Method for spraying film

Abstract

The invention discloses a method for spraying a film, which is different from a spray mode of fog drops, adopts a spray head structure in a gap form, and sprays a water-based coating with certain characteristics in a form of a thin film to uniformly cover the surface of an implement. The coating thickness is controlled through the flow of a conveying pump, the width of a nozzle gap, the rotating speed of a sprayed object, the moving speed of a gap nozzle and the like. In the spraying process, the utensil rotates at a certain speed, the gap nozzle linearly moves at a constant speed in the direction parallel to the rotating face or adjusts the dip angle of the nozzle, a coating film with a certain thickness can evenly sweep the surface of the utensil, and spraying is completed. According to the method, compressed air is not needed, and the problems that in the traditional spraying process, fog drop covering is uneven, fog drops are prone to drying, a spray head is prone to being blocked, and paint waste is large can be effectively solved.

Description

Technical Field

[0001] This invention relates to a method, specifically a method for spraying water-based coatings in the form of a coating film. Background Technology

[0002] Traditional spraying, as a fundamental process in industrial coating, is widely used in five core industries: automotive, furniture, hardware, construction, and electronics, becoming a crucial link in ensuring product appearance and protective performance. Spraying is a coating method that disperses liquid coating material into uniform and fine droplets using spray guns or disc atomizers, applying it to the surface of the workpiece. Mainstream spraying methods include compressed air spraying, high-pressure airless spraying, and electrostatic spraying. Compressed air spraying uses high-speed jets of compressed air to atomize the coating into fine particles that adhere to the workpiece surface. High-pressure airless spraying uses a high-pressure pump to pressurize the coating to 10-25 MPa, atomizing it through a specialized nozzle, eliminating the need for compressed air. Electrostatic spraying involves charging the coating during atomization, grounding the workpiece to generate an electrostatic field, and causing the coating particles to adhere to the workpiece surface under the influence of this electric field.

[0003] Atomized spraying involves breaking down a liquid coating into fine droplets, which are then sprayed at high speed onto the object. A large number of tiny droplets accumulate on the surface to form a coating. However, for thinner coatings, traditional atomized spraying suffers from uneven droplet accumulation and missed areas, resulting in minor coating defects after the surface dries. These defects are unacceptable for containers with high barrier properties, such as disposable paper-plastic plates and food containers. Multiple coats can compensate for these defects, but this leads to reduced production efficiency and a significant increase in costs.

[0004] During the spraying process, atomized droplets scatter everywhere, polluting the environment. These droplets solidify rapidly, making them difficult to recover and severely impacting paint utilization, leading to a significant increase in costs. Paint utilization varies considerably between different spraying methods, with air spraying exhibiting the most significant waste. For example, when processing furniture carvings or complex metal shapes, some paint may be lost because it cannot adhere to the substrate surface, resulting in a utilization rate of only 50%-60%. Furthermore, the atomized droplets easily dry and solidify in the air, clogging the nozzles when they fall into the recycled paint solution, severely affecting spraying quality and production continuity.

[0005] The invention patent "Workpiece Water-Based Coating Production Line and Process (Application No.: CN202211540063)" proposes a workpiece water-based coating production line and process, aiming to solve the technical problem of poor coating quality caused by traditional manual spraying of water-based coatings. By establishing a spray booth equipped with multiple six-axis spraying robots with mixed-air nozzles, air inlet and outlet pipes, a paint mist collection box, a centralized paint supply and mixing system, and a drying zone, defects such as orange peel on the paint film surface are prevented, thereby improving the overall coating quality. This patent uses compressed air spraying and does not address how to solve the problem of uniform spray droplet coverage when applying thinner coatings. Furthermore, it does not address the issue of easy drying of the sprayed droplets and the problem of recycled material clogging the nozzles. The invention patent "A Batch Spraying Device for the Outer Wall of Straight Pipe Fittings with Water-Based Coating Recycling Function (Application No.: CN202411731220)" discloses a high-efficiency spraying device that can improve coating utilization and prevent coating overflow, achieving integrated spraying, drying, and recycling. This invention integrates spraying, recycling, and drying functions through a spraying mechanism, a drying mechanism, and a recycling mechanism. While performing high-quality batch spraying on pipe fittings, it also achieves coating recycling, prevents coating spillage and environmental pollution, and improves production efficiency. However, it does not describe how to solve the problem of uniform coating droplet coverage when applying thinner coatings.

