Copper paste for screen printing and preparation method thereof

Abstract

The invention discloses copper paste for screen printing and a preparation method thereof, and belongs to the technical field of metal paste. The copper paste is composed of 80-93 parts by weight of copper powder and an organic carrier, and the organic carrier comprises 0.4-2 parts by weight of polyurethane resin, 0.5-5 parts by weight of epoxy resin, 0.1-2 parts by weight of a curing agent, 4-15 parts by weight of a diluent, 0.1-2 parts by weight of a thixotropic agent and 0.01-0.5 part by weight of a silane coupling agent. The preparation method comprises the following steps: modifying the surface of the copper powder by using a modifier; blending the polyurethane resin with a part of the diluent to obtain a first component; blending the epoxy resin, the curing agent, the residual diluent, the thixotropic agent and the coupling agent to obtain a second component; blending the first component and the second component to obtain an organic carrier; mixing an organic carrier with the copper powder containing the modifier on the surface; the copper paste for screen printing is suitable for large-scale mass production, and has a wide application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal slurries, and in particular relates to a copper slurry for screen printing and a preparation method thereof. Background Art

[0002] Silk screen printing is a common printing technique in the electronics manufacturing industry, creating conductive circuits by printing a conductive paste onto a substrate. However, in recent years, the cost of silver raw materials has increased, and silver paste is prone to migration at high temperatures, affecting circuit reliability. Consequently, conductive silver paste is increasingly being considered as a replacement for copper paste, a material with similar conductivity, for applications in integrated circuits, wafer devices, light-emitting diodes, display screens, electromagnetic shielding, photovoltaics, and other fields.

[0003] The existing technology mostly adopts the silver-coated copper model to prepare conductive paste, and the copper is isolated from the air by forming a silver layer on the copper particles, thereby forming a protective layer. For example, patent CN115376719A discloses a low-temperature silver-coated copper paste for solar cells. The paste is modified by a silver precursor and a reducing component. New filled nano-silver particles can be continuously generated during the curing process, that is, the paste and the grid lines are formed to provide secondary patch-like protection for the silver-coated copper paste, thereby improving the conductivity. However, the above-mentioned technology of effectively coating the surface of copper powder with elemental silver is more difficult, and the preparation process is more complicated. Compared with pure copper materials, there is still a large gap in production cost, and the cost reduction goal cannot be effectively achieved. Nano copper paste technology has received widespread attention worldwide, but there is still a certain gap from the realization of large-scale industrialization, and continuous technical research and innovation are needed.

[0004] In order to improve the oxidation resistance of pure copper paste that does not contain silver, flake copper is usually used for preparation. For example, patent CN105405489A introduces a low-temperature curable solderable highly conductive paste and its preparation method. It has strong printing adaptability, a single component, can be quickly cured at low temperature, and is suitable for 100-200 mesh screen printing. However, due to the easy stacking between the flakes, according to production experience, this paste is prone to problems such as screen blocking and false printing when used in higher mesh printing scenarios.

[0005] At present, the low-temperature copper paste technology on the market is still in the rising stage. Due to the active chemical properties of the copper material itself, it is easy to oxidize into oxides when used in an air environment, resulting in a sharp drop in conductivity. Therefore, the control requirements for various details from copper powder preparation to post-processing, formulation, additives, sintering details, etc. are very strict. In addition, the copper paste that matches the existing silk screen printing process also needs to have certain comprehensive properties such as oxidation resistance, printability, adhesion and conductivity. The rheological properties of nano copper paste also restrict its application in silk screen printing (too high viscosity will affect the ink penetration efficiency, and too low viscosity will cause the paste to overflow and affect the silk screen accuracy). It is difficult to prepare copper paste technology that is suitable for the existing silk screen printing process. If the problems of copper oxidation, sintering diffusion and adhesion can be solved, pure copper paste may be an ideal solution for reducing the cost of metallization in the existing printing field.

[0006] Overall, the existing technology needs to be improved, and there is an urgent need to develop a copper paste material that is suitable for the existing silk screen printing process and has excellent conductive properties to provide support for reducing costs and increasing efficiency in industry production. Summary of the Invention

[0007] The main purpose of the present invention is to provide a copper paste for screen printing and a preparation method thereof, so as to solve the problems in the prior art that copper paste materials are difficult to be applied to screen printing and have poor conductivity.

