Operational points
Vacuum adsorption coating technology is a key process in the preparation of flexible electronics, functional coatings and new materials. This technology uses vacuum negative pressure to flatten the flexible substrate to adsorb on the coating platform, combined with precision coating, which can effectively reduce wrinkles, bubbles and other defects, and improve the uniformity and consistency of the coating. Its operation needs to take into account many factors such as equipment, materials and environment.
A comprehensive inspection of the equipment is required before operation. Confirm that the vacuum pump is running smoothly and there is no abnormal noise; Check the sealing of the vacuum pipeline and the adsorption platform to ensure that there is no leakage; Clean the surface of the adsorption platform and the coating head to avoid dust or residue affecting the quality of the coating film. For flexible substrates, the adsorption negative pressure range should be adjusted according to its material (such as polyimide, polyethylene terephthalate, flexible glass, etc.) to prevent excessive stretching or deformation. It is recommended to refer to the equipment manual and relevant process standards for parameter presetting.
The pretreatment of flexible substrates directly affects the coating effect. First, the substrate needs to be cleaned to remove surface grease, particles and other contaminants, and common methods include dust-free wipe wiping and low-power plasma treatment. Subsequently, the substrate is laid flat on the adsorption platform and the vacuum adsorption system is activated to ensure an even fit. During the adsorption process, it can be observed whether there is a local non-fit phenomenon on the surface of the substrate, and if so, it is necessary to reposition or check the vacuum distribution. The substrate size should be slightly larger than the adsorption area to ensure a secure hold.
The coating parameters need to be set precisely according to the characteristics of the coating material and the target thickness. The main parameters include coating speed, coating gap, feeding pressure and vacuum degree. The coating speed v and the coating thickness h often satisfy the relationship: h ∝ Q/(v·w), where Q is the feed flow rate and w is the coating width. In practice, it is necessary to determine the combination of parameters through pre-experiments to avoid streaks, shrinkage holes or edge effects of the coating. Due to the high coefficient of thermal expansion, the ambient temperature T needs to be controlled when necessary, and its relationship with the change of substrate size ΔL can be approximately expressed as ΔL = α· L0ΔT, α is the coefficient of thermal expansion, L0is the initial length.
During the coating process, the coating status and equipment operation data need to be monitored in real time. Observe whether the coating is spread evenly, paying special attention to the difference between the edge of the substrate and the center area; Monitor the vacuum pressure value to ensure stable adsorption; Record the temperature and humidity of the environment to avoid fluctuations in external conditions affecting the curing or drying of the coating. If multiple layers are used, ensure that the solvent is fully volatilized or pre-cured after each layer is completed before proceeding to the next layer.
After the coating film is completed, the vacuum needs to be released first, and then gently peel off the substrate after the adsorption force is completely removed. Avoid rapid tearing that can cause coating damage or deformation of the substrate. The stripped substrate should be cured, annealed or dried according to the coating material requirements. During the treatment process, attention should be paid to the upper limit of the temperature resistance of the flexible substrate to prevent the performance from degrading due to thermal stress.
FAQs
The following are common phenomena and countermeasures in flexible substrate coatings.
| Regular streaks appear on the coating | Check the flatness of the coating head and adjust the coating gap and speed |
| The substrate is locally wrinkled or deformed | Reduce the negative adsorption pressure and check the uniformity of the thickness of the substrate |
| The coating is thick at the edges and thin in the middle | Adjust the feed pressure distribution and optimize the design parameters of the coating head |
| Insufficient vacuum adsorption | Clean the adsorption holes, check the pipeline seal and pump performance |
| Poor coating adhesion | Improve the surface pretreatment of the substrate to match the coating material with the surface energy of the substrate |
Notes:
Operators should wear appropriate protective equipment and avoid contact with organic solvents or high-temperature components. When the equipment is out of service for a long time, the vacuum should be released, and critical components should be cleaned and covered. Calibrate the metering unit such as vacuum gauges and pressure sensors regularly and replace consumables as recommended by the manufacturer. All operations should comply with laboratory safety codes and relevant process standards.