Copper paste for screen printing and preparation method thereof

Abstract

The invention discloses copper paste for silk-screen printing and a preparation method thereof, the copper paste for silk-screen printing comprises the following components in parts by mass: 80-92 parts of copper powder and 8-20 parts of an organic carrier, the copper powder comprises copper powder A with D90 of 5-10 [mu] m, copper powder B with D90 of 500-900 nm and copper powder C with D90 of 50-200 nm; the surface of the copper powder B is provided with a ligand, and the surface of the copper powder C is provided with a surfactant. When the copper paste is used in a silk-screen circuit, the height-width ratio is 0.4-0.7, the shading area is reduced, and the photoelectric conversion efficiency of a battery is improved; the conductive copper paste has the advantages that the conductivity meets the requirements of photovoltaic copper paste, the resistivity is 0.086-0.172 m omega.mm, the viscosity is 200-300 Pa.s, the wire drawing property is reduced, the silk-screen effect is good, and the application prospect is good.

Description

Technical Field

[0001] The invention belongs to the field of screen printing of circuit boards, and in particular relates to a copper paste for screen printing and a preparation method thereof. Background Art

[0002] Currently, printed circuit boards are primarily manufactured using an etching method, where excess copper is removed from a complete copper layer to form the designed circuit pattern. This process can have serious environmental and human health impacts. Furthermore, the etching solution contains strong oxidants, and the wastewater after etching contains large amounts of copper ions, significantly increasing the difficulty of post-processing the wastewater.

[0003] Photovoltaic printing technology uses large-scale printing equipment that can process multiple panels simultaneously, greatly improving production efficiency. Compared to traditional manual assembly methods, photovoltaic printing can save significant time and labor. The principle of photovoltaic screen printing is to use screen printing technology to evenly apply conductive paste to the solar cell to form electrodes and conductors. The conductive material in the conductive paste has excellent electrical conductivity and provides a current transmission path. Screen printing technology can control the thickness and shape of the paste to meet the design requirements of the solar cell. During the sintering process, the conductive paste is combined with the substrate to form a stable electrode and conductor structure. However, even the most mature silver paste currently suffers from high sintering temperature and high cost. The cost-effective copper paste has inherent problems such as easy oxidation and poor sintering performance. Therefore, how to improve the low-temperature sintering performance, conductivity, and printing reliability of metal conductive pastes to ensure smooth current flow through the cell and thus improve photoelectric conversion efficiency is a technical problem that needs to be solved urgently. Summary of the Invention

[0004] The main purpose of the present invention is to provide a copper paste for screen printing and a preparation method thereof, which solves the technical problem in the prior art that the conductivity and printing reliability of the copper paste are difficult to meet the screen printing requirements of the photovoltaic industry.

[0005] In the first aspect, the present invention provides a copper paste for screen printing, which comprises, by mass, 80 to 92 parts of copper powder and 8 to 20 parts of an organic vehicle, wherein the copper powder comprises D 90 =5~10μm copper powder A, D 90 = 500~900nm copper powder B and D 90 =50~200nm copper powder C; the copper powder B has a ligand on its surface, and the copper powder C has a surfactant on its surface.

[0006] Furthermore, the organic vehicle comprises 1 to 5 parts of resin, 1 to 5 parts of binder, 5 to 10 parts of solvent, 0.2 to 2 parts of plasticizer and 0.2 to 2 parts of thixotropic additive.

[0007] Furthermore, the mass ratio of copper powder A, copper powder B, and copper powder C is (1-10):(1-10):(0.5-5).

[0008] Furthermore, the resin is selected from at least one of acrylic resin, polyurethane, polyvinyl butyral or polyvinyl acetal; and / or the binder is selected from at least one of ethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose or hydroxypropyl methyl fiber; and / or the solvent is selected from at least one of terpineol, isopropyl alcohol, isophorone, cyclohexanone, n-butyl acetate, diethylene glycol butyl ether acetate, ethylene glycol monomethyl ether acetate or dipropylene glycol methyl ether acetate; and / or the plasticizer is selected from at least one of tributyl phosphate, triphenyl phosphate, dimethyl phthalate, dibutyl phthalate or dioctyl phthalate; and / or the thixotropic agent is selected from at least one of hydrogenated castor oil, polyamide-modified hydrogenated castor oil, polyamide wax slurry, fumed silica or organic bentonite.

[0009] Among them, the molecular structure of the plasticizer in the organic carrier solvent contains a polar part. When mixed with polar polymers such as ethyl cellulose at a higher temperature, the polar parts attract each other to form a multi-dimensional network structure, making the organic carrier a pseudoplastic liquid suitable for screen printing.

