Ultrafine silver particle dispersion, method for producing the same, and method for producing conductive film

Abstract

This invention discloses an ultrafine silver particle dispersion and its preparation method, as well as a method for preparing a conductive film, belonging to the field of dispersion technology. The ultrafine silver particle dispersion includes: ultrafine silver particles, a solvent, and ethyl cellulose. The preparation method includes: Step S1: Preparation of the ultrafine silver particle aqueous dispersion: Pure water is added to a reactor, followed by the addition of octylamine and 80% hydrazine hydrate. After stirring, an aqueous solution of silver nitrate is added to the reactor, and stirring is continued to obtain an ultrafine silver particle aqueous dispersion containing octylamine-coated particles; Step S2: Collection of wet ultrafine silver particles: The wet ultrafine silver particles in the above aqueous dispersion are collected by centrifugation; Step S3: Preparation of the ultrafine silver particle dispersion: Ethyl cellulose is dissolved in diethylene glycol monobutyl ether and stirred and mixed. The above-separated wet ultrafine silver particles are added to the mixture and dried to obtain the ultrafine silver particle dispersion.

Description

Technical Field

[0001] This invention relates to the field of dispersion technology, and in particular to an ultrafine silver particle dispersion and its preparation method, as well as a method for preparing a conductive film. Background Technology

[0002] Ultrafine silver particle dispersions, formed by dispersing ultrafine silver particles in a solvent, are used to form a conductive film that can be used to construct circuits, electrodes, or conductive bonding layers. To obtain an ultrafine silver particle dispersion with good resistivity, and to use this dispersion to prepare a conductive film with low resistivity, a method for preparing the ultrafine silver particle dispersion and a method for preparing the conductive film are needed. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide an ultrafine silver particle dispersion and its preparation method, as well as a method for preparing a conductive film. The dispersion has good resistance stability, so as to prepare a conductive film with low resistivity.

[0004] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0005] This invention discloses an ultrafine silver particle dispersion, the ultrafine silver particle dispersion comprising:

[0006] The ultrafine silver particles comprise 65% to 95.4% by weight, wherein the average primary particle size of the ultrafine silver particles is 10 to 190 nm, and wherein 25% by weight of the ultrafine silver particles have a primary particle size greater than or equal to 100 nm.

[0007] Solvents with a weight percentage of 4.5% to 34.5%;

[0008] And 0.1% to 1.0% by weight of ethyl cellulose, wherein the average molecular weight of the ethyl cellulose is 10,000 to 120,000.

[0009] Another aspect of the present invention discloses a method for preparing the ultrafine silver particle dispersion, the method comprising:

[0010] Step S1: Preparation of ultrafine silver particle aqueous dispersion

[0011] Pure water was added to the reactor as the reaction medium and the temperature was adjusted to 40°C. Then, octylamine, an organic protective material, and 80% hydrazine hydrate, a reducing agent, were added to the reactor. The mixture in the reactor was stirred, and nitrogen gas was blown into the reactor as an inert gas. An aqueous solution of silver nitrate was added to the reactor, and the mixture was stirred in the reactor at a speed of 156-160 rpm for another 2-3 minutes to obtain an aqueous dispersion of ultrafine silver particles coated with octylamine.

[0012] Step S2: Collection of wet ultrafine silver particles

[0013] The wet ultrafine silver particles in the above aqueous dispersion were collected by centrifugation, which also separated most of the liquid.

[0014] Step S3: Preparation of ultrafine silver particle dispersion

[0015] Ethyl cellulose was dissolved in diethylene glycol monobutyl ether (DGBE) and stirred at 60°C for 5–7 hours with a stirring speed of 900–1100 rpm. The separated wet ultrafine silver particles were added to the mixture and then vacuum dried at 30°C for 7–9 hours to remove the moisture, thereby obtaining an ultrafine silver particle dispersion.

[0016] Preferably, in step S1, the molar ratio of octylamine to silver is 2:1.

[0017] Preferably, in step S1, the mass ratio of 80% hydrazine hydrate to silver nitrate aqueous solution is 1.8 to 2.2:1.

[0018] Another aspect of the present invention discloses a method for preparing a conductive film using the aforementioned ultrafine silver particle dispersion, the method comprising the following steps:

[0019] Liquid ultrafine silver particle dispersion is coated onto a substrate;

[0020] The coated fine silver particle dispersion was heated, dried, and solidified to form an ultrafine silver particle dispersion, which was then used to prepare a conductive film.

[0021] Preferably, the volume resistivity of the conductive film is 6 to 7 μΩ·cm.

[0022] The above technical solution has the following beneficial effects:

[0023] This application provides an ultrafine silver particle dispersion with good resistivity, which is used to prepare a conductive film with low resistivity. Detailed Implementation

[0024] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] Example 1

[0026] An ultrafine silver particle dispersion, specifically comprising:

[0027] The ultrafine silver particles comprise 65% to 95.4% by weight, with an average primary particle size of 10 to 190 nm, and 25% by weight of the ultrafine silver particles having a primary particle size greater than or equal to 100 nm.

