An electrostatic spraying film and its preparation method

Abstract

The present application relates to a kind of electrostatic spray film and its preparation method, belong to surface spraying processing technical field.A kind of electrostatic spray film, transparent conductive layer and electrostatic spray layer are sequentially arranged from bottom to top based on substrate surface;Substrate is one of glass, polyethylene terephthalate, polyimide material;Transparent conductive layer is one of doped aluminum zinc oxide, silver nanowire;The main component of electrostatic spray layer film-forming substance is one or two of SiO2, TiO2.The method includes the following steps: remove oil dirt and dust on the surface of substrate, dry moisture of substrate after cleaning and cool to below 40 DEG C;Preparation transparent conductive layer on the surface of substrate;By electrostatic spray equipment, spray electrostatic spray layer on transparent conductive layer and solidification.The present application is high to coating utilization rate, less pollution to atmosphere, and high coating efficiency, easy to automate flow operation.The quality of coating film is good, charged coating particles are affected by electric field to produce embrace effect, and the coating film obtained is uniform, smooth and smooth.

Description

Technical Field

[0001] This invention relates to the field of surface spraying technology, specifically to an electrostatic spraying film and its preparation method. Background Technology

[0002] Spraying is an important method of coating. Compared with roller coating, scraping coating, and slot coating, spraying has a fast speed and can be applied not only to flat substrates, but also to substrates of other shapes.

[0003] Electrostatic spraying is a spraying method that uses a high-voltage electrostatic field to cause paint particles to move directionally under the influence of the electric field, and then adsorb the paint particles onto the surface of a workpiece with opposite charges. Electrostatic coating can be carried out in an electrostatic spraying chamber, greatly improving the coating environment and offering advantages such as high paint utilization and high coating efficiency. In electrostatic coating, paint particles are adsorbed onto the workpiece surface by the force of the electric field, significantly reducing scattering and rebound, thus greatly improving paint utilization—1 to 2 times higher than air spraying.

[0004] Patent application number 201510036343.8 uses Q235 steel as a substrate. First, an epoxy resin layer is brushed on, then SiO2 mixed powder is electrostatically sprayed onto it. The electrostatic spraying voltage is 50-60 V, forming a particle size gradient from the surface inwards to prepare a composite wear-resistant coating. This technical solution is a low-pressure spraying method, which is not conducive to air ionization and cannot efficiently charge and fully disperse the SiO2 mixed powder, thus hindering the improvement of film uniformity.

[0005] Application number 202110539374.0 discloses an electrostatic spraying apparatus and a method for preparing large-area thin films using the apparatus. During the spraying process, a thermally conductive glass plate is covered with aluminum foil and grounded. A spraying needle connected to the positive terminal of a high-voltage power supply moves along a pre-set zigzag pattern, spraying the coating solution onto the substrate surface on a heating unit at 10-20 kV to form a film. The spraying time is 3-6 hours. This technical solution uses a moving spraying needle for coating, and the excessively long spraying time results in low production efficiency, making it unsuitable for continuous production lines. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing spraying processes in the preparation of coatings for transparent substrates, such as poor film formation, uneven coating, and low spraying efficiency, by providing an electrostatic spraying film and its coating method. It adopts the following technical solution:

[0007] An electrostatic spraying film layer has a film structure based on a transparent conductive layer and an electrostatic spraying layer sequentially arranged from the inside to the outside on the surface of a substrate; the substrate is one of glass, polyethylene terephthalate, and polyimide; the substance constituting the transparent conductive layer is one of aluminum-doped zinc oxide and silver nanowires; the main component of the electrostatic spraying coating film is one or two of SiO2 and TiO2.

[0008] Furthermore, the coating solution used to prepare the transparent conductive layer with aluminum-doped zinc oxide has the following composition by mass fraction: 12.5%~16.5% zinc acetate dihydrate, 0.085%~0.185% aluminum nitrate nonahydrate, 75.2%~85.6% ethylene glycol methyl ether, and 3.20%~4.90% diethanolamine; the curing temperature of the film layer is 500℃~600℃, the holding time is 0.2 h~2 h, and the sheet resistance of the transparent conductive layer with aluminum-doped zinc oxide is 5 Ω / □~25 Ω / □.

