Masking and stripping method for electrostatic painting and automated painting system

Abstract

The application relates to the technical field of automobile coating processing, and discloses a shielding peeling method for electrostatic spraying and an automatic coating system. The shielding peeling method comprises the following steps: setting a shielding area according to a preset coating effect of a workpiece, applying water-based shielding slurry to the shielding area, wherein the water-based shielding slurry comprises a peelable water-based acrylic emulsion, the peelable water-based acrylic emulsion contains silicon, drying the workpiece coated with the water-based shielding slurry to form a shielding film, electrostatically spraying powder coating on the surface of the workpiece, wherein the powder coating contains epoxy resin, the powder coating covers the shielding film, performing curing treatment on the workpiece electrostatically sprayed with the powder coating to obtain a shielding composite film, performing cooling treatment on the workpiece after the curing treatment, and peeling the shielding composite film to obtain the workpiece with the preset coating effect. The application has good shielding effect, the shielding film can be completely peeled without residues, and is suitable for automobile coating processes.

Description

Technical Field

[0001] This invention relates to the field of automotive coating processing technology, and in particular to a masking and peeling method and an automated coating system for electrostatic spraying. Background Technology

[0002] During the manufacturing process of automotive parts, the surface of the parts needs to be sprayed, such as with paint or powder, to improve the gloss and appearance of the parts. During the spraying process, non-sprayed areas (masked areas) are masked for protection. Masking protection generally uses cloth tape, high-temperature masking tape, PVC tape, and aluminum foil tape, as well as matching masking paper and masking film.

[0003] To facilitate powder coating application, high-temperature tapes or masking films that can withstand high temperatures are generally selected. The tapes are suitable for various complex shapes and are easy to use. However, high-temperature tapes tend to melt and adhere to the powder coating at high temperatures, resulting in high peeling resistance and easy residue, which can damage the workpiece substrate and the surface of the formed coating. Moreover, the manual application, removal, and residue cleaning processes are cumbersome, resulting in high labor costs and low production efficiency.

[0004] Chinese patent CN 113583328 A discloses a high-temperature resistant protective film suitable for automotive paint masking. The high-temperature resistant protective film comprises: 34.60-36.80% polyethylene resin, 9.60-10.60% silicone resin, 0.30-0.50% antioxidant, 0.30-0.50% UV absorber, 15.50-17.30% composite modified filler, and the remainder being organic solvent. It can effectively improve the high-temperature resistance, anti-aging properties, and peel-off removal effect of the high-temperature resistant protective film for automotive paint masking, preventing masking film damage and residue on the car surface. This patent utilizes a high-temperature resistant hydrogel composite incorporated into a masking film. After drying and cooling, the masking film can be directly sprayed with water to induce swelling, improving its surface wetting and expansion properties. This allows for rapid separation of the masking film from the car surface, preventing residue. It is suitable for automotive painting processes where painting involves baking at 150°C for 30 minutes. However, powder coatings typically cure at temperatures as high as 220°C. The patented high-temperature protective film is ill-suited to the high-temperature curing requirements of powder coatings, leading to easy damage, peeling, difficulty in tearing, and residual powder. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a masking and peeling method for electrostatic spraying, which has a good masking effect, the masking film is easy to peel off, and can be completely peeled off without residue.

[0006] The technical problem that this invention also aims to solve is to provide an automated coating system that enables automated coating of automotive workpiece surfaces.

[0007] To address the aforementioned problems, a masking and stripping method for electrostatic spraying includes the following steps: The masking area is set according to the preset coating effect of the workpiece, and an aqueous masking paste is applied to the masking area. The aqueous masking paste includes a peelable aqueous acrylic emulsion, which contains silicone. The workpiece coated with water-based masking slurry is dried to form a masking film; An electrostatic powder coating is applied to the surface of a workpiece, the powder coating containing epoxy resin, and the powder coating covers the masking film. A workpiece coated with electrostatic powder coating is cured to obtain a masking composite film; the hydroxyl or epoxy groups of the powder coating form an interfacial bond structure with the carboxyl groups of the peelable waterborne acrylic emulsion. Cool the workpiece after it has been cured. The masking composite film is peeled off to obtain a workpiece with the preset coating effect.

[0008] As an improvement to the above technical solution, the hydroxyl or epoxy groups of the epoxy resin in the powder coating react with the residual carboxyl groups of the silicone-containing peelable waterborne acrylic emulsion to form ester bonds.

[0009] As an improvement to the above technical solution, the peelable waterborne acrylic emulsion is a silicone-modified acrylic emulsion, which is obtained by the polymerization reaction of silicone monomers and acrylic emulsion. The silicone content of the peelable waterborne acrylic emulsion is 2wt%~25wt%.

[0010] As an improvement to the above technical solution, the peelable waterborne acrylic emulsion is an organosilicon-modified acrylic emulsion, which is obtained by the polymerization reaction of siloxane monomers and acrylic emulsion. The silicone content of the peelable waterborne acrylic emulsion is 3wt%~20wt%.

[0011] As an improvement to the above technical solution, the organosilicon monomer is one or more of the following: triphenyl-hydroxysilane, (3-methacryloyloxy-2-hydroxypropoxy)propylbis(trimethylsiloxy)methylsilane, (3-epoxypropoxypropyl)dimethylethoxysilane, tris(epoxypropoxypropyldimethylsiloxy)phenylsilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and γ-methacryloyloxypropyltriethoxysilane.

[0012] As an improvement to the above technical solution, the pH value of the peelable aqueous acrylic emulsion is 3.5~6.0.

[0013] As an improvement to the above technical solution, the peelable waterborne acrylic emulsion is one or a combination of peelable waterborne soft acrylic emulsion and peelable waterborne hard acrylic emulsion, wherein the Tg of the peelable waterborne soft acrylic emulsion is -30℃ to 10℃, and the Tg of the peelable waterborne hard acrylic emulsion is 0℃ to 50℃.

