Quick-drying low-temperature silver paste and preparation method thereof

Abstract

The invention discloses quick-drying low-temperature silver paste and a preparation method thereof. The conductive silver paste comprises the following components: 3-7 parts of polymer resin, 20-40 parts of a mixed solvent, 0.5-2 parts of an adhesion promoter, 1-3 parts of a dispersant and 55-70 parts of conductive silver powder, wherein the polymer resin is thermoplastic acrylic resin; the mixed solvent is a mixture of ester solvents; the adhesion promoter is a silane coupling agent; the dispersing agent is an acrylate dispersing agent; the conductive silver powder is a combination of micron-sized spherical silver powder and micron-sized flaky silver powder. The silver paste has the advantages that the good printing adaptability of the silver paste is kept, a film can be rapidly formed during heating and drying, lap joint of conductive paths between silver powder is achieved, meanwhile, use of a thickening thixotropic agent with high solvent adsorbability is avoided, and the environment-friendly requirement is met; and meanwhile, micron-sized spherical silver powder is used as a main conductive filler, so that the dispersion of the silver powder in a binding phase is further improved, and the silver paste achieves the effects of high conductivity and high resistance stability after being quickly dried.

Description

Technical Field

[0001] The invention relates to a slurry preparation technology, and in particular to a quick-drying low-temperature silver paste and a preparation method thereof. Background Art

[0002] Low-temperature silver paste is a special paste composed of silver powder, polymer resin, solvent and additives. It is usually dried at a temperature below 200°C and attached to substrates that are not resistant to high-temperature sintering, such as PET, TPU, Teslin, PI, etc., to form a conductive circuit or film layer. Low-temperature silver paste has good conductivity, adhesion, flexibility, printability and other characteristics. It is widely used in touch display, membrane switch, printed circuit board, electromagnetic shielding, electric heating film and other fields. Its research and development and application have attracted wide attention.

[0003] The film formation of low-temperature silver paste requires a certain drying temperature, and the solvent in the components evaporates, so that the polymer resin as the bonding phase precipitates and forms a film. The drying speed of low-temperature silver paste depends on the boiling point and volatilization rate of the solvent itself, the adsorption of the silver powder and other powder fillers (such as thickening thixotropic agents) on the solvent in the silver paste, the combination of the polymer resin and the solvent, and the microscopic volatilization channel of the solvent in the silver paste.

[0004] At present, according to the difference in composition, the conventional low-temperature silver paste drying temperature is generally 120~150℃, and the drying time is 20~60min. In actual application, the longer drying time leads to the decline of production efficiency and energy consumption of the silver paste user, while shortening the drying time often leads to excessive resistance and loss of adhesion. Therefore, how to reduce the process cost and difficulty of using low-temperature silver paste has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a quick-drying low-temperature silver paste which can be dried quickly and maintain good conductivity and adhesion, and a preparation method thereof.

[0006] In order to solve the above technical problems, the quick-drying low-temperature silver paste of the present invention comprises the following components in parts by weight: High molecular resin: 3-7 parts Mixed solvent: 20-40 parts Adhesion promoter: 0.5-2 parts Dispersant: 1-3 parts Conductive silver powder: 55-70 parts; Among them, the polymer resin is a thermoplastic acrylic resin; the mixed solvent is a mixture of ester solvents; the adhesion promoter is a silane coupling agent; the dispersant is an acrylic ester dispersant; and the conductive silver powder is a combination of micron-sized spherical silver powder and micron-sized flaky silver powder.

[0007] Furthermore, the molecular weight of the thermoplastic acrylic resin is 150,000 to 300,000, and Tg is ≥ 80°C.

[0008] Furthermore, the mixed solvent is a mixture of propylene glycol methyl ether acetate, ethylene glycol butyl ether acetate and DBE.

[0009] Furthermore, the weight ratio of propylene glycol methyl ether acetate, ethylene glycol butyl ether acetate and DBE is 1:2-3.5:1-2.2.

[0010] Furthermore, the silane coupling agent is a combination of one or more of silane coupling agent KH151, silane coupling agent KH171, silane coupling agent KH172, silane coupling agent KH560, silane coupling agent KH570, and silane coupling agent KH792.

[0011] Furthermore, the acrylate dispersant is a combination of one or more of the acrylate dispersants EFKA-4401, EFKA-4402, DISPERBYK-191, DISPERBYK-2008, DISPERBYK-2055, Dispex Ultra PA 4550, and Dispex Ultra PA 4560.

