Electrodeposition process for ultrasonic-assisted preparation of microstructure optical mold with surface passivation performance

Abstract

The invention discloses an ultrasonic-assisted electrodeposition process for preparing a microstructure optical mold with surface passivation performance, and aims to provide a cathode direct vibration mode, improve mass transfer in an electroplating bath, homogenize the concentration of lubricant particles near a cathode plate, homogenize a deposited lubricant to form a nano passivation layer, and improve the surface passivation performance of the microstructure optical mold. Auxiliary electroforming demolding and hot stamping demolding are achieved at the same time, the service life of the mold is prolonged, the product quality is improved, ultrasonic parameters can be conveniently adjusted through an ultrasonic power source in production, electrodeposition of a mold passivation layer can be conveniently achieved through an electroplating method in production, and the production efficiency is improved. The thickness and content of the passivation layer can be controlled by adjusting electroplating parameters and component concentration.

Description

Technical Field

[0001] The invention relates to the technical field of composite electroplating, and in particular to an ultrasonic-assisted electroplating process for preparing a microstructure optical mold with surface passivation performance. Background Art

[0002] Reflective materials rely on nickel molds for mass production. In order to ensure the directionality of light transmission, the shape accuracy and geometric accuracy of the surface microstructure are required to reach the nanometer level on a meter-sized mold, which poses a challenge to the electroforming demolding accuracy of the nickel mold. At present, potassium dichromate solution is used for electroforming demolding of microstructure optical molds, but potassium dichromate contains hexavalent chromium, which is carcinogenic and toxic, and is difficult to process later. The uniformity of the nano-passivation film formed on the surface of the microstructure cannot be guaranteed, which often causes local tearing during demolding. In addition, the passivation film formed by the potassium dichromate solution is destroyed after electroforming demolding, and cannot assist in the demolding between the polymer and the nickel mold during the subsequent hot stamping process. For this reason, it is urgent to find an environmentally friendly mold nano-level passivation layer preparation technology that meets the optical properties of the microstructure.

[0003] With the rapid development of materials science and technology, and modern processing technology, people's requirements for environmental protection are getting higher and higher. Reflective materials themselves do not need a light source, and use the micron-level structure on their surface to control the direction of light propagation. Their mold manufacturing belongs to the field of ultra-precision processing. In many manufacturing links, the electroforming of nickel molds has always been unable to be separated from the potassium dichromate solution. This problem has been highly valued by material researchers in various countries.

[0004] Invention patent CN111304701A discloses a process for preparing a graphene-assisted demolding layer. A graphene dispersion is coated on the surface of the cathode mold, and then the cathode is placed in a casting tank for electroforming. After the cathode is demolded, a high-quality mold is obtained. This technology can solve the problem of electroforming demolding accuracy, but it is not helpful for subsequent hot stamping demolding.

[0005] Invention patent CN201811172751.6 discloses a method for preparing an ultra-thin metal layer, by preparing an ultra-thin metal layer on a substrate, by preparing a high-concentration electroforming liquid to ensure the transient nucleation of metal ions, and at the same time, combined with current density control, so that the working potential exceeds the deposition potential of the metal ions, to ensure that an ultra-thin metal layer less than 1 micron is formed on the surface of the substrate. This technology can solve the problem of electroforming demolding accuracy, but it is of no help for subsequent hot embossing demolding.

[0006] Invention patent CN201210092952.1 uses a glass sheet or a silicon wafer as a substrate, spin-coats a layer of SU-8 photoresist with a thickness of 2 microns on the surface of the pretreated substrate, and bakes it at 85-95°C for 15-25 minutes to obtain the SU-8 photoresist layer to be imprinted; spin-coats a layer of release agent on the pretreated grating template, and then places it on a hot plate at 85-95°C for heating for 10-20 minutes, and obtains the grating template for imprinting after natural cooling.

[0007] Multiple hot pressings require multiple cleaning of residual release agent and spin coating of new release agent layers, which greatly reduces efficiency.

