Solvent-free drawing silver paste and preparation method thereof

Abstract

This invention discloses a solvent-free stretchable silver paste and its preparation method, belonging to the field of electronic materials technology. The raw materials of the solvent-free stretchable silver paste of this invention, by mass parts, include: 60-70 parts silver-aluminum powder, 20-30 parts resin carrier, 4-7 parts diluent, 1-3 parts silane coupling agent, and 1-3 parts stabilizer; the resin carrier does not contain organic solvents. To solve the problems of foaming and performance instability caused by the use of organic solvents in the preparation process of traditional silver pastes containing organic solvents, and to improve the conductivity, adhesion, and extrusion process adaptability of the silver paste, this invention uses a highly stretchable silicone resin as a carrier and increases the amount of conductive filler silver-aluminum powder, thus designing a solvent-free stretchable silver paste solution. The resulting product has achieved significant progress in improving stretchability, preventing high-temperature solvent boiling and foaming, adapting to extrusion processing, and improving electrical properties, and has good application value.

Description

Technical Field

[0001] This invention relates to the field of electronic materials technology, and in particular to a solvent-free stretching silver paste and its preparation method. Background Technology

[0002] In the traditional preparation of silver paste, organic solvents are typically introduced as dispersion media to improve the dispersion of silver powder and adjust the leveling properties of the paste. However, in actual processing, especially during high-temperature extrusion of adhesive strips, the use of such organic solvents can easily cause boiling due to high temperatures. This leads to bubbling at the interface between the silver paste layer and the substrate, resulting in protrusions on the silver layer surface. Consequently, this causes a series of problems such as appearance defects, deterioration of electrical properties, decreased adhesion, and unstable tensile properties, ultimately affecting the conductivity reliability and overall quality of the product.

[0003] To address the aforementioned issues, efforts have been made in the field to develop low-solvent or solvent-free silver paste products. However, existing solvent-free silver paste solutions often rely on complex preparation processes for their resin carrier systems, resulting in high production costs. Furthermore, there is still room for improvement in overall performance aspects such as tensile properties, conductivity, adhesion, and process adaptability. While some products have achieved solvent-free status, insufficient dispersion between the conductive filler and the resin carrier leads to poor stability of the conductive network under dynamic bending or stretching conditions.

[0004] Therefore, developing a solvent-free stretchable silver paste that combines excellent stretchability, good conductivity, reliable adhesion, good process adaptability, and environmental friendliness has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a solvent-free stretchable silver paste and its preparation method to solve the aforementioned problems in the background art. To address the foaming and performance instability issues caused by the use of organic solvents in the preparation process of traditional silver pastes containing organic solvents, and to improve the conductivity, adhesion, and extrusion process adaptability of the silver paste, this invention uses a highly stretchable silicone resin as a carrier and increases the amount of conductive filler silver-aluminum powder, thereby designing a solvent-free stretchable silver paste solution.

[0006] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention is to provide a solvent-free stretchable silver paste, wherein the raw materials, by mass parts, include: 60-70 parts silver aluminum powder, 20-30 parts resin carrier, 4-7 parts diluent, 1-3 parts silane coupling agent and 1-3 parts stabilizer; The resin carrier does not contain organic solvents.

[0007] Preferably, the silver-aluminum powder has a mesh size of 1500-2000 mesh.

[0008] Preferably, the resin carrier is liquid silicone rubber resin.

[0009] More preferably, the raw materials of the liquid silicone rubber resin include silicone rubber resin, vinyl silicone oil, dimethyl silicone oil, dispersant, silane coupling agent and diluent.

[0010] Preferably, the diluent is hydrogenated polyisobutylene.

[0011] Preferably, the solvent-free stretching silver paste is made from the following raw materials in parts by weight: 65 parts silver aluminum powder, 25 parts resin carrier, 6 parts diluent, 2 parts silane coupling agent and 2 parts stabilizer.

[0012] The second technical solution of the present invention provides a method for preparing the above-mentioned solvent-free stretching silver paste, comprising the following steps: The raw materials are mixed and ground to obtain a precursor liquid with a fineness of ≤10μm, and then vacuum degassing is performed to obtain the solvent-free stretching silver paste.

