Stretchable low-temperature silver paste and preparation method thereof

Abstract

The invention discloses stretchable low-temperature silver paste suitable for a flexible circuit and a preparation method of the stretchable low-temperature silver paste. The conductive silver paste comprises the following components in parts by weight: 5-15 parts of elastomer rubber, 20-35 parts of an organic solvent, 1.5-5 parts of a curing agent, 1.5-3 parts of a functional aid and 50-70 parts of modified silver powder, wherein the elastomer rubber is ternary ethylene acrylate rubber; the curing agent is a combination of an aliphatic amine curing agent and a polyether polyamine curing agent. The silver paste has the advantages that the silver paste has good adhesive force to a base material while achieving 200% stretch rate, the adhesive force and conductivity are kept stable after stretching, and the problem that existing silver paste cannot achieve stretching and good adhesive force at the same time is solved; tensile fracture caused by uneven distribution of silver paste components is avoided, and the conductivity is improved; the formula is reasonable, so that the silver paste has the characteristic of high flexibility, is good in adhesive force with a flexible substrate, can resist repeated deformation at the stretching rate of 200%, and keeps stable conductivity.

Description

Technical Field

[0001] The present invention relates to a conductive silver paste production technology, in particular to a stretchable low-temperature silver paste applicable to flexible circuits and a preparation method thereof. Background Art

[0002] In recent years, with the development of the electronic information industry, the requirements for the portability, flexibility, and integration of electronic products in application fields such as touch display, medical health, smart home, and automotive manufacturing have gradually increased, providing development opportunities for flexible electronic technology. Compared with traditional electronic technologies, flexible electronic technology enables electronic devices to have original functions while achieving various forms such as foldable, wearable, stretchable, and twistable, thereby endowing various new electronic devices with greater flexibility. Due to its excellent electrical conductivity and adhesion, conductive silver paste is often used in the electronic industry to form conductive structures on various flexible or rigid substrates through processes such as screen printing, gravure printing, pad printing, and spraying, to prepare electrodes or form conductive connections between electronic devices.

[0003] In conductive silver paste, high-temperature silver paste uses glass powder as the binder phase, and it becomes hard after sintering and thus does not have flexibility; low-temperature silver paste uses polymer resin as the binder phase. When using flexible resin systems such as polyurethane or silicone, it has certain flexibility and bendability after curing, but it cannot maintain good electrical conductivity and adhesion under repeated high stretching, bending, and curling deformations. For example, the halogen-free thin-film switch silver paste and keyboard circuit silver paste on the market are usually polyurethane resin systems. Polyurethane resin has certain stretchability, but its stretchability significantly decreases after adding silver powder. Although it can withstand more than 10 times of forward and reverse bending and maintain circuit conduction, the film layer will break when the elongation rate is within 10%. The silicone resin system has self-supporting and excellent stretchability, but due to its low surface energy after curing, the low-temperature silver paste prepared from it has poor adhesion to substrates such as PET, PI, and TPU. Adding a large amount of tackifier can improve adhesion but cause a significant decrease in electrical conductivity. Therefore, to realize the application of conductive silver paste in new flexible electronic technology, it is of great significance to develop a conductive silver paste with high flexibility, resistance to deformation, good adhesion, and stable performance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a stretchable conductive silver paste with high flexibility, resistance to deformation, good adhesion, and stable performance, and a preparation method thereof.

[0005] To solve the above technical problem, the stretchable conductive silver paste of the present invention, by weight, comprises the following components:

[0006] Elastomeric rubber: 5 - 15 parts

[0007] Organic solvent: 20 - 35 parts

[0008] Curing agent: 1.5 - 5 parts

[0009] Functional additive: 1.5 - 3 parts

[0010] Modified silver powder: 50 - 70 parts

[0011] Among them, the elastomer rubber is ethylene acrylic acid ester rubber; the curing agent is a combination of aliphatic amine curing agent and polyether polyamine curing agent.

[0012] The organic solvent is a combination of ketone solvent and ester solvent.

[0013] The ketone solvent is one or a combination of cyclohexanone, diisobutyl ketone or isophorone, and the ester solvent is one or a combination of ethylene glycol monoethyl ether acetate, ethylene glycol diacetate, ethylene glycol monobutyl ether acetate, DBE, dimethyl adipate or diethylene glycol monoethyl ether acetate.

