Ultrafine copper powder suitable for flexible conductive ink as well as preparation method and application of ultrafine copper powder

Abstract

The invention provides a preparation method of superfine copper powder suitable for flexible conductive ink, which comprises the following steps: A, preparing 0.01-1 mol / L of copper salt aqueous solution and at least 2 parts of ascorbic acid aqueous solution, and the molar ratios of the ascorbic acid aqueous solution to the copper salt are different; b, the at least two parts of ascorbic acid aqueous solution are sequentially added into the copper salt aqueous solution, the reaction temperature of each part of ascorbic acid aqueous solution and the copper salt aqueous solution is sequentially increased by 10-40 DEG C, and copper powder suspension liquid is formed; and C, the copper powder suspension liquid is cleaned and dried, and the superfine copper powder is obtained. The preparation method of the superfine copper powder of the flexible conductive ink aims at providing the copper powder with the superfine particle size and improving the stability and oxidation resistance of the copper powder. The invention further provides the superfine copper powder suitable for the flexible conductive ink and application of the superfine copper powder.

Description

Technical Field

[0001] The invention relates to the technical field of copper powder preparation, and in particular to an ultrafine copper powder suitable for flexible conductive ink, a preparation method and application thereof. Background Art

[0002] Wearable electronics have become smaller, thinner, and lighter, and have been applied to circuit boards, displays, wearable devices, and electronic devices. Liquid metal inks are directly printed on flexible substrates, which improves manufacturing efficiency; in turn, the demand for nanometal inks has increased. Therefore, the preparation of stable and oxidation-resistant CuNPs is often the focus of research and development.

[0003] Unfortunately, CuNPs (copper nanoparticles) are easily oxidized, and when used in conductive inks, a high sintering temperature is required to eliminate the oxide layer on the surface of CuNPs. In addition, studies on the preparation of CuNPs often use strong reducing agents, such as sodium borohydride or hydrazine, to make smaller particles or shorten the reduction time. However, these types of reducing agents are typically highly toxic, causing environmental pollution, while weaker reducing agents will produce larger metal particles and require longer reduction times.

[0004] Since CuNPs are easily oxidized, especially at high temperatures, the oxidation rate is accelerated and sintering must be carried out in an inert environment. Therefore, research on low-temperature sintering and the application of CuNPs on flexible substrates is relatively limited. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for preparing ultrafine copper powder suitable for flexible conductive ink, aiming to provide copper powder with ultrafine particle size and improve the stability and oxidation resistance of the copper powder.

[0006] The method for preparing ultrafine copper powder suitable for flexible conductive ink provided by the present invention comprises the following steps: A. preparing a 0.01-1 mol / L copper salt aqueous solution and at least 2 parts of an ascorbic acid aqueous solution, wherein the molar ratio of the ascorbic acid aqueous solution to the copper salt is different; B. adding the at least 2 parts of the ascorbic acid aqueous solution to the copper salt aqueous solution in sequence, and raising the reaction temperature of each part of the ascorbic acid aqueous solution and the copper salt aqueous solution by 10-40° C. in sequence to form a copper powder suspension; C. Washing and drying the copper powder suspension to obtain ultrafine copper powder.

[0007] In one embodiment, the molar ratio of ascorbic acid to copper salt is 30-100.

[0008] In one embodiment, in step B, after adding the first portion of the ascorbic acid aqueous solution to the copper salt aqueous solution, the reaction is maintained at a constant temperature of 50-80° C. for 5-15 min, preferably 10 min, and then the remaining ascorbic acid aqueous solution is added.

[0009] In one embodiment, the reaction time of the remaining ascorbic acid aqueous solution and the copper salt aqueous solution exceeds 1 hour.

[0010] In one embodiment, the reaction temperature of the remaining ascorbic acid aqueous solution and the copper salt aqueous solution is a constant temperature of 60-90°C.

[0011] In one embodiment, in step B, the at least 2 portions of the ascorbic acid aqueous solution are added to the copper salt aqueous solution in descending molar ratio to the copper salt.

[0012] In one embodiment, in step A, the pH value of the copper salt aqueous solution is further adjusted to be alkaline, preferably to a pH of 10, 10.5 or 11.