[0008] Apparently, there is no passivation layer that can be used for both electroforming and hot stamping demolding of optical molds, especially a nanometer-thick functional coating that has a simple process and can achieve lubrication and hardness improvement at the same time. Summary of the invention

[0009] The purpose of the present invention is to provide a method for preparing a nickel mold by improving mass transfer in an electroplating tank by direct cathode vibration, uniformizing the concentration of lubricant particles near the cathode plate, and then homogenizing the deposited lubricant to form a nano passivation layer, while achieving optical mold electroforming demolding and hot embossing demolding.

[0010] The present invention comprises the following steps: 1) preparing electroforming solution: adding deionized water to the electroforming tank, then adding nickel sulfate hexahydrate and nickel chloride in sequence, adding deionized water to the container, then adding boric acid and boiling, then adding sodium dodecyl sulfate, dissolving and pouring into the electroforming tank, adding saccharin and 1,4-butynediol to the electroforming tank, then injecting deionized water to fill the electroforming tank, and adjusting the pH to 3.0-5.0; the amount of the nickel sulfate hexahydrate, nickel chloride, boric acid, sodium dodecyl sulfate, saccharin and 1,4-butynediol added is (6000-12000) : (600-1400) : (600-1500) : (1-20) : (2-20) : (4-10) in terms of mass ratio; In step 1), the temperature of the water may be 50-60°C, preferably 55°C; the mass-volume concentration of the nickel sulfate hexahydrate may be 400-600 g / L, the mass-volume concentration of the nickel chloride may be 40-70 g / L, the mass-volume concentration of the boric acid may be 40-75 g / L, the mass-volume concentration of the sodium dodecyl sulfate may be 0.1-1 g / L, the mass-volume concentration of the saccharin may be 0.1-1.5 g / L, and the mass-volume concentration of the 1,4-butynediol may be 0.3-0.6 g / L; the boiling time may be 30-50 min, preferably 40 min; the pH is adjusted to 4.0 using a sulfuric acid solution with a mass-volume concentration of 30%, and after the pH is adjusted to 4.0, the solution is kept warm at 45-55°C for 8-12 h, preferably at 50°C for 10 h.

[0011] 2) Prepare lubricant liquid: put deionized water in a beaker, add lubricant dispersion and fluorocarbon surfactant in sequence and mix them by ultrasonic. The lubricant includes particles with lubricating properties such as polytetrafluoroethylene or molybdenum disulfide, and the particle size is 1 to 2 μm. In step 2), the ultrasonic time can be 20 to 30 minutes; the added amount of the oxidized lubricant dispersion can be 1 to 2.5 g / L in terms of mass-volume concentration, and the added amount of the fluorocarbon surfactant can be (10 to 30)×10-6 g / 1000L in terms of mass-volume concentration.

[0012] 3) Place the anode nickel plate into the anode basket and connect it to the positive electrode, place the lubricant liquid into the electroforming liquid, stir ultrasonically for 30 to 60 minutes, then connect the nickel original mold to the negative electrode, adjust the ultrasonic power to 210 to 300 W, the frequency to 20 to 50 kHz, adjust the current density to 2 to 3 A / dm2, electroform for 10 to 20 minutes, then turn off the ultrasonic power supply, continue electroplating for 8 to 12 hours, stop electroplating when the required thickness of the mold is reached, and obtain a high-quality mold after cathode demolding.

[0013] In step 3), the electroplating time is 8.5 to 13 hours, and the electroplating temperature is 45 to 55°C.

[0014] The microstructure on the nickel mold is transferred to the polymer surface by using a hot embossing machine, and then demolded to obtain a reflective film product.

[0015] In step 4), the hot stamping time is 5 to 10 seconds and the temperature is 200 to 250°C.

[0016] The present invention directly applies ultrasonic vibration excitation to the cathode plate at the beginning of electroplating to excite the high-frequency natural vibration mode of the cathode plate, and then applies the high-frequency vibration mode of the cathode plate to the electroplating solution to generate a high-frequency three-dimensional oscillating flow. The mechanism is as follows: the ultrasonic vibration of the cathode plate causes the electroplating solution to generate numerous eddies in its boundary layer, and the rotation direction thereof is alternately changed at the ultrasonic frequency, which makes the lubricant particles in the boundary layer more uniform, reduces the thickness of the boundary layer and the lubricant concentration gradient, reduces the concentration polarization of the solution, and accelerates the process of the electrode reaction, thereby greatly improving the electrodeposition speed, uniformly distributing the lubricant, and also refining the grains and improving the hardness of the coating.

