TW202118820A - Polyimide film for graphitization - Google Patents

Abstract

The invention provides a polyimide film for graphitization, which comprises a polyimide polymer polymerized by diamine and diacid anhydride monomers; an inorganic particle whose weight accounts for 0.50wt% or less of the total weight of the film; an organic particle whose weight accounts for more than 0.05wt% of the total weight of the film, and the median particle diameter (D50) of the organic particle is 1-20 microns, and the maximum particle diameter (Dmax) is less than 30 microns; and the core void volume (Vvc) of the polyimide film is made higher than 0.040 cubic micrometer/square micrometer ([mu]m3/[mu]m2), so as to avoid the formation of sticking and discoloration during the graphitization process.

Description

Polyimide film for graphitization

The present invention relates to a polyimide film for graphitization. After the film undergoes a high-temperature process, a graphite film with good appearance and thermal diffusion characteristics can be obtained.

The development of thinner and lighter mobile devices has been the current development trend of electronic products. The reduction of electronic components has resulted in compact stacking of components. Therefore, heat dissipation issues such as chips, backlight modules, and batteries have become an important issue. When the requirements for heat conduction and heat dissipation are becoming stricter, the introduction of artificial soft graphite film has allowed these problems to be solved. Compared with traditional metal copper or aluminum heat dissipation materials, artificial graphite film has better thermal conductivity, flexibility and lower density (lightweight), allowing graphite films to be used in large numbers on mobile devices.

The high thermal conductivity artificial graphite film is manufactured by the high aromatic structure polymer film through a series of high temperature pyrolysis reactions and atomic rearrangement processes. These high temperature treatment processes are called carbonization and graphitization. The main function of the carbonization process is thermal cracking of non-carbon elements, and the treatment temperature is about 500-1500°C. The function of graphitization is to push the carbon atoms through high temperature and rearrange the carbon atoms to form a continuous and orderly layered structure. In the process, it will act as a foaming phenomenon to form a foamed graphite layer structure. Its operation The temperature occurs between 2000-3000°C. After rolling the obtained foamed graphite film, a flexible graphite film can be obtained, which is suitable for heat dissipation and electromagnetic wave shielding layer in electronic equipment.

The known manufacturing process of graphite film is to cut the polymer film, especially the polyimide film, into a sheet, stack multiple sheets together as a layer, and then separate the layers of the polyimide film with a graphite gasket Afterwards, heat treatment is carried out, which is called stack firing; for another example, the polyimide film is heat-treated in a roll film larger than 5 meters, which is called roll firing. Regardless of stacking or rolling, in order to increase the production capacity of graphite film per batch, it is usually used to increase the feed rate per furnace. Therefore, it is necessary to increase the packing density of the raw material film in the furnace and compress the space between the film and the film, resulting in Obstruction of tar discharge during the carbonization process. This phenomenon causes sticking, breakage, and surface chromatic aberration between the graphite film and the film, as shown in Figure 1 and 10.

In the past, in order to improve the aforementioned phenomenon, the surface roughness of the film surface can be increased by adding a certain proportion of inorganic particles, so that the polymer film and the film have the effect of antistatic adsorption. However, the added amount of inorganic particles to achieve the antistatic adsorption effect will cause the thermal diffusion characteristics of graphitization to decrease, which is a disadvantage.

The function of inorganic particles in the polyimide film, in addition to avoiding the above-mentioned electrostatic adsorption, can also be used as a foaming agent to help graphite foam. A proper amount of inorganic particles can make the polyimide film foam smoothly during graphitization, and the foamed graphite film has better flexibility after rolling. However, with the presence of inorganic particles, during the graphitization process, non-carbon heteroatoms will be doped in the lattice or lattice gaps, causing defects in the structure of the graphite film, resulting in a decrease in the thermal conductivity of graphite, so it is usually not added 1wt% of the total weight of the imine film.

However, the above-mentioned limited amount of inorganic particles cannot achieve an effective anti-sticking effect. In addition, inorganic particles usually have a high specific gravity and are not easy to produce roughness on the surface of the film. Therefore, increasing their addition ratio will not effectively reduce the electrostatic adsorption between the polyimide film and the film, but will also reduce the characteristics of the graphite film.

In addition, increasing the particle size of the inorganic particles can also slightly improve the antistatic effect, but the larger size of the inorganic particles will cause protrusions or bright spots on the surface of the graphite film, which will adversely affect the appearance.