[0006] The utility model patent "A surface curing device for deep-processed glass products (application number: 202220415390.9)" provides a surface curing device for deep-processed glass that combines spraying and surface curing. During the curing process, the glass bottle rotates, improving curing efficiency, saving time, and improving product quality. However, it does not provide solutions to the problems inherent in spraying. The utility model patent "A rotary cup electrostatic spraying device (application number: CN202323528461)" improves the surface drying problem of the rotary cup by optimizing the rotating cup structure and adding a cooling device, resulting in better liquid atomization. However, this patent does not address how to solve the problem of uniform coverage of spray droplets when applying thinner coatings. The utility model patent "A spray booth for spraying water-based coatings (application number: CN202123212492)" provides a spray booth for spraying water-based coatings, but only addresses the problem of low paint mist recovery rate. The utility model patent "Automatic Water-Based Coating Spraying Device (Application No.: 201821662646.6)" only solves the problems of uneven manual spraying and difficulty in recovering spray droplets. The utility model patent "Anti-Clogging Spraying Device for Water-Based Coatings (Application No.: CN202421147285)" addresses the issue of residual, solidified coating adhering to the inner wall of the coating bucket, causing clumping and clogging the spraying machine. It also does not address the problem of atomized coating escaping and polluting the surrounding environment, resulting in waste. The utility model patent "A Water-Based Coating Spraying Device (Application No.: CN201920017028)" improves spraying accuracy and uniformity by moving the coating delivery pipe up, down, left, and right, and promptly dries the coating after spraying to prevent coating residue from clinging to objects. However, it does not address how to solve the problem of uniform spray droplet coverage for thin coatings or how to prevent the sprayed droplets from drying out easily. The utility model patent "A Novel Water-Based Coating Spraying Device (Application No.: CN202421147285)" solves the problems of poor spraying effect and difficulty in recycling water-based coatings that slip off the coating when spraying onto workpieces by setting up a rotating turntable on a carrier plate, a return trough on the carrier plate, a coating filter collection box, and multiple vertically arranged spray pipes and nozzles. However, it does not describe how to solve the problem of uniform coverage of the spray droplets or how to solve the problem of the sprayed droplets drying out easily.

[0007] This demonstrates that current traditional spraying methods struggle to address issues such as uneven droplet coverage and missed areas when applying thin coatings. Furthermore, problems like droplet drying, nozzle clogging, and low paint utilization remain. Therefore, there is a need to develop an environmentally friendly spraying method that significantly improves coating coverage and reduces dry material loss. Summary of the Invention

[0008] This invention provides a method for spraying a coating film. This method differs from droplet spraying by employing a slit-type nozzle structure to spray a water-based coating with specific properties in the form of a thin film, uniformly covering the surface of an object. The coating thickness is controlled by factors such as the pump flow rate, nozzle slit width, the rotation speed of the object being sprayed, and the movement speed of the slit nozzle. During spraying, the object rotates at a certain speed, and the slit nozzle moves linearly at a constant speed parallel to the plane of rotation, or the nozzle angle is adjusted, allowing a coating film of a certain thickness to be evenly swept across the object's surface, completing the spraying process. This method eliminates the need for compressed air, effectively solving problems such as uneven droplet coverage, easy drying of droplets, nozzle clogging, and significant paint waste in traditional spraying processes.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] (1) The object 6 to be sprayed is placed on a platform 5 that can rotate horizontally, vertically, or at a certain angle of inclination, and is held and fixed. The spraying surface of the object 6 can face upward, to the side, or downward. The slit nozzle 2 faces the spraying surface and is spaced at a certain distance. The sprayed paint film 4 can form a radial fan-shaped surface, a basically parallel rectangular surface, a curved cylindrical surface (side) or a conical surface (side) depending on the structure of the slit nozzle 2. During the spraying process, the slit nozzle 2 faces the rotating object 6. The sprayed paint film 4 enters from one end, passes through the center of rotation 9 of the platform, and exits from the other end, thus completing the spraying of the object 6.

[0011] (2) The object 6 is placed on the platform 5, with its center on the rotation center 9 of the platform. The object 6 is fixed on the platform 5 by one or more combinations of magnetic attraction, adhesive, mechanical claw gripping, bolt, vacuum suction, etc. The rotation speed of the platform 5 is adjustable, with an adjustment range of 0-500 rpm.

[0012] (3) The slit nozzle 2 faces the platform 5, and the distance from the nozzle outlet 3 to the platform 5 is adjustable so that the distance from the slit nozzle outlet 3 to the surface of the fixed object 6 is maintained between 10mm and 500mm.