[0017] The present invention has the following outstanding advantages: At the same time, auxiliary electroforming demoulding and hot embossing demoulding are realized to increase the mold life and improve product quality.

[0018] In production, ultrasonic parameters can be easily adjusted using an ultrasonic power supply.

[0019] 3) In production, the electroplating method can be conveniently used to realize the electrodeposition of the mold passivation layer.

[0020] 4) The thickness and content of the passivation layer can be controlled by adjusting the electroplating parameters and component concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the schematic diagram of cathode vibration electroplating.

[0022] Figure 2 This is a micrograph of the mold surface after electroforming demoulding and a micrograph of the reflective film surface after hot embossing in this method. DETAILED DESCRIPTION

[0023] The following embodiments will further illustrate the present invention in conjunction with the accompanying drawings.

[0024] Example 1 Preparation of electroforming liquid: According to the total volume of the electroforming tank, weigh 450g of nickel sulfate, 40g of nickel chloride, 40g of boric acid, 0.5g of sodium dodecyl sulfate, 0.1g of saccharin and 0.3g of 1,4-butynediol. Add deionized water to the electroforming tank, heat it to 50°C, add the weighed nickel sulfate and nickel chloride in turn, stir and keep warm for 4h. Take another beaker, rinse with deionized water, dry it, add deionized water, stir and heat to boiling, add weighed boric acid and boil for 0.5h, then add sodium dodecyl sulfate, and after sodium dodecyl sulfate is fully dissolved, slowly pour it into the electroforming tank, add saccharin and butynediol to the casting tank, and then add deionized water to fill the electroforming tank, stir well, keep warm at 45°C for 12h, measure its pH value with pH test paper, and adjust it to pH=3.0 with 30% sulfuric acid solution. The casting liquid ensures mass-volume concentration: nickel sulfate 450g / L, nickel chloride 40g / L, boric acid 40g / L, sodium dodecyl sulfate 0.5g / L, saccharin 0.1g / L, butynediol 0.3g / L.

[0025] Prepare lubricant liquid: Take polytetrafluoroethylene particles with a size of 1 to 2 μm and a mass of 0.1 g, drop 1×10-9 g of fluorocarbon surfactant into it, prepare 0.1 L of the mixed solution, and then mix the above solution by ultrasonication for 20 minutes.

[0026] Electroplating: Place the anode nickel plate into the anode basket and connect it to the positive electrode, place the lubricant liquid into the electroforming liquid, ultrasonically stir for 30 minutes, then connect the nickel master mold to the negative electrode, adjust the ultrasonic power to 210W, the frequency to 20kHz, adjust the current density to 2A / dm2, electroplate for 20 minutes, then turn off the ultrasonic power and continue electroplating for 12 hours.

[0027] Post-processing of electroplated parts: plated parts out of the tank → demoulding → pure water washing multiple times → hot water washing → drying → hot pressing for 5s, the temperature is 200℃. Use electron microscope to test the microscopic morphology of the mold after two demoulding, such as Figure 2 (a) and Figure 2 As shown in (b), the surface is smooth and there is no demoulding tearing phenomenon.

[0028] Example 2 Preparation of nickel sulfate electroforming solution: According to the total volume of the electroforming tank, first weigh 500g of nickel sulfate, 55g of nickel chloride, 50g of boric acid, 0.1g of sodium dodecyl sulfate, 0.8g of saccharin and 0.45g of 1,4-butynediol. Add deionized water to the electroforming tank, heat it to 55°C, add the weighed nickel sulfate and nickel chloride in turn, stir and keep warm for 3.5h. Take another beaker, rinse with deionized water, dry it, add deionized water, stir and heat to boiling, add weighed boric acid and boil for 40min, then add sodium dodecyl sulfate, and after sodium dodecyl sulfate is fully dissolved, slowly pour it into the electroforming tank, add saccharin and butynediol to the casting tank, and then add deionized water to fill the electroforming tank, stir well, keep warm at 50°C for 10h, measure its pH value with pH test paper, and adjust it to pH=4.0 with 30% sulfuric acid solution. The casting liquid ensures mass-volume concentration: nickel sulfate 500g / L, nickel chloride 55g / L, boric acid 50g / L, sodium dodecyl sulfate 0.1g / L, saccharin 0.8g / L, butynediol 0.45g / L.

