Corrosion-resistant double-layer rough conductive microsphere and preparation method thereof

Abstract

The invention provides a corrosion-resistant double-layer rough conductive microsphere and a preparation method thereof, and belongs to the technical field of nickel-plated conductive microspheres. The preparation method comprises the following steps: carrying out roughening treatment on polymer microspheres to obtain roughened microspheres; activating the coarsened microspheres to obtain activated microspheres; performing nickel pre-plating treatment on the activated microspheres to obtain nickel pre-plated microspheres, wherein the nickel pre-plating treatment is to deposit nickel particles on the surfaces of the activated microspheres through a chemical reduction method; the nickel pre-plated microspheres are sequentially subjected to chemical plating twice, the first chemical plating adopts an alkaline plating solution to obtain inner-layer conductive microspheres, and the second chemical plating adopts an acid plating solution containing cerous nitrate to obtain the corrosion-resistant double-layer rough conductive microspheres. The corrosion-resistant double-layer rough conductive microsphere prepared by the method comprises an inner coating with the phosphorus content of 2-3wt% and an outer coating with the phosphorus content of more than or equal to 10wt%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nickel-plated conductive microspheres, and particularly relates to a corrosion-resistant double-layer rough conductive microsphere and a preparation method thereof. BACKGROUND

[0002] The nickel-plated conductive microsphere is a kind of functional material taking a polymer microsphere as a substrate and forming a nickel-based conductive coating on the surface of the substrate through a chemical plating or electroplating process. The nickel-plated conductive microsphere is widely used in the fields of flexible circuits and precision connectors and is an important carrier for realizing electrical signal transmission in microelectronic products due to the lightweight characteristics of the substrate and the conductive performance of the coating.

[0003] There are two main types of preparation technologies for the existing nickel-plated conductive microspheres: one is single-layer chemical plating, that is, a single alkaline or acid plating solution is used to form a single-layer nickel coating. The process is simple, but the phosphorus content of the coating is single, and the low-phosphorus coating is prone to micro-cracks due to high crystallinity, which becomes a channel for the penetration of corrosive media. Although the high-phosphorus coating has a dense structure, the adhesion between the coating and the substrate is weak, and peeling may occur during long-term use, resulting in insufficient corrosion resistance. The other is multi-layer chemical plating. Although the thickness of the coating is increased through multiple plating, the same system plating solution or only a slight adjustment of the formula is used in mass production, and the differences in structure and composition of the coating are small. In a corrosive environment, coating defects tend to accumulate between layers, and the coating may still fall off, affecting the stability of the electrical conductivity.

[0004] Therefore, it is of great significance to design a preparation method for a nickel-plated conductive microsphere composed of multiple layers, with obvious differences in structure and composition between the layers, and capable of forming a functionally complementary coating, to solve the problems of existing coatings being easily corroded and having insufficient electrical stability and to improve the performance of the coating in complex environments. SUMMARY

[0005] The application overcomes the shortcomings of the prior art and provides a corrosion-resistant double-layer rough conductive microsphere and a preparation method thereof.

[0006] To achieve the above-mentioned purpose, the application adopts the technical scheme of a preparation method for a corrosion-resistant double-layer rough conductive microsphere, comprising the following steps:

[0007] S1, roughening treatment is performed on a polymer microsphere to obtain a roughened microsphere;

[0008] S2, activation treatment is performed on the roughened microsphere to obtain an activated microsphere;

[0009] S3, pre-nickel plating treatment is performed on the activated microsphere to obtain a pre-nickel plated microsphere, wherein the pre-nickel plating treatment is to deposit nickel particles on the surface of the activated microsphere by a chemical reduction method;

[0010] S4, the pre-plated nickel microspheres are sequentially subjected to two times of electroless plating; wherein the first electroless plating adopts an alkaline plating solution, and after reaction, inner-layer conductive microspheres are obtained; the second electroless plating adopts an acid plating solution, and after reaction, corrosion-resistant double-layer rough conductive microspheres are obtained.

[0011] Further, the alkaline plating solution in step S4 comprises:

[0012] nickel sulfate 80-150 g / L;

[0013] sodium citrate 50-100 g / L;

[0014] succinic acid 15-30 g / L;

[0015] sodium hypophosphite 100-150 g / L;

[0016] thiourea 3-6 mg / L;

[0017] pH value is 9.0-11.0.

[0018] Further, the acid plating solution in step S4 comprises:

[0019] nickel sulfate 10-40 g / L;

[0020] citric acid 5-20 g / L;

[0021] lactic acid 5-10 g / L;

[0022] sodium hypophosphite 20-50 g / L;

[0023] cerium nitrate 1-5 mg / L;

[0024] pH value is 4.0-5.5.