The polyimide film used for graphitization of the present invention includes: a polyimide polymer polymerized by diamine and dianhydride monomers; an inorganic particle whose weight accounts for 0.50 wt of the total weight of the film % Or less; an organic particle whose weight accounts for more than 0.05wt% of the total weight of the film, and the median particle size (D50) of the organic particle is 1-20 microns, and the maximum particle size (Dmax) is less than 30 microns; and The core void volume (Vvc) of the polyimide membrane is higher than 0.040 cubic micrometer/square micrometer (μm ³ /μm ² ).

The effect of the present invention is to improve the adhesion and discoloration of the polyimide film after graphitization, and maintain good thermal diffusivity.

10‧‧‧The Graphite Film of the Known

12‧‧‧The graphite film of the present invention

The first picture shows the sticky and damaged appearance of the conventional graphite film.

Figure 2 shows the appearance of the graphite film made by the present invention.

The polyimide film used for graphitization of the present invention includes: a polyimide polymer polymerized by diamine and dianhydride monomers; an inorganic particle whose weight accounts for 0.50 wt of the total weight of the film % Or less; an organic particle whose weight accounts for more than 0.05wt% of the total weight of the film, and the median particle size (D50) of the organic particle is 1-20 microns, and the maximum particle size (Dmax) is less than 30 microns; and The core void volume (Vvc) of the polyimide membrane is higher than 0.040 cubic micrometer/square micrometer (μm ³ /μm ² ).

Please refer to Figure 2. The polyimide film is carbonized and graphitized at a high temperature to produce a flat graphite film 12 without sticking or discoloration.

In the present invention, inorganic and organic particles are added to the polyimide film to increase the void volume of the core.

The specific concept of anti-graphitization sticking and discoloration of the present invention is to increase the gap between the film and the film, that is, increase the void volume of the core, so that the tar of high temperature cracking can be discharged from the gap, and the tar residue on the film and the film is reduced. Sticking between them, or remaining on the inner side of the film surface, resulting in different colors caused by the inconsistency of the inner color and the outer edge of the tar removal state.

The gap between the film and the film is created by the space between the tiny undulations on the surface of the polyimide film. The method of controlling the fluctuation of the film surface is called the control of the surface topography in the present invention.

The invention uses inorganic and organic particles to be dispersed in the main polyimide polymer. The advantage of this method is that it has flexible control and production operability.

Surface topography analysis

In the present invention, the surface morphology is evaluated based on the core void volume (Vvc) of the membrane surface.

The surface topography measurement of the present invention is measured based on the definition method of the ISO 25178 specification. The core void volume is generated by the fine protrusion morphology of the membrane surface. The core space is defined as the volume with a unit area of 10% to 80% of the protrusion height. The core void volume is the core physical volume (Core Core space other than material volume (Vmc).

The index of the present invention for the surface morphology analysis of the polyimide film is not limited to the expression of the core void volume Vvc, and the surface morphology parameters of other ISO25178 specifications can also correspond to The features described in the present invention, such as: height parameters (average height Sa, maximum height Sz, root mean square height Sq, skewness Ssk, kurtosis Sku, maximum peak height Sp, maximum valley depth Sv), spatial parameters (minimum free Relevant length Sal, surface property aspect ratio Str, surface property direction Std), mixing parameters (root mean square slope Sdq, interface development area ratio Sdr), functional parameters (load area ratio Smr, reverse load area ratio Smc, core height Difference Sk, height of peak part Spk, depth of peak part Svk, load factor area Smr1 between peak part and core part, load factor area Smr2 between peak part and core part, Smr2, Sxp pole height), functional volume parameter ( The void volume of the trough part Vvv, the volume of the peak part Vmp, the volume of the core part Vmc) and so on.

The composition of polyimide

The polyimide film of the present invention can be polymerized by using one diamine and one dianhydride monomer, or two or more diamines or dianhydrides to obtain a polyimide solution and then coating.

In the present invention, the preferred diamine monomers are 4,4'-oxydianiline (4,4'-ODA) and phenylenediamine (p-PDA) ), and a small amount of one or more other diamines can be added without affecting the effect of the present invention; the preferred dianhydride monomer is pyromellitic dianhydride (PMDA) and 3,3' ,4,4'-Biphenyltetracarboxylic dianhydride (3,3',4,4'-Biphenyltetracarboxylic dianhydride (BPDA)), and a small amount of one or more than two can be added without affecting the effect of the present invention Other dianhydrides.

