A zinc oxide ring varistor and silver paste used for electrode sintering

Abstract

The invention discloses a zinc oxide annular varistor silver paste, which is characterized in that the resistor silver paste comprises: precious metal powder, organic binder, organic solvent, additive, glass powder, strong reducing base metal powder, and silver electrode recycled material powder on the zinc oxide annular varistor substrate; the technical solution of the application directly adds the silver electrode material peeled from the waste sheet when preparing the silver paste from the perspective of re-putting the waste sheet into production and recycling, and overcomes the inability to form the varistor voltage caused by the segregation of the silver paste components, so as to achieve a balance between the contradictory bodies of silver electrode solderability and adhesion, and the number of zinc oxide solid waste sheets after infiltration handed over to the recycling organization by the production enterprise is greatly reduced, and various harms to the environment and human body caused by strong acid are reduced, and the high energy consumption caused by smelting is reduced; from the utilization of silver ingots to the direct recycling of varistor production, the production process is greatly shortened, and the precious and base metals and glass bodies can be recycled.

Description

Technical Field

[0001] The invention relates to the recycling of metal materials, in particular to the recycling of waste zinc oxide annular varistor sheets. Background Art

[0002] The Schottky barrier formed by the electron depletion layer at the contact interface between the metal and the semiconductor ceramic substrate causes the conduction of the current under the external voltage to be affected by the direction and position, and has rectification. The metal electrode and the ceramic bonding interface burned into the surface of the semiconductor zinc oxide ceramic substrate must meet the ohmic contact, and the carriers crossing the Schottky barrier must meet the ohmic contact. The electrode surface must meet the solderability and the bottom of the electrode must have sufficient adhesion. The challenge of electrode function comes not only from the guarantee of the high-pass, low-resistance, nonlinear clamping protection function of the stepped series voltage threshold of the semiconductor device, but also from the rigorous coordination of the various components of the silver paste used for electrode burning to meet the above-mentioned multiple functions at the same time.

[0003] Because its electrodes contain at least one precious metal such as gold, silver, palladium, and at least one base metal such as aluminum, copper, tin, zinc, and nickel, varistor waste sheets are highly favored for recycling. At present, varistor manufacturers directly hand over waste sheets to specialized recycling agencies for processing:

[0004] Publication (Announcement) No.: KR101951352B1 (1) leaching silver by adding nitric acid to an electrode process byproduct; (2) filtering the silver-containing leachate to remove solid residues; (3) adding hydrochloric acid to the leachate from which the solid residues have been removed to precipitate silver chloride, and recovering them separately. (4) preparing a silver nitrate aqueous solution by dissolving silver chloride in an ammonia aqueous solution having a concentration of 30 to 50% by weight. And (5) adding a reducing agent including polyethylene glycol (PEG), sodium borohydride (adding NaBH4), polyacrylic acid (PAA), polypropylene glycol-based or a mixture thereof to a silver nitrate aqueous solution, and centrifuging silver nanoparticles to recover silver from an electrode process byproduct including a recovery step. Leaching silver from nitric acid is harmful to the five senses of operators due to its volatility, acidic corrosion to the surrounding environment and equipment, and the waste acidifies the soil, causing a new round of damage to the environment.

[0005] Announcement No.: CN107419103B, A method for recycling waste varistor, discloses a method for recycling waste varistor, including solvent mixing flow to remove insulating paint, low-temperature liquid nitrogen freezing mechanical collision to remove nickel-iron alloy wire and solder, high-temperature scraping and reciprocating screening to recover silver flakes, etc. The solvents used are not friendly to the environment, and the final recycled material must be melted into ingots, which is high energy consumption.

[0006] How to improve the various deficiencies of the above-mentioned recovery process, reduce the use of strong acid, reduce carbon emissions to achieve low-consumption recovery and efficient utilization, this is the problem to be solved in this application. Summary of the invention

[0007] A zinc oxide annular varistor silver paste, comprising: precious metal micropowder, organic binder, organic solvent, additive, glass powder, strong reducing base metal micropowder, and silver electrode recycled material micropowder on the zinc oxide annular varistor substrate;

[0008] Furthermore, the weight ratio of the precious metal powder: glass powder: strong reducing base metal powder: silver electrode recycled material powder is [65,75]: [1,5]: [5,10]:

[10] max ;

[0009] Furthermore, the silver electrode recycled material is derived from the stripping of the silver electrode on the zinc oxide varistor waste sheet before infiltration, and contains zinc oxide substrate debris, silver electrode debris and impurities;

