阅读说明：本技术 一种氧化石墨烯膜及其制备方法 (Graphene oxide film and preparation method thereof ) 是由 卢静 周步存 周仁杰 李峰 于 2019-08-22 设计创作，主要内容包括：本发明提供一种石墨烯导热膜及其制备方法。本发明主要采用的方法是,将氧化石墨烯在高压剪切、高速撞击和强烈的空穴作用下超微细化,减小氧化石墨烯的片径,从而降低氧化石墨烯浆料的粘度,提升氧化石墨烯浆料的固含量,使氧化石墨烯浆料涂布成氧化石墨烯膜的效率提高。(The invention provides a graphene heat-conducting film and a preparation method thereof. The method mainly adopted by the invention is characterized in that the graphene oxide is micronized under the actions of high-pressure shearing, high-speed impact and strong cavitation, and the sheet diameter of the graphene oxide is reduced, so that the viscosity of the graphene oxide slurry is reduced, the solid content of the graphene oxide slurry is improved, and the efficiency of coating the graphene oxide slurry into the graphene oxide film is improved.)

1. A preparation method of a graphene heat-conducting film is characterized in that,

mixing, dispersing and ultra-fining graphene oxide and a solvent to reduce the average sheet diameter of the graphene oxide and obtain low-viscosity graphene oxide slurry;

defoaming the low-viscosity graphene oxide slurry, coating the defoamed graphene oxide slurry on the surface of a substrate, drying and stripping to obtain a graphene oxide film;

carrying out heat treatment and calendering on the graphene oxide film to obtain a graphene heat-conducting film;

the method for ultra-micronization comprises the steps of applying pressure to a mixture of graphene oxide and a solvent, allowing the mixture to pass through a slit, subjecting the mixture to high-pressure shearing and high-speed impact during the passage through the slit, and generating strong cavitation due to instantaneous release of pressure energy after the mixture passes through the slit, wherein the applied pressure in the ultra-micronization is 50-250 MPa.

2. The method for producing a graphene thermal conductive film according to claim 1, wherein the pressure applied in the ultra-fining is 100 MPa;

preferably, micronizing to obtain graphene oxide with average sheet diameter of 2-3 μm;

preferably, the viscosity of the graphene oxide slurry before ultra-micronization is 100000-200000 mPa-s;

preferably, the viscosity of the graphene oxide slurry after ultra-micronization is 10000-50000mPa & s; more preferably, the viscosity of the graphene oxide slurry after ultra-micronization is 20000mPa · s.

3. The method for preparing the graphene thermal conductive film according to claim 1, wherein the solid content of the graphene oxide slurry is 5-10%; preferably, the solid content of the graphene oxide slurry is 8%;

preferably, the graphene oxide is prepared by a Hummers method;

preferably, in the graphene oxide, the molar ratio of oxygen to carbon is 0.6-0.7; further preferably, in the graphene oxide, the molar ratio of oxygen to carbon is 0.65;

preferably, the solvent is water.

4. The method for preparing a graphene thermal conductive film according to claim 1, wherein the linear velocity of the dispersion is 2 to 20 m/s; preferably, the linear velocity of the dispersion is 5 m/s;

preferably, the dispersing time is 1-5 h; further preferably, the time of dispersion is 2 h;

preferably, the defoaming is vacuum defoaming, and the vacuum value of the vacuum defoaming is-95 to-50 kPa; further preferably, the vacuum value of the vacuum defoamation is-80 kPa;

preferably, the defoaming adopts an online continuous defoaming machine.

5. The preparation method of the graphene thermal conductive film according to claim 1, wherein the coating is performed by blade coating or extrusion coating, and the coating speed is 1-10 m/min; preferably, the speed of the coating is 3 m/min;

preferably, the thickness of the coating is 0.5-5.0 mm; further preferably, the thickness of the coating is 1.5 mm;

preferably, the temperature of the drying is 70-130 ℃; further preferably, the temperature of the drying is 100 ℃;

preferably, the drying time is 8-80 min; further preferably, the drying time is 27-30 min.

6. The method according to claim 1, wherein the graphene oxide film has a thickness of 50 to 500 μm; further preferably, the graphene oxide film has a thickness of 200 μm.

7. The method for preparing the graphene thermal conductive film according to claim 1, wherein the temperature of the thermal treatment is 1000-3000 ℃; preferably, the temperature of the heat treatment is 2000 ℃;

preferably, the graphene oxide film has a density of 0.1 to 1.0g/cm after heat treatment³(ii) a Further preferably, the density of the graphene oxide film after heat treatment is preferably 0.3g/cm³。

8. The method for preparing the graphene thermal conductive film according to claim 1, wherein the calendering pressure is 50-200 t; further preferably, the pressure of the calendering is 100 t.

9. A graphene thermal conductive film prepared by the method of any one of claims 1 to 6.

10. The graphene thermal conductive film according to claim 9, wherein the thermal conductivity of the graphene thermal conductive film is 1000-1600W/m-K;

preferably, the thermal conductivity of the graphene thermal conductive film is 1500W/m.K;

preferably, the density of the graphene heat conduction film is 1.5-2.2g/cm³(ii) a Further preferably, the density of the graphene heat conduction film is 2.0g/cm³；

Preferably, the thickness of the graphene heat conduction film is 10-150 μm; further preferably, the thickness of the graphene thermal conductive film is 40 μm.