[0014] The aliphatic amine curing agent is one of ethylenediamine, hexamethylenediamine or diethylenetriamine, preferably hexamethylenediamine, and the polyether polyamine curing agent is one of Huntsman D - 205, Huntsman D - 230, Huntsman D - 400 or Huntsman T - 403. By weight ratio, the ratio of aliphatic amine curing agent to polyether polyamine curing agent is 1:3 - 5.5.

[0015] The functional additive is a combination of silane coupling agent and carbon fiber powder.

[0016] The silane coupling agent is a silane coupling agent without active amine groups, and the carbon fiber powder is carbon fiber powder with a mesh number of 1000 - 2500 meshes.

[0017] The modified silver powder is obtained by surface cleaning and coating with a dispersant of micron - sized flaky silver powder.

[0018] The micron - sized flaky silver powder has a particle size of 2.0 - 5.0 μm and a tapped density of 2.0 - 3.0 g / cm 3 3

[0019] The dispersant is a dispersant without active amine groups.

[0020] A preparation method of the stretchable low - temperature silver paste as described above includes the following steps:

[0021] (1) Surface cleaning of silver powder:

[0022] Mix the micron - sized flaky silver powder and acetone at a rotation speed of 1000 - 1500 rpm for cleaning for 2 - 4 h. After cleaning, filter out the silver powder using a sieve and dry it at 40 - 50 °C for 2 - 4 h. Repeat the above process 3 times to obtain the surface - cleaned silver powder.

[0023] (2) Coating modification of silver powder:

[0024] Dissolve the dispersant in propylene glycol methyl ether acetate to prepare a 5wt% dispersant solution. Weigh the surface-cleaned silver powder and the dispersant solution in step (1) at a weight ratio of 5:1, and perform dispersion mixing at a rotation speed of 800 - 1200 rpm for 1 - 3 h. After dispersion, dry at 85 - 95 °C for 2 - 4 h to obtain modified silver powder;

[0025] (3) Preparation of organic carrier:

[0026] Weigh the elastomer rubber and the organic solvent according to the weight ratio, mix and stir at 75 - 85 °C until uniformly dissolved and dispersed, with a stirring speed of 300 - 600 rpm. After dissolution, use a 300 - 500 mesh filter to remove impurities, and cool to room temperature for standby;

[0027] (4) Preparation of silver paste matrix:

[0028] Weigh the organic carrier, curing agent and functional additives prepared in step (3) according to the weight ratio, mix them evenly in a planetary disperser at a dispersion speed of 1200 - 1800 rpm for 1 - 2 h, and then put them into a three-roll mill for grinding. After grinding to a fineness of less than 20 μm, a silver paste matrix is obtained;

[0029] (5) Preparation of low-temperature silver paste:

[0030] Weigh the silver paste matrix prepared in step (4) and the modified silver powder prepared in step (2) according to the weight ratio, mix them evenly in a planetary disperser at a dispersion speed of 1200 - 1800 rpm for 1 - 2 h, and then put them into a three-roll mill for grinding. After grinding to a fineness of less than 15 μm, the stretchable low-temperature silver paste is obtained.

[0031] The advantages of the present invention are:

[0032] Using ethylene acrylic acid terpolymer rubber as the binder phase of the low-temperature silver paste and a specific screening combination of curing agents, the silver paste can achieve a 200% elongation rate while having good adhesion to the substrate, and maintaining the stability of adhesion and conductivity after stretching, overcoming the problem that existing silver pastes cannot achieve stretchability and good adhesion at the same time; by modifying conventional silver powder, the adverse effect of the original surface treatment agent of silver powder on the curing effect is avoided, and uniform dispersion in the silver paste system is achieved through coating treatment with a dispersant, avoiding tensile fracture caused by uneven distribution of silver paste components and improving conductivity; at the same time, through the selection of functional additives, the adhesion, conductivity and stretch resistance of the silver paste are further improved. Its formula is reasonable, making the silver paste have high flexibility, good adhesion to flexible substrates, and can withstand repeated deformation at a 200% elongation rate and maintain stable conductivity. Specific embodiments

[0033] The stretchable conductive silver paste of the present invention and its preparation method will be further described in detail below in conjunction with specific embodiments.