[0012] Furthermore, in terms of weight ratio, the ratio of micron-sized spherical silver powder to micron-sized flaky silver powder in the conductive silver powder is 5-8:1.

[0013] Furthermore, the particle size of the micron-sized spherical silver powder is 0.8 to 2.0 μm, and the particle size of the micron-sized flaky silver powder is 1.5 to 3.0 μm.

[0014] A method for preparing the quick-drying low-temperature silver paste as described above comprises the following steps: (1) Weighing a polymer resin and a mixed solvent according to a weight ratio, mixing and stirring at 70 to 90° C. until they are uniformly dissolved and dispersed, with a stirring speed of 300 to 800 rpm, filtering with a filter to remove impurities, cooling to room temperature for use, and preparing an organic carrier; (2) weighing the organic carrier, adhesion promoter and dispersant prepared in the above step (1) according to the weight ratio and uniformly mixing them in a planetary disperser at a speed of 1000 to 1500 rpm for 30 to 60 minutes to prepare a silver paste matrix; (3) The silver paste matrix and the conductive silver powder prepared in step (2) are weighed according to a weight ratio, and mixed evenly in a planetary disperser at a dispersion speed of 1000 to 1500 rpm for 30 to 60 min. The mixture is then put into a three-roll grinder for grinding until the fineness is less than 5 μm, thereby obtaining the quick-drying low-temperature silver paste.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The invention uses a high molecular weight thermoplastic acrylic resin and a prepared mixed ester solvent, so that the silver paste can maintain good printing adaptability, and can quickly form a film when heated and dried, so as to achieve the overlap of the conductive paths between the silver powders, and at the same time avoid the use of a thickening thixotropic agent with high solvent adsorption, and meet the environmental protection requirements; at the same time, micron-sized spherical silver powder is used as the main conductive filler, which is easy to obtain and low in cost compared with nano silver powder, and provides more volatilization channels for the solvent when drying, and is matched with a dispersant with a structure similar to that of the polymer resin, so as to further improve the dispersion of the silver powder in the bonding phase, so that the silver paste can achieve the effects of high conductivity and high resistance stability after rapid drying, and the silver paste can adapt to the screen printing process, and has the effect of complete drying at a drying temperature of 120°C for 5 minutes, so that the silver paste has the characteristics of rapid drying and has good conductivity and adhesion. DETAILED DESCRIPTION

[0016] The quick-drying low-temperature silver paste and the preparation method thereof of the present invention are further described in detail below in conjunction with specific embodiments. Example 1

[0017] The quick-drying low-temperature silver paste of this embodiment comprises the following components in parts by weight: High molecular resin: 3-7 parts Mixed solvent: 20-40 parts Adhesion promoter: 0.5-2 parts Dispersant: 1-3 parts Conductive silver powder: 55-70 parts; Among them, the polymer resin is a thermoplastic acrylic resin. Preferably, the molecular weight of the thermoplastic acrylic resin is 150,000 to 300,000, Tg ≥ 80°C. Acrylic resin is used as the bonding phase of low-temperature silver paste. Acrylic resin has the characteristics of rapid shrinkage during solvent drying, which is conducive to the rapid film formation of silver paste and the formation of contact between silver powders, thereby achieving high conductivity and stable resistance. Compared with chlorovinyl resin, which also has the characteristics of rapid shrinkage, acrylic resin does not contain halogen and can meet the increasingly stringent halogen-free requirements in industrial products. When the molecular weight of the polymer resin increases, the longer its molecular chain, the greater the interaction between molecules, and the viscosity of the polymer resin after being dissolved by the solvent increases. Therefore, using ultra-high molecular weight acrylic resin as the bonding phase of low-temperature silver paste can directly make the viscosity of the silver paste reach a printable level, without the need to use powder-type thickening and thixotropic agents such as carbon black, fumed silica, and organic bentonite to increase the viscosity of the silver paste to meet the requirements of printability. Thickening and thixotropic agents usually have a higher specific surface area and oil absorption, and have a stronger adsorption effect on solvents, which is not conducive to the volatilization of solvents during the drying process. Avoiding the addition of thickening and thixotropic agents can speed up the drying of low-temperature silver paste and avoid solvent residues.