[0025] Further, the method of the first electroless plating in step S4 comprises:

[0026] dispersing the pre-plated nickel microspheres in water at a concentration of 5-50 g / L;

[0027] dropping the alkaline plating solution at a flow rate of 0.5-2 mL / min, and the initial stirring speed is 100-200 r / min;

[0028] after reaction for 10-20 min, adjusting the flow rate to 5-10 mL / min, and increasing the stirring speed to 200-800 r / min;

[0029] total reaction time is 30-90 min;

[0030] after reaction, maintaining stirring for 5-15 min, filtering and washing to obtain the inner-layer conductive microspheres.

[0031] Further, the method of the second electroless plating in step S4 comprises:

[0032] The inner layer of conductive microspheres is dispersed in water at a concentration of 5-50 g / L;

[0033] An acidic plating solution is added, and the stirring speed is 200-800 r / min;

[0034] The reaction time is 20-60 min;

[0035] After the reaction is completed, stirring is maintained for 5-15 min, and then filtration and washing are performed to obtain the corrosion-resistant double-layer rough conductive microspheres.

[0036] Further, the roughening treatment method in step S1 includes:

[0037] The high-molecular microspheres are dispersed in concentrated sulfuric acid at a concentration of 50-200 g / L;

[0038] Stirring is performed at 60-70°C for 60-90 min;

[0039] After filtration and washing, the roughened microspheres are obtained after drying.

[0040] Further, the activation treatment method in step S2 includes:

[0041] The roughened microspheres are dispersed in methanol at a concentration of 30-100 g / L, and a palladium chloride solution with a concentration of 0.1-1.5 g / L is added, and stirring is performed at 20-40°C for 1-3 h; after filtration and washing, the activated microsphere intermediate is obtained after drying;

[0042] The activated microsphere intermediate is dispersed in methanol at a concentration of 30-100 g / L, and a sodium borohydride methanol solution with a concentration of 1-3 g / L is added dropwise under stirring at 20-40°C; after the dropwise addition is completed, stirring is continued for 5-10 min, and then filtration and washing are performed, and the activated microspheres are obtained after drying.

[0043] Further, the chemical reduction method in step S3 includes:

[0044] The activated microspheres are dispersed in water, and a nickel sulfate solution with a concentration of 10-50 g / L is added and mixed, and stirring is performed at a pH of 1.5-3.0 for 1.5-2.5 h, and then filtration is performed to obtain the pre-plated nickel microsphere intermediate;

[0045] The pre-plated nickel microsphere intermediate is dispersed in water, and a sodium phosphite solution with a concentration of 5-15 g / L is added and mixed and stirred for 5-15 min, and then filtration is performed to obtain the pre-plated nickel microspheres.

[0046] Further, step S3 further includes pretreating the activated microspheres before pre-plating nickel; the pretreatment includes grinding the activated microspheres and then passing them through a 300-500 mesh sieve.

[0047] The application provides a further technical scheme: a corrosion-resistant double-layer rough conductive microsphere prepared based on the preparation method and comprising an inner layer plating layer with a phosphorus content of 2-3 wt% and an outer layer plating layer with a phosphorus content of greater than or equal to 10 wt%.

[0048] The application solves the defects in the background art and has the following beneficial effects:

[0049] The application forms a double-layer plating layer through two chemical platings, the first chemical plating adopts an alkaline plating solution to form an inner layer plating layer, and the second chemical plating adopts an acidic plating solution to form an outer layer plating layer. The inner layer plating layer formed under the condition of the alkaline plating solution has a higher crystallinity, although there are small cracks and pores, but is firmly combined with the surface of the pre-plated nickel microsphere and can provide a stable substrate for subsequent acid nickel plating. The outer layer plating layer formed under the condition of the acidic plating solution has an amorphous structure and excellent compactness, can cover the defects of the inner layer plating layer, and the two plating layers form a potential difference due to the difference in phosphorus content, which can change the penetration path of the corrosion medium. Compared with the prior art, the corrosion-resistant double-layer rough conductive microsphere prepared by the application can more effectively block the corrosion medium and reduce the influence of corrosion on the conductive performance.

[0050] The application adds 1-5 mg / L of cerium nitrate to the acidic plating solution as a rare earth compound to control the structure of the outer layer plating layer. The cerium nitrate ions can be preferentially adsorbed on the crystal defects on the surface of the microsphere, promote the directional adsorption and reduction of nickel ions and hypophosphorous acid on the surface of the microsphere, and refine the cellular particles of the outer layer plating layer. At the same time, the interaction between cerium nitrate and nickel ions can reduce the activity of both and increase the mutual solubility, so that the structure of the outer layer plating layer is more uniform. When the concentration of cerium nitrate is in the range of 1-5 mg / L, the above effects can be stably exerted; if the concentration is too low, the refining effect is insufficient, and if the concentration is too high, the plating solution is prone to self-catalytic decomposition, causing local defects in the outer layer plating layer. Compared with the prior art, by controlling the concentration of cerium nitrate in the acidic plating solution, the application optimizes the structure of the outer layer plating layer, enhances the compactness of the outer layer plating layer, and improves the blocking ability of the corrosion medium.