[0014] As an improvement to the above technical solution, the peelable waterborne acrylic emulsion includes a peelable waterborne soft acrylic emulsion and a peelable waterborne hard acrylic emulsion, wherein the weight ratio of the peelable waterborne soft acrylic emulsion to the peelable waterborne hard acrylic emulsion is 1:1 to 2:1.

[0015] As an improvement to the above technical solution, the water-based masking slurry comprises the following raw materials in parts by weight: 35 to 100 parts of peelable water-based acrylic emulsion, 0 to 8 parts of functional additives, and 0 to 14 parts of inorganic filler.

[0016] As an improvement to the above technical solution, the water-based masking slurry comprises the following raw materials in parts by weight: 35 to 100 parts of peelable water-based acrylic emulsion, 2 to 8 parts of functional additives, and 4 to 14 parts of inorganic filler.

[0017] As an improvement to the above technical solution, the functional additives include one or more of film-forming aids, wetting agents, defoamers, neutralizers, thickeners, and functional color pastes.

[0018] As an improvement to the above technical solution, the curing temperature of the powder coating is 120℃~220℃, and the curing time is 8min~30min; The drying temperature of the water-based masking slurry is 40℃~150℃, and the drying time is 5min~60min.

[0019] As an improvement to the above technical solution, the epoxy resin accounts for 20% to 90% of the powder coating by weight.

[0020] As an improvement to the above technical solution, the powder coating is selected from one or more of pure epoxy powder coating, epoxy polyester powder coating, and epoxy acrylic powder coating.

[0021] As an improvement to the above technical solution, the pure epoxy powder coating is mainly composed of 55%~80% epoxy resin, 5%~10% curing agent, 5%~10% functional additives and 0%~30% filler by weight percentage. The epoxy polyester powder coating is mainly composed of 25%~50% carboxylated polyester, 25%~50% epoxy resin, 5%~10% functional additives and 0%~30% filler. The epoxy acrylic powder coating is mainly composed of 25%~50% epoxy resin, 25%~50% acrylic resin, 5%~10% functional additives and 0%~30% filler.

[0022] As an improvement to the above technical solution, the D of the powder coating 50 The range is 20μm to 70μm; The thickness of the shielding film is 30μm~120μm; The thickness of the powder coating is 60μm~450μm.

[0023] Accordingly, the present invention also discloses an automated coating system that performs the above-described masking and stripping method for electrostatic spraying, comprising a transmission module, a coating module, a drying module, a spraying module, a curing module, a cooling module, and a stripping module; wherein the coating module, drying module, spraying module, curing module, cooling module, and stripping module are sequentially connected via the transmission module; The coating module is used to apply water-based masking slurry to the masked area; The drying module is used to dry the workpiece coated with water-based masking slurry; The spraying module is used for electrostatic spraying of powder coating on the surface of the workpiece; The curing module is used to cure workpieces coated with electrostatic powder coating. The cooling module is used to cool the workpiece after it has been cured. The peeling module is used to peel off the masking composite film; The transmission module is used for conveying the workpiece.

[0024] Implementing this invention has the following beneficial effects: The masking and peeling method for electrostatic spraying provided by the present invention first applies an aqueous masking slurry to the masking area to form a masking film; then sprays powder coating, and after curing, obtains a masking composite film; after cooling, the masking composite film is peeled off. This method can be adapted to the high-temperature working conditions of electrostatic powder spraying and realizes continuous operation of the entire process of masking, spraying, curing, and automatic peeling.

[0025] First, the water-based masking slurry is evenly applied to the non-coated masking area of ​​the workpiece to ensure uniform coating without any missed areas or sagging defects. The water-based masking slurry used in the masking film is a peelable water-based acrylic emulsion containing silicone. After drying, the masking film formed on the workpiece has low adhesion to the workpiece and is easy to peel off, providing a stable structural basis for the subsequent interfacial reaction with the powder coating.

[0026] Secondly, during the curing process, the powder coating and masking film of electrostatic spraying form an interfacial bond structure. The residual carboxyl groups of the silicone-containing peelable waterborne acrylic emulsion react with the hydroxyl or epoxy groups of the epoxy resin in the powder coating to form ester bonds. The adhesion between the powder coating and the masking film is greater than the adhesion between the masking film and the workpiece. This ensures that the masking film does not fall off during the high-temperature curing process and also prevents the molten powder resin from penetrating into the film layer. This ensures that the masking film is easy to peel off and can be completely peeled off without residue.

[0027] Secondly, after the powder coating has cured, it is cooled down. By utilizing the difference in the coefficient of thermal expansion between the masking composite film and the workpiece, the masking composite film undergoes linear shrinkage, which greatly reduces the overall peeling resistance of the masking composite film and achieves complete peeling of the masking composite film.

[0028] Therefore, this method has a good masking effect, the masking film is easy to peel off, and it can be completely peeled off without residue, meeting the needs of high-quality coating for automotive parts and new energy power battery module components. Attached Figure Description

[0029] Figure 1 This is a schematic flowchart of the masking and stripping method for electrostatic spraying provided by the present invention. Figure 2 This is a schematic diagram of the flat workpiece after the shielding film is formed in Application Example 1 of the present invention; Figure 3 This is a schematic diagram of the powder coating masking composite film in Application Example 1 of the present invention; Figure 4 This is a schematic diagram of the peeled-off masking composite film in Application Example 1 of the present invention; Figure 5 This is a schematic diagram of the finished workpiece in Application Example 1 of the present invention; Figure 6 This is a schematic diagram of the finished workpiece in Application Example 2 of the present invention; Figure 7 This is a schematic diagram of the finished workpiece in Example 3 of the application of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below.

[0031] This invention provides a masking and peeling method for electrostatic spraying, which provides good masking effect, easy peeling of the masking film, and complete peeling without residue, making it suitable for automotive painting processes. Figure 1 As shown, the masking and stripping method includes the following steps: S1. Set the masking area according to the preset coating effect of the workpiece, and apply water-based masking paste to the masking area. The water-based masking paste includes a peelable water-based acrylic emulsion, which contains silicone.