[0009] Furthermore, the silver nanowire dispersion used in the transparent conductive layer prepared by silver nanowires has a mass concentration of 0.10%~3.50%, the silver nanowires have a diameter of 5 nm~30 nm and a length of 1 μm~20 μm, and the dispersant used is one of ethanol, isopropanol, and ethylene glycol; the sheet resistance of the silver nanowire conductive layer is 10 Ω / □~30 Ω / □.

[0010] Furthermore, the resistivity of the coating liquid used in the electrostatic spraying coating is 10–40 MΩ·cm, and the kinematic viscosity at room temperature is 20–60 mm² / s; the mass ratio of raw materials used in the preparation of the coating liquid is: 85%–95% SiO2 sol or TiO2 sol or a mixture of the two, 3%–9% antistatic agent, and 0.5%–2.5% nano-SiO2 particles or nano-TiO2 particles or a mixture of the two; wherein the antistatic agent is one or more of polyethylene oxide and hydrophilic organosilanes, the particle size range of the added nano-SiO2 particles is 5 nm–50 nm, and the particle size range of TiO2 particles is 5 nm–60 nm.

[0011] A method for preparing an electrostatic spray coating film is provided, which is prepared using an electrostatic spraying equipment. The equipment includes a set of metal conveyor rollers, on which an electrostatic spraying chamber and a curing oven are arranged in sequence. The electrostatic spraying chamber is equipped with a ventilation device. The electrostatic spraying chamber is equipped with a set of spray guns arranged side by side along the width direction of the substrate. The spray guns can move back and forth at a certain speed in the direction parallel to the rollers and can be vertically moved to adjust the height from the workpiece to be sprayed. The curing oven is equipped with a heating element.

[0012] The preparation method includes the following steps:

[0013] S1. Remove oil and dust from the surface of the substrate, dry the cleaned substrate and cool it to below 40°C;

[0014] S2. A transparent conductive layer is prepared on the surface of the substrate. The transparent conductive layer is made of aluminum-doped zinc oxide and the curing temperature is 500℃~600℃ and the holding time is 0.2 h~2 h. The transparent conductive layer is made of silver nanowires and the curing temperature is 40℃~90℃ and the holding time is 2 min~20 min.

[0015] S3. Apply an electrostatic spraying layer to the transparent conductive layer using an electrostatic spraying device and then cure it.

[0016] The advantages of this invention compared to the prior art are as follows:

[0017] In this invention, charged paint particles exhibit a wrapping effect under the influence of an electric field. That is, as the paint is atomized by the electrostatic spray gun, it acquires a static charge. Under the influence of the electrostatic field, a larger proportion of the charged paint particles reach the grounded workpiece without deviating from the target or being carried away by the surrounding airflow. This results in high paint utilization, less air pollution, and high coating efficiency. This electrostatic coating method allows for fixed spray gun positions or horizontal movement relative to the workpiece's direction of motion, facilitating automated assembly line operations. The coating liquid used for the surface film combines compatibility with electrostatic spraying processes and film-forming properties, resulting in a uniform and smooth film layer. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of an electrostatic spraying film layer according to the present invention;

[0019] Figure 2 This is a front view schematic diagram of the electrostatic spraying equipment of the present invention;

[0020] Figure 3 This is a top view schematic diagram of the electrostatic spraying equipment of the present invention;

[0021] Figure 4 SEM morphology image of the coating surface prepared in Example 1 of this invention;

[0022] Figure 5 SEM morphology image of the coating surface prepared in Example 2 of this invention;

[0023] Figure 6 SEM morphology image of the coating surface prepared in Example 3 of this invention;

[0024] Figure 7 SEM morphology image of the coating surface prepared in Example 4 of this invention.