Technical Field

The invention relates to the field of graphene materials, in particular to a process for improving the preparation efficiency of a graphene heat-conducting film prepared by a thermal reduction method.

Background

Since the discovery in 2004, graphene has been widely researched and applied in the fields of sensing devices, photoelectricity, and energy materials due to its ultra-large specific surface area, high conductivity, excellent chemical stability and thermodynamic stability, and physical properties and mechanical properties.

In the prior art, the main method for preparing the graphene heat-conducting film with good heat-conducting property is as follows: firstly, dispersing a graphene oxide filter cake prepared by a Hummers method into slurry, coating the slurry on a substrate, drying to prepare a graphene oxide film, and then carrying out high-temperature thermal reduction on the graphene oxide film to obtain the graphene heat-conducting film.

However, due to the high viscosity of the graphene oxide slurry, the solid content of the graphene oxide slurry can reach 2.0-4.0% at most. The solid content is limited to be low, so that the coating efficiency of the graphene oxide slurry is low, and the large-scale production is greatly limited.

The statements in the background section are merely prior art as they are known to the inventors and do not, of course, represent prior art in the field.

Disclosure of Invention

Aiming at one or more problems in the prior art, the technical problem to be solved by the invention is to improve the coating efficiency of the graphene oxide slurry, and the method mainly adopts the steps of carrying out ultra-fine thinning on the graphene oxide through high-pressure shearing, high-speed impact and strong cavitation, reducing the sheet diameter of the graphene oxide, reducing the viscosity of the graphene oxide slurry, and improving the solid content of the graphene oxide slurry, so that the coating efficiency of the graphene oxide slurry is improved.

The invention provides a graphene oxide slurry with low viscosity, wherein the solid content of the graphene oxide slurry is 5-10%, and 8% is preferred.

According to an aspect of the present invention, the viscosity of the graphene oxide slurry is 10000-.

The coating is not facilitated due to over-high and over-low viscosity, and the graphene oxide slurry is not facilitated due to the viscosity higher than 50000mPa & s; the viscosity is less than 10000mPa · s, and the fluidity of the graphene oxide slurry is too high, which is not beneficial to controlling the coating thickness.

Preferably, the low-viscosity graphene oxide slurry is graphene oxide micro-sheets, and the average sheet diameter is 2-3 μm.

The invention also provides a preparation method of the graphene oxide slurry with low viscosity, which is characterized in that graphene oxide and a solvent are mixed, dispersed and subjected to ultra-fine refinement to reduce the average sheet diameter of the graphene oxide and obtain the graphene oxide slurry with low viscosity.

The graphene oxide contains very rich oxygen-containing functional groups, and during the oxidation process, the edges and the middle of the sheets generate 'defects' due to the presence of the functional groups, and the defects are easily broken under the action of high-pressure viscosity reduction equipment (a cavity effect and an impact effect shearing effect), so that the sheet diameter of the graphene oxide can be reduced to 2-3 μm from 17-18 μm on average. And the oxygen-containing functional group of the graphene oxide has a hydrophilic effect, so that the graphene oxide can be dispersed in water. Under a certain range of oxidation degree, the smaller the sheet diameter of the graphene oxide, the smaller the internal friction force, and correspondingly, the macroscopically reduced viscosity appears, so that the solid content of the graphene oxide slurry can be improved, and the coating efficiency of the graphene oxide slurry on the substrate can be improved.

According to one aspect of the present invention, the graphene oxide is prepared by Hummers method.

Preferably, the graphene oxide has a molar ratio of oxygen to carbon of 0.6 to 0.7, preferably 0.65.

Preferably, the solvent is water.

Preferably, the linear velocity of the dispersion is 2 to 20m/s, preferably 5 m/s.

Further preferably, the time of dispersion is 1 to 5h, preferably 2 h.

During dispersion, the graphene oxide sheets are opened in water and uniformly dispersed.

According to an aspect of the present invention, a method of ultra-micronization comprises applying pressure to a mixture of graphene oxide and a solvent, passing the mixture through a slit, subjecting the mixture to high-pressure shear and high-speed impact during the passage through the slit, and generating strong cavitation due to instantaneous release of pressure energy after the passage through the slit.

Preferably, the pressure applied is from 50 to 250MPa, preferably 100 MPa.

Preferably, the graphene oxide is ultra-finely divided so that the average sheet diameter of the graphene oxide is 2 to 3 μm.

The ultra-fining is to make liquid material flow through narrow gap at high speed under the action of high pressure to produce strong cavity effect similar to explosion effect in the narrow area, and to make the liquid material break through the fining effect of the slit and the high speed impact effect of the impact inside the cavity, so as to obtain ultra-fining for liquid matter or solid particle with liquid as carrier and fine graphene oxide sheet. The pressure exerted on the mixture of the graphene oxide and the solvent by ultra-micronization is set to be 50-250MPa, the sheet diameter of the graphene oxide can be thinned to 2-3 μm from 17-18 μm on average, if the pressure is too small and is less than 50MPa, the micronization effect is insufficient, and the sheet diameter of the graphene oxide cannot reach 2-3 μm, so that the viscosity reduction effect cannot be achieved; if the pressure is more than 250MPa, the machine is easily damaged, and the higher the damage frequency is, the higher the manufacturing cost is.

