Silver-nickel paste for radio frequency identification antenna and preparation method of silver-nickel paste

Abstract

The invention belongs to the technical field of electronic paste, and particularly relates to silver-nickel paste for a radio frequency identification antenna and a preparation method of the silver-nickel paste. The silver-nickel paste comprises the following components in percentage by mass: 50-60% of conductive metal powder, 5-20% of polymer resin and a solvent, the conductive metal powder comprises first-stage powder, second-stage powder and third-stage powder, the particle size D50 of the first-stage powder, the particle size D50 of the second-stage powder and the particle size D50 of the third-stage powder are decreased step by step, the first-stage powder is nickel powder, and the second-stage powder and the third-stage powder are silver powder; the conductive metal powder comprises nickel powder and silver powder; the macromolecular resin comprises vinyl chloride-vinyl acetate resin and polyester resin; the solvent is dibasic acid ester. The silver-nickel paste capable of replacing pure silver conductive paste is firstly provided, on one hand, the material cost of the radio frequency identification antenna printing paste is reduced, and on the other hand, the particle size design and metal model selection are combined to optimize the conductive performance after nickel replacement.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electronic paste, and particularly relates to a silver-nickel paste for a radio frequency identification antenna and a preparation method thereof. BACKGROUND

[0002] Radio frequency identification (RFID) is a non-contact automatic identification technology, which is widely applied to article tracking, identity recognition, anti-counterfeiting and the like. A common RFID tag is mainly composed of a substrate, an antenna and a chip. When an RFID reader sends a signal of a specific frequency to the tag, the RFID tag receives the signal and excites a current through electromagnetic induction to power the chip, and then the chip sends the stored data to the reader in the form of a radio frequency signal.

[0003] Common radio frequency identification antennas are manufactured through a printing process, and the printing materials include conductive silver paste, silver-coated copper paste and graphene ink, etc. From the application performance, the conductive silver paste has the lowest volume resistivity and the strongest substrate adhesion, and occupies a dominant position due to the comprehensive performance advantages. For example, patent CN 105632588 B proposes a high silver-nickel paste, in which the mass percentage of silver powder reaches 63%-75%.

[0004] Although high silver content can control the volume resistivity of the paste, the cost is high. At present, the silver price is close to 10,000 yuan / kg, and the silver powder accounts for usually 60%-80% in the conductive silver paste, resulting in that the material cost of a single kilogram of conductive silver paste is at least 6000-8000 yuan, and the electronic paste industry is facing great cost pressure. SUMMARY

[0005] Therefore, the application hopes to propose a silver-nickel paste for a radio frequency identification antenna, which can greatly reduce the cost of the paste while maintaining good conductivity.

[0006] The application is implemented through the following technical solutions:

[0007] A silver-nickel paste for a radio frequency identification antenna, comprising, by mass fraction, 50%-60% of conductive metal powder, 5%-20% of high molecular resin and solvent;

[0008] The conductive metal powder comprises primary powder, secondary powder and tertiary powder, and the particle size D 50 The primary powder, the secondary powder and the tertiary powder are gradually decreased, the primary powder is nickel powder, and the secondary powder and the tertiary powder are silver powder;

[0009] The conductive metal powder comprises nickel powder and silver powder;

[0010] The high molecular resin comprises chlorovinyl resin and polyester resin;

[0011] The solvent is a binary acid ester.

[0012] As preferred, the particle size D 90 not more than 30 μm, the particle size D 50 not more than 15 μm.

[0013] As preferred, the D 50 The ratio of the particle sizes is 9-11:7-9:4-6.

[0014] As preferred, the morphology of the silver powder is flaky.

[0015] As preferred, the morphology of the nickel powder includes at least one of acicular and flaky.

[0016] As preferred, the nickel powder is a pretreated nickel powder with polyvinylpyrrolidone on the surface.

[0017] As preferred, the type of the polyvinylpyrrolidone is K60.

[0018] As preferred, the number average molecular weight (Mn) of the chlorovinyl resin is 10000-100000; and / or, the number average molecular weight (Mn) of the polyester resin is 5000-50000.

