Composite ink, preparation method thereof and application of composite ink in aerosol jet printing conformal circuit

Abstract

The invention discloses composite ink, a preparation method thereof and application of the composite ink in an aerosol jet printing conformal circuit, and belongs to the technical field of common circuit preparation. The invention provides the composite ink which can be sintered in situ at a low post-processing temperature, and a conformal circuit is prepared on a polymer substrate by adopting an aerosol jet printing mode. According to the invention, silver nanoparticles and silver ions are compounded to prepare the composite ink for preparing a conformal circuit by aerosol jet printing. According to the composite ink, gaps among particles are filled with ink containing silver ions by utilizing the capillary action among the particles after nano-silver particle ink with high solid content is deposited on a substrate, the silver ions are reduced in situ on the heated substrate, the gaps of the original nano-particles are filled with the generated nano-silver particles, and the nano-silver particles are formed. And the conductivity of the conformal circuit is greatly improved. When the composite ink is used for aerosol jet printing, the conductivity of a prepared conformal circuit reaches 22.4 mu omega.cm at the post-processing temperature of 100 DEG C.

Description

Technical Field

[0001] The invention relates to a composite ink and a preparation method thereof and application in aerosol jet printing conformal circuits, belonging to the technical field of conformal circuit preparation. Background Art

[0002] Conformal electronics has become a hot topic in academia and industry because it brings new features and functions to integrated electronic systems on curved surfaces. On the one hand, conformal electronics can accurately respond to external stimuli on non-planar and dynamic surfaces, meeting the strong demand for next-generation sensing devices in the fields of safety, environment, and health monitoring. On the other hand, conformal electronics is not limited by installation space and has the advantages of miniaturization and lightweight. It has been applied in the fields of smart implants, conformal displays, conformal antennas, etc. The huge advantages and wide applications of conformal electronics urgently require high-resolution, high-conductivity conformal circuits.

[0003] Traditional circuit manufacturing technology provides nanometer-level resolution, but processes such as lithography, etching, and doping are not compatible with curved surfaces. Existing transfer technology can indirectly produce large-area curved graphics, but only provides millimeter-level resolution. And assembling electronic products from flat surfaces to curved surfaces is another method, but the complex process and potential threats of residual stress limit its application. Other methods, such as non-planar lithography and laser direct writing can achieve fine patterns on curved substrates, but rely on expensive equipment and lead to higher costs. In contrast, inkjet printing, as an additive manufacturing technology, offers advantages such as wide material compatibility, high resolution, environmental protection, and cost-effectiveness.

[0004] Aerosol jet printing is one of the inkjet printing technologies. Due to the sheath gas focusing effect, its working distance exceeds 2 mm. The higher working distance enables it to adapt to various complex surface morphologies. In addition, due to the protection of the sheath gas, aerosol jet printing can be compatible with inks with a solid content of up to 50% without nozzle clogging. The high solid content of the ink ensures the excellent adhesion of the printed pattern to three-dimensional substrates of various materials. Therefore, aerosol jet printing is considered to be the most promising technology for conformal circuit preparation.

[0005] However, the aerosol printing ink currently used for the preparation of conformal circuits is mainly nanosilver ink. However, its post-processing temperature often exceeds 150°C, which is not suitable for polymer substrates such as epoxy resin and PET, greatly limiting the application scope of conformal circuits. Therefore, it is necessary to develop silver-based aerosol inks with low post-processing temperature and high conductivity to adapt to different types of substrate materials and promote the development of conformal electronics. Summary of the invention

[0006] In view of the above-mentioned technical problems and development bottlenecks of existing conformal circuits, the present invention provides a composite ink that can be in-situ sintered at a low post-processing temperature, so as to realize the preparation of conformal circuits on polymer substrates by aerosol printing.

[0007] The technical solution of the present invention:

[0008] One of the purposes of the present invention is to provide a composite ink, which is prepared by mixing silver nanoparticle ink and silver ion ink; the silver nanoparticle ink comprises spherical silver nanoparticles, additives and a mixed solvent; the silver ion ink comprises a silver source, a solvent, a complexing agent and a reducing agent.

