A UV-cured conductive silver paste and a preparation method thereof

Abstract

The present application relates to the technical field of new material preparation, in particular to a kind of UV curing conductive silver paste and preparation method thereof.A kind of UV curing conductive silver paste preparation method, it includes the following steps: step 1: under heating condition, photoinitiator is dissolved in active diluent, after cooling, photoinitiating curing liquid is obtained;Step 2: prepolymer, conductive additive and conductive powder are added to the photoinitiating curing liquid of step 1, grinding, to obtain conductive glue;Wherein, the conductive additive includes at least one of tetra-neooxy double (didecyl phosphoric acid acyloxy) titanate, isopropoxy di-oil acid acyloxy (dioctyl phosphoric acid acyloxy) titanate, isopropoxy tri-oil acid acyloxy titanate.The present application innovatively introduces the titanate coupling agent with special structure as conductive additive, which can effectively reduce the amount of silver powder and improve the conductivity of silver paste, while enhancing the flexibility of silver paste after curing and improving the bending resistance.

Description

Technical Field

[0001] This invention relates to the field of conductive silver paste preparation technology, specifically to a UV-curable conductive silver paste and its preparation method. Background Technology

[0002] Conductive silver paste is an important component in electronic products, widely used in printed circuits, semiconductor packaging, and solar cells. Existing conductive silver pastes are mostly epoxy resin-based, which suffers from problems such as high curing temperature, long curing time, and solvent evaporation. In recent years, UV-curable conductive silver paste has emerged, offering advantages such as high curing efficiency, no solvent emissions, and energy saving and environmental friendliness, and is gradually becoming a new trend in conductive silver paste development. Currently, to achieve high conductivity, UV-curable conductive silver paste often requires a silver powder filling content of over 80%. This high silver powder filling content increases cost and negatively impacts the adhesion and flexural strength of the cured silver paste. Summary of the Invention

[0003] The purpose of this invention is to provide a UV-curable conductive silver paste. Based on extensive creative work, this invention selects a titanate coupling agent with a special structure as a conductive additive, which can effectively reduce the amount of silver powder used and improve the conductivity of the silver paste. At the same time, it can enhance the flexibility of the silver paste after curing and improve its bending resistance.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for preparing a UV-curable conductive silver paste, comprising the following steps:

[0006] Step 1: Under heating conditions, the photoinitiator is dissolved in an active diluent, and after cooling, a photoinitiated curing solution is obtained;

[0007] Step 2: Add the prepolymer, conductive additives, and conductive powder to the photoinitiating curing solution from Step 1, and grind to obtain the conductive adhesive;

[0008] The conductive additive includes at least one of tetraneoalkoxybis(decylphosphite)titanate (CAS64157-14-8), isopropoxydioleoyloxy(dioctylphosphite)titanate (CAS 61417-49-0), and isopropoxytrioleoyloxytitanate (CAS 136144-62-2).

[0009] In a preferred embodiment of the preparation method of the UV-curable conductive silver paste provided by the present invention, in step 2, the weight ratio of the prepolymer: conductive additive: silver powder: photoinitiator curing liquid is (15-25):(0.5-1):(60-75):(6-12).

[0010] In a preferred embodiment of the preparation method of the UV-curable conductive silver paste provided by the present invention, the weight ratio of photoinitiator to reactive diluent in step 1 is (0.6-1.2):(30-60).

[0011] In a preferred embodiment of the preparation method of the UV-curable conductive silver paste provided by the present invention, the conductive powder is silver powder.

[0012] In a preferred embodiment of the preparation method of the UV-curable conductive silver paste provided by the present invention, the silver powder includes at least one of 0.2-10μm flake silver powder, 0.1-2μm spherical silver powder, 0.5-3μm spherical silver-coated copper powder, and 1-10μm flake silver-coated copper powder.

[0013] In a preferred embodiment of the preparation method of the UV-curable conductive silver paste provided by the present invention, the prepolymer includes at least one of polyester acrylate, polyurethane acrylate, and epoxy acrylate.