[0019] As preferred, further including a thickening agent, a curing agent and a coupling agent;

[0020] The thickening agent is fumed silica; and / or, the curing agent includes isocyanate curing agent, amine curing agent, imidazole curing agent and acid anhydride curing agent; and / or, the coupling agent includes silane coupling agent, titanate coupling agent, aluminate coupling agent and phosphate coupling agent.

[0021] A preparation method of a silver-nickel paste for radio frequency identification antenna, comprising the following steps:

[0022] S1, preparing a nickel powder, the particle size D 90 not more than 30 μm, the particle size D 50 not more than 15 μm, including at least one of acicular and flaky morphologies; performing polyvinylpyrrolidone coating treatment on the nickel powder to obtain a pretreated nickel powder;

[0023] S2, uniformly mixing a system containing the pretreated nickel powder, silver powder, chlorovinyl resin, polyester resin and solvent according to the mass fraction of any one of the preceding, and grinding and rolling to obtain the silver-nickel paste.

[0024] As preferred, in the preparation method, the chlorovinyl resin is first configured as a chlorovinyl resin solution, and the polyester resin is configured as a polyester resin solution.

[0025] A radio frequency identification tag printed with any of the aforementioned silver-nickel paste.

[0026] This invention first proposes a silver-nickel paste that can replace pure silver conductive paste. Since nickel has a significantly higher resistivity than silver, while replacing some silver with nickel reduces material costs, the conductivity of the silver-nickel paste will inevitably decrease. Therefore, this invention combines particle size design with metal selection to optimize the conductivity after nickel substitution.

[0027] This invention employs a three-stage gradient of powder particle sizes, where the primary powder is nickel powder, and the secondary and tertiary powders are both silver powder. The silver powder of different particle sizes can fill the gaps between the nickel powder particles, thereby improving the conductivity of the slurry. The main reason for choosing nickel powder as the primary powder, rather than the secondary or tertiary powder, is that smaller particle sizes result in a larger specific surface area, which translates to higher conductivity. Using silver powder, with its relatively smaller particle size in the secondary and tertiary stages, maximizes the utilization of the surface contact characteristics of silver powder, thereby improving the overall conductivity.

[0028] Furthermore, micron-sized metal powders possess various morphologies, including flakes, spheres, and spiky spheres. From an electrical conductivity perspective, flake powders primarily exhibit surface or line contact, which is superior to the point contact of spherical powders. Therefore, coatings prepared from flake powders exhibit better conductivity. Consequently, this invention selects flake silver powder as both the secondary and tertiary powders.

[0029] The morphology of micron-sized particles also affects the dispersion ability of powders. The aggregation state of micron-sized particles includes aggregates and agglomerates. Agglomerates are bound together by surface contact, resulting in a stable structure that is difficult to redisperse; agglomerates are connected by edges and corners, resulting in a looser structure. If the conductive metal powder in the conductive slurry is aggregated, it will undoubtedly increase the difficulty of slurry dispersion, thereby reducing the conductivity of the prepared conductive slurry. Furthermore, for nickel powder, which already has a high resistivity, insufficient dispersion will further lead to a decrease in conductivity. Nickel powder has various morphologies such as flakes, spheres, spiky spheres, and chain-like structures. This invention selects a mixture of flake / spiky sphere nickel powder. Spiky sphere nickel powder is connected by points and corners, resulting in good dispersibility and easy separation of individual components. When mixed with silver powder, the spiky structure on the surface of the spheres can act as a skeleton in the slurry, providing space for the flake silver and flake nickel powder, thus ensuring that the conductive metal powder as a whole possesses both dispersibility and conductivity.