[0018] The mixed solvent is a mixture of ester solvents, and the mixed solvent can be a mixture of propylene glycol methyl ether acetate, ethylene glycol butyl ether acetate and DBE. Preferably, the weight ratio of propylene glycol methyl ether acetate, ethylene glycol butyl ether acetate and DBE is 1:2-3.5:1-2.2, the boiling point of propylene glycol methyl ether acetate is 145°C, the boiling point of ethylene glycol butyl ether acetate is 192°C, and the boiling range of DBE is 196-225°C. Compared with alcohol and ether solvents, ester solvents have better solubility for polymer resins, and have lower odor and lower toxicity than highly soluble ketone solvents, and have better comprehensive performance among organic solvents. Mixed ester solvents with different boiling points are used to balance the overall volatility of the solvent, so that the silver paste does not dry the plate or block the screen during normal temperature printing, and evaporates quickly during the drying process, so that the silver paste forms a film quickly and stabilizes the resistance.

[0019] The adhesion promoter is a silane coupling agent. Preferably, the silane coupling agent is a combination of one or more of silane coupling agent KH151, silane coupling agent KH171, silane coupling agent KH172, silane coupling agent KH560, silane coupling agent KH570, and silane coupling agent KH792. The use of silane coupling agent can effectively improve the adhesion of silver paste to the substrate after rapid drying.

[0020] The dispersant is an acrylate dispersant. Preferably, the acrylate dispersant is a combination of one or more of the acrylate dispersants EFKA-4401, EFKA-4402, DISPERBYK-191, DISPERBYK-2008, DISPERBYK-2055, Dispex UltraPA 4550, and Dispex Ultra PA 4560. The use of the acrylate dispersant can utilize its similar and compatible properties with the thermoplastic acrylic resin molecular structure to effectively improve the uniform dispersion of silver powder in the low-temperature silver paste system and maintain the stability of the silver paste resistance.

[0021] The conductive silver powder is a combination of micron-sized spherical silver powder and micron-sized flaky silver powder. Preferably, the ratio of micron-sized spherical silver powder to micron-sized flaky silver powder in the conductive silver powder is 5-8:1 by weight. Preferably, the particle size of the micron-sized spherical silver powder is 0.8-2.0 μm, and the particle size of the micron-sized flaky silver powder is 1.5-3.0 μm. The use of micron-sized spherical silver powder as the main conductive filler can provide more volatilization channels for the solvent during the drying process of the silver paste, avoiding the large-diameter flaky silver powder in the conventional low-temperature silver paste from covering the solvent volatilization, causing the solvent inside the silver paste film layer to be difficult to volatilize, the drying speed inside the film layer is slower than the surface, and the drying speed is uneven. Use small-diameter flaky silver powder as an auxiliary conductive filler, and form a spherical compound with micron-sized spherical silver powder to improve the conductivity of the silver paste. The combination of micron-sized spherical silver powder and flaky silver powder in an appropriate proportion can achieve a balance between the drying speed and conductivity of the silver paste. Example 2

[0022] The quick-drying low-temperature silver paste of this embodiment is prepared by the following steps: (1) Weigh 50 g of thermoplastic acrylic resin, 55 g of propylene glycol methyl ether acetate, 156 g of ethylene glycol butyl ether acetate and 89 g of DBE, stir and disperse them at 80°C until they are uniformly dispersed, and the stirring speed is 500 rpm. After the dissolution is completed, filter with a 400-mesh filter to remove impurities, cool to room temperature for use, and prepare an organic carrier.

[0023] (2) The organic carrier prepared in step (1), 10 g of silane coupling agent KH-570 and 20 g of acrylate dispersant EFKA-4402 were uniformly mixed in a planetary disperser at a dispersing speed of 1200 rpm for 45 min to prepare a silver paste matrix.

[0024] (3) The silver paste matrix prepared in step (2), 532 g of micron-sized spherical silver powder (particle size of 0.8 to 2.0 μm) and 88 g of micron-sized flaky silver powder (particle size of 1.5 to 3.0 μm) are uniformly mixed in a planetary disperser at a dispersion speed of 1200 rpm for 45 min, and then placed in a three-roll grinder for grinding until the fineness is less than 5 μm to obtain the quick-drying low-temperature silver paste of the present invention. Example 3

[0025] The quick-drying low-temperature silver paste of this embodiment is prepared by the following steps: (1) Weigh 38 g of thermoplastic acrylic resin, 46.5 g of propylene glycol methyl ether acetate, 139.5 g of ethylene glycol butyl ether acetate and 93 g of DBE, stir and disperse them at 80°C until they are uniformly dispersed, and the stirring speed is 500 rpm. After the dissolution is completed, filter with a 400-mesh filter to remove impurities, cool to room temperature for use, and prepare an organic carrier.