[0008] In a first aspect, the present invention provides a copper paste for silk screen printing, which is composed of copper powder and an organic carrier, wherein the copper powder is 80 to 93 parts by weight; the organic carrier includes 0.4 to 2 parts of polyurethane resin, 0.5 to 5 parts of epoxy resin, 0.1 to 2 parts of curing agent, 4 to 15 parts of diluent, 0.1 to 2 parts of thixotropic agent and 0.01 to 0.5 parts of silane coupling agent.

[0009] Furthermore, the copper powder includes submicron copper powder and micron copper powder, the size of the submicron copper powder is 0.1~1μm, the size of the micron copper powder is 1~10μm, the morphology of the copper powder is spherical or quasi-spherical or a mixture of the two, and the mass ratio of the submicron copper powder to the micron copper powder is (1~2):(1~4).

[0010] Furthermore, the surface of the copper powder is modified by a modifier, and the modifier is selected from at least one of an organic acid having 3 to 18 carbon atoms, such as ascorbic acid, oxalic acid, lactic acid, malonic acid, fumaric acid, tartaric acid, ascorbic acid, citric acid, octanoic acid, dodecanoic acid, myristic acid, stearic acid, and oleic acid.

[0011] Furthermore, the molar ratio of the copper powder to the modifier is (5-10):1.

[0012] Furthermore, the polyurethane resin is selected from at least one of BASF Laromer LR9100, Desmopan 2100P, Jiurui DL2126, Jiurui GL2126, Estane 5719, and Irocoat 5836, and the epoxy equivalent of the epoxy resin is 150-200 g / eq and the viscosity is 8000-20000 mPa·s.

[0013] Furthermore, the curing agent is selected from at least one of aromatic amine curing agents, phenolic amine curing agents, alicyclic amine curing agents, low molecular weight polyamide curing agents, polyether amine curing agents, alcohol amine curing agents, and acid anhydride curing agents.

[0014] Furthermore, the diluent includes an active diluent and an inactive diluent, and the mass ratio of the active diluent to the inactive diluent is 1: (1 to 4); the active diluent is a multifunctional epoxy monomer, preferably, the active diluent is selected from at least one of trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, glycerol triglycidyl ether, sorbitol glycidyl ether, propoxyglycerol triglycidyl ether, and 1,4-butanediol diglycidyl ether; and / or, the inactive diluent is selected from mixed divalent acid esters, ethylene glycol diacetate, tributyl citrate, alcohol ester-12, cyclohexanone, isophorone, 4-ethylcyclohexanone, oxidized isophorone, 4-methylcyclohexanone, 2,6,6-trimethyl-2-cyclohexene-1,4-dione, ethylene glycol dimethyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, At least one of, wherein X and Y are independently selected from C1-C4 alkyl.

[0015] Furthermore, the thixotropic agent is selected from at least one of polyamide wax, hydrogenated castor oil, bentonite, and fumed silica.

[0016] Furthermore, the silane coupling agent is selected from at least one of KH550, KH551, KH560, KH570 or KH580.

[0017] In a second aspect, the present invention provides a method for preparing a screen printing copper paste, the method comprising the following steps:

[0018] Modifying the surface of the copper powder using a modifier;

[0019] blending the polyurethane resin with a portion of the diluent to obtain a first component;

[0020] blending the epoxy resin, curing agent, remaining diluent, thixotropic agent and coupling agent to obtain a second component;

[0021] blending the first component and the second component to obtain an organic vehicle;

[0022] The organic carrier is mixed with copper powder containing a surface modifier.

[0023] Furthermore, the organic carrier is mixed with copper powder containing a surface modifier, and the copper slurry is ground and dispersed to a fineness of ≤10 μm; the portion of the diluent blended with the polyurethane resin accounts for 20-50% of the total mass of the diluent.

[0024] Specifically, the preparation method comprises the following steps:

[0025] (1) Surface modification of copper powder:

[0026] S11. Dissolve and disperse the modifier in a solvent to prepare solution A; wherein the concentration of the modifier in the solvent is 0.05 to 0.5 mol / L;

[0027] S12. Weigh the copper powder and add it to solution A. Stir the reaction at 60 to 80 ° C for 10 to 30 minutes to obtain a pretreated copper powder dispersion B.

[0028] S13. Centrifugation, washing, and drying;

[0029] (2) Preparation of copper slurry:

[0030] S21. Blending a polyurethane resin and an inactive diluent in a mass ratio of 1:(0.1-5) to obtain a first component;

[0031] S22. The thermosetting resin, curing agent, reactive diluent, inactive diluent, thixotropic agent and coupling agent are blended to obtain a second component;

[0032] S23. The first component and the second component are blended to obtain an organic vehicle;

[0033] S24. Add the organic carrier to the surface-modified copper powder obtained after pretreatment, mix at 1000-2000 rpm for 5-20 minutes, and fully grind and disperse to a fineness of ≤10 μm to obtain a copper slurry.

