition, within the first to third graphitization temperature range and the first to third graphitization temperature increase rate, the discharge of gas generated during the manufacture of the graphite sheet proceeds stably, further preventing surface damage, It is possible to further reduce the surface damage rate of Equations 1 and 2 described above to near zero.

The high-thickness graphite sheet manufacturing method includes a cooling step of cooling the graphitized graphite sheet at a rate of 5° C./min to 10° C./min after performing the step of preparing the graphite sheet; may additionally include. In such a case, the brittleness of the graphite sheet may be further lowered, and the surface quality may be further improved.

Another embodiment of the present invention relates to a high-thickness graphite sheet manufactured by the above-described high-thickness graphite sheet manufacturing method.

The high-thickness graphite sheet has a thickness of 50 μm to 100 μm. In this case, since the heat capacity is excellent, it has more advantageous properties to be used as a heat dissipation means applied to an electronic device.

The high-thickness graphite sheet is formed from a polyimide film having a thickness of 100 μm to 200 μm. In addition, the high-thickness graphite sheet may be a carbonized and graphitized sheet of a polyimide film having a thickness of 100 μm to 200 μm. In this case, the high-thickness graphite sheet is formed to have a thickness of 50 μm to 100 μm, and has excellent heat capacity, so it has more advantageous properties to be used as heat dissipation means applied to electronic devices.

The high-thickness graphite sheet implements excellent surface quality with a second surface damage rate of 0% or 0.001% to 0.004% of the second surface damage rate represented by Equation 2 above. In this case, it has more advantageous properties to be used as a heat dissipation means applied to an electronic device.

In addition, the high-thickness graphite sheet may have a thermal conductivity of 800 W/m·K or more in the plane direction, specifically 800 W/m·K to 1,200 W/m·K. In this case, it has more advantageous properties to be used as a heat dissipation means applied to an electronic device.

Example

Hereinafter, through specific examples of the invention, the operation and effect of the invention will be described in more detail. However, these embodiments are merely presented as an example of the invention, and the scope of the invention is not defined thereby.

Example 1

In a 0.5 L reactor under nitrogen atmosphere, oxydianiline (ODA, 3,3'-oxydianiline) as a diamine monomer in dimethylformamide (DMF) as an organic solvent and pyromellitic dianhydride (PMDA) as a dianhydride monomer , pyromellitic dianhydride) was added in a weight ratio of 1:1 and then polymerized to prepare a polyamic acid solution. At this time, the weight ratio of the solid content to the solvent in the total reactant was 20:80.

2,500 ppm of calcium phosphate having an average particle diameter of 3 μm was added to the polyamic acid solution as an inorganic filler and stirred to obtain a precursor composition.

Then, beta-picoline as an imidization catalyst was added in an amount of 0.17 molar ratio to 1 mol of the amic acid group, and then uniformly mixed and defoamed to prepare a composition for forming a polyimide film.

The composition for forming a polyimide film was cast to 500 μm using a doctor blade on a SUS plate (100SA, Sandvik) as a support, and dried in a hot air method at a temperature of 100° C. to 200° C. to prepare a sheet-shaped gel. .

Then, the sheet-shaped gel is peeled off the SUS Plate, fixed to a pin frame, transferred to a high-temperature tenter, and after performing primary imidization at a temperature of 200°C to 400°C for 10 minutes in the high-temperature tenter, 300°C to 500°C Secondary imidization was performed at a temperature of °C for 10 minutes. The polyimide film filmed by the primary and secondary imidization was cooled at 25° C. and then separated from the pin frame to obtain a polyimide film having a size of 20 cm×2.5 cm and a thickness of 125 μm.

Examples 2 to 3

Thickness in the same manner as in Example 1, except that the solvent content of the polyamic acid solution and the molar ratio (content) of the imidization catalyst (beta-picoline) in the composition for forming a polyimide film were changed as shown in Table 1 below. A 125 μm polyimide film was prepared.

Example 4

The polyimide film prepared in Example 1 was subjected to carbonization heat treatment from 50° C. to 1,200° C. at a temperature increase rate of 1° C./min to prepare a carbonized sheet.

Then, a graphite sheet having a final thickness of 50 μm was prepared by performing a graphitization heat treatment in which the carbonized sheet was fired while changing the temperature increase rate in stages from 1st to 3rd in a temperature range of 1,200°C to 2,800°C. At this time, the primary graphitization was heated at a rate of 1.5 °C/min from 1,200 °C to 2,200 °C, the secondary graphitization was heated at a rate of 0.4 °C/min from 2,200 °C to 2,500 °C, and the third graphitization was 2,500 °C. The temperature was raised from ℃ to 2,800 ℃ at a rate of 8.5 ℃ / min.

Example 5

A graphite sheet having a final thickness of 50 μm was prepared in the same manner as in Example 4, except that the polyimide film was changed to the polyimide film prepared in Example 2.

