Abstract:

Objective With the development of hyperspectral remote sensing detection technology, conventional vegetation-like camouflage fabrics are easily detected due to the phenomenon of "metamerism" based on differences in near-infrared bands, which pose a serious threat to the target's battlefield survival. The use of dyes to prepare vegetation-like camouflage fabrics still faces the problems in complex printing and dyeing processes and low efficiency. Therefore, simple and rapid preparation of camouflage fabrics with a high degree of fit with the vegetation background by the direct printing method of disperse dyes is of great significance for the development of military textiles.
Method Based on the principle of subtractive color mixing, the disperse dyes that meet the requirements of vegetation-like camouflage were screened by disperse dye direct printing, then the vegetation-like Vis-NIR reflection spectrum characteristics of the printed fabrics were prepared. The influence of the types and contents of disperse dyes, the types and proportions of dye combinations, fabric specifications and water content on the characteristics of the Vis-NIR reflection spectrum of polyester printed fabrics were studied. The vegetation-like Vis-NIR camouflage performance was analyzed by calculating the Euclidean distance, the spectral angle, and the spectral correlation coefficient between the printed fabric and the leaf reflection spectrum, and the color fastness performance were evaluated.
Results Different species of green leaves have similar spectral characteristics of Vis-NIR reflectance. Selecting suitable disperse dyes to directly print polyester fabrics can provide them with good vegetation-like Vis-NIR camouflage properties. The type and content of blue disperse dyes were found to be the keys to affect the starting position and slope of the "red edge". For Disperse Blue NP-SBG, Disperse Blue S-GL and Disperse Blue RD-GL dyes, the starting position of "red edge" was not influenced by the change of dye content, but the slope of "red edge" decreased when increasing dye content. For Disperse Dark Blue HGL, Disperse Navy Blue S-2G, Disperse Dark Blue S-3BG, Disperse Brilliant Blue 2BLN, Disperse Blue LF-B and Disperse Blue ACE dyes, as the dye content increases, the starting position of the "red edge" red shifted with a slope increase. The decrease of fabric thickness and the increase of water content both caused reduction in the reflectivity of "near-infrared plateau" of the fabric. The water content of the fabric was identified as the fundamental cause for the formation of the "water absorption valley" in the spectral curve. With the increase of water content, the position of the absorption valley remained unchanged and the reflectance decreased. With the 240 g/m² woven natural white polyester fabric as the base fabric, the printed fabric was prepared under the condition that the mass ratio of Disperse Blue NP-SBG, Disperse Orange 30 and Disperse Dark Blue HGL was set to 2.5:2.0:1.1. When the moisture content was 120.9% (Fig.5), its spectral reflectance curve was found similar to the Vis-NIR reflection spectrum of green vegetation. The Euclidean distance to the spectral curve of Everyreen leaves was 0.346, the spectral angle was 0.169° at 400-780 nm, 0.009° at 780-1 350 nm, 0.094° at 1 450-1 780 nm, and 0.107° at 2 000-2 350 nm, with the spectral correlation coefficient of 0.997 (Tab.3), which meets the first-level hyperspectral camouflage requirements. In addition, the fastness of the printed fabric against fading, staining, dry rubbing and wet rubbing all reached grade 5.
Conclusion The disperse dye-printed fabrics with vegetation-like Vis-NIR reflection spectrum characteristics have good field visible light camouflage performance and Vis-NIR spectral camouflage performance, and the overall color fastness performance is excellent. In the actual application process, a soft and high-strength colorless transparent plastic film was adopted to encapsulate the wet camouflage fabric to keep its moisture content unchanged, which can be used as military tents, camouflage nets, material covers and various weapons and equipment smocks.

Key words: imitation vegetation, Vis-NIR camouflage, reflectance spectrum, disperse dye, polyester fabric, printed fabric