Boiling-resistant conductive silver paste and preparation and application thereof

Abstract

The invention relates to the technical field of conductive silver paste, in particular to boiling-resistant conductive silver paste and preparation and application thereof. The boiling-resistant conductive silver paste provided by the invention comprises the following components in percentage by mass: 40-55% of conductive silver powder; 4%-8% of polymer resin; 1%-4% of an auxiliary agent; 45%-55% of a solvent; wherein the sum of the mass percentages of all the components is 100%. Compared with the existing conductive silver paste, the boiling-resistant conductive silver paste provided by the invention has excellent printing performance, conductivity and adhesion performance, is free from delamination and serious powder falling after being subjected to water bath at 80 DEG C for 200 hours, has a cross-cut grade of greater than or equal to 2, and has excellent boiling resistance and weather resistance.

Description

Technical Field

[0001] The invention relates to the technical field of conductive silver paste, in particular to a boiling-resistant conductive silver paste and the preparation and application thereof. Background Art

[0002] The rapid development of the electronic information industry has driven the development of the electronic paste industry. Silver plays an extremely important role in the electronics industry due to its excellent application properties such as high electrical conductivity. Conductive silver paste is an indispensable basic and key functional material for the production of various electronic components.

[0003] Conductive silver paste is widely used in electronic industries such as computers, mobile phone keyboards, membrane switches, touch screens, smart cards, and radio frequency identification. The most widely used conductive silver pastes include: low-temperature silver paste for membrane switches and flexible circuit boards based on PET, low-temperature conductive silver paste for touch screens, paste for single-board ceramic capacitors, silver paste for varistors and thermistors, silver paste for piezoelectric ceramics, and silver electrode paste for carbon film potentiometers.

[0004] Low-temperature curing environmentally friendly conductive silver paste is composed of metallic silver powder, high molecular organic polymer system, organic solvent and additives. The above components are mixed evenly and prepared into a viscous paste. After the corresponding circuit pattern is made by screen printing process, it is cured at a lower temperature to obtain a circuit conductor with good adhesion to the substrate. The main characteristics of low-temperature curing conductive silver paste are low curing temperature, high bonding strength, stable electrical properties, and suitable for screen printing. It is suitable for conductive and thermal bonding in low-temperature curing welding occasions.

[0005] The conductive silver paste used in PLDC has certain weather resistance and water boiling resistance requirements. However, due to the poor water boiling resistance of the coating, it is often in contact with water vapor for a long time in a high temperature and high humidity environment during storage or use, which causes the coating surface to change color and poor adhesion. Therefore, it is very important to ensure that the coating has good water boiling resistance. With the continuous improvement of people's living standards, the requirements for the water boiling resistance and salt spray resistance of the conductive silver paste itself are constantly increasing. Therefore, the water boiling resistance and salt spray resistance of the existing conductive silver paste need to be improved.

[0006] Patent CN113674893A discloses a conductive silver paste for low-temperature wear-resistant and acetone-resistant PCB boards and its preparation method. The raw materials use the following components and weight percentages: 30% to 50% metallic silver powder, 5% to 15% polymer resin, 35% to 45% organic solvent, and 1% to 10% functional additives. The patent mentions that it has the property of being resistant to boiling water, but the patent focuses on acetone resistance and strong adhesion on PCB circuits, and its test conditions are at room temperature, which is no longer in line with the current situation of resistance to boiling water in a hot and humid environment during use.

[0007] Patent CN107236099A discloses an acrylate-polyurethane copolymer resin and a conductive silver paste containing the resin. The raw materials are prepared by the following components and weight percentages: 30% to 80% micron silver powder, 0.1% to 25% nano silver powder, 10% to 35% solvent, 4% to 20% synthetic resin, and 0.3% to 8% auxiliary agent; the structure of the acrylate-polyurethane copolymer resin is: (PA-b-PB)-co-PU, wherein PA-b-PB is a block copolymer of acrylate resin, PU is a polyurethane resin, and co represents copolymerization. This patent mainly realizes the requirement of optimizing the boiling resistance of conductive silver paste by resin modification, but its resin modification process is relatively cumbersome, with more by-products, and it is difficult to ensure the stability of the polymer carrier of the conductive silver paste. Moreover, it does not optimize the formula of the conductive silver paste too much, and cannot meet a wide range of needs. Summary of the invention

[0008] In order to solve the above problems, the purpose of the present invention is to provide a boiling-resistant conductive silver paste and its preparation and application. The boiling-resistant conductive silver paste provided by the present invention can effectively avoid the adverse effects on the resistance, adhesion and oxidation resistance of the conductive silver paste under hot and humid conditions, thereby improving the application range and life of the conductive silver paste.