Example 6

A graphite sheet having a final thickness of 50 μm was prepared in the same manner as in Example 4, except that the polyimide film was changed to the polyimide film prepared in Example 3.

Comparative Example 1

As shown in Table 1 below, a polyimide film having a thickness of 125 μm was prepared in the same manner as in Example 1, except that the molar ratio (content) of the imidization catalyst (beta-picoline) was changed.

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Comparative Example 2

As shown in Table 1 below, a polyimide film having a thickness of 125 μm was prepared in the same manner as in Example 1, except that the molar ratio (content) of the imidization catalyst (beta-picoline) was changed.

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Comparative Examples 3 to 4

Thickness in the same manner as in Example 1, except that the solvent content of the polyamic acid solution and the molar ratio (content) of the imidization catalyst (beta-picoline) in the composition for forming a polyimide film were changed as shown in Table 1 below. A 125 μm polyimide film was prepared.

Comparative Example 5

The polyimide film prepared in Comparative Example 1 was subjected to carbonization heat treatment from 50° C. to 1,200° C. at a temperature increase rate of 1° C./min to prepare a carbonized sheet.

Then, a graphite sheet having a final thickness of 50 μm was prepared by performing a graphitization heat treatment in which the carbonized sheet was fired while changing the temperature increase rate in stages from 1st to 3rd in a temperature range of 1,200°C to 2,800°C. At this time, the primary graphitization was heated at a rate of 1.5 °C/min from 1,200 °C to 2,200 °C, the secondary graphitization was heated at a rate of 0.4 °C/min from 2,200 °C to 2,500 °C, and the third graphitization was 2,500 °C. The temperature was raised from ℃ to 2,800 ℃ at a rate of 8.5 ℃ / min.

Comparative Example 6

A graphite sheet having a final thickness of 50 μm was prepared in the same manner as in Example 6, except that the polyimide film of Comparative Example 5 was changed to the polyimide film of Comparative Example 2.

Comparative Example 7

A graphite sheet having a final thickness of 50 μm was prepared in the same manner as in Example 6, except that the polyimide film of Comparative Example 5 was changed to the polyimide film of Comparative Example 3.

Comparative Example 8

A graphite sheet having a final thickness of 50 μm was prepared in the same manner as in Example 6, except that the polyimide film of Comparative Example 5 was changed to the polyimide film of Comparative Example 4.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 polyamic acid
(parts by weight) 100 100 100 100 100 100 100 solvent 400 400 400 400 400 400 400 imidization catalyst
(molar ratio) 0.17 0.20 0.15 0 0.28 0.25 0.24 imidization catalyst
(parts by weight) 27 29 25 0 36 33 32 inorganic filler 2,500
ppm 2,500
ppm 2,500
ppm 2,500
ppm 2,500
ppm 2,500
ppm 2,500
ppm Thickness (μm) 125 125 125 125 125 125 125

Example 4 Example 5 Example 6 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 polyimide film Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 carbonization temperature
(℃) 50℃
~1200℃ 50℃
~1200℃ 50℃
~1200℃ 50℃
~1200℃ 50℃
~1200℃ 50℃
~1200℃ 50℃
~1200℃ Primary graphitization temperature (℃) 1,200℃
~2,200℃ 1,200℃
~2,200℃ 1,200℃
~2,200℃ 1,200℃
~2,200℃ 1,200℃
~2,200℃ 1,200℃
~2,200℃ 1,200℃
~2,200℃ Secondary graphitization temperature (℃) 2,200℃
~2,500℃ 2,200℃
~2,500℃ 2,200℃
~2,500℃ 2,200℃
~2,500℃ 2,200℃
~2,500℃ 2,200℃
~2,500℃ 2,200℃
~2,500℃ Tertiary graphitization temperature (℃) 2,500℃
~2,800℃ 2,500℃
~2,800℃ 2,500℃
~2,800℃ 2,500℃
~2,800℃ 2,500℃
~2,800℃ 2,500℃
~2,800℃ 2,500℃
~2,800℃ Thickness (μm) 50 50 50 50 50 50 50

<Evaluation of physical properties>

(1) Surface quality evaluation 1

The high-thickness graphite sheets prepared in Examples 4 to 6 and Comparative Examples 5 to 8 were visually evaluated for surface quality. Specifically, for surface quality evaluation, cracks or cracks were observed on the surface of each high-thickness graphite sheet through the naked eye.

If no cracks or cracks occurred within the observation area (width 20 cm, length 2.5 cm), the surface quality is indicated as “excellent”, and when the number of cracks or cracks is 1 to 5, the surface quality is indicated as “ When the number of cracks or cracks exceeds 5, or when graphitization is not performed, the surface quality was evaluated as “poor”. The results are shown in FIGS. 1 to 3 and Table 3 below.

(2) Surface damage rate evaluation

For the high-thickness graphite sheets prepared in Examples 4 to 6 and Comparative Examples 5 to 8, the second surface damage rate expressed by the following formula 2 is measured, and if the second surface damage rate exceeds 0.004%, "unsuitable" " was evaluated. The results are shown in Table 3 below.