[0026] (2) The organic carrier prepared in step (1), 15 g of silane coupling agent KH-560 and 20 g of acrylate dispersant DISPERBYK-2008 were uniformly mixed in a planetary disperser at a dispersing speed of 1200 rpm for 45 min to prepare a silver paste matrix.

[0027] (3) The silver paste matrix prepared in step (2), 572 g of micron-sized spherical silver powder (particle size of 0.8 to 2.0 μm) and 76 g of micron-sized flaky silver powder (particle size of 1.5 to 3.0 μm) are uniformly mixed in a planetary disperser at a dispersion speed of 1300 rpm for 50 min, and then placed in a three-roll grinder for grinding until the fineness is less than 5 μm to obtain the quick-drying low-temperature silver paste of the present invention. Example 4

[0028] The quick-drying low-temperature silver paste of this embodiment is prepared by the following steps: (1) Weigh 60 g of thermoplastic acrylic resin, 76 g of propylene glycol methyl ether acetate, 166 g of ethylene glycol butyl ether acetate and 98 g of DBE, stir and disperse them at 80°C until they are uniformly dispersed, and the stirring speed is 700 rpm. After the dissolution is completed, filter with a 400-mesh filter to remove impurities, cool to room temperature for use, and prepare an organic carrier.

[0029] (2) The organic carrier prepared in step (1), 10 g of silane coupling agent KH-171 and 15 g of acrylate dispersant Dispex Ultra PA 4560 were uniformly mixed in a planetary disperser at a dispersing speed of 1300 rpm for 50 min to prepare a silver paste matrix.

[0030] (3) The silver paste matrix prepared in step (2), 484 g of micron-sized spherical silver powder (particle size of 0.8 to 2.0 μm) and 91 g of micron-sized flaky silver powder (particle size of 1.5 to 3.0 μm) are mixed uniformly in a planetary disperser at a dispersion speed of 1200 rpm for 45 min, and then placed in a three-roll grinder for grinding until the fineness is less than 5 μm to obtain the quick-drying low-temperature silver paste of the present invention.

[0031] Comparative Example 1 The method is basically the same as Example 2, except that the polymer resin is a saturated polyester resin commonly used in low-temperature silver paste on the market, with a molecular weight of 20,000 to 50,000, Tg ≥ 50°C, and the added amount remains unchanged.

[0032] Comparative Example 2 The method is basically the same as Example 2, except that the amount of propylene glycol methyl ether acetate added is 92 g, the amount of ethylene glycol butyl ether acetate added is 116 g, and the amount of DBE added is 92 g.

[0033] Comparative Example 3 The method is basically the same as Example 2, except that the amount of propylene glycol methyl ether acetate added is 27 g, the amount of ethylene glycol butyl ether acetate added is 162 g, and the amount of DBE added is 109 g.

[0034] Comparative Example 4 Basically the same as Example 2, the amount of micron-sized spherical silver powder added (particle size of 0.8-2.0 μm) is 465 g, and the amount of micron-sized flaky silver powder added (particle size of 1.5-3.0 μm) is 155 g.

[0035] Comparative Example 5 The process is basically the same as Example 2, except that the acrylate dispersant EFKA-4402 is not added.

[0036] Performance Testing The low-temperature silver paste prepared in Examples 2 to 4 of the present invention and Comparative Examples 1 to 5 was printed on a PET film by screen printing. The screen was 300 mesh and the thickness of the photosensitive adhesive was 10 μm. The viscosity of the silver paste was tested using a Liyin viscometer VT-06. The drying temperature was 120°C, and the square resistance was tested using a four-probe tester at drying times of 5 min, 10 min, and 20 min, respectively. After drying, the film printing quality of the silver paste was observed using a backlight, the hardness was tested using a pencil hardness tester, and the adhesion was tested using the hundred-grid method. The test results are shown in Table 1: Table 1

