RU2724228C1 - Graphene based heater manufacturing method - Google Patents

Abstract

FIELD: nanotechnologies.SUBSTANCE: invention relates to nanotechnology and specifically to the use of novel materials, such as polymer-graphene composites, obtained by chemical vapor deposition (CVD). Method of producing graphene based heater containing transparent polymer substrate with graphene layer and metal electrodes includes annealing of copper catalyst substrate, synthesis of graphene on copper catalytic substrate by chemical vapor deposition (CVD) method, mechanical transfer of graphene layer onto transparent polymer substrate and connection of metal electrodes to graphene layer. Prior to annealing, copper catalytic substrate is washed successively in acetone, ethyl alcohol and distilled water under ultrasound and dried. Copper catalyst substrate is annealed for 30±1 min in the flow of Hat temperature of 1,070±3 °C. Synthesis of graphene is performed for 10±1 minute at temperature of 1,070±3 °C. gas mixture and quickly cooled in the same gas mixture. Graphene is transferred onto a transparent polymer substrate by hot lamination. Metal electrodes are connected to polymer-graphene composite by mechanical method and crimped. Obtained heaters have characteristics including resistance of 0.8–1 kOhm per square, integral transmittance in visible range of 85–90 %, surface power of infrared radiation of 100–150 W/dm, minimum bending radius of 1 cm and operating temperature range of 20–100 °C.EFFECT: production of a heater having high transparency and elasticity, high surface power of infrared radiation and high fire safety.5 cl, 6 dwg

Description

The invention relates to the field of nanotechnology. The invention relates to the field of use of new materials, such as polymer-graphene composites obtained by chemical vapor deposition (CVD).

The invention can find application in electronics, in household heating devices, such as heated glass in rooms, heated floor systems, heated glass of automobile and air transport.

The main representative of a transparent heater is a film of ITO (indium - tin oxide). ITOs are used in hard displays, touch screens, LEDs and solar cells because they have high electrical conductivity and transparency.

The disadvantages of ITO include cost-related limitations and, most importantly, the fragility of ITO films and chemical instability, which makes them impossible to use in flexible systems. Parameters of ITO films: transparency about 90%, conductivity 10-50 Ohms per square.

There are also heating systems based on the organization of design from conductive materials (metal wires, carbon nanotubes, thin films of metals and oxides). However, all these systems have the main drawback of a strong attenuation of the optical signal and scattering on the inhomogeneities (glare) of the surface.

Graphene has great potential as an electrothermal heater due to its high thermal conductivity and low thermal mass even at higher temperatures. Graphene-based heaters exhibit unique properties such as flexibility, mechanical strength, high transparency (2.3%), chemical stability to various environments.

J.-H.AhnandB. H. Hong, Nat. Nanotechnol, 2010, 5, 574-578.], что сопоставимо с показателями ITO.Graphene films grown by chemical vapor deposition (CVD) have low sheet resistance (~ 30 Ohms per square) and high optical transmittance (~ 90%) [S.Bae, N. Kim, Y. Lee, X. Xu , J.-S. Park, Y. Zheng, Balakrishnan, T. Lei, HRKim, YI Song, Y.-J. Kim, S. Kim,

J.-H.AhnandB. H. Hong, Nat. Nanotechnol, 2010, 5, 574-578.], Which is comparable with ITO indicators.

The potential possibilities of creating heaters based on graphene and its composites and the possibility of miniaturization are shown in the articles:

- Usman Khan, Tae-No Kim, Kang Hyuck Lee, Ju-Hyuck Lee, Hong-Joon Yoon, Ravi Bhatia, Ivaturi Sameera, Wanchul Seung, Hanjun Ryu, Christian Falcon, Sang-Woo Kim. Self-powered transparent flexible graphene microheaters. Nano Energy (2015) 17, 356-365;

- Junmo Kang, Yonghee Jang, Youngsoo Kim, Seung-Hyun Cho, Jonghwan Suhr, Byung Her Hong, Jae-Boong Choi and Doyoung Byun. An Aggrid / graphene hybrid structure for large-scale, transparent, flexible heaters. Nanoscale, 2015, 7, 6567-6573-2;

- Dong Sui, Yi Huang, Lu Huang, Jiajie Liang, Yanfeng Ma, and Yongsheng Chen. Flexible and Transparent Electrothermal Film Heaters Based on Graphene Materials, small 2011, 7, No. 22, 3186-3192;