[0009] It is further defined that the particle size range of the spherical silver nanoparticles is 20 to 60 nm, and the surface coating agent is citrate.

[0010] Further defined, the mixed solvent includes isopropyl alcohol, ethylene glycol, terpineol and deionized water.

[0011] It is further defined that the mixed solvent comprises, by volume percentage, 40-55 vol% isopropyl alcohol, 10-15 vol% ethylene glycol, 0.5-2 vol% terpineol, and the remainder is deionized water.

[0012] It is further defined that the additive comprises a fluorocarbon surfactant and a leveling agent.

[0013] It is further defined that the content of the leveling agent in the silver nanoparticle ink is 1 to 3 wt %, the content of the fluorocarbon surfactant is 0.1 to 0.2 wt %, and the content of the spherical silver nanoparticles is 35 to 45 wt %.

[0014] It is further defined that the leveling agent is a 10% by mass aqueous solution of carboxypropyl methylcellulose, and the molecular weight of the carboxypropyl methylcellulose is 66000;

[0015] It is further defined that the silver source is one or a mixture of silver acetate, silver tartrate, silver citrate, silver oxalate, and silver carbonate.

[0016] It is further defined that the solvent is one or a mixture of methanol, ethanol, isopropanol, and ethylene glycol.

[0017] It is further defined that the complexing agent is one or a mixture of ethylamine, propylamine, ethylenediamine, and propylenediamine.

[0018] In a further embodiment, the reducing agent is formic acid and / or diethanolamine.

[0019] It is further defined that the ratio of the molar content of the amino groups in the complexing agent to the molar content of the silver ions in the silver source is 2:1.

[0020] The second object of the present invention is to provide a method for preparing the composite ink, which comprises:

[0021] Firstly, spherical silver nanoparticles are dispersed in a mixed solvent, and an additive is added and stirred to obtain silver nanoparticle ink;

[0022] Then, the silver source is dispersed in a solvent, a complexing agent and a reducing agent are added and stirred evenly to obtain a silver ion ink;

[0023] Finally, the silver nanoparticle ink and the silver ion ink are mixed to obtain a composite ink.

[0024] It is further defined that the volume ratio of the silver nanoparticle ink to the silver ion ink is 2:0.05-0.08.

[0025] A third object of the present invention is to provide an application of the above composite ink, specifically for aerosol printing of conformal circuits.

[0026] It is further defined that the aerosol printing parameters are: atomization voltage 20-47V, carrier gas flow rate 0-100sccm, sheath gas flow rate 0-200sccm, carrier gas flow rate>1.5, printing speed 0.1-40mm / s, substrate temperature 50-150℃, and after printing, it is stored in a constant temperature box at 50-150℃ for 15-60min to obtain a common circuit.

[0027] Beneficial effects:

[0028] (1) The present invention provides a composite ink for preparing conformal circuits by aerosol printing. The composite ink is compounded with silver nanoparticles and silver ions. Since the solid content of the ink is about 40%, and after being dried and subjected to high-speed sheath gas after being formed into an aerosol, the solvent will further evaporate, and the aerosol droplets deposited on the substrate contain only a very low liquid component. After the nanosilver particle ink with a high solid content is deposited on the substrate, the capillary action between the particles is utilized, so that the ink containing silver ions fills the gaps between the nanoparticles. The high-viscosity deposit provides excellent adhesion and conformal performance compatible with substrates of various materials. In addition, the silver ions in the liquid component of the ink are rapidly reduced in situ under the combined action of the heated substrate and the reducing agent to form new nanosilver particles. As the reduction reaction proceeds further, the generated silver nanoparticles continue to grow and fill the gaps of the original nanosilver particles, realizing the interconnection between the nanoparticles, thereby improving the conductivity of the circuit. The composite ink is used for aerosol printing, and the conductivity of the prepared conformal circuit reaches 22.4μΩ·cm at a post-processing temperature of 100°C. The printed conformal wires can achieve high-density electrical interconnections on curved substrates, thereby greatly reducing the weight of the equipment.