[0009] The purpose of the present invention can be achieved by the following technical solutions:

[0010] The first object of the present invention is to provide a boiling-resistant conductive silver paste, comprising the following components in percentage by mass:

[0011] Conductive silver powder 40% to 55%; polymer resin 4% to 8%; additive 1% to 4%; solvent 45% to 55%;

[0012] The sum of the mass percentages of the various components is 100%.

[0013] In one embodiment of the present invention, the conductive silver powder is a mixture of flaky silver powder and spherical silver powder, the mass ratio of flaky silver powder to spherical silver powder is 4:1, the D50 particle size of the flaky silver powder is 4.0-6.0 μm, the tap density is 2.0-2.5 g / mL, and the loose density is 1.0-1.5 g / mL; the D50 particle size of the spherical silver powder is 0.5-1.0 μm, the tap density is 3.0-4.5 g / mL; and the loose density is 1.5-2.0 g / mL.

[0014] In one embodiment of the present invention, the polymer resin is selected from one or more of chloroacetic acid resin, polyurethane resin, polyester resin, amino resin or epoxy resin; the relative molecular mass of the polymer resin is 15000-30000.

[0015] In one embodiment of the present invention, the auxiliary agent includes a curing agent, a defoaming agent, a leveling agent, a thixotropic agent and an adhesion promoter.

[0016] In one embodiment of the present invention, the curing agent is selected from one of blocked isocyanate, methylimidazole and benzyl glycidyl ether;

[0017] The defoaming agent is selected from polyether and silicone;

[0018] The leveling agent is selected from one of silicone or acrylate;

[0019] The thixotropic agent is selected from one of carbon black, organic bentonite, hydrogenated castor oil, polyamide wax or fumed silica;

[0020] The adhesion promoter is selected from a silane coupling agent or a phthalate coupling agent.

[0021] In one embodiment of the present invention, the solvent is selected from one or more of butyl acetate, butyl ether, diethylene glycol ethyl ether acetate, isophorone, PMA or DBE.

[0022] A second object of the present invention is to provide a method for preparing a boiling-resistant conductive silver paste, comprising the following steps:

[0023] (S1) mixing a polymer resin and a solvent, heating and stirring, and then filtering to remove impurities to obtain an organic carrier;

[0024] (S2) mixing the conductive silver powder, the organic carrier prepared in step (S1), a curing agent, a defoaming agent, a leveling agent, a thixotropic agent, an adhesion promoter and a solvent, and dispersing them at high speed to obtain a mixed slurry;

[0025] (S3) Grinding and vacuum degassing the mixed slurry prepared in step (S2) to obtain a water-boiling-resistant conductive slurry.

[0026] In one embodiment of the present invention, in step (S1), during the heating process, the temperature is 50 to 90°C;

[0027] In step (S2), during the high-speed dispersion process, the high-speed dispersion rate is 1800-2200 rpm / min, and the time is 3-5 min;

[0028] In step (S3), during the vacuum degassing process, the vacuum degree is -0.2 to -0.01 MPa and the time is 10 to 15 minutes.

[0029] In one embodiment of the present invention, in step (S3), the fineness of the water-boiling-resistant conductive paste is less than 10 μm, and the viscosity is 10 to 15 Pa·s.

[0030] The third object of the present invention is to provide an application of boiling-resistant conductive silver paste in the preparation of a membrane switch.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The water-boiling conductive silver paste of the present invention belongs to the low-temperature quick-drying conductive silver paste. It can be completely cured and dried at 90°C to 100°C within 5min to 8min. The square resistance is less than 7mΩ / □ / 25.4μm and the resistivity is less than 8*10 -5 Ωcm;.

[0033] (2) The conductive silver powder of the boiling-resistant conductive silver paste of the present invention is a mixture of flaky silver powder and spherical silver powder. The flaky silver powder is mainly in surface contact or line contact with a certain gap or "slip". The spherical silver powder is added to make point or surface contact between the flaky silver powders, reducing the "slip" between the flaky silver powders, effectively improving the density of the conductive silver powder, effectively reducing the contact resistance, making the conductive network denser, and having better conductive performance.

[0034] (3) The resin, silver powder, solvent and additives of the water-boiling conductive silver paste of the present invention are reasonably matched. After curing, the conductive silver paste has an adhesion of 5B, a hardness of more than 3H, a printing thickness of 3 to 4 um, good light-shielding properties, and excellent line edge quality.