[0030] In further optimization scheme, the flaky / stick ball-shaped mixed nickel powder is pretreated by polyvinylpyrrolidone (PVP) and then mixed with other components. As a comparison, the prior art usually adds dispersant PVP in the process of dispersion and mixing. The principle is to use the amphiphilic property of PVP molecules, and the hydrophilic group and the hydrophobic group are connected to the dispersed powder and the dispersion medium respectively, to organize the particles to approach each other by steric hindrance, and to increase the compatibility with the dispersion medium. In this scheme, the stick ball-shaped nickel powder can be well dispersed by the thorn structure without the aid of dispersant. The longer the thorn length, the greater the particle spacing, and the more loose the accumulation. If PVP is added during the mixing of raw materials, the thorn structure of the stick ball-shaped nickel powder will be worn and shortened during the collision with other powders, resulting in a tight accumulation between the stick ball-shaped nickel powders, a decrease in the filling homogeneity of the flaky silver powder and the flaky nickel powder, and a decrease in the dispersibility of the conductive metal powder. This scheme mainly uses the film forming property of PVP to protect the thorn structure of the nickel powder, avoids the wear problem of the thorn structure in the mixing step, and maintains the accumulation state of the thorn nickel powder, so that the PVP pretreatment is only for the nickel powder.

[0031] In the selection of PVP, although K30 and K60 both belong to medium K value type, the molecular weight of K30 is 45000-58000, and the molecular weight of K60 is 270000-400000. The film formed by the PVP with larger molecular weight has thicker thickness and greater mechanical strength, and the protection effect on the thorn structure is better. Therefore, the application preferably selects K60 as the PVP model. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 It is a schematic diagram of the thorn ball shape and flaky shape of the nickel powder. DETAILED DESCRIPTION

[0033] The application will be further described below in conjunction with the drawings and specific examples in the specification. Those skilled in the art will be able to implement the application based on these descriptions. In addition, the embodiments of the application involved in the following description are generally only a part of the embodiments of the application, not all the embodiments. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments in the application without creative labor should be within the scope of protection of the application.

[0034] I. Information of raw materials and reagents used in the examples

[0035] #1 silver powder, flaky, particle size D 10 2.81 μm, D 50 7.72 μm, D 90 17.49 μm;

[0036] #2 Silver powder, flaky, particle size D 10 was 1.83 pm, D 50 was 4.97 pm, D 90 was 25.87 pm;

[0037] #1 Nickel powder, mixed flaky and acicular morphology, particle size D 10 was 3.09 pm, D 50 was 9.71 pm, D 90 was 13.51 pm;

[0038] #2 Nickel powder, mixed flaky and acicular morphology, K60 PVP coated (pretreatment), particle size D 10 was 3.09 pm, D 50 was 9.71 pm, D 90 was 13.51 pm;

[0039] #3 Nickel powder, mixed flaky and acicular morphology, K60 PVP coated (pretreatment), particle size D 50 was 5.61 pm;

[0040] #4 Nickel powder, mixed flaky and acicular morphology, K30 PVP coated (pretreatment), particle size D 10 was 3.09 pm, D50 was 9.71 pm, D 90 was 13.51 pm.

[0041] Thickening agent was De Gussa R972 fumed silica;

[0042] Curing agent was Covestro BL3370 MPA blocked isocyanate curing agent;

[0043] Coupling agent was Dow OFS-6011 silane coupling agent;

[0044] Solvent was dibasic ester (DBE) solvent.

[0045] II. Experimental steps involved in the examples

[0046] S1, pretreatment of nickel powder:

[0047] S1.1, polyvinylpyrrolidone PVP (K60) and anhydrous ethanol were mixed at room temperature according to a mass ratio of 1:50 to prepare a PVP ethanol solution;

[0048] S1.2, 100 grams of nickel powder were mixed with 100 grams of the above PVP ethanol solution, and then ultrasonic dispersion was performed for 30 minutes. Next, the mixed solution was placed in a 50°C constant temperature oil bath and stirred at a uniform speed (stirring speed 200 revolutions / minute) for 3 hours;

[0049] S1.3, After the surface treatment is completed, the nickel powder solution is washed with alcohol by centrifugation 5 times to remove excess PVP, and then the obtained wet nickel powder is placed in an oven at 60°C to dry, obtaining the pretreated nickel powder.