[0029] (2) The spherical silver nanoparticles used in the present invention are coated with citrate and have hydrophilicity. At the same time, the amino complexing agent is used to form a coordination bond with the metal ions, thereby reducing the binding force of the anions to the metal ions, thereby greatly improving the solubility of silver and reducing the post-processing temperature.

[0030] (3) The ratio of silver nanoparticle ink to silver ion ink in the present invention is a key parameter. If the silver ion ink content is too high, the composite ink solid content is low and cannot maintain good adhesion to the substrate, affecting conformal printing performance. If the silver ion ink content is too low, only a small amount of silver ions are reduced after post-treatment, and a high conductivity cannot be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the low temperature post-processing process of the composite ink provided for this application;

[0032] In the figure, 1-liquid component of the composite ink, 2-silver nanoparticles in the composite ink, 3-reduced silver atoms, 4-silver nanoparticles, and 5-substrate. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0034] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0035] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0036] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art, and the purity of the solid and liquid reagents used is analytically pure.

[0037] Example 1

[0038] The process of preparing the composite ink in this embodiment is as follows:

[0039] (1) Configuration of silver nanoparticle ink;

[0040] First, 1.0 g of spherical silver nanoparticles with an average particle size of 20 nm was weighed. The surface coating agent of the spherical silver nanoparticles was citrate, which was hydrophilic.

[0041] Then, isopropyl alcohol, ethylene glycol, terpineol, and deionized water were uniformly mixed in a volume ratio of 40:15:0.5:44.5 to obtain a mixed solvent.

[0042] Finally, the spherical silver nanoparticles were dispersed in 2 ml of a mixed solvent, 0.25 g of a 10% carboxypropyl methylcellulose aqueous solution with a molecular weight of 66,000 and 3 mg of a fluorocarbon surfactant (FS-50) were added, and the mixture was stirred at 600 r / min for 20 min to obtain a silver nanoparticle ink.

[0043] (2) Configuration of silver ion ink;

[0044] Silver acetate is selected as the silver source, ethanol is selected as the solvent, isopropanolamine is selected as the complexing agent, and formic acid is selected as the reducing agent.

[0045] 0.5 g of silver acetate was weighed and dispersed in 1.5 ml of ethanol, 0.9 g of isopropanolamine and 0.15 g of formic acid were added, and stirred at 600 r / min for 30 min. The obtained solution was filtered using a 5 μm needle filter to obtain a silver ion ink.

[0046] (3) Configuration of silver nanoparticle / silver ion composite ink

[0047] 0.08 ml of silver ion ink was added to 2 ml of silver nanoparticle ink, stirred at 600 r / min for 30 min and subjected to water bath ultrasound for 20 min to obtain a composite ink.

[0048] The composite ink prepared in this embodiment is used to prepare a conformal circuit by aerosol printing. The specific process is as follows:

[0049] CAD software was used to draw a spiral line on an arc surface with a curvature radius of 1.5 cm. The G-code of the five-axis machine tool was written according to the drawn common circuit, so that the nozzle was always located in the normal direction of the substrate during the printing process and the relative speed with the substrate surface was kept constant.

[0050] The composite ink was loaded into the ink tank and ultrasonic atomization was used to adjust the printing parameters, including atomization voltage of 40V, carrier gas flow rate of 10sccm, sheath gas flow rate of 80sccm, and printing speed of 5mm / s. The curved substrate was heated to 100℃. The G-code code was run for printing, and the aerosol beam was deposited on the substrate and in-situ sintering was achieved. After printing, it was stored in a constant temperature box at 100℃ for 60min. The resistivity of the circuit was measured to be 22.4μΩ·cm.

[0051] The printed conformal wires can achieve high-density electrical interconnections on curved substrates, thereby greatly reducing the weight of the equipment.