[0013] In one embodiment, the copper salt is one or more of copper sulfate, copper nitrate, copper chloride, copper hydroxide, and copper acetate.

[0014] In step C, the copper powder suspension is washed with deionized water and ethanol for 4-5 times, and then dried under vacuum at 40° C. for 5 h.

[0015] Compared with the prior art, the preparation method of the present invention has the following beneficial effects: (1) Reducing agent is one of the important factors affecting the growth and aggregation of CuNPs. It can be controlled not only by selecting the reagent and concentration, but also by adding or reducing multiple times. Ascorbic acid is a medium-strength reducing agent that easily aggregates in aqueous solution and produces large CuNPs. Therefore, this paper repeatedly adds reducing agent in batches to adjust the progress of the reduction reaction and facilitate the control of the particle size of CuNPs.

[0016] (2) Because the ascorbic acid content is too high during the reduction process, the lone pair of electrons in the polar group of L-ascorbic acid can occupy the two spatial orbitals of the copper ion to form a complex compound, which plays the role of a stabilizer.

[0017] (3) Dehydroascorbic acid formed after oxidation of ascorbic acid obtains a polyhydroxy structure through irreversible hydrolysis of ester bonds. A large number of hydroxyl groups can promote the complexation of copper nanoparticles with the molecular matrix through intermolecular and intramolecular hydrogen bonds, thereby preventing the aggregation of copper nanoparticles.

[0018] (4) Ascorbic acid is a natural mild reducing agent with certain antioxidant properties. It can extend the storage period without adding antioxidants.

[0019] (5) Since ascorbic acid has a weak reducing property, the reaction often takes a long time. Therefore, by strictly controlling the temperature and addition method, the reaction time can be shortened and the industrial feasibility of the process can be improved.

[0020] (6) Increasing the molar ratio of ascorbic acid and copper salt plays a role as a stabilizer, reduces or avoids the addition of dispersants, and reduces the impact of additives on sedimentation and other steps. It also simplifies the preparation process of copper powder and saves costs in many aspects.

[0021] (7) Since the present invention adopts a multiple reduction method to promote the full reduction of the copper salt, and at the same time appropriately increases the reaction temperature to further promote the oxidation of ascorbic acid to form dehydroascorbic acid containing hydrogen bonds, thereby more effectively preventing the aggregation of nano-copper particles.

[0022] The present invention also provides an ultrafine copper powder prepared by the above-mentioned method for preparing ultrafine copper powder suitable for flexible conductive ink and application of the ultrafine copper powder in flexible conductive ink. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below.

[0024] Figure 1 This is a scanning electron microscope photograph of the copper powder obtained in Example 1 of the present invention.

[0025] Figure 2 This is a scanning electron microscope photo of the copper powder obtained in Example 3 of the present invention. Implementation

[0026] The specific embodiments of the present invention are described in detail below. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the description of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The terms "comprises," "comprising," or any other variations thereof, are intended to cover a non-exclusive inclusion of the elements listed and may also include additional elements not expressly listed.

[0028] It is worth mentioning that the present invention only lists a number of representative specific implementations, which is intended to reflect the beneficial effects of the present invention, and is not equivalent to the implementations shown below being all implementations of the present invention. Example 1

[0029] The present invention provides a method for preparing copper powder, comprising the steps of: A. preparing a copper salt aqueous solution having a pH of 10.5 and a concentration of 0.5 mol / L and 3 parts of an ascorbic acid aqueous solution, wherein the 3 parts of the ascorbic acid aqueous solution are specifically ascorbic acid a solution, ascorbic acid b solution and ascorbic acid c solution having a molar ratio of 90, 60 and 30 with the copper salt, respectively; B. firstly add ascorbic acid solution a to the copper salt aqueous solution, and react at a constant temperature of 60° C. for 10 min, then add ascorbic acid solution b at a constant temperature of 75° C., react for 1 h, and then add ascorbic acid solution c at a constant temperature of 90° C., react for 1 h, to form a copper powder suspension; C. The copper powder suspension was washed with deionized water and ethanol for 4-5 times, and vacuum dried at 40°C for 5 hours to obtain ultrafine copper powder. Example 2