[0051] The application covers defects and controls corrosion direction through the double-layer plating layer with obvious differences in structure and composition, and further refines the cellular particles of the outer layer plating layer and reduces the porosity by using cerium nitrate, so that the corrosion medium is difficult to penetrate the dense structure of the outer layer and cannot quickly diffuse through the defects of the inner layer plating layer. The blocking ability of the corrosion medium makes the comprehensive stability of corrosion resistance and conductivity more optimal. BRIEF DESCRIPTION OF DRAWINGS

[0052] In order to make the technical solutions in the embodiments of the present application or the prior art clearer, the accompanying drawings needed in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only represent some embodiments described in the present application, and other drawings can be obtained by those of ordinary skill in the art without any creative effort.

[0053] Figure 1 A preparation method flow chart of the corrosion-resistant double-layer rough conductive microspheres;

[0054] Figure 2 An SEM image of the conductive microspheres prepared in Example 1;

[0055] Figure 3 An SEM image of the conductive microspheres prepared in Comparative Example 1;

[0056] Figure 4 An SEM image of the conductive microspheres prepared in Comparative Example 6. DETAILED DESCRIPTION

[0057] The technical solutions in the embodiments of the present application will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments only represent some embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all the other embodiments obtained by those of ordinary skill in the art without any creative effort belong to the protection scope of the present application.

[0058] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application. However, the present application can be practiced without the specific details, other than those described herein, and therefore, the scope of the present application is not limited to the specific embodiments disclosed herein.

[0059] In the following description, all the raw materials can be obtained from commercial sources or prepared by conventional methods in the art, unless otherwise specified. Among them, cerium nitrate (cerium nitrate hexahydrate) and nickel sulfate (nickel sulfate hexahydrate) are purchased from Sinopharm, and the specifications are both analytical pure.

[0060] SUMMARY:In the field of nickel-plated conductive microspheres, in order to improve corrosion resistance, the industry generally tends to use similar composition and property plating solution system for multi-layer plating, for fear that the combination will not be firm or the interface will fail due to too large differences in structure and physical properties between the heterogeneous plating layers. However, the present invention overcomes this technical prejudice and unexpectedly finds that by strictly following the "alkaline first and then acidic" sequence for double-layer chemical plating and introducing a narrow concentration range of cerium nitrate in the acidic plating solution, not only will the interlayer bonding not be weakened, but a stable heterogeneous structure of low-phosphorus crystalline inner layer and high-phosphorus amorphous outer layer can be constructed. In this structure, the inner layer provides a firm base, and the dense outer layer optimized by cerium nitrate effectively seals the possible micro defects in the inner layer, and the combination of the two produces corrosion resistance beyond simple addition. In particular, the specific concentration of cerium nitrate in the acidic plating solution, too low will not show effect, too high will easily lead to unstable plating solution, this discovery provides a new solution to the problem of balancing density and stability of high-phosphorus plating layer.

[0061] Exemplary method:

[0062] As shown in Figure 1 A method for preparing a corrosion-resistant double-layer rough conductive microsphere, comprising the following steps:

[0063] S1: roughening treatment of high polymer microspheres to obtain roughened microspheres;

[0064] S2: activation treatment of roughened microspheres to obtain activated microspheres;

[0065] S3: pre-plating nickel treatment of activated microspheres to obtain pre-plated nickel microspheres; wherein the pre-plating nickel treatment is to deposit nickel particles on the surface of the activated microspheres by chemical reduction method;

[0066] S4: two chemical platings in sequence on the pre-plated nickel microspheres; wherein the first chemical plating uses alkaline plating solution, and the inner layer conductive microspheres are obtained after reaction; the second chemical plating uses acidic plating solution, and the corrosion-resistant double-layer rough conductive microspheres are obtained after reaction.

[0067] In the following, each step will be described in detail.

[0068] Step S1 etches the surface of high polymer microspheres by the strong oxidizing property of concentrated sulfuric acid to increase the roughness of the surface of high polymer microspheres. The roughening treatment method includes:

[0069] Disperse the high polymer microspheres in 70-98wt% concentrated sulfuric acid at a concentration of 50-200g / L;

[0070] Stir at 60-70℃ for 60-90min;

[0071] Filter and wash, and dry to obtain roughened microspheres.

[0072] The high-molecular microspheres are one or more of polystyrene microspheres, polymethyl methacrylate microspheres, polyvinyl chloride microspheres and polyethylene microspheres, and the particle size is 3-20 μm.