[0028] Solvents with a weight percentage of 4.5% to 34.5%;

[0029] And 0.1% to 1.0% by weight of ethyl cellulose, with an average molecular weight of 10,000 to 120,000.

[0030] Specifically, the solvent can be diethylene glycol monobutyl ether (DGBE), a polar solvent with a boiling point of 230°C and a solubility parameter of 9.5. The ultrafine silver particle dispersion includes ultrafine silver particles, solvent, and ethyl cellulose, wherein the total weight percentage of the three is 100%. Specifically, the ultrafine silver particle dispersion may include 95.4% ultrafine silver particles, 4.5% solvent, and 0.1% ethyl cellulose by weight. The ultrafine silver particle dispersion may also include 74.5% ultrafine silver particles, 24.5% solvent, and 1.0% ethyl cellulose by weight.

[0031] Furthermore, the average primary particle size of the ultrafine silver particles is 10–190 nm, with 25% by weight of the ultrafine silver particles having a primary particle size greater than or equal to 100 nm, while the primary particle size of the remaining ultrafine silver particles is still between 10 and 190 nm. The average primary particle size corresponds to the particle size of the ultrafine silver particles in the preparation process, i.e., when the aqueous dispersion contains fine silver particles coated with octylamine. To measure the primary particle size of the ultrafine silver particles, a few drops of the aqueous dispersion were dropped onto a glass substrate, and the aqueous dispersion on the glass substrate was dried at 60 °C to retain the ultrafine silver particles. The image of the ultrafine silver particles remaining on the glass substrate was taken with a scanning electron microscope at a magnification of 50,000 times, and the primary particle size was obtained using image analysis software. SEM images with aggregated particles and irregularly shaped particles were determined to be unmeasurable.

[0032] Example 2

[0033] A method for preparing the ultrafine silver particle dispersion includes the following steps:

[0034] Step S1: Preparation of ultrafine silver particle aqueous dispersion

[0035] Pure water was added to the reactor as the reaction medium and the temperature was adjusted to 40°C. Then, octylamine, an organic protective material, and 80% hydrazine hydrate, a reducing agent, were added to the reactor. The mixture in the reactor was stirred, and nitrogen gas was blown into the reactor as an inert gas. An aqueous solution of silver nitrate was added to the reactor, and the mixture was stirred in the reactor at a speed of 156-160 rpm for another 2-3 minutes to obtain an aqueous dispersion of ultrafine silver particles coated with octylamine.

[0036] Specifically, 125.7 kg of purified water was weighed and injected into a 200-liter reactor as the reaction medium, and the temperature was adjusted to 40°C. Then, 2431.2 g of octylamine, an organic protective material, and 230.7 g of 80% hydrazine hydrate as a reducing agent were added to the reactor. The mixture in the reactor was stirred at 158 ​​rpm by a stirring rod with an impeller. At the same time, nitrogen gas was blown into the reactor as an inert gas at a rate of 20 L / min. 1253.6 g of an aqueous solution of silver nitrate was added to the reactor. By stirring the mixture in the reactor at 158 ​​rpm and continuing to stir for two minutes, an aqueous dispersion containing fine silver particles coated with octylamine was obtained. The molar ratio of octylamine to silver was 2:1, and the mass ratio of 80% hydrazine hydrate to silver was 1.8 to 2.2:1, specifically 1.8:1, 2.2:1, or 2:1.

[0037] To measure the primary particle size of the ultrafine silver particles in the above aqueous dispersion, a few drops of the aqueous dispersion were dropped onto a glass substrate. The aqueous dispersion on the glass substrate was dried at 60°C to retain the ultrafine silver particles. The image of the ultrafine silver particles remaining on the glass substrate was captured by scanning electron microscopy at a magnification of 50,000 times, and the primary particle size was obtained using image analysis software. The measured average primary particle size was 57.8 nanometers. In this dispersion system, the silver particles account for 5% or less by quantity, and their primary particle diameter is greater than or equal to 100 nanometers.

[0038] Step S2: Collection of wet ultrafine silver particles

[0039] The wet ultrafine silver particles in the above aqueous dispersion were collected by centrifugation, which also separated most of the liquid.

[0040] Step S3: Preparation of ultrafine silver particle dispersion

[0041] Ethyl cellulose was dissolved in diethylene glycol monobutyl ether (DGBE) and stirred at 60°C for 5–7 hours with a stirring speed of 900–1100 rpm. The separated wet ultrafine silver particles were added to the mixture and then vacuum dried at 30°C for 7–9 hours to remove the moisture, thereby obtaining an ultrafine silver particle dispersion.