[0032] Water-based masking slurry is applied to the masked area using methods such as spraying, roller coating, dip coating, and brush coating. Spraying uses compressed air to atomize the water-based masking slurry and spray it onto the workpiece surface through a spray gun, resulting in high efficiency, a uniform and smooth coating, and suitability for complex-shaped workpieces. Roller coating uses rotating rollers to evenly transfer the water-based masking slurry onto a flat substrate, suitable for large-area operations on factory production lines, saving paint and eliminating air pollution. Dip coating involves completely immersing the workpiece in a tank containing water-based masking slurry, ensuring no dead corners, high efficiency, simple equipment, and high paint utilization. Brush coating uses a brush to apply the water-based masking slurry by wiping, offering simple tools, high flexibility, paint savings, and good adhesion.

[0033] The workpiece can be made of one or more of the following: metal, plastic, glass, and synthetic fiber composite materials.

[0034] The masking and peeling method for electrostatic spraying provided by this invention first involves uniformly applying an aqueous masking slurry to the non-coated masking area of ​​the workpiece, ensuring uniform coating without missed areas or sagging defects, thus forming a masking film. Ordinary acrylic emulsions are prone to defects such as tensile fracture, discontinuous film formation, pinholes, and craters, exhibiting poor masking stability and difficulty in adapting to the high-temperature curing process of powder coatings. This results in uncontrollable peeling force, leading to problems such as difficulty in film removal and peeling, and residual powder.

[0035] The peelable waterborne acrylic emulsion of the present invention comprises a silicone-modified acrylic emulsion, which is obtained by polymerization of silicone monomers and acrylic emulsion. In the acrylic emulsion, acrylic polymers are the main component, providing excellent film-forming properties, weather resistance, and water resistance. The addition of silicone monomers imparts low surface tension to the coating. The masking film formed on the workpiece after drying has low adhesion to the workpiece, is easy to peel off, and provides a stable structural basis for subsequent interfacial reactions with powder coatings.

[0036] Preferably, the peelable aqueous acrylic emulsion includes a silicone-modified acrylic emulsion, which is obtained by polymerization of a siloxane monomer and an acrylic emulsion.

[0037] In some embodiments, the organosilicon monomer is one or more of the following: triphenyl-hydroxysilane, (3-methacryloyloxy-2-hydroxypropoxy)propylbis(trimethylsiloxy)methylsilane, (3-epoxypropoxypropyl)dimethylethoxysilane, tris(epoxypropoxypropyldimethylsiloxy)phenylsilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and γ-methacryloyloxypropyltriethoxysilane, but is not limited thereto.

[0038] In some embodiments, the organosilicon monomer includes a first organosilicon monomer and a second organosilicon monomer, wherein the ratio of the first organosilicon monomer to the second organosilicon monomer is 3:1 to 1:3. The first organosilicon monomer is one or more of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and γ-methacryloyloxypropyltriethoxysilane, but is not limited thereto. The second organosilicon monomer is one or more of triphenyl-hydroxysilane, (3-methacryloyloxy-2-hydroxypropoxy)propylbis(trimethylsiloxy)methylsilane, (3-epoxypropoxypropyl)dimethylethoxysilane, and tris(epoxypropoxypropyldimethylsiloxy)phenylsilane, but is not limited thereto.

[0039] In the polymerization reaction between organosilicon monomers and acrylic emulsions, the first organosilicon monomer is vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, etc., which provides peelability and flexibility. The second organosilicon monomer is triphenyl-hydroxysilane, (3-methacryloyloxy-2-hydroxypropoxy)propylbis(trimethylsiloxy)methylsilane, etc., whose hydroxyl groups can act as reactive sites, partially condensing with the acrylic monomer to prevent the migration and precipitation of the first organosilicon monomer and improve the stability of the polymerization process.

[0040] In some embodiments, the silicone content of the peelable waterborne acrylic emulsion is 2wt%~25wt%, preferably 3wt%~20wt%, and more preferably 3wt%~15wt%. The silicone can spontaneously migrate to the film surface after film formation to form a siloxane barrier layer, blocking the deep penetration of the powder resin. If the silicone content is less than 2wt%, the release effect is insufficient, resulting in high adhesion to the workpiece. Furthermore, molten powder coatings easily penetrate into the film layer, producing residual powder and adhesive. If the silicone content is greater than 25wt%, the film surface energy is too low, and the film layer easily peels off in whole pieces during the electrostatic spraying stage.

[0041] It is understandable that silicone monomer-modified acrylic emulsions are formed through a copolymerization reaction between acrylic monomers and silicone monomers. The amount of acrylic monomer added is 75wt%~98wt%, and the amount of silicone monomer added is 2wt%~25wt%.

[0042] Examples of the amounts of acrylic monomer added are 75 wt%, 78 wt%, 80 wt%, 82 wt%, 85 wt%, 88 wt%, 90 wt%, 92 wt%, 95 wt%, and 98 wt%, but are not limited thereto. Preferably, the amount of acrylic monomer added is 80 wt% to 97 wt%. More preferably, the amount of acrylic monomer added is 85 wt% to 97 wt%.

[0043] Examples of the amounts of silicone monomers added are 2 wt%, 4 wt%, 5 wt%, 8 wt%, 10 wt%, 13 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, and 25 wt%, but are not limited thereto. Preferably, the amount of silicone monomers added is 3 wt% to 20 wt%. More preferably, the amount of silicone monomers added is 3 wt% to 15 wt%.

[0044] The acrylic monomer may be one or more of methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, and hydroxyethyl methacrylate.

[0045] Acrylic monomers and organosilicon monomers undergo a copolymerization reaction to form an organosilicon-modified acrylic emulsion. The residual carboxyl groups react with the hydroxyl or epoxy groups in the powder coating to form an interfacial bond structure. In some embodiments, the residual carboxyl group content is controlled by adjusting the pH value of the peelable aqueous acrylic emulsion to improve the stability of the interfacial bond structure formed with the powder coating. The pH value of the organosilicon-modified acrylic emulsion is 3.5–6.0. ​​Preferably, the pH value of the organosilicon-modified acrylic emulsion is 4.0–6.0. ​​More preferably, the pH value of the organosilicon-modified acrylic emulsion is 4.5–5.5.