[0073] Step S2 forms catalytic active sites on the roughened microsphere surface through activation treatment. The activation treatment method includes:

[0074] The roughened microspheres are dispersed in methanol at a concentration of 30-100 g / L, and a palladium chloride solution is added at a concentration of 0.1-1.5 g / L, and stirred at 20-40 °C for 1-3 h; after filtration and washing, the activated microsphere intermediate is obtained after drying;

[0075] The activated microsphere intermediate is dispersed in methanol at a concentration of 30-100 g / L, and a sodium borohydride methanol solution is added dropwise at a concentration of 1-3 g / L under stirring at 20-40 °C; after the dropwise addition, the stirring is continued for 5-10 min, and the activated microspheres are obtained after filtration and washing and drying.

[0076] The palladium chloride solution adopts a palladium chloride-hydrochloric acid-methanol system, specifically: first dissolve the palladium chloride in dilute hydrochloric acid to assist dissolution, and then dilute with anhydrous methanol.

[0077] Step S3 forms initial nickel particles on the surface of the activated microspheres by chemical reduction method, providing a conductive substrate for two chemical platings. The chemical reduction method specifically includes:

[0078] The activated microspheres are dispersed in water, and a nickel sulfate solution is added at a concentration of 10-50 g / L and mixed, and stirred at pH 1.5-3.0 for 1.5-2.5 h, and the pre-plated nickel microsphere intermediate is obtained after filtration;

[0079] The pre-plated nickel microsphere intermediate is dispersed in water, and a sodium phosphite solution is added at a concentration of 5-15 g / L and mixed and stirred for 5-15 min, and the pre-plated nickel microspheres are obtained after filtration.

[0080] Optionally, the activated microspheres are pretreated before pre-plating nickel, including grinding the activated microspheres and passing them through a 300-500 mesh sieve.

[0081] Step S4 forms a double-layer plating layer through two chemical platings of alkaline nickel plating and then acid nickel plating.

[0082] The alkaline plating solution includes:

[0083] Nickel source: nickel sulfate 80-150 g / L;

[0084] Complexing agent: sodium citrate 50-100 g / L;

[0085] Buffer: succinic acid 15-30 g / L;

[0086] Reducing agent: sodium hypophosphite 100-150 g / L;

[0087] Stabilizer: Thiourea 3-6 mg / L;

[0088] pH value is 9.0-11.0.

[0089] The first electroless plating method comprises:

[0090] Disperse the pre-plated nickel microspheres in water at a concentration of 5-50 g / L;

[0091] Drop the alkaline plating solution at a flow rate of 0.5-2 mL / min, and the initial stirring speed is 100-200 r / min;

[0092] After 10-20 min of reaction, adjust the flow rate to 5-10 mL / min, and increase the stirring speed to 200-800 r / min;

[0093] The total reaction time is 30-90 min;

[0094] After the reaction is completed, maintain stirring for 5-15 min, filter and wash to obtain the inner layer conductive microspheres.

[0095] The acidic plating solution comprises:

[0096] Nickel source: Nickel sulfate 10-40 g / L;

[0097] Complexing agent: Citric acid 5-20 g / L;

[0098] Buffer: Lactic acid 5-10 g / L;

[0099] Reducing agent: Sodium hypophosphite 20-50 g / L;

[0100] Rare earth compound: Cerium nitrate 1-5 mg / L;

[0101] pH value is 4.0-5.5.

[0102] The second electroless plating method comprises:

[0103] Disperse the inner layer conductive microspheres in water at a concentration of 5-50 g / L;

[0104] Add the acidic plating solution, and the stirring speed is 200-800 r / min;

[0105] Reaction time is 20-60 min;

[0106] After the reaction is completed, maintain stirring for 5-15 min, filter and wash to obtain the corrosion-resistant double-layer rough conductive microspheres.

[0107] Example 1:

[0108] As Figure 1As shown, a kind of corrosion-resistant double-layer rough conductive microspheres is prepared by the following steps:

[0109] S1: polystyrene microspheres with a particle size of 5 μm are dispersed in 98 wt% concentrated sulfuric acid at a concentration of 100 g / L, stirred at 65 ℃ for 75 min; after the reaction is completed, filter, repeatedly wash with water until the filtrate is neutral, and dry in a 60 ℃ oven to obtain roughened microspheres.

[0110] S2: the roughened microspheres are dispersed in methanol at a concentration of 50 g / L, and a palladium chloride-hydrochloric acid-methanol solution (palladium chloride is first dissolved in 5 wt% dilute hydrochloric acid to assist dissolution, and then diluted with anhydrous methanol) with a concentration of 1.0 g / L is added, and stirred at 30 ℃ for 2 h; after filtration, wash with methanol for 3 times, and dry at 60 ℃ to obtain activated microsphere intermediates.

[0111] The activated microsphere intermediates are dispersed in methanol at a concentration of 50 g / L, and a sodium borohydride methanol solution with a concentration of 2 g / L is added dropwise under the condition of stirring at 30 ℃ and 200 r / min, and continue to stir for 8 min after dropping; after filtration, wash with methanol for 3 times, and dry at 60 ℃ to obtain activated microspheres.