Ritu Gupta, K. D. M. Rao, S. Kiruthika, and Giridhar U. Kulkarni Visibly Transparent Heaters. ACS Appl. Mater. Interfaces April 21, 2016;

- Junmo Kang, Hyeongkeun Kim, Keun Soo Kim, Seoung-Ki Lee, Sukang Bae, Jong-Hyun Ahn, Young-Jin Kim, Jae-Boong Choi, and ByungHee Hong High-Performance Graphene-Based Transparent Flexible Heaters, Nano Lett. 2011, 11, 5154-5158;

- Siqi Yanl, Xiaolong Zhu, Lars Hagedorn Frandsen, Sanshui Xiao, N. Asger Mortensen, Jianji Dong, Yunhong Ding Slow-light-enhanced energy efficiency for graphene microheaters on silicon photonic crystal waveguides. NATURE COMMUNICATIONS, 2017;

- Daniel Schall, Muhammad Mohsin, Abhay A. Sagade, Martin Otto, Bartos Chmielak, Stephan Suckow, Anna Lena Giesecke, Daniel Neumaier, and Heinrich Kurz Infrared transparent graphene heater for silicon photonic integrated circuits. OPTICS EXPRESS. Apr 2016 | Vol.24, No. 8.

However, in these works, to obtain graphene-based heaters, they use complex technologies, complex structures of heaters that are not suitable for industrial use.

The graphene transfer method used has a significant effect on the quality of the graphene-based heater. Chemical etching of the metal substrate in comparison with mechanical separation has a milder effect on graphene. However, for the practical implementation of graphene, transfer methods are required while preserving the copper substrate for its reuse, which will significantly reduce the cost of producing transparent electrodes.

The method of mechanical separation is recognized as the simplest and cheapest when copper is removed by cleaving it from the polymer surface, but graphene deformations occur under the action of shear stresses. With this method, the obtained film resistance is at least 10 kOhm per square.

For example, there is a known method of graphene transfer described in the article [Ilya A. Kostogruda, Evgeniy V. Boykoa, Dmitry V. Smovzh. CVD Graphene Transferfrom Copper Substrateto Polymer. Materials Today: Proceedings 4 (2017) 11476-11479], comprising the following steps: a copper substrate with graphene is placed between two layers of polyethylene terephthalate / ethylene vinyl acetate (PET / EVA) and baked at 180 ° C under pressure for 10 minutes; the resulting composite is cooled to room temperature and mechanically split to obtain a graphene / PET / EVA composite.

In this work, graphene was badly damaged during separation, which led to a significant increase in its resistance, which was 21 kOhm per square.

In the patent [RF patent No. 2688628, 01/10/2018, С01В 32/00, В82 В 1/00] a method for transferring graphene obtained by the CVD method from copper to a polymeric material (PET / EVA) to produce a composite (PET / EVA) is proposed / graphene. The method includes placing a graphene / copper substrate / graphene composite between two layers of PET / EVA polymer, hot pressing at a pressure of 0.1-0.3 kgf / cm ² and a temperature of 181-190 ° C for 10 minutes, cooling the resulting composite to room temperature temperature and mechanical transfer with stabilization between two rigid plates. Achievable result - obtaining a simple method for transferring graphene from a metal substrate to a polymer suitable for industrial use, and obtaining high quality graphene.

Known CVD-graphene transparent heat-generating film [CN 109526073 (A), 2019-03-26, C09D 125/18; C09D 129/04; C09D 133/02; C09D 171/02; C09D 7/63; Н05В 3/14; H05B 3/34] containing a transparent substrate, a graphene layer and an electrode layer that are laminated in this order, and the adhesion between the transparent substrate and the graphene layer is provided by an adhesion-enhancing polymer layer. A method of obtaining a transparent heat-generating film includes the following steps:

1. obtaining a transparent liquid polymer;

2. spraying a transparent liquid polymer onto a single-layer graphene film prepared in advance by CVD;

3. transfer of graphene film to a transparent PET substrate;

4. curing the liquid polymer with ultraviolet radiation to form adhesion between the transparent substrate and the graphene layer;

5. removal of copper foil by etching in solution, purification and drying of a layer of graphene;

6. obtaining an electrode layer by screen printing on the surface of a graphene layer.

After 20,000 fold bending (bending radius 5 mm) of the film obtained in this way, the uniformity of infrared radiation is well preserved.

The specified technical solution uses sophisticated technology. The heat-generating films obtained in this way are inferior to those proposed in elasticity.