[0010] Furthermore, the ligand on the surface of the copper powder B is selected from at least one of nonanoic acid, decanoic acid, undecyl acid, undecenoic acid, dodecyl acid, dodecenoic acid, tetradecyl acid, tetradecenoic acid, hexadecyl acid, hexadecenoic acid, octadecenoic acid, octadecyl acid, octylamine, nonylamine, aniline, benzylamine, p-methylaniline, toluidine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine or octadecylamine; and / or, the surfactant is selected from at least one of polyoxyethylene stearate-30, polyoxyethylene stearate-40, triethanolamine oleate, sorbitan laurate, polyoxyethylene lauryl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monopalmitate or polyoxyethylene sorbitan stearate.

[0011] Furthermore, the preparation method of the copper powder A comprises the following steps: adding ammonia water to a solution containing a copper salt to allow the ammonia water to complex with copper ions, and then adding a reducing agent to react to obtain copper powder A;

[0012] The preparation method of the copper powder B comprises the following steps: adding a growth regulator to a solution containing a copper salt to obtain a mixed solution; adding a sodium hydroxide solution to a solution containing a reducing agent, heating and stirring, adding the mixed solution to continue the reaction, and reacting the reaction product with a ligand to obtain copper powder B;

[0013] The preparation method of the copper powder C comprises the following steps: adding a sodium hydroxide solution to a solution containing a copper salt, reacting the solution with a reducing agent, and reacting the reaction product with a surfactant to obtain the copper powder C.

[0014] Furthermore, the aspect ratio of the screen-printed circuit of the copper paste is 0.4-0.7, the resistivity is 0.086-0.172 mΩ·mm, and the viscosity is 200-300 Pa·s.

[0015] In a second aspect, the present invention provides a method for preparing a copper paste for screen printing, the method comprising the following steps:

[0016] Mix copper powder A, copper powder B and copper powder C in proportion;

[0017] The resin, binder, solvent, plasticizer and thixotropic agent are mixed in proportion to obtain an organic carrier;

[0018] The mixed copper powder and the organic carrier are mixed and ground according to a certain proportion to obtain the copper paste for screen printing.

[0019] Specifically include:

[0020] The copper salt is dissolved in a solvent, and then ammonia is added to complex with the copper ions to obtain a copper complex solution; the reducing agent is dissolved in the solvent, and the solution containing the reducing agent is added dropwise to the copper complex solution and heated to react to obtain copper powder A;

[0021] The copper salt is dissolved in a solvent, and a growth regulator is added and stirred evenly; sodium hydroxide and a reducing agent are dissolved in a solvent respectively, the sodium hydroxide solution is dripped into the reducing agent solution to obtain a mixed solution, and the copper salt solution is dripped into the mixed solution to react and obtain a product; the product is added to a weak polar solvent, a ligand is added, and the reaction is stirred at room temperature to obtain copper powder B;

[0022] A copper salt is dissolved in a solvent, and a sodium hydroxide solution is added dropwise, followed by stirring for reaction. A two-step reduction process is then performed, wherein a weak reducing agent is first added for reaction at room temperature, followed by a strong reducing agent for reaction by heating to obtain copper powder. A solvent is added to the dried copper powder, followed by a surfactant and reaction to obtain copper powder C coated with a surfactant.

[0023] Copper powder A, copper powder B, and copper powder C are mixed in proportion, and then mixed evenly with an organic vehicle to obtain the copper paste for screen printing.

[0024] Furthermore, the copper salt is selected from at least one of copper sulfate pentahydrate, copper hydroxide, copper nitrate, copper formate, copper acetate monohydrate or copper chloride.

[0025] Furthermore, during the preparation of the copper powder A, the particles grow faster and the generated particles are larger in size.

[0026] Furthermore, in the process of preparing the copper powder B, a growth regulator is first added to a solution containing a copper salt to obtain a mixed solution, and the addition of the growth regulator helps to accelerate nucleation, so that the generated particles are smaller in size; the product obtained by the reaction reacts with a ligand to obtain copper powder B, and the ligand completely replaces the above-mentioned growth regulator, which helps to reduce the wire drawing property of the final product; the growth regulator is selected from at least one of polyacrylic acid, polyvinyl pyrrolidone, carboxymethyl cellulose, polyvinyl alcohol, polyethylene glycol, styrene-maleic acid copolymer, oxalic acid, formic acid or gluconic acid; and / or the ligand is selected from at least one of nonanoic acid, decanoic acid, undecyl acid, undecenoic acid, dodecyl acid, dodecenoic acid, tetradecyl acid, tetradecenoic acid, hexadecyl acid, hexadecenoic acid, octadecenoic acid, octadecyl acid, octylamine, nonylamine, aniline, benzylamine, p-methylaniline, monotoluidine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine or octadecenylamine.