[0013] Preferably, the vacuum degassing is performed for 20 minutes under a vacuum of -0.1 MPa.

[0014] The third technical solution of the present invention provides an extrusion molding method for the above-mentioned solvent-free stretchable silver paste, comprising the following steps: Cold die extrusion molding: Solvent-free stretch silver paste is extruded through a cold die into a strip of the desired shape, avoiding the viscosity abrupt change caused by high-temperature pre-forming; Rapid heating in a high-temperature furnace: A short high-temperature treatment at 300℃ for 3-5 seconds promotes neck connections between silver and aluminum powders, rapidly forming a continuous conductive network; Tunnel oven curing: The resin carrier is fully cross-linked at 180℃~200℃ for 20 minutes to ensure the density and mechanical stability of the silver layer.

[0015] The beneficial technical effects of the present invention are as follows: To address the problems of foaming and performance instability caused by the use of organic solvents in the preparation of traditional silver pastes, and to improve the conductivity, adhesion, and extrusion process adaptability of the silver paste, this invention uses a highly stretchable silicone resin as a carrier and increases the amount of conductive filler silver-aluminum powder, thus designing a solvent-free stretchable silver paste solution. The resulting product shows significant progress in improving stretchability, preventing high-temperature solvent boiling and foaming, adaptability to extrusion processing, and enhancing electrical properties, and has great application value. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the extrusion molding process of the solvent-free stretch silver paste of the present invention.

[0018] Figure 2 This is a schematic diagram of the structure of the solvent-free stretched silver paste and solid silicone substrate of the test sample of the present invention. Detailed Implementation

[0019] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0020] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0021] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. It should be noted that any aspects of this invention not described in detail are conventional practices in the art and are not the focus of this invention.

[0022] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0023] This invention designs a solvent-free stretchable silver paste. Through the solvent-free design of the resin carrier and the synergistic optimization of process parameters, it achieves excellent technical results in eliminating solvent boiling defects, improving stretching reliability, adapting to flexible electronic manufacturing processes, and ensuring electrical performance stability.

[0024] I. Solvent-free systems eliminate the risk of volatilization and improve process adaptability Traditional solvent-based silver pastes often contain organic solvents (such as octane and undecane). During high-temperature extrusion or curing, the rapid vaporization of these solvents can cause blistering at the interface between the silver paste layer and the substrate, resulting in voids and bulges. This invention, however, employs a solvent-free system, completely eliminating the introduction of volatile organic compounds (VOCs) through formulation design. This not only achieves zero VOC emissions but also fundamentally avoids interface defects caused by vaporization, ensuring the density and integrity of the cured silver layer. Furthermore, the viscosity of this solvent-free silver paste can be flexibly adjusted within the range of 1000-5000 mPa·s, making it suitable for various processing techniques such as screen printing, inkjet printing, and extrusion coating. It also eliminates the need for preheating or staged heating, significantly simplifying the production process and reducing the difficulty of process control.

[0025] II. High tensile properties and dynamic conductivity reliability The silver paste prepared by this invention exhibits excellent tensile properties, with an elongation rate exceeding 300%, while maintaining a low rate of change in resistivity, making it suitable for dynamic applications requiring protection against sudden breakage of hard connections. Through the chemical bonding between the elastomer resin and silver powder, the interfacial adhesion is significantly enhanced, enabling the silver paste to maintain stable conductivity during repeated stretching and significantly improving fatigue resistance, making it suitable for high-frequency dynamic applications such as wearable devices and electronic skin. Experimental data shows that under 100% tensile strain conditions, no cracks are generated in the silver paste layer, and the conductive network remains intact, fully demonstrating its conductive network stability under high deformation conditions.

[0026] III. Excellent resistance to environmental aging and migration The silver paste of this invention exhibits excellent long-term reliability under harsh environmental conditions. After 1000 hours of aging test in a high temperature and high humidity environment of 85℃ / 85%RH, the resistance change rate is less than 5%; no electrochemical migration short circuit occurred after 1000 hours of continuous operation at a 10V bias voltage, meeting the application requirements of scenarios with strict requirements for weather resistance and anti-migration performance, such as automotive displays and power battery modules.