[0046] If the pH is too low, there will be too many residual carboxyl groups, which will reduce the water resistance and increase the viscosity of the masking film after drying, thus adversely affecting the performance of the masking film. If the pH is too high, the carboxyl groups will be consumed through cross-linking reaction, making it difficult to form a stable interfacial bond structure with the powder coating.

[0047] Optionally, the peelable waterborne acrylic emulsion is one or a combination of peelable waterborne soft acrylic emulsion and peelable waterborne hard acrylic emulsion. The peelable waterborne soft acrylic emulsion is used to construct the flexible main framework of the film layer, match the interfacial adhesion of the powder coating, resist high-speed impact from electrostatic powder, and prevent the film layer from peeling off. Preferably, the Tg of the peelable waterborne soft acrylic emulsion is -30℃ to 10℃, more preferably -25℃ to 0℃, and even more preferably -25℃ to -5℃, which is beneficial for forming a soft and tough, rather than hard and brittle, masking film that is easy to peel off.

[0048] However, in some embodiments, the coefficient of thermal expansion of the peelable water-based soft acrylic emulsion is close to that of metal components such as aluminum alloys, resulting in poor release performance. This embodiment uses a combination of a peelable water-based hard acrylic emulsion and a peelable water-based soft acrylic emulsion to simultaneously solve problems such as difficult film formation, brittle texture, low strength, poor heat resistance, easy sticking, and poor release performance, achieving high-temperature resistance and anti-adhesion, thereby ensuring easy peeling of the masking film. Preferably, the Tg of the water-based hard acrylic emulsion is 0℃~50℃, more preferably 5℃~40℃, and even more preferably 20℃~30℃, which can improve the high-temperature resistance, anti-adhesion, and water resistance of the film layer, achieving high-temperature resistance of 200℃~220℃. The peelable water-based hard acrylic emulsion provides good cohesive strength, achieving high-temperature resistance and anti-adhesion, thereby ensuring easy peeling of the masking film. The large difference in the coefficient of thermal expansion between the water-based hard acrylic emulsion and metal components such as aluminum alloys facilitates release.

[0049] Preferably, the peelable waterborne acrylic emulsion includes a peelable waterborne soft acrylic emulsion and a peelable waterborne hard acrylic emulsion, wherein the weight ratio of the peelable waterborne soft acrylic emulsion to the peelable waterborne hard acrylic emulsion is 1:1 to 2:1, with exemplary ratios of 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, and 2:1, but not limited thereto. By controlling the mass ratio of the peelable waterborne soft acrylic emulsion to the peelable waterborne hard acrylic emulsion, problems such as difficult film formation, brittle texture, low strength, poor heat resistance, easy stickiness, and poor release effect can be solved simultaneously, achieving a synergistic improvement in the performance of the masking film layer and the release effect.

[0050] In some embodiments, the water-based masking paste comprises the following raw materials in parts by weight: 35 to 100 parts of peelable water-based acrylic emulsion, 0 to 8 parts of functional additives, and 0 to 14 parts of inorganic filler.

[0051] Preferably, the water-based masking paste comprises the following raw materials in parts by weight: 35 to 100 parts of peelable water-based acrylic emulsion, 2 to 8 parts of functional additives, and 4 to 14 parts of inorganic filler.

[0052] The inorganic filler has a weight ratio of 0 to 14 parts, preferably 4 to 14 parts, and more preferably 8 to 14 parts. The inorganic filler can fill the acrylic network. If the weight ratio of the inorganic filler is higher than 14 parts, the film rigidity is too high, and it is prone to breakage during peeling. Specifically, the inorganic filler can be one or more of nano-silica, nano-titanium dioxide, nano-alumina, zinc oxide powder, calcium silicate powder, aluminum hydroxide powder, and magnesium silicate powder.

[0053] The functional additives may include one or more of the following: film-forming aids, wetting agents, defoamers, pH adjusters, thickeners, and color pastes.

[0054] Among them, film-forming aids can ensure continuous film formation of each component at low temperatures and eliminate pinholes. Specifically, film-forming aids can be one or more of ethylene glycol, glycerol, and dodecyl alcohol ester.

[0055] Wetting agents can improve the wettability and spreadability of the substrate, preventing coating pinholes. Too low a weight percentage will result in poor wetting and discontinuous film layers; too high a weight percentage will increase air bubbles in the system, leading to pinhole defects. Specifically, polyether wetting agents or silicone wetting agents can be selected.

[0056] Defoamers are used to eliminate air bubbles in the coating process and prevent pinholes from causing the powder coating to directly adhere to the substrate. Insufficient defoamer leads to more pinholes, while excessive defoamer weakens the adhesion between the film and the substrate. Specifically, water-based polyether defoamers or modified silicone defoamers can be used.

[0057] Neutralizing agents are used to adjust the pH of the system, thereby controlling the thickness and quality of the film. Specifically, AMP-95 neutralizing agent can be selected.

[0058] Thickeners can adjust the viscosity for application and prevent sagging during vertical coating. Specifically, alkali-soluble thickeners can be selected.

[0059] Functional pigments give the film layer visual characteristics, making it suitable for automated visual positioning and recognition.

[0060] In one embodiment, based on the aqueous masking slurry, the functional additives comprise the following components in parts by weight: 1.5 to 3.5 parts film-forming aid, 0.1 to 1 part wetting agent, 0.1 to 1 part defoamer, 0.1 to 1 part neutralizer, 0.1 to 1 part thickener, and 0.1 to 2 parts functional color paste.

[0061] In the above formula, the solid content and application viscosity of the slurry are adjusted in conjunction with the mass fraction range of each component to control the film thickness and adapt to the interfacial bonding requirements of the powder coating under different film thicknesses.

[0062] In some embodiments, the aqueous masking slurry is prepared by the following method: (1) Acrylic monomer, organosilicon monomer, water, emulsifier and initiator are added to a reaction vessel to prepare a peelable waterborne acrylic emulsion; (2) Functional additives and inorganic fillers are added to the peelable waterborne acrylic emulsion to obtain waterborne masking slurry.