[0034] Furthermore, the step S13 specifically includes: S131. treating the copper powder dispersion B using a low-speed centrifuge at 2000-4000 rpm for 5-10 minutes, pouring out the generated clear liquid after separation and adding a solvent for dispersion and cleaning; S132. repeating S131 once, pouring out the upper clear liquid, and placing the obtained centrifuged product under a vacuum environment to dry to obtain surface-modified copper powder.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The copper paste has good adhesion to the substrate, with an adhesion performance of up to 5B. After curing at 200°C, the volume resistivity is ≤17.2μm·cm. It has excellent electrical conductivity, excellent product circuit conductivity, and high energy utilization efficiency.

[0037] (2) The copper paste has good printing performance, which is manifested in high screen transmittance, smooth and unbroken lines, good formability, and can achieve a printing effect with an aspect ratio of ≥0.4 after curing;

[0038] (3) The copper slurry has good stability. After being stored in a sealed and frozen state for 6 months, the resistivity change is ≤10%, and the slurry is stable and does not separate into phases.

[0039] (4) The copper paste does not volatilize toxic or irritating substances during the preparation and curing process, is simple to operate, has a good working environment, and has low production costs, thus meeting green environmental protection and economic goals;

[0040] (5) The copper paste can be widely used in the fields of precision interconnection, photovoltaic grid lines, printed circuits, chip mounting, microwave communications, flexible circuits, etc., is suitable for large-scale mass production, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is the slurry morphology;

[0042] Figure 2 This is the morphology of micron copper powder particles;

[0043] Figure 3 This is the morphology of submicron copper powder particles;

[0044] Figure 4 This is the printed line graph of Example 1. DETAILED DESCRIPTION

[0045] 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.

[0046] At present, the cost of silver raw materials has increased, and silver paste is prone to migration at high temperatures, affecting the reliability of the circuit. Therefore, conductive silver paste is gradually being considered as a replacement for copper paste materials with similar conductive properties, and is used in integrated circuits, wafer devices, light-emitting diodes, display screens, electromagnetic shielding protection, photovoltaics and other fields. However, due to the active chemical properties of the copper material itself, it is easy to oxidize into oxides when used in an air environment, resulting in a sharp drop in conductivity. Therefore, the control requirements for various details from copper powder preparation to post-processing, formulation, additives, sintering details, etc. are very strict. In addition, the copper paste that matches the existing silk screen printing process also needs to have certain comprehensive properties such as oxidation resistance, printability, adhesion and conductivity. The rheological properties of nano copper paste also restrict its application in the silk screen printing process (too high viscosity will affect the ink penetration efficiency, and too low viscosity will cause the paste to overflow and affect the silk screen accuracy). The preparation of copper paste that is suitable for the existing silk screen printing process is technically difficult.

[0047] In a first aspect, the present invention provides a copper paste for silk screen printing, which is composed of copper powder and an organic carrier, wherein, by weight, the copper powder is 80 to 93 parts, and the organic carrier includes 0.4 to 2 parts of polyurethane resin, 0.5 to 5 parts of epoxy resin, 0.1 to 2 parts of curing agent, 4 to 15 parts of diluent, 0.1 to 2 parts of thixotropic agent and 0.01 to 0.5 parts of silane coupling agent.

[0048] Typically but not limitatively, the screen printing copper paste comprises, by weight, 80 parts, 83 parts, 86 parts, 89 parts, 93 parts or a range consisting of any two of their copper powders, 0.4 parts, 0.5 parts, 1.0 parts, 1.5 parts, 2.0 parts or a range consisting of any two of their polyurethane resins, 0.5 parts, 1.0 parts, 1.5 parts, 2.0 parts, 2.5 parts, 3.0 parts, 3.5 parts, 4.0 parts, 4.5 parts, 5.0 parts or a range consisting of any two of their epoxy resins, 0.1 parts, 0.4 parts, 0.5 parts, 1.0 parts, 1.5 parts, 2.0 parts, 2.5 parts, 3.0 parts, 3.5 parts, 4.0 parts, 4.5 parts, 5.0 parts or a range consisting of any two of their epoxy resins, 7 parts, 1.0 parts, 1.3 parts, 1.6 parts, 2.0 parts or a range consisting of any two of the above mentioned curing agents; 4 parts, 5 parts, 7 parts, 9 parts, 11 parts, 13 parts, 15 parts or a range consisting of any two of the above mentioned diluents; 0.1 parts, 0.4 parts, 0.7 parts, 1.0 parts, 1.3 parts, 1.6 parts, 2.0 parts or a range consisting of any two of the above mentioned thixotropic agents; 0.01 parts, 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts or a range consisting of any two of the above mentioned silane coupling agents.