[0027] IV. Rheological property optimization to adapt to extrusion processing technology This invention achieves uniform dispersion of raw materials through mechanical grinding and the action of various additives, avoiding excessive agglomeration. A vacuum degassing machine and a three-roll mill are used to ensure high particle size concentration and dispersibility of over 95% in the silver paste, meeting the uniformity requirements of extrusion processes. By adjusting the resin ratio, the viscosity and thixotropy of the silver paste are optimized, maintaining a stable flow rate during extrusion and reducing line breakage or accumulation. The viscosity can be controlled between 2000-4000 mPa·s, making it suitable for precision processing techniques such as slot coating and 3D printing. Furthermore, the solvent-free system eliminates the need for a solvent recovery system, reducing equipment investment and maintenance costs. It also avoids the conductive layer peeling or corrosion problems that may result from solvent residue, increasing the overall yield rate to over 98%.

[0028] V. Superior electrical performance and long-term stability This invention's silver paste achieves a volume resistivity as low as 1.8 mΩ·cm by forming a dense conductive network, meeting the low resistivity requirements of high-precision applications such as high-frequency 5G communication and flexible electronics. Under high temperature and humidity conditions of 85℃ / 85%RH, the resistance change rate is less than 5%, and the life test (dual 85 test) exceeds 1000 hours, making it suitable for applications with stringent long-term stability requirements, such as automotive electronics and industrial control.

[0029] Unless otherwise specified, the parts in this invention are calculated by weight.

[0030] The silver-aluminum powder used in this invention has a mesh size of 2000 and was purchased from Foshan Meijiacai Chemical Co., Ltd. The silane coupling agent used is Dow Corning's 6040 silane coupling agent; the diluent used is BASF's hydrogenated polyisobutylene OPPANOL B10SFN; the dispersant used is Chenghe Technology's CHT-101; the surface wetting agent used is Tego Wet 270; the flow modifier used is BYK-333 from BYK Chemical; the silicone rubber resin used is Shin-Etsu Chemical's KEG-2000 series; the vinyl silicone oil used is Xin'an Chemical's XJ-305 series; the dimethyl silicone oil used is purchased from Dow Corning and has a viscosity of 80 mPa·s; and the plasticizer used is Dow Chemical's PMX-200.

[0031] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0032] Example 1 A solvent-free stretchable silver paste is made from the following raw materials by weight percentage: Silver aluminum powder: 65 wt%; liquid silicone rubber resin carrier: 25 wt%; diluent: 6 wt%; silane coupling agent: 2 wt%; stabilizer: 2 wt%.

[0033] The preparation method of the liquid silicone rubber resin carrier is as follows: preheat the double planetary mixer to 25°C, then add 63 parts of silicone rubber resin, 7 parts of vinyl silicone oil, 7 parts of dimethyl silicone oil, 3 parts of dispersant, 2 parts of silane coupling agent, and 18 parts of diluent in sequence, and mix them until uniform under stirring conditions to obtain the liquid silicone rubber resin carrier as the silver paste resin system.

[0034] The stabilizer is prepared by preheating a double planetary mixer to 25°C, adding 67 parts of flow modifier, 22 parts of plasticizer, and 11 parts of surface wetting agent in sequence, and stirring until uniformly mixed to obtain the stabilizer.

[0035] The specific preparation method of this solvent-free stretching silver paste is as follows: The above raw materials were added to a double planetary mixer and mixed for 30 minutes. After uniform mixing, the mixture was transferred to a three-roll mill for three-stage grinding, with each stage lasting 10 minutes, to obtain a precursor liquid with a fineness ≤10μm. After grinding, the ground slurry was placed in a vacuum degassing machine and degassed for 20 minutes under a vacuum of -0.1 MPa. Finally, the degassed slurry was sealed and packaged to obtain solvent-free stretchable silver paste.

[0036] Figure 1 This is a schematic diagram of the extrusion molding process of the solvent-free stretch silver paste of the present invention.