[0063] In the preparation of peelable waterborne acrylic emulsions, various existing polymerization processes can be used, such as the batch process, in which all raw materials are added to the reactor at once, and the product is discharged after polymerization. A semi-continuous process can also be used, in which acrylic monomers, organosilicon monomers, a portion of the emulsifier, and water are first stirred at high speed to form a pre-emulsion; then the remaining emulsifier and water are added to the reactor, followed by the uniform dropwise addition of the pre-emulsion containing an initiator; finally, a neutralizing agent is used to adjust the pH.

[0064] S2. Dry the workpiece coated with water-based masking slurry to form a masking film.

[0065] The workpiece coated with water-based masking slurry is dried. This drying can be oven drying or room temperature drying. The drying temperature is 40℃~150℃ and the drying time is 5min~60min.

[0066] In one embodiment, the drying is oven drying, with a drying temperature of 90℃~150℃, exemplarily 90℃, 95℃, 100℃, 110℃, 120℃, 130℃, 140℃, and 150℃, but not limited thereto; and a drying time of 5min~15min, exemplarily 5min, 6min, 8min, 10min, 11min, 12min, 14min, and 15min, but not limited thereto. Oven drying allows the water-based masking slurry to fully form a film, curing it to form a peelable masking film. The masking film has low adhesion to the workpiece, is easy to peel off, and provides a stable structural basis for subsequent interfacial reactions with powder coatings.

[0067] S3. Electrostatically spray powder coating onto the surface of the workpiece.

[0068] The powder coating contains epoxy resin. The workpiece coated with the electrostatically sprayed powder coating is cured, and the hydroxyl or epoxy groups of the powder coating form an interfacial bond structure with the carboxyl groups of the peelable waterborne acrylic emulsion. The epoxy resin accounts for 20% to 90% of the powder coating by weight, exemplary values ​​being 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90%, but not limited thereto. Preferably, the epoxy resin accounts for 30% to 85% of the powder coating by weight. More preferably, the epoxy resin accounts for 35% to 80% of the powder coating by weight.

[0069] During the curing process, the powder coating and masking film of electrostatic spraying form an interfacial bond structure. This allows the residual carboxyl groups of the water-based acrylic emulsion to react with the hydroxyl or epoxy groups of the epoxy resin in the powder coating to form ester bonds. The adhesion between the powder coating and the masking film is greater than that between the masking film and the workpiece. This ensures that the masking film does not fall off during high-temperature curing and also prevents the molten powder resin from penetrating into the film layer. This ensures that the masking film is easy to peel off and can be completely peeled off without residue.

[0070] In some embodiments, the powder coating is selected from one or more of pure epoxy powder coating, epoxy polyester powder coating, and epoxy acrylic powder coating. The powder coating contains epoxy resin, which is rich in polar groups such as hydroxyl and epoxy groups, and can form an interfacial bond structure with the carboxyl groups of the peelable waterborne acrylic emulsion.

[0071] In some embodiments, the pure epoxy powder coating is mainly composed of 55% to 80% epoxy resin, 5% to 10% curing agent, 5% to 10% functional additives and 0% to 30% filler by weight percentage. The epoxy polyester powder coating is mainly composed of 25%~50% carboxylated polyester, 25%~50% epoxy resin, 5%~10% functional additives and 0%~30% filler. The epoxy acrylic powder coating is mainly composed of 25%~50% epoxy resin, 25%~50% acrylic resin, 5%~10% functional additives and 0%~30% filler.

[0072] The functional additives may be selected from one or more of curing accelerators, defoamers, dispersants, leveling agents, and degassing agents, but are not limited thereto. The fillers may be selected from one or more of barium sulfate, calcium carbonate, talc, mica powder, kaolin, silica, and wollastonite, but are not limited thereto.

[0073] In some embodiments, the epoxy resin includes phenolic epoxy vinyl ester resin and bisphenol A type epoxy resin, with a weight ratio of phenolic epoxy vinyl ester resin to bisphenol A type epoxy resin of 1:(5~7). The phenolic epoxy vinyl ester resin and bisphenol A type epoxy resin have different epoxy equivalents. By controlling the weight ratio of phenolic epoxy vinyl ester resin to bisphenol A type epoxy resin, the masking film layer adheres tightly to the powder coating during the high-temperature curing stage without powder leakage, thus ensuring the flexibility of the masking composite film.

[0074] The powder coating and masking film of this invention form an interfacial bond structure during curing, which effectively resists the impact of high-speed powder and the electrostatic adsorption during electrostatic spraying. This ensures stable film adhesion throughout the process, preventing edge lifting, peeling, and displacement, achieving precise masking protection and avoiding electrostatic powder penetration and deposition into the gaps between the substrate and the film layer. In some embodiments, the electrostatic spraying voltage is 60kV~90kV, the spraying speed is 800mm / s~1000mm / s, the distance between the spray gun and the workpiece is 80mm~100mm, and the angle between the spray gun and the plane of the workpiece is 60°~70°. By controlling the electrostatic spraying process conditions, the uniformity of the powder coating in the masking film coverage area is ensured.

[0075] To further improve the peeling effect, the D of the powder coating 50 With a thickness of 20μm to 70μm, it can ensure the stability of powder output and spraying, and is conducive to forming a masking composite film with ideal leveling and surface smoothness.

[0076] The thickness of the masking film is 30 μm to 120 μm, with exemplary values ​​of 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, and 120 μm, but not limited thereto. The thickness of the masking film is preferably 35 μm to 100 μm, and more preferably 40 μm to 90 μm.

[0077] If the masking film is too thin (<30μm), the powder coating will penetrate the masking film. In addition, the masking film is too thin and lacks elasticity, making it impossible to form a complete film, resulting in peeling failure. If the masking film is too thick (>120μm), it is prone to blistering during drying and shrinkage, and is prone to breakage during cooling and peeling.