[0112] S3: after the activated microspheres are ground and passed through a 400 mesh sieve, the undersize is dispersed in water, and a nickel sulfate solution with a concentration of 10 g / L is added and mixed, and the pH is adjusted to 2.0 with dilute sulfuric acid, and stirred at 25 ℃ for 2 h, and after filtration, a pre-plated nickel microsphere intermediate is obtained;

[0113] The pre-plated nickel microsphere intermediate is dispersed in water and a sodium phosphite solution with a concentration of 10 g / L is added, and after stirring for 10 min, filtration is performed to obtain a pre-plated nickel microsphere.

[0114] S4: the pre-plated nickel microspheres are dispersed in water at a concentration of 10 g / L, and under the condition of constant temperature at 40 ℃, a basic plating solution (composition: nickel sulfate 130 g / L, sodium citrate 67 g / L, succinic acid 23 g / L, sodium hypophosphite 120 g / L, thiourea 5 mg / L, and the pH value is adjusted to 10.6) is added dropwise at a flow rate of 1 mL / min, and the initial stirring speed is 200 r / min; after 10 min of reaction, the flow rate is adjusted to 8 mL / min and the speed is adjusted to 300 r / min, and the total reaction time is 60 min; after the reaction is completed, maintain stirring for 10 min, filter and wash with water for 3 times to obtain inner-layer conductive microspheres.

[0115] The inner layer conductive microspheres are dispersed in water at a concentration of 10 g / L, stirred at 250 r / min under constant temperature of 40℃, and then an acid plating solution (consisting of nickel sulfate 20 g / L, citric acid 10 g / L, lactic acid 7.5 g / L, sodium hypophosphite 35 g / L, cerous nitrate 2 mg / L, and adjusted to pH 4.6) is added, and the reaction is carried out for 40 min; after the reaction, the stirring is maintained for 10 min, and then the product is filtered, washed with water for 3 times, and dried at 60℃ to obtain the corrosion-resistant double-layer rough conductive microspheres.

[0116] Example 2:

[0117] The preparation process of this example is similar to that of Example 1, except that the acid plating solution in step S4 of this example contains cerous nitrate at a concentration of 1 mg / L.

[0118] Example 3:

[0119] The preparation process of this example is similar to that of Example 1, except that the acid plating solution in step S4 of this example contains cerous nitrate at a concentration of 5 mg / L.

[0120] Comparative Example 1:

[0121] As shown in the following table, the preparation process of this comparative example is similar to that of Example 1, except that in step S4 of this comparative example, a first chemical plating is carried out by using an acid plating solution, and then a second chemical plating is carried out by using an alkaline plating solution. Figure 3 Comparative Example 2:

[0122] The preparation process of this comparative example is similar to that of Example 1, except that in step S4 of this comparative example, the pH of the acid plating solution is adjusted to 10.6.

[0123] Comparative Example 3:

[0124] The preparation process of this comparative example is similar to that of Example 1, except that in step S4 of this comparative example, the pH of the alkaline plating solution is adjusted to 4.6.

[0125] Comparative Example 4:

[0126] The preparation process of this comparative example is similar to that of Example 1, except that in step S4 of this comparative example, only the first chemical plating of the two chemical platings is carried out.

[0127] Comparative Example 5:

[0128] The preparation process of this comparative example is similar to that of Example 1, except that in step S4 of this comparative example, only the second chemical plating of the two chemical platings is carried out.

[0129] Comparative Example 6:

[0130] As shown in the following table, the preparation process of this comparative example is similar to that of Example 1, except that in step S4 of this comparative example, a first chemical plating is carried out by using an acid plating solution, and then a second chemical plating is carried out by using an alkaline plating solution.

[0131] Figure 4 ​As shown, the preparation process of the present comparative example is similar to that of Example 1, except that the acidic plating solution in step S4 of the present comparative example does not include cerium nitrate.

[0132] Experimental Example 1:

[0133] The finished microspheres prepared based on Examples 1-3 and Comparative Examples 1-6 were taken for the following detections.

[0134] 1. Phosphorus content detection of the plating layer (scanning electron microscope-energy dispersive X-ray spectroscopy, SEM-EDS)

[0135] (1) Sample pretreatment:

[0136] The finished microspheres of each example and comparative example were taken as samples, and cold inlay fixation was performed using epoxy resin. After the resin was cured, the samples were ground and polished to prepare metallographic samples that could expose the cross sections of the microspheres.