[0049] In some specific embodiments, the copper powder includes submicron copper powder and micron copper powder, the size of the submicron copper powder is 0.1-1 μm, the size of the micron copper powder is 1-10 μm, the morphology of the copper powder is spherical or quasi-spherical or a mixture of the two, and the mass ratio of the submicron copper powder to the micron copper powder is (1-2): (1-4). The copper paste prepared by the present invention is composed of two sizes of particles. The small-particle copper powder has the advantages of large specific surface area, strong surface activity, low sintering temperature, good electrical conductivity and thermal conductivity, but it is easy to agglomerate and oxidize, and the volume shrinkage during the solidification process is large, which is easy to crack; large particles are not easy to oxidize relative to small particles and are not easy to agglomerate between particles, but the gaps are large, and the sintering conductivity is poor. Therefore, a reasonable combination of large and small particles can enable small particles to effectively fill the gaps between large particles. The advantages are: ① forming multi-site sintering necks, so that a three-dimensional network conductive structure is formed between copper particles, and good low-temperature sintering conductivity is obtained; ② obtaining good shape retention, and the material is not easy to collapse; ③ storage stability and not easy to oxidize.

[0050] In some specific embodiments, the surface of the copper powder is modified by a modifier, and the modifier is selected from at least one of an organic acid having 3 to 18 carbon atoms, such as ascorbic acid, oxalic acid, lactic acid, malonic acid, fumaric acid, tartaric acid, ascorbic acid, citric acid, octanoic acid, dodecanoic acid, myristic acid, stearic acid, and oleic acid.

[0051] In some specific embodiments, the molar ratio of the copper powder to the modifier is (5-10): 1. The mechanism of action of the modifier in modifying the copper powder is as follows: ① The modifier can combine with the surface of the copper particles to form a coordination bond, uniformly coating the surface of the copper particles, forming a surface barrier that isolates water and oxygen in the air; ② The modifier can activate the surface activity of the copper particles, improve low-temperature sintering, and promote melt bonding between the particles at a lower curing temperature to achieve good conduction effect; ③ The modifier can improve the compatibility of the copper particles with the organic carrier, reduce problems such as particle agglomeration and sedimentation, and achieve good uniformity.

[0052] In some specific embodiments, the polyurethane resin is selected from at least one of BASF Laromer LR9100, Desmopan 2100P, Jiurui DL2126, Jiurui GL2126, Estane 5719, and Irocoat 5836. The epoxy resin has an epoxy equivalent weight of 150 to 200 g / eq and a viscosity of 8,000 to 20,000 mPa·s, and can be specifically selected from bisphenol A epoxy resin. The copper paste resin prepared in the present invention is mainly composed of two specific resins: a polyurethane resin and a thermosetting epoxy resin. The use of a compounding scheme of the two specific resins can achieve the effect of combining the reinforcing effect of the thermosetting epoxy resin with the toughening effect of the polyurethane resin, resulting in excellent adhesion and flexibility after curing of the copper paste. The polyurethane resin contains a large number of polar groups such as carbamate groups and urea groups. The polar groups are easily adsorbed on the surface of the modified copper powder, which can fully wet the copper powder particles and uniformly disperse them in the organic carrier. Good wettability can also promote the uniform coating of the binder phase on the surface of the copper powder, effectively control the agglomeration of the copper powder, and form a good conductive path, ultimately achieving good electrical conductivity.

[0053] In some specific embodiments, the curing agent is selected from at least one of aromatic amine curing agents, phenolic amine curing agents, alicyclic amine curing agents, low molecular weight polyamide curing agents, polyether amine curing agents, alcohol amine curing agents, and acid anhydride curing agents.

[0054] In some specific embodiments, the diluent includes a reactive diluent and an inactive diluent, and the mass ratio of the reactive diluent and the inactive diluent is 1:(1-4). The diluent preferably is suitable for the modified copper powder selected in this scheme. ① It can improve the dispersion uniformity of the copper powder in the formula while adjusting the material viscosity and printability. ② During the curing process, part of the diluent evaporates, causing the material volume to shrink and forming a denser conductive path. ③ The selected epoxy monomer reactive diluent can cooperate with the curing agent to participate in the ring-opening reaction, thereby forming a pre-crosslinked structure with the resin system, achieving better toughness and uniformity.