Inorganic particles

A proper amount of inorganic particles can make the polyimide film foam smoothly during graphitization, and the foamed graphite film has better flexibility after rolling. Phosphate can be used as inorganic particles for foaming Phosphates, carbonates, metal oxides, silicon dioxide, titanium dioxide, boron nitride, etc., preferably phosphates, such as calcium dihydrogen phosphate, calcium hydrogen phosphate, and calcium phosphate. However, with the presence of inorganic particles, during the graphitization process, non-carbon heteroatoms will be doped in the lattice or lattice gaps, causing defects in the structure of the graphite film, resulting in a decrease in the thermal conductivity of graphite. Therefore, the amount of inorganic particles added is It is preferably 0.5wt% or less of the total weight of the film.

However, the above-mentioned limited amount of inorganic particles cannot reach the effective core void volume. In addition, inorganic particles usually have a relatively high specific gravity. Therefore, increasing their addition ratio will not effectively increase the void volume of the core, but will also decrease the properties of the graphite film. In addition, increasing the particle size of inorganic particles can slightly improve the surface roughness, but larger inorganic particles will cause protrusions on the surface of the graphite film, which will adversely affect the appearance. The median diameter of the particle size distribution (D50 ) Should be less than 1μm, and the maximum particle size (Dmax) should be less than 10μm.

The particle size of the inorganic particles can be screened by the input material, and some of them need to be ground to achieve the desired particle size. The method of grinding is not particularly limited. In the present invention, bead milling is preferred, supplemented by a 5-15 micron filter for screening.

Organic particles

The addition of organic particles can effectively increase the void volume of the core. The mechanism is: the specific gravity of organic particles is smaller than that of inorganic particles, so the same addition ratio, organic particles have a greater effect on improving the void volume of the core. In addition, the organic particles are cracked during the carbonization process and will not remain in the film, or they are cracked into carbon and remain in the carbonized film. Graphitization is not easy to cause defects in the graphite structure, or it can be graphite together with the polyimide film. It has limited influence on the characteristics of graphite film.

The median diameter (D50) of the particle size distribution of organic particles is between 1-20μm, and the maximum particle size (Dmax) should be less than 30μm. When the addition ratio accounts for more than 0.05% of the total solid content of the film, it will affect the surface morphology.

The types of organic particles can be: acrylic, polyamide, polyethylene, polypropylene, polyimide, palm wax, synthetic wax, lanolin wax, etc.

The particle size of the organic particles can be controlled through the screening of the initial raw materials, and some of them need to be ground to achieve the desired particle size. The grinding method is not particularly limited. In the present invention, bead milling is preferred, supplemented by a 5-15 micron filter for screening. .

Manufacturing method of polyimide film

The manufacturing method of polyimide film is to coat polyimide acid solution into a film, and then it is obtained by dehydration and solvent volatilization at a high temperature above 200℃. It is called thermal closed loop method; or mixed and dehydrated in polyimide acid solvent. Agents such as acetic anhydride, and catalysts such as triethylamine, pyridine, isoquinoline or picoline, etc., are chemically dehydrated and cyclized to obtain a gelatinous film, and then the solvent is removed at a high temperature to obtain a polyimide film. The chemical closed-loop method. In the present invention, the coating method does not affect the evaluation effect of improving the appearance of the present invention, but the chemical closed loop method is preferred in consideration of the evaluation of characteristics after graphitization.

Carbonized film

The polyimide is under reduced pressure or an inert gas environment, and at the same time, under reduced pressure while passing inert gas for heat treatment. The highest heat treatment temperature in the carbonization step must also be 1000°C or higher, and more preferably 1300°C or higher.

Graphite film

The above-mentioned carbonized film is carried out under reduced pressure or in an inert gas. The maximum heat treatment temperature of the graphitization step is 2400°C or higher, more preferably 2800°C or higher.

The film placement method of the carbonization and graphitization of the polyimide film of the present invention is not particularly limited. For example, the polyimide film is cut into pieces, and multiple pieces are stacked as a layer, and then a graphite gasket is used. Separate the layers of the polyimide and perform the sintering treatment; for another example, the polyimide film is subjected to the sintering treatment with a roll film larger than 5 meters.

The heating device and method required to be used in the present invention are not particularly limited, for example, a high-temperature furnace such as a graphite resistance heater or an induction heater. Another example is the Acheson method high-temperature furnace.