[0137] (2) Detection steps:

[0138] The prepared cross section samples were subjected to carbon spraying treatment to ensure good electrical conductivity thereof;

[0139] Field emission scanning electron microscopy (FE-SEM) was used to observe the plating layer morphology, thickness and bonding of the cross section of the microspheres;

[0140] EDS was used to analyze the composition of the micro area:

[0141] First layer (inner layer) phosphorus content determination: In the cross section area of the microspheres, the focal point of the EDS point analysis or small range face scanning (less than 1 μm 2 The average value of the weight percentage (wt%) of phosphorus (P) elements was taken as the first layer phosphorus content of the sample;

[0142] Second layer (outer layer) phosphorus content determination: The same method was used to analyze the point in the center area of the outer layer plating layer, and the average value of the obtained phosphorus content was the second layer phosphorus content of the sample.

[0143] 2. Initial resistance detection (four-probe method)

[0144] (1) The finished microspheres were uniformly spread on the surface of the conductive glass, and a tablet press was used to apply a pressure of 5 N to form a dense microsphere layer;

[0145] (2) A four-probe resistance tester was used, and the probe was lightly pressed vertically on the surface of the microsphere layer. The resistance value was recorded, and the average value of 5 parallel tests was taken as the initial resistance.

[0146] 3. Salt spray test (neutral salt spray test)

[0147] (1) Test conditions: 5 w% sodium chloride solution (pH 6.5-7.2), temperature 35℃, salt spray deposition amount 1-2 mL / (h·80cm 2 );

[0148] (2) Fix the finished microspheres on the sample holder and place them in the center of the salt spray chamber, and conduct 24h and 96h salt spray tests respectively, and record the 24h salt spray resistance and 96h salt spray resistance;

[0149] (3) After the test, the sample is taken out, the surface salt is washed with water, dried at 60℃, and the surface corrosion is observed.

[0150] All test items are tested in parallel for 3 times, and the results are averaged to obtain the results as shown in the following table:

[0151] Table 1 Comparison table of experimental results

[0152] Group First layer phosphorus content (wt%) Second layer phosphorus content (wt%) Initial resistance (Ω) 24h salt spray resistance (Ω) 96h salt spray resistance (Ω) Example 1 2.10 11.36 1.26 1.32 1.34 Example 2 2.14 10.78 1.3 1.44 1.58 Example 3 2.51 11.24 1.26 1.66 1.95 Comparative Example 1 10.78 2.34 1.36 2.44 3.25 Comparative Example 2 2.25 2.41 1.26 2.56 3.88 Comparative Example 3 10.88 11.02 3.52 3.66 3.68 Comparative Example 4 2.27 / 2.25 4.23 6.36 Comparative Example 5 12.63 / 4.36 4.88 5.27 Comparative Example 6 2.52 10.37 1.21 2.54 3.21

[0153] As can be seen from Table 1, Example 1 ( Figure 2 ) uses two chemical plating of alkaline nickel plating and then acid nickel plating, the first layer phosphorus content is 2.10wt%, the second layer phosphorus content is 11.36wt%, the initial resistance is 1.26Ω, the 24h salt spray resistance is 1.32Ω, and the 96h salt spray resistance is 1.34Ω, showing excellent corrosion resistance. This is because the inner layer of low phosphorus plating layer formed by the alkaline plating solution under the condition of pH 10.6, although there are micro cracks and pores due to high crystallinity, but provides a stable substrate for subsequent acid nickel plating; The outer layer of high phosphorus plating layer formed by the acid plating solution under the condition of pH 4.6 is amorphous structure, good in compactness, covering the defects of the inner layer, and the potential difference is formed between the two layers due to the difference in phosphorus content, when the corrosion medium penetrates the outer layer to reach the inner layer, it can convert the longitudinal corrosion to transverse corrosion, delaying the corrosion time of the substrate.

[0154] Comparative Example 1 ( Figure 3 ) uses the reverse order of acid nickel plating and then alkaline nickel plating, the first layer phosphorus content is 10.78wt%, the second layer phosphorus content is 2.34wt%, the 96h salt spray resistance rises to 3.25Ω, and the corrosion resistance decreases significantly. This is because the outer layer of low phosphorus plating layer formed by the alkaline plating solution has coarse grains and high porosity, which is difficult to block the corrosion medium, and cannot play a protective role, but becomes the starting point of corrosion.

[0155] Comparative Example 2 uses two times of alkaline electroless nickel plating, the first layer phosphorus content is 2.25wt%, the second layer is 2.41wt%, the 96h salt spray resistance rises to 3.88Ω. After the pH of the acid plating solution is adjusted to alkaline, the plating solution system is close to the alkaline environment of the first electroless plating, which leads to a significant decrease in the phosphorus content of the outer layer (from 11.36wt% in Example 1 to 2.41wt%), forming a low-phosphorus crystalline structure. The structure has coarse grains and high porosity, which cannot cover the possible defects in the inner layer, and the corrosion medium can easily penetrate the double-layer coating, resulting in a sharp rise in resistance.