[0055] In some specific embodiments, the reactive diluent is a multifunctional epoxy monomer, preferably, the reactive diluent is selected from at least one of trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, glycerol triglycidyl ether, sorbitol glycidyl ether, propoxyglycerol triglycidyl ether, and 1,4-butanediol diglycidyl ether; and / or, the inactive diluent is selected from mixed divalent acid esters, ethylene glycol diacetate, tributyl citrate, alcohol ester-12, cyclohexanone, isophorone, 4-ethylcyclohexanone, oxidized isophorone, 4-methylcyclohexanone, 2,6,6-trimethyl-2-cyclohexene-1,4-dione, ethylene glycol dimethyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, At least one of, wherein X and Y are independently selected from C1-C4 alkyl.

[0056] In some specific embodiments, the thixotropic agent is selected from at least one of polyamide wax, hydrogenated castor oil, bentonite, and fumed silica.

[0057] In some specific embodiments, the silane coupling agent is selected from at least one of KH550, KH551, KH560, KH570, or KH580.

[0058] In a second aspect, the present invention provides a method for preparing a screen printing copper paste, the method comprising the following steps:

[0059] Modifying the surface of the copper powder using a modifier;

[0060] blending the polyurethane resin with a portion of the diluent to obtain a first component;

[0061] blending the epoxy resin, curing agent, remaining diluent, thixotropic agent and coupling agent to obtain a second component;

[0062] blending the first component and the second component to obtain an organic vehicle;

[0063] The organic carrier is mixed with copper powder containing a surface modifier.

[0064] In some specific embodiments, the organic vehicle is mixed with copper powder containing a surface modifier, and then the copper slurry is ground and dispersed to a fineness of ≤10 μm.

[0065] Specifically, the preparation method comprises the following steps:

[0066] (1) Surface modification of copper powder:

[0067] S11. Dissolve and disperse the modifier in a solvent to prepare solution A; wherein the concentration of the modifier in the solvent is 0.05 to 0.5 mol / L;

[0068] S12. Weigh the copper powder and add it to solution A. Stir the reaction at 60 to 80 ° C for 10 to 30 minutes to obtain a pretreated copper powder dispersion B.

[0069] S13. Centrifugation, washing, and drying;

[0070] (2) Preparation of copper slurry:

[0071] S21. Blending a polyurethane resin and an inactive diluent in a mass ratio of 1:(0.1-5) to obtain a first component;

[0072] S22. The thermosetting resin, curing agent, reactive diluent, inactive diluent, thixotropic agent and coupling agent are blended to obtain a second component;

[0073] S23. The first component and the second component are blended to obtain an organic vehicle;

[0074] S24. Add the organic carrier to the surface-modified copper powder obtained after pretreatment, mix at 1000-2000 rpm for 5-20 minutes, and fully grind and disperse to a fineness of ≤10 μm to obtain a copper slurry.

[0075] In some specific embodiments, the step S13 specifically includes: S131. The copper powder dispersion B is treated using a low-speed centrifuge at 2000-4000 rpm for 5-10 minutes, and after separation, the generated clear liquid is poured out and a solvent is added for dispersion and cleaning; S132. S131 is repeated once, the upper clear liquid is poured out, and the obtained centrifuged product is placed in a vacuum environment and dried to obtain surface-modified copper powder.

[0076] Three-stage curing mechanism: ① When the copper paste is at a lower temperature at the initial stage of curing, the viscosity of the organic carrier decreases, the steric hindrance is small, the copper particles can obtain a certain fluidity, and the sequence is easily reorganized to form a spatial position relationship of stacking and overlapping. At the same time, the low-boiling point components in the system volatilize to promote the volume shrinkage of the paste, obtain a denser spatial structure, and improve the contact effectiveness of the copper particles; ② In the middle stage of curing, the diluent component further evaporates and shrinks in volume, the material density is further improved, and the epoxy resin is cross-linked and cured; ③ At the end of curing, the temperature drops, the epoxy resin system completes cross-linking and curing to form a dense resin cross-linking network, the polyurethane resin chain segments shrink, and the copper particles are more densely bonded to avoid internal voids. The internal shrinkage of the paste is strengthened to form a conductive path while obtaining good surface hardness and bonding properties.

