The coating machine applies a moisturizing lotion retention layer on the surface of the nonwoven fabric.

This article introduces the process of applying a moisturizing lotion retention layer on nonwoven fabric surfaces using a coating machine. The coating machine evenly applies the lotion onto the nonwoven fabric through methods such as blade coating, roller coating, or slot-die extrusion, and its rheological properties must conform to the power-law model. The equipment mainly consists of unwinding, coating head, drying, and rewinding sections. Coating quality is ensured by controlling parameters such as coating speed, drying temperature, substrate tension, and lotion viscosity. Key considerations in the process include controlling the coating amount, setting the drying temperature, and pre-treating the nonwoven fabric. The retention amount and uniformity of the coating are evaluated using gravimetric and optical methods. The production environment must be kept clean, and equipment should be regularly maintained to adapt to different materials and lotion batches, thereby stabilizing product quality and improving production efficiency.

Introduction

In the manufacture of personal care materials, it is a common process to build an emollient retention layer on the surface of a nonwoven fabric. As a key equipment, the coating process control directly affects the uniformity of the coating, the retention rate of the emulsion, and the performance of the final product. This article will systematically explain the implementation points of the coating machine in this application from the aspects of technical principles, process parameters and quality control.

Coating principle

The coating machine mechanically applies the emollient lotion evenly to the surface of the non-woven substrate. The main coating methods include scraper type, roller coating type and slit extrusion type. The rheological characteristics of emollient emulsion are usually oil-in-water or water-in-oil emulsion systems, and their rheological characteristics conform to the power law model: τ = Kγⁿ, where τ is the shear stress, K is the consistency coefficient, γ is the shear rate, and n is the flow behavior index. During the coating process, the emulsion needs to maintain proper viscosity and surface tension to ensure good wetting and penetration control of the nonwoven fibers.

Equipment composition

A typical film coating machine is composed of a unwinding unit, a coating head, a drying section, a winding unit and a control system. The coating head is responsible for the quantitative conveying and leveling of the emulsion; The drying section mostly uses infrared or hot air to promote water volatilization to form a retaining layer. The control system can adjust the coating speed, thickness and drying temperature.

Coating speed	Affects emulsion penetration and coating thickness
Drying temperature	Relationship between solvent volatilization rate and composition stability
Substrate tension	Ensure the flatness and uniform coating of non-woven fabrics
Emulsion viscosity	Determine the leveling and retention

Process control

The amount of coating can be controlled by adjusting the scraper gap or the pressure between the rolls, and the common range is 10-50 g/m². The drying temperature should be set according to the flash point of the emulsion and the heat-sensitive components to avoid excessive heating leading to emulsion demulsification or degradation of active substances. Non-woven fabric pretreatments such as corona treatment can improve surface energy and enhance emulsion adhesion. The online monitoring system can detect coating thickness and defects in real time.

Performance evaluation

Coating performance evaluation includes retention determination, uniformity analysis, and simulation testing. The amount of retention can be calculated by gravimetric method: W_r = (W_c - W_b/A, where W_ris the reserved amount per unit area, W_cis the weight of the substrate after coating, W_bis the original weight of the substrate, and A is the sample area. Uniformity can be characterized by light microscopy or infrared imaging.

Notes:

The production environment should be kept clean to prevent dust from affecting the integrity of the coating. The emulsion needs to be filtered regularly to prevent solid particles from clogging the coating head. Equipment maintenance should pay attention to the wear of scrapers or rollers, and calibrate the metering unit regularly. The process parameters need to be adjusted according to the weight of the non-woven fabric, fiber density and emulsion batch.

Epilogue

In the application of coating emollient retention layer on the surface of non-woven fabrics, the coating machine can achieve stable output of coating performance through reasonable equipment selection and fine process control. Continuous optimization of coating efficiency and material utilization can help improve product quality and production process economy.

References

1. Fundamentals of Coating Technology, Journal of Materials Processing, No. 3, 2020;
2. Review of nonwovens surface treatment technology, Progress in Textile Science and Technology, 2019;
3. Research on the Influence of Rheological Properties of Emulsions on Coating, Fluid Engineering, No. 5, 2021.