[0042] Specifically, ethyl cellulose (molecular weight 77180, glass transition temperature 130°C, Dow Chemical Company) was dissolved in diethylene glycol monobutyl ether (DGBE) and stirred at 60°C for 6 hours using a magnetic stirrer at a stirring speed of 1000 rpm. The wet ultrafine silver particles obtained in the above process were dispersed in ethyl cellulose and diethylene glycol monobutyl ether. The mixture of wet ultrafine silver particles and solution was vacuum dried at 30°C for 8 hours to remove the water content, thereby obtaining a dispersion of ultrafine silver particles.

[0043] At this point, the secondary particle diameter of the ultrafine silver particles in the dispersion can be measured. The method for diluting the fine silver particle dispersion by 10,000 times is as follows: add diethylene glycol monobutyl ether (DGBE) to the fine silver particle dispersion, then perform ultrasonic treatment with an ultrasonic cleaner, and use the diluted fine silver particle dispersion to measure the particle diameter (D50).

[0044] Example 3

[0045] A method for preparing a conductive film using the above-mentioned ultrafine silver particle dispersion specifically includes the following steps:

[0046] Liquid ultrafine silver particle dispersion is coated onto a substrate;

[0047] The coated fine silver particle dispersion was heated, dried and solidified to form an ultrafine silver particle dispersion, which was then used to prepare a conductive film.

[0048] The volume resistivity of the conductive film is 6–7 μΩ·cm;

[0049] Specifically, a liquid ultrafine silver particle dispersion is coated onto a glass substrate and baked at 130°C for 30–60 minutes using a hot air dryer. The specific drying temperature can be between 120 and 140°C to prepare a conductive film. The volume resistivity of the conductive film was tested using the four-probe method and found to be 6.4 μΩ·cm. The conductive film can be used to construct circuits, electrodes, or conductive bonding layers.

[0050] In addition, a portion of the ultrafine silver particle dispersion was stored at 25°C for 3 months and a conductive film was prepared in the same manner. The measured volume resistivity was still 6.4 μΩ·cm. This dispersion has good resistance stability and can be used to prepare a conductive film with low resistivity.

[0051] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. An ultrafine silver particle dispersion, characterized in that, The ultrafine silver particle dispersion comprises: The ultrafine silver particles comprise 65% to 95.4% by weight, wherein the average primary particle size of the ultrafine silver particles is 10 to 190 nm, and wherein 25% by weight of the ultrafine silver particles have a primary particle size greater than or equal to 100 nm. Solvents with a weight percentage of 4.5% to 34.5%; And 0.1% to 1.0% by weight of ethyl cellulose, wherein the average molecular weight of the ethyl cellulose is 10,000 to 120,000.

2. A method for preparing the ultrafine silver particle dispersion as described in claim 1, characterized in that, The preparation method includes: Step S1: Preparation of ultrafine silver particle aqueous dispersion Pure water as the reaction medium was added to the reactor and the temperature was adjusted to 40°C. Then, octylamine, an organic protective material, and 80% hydrazine hydrate as a reducing agent were added to the reactor. The mixture in the reactor was stirred, and nitrogen gas was blown into the reactor as an inert gas. An aqueous solution of silver nitrate was added to the reactor, and the mixture was stirred in the reactor at a speed of 156-160 rpm for another 2-3 minutes to obtain an aqueous dispersion of ultrafine silver particles coated with octylamine. Step S2: Collection of wet ultrafine silver particles The wet ultrafine silver particles in the above aqueous dispersion were collected by centrifugation, which also separated most of the liquid. Step S3: Preparation of ultrafine silver particle dispersion Ethyl cellulose was dissolved in diethylene glycol monobutyl ether and stirred with a magnetic stirrer at 60°C for 5–7 hours at a stirring speed of 900–1100 rpm. The separated wet ultrafine silver particles were added to the mixture and then vacuum dried at 30°C for 7–9 hours to remove the moisture, thereby obtaining an ultrafine silver particle dispersion.

3. The method for preparing the ultrafine silver particle dispersion according to claim 2, characterized in that, In step S1, the molar ratio of octylamine to silver is 2:

1.

4. The method for preparing the ultrafine silver particle dispersion according to claim 2, characterized in that, In step S1, the mass ratio of 80% hydrazine hydrate to silver nitrate aqueous solution is 1.8 to 2.2:

1.

5. A method for preparing a conductive film using the ultrafine silver particle dispersion described in claim 1, characterized in that, The method includes the following steps: Liquid ultrafine silver particle dispersion is coated onto a substrate; The coated fine silver particle dispersion is heated, dried and solidified to form an ultrafine silver particle dispersion, which is then used to prepare a conductive film.

6. The method for preparing a conductive film from the ultrafine silver particle dispersion according to claim 5, characterized in that, The volume resistivity of the conductive film is 6–7 μΩ·cm.