[0052] The principle of low temperature post-treatment of the present invention is described as follows:

[0053] like Figure 1 As shown, the process of low-temperature post-processing of the above composite ink is demonstrated. Since the solid content of the composite ink is about 40%, after being atomized into an aerosol, the solvent will evaporate further after drying and the action of high-speed sheath gas. The aerosol droplets deposited on the substrate contain only very low liquid components. Due to capillary action, the liquid component 1 of the ink will fill the gaps of the silver nanoparticles 2 in the composite ink. The high-viscosity deposit provides excellent adhesion and conformal properties compatible with various material substrates. The silver ions in the liquid component 1 of the composite ink are quickly reduced under the combined action of the heated substrate 5 and the reducing agent to form new nanosilver particles 4. As the reduction reaction proceeds further, the generated silver nanoparticles 4 continue to grow and fill the gaps of the original nanosilver particles, realizing the interconnection between the nanoparticles, thereby improving the conductivity of the circuit.

[0054] In addition, in this embodiment, isopropanolamine is used as a complexing agent, and the amine groups contained therein form coordination bonds with silver ions, thereby reducing the binding force of acetate ions to silver ions, thereby greatly improving the solubility of silver and reducing the post-treatment temperature.

[0055] Example 2

[0056] The process of preparing the composite ink in this embodiment is as follows:

[0057] (1) Configuration of silver nanoparticle ink;

[0058] First, 1.0 g of spherical silver nanoparticles with an average particle size of 50 nm was weighed. The surface coating agent of the spherical silver nanoparticles was citrate, which was hydrophilic.

[0059] Then, isopropyl alcohol, ethylene glycol, terpineol, and deionized water were uniformly mixed in a volume ratio of 40:10:2:48 to obtain a mixed solvent.

[0060] Finally, the spherical silver nanoparticles were dispersed in 2 ml of a mixed solvent, 0.15 g of a 10% carboxypropyl methylcellulose aqueous solution with a molecular weight of 66,000 and 3 mg of a fluorocarbon surfactant (FS-50) were added, and the mixture was stirred at 600 r / min for 40 min to obtain a silver nanoparticle ink.

[0061] (2) Configuration of silver ion ink;

[0062] Silver oxalate is selected as the silver source, methanol and ethylene glycol are selected as the solvent, propylene diamine is selected as the complexing agent, and diethanolamine is selected as the reducing agent.

[0063] 0.5 g of silver oxalate was weighed and dispersed in a mixed solvent of 1.2 ml of methanol and 0.6 ml of ethylene glycol, 0.58 g of propylene diamine and 0.25 g of diethanolamine were added, and stirred at 600 r / min for 40 min. The obtained solution was filtered using a 5 μm needle filter to obtain a silver ion ink.

[0064] (3) Configuration of silver nanoparticle / silver ion composite ink

[0065] 0.05 ml of silver ion ink was added to 2 ml of silver nanoparticle ink, stirred at 600 r / min for 30 min and subjected to water bath ultrasound for 30 min to obtain a composite ink.

[0066] The composite ink prepared in this embodiment is used to prepare a conformal temperature sensor by aerosol printing. The specific process is as follows:

[0067] Use CAD software to draw a serpentine line on an arc surface with a curvature radius of 35cm; write the G-code code of the five-axis machine tool according to the common circuit drawn, so that the nozzle is always located in the normal direction of the substrate during printing and the relative speed with the substrate surface remains constant; adjust various printing parameters, including atomization voltage 47V, carrier gas flow rate 10sccm, sheath gas flow rate 120sccm, and printing speed 10mm / s. Set the substrate temperature to 120℃. Run the G-code code for printing, and store it in a constant temperature box at 150℃ for 60min after printing. The temperature monitoring range of the prepared temperature sensor is 25-200℃, and the resistance temperature coefficient is >0.002.

[0068] Comparative Example 1

[0069] The difference between this comparative example and Example 1 is that no silver ion ink is added, and only silver nanoparticle ink is used. The remaining process steps and parameter settings are the same as those in Example 1.

