CN117672595A

CN117672595A - Low-temperature conductive paste suitable for 3D printing, preparation method and application thereof

Info

Publication number: CN117672595A
Application number: CN202211054460.3A
Authority: CN
Inventors: 朱晓艳; 严俊秋; 沈剑铧; 赵怀远; 陈小朋
Original assignee: Corevoxel Hangzhou Technology Development Co ltd
Current assignee: Corevoxel Hangzhou Technology Development Co ltd
Priority date: 2022-08-31
Filing date: 2022-08-31
Publication date: 2024-03-08

Abstract

The invention relates to the field of conductive paste, in particular to low-temperature conductive paste suitable for 3D printing, a preparation method and application thereof, wherein the low-temperature conductive paste comprises silver nano particles, a diluent and a binder; wherein the surface of the silver nanoparticle is coated with a ligand; the diluent is an organic alcohol substance; the binder is an alcohol-soluble resin. The invention aims to overcome the defects of easy agglomeration of silver nano particles and poor dispersibility after long-term storage of the conductive paste in the prior art, which cause easy blockage of a needle head in 3D printing and poor sintering conductivity and adhesiveness, and the low-temperature conductive paste prepared by the invention not only has good dispersibility and stability, but also has good compactness and conductivity after sintering, and can realize high-precision direct-writing 3D printing of 10 mu m or less.

Description

Low-temperature conductive paste suitable for 3D printing, preparation method and application thereof

Technical Field

The invention relates to the field of conductive paste, in particular to low-temperature conductive paste suitable for 3D printing, a preparation method and application thereof.

Background

The precise 3D printing technology is a global frontier advanced manufacturing technology, can realize the preparation of a complex micro-nano scale three-dimensional structure through printing control of different dimensions, is widely focused in the fields of precise optics, micro-nano chips, printed electronics and the like, and has great industrial potential.

The technology is applied to the microelectronics industry, and has higher requirements on performance indexes of conductive slurry, and the used slurry has excellent shape retention and conductivity on the basis of meeting smooth discharging of a fine nozzle. At present, conductive metal paste prepared from nano silver particles is mainly used in the market, and the paste generally has higher conductivity and is concerned by the field of three-dimensional integrated electronics.

The existing preparation methods of silver nanoparticles can be generally summarized into two types of physical methods (plasma and atomization methods) and chemical methods (silver nitrate thermal decomposition method and liquid phase reduction method). Among them, the liquid phase reduction method is currently the most dominant method for preparing silver nanoparticles. The liquid phase reduction method is to dissolve silver salt (such as silver nitrate, etc.) in water, add chemical reducing agent, prepare silver nano particles with corresponding size, and then purify the silver nano particles by centrifugation.

For example, patent CN110842191B discloses a preparation method of spherical silver powder for photovoltaic positive and negative electrodes, which adopts a liquid phase reduction method to prepare spherical silver powder with the advantages of high dispersibility, good sphericity, high tap density, narrow particle size distribution and the like, but the subsequent slurry preparation of the patent is to treat the surface of the spherical silver powder by a surface treatment agent such as oleic acid, then disperse the spherical silver powder in a corresponding oil-soluble diluent, and the process can cause incomplete surface treatment or ligand loss, so that silver nanoparticles are easy to agglomerate in the diluent.

Patent CN113593750a discloses a preparation method of water-soluble nano metal slurry, which improves the adhesiveness of the slurry on the surfaces of different substrates by introducing water-soluble resin, but in the practical use process, we can find that water is used as a diluent of the slurry, and the problem that the water is easy to volatilize is caused in the long-term use process, so that the problem of agglomeration easily occurs.

Disclosure of Invention

The invention aims to overcome the defects of the conductive paste in the prior art, and therefore provides a low-temperature conductive paste suitable for 3D printing, a preparation method and application thereof.

In order to achieve the aim of the invention, the invention is realized by the following technical scheme:

in a first aspect, the present invention provides a low temperature conductive paste suitable for 3D printing,

comprises silver nano particles, a diluent and a binder; wherein,

the surface of the silver nanoparticle is coated with a ligand;

the diluent is an organic alcohol substance;

the binder is an alcohol-soluble resin.

The surface of the silver nano particles in the conductive paste is coated with the ligand, so that the problem of agglomeration among the silver nano particles caused by factors such as physical adsorption or electrostatic adsorption can be avoided, and the silver nano particles have good dispersibility and stability. Therefore, the conductive paste is suitable for a high-precision direct-writing 3D printing process with the thickness of 10 mu m or less, and the problem of blocking does not occur during long-time working.