According to an aspect of the present invention, the viscosity of the graphene oxide slurry before ultra-micronization is 100000-200000 mPa-s.

Preferably, the viscosity of the graphene oxide slurry after ultra-micronization is 10000-50000 mPas, preferably 20000 mPas.

Further preferably, the solid content of the graphene oxide slurry is 5-10%, preferably 8%.

The invention also provides a graphene oxide film, wherein the average sheet diameter of graphene oxide in the graphene oxide film is 2-3 mu m.

According to one aspect of the invention, the graphene oxide film has a thickness of 50 to 500 μm, preferably 200 μm.

Preferably, the graphene oxide film has a density of 1.0-2.0g/cm³。

The invention also provides a preparation method of the graphene oxide film, the graphene oxide slurry with low viscosity is prepared by adopting the preparation method of the graphene oxide slurry with low viscosity, and is coated on the surface of a substrate after defoaming treatment, and the graphene oxide film is obtained after drying and stripping.

The substrate is a carrier coated and dried by graphene oxide slurry, and a graphene oxide film is formed on the surface of the substrate after the graphene oxide slurry is coated and dried.

According to one aspect of the invention, the degassing is vacuum degassing having a vacuum value of-95 to-50 kPa, preferably-80 kPa.

Preferably, the defoaming adopts an online continuous defoaming machine.

According to one aspect of the invention, the coating is blade coating or extrusion coating, the coating rate being 1-10m/min, preferably 3 m/min.

Preferably, the thickness of the coating is 0.5-5.0mm, preferably 1.5 mm.

According to one aspect of the invention, the temperature of the drying is 70 to 130 ℃, preferably 100 ℃.

Preferably, the drying time is 8-80min, preferably 27-30 min.

Preferably, the graphene oxide film has a thickness of 50 to 500 μm, preferably 200 μm.

Due to the fact that the solid content of the graphene oxide slurry is improved, the coating thickness is reduced, the coating speed is improved, and the coating efficiency in unit time is improved. The drying time is adjusted according to the length of the drying oven of the coating machine and the coating speed, and the drying time is shortened due to the increase of the coating speed, so that the preparation efficiency of the graphene oxide film is greatly improved.

The invention also provides a graphene heat-conducting film, wherein the heat-conducting coefficient of the graphene heat-conducting film is 1000-1600W/m.k, and is preferably 1500W/m.k.

Preferably, the density of the graphene heat conduction film is 1.5-2.2g/cm³Preferably 2.0g/cm³。

Preferably, the thickness of the graphene thermal conductive film is 10-150 μm, preferably 40 μm.

The invention also provides a preparation method of the graphene heat-conducting film, the graphene oxide film is prepared by the preparation method of the graphene oxide film, and the graphene heat-conducting film is obtained through heat treatment and calendering.

Preferably, the temperature of the heat treatment is 1000-3000 ℃, preferably 2000 ℃.

Preferably, the graphene oxide film has a density of 0.1 to 1.0g/cm after heat treatment³Preferably 0.3g/cm³。

Further preferably, the calendering pressure is between 50 and 200t, preferably 100 t.

The invention has the beneficial effects that:

according to the invention, the graphene oxide micro-sheets are refined, so that the sheet diameter of the graphene oxide is reduced to 2-3 μm from 17-18 μm on average, the viscosity of the graphene oxide slurry is reduced, and the solid content of the slurry is increased to 5-10%. The advantages of the present invention are illustrated by the following points:

(1) due to the fact that the solid content of the graphene oxide slurry is increased, the coating thickness is reduced, the coating speed is increased, the coating efficiency is increased to be more than 300%, and the unit productivity is greatly improved.

(2) Because the thickness of the coating is thin, the drying can be carried out at a higher temperature without bubbling the graphene oxide film; in addition, the water content of the graphene oxide slurry is reduced, so that the graphene oxide film can remove water molecules more easily, the drying time is shortened, and the efficiency of preparing the graphene oxide film is improved.

(3) Due to the fact that the efficiency of preparing the graphene oxide film is improved, the preparation cost is greatly reduced, and the method is suitable for industrial large-scale production.

(4) Compared with the prior art, the graphene heat-conducting film prepared by the invention has normal performance tests of appearance, thickness, density, heat conductivity coefficient, cohesion and the like.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is a schematic representation of AFM before graphene oxide sheet diameter reduction;

FIG. 2 is a schematic representation of AFM after graphene oxide sheet diameter reduction;

FIG. 3 is an AFM particle size distribution diagram before viscosity reduction of graphene oxide, wherein the abscissa represents the size of graphene oxide sheet diameter (μm) and the ordinate represents frequency (counts);

FIG. 4 is an AFM particle size distribution diagram after graphene oxide viscosity reduction, wherein the abscissa represents the size (mum) of graphene oxide sheet diameter and the ordinate represents frequency (counts);

FIG. 5 is a step diagram of a sixth embodiment of the present invention;

fig. 6 is a pictorial view of a graphene oxide film of example 1;

fig. 7 is a physical diagram of the graphene thermal conductive film of example 1;

fig. 8 is a pictorial view of a graphene oxide film of example 2;

fig. 9 is a pictorial view of a graphene oxide film of example 3;

fig. 10 is a pictorial representation of a graphene oxide membrane of comparative example 5;

fig. 11 is a physical diagram of the graphene thermal conductive film of comparative example 5;

fig. 12 is a physical representation of a graphene oxide film that yields blistering when a 6.0mm thick graphene oxide film is dried at 100 ℃.