[0034] The stretchable low-temperature silver paste of the present invention, in parts by weight, comprises the following components: elastomeric rubber: 5 to 15 parts, organic solvent: 20 to 35 parts, curing agent: 1.5 to 5 parts, functional additive: 1.5 to 3 parts, modified silver powder: 50 to 70 parts;

[0035] Among them, the elastomeric rubber is ethylene acrylic terpolymer rubber; ethylene acrylic ester rubber is abbreviated as AEM rubber, and ethylene acrylic terpolymer rubber consists of three parts: ethylene (E) chain segment / methyl acrylate (MA) chain segment / monomer providing curing sites; among them, the ethylene chain segment is a flexible chain segment, and the ethylene unit endows AEM rubber with high elasticity; in the methyl acrylate chain segment, the ester structure is located on the side chain, and as a polar group, it can form hydrogen bonds and van der Waals forces with the polar groups on the surface of the substrate to be adhered, so that the AEM rubber system has good adhesion to the substrate. In the monomer providing curing sites, the active group is usually a carboxyl group, which can react with amine curing agents to form amide bonds, crosslinking and curing AEM rubber into an integral body with mechanical strength; due to the presence of polar groups, AEM rubber cannot be dissolved in non-polar solvents such as mineral oil, but is soluble in organic solvents such as esters and ketones. In the present invention, ethylene acrylic terpolymer rubber is used as the binder phase, which can be dissolved in common organic solvents such as esters and ketones to be formulated into the carrier of the silver paste, and after curing, it can simultaneously have excellent stretchability and adhesion;

[0036] Preferably, the above ethylene acrylic terpolymer rubber is one or a combination of more than one of Vamac G, Vamac GXF, Vamac GLS, Vamac Ultra XF, Vamac Ultra IP, Vamac Ultra HT, Vamac Ultra HT-OR and Vamac Ultra LS manufactured by Celanese Corporation.

[0037] The organic solvent is a combination of a ketone solvent and an ester solvent. Among them, the ketone solvent is one or a combination of more than one of cyclohexanone, diisobutyl ketone or isophorone, and the above ester solvent is one or a combination of more than one of ethylene glycol monoethyl ether acetate, ethylene glycol diacetate, ethylene glycol monobutyl ether acetate, DBE, dimethyl adipate or diethylene glycol monoethyl ether acetate.

[0038] The curing agent is a combination of a fatty amine curing agent and a polyether polyamine curing agent. Preferably, the fatty amine curing agent is one of ethylenediamine, hexamethylenediamine or diethylenetriamine, preferably hexamethylenediamine, and the polyether polyamine curing agent is one of Huntsman D-205, Huntsman D-230, Huntsman D-400 or Huntsman T-403, preferably Huntsman T-403. In terms of weight ratio, the ratio of the fatty amine curing agent to the polyether polyamine curing agent is 1:3-5.5. The present invention uses a combination of a fatty amine curing agent and a polyether polyamine curing agent as a curing agent system, the purpose of which is to achieve the optimal effect of mechanical strength and stretchability. The use of a fatty amine curing agent or a polyether polyamine curing agent alone can cure the low-temperature silver paste of the present invention, but both have performance defects. The fatty amine curing agent is a short carbon chain structure, and its cured product has the characteristics of high tensile strength and fast curing speed, but low elongation at break and insufficient flexibility. The main chain of the polyether polyamine curing agent is a highly flexible polyether structure. The cured product has good flexibility, high elongation at break but low tensile strength. It is easy to produce cracks during repeated deformation, causing the silver paste film layer to break. Therefore, the two curing agents are used in combination and the cross-linking density can be optimized through proportional adjustment, thereby overcoming the defects when used alone and achieving a balance between mechanical strength and tensile effect. According to experiments by the inventor, when the ratio of fatty amine curing agent to polyether polyamine curing agent is in the range of 1:3-5.5 by weight, the performance target of the present invention can be achieved.