[0027] Furthermore, in the process of preparing the copper powder B, the product obtained by the reaction is pre-dissolved in a weak polar solvent before reacting with the ligand. The reason is that according to the principle of like dissolves like, the ligand is exchanged with the original substance on the surface of the copper powder. The weak polar solvent is selected from at least one of n-hexane, dichloromethane, chloroform, acetone, cyclohexane or N,N-dimethylformamide.

[0028] Furthermore, the reducing agent used in the process of preparing the copper powder A or B is selected from at least one of glucose, sodium hypophosphite, citric acid, sodium citrate, ascorbic acid, sodium borohydride, hydrazine hydrate or hypophosphorous acid.

[0029] Furthermore, the reducing agent used in the process of preparing the copper powder C includes a weak reducing agent and a strong reducing agent. The weak reducing agent is first added to generate cuprous oxide, and then the strong reducing agent is added to reduce the cuprous oxide to copper. The two-step reduction method can synthesize smaller copper particles; the weak reducing agent is selected from at least one of glucose, sodium hypophosphite, citric acid or sodium citrate; and / or the strong reducing agent is selected from at least one of ascorbic acid, sodium borohydride, hydrazine hydrate or hypophosphorous acid.

[0030] Furthermore, in the process of preparing the copper powder A, the concentration of the solution containing copper salt is 0.1-10 mol / L, the concentration of the ammonia water is 1-20 mol / L, the concentration of the reducing agent dissolved in the solvent is 0.5-10 mol / L, the reaction temperature is 60-80°C, and the reaction time is 1 hour or more.

[0031] Furthermore, in the process of preparing the copper powder B, the concentration of the solution containing the copper salt is 0.5-10 mol / L, the concentration of the growth regulator in the solution is 0.01-0.1 mol / L, the concentration of the sodium hydroxide solution is 10-50 mol / L, the concentration of the reducing agent solution is 1-20 mol / L, the heating and stirring temperature is 60-80°C, the heating and stirring time is 5-10 minutes, and the mixed solution is added and the reaction time is continued for 1 hour or more. The amount of the ligand used is 1-5 wt.% of the copper powder, and the reaction is stirred at room temperature for 1 hour or more.

[0032] Furthermore, in the process of preparing the copper powder C, the concentration of the solution containing copper salt is 0.5-10 mol / L, the concentration of the sodium hydroxide solution is 10-50 mol / L, the concentration of the weak reducing agent solution is 1-10 mol / L, the concentration of the strong reducing agent solution is 1-20 mol / L, the reaction is carried out at room temperature for 0.5 h or more, the heating temperature for the strong reducing agent to reduce cuprous oxide to copper is 60-80°C, the reaction time is 1 h or more, the amount of the surfactant used is 0.1-2 wt.% of the copper powder, and the ultrasonic treatment is carried out for 5-10 min after the surfactant is added.

[0033] Among them, copper powder A has the largest particle size, a smaller specific surface area, and a small contact site with the organic phase, which can reduce the overall viscosity of the slurry, adjust the slurry viscosity to a level suitable for screen printing, and provide conductivity. Copper powder B has a moderate particle size, and after ligand treatment, its surface is oily and has no hydrogen bonding, which can reduce the overall wire drawing property of the slurry and effectively avoid problems such as screen adhesion and poor line uniformity during screen printing. Copper powder C has the smallest particle size. On the one hand, it can fill the gaps between large particles, thereby improving the density and conductivity of the slurry after sintering. On the other hand, due to its large specific surface area, after treatment, the surfactant has more cross-linking sites with the resin in the organic phase, forming a dense network structure, giving the slurry a certain degree of conformality, preventing line collapse after screen printing, and ensuring that the screen printed lines have a high aspect ratio. In addition, the copper powder surface treated by the above method is protected from organic matter, which can also isolate water and oxygen in the air to a certain extent, reducing the problem of copper powder oxidation. Overall, the synergistic effect of the above three copper powders and the organic carrier makes the final copper paste have relatively excellent technical effects in screen printing.

[0034] The copper paste for screen printing and the preparation process thereof provided by the present invention have the following beneficial effects:

[0035] (1) The aspect ratio of the screen printed circuit is 0.4 to 0.7, which is beneficial to reducing the shading area and improving the photoelectric conversion efficiency of the battery; some of the additives added in the present invention can produce internal cross-linking with the organic phase, so that the slurry has a certain degree of shape retention;

[0036] (2) The electrical conductivity meets the requirements of photovoltaic copper paste, with a resistivity of 0.086 to 0.172 mΩ·mm;

[0037] (3) The viscosity is 200-300 Pa·s, the wire drawing property is reduced, and the screen printing effect is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The figures are the screen printing effect and wire drawing effect of the copper paste prepared in Example 1;

[0039] Figure 2 These are the screen printing effect and wire drawing effect of the copper paste prepared in Comparative Example 7. DETAILED DESCRIPTION

[0040] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0041] As mentioned in the background of this invention, even the most mature silver paste currently suffers from issues such as high sintering temperature and high cost. Meanwhile, copper paste, which offers cost advantages, has inherent issues such as susceptibility to oxidation and poor sintering performance. Therefore, improving the low-temperature sintering performance, conductivity, and printing reliability of metallic conductive pastes to ensure smooth current flow through the cell and thus improve photoelectric conversion efficiency is a pressing technical challenge.