[0078] The thickness of the powder coating is 60μm to 450μm, with exemplary thicknesses of 60μm, 80μm, 90μm, 100μm, 150μm, 200μm, 250μm, 300μm, 350μm, 400μm, and 450μm, but not limited to these. The preferred thickness of the powder coating is 80μm to 400μm, and more preferably 100μm to 400μm.

[0079] If the powder coating is applied too thinly (<60μm), the interfacial ester bond strength is insufficient, making it prone to powder shedding and exposing the substrate, and failing to guarantee complete and residue-free removal of the masking film. If the powder coating is applied too thickly (>450μm), it is difficult to apply powder, and it may also damage the peeling mechanism, leading to difficulties in removing the film.

[0080] S4. The workpiece coated with electrostatic powder coating is cured to obtain a masking composite film.

[0081] Under specific temperature and time conditions, the powder coating melts, flows, cross-links, and cures, forming a uniform powder coating on the workpiece surface. The curing temperature of the powder coating is 120℃~220℃, exemplarily 120℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, and 220℃, but not limited to these. The curing time is 8min~30min, exemplarily 8min, 10min, 12min, 15min, 18min, 20min, 25min, and 30min, but not limited to these. Preferably, the curing temperature is 120℃~200℃, and the curing time is 8min~25min. More preferably, the curing temperature is 120℃~180℃, and the curing time is 8min~20min.

[0082] In some embodiments, if the curing temperature exceeds 220°C, the carboxyl groups of acrylic acid react with metal components such as aluminum, resulting in enhanced adhesion. However, the ester bonds formed by the reaction of epoxy groups, hydroxyl groups, and carboxyl groups of acrylic acid undergo high-temperature aging, leading to a severe decrease in bonding strength and resulting in high-temperature peeling failure.

[0083] In one embodiment, the curing method is infrared curing, with a curing temperature of 120℃~180℃ and a curing time of 8min~15min. Infrared curing has a fast heating rate, allowing the powder coating outside the area covered by the masking film to quickly melt, level, cross-link, and cure, forming a stable powder coating. The powder coating on the masking film and the masking film quickly form an interfacial bonding structure.

[0084] In one embodiment, the curing method is hot air curing, with a curing temperature of 120℃~220℃ and a curing time of 10min~30min. Hot air curing provides uniform heating, a dense coating with fewer defects, and a wide range of applications.

[0085] S5. Cool the workpiece after curing.

[0086] After the powder coating cures, a cooling process is performed. Utilizing the difference in expansion coefficients between the masking composite film and the workpiece, the masking composite film undergoes linear shrinkage, significantly reducing the overall peel resistance and achieving complete peeling. Specifically, rapid cooling is achieved using methods such as air cooling.

[0087] S6. Peel off the masking composite film to obtain a workpiece with the preset coating effect.

[0088] Specifically, a flexible rolling mechanism can be used to automatically and continuously peel off the masking area of ​​the workpiece, achieving complete peeling of the masking composite film without breakage or residue, and the waste film is collected and recycled uniformly. After the masking composite film is peeled off, the workpiece coating is smooth and clean, and the substrate is undamaged, so it can be directly and automatically transferred to the next production process without human intervention, realizing large-scale, continuous and automated coating production.

[0089] The masking and peeling method for electrostatic spraying provided in this embodiment offers excellent masking performance, easy and complete peeling of the masking film without residue, meeting the high-quality coating requirements of automotive parts and new energy power battery module components, such as battery housings, battery liquid cooling plates, and battery busbars. Automotive parts and new energy power battery module components are made of one or more of metals, plastics, glass, and synthetic fiber composite materials. This embodiment meets the requirements for high-quality masking coating on workpieces made of metals, plastics, glass, and synthetic fiber composite materials.

[0090] Accordingly, the present invention also provides an automated coating system, including a transmission module, a coating module, a drying module, a spraying module, a curing module, a cooling module, and a stripping module; the coating module, drying module, spraying module, curing module, cooling module, and stripping module are connected sequentially through the transmission module; The coating module is used to apply water-based masking slurry to the masked area; The drying module is used to dry the workpiece coated with water-based masking slurry; The spraying module is used for electrostatic spraying of powder coating on the surface of the workpiece; The curing module is used to cure workpieces coated with electrostatic powder coating. The cooling module is used to cool the workpiece after it has been cured. The peeling module is used to peel off the masking composite film; The transmission module is used for conveying the workpiece.

[0091] The present invention will be further described below with reference to specific embodiments: Example 1 This embodiment provides a masking and stripping method for electrostatic spraying, including the following steps: (1) Set the masking area according to the preset coating effect of the workpiece, and apply water-based masking paste to the masking area.

[0092] The water-based masking paste comprises the following raw materials in parts by weight: 100 parts of peelable water-based acrylic emulsion. The peelable water-based acrylic emulsion is a silicone-containing peelable water-based acrylic emulsion with a pH of 4.5 and an organosilicon content of 10 wt%.

[0093] (2) Dry the workpiece coated with water-based masking slurry to form a masking film.

[0094] The drying temperature is 100℃, the drying and heat preservation time is 10 min, and the thickness of the masking film is 50μm.

[0095] (3) Electrostatically spray powder coating onto the surface of the workpiece, and cover the powder coating with a masking film.

[0096] D of powder coating 50 The thickness of the powder coating is 20μm~70μm, and the thickness of the powder coating spraying is 200μm. The powder coating includes the following raw materials in parts by weight: 85 parts of bisphenol A type epoxy resin and 15 parts of curing agent.

[0097] (4) The workpiece coated with electrostatic powder coating is cured to obtain a masking composite film.

[0098] The curing method is infrared curing, the curing temperature is 180℃, and the curing time is 8 minutes.

[0099] (5) Cool the workpiece after curing.

[0100] (6) Roller peeling off the masking composite film to obtain the workpiece with the preset coating effect.