In addition, the preparation method of silver nano particles in the prior art is mostly aqueous phase synthesis, and the obtained silver particle surface ligand is mostly aqueous ligand, so that water is usually adopted as a diluent of the slurry after the silver nano particles are prepared into the slurry, and the problem that the water is extremely volatile, so that the silver nano particles are easy to agglomerate in the long-term use process is caused.

The diluent selected in the invention is an organic alcohol substance, which not only ensures good dispersibility of silver nano particles synthesized in water phase, but also has good dispersibility to corresponding alcohol-soluble resin, thus realizing preparation of high-dispersibility silver paste. The main solvent of the slurry obtained by water phase synthesis is water, and the slurry is easy to agglomerate when stored for a long time due to easy volatilization, and the water is replaced by the alcohol-soluble solvent which is not easy to volatilize as a diluent, so that the silver nano particles can be uniformly dispersed, and the storage stability of the silver nano particles is improved.

Preferably, the silver nanoparticle preparation method comprises the following steps:

(1) Adding a silver precursor into a solution containing a ligand to form a mixed solution;

(2) Adding a reducing agent into the mixed solution to reduce the silver precursor to obtain silver nano particles;

(3) Washing the obtained silver nano particles by a mixed solvent;

the reducing agent in the step (2) is a compound with a general formula of HO-X-NH ₂ Wherein X is an alkane chain having 2.ltoreq.C.ltoreq.6.

In the prior art, polyalcohol amine such as diethanolamine is generally used as a reducing agent in the preparation of silver nano-particles. However, in the preparation process, the applicant finds that the adoption of polyalcohol amine as a reducing agent can cause the increase of the crosslinking degree between free organic ligands in the slurry, so that the purification is difficult to be clean in the subsequent purification process, and the existing silver nano particles can obtain good conductivity only at a higher sintering temperature (such as 300 ℃); meanwhile, the free organic ligand is gasified and decomposed in the sintering process, so that the porosity in the sintered silver wire is obviously increased, and the conductivity is reduced.

Therefore, the reducing agent adopted by the invention is a reducing agent with the general formula of HO-X-NH ₂ Can ensure that no side products of cross-linking ligand appear in the process of synthesizing silver nano particles, thereby realizing the purpose of low-temperature sintering. In addition, the reducing agent can ensure the cleaning effect on the redundant free organic ligand in the subsequent purification process.

Preferably, in the step (3):

the mixed solvent consists of a good solvent with stronger dissolving capacity for the ligand and a secondary good solvent with weaker dissolving capacity for the ligand;

the good solvent contains hydroxyl or carbonyl;

the secondary solvent contains an ester group.

In the prior art, after the preparation of the silver nanoparticles is finished, the silver nanoparticles are usually directly used after centrifugation, however, more reducing agent and ligand which is not combined with the silver nanoparticles still remain in the silver nanoparticles obtained in the way, and impurities remained in the silver nanoparticles have obvious influence on conductivity and adhesion after sintering. Thus, in some documents, the silver nanoparticles are further purified by a plurality of times using a solvent having a relatively high polarity (e.g., water, ethanol) after being prepared, however, although this technique can remove the free ligand which is not bound to the silver nanoparticles, the ligand bound to the surface of the silver nanoparticles can also be destroyed. Thereby causing the loss of ligand on the surface of the silver nano-particles in the purification and subsequent treatment processes, so that part of silver atoms or ions are exposed on the surface of the silver particles. Therefore, agglomeration problems caused by physical adsorption or electrostatic adsorption are easy to occur among particles, so that uniformity of particle dispersion of slurry is influenced, and the problem of needle blockage is easy to cause in a 3D printing process, and the method is not suitable for a 3D printing process.

Therefore, the invention optimizes the purification process to a certain extent in the purification process of the silver nano-particles, firstly selects the combination of the good solvent and the mixed solvent of the inferior good solvent in the purification process, and can properly reduce the polarity of the purification solvent, so that on the premise of effectively removing free ligand in the purification process, enough organic ligand can be reserved on the surface of the silver nano-particles, the stability of the slurry in the storage process and the surface compactness after sintering are ensured, and the overall stability of the slurry and the conductivity after sintering are improved.

Preferably, the good solvent is any one or a combination of methanol, ethanol and acetone;

the secondary good solvent is any one or combination of ethyl acetate, propyl acetate and butyl acetate.

In the invention, organic alcohols are selected as diluents.

Preferably, the diluent is an organic alcohol substance with carbon number/hydroxyl group not more than 4 and hydroxyl number not less than 2.

