Patent Number: 051035049
Section: summary

From DE-A-29 23 286, a textile fabric is known whose orthogonally crossing warp threads and weft threads are made of spun mixed yarn of steel fibres of stainless steel and of textile fibres. The steel fibres may be extremely thin, less than 25 micrometers in diameter, for example. According to this document, the mesh is proposed to measure at least 0.5 cm. This textile fabric is designed for carpet floors or working garments, for example, in order to obtain an antistatic network and thus prevent electrostatic charging. However, such a fabric does not provide effective protection against microwaves and other electromagnetic radiation, to which in particular the hospital personnel, for example, when operating electromedical equipment such as X-ray, ECG and EEG apparatus and the like, and the personnel for operating radar installations, for example, are exposed. In the course of electronization, also heart pacemakers are miniaturized and refined, but at the same time rendered susceptible to electromagnetic radiation interference such as occurs in everyday life due to, for example, broadcast and TV stations and various electrical apparatus, electric motors, electrical and electronic ignition control devices in motor vehicles, shavers, electrical household appliances, and electronic computer installations and the like. Modern heart pacemakers are designed so as to take over the pacemaker function only when the normal heart rhythm is disturbed, but not to interfere when the heart rhythm is normal. The occurrence of electromagnetic radiation, however, may result in a disturbance of the heart pacemaker control such that incorrect information on the current heart activity may be received and the control may fail in that case. While it is true that clothing which shields against electromagnetic radiation exist, such as the vest known from US-A-4 196 355. However, this vest, due to its construction and weight, is much too heavy and uncomfortable to be suitable for normal applications. According to the invention, a textile fabric and clothing made thereof are provided, which are effectively suitable for shielding against electromagnetic radiation, in particular in the microwave range, and, at the same time, do not restrict the wearing comfort of usual clothing. The invention is based on the perception that total shielding against electromagnetic radiation is not necessary, since radiation below certain intensities can be accepted without health impairment, and that this provides the possibility of achieving sufficient shielding by means of clothing even without restriction on the wearing comfort. For shielding against electromagnetic radiation, the invention provides a textile fabric whose orthogonally crossing warp threads and weft threads are made of spun mixed yarn of steel fibers of stainless steel and of textile fibers. To this end, the textile fabric has the quality of fabrics for usual clothing, wherein the textile fibers comprise cotton fibers and are twined with the steel fibers which measure 6 to 10 micrometers in diameter and constitute a content of 10 to 15% per weight of the mixed yarn, the distribution of the warp threads and the weft threads in the fabric and the composition of the warp threads and the weft threads being substantially the same, the number of mixed yarn threads in warp direction and in weft direction each is 18 to 20 threads per cm, and the yarn fineness of the textile fabric is in the range of 30 to 50 tex (g per km), especially of 38 to 40 tex, such that a shielding by 20 to 40 dB against electromagnetic radiation at a frequency of 10 GHz is established by the fabric. Owing to the content and fineness of steel fibers suggested in accordance with the invention, a textile fabric suitable for effective shielding against excessive electromagnetic microwave radiation can be obtained in a clothing fabric quality, which textile fabric is not too stiff. Hence, clothing can be made which is comparable to clothing without steel fibers. For the shielding effect, it is essential that the steel fibers and the textile fibers are spun and twined with each other in a manner such that a substantial part of the steel fibers is exposed on the exterior surface of the mixed yarn and sufficient mutual electrical contact of the fibers is achieved in the warp and weft threads at the crossings of the fabric to form a Faraday cage. The average number of the steelfibers in the yarn cross-section is preferably 10 to 15. Preferably, the thickness of the steel fibers measures 8 micrometers, and the content of the steel fibers in the mixed yarn is preferably 13.5% per weight. The length of the steel fibers is preferably in the range of the length of the cotton fibers and, hence, measures 3 to 10 centimeters. Although it is further possible to provide a mixture of cotton fibers and polyamide fibers, it is preferred to provide textile fibers exclusively of cotton. Cotton is capable of absorbing moisture and improves the electrical conductibility with increasing moisture absorption. Although a twined one-thread yarn, i.e., a yarn only single-twined, may be used, it is preferred to use a mixed yarn made of double-twined mixed yarn threads, each of which is made of textile fibers and steel fibers in a twined manner, wherein the single threads have a yarn fineness of 16 to 20 tex and a degree of turns of 550 to 650 turns, especially Z-turns, per m, and wherein the degree of turns of the double-threads is 400 to 480 turns, especially Z-turns, per m. The textile fabric according to the invention is light (the weight of the