Example 1

Preparation of the polyimide film of the present invention

Polyamide acid solution preparation

Combine 20Kg (100mole%) of 4'-diaminodiphenyl ether (4,4'-oxydianiline (4,4'-ODA)) and 21.8Kg (100mole%) of pyromellitic dianhydride (PMDA)) Dissolve in 157Kg of dimethylacetamide (DMAc) for reaction, then add 0.077Kg of calcium hydrogen phosphate with a median diameter (D50) of 0.6μm and a maximum particle size (Dmax) of 7μm in the particle size distribution Calcium hydrogen phosphate accounts for 0.2wt% of the total solid content of the film, and the addition of polyamide powder with a median diameter (D50) of 7.3μm and a maximum particle size (Dmax) of 20μm in the particle size distribution is 0.077kg, and the polyamide powder accounts for 0.2wt% of the total solid content of the film, to obtain a 21% polyamide acid solution.

Inorganic/organic particle size analysis

A laser diffraction particle size analyzer (HORIBA LA-950V2) was used to analyze the inorganic/organic particle dispersion, and the median diameter D50 and the maximum particle diameter Dmax were used as the particle size judgment.

Polyimide membrane preparation

The above polyamide acid solution is mixed with dehydrating agent and catalyst, and the ratio of addition is that the molar ratio of polyamide acid: dehydrating agent: catalyst is 1:2:1. Coat the steel strip and put it in an oven at 80°C. Heat to remove most of the solvent, and then peel off the polyimide film and enter it into an oven at 170°C~370°C for heating and biaxial stretching to form a 50-micron polyimide film.

Analysis of the surface morphology of the polyimide film

A white light interferometer (zygo NewView 8000) was used to analyze the surface morphology of the polyimide film. Use 5.5x objective lens and 1x eyepiece magnification. According to the definition of ISO 25178, the filter type is High pass Gaussian spline Fixed, and the cutoff mode is period (Long period: 250μm). The void volume (Vvc) of the core of the membrane surface was analyzed.

Carbonized film preparation

Cut the polyimide film into a width of 257mm, take a length of 50 meters and wind it around a graphite inner tube, place it in a graphite crucible, and increase the temperature in a reduced pressure environment. The heating rate is divided into the following sections: room temperature to 500°C is 5°C per minute, 500 to 800°C is 0.5°C per minute, and 800 to 1300°C is 1°C per minute.

Graphite film preparation

The above-mentioned carbonized film is graphitized under normal pressure and heated under argon gas. The heating rate is: room temperature to 2000°C is 10°C per minute, 2000 to 2200°C is 5°C per minute, and 2200°C to 2850°C is every minute. 1 ℃ minute, 2850 ℃ constant temperature for 1 hour.

Characteristic evaluation

A laser flash thermal diffusion analyzer (Netzsch LFA 467) was used to analyze the thermal diffusivity of the graphite film after calendering. The test was performed in in-plane mode with a voltage of 260V and a pulse width of 0.050ms.

Thermal diffusion evaluation: A: more than 800 mm ² /sec; B: less than 800 mm ² /sec.

Appearance evaluation

Adhesion, discoloration, bumps, etc. are evaluated visually

Adhesion evaluation: the number of adhesion per square meter. A: less than 3 points; B: between 3 to 5 points; C: more than 5 points of sticking point.

Heterochromic evaluation: the edge heterochromatic distance per square meter is average. A: less than 5mm; B: between 5~10mm; C: greater than 10mm.

Convex rating: the number of bumps per square meter. A: less than 3 points; B: between 3 and 5 points; C: more than 5 points.

Example 2

The steps of Example 1 were repeated, but the organic particles were changed to polyethylene, and the median diameter (D50) of the particle size distribution was 9.0 μm, and the maximum diameter (Dmax) was 22 μm.

Example 3

The steps of Example 1 were repeated, but the organic particles were changed to polyimide, the median diameter (D50) of the particle size distribution was 9.0 μm, and the maximum diameter (Dmax) was 20 μm.

Example 4

The steps of Example 1 were repeated, but the organic particles were changed to lanolin wax, the median diameter (D50) of the particle size distribution was 3.7 μm, and the maximum particle diameter (Dmax) was 12 μm.

Example 5

The steps of Example 3 were repeated, except that the median diameter (D50) of the particle size distribution of the organic particulate polyimide was 6.0 μm and the maximum diameter (Dmax) was 17 μm.

Example 6

The steps of Example 3 were repeated, except that the median diameter (D50) of the particle size distribution of the organic particulate polyimide was 11.0 μm and the maximum diameter (Dmax) was 26 μm.

Example 7

Repeat the steps of Example 5, but the addition amount of the organic particulate polyimide is 0.05wt% (0.019Kg) of the total solid weight.

Example 8

Repeat the steps of Example 5, but the addition amount of the organic particulate polyimide is 0.4wt% (0.154Kg) of the total solid weight.