The method can ensure good dispersibility of the silver nano particles synthesized in the water phase and good dispersibility of the corresponding alcohol-soluble resin, and can realize preparation of high-dispersibility silver paste. And the volatility of the water-based paint can be effectively reduced in the use process, and the possibility of agglomeration in the long-term use process is further reduced.

Preferably, the diluent comprises any one or more of ethylene glycol, glycerol, 1, 4-butanediol, isoprene glycol and trimethylolpropane.

Preferably, the alcohol-soluble resin comprises any one or more of alcohol-soluble epoxy resin, alcohol-soluble acrylic resin and alcohol-soluble polyurethane.

Preferably, the ligand comprises any one or more of PAA, PVP, triton and PEG.

Preferably, the solid content of the low-temperature conductive paste is 50-90%;

the conductivity of the low-temperature conductive slurry after sintering is more than or equal to 6.3 x 10 at any temperature of 150-200 DEG C ⁶ S/m；

The adhesion performance after sintering was 4B and above according to ASTM D3359-2017 test Standard test results.

In a second aspect of the present invention, there is also provided a method for preparing the conductive paste, comprising the steps of:

(S.1) preparation of silver nanoparticles;

(s.2) mixing silver nanoparticles with a diluent and a binder to obtain the conductive paste.

In a third aspect, the invention also provides application of the conductive paste in the fields of high-precision direct-writing 3D printing, precision optics, micro-nano chips, photovoltaics or printed electronics with the thickness of 10 mu m and below.

Therefore, the invention has the following beneficial effects:

(1) The invention uses low boiling point alcohol amine as the reducing agent, and can obtain low temperature sintered nano silver paste at any temperature of 150-200 DEG CAt a temperature, the electrical conductivity after sintering is more than or equal to 6.3 x 10 ⁶ S/m, and good compactness after sintering;

(2) Meanwhile, after the silver nano particles are reduced, the purification mode of combining a good solvent and a secondary good solvent is used, free ligands can be fully washed off, the ligands on the surfaces of the silver nano particles are reserved, the dispersibility and sintering performance of the nano silver particles are improved, the mutual solubility of the nano silver particles and alcohol-soluble resin is facilitated, the adhesion after the slurry is sintered is improved, the alcohol-soluble diluent and the silver slurry of the alcohol-soluble resin are added, the adhesion after the sintering at 200 ℃ is obviously improved, and the adhesion is 4B or more through the hundred-gram cross-hatch test of ASTM D3359-2017 test standard;

(3) The stability of the slurry stored for a long time is obviously improved, the slurry can be stably discharged for more than 4 hours at a needle head with the diameter of 10 mu m after being stored for more than 3 months in a room temperature environment;

(4) The low-temperature conductive paste is stored for more than 3 months in a room temperature environment, and the change amplitude of the conductivity of the low-temperature conductive paste after sintering is less than or equal to 10 percent.

Drawings

Fig. 1 is an SEM photograph of the silver nanoparticle (A1) prepared in example 1.

Fig. 2 is an SEM photograph of the low-temperature conductive paste (B1) prepared in example 1 after sintering.

Fig. 3 is an SEM photograph of the silver nanoparticle (A2) prepared in example 2.

Fig. 4 is an SEM photograph of the low temperature conductive paste (B2) prepared in example 2 after sintering.

Fig. 5 is an SEM photograph of the silver nanoparticle (A3) prepared in example 3.

Fig. 6 is an SEM photograph of the low temperature conductive paste (B3) prepared in example 3 after sintering.

Fig. 7 is an SEM photograph of the silver nanoparticle (A4) prepared in example 4.

Fig. 8 is an SEM photograph of the low-temperature conductive paste (B4) prepared in example 4 after sintering.

Fig. 9 is an SEM photograph of the silver nanoparticle (A5) prepared in example 5.

Fig. 10 is an SEM photograph of the low-temperature conductive paste (B5) prepared in example 5 after sintering.

Fig. 11 is an SEM photograph of the silver nanoparticle (A6) prepared in example 6.

Fig. 12 is an SEM photograph of the low-temperature conductive paste (B6) prepared in example 6 after sintering.

Fig. 13 is an SEM photograph of the silver nanoparticle (A7) prepared in example 7.

Fig. 14 is an SEM photograph of the low-temperature conductive paste (B7) prepared in example 7 after sintering.

Fig. 15 is an SEM photograph of the silver nanoparticle (A8) prepared in example 8.

Fig. 16 is an SEM photograph of the low-temperature conductive paste (B8) prepared in example 8 after sintering.

Fig. 17 is an SEM photograph of the silver nanoparticle (A9) prepared in comparative example 1.

