GRAPHITE SHEET PRODUCED FROM POLYIMIDE FILM HAVING EXCELLENT ORIENTATION PROPERTIES, AND METHOD FOR PRODUCING SAME

Abstract

Disclosed are a graphite sheet formed from a polyimide film having a molecular orientation ratio of at least about 1.25, and a method for producing the same.

Claims

1. A graphite sheet formed from a polyimide film, wherein the polyimide film has a molecular orientation ratio of about 1.25 or more.

2. The graphite sheet of claim 1, wherein the polyimide film has a molecular orientation ratio of about 1.25 to about 1.32.

3. The graphite sheet of claim 1, wherein the polyimide film has a thickness of about 20 μm to about 100 μm.

4. The graphite sheet of claim 1, which is produced by carbonizing, graphitizing, or carbonizing and graphitizing the polyimide film.

5. The graphite sheet of claim 1, which has a thermal conductivity of about 1,400 W/m.Math.K or more.

6. The graphite sheet of claim 1, which has a thermal conductivity of about 1,400 W/m.Math.K to about 1,450.6 W/m.Math.K.

7. A method for producing a graphite sheet, the method comprising carbonizing, graphitizing, or carbonizing and graphitizing a polyimide film having a molecular orientation ratio of about 1.25 or more.

8. The method of claim 7, wherein the polyimide film has a molecular orientation ratio of about 1.25 to about 1.32.

9. The method of claim 7, wherein the carbonizing is performed at a temperature of about 800° C. to about 1,500° C. for about 1 hour to about 20 hours.

10. The method of claim 7, wherein the graphitizing comprises a step of heat-treating the polyimide film by raising a temperature of the polyimide film from about 1,000° C. to a temperature of about 2,500° C. to about 3,000° C.

Description

BEST MODE

[0167] Hereinafter, the operation and effect of the present disclosure will be described in more detail with reference to specific examples of the present disclosure. However, these examples serve merely to illustrate the present disclosure, and the scope of the present disclosure is not determined thereby.

Example 1

[0168] Step (a) of the production method according to the present disclosure was performed as follows: [0169] 200 kg of DMF was placed in a 300-liter reactor and set to a temperature of 20° C. Next, 20.3 kg of 4,4-ODA as a first monomer (diamine) was added thereto and dissolved therein.

[0170] Then, step (b) of the production method according to the present disclosure was performed as follows: [0171] PMDA as a second monomer (dianhydride) was added in portions three times. The PMDA was added three times in amounts of 7.15 kg, 7.15 kg and 7.15 kg, respectively, and the additions were performed continuously at intervals of about 10 minutes. The reactor was allowed to stand for a time period from the time when the last addition was completed to the time when about 20 minutes had elapsed. At this time, the amount of second monomer added was about 97 mol % relative to the total moles of the first monomer.

[0172] Subsequently, step (c) of the production method according to the present disclosure was performed as follows: [0173] PMDA as the second monomer (dianhydride) was added in portions five times. At the time of addition of the first portion, the allowing-to-stand of step (b) was completed. The PMDA was added sequentially in amounts of 150 g, 150 g, 150 g, 150 g and 60 g, and the additions were performed continuously at intervals of about 20 minutes. At this time, the amount of second monomer added was about 99.8 mol % relative to the total moles of the first monomer.

[0174] Then, step (d) of the production method according to the present disclosure was performed as follows: [0175] The reactor was allowed to stand for a time period from the time when the last addition of the second monomer in step (c) was completed to the time when about 4 minutes had elapsed. Then, a precursor composition containing 15 wt % of polyamic acid solids was recovered from the reactor. Then, 7 kg of beta-picoline as an imidizing agent and 48.5 kg of acetic anhydride as a dehydrating agent were added to the precursor composition, thus preparing a final precursor composition (a film-forming composition).

[0176] At this time, the ratio between the time required (T.sub.b) in step (b), the time required (T.sub.c) in step (c) and the allowing-to-stand time (T.sub.d) in step (d) was 1:2:0.1.

[0177] Then, step (e) of the production method according to the present disclosure was performed as follows: [0178] (e-1) A film intermediate was produced by applying the precursor composition to an endless stainless plate in a dryer and drying the applied precursor composition at a temperature of about 90° C. [0179] (e-2) The produced film intermediate was placed in a tenter, and then stretched at about 130% in the machine direction (MD) by adjusting the speed of transfer rollers while being transferred to a heat-treatment device (including a plurality of zones having different temperatures). [0180] (e-3) The stretched film intermediate was fixed at both ends thereof in the transverse direction (TD) with respect to the MD, and then transferred in a non-stretched state with respect to the TD. The stretched film intermediate being transferred was subjected sequentially to first heat-treatment and second heat-treatment while it was passed through a heat-treatment device including a plurality of zones having different temperatures. At this time, the first heat-treatment was performed by raising the temperature from 20° C. to 400° C. at a temperature rise rate of 300° C./min to 350° C./min. The second heat-treatment was performed by raising the temperature from 400° C. to 600° C. at a temperature rise rate of 50° C./min to 100° C./min. [0181] (e-4) After completion of the heat treatment, a polyimide film having a thickness of about 50 μm was obtained.