[0013] (4) The length of the slit outlet 2 from left to right along the outer surface of the outlet 3 is 5mm to 500mm, and the width of the slit outlet 3 formed by the front and rear blades of the nozzle 2 is 0.01mm to 5mm.

[0014] (5) The paint is evenly distributed in the internal cavity of the slit nozzle 2, and the paint flow velocity at the outlet 3 is >1m / s;

[0015] (6) During spraying, the slit nozzle 2 moves at a constant speed along a straight line and passes through the rotation center 9 of the platform. The moving speed is 1-1000mm / s. The angle of the spraying direction of the slit nozzle 2 can also be adjusted at a constant speed. The rotation speed is 1-180° / s. It passes through the rotation center 9 of the platform, from one end 8 to the other end 10, and sweeps across the surface of the object 6. The angle between the plane of the spray film 4 and its moving trajectory is <80 degrees.

[0016] (7) Opposite to the slit nozzle 2, that is, behind the platform 5, there is a paint recovery baffle 7 or the inner wall of the recovery tank, covering the area that the paint film 4 can sweep, for collecting the liquid material.

[0017] (8) The sprayed coating is a water-based coating with a dynamic surface tension ≤40mN / m, an Euler number of the coating's elongation characteristics above 1.5, a low shear viscosity of the coating controlled in the range of 50 to 500cp, and a solid content of the coating not higher than 50%.

[0018] (9) After spraying, adjust the speed of the rotating platform 5 and continue rotating for 5–300 s to evenly distribute the coating on the surface of the object 6 using centrifugal force. The coating amount of a single spray is ≥5 g / m². 2 .

[0019] This invention provides a method for spraying a coating film. Utilizing a slit-film formation mechanism, water-based paint is sprayed from a slit nozzle, forming a thin film that covers the surface of an object. Through the rotation of the platform and the movement of the slit nozzle (including parallel movement and changes in tilt angle), the paint film sweeps across the object's surface in a spiral shape. The spiral paint films have slight overlap areas. The delayed rotation of the platform ensures even distribution of the paint on the object's surface, resulting in a uniform, leak-proof coating. Furthermore, this method avoids the formation of tiny paint droplets, significantly reducing the problems of dried paint and environmental pollution. The sprayed paint film is recycled using a paint recovery baffle, significantly reducing paint waste. By controlling the surface tension and elongation rheological properties of the paint, this invention significantly improves the flexibility and stability of the paint film leaving the slit nozzle during spraying. It is less prone to breakage during coating stretching, thereby improving the coverage performance of the paint sprayed onto the object's surface and significantly reducing the problem of leaks caused by uneven accumulation in conventional atomized spraying. Attached Figure Description

[0020] Figures 1-3 This is a cross-sectional structural diagram of the three types of slit nozzles in this patent.

[0021] Figures 4-6 This is a schematic diagram showing the shape of the coating film sprayed from the three types of slit nozzles in this patent.

[0022] Figure 7 This is a schematic diagram of the spraying process of this patent. The slit nozzle moves in a straight line to complete the spraying and liquid recovery.

[0023] Figures 8-9 This is a schematic diagram of the spraying process of this patent, showing how the spraying and liquid recovery are completed by adjusting the angle of the slit nozzle.

[0024] In the diagram: 1. Feed inlet; 2. Slit nozzle; 3. Slit outlet; 4. Coating film; 5. Platform; 6. Object to be coated; 7. Coating recovery baffle; 8. Coating film entry position A; 9. Coating film rotation center position B after passing the platform; 10. Coating film exit position C. Detailed Implementation

