ARTIFICIAL GRAPHITE FLAKE MANUFACTURING METHOD

Abstract

An artificial graphite flake manufacturing method mainly using PI (Polyimide) film as a material comprising steps of perforating holes and stacking and compacting various graphite auxiliary materials so as to stabilize the quality of heating and sintering, ensure product flatness, and further proceed step-by-step regulation during the heating process, making the carbonization and graphitization reaction more complete, and indeed improving the quality and yield of manufacturing.

Claims

1. An artificial graphite flake manufacturing method for manufacturing artificial graphite flakes by using PI (polyimide) films as a material, comprising the following steps: (a) a step for providing a plurality of PI films; (b) a step for perforating a plurality of holes with a diameter of 0.11 mm on each of the artificial graphite flakes and an interval between any two adjacent holes is between 0.15 mm; (c) a step for alternately stacking said PI films and natural graphite dust papers so that each PI film is sandwiched by two of the natural graphite dust papers; (d) a step for pressing said alternately stacked PI films and natural graphite dust papers with at least a graphite board and accommodating them into a graphite box in which there is reserved a predetermined space for inflation; (e) a step for accommodating said graphite box into a temperature increasing environment and starting to proceed a continuous heating; (f) a step for injecting a stabilizing gas for degumming when the temperature rises to about 400 C., the injection amount gradually increasing with the temperature in the range of 10 to 60 L/min while stopping the increase of the stabilizing gas injection when the temperature rises to about 600 C., the amount being adjusted to 1030 L/min; (g) a step for adjusting the stabilization gas injection amount to 60 L/min when the temperature rises to about 2300 C.; and (h) a step for cooling and then obtaining artificial graphite flakes from carbonized and graphitized PI films when the continuous heating process is finished after the temperature rises to 25003000 C.

2. The artificial graphite flake manufacturing method as claimed in claim 1, wherein a thickness of each said PI film provided on the step (a) is less than 300 m.

3. The artificial graphite flake manufacturing method as claimed in claim 1, wherein said stabilizing gas on steps (f) and (g) is nitrogen or an inert gas, said inert gas being any of helium, neon, argon, krypton, xenon or radon.

4. The artificial graphite flake manufacturing method as claimed in claim 2, wherein said holes perforated on step (b) are distributed in an array or a plurality of slope lines.

5. The artificial graphite flake manufacturing method as claimed in claim 4, wherein throughout the continuous heating process on step (e) to step (h), said temperature increasing environment is provided by a resistive heating furnace or induction heating furnace.

6. The artificial graphite flake manufacturing method as claimed in claim 3, wherein the continuous heating on step (e) starts to proceed from a vacuum state and the vacuum state ends on step (g).

7. The artificial graphite flake manufacturing method as claimed in claim 6, wherein a degree of said vacuum state is 810.sup.2 Pa810.sup.4 Pa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 is a flowchart in accordance with an embodiment of the present invention.

[0034] FIG. 2 and FIG. 3 are flowcharts in accordance with other embodiments of the present invention.

[0035] FIG. 4 is a schematic view of a stacking status in accordance with an embodiment of the present invention.

[0036] FIG. 5 is a schematic view of the appearance and partial enlargement of an artificial graphite flake in accordance with an embodiment of the present invention.

[0037] FIG. 6 is a top view of the partial structure of an artificial graphite flake in accordance with an embodiment of the present invention.

[0038] FIG. 6a and FIG. 6b are schematic views of the partial structures of artificial graphite flakes in accordance with other embodiments of the present invention.

[0039] FIG. 7FIG. 10 are schematic views of graphite substrate stacking structures in accordance with the embodiments of the present invention.

REPRESENTATIVE FIGURE

[Representative Figure of the Invention]: FIG. 2

[Element Description of the Representative Figure]:

[0040] S1 Stacking step [0041] S2 First heating step [0042] S3 Second heating step [0043] S4 Rolling & forming [0044] S0 Perforation step

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Please refer to FIG. 1; the main flow of the artificial graphite flake manufacturing method in accordance with the present invention includes a stacking step S1, a first heating step S2, a second heating step S3, rolling and forming S4, etc.; of course, before stacking, it is necessary to select a predetermined material, polyimide (PI), and then cut the material into a plurality of PI films with predetermined size; then, the process proceeds to the stacking step S1.