[0025] Explanation of reference numerals in the attached drawings: 1. Spray gun; 2. Substrate; 3. Metal conveyor roller; 4. Curing oven; 5. Heating element; 6. Electrostatic spraying chamber; 7. Ventilation device; 8. Online tracking reciprocating mechanism. Detailed Implementation

[0026] To make the present invention clearer, an electrostatic spraying film layer and its coating method according to the present invention will be further described below with reference to the accompanying drawings. The specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0027] like Figure 1 The diagram shows a cross-sectional structure of an electrostatic spraying film, wherein the film structure consists of a transparent conductive layer B and an electrostatic coating layer C arranged sequentially from bottom to top on the surface of a substrate A.

[0028] like Figure 2 , Figure 3 As shown, the electrostatic spraying equipment structure for applying an electrostatic coating layer C includes a set of metal conveyor rollers 3, which are used to transport the substrate 2 after it has been coated with a transparent conductive layer B. An electrostatic spraying chamber 6 and a curing oven 4 are sequentially arranged on the metal conveyor rollers 3. A ventilation device 7 is provided inside the electrostatic spraying chamber 6, with air inlets and outlets located on opposite sides of the chamber. An online tracking reciprocating mechanism 8 is provided inside the electrostatic spraying chamber 6, and a set of spray guns 1 arranged side-by-side along the width of the substrate are mounted on the mechanism 8. The spray guns 1 are located below the ventilation device 7 and are rotary cup electrostatic spray guns. The number of spray guns is determined according to the width of the substrate; two are shown in the figure. The online tracking reciprocating mechanism 8 is existing technology and often uses a combination of a servo motor and a linear reciprocating mechanism to form a precise horizontal and longitudinal reciprocating movement function, for example, commonly used in CNC gantry machine tools. The spray gun 1 can spray paint at a certain speed while moving forward or backward in the parallel roller direction via an online tracking reciprocating mechanism 8, and stops spraying when it reaches a set position and quickly returns to its original position to await the next workpiece. Using the online tracking reciprocating mechanism as the transmission mechanism allows for adjustment of the coating rate and film-forming properties by changing the relative speed of the spray gun in the horizontal direction with or against the workpiece, when changing the workpiece conveying speed is economically or technically unsuitable. When the spray gun moves in the same direction as the workpiece, the spraying time can be extended, increasing the coating film thickness without reducing the production rate; when the spray gun moves in the opposite direction, the spraying time can be shortened, reducing the coating film thickness. Furthermore, the spray gun can be vertically moved to adjust its height from the workpiece to accommodate electrostatic spraying coatings with different viscosities, particle sizes, and resistivities, promoting coating uniformity. The curing oven 4 is equipped with heating elements 5 for curing the sprayed film. Additionally, a paint return trough is located below the metal conveying rollers, where the received paint is filtered and returned to the paint tank (not shown in this structural diagram). Example 1

[0029] Using glass as the substrate, remove surface oil and dust, dry the cleaned glass, and cool it to below 40°C. Prepare a coating solution for the transparent conductive layer of aluminum-doped zinc oxide (AZO) by measuring 13.5% zinc acetate dihydrate, 0.135% aluminum nitrate nonahydrate, 79.0% ethylene glycol methyl ether, and 4.20% diethanolamine by mass fraction. The heat treatment temperature for coating is 520°C, and the holding time is 0.5 h to allow the film to crystallize and solidify. The sheet resistance of the AZO transparent conductive layer is 15~20 Ω / □, which is beneficial for serving as the positive electrode in electrostatic spraying and for timely conduction of the charge accumulated during the spraying process.