<Equation 2>

Second surface damage rate (%) = { ( B ₁ / B ₀ ) × 100 }

In Equation 2, B ₀ ^{is the area (mm 2} ) measured by photographing the graphite sheet specimen at 10 magnification, and B ₁ is the area of the damaged area measured by photographing the graphite sheet specimen at 10 magnification (mm). ² ) is.

(3) thermal conductivity

The thermal diffusivity was measured in the plane direction of the graphite sheet specimens of Examples and Comparative Examples by the laser flash method using a thermal diffusivity measuring device (model name LFA 467, Netsch Co.), and the density (weight/volume) in the thermal diffusivity measurement value and specific heat (measured specific heat using DSC) to calculate thermal conductivity. In addition, in the (1) surface quality evaluation, cracks or cracks occurred, or the specimen that was not graphitized could not be measured, so it was indicated as impossible to measure. The results are shown in Table 3 below.

(4) Evaluation of occurrence of bright spots

The number of bright spots is a factor that causes surface defects of the graphite sheet, and the number of protrusions having a size of 0.05 mm or more inside a 50 mm × 50 mm square of the sheet was measured. In addition, in the (1) surface quality evaluation, cracks or cracks occurred, or the specimen that was not graphitized could not be measured, so it was indicated as impossible to measure. The results are shown in Table 3 below.

Example 4 Example 5 Example 6 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 cracks or cracks does not exist does not exist does not exist Occur Occur Occur Occur surface quality Great Great Great error error usually usually Second surface damage rate 0% 0% 0% incongruity incongruity incongruity incongruity Planar thermal conductivity (W/m·K) 1,000 800 1,100 measurement
impossible measurement
impossible measurement
impossible measurement
impossible Number of bright spots (EA) One 2 0 measurement
impossible measurement
impossible measurement
impossible measurement
impossible drawing Figure 1 - - Fig. 3 - Figure 2 -

Although the above has been described with reference to the embodiments of the present invention, those of ordinary skill in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Claims (10)

A graphite sheet having a thickness of 50 μm to 100 μm, and a second surface damage rate of 0% or 0.001% to 0.004% represented by the following Formula 2:
<Equation 2>
Second surface damage rate (%) = { ( B ₁ / B ₀ ) × 100 }
In Equation 2, B ₀ ^{is the area (mm 2} ) measured by photographing the graphite sheet specimen at 10 magnification, and B ₁ is the area of the damaged area measured by photographing the graphite sheet specimen at 10 magnification (mm). ² ) is.
According to claim 1,
The graphite sheet is a graphite sheet formed from a polyimide film having a thickness of 100 μm to 200 μm.
According to claim 1,
The graphite sheet is a graphite sheet which is a carbonized and graphitized sheet of a polyimide film having a thickness of 100 μm to 200 μm.
According to claim 1,
The graphite sheet has a thermal conductivity of 800 W/m·K to 1,200 W/m·K in the plane direction.
Preparing a carbonized sheet by heat-treating the polyimide film from 15° C. to 1,200° C.; and graphitizing the carbonized sheet while changing the temperature increase rate step by step from 1,200° C. to 2,800° C. to prepare a graphite sheet having a thickness of 50 μm to 100 μm; including,
The graphite sheet is a graphite sheet manufacturing method having a second surface damage rate of 0% or 0.001% to 0.004% represented by the following formula 2:
<Equation 2>
Second surface damage rate (%) = { ( B ₁ / B ₀ ) × 100 }
In Equation 2, B ₀ ^{is the area (mm 2} ) measured by photographing the graphite sheet specimen at 10 magnification, and B ₁ is the area of the damaged area measured by photographing the graphite sheet specimen at 10 magnification (mm). ² ) is.
6. The method of claim 5,
Manufacturing the carbonized sheet comprises thermally decomposing the polyimide film while heating the polyimide film at a rate of 1° C./min to 5° C./min.
6. The method of claim 5,
The step of preparing the graphite sheet is after primary graphitization of the carbonized sheet while raising the temperature from 1,200 °C to 2,200 °C, and then secondary graphitization while raising the temperature from 2,200 °C to 2,500 °C, and then from 2,500 °C to 2,800 °C 3 A method for producing a graphite sheet, comprising primary graphitizing.
8. The method of claim 7,
The temperature increase rate of the primary graphitization is 1.5 ℃ / min to 5 ℃ / min,
The temperature increase rate of the secondary graphitization is 0.4 ℃ / min to 1.3 ℃ / min,
The temperature increase rate of the tertiary graphitization is 8.5 °C / min to 20 °C / min, the graphite sheet manufacturing method.
6. The method of claim 5,
The polyimide film is a graphite sheet manufacturing method having a thickness of 100 μm to 200 μm.
6. The method of claim 5,
The graphite sheet has a thermal conductivity of 800 W/m·K to 1,200 W/m·K in the plane direction.

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