[0050] S2, Preparation of resin carrier:

[0051] S2.1, 250 grams of chlorovinyl resin and 750 grams of dibasic acid ester (DBE, purity > 99%) solvent are mixed and added to the reaction kettle, the stirring paddle is set to 200 revolutions per minute, the temperature is set to 80°C, and the resin is dissolved by stirring for about 4 hours until the resin is completely dissolved. After cooling to room temperature, a chlorovinyl resin solution is obtained.

[0052] S2.2, 250 grams of polyester resin and 750 grams of dibasic acid ester (DBE, purity > 99%) solvent are mixed and added to the reaction kettle, the stirring paddle is set to 200 revolutions per minute, the temperature is set to 80°C, and the resin is dissolved by stirring for about 4 hours until the resin is completely dissolved. After cooling to room temperature, a polyester resin solution is obtained.

[0053] S3, Preparation of silver-nickel paste:

[0054] S3.1, The organic components such as chlorovinyl resin solution, polyester resin solution, additives and solvents obtained in the previous steps are added to the reaction kettle according to the mass ratio, and the mixture is stirred uniformly.

[0055] S3.2, Silver powder and pretreated nickel powder are added to the system according to the mass ratio, and a homogenizer is used to stir uniformly. After passing through a three-roll mill, the fineness is reduced to less than 10 microns, obtaining a silver-nickel paste.

[0056] III. Performance test methods used in examples and comparative examples

[0057] Tap density: BT-1000 powder comprehensive performance tester produced by Dandong Bitai Instrument Co., Ltd. is used to test according to national standard GB / T 5162-2021.

[0058] Particle size distribution: BT-2003 laser particle size analyzer produced by Dandong Bitai Instrument Co., Ltd. is used to test according to national standard GB / T 19077-2016, and D 10 , D 50 , D 90 , etc. particle size data of each metal powder are obtained.

[0059] Sheet resistance: The silver on copper paste was screen printed on a PET or copper clad paper substrate with a total length of 1000 mm and a width of 0.3 mm circuit. The printed circuit was baked at 120 °C for 30 minutes, and then the resistance R of the circuit was measured using a multimeter, with units of Ω. The film thickness of the circuit after baking can be measured by a Mitutoyo thickness gauge, with units of μm. The sheet resistance R□ of the silver nickel paste (units of mΩ / □) can be calculated by the following formula:

[0060] R□= R * 0.3 * h / 25.4

[0061] Hardness test: Referring to the national standard GB / T6739-2006, the pencil hardness tester QHQ-A produced by the Ai Ruipu Company was used for testing.

[0062] Adhesion: Referring to the international standard ASTM D3359, the crosshatch knife tool produced by the Ningbo Kemai Company was used to test the 10x10 1mm x 1mm small grid, and the No. 600 tape produced by the 3M Company was used for testing.

[0063] Scanning electron microscope: The Sigma 300 model produced by the Zeiss Company was used for testing.

[0064] IV. Actual formula parameters of each embodiment and comparative example

[0065] Table 1 Formula of Examples 1-5

[0066] Formulation Example 1 Example 2 Example 3 Example 4 Example 5 Chlorovinyl resin solution 14.50 14.26 14.35 14.05 13.96 Polyester resin solution 16.70 16.32 16.13 15.67 15.69 R972 0.30 0.30 0.31 0.30 0.30 BL3370 MPA 0.50 0.50 0.51 0.49 0.50 OFS-6011 1.00 1.00 0.99 1.00 1.00 PVP-K60 0.00 0.00 0.00 0.00 0.00 DBE 12.00 12.62 12.71 13.49 13.55 #1 nickel powder 0.00 0.00 0.00 0.00 0.00 #2 nickel powder 35.00 30.00 25.00 20.00 15.00 #3 nickel powder 0.00 0.00 0.00 0.00 0.00 #4 nickel powder 0.00 0.00 0.00 0.00 0.00 #1 silver powder 15.00 20.00 25.00 30.00 35.00 #2 silver powder 5.00 5.00 5.00 5.00 5.00 Silver content (%) 20.00 25.00 30.00 35.00 40.00 Nickel content (%) 35.00 30.00 25.00 20.00 15.00 Sheet resistance (mΩ / □) 62.54 33.67 21.96 16.19 11.48 Pencil hardness 4H 4H 4H 4H 4H Adhesion 5B 5B 5B 5B 5B