[0029] Prepare lubricant liquid: Take polytetrafluoroethylene particles with a size of 1.5 μm and a mass of 0.15 g, drop them into a fluorocarbon surfactant with a mass-volume concentration of 2×10-9 g, prepare 0.1 L of the mixed solution, and then mix the above solution by ultrasonication for 25 minutes.

[0030] Electroplating: Place the anode nickel plate into the anode basket and connect it to the positive electrode, place the lubricant liquid into the electroforming liquid, stir ultrasonically for 45 minutes, then connect the nickel master mold to the negative electrode, adjust the ultrasonic power to 300W, the frequency to 50kHz, adjust the current density to 2.5A / dm2, electroplate for 15 minutes, then turn off the ultrasonic power and continue electroplating for 10 hours.

[0031] Post-processing operations of electroplated parts: plated parts out of the tank → demoulding → pure water washing multiple times → hot water washing → drying → hot pressing for 8s, temperature is 220℃.

[0032] Example 3 Preparation of nickel sulfate electroforming solution: According to the total volume of the electroforming tank, first weigh 600g of nickel sulfate, 70g of nickel chloride, 75g of boric acid, 1g of sodium dodecyl sulfate, 1.5g of saccharin and 0.6g of 1,4-butynediol. Add 1 / 2 volume of deionized water to the electroforming tank, heat it to 60°C, add weighed nickel sulfate and nickel chloride in turn, stir and keep warm for 3h. Take another beaker, rinse with deionized water, dry it, add deionized water, stir and heat to boiling, add weighed boric acid and boil for 50min, then add sodium dodecyl sulfate, and after sodium dodecyl sulfate is fully dissolved, slowly pour it into the electroforming tank, add saccharin and butynediol to the casting tank, and then add deionized water to fill the electroforming tank, stir well, keep warm at 55°C for 8h, measure its pH value with pH test paper, and adjust to pH=5.0 with 30% sulfuric acid solution. The casting liquid has the following guaranteed mass-volume concentrations: nickel sulfate 600 g / L, nickel chloride 70 g / L, boric acid 75 g / L, sodium dodecyl sulfate 1 g / L, saccharin 1.5 g / L, butynediol 0.6 g / L.

[0033] Prepare lubricant liquid: Take molybdenum disulfide particles with a size of 2 μm and a mass of 0.25 g, drop them into a fluorocarbon surfactant with a mass-volume concentration of 3×10-9 g, prepare 0.1 L of the mixed solution, and then mix the above solution by ultrasonication for 30 minutes.

[0034] Pretreatment of anode and cathode: Place the anode nickel plate in hydrochloric acid for 25 minutes. After the surface is fully activated, rinse it with deionized water.

[0035] Electroplating: Place the anode nickel plate into the anode basket and connect it to the positive electrode, place the lubricant liquid into the electroforming liquid, ultrasonically stir for 60 minutes, then connect the nickel original mold to the negative electrode, adjust the ultrasonic power to 300W, the frequency to 40kHz, adjust the current density to 3A / dm2, electroplate for 20 minutes, then turn off the ultrasonic power and continue electroplating for 8 hours.

[0036] Post-processing operations of electroplated parts: plated parts out of the tank → demoulding → pure water washing multiple times → hot water washing → drying → hot pressing for 10s, the temperature is 250℃.

