The necessity of production and use of metallized textile materials becomes more and more actual. Such materials are required nowadays and in the nearest future the demand for them will increase. First of all it is connected with growth of number of electromagnetic environment “contamination” sources caused by emergence of mobile communications, personal computers and other radio frequency and microwave radiation sources.
The production of special clothes for electromagnetic fields shielding, infrared radiation protection, obtaining textile materials with antistatic, bactericidal, electrical conductive, radio absorbing, heat reflective and other special properties requires for use of metalized textile materials. Metallized fabrics and non-woven materials are more universal for using than metallized films, which are produced now, but which can not be applied for sewing clothes and other goods. Metallized textile material are something different than films. It is well known that air and water vapor very easy pass through textile materials. Texiles are draped well, form-fit every bulge and hollow of covered surfaces perfectly, resistant to physical- and mechanical effects and finally their service life is longer than the service life of films.
Existing methods of metallizing fabrics by means of electrolyte solutions are harmful because their production need to use aggressive and toxic substances which must be utilized.
Textile materials metallized by an electrochemical method are looking bad, they have a hard touch; adhesion of coating to a substrate is poor.
Besides of this the presented method doesn’t allow to control the conductivity of the fabrics and their other properties with good accuracy which is very important for further application.
There is a possibility to metallize textile materials by vacuum thermal evaporation. However this method is limited by a possibility to coat the textile materials by thin aluminium films only, that reduces its application significantly.
Furthermore this process is difficult to control and it is very difficult to receive thin aluminium films of specific thickness (resistance).
We suggest to metallize textile fabrics through a magnetron sputtering method, which is widely applicable in the microelectronics, however it has not yet been used in the textile industry. The method is based on use of an anomalous glow discharge in the inert gas by imposition on it of an annular zone of crossed inhomogeneous electrical and magnetic fields localizing and stabilizing gaseous plasma in a cathode area. Positive ions created in a discharge are accelerated to the cathode direction and bombard cathode surface in the erosion area. Sputtering of target surface takes place. Leaving particles are deposited onto a substrate (fabric, film). A high kinetic energy of the particles provides a good level of film adhesion to the substrate.
The magnetron sputtering method is realized at quite deep vacuum (about 5 х 10-5mm Hg) and allows to coat the substrates by thin films of copper, aluminium, titanium, brass, silver, stainless steel, bronze and other metals and their alloys. The method permits to coat the fabrics by compounds of some metals with oxygen or nitrogen. For example, to obtain a gold-like fabric titanium nitride can be applicated onto a fabric surface.
It is necessary to underline the fact, that the presented method practically doesn’t contaminate environment. There is no need to use any chemical materials, i.e. sewage water treatment is not required, which must compensate costs connected with an increased power consumption by the equipment because of a necessity to perform an essentially deep degassing and to use a magnetron. Installing the equipment doesn’t require presence of special engineering communications: sewage water treatment plants, steam generators and steam lines, chemical stations etc. It is allows to use this equipment even under working conditions of so-called small enterprises.
Recently we have started up a pilot plant, type UMN-180 produced and installed in the area of the “Ivtechnomash”Ltd. ( Ivanovo). The plant has a working width of 180 cm and can metallize fabrics, non-woven fabrics and films up to 170 cm width. Thin film of the real metal or alloy is deposited onto a fabric surface, which gives to the fabrics a noble and original color nuance, for example, mother-of-pearl color or metallic luster of stainless steel, titanium, gold, silver, aluminium, bronze etc. The specified fabrics colors and nuances are impossible to obtain by no one from the famous nowadays methods for treatment of textiles: dyeing, pigment printing, metallizing by means of electrolyte solutions, thermal vacuum evaporation.
As the treatment of fabrics is performed under soft conditions of so-called “low - temperature plasma” the fabric remains soft to the touch, maintains its permeability to air and moisture, drapability and strength.
Fig.1 Conductivity of polyamide fabric art. 5369-06 like funtion of sputtering time.
Fig.2. Transmittance of a polyamide fabric, art. 52001 metalized by aluminium in a frequency range from 1 to 1250 MHz
Application of a metal coating by sputtering causes electrical conductivity of the fabric (Fig. 1). Unlike other metallizing methods the magnetron sputtering method allows to regulate the thickness of a metal coating with enough accuracy and in consequence – its resistance, which is very important for formation of structures with a definite conductivity.
Because of conductivity synthetic fabrics or non-woven materials obtain antistatic properties. It is important, for example, for manufacture spark proof filters used in explosive productions (coal-mining industry, woodworking industry, food industry).
Conductive fabrics give the possibility to obtain materials shielding electromagnetic radiation. It could be used to obtaining light, strong, serviceable, long-run and attractive materials, shielding electromagnetic interference and masking in a wide frequency range (from infra-red to microvawes), fig. 2.
Fig. 3. Different kinds (a,b) of camouflage coating used for masking of defense objects upon a summer vegetal ground from optical and radar detection (produced on the base of metal coated fabrics “Ivtechnomash” Ltd).
The magnetron sputtering method is very economical. It is possible to deposit a very small quantity of metal at certain treatment parameters. This is useful during sputtering expensive metals and alloys, for example: silver, a small quantity of which as you know, can give to the materials bactericidal properties; or, for example, metals of platinum group used like catalysts.
Fig.4. Polyester fabrics, coated by silver
Previous researches have shown that cotton gauze covered by silver is bactericidal active to Staphylococcus, Pyosyaneus bacillus, Enterobacter cl., Proteus (fig. 5).
Fig. 5 Bactericidal properties of gauze covered by a thin film of silver
A preliminary conclusion has been made stating that gauze coated by thin silver film has a bactericidal effectiveness sufficient for its practical application in medicine. After sterilization such type of gauze was used for local treatment of surface burn wounds. The wounds healed faster in areas covered with a silvered material.
Preliminary evaluations state that the price for bandaging material manufactured on base of metalized gauze will be lower than the price for imported napkins on base of special ointments. Such bandage will have practically unlimited expiration life, whereas the expiration life of the above mentioned imported napkins is several years.
Dr. B. L. Gorberg
Chief of a laboratory of ion – plasma processes of Ivanovo State University of Chemistry and Technology