[0039] The functional additive is a combination of a silane coupling agent and carbon fiber powder. Preferably, the silane coupling agent is a silane coupling agent that does not contain an active amine group, and can be one of the commercially available silane coupling agents KH-151, KH-171, KH-172, KH-560 or KH-570. The function of the silane coupling agent is to enhance the adhesion between the silver paste film layer and the substrate. The carbon fiber powder is a carbon fiber powder with a mesh size of 1000-2500 meshes. As a conductive toughening agent, the carbon fiber powder has good conductivity on the one hand, and is overlapped between the silver powders to improve the conductivity of the low-temperature silver paste. On the other hand, through the toughening effect, the risk of the silver paste film layer breaking when subjected to deformation such as stretching is reduced.

[0040] Furthermore, the modified silver powder is obtained by surface cleaning and dispersant coating of commercially available micron-sized flaky silver powder.

[0041] Preferably, the micron-sized flaky silver powder has a particle size of 2.0 to 5.0 μm and a tap density of 2.0 to 3.0 g / cm 3, the purpose of surface cleaning is to remove the original surface treatment agent of the silver powder. Since the surface of the silver powder usually has an amine coating agent, and there is a reaction activity between the amine surface coating agent and the carboxyl group in the ethylene acrylic acid ester rubber adopted in the present invention, which participates in the cross-linking reaction and causes an abnormal increase in the cross-linking density, damaging the stretching effect; the purpose of the dispersant coating treatment is to improve the dispersibility of the silver powder after surface cleaning, so that the silver powder is stably and uniformly dispersed in the silver paste system, avoiding tensile fracture caused by silver powder aggregation and uneven distribution of silver paste components, and at the same time improving the conductivity.

[0042] The above-mentioned dispersant is a dispersant without active amine groups, preferably a phosphate ester type dispersant or a hyperbranched polyester type dispersant. Preferably, the above-mentioned phosphate ester type dispersant is one of DISPERBYK-110 or DISPERBYK-111, and the above-mentioned hyperbranched polyester type dispersant is one of DISPERBYK-2152, DISPERBYK-2200 or Silok7631.

[0043] The effects of the present invention are verified below in combination with specific examples and comparative examples:

[0044] Example 1

[0045] The preparation method of the stretchable low-temperature silver paste in this example includes the following steps:

[0046] (1) Surface cleaning of silver powder:

[0047] Mix commercially available micron-sized flaky silver powder (particle size 2.0 - 3.5μm, tapped density 2.8g / cm 3 ) with acetone at a rotation speed of 1200rpm for cleaning for 3h. After cleaning, filter out the silver powder using a sieve and dry it at 45°C for 3h. Repeat the above process 3 times to obtain the silver powder after surface cleaning.

[0048] (2) Coating modification of silver powder:

[0049] Dissolve the phosphate ester type dispersant DISPERBYK-110 in propylene glycol monomethyl ether acetate to prepare a 5wt% DISPERBYK-110 dispersant solution. Weigh the silver powder after surface cleaning in step (1) and the DISPERBYK-110 dispersant solution at a weight ratio of 5:1, and disperse and mix them at a rotation speed of 1000rpm for 2h. After dispersion, dry it at 90°C for 3h to obtain modified silver powder.

[0050] (3) Preparation of organic carrier:

[0051] Weigh 6 parts of ethylene acrylic acid ester rubber Vamac G, 12 parts of isophorone and 12 parts of DBE by weight, mix and stir at 80 °C until uniformly dissolved and dispersed, with a stirring speed of 450 rpm. After dissolution, use a 400-mesh filter screen to remove impurities, and cool to room temperature for standby.

[0052] (4) Preparation of silver paste matrix:

[0053] Weigh 30 parts of the organic carrier prepared in step (3), 0.3 part of fatty amine curing agent hexamethylenediamine, 1.5 parts of polyether polyamine curing agent Huntsman T-403, 1 part of silane coupling agent KH-171 and 1.2 parts of 1500-mesh carbon fiber powder by weight, mix them evenly in a planetary disperser at a dispersion speed of 1500 rpm for 1.5 h, and then put them into a three-roll mill for grinding. After grinding to a fineness of less than 20 μm, a silver paste matrix is obtained.