[0077] Example 1

[0078] 1. Surface modification of copper powder:

[0079] (1) Dissolve 18 g of n-octanoic acid in anhydrous ethanol to prepare solution A.

[0080] (2) 64 g of micron copper powder was added to solution A and magnetically stirred at 60° C. for 15 min to obtain a pretreated copper powder dispersion B;

[0081] (3) The copper powder dispersion B was centrifuged at 4000 rpm for 5 min. After separation, the supernatant was removed and 500 g of ethanol was added for dispersion and cleaning.

[0082] (4) Repeat S3 once, remove the supernatant, and dry the centrifuged product under vacuum to obtain surface-modified micron copper powder. The micron copper powder particle morphology is shown in FIG. Figure 2 As shown;

[0083] (5) The surface modified submicron copper powder was prepared by the same steps 1-4 as above. The morphology of the submicron copper powder particles is shown in FIG. Figure 3 shown.

[0084] 2. Preparation of copper paste:

[0085] (1) 1 g of Laromer LR9100 was blended with 2.5 g of a mixed dibasic acid ester to obtain a first component;

[0086] (2) 3.5 g of bisphenol A epoxy resin, 1 g of 1,3-cyclohexanedimethylamine, 2.5 g of 1,4-butanediol diglycidyl ether, 4 g of ethylene glycol diacetate, 0.4 g of hydrogenated castor oil, and 0.1 g of KH550 were blended to obtain a second component;

[0087] (3) blending the first component and the second component to obtain an organic carrier;

[0088] (4) Weigh 64 g of surface-modified micron copper powder and 21 g of surface-modified submicron copper powder, add 15 g of the organic vehicle to the copper powder, use a Thinky planetary mixer at 1500 rpm to mix for 10 min, and grind and disperse the mixture on a three-roll mill to a fineness of ≤10 μm to obtain a copper slurry;

[0089] (5) The obtained copper slurry is sealed in a can and stored at -20°C.

[0090] The morphology of the copper slurry obtained in Example 1 is as follows: Figure 1 As shown, the printed line graph used for printing is as follows Figure 4 shown.

[0091] Example 2

[0092] The difference from Example 1 is that the total mass of the copper powder is 80 g (60 g of surface-modified micron copper powder and 20 g of surface-modified submicron copper powder), and the remaining steps are the same as in Example 1.

[0093] Example 3

[0094] The difference from Example 1 is that the amount of copper powder is 93 g (68 g of surface-modified micron copper powder and 25 g of surface-modified submicron copper powder), and the remaining steps are the same as in Example 1.

[0095] Example 4

[0096] The difference from Example 1 is that the amount of polyurethane resin is 0.5 g, and the remaining steps are the same as Example 1.

[0097] Example 5

[0098] The difference from Example 1 is that the amount of polyurethane resin is 1.25 g, and the remaining steps are the same as Example 1.

[0099] Example 6

[0100] The difference from Example 1 is that the amount of epoxy resin is 0.5 g, and the remaining steps are the same as in Example 1.

[0101] Example 7

[0102] The difference from Example 1 is that the epoxy resin is 5g, and the other steps are the same as Example 1.

[0103] Example 8

[0104] The difference from Example 1 is that the amount of curing agent is 0.1 g, and the remaining steps are the same as Example 1.

[0105] Example 9

[0106] The difference from Example 1 is that the amount of curing agent is 2 g, and the remaining steps are the same as Example 1.

[0107] Example 10

[0108] The difference from Example 1 is that the total amount of diluent is 5 g, and in the copper slurry preparation process, step (1) is: blending 1 g of Laromer LR9100 with 2 g of mixed dibasic acid ester to obtain a first component; step (2) is: blending 3.5 g of bisphenol A epoxy resin, 1 g of 1,3-cyclohexanedimethylamine, 2.5 g of 1,4-butanediol diglycidyl ether, 0.5 g of ethylene glycol diacetate, 0.4 g of hydrogenated castor oil and 0.1 g of KH550 to obtain a second component, and the remaining steps are the same as in Example 1.

[0109] Example 11

[0110] The difference from Example 1 is that: the total amount of diluent is 15 g; in the copper slurry preparation process, step (1) is: blending 1 g of Laromer LR9100 with 5 g of mixed dibasic acid ester to obtain a first component; step (2) is: blending 3.5 g of bisphenol A epoxy resin, 1 g of 1,3-cyclohexanedimethylamine, 4.5 g of 1,4-butanediol diglycidyl ether, 5.5 g of ethylene glycol diacetate, 0.4 g of hydrogenated castor oil and 0.1 g of KH550 to obtain a second component; the remaining steps are the same as in Example 1.