[0025] Implementation Method 1

[0026] This invention patent uses a spray coating method, and the slit nozzle 2 is shown in the attached drawing of the specification. Figure 1 The structure shown includes an inlet 1 and a slit outlet 3; the object to be coated 6 is a container, which is adhered and fixed to the center of a vertically rotating stage 5, with the coating surface of the object 6 facing the side; the stage 5 rotates at a speed of 50-100 rpm; the distance between the slit nozzle 2 and the object to be coated 6 is 100-150 mm; the coated film 4 is as shown in the attached diagram of the instruction manual. Figure 4 As shown in the diagram, the slit nozzle 2 has a slit outlet 3 with a length of 30mm from left to right along its outer surface. The width of the slit outlet 3 formed by the two nozzle blades is 0.1mm. The paint is evenly distributed through the internal cavity of the slit nozzle 2, and the paint flow velocity at the outlet is 1.5-2m / s. During spraying, as shown in the attached diagram of the instruction manual... Figure 7 As shown, the slit nozzle 2 moves at a constant speed along a straight line and passes through the center of rotation 9 of the stage, with a moving speed of 200 mm / s; behind the stage 5 is a paint recovery baffle 7, covering the area that the paint film 4 can sweep; the properties of the sprayed water-based paint are adjusted by adding additives to adjust the dynamic surface tension and elongation rheological properties, with a dynamic surface tension of 35 mN / m, an elongation characteristic Euler number of 1.8, a low shear viscosity controlled in the range of 100-150 cp, and a solid content of 40%; after spraying, the speed of the rotating stage 5 is adjusted to 30 rpm and rotated continuously for 30 s, with a coating amount of 10 g / m² per spray. 2 The coating is evenly applied with no missed areas, and there is no issue of dry material during the spraying process. The paint is also recyclable.

[0027] Implementation Method 2

[0028] This invention employs a spray coating method, with the slit nozzle 2 shown in the accompanying drawings. Figure 2The structure shown includes an inlet 1 and a slit outlet 3; the object to be coated 6 is a container, which is adhered and fixed to the center of a vertically rotating platform 5, with the coating surface of the object 6 facing the side; the platform 5 rotates at a speed of 100-150 rpm; the distance between the slit nozzle 2 and the object to be coated 6 is 500-100 mm; the coated film 4 is as shown in the attached diagram of the instruction manual. Figure 5 The fan-shaped planar shape shown indicates that the slit nozzle 2 has a slit outlet 3 with a length of 50mm from left to right along its outer surface. The width of the slit outlet 3 formed by the two sections of the nozzle is 0.15mm. The paint is evenly distributed through the internal cavity of the slit nozzle 2, and the paint flow velocity at the outlet is 1.0-1.5m / s. During spraying, as shown in the attached diagram of the instruction manual... Figure 9 As shown, the spray angle of the slit nozzle 2 is adjusted uniformly at a rotation speed of 45° / s, passing through the rotation center 9 of the stage. Behind the stage 5 is a paint recovery baffle 7, covering the area that the paint film 4 can sweep. The properties of the sprayed water-based paint are adjusted by adding additives to control its dynamic surface tension and elongation rheological properties. Its dynamic surface tension is 30 mN / m, the elongation characteristic Euler number is 2.2, the low shear viscosity is controlled within the range of 150-200 cp, and the solid content is 35%. After spraying, the rotation speed of the stage is adjusted to 20 rpm and maintained for 10 seconds. The coating amount per spray is 15 g / m². 2 The coating is evenly applied with no missed areas, and there is no issue of dry material during the spraying process. The paint is also recyclable.

[0029] Implementation Method 3

[0030] This invention employs a spray coating method, with the slit nozzle 2 shown in the accompanying drawings. Figure 3 The structure shown includes an inlet 1 and a slit outlet 3; the object to be coated 6 is a container, magnetically fixed to the center of a vertically rotating platform 5, with the coating surface of the object 6 facing to the side; the platform 5 rotates at a speed of 50-80 rpm; the distance between the slit nozzle 2 and the object to be coated 6 is 50-70 mm; the coated film 4 is as shown in the attached diagram of the instruction manual. Figure 6The curved surface shape shown has a slit nozzle 2 with a slit outlet 3 that is 100mm long from left to right along the outer surface of the outlet. The width of the slit outlet 3 formed by the two blades before and after the nozzle is 0.11mm. The paint is evenly distributed through the internal cavity of the slit nozzle 2, and the paint flow velocity at the outlet is 1.5-2m / s. During spraying, the slit nozzle 2 moves at a constant speed in a straight line and passes through the rotation center 9 of the stage, with a moving speed of 100mm / s. Behind the stage 5 is a paint recovery baffle 7, which covers the area that the paint film 4 can sweep. The performance of the sprayed water-based paint is adjusted by adding additives to adjust the dynamic surface tension and elongation rheological properties. Its dynamic surface tension is 33mN / m, the elongation characteristic Euler number of the paint is 2.0, the low shear viscosity of the paint is controlled in the range of 80-100cp, and the solid content of the paint is 40%. After spraying, the rotation speed of the stage is adjusted to 30rpm and rotated continuously for 30s. The coating amount of a single spray is 20g / m. 2 The coating is evenly applied with no missed areas, and there is no issue of dry material during the spraying process. The paint is also recyclable.