[0037] It can be seen from the above test results that the low-temperature silver paste prepared by the present invention in Examples 2 to 4 has good printability, stable resistance under rapid drying, basically no change in conductivity after 5 minutes of drying, and good hardness and adhesion. In Comparative Example 1, the use of conventional saturated polyester resin cannot achieve the quick-drying effect of the present invention due to the slow shrinkage of the resin and poor conductivity. In Comparative Example 2, the proportion of low-boiling point propylene glycol methyl ether acetate is relatively large, resulting in dry plates and virtual printing, causing a decrease in resistance and adhesion. In Comparative Example 3, the proportion of high-boiling point solvents is too large, although printability can be maintained, the drying speed is slow. In Comparative Example 4, the proportion of micron-sized spherical silver powder is low, resulting in a reduction in solvent volatilization channels, slowing down the quick-drying performance of the silver paste. In Comparative Example 5, due to the lack of acrylic ester dispersant, the dispersion effect of the silver powder is poor, and the agglomeration of the silver powder in the silver paste matrix causes a decrease in printing quality and a weakening of conductivity. In summary, the low-temperature silver paste of the present invention has the characteristics of rapid drying and excellent comprehensive performance, and has a broad application space.

[0038] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A quick-drying low-temperature silver paste, characterized in that: In parts by weight, it contains the following components: High molecular resin: 3-7 parts Mixed solvent: 20-40 parts Adhesion promoter: 0.5-2 parts Dispersant: 1-3 parts Conductive silver powder: 55-70 parts; Among them, the polymer resin is a thermoplastic acrylic resin; the mixed solvent is a mixture of ester solvents; the adhesion promoter is a silane coupling agent; the dispersant is an acrylic ester dispersant; and the conductive silver powder is a combination of micron-sized spherical silver powder and micron-sized flaky silver powder.

2. The quick-drying low-temperature silver paste according to claim 1, characterized in that: The molecular weight of the thermoplastic acrylic resin is 150,000 to 300,000, and Tg is ≥80°C.

3. The quick-drying low-temperature silver paste according to claim 1 or 2, characterized in that: The mixed solvent is a mixture of propylene glycol methyl ether acetate, ethylene glycol butyl ether acetate and DBE.

4. The quick-drying low-temperature silver paste according to claim 3, characterized in that: The weight ratio of propylene glycol methyl ether acetate, ethylene glycol butyl ether acetate and DBE is 1:2-3.5:1-2.

2.

5. The quick-drying low-temperature silver paste according to claim 1, 2 or 4, characterized in that: The silane coupling agent is a combination of one or more of silane coupling agent KH151, silane coupling agent KH171, silane coupling agent KH172, silane coupling agent KH560, silane coupling agent KH570, and silane coupling agent KH792.

6. The quick-drying low-temperature silver paste according to claim 5, characterized in that: The acrylate dispersant is a combination of one or more of the acrylate dispersants EFKA-4401, EFKA-4402, DISPERBYK-191, DISPERBYK-2008, DISPERBYK-2055, Dispex Ultra PA 4550, and Dispex Ultra PA 4560.

7. The quick-drying low-temperature silver paste according to claim 1, 2, 4 or 6, characterized in that: In terms of weight ratio, the ratio of micron-sized spherical silver powder to micron-sized flaky silver powder in the conductive silver powder is 5-8:

1.

8. The quick-drying low-temperature silver paste according to claim 7, characterized in that: The particle size of the micron-sized spherical silver powder is 0.8 to 2.0 μm, and the particle size of the micron-sized flaky silver powder is 1.5 to 3.0 μm.

9. A method for preparing the quick-drying low-temperature silver paste according to any one of claims 1 to 8, characterized in that: The following steps are involved: (1) Weighing a polymer resin and a mixed solvent according to a weight ratio, mixing and stirring at 70 to 90° C. until they are uniformly dissolved and dispersed, with a stirring speed of 300 to 800 rpm, filtering with a filter to remove impurities, cooling to room temperature for use, and preparing an organic carrier; (2) weighing the organic carrier, adhesion promoter and dispersant prepared in the above step (1) according to the weight ratio and uniformly mixing them in a planetary disperser at a speed of 1000 to 1500 rpm for 30 to 60 minutes to prepare a silver paste matrix; (3) The silver paste matrix and the conductive silver powder prepared in step (2) are weighed according to a weight ratio, and mixed evenly in a planetary disperser at a dispersion speed of 1000 to 1500 rpm for 30 to 60 min. The mixture is then put into a three-roll grinder for grinding until the fineness is less than 5 μm, thereby obtaining the quick-drying low-temperature silver paste.

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