[0010] Furthermore, the waste zinc oxide varistor sheets before infiltration are selected from at least one of a defective substrate and a defective printed electrode in the production process of the zinc oxide ring varistor;

[0011] Furthermore, the noble metal is at least one of gold, silver, platinum, ruthenium, rhodium, palladium, osmium, iridium, single substance or ions, compounds, and salts; the strong reducing base metal is at least one of iron, aluminum, tin, zinc, copper, tungsten, molybdenum, tantalum, magnesium, cobalt, bismuth, cadmium, titanium, zirconium, antimony, manganese, beryllium, chromium, germanium, vanadium, gallium, hafnium, indium, niobium, rhenium, and thallium, single substance or ions, compounds, and salts;

[0012] Still further, the compound is an oxide;

[0013] Furthermore, the recycling method of the silver electrode recycled material is ultrasonic cleaning, placing the zinc oxide varistor waste sheets before the silver electrode infiltration in a solvent containing at least one of alcohol and deionized water, starting the ultrasonic vibration cleaning equipment loaded with the waste sheets and the solvent, obtaining a precipitate including zinc oxide substrate debris, silver electrode debris and impurities, washing and filtering the precipitate, drying at 100-120° C., ball milling and sieving to obtain electrode recycled materials, and the washed varistor substrate is selected and reused;

[0014] Furthermore, the heating function is not turned on when the ultrasonic vibration cleaning device is turned on.

[0015] The preparation method of the silver paste for any of the above-mentioned zinc oxide annular varistors is as follows: step A: batching, wherein silver electrode recycled material, precious metal powder, glass powder, and strongly reducing base metal powder are batched in proportion; step B: mixing and ball milling, and then mixing and rolling with an organic adhesive and an organic solvent, and the obtained slurry is sieved, and the fineness does not exceed 3μm.

[0016] A zinc oxide annular varistor comprises a semi-conductive zinc oxide substrate and a silver electrode, wherein the silver electrode is formed by printing a silver paste of any of the above zinc oxide annular varistor on the surface of the zinc oxide substrate and then sintering;

[0017] Further, the number of silver electrodes is one of three electrodes, five electrodes, six electrodes, ten electrodes, and twelve electrodes, and the silver electrode printing position is one of the upper and lower planes, inner and outer sides of the annular varistor, or a combination of at least two;

[0018] Further, the voltage E10 value of the annular varistor is a series specification of 1.5-3.5V of 015 to 60.0-100.0V of 600 that matches the voltage of the micro DC motor;

[0019] Furthermore, the nonlinear coefficient α of the annular varistor is 2.5-7.0;

[0020] Furthermore, the inner and outer diameters and thickness specifications of the annular varistor are series specifications of 060 to 200 that match the DC micromotor installation.

[0021] The preparation method of any of the above-mentioned zinc oxide annular varistors is as follows: step A, pre-sintering zinc oxide powder, donor doping, ball milling and granulation to form particles with a normal distribution and a median particle size of 3μm; forming and molding into annular embryonic sheets; debinding and sintering to form a semiconducting substrate of the annular varistor; step B: printing silver paste on the surface of any of the zinc oxide annular varistor described in claims 1 to 8, sintering and infiltrating to form electrodes, the sintering and infiltration temperature is 750-830℃, and obtaining annular varistors with nonlinear volt-ampere characteristics of a series of voltage specifications.

[0022] A direct current micro motor is provided, on which any of the above-mentioned annular varistor is installed. Beneficial Effects

[0023] The technical solution of this application takes the perspective of recycling waste sheets back into production. The silver electrode material peeled from the waste sheets is directly added when the silver paste is prepared. At the same time, the inability to form a varistor voltage caused by the segregation of the silver paste components is overcome, and the balance between the solderability and adhesion of the silver electrode is achieved, thereby realizing the direct reuse of waste sheets within the production enterprise.

