Application of Small Coating Machine in Polyimide Slurry
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Polyimide (PI) is a high-performance polymer material widely used in aerospace, electronic and electrical, automotive industries, and other fields due to its excellent heat resistance, mechanical properties, electrical insulation properties, and chemical corrosion resistance. As one of the basic forms of PI materials, the uniform coating of polyimide slurry is crucial for its subsequent performance. Small coating machines have become important tools in laboratories and small-scale production due to their easy operation, low cost, and strong applicability. This article will explore the application technology of small coating machines in polyimide slurries, including the working principle of coating machines, control of process parameters, common problems and solutions, etc.
Working principle of coating machine
The basic principle of a coating machine is to evenly coat liquid or semi liquid materials onto the surface of a substrate, forming a coating of a certain thickness. According to different coating methods, coating machines can be divided into knife scraping coating, roller coating, spray coating, groove coating, and other types. Small coating machines mainly use two methods: knife scraping coating and roller coating, which will be introduced separately below.
Knife scraping coating
Scrape coating is a method of controlling coating thickness by adjusting the gap between the scraper and the substrate. The knife scraper coating machine consists of a scraper, a coating platform, a drive system, and a control system. The working process is as follows: pour the polyimide slurry onto the coating platform. Adjust the gap between the scraper and the substrate according to the required coating thickness. Start the coating machine and drive the scraper or substrate to move, so that the slurry is evenly coated on the surface of the substrate under the action of the scraper. After coating, send the coated substrate into an oven for drying and curing.
Roller coating
Roller coating is a method of uniformly transferring slurry onto the surface of a substrate through rollers. The roller coating machine consists of an upper coating roller, a lower coating roller, a coating tank, a drive system, and a control system. The working process is as follows: pour the polyimide slurry into the coating tank. Adjust the gap between the upper and lower coating rollers according to the required coating thickness. The driving system drives the rollers to rotate, so that the slurry is evenly coated on the surface of the substrate under the action of the rollers. After coating, send the coated substrate into an oven for drying and curing.
Control of Coating Process Parameters
The control of coating process parameters is crucial for obtaining a uniform polyimide coating. The main process parameters include slurry viscosity, coating speed, scraper/roller gap, drying temperature and time, etc.
Slurry viscosity
The viscosity of polyimide slurry directly affects the coating effect. Excessive viscosity makes it difficult to evenly apply the slurry; Low viscosity makes the slurry easy to flow and difficult to form a uniform coating. Generally speaking, the viscosity of the slurry should be controlled between 500-2000 mPa · s. The viscosity can be controlled by adjusting the solvent content, temperature, and other methods of the slurry.
Coating speed
Coating speed refers to the movement speed of the scraper or roller during the coating process. The coating speed is too fast, and the slurry is prone to splashing, forming uneven coatings; The coating speed is too slow, and the slurry is prone to accumulate, forming uneven thickness coatings. Generally speaking, the coating speed should be controlled between 0.1-1 m/min.
Scraper/roller gap
The gap between the scraper/roller refers to the distance between the scraper and the substrate or upper and lower rollers. The gap is too large, the coating thickness is too thick, and it is easy to cause sagging phenomenon; The gap is too small and the coating thickness is too thin, which can easily lead to incomplete coating. Generally speaking, the gap between the scraper/roller should be controlled between 10-100 μ m.
Drying temperature and time
Drying temperature and time refer to the temperature and time required for drying and curing after coating. Excessive temperature can easily cause coating cracking; The temperature is too low, making it difficult for the coating to fully cure. Excessive time affects production efficiency; The coating is difficult to fully cure due to the short time. Generally speaking, the drying temperature should be controlled between 150-250 ℃, and the drying time should be controlled between 30-60 minutes.
Common problems and solutions
During the process of coating polyimide slurry on a small coating machine, some problems are often encountered that affect the coating effect. The following are common problems and their solutions.
1) Uneven coating thickness
Uneven coating thickness is a common problem in the coating process, mainly due to uneven viscosity of the slurry, uneven clearance between the scraper/roller, and uneven coating speed. The solutions include:
Adjusting the viscosity of the slurry - By adjusting the solvent content, temperature, and other methods, the viscosity of the slurry can be made uniform.
Adjust the gap between the scraper/roller - by precisely adjusting the gap between the scraper/roller to maintain uniformity.
Adjust coating speed - by precisely controlling the coating speed to maintain uniformity.
2) Coating cracking
The main reasons for coating cracking include excessive drying temperature, prolonged time, and thick coating thickness. The solutions include:
Reduce drying temperature - control the drying temperature within a reasonable range, generally 150-250 ℃.
Shorten drying time - Control the drying time within a reasonable range, usually 30-60 minutes.
Reduce coating thickness - By adjusting the gap between the scraper/roller, reduce the coating thickness.
3) Coating flow hanging
The main reasons for coating sagging include low viscosity of the slurry, too fast coating speed, and excessive coating thickness. The solutions include:
Improve slurry viscosity - By reducing solvent content, lowering temperature, and other methods, the viscosity of the slurry can be increased.
Slow down the coating speed - By slowing down the coating speed, the phenomenon of sagging can be reduced.
Reduce coating thickness - By adjusting the gap between the scraper/roller, reduce the coating thickness.
4) Incomplete coating
The main reasons for incomplete coating include high viscosity of the slurry, slow coating speed, and small clearance between the scraper/roller. The solutions include:
Reduce the viscosity of the slurry - by increasing the solvent content, raising the temperature, and other methods, the viscosity of the slurry can be reduced.
Accelerate coating speed - By speeding up the coating speed, the coating effect can be improved.
Increase the gap between the scraper/roller - By adjusting the gap between the scraper/roller, the coating thickness can be increased.
conclusion
The application of small coating machines in polyimide slurries provides a convenient solution for laboratories and small-scale production. By reasonably controlling the coating process parameters and solving common problems during the coating process, uniform and high-quality polyimide coatings can be obtained.
2024-07-24 15:36
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