[0030] A surface film was prepared by electrostatic spraying based on the aforementioned transparent conductive layer. The raw material ratio of the coating solution for this film layer was: 93.8% SiO2 sol, 5% antistatic agent, and 1.2% nano-SiO2 particles; wherein the antistatic agent was polyethylene oxide, and the particle size range of the added nano-SiO2 particles was 5 nm ~ 50 nm; the resistivity of the coating solution used for the electrostatic spraying layer was 30 MΩ·cm, and the kinematic viscosity at room temperature was 50 mm² / s. A 300 mm × 300 mm glass substrate entered the electrostatic spraying chamber through a metal conveyor roller 3. Two evenly arranged rotary cup electrostatic spray guns were fixed above the metal conveyor roller in the spraying chamber 6, with a spraying voltage of 60 kV and a spraying distance of 20 cm. The substrate moves at a constant speed of 30 cm / s under the spray gun 1. The spray gun 1 is connected to the negative electrode and the spray flow rate is set to 220 cc / min. The paint delivered to the spray gun by the gear pump reaches the surface of the substrate under the dual impetus of electric field force and compressed air pressure. It forms a uniform coating on the surface of the transparent conductive layer by electrostatic attraction.

[0031] After spraying, the workpiece is conveyed out of the spraying chamber 6 and enters the curing oven 4 for curing at 250℃ to solidify the coating. Before and during spraying, the film and substrate are fully grounded through the electrostatic spraying equipment. The ventilation device 7 above the roller conveyor in the electrostatic spraying chamber has an air velocity controlled at 0.3–0.4 m / s to promptly remove residual spray. The coating image obtained by scanning electron microscopy is shown below. Figure 4 As shown, the secondary electron image exhibits uniform brightness, and the coating surface is smooth with no obvious undulations, only scattered particles adhering to it. The thickness of the obtained coating sample was measured to be 2.2 ± 0.1 μm, and the average visible light transmittance was 85 ± 1%. Example 2

[0032] A transparent conductive layer was prepared on the surface of a substrate according to Example 1. Then, a surface film was prepared by electrostatic spraying on this transparent conductive layer. The coating solution used for this film had the following raw material mass ratio: 94.0% TiO2 sol, 4.5% antistatic agent, and 1.5% nano-TiO2 particles; wherein the antistatic agent was polyethylene oxide, and the average particle size of the added nano-TiO2 particles was 15 nm ~ 25 nm; the resistivity of the coating solution used for the electrostatic spraying layer was 32 MΩ·cm, and the kinematic viscosity at room temperature was 37 mm² / s. A 300 mm × 300 mm glass substrate entered the electrostatic spraying chamber via a metal conveyor roller 3. Two evenly arranged rotary cup electrostatic spray guns were fixed above the metal conveyor roller in the spraying chamber 6, with a spraying voltage of 60 kV and a spraying distance of 18 cm. Spray gun 1 is connected to the negative terminal. When the substrate passes under spray gun 1 at a moving speed of 30 cm / s, the spray gun moves in the opposite direction to the substrate at a speed of 30 cm / s. The spray flow rate is set to 200 cc / min. The paint delivered to the spray gun by the gear pump reaches the substrate surface under the dual impetus of electric field force and compressed air pressure. A uniform coating is formed on the surface of the transparent conductive layer by electrostatic attraction. Then the spray gun stops spraying and returns to its original position, waiting for the next workpiece to enter the initial spraying position.

[0033] After spraying, the workpiece is conveyed out of the spraying chamber 6 and enters the curing oven 4 for curing at 250℃ to solidify the coating. Before and during spraying, the film and substrate are fully grounded through the electrostatic spraying equipment. The ventilation device 7 above the roller conveyor in the electrostatic spraying chamber has an air velocity controlled at 0.3–0.4 m / s to promptly remove residual spray. The coating image obtained by scanning electron microscopy is shown below. Figure 5 As shown, the secondary electron image exhibits uniform brightness, and the coating surface is smooth with no obvious undulations, only scattered particles adhering to it. The obtained coating sample has a thickness of 1.3±0.1 μm and an average visible light transmittance of 86±1%. Example 3