[0024] The amount of solid waste zinc oxide flakes after burning and infiltration that the production enterprises hand over to recycling institutions for treatment is greatly reduced, reducing the various harms to the environment and human body caused by strong acids, and reducing the high energy consumption caused by smelting;

[0025] From the reuse of recycled silver ingots to the direct recycling of varistor waste sheets, the production process is greatly shortened, energy consumption and emissions are greatly reduced, and precious and base metals and glass can be recycled;

[0026] The technical solution of the present application can be mass-produced, and can also be extended to the production of other electronic ceramics, such as chip zinc oxide varistors, strontium titanate ring varistors, thermistors, etc., on the premise of meeting the requirements of ohmic contact, solderability, and sufficient strength. It has versatility and helps to achieve the production requirements of green factories. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] . Figure 1 This is the process flow chart of the technical solution of this application;

[0028] Figure 2 This is a comparison diagram of the appearance of the varistor of the specific embodiment 1 of the technical solution of this application and the comparative example 1, the lower three pieces are the embodiment 1, and the upper three pieces are the comparative example 1;

[0029] Figure 3 This is the appearance diagram of comparative example 2 before and after welding;

[0030] Figure 4 This is a comparison diagram of the appearance of the varistors of specific embodiment 2 and comparative example 3 of the technical solution of the present application. The three pieces on the right are embodiment 2, and the three pieces on the left are comparative example 3. Implementation

[0031] The technical solution is further described below in conjunction with the accompanying drawings, and the relevant descriptions involved in the specification are first explained as follows:

[0032] Weldability: It refers to the welding of the wire on the armature winding on the surface of the silver electrode when the varistor is installed in the motor. The stronger the metallic property of the silver electrode, the better the weldability.

[0033] Ohmic contact: There is no rectification when the silver electrode and the ceramic substrate are conducting, and the resistance does not change with the position and direction. This is the guarantee for the accurate performance of the nonlinear volt-ampere characteristic of the varistor. The segregation of the components of noble and base metals will affect the ohmic contact.

[0034] Tin drop: the reduction in varistor voltage after the wire on the motor armature is welded to the annular varistor electrode. The smaller the tin drop, the better.

[0035] Adhesion: Electrode adhesion is tested by tensile strength test, which is also the peel strength of equivalent silver electrode. Adhesion is related to glass and organic adhesive, and is contradictory to solderability.

[0036]

[10] max The maximum value of recycled powder added; [1,5] represents the set of rational numbers between the end values ​​1 and 5, and so on.

[0037] A zinc oxide annular varistor silver paste comprises a powder m1 containing at least one of a silver metal single substance or ions, compounds and salts, an organic binder, an organic solvent, an additive, a glass powder m2, a powder m3 containing at least one of a strong reducing base metal single substance or ions, compounds and salts, and a silver electrode recovery material m4 on a zinc oxide annular varistor substrate; wherein the mass ratio of m1:m2:m3:m4 is

[75] :[5]:

[10] :

[10] ; the silver electrode recovery material is stripped from zinc oxide waste sheets before silver electrode sintering, the stripped material comprises zinc oxide substrate debris and electrode debris and impurities, and the waste sheet is selected from at least one of a defective substrate and a printed electrode in the production process of the zinc oxide annular varistor;

[0038] Among them, m1 is silver powder; m3 is strong reducing metal powder, which is a mixture of Cu, Al and Sn single substances and their oxides.

[0039] Reference Figure 1 Process flow chart of the technical solution of this application:

[0040] The recycling method of the silver electrode recycling material m4 is ultrasonic cleaning, 2 kg of zinc oxide waste sheets before sintering are placed in alcohol, and the ultrasonic vibration cleaning equipment loaded with the above waste sheets and alcohol is turned on, and the heating function is not turned on. After cleaning for 10 minutes, the substrate is free of silver paste, and the precipitate including zinc oxide substrate debris and electrode debris under the solvent is obtained, which is successively washed with clean water, and then dried at 100-120°C. After passing through 60 mesh, it is the electrode recycling material m4. The annular zinc oxide resistor substrate is cleaned and the appearance is selected to be reused; the ultrasonic vibration cleaning equipment used is 2400W, the ultrasonic frequency is 28KHz, the model is JT-F2840D, and it is produced by Shenzhen Jietuo Ultrasonic Cleaning Equipment Co., Ltd.;

[0041] The components of the electrode recycling material m4 were detected by X-ray energy dispersive spectrometer (EDS) and X-ray fluorescence spectrometer (XRF), which were Ag, O, Si, Bi, Fe, Ba, Cl, Ti, Cs, Cu, Ca, Al, Sr, Sm, W, Mg, Ni, Mn, Mo, Pt, Co, Sx, and Cr.