Detailed Description

In the following, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.

As a first embodiment of the present invention, a graphene oxide slurry with low viscosity is presented, the solid content of the graphene oxide slurry is 5-10%, for example: 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, etc. As a preferred embodiment, the graphene oxide slurry has a solid content of 8%. The viscosity of the graphene oxide slurry is 10000-: 10000 mPas, 11000 mPas, 12000 mPas, 15000 mPas, 20000 mPas, 22000 mPas, 23000 mPas, 25000 mPas, 30000 mPas, 32000 mPas, 35000 mPas, 40000 mPas, 42000 mPas, 45000 mPas, 48000 mPas, 50000 mPas, etc. In a preferred embodiment, the viscosity of the graphene oxide slurry is 20000mPa · s. The viscosity is not favorable for coating when being too high or too low, and is not favorable for graphene oxide slurry to flow out when being higher than 50000mPa & s; the viscosity is less than 10000mPa · s, and the fluidity of the graphene oxide slurry is too high, which is not beneficial to controlling the coating thickness. Graphene oxide is graphene oxide nanoplatelets with an average platelet size of 2-3 μm, for example: 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, etc.

As a second embodiment of the present invention, a method for preparing a graphene oxide slurry having a low viscosity is disclosed, in which graphene oxide is mixed with a solvent, dispersed, and ultra-finely divided to reduce the average sheet diameter of the graphene oxide, thereby obtaining a graphene oxide slurry having a low viscosity.

The graphene oxide contains very rich oxygen-containing functional groups, and during the oxidation process, the edges and the middle of the sheets generate 'defects' due to the presence of the functional groups, and the defects are easily broken under the action of high-pressure viscosity reduction equipment (a cavity effect and an impact effect), so that the sheet diameter of the graphene oxide is reduced to 2-3 μm from 17-18 μm on average. And the oxygen-containing functional group of the graphene oxide has a hydrophilic effect, so that the graphene oxide can be dispersed in water. Under a certain range of oxidation degree, the smaller the sheet diameter of the graphene oxide, the smaller the internal friction force, and correspondingly, the macroscopically reduced viscosity appears, so that the solid content of the graphene oxide slurry can be improved, and the coating efficiency of the graphene oxide slurry on the substrate can be improved.

The graphene oxide is prepared by a Hummers method. In the graphene oxide, the molar ratio of oxygen to carbon is 0.6 to 0.7, for example: 0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, etc. In a preferred embodiment, the graphene oxide has a molar ratio of oxygen to carbon of 0.65. The solvent is water. The linear velocity of the dispersion is from 2 to 20m/s, for example: 2m/s, 3m/s, 4m/s, 5m/s, 6m/s, 7m/s, 8m/s, 9m/s, 10m/s, 11m/s, 12m/s, 13m/s, 14m/s, 15m/s, 16m/s, 17m/s, 18m/s, 19m/s, 20m/s, and the like. In a preferred embodiment, the linear velocity of dispersion is 5 m/s.

The dispersion time is 1-5h, for example: 1h, 1.2h, 1.5h, 1.8h, 2h, 2.2h, 2.5h, 2.8h, 3h, 3.2h, 3.5h, 3.8h, 4h, 4.2h, 4.5h, 4.8h, 5h, and the like. In a preferred embodiment, the time for dispersion is 2 hours. The method of ultra-micronization includes applying pressure to a mixture of graphene oxide and a solvent, passing the mixture through a slit, subjecting the mixture to high-pressure shear and high-speed impact during the passage through the slit, and generating strong cavitation due to sudden release of pressure energy after passing through the slit. The pressure applied is 50-250MPa, for example: 50MPa, 51MPa, 52MPa, 53MPa, 54MPa, 55MPa, 56MPa, 57MPa, 58MPa, 59MPa, 60MPa, 70MPa, 80MPa, 90MPa, 100MPa, 110MPa, 120MPa, 130MPa, 140MPa, 150MPa, 160MPa, 170MPa, 180MPa, 190MPa, 200MPa, 210MPa, 220MPa, 230MPa, 240MPa, 245MPa, 246MPa, 247MPa, 248MPa, 249MPa, 250MPa, etc. In a preferred embodiment, the pressure for ultrafinely shattering organic granular substances is 100 MPa. Ultra-fine to an average sheet diameter of 2 to 3 μm of graphene oxide, for example: 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, etc. As can be seen from fig. 1, the sheet diameter of graphene oxide is larger than that of a 50 μm scale bar, and the sheet diameter of some graphene oxides can reach 25 μm, and the bar scale on the right side indicates the height of the graphene oxide. As can be seen in fig. 2, the sheet diameter of the graphene oxide is small compared to the 20 μm scale bar, and is substantially less than 3 μm, and the bar scale on the right side indicates the height of the graphene oxide. As shown in fig. 3 and 4, the sheet diameters of the graphene oxide before viscosity reduction are concentrated in a range of 15-25 μm, the average value of the sheet diameters is 18.236 μm, and the standard deviation is 1.012; the sheet diameters of the viscosity-reduced graphene oxide are concentrated in a range of 1.6-4 microns, the average value of the sheet diameters is 2.495 microns, the standard deviation is 0.936, the sheet diameters of the viscosity-reduced graphene oxide are reduced, and the sheet diameter distribution is more even.