[0035] (4) The water-boiling-resistant conductive silver paste of the present invention has no delamination and serious powder loss after being placed in a water bath at 80° C. for 200 hours, and the grid knife grade is ≥2, and has excellent water-boiling resistance and weather resistance. DETAILED DESCRIPTION

[0036] The present invention is described in detail below with reference to specific embodiments.

[0037] In the following examples, unless otherwise specified, all reagents used are commercially available reagents, and all detection means and methods used are conventional detection means and methods in the art.

[0038] The percentages mentioned below are all the proportions in the water-boiling resistant conductive silver paste.

[0039] Example 1

[0040] This embodiment provides a boiling-resistant conductive silver paste, comprising the following components in percentage by weight:

[0041] Conductive silver powder 40%; polymer resin 8%; curing agent 1%; defoaming agent 0.5%; leveling agent 0.2%; thixotropic agent 0.5%; adhesion promoter 0.5%; solvent 49.3%.

[0042] The conductive silver powder is a mixture of flaky silver powder and spherical silver powder, the mass ratio of flaky silver powder to spherical silver powder is 4:1, the D50 particle size of the flaky silver powder is 4.0-6.0 μm, the tap density is 2.0-2.5 g / mL, and the loose density is 1.0-1.5 g / mL; the D50 particle size of the spherical silver powder is 0.5-1.0 μm, the tap density is 3.0-4.5 g / mL, and the loose density is 1.5-2.0 g / mL.

[0043] The polymer resin is a hydroxyl-modified ternary chloroacetic acid resin, the model is LPOH, and the manufacturer is Wuxi Honghui;

[0044] The curing agent is a blocked isocyanate curing agent, model NX-2026, manufactured by Cardolite;

[0045] The defoamer is a polyether, model HF-910, manufactured by Shandong Hengfu;

[0046] The leveling agent is organic silicon, model HY-5030, and the manufacturer is Maier Chemical;

[0047] The thixotropic agent is hydrogenated castor oil, model PEG-40, produced by Beijing Coupling;

[0048] The adhesion promoter is a silane coupling agent, model KH-550, manufactured by Nanjing Nengde;

[0049] The solvent is a mixture of butyl acetate, PMA and DBE in a ratio of 1:1:2.

[0050] The boiling-resistant conductive silver paste provided in this embodiment is prepared by the following method:

[0051] (S1) Preparation of an organic carrier: a hydroxy-modified ternary chloroacetic acid resin VAGH is mixed with butyl acetate, PMA, and DBE solvents, and then heated to 80° C. and kept at a constant temperature. After the modified ternary chloroacetic acid resin is completely dissolved, it is filtered on a 400-mesh mesh to remove impurities, thereby obtaining an organic carrier;

[0052] (S1) Preparation of conductive silver paste: Flake and spherical conductive silver powder, organic carrier, blocked curing agent, defoamer, leveling agent, thixotropic agent, and adhesion promoter are fully mixed in a mixer, and then high-speed dispersant is used for high-speed dispersion (high-speed dispersion rate is 2000 rpm / min, time is 5 min), so as to obtain a uniform mixed slurry;

[0053] (S1) Production of conductive silver paste: The mixed slurry obtained in step (S2) is ground in a three-roll mill, and the fineness of the silver paste is controlled to be below 10 μm and the viscosity is 16000 mPa·S by fine adjustment of the rollers to obtain a water-resistant conductive silver paste.

[0054] Example 2

[0055] This embodiment provides a boiling-resistant conductive silver paste, comprising the following components in percentage by weight:

[0056] Conductive silver powder 50%; polymer resin 6%; curing agent 0.5%; defoaming agent 0.5%; leveling agent 0.5%; thixotropic agent 0.5%; adhesion promoter 0.5%; solvent 41.5%.

[0057] The conductive silver powder is a mixture of flaky silver powder and spherical silver powder, the mass ratio of flaky silver powder to spherical silver powder is 4:1, the D50 particle size of the flaky silver powder is 4.0-6.0 μm, the tap density is 2.0-2.5 g / mL, and the loose density is 1.0-1.5 g / mL; the D50 particle size of the spherical silver powder is 0.5-1.0 μm, the tap density is 3.0-4.5 g / mL, and the loose density is 1.5-2.0 g / mL.

