Overview
Applying a plaster adhesive layer to the backing layer is a process in which a specific formulation of adhesive is applied evenly to the surface of the backing material through a film applicator. This process aims to create a uniform thickness, adhesive stable and defect-free adhesive film to ensure reliable adhesion and comfort in use of the final product. The coating quality directly affects the adhesion time, skin adaptability and peeling characteristics of the product.
Coating machine working principle
The film coating machine is usually composed of a feeding system, a coating head, a backing conveying system, a drying unit and a winding device. During operation, the adhesive is transported by the feeding system to the coating head, which mechanically or pneumatically applies the adhesive to the uniformly moving backing layer at a set thickness. The coated material then enters the drying zone, where the solvent volatilizes or the adhesive layer solidifies by controlling the temperature and airflow, and is finally collected into a roll by the winding device. The coating thickness can be controlled by adjusting the scraper clearance, roll speed ratio, or pumping pressure.
Adhesive properties
The rheological properties of adhesives, such as viscosity and thixotropy, have a significant impact on coating uniformity. High viscosity adhesives require higher coating pressures, while low viscosity materials need to prevent flow. Parameters such as coating speed, backing tension, and drying temperature should be optimized according to the adhesive formulation and backing material. The coating thickness T can be approximated by the formula: T = Q / (W × V), where Q is the volume flow rate of the adhesive, W is the coating width, and V is the backing movement speed. In actual production, it is necessary to maintain stable thickness through online monitoring and feedback adjustment.
Backing layer pretreatment requirements
The surface energy, roughness and chemical compatibility of the backing layer affect the wetting and adhesion of the adhesive. Corona treatment or primer treatment is often required before coating to improve surface wettability. The treated surface tension should be higher than the adhesive surface tension to ensure good spreading. The backing material needs to have a certain tensile strength and dimensional stability to withstand mechanical stress during the coating process.
FAQs
The coating process needs to monitor the thickness, uniformity, and presence of bubbles or streaks. Thickness can be measured with an in-line thickness gauge, and uniformity can be assessed by light transmission observation or viscosity test. Common problems include uneven coating, edge thickening, under-drying or over-drying, etc., which can be improved by adjusting the coating head accuracy, drying conditions, or ambient humidity. The following table lists some of the problems and adjustment directions:
| Coating stripes | Check the flatness of the scraper and adjust the backing tension |
| The thickness of the adhesive layer fluctuates | Calibrate the feed pump to stabilize the backing speed |
| Insufficient viscosity after drying | Optimize drying temperature and time |
| Backing curl | Adjust the wind speed in the drying area to balance the humidity on both sides |
Relevant standards
The coating process should refer to the requirements of the industry standard for adhesive biocompatibility, volatile content and peel strength. The operating environment should control dust and static electricity to avoid contaminating the adhesive layer. The equipment needs to be cleaned regularly to prevent adhesive residue from affecting the coating quality. Personnel should wear protective equipment when operating and ensure that the ventilation system is operating effectively.
References
1. Coating Technology Handbook, Material Processing Press, 2020, Chapter 3 "Precision Coating Technology".
2. Adhesive Rheology and Coating Applications, International Journal of Coating Technology, 2019, Vol. 12, No. 3.
3. Surface Treatment Standard for Backing Materials, Industrial Materials Association, 2021, Standard No. IMS-TY2021.