[0042] The present invention provides a copper paste for screen printing, which comprises, by weight, 80 to 92 parts of copper powder and 8 to 20 parts of an organic vehicle, wherein the copper powder comprises D 90 =5~10μm copper powder A, D 90 = 500~900nm copper powder B and D 90 =50~200nm copper powder C; the copper powder B has a ligand on its surface, and the copper powder C has a surfactant on its surface.

[0043] In some specific embodiments, the organic carrier includes 1 to 5 parts of resin, 1 to 5 parts of binder, 5 to 10 parts of solvent, 0.2 to 2 parts of plasticizer and 0.2 to 2 parts of thixotropic agent, wherein the resin is selected from at least one of acrylic resin, polyurethane, polyvinyl butyral or polyvinyl acetal; and / or the binder is selected from at least one of ethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose or hydroxypropyl methylcellulose; and / or the plasticizer is selected from at least one of tributyl phosphate, triphenyl phosphate, dimethyl phthalate, dibutyl phthalate or dioctyl phthalate; and / or the thixotropic agent is selected from at least one of hydrogenated castor oil, polyamide-modified hydrogenated castor oil, polyamide wax slurry, fumed silica or organic bentonite.

[0044] In some specific embodiments, the mass ratio of copper powder A, copper powder B, and copper powder C is (1-10):(1-10):(0.5-5).

[0045] In some specific embodiments, the organic carrier further includes 5 to 10 parts of a solvent, and the solvent is selected from at least one of terpineol, isopropyl alcohol, isophorone, cyclohexanone, n-butyl acetate, diethylene glycol butyl ether acetate, ethylene glycol monomethyl ether acetate or dipropylene glycol methyl ether acetate.

[0046] In some specific embodiments, the ligand on the surface of the copper powder B is selected from at least one of nonanoic acid, decanoic acid, undecyl acid, undecenoic acid, dodecyl acid, dodecenoic acid, tetradecyl acid, tetradecenoic acid, hexadecyl acid, hexadecenoic acid, octadecenoic acid, octadecyl acid, octylamine, nonylamine, aniline, benzylamine, p-methylaniline, toluidine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine or octadecylamine; and / or, the surfactant is selected from at least one of polyoxyethylene stearate-30, polyoxyethylene stearate-40, triethanolamine oleate, sorbitan laurate, polyoxyethylene lauryl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monopalmitate or polyoxyethylene sorbitan stearate.

[0047] Furthermore, the preparation method of the copper powder A comprises the following steps: adding ammonia water to a solution containing a copper salt to allow the ammonia water to complex with copper ions, and then adding a reducing agent to react to obtain copper powder A;

[0048] The preparation method of the copper powder B comprises the following steps: adding a growth regulator to a solution containing a copper salt to obtain a mixed solution; adding a sodium hydroxide solution to a solution containing a reducing agent, heating and stirring, adding the mixed solution to continue the reaction, and reacting the reaction product with a ligand to obtain copper powder B;

[0049] The preparation method of the copper powder C comprises the following steps: adding a sodium hydroxide solution to a solution containing a copper salt, reacting the solution with a reducing agent, and reacting the reaction product with a surfactant to obtain the copper powder C.

[0050] In some specific embodiments, the copper salt is selected from at least one of copper sulfate pentahydrate, copper hydroxide, copper nitrate, copper formate, copper acetate monohydrate or copper chloride.

[0051] In some specific embodiments, during the preparation of the copper powder B, a growth regulator is first added to a solution containing a copper salt to obtain a mixed solution; the product obtained by the reaction reacts with a ligand to obtain copper powder B; the growth regulator is selected from at least one of polyacrylic acid, polyvinyl pyrrolidone, carboxymethyl cellulose, polyvinyl alcohol, polyethylene glycol, styrene-maleic acid copolymer, oxalic acid, formic acid or gluconic acid; and / or the ligand is selected from at least one of nonanoic acid, decanoic acid, undecyl acid, undecenoic acid, dodecyl acid, dodecenoic acid, tetradecyl acid, tetradecenoic acid, hexadecyl acid, hexadecenoic acid, octadecenoic acid, octadecyl acid, octylamine, nonylamine, aniline, benzylamine, p-methylaniline, monotoluidine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine or octadecylamine.