[0054] (5) Preparation of low-temperature silver paste:

[0055] Weigh 34 parts of the silver paste matrix prepared in step (4) and 66 parts of the modified silver powder prepared in step (2) by weight, mix them evenly in a planetary disperser at a dispersion speed of 1500 rpm for 1.5 h, and then put them into a three-roll mill for grinding. After grinding to a fineness of less than 15 μm, the stretchable low-temperature silver paste applicable to flexible circuits of the present invention is obtained.

[0056] Example 2

[0057] The preparation method of the stretchable low-temperature silver paste in this example includes the following steps:

[0058] (1) Surface cleaning of silver powder:

[0059] Mix commercially available micron-sized flaky silver powder (particle size 2.0 - 3.5 μm, tapped density 2.8 g / cm 3 ) with acetone at a rotation speed of 1200 rpm for cleaning for 3 h. After cleaning, filter out the silver powder using a sieve and dry it at 45 °C for 3 h. Repeat the above process 3 times to obtain the surface-cleaned silver powder.

[0060] (2) Coating modification of silver powder:

[0061] Dissolve the phosphate ester dispersant DISPERBYK-110 in propylene glycol methyl ether acetate to prepare a 5 wt% DISPERBYK-110 dispersant solution. Weigh the surface-cleaned silver powder and the DISPERBYK-110 dispersant solution in a weight ratio of 5:1, disperse and mix them at a rotation speed of 1000 rpm for 2 h. After dispersion, dry them at 90 °C for 3 h to obtain modified silver powder.

[0062] (3) Preparation of organic carrier:

[0063] Weigh 8 parts by weight of ethylene acrylic acid ester rubber Vamac G, 13 parts of isophorone and 13 parts of DBE. Mix and stir them at 80 °C until they are uniformly dissolved and dispersed. The stirring speed is 450 rpm. After dissolution, use a 400-mesh filter screen to remove impurities, and cool to room temperature for standby.

[0064] (4) Preparation of silver paste matrix:

[0065] Weigh 34 parts by weight of the organic carrier prepared in step (3), 0.4 part of fatty amine curing agent hexamethylenediamine, 2 parts of polyether polyamine curing agent Huntsman T-403, 1.2 parts of silane coupling agent KH-171 and 1.2 parts of 1500-mesh carbon fiber powder. Mix them evenly in a planetary disperser. The dispersion speed is 1500 rpm and the time is 1.5 h. Then put them into a three-roll grinder for grinding. After grinding to a fineness less than 20 μm, the silver paste matrix is obtained.

[0066] (5) Preparation of low-temperature silver paste:

[0067] Weigh 38.8 parts by weight of the silver paste matrix prepared in step (4) and 61.2 parts of the modified silver powder prepared in step (2). Mix them evenly in a planetary disperser. The dispersion speed is 1500 rpm and the time is 1.5 h. Then put them into a three-roll grinder for grinding. After grinding to a fineness less than 15 μm, the stretchable low-temperature silver paste applicable to flexible circuits of the present invention is obtained.

[0068] Example 3

[0069] The preparation method of the stretchable low-temperature silver paste in this example includes the following steps:

[0070] (1) Surface cleaning of silver powder:

[0071] Mix the commercially available micron-sized flaky silver powder (particle size 3.0 - 5.0 μm, tapped density 2.2 g / cm 3 ) with acetone and mix them at a rotation speed of 1200 rpm for cleaning for 3 h. After cleaning, use a sieve to filter out the silver powder and dry it at 45 °C for 3 h. Repeat the above process 3 times to obtain the silver powder after surface cleaning.

[0072] (2) Coating modification of silver powder:

[0073] Dissolve the hyperbranched polyester dispersant Silok 7631 in propylene glycol methyl ether acetate to prepare a 5 wt% dispersant Silok 7631 solution. Weigh the silver powder after surface cleaning in step (1) and the dispersant Silok 7631 solution at a weight ratio of 5:1, and perform dispersion mixing at a rotation speed of 1000 rpm for 2 h. After dispersion, dry at 90 °C for 3 h to obtain modified silver powder.