[0014] In a preferred embodiment of the preparation method of the UV-curable conductive silver paste provided by the present invention, in step 1, the photoinitiator includes at least one of 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, isopropylthioxanthone, and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide; the reactive diluent includes one or more of acrylic acid, isobornyl acrylate, N-vinylpyrrolidone, diethylene glycol diacrylate, 1,4-hexanediol diacrylate, neopentyl glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and ditrimethylolpropane tetraacrylate.

[0015] As a preferred embodiment of the preparation method of the UV-curable conductive silver paste provided by the present invention, the preparation method further includes step 3: printing the conductive adhesive from step 2 onto the substrate, curing it first with UV light under a nitrogen atmosphere, and then baking it to obtain the UV-curable conductive silver paste.

[0016] In a preferred embodiment of the UV-curable conductive silver paste preparation method provided by the present invention, in step 3, the UV light irradiation energy is 1000-3000 mW / cm². 2 The baking conditions are 100℃ for 10 minutes.

[0017] A UV-curable conductive silver paste, which is prepared by any of the above-described methods for preparing UV-curable conductive silver paste.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] (1) This invention innovatively introduces a special structured titanate coupling agent as a conductive additive. The polar groups of the special structured titanate coupling agent have a good wetting effect on inorganic fillers, which can improve the dispersion of fillers. Moreover, its structure has high functionality and can react with hydroxyl, carboxyl, and amine groups in the prepolymer resin at 100°C, causing the resin volume to shrink continuously. This reduces the distance between conductive powder particles, forming a better conductive path. In addition, the long-chain alkane structure can intertwine with the molecular chains of the resin and also undergo a certain degree of volume shrinkage after baking, enhancing the conductivity. This makes the conductive powder per unit mass more tightly contacted, effectively reducing the amount of conductive powder used and lowering costs. At the same time, the long carbon chain structure has good flexibility, which can increase the distance between rigid groups in the resin molecules and weaken the interaction between molecular chains to a certain extent. Under load or impact, the molecular chains have greater freedom, which has a toughening effect, that is, it can enhance the flexibility of the silver paste after curing and improve the bending resistance.

[0020] (2) This invention uses UV curing to prepare conductive silver paste, with no solvent emissions throughout the process, resulting in high efficiency and energy saving, in line with the development concept of green chemistry. The prepared conductive silver paste not only has excellent conductivity but can also be stored for a long time and remain stable. Attached Figure Description

[0021] Figure 1 This is a SEM image of the UV-cured conductive silver paste obtained in Example 3 of the present invention after bending.

[0022] Figure 2 SEM image of UV-cured conductive silver paste prepared in Comparative Example 2 after bending.

[0023] As can be seen from the two SEM images above, Example 3 formed many micro-silver ripple structures at the bending point, which can effectively disperse stress and thus still have good conductivity after bending; while Comparative Example 2 broke directly after bending and could no longer form a conductive path. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The specific embodiments described below further illustrate the present invention.

[0025] Example 1

[0026] This embodiment illustrates a method for preparing UV-curable conductive silver paste, specifically including the following steps:

[0027] Step 1: Weigh 0.5 parts of 1-hydroxycyclohexylphenyl ketone, 0.25 parts of isopropylthioxanthone, 1 part of acrylic acid, and 4 parts of 1,4-hexanediol diacrylate and add them to the reaction vessel. Heat to 50°C and stir at high speed to fully dissolve the initiator. Then cool to room temperature to obtain the photoinitiated curing solution.

[0028] Step 2: Weigh 8 parts of polyester acrylate, 10 parts of polyurethane acrylate, 0.25 parts of tetraneoalkoxybis(dicylphosphite)titanate and 76 parts of 500nm spherical silver powder and add them to the initiator curing solution in Step 1. Grind the mixture with a three-roll mill until it becomes a conductive adhesive with a fineness of less than 5μm.