[0046] The stacking step S1 is to alternately stack the PI films and natural graphite dust papers so as to make each PI film is sandwiched by two natural graphite dust papers. Regarding the type of the stacking, as shown in FIG. 4, the PI films 20 and the natural graphite dust papers 12 are alternately stacked to the predetermined layer number or height; then at least two graphite boards 12 are inserted into the stacked PI films 20 and the natural graphite dust papers 12, and press the top and the bottom of the stacked PI films 20 and the natural graphite dust papers 12; afterward, all of which are putted into and fixed in a graphite box 10, and the stacking height is slightly lower than the depth of the graphite box 10; therefore, the graphite box 10 can have a predetermined space 13 for the inflation due to the following heating processing steps.

[0047] After the stacking step S1 is finished, the first heating step S2 is performed first, which puts the graphite box 10 into the low-temperature heating furnace, and then perform the carbonization operation via 10001200 C. heating in stages so as to carbonize the PI films 20 to be the half-finished product; after the first heating step S2 is finished, the second heating step S3 is executed, which takes out the half-finished product and then puts the half-finished product into the high-temperature heating furnace so as to graphitize the half-finished product via 25003000 C. heating in stages; then, the half-finished product can be graphitized to be the artificial graphite flake 20; after the above process is finished, the stacking structure is taken out and then disassembled; afterward, the finished product of the artificial graphite flake 20 is obtained after the rolling step and the forming step.

[0048] In a preferred embodiment, the heating furnace may be a resistance-type heating furnace or a sensing-type heating furnace; the heating furnace adopted by the carbonization reaction is a low-temperature carbonization furnace, and the heating furnace of the graphitization reaction is a high-temperature heating furnace.

[0049] Please refer to FIG. 2, FIG. 3 and FIG. 5; a perforation step S0, S5 can be further added into the manufacturing process of the embodiment, which can form a plurality of holes 21 with diameter of 0.11 mm. As shown in FIG. 2, the perforation step S0 is to execute the perforation operation before the stacking step S1, and the holes formed by which can provide the space for the inflation due to heating so as to increase the defect-free rate and the smoothness of the artificial graphite flake 20 after heating reaction; thus, the diameter of the holes 21 after the heating reaction will have the contract ratio of 5-15%; for example, if the diameter of the holes of the PI films 20 is 1 mm, the diameter of the holes 21 of artificial graphite flake 20 will contract to be 0.850.95 mm after the heating reaction; as shown in FIG. 3, the perforation operation is executed after the second heating step S2, which can accurately control the size of the holes 21 to keep stable heat diffusion and the air permeability.

[0050] Accordingly, via the hole structure formed by the holes 21 on the PI films 20 and the artificial graphite flakes 20 during the perforation step S0, S5, the heat diffusion area and the air permeability of the artificial graphite flakes 20 can be increased; thus, the heat diffusion function and the heat conduction function of the artificial graphite flakes 20 can be much better than conventional graphite flakes; further, the holes 20 can form the space for inflation or contracting; therefore, the defect-free rate and the smoothness can be increased in either the heating process or the following process of pressing the artificial graphite flakes to form the heat dissipation substrates.

[0051] In a preferred embodiment, the holes 21 formed by the perforation step S0, S5 (or the holes 21 of the artificial graphite flakes 20) can be distributed to form an array (as shown in FIG. 6) or a plurality of sloping lines (as shown in FIG. 6a); besides, the interval d of any two adjacent holes 21 is between 0.15 mm. Further, the holes 21 not only can be circular, but also can be hexangular holes 21 outside the inscribed circle (or inside the circumscribed circle) with diameter of 0.11 mm; as shown in FIG. 6b, the holes 21 of the artificial graphite flakes 20 are the hexangular holes 21 outside the inscribed circle.