[0156] Comparative Example 3 uses two times of acid electroless nickel plating, the first layer phosphorus content is 10.88wt%, the second layer is 11.02wt%, the 96h salt spray resistance rises to 3.68Ω. In the acid pH condition, the reduction rate of nickel ions in alkaline plating solution changes, leading to the formation of a high-phosphorus amorphous structure in the inner layer (phosphorus content 10.88wt%), and the structural difference between the outer layer high-phosphorus coating (11.02wt%) is reduced. Although both layers are high-phosphorus amorphous, the density is good, but the low-phosphorus crystalline structure of the inner layer, which should be a rigid substrate, is destroyed, resulting in a decrease in interlayer adhesion (initial resistance rises to 3.52Ω, much higher than 1.26Ω in Example 1).

[0157] Comparative Example 4 only uses alkaline electroless nickel plating in Example 1 twice to generate a single low-phosphorus coating, the first layer phosphorus content is 2.27wt%, the initial resistance is 2.25Ω, and the 96h salt spray resistance is 6.36Ω. The single low-phosphorus coating has high crystallinity, and there are micro-cracks and pores on the surface. The corrosion medium directly invades the substrate in the salt spray environment, resulting in a nearly 3-fold increase in resistance within 96h. As can be seen from Example 1, a single low-phosphorus coating cannot meet the corrosion resistance requirements.

[0158] Comparative Example 5 only uses acid electroless nickel plating in Example 1 twice to generate a single high-phosphorus coating, the first layer phosphorus content is 12.63wt%, the initial resistance is 4.36Ω, and the 96h salt spray resistance is 5.27Ω. When only the outer layer of high-phosphorus amorphous coating is deposited, the adhesion between the coating and the high-molecular microsphere substrate is significantly reduced due to the lack of the conductive support and mechanical anchoring of the inner layer low-phosphorus crystalline substrate (the initial resistance is as high as 4.36Ω, much higher than 1.26Ω in Example 1). In the salt spray test, the corrosion medium directly erodes the substrate through the weakly bonded area, causing the resistance to increase by 21% within 96h. Although the corrosion resistance is better than that of a single low-phosphorus coating (Comparative Example 4), it is far inferior to that of a double-layer structure (the resistance of Example 1 only increases by 6.3%).

[0159] It can also be seen from Table 1 that the phosphorus content of the second layer of Example 1 is 11.36wt% with 2mg / L cerium nitrate added in the acidic plating solution, and the 96h salt spray resistance is 1.34Ω, and the corrosion resistance is optimal. This is because cerium nitrate is preferentially adsorbed on the crystal defects of the microspheres in the form of ions, promotes the adsorption of complex nickel ions and reducing agent hypophosphite to the metal surface, increases the catalytic activity, speeds up the deposition rate, makes the cellular particles of the plating layer small and arranged densely, reduces the porosity, and reduces the probability of contact between the corrosion medium and the substrate. At the same time, cerium nitrate and nickel ions reduce the activity of each other, increase the mutual solubility, and further optimize the structure of the plating layer.

[0160] In Example 2, 1mg / L cerium nitrate is added to the acidic plating solution, the phosphorus content of the second layer is 10.78wt%, the 96h salt spray resistance is 1.58Ω, and the corrosion resistance is slightly lower than that of Example 1. This is because when the concentration of cerium nitrate is too low, the coverage of crystal defects and the promotion of catalytic activity are limited, the cellular particle refinement effect of the plating layer is insufficient, the density is slightly poor, and the corrosion medium is more easily penetrated.

[0161] In Example 3, 5mg / L cerium nitrate is added to the acidic plating solution, the phosphorus content of the second layer is 11.24wt%, the 96h salt spray resistance is 1.95Ω, and the corrosion resistance decreases. This is because the high concentration of cerium nitrate will become an active ion in the plating solution, form an additional catalytic core, trigger the autocatalytic reaction of the plating solution, increase the decomposition trend of the plating solution, and reduce the deposition capacity of the microspheres, resulting in local defects in the plating layer, thereby reducing the corrosion resistance.

[0162] Comparative Example 6 Figure 4 Using an acidic plating solution without adding cerium nitrate, the phosphorus content of the second layer is 10.37wt%, and the 96h salt spray resistance is 3.21Ω. Without adding cerium nitrate, the density of the outer layer high-phosphorus plating layer is insufficient (the phosphorus content is reduced by 1wt% compared to Example 1), and the corrosion medium is easily penetrated to the inner layer. Compared with Example 1, the cellular particles of the plating layer without cerium nitrate are large, the porosity is increased, resulting in an increase in the 96h salt spray resistance (from 1.34Ω to 3.21Ω).

[0163] In summary, the optimal concentration range of cerium nitrate in the acidic plating solution is about 2mg / L, and within this range, the corrosion resistance of the plating layer can be significantly improved by refining the grains and increasing the density. Too high or too low concentration will result in increased structural defects and reduced performance.

[0164] Based on the ideal embodiments of the present application, related personnel can make various changes and modifications without deviating from the technical concept of the present application. The technical scope of the present application is not limited to the contents of the specification, and must be determined by the scope of the claims.