Fig. 18 is an SEM photograph of the low-temperature conductive paste (B9) prepared in comparative example 1 after sintering.

Fig. 19 is an SEM photograph of the silver nanoparticle (a 10) prepared in comparative example 2.

Fig. 20 is an SEM photograph of the low temperature conductive paste (B10) prepared in comparative example 2 after sintering.

Fig. 21 is an SEM photograph of the silver nanoparticle (a 11) prepared in comparative example 3.

Fig. 22 is an SEM photograph of the low temperature conductive paste (B11) prepared in comparative example 3 after sintering.

Detailed Description

The invention is further described below with reference to the drawings and specific examples. Those of ordinary skill in the art will be able to implement the invention based on these descriptions. In addition, the embodiments of the present invention referred to in the following description are typically only some, but not all, embodiments of the present invention. Therefore, all other embodiments, which can be made by one of ordinary skill in the art without undue burden, are intended to be within the scope of the present invention, based on the embodiments of the present invention.

[ preparation of silver paste ]

Example 1

[ preparation of silver paste ]

(1) Taking 20g of AgNO ₃ (118 mmol) in 20g deionized water to prepare silver nitrate solution, adding 50g deionized water into a conical flask, sequentially adding 3g of PAA (MW 3000) and 1g of PAA (MW 20,000), starting stirring, dropwise adding the silver nitrate solution into the conical flask, finally pouring 18g (295 mmol) of ethanolamine into the conical flask at a high speed, and stirring at a rotating speed of 300r/min for 2h;

(2) Heating and stirring for 2h on a hot table at 120 ℃;

(3) Cooling to room temperature, adding 100ml of ethyl acetate, adding 300ml of ethanol in portions, stirring for 10min, separating out a product in the form of flocculent precipitate, removing supernatant, transferring the precipitate to a 50ml centrifuge tube, and centrifuging at 9000rpm for 20min;

(4) Removing supernatant, adding deionized water to 15mL, shaking uniformly, filtering with a10 μm filter screen for 1 time, filtering with A1 μm filter screen for 1 time again, adding ethyl acetate 10mL, adding ethanol to 50mL, shaking uniformly, centrifuging at 9000rpm for 20min, removing supernatant, and mixing uniformly to obtain silver nanoparticle (A1), wherein SEM photograph shows that particle size is less than 400nm.

[ preparation of Low-temperature conductive paste ]

The silver paste obtained above was treated with 5% ethylene glycol and then added with epoxy-ethylene glycol (9:1) (epoxy resin content 3 wt%) and mixed uniformly to obtain a low-temperature conductive paste (B1) having a solid content of 87%, and SEM photograph of the silver film obtained after sintering thereof was shown in fig. 2.

Example 2

(1) Taking 20g of AgNO ₃ (118 mmol) in 20g deionized water to prepare silver nitrate solution, adding 50g deionized water into a conical flask, sequentially adding 3g of PAA (MW 3000) and 1g of PAA (MW 20,000), starting stirring, dropwise adding the silver nitrate solution into the conical flask, finally pouring 22g (295 mmol) of propanolamine into the conical flask at a high speed, and stirring at a rotating speed of 300r/min for 2h;

(2) Heating and stirring for 2h on a hot table at 120 ℃;

(4) Removing supernatant, adding deionized water to 15mL, shaking uniformly, filtering with a10 μm filter screen for 1 time, filtering with a1 μm filter screen for 1 time again, adding ethyl acetate 10mL, adding ethanol to 50mL, shaking uniformly, centrifuging at 9000rpm for 20min, removing supernatant, and mixing uniformly to obtain silver nanoparticles (A2), wherein SEM photograph shows that particle size is less than 400nm.

[ preparation of Low-temperature conductive paste ]

The silver paste obtained above was treated with 5% ethylene glycol and then added with epoxy-ethylene glycol (9:1) (epoxy resin content 3 wt%) and mixed to obtain a low-temperature conductive paste (B2) having a solid content of 84%, and SEM photograph of the silver film obtained after sintering thereof was shown in fig. 4.

Example 3

(1) Taking 20g of AgNO ₃ (118 mmol) in 20g deionized water to prepare silver nitrate solution, adding 50g deionized water into a conical flask, sequentially adding 3g of PAA (MW 3000) and 1g of PAA (MW 20,000), starting stirring, dropwise adding the silver nitrate solution into the conical flask, finally pouring 26g (295 mmol) of butanolamine into the conical flask at a high speed, and stirring at a rotating speed of 300r/min for 2h;

(2) Heating and stirring for 2h on a hot table at 120 ℃;

(4) Removing supernatant, adding deionized water to 15mL, shaking uniformly, filtering with a10 μm filter screen for 1 time, filtering with a1 μm filter screen for 1 time again, adding ethyl acetate 10mL, adding ethanol to 50mL, shaking uniformly, centrifuging at 9000rpm for 20min, removing supernatant, and mixing uniformly to obtain silver nanoparticles (A3), wherein SEM photograph shows that particle size is less than 400nm.