[0074] (3) Preparation of organic carrier:

[0075] Weigh 9 parts of terpolymer ethylene acrylic ester rubber Vamac Ultra XF, 7 parts of diisobutyl ketone, and 20 parts of ethylene glycol monobutyl ether acetate by weight, mix and stir at 80 °C until uniformly dissolved and dispersed, with a stirring speed of 450 rpm. After dissolution, use a 400-mesh filter screen to remove impurities, and cool to room temperature for standby.

[0076] (4) Preparation of silver paste matrix:

[0077] Weigh 36 parts of the organic carrier prepared in step (3), 0.5 part of aliphatic amine curing agent hexamethylenediamine, 2 parts of polyether polyamine curing agent Huntsman T-403, 1.2 parts of silane coupling agent KH-560, and 1.3 parts of 1500-mesh carbon fiber powder by weight, mix uniformly in a planetary disperser at a dispersion speed of 1500 rpm for 1.5 h, and then put it into a three-roll mill for grinding. After grinding to a fineness of less than 20 μm, a silver paste matrix is obtained.

[0078] (5) Preparation of low-temperature silver paste:

[0079] Weigh 41 parts of the silver paste matrix prepared in step (4) and 59 parts of the modified silver powder prepared in step (2) by weight, mix uniformly in a planetary disperser at a dispersion speed of 1500 rpm for 1.5 h, and then put it into a three-roll mill for grinding. After grinding to a fineness of less than 15 μm, the stretchable low-temperature silver paste applicable to flexible circuits of the present invention is obtained.

[0080] Example 4

[0081] The preparation method of the stretchable low-temperature silver paste in this example includes the following steps:

[0082] (1) Surface cleaning of silver powder:

[0083] Mix commercially available micron-scale flaky silver powder (particle size 3.0 - 5.0 μm, tapped density 2.2 g / cm 3 ) with acetone and mix for cleaning at a rotation speed of 1200 rpm for 3 h. After cleaning, filter out the silver powder using a sieve and dry at 45 °C for 3 h. Repeat the above process 3 times to obtain the silver powder after surface cleaning.

[0084] (2) Coating modification of silver powder:

[0085] Dissolve the hyperbranched polyester dispersant Silok 7631 in propylene glycol methyl ether acetate to prepare a 5 wt% dispersant Silok 7631 solution. Weigh the surface-cleaned silver powder from step (1) and the dispersant Silok 7631 solution at a weight ratio of 5:1, and perform dispersion mixing at a rotation speed of 1000 rpm for 2 h. After dispersion, dry at 90 °C for 3 h to obtain modified silver powder.

[0086] (3) Preparation of organic carrier:

[0087] Weigh 12 parts of ethylene acrylic acid ester rubber Vamac Ultra XF, 7 parts of diisobutyl ketone, and 21 parts of ethylene glycol butyl ether acetate by weight. Mix and stir at 80 °C until uniformly dissolved and dispersed, with a stirring speed of 450 rpm. After dissolution, use a 400-mesh filter to remove impurities, and cool to room temperature for standby.

[0088] (4) Preparation of silver paste matrix:

[0089] Weigh 40 parts of the organic carrier prepared in step (3), 0.7 part of fatty amine curing agent hexamethylenediamine, 2.3 parts of polyether polyamine curing agent Huntsman T-403, 0.6 part of silane coupling agent KH-560, and 1.2 parts of 1500-mesh carbon fiber powder by weight. Mix them uniformly in a planetary disperser at a dispersion speed of 1500 rpm for 1.5 h, and then put them into a three-roll mill for grinding. After grinding to a fineness of less than 20 μm, a silver paste matrix is obtained.

[0090] (5) Preparation of low-temperature silver paste:

[0091] Weigh 44.8 parts of the silver paste matrix prepared in step (4) and 55.2 parts of the modified silver powder prepared in step (2) by weight. Mix them uniformly in a planetary disperser at a dispersion speed of 1500 rpm for 1.5 h, and then put them into a three-roll mill for grinding. After grinding to a fineness of less than 15 μm, the stretchable low-temperature silver paste applicable to flexible circuits of the present invention is obtained.

[0092] Comparative Example 1

[0093] Basically the same as Example 1, except that 6 parts of ethylene acrylic acid ester rubber are replaced with 6 parts of saturated polyurethane resin, and the curing agent (1.8 parts in total) is replaced with 1.8 parts of the commonly used isocyanate curing agent for polyurethane resin, and the remaining components and weight ratios remain unchanged.