[0030] The present invention provides a method for preparing copper powder, which is different from Example 1 in that the steps are: A. preparing a copper salt aqueous solution having a pH of 10 and a concentration of 0.5 mol / L and 2 parts of an ascorbic acid aqueous solution, wherein the 2 parts of the ascorbic acid aqueous solution are specifically an ascorbic acid a solution and an ascorbic acid b solution having a molar ratio of 80 to the copper salt and 40 to the copper salt, respectively; B. First, add ascorbic acid solution a to the copper salt aqueous solution, and react at a constant temperature of 70°C for 10 minutes, then add ascorbic acid solution b at a constant temperature of 80°C and react for 1 hour; C. The copper powder suspension was washed with deionized water and ethanol for 4-5 times, and vacuum dried at 40°C for 5 hours to obtain ultrafine copper powder. Example 3

[0031] The present invention provides a method for preparing copper powder, which is different from Example 1 in that the steps are: A. preparing a copper salt aqueous solution having a pH of 11 and a concentration of 0.5 mol / L and an ascorbic acid aqueous solution having a molar ratio of 1 part to the copper salt of 50; B. adding ascorbic acid aqueous solution to the copper salt aqueous solution, and reacting at a constant temperature of 50° C. for 10 min, then adding ascorbic acid b solution at a constant temperature of 80° C. and reacting for 1 h; C. The copper powder suspension was washed with deionized water and ethanol for 4-5 times, and vacuum dried at 40°C for 5 hours to obtain ultrafine copper powder. Example 4

[0032] The present invention provides a method for preparing copper powder, which is different from Example 1 in that the steps are: A. preparing a copper salt aqueous solution having a pH of 10.5 and a concentration of 0.5 mol / L and 3 parts of an ascorbic acid aqueous solution, wherein the 3 parts of the ascorbic acid aqueous solution are specifically ascorbic acid a solution, ascorbic acid b solution and ascorbic acid c solution having a molar ratio of 90, 60 and 30 with the copper salt, respectively; B. firstly adding ascorbic acid solution a to the copper salt aqueous solution, and reacting at a constant temperature of 60° C. for 10 min, then adding ascorbic acid solution b at a constant temperature of 60° C. for 1 h, and then adding ascorbic acid solution c at a constant temperature of 60° C. for 1 h to form a copper powder suspension; C. The copper powder suspension was washed with deionized water and ethanol for 4-5 times, and vacuum dried at 40°C for 5 hours to obtain ultrafine copper powder. Example 5

[0033] The present invention provides a method for preparing copper powder, which is different from Example 1 in that the steps are: A. preparing a copper salt aqueous solution having a pH of 10.5 and a concentration of 0.5 mol / L and 3 parts of a formaldehyde aqueous solution, wherein the 3 parts of the ascorbic acid aqueous solution are specifically formaldehyde a solution, formaldehyde b solution and formaldehyde c solution in a molar ratio of 90, 60 and 30 to the copper salt, respectively; B. First, add formaldehyde solution a to the copper salt aqueous solution, and react at a constant temperature of 60°C for 10 minutes, then add formaldehyde solution b at a constant temperature of 75°C, react for 1 hour, and then add formaldehyde solution c at a constant temperature of 90°C, react for 1 hour to form a copper powder suspension; C. The copper powder suspension was washed with deionized water and ethanol for 4-5 times, and vacuum dried at 40°C for 5 hours to obtain ultrafine copper powder.

[0034] Preparation Example 1 The present invention provides a flexible conductive ink. The raw materials for preparing the flexible conductive ink include copper powder prepared by the method for preparing the copper powder described in Example 1, an epoxy resin defoamer, a wetting dispersant, a nano rubber powder and a mixed solvent. The raw materials are first added into a dispersion kettle and stirred evenly, then ultrasonically dispersed evenly, and ground to a desired particle size to obtain the epoxy resin polyetheramine flexible conductive ink.

[0035] Preparation Example 2 The present invention provides a flexible conductive ink. The raw materials for preparing the flexible conductive ink include copper powder prepared by the copper powder preparation method described in Example 5, epoxy resin defoamer, wetting dispersant, nano rubber powder and mixed solvent, which are first added into a dispersion kettle and stirred evenly, then ultrasonically dispersed evenly, and ground to a desired particle size to obtain the epoxy resin polyetheramine flexible conductive ink.