As a prototype, a heat-generating film based on graphene was selected [CN 109618428 (A), 2019-04-12, A61N 5/06; СВВ 32/186; СВВ 32/194; Н05В 3/03; Н05В 3/14; H05B 3/20], which contains a transparent substrate, a rough composite graphene layer, an electrode layer and a packing layer, which are successively stacked from top to bottom. A graphene composite layer is a layer formed by cured adhesive and a thin film of graphene. A method of obtaining the specified heat-generating film based on graphene includes the following steps:

1. obtaining a rough catalytic substrate using an annealing process and chemical micro-etching;

2. obtaining a graphene film by CVD on a rough catalytic substrate;

3. transferring the graphene film to the surface of the transparent substrate using liquid glue and removing the growth substrate by dissolution;

4. joining the electrodes to the graphene film.

In this invention, the problem of film quality is solved, because The proposed method for transferring a graphene layer allows one to reduce its damage and achieve high infrared radiation power by the film surface. The resulting films have a surface infrared power of 1-50 W / dm ² (preferably 3-15 W / dm ² ), and the emissivity of the normal phase is 0.85-0.95.

In the indicated technical solution, a sophisticated technology is used to improve the quality of the graphene layer for a heat-generating film. The specified method involves the destruction of the catalytic substrate, which significantly increases the cost of the production process. The heat-generating films obtained in this way are 2-3 times inferior to the present invention in the surface power of infrared radiation.

Thus, the known methods for producing graphene-based heaters are complex and have a high cost, while the surface power of the infrared radiation of the resulting films leaves much to be desired. In addition, the known methods for producing graphene-based heaters do not allow producing large-sized heaters.

The problem to which the present invention is directed, is to create a heater having high transparency and elasticity, high surface power of infrared radiation, high fire safety, the basis of which is a heat-generating film based on graphene, obtained in a simple and cheap way, suitable for industrial use.

The problem is solved by using to create a heater, which is a transparent polymer substrate with a graphene layer and metal electrodes, a simple method containing the following steps:

1. preparation of a copper catalytic substrate,

2. synthesis of graphene on a copper catalytic substrate by the method of CVD,

3. mechanical transfer of the graphene layer to a transparent polymer substrate,

4. joining metal electrodes to the graphene layer.

According to the invention, the copper catalyst support is washed successively in acetone (10 min.), Distilled water (5 min.), Ethanol (10 min.) And distilled water (5 min.) Under the action of ultrasound and dried, and then annealed for 30 ± 1 minute. in the H ₂ duct at a temperature of 1070 ± 3 ° C.

According to the invention, the synthesis of graphene is carried out for 10 ± 1 min. at a temperature of 1070 ± 3 ° C in a mixture of gases Ar / H ₂ / CH ₄ and quickly cooled in the same mixture of gases, and the ratio of the mass flow rate of the components of the mixture of gases is 450: 100: 1 (± 2%).

According to the invention, graphene is transferred onto a transparent polymer substrate (polyethylene terephthalate (PET)) by hot lamination.

According to the invention, metal electrodes are mechanically attached to the polymer-graphene composite and crimped with a force of 10 ⁻⁵ −10 ⁻⁴ N / m ² .

According to the invention, the heaters obtained with this have the following characteristics: resistance 0.8-1 kOhm per square, integral transmittance in the visible range 85-90%, surface infrared power 100-150 W / dm ² , minimum bending radius 1 cm, operating temperature range 20-100 ° С.

The heater is a transparent polymer substrate with a graphene layer and metal electrodes.

Heater Specifications:

1. Resistance per square 0.8-1.0 kOhm.

2. The maximum removable power of 10 kW / m ² .

3. The maximum surface temperature is 95 ° C.

4. The shape of the radiating surface is arbitrary (the curvature is not more than 1 cm).

5. The thickness of the radiating surface is 50-150 microns.

6. Transparency 80-95%.

7. The range of operating temperatures of the heater is from 20 to 100 ° C.

In FIG. 1 is a model diagram of a polycrystalline graphene film heater, where 1 are graphene crystals, 2 are contact areas of graphene crystals, where the main heat is released. The characteristic size of graphene crystals is about 200 microns.

A method of producing a graphene-based heater includes the following steps:

1. obtaining a catalytic substrate;

The copper substrate is washed in acetone, ethyl alcohol and distilled water under the influence of ultrasound, dried and placed in a gas chamber. Annealing the copper substrate is carried out for 30 ± 1 minutes in a H ₂ flow at a temperature of 1070 ± 3 ° C.