[0070] After the composite ink was printed, it was stored in a constant temperature box at 100°C, 150°C, and 200°C for 60 minutes. The measured resistivity of the circuit was 1.2×10 5 μΩ·cm, 76.7 μΩ·cm, 14.1 μΩ·cm.

[0071] Comparative Example 2

[0072] The difference between this comparative example and Example 1 is that no complexing agent is added during the preparation of the silver ion ink, and the remaining process steps and parameter settings are the same as those in Example 1.

[0073] After the composite ink was printed, it was stored in a constant temperature box at 100°C for 60 minutes. The resistivity of the circuit was measured to be 237.2μΩ·cm.

[0074] Comparative Example 3

[0075] The difference between this comparative example and Example 1 is that no reducing agent is added during the preparation of the silver ion ink, and the remaining process steps and parameter settings are the same as those in Example 1.

[0076] After the composite ink was printed, it was stored in a constant temperature box at 100°C for 60 minutes. The resistivity of the circuit was measured to be 5.6×10 3 μΩ·cm.

[0077] Although the present invention has been disclosed as above in the preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A composite ink, characterized in that: The composite ink is prepared by mixing silver nanoparticle ink and silver ion ink; the silver nanoparticle ink comprises spherical silver nanoparticles, additives and a mixed solvent; and the silver ion ink comprises a silver source, a solvent, a complexing agent and a reducing agent.

2. The composite ink according to claim 1, characterized in that: The particle size of the spherical silver nanoparticles ranges from 20 to 60 nm, the surface coating agent is citrate, the additives include fluorocarbon surfactant and leveling agent, and the mixed solvent includes isopropyl alcohol, ethylene glycol, pinene alcohol and deionized water.

3. The composite ink according to claim 2, characterized in that: The content of the leveling agent in the silver nanoparticle ink is 1-3wt%, the content of the fluorocarbon surfactant is 0.1-0.2wt%, and the content of the spherical silver nanoparticles is 35-45wt%.

4. The composite ink according to claim 2, characterized in that: The mixed solvent comprises, by volume percentage, 40-55 vol% of isopropyl alcohol, 10-15 vol% of ethylene glycol, 0.5-2 vol% of terpineol, and the remainder is deionized water.

5. The composite ink according to claim 2, characterized in that: The leveling agent is a 10% by mass carboxypropyl methylcellulose aqueous solution, and the molecular weight of the carboxypropyl methylcellulose is 66,000.

6. The composite ink according to claim 1, characterized in that: The silver source is one or a mixture of silver acetate, silver tartrate, silver citrate, silver oxalate and silver carbonate; the solvent is one or a mixture of methanol, ethanol, isopropanol and ethylene glycol; the complexing agent is one or a mixture of ethylamine, propylamine, ethylenediamine and propylenediamine; and the reducing agent is formic acid and / or diethanolamine.

7. The composite ink according to claim 1 or 6, characterized in that: The ratio of the molar content of the amino group in the complexing agent to the molar content of the silver ion in the silver source is 2:

1.

8. A method for preparing the composite ink according to any one of claims 1 to 7, characterized in that: First, spherical silver nanoparticles are dispersed in a mixed solvent, and an additive is added and stirred to obtain silver nanoparticle ink; then, a silver source is dispersed in a solvent, and a complexing agent and a reducing agent are added and stirred to obtain silver ion ink; finally, the silver nanoparticle ink and the silver ion ink are mixed to obtain a composite ink.

9. Use of the composite ink according to any one of claims 1 to 7, characterized in that: For aerosol printing of conformal circuits.

10. The use of the composite ink according to claim 9, characterized in that: Aerosol printing parameters are: atomization voltage 20-47V, carrier gas flow rate 0-100sccm, sheath gas flow rate 0-200sccm, carrier gas flow rate>1.5, printing speed 0.1-40mm / s, substrate temperature 50-150℃, after printing, keep in a constant temperature box at 50-150℃ for 15-60min to obtain a common circuit.

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