The ultra-fining is to make liquid material flow through narrow gap at high speed under the action of high pressure to produce strong cavity effect similar to explosion effect in the narrow area, and to make the liquid material break through the fining effect of the slit and the high speed impact effect of the impact inside the cavity, so as to obtain ultra-fining for liquid matter or solid particle with liquid as carrier and fine graphene oxide sheet. The pressure exerted on the mixture of the graphene oxide and the solvent by ultra-micronization is set to be 50-250MPa, the sheet diameter of the graphene oxide can be thinned to 2-3 μm from 17-18 μm on average, if the pressure is too small and is less than 50MPa, the micronization effect is insufficient, and the sheet diameter of the graphene oxide cannot reach 2-3 μm, so that the viscosity reduction effect cannot be achieved; if the pressure is more than 250MPa, the machine is easily damaged, and the higher the damage frequency is, the higher the manufacturing cost is.

The viscosity of the graphene oxide slurry before ultra-micronization is 100000-200000mPa · s, for example: 100000 mPas, 105000 mPas, 110000 mPas, 115000 mPas, 120000 mPas, 125000 mPas, 130000 mPas, 135000 mPas, 140000 mPas, 145000 mPas, 150000 mPas, 160000 mPas, 170000 mPas, 180000 mPas, 190000 mPas, 195000 mPas, 200000 mPas, and the like. The viscosity of the graphene oxide slurry after ultra-micronization is 10000-50000 mPas, for example: 10000 mPas, 11000 mPas, 12000 mPas, 15000 mPas, 20000 mPas, 22000 mPas, 23000 mPas, 25000 mPas, 30000 mPas, 32000 mPas, 35000 mPas, 40000 mPas, 42000 mPas, 45000 mPas, 48000 mPas, 50000 mPas, etc. In a preferred embodiment, the viscosity of the graphene oxide slurry after ultra-micronization is 20000mPa · s. The solid content of the graphene oxide slurry is 5-10%, for example: 5%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 9.6%, 9.7%, 9.8%, 9.9%, 10%, etc. As a preferred embodiment, the graphene oxide slurry has a solid content of 8%.

As a third embodiment of the present invention, a graphene oxide film is shownThe average sheet diameter of the graphene oxide in the graphene oxide film is 2 to 3 μm, for example: 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, etc. The thickness of the graphene oxide film is 100-500 μm, for example: 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, 220 μm, 250 μm, 280 μm, 300 μm, 320 μm, 350 μm, 380 μm, 400 μm, 420 μm, 450 μm, 480 μm, 500 μm, and the like. In a preferred embodiment, the graphene oxide film has a thickness of 200 μm. The density of the graphene oxide film is 1.0-2.0g/cm³For example: 1.0g/cm³、1.1g/cm³、1.2g/cm³、1.3g/cm³、1.4g/cm³、1.5g/cm³、1.6g/cm³、1.7g/cm³、1.8g/cm³、1.9g/cm³、2.0g/cm³And so on.

In a fourth embodiment of the present invention, a method for preparing a graphene oxide film is shown, in which a graphene oxide slurry with low viscosity is prepared by the method of the second embodiment of the present invention, and after a defoaming treatment, the defoamed graphene oxide slurry is applied to a substrate surface, and then dried and peeled off to obtain the graphene oxide film.

The substrate is a carrier coated and dried by graphene oxide slurry, and a graphene oxide film is formed on the surface of the substrate after the graphene oxide slurry is coated and dried.