[ preparation of Low-temperature conductive paste ]

The silver paste obtained above was treated with 5% ethylene glycol and then added with epoxy-ethylene glycol (9:1) (epoxy resin content 3 wt%) and mixed to obtain a low-temperature conductive paste (B3) having a solids content of 82%, and an SEM photograph of the silver film obtained after sintering thereof was shown in fig. 6.

Example 4

[ preparation of silver paste ]

(2) Heating and stirring for 2h on a hot table at 120 ℃;

(4) Removing supernatant, adding deionized water to 15mL, shaking uniformly, filtering with a10 μm filter screen for 1 time, filtering with a1 μm filter screen for 1 time again, adding ethyl acetate 10mL, adding ethanol to 50mL, shaking uniformly, centrifuging at 9000rpm for 20min, removing supernatant, and mixing uniformly to obtain silver nanoparticles (A4), wherein SEM photograph shows that particle size is less than 400nm.

[ preparation of Low-temperature conductive paste ]

After the silver paste obtained above was treated with 5% glycerol (with an adjustable solid content), epoxy-glycerol (9:1) (epoxy resin content 3 wt%) was added and mixed uniformly to obtain a low-temperature conductive paste (B4) with a solid content of 87%, and an SEM photograph of the silver film obtained after sintering thereof was shown in fig. 8.

Example 5

[ preparation of silver paste ]

(1) Taking 20g of AgNO ₃ （118mmol) Dissolving in 20g of deionized water to prepare a silver nitrate solution, adding 50g of deionized water into a conical flask, sequentially adding 3g of PAA (MW 3000) and 1g of PAA (MW 20,000), starting stirring, dropwise adding the silver nitrate solution into the conical flask, finally pouring 18g (295 mmol) of ethanolamine into the conical flask at a high speed, and stirring for 2 hours at a rotating speed of 300 r/min;

(2) Heating and stirring for 2h on a hot table at 120 ℃;

(4) Removing supernatant, adding deionized water to 15mL, shaking uniformly, filtering with a10 μm filter screen for 1 time, filtering with a1 μm filter screen for 1 time again, adding ethyl acetate 10mL, adding ethanol to 50mL, shaking uniformly, centrifuging at 9000rpm for 20min, removing supernatant, and mixing uniformly to obtain silver nanoparticles (A5), wherein SEM photograph shows that particle size is less than 400nm.

[ preparation of Low-temperature conductive paste ]

After the silver paste obtained above was treated with 5% trimethylolpropane (solid content was adjustable), epoxy-trimethylolpropane (9:1) (epoxy resin content 3 wt%) was added and mixed uniformly to obtain a low-temperature conductive paste (B5) having a solid content of 87%, and SEM photograph of the silver film obtained after sintering thereof was shown in fig. 10.

Example 6

[ preparation of silver paste ]

(2) Heating and stirring for 2h on a hot table at 120 ℃;

(3) Cooling to room temperature, adding 150ml of butyl acetate, adding 250ml of methanol in portions, stirring for 10min, separating out a product in the form of flocculent precipitate, removing supernatant, transferring the precipitate to a 50ml centrifuge tube, and centrifuging at 9000rpm for 20min;

(4) Removing supernatant, adding deionized water to 15mL, shaking uniformly, filtering with a10 μm filter screen for 1 time, filtering with a1 μm filter screen for 1 time again, adding 13mL of butyl acetate, adding methanol to 50mL of shaking uniformly, centrifuging at 9000rpm for 20min, removing supernatant, and mixing uniformly to obtain silver nanoparticles (A6), wherein SEM photograph shows that particle size is less than 400nm.

[ preparation of Low-temperature conductive paste ]

The silver paste obtained above was treated with 5% ethylene glycol and then added with epoxy-ethylene glycol (9:1) (epoxy resin content 3 wt%) and mixed to obtain a low-temperature conductive paste (B6) having a solid content of 87%, and SEM photograph of the silver film obtained after sintering thereof was shown in fig. 12.