Claims

1. An ultrasonic-assisted electrodeposition process for preparing a microstructured optical mold with surface passivation performance, characterized in that: The following steps are involved: Step S1, preparing an electroforming solution: adding deionized water to an electroforming tank, then adding nickel sulfate hexahydrate and nickel chloride in sequence, adding deionized water to a container and then heating it, then adding boric acid and boiling it, then adding sodium dodecyl sulfate, and pouring it into the electroforming tank after dissolving, adding saccharin and 1,4-butynediol to the electroforming tank, then injecting deionized water to fill the electroforming tank, and adjusting the pH to 3.0-5.0; the amount of the nickel sulfate hexahydrate, nickel chloride, boric acid, sodium dodecyl sulfate, saccharin and 1,4-butynediol added is (6000-12000) : (600-1400) : (600-1500) : (1-20) : (2-20) : (4-10) in terms of mass ratio; Step S2, preparing lubricant liquid: putting deionized water in a beaker, adding lubricant dispersion liquid and fluorocarbon surfactant in sequence, and then ultrasonically mixing, wherein the lubricant is particles having lubricity itself; Step S3, placing the anode nickel plate into the anode basket and connecting it to the positive electrode, placing the lubricant liquid into the electroforming liquid, ultrasonically stirring, and then connecting the nickel original mold to the negative electrode, adjusting the ultrasonic power to 210-300W, the frequency to 20-50kHz, and the current density to 2-3A / dm2, electroforming for 10-20min, then turning off the ultrasonic power supply, continuing electroplating for 8-13h, stopping electroplating after reaching the required thickness of the mold, and obtaining a high-quality mold after cathode demolding. Step S4: using a hot embossing machine to perform hot embossing to transfer the microstructure on the nickel mold to the polymer surface, and demolding to obtain a reflective film product.

2. The ultrasonic-assisted electrodeposition process for preparing a microstructure optical mold with surface passivation performance according to claim 1, characterized in that: The size of the lubricating particles is 1 to 2 μm.

3. The ultrasonic-assisted electrodeposition process for preparing a microstructure optical mold with surface passivation performance according to claim 2, characterized in that: The temperature of adding deionized water into the container and then heating is 50-60° C., the mass-volume concentration of nickel sulfate hexahydrate is 400-600 g / L, the mass-volume concentration of nickel chloride is 40-70 g / L, the mass-volume concentration of boric acid is 40-75 g / L, the mass-volume concentration of sodium dodecyl sulfate is 0.1-1 g / L, the mass-volume concentration of saccharin is 0.1-1.5 g / L, and the mass-volume concentration of 1,4-butynediol is 0.3-0.6 g / L; the boiling time is 30-50 min, the pH is adjusted to 4.0 using a sulfuric acid solution with a mass-volume concentration of 30%, and after the pH is adjusted to 4.0, the temperature is kept at 45-55° C. for 8-12 hours.

4. The ultrasonic-assisted electrodeposition process for preparing a microstructure optical mold with surface passivation performance according to claim 3, characterized in that: The temperature of adding deionized water into the container and then heating is 55° C., the boiling time is 40 minutes, and the pH is adjusted to 4.0 and then kept warm at 50° C. for 10 hours.

5. The ultrasonic-assisted electrodeposition process for preparing a microstructure optical mold with surface passivation performance according to claim 2, characterized in that: The ultrasonic time is 20 to 30 minutes; the added amount of the lubricant dispersion is 1 to 2.5 g / L in terms of mass-volume concentration, and the added amount of the fluorocarbon surfactant is (10 to 30)×10-6 g / 1000L in terms of mass-volume concentration.

6. The ultrasonic-assisted electrodeposition process for preparing a microstructure optical mold with surface passivation performance according to claim 1, characterized in that: The electroplating time is 8.5 to 13 hours, and the electroplating temperature is 45 to 55°C.

7. The ultrasonic-assisted electrodeposition process for preparing a microstructure optical mold with surface passivation performance according to claim 1, characterized in that: The hot stamping time is 5 to 10 seconds, and the temperature is 200 to 250°C.

8. The ultrasonic-assisted electrodeposition process for preparing a microstructure optical mold with surface passivation performance according to claim 1, characterized in that: The ultrasonic stirring time is 30 to 60 minutes.

9. The ultrasonic-assisted electrodeposition process for preparing a microstructure optical mold with surface passivation performance according to claim 2, characterized in that: The particles with lubricating properties are polytetrafluoroethylene.

10. The ultrasonic-assisted electrodeposition process for preparing a microstructure optical mold with surface passivation performance according to claim 2, characterized in that: The particles having lubricating properties are molybdenum disulfide.

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