[0067] Table 2 Formula of Comparative Examples 1-8

[0068] Formulation Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Chlorovinyl resin solution 15.50 30.00 18.75 14.65 14.90 15.75 14.80 14.50 Polyester resin solution 18.00 33.00 20.63 16.05 16.80 16.45 16.10 16.00 R972 0.29 0.33 0.33 0.30 0.30 0.30 0.30 0.30 BL3370 MPA 0.50 0.50 0.51 0.50 0.50 0.50 0.50 0.50 OFS-6011 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 PVP-K60 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.10 DBE 9.71 5.17 3.78 12.50 11.50 11.00 12.30 12.60 #1 nickel powder 0.00 0.00 0.00 25.00 0.00 0.00 0.00 25.00 #2 nickel powder 55.00 0.00 0.00 0.00 25.00 0.00 0.00 0.00 #3 nickel powder 0.00 0.00 0.00 0.00 0.00 25.00 0.00 0.00 #4 nickel powder 0.00 0.00 0.00 0.00 0.00 0.00 25.00 0.00 #1 silver powder 0.00 25.00 50.00 25.00 30.00 25.00 25.00 25.00 #2 silver powder 0.00 5.00 5.00 5.00 0.00 5.00 5.00 5.00 Silver content (%) 0.00 30.00 55.00 30.00 30.00 30.00 30.00 30.00 Nickel content (%) 55.00 0.00 0.00 25.00 25.00 25.00 25.00 25.00 Sheet resistance (mΩ / □) 22540.55 207.87 6.84 26.99 25.76 28.99 28.68 24.43 Pencil hardness 4H 4H 4H 4H 4H 4H 4H 4H Adhesion 5B 5B 5B 5B 5B 5B 5B 5B

[0069] V. Performance test results of Examples 1-5 and Comparative Examples 1-8

[0070] From the test results, it can be seen that Examples 1-5 use nickel powder coated with PVP (#2 nickel powder), #1 silver powder and #2 silver powder, and the silver content increases in turn, which is 20.00%, 25.00%, 30.00%, 35.00%, and 40.00%, and the sheet resistance of Examples 1-5 is 62.54 mΩ / □, 33.67 mΩ / □, 21.96 mΩ / □, 16.19 mΩ / □ and 11.48 mΩ / □, respectively, and the sheet resistance gradually decreases with the increase of silver content. The silver nickel paste prepared in Examples 1-5 has excellent hardness and adhesion, and the hardness is 4H and the adhesion is 5B.

[0071] Comparative Example 1 is a nickel paste prepared using pure nickel powder, and the sheet resistance is 22540.55 mΩ / D. Although the metal powder content of Comparative Example 1 and Examples 1-5 is about 55%, the sheet resistance of Comparative Example 1 is several hundred to several thousand times higher than that of Examples 1-5, which is mainly due to the fact that the conductivity of nickel powder is much lower than that of silver powder.

[0072] Comparative Examples 2 and 3 do not contain #2 nickel powder, and are pure silver pastes. The sheet resistance of Comparative Example 2 is measured to be 207.87 mΩ / D, which is about 10 times higher than that of Example 3 silver-nickel paste with the same silver content of 30%, which is mainly due to the fact that the nickel powder in Example 3 plays a certain conductive role. The sheet resistance of Comparative Example 3 is measured to be 6.84 mΩ / D, which is excellent in terms of conductivity, but the silver content is 55%, which is much higher than the maximum silver content of 40% in Examples 1-5, and Comparative Example 3 does not have a cost advantage.

[0073] Comparative Example 4 uses #1 nickel powder that has not been coated with PVP, and is used as a control for Example 3. The sheet resistance of Comparative Example 4 is more than 20% higher than that of Example 3, which is mainly due to the fact that the #2 nickel powder coated with PVP has a more complete thorn ball structure, and has better dispersibility and stability in the paste.