[0058] The polymer resin is polyester resin and amino resin, the polyester resin model is PB-230, the manufacturer is Suzhou Jianxing Huaxue, the amino resin model is Resimene 717, the manufacturer is Ineos;

[0059] The curing agent is a blocked isocyanate curing agent, model NX-2026, manufactured by Cardolite;

[0060] The defoamer is a polyether, model HF-910, manufactured by Shandong Hengfu;

[0061] The leveling agent is organic silicon, model HY-5030, and the manufacturer is Maier Chemical;

[0062] The thixotropic agent is hydrogenated castor oil, model PEG-40, produced by Beijing Coupling;

[0063] The adhesion promoter is a silane coupling agent, model KH-550, manufactured by Nanjing Nengde;

[0064] The solvent is a mixture of isophorone, PMA and DBE in a ratio of 1:1:1.

[0065] The boiling-resistant conductive silver paste provided in this embodiment is prepared by the following method:

[0066] (S1) Preparation of an organic carrier: a polyester resin and an amino resin are mixed with isophorone, PMA and DBE, and then heated to 80° C. and kept at a constant temperature. After the polyester resin and the amino resin are completely dissolved, the mixture is filtered on a 400-mesh mesh to remove impurities, thereby obtaining an organic carrier;

[0067] (S1) Preparation of conductive silver paste: Flake and spherical conductive silver powder, organic carrier, blocked curing agent, defoamer, leveling agent, thixotropic agent, and adhesion promoter are fully mixed in a mixer, and then dispersed at high speed (2000 rpm / min, time is 5 min) using a high-speed dispersant to obtain a uniform mixed slurry;

[0068] (S1) Production of conductive silver paste: The mixed slurry obtained in step (S2) is ground in a three-roll mill, and the fineness of the silver paste is controlled to be below 10 μm and the viscosity is 18000 mPa·S by fine adjustment of the rollers to obtain a water-resistant conductive silver paste.

[0069] Example 3

[0070] This embodiment provides a boiling-resistant conductive silver paste, comprising the following components in percentage by weight:

[0071] Conductive silver powder 55%; polymer resin 6%; curing agent 0.5%; defoaming agent 0.5%; leveling agent 0.5%; thixotropic agent 1%; adhesion promoter 0.5%; solvent 36%.

[0072] The conductive silver powder is a mixture of flaky silver powder and spherical silver powder, the mass ratio of flaky silver powder to spherical silver powder is 4:1, the D50 particle size of the flaky silver powder is 4.0-6.0 μm, the tap density is 2.0-2.5 g / mL, and the loose density is 1.0-1.5 g / mL; the D50 particle size of the spherical silver powder is 0.5-1.0 μm, the tap density is 3.0-4.5 g / mL, and the loose density is 1.5-2.0 g / mL.

[0073] The polymer resins are chloroacetic acid resin and epoxy resin. The chloroacetic acid resin model is LPOH, manufactured by Wuxi Honghui, and the epoxy resin model is 102C-1, manufactured by Hengxin New Materials.

[0074] The curing agent is methylimidazole, model NP-49, and the manufacturer is Shandong Deke Biological;

[0075] The defoamer is organic silicon, model ZBH-309, and the manufacturer is Qingdao Zhongbao;

[0076] The leveling agent is organic silicon, model HY-5030, and the manufacturer is Maier Chemical;

[0077] The thixotropic agent is polyamide wax, model MT6900-20X, manufactured by Taiyuan Meitexiang;

[0078] The adhesion promoter is a phthalate coupling agent, model FT201, manufactured by Nanjing Feiteng;

[0079] The solvent is a mixture of isophorone, PMA and DBE in a mass percentage of 1:1:2.

[0080] The boiling-resistant conductive silver paste provided in this embodiment is prepared by the following method:

[0081] (S1) Preparation of an organic carrier: a chloroacetic acid resin and an epoxy resin are mixed with isophorone, PMA and DBE, and then heated to 80° C. and kept at a constant temperature. After the chloroacetic acid resin and the epoxy resin are completely dissolved, the mixture is filtered on a 400-mesh mesh to remove impurities, thereby obtaining an organic carrier;

[0082] (S1) Preparation of conductive silver paste: Flake and spherical conductive silver powder, organic carrier, blocked curing agent, defoamer, leveling agent, thixotropic agent, and adhesion promoter are fully mixed in a mixer, and then high-speed dispersant is used for high-speed dispersion (high-speed dispersion rate is 2000 rpm / min, time is 5 min), so as to obtain a uniform mixed slurry;

[0083] (S1) Production of conductive silver paste: The mixed slurry obtained in step (S2) is ground in a three-roll mill, and the fineness of the silver paste is controlled to be below 10 μm and the viscosity is 18700 mPa·S by fine adjustment of the rollers, thereby obtaining a water-resistant conductive silver paste.