[0052] In some specific embodiments, during the preparation of the copper powder B, the product obtained by the reaction is pre-dissolved in a weak polar solvent before reacting with the ligand, and the weak polar solvent is selected from at least one of n-hexane, dichloromethane, chloroform, acetone, cyclohexane or N,N-dimethylformamide.

[0053] Furthermore, the reducing agent used in the process of preparing the copper powder A or B is selected from at least one of glucose, sodium hypophosphite, citric acid, sodium citrate, ascorbic acid, sodium borohydride, hydrazine hydrate or hypophosphorous acid.

[0054] In some specific embodiments, the reducing agent used in the process of preparing the copper powder C includes a weak reducing agent and a strong reducing agent; the weak reducing agent is selected from at least one of glucose, sodium hypophosphite, citric acid or sodium citrate; and / or, the strong reducing agent is selected from at least one of ascorbic acid, sodium borohydride, hydrazine hydrate or hypophosphorous acid.

[0055] A second aspect of the present invention provides a method for preparing a copper paste for screen printing, the method comprising the following steps:

[0056] Mix copper powder A, copper powder B and copper powder C in proportion;

[0057] The resin, binder, solvent, plasticizer and thixotropic agent are mixed in proportion to obtain an organic carrier;

[0058] The mixed copper powder and the organic carrier are mixed and ground according to a certain proportion to obtain the copper paste for screen printing.

[0059] Typically but not limitatively, the copper paste for silk screen printing comprises, by mass, 80 parts, 82 parts, 84 parts, 86 parts, 88 parts, 90 parts, 92 parts or a range of values ​​consisting of any two of their values ​​of copper powder and 8 parts, 10 parts, 12 parts, 14 parts, 16 parts, 18 parts, 20 parts or a range of values ​​consisting of any two of their values ​​of organic carrier.

[0060] Typically but not limitatively, the organic vehicle comprises, by mass, 1 part, 2 parts, 3 parts, 4 parts, 5 parts or a range consisting of any two of the resins; 1 part, 2 parts, 3 parts, 4 parts, 5 parts or a range consisting of any two of the binders; 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts or a range consisting of any two of the solvents; 0.2 parts, 0.5 parts, 0.8 parts, 1.1 parts, 1.4 parts, 1.7 parts, 2 parts or a range consisting of any two of the plasticizers; and 0.2 parts, 0.5 parts, 0.8 parts, 1.1 parts, 1.4 parts, 1.7 parts, 2 parts or a range consisting of any two of the thixotropic additives.

[0061] Example 1

[0062] Preparation method of copper powder:

[0063] Preparation of Copper Powder A: Dissolve copper sulfate pentahydrate in deionized water to a concentration of 1.6 mol / L. Then, add ammonia to complex the copper ions at a concentration of 16 mol / L. Dissolve ascorbic acid in deionized water to a concentration of 3.8 mol / L. Add the ascorbic acid solution dropwise to the copper complex solution, heat at 70°C for 1 hour, cool, and allow to stand to precipitate copper powder. Wash with deionized water and ethanol, shake, centrifuge, and dry to obtain Copper Powder A.

[0064] Preparation method of copper powder B: copper sulfate pentahydrate is dissolved in deionized water to a concentration of 3.5 mol / L, and polyvinyl pyrrolidone is added and stirred evenly to a concentration of 0.05 mol / L; sodium hydroxide is dissolved in deionized water to a concentration of 26 mol / L; sodium citrate is dissolved in deionized water to a concentration of 6 mol / L, sodium hydroxide is dropped into the sodium citrate solution, heated and stirred at 60-80°C for 5 minutes, and the copper salt solution is added dropwise to the above mixed solution to react for 1 hour. The solution is cooled and allowed to stand to obtain a copper powder precipitate, which is washed with deionized water and ethanol, centrifuged, and then dried for later use.

[0065] Pretreatment method: add 20 g of dried copper powder to 100 ml of n-hexane, add 0.4 g of octadecenoic acid, stir at room temperature for 1 hour, let stand for 0.5 hour, shake and wash with ethyl acetate, centrifuge, and dry to obtain copper powder B.

[0066] Preparation method of copper powder C: copper sulfate pentahydrate is dissolved in deionized water to a concentration of 2 mol / L; sodium hydroxide is dissolved in deionized water to a concentration of 15 mol / L; the sodium hydroxide solution is dropped into the copper salt solution and stirred to react evenly, followed by a two-step reduction method: first, a weak reducing agent, glucose, is added to react at room temperature for 0.5 h to generate cuprous oxide, and the concentration of the glucose solution is 4 mol / L; then, a strong reducing agent, ascorbic acid, is added to reduce the cuprous oxide to copper, and the reaction is heated at 65°C for 1 h, and the concentration of the ascorbic acid solution is 4 mol / L.