2. synthesis of graphene on a catalytic substrate;

The synthesis of graphene is carried out by the method of CVD on copper foil. After annealing the copper substrate, gases are introduced into the chamber for the synthesis of Ar, H ₂ and CH ₄ . The mass flow ratio of the constituent gas mixture Ar / H ₂ / CH ₄ to the chamber is 450: 100: 1 (accuracy 2%). The synthesis of graphene on a copper substrate is carried out in a gas mixture of Ar / H ₂ / CH ₄ for 10 ± 1 minutes at a temperature of 1070 ± 3 ° C and atmospheric pressure. The process is completed by rapid cooling in a mixture of synthesis gases.

3. transfer of graphene to the surface of a transparent substrate by hot lamination;

Graphene transfer is carried out in a manner similar to that proposed in the RF patent No. 2688628 [RF patent No. 2688628.01.10.2018, C01B 32/00, B82B 1/00]. The copper substrate with a graphene layer is coated with a laminating film consisting of PET as a carrier layer and EVA as a polymer (coating sequence: copper-graphene-EVA-PET). Coat bake at a temperature of 181-190 ± 1 ° C under a press with a pressure of 0.1-0.3 kgf / cm ² . Separation of copper from the graphene-EVA-PET composite is carried out with mechanical stabilization, which involves the use of rigid plates, which prevents the occurrence of deformations and bends of the copper substrate and polymer. The plates are glued to copper and PET so that the plate-copper adhesive force and the plate-PET adhesive force are higher than the graphene-copper adhesive force. Then, separation is made on the graphene-copper interface and the plates are peeled off.

4. the attachment of metal contacts to the graphene layer.

Metal (copper) contacts are connected to the graphene-EVA-PET composite from opposite sides mechanically and crimped with a force of 10 ^-5 -10 ^-4 N / m ² .

The width of the contacts is equal to the width of the radiating element. The distance between the contacts is arbitrary. Any contact design is possible, everything is tied to the production of graphene. You can dial a heater from several bands.

The advantages obtained by the proposed method of heaters over known from the technical field:

- high transparency (integrated transmittance in the visible range of 85-90%),

- low resistance of 0.8-1 kOhm per square,

- high elasticity (the ability to bend to a radius of curvature of at least 1 cm, while the resistance changes by no more than 1%),

- high power per square, about 1-1.5 W s cm ² (100-150 W s dm ² ),

- the lack of local heat during the failure of the heaters, which eliminates the possibility of heating the surrounding space to temperatures above 100 ° C and increases the fire safety of using the device.

In addition, by the proposed method, it is possible to obtain cheap and high-quality heaters of any size on an industrial scale, since the method is simple and allows you to scale the heating element from 3 × 1 mm to unlimited size by sequential transfer of graphene layers to PET with a coating of a given area.

Graphene was synthesized by the AP-CVD method on AlfaAesar 13382 copper foil (99.8% Cu) 25 μm thick. Methane was used as a carbon precursor. The CVD synthesis unit was a furnace with the possibility of heating to 1200 ° C. Before synthesis, the copper substrate was washed successively in acetone, ethyl alcohol, and distilled water under the action of ultrasound, dried, and placed in a gas chamber. The chamber was pumped out, filled with argon, and heated to an annealing temperature of 1070 ° C.

Annealing of the copper substrate was carried out for 30 min in an H ₂ duct. After annealing, Ar, Н ₂ , and CH ₄ gases were supplied to the chamber for the synthesis of graphene for 10 min at a temperature of 1070 ° С. The process ended with rapid cooling in a mixture of synthesis gases. The mass flow ratio of the constituent gas mixture Ar / H ₂ / CH ₄ supplied to the chamber was 450: 100: 1.

The analysis of the obtained samples was carried out on a RamanspectrometerT64000 HoribaJobinYvon spectrometer. Optical surface images were obtained using an Olympus BX51M optical microscope.

Raman spectra of synthesized graphene are shown in FIG. 2. The ratio of the intensities of the Raman peaks I (D) / I (G) = 0.09, I (G) / I (2D) = 0.62, the half-width at half maximum D peak = 34 cm ^-1 , these spectra correspond to a single-layer graphene coverage.

In FIG. 3 shows an optical image of the material after annealing. An optical microscope analysis of copper samples coated with graphene after oxidation in air at a temperature of 200 ° C showed that the entire surface of copper is protected from atmospheric oxygen by a graphene coating, FIG. 3. With an incomplete coating, an interference pattern is observed on the surface of copper associated with the presence of oxide layers of different thicknesses.