[0036] Average particle size The copper powder particles obtained by the preparation methods described in Examples 1 to 5 were observed for their particle sizes using a scanning electron microscope. The specific particle sizes are shown in Table 1: Table 1 sample Example 1 Example 2 Example 3 Example 4 Example 5 Average particle size / nm 80 200 450 150 100 Performance Testing The flexible conductive inks of Preparation Example 1 and Preparation Example 2 were tested for resistance stability and oxidation resistance. After being stored at room temperature for a period of time, the resistance was measured with a four-point probe. The results are shown in Table 2: Table 2 Characterization Project <![CDATA[Resistivity (10 -3 Ω·cm)]]> Antioxidant Preparation Example 1 1.67 No resistance change within 60 days Preparation Example 2 10.26 No resistance change within 10 days Please refer to the attached Figure 1 , Attachment Figure 2 As well as the data in Table 1, compared with Example 1, the difference between the other embodiments is that Example 1 is reduced three times, while Example 2 is reduced twice and Example 3 is reduced once. It can be seen that the copper powder obtained by the three reductions has a smaller particle size; no reaction temperature difference is set between the three reductions in Example 4, while a certain temperature difference is formed between the reaction temperatures of the three reduction reactions in Example 1, and the particle size is smaller in comparison.

[0037] Please continue to refer to Table 2. The difference between Preparation Example 1 and Preparation Example 2 is that the reducing agent for preparing the copper powder in Preparation Example 1 is an aqueous ascorbic acid solution, which can maintain a low resistivity (good circuit stability) and antioxidant properties without adding a stabilizer and an antioxidant, while the reducing agent for preparing the copper powder in Preparation Example 2 is a formaldehyde aqueous solution, which cannot play the role of a stabilizer and an antioxidant.

[0038] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing ultrafine copper powder suitable for flexible conductive ink, characterized in that: The following steps are involved: A. preparing a 0.01-1 mol / L copper salt aqueous solution and at least 2 parts of an ascorbic acid aqueous solution, wherein the molar ratio of the ascorbic acid aqueous solution to the copper salt is different; B. adding the at least 2 parts of the ascorbic acid aqueous solution to the copper salt aqueous solution in sequence, and raising the reaction temperature of each part of the ascorbic acid aqueous solution and the copper salt aqueous solution by 10-40° C. in sequence to form a copper powder suspension; C. Washing and drying the copper powder suspension to obtain ultrafine copper powder.

2. The method for preparing ultrafine copper powder suitable for flexible conductive ink according to claim 1, characterized in that: The molar ratio of ascorbic acid to copper salt is 30-100.

3. The method for preparing ultrafine copper powder suitable for flexible conductive ink according to claim 1, characterized in that: In step B, after adding the first portion of the ascorbic acid aqueous solution to the copper salt aqueous solution, the reaction is maintained at a constant temperature of 50-80° C. for 5-15 minutes and then the remaining ascorbic acid aqueous solution is added.

4. The method for preparing ultrafine copper powder suitable for flexible conductive ink according to claim 3, characterized in that: The reaction time of the remaining ascorbic acid aqueous solution and the copper salt aqueous solution is more than 1 hour.

5. The method for preparing ultrafine copper powder suitable for flexible conductive ink according to claim 3, characterized in that: The reaction temperature of the remaining ascorbic acid aqueous solution and the copper salt aqueous solution is a constant temperature of 60-90°C.

6. The method for preparing ultrafine copper powder suitable for flexible conductive ink according to claim 1, characterized in that: In step B, the at least 2 portions of the ascorbic acid aqueous solution are added to the copper salt aqueous solution in descending molar ratio to the copper salt.

7. The method for preparing ultrafine copper powder suitable for flexible conductive ink according to claim 1, characterized in that: In step A, the pH value of the copper salt aqueous solution is adjusted to be alkaline.

8. The method for preparing ultrafine copper powder suitable for flexible conductive ink according to claim 7, characterized in that: The copper salt is one or more of copper sulfate, copper nitrate, copper chloride, copper hydroxide and copper acetate.

9. The ultrafine copper powder obtained by the method for preparing ultrafine copper powder suitable for flexible conductive ink according to any one of claims 1 to 8.

10. Use of the ultrafine copper powder as claimed in claim 9 in flexible conductive ink.

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