Example 2

[0182] A polyimide film having a thickness of about 50 μm was obtained in the same manner as in Example 1, except that (e-2) in step (e) of the production method according to the present disclosure was modified as follows: [0183] (e-2) The produced film intermediate was placed in a tenter, and then stretched at about 160% in the machine direction (MD) by adjusting the speed of transfer rollers while being transferred to a heat-treatment device.

Example 3

[0184] A polyimide film having a thickness of about 50 μm was obtained in the same manner as in Example 1, except that (e-2) and (e-3) in step (e) of the production method according to the present disclosure were modified as follows: [0185] (e-2) The produced film intermediate was placed in a tenter, and then stretched at about 160% in the machine direction (MD) by adjusting the speed of transfer rollers while being transferred to a heat-treatment device. [0186] (e-3) First heat-treatment was performed by raising the temperature from 20° C. to 400° C. at a variable temperature rise rate of 450° C./min to 500° C./min.

Comparative Example 1

[0187] A polyimide film having a thickness of about 50 μm was obtained in the same manner as in Example 1, except that (e-1) in step (e) of the production method according to the present disclosure was modified as follows: [0188] (e-1) A film intermediate was produced by applying the precursor composition to an endless stainless plate in a dryer and drying the applied precursor composition at a temperature of about 110° C.

Comparative Example 2

[0189] A polyimide film having a thickness of about 50 μm was obtained in the same manner as in Example 1, except that (e-1) in step (e) of the production method according to the present disclosure was modified as follows and (e-2) was omitted: [0190] (e-1) A film intermediate was produced by applying the precursor composition to an endless stainless plate in a dryer and drying the applied precursor composition at a temperature of about 110° C.

Comparative Example 3

[0191] A polyimide film having a thickness of about 50 μm was obtained in the same manner as in Example 1, except that (e-1) in step (e) of the production method according to the present disclosure was modified as follows and (e-2) was omitted: [0192] (e-1) A film intermediate was produced by applying the precursor composition to an endless stainless plate in a dryer and drying the applied precursor composition at a temperature of about 130° C.

Comparative Example 4

[0193] A polyimide film having a thickness of about 50 μm was obtained in the same manner as in Example 1, except that (e-2) in step (e) of the production method according to the present disclosure was modified as follows and the first heat-treatment in (e-3) was modified as follows: [0194] (e-2) The produced film intermediate was placed in a tenter, and then stretched at about 160% in the machine direction (MD) by adjusting the speed of transfer rollers while being transferred to a heat-treatment device. [0195] (e-3) First heat-treatment was performed by raising the temperature from 20° C. to 400° C. at a temperature rise rate of 100° C./min to 110° C./min.

Comparative Example 5

[0196] The production of a polyimide film having a thickness of about 50 μm was attempted in the same manner as in Example 1, except that (e-2) in step (e) of the production method according to the present disclosure was modified as follows and the first heat-treatment in (e-3) was modified as follows, but the production of the polyimide film failed due to breakage of the film intermediate in the (e-3) process: [0197] (e-2) The produced film intermediate was placed in a tenter, and then stretched at about 160% in the machine direction (MD) by adjusting the speed of transfer rollers while being transferred to a heat-treatment device. [0198] (e-3) First heat-treatment was performed by raising the temperature from 20° C. to 400° C. at a temperature rise rate of 600° C./min to 650° C./min

Comparative Example 6

[0199] A polyimide film having a thickness of about 50 μm was obtained in the same manner as in Example 1, except that the time interval between the additions of the second monomer in step (c) was adjusted to be shorter so that the ratio between the time required (T.sub.b) in step (b), the time required (T.sub.c) in step (c) and the allowing-to-stand time (T.sub.d) in step (d) was 1:1:0.1.

Comparative Example 7

[0200] A polyimide film having a thickness of about 50 μm was obtained in the same manner as in Example 1, except that the allowing-to-stand time (T.sub.d) in step (d) was adjusted to be longer so that the ratio between the time required (T.sub.b) in step (b), the time required (T.sub.c) in step (c) and the allowing-to-stand time (T.sub.d) in step (d) was 1:2:0.5.

Comparative Example 8

[0201] The production of a polyimide film was attempted in the same manner as in Example 1, except that (e-1) in step (e) of the production method according to the present disclosure was modified as follows, but the production of the polyimide film failed due to breakage of the film intermediate in the (e-2) process: [0202] (e-1) A film intermediate was produced by applying the precursor composition to an endless stainless plate in a dryer and drying the applied precursor composition at a temperature of about 130° C.