[0094] Comparative Example 2

[0095] Basically the same as Example 1, except that 6 parts of ethylene acrylic acid ester rubber are replaced by 6 parts of heat-curable silicone resin-based glue, 24 parts of organic solvent are replaced by 24 parts of undecane soluble in silicone resin, and 1.8 parts of curing agent are replaced by 1.8 parts of silicone resin vulcanizing agent, and the other components and their weight ratios remain unchanged.

[0096] Comparative Example 3

[0097] Basically the same as Example 1, except that the commercially available micron-sized flaky silver powder is not subjected to surface cleaning and dispersant coating treatment and is directly added to the silver paste matrix, and the other components and their weight ratios remain unchanged.

[0098] Comparative Example 4

[0099] Basically the same as Example 1, except that the commercially available micron-sized flaky silver powder is only subjected to surface cleaning and not subjected to dispersant coating treatment, and the other components and their weight ratios remain unchanged.

[0100] Performance Test

[0101] The following tests were carried out on the low-temperature silver pastes prepared in Examples 1 to 4 and Comparative Examples 1 to 4:

[0102] 1. Each silver paste was printed on a PET film using a 150-mesh screen with a photosensitive glue thickness of 15 μm, printed into a 50 mm × 10 mm rectangular pattern, cured at 130 °C for 30 min, and then the resistivity was measured using a four-probe tester, and the adhesion was measured using the cross-cut method.

[0103] 2. Each silver paste was printed on an elastic TPU film using a 150-mesh screen with a photosensitive glue thickness of 15 μm, printed into a 50 mm × 10 mm rectangular pattern, cured at 130 °C for 30 min, and then the resistivity was measured using a four-probe tester, and the adhesion was measured using the cross-cut method. After stretching the silver paste sample strip to 150 mm (elongation rate 200%) at a speed of 5 mm / s and then recovering to the original length, the resistivity change was measured after 100 cycles.

[0104] 3. Each silver paste was scraped onto a release paper to form a 50 mm × 10 mm rectangular pattern with a thickness of 30 μm, cured at 130 °C for 30 min, and then the resistivity was measured using a four-probe tester. The silver paste was peeled off from the release paper to obtain a self-supporting silver paste sample strip. After stretching the silver paste sample strip to 150 mm (elongation rate 200%) at a speed of 5 mm / s and then recovering to the original length, the resistivity change was measured after 100 cycles. The test results are shown in Table 1:

[0105] Table 1

[0106]

[0107] As can be seen from the above test results, the low-temperature silver pastes prepared in Examples 1 to 4 of the present invention have good conductivity and adhesion. When printed on an elastic substrate or used as a self-supporting conductive film layer, they all exhibit excellent stretchability, can withstand repeated tensile deformation, do not break, and have a small change in resistivity. In Comparative Example 1, a polyurethane resin system was used to prepare a low-temperature silver paste, which showed good conductivity and adhesion on a common PET substrate, but could not withstand tensile deformation and broke after stretching. In Comparative Example 2, a silicone resin system was used to prepare a low-temperature silver paste, which could form a self-supporting film layer with good stretchability, but had poor adhesion to PET and elastic TPU substrates and could not form a highly reliable conductive circuit on the substrate. In Comparative Example 3, the micron-sized flaky silver powder used was not subjected to surface cleaning and dispersant coating treatment, and the amine coating agent on its surface participated in the cross-linking reaction, resulting in a relatively high hardness and insufficient stretchability of the cured silver paste. In Comparative Example 4, the silver powder used was not modified with a dispersant after cleaning, resulting in poor dispersibility in the silver paste system, and an increase in resistance and tensile fracture due to silver powder aggregation. In summary, the stretchable low-temperature silver paste prepared by the present invention for flexible circuits has excellent stretchability, stable resistance after repeated stretching, good adhesion to flexible substrates, and has broad application prospects in new flexible electronic technologies.