Example 7

[ preparation of silver paste ]

(2) Heating and stirring for 2h on a hot table at 120 ℃;

(3) Cooling to room temperature, adding 200ml of propyl acetate, adding 200ml of acetone in portions, stirring for 10min, separating out product in flocculent precipitate, removing supernatant, transferring the precipitate to a 50ml centrifuge tube, and centrifuging at 9000rpm for 20min;

(4) Removing supernatant, adding deionized water to 15mL, shaking uniformly, filtering with a10 μm filter screen for 1 time, filtering with a1 μm filter screen for 1 time again, adding 17.5mL of propyl acetate, adding acetone to 50mL of shaking uniformly, centrifuging at 9000rpm for 20min, removing supernatant, and mixing uniformly to obtain silver nanoparticle (A7), wherein SEM photograph shows that particle size is <400nm.

[ preparation of Low-temperature conductive paste ]

The silver paste obtained above was treated with 5% ethylene glycol and then added with epoxy-ethylene glycol (9:1) (epoxy resin content 3 wt%) and mixed to obtain a low-temperature conductive paste (B7) having 86% solids content, and SEM photograph of the silver film obtained after sintering thereof was shown in fig. 14.

Example 8

[ preparation of silver paste ]

(2) Heating and stirring for 2h on a hot table at 120 ℃;

(4) Removing supernatant, adding deionized water to 15mL, shaking uniformly, filtering with a10 μm filter screen for 1 time, filtering with a1 μm filter screen for 1 time again, adding ethyl acetate 10mL, adding ethanol to 50mL, shaking uniformly, centrifuging at 9000rpm for 20min, removing supernatant, and mixing uniformly to obtain silver nanoparticles (A8), wherein SEM photograph shows that particle size is <400nm.

[ preparation of Low-temperature conductive paste ]

The silver paste obtained above was treated with 40% ethylene glycol and then added with epoxy-ethylene glycol (9:1) (epoxy resin content 3 wt%) and mixed to obtain a low-temperature conductive paste (B8) having a solid content of 54%, and an SEM photograph of the silver film obtained after sintering thereof was shown in fig. 16.

Comparative example 1

[ preparation of silver paste ]

(1) Taking 20g of AgNO ₃ (118 mmol) was dissolved in 20g deionized water to prepare a silver nitrate solution, 50g deionized water was added to a Erlenmeyer flask, followed by sequential addition3g of PAA (MW 3000), 1g of PAA (MW 20,000), starting stirring, dropwise adding a silver nitrate solution into a conical flask, and finally pouring 31g (295 mmol) of diethanolamine into the conical flask at a faster speed, and stirring at a rotating speed of 300r/min for 2 hours;

(2) Heating and stirring for 2h on a hot table at 120 ℃;

(4) Removing supernatant, adding deionized water to 15mL, shaking uniformly, filtering with a10 μm filter screen for 1 time, filtering with a1 μm filter screen for 1 time again, adding ethyl acetate 10mL, adding ethanol to 50mL, shaking uniformly, centrifuging at 9000rpm for 20min, removing supernatant, and mixing uniformly to obtain silver nanoparticles (A9), wherein SEM photograph shows that particle size is <400nm as shown in figure 17.

[ preparation of conductive paste ]

The silver paste obtained above was treated with 5% ethylene glycol and then added with epoxy-ethylene glycol (9:1) (epoxy resin content 3 wt%) and mixed to obtain a conductive paste (B9) having a solid content of 75%, and SEM photograph of the silver film obtained after sintering thereof was shown in fig. 18.

Comparative example 2

[ preparation of silver paste ]

(2) Heating and stirring for 2h on a hot table at 120 ℃;

(3) Cooling to room temperature, adding 400ml of ethanol, adding in portions, stirring for 10min, separating out product in flocculent precipitate, removing supernatant, transferring the precipitate to a 50ml centrifuge tube, and centrifuging at 9000rpm for 20min;

(4) Removing supernatant, adding deionized water to 15mL, shaking uniformly, filtering with a10 μm filter screen for 1 time, filtering with A1 μm filter screen for 1 time, adding ethanol to 60mL, shaking uniformly, centrifuging at 9000rpm for 20min, removing supernatant, and mixing uniformly to obtain silver nanoparticle (A10), wherein SEM photograph shows that particle size is less than 400nm.

[ preparation of conductive paste ]

The silver paste obtained above was treated with 5% ethylene glycol and then added with epoxy-ethylene glycol (9:1) (epoxy resin content 3 wt%) and mixed to obtain a conductive paste (B10) having a solids content of 88%, and SEM photograph of the silver film obtained after sintering thereof was shown in fig. 20.