[0029] Step 3: Print the conductive adhesive onto the PET film using a 300-mesh screen, then apply 1500mW / cm² of adhesive. 2 The silver paste is cured by UV light, and then baked in a 100℃ oven for 10 minutes to obtain a UV-cured conductive silver paste with high conductivity.

[0030] Performance Testing: The conductivity of the conductive silver paste was measured to be 214 S / mm using a four-probe impedance tester, and the adhesion of the conductive silver paste was 5B in the cross-cut adhesion test. The bending resistance test method was as follows: First, the conductivity of the cured conductive silver paste line was measured using a four-probe tester; then, the cured conductive silver paste line was folded in half along a straight line; a 2kg weight was then applied to the fold line and held for 1 minute; the cured conductive silver paste line was then folded in the opposite direction and pressure was applied for the same duration, repeating the above steps 10 times; finally, the conductivity of the bent and cured conductive silver paste line was measured. The conductivity after 10 bends was 170 S / mm.

[0031] Example 2

[0032] This embodiment illustrates a method for preparing UV-curable conductive silver paste, specifically including the following steps:

[0033] Step 1: Weigh 0.5 parts of 1-hydroxycyclohexylphenyl ketone, 0.25 parts of isopropylthioxanthone, 1 part of acrylic acid, and 5 parts of 1,4-hexanediol diacrylate and add them to the reaction vessel. Heat to 55°C and stir at high speed to fully dissolve the initiator. Then cool to room temperature to obtain the photoinitiated curing solution.

[0034] Step 2: Weigh 13 parts of polyester acrylate, 10 parts of polyurethane acrylate, 0.25 parts of tetraneoalkoxybis(dicylphosphite)titanate and 70 parts of 500nm spherical silver powder and add them to the initiator curing solution in Step 1. Grind the mixture with a three-roll mill until it becomes a conductive adhesive with a fineness of less than 5μm.

[0035] Step 3: Print the conductive adhesive onto the PE film using a 400-mesh screen, then apply 1500mW / cm² of heat.2 The silver paste is cured by UV light, and then baked in a 100℃ oven for 10 minutes to obtain a UV-cured conductive silver paste with high conductivity.

[0036] Performance Testing: The conductivity of the conductive silver paste was measured to be 193 S / mm using a four-probe impedance tester, and the adhesion of the conductive silver paste was 5B in the cross-cut adhesion test. The bending resistance test method was as follows: First, the conductivity of the cured conductive silver paste line was measured using a four-probe tester; then, the cured conductive silver paste line was folded in half along a straight line; a 2kg weight was then applied to the fold line and held for 1 minute; the cured conductive silver paste line was then folded in the opposite direction and pressure was applied for the same duration, repeating the above steps 10 times; finally, the conductivity of the bent and cured conductive silver paste line was measured. The conductivity after 10 bends was 151 S / mm.

[0037] Example 3

[0038] This embodiment illustrates a method for preparing UV-curable conductive silver paste, specifically including the following steps:

[0039] Step 1: Weigh 0.5 parts of 1-hydroxycyclohexylphenyl ketone, 0.25 parts of isopropylthioxanthone, 1.5 parts of acrylic acid, and 5 parts of 1,4-hexanediol diacrylate and add them to the reaction vessel. Heat to 45°C and stir at high speed to fully dissolve the initiator. Then cool to room temperature to obtain the photoinitiated curing solution.

[0040] Step 2: Weigh 10 parts of polyester acrylate, 10 parts of polyurethane acrylate, 0.75 parts of tetraneoalkoxybis(dicylphosphite)titanate and 72 parts of 200nm flake silver powder and add them to the initiator curing solution in Step 1. Grind the mixture with a three-roll mill until it becomes a conductive adhesive with a fineness of less than 5μm.

[0041] Step 3: Print the conductive adhesive onto the PC film using a 500-mesh screen, then apply 2500mW / cm² of heat. 2 The silver paste is cured by UV light, and then baked in a 100℃ oven for 10 minutes to obtain UV-cured conductive silver paste.