[0031] The embodiments of this invention form a thin coating film using a slit-structured spray nozzle. During spraying, the nozzle sweeps evenly across the surface of the object in a spiral motion, creating a uniform, unobstructed surface. This avoids the problems of easy drying of micro-droplets in traditional atomized coatings and the environmental pollution associated with atomized coatings. Furthermore, a coating recovery baffle can recover coatings that have spilled onto the object, significantly reducing coating waste. This spraying method is also suitable for coatings with high viscosity and significantly reduces uneven coating and dripping issues, improving coating quality. Compared to traditional atomized spraying, slit spraying effectively reduces coating thickness while maintaining the same coverage, thus saving on coating costs.

[0032] Compared to curtain coating, the spraying method of this invention has a significantly higher coating film flow rate at the slit exit than curtain coating (in curtain coating, the coating film flow rate at the die exit is usually no more than 0.5 m / s). In curtain coating, the curtain has a free fall phase after exiting the die, which increases the curtain speed and thins the curtain. In contrast, the coating film of this invention is sprayed directly by adjusting the slit width and the feed flow rate, without the need for a free fall acceleration process. Furthermore, the spraying direction of this method is not restricted, while the curtain of curtain coating can only face downwards.

Claims

1. A method for spraying a film, characterized in that: The object 6 to be sprayed is placed on a platform 5 that can rotate horizontally, vertically, or at a certain angle, and is held and fixed. The spraying surface of the object 6 can face upward, to the side, or downward. The slit nozzle 2 faces the spraying surface and is spaced at a certain distance. The sprayed paint film 4, depending on the structure of the slit nozzle 2, can form a radial fan-shaped surface, a basically parallel rectangular surface, a curved cylindrical surface (side), or a conical surface (side). The sprayed paint film 4 sweeps across the object 6, completing the spraying.

2. The method for spraying a film as described in claim 1, characterized in that: The object 6 is placed on the stage 5, with its center at the rotation center 9 of the stage. The object 6 is fixed to the stage 5 by one or more methods such as magnetic attraction, adhesive, mechanical gripping, bolts, and vacuum suction. The rotation speed of the stage 5 is adjustable, with an adjustment range of 0-500 rpm.

3. The method for spraying a film as described in claim 1, characterized in that: The slit nozzle 2 faces the platform 5, and the distance from the nozzle outlet 3 to the platform 5 is adjustable, so that the distance from the slit nozzle outlet 3 to the surface of the fixed object 6 is maintained between 10mm and 500mm.

4. The method for spraying a film as described in claim 1, characterized in that: The slit nozzle 2 has a slit outlet length of 5mm to 500mm from left to right along the outer surface of the outlet 3, and the slit outlet 3 formed by the two front and rear blades of the nozzle 2 has a width of 0.01mm to 5mm.

5. The method for spraying a film as described in claim 1, characterized in that: The paint is evenly distributed inside the cavity of the slit nozzle 2, and the paint flow velocity at the outlet 3 is >1m / s.

6. The method for spraying a film as described in claim 1, characterized in that: During spraying, the slit nozzle 2 moves at a constant speed along a straight line. The sprayed paint film 4 enters from one end 8, passes through the center of rotation 9 of the platform, and exits from the other end 10. The moving speed is 1-1000mm / s. The angle of the spraying direction of the slit nozzle 2 can also be adjusted at a constant speed. The rotation speed is 1-180° / s. It passes through the center of rotation 9 of the platform, from one end 8 to the other end 10, and sweeps across the surface of the object 6. The angle between the plane of the sprayed film 4 and its moving trajectory is <80 degrees.

7. The method for spraying a film as described in claim 1, characterized in that: Opposite to the slit nozzle 2, behind the platform 5, there is a paint recovery baffle 7 or the inner wall of the recovery tank, covering the area that the paint film 4 can sweep over, for collecting the liquid material.

8. The method for spraying a film as described in claim 1, characterized in that: The sprayed coating is a water-based coating with a dynamic surface tension ≤40mN / m, an Euler number of 1.5 or higher, a low shear viscosity of 50-500cp, and a solid content of no more than 50%.

9. The method for spraying a film as described in claim 1, characterized in that: After spraying, adjust the speed of the rotating stage 5 and continue rotating for 5–300 seconds to evenly distribute the coating on the surface of the object 6 using centrifugal force. The coating amount of a single spray is ≥5 g / m². 2 .

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