Comparative example 3

[ preparation of silver paste ]

(1) Taking 20g of AgNO3 (118 mmol), dissolving in 20g of deionized water to prepare a silver nitrate solution, adding 50g of deionized water into a conical flask, sequentially adding 3g of PAA (MW 3000) and 1g of PAA (MW 20,000), starting stirring, dropwise adding the silver nitrate solution into the conical flask, and finally pouring 18g (295 mmol) of ethanolamine into the conical flask at a high speed, and stirring for 2 hours at a rotating speed of 300 r/min;

(2) Heating and stirring for 2h on a hot table at 120 ℃;

(4) Removing supernatant, adding deionized water to 15mL, shaking uniformly, filtering with a10 μm filter screen for 1 time, filtering with A1 μm filter screen for 1 time again, adding ethyl acetate 10mL, adding ethanol to 50mL, shaking uniformly, centrifuging at 9000rpm for 20min, removing supernatant, and mixing uniformly to obtain silver nanoparticles (A11), wherein SEM photograph shows that particle size is less than 400nm.

[ preparation of conductive paste ]

The silver paste obtained above was treated with 5% ethanol, then epoxy-ethanol (9:1) (epoxy resin content 3 wt%) was added and mixed to obtain a conductive paste (B11) having a solid content of 87%, and SEM photograph of the silver film obtained after sintering thereof was shown in fig. 22.

[ Performance test ]

(1) Particle size observation: the silver nanoparticle size and morphology were characterized using a flying scanning electron microscope.

The specific method is as follows: (1) a small amount of silver paste was taken to 1:1000 in deionized water or organic solvent; (2) fully dispersing the diluent, sucking a small amount of liquid drop on the surface of the carrier by a dropper, and heating to remove the redundant solvent; (3) and (5) after sample preparation and metal spraying, sample feeding and observation are carried out to obtain the size and morphology image information of the silver nano particles.

(2) Resistivity test: the resistivity of the silver paste and the low-temperature conductive paste added with the resin was tested using a Rayleigh Ke Weiye FT-340 four-probe sheet resistance tester.

The specific method is as follows: (1) spreading the prepared silver paste and low-temperature conductive paste on a glass original plate by a coater, and sintering at 200 ℃ in air for 60min to obtain a conductive silver film; (2) measuring the thickness of the sintered silver film sample by means of a step instrument; (3) setting corresponding parameters in Fang Zuyi, and adjusting the four probes to vertically press down and touch the sample to be measured; (4) and after the number to be read is stable, recording data such as sheet resistance, resistivity and the like.

(3) Adhesion test

(1) The prepared low-temperature conductive paste is coated on a glass original plate by a coating machine, and sintered for 60 minutes at 200 ℃ in air to obtain a conductive silver film;

(2) using ASTM D3359-2017 as a test standard, using a hundred-knife to cut at a cutting speed of 20-50mm/s on the surface of the test piece;

(3) rotating the test piece by 90 degrees, and repeating the above operation on the cut to form a lattice pattern;

(4) brushing diagonal lines on two sides of the lattice pattern by using soft brush, and slightly brushing for 5 times in front and back respectively;

(5) the 3M 600-1PK test was used to test the dedicated tape, peel test, and evaluate the material adhesion properties.

(4) Stability test

The prepared low-temperature conductive paste is stored in a sealed manner in a room temperature environment, the state of the paste after 90 days of storage is monitored, the stable appearance time of a needle with the diameter of 10 mu m is tested, and the monitoring time is 4 hours.

[ characterization of experimental results ]

The performance test results of the silver nanoparticles (A1) to (a 11) obtained in examples 1 to 8 and comparative examples 1 to 3 are shown in table 1 below:

table 1 shows the results of the performance test of silver nanoparticles (A1) to (A11) in examples 1 to 8 and comparative examples 1 to 3

。

The results of performance tests of the conductive pastes (B1) to (B11) prepared in examples 1 to 8 and comparative examples 1 to 3 are shown in table 2 below:

table 2 Table of results of Performance test of conductive pastes (B1) to (B11) in examples 1 to 8 and comparative examples 1 to 3

。

[ Performance analysis ]

As can be seen from the data in tables 1 and 2, the silver nanoparticles (A1) to (A8) and the conductive pastes (B1) to (B8) prepared by the methods in examples 1 to 8 of the present invention have significantly better properties than the silver nanoparticles (A9) to (a 11) and the conductive pastes (B9) to (B11) prepared by the methods in comparative examples 1 to 3, respectively.