[0042] Performance Testing: The conductivity of the conductive silver paste was measured to be 241 S / mm using a four-probe impedance tester, and the adhesion of the conductive silver paste was 5B in the cross-cut adhesion test. The bending resistance test method was as follows: First, the conductivity of the cured conductive silver paste line was measured using a four-probe tester; then, the cured conductive silver paste line was folded in half along the straight direction; a 2kg weight was then applied to the fold line and held for 1 minute; the cured conductive silver paste line was then folded in the opposite direction and pressure was applied for the same duration, repeating the above steps 10 times; finally, the conductivity of the bent and cured conductive silver paste line was measured. The conductivity after 10 bends was 205 S / mm.

[0043] Comparative Example 1

[0044] This embodiment illustrates a method for preparing UV-curable conductive silver paste, specifically including the following steps:

[0045] Step 1: Weigh 0.5 parts of 1-hydroxycyclohexylphenyl ketone, 0.5 parts of isopropylthioxanthone, 1 part of acrylic acid, and 4 parts of 1,4-hexanediol diacrylate and add them to the reaction vessel. Heat to 50°C and stir at high speed to fully dissolve the initiator. Then cool to room temperature to obtain the photoinitiated curing solution.

[0046] Step 2: Weigh 8 parts of polyester acrylate, 8 parts of polyurethane acrylate, and 78 parts of 500nm spherical silver powder and add them to the initiator curing solution in Step 1. Grind them with a three-roll mill until the fineness is less than 5μm of conductive adhesive.

[0047] Step 3: Print the conductive adhesive onto the PET film using a 300-mesh screen, then apply 1500mW / cm² of adhesive. 2 The silver paste is cured by UV light, and then baked in a 100℃ oven for 10 minutes to obtain UV-cured conductive silver paste.

[0048] Performance Testing: The conductivity of the conductive silver paste was measured to be 172 S / mm using a four-probe impedance tester, and the adhesion of the conductive silver paste was 5B in the cross-cut adhesion test. The bending resistance test method was as follows: First, the conductivity of the cured conductive silver paste line was measured using a four-probe tester; then, the cured conductive silver paste line was folded in half along the straight direction; a 2kg weight was then applied to the fold line and held for 1 minute; the cured conductive silver paste line was then folded in the opposite direction and pressure was applied for the same duration, repeating the above steps 10 times; finally, the conductivity of the bent and cured conductive silver paste line was measured. The conductivity after 10 bends was 21 S / mm.

[0049] Comparative Example 2

[0050] This embodiment illustrates a method for preparing UV-curable conductive silver paste, specifically including the following steps:

[0051] Step 1: Weigh 0.5 parts of 1-hydroxycyclohexylphenyl ketone, 0.25 parts of isopropylthioxanthone, 1.5 parts of acrylic acid, and 5 parts of 1,4-hexanediol diacrylate and add them to the reaction vessel. Heat to 50°C and stir at high speed to fully dissolve the initiator. Then cool to room temperature to obtain the photoinitiated curing solution.

[0052] Step 2: Weigh 10 parts polyester acrylate, 10 parts polyurethane acrylate, 0.75 parts di(triethylamine) titanate diisopropyl ester (NXH-501 titanate coupling agent) and 72 parts 500nm spherical silver powder and add them to the initiator curing solution in Step 1. Grind the mixture with a three-roll mill until it becomes a conductive adhesive with a fineness of less than 5μm.

[0053] Step 3: Print the conductive adhesive using a 300-mesh screen, then apply 2500mW / cm² of heat. 2 The silver paste is cured by UV light, and then baked in a 100℃ oven for 10 minutes to obtain UV-cured conductive silver paste.