[0101] Example 2 This embodiment provides a masking and stripping method for electrostatic spraying, which differs from Embodiment 1 in that the water-based masking slurry comprises the following raw materials in parts by weight: 88 parts of peelable water-based acrylic emulsion, 2.5 parts of alcohol ester dodecyl film-forming aid, 0.2 parts of polyether wetting agent, 0.15 parts of water-based polyether defoamer, 0.1 parts of AMP-95 neutralizer, 0.25 parts of alkali-swelling thickener, 8 parts of light calcium carbonate inorganic filler, and 0.8 parts of functional color paste. The peelable water-based acrylic emulsion is a silicone-containing peelable water-based acrylic emulsion with a pH of 5 and an organosilicon content of 20 wt%.

[0102] The powder coating is cured by infrared curing at a temperature of 160℃ for 10 minutes.

[0103] Everything else is the same as in Example 1.

[0104] Example 3 This embodiment provides a masking and stripping method for electrostatic spraying, which differs from Embodiment 1 in that the water-based masking slurry includes the following raw materials in parts by weight: 84.55 parts of peelable water-based acrylic emulsion, 2.5 parts of alcohol ester twelve film-forming aid, 0.3 parts of polyether wetting agent, 0.2 parts of water-based polyether defoamer, 0.15 parts of AMP-95 neutralizer, 0.3 parts of alkali-swelling thickener, 11 parts of light calcium carbonate inorganic filler, and 1 part of functional color paste.

[0105] The peelable waterborne acrylic emulsion includes a peelable waterborne soft acrylic emulsion and a peelable waterborne hard acrylic emulsion, with a mass ratio of 1.5:1. The peelable waterborne soft acrylic emulsion has a pH of 5.5, a Tg of -25℃ to 0℃, and an organosilicon content of 25wt%; the peelable waterborne hard acrylic emulsion has a pH of 5.5, a Tg of 5℃ to 40℃, and an organosilicon content of 25wt%.

[0106] The powder coating is cured by infrared curing at a temperature of 180℃ for 9 minutes.

[0107] Everything else is the same as in Example 1.

[0108] Comparative Example 1 This comparative example provides a masking and stripping method for electrostatic spraying, which differs from Example 1 in that the aqueous masking slurry includes the following raw materials in parts by weight: 100 parts of a peelable aqueous acrylic emulsion. The peelable aqueous acrylic emulsion is a silicone-containing peelable aqueous acrylic emulsion with a pH of 3.5, an organosilicon content of 1 wt%, and forms a masking film with a thickness of 20 μm.

[0109] Everything else is the same as in Example 1.

[0110] Comparative Example 2 This comparative example provides a masking and stripping method for electrostatic spraying, which differs from Example 1 in that the water-based masking slurry includes the following raw materials in parts by weight: 100 parts of a peelable water-based acrylic emulsion. The peelable water-based acrylic emulsion is a silicone-containing peelable water-based acrylic emulsion with a pH of 6.5 and an organosilicon content of 10 wt%. The powder coating is cured by infrared curing, and the curing temperature is 230℃.

[0111] Everything else is the same as in Example 1.

[0112] The performance of the masking composite films obtained in Examples 1 to 3, Comparative Example 1, and Comparative Example 2 was tested. The peel strength of the masking composite films was tested according to GB / T 2792-2014, and the peeling condition of the masking composite films was recorded.

[0113] The specific results are as follows:

[0114] Application Example 1 The masking and peeling method of Example 1 is applied to a flat workpiece 1 with a frame. The internal area of ​​the flat workpiece 1 is the area that needs to be powder coated, and the frame is the area that does not need to be powder coated.

[0115] Masking and stripping methods include: The masking area is defined as the four edges of the frame. A water-based masking slurry is applied to the masking area, and the workpiece coated with the water-based masking slurry is dried to form a masking film 2. Figure 2 As shown.

[0116] A powder coating is electrostatically sprayed onto the surface of a workpiece, and a masking film is then applied over the powder coating. The workpiece with the electrostatically sprayed powder coating is then cured to obtain a masking composite film 3. Figure 3 As shown.

[0117] After curing, the workpiece is cooled and then the masking composite film 3 is rolled off to obtain the workpiece with the preset coating effect. Figure 4 For the peeled-off masking composite film 3, Figure 5 The finished product is a flat workpiece with a border.

[0118] Application Example 2 The masking and peeling method of Comparative Example 1 is applied to a flat workpiece 1.

[0119] Masking and stripping methods include: The entire flat surface is designated as the masking area. First, a water-based masking slurry is applied to the masking area, and after drying, a masking film is formed. Then, powder coating is electrostatically sprayed onto the workpiece surface, covering the masking film 2. After curing, a masking composite film is obtained. Finally, the masking composite film 3 is peeled off by cooling and rolling, with the result as follows. Figure 6 As shown.

[0120] Depend on Figure 6 It is known that the thickness of the masking film 2 is 20μm. The masking film is too thin and lacks elasticity. The superimposed powder coating penetrates the masking film, resulting in the inability to form a peelable masking composite film 3, and the peeling fails.

[0121] Application Example 3 The masking and stripping method of Comparative Example 2 was applied to a flat workpiece 1 with a through hole.

[0122] Masking and stripping methods include: The area surrounding the through-hole is designated as the masking region. First, a water-based masking slurry is applied to this region, and after drying, it forms a masking film 2. Then, powder coating is electrostatically sprayed onto the workpiece surface to form a powder coating 3 covering the masking film. After curing, a masking composite film is obtained, which is a composite layer of masking film 2 and powder coating 3. Finally, the masking composite film is peeled off by cooling and rolling, with the following result: Figure 7 As shown.

[0123] Depend on Figure 7 It can be seen that under high temperature curing conditions, the black powder coating 3 and the masking film 2 are separated. During peeling, the adhesion between the powder coating and the masking film is less than the adhesion between the masking film and the workpiece. The carboxyl groups of acrylic acid in the masking film react with the metallic aluminum, while the ester bonds formed by the reaction of epoxy groups and hydroxyl groups in the powder coating with the carboxyl groups of acrylic acid break. The masking film becomes brittle and powdery, leading to peeling failure.