Comparing example 1 with comparative example 1, we find that example 1 differs from comparative example 1 in that the reducing agent used in example 1 is ethanolamine and the reducing agent used in comparative example 1 is diethanolamine. As can be seen from the comparison of fig. 1 and 17, the surface of the silver nanoparticles in the silver paste synthesized in example 1 using ethanolamine as a reducing agent is smoother, while the surface of the silver nanoparticles in the silver paste synthesized in comparative example 1 using diethanolamine as a reducing agent is rougher, indicating that the diethanolamine has a by-product of crosslinking ligand during the reduction.

As can be seen from SEM photographs of the silver film obtained by sintering the conductive paste, the silver nanoparticles obtained by reduction of ethanolamine are well densified (as shown in fig. 2) after being prepared into the conductive paste, so that the conductivity of the silver film is better; and silver nanoparticles obtained by reduction of diethanolamine are less dense (as shown in fig. 18) and have higher resistivity after being sintered to obtain a silver film after being prepared into conductive paste.

Comparing example 1 with comparative example 2, we found that the polarity of the solvent during the purification process had a significant effect on the conductivity of the stability of the final conductive paste. When the silver paste is cleaned by using stronger ethanol as a solvent, the ligand attached to the surface of the silver nano particles can be removed to a certain extent, so that the dispersibility and the adhesion performance of the nano silver particles after sintering are reduced, and the sintered silver film is easy to crack. In the embodiment 1, the combination of the polar solvent and the secondary good solvent can properly reduce the polarity of the purifying liquid, so that on the premise of effectively removing free ligand in the purifying process, enough organic ligand can be reserved on the surface of the silver nano particles, the stability of the slurry in the storage process and the adhesion after sintering are ensured, and the overall stability of the slurry and the adhesion performance after sintering are improved.

Comparing example 1 with comparative example 3, we found that in comparative example 3, the conductive paste was prepared using ethanol which is volatile as a diluent, and because of its high volatility, the silver nanoparticles in the paste were agglomerated during long-term use, resulting in a decrease in storage stability, and delamination of ethanol from silver paste, and almost no film formation, and a rapid drying rate. The diluent selected in the embodiment 1 is ethylene glycol with weaker volatility, which not only ensures good dispersibility of the silver nanoparticles synthesized in the water phase, but also has good dispersibility of the corresponding alcohol-soluble resin, thus realizing preparation of high-dispersibility silver paste, so that the silver nanoparticles can be uniformly dispersed, and the storage stability of the silver nanoparticles is improved.

Claims

1. A low-temperature conductive paste suitable for 3D printing is characterized in that,

comprises silver nano particles, a diluent and a binder; wherein,

the surface of the silver nanoparticle is coated with a ligand;

the diluent is an organic alcohol substance;

the binder is an alcohol-soluble resin.

2. A low temperature conductive paste suitable for 3D printing according to claim 1 wherein,

the preparation method of the silver nano-particles comprises the following steps:

(3) Purifying the obtained silver nano particles by using a mixed solvent;

3. A low temperature conductive paste suitable for 3D printing according to claim 2 wherein,

the mixed solvent is composed of a good solvent containing hydroxyl or carbonyl and a secondary good solvent containing ester groups.

4. A low temperature conductive paste suitable for 3D printing according to claim 1 or 2 wherein,

the ligand comprises any one or more of PAA, PVP, triton and PEG.

5. A low temperature conductive paste suitable for 3D printing according to claim 1 wherein,

the diluent is an organic alcohol substance with carbon number/hydroxyl group not more than 4 and hydroxyl number not less than 2.

6. A low temperature conductive paste suitable for 3D printing according to claim 1 wherein,

the alcohol-soluble resin comprises any one or a combination of a plurality of alcohol-soluble epoxy resin, alcohol-soluble acrylic resin and alcohol-soluble polyurethane.

7. A low temperature conductive paste suitable for 3D printing according to claim 1 wherein,

the solid content of the low-temperature conductive paste is 50-90%;

8. A low temperature conductive paste suitable for 3D printing according to claim 1 wherein,

the low-temperature conductive paste can be stably discharged for more than 4 hours on a needle with the diameter of 10 mu m after being stored for more than 3 months in a room temperature environment;

the low-temperature conductive paste is stored for more than 3 months in a room temperature environment, and the change amplitude of the conductivity of the low-temperature conductive paste after sintering is less than or equal to 10 percent.

9. A method for preparing the electroconductive paste according to any one of claims 1 to 8, characterized in that,

the method comprises the following steps:

(S.1) preparation of silver nanoparticles;

(s.2) mixing silver nanoparticles with a diluent and an organic carrier to obtain the conductive paste.

10. The use of the electroconductive paste according to any one of claims 1 to 8 in the fields of high-precision direct-write 3D printing, precision optics, micro-nano chips, photovoltaics or printed electronics of 10 μm or less.