[0108] 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 those skilled in the art within the scope of the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A stretchable conductive silver paste, characterized in that: In parts by weight, it contains the following components: Elastomer rubber: 5-15 parts Organic solvent: 20-35 parts Curing agent: 1.5-5 parts Functional additives: 1.5-3 parts Modified silver powder: 50-70 parts Wherein, the elastomeric rubber is ternary ethylene acrylate rubber; and the curing agent is a combination of a fatty amine curing agent and a polyether polyamine curing agent.

2. The stretchable conductive silver paste according to claim 1, characterized in that: The organic solvent is a combination of a ketone solvent and an ester solvent.

3. The stretchable conductive silver paste according to claim 2, characterized in that: The ketone solvent is a combination of one or more of cyclohexanone, diisobutyl ketone or isophorone, and the ester solvent is a combination of one or more of ethylene glycol ethyl ether acetate, ethylene glycol diacetate, ethylene glycol butyl ether acetate, DBE, dimethyl adipate or diethylene glycol ethyl ether acetate.

4. The stretchable conductive silver paste according to claim 1, 2 or 3, characterized in that: The fatty amine curing agent is one of ethylenediamine, hexamethylenediamine or diethylenetriamine, preferably hexamethylenediamine, and the polyether polyamine curing agent is one of Huntsman D-205, Huntsman D-230, Huntsman D-400 or Huntsman T-403. The ratio of the fatty amine curing agent to the polyether polyamine curing agent is 1:3-5.5 in terms of weight ratio.

5. The stretchable conductive silver paste according to claim 1, characterized in that: The functional additive is a combination of a silane coupling agent and carbon fiber powder.

6. The stretchable conductive silver paste according to claim 5, characterized in that: The silane coupling agent is a silane coupling agent without active amine groups, and the carbon fiber powder is a carbon fiber powder with a mesh number of 1000 to 2500.

7. The stretchable conductive silver paste according to claim 1, characterized in that: The modified silver powder is micron-sized flaky silver powder obtained by surface cleaning and dispersant coating.

8. The stretchable conductive silver paste according to claim 7, characterized in that: The micron-scale flaky silver powder has a particle size of 2.0 to 5.0 μm and a tap density of 2.0 to 3.0 g / cm 3 .

9. The stretchable conductive silver paste according to claim 7, characterized in that: The dispersant is a dispersant that does not contain active amine groups.

10. A method for preparing the stretchable low-temperature silver paste according to claims 1-9, comprising the following steps: (1) Surface cleaning of silver powder: The micron-sized flaky silver powder is mixed with acetone at a rotation speed of 1000-1500 rpm for washing for 2-4 hours. After washing, the silver powder is filtered out using a sieve and dried at 40-50° C. for 2-4 hours. The above process is repeated 3 times to obtain the surface-cleaned silver powder. (2) Coating modification of silver powder: The dispersant is dissolved in propylene glycol methyl ether acetate to prepare a 5 wt% dispersant solution, the silver powder after surface cleaning in step (1) and the dispersant solution are weighed in a weight ratio of 5:1, and dispersed and mixed at a speed of 800-1200 rpm for 1-3 hours. After the dispersion is completed, the mixture is dried at 85-95° C. for 2-4 hours to obtain a modified silver powder; (3) Preparation of organic carrier: Weigh the elastomer rubber and the organic solvent according to the weight ratio, mix and stir at 75-85°C until they are evenly dissolved and dispersed, with a stirring speed of 300-600rpm. After dissolution, use a 300-500 mesh filter to remove impurities, and cool to room temperature for use; (4) Preparation of silver paste matrix: The organic carrier, curing agent and functional additive prepared in step (3) are weighed according to the weight ratio, and mixed evenly in a planetary disperser at a dispersion speed of 1200-1800 rpm for 1-2 hours, and then put into a three-roll grinder for grinding until the fineness is less than 20 μm to obtain a silver paste matrix; (5) Preparation of low-temperature silver paste: The silver paste matrix prepared in step (4) and the modified silver powder prepared in step (2) are weighed according to the weight ratio, and mixed evenly in a planetary disperser at a dispersion speed of 1200 to 1800 rpm for 1 to 2 hours. The mixture is then placed in a three-roll grinder for grinding until the fineness is less than 15 μm to obtain the stretchable low-temperature silver paste.

Images