[0054] Performance Testing: The conductivity of the conductive silver paste was measured to be 220 S / mm using a four-probe impedance tester, and the adhesion of the conductive silver paste was 5B in the cross-cut adhesion test. The bending resistance test method was as follows: First, the conductivity of the cured conductive silver paste line was measured using a four-probe tester; then, the cured conductive silver paste line was folded in half along a straight line; a 2kg weight was then applied to the fold line and held for 1 minute; the cured conductive silver paste line was then folded in the opposite direction and pressure was applied for the same duration, repeating the above steps 10 times; finally, the conductivity of the bent and cured conductive silver paste line was measured. The conductivity after 10 bends was 0 S / mm.

[0055] Comparative Example 3

[0056] This embodiment illustrates a method for preparing UV-curable conductive silver paste, specifically including the following steps:

[0057] Step 1: Weigh 0.5 parts of 1-hydroxycyclohexylphenyl ketone, 0.25 parts of isopropylthioxanthone, 1.5 parts of acrylic acid, and 5 parts of 1,4-hexanediol diacrylate and add them to the reaction vessel. Heat to 50°C and stir at high speed to fully dissolve the initiator. Then cool to room temperature to obtain the photoinitiated curing solution.

[0058] Step 2: Weigh 10 parts of polyester acrylate, 10 parts of polyurethane acrylate, 0.75 parts of diisopropyl di(acetylacetonyl)titanate and 72 parts of 500nm spherical silver powder and add them to the initiator curing solution in Step 1. Grind the mixture with a three-roll mill until it becomes a conductive adhesive with a fineness of less than 5μm.

[0059] Step 3: Print the conductive adhesive using a 300-mesh screen, then cure it with 2500mW / cm2 UV light. Place the cured silver paste in a 100℃ oven and bake for 10 minutes to obtain UV-cured conductive silver paste.

[0060] Performance Testing: The conductivity of the conductive silver paste was measured to be 192 S / mm using a four-probe impedance tester, and the adhesion of the conductive silver paste was 5B in the cross-cut adhesion test. The bending resistance test method was as follows: First, the conductivity of the cured conductive silver paste line was measured using a four-probe tester; then, the cured conductive silver paste line was folded in half along a straight line; a 2kg weight was then applied to the fold line and held for 1 minute; the cured conductive silver paste line was then folded in the opposite direction and pressure was applied for the same duration, repeating the above steps 10 times; finally, the conductivity of the bent and cured conductive silver paste line was measured. The conductivity after 10 bends was 0 S / mm.

[0061] The above experimental results show that the introduction of titanate coupling agents can significantly improve the conductivity of UV conductive silver paste. Furthermore, within a certain range, increasing the amount of titanate coupling agent can reduce the amount of silver powder used while achieving better conductivity (as in Example 3). While commonly used titanate coupling agents can achieve similar effects (e.g., Comparative Examples 2 and 3), they significantly worsen the bending resistance of the silver paste. That is, after bending, stress concentration occurs at the bending point, causing direct breakage and loss of conductivity, thus limiting the application of silver paste in flexible conductive fields. It is evident that adding conventional titanate coupling agents is insufficient to obtain high-performance UV-cured conductive silver paste. However, the long-chain structure of the titanate in this case does not exhibit this problem. This is because the long carbon chain structure has better flexibility, increasing the distance between rigid groups in the resin molecule and weakening the interaction between molecular chains to some extent. Under load or impact, this allows the molecular chains greater freedom, resulting in a toughening effect.

[0062] Comparative Example 4

[0063] This embodiment illustrates a method for preparing UV-curable conductive silver paste, specifically including the following steps:

[0064] Step 1: Weigh 0.5 parts of 1-hydroxycyclohexylphenyl ketone, 0.25 parts of isopropylthioxanthone, 1 part of acrylic acid, and 4 parts of 1,4-hexanediol diacrylate and add them to the reaction vessel. Heat to 50°C and stir at high speed to fully dissolve the initiator. Then cool to room temperature to obtain the photoinitiated curing solution.