[0111] Example 12

[0112] The difference from Example 1 is that the amount of thixotropic agent is 0.1 g, and the remaining steps are the same as Example 1.

[0113] Example 13

[0114] The difference from Example 1 is that the amount of thixotropic agent is 2 g, and the remaining steps are the same as Example 1.

[0115] Example 14

[0116] The difference from Example 1 is that the amount of silane coupling agent is 0.01 g, and the remaining steps are the same as Example 1.

[0117] Example 15

[0118] The difference from Example 1 is that the amount of silane coupling agent is 0.5 g, and the remaining steps are the same as Example 1.

[0119] Comparative Example 1

[0120] The difference from Example 1 is that the surface of the copper particles is not modified and they are directly used for the preparation of the copper slurry. The remaining steps are the same as those in Example 1.

[0121] Comparative Example 2

[0122] The difference from Example 1 is that the polyurethane resin Laromer LR9100 is not added to the first component in step (1), that is, only 2.5 g of mixed dibasic acid ester is used as the first component, and the remaining steps are the same as in Example 1.

[0123] Comparative Example 3

[0124] The difference from Example 1 is that bisphenol A epoxy resin is not added to the second component, and the remaining steps are the same as Example 1.

[0125] Comparative Example 4

[0126] The difference from Example 1 is that the active diluent 1,4-butanediol diglycidyl ether is not added to the second component, and the remaining steps are the same as Example 1.

[0127] Comparative Example 5

[0128] The difference from Example 1 is that all inactive diluents are replaced by an equal amount of active diluent 1,4-butanediol diglycidyl ether, and the remaining steps are the same as Example 1.

[0129] Experimental characterization methods

[0130] 1. Volume resistivity test method: It is measured using a four-probe square resistivity tester. Specifically, the obtained copper paste is scraped onto a glass original plate to form a uniform film of about 20μm in thickness. After curing at 200℃, the film thickness is tested using a step profiler. The obtained film thickness value is input into the device to obtain the corresponding resistivity value ρ0.

[0131] 2. Adhesion test method: The 100-grid knife scratch test method (according to ASTM D3359-2017) is used. Specifically, the corresponding grid area is cut on the surface of the cured copper film with a 100-grid knife. The glass test is performed using 3M 600 special tape. The adhesion ability of the copper film and the silicon wafer is evaluated against the standard example.

[0132] 3. Stability evaluation method: Store the copper paste in a sealed container at -20°C, take it out after 30 days and 180 days, and evaluate the conductivity of the material cured at 200°C under the corresponding storage time, and record it as ρ 30 and ρ 180 , the resistivity change before and after 30 days of storage A=(ρ 30 -ρ0) / ρ0, the same applies to 180 days.

[0133] 4. Printability evaluation method: Use a silk screen to print the copper paste material on the solar panel at 300mm / s, observe the completion of the circuit, observe the circuit phenomenon after curing, and use a step meter and super-vision microscope equipment to test the line height and line width of the corresponding positions respectively, and calculate the line aspect ratio.

[0134] The test results are listed in Table 1 and Table 2.

[0135] Table 1 Basic performance test

[0136]

[0137]

[0138] Table 2 Printing performance test

[0139] Test number Printability Aspect ratio after curing Overall linear shape after curing Example 1 Smooth and uninterrupted 0.45 good Example 2 Smooth and uninterrupted 0.44 good Example 3 Smooth and uninterrupted 0.46 good Example 4 Smooth and uninterrupted 0.42 good Example 5 Smooth and uninterrupted 0.47 good Example 6 Smooth and uninterrupted 0.42 good Example 7 Smooth and uninterrupted 0.40 good Example 8 Smooth and uninterrupted 0.41 good Example 9 Smooth and uninterrupted 0.45 good Example 10 Smooth and uninterrupted 0.43 good Example 11 Smooth and uninterrupted 0.46 good Example 12 Smooth and uninterrupted 0.49 good Example 13 Smooth and uninterrupted 0.50 good Example 14 Smooth and uninterrupted 0.46 good Example 15 Smooth and uninterrupted 0.48 good Comparative Example 1 There is a disconnection / Many breakpoints Comparative Example 2 Smooth and uninterrupted 0.23 Line width is too large Comparative Example 3 Smooth and uninterrupted / Line width is too large Comparative Example 4 There is a disconnection / Many breakpoints Comparative Example 5 Smooth and uninterrupted / Poor uniformity

[0140] As can be seen from the above table, the present invention selects two specific resins to match active diluents and inactive diluents to cooperate with other components to form an organic carrier, and mixes the organic carrier with two copper powders modified by a modifier to prepare a copper paste. The prepared screen printing copper paste has good conductivity and adhesion after low-temperature curing (adhesion performance to the substrate can reach 5B, and volume resistivity ≤17.2μm·cm after curing at 200°C). It is stable and not easy to separate after being frozen and stored for 6 months. At the same time, it has good printing performance, manifested as high screen transmittance, smooth and unbroken lines, good formability, and can achieve a printing effect with an aspect ratio ≥0.4 after curing. It can be applied to fields such as electronic printing.