Comparative Example 9

[0203] The production of a polyimide film was attempted in the same manner as in Example 1, except that (e-1) and (e-2) in step (e) of the production method according to the present disclosure were modified as follows, but the production of the polyimide film failed due to breakage of the film intermediate in the (e-2) process: [0204] (e-1) A film intermediate was produced by applying the precursor composition to an endless stainless plate in a dryer and drying the applied precursor composition at a temperature of about 110° C. [0205] (e-2) The produced film intermediate was placed in a tenter, and then stretched at about 160% in the machine direction (MD) by adjusting the speed of transfer rollers while being transferred to a heat-treatment device.

Comparative Example 10

[0206] The production of a polyimide film was attempted in the same manner as in Example 1, except that (e-2) in step (e) of the production method according to the present disclosure was modified as follows, but the production of the polyimide film failed due to breakage of the film intermediate in the (e-2) process: [0207] (e-2) The produced film intermediate was placed in a tenter, and then stretched at about 200% in the machine direction (MD) by adjusting the speed of transfer rollers while being transferred to a heat-treatment device.

TABLE-US-00001 TABLE 1 (e-1) drying (e-2) Temperature rise Time ratio temperature elongation rate (° C./min) in Film (T.sub.b:T.sub.c:T.sub.d) (° C.) rate (%) first heat treatment breakage Example 1 1:2:0.1 90 130 300 to 350 x Example 2 1:2:0.1 90 160 300 to 350 x Example 3 1:2:0.1 90 160 450 to 500 x Comparative 1:2:0.1 110 130 300 to 350 x Example 1 Comparative 1:2:0.1 110 100 300 to 350 x Example 2 Comparative 1:2:0.1 130 100 300 to 350 x Example 3 Comparative 1:2:0.1 90 160 100 to 110 x Example 4 Comparative 1:2:0.1 90 160 600 to 650 ∘ Example 5 Comparative 1:1:0.1 90 130 300 to 350 x Example 6 Comparative 1:2:0.5 90 130 300 to 350 x Example 7 Comparative 1:2:0.1 130 130 300 to 350 ∘ Example 8 Comparative 1:2:0.1 110 160 300 to 350 ∘ Example 9 Comparative 1:2:0.1 90 200 300to 350 ∘ Example 10

Experimental Example 1: Measurement of Molecular Orientation Ratios of Polyimide Films

[0208] The molecular orientation ratios of the polyimide films produced in Examples 1 to 3 and Comparative Examples 1 to 4, 6 and 7 were measured using a microwave transmission-type molecular orientation meter MOA 7015, and the results of the measurement are shown in Table 2 below.

TABLE-US-00002 TABLE 2 Molecular orientation ratio Example 1 1.25 Example 2 1.27 Example 3 1.32 Comparative 1.16 Example 1 Comparative 1.08 Example 2 Comparative 1.09 Example 3 Comparative 1.13 Example 4 Comparative 1.15 Example 6 Comparative 1.03 Example 7

[0209] As shown in Table 2 above, the polyimide films produced according to the Examples had remarkably excellent molecular orientation ratios compared to those of the Comparative Examples, indicating that polymer chains constituting each of the polyimide films were well oriented.

Experimental Example 2: Evaluation of Thermal Conductivity of Graphite Sheet

[0210] Each of the polyimide films obtained in Examples 1 to 3 and Comparative Examples 1 to 4, 6 and 7 was heated to 1,200° C. at a rate of 1° C./min under nitrogen gas by means of an electric furnace capable of carbonization and maintained at this temperature for about 2 hours (carbonization). Then, each polyimide film was heated to 2,800° C. at a temperature rise rate of 20° C./min under argon gas by means of the electric furnace and maintained at this temperature for 8 hours, followed by cooling to obtain graphite sheets.

[0211] The thermal diffusivity of each of the graphite sheets was measured by a laser flash method using a thermal diffusivity measurement system (model name LFA 447, Netsch), and the specific heat capacity of each graphite sheet could be measured using a specific heat measurement system (model name DSC 204F1, Netsch).

[0212] The thermal conductivity of each graphite sheet was calculated by multiplying the measured thermal diffusivity and DSC values by the density (weight/volume), and the results are shown in Table 3 below.

TABLE-US-00003 TABLE 3 Thermal conductivity (W/m .Math. K) Example 1 1402.5 Example 2 1419.2 Example 3 1450.6 Comparative 1337.4 Example 1 Comparative 1331.0 Example 2 Comparative 1312.8 Example 3 Comparative 1298.4 Example 4 Comparative 1356.4 Example 6 Comparative 1255.6 Example 7

[0213] As shown in Table 3 above, the graphite sheets produced from the polyimide films produced according to the Examples exhibited remarkably excellent thermal conductivities compared to those of the Comparative Examples. From the results in Table 3 and Table 2 above, it can be seen that the Example of the present invention is preferred for the production of a polyimide film having excellent orientation, and also plays a major role in obtaining a graphite sheet having excellent thermal conductivity.

[0214] Although the above description has been made with reference to the embodiments of the present disclosure, any person skilled in the art to which the present disclosure pertains will appreciate that various applications and modifications are possible within the scope of the present disclosure based on the above-described contents.