[0084] Comparative Example 1

[0085] Compared with Example 3, this comparative example is consistent with Example 3 except for the following contents:

[0086] The conductive silver powder is flaky silver powder, the D50 particle size of the flaky silver powder is 4.0-6.0 μm, the tap density is 2.0-2.5 g / mL, and the loose density is 1.0-1.5 g / mL.

[0087] Comparative Example 2

[0088] Compared with Example 3, this comparative example is consistent with Example 3 except for the following contents:

[0089] The conductive silver powder is spherical silver powder, the D50 particle size of the spherical silver powder is 0.5-1.0 μm, the tap density is 3.0-4.5 g / ml, and the loose density is 1.5-2.0 g / ml.

[0090] The conductive silver pastes prepared in Examples 1-3 and Comparative Examples 1-2 were tested for basic properties and high temperature and high humidity. The test results are listed in Table 1:

[0091] Table 1: Conductive silver paste performance test results

[0092]

[0093]

[0094] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the explanation of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A boiling-resistant conductive silver paste, characterized in that: The following components are included in mass percentage: Conductive silver powder 40% to 55%; polymer resin 4% to 8%; additive 1% to 4%; solvent 45% to 55%; The sum of the mass percentages of the various components is 100%.

2. The boiling-resistant conductive silver paste according to claim 1, characterized in that: The conductive silver powder is a mixture of flaky silver powder and spherical silver powder, the mass ratio of the flaky silver powder to the spherical silver powder is 4:1, the D50 particle size of the flaky silver powder is 4.0-6.0 μm, the tap density is 2.0-2.5 g / mL, and the loose density is 1.0-1.5 g / mL; the D50 particle size of the spherical silver powder is 0.5-1.0 μm, the tap density is 3.0-4.5 g / mL; and the loose density is 1.5-2.0 g / mL.

3. The boiling-resistant conductive silver paste according to claim 1, characterized in that: The polymer resin is selected from one or more of chloroacetic acid resin, polyurethane resin, polyester resin, amino resin or epoxy resin; the relative molecular mass of the polymer resin is 15000-30000.

4. The boiling-resistant conductive silver paste according to claim 1, characterized in that: The auxiliary agents include curing agent, defoaming agent, leveling agent, thixotropic agent and adhesion promoter.

5. The boiling-resistant conductive silver paste according to claim 4, characterized in that: The curing agent is selected from one of blocked isocyanate, methylimidazole and benzyl glycidyl ether; The defoaming agent is selected from polyether and silicone; The leveling agent is selected from one of silicone or acrylate; The thixotropic agent is selected from one of carbon black, organic bentonite, hydrogenated castor oil, polyamide wax or fumed silica; The adhesion promoter is selected from a silane coupling agent or a phthalate coupling agent.

6. The boiling-resistant conductive silver paste according to claim 1, characterized in that: The solvent is selected from one or more of butyl acetate, butyl ether, diethylene glycol ethyl ether acetate, isophorone, PMA or DBE.

7. A method for preparing the boiling-resistant conductive silver paste according to any one of claims 1 to 6, characterized in that: The following steps are involved: (S1) mixing a polymer resin and a solvent, heating and stirring, and then filtering to remove impurities to obtain an organic carrier; (S2) mixing the conductive silver powder, the organic carrier prepared in step (S1), a curing agent, a defoaming agent, a leveling agent, a thixotropic agent, an adhesion promoter and a solvent, and dispersing them at high speed to obtain a mixed slurry; (S3) Grinding and vacuum degassing the mixed slurry prepared in step (S2) to obtain a water-boiling-resistant conductive slurry.

8. The method for preparing a boiling-resistant conductive silver paste according to claim 7, characterized in that: In step (S1), during the heating process, the temperature is 50 to 90°C; In step (S2), during the high-speed dispersion process, the high-speed dispersion rate is 1800-2200 rpm / min, and the time is 3-5 min; In step (S3), during the vacuum degassing process, the vacuum degree is -0.2 to -0.01 MPa and the time is 10 to 15 minutes.

9. The method for preparing a boiling-resistant conductive silver paste according to claim 7, characterized in that: In step (S3), the fineness of the water-boiling-resistant conductive paste reaches less than 10 μm, and the viscosity is 10 to 15 Pa·s.

10. Use of the boiling-resistant conductive silver paste according to any one of claims 1 to 6 in preparing a membrane switch.

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