[0052] As to the heating process, except employing the above-mentioned operation method in which the carbonization operation is performed in a low-temperature heating furnace and the graphitization operation is completed in a high-temperature heating furnace, in the case where the equipment can meet the requirements, the heating environment provided by a single device can also be used to precisely regulate and control the conditions required for each temperature stage during continuous heating, such as pressure conversion and exhaust volume adjustment according to temperature. And by using a single-temperature one-time heating and sintering mode, the work hour and cost will be saved, the quality stabilized and the damage rate lowered.

[0053] The primary procedure of the above-mentioned embodiments in which the single equipment is continuously heated in stages includes a pre-processing before heating treatment and a heating control, wherein the pre-processing mainly comprises:

(a) a step for preparing a material which is cut into a plurality of PI films 20 having a thickness of 300 m or less according to a predetermined size specification;
(b) a step for using a processing apparatus to proceed a hole processing operation, wherein a plurality of holes 21 are formed on the PI films 20, and the holes 21 have a diameter of 0.1 to 1 mm and an interval of 0.1 to 5 mm;
(c) a step for proceeding a preparation before heating, wherein the PI films 20 are alternately stacked with the natural graphite dust papers 12 so that each PI films 20 can be interposed between the two natural graphite dust papers 12; and
(d) a step for pressing and fixing a plurality of graphite boards 11 wherein each time the PI films 20 and the natural graphite dust papers 12 are alternately stacked to a predetermined number of layers, a graphite board 11 is used for pressing, and after being stacked to a certain height, they are accommodated in a graphite box 10 to form a combination with a predetermined space 13 reserved for inflation in the graphite box 10.

[0054] After steps (a) to (d) of the pre-processing are completed, a continuous heating and a regulation and control start to proceed, and the process comprises:

(e) a step for smoothly accommodating the pre-processed graphite box 10 into a high-efficient heating furnace with a precisely regulated and controlled heating environment to meet the needs to proceed regulation and control in stages during continuous heating wherein when the temperature increases, the vacuum valve is opened for the heating environment to start to proceed heating in a vacuum state of a degree of 810.sup.2 Pa to 810.sup.4 Pa;
(f) a step for injecting nitrogen gas when the temperature continuously rises to about 400 C., the nitrogen injection amount being in the range of 10 to 60 L/min and gradually increasing with the increase of temperature, while the injection amount of nitrogen gas stop increasing when the temperature continuously rises to about 600 C. and the nitrogen gas is adjusted to a steady injection amount of 10 to 30 L/min to continuously proceed heating;
(g) a step for closing the vacuum valve to end the vacuum state when the temperature continuously rises to about 2300 C., the heating environment being returned to the normal pressure state, and the injection amount adjusted to 60 L/min; and
(h) a step for continuously heating up to the final temperature (25003000 C., preferably 2850 C.) and keeping steady for a period of time to finally complete the heating process, wherein after cooling, artificial graphite flakes are obtained from the carbonized and graphitized PI films.

[0055] In the above embodiments, the gas regulated and controlled to be injected on steps (f) and (g) may be selected from any of inert gases such as helium, neon, argon, krypton, xenon and radon, in addition to nitrogen, which can react with the residual gum to achieve the degumming effect. By regulating and controlling the injection amount of the gases at a specific temperature, the degumming effect can be efficiently achieved. In addition to avoiding damage to the equipment caused by the residual gum after sintering, it can make the process of carbonization and graphitization of the sintered PI film 20 more stable.

[0056] Furthermore, by controlling the pressure during the heating process, the quality of the carbonized and graphitized PI film 20 can be stabilized. In the present embodiment, the vacuum is further converted to a positive pressure at a temperature of about 2300 C., and the graphitized lattice chain structure can be made more complete during the graphitization of the PI film 20 to achieve a standard qualified graphitized structure.