[0141] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations shall all fall within the scope defined by the present invention.

Claims

1. A copper paste for screen printing, characterized in that: The invention is composed of copper powder and an organic carrier. The copper powder accounts for 80 to 93 parts by weight, and the organic carrier comprises 0.4 to 2 parts of polyurethane resin, 0.5 to 5 parts of epoxy resin, 0.1 to 2 parts of curing agent, 4 to 15 parts of diluent, 0.1 to 2 parts of thixotropic agent and 0.01 to 0.5 parts of silane coupling agent.

2. The copper paste for screen printing according to claim 1, characterized in that The copper powder includes submicron copper powder and micron copper powder. The size of the submicron copper powder is 0.1-1 μm, the size of the micron copper powder is 1-10 μm, and the shape of the copper powder is spherical or quasi-spherical or a mixture of the two.

3. The copper paste for screen printing according to claim 1 or 2, characterized in that The surface of the copper powder is modified by a modifier, and the modifier is selected from organic acids with 3 to 18 carbon atoms.

4. The copper paste for screen printing according to claim 3, characterized in that The mass ratio of the surface-modified submicron copper powder to the surface-modified micron copper powder is (1-2): (1-4).

5. The copper paste for screen printing according to claim 3, characterized in that The molar ratio of the copper powder to the modifier is (5-10):

1.

6. The copper paste for screen printing according to claim 1, characterized in that The polyurethane resin is selected from at least one of BASF Laromer LR9100, Desmopan 2100P, Jiurui DL2126, Jiurui GL2126, Estane 5719, and Irocoat5836. The epoxy resin has an epoxy equivalent of 150 to 200 g / eq and a viscosity of 8000 to 20000 mPa·s.

7. The copper paste for screen printing according to claim 1, characterized in that The curing agent is selected from at least one of aromatic amine curing agents, phenolic amine curing agents, alicyclic amine curing agents, low molecular weight polyamide curing agents, polyether amine curing agents, alcohol amine curing agents, and acid anhydride curing agents.

8. The copper paste for screen printing according to claim 1, characterized in that The diluent includes an active diluent and an inactive diluent, the mass ratio of the active diluent to the inactive diluent is 1: (1-4), the active diluent is selected from at least one of trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, glycerol triglycidyl ether, sorbitol glycidyl ether, propoxyglycerol triglycidyl ether, and 1,4-butanediol diglycidyl ether; and / or, the inactive diluent is selected from mixed divalent acid esters, ethylene glycol diacetate, tributyl citrate, alcohol ester-12, cyclohexanone, isophorone, 4-ethylcyclohexanone, oxidized isophorone, 4-methylcyclohexanone, 2,6,6-trimethyl-2-cyclohexene-1,4-dione, ethylene glycol dimethyl ether, propylene glycol methyl ether, propylene glycol ethyl ether, At least one of, wherein X and Y are independently selected from C1-C4 alkyl.

9. The copper paste for screen printing according to claim 1, characterized in that The thixotropic agent is selected from at least one of polyamide wax, hydrogenated castor oil, bentonite, and fumed silica.

10. The copper paste for screen printing according to claim 1, characterized in that The silane coupling agent is selected from at least one of KH550, KH551, KH560, KH570, and KH580.

11. A method for preparing the copper paste for screen printing according to any one of claims 1 to 10, characterized in that: The steps include: Modifying the surface of the copper powder using a modifier; blending the polyurethane resin with a portion of the diluent to obtain a first component; blending the epoxy resin, curing agent, remaining diluent, thixotropic agent and coupling agent to obtain a second component; blending the first component and the second component to obtain an organic vehicle; The organic carrier is mixed with copper powder containing a surface modifier.

12. The method for preparing the copper paste for screen printing according to claim 11, characterized in that: After mixing, the copper slurry is ground and dispersed to a fineness of ≤10μm.

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