[0037] Effect verification 1. Coating and curing The solvent-free stretchable silver paste prepared in Example 1 was coated and cured onto the surface of a solid silicone substrate (solid base adhesive). The coating thickness was controlled at 20-30 μm, and then cured at 150°C for 60 minutes to obtain the test sample (see schematic diagram). Figure 2 The test samples were subjected to performance testing according to the following methods.

[0038] (1) Volume resistivity test The sheet resistance of the cured silver paste layer of the test sample was measured using a four-probe tester, and the volume resistivity was calculated in combination with the film thickness. The test results showed that the volume resistivity of the solvent-free stretched silver paste was 1.8 mΩ·cm, which is less than 2 mΩ·cm, indicating that it has excellent conductivity.

[0039] (2) Adhesion test The test was conducted according to GB / T 9286-2021 "Paints and Varnishes - Cross-cut Test" (100-square test). One hundred 1mm × 1mm squares were drawn on the surface of the cured silver paste layer of the test sample using a cross-cut tester. 3M 600 tape was then applied and quickly peeled off, and the coating peeling was observed. The test results showed that the coating did not peel off at all, the edges of the cross-cut were smooth, and the adhesion reached grade 5B, indicating that the solvent-free stretchable silver paste of this invention has good interfacial bonding strength with the solid silicone substrate.

[0040] (3) Tensile property test The tests were conducted according to GB / T 528-2009, "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber". The cured test samples were cut into dumbbell-shaped standard specimens and subjected to uniaxial tensile testing using a universal testing machine at a tensile rate of 50 mm / min. A digital multimeter was used to monitor the resistance change during the tensile process in real time. The test results are as follows: Visual inspection: When stretched to 100% strain, no cracks were generated on the surface of the silver paste layer, the coating remained intact and continuous, and no peeling or cracking was observed.

[0041] Resistance growth rate: When stretched to 100% strain, the resistance growth rate (ΔR / R0×100%) is 12.5%, which is less than 15%, indicating that the conductive network of the silver paste remains stable under tension and has good dynamic conductivity reliability.

[0042] 2. Extrusion curing The solvent-free stretching silver paste prepared in Example 1 was extruded through a cold die to form a strip with a diameter of 2 mm. Then, it was cured in a 300°C high-temperature oven (4 seconds) and a 190°C tunnel oven (20 minutes) in sequence. The appearance was observed and the performance was tested. Appearance: The silver paste layer has a tight interface; Volume resistivity: 1.9 mΩ·cm, comparable to that of the coated and cured sample; Tensile properties: The resistance increase rate at 100% strain is 13.2%, which remains at a stable level of less than 15%, proving the conductivity reliability under the extrusion process.

[0043] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A solvent-free stretchable silver paste, characterized in that, Raw materials, by mass parts, include: 60-70 parts silver aluminum powder, 20-30 parts resin carrier, 4-7 parts diluent, 1-3 parts silane coupling agent and 1-3 parts stabilizer; The resin carrier does not contain organic solvents.

2. The solvent-free stretchable silver paste according to claim 1, characterized in that, The silver-aluminum powder has a mesh size of 1500-2000 mesh.

3. The solvent-free stretchable silver paste according to claim 1, characterized in that, The resin carrier is liquid silicone rubber resin.

4. The solvent-free stretchable silver paste according to claim 3, characterized in that, The raw materials of the liquid silicone rubber resin include silicone rubber resin, vinyl silicone oil, dimethyl silicone oil, dispersant, silane coupling agent and diluent.

5. The solvent-free stretchable silver paste according to claim 1, characterized in that, The diluent is hydrogenated polyisobutylene.

6. The solvent-free stretchable silver paste according to claim 1, characterized in that, The solvent-free stretching silver paste is made from the following raw materials in parts by weight: 65 parts silver aluminum powder, 25 parts resin carrier, 6 parts diluent, 2 parts silane coupling agent and 2 parts stabilizer.

7. A method for preparing solvent-free stretchable silver paste according to any one of claims 1-6, characterized in that, Includes the following steps: The raw materials are mixed and ground to obtain a precursor liquid with a fineness of ≤10μm, and then vacuum degassing is performed to obtain the solvent-free stretching silver paste.

8. The preparation method according to claim 7, characterized in that, The vacuum degassing is performed for 20 minutes under a vacuum of -0.1 MPa.

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