The deaeration is carried out in vacuum, and the vacuum value of the vacuum deaeration is-95 to-50 kPa, for example: -95kPa, 90kPa, -85kPa, -80kPa, -75kPa, -70kPa, -65kPa, -60kPa, -55kPa, -50kPa, etc. In a preferred embodiment, the vacuum value for vacuum degassing is-80 kPa. The defoaming adopts an online continuous defoaming machine. The coating is carried out by means of blade coating or extrusion coating, and the coating speed is 1-10m/min, for example: 1m/min, 1.1m/min, 1.2m/min, 1.3m/min, 1.4m/min, 1.5m/min, 2m/min, 2.5m/min, 3m/min, 3.5m/min, 4m/min, 4.5m/min, 5m/min, 5.5m/min, 6m/min, 6.5m/min, 7m/min, 7.5m/min, 8m/min, 8.5m/min, 9m/min, 9.5m/min, 9.6m/min, 9.7m/min, 9.8m/min, 9.9m/min, 10m/min, and the like. As a preferred embodiment, the coating rate is 3 m/min. The thickness of the coating is 0.5-5.0mm, for example: 0.5mm, 0.52mm, 0.55mm, 0.58mm, 0.6mm, 0.62mm, 0.65mm, 0.68mm, 0.7mm, 0.75mm, 0.76mm, 0.77mm, 0.78mm, 0.79mm, 0.8mm, 0.9mm, 1mm, 1.2mm, 1.3mm, 1.5mm, 1.6mm, 1.8mm, 2mm, 2.1mm, 2.2mm, 2.5mm, 2.6mm, 2.7mm, 2.8mm, 2.9mm, 2.93mm, 2.95mm, 2.97mm, 2.98mm, 2.99mm, 3.0mm, 3.5mm, 4mm, 4.2mm, 4.5mm, 4.8mm, 5mm, etc. In a preferred embodiment, the thickness of the coating is 1.5 mm. Due to the fact that the solid content of the graphene oxide slurry is improved, the coating thickness is reduced, the coating speed is improved, and the coating efficiency in unit time is improved. The temperature of drying is 70-130 ℃, for example: 70 ℃, 71 ℃, 72 ℃, 73 ℃, 75 ℃, 78 ℃, 80 ℃, 82 ℃, 85 ℃, 88 ℃, 90 ℃, 92 ℃, 95 ℃, 98 ℃, 100 ℃, 102 ℃, 105 ℃, 108 ℃, 110 ℃, 112 ℃, 115 ℃, 118 ℃, 120 ℃, 122 ℃, 125 ℃, 126 ℃, 127 ℃, 128 ℃, 129 ℃, 130 ℃, and the like. In a preferred embodiment, the drying temperature is 100 ℃. The drying time is 8-80min, for example: 8min, 9min, 10min, 12min, 15min, 16min, 18min, 20min, 22min, 24min, 25min, 27min, 28min, 29min, 30min, 32min, 34min, 35min, 38min, 40min, 45min, 50min, 55min, 60min, 65min, 70min, 75min, 78min, 80min, and the like. As a preferred embodiment, the drying time is 27-30min, for example: 27min, 28min, 29min, 30min, etc. The graphene oxide film has a thickness of 50 to 500 μm, for example: 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 150 μm, 180 μm, 200 μm, 220 μm, 250 μm, 280 μm, 300 μm, 320 μm, 350 μm, 380 μm, 400 μm, 420 μm, 450 μm, 480 μm, 490 μm, 500 μm, and the like. In a preferred embodiment, the graphene oxide film has a thickness of 200 μm.

As a fifth embodiment of the present invention, a graphene thermal conductive film is shown, wherein the thermal conductivity of the graphene thermal conductive film is 1000-: 1000W/m.k, 1100W/m.k, 1200W/m.k, 1300W/m.k, 1400W/m.k, 1500W/m.k, 1600W/m.k, etc. In a preferred embodiment, the graphene thermal conductive film has a thermal conductivity of 1500W/m · k. The density of the graphene heat-conducting film is 1.5-2.2g/cm³Example ofSuch as: 1.5g/cm³、1.6g/cm³、1.7g/cm³、1.8g/cm³、1.9g/cm³、2.0g/m³、2.1g/cm³、2.2g/cm³、2.2g/cm³And so on. In a preferred embodiment, the graphene thermal conductive film has a density of 2.0g/m³. The thickness of the graphene heat conduction film is 10-150 μm, for example: 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, and the like. In a preferred embodiment, the graphene thermal conductive film has a thickness of 40 μm.

As a sixth embodiment of the present invention, a method for preparing a graphene thermal conductive film is presented, wherein a graphene oxide film is prepared by the method of the fourth embodiment of the present invention, and is subjected to heat treatment and rolling to obtain the graphene thermal conductive film. The specific preparation process is shown in fig. 5, firstly, mixing the graphene oxide filter cake prepared by the Hummers method with a solvent, and stirring and dispersing to obtain graphene oxide slurry; then carrying out ultra-fine thinning viscosity reduction on the graphene oxide slurry to obtain low-viscosity graphene oxide slurry; then defoaming the graphene oxide slurry with low viscosity, coating the graphene oxide slurry on a substrate, drying and stripping to obtain a graphene oxide film; carrying out heat treatment on the graphene oxide film to obtain a graphene foam film; and finally, carrying out calendaring treatment on the graphene foam film to obtain the graphene heat-conducting film. The solid content of the graphene oxide slurry is 5-10%, and the coating efficiency is improved. The appearance, density, heat conductivity coefficient, cohesion, tensile strength and the like of the graphene heat-conducting film are equivalent to those of graphene heat-conducting films prepared from graphene oxide slurry which is not subjected to viscosity reduction treatment and has a solid content of 2-4%, but the preparation efficiency is higher.

The temperature of the heat treatment is 1000-3000 ℃, for example: 1000 ℃, 1100 ℃, 1200 ℃, 1300 ℃, 1400 ℃, 1500 ℃, 1600 ℃, 1700 ℃, 1800 ℃, 1900 ℃, 2000 ℃, 2100 ℃, 2200 ℃, 2300 ℃, 2400 ℃, 2500 ℃, 2600 ℃, 2700 ℃, 2800 ℃, 2900 ℃, 3000 ℃, etc. In a preferred embodiment, the temperature of the heat treatment is 2000 ℃. The density of the graphene oxide film after heat treatment is 0.1-1.0g/cm³For example: 0.1g/cm³、0.2g/cm³、0.3g/cm³、0.4g/cm³、0.5g/cm³、0.6g/cm³、0.7g/cm³、0.8g/cm³、0.9g/cm³、1.0g/cm³And so on. In a preferred embodiment, the graphene oxide film has a density of 0.3g/cm after heat treatment³. The calendering pressure is 50 to 200t, for example: 50t, 60t, 70t, 80t, 90t, 100t, 110t, 120t, 130t, 140t, 150t, 160t, 170t, 180t, 190t, 200t, etc. In a preferred embodiment, the pressure for rolling is 100 t.