[0057] In the foregoing embodiments of the present invention, the auxiliary materials such as the graphite box 10, the graphite board 11, and natural graphite dust paper 12 etc., are used to assist in sintering. In addition to using the high-speed heat conduction effect of the graphite material to make the temperature rise of the PI film 20 more uniform and consistent, it can provide the effect of plane pressing and auxiliary fixing, and the holes 21 perforated on the PI film 20 can greatly reduce the impact caused by shrinkage and expansion during heating and sintering to ensure the flatness of the sintered product and improve the yield.

[0058] Please refer to FIG. 7, which is a schematic view of the stacking structure of the graphite substrate 3 manufactured by further processing the aforementioned artificial graphite flake 20; the structure includes an artificial graphite flake 20, a base layer 30, at least one conducting layer 32 and at least one isolating layer 31; more specifically, the base layer 30 is disposed below the artificial graphite flake 20 and made of metal, resin or wood fiber; the conducting layer 32 is disposed above the artificial graphite flake 20 and made of the conducting material; the isolating layer 31 is corresponding to the conducting layer 32 and attached to the bottom of the conducting layer 32, wherein the isolating layer 31 is made of isolating composite material.

[0059] The stacking structure of the graphite substrate 3 shown in FIG. 7 is an embodiment of a single-layer graphite substrate 3; of course, as shown in FIG. 8, an additional isolating layer 33 can be inserted between the base layer 30 and the artificial graphite flake 20 according to the requirements to form anther embodiment of the single-layer graphite substrate 3; the material of the additional isolating layer 33 is the same with the isolating layer 31 and can be made of isolating composite material.

[0060] In addition, a plurality of conducting layers 32 can be disposed above the artificial graphite flake 20 according to the requirements to form a multi-layer graphite substrate 3; as shown in FIG. 9, two conducting layers 32 are disposed above the artificial graphite flake 20, and the bottom of each of the conducting layers 32 is disposed with the corresponding isolating layer 31, whereby the stacking structure of a double-layer graphite substrate 3 is formed.

[0061] Furthermore, as shown in FIG. 10, at least perfusion hole 34 can be formed at the conducting layer 32 at the top and the corresponding isolating layer 31 of the graphite substrate 3, and the perfusion material 35 is injected into perfusion hole 34 so as to match the circuit structure of electronic equipment and enhance the heat transmission ability of the vertical direction of the graphite substrate 3; more specifically, the perfusion material 35 can be cooper paste, silver paste, resin or electroplating copper.

[0062] In all embodiments of the present invention, the material of the isolating layer 31 can be heat curing resin or polymeric resin; the material of the conducting layer 32 can be conducting metal material (such as copper foil). Besides, the material of the base layer 30, the isolating layer 31 and the conducting layer 32 can be properly selected according to the actual requirements and be of appropriate thickness; more specifically, compared the material cost and the heat conducting performance, the preferred base layer 20 can be an aluminum layer with thickness of 103000 m, a copper layer with thickness of 10175 m, a resin layer with thickness of 103000 m or a wood fiber layer with thickness of 10200 m; the preferred isolating layer 31 can be a PP (prepreg) layer with thickness of 10130 m; the preferred conducting layer 32 can be a copper layer with thickness of 10175 m.

[0063] While the means of specific embodiments in present invention has been described by reference drawings, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope and spirit of the invention set forth in the claims. The modifications and variations should in a range limited by the specification of the present invention.

DESCRIPTION OF ELEMENTS

[0064] S1 Stacking step [0065] S2 First heating step [0066] S3 Second heating step [0067] S4 Rolling & forming [0068] S0, S5 Perforation step [0069] 20 PI (Polyimide) film [0070] 10 Graphite box [0071] 11 Graphite board [0072] 12 Natural graphite dust paper [0073] 13 Predetermined space [0074] 20 Artificial graphite flake [0075] 21 Hole [0076] d Interval [0077] 3 Graphite substrate [0078] 30 Base layer [0079] 31 Isolating layer [0080] 32 Conducting layer [0081] 33 Additional isolating layer [0082] 34 Perfusion hole [0083] 35 Perfusion material