Example 9

Repeat the steps of Example 5, but the addition amount of the organic particulate polyimide is 1wt% (0.385Kg) of the total solid weight.

Example 10

Repeat the steps of Example 5, but the addition amount of the organic particulate polyimide is 2wt% (0.77Kg) of the total solid weight.

Example 11

Repeat the steps of Example 8, but the thickness is 38 microns.

Example 12

Repeat the steps of Example 8, except that the thickness is 125 microns.

Example 13

Repeat the steps of Example 8, except that the addition amount of the inorganic particulate calcium hydrogen phosphate is 0.5wt% (0.193Kg) of the total solid weight.

Comparative example 1

Repeat the steps of Example 1, but did not add any organic particles.

Comparative example 2

Repeat the steps of Comparative Example 1, but the particle size distribution of the inorganic particles of calcium hydrogen phosphate is D50: 1.2 microns, Dmax: 11 microns.

Comparative example 3

Repeat the steps of Comparative Example 1, except that the addition amount of the inorganic particulate calcium hydrogen phosphate is 1.0wt% (0.77Kg) of the total solid weight.

Comparative example 4

Repeat the steps of Comparative Example 2, except that the addition amount of the inorganic particulate calcium hydrogen phosphate is 1.0wt% (0.77Kg) of the total solid weight.

Comparative example 5

Repeat the steps of Example 3, except that the particle size of the organic particulate polyimide is D50: 0.8 μm and Dmax: 10 μm.

The relevant parameters and results in Examples 1 to 18 and Comparative Examples 1 to 5 are compiled in a list.

[00100] Comparing Examples 1 to 4 with Comparative Examples 1 to 4, if only inorganic particles are added, even if the addition amount and particle size are increased, the surface characteristics of the graphite film Vvc will be limited, but the thermal diffusion will decrease and bumps will be caused. . When organic particles are added, the organic particles have different effects on the surface of the polyimide film due to different types and particle size distributions, but all of them can significantly increase the Vvc, so that the appearance evaluation of graphitization is upgraded to A, and the heat is maintained. The performance of diffusion.

[00101] Comparing Example 3, Example 5, Example 6 and Comparative Example 5, increasing the particle size of organic particles can increase Vvc; Comparative Example 5 has a smaller particle size, which has a limited effect on improving Vvc.

[00102] Comparing Example 5 and Examples 7 to 10, it is shown that increasing the amount of organic particles can increase the Vvc, and the characteristics and appearance evaluation are both A.

[00103] Comparing Example 8, Examples 11 and 12, the method of the present invention has no significant effect on Vvc by changing the thickness, and the characteristics and appearance evaluation are both A. .

[00104] The property evaluation and appearance evaluation of Examples 1-13 (with organic particles added) are both A, and each evaluation is better than Comparative Examples 1 to 4 (only inorganic particles are added).

[00105] The content of the above specific embodiments is to describe the present invention in detail. However, these embodiments are for illustration only and are not intended to limit the present invention. Those skilled in the art can understand that various changes or modifications made to the present invention without departing from the scope defined by the appended patent application fall into a part of the present invention.

12‧‧‧Graphite film

Claims (4)

A polyimide film for graphitization, which includes: Polyimide polymer formed by polymerization of diamine and dianhydride monomers; An inorganic particle whose weight accounts for less than 0.50wt% of the total weight of the film; An organic particle whose weight accounts for more than 0.05wt% of the total weight of the film, and the median particle size (D50) of the organic particle is 1-20 microns, and the maximum particle size (Dmax) is less than 30 microns; and The core void volume (Vvc) of the polyimide film is higher than 0.040 cubic micrometer/square micrometer (μm ³ /μm ² ). The polyimide film used for graphitization as described in item 1 of the scope of patent application, wherein the inorganic particles can be calcium dihydrogen phosphate, calcium hydrogen phosphate and calcium phosphate. The polyimide film used for graphitization as described in item 1 of the scope of patent application, wherein the organic particles can be acrylic, polyamide, polyethylene, polypropylene, polyimide, palm wax, synthetic Wax and lanolin wax. The polyimide film used for graphitization as described in item 1 of the scope of patent application, the diamine monomer of the film is 4,4'-oxydianiline (4,4'-oxydianiline(4, 4'-ODA)) and phenylenediamine (p-PDA), and a small amount of one or more other diamines can be added without affecting the effect of the present invention; the preferred dianhydride monomer is Pyromellitic dianhydride (PMDA) and 3,3',4,4'-Biphenyltetracarboxylic dianhydride (BPDA), and A small amount of one or more other dianhydrides can be added without affecting the effect of the present invention.

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