[0034] Using polyethylene terephthalate (PET) as the substrate, surface oil and dust were removed, and the cleaned substrate was dried and cooled to below 35°C. A transparent conductive layer was prepared on the PET substrate using silver nanowires. The silver nanowire dispersion had a mass concentration of 3.10%, with diameters ranging from 10 nm to 25 nm and lengths from 1 μm to 12 μm. Isopropanol was used as the dispersant. The curing temperature after coating was 80°C, and the holding time was 8 min. The sheet resistance of the silver nanowire conductive layer was 10 Ω / □ to 15 Ω / □, which facilitates its use as the positive electrode for electrostatic spraying, enabling timely conduction of the charge accumulated during the spraying process.

[0035] A surface film was prepared by electrostatic spraying based on the aforementioned transparent conductive layer. The coating solution for this film was prepared using the following raw material mass ratio: 93% SiO2 sol, 5% antistatic agent, and 2% nano-SiO2 particles; the antistatic agent was polyethylene oxide, and the added nano-SiO2 particles had a particle size range of 30 nm to 45 nm; the resistivity of the coating solution used for the electrostatic spraying layer was 27 MΩ·cm, and the kinematic viscosity at room temperature was 44 mm² / s. A 1000 mm × 300 mm PET substrate entered the electrostatic spraying chamber via a metal conveyor roller. Two evenly arranged rotary cup electrostatic spray guns were fixed above the conveyor roller in the spraying chamber, with a spraying voltage of 70 kV and a spraying distance of 25 cm. The substrate moves uniformly past the spray gun at a speed of 40 cm / s. The spray gun is connected to the negative electrode, creating an electric field between the spray gun and the substrate. The spray flow rate is set to 400 cc / min. The coating material, delivered to the spray gun by a gear pump, reaches the substrate surface under the combined force of the electric field and compressed air pressure. A uniform coating layer forms on the surface of the transparent conductive layer due to electrostatic attraction. The coating is then conveyed out of the spraying chamber and into a curing oven at 200℃ for curing. Before and during spraying, the film layer and substrate are fully grounded through the electrostatic spraying equipment. A ventilation device is installed above the roller conveyor in the electrostatic spraying chamber, and the air velocity should be controlled between 0.5 and 0.6 m / s to promptly remove residual spray. The secondary electron image of the coating obtained by scanning electron microscopy is shown below. Figure 6 As shown, due to the increase in the amount of nanoparticles added and the coating thickness, the relative Figure 4 and Figure 5 In terms of morphology, the surface is relatively rough, but the coating surface is still smooth without obvious undulations. The thickness of the obtained coating sample is 4.3±0.1 μm, and the average transmittance of visible light is 83±1%. Example 4

[0036] Using polyimide as the substrate, the surface is cleaned to remove oil and dust, then dried and cooled to below 35°C. The coating solution for the AZO transparent conductive layer is prepared by measuring 15.5% zinc acetate dihydrate, 0.175% aluminum nitrate nonahydrate, 78% ethylene glycol methyl ether, and 4.30% diethanolamine by mass fraction. The curing temperature is 580°C, and the holding time is 0.2 h. The resulting AZO transparent conductive layer has a sheet resistance of 5 Ω / □ ~ 15 Ω / □.