[0074] Comparative Example 5 does not contain #2 silver powder, that is, the conductive metal powder only includes primary powder and secondary powder, and is used as a control for Example 3. The sheet resistance of Comparative Example 5 is 25.76 mΩ / D, which is significantly higher than that of Example 3 (21.96 mΩ / D) with the same silver content, which shows that the use of silver powder with two particle size distributions helps to reduce the sheet resistance.

[0075] Comparative Example 6 uses a combination of large particle size silver powder / medium particle size nickel powder / small particle size silver powder, and the particle size D 50 of #3 nickel powder is 5.61 μm, which is between that of #1 silver powder and #3 silver powder, and the sheet resistance is measured to be 28.99 mΩ / D, which shows that its conductivity is significantly lower than that of the large particle size nickel powder / medium particle size silver powder / small particle size silver powder combination.

[0076] Comparative Example 7 is PVP-treated nickel powder with a type of K30, and the sheet resistance is 28.68 mΩ / D, which shows that the dispersing effect of K30 is lower than that of K60.

[0077] Comparative Example 8 uses #1 nickel powder that has not been treated with PVP, and 0.1% PVP-K60 is added in step S3.2 of preparing the silver-nickel paste, and the sheet resistance is measured to be 24.43 mΩ / D, which shows that the effect of adding PVP in the powder mixing step is not as good as using PVP to pretreat the nickel powder. In addition to being able to optimize the dispersibility of the powder, PVP can also protect the thorn structure of the nickel powder thorn ball morphology, and improve the distribution uniformity of the flaky silver powder and flaky nickel powder.

Claims

1. A silver nickel paste for radio frequency identification antennas, characterized in that, Comprising: by mass fraction, conductive metal powder 50%~60%, high polymer resin 5%~20% and solvent; The conductive metal powder includes a particle size D 50 The stepwise decreasing primary powder, secondary powder and tertiary powder, the primary powder is nickel powder, and the secondary powder and the tertiary powder are silver powder. The conductive metal powder comprises nickel powder and silver powder; The high polymer resin comprises chlorovinyl acetate resin and polyester resin; The solvent is dibasic acid ester.

2. The silver nickel paste of claim 1, wherein, The particle size D of the electrically conductive metal powder 90 not more than 30 μm, the particle size D 50 not more than 15 μm.

3. The silver nickel paste of claim 2, wherein, The D50 of the primary powder, the secondary powder, and the tertiary powder is 9-11: 7-9: 4-6. 50 The ratio of the particle sizes is 9-11: 7-9: 4-6.

4. The silver nickel paste of claim 1, wherein, The morphology of the nickel powder comprises at least one of thorn ball shape and flake shape.

5. The silver nickel paste of claim 4, wherein, The nickel powder is pretreated nickel powder with surface treated by polyvinylpyrrolidone.

6. The silver nickel paste of claim 5, wherein, The type of the polyvinylpyrrolidone is K60.

7. The silver nickel paste of claim 1, wherein, The morphology of the silver powder is flake shape.

8. The silver nickel paste of claim 1, wherein, Further comprising thickening agent, curing agent and coupling agent; the thickening agent is selected from at least one of fumed silica, BYK 410, Degos Rheo 8600 and Hennes THIXCIN R; the curing agent is selected from at least one of isocyanate curing agent, amine curing agent, imidazole curing agent and acid anhydride curing agent; the coupling agent is selected from at least one of silane coupling agent, titanate coupling agent, aluminate coupling agent and phosphate coupling agent.

9. A method for preparing a silver nickel paste for radio frequency identification antennas, characterized by, Comprising the following steps: S1, preparing nickel powder with particle size D 90 not more than 30 μm, particle size D 50 not more than 15 μm, including at least one of thorn ball morphology and flake morphology; performing polyvinylpyrrolidone coating treatment on the nickel powder to obtain pretreated nickel powder; S2, according to any one of claims 1~8 by mass fraction, uniformly mixing the system comprising the pretreated nickel powder, silver powder, chlorovinyl acetate resin, polyester resin and solvent, grinding and rolling to obtain the silver nickel paste.

10. A radio frequency identification tag, characterized by Printed with the silver nickel paste according to any one of claims 1~9.

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