[0067] Pretreatment method: ethanol was added to 20 g of dried copper powder, and 0.2 g of surfactant polyoxyethylene lauryl ether was added while stirring, followed by ultrasonic treatment for 10 min. The ethanol was removed by stirring and heating at 70°C in a nitrogen atmosphere to obtain copper powder with a surface-coated surfactant, thereby obtaining copper powder C.

[0068] Preparation of copper paste:

[0069] Copper powder ratio is based on copper powder A (D 90 :6μm):Copper powder B(D 90 :600nm):Copper powder C(D 90 :150nm) in a mass ratio of 1:1:0.5, and then an organic vehicle was added. The mixture was first mixed three times using a high-speed disperser and then ground using a three-roll mill for screen printing.

[0070] The masses of the components in the copper paste are: 88 g of copper powder, 2 g of acrylic resin, 6 g of isophorone, 3 g of ethyl cellulose, 0.5 g of tributyl phosphate, and 0.5 g of thixotropic agent.

[0071] Example 2

[0072] The difference from Example 1 is that the copper slurry contains 50 g of copper powder.

[0073] Example 3

[0074] The difference from Example 1 is that the copper slurry contains 135 g of copper powder.

[0075] Example 4

[0076] The difference from Example 1 is that the copper paste contains 1 g of acrylic resin.

[0077] Example 5

[0078] The difference from Example 1 is that the copper paste contains 5 g of acrylic resin.

[0079] Example 6

[0080] The difference from Example 1 is that the copper slurry contains 5 g of isophorone.

[0081] Example 7

[0082] The difference from Example 1 is that 10 g of isophorone is contained in the copper slurry.

[0083] Example 8

[0084] The difference from Example 1 is that the copper slurry contains 1 g of ethyl cellulose.

[0085] Example 9

[0086] The difference from Example 1 is that the copper slurry contains 5 g of ethyl cellulose.

[0087] Example 10

[0088] The difference from Example 1 is that the copper slurry contains 0.2 g of tributyl phosphate.

[0089] Example 11

[0090] The difference from Example 1 is that the copper slurry contains 2 g of tributyl phosphate.

[0091] Example 12

[0092] The difference from Example 1 is that the copper paste contains 0.2 g of thixotropic agent.

[0093] Example 13

[0094] The difference from Example 1 is that the copper paste contains 2 g of thixotropic agent.

[0095] Example 14

[0096] The difference from Example 1 is that the mass ratio of copper powder A:copper powder B:copper powder C is 10:1:0.5.

[0097] Example 15

[0098] The difference from Example 1 is that the mass ratio of copper powder A:copper powder B:copper powder C is 10:10:0.5.

[0099] Example 16

[0100] The difference from Example 1 is that the mass ratio of copper powder A:copper powder B:copper powder C is 10:1:5.

[0101] Example 17

[0102] The difference from Example 1 is that the mass ratio of copper powder A:copper powder B:copper powder C is 5:5:3.

[0103] Example 18

[0104] The difference from Example 1 is that "polyvinyl pyrrolidone" is replaced by "polyacrylic acid".

[0105] Example 19

[0106] The difference from Example 1 is that "octadecenoic acid" is replaced by "decanoic acid".

[0107] Example 20

[0108] The difference from Example 1 is that "glucose" is replaced by "citric acid".

[0109] Example 21

[0110] The difference from Example 1 is that "ascorbic acid" is replaced by "hypophosphorous acid".

[0111] Comparative Example 1

[0112] The difference from Example 1 is that copper powder A is not added.

[0113] Comparative Example 2

[0114] The difference from Example 1 is that copper powder B is not added.

[0115] Comparative Example 3

[0116] The difference from Example 1 is that copper powder C is not added.

[0117] Comparative Example 4

[0118] The difference from Example 1 is that the preparation method of copper powder B does not include a pretreatment step.

[0119] Comparative Example 5

[0120] The difference from Example 1 is that the preparation method of copper powder C does not include a pretreatment step.

[0121] Comparative Example 6

[0122] The difference from Example 1 is that no plasticizer is added.

[0123] Comparative Example 7

[0124] The difference from Example 1 is that no thixotropic agent is added.

[0125]

Performance test

[0126] (1) Particle size observation: Use scanning electron microscopy to characterize the size and morphology of copper nanoparticles: ① Take a small amount of slurry and dilute it in deionized water or organic solvent at a ratio of 1:500; ② Ultrasonicate the dilution to fully disperse it, pipette a small amount and add it to the surface of the silicon wafer and heat it to remove excess solvent; ③ Prepare the sample and spray it with gold to obtain the image information of the size and morphology of the copper nanoparticles.