[0037] A surface film was prepared by electrostatic spraying based on the aforementioned transparent conductive layer. The coating solution for this film was prepared using the following raw material mass ratio: 90% SiO2 and TiO2 mixed sol (molar ratio 1.5:1), 7.5% antistatic agent, and 2.5% nano-SiO2 particles; the antistatic agent was an organosilane containing hydrophilic groups, and the added nano-SiO2 particles had a particle size range of 15 nm to 50 nm. The resistivity of the coating solution used for the electrostatic spraying layer was 25 MΩ·cm, and the kinematic viscosity at room temperature was 42 mm² / s. A 500 mm × 300 mm polyimide sheet entered the electrostatic spraying chamber via a metal conveyor roller. Two evenly arranged rotary cup electrostatic spray guns were fixed above the conveyor rollers inside the spraying chamber, with a spraying voltage of 80 kV and a spraying distance of 30 cm. The substrate moves uniformly at a speed of 50 cm / s beneath the spray gun. The electrostatic spray gun is connected to the negative electrode, creating an electric field between the spray gun and the substrate. The spray flow rate is set to 500 cc / min. The coating material, delivered to the spray gun by a gear pump, reaches the substrate surface under the combined force of the electric field and compressed air pressure. A uniform coating layer forms on the surface of the transparent conductive layer due to electrostatic attraction. The coating is then conveyed out of the spray chamber and into a curing oven at 250℃ for curing. Before and during spraying, the film layer and substrate are fully grounded through the electrostatic spraying equipment. A ventilation device covers the roller conveyor inside the electrostatic spraying chamber, and the air velocity should be controlled at 0.6–0.7 m / s to promptly remove residual spray. The secondary electron image of the coating obtained by scanning electron microscopy is shown below. Figure 7 As shown, due to the increase in the amount of nanoparticles added and the coating thickness, the relative Figure 4 and Figure 5 In terms of morphology, the surface is relatively rough. However, the coating surface is still smooth without obvious undulations. The thickness of the obtained coating sample is 6.2±0.1 μm, and the average transmittance of visible light is 80±1%.

[0038] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. However, obvious variations or modifications derived from the essential spirit of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for preparing an electrostatic spraying film layer, the film system structure of which is a transparent conductive layer and an electrostatic spraying layer arranged in turn from the inside to the outside based on the surface of a substrate; the substrate is one of glass, polyethylene terephthalate and polyimide material; the substance constituting the transparent conductive layer is aluminum-doped zinc oxide; the main component of the film-forming substance of the electrostatic spraying layer is SiO2; The coating solution used for preparing the transparent conductive layer prepared from aluminum-doped zinc oxide has the following composition by mass fraction: 12.5%-16.5% zinc acetate dihydrate, 0.085%-0.185% aluminum nitrate nonahydrate, 75.2%-85.6% ethylene glycol methyl ether, 3.20%-4.90% diethanolamine; the sheet resistance of the transparent conductive layer of aluminum-doped zinc oxide is 5Ω / □-25Ω / □; The resistivity of the coating solution used for the electrostatic spraying layer is 10-40MΩ·cm, and the kinematic viscosity at room temperature is 20-60mm² / s; the mass ratio of raw materials used for preparing the coating solution is: 85%-95% SiO2sol, 3%-9% antistatic agent, and 0.5%-2.5% nano-SiO2particles; the antistatic agent is one or several of polyethylene oxide and hydrophilic group-containing organosilane, and the added nano-SiO2particles have a particle size range of 5nm-50nm; characterized in that The electrostatic spraying equipment used for preparation includes a set of metal conveying roller (3), an electrostatic spraying chamber (6) and a curing furnace (4) arranged in turn on the metal conveying roller (3), a ventilation device (7) arranged in the electrostatic spraying chamber (6), an on-line tracking reciprocating mechanism (8) arranged in the electrostatic spraying chamber (6), a set of spraying guns (1) arranged side by side along the width direction of the substrate on the on-line tracking reciprocating mechanism (8), the spraying guns can move back and forth at a certain rate in the direction parallel to the roller, and can be vertically moved to adjust the height from the workpiece to be sprayed, and a heating element (5) arranged in the curing furnace (4); The method for preparing the electrostatic spraying film layer comprises the following steps: S1, removing oil stains and dust from the surface of the substrate, drying the cleaned substrate and cooling it to below 40℃; S2, preparing a transparent conductive layer on the surface of the substrate, wherein the transparent conductive layer adopts aluminum-doped zinc oxide, the film curing temperature of which is 500℃-600℃, and the holding time is 0.2h-2h; S3, spraying an electrostatic spraying layer on the transparent conductive layer by the electrostatic spraying equipment and curing.

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