The advantages of the invention are further illustrated by the following examples and comparative examples:

example 1:

step 1): dispersing a graphene oxide filter cake with the solid content of 5.0% in deionized water by using dispersing equipment, wherein the linear velocity of the dispersion is 5m/s, and the viscosity of graphene oxide slurry obtained after the dispersion is carried out for 2 hours is 100000mPa & s;

step 2): carrying out ultramicro refinement on the graphene oxide slurry, wherein the pressure is 50MPa, and the viscosity of the obtained low-viscosity graphene oxide slurry is 20000mPa s;

step 3): defoaming the low-viscosity graphene oxide slurry obtained in the step 2) by using defoaming equipment, wherein the vacuum value is-80 kPa;

step 4): coating the slurry after defoaming in the step 3) on a PET film in a scraper coating mode, drying at 80 ℃ for 75min to obtain a graphene oxide film, directly stripping and rolling, wherein the coating thickness is 2.5mm, and the coating speed is 1.2 m/min;

step 5): cutting the graphene oxide film coiled material obtained by rolling in the step 4), and obtaining a graphene oxide film with the size of 300mm x 300mm as shown in fig. 6;

step 6): carrying out high-temperature heat treatment at 2000 ℃ on the graphene oxide film obtained in the step 5) to obtain the graphene oxide film with the density of 0.3g/cm³The graphene foam film of (1);

step 7): calendering the graphene foam film of step 6) using a pressure of 100t, as shown in FIG. 7, to give a density of 2.0g/cm³Graphene heat-conducting film with thickness of 40 mu m and heat conductivity coefficient of 1500W/m.K。

Example 2:

step 1): dispersing a graphene oxide filter cake with a solid content of 10.0% in deionized water by using dispersing equipment, wherein the linear velocity of the dispersion is 5m/s, and the viscosity of the graphene oxide slurry obtained after the dispersion is carried out for 2 hours is 200000mPa s;

step 2): carrying out ultra-fine refinement on the graphene oxide slurry, wherein the pressure is 100MPa, and the viscosity of the obtained low-viscosity graphene oxide slurry is 20000mPa s;

step 3): defoaming the low-viscosity graphene oxide slurry obtained in the step 2) by using defoaming equipment, wherein the vacuum value is-80 kPa;

step 4): coating the slurry after defoaming in the step 3) on a PET film in a scraper coating mode, drying at 120 ℃ for 11min to obtain a graphene oxide film, directly stripping and rolling, wherein the coating thickness is 0.75mm, and the coating speed is 8.0 m/min;

step 5): cutting the graphene oxide film coiled material obtained by rolling in the step 4), and obtaining a graphene oxide film with the size of 300mm x 300mm as shown in fig. 8;

step 6): carrying out high-temperature heat treatment at 2000 ℃ on the graphene oxide film obtained in the step 5) to obtain the graphene oxide film with the density of 0.3g/cm³The graphene foam film of (1);

step 7): calendering the graphene foam film obtained in the step 6) by using the pressure of 100t to obtain the density of 2.0g/cm³The graphene heat-conducting film is 20 mu m thick and 1500W/m.K in heat conductivity coefficient.

Example 3:

step 1): dispersing the graphene oxide filter cake with the solid content of 8.0% in deionized water by using dispersing equipment, wherein the linear velocity of the dispersion is 5m/s, and the viscosity of the graphene oxide slurry obtained after the dispersion is carried out for 2 hours is 150000mPa & s;

step 2): carrying out ultra-fine refinement on the graphene oxide slurry, wherein the pressure is 100MPa, and the viscosity of the obtained low-viscosity graphene oxide slurry is 20000mPa s;

step 3): defoaming the low-viscosity graphene oxide slurry obtained in the step 2) by using defoaming equipment, wherein the vacuum value is-80 kPa;

step 4): coating the slurry after defoaming in the step 3) on a PET film in a scraper coating mode, drying at 100 ℃ for 30min to obtain a graphene oxide film, directly stripping and rolling, wherein the coating thickness is 1.5mm, and the coating speed is 3 m/min;

step 5): cutting the graphene oxide film coiled material obtained by rolling in the step 4), and obtaining a graphene oxide film with the size of 300mm x 300mm as shown in fig. 9;

step 6): carrying out high-temperature heat treatment at 2000 ℃ on the graphene oxide film obtained in the step 5) to obtain the graphene oxide film with the density of 0.3g/cm³The graphene foam film of (1);

step 7): calendering the graphene foam film obtained in the step 6) by using the pressure of 100t to obtain the density of 2.0g/cm³The graphene heat-conducting film is 40 mu m thick and 1500W/m.K in heat conductivity coefficient.