[0127] (2) Aspect ratio test: Use an ultra-depth-of-field microscope to observe and measure the line width of the printed circuit; use a step meter to measure the line height at the corresponding position.

[0128] (3) Resistivity test: Use the Ruike Weiye FT-340 four-probe square resistance tester to test the resistivity of the slurry: ① The prepared conductive slurry is coated on the glass original plate through a coating machine, and sintered at 200℃ for 1h under a nitrogen atmosphere to obtain a conductive copper film; ② The thickness of the metal film sample after high-temperature sintering is measured with the help of a step meter; ③ Set the corresponding parameters in the square resistance meter, adjust the four probes above the sample to be tested, and press down vertically to touch; ④ Record the resistivity data after the reading stabilizes.

[0129] (4) Viscosity test: Use Brookfield's DVNextCP cone-plate viscometer to measure the viscosity of the copper slurry: ① Adjust the torque to zero and adjust the cone-plate spacing to 0.0005 inches; ② Take a volume of 0.5 ml of conductive copper slurry and place it in the center of the sample cup, set the speed and test time, where the speed is 1 rpm; ③ Test to obtain material viscosity information and record it.

[0130]

Test results

[0131] The products obtained in the above examples and comparative examples were tested for relevant indicators to obtain the following table.

[0132] project Aspect ratio test Resistivity (mΩ·mm) Viscosity (Pa·s) Example 1 0.55 0.134 251.6 Example 2 0.45 0.167 204.2 Example 3 0.64 0.109 297.8 Example 4 0.52 0.130 247.4 Example 5 0.59 0.158 240.1 Example 6 0.57 0.123 253.2 Example 7 0.49 0.162 204.7 Example 8 0.51 0.127 276.9 Example 9 0.58 0.150 258.1 Example 10 0.53 0.125 250.3 Example 11 0.60 0.148 249.6 Example 12 0.48 0.122 246.4 Example 13 0.66 0.146 268.7 Example 14 0.43 0.171 207.3 Example 15 0.41 0.166 229.6 Example 16 0.50 0.124 231.9 Example 17 0.56 0.105 254.2 Example 18 0.52 0.095 250.9 Example 19 0.49 0.145 247.8 Example 20 0.52 0.119 233.9 Example 21 0.56 0.172 260.4 Comparative Example 1 0.36 0.324 280.7 Comparative Example 2 0.32 0.364 219.4 Comparative Example 3 0.24 0.817 176.2 Comparative Example 4 0.28 1.215 345.8 Comparative Example 5 0.35 0.769 231.3 Comparative Example 6 0.32 0.486 203.1 Comparative Example 7 0.25 0.427 176.7

[0133] from Figure 1 It can be seen from the figure that the lines after screen printing in Example 1 are full and uniform, without line collapse; the state of the slurry can also correspond to this. When the slurry is lifted by the scraper, it presents a large sharp angle and no tailing and drawing phenomenon. From the test result table, it can be seen that the present invention provides a mixture of large and small particles with three different proportions, different sizes, and different processing methods, and uses a suitable organic carrier to prepare a conformal copper paste with an aspect ratio of 0.4 to 0.7, a resistivity of 0.086 to 0.172 mΩ·mm, and a viscosity of 200 to 300 Pa·s; Figure 2 It can be seen that the circuit collapse phenomenon and solvent overflow occurred in the slurry of Comparative Example 7 after screen printing, indicating that no thixotropic agent was added, the cross-linking between the components in the organic phase was weak, and no supporting network could be formed with the copper powder; from the state of the slurry, when the slurry was lifted by the scraper, it showed a wire drawing and tailing phenomenon, and had no conformality, so the aspect ratio of the screen-printed circuit was only 0.25.

Claims

1. A copper paste for screen printing, characterized in that: By mass, it comprises 80 to 92 parts of copper powder and 8 to 20 parts of organic carrier, wherein the copper powder comprises D 90 =5~10 μm copper powder A, D 90 = 500~900 nm copper powder B and D 90 =50~200 nm copper powder C; the copper powder B has a ligand on its surface, and the copper powder C has a surfactant on its surface.

2. The copper paste for screen printing according to claim 1, characterized in that The organic carrier comprises 1 to 5 parts of resin, 1 to 5 parts of binder, 5 to 10 parts of solvent, 0.2 to 2 parts of plasticizer and 0.2 to 2 parts of thixotropic additive.

3. The copper paste for screen printing according to claim 1, characterized in that The mass ratio of the copper powder A, copper powder B and copper powder C is (1-10): (1-10): (0.5-5).