[0065] Step 2: Weigh 8 parts of polyester acrylate, 10 parts of polyurethane acrylate, 0.25 parts of tetraneoalkoxybis(dicylphosphite)titanate and 76 parts of 500nm spherical silver powder and add them to the initiator curing solution in Step 1. Grind the mixture with a three-roll mill until it becomes a conductive adhesive with a fineness of less than 5μm.

[0066] Step 3: Print the conductive adhesive onto the PET film using a 300-mesh screen, then bake it in a 100℃ oven for 10 minutes, and then use 1500mW / cm 2 UV curing is performed to obtain UV-cured conductive silver paste.

[0067] Performance Testing: The conductivity of the conductive silver paste was measured to be 42 S / mm using a four-probe impedance tester, and the adhesion of the conductive silver paste was 3B in the cross-cut adhesion test. The bending resistance test method was as follows: First, the conductivity of the cured conductive silver paste line was measured using a four-probe tester; then, the cured conductive silver paste line was folded in half along a straight line; a 2kg weight was then applied to the fold line and held for 1 minute; the cured conductive silver paste line was then folded in the opposite direction and pressure was applied for the same duration, repeating the above steps 10 times; finally, the conductivity of the bent and cured conductive silver paste line was measured. The conductivity after 10 bends was 0 S / mm.

[0068] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing a UV-curable conductive silver paste, characterized in that, It comprises the following steps: Step 1: under heating condition, dissolving a photoinitiator in an active diluent, and obtaining a photoinitiation curing liquid after cooling; Step 2: adding a prepolymer, a conductive assistant and a conductive powder into the photoinitiation curing liquid of step 1, and grinding to obtain a conductive adhesive; The conductive assistant comprises at least one of tetra-neooxy bis (didecyl phosphoric acid acyloxy) titanate, isopropoxy dioleic acid acyloxy (dioctyl phosphoric acid acyloxy) titanate and isopropoxy trioleic acid acyloxy titanate. In step 2, the weight ratio of the prepolymer: conductive assistant: silver powder: photoinitiation curing liquid is (15-25):(0.5-1):(60-75):(6-12). The prepolymer is at least one of polyester acrylate, polyurethane acrylate and epoxy acrylate; the prepolymer contains hydroxyl, carboxyl and amine groups. The preparation method further comprises step 3: printing the conductive adhesive of step 2 onto a substrate, and curing under UV light irradiation in a nitrogen atmosphere, and then baking to obtain a UV cured conductive silver paste. In step 3, the UV light energy is 1000-3000 mW / cm 2 , and the baking condition is 100 °C, 10 min.

2. The method of claim 1, wherein the UV-curable conductive silver paste is prepared by mixing the silver powder, the organic vehicle, the photoinitiator, the dispersant, and the surfactant. In step 1, the weight ratio of the photoinitiator: active diluent is (0.6-1.2):(30-60).

3. The method of claim 1, wherein the UV-curable conductive silver paste is prepared by mixing silver powder, a binder, a solvent, a dispersant, a surfactant, and a photoinitiator. The conductive powder is silver powder.

4. The method of claim 3, wherein the UV-curable conductive silver paste is prepared by mixing the silver powder, the organic vehicle, the photoinitiator, the dispersant, and the surfactant. The silver powder comprises at least one of 0.2-10 μm flaky silver powder, 0.1-2 μm spherical silver powder, 0.5-3 μm spherical silver-coated copper powder and 1-10 μm flaky silver-coated copper powder.

5. The method of claim 1 to 4, characterized in that In step 1, the photoinitiator comprises at least one of 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, phenyl bis (2,4,6-trimethyl benzoyl) phosphine oxide, isopropyl thioxanthone and diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide; and the active diluent comprises one or more of acrylic acid, isobornyl acrylate, N-vinyl pyrrolidone, diethylene glycol diacrylate, 1,4-hexanediol diacrylate, neopentyl glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate and ditrimethylolpropane tetraacrylate.

6. A UV-cured conductive silver paste, characterized in that, The UV cured conductive silver paste is prepared by the preparation method of claim 1 to 5.

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