Comparative example 4:

step 1): dispersing a graphene oxide filter cake with the solid content of 2.0% in deionized water by using dispersing equipment, wherein the linear velocity of the dispersion is 2m/s, and the viscosity of the graphene oxide slurry obtained after the dispersion is carried out for 2 hours is 20000mPa s;

step 2): carrying out vacuum defoaming on the graphene oxide slurry obtained in the step 1) by using defoaming equipment, wherein the vacuum value is-80 kPa;

step 3): coating the slurry after defoaming in the step 2) on a PET film in a scraper coating mode, drying at 70 ℃ for 5 hours to obtain a graphene oxide film, and directly stripping and rolling the graphene oxide film, wherein the coating thickness is 6.0mm, and the coating speed is 0.3 m/min;

step 4): cutting the graphene oxide film coiled material obtained by rolling in the step 3) to obtain a graphene oxide film with the size of 300mm x 300 mm;

step 5): carrying out high-temperature heat treatment at 2000 ℃ on the graphene oxide film obtained in the step 4) to obtain the graphene oxide film with the density of 0.3g/cm³The graphene foam film of (1);

step 6): calendering the graphene foam film obtained in the step 5) by using the pressure of 100t to obtain the density of 2.0g/cm³The graphene heat-conducting film is 40 mu m thick and 1500W/m.K in heat conductivity coefficient.

Comparative example 5:

step 1): dispersing the graphene oxide filter cake with the solid content of 8.0% in deionized water by using dispersing equipment, wherein the linear velocity of the dispersion is 5m/s, and the viscosity of the graphene oxide slurry obtained after the dispersion is carried out for 2 hours is 150000mPa & s;

step 2): defoaming the graphene oxide slurry obtained in the step 1) in vacuum by using defoaming equipment, wherein bubbles in the slurry cannot be completely removed by using the existing defoaming technology;

step 3): coating the slurry after the deaeration in the step 2) on a PET film by using a scraper coating mode, and drying at 100 ℃ to obtain a graphene oxide film which is directly peeled and rolled, wherein the coating thickness is 1.5mm, the coating speed is 3m/min, and as shown in figure 10, the appearance of the dried graphene oxide film has defects;

step 4): cutting the graphene oxide film coiled material obtained by rolling in the step 3) to obtain a graphene oxide film with the size of 300mm x 300 mm;

step 5): carrying out high-temperature heat treatment at 2000 ℃ on the graphene oxide film obtained in the step 4) to obtain the graphene oxide film with the density of 0.3g/cm³The graphene foam film of (1);

step 6): calendering the graphene foam film obtained in the step 5) by using the pressure of 100t to obtain the density of 2.0g/cm³The graphene thermal conductive film with a thickness of 40 μm and a thermal conductivity of 900W/m.K has defects in appearance as shown in FIG. 11.

The graphene oxide slurry with the solid content of 8% in the comparative example 5 has an excessively high viscosity without the ultra-fine refinement of the present invention, which may result in the following consequences:

(1) under the existing defoaming technology, bubbles in the graphene oxide slurry cannot be completely removed, and the bubbles can influence the appearance of the dried graphene oxide film, so that the defect of the graphene oxide film is caused; seriously, it is also possible that pipeline transportation cannot be accomplished due to poor fluidity of the graphene oxide slurry.

(2) Under the existing coating technology, the high viscosity can cause uneven coating thickness and uneven coating appearance, which affects the thickness uniformity and appearance of the graphene oxide film after coating and drying, and further affects the thickness uniformity and appearance of the graphene heat-conducting film, as shown in fig. 11; seriously, due to poor fluidity of the graphene oxide slurry, the graphene oxide slurry can block the pipeline when being coated.

(3) Due to the fact that viscosity of slurry obtained after dispersion is too high, graphene oxide cannot be uniformly dispersed in water, lamella cannot be fully opened, heat conducting performance of a final heat conducting film is affected, and heat conducting performance of a graphene heat conducting film with the thickness of 40 mu m is only 900W/m.K.

From examples 1 to 3, it can be seen that the viscosity of the graphene oxide slurry can be reduced and the solid content can be increased by using the ultra-micronization method of the present invention, so as to achieve the following effects:

(1) also, the graphene oxide slurry having a viscosity of 20000mPa · s, comparative example 4 can achieve only a solid content of 2%, but examples 1 to 3 of the present invention can achieve a solid content of 5 to 10%. The graphene oxide slurry in the embodiments 1 to 3 of the present invention has a high solid content, and can achieve the same thermal conductivity as the graphene thermal conductive film obtained by coating the graphene oxide slurry in the comparative example 4 with a thickness of 6mm by coating the graphene oxide slurry with a thickness of 0.75 to 2.5 mm.

(2) In examples 1 to 3, the solid content was high, the coating thickness was thin, the coating speed was increased, and the coating speed could reach 1.2 to 8m/min, resulting in an improvement in the coating efficiency. Comparative example 4, since the solid content of graphene oxide is low, a thickness of 6.0mm is required to be coated to achieve a good heat conduction effect, and at this thickness, if the drying temperature is too high, and reaches 100 ℃, water molecules in graphene oxide are difficult to escape, which may cause formation of cavities between graphene oxide film layers, resulting in formation of a graphene oxide film as shown in fig. 12, and thus, in order to ensure the appearance of the graphene oxide film, the drying temperature may be only reduced to 70 ℃. However, since the drying temperature is low and the thickness is thick, the graphene oxide film can be sufficiently dried only by reducing the coating rate and setting the coating rate to 0.3 m/min.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.