[0042] The specific implementation method of the technical solution is as follows: step A: mixing ingredients, wherein the mass ratio of m1:m2:m3:m4 is

[75] :[5]:

[10] :

[10] ; step B: mixing and ball milling, rolling, mixing with an organic binder and an organic solvent after ball milling, rolling, and sieving, wherein the slurry fineness does not exceed 3 μm;

[0043] The organic binder and the organic solvent are heated, stirred, mixed and diluted in advance, and the composition, heating temperature, duration, amount and other processes are prior art; the softening point of the glass powder m2 is 600~700℃, the median particle size D50≤3μm, the composition and preparation are prior art, and will not be described in detail here;

[0044] The specific implementation method of the technical solution is as follows: step A, pre-sintering zinc oxide powder, donor doping, ball milling, and granulation to form particles with a normal distribution and a median particle size of 3μm; forming, molding into annular embryonic sheets; debinding and sintering to form an annular varistor semiconductor substrate with nonlinear varistor characteristics; step B: printing the above-prepared silver paste on its surface and sintering it into a silver electrode at a sintering temperature of 760°C to obtain a zinc oxide annular varistor of Examples 1 and 2.

[0045] Comparative Example 1 is a conventionally produced zinc oxide varistor specification, which is different from the technical solution of the present application in that the ingredients for preparing the silver paste do not contain the recycled material m4.

[0046] Comparative Example 2 is a conventionally produced zinc oxide varistor specification, which is different from the technical solution of the present application in that the ingredients used in preparing the silver paste only include the recycled material m4, without m1, m2, and m3, and the silver electrode sintering temperature is 785°C.

[0047] The size specifications, E10 value specifications, and electrode specifications of the zinc oxide annular varistors of the embodiments and comparative examples are recorded in Table 1; the voltage and capacitance consistency test data are recorded in Table 2; and the tin drop and tensile test data are recorded in Table 3.

[0048] The cleaned zinc oxide annular substrate was put back into use after full appearance inspection and crushing strength sampling inspection. After the printed electrode was burned and infiltrated, Example 3 and Example 4 were obtained. The pulse tin drop detection data are recorded in Table 4 and Table 5.

[0049] Any of the annular varistors obtained in Examples 1, 2, 3, and 4 can be installed and used on a DC micromotor.

[0050]

[0051]

[0052] Remark:

[0053] E1 and E10 are the voltage values ​​when the current is 1mA and 10mA respectively;

[0054] The three silver electrodes of each varistor were randomly named ABC. Each set of E1 value or E10 value measured 3 values ​​from A to B, B to C, and C to A. The difference between the maximum and minimum values ​​was the three-pole difference. R1 and R10 were the three-pole differences of E1 value and E10 value, respectively.

[0055] The statistical results include the minimum value MIN, the maximum value MAX, and the average value X. The statistics of each data in the table are based on 20 varistor samples randomly selected from 10,000 pieces, and the statistical results after 20 groups of data are detected; due to space limitations, only the statistical result values ​​are retained in Table 2, and the same is true for Tables 3, 4, and 5 below.

[0056] Analysis 1:

[0057] In Table 2, the R1 and R10 values ​​of Example 1 and Comparative Example 1 are comparable, and the discreteness of the E1 and E10 values ​​of the two are comparable. It can be seen that the ohmic contact between the silver electrode and the semiconductor substrate interface of the embodiment of the technical solution can be formed;

[0058] As can be seen from the comparison of the a value in Table 2, the nonlinear volt-ampere characteristic of the varistor of the embodiment is guaranteed;

[0059] The comparison in Table 2 shows that the capacitance value of the present technical solution does not deteriorate due to the addition of recycled materials.

[0060] Analysis 2:

[0061] in accordance with Figure 3 Comparison of appearance before and after welding and test results in Table 2: The silver electrode of Comparative Example 2 has almost no adhesion before welding, and welding cannot be completed; the average value X of the voltage E10 value is 1.40~3.5V, and the silver burning temperature is 20°C higher than that of Examples 1 and 2, but the result is still far below the requirement of 6~9V of the product specification. It can be seen that the use of silver electrode recycled materials alone cannot form a varistor voltage on the substrate, the silver electrode has no adhesion on the substrate, and the other electrical properties of the varistor, ohmic contact and tensile strength, cannot be achieved and corresponding tests cannot be performed.

[0062]

[0063] Analysis 3:

[0064] Compared with the normal supply of comparative example 1 and comparative example 3, embodiments 1 and 2 of the present technical solution can meet the normal production requirements. The tensile data show that the bottom of the silver electrode has sufficient adhesion, and the welding performance and tin drop meet the product specification requirements.

[0065] In the above specific embodiments 1-2, a maximum of 10% of silver electrode recycled material is added, and various proportions of addition below 10% can also meet various requirements of actual product specifications.

