The Research And Practice Of Infrared Camouflage Fabric

The study of infrared camouflage fabrics has given rise to a great attention in the military affairs in the world. The equipment of infrared camouflage uniforms with high performance not only increases the chance of survival and safety of soldiers in the battlefield, but also strengthens the battle effectiveness of the army. In recent years, with the development of thermal imaging technology and the application of detector, the pattern painting camouflage uniform has made a great progress in the near-infrared camouflage as well as in the thermal infrared camouflage, and so they can satisfy the requirement of campaign in different environment. In this paper, on the basis of infrared physics and electromagnetic radiation theory, infrared camouflage fabrics have been carried out in terms of human body. In the near-infrared camouflage aspect, the green leaves were chosen as a simulating object at first, and then the PET and cotton fabrics were dyed with disperse dyes and vat dyes respectively, and eventually the relationship between dye structure and reflected spectrum was discussed. In the thermal infrared camouflage aspect, the low emissivity fabrics were made by means of electroless plating. The hollow cenospheres coated with a layer of different metals were also produced, and then added to the adhesive and coated on the fabric surface. Results show that they have a good electric conductibility and anti-electromagnetic effectiveness.In order to simulate the reflected spectrum of green leaf in the near-infrared band, PET and cotton fabrics were dyed with disperse and vat dyes respectively. Results show that the PET fabric dyed by disperse blue E-4R, disperse yellow E-3RL and disperse black S-2BL has the ability of near-infrared green camouflage. The near-infrared green camouflage performance can also be obtained by using vat light yellow L-2LY, vat yellow L-LDY, vat blue L-MG (or blue 8396) and vat black R for cotton fabrics. Disperse blue E-4R and vat blue L-MG are two important dyes which play a crucial role in near-infrared camouflage. As the concentration (owf %) of disperse blue E-4R (or vat blue L-MG) increases, the reflectivity of dyed fabric decreases gradually, but the wavelength at which it has the max absorbance to dye is not changed. When the concentration of dye is 1～2%, the reflected spectrum of dyed fabric is very close to that of green leaf in the region of 0.67～0.78μm (called section A). The reflected spectrum of fabric by using a combination of dyes is greatly influenced by its composition, and it is only determined by one of dyes of it's reflected spectrum occurs close to the long wave band. The weave has little effect on the near-infrared reflected spectrum for the same dye formula. The near-infrared camouflage capability for PET/cotton fabric mainly depends on cotton fiber dyeing properties.Based on electroless plating technology, PET fabrics were coated with nickel, copper and sliver to obtain low emissivity fabric respectively, and a better electric conductibility and electromagnetic shielding effectiveness was also obtained. Some results show that yarn structure and fabric's cover tightness have effect on the electroless plating process to some extent. As the weight increasing rate is the same, the shielding effectiveness (SE) processed in acidic bath is better than that in alkaline bath. As the plating thickness increases, the surface resistance decreases, and the electromagnetic SE increases at first, and then reach to a certain level. The abrasion of nickel and copper plating fabrics are better than that of silver plating fabric. The coating structure and crystal grain of silver plating fabric are different by using different reducing agent, and the content of silver is beyond 95% and it's crystallinity is in the range of 45～60%. C₁₂H₂₂O₁₁ was the most suitable reducing agent which bring high quality coating structure, and its crystal grain is relatively small compared with H₂NNH₂, KNaC₄H₄O₆ and HCHO. The SE increased at first, and then reached to a certain level with weight increasing rate. As the chemical reaction was not carried out completely by using C₆H₁₂O₆, the SE was greatly influenced. With regard to ultrasonic wave enhanced treatment on electroess silver plating, the optimum parameters are given in the following: AgNO₃ 5.4g/L, NH₃·H₂O 12g/L, C₁₂H₂₂O₁₁ 25g/L, KOH 3.5g/L, CH₃CH₂OH 100ml/L, pH=12.5, the temperature is about 35℃.With cenosphere as core, the electroless metal-plating experiments such as nickel plating, copper plating and silver plating have been done so that the conductive powder with perfect low emissivity metal-coating has been obtained. The coated fabrics were also fabricated by using different powders. Results show that the treatment before plating has a great effect on coating quality. The coating fastness and the deposit rate can be improved by using coupling agents. The coating structures are different from each other for different reducing agent, but their crystal structures are all silver. For coated fabric, C₆H₁₂O₆ is the most suitable reducing agents to obtain a better electromagnetic SE. As the cenosphere add-on increases, the electric resistance decreases and the SE increases. The anti-heat radiation properties are improved, and the order against heat radiation is given as follow: untreated cenosphere＞silver plating cenosphere (C₆H₁₂O₆)＞copper plating cenosphere＞nickel plating cenosphere.Combined with a special made blackbody, a Fourier transform infrared (FT-IR) spectral radiometer has developed to measure the thermal characteristics of common fabric, such as cotton, wool, linen, PET, nylon and so on, electroless plating fabrics and coated fabrics in the thermal infrared region between::8, and 14μm at near ambient temperature. The mathematical model for measuring surface emissivity of fabric was put forward by the author. Results show that fabric's cover tightness has great effect on transmitting properties of thermal infrared radiant energy. As cover tightness increases, transmittivity significantly decreases. As for cotton fabrics, the transmittivities are less than 65%, but for PET fabrics, they are less than 75%. Transmittivity was not equal to zero even for compact fabrics. The hairiness in the fabric, especially made of staple yarn, plays an important role in shading some parts of infrared radiation energy. The relationship between transmittivity and cover tightness is very complicated for different fabrics, exemplified by the exponential function for cotton fabrics, the linear function for PET fabrics. Similarly, the exponential relationship between transmittivity and fabric's thickness, the linear relationship between transmittivity and fabric's area density were deduced on the basis of statistical analysis. The surface emissivities of fabrics made from different materials are able to differentiate one kind of material from another, and the order is given as follow: polyamide＞PET＞wool＞cotton＞electroless plating fabrics. The surface emissivity of blended fabric is determined by the characteristics of textile materials it constitutes. For coated fabric, surface emissivity is greatly influenced by the binder contained on the fabric surface. The color has no effect on surface emissivity for the same kind of fabric within the range of 8～14μm. The fabric emissivity can be reduced distinctly by improving the reflectivity of infrared rays. The transmittivity and emissivity of fabric are not influenced by the ambient temperature if not exceeding 200℃. The thermal imaging results show that electroless plating fabric and coated fabric with cenosphere have the ability of thermal infrared camouflage.