4. The copper paste for screen printing according to claim 1, characterized in that The ligand is selected from at least one of nonanoic acid, decanoic acid, undecyl acid, undecenoic acid, dodecyl acid, dodecenoic acid, tetradecyl acid, tetradecenoic acid, hexadecyl acid, hexadecenoic acid, octadecenoic acid, octadecyl acid, octylamine, nonylamine, aniline, benzylamine, p-methylaniline, monotoluidine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine or octadecylamine; and / or, The surfactant is selected from at least one of polyoxyethylene stearate-30, polyoxyethylene stearate-40, triethanolamine oleate, sorbitan laurate, polyoxyethylene lauryl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monopalmitate or polyoxyethylene sorbitan stearate.

5. The copper paste for screen printing according to claim 2, characterized in that The resin is selected from at least one of acrylic resin, polyurethane, polyvinyl butyral or polyvinyl acetal; and / or, The binder is selected from at least one of ethyl cellulose, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose or hydroxypropyl methyl cellulose; and / or, The solvent is at least one selected from terpineol, isopropyl alcohol, isophorone, cyclohexanone, n-butyl acetate, diethylene glycol butyl ether acetate, ethylene glycol monomethyl ether acetate, and dipropylene glycol methyl ether acetate; and / or, The plasticizer is selected from at least one of tributyl phosphate, triphenyl phosphate, dimethyl phthalate, dibutyl phthalate or dioctyl phthalate; and / or, The thixotropic agent is selected from at least one of hydrogenated castor oil, polyamide-modified hydrogenated castor oil, polyamide wax slurry, fumed silica or organic bentonite.

6. The copper paste for screen printing according to claim 1, characterized in that The preparation method of the copper powder A comprises the following steps: adding ammonia water to a solution containing copper salt to complex the ammonia water with copper ions, and then adding a reducing agent to react to obtain copper powder A.

7. The copper paste for screen printing according to claim 1, characterized in that The preparation method of the copper powder B comprises the following steps: adding a growth regulator to a solution containing a copper salt to obtain a mixed solution; adding a sodium hydroxide solution to a solution containing a reducing agent, heating and stirring, adding the mixed solution to continue the reaction, and reacting the reaction product with a ligand to obtain copper powder B.

8. The copper paste for screen printing according to claim 7, characterized in that The growth regulator is selected from at least one of polyacrylic acid, polyvinyl pyrrolidone, carboxymethyl cellulose, polyvinyl alcohol, polyethylene glycol, styrene-maleic acid copolymer, oxalic acid, formic acid or gluconic acid; and / or, The ligand is selected from at least one of nonanoic acid, decanoic acid, undecyl acid, undecenoic acid, dodecyl acid, dodecenoic acid, tetradecyl acid, tetradecenoic acid, hexadecyl acid, hexadecenoic acid, octadecenoic acid, octadecyl acid, octylamine, nonylamine, aniline, benzylamine, p-methylaniline, monotoluidine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine or octadecylamine; In the process of preparing the copper powder B, the product obtained by the reaction is pre-dissolved in a weak polar solvent before reacting with the ligand, and the weak polar solvent is selected from at least one of n-hexane, dichloromethane, chloroform, acetone, cyclohexane or N,N-dimethylformamide.

9. The copper paste for screen printing according to claim 1, characterized in that The preparation method of the copper powder C comprises the following steps: adding a sodium hydroxide solution to a solution containing a copper salt, reacting the solution with a reducing agent, and reacting the reaction product with a surfactant to obtain the copper powder C; The reducing agent used in the process of preparing the copper powder C includes a weak reducing agent and a strong reducing agent; the weak reducing agent is selected from at least one of glucose, sodium hypophosphite, citric acid, sodium citrate, or; and / or, the strong reducing agent is selected from at least one of ascorbic acid, sodium borohydride, hydrazine hydrate, or hypophosphorous acid.

10. The copper paste for screen printing according to claim 6, 7 or 9, characterized in that: The copper salt is selected from at least one of copper sulfate pentahydrate, copper hydroxide, copper nitrate, copper formate, copper acetate monohydrate or copper chloride.

11. The copper paste for screen printing according to claim 1, characterized in that The aspect ratio of the screen-printed circuit of the copper paste is 0.4-0.7, the resistivity is 0.086-0.172 mΩ·mm, and the viscosity is 200-300 Pa·s.

12. A method for preparing the copper paste for screen printing according to any one of claims 1 to 11, characterized in that: The steps include: Mix copper powder A, copper powder B and copper powder C in proportion; The resin, binder, solvent, plasticizer and thixotropic agent are mixed in proportion to obtain an organic carrier; The mixed copper powder and the organic carrier are mixed and ground according to a certain proportion to obtain the copper paste for screen printing.

Images