[0124] The above description is a preferred embodiment of the invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the invention, and these improvements and modifications are also considered to be within the scope of protection of the invention.

Claims

1. A masking and stripping method for electrostatic spraying, characterized in that, Includes the following steps: The masking area is set according to the preset coating effect of the workpiece, and an aqueous masking paste is applied to the masking area. The aqueous masking paste includes a peelable aqueous acrylic emulsion, which contains silicone. The workpiece coated with water-based masking slurry is dried to form a masking film; An electrostatic powder coating is applied to the surface of a workpiece, the powder coating containing epoxy resin, and the powder coating covers the masking film. A workpiece coated with electrostatic powder coating is cured to obtain a masking composite film; the hydroxyl or epoxy groups of the powder coating form an interfacial bond structure with the carboxyl groups of the peelable waterborne acrylic emulsion. Cool the workpiece after it has been cured. The masking composite film is peeled off to obtain a workpiece with the preset coating effect.

2. The masking and peeling method as described in claim 1, characterized in that, The hydroxyl or epoxy groups of the epoxy resin in the powder coating react with the residual carboxyl groups of the silicone-containing peelable waterborne acrylic emulsion to form ester bonds.

3. The masking and peeling method as described in claim 1, characterized in that, The peelable waterborne acrylic emulsion is a silicone-modified acrylic emulsion, which is obtained by the polymerization reaction of silicone monomers and acrylic emulsion. The silicone content of the peelable waterborne acrylic emulsion is 2wt%~25wt%.

4. The masking and peeling method as described in claim 3, characterized in that, The peelable waterborne acrylic emulsion is a silicone-modified acrylic emulsion, which is obtained by the polymerization reaction of siloxane monomers and acrylic emulsion. The silicone content of the peelable waterborne acrylic emulsion is 3wt%~20wt%.

5. The masking and peeling method as described in claim 3, characterized in that, The organosilicon monomer is one or more of the following: triphenyl-hydroxysilane, (3-methacryloyloxy-2-hydroxypropoxy)propylbis(trimethylsiloxy)methylsilane, (3-epoxypropoxypropyl)dimethylethoxysilane, tri(epoxypropoxypropyldimethylsiloxy)phenylsilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and γ-methacryloyloxypropyltriethoxysilane.

6. The masking and stripping method as described in claim 1, characterized in that, The pH value of the peelable waterborne acrylic emulsion is 3.5 to 6.0, in order to control the residual carboxyl groups in the silicone-containing peelable waterborne acrylic emulsion.

7. The masking and stripping method as described in claim 1, characterized in that, The peelable waterborne acrylic emulsion is one or a combination of peelable waterborne soft acrylic emulsion and peelable waterborne hard acrylic emulsion, wherein the Tg of the peelable waterborne soft acrylic emulsion is -30℃ to 10℃, and the Tg of the peelable waterborne hard acrylic emulsion is 0℃ to 50℃.

8. The masking and stripping method as described in claim 7, characterized in that, The peelable waterborne acrylic emulsion includes a peelable waterborne soft acrylic emulsion and a peelable waterborne hard acrylic emulsion, wherein the weight ratio of the peelable waterborne soft acrylic emulsion to the peelable waterborne hard acrylic emulsion is 1:1 to 2:

1.

9. The masking and peeling method as described in claim 1, 3, or 4, characterized in that, The water-based masking slurry comprises the following raw materials in parts by weight: 35 to 100 parts of peelable water-based acrylic emulsion, 0 to 8 parts of functional additives, and 0 to 14 parts of inorganic filler.

10. The masking and peeling method as described in claim 9, characterized in that, The water-based masking slurry comprises the following raw materials in parts by weight: 35 to 100 parts of peelable water-based acrylic emulsion, 2 to 8 parts of functional additives, and 4 to 14 parts of inorganic filler.

11. The masking and peeling method as described in claim 10, characterized in that, The functional additives include one or more of the following: film-forming aids, wetting agents, defoamers, neutralizing agents, thickeners, and functional color pastes.

12. The masking and stripping method as described in claim 1, characterized in that, The curing temperature of the powder coating is 120℃~220℃, and the curing time is 8min~30min; The drying temperature of the water-based masking slurry is 40℃~150℃, and the drying time is 5min~60min.

13. The masking and stripping method as described in claim 1, characterized in that, The epoxy resin accounts for 20% to 90% of the weight of the powder coating.

14. The masking and stripping method as described in claim 13, characterized in that, The powder coating is selected from one or more of pure epoxy powder coating, epoxy polyester powder coating, and epoxy acrylic powder coating.

15. The masking and peeling method as described in claim 14, characterized in that, By weight percentage, the pure epoxy powder coating is mainly composed of 55% to 80% epoxy resin, 5% to 10% curing agent, 5% to 10% functional additives and 0% to 30% filler; The epoxy polyester powder coating is mainly composed of 25%~50% carboxylated polyester, 25%~50% epoxy resin, 5%~10% functional additives and 0%~30% filler. The epoxy acrylic powder coating is mainly composed of 25%~50% epoxy resin, 25%~50% acrylic resin, 5%~10% functional additives and 0%~30% filler.

16. The masking and stripping method as described in claim 1, characterized in that, The powder coating's D 50 The range is 20μm to 70μm; The thickness of the shielding film is 30μm~120μm; The thickness of the powder coating is 60μm~450μm.

17. An automated coating system, performing the masking and stripping method for electrostatic spraying as described in any one of claims 1 to 16, characterized in that, It includes a transmission module, a coating module, a drying module, a spraying module, a curing module, a cooling module, and a peeling module; the coating module, drying module, spraying module, curing module, cooling module, and peeling module are connected sequentially through the transmission module; The coating module is used to apply water-based masking slurry to the masked area; The drying module is used to dry the workpiece coated with water-based masking slurry; The spraying module is used for electrostatic spraying of powder coating on the surface of the workpiece; The curing module is used to cure workpieces coated with electrostatic powder coating. The cooling module is used to cool the workpiece after it has been cured. The peeling module is used to peel off the masking composite film; The transmission module is used for conveying the workpiece.

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