textile fabric is preferable in the region of 160 g per m.sup.2) and permeable to air and washable like other cloths without impairment of the shielding effect against electromagnetic radiation as would be the case if there were no discrete steel fibers but, instead, for example, a metal coating of the textile fibers. Moreover, the textile fabric according to the invention may be dyed such that pleasing and fashionable articles of clothing can be made of it. A textile fabric according to the invention having been proved and being excellently effective to shield heart pacemaker against microwave radiation was made of pure cotton with spun with steel fibers. The warp threads and weft threads were made of double-twined yarn of a fineness of R 38 to 40 tex made of single-threads of a fineness of R 16 to 18 tex. The degree of turns of the single threads was 590 to 640 Z per m and that of the Yarn was 420 to 440 Z per m. The content of steel fibers spun into the single-threads was about 13.5% per weight of the mixed yarn. The thread density of the textile fabric was 18 to 20 threads per cm, each, in warp direction and in weft direction and the average weight of the textile fabric was 160 g per m.sup.2. The textile fabric had an elongation of 9 to 14% at a breaking force of 638 to 672 N. The clothing according to the invention is completely or partly made of a textile fabric according to the invention. This textile fabric may completely form the clothing or may be provided as its interior lining. It is also possible to line the textile fabric itself with a lining of different textile material. For the manufacture of this textile fabric, usual pieces of fabric are cut out which are sewed together along joint seams. According to the invention, it is essential that the textile fabric is made of the above-presented textile/steel-fiber fabric according to the invention and covers at least the upper part of the body and the hip area of the person wearing the clothing as well as at least the person's upper arms approximately to the elbows. To avoid interruption of the shielding effect in the area of the joint seams, the joint seams should be turned up into each other and sewed together by at least two seams with a sewing yarn that is also a textile-fiber/steel-fiber mixed yarn of the kind according to the invention. However, the content of steel fibers in the sewing yarn may possibly be greater than the content in the threads of the textile fabric. All fasteners of the clothing, such as zip and button fasteners, should be free of metal and be underlayed with an interior border band or flap made of the textile-fiber/steel-fiber fabric according to the invention and provide an overlap breadth of at least 5 and preferably 7 centimeters. If pockets are provided in the textile fabric, these pockets should not be inserted into but put on the fabric, in order to avoid interruptions of the shielding effect. In a preferred embodiment of a clothing according to the invention, the clothing is in the form of a shirt or T-shirt which has at least elbow-length sleeves, covers the hip area of the person wearing the shirt and is provided with a closable neckline that, even when not closed, is covered by an interior flap made of the textile-fiber/steel-fiber fabric according to the invention. As proven by numerous experiments, such a clothing is most suitable for wearers of heart pacemakers to attain an effective shielding of the heart pacemaker against electromagnetic radiation disturbances and, at the same time, achieving the wearing comfort of other shirts or T-shirts. Owing to the invention, shirts or T-shirts of this kind may be manufactured in such a way that they look like other shirts or T-shirts and, hence, the fact that a person needs a heart pacemaker is not discernible from this kind of clothing. In another preferred embodiment, clothing according to the invention suitable for the personnel of radar installations takes the shape of an overall, in which the textile-fiber/steel-fiber fabric according to the invention covers the upper part of the body as well as at least the upper arms and the hip area, at least down to the knees. As protective clothing for hospital staff against the influence of electromagnetic radiation emitted by electromedical apparatus, two-piece clothing consisting of a jacket or blouse and a pair of trousers is suggested, wherein the pair of trousers is overlapped by the jacket or blouse by at least 10 centimeters and the jacket or blouse in its chest area has overlapping parts of textile-fiber/steel-fiber fabric held together by Velcro-type fasteners. Since clothing according to the invention is made of comfortable textile material, it can be worn completely closed, while the Velcro-type fasteners prevent the jacket or blouse from being worn open. In this arrangement, one of the overlapping parts of textile fabric preferably extends to ne shoulder of the wearing person, and the other part of textile fabric extends at least to the middle of the person's body. The waist measurement of the trousers of this clothing is preferably also adjustable by means of Velcro-type fasteners. In such clothing according to the invention, an interior lining may be formed of the textile-fiber/steel-fiber fabric according to the invention, while the exterior side of the clothing may, for example, made of light cotton cloth of a quality usual for hospital clothing. When the clothing according to the invention is embodied by an overall or two-piece suit, a stand-up collar containing textile fabric material according to the invention is preferably additionally provided.