Graphene was transferred using a polyethylene terephthalate / ethylene vinyl acetate (PET / EVA) polymer. The light transmission of PET polymers depends on the manufacturer and the thickness of the sheet. We used polymers from Helvetik - Prikamye with a thickness of 0.3-3 mm, the light transmission of which in the visible range is 88-90%. Light transmission in the visible range of laminator films with a thickness of 300 μm is 90%, and a thickness of 50 μm is 97-98%.

A copper substrate with a graphene layer was coated with a lamination film consisting of PET and EVA. Then the coating was baked at a temperature of 190 ° C under a press with a pressure of 0.1 kg / cm. Separation of copper from the graphene-EVA-PET composite was carried out with mechanical stabilization.

Measurement of current-voltage characteristics (CVC).

From the DC power source, a predetermined voltage was applied to the contacts. Using multimeters, the voltage drop across the sample and the current in the circuit were measured. The data obtained were used to determine the resistance of the graphene-polymer composite and power consumption. To determine the temperature of the sample, a thermocouple was attached to the polymer. Experiments on the resistive heating of a graphene film on a polymer were carried out in air.

In FIG. Figures 4 and 5 show the current – voltage characteristics that determine the dependence of the current I (mA) on the magnitude and also the polarity of the applied voltage U (V) of heating elements based on PET-EVA-graphene.

In FIG. Figure 4 shows the I – V characteristic of a heating element based on PET-graphene in air at a temperature of 21 ° C.

In FIG. 5 shows the I – V characteristic of a heating element based on PET-EVA-graphene in water.

The I – V characteristic shows a high conductivity of the heater both in air and in water.

In FIG. 6 shows the dependence of the resistance per square R (Ohm) of a heater based on PET-EVA-graphene on temperature T (° C). The range of operating temperatures of the heater is from 20 to 100 ° C, which indicates the exclusion of the possibility of heating the surrounding space to temperatures above 100 ° C, i.e. high fire safety of using such a heater.

The presented heater can be used up to temperatures of 100 ° C. The power of the heater in air is limited by heat exchange with the environment and amounts to 1.5 W / cm ² , for water the maximum power is 7 W / cm ² .

The heater can be used in household heating devices, such as: heated glass in rooms, heated floor systems, heated glass for cars and air transport.

Thus, films with the following characteristics were obtained:

- integrated transmittance in the visible range of 85-90%,

- resistance 0.8-1 kOhm per square,

- the possibility of bending to a radius of curvature of at least 1 cm, while the resistance varies by no more than 1%,

- power per square, about 1-1.5 W s cm ² (100-150 W s dm ² ),

- range of operating temperatures 20-100 ° C,

- heat flow in air 15 kW / m ² in water 70 kW / m ² .

Claims (5)

1. A method of manufacturing a heater based on graphene containing a transparent polymer substrate with a graphene layer and metal electrodes, including annealing a copper catalyst substrate, synthesis of graphene on a copper catalyst substrate by chemical vapor deposition (CVD), mechanical transfer of a graphene layer onto a transparent polymer substrate and attaching metal electrodes to the graphene layer, characterized in that the copper catalytic substrate is washed successively in acetone, ethanol and distilled water under an ultrasound before annealing, and dried, the copper catalytic substrate is annealed for 30 ± 1 min in an H ₂ duct at a temperature of 1070 ± 3 ° С, graphene synthesis is carried out for 10 ± 1 min at a temperature of 1070 ± 3 ° С in a gas mixture and is quickly cooled in the same gas mixture, graphene is transferred onto a transparent polymer substrate by hot lamination, metal electrodes are attached to the polymer-graphene composite by mechanical method and crimping They are equipped with heaters of 0.8-1 kOhm per square, integral transmittance in the visible range of 85-90%, surface infrared power of 100-150 W / dm ² , a minimum bending radius of 1 cm and a range operating temperatures of 20-100 ° C. 2. The method according to p. 1, characterized in that the synthesis of graphene is carried out in a mixture of gases Ar / H ₂ / CH ₄ . 3. The method according to p. 1, characterized in that the synthesis of graphene is carried out in a mixture of gases at a ratio of the mass flow rate of the components Ar: H ₂ : CH _{4 of} 450: 100: 1. 4. The method according to p. 1, characterized in that the transparent polymer substrate is made of polyethylene terephthalate (PET) with a layer of ethylene vinyl acetate (EVA). 5. The method according to p. 1, characterized in that the metal electrodes attached to the polymer-graphene composite by a mechanical method are crimped with a force of 10 ^-5 -10 ^-4 N / m ² .

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