[0066]

[0067]

[0068] Note: Pulse detection, E10 voltage * 3 times = about 75V (peak voltage), impact 10 times, impact frequency 0.5 / second.

[0069] Analysis 4:

[0070] After the recycled substrates in Table 4 and Table 5 are put back into use, they have good pulse resistance characteristics. The varistor of this embodiment can continue to be durable, and the tin drop data show that the performance after welding is within the acceptable range of product specifications.

Claims

1. A zinc oxide ring varistor silver paste, characterized by: The resistor silver paste comprises: precious metal powder, organic binder, organic solvent, additive, glass powder, strong reducing base metal powder, and silver electrode recycled material powder on the zinc oxide annular varistor substrate; the weight ratio of the precious metal powder: glass powder: strong reducing base metal powder: silver electrode recycled material powder is: (65-75): (1-5): (5-10): (0-10), wherein the content of the silver electrode recycled material powder is not 0; the silver electrode recycled material is recycled by ultrasonic cleaning, the zinc oxide varistor waste sheets before silver electrode sintering are placed in a solvent containing at least one of alcohol and deionized water, and an ultrasonic vibration cleaning device loaded with the waste sheets and the solvent is turned on to obtain a precipitate including zinc oxide substrate fragments, silver electrode fragments and impurities, the precipitate is cleaned and filtered, dried at 100-120°C, ball milled and sieved to obtain electrode recycled material, and the cleaned varistor substrate is selected and reused.

2. The zinc oxide ring varistor silver paste according to claim 1, characterized in that: The silver electrode recycling material is derived from the stripping of the silver electrode on the zinc oxide varistor waste sheet before infiltration, and contains zinc oxide substrate debris, silver electrode debris and impurities.

3. The zinc oxide ring varistor silver paste according to claim 2, characterized in that: The waste zinc oxide varistor sheets before infiltration are selected from at least one of a defective substrate and a defective printed electrode in the production process of the zinc oxide ring varistor.

4. The zinc oxide ring varistor silver paste according to claim 1, characterized in that: The precious metal is at least one of gold, silver, platinum, ruthenium, rhodium, palladium, osmium, and iridium; the strong reducing base metal is at least one of iron, aluminum, tin, zinc, copper, tungsten, molybdenum, tantalum, magnesium, cobalt, bismuth, cadmium, titanium, zirconium, antimony, manganese, beryllium, chromium, germanium, vanadium, gallium, hafnium, indium, niobium, rhenium, and thallium.

5. The zinc oxide ring varistor silver paste according to claim 1, characterized in that: The heating function is not turned on when the ultrasonic vibration cleaning device is turned on.

6. A zinc oxide annular varistor, comprising a semiconducting zinc oxide substrate and a silver electrode, characterized in that: The silver electrode is formed by printing the silver paste of the zinc oxide annular varistor as claimed in any one of claims 1 to 5 on the surface of the zinc oxide substrate and then sintering it.

7. The zinc oxide ring varistor according to claim 6, characterized in that: The number of silver electrodes is one of three, five, six, ten, and twelve, and the silver electrode printing position is one of the upper and lower planes, inner and outer sides of the annular varistor, or a combination of at least two.

8. The zinc oxide ring varistor according to claim 6, characterized in that: The voltage E10 value of the annular varistor is a series specification of 1.5-3.5V of 015 to 60.0-100.0V of 600, which matches the voltage of the micro DC motor.

9. The zinc oxide ring varistor according to claim 6, characterized in that: The nonlinear coefficient α of the annular varistor is 2.5-7.

0.

10. The zinc oxide ring varistor according to claim 6, characterized in that: The inner and outer diameters and thickness specifications of the annular varistor are series specifications of 060 to 200 that match the DC micromotor installation.

11. A zinc oxide ring varistor according to any one of claims 6 to 10, characterized in that: The preparation method comprises the following steps: step A: pre-sintering zinc oxide powder, donor doping, ball milling and granulation to form granules with a normal distribution and a median particle size of 3 μm; forming and molding into annular embryonic sheets; debinding and sintering to form an annular varistor semiconductor substrate; step B: printing a zinc oxide annular varistor silver paste as described in any one of claims 1 to 5 on its surface, sintering and infiltrating to form electrodes, and the sintering and infiltration temperature is 750-830°C to obtain annular varistor with a series of voltage specifications and nonlinear volt-ampere characteristics.

12. A DC micromotor, characterized in that: An annular varistor as claimed in any one of claims 6 to 11 is installed on the motor.

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