Claims

1. A method for preparing a corrosion resistant double-layer rough conductive microsphere, characterized in that, The method comprises the following steps: S1, roughening treatment is performed on the polymer microspheres to obtain roughened microspheres; S2, activation treatment is performed on the roughened microspheres to obtain activated microspheres; S3, pre-nickel plating treatment is performed on the activated microspheres to obtain pre-nickel plated microspheres; wherein the pre-nickel plating treatment is to deposit nickel particles on the surface of the activated microspheres by a chemical reduction method; S4, the pre-nickel plated microspheres are sequentially subjected to two times of chemical plating; wherein the first time of chemical plating adopts an alkaline plating solution, and after reaction, inner layer conductive microspheres are obtained; the second time of chemical plating adopts an acidic plating solution, and after reaction, corrosion-resistant double-layer rough conductive microspheres are obtained.

2. The production method according to claim 1, characterized by, The alkaline plating solution in step S4 comprises: nickel sulfate 80-150 g / L; sodium citrate 50-100 g / L; succinic acid 15-30 g / L; sodium hypophosphite 100-150 g / L; thiourea 3-6 mg / L; pH value is 9.0-11.

0.

3. The preparation method according to claim 1, characterized in that, The acidic plating solution in step S4 comprises: nickel sulfate 10-40 g / L; citric acid 5-20 g / L; lactic acid 5-10 g / L; sodium hypophosphite 20-50 g / L; cerium nitrate 1-5 mg / L; pH value is 4.0-5.

5.

4. The preparation method according to claim 1, characterized in that, The method of the first time of chemical plating in step S4 comprises: the pre-nickel plated microspheres are dispersed in water at a concentration of 5-50 g / L; the alkaline plating solution is added dropwise at a flow rate of 0.5-2 mL / min, and the initial stirring speed is 100-200 r / min; after reaction for 10-20 min, the flow rate is adjusted to 5-10 mL / min, and the speed is increased to 200-800 r / min; the total reaction time is 30-90 min; after reaction, stirring is maintained for 5-15 min, then filtration and washing are performed, and the inner layer conductive microspheres are obtained.

5. The preparation method according to claim 1, characterized in that, The method of the second time of chemical plating in step S4 comprises: the inner layer conductive microspheres are dispersed in water at a concentration of 5-50 g / L; the acidic plating solution is added, and the stirring speed is 200-800 r / min; the reaction time is 20-60 min; after reaction, stirring is maintained for 5-15 min, then filtration and washing are performed, and the corrosion-resistant double-layer rough conductive microspheres are obtained.

6. The method of claim 1, wherein, The method of the roughening treatment in step S1 comprises: the polymer microspheres are dispersed in concentrated sulfuric acid at a concentration of 50-200 g / L; stirring is performed at 60-70 °C for 60-90 min; filtration and washing are performed, and after drying, the roughened microspheres are obtained.

7. The preparation method according to claim 1, characterized in that, The method of the activation treatment in step S2 comprises: the roughened microspheres are dispersed in methanol at a concentration of 30-100 g / L, and a palladium chloride solution with a concentration of 0.1-1.5 g / L is added, stirring is performed at 20-40 °C for 1-3 h; filtration and washing are performed, and after drying, an activated microsphere intermediate is obtained; the activated microsphere intermediate is dispersed in methanol at a concentration of 30-100 g / L, and a sodium borohydride methanol solution with a concentration of 1-3 g / L is added dropwise under stirring at 20-40 °C; after dropping, stirring is continued for 5-10 min, then filtration and washing are performed, and after drying, the activated microspheres are obtained.

8. The method of claim 1, wherein, The chemical reduction method in step S3 comprises: The activated microspheres are dispersed in water, mixed with a nickel sulfate solution at a concentration of 10-50 g / L, stirred at a pH of 1.5-3.0 for 1.5-2.5 h, and filtered to obtain a pre-plated nickel microsphere intermediate; The pre-plated nickel microsphere intermediate is dispersed in water, mixed with a sodium hypophosphite solution at a concentration of 5-15 g / L, stirred for 5-15 min, and filtered to obtain the pre-plated nickel microspheres.

9. The method of claim 1, wherein, Step S3 further comprises pretreating the activated microspheres before pre-plating nickel; the pretreatment comprises grinding the activated microspheres and then passing them through a 300-500 mesh sieve.

10. A corrosion resistant double-layer rough conductive microsphere, prepared based on the preparation method of any one of claims 1-9, characterized in that, The inner layer plating layer comprises phosphorus at a content of 2-3 wt%, and the outer layer plating layer comprises phosphorus at a content of ≥10 wt%. The inner layer plating layer comprises phosphorus at a content of 2-3 wt%, and the outer layer plating layer comprises phosphorus at a content of ≥10 wt%.

Images