| Method for producing compressed, plastic-coated rovings -> Monitor Keywords |
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Method for producing compressed, plastic-coated rovingsRelated Patent Categories: Adhesive Bonding And Miscellaneous Chemical Manufacture, Methods, Surface Bonding And/or Assembly Therefor, Bonding Of Flexible Filamentary Material While In Indefinite Length Or Running Length, Of Filamentary Material Only To Form Article, Article Is Sheet Or WebMethod for producing compressed, plastic-coated rovings description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070175570, Method for producing compressed, plastic-coated rovings. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention relates to a method for producing compressed, plastic-coated fibers or rovings, consisting of substantially unidirectional parallel filaments. In particular, the present invention relates to a method for producing sized and compressed thin threads or tapes which consist of substantially parallel filaments which are used, for example, for producing sized thin threads, in particular saw threads for cutting out precise workpieces in the electronics industry, or for producing tapes and prepregs, fiber-reinforced plastic granules and fiber-reinforced shaped articles, and in extrusion. [0002] The production of plastic-coated fibers and rovings which preferably consist of substantially parallel filaments, also in the form of tapes or prepregs, is known per se. Usually, rovings which consist of filaments are coated with a plastic or a mixture of plastics which may contain various additives and are processed in further processing stages, depending on the intended use, to give threads, granules, fiber-reinforced shaped articles or pultruded or extruded profiles. [0003] Thus, it is known that rovings to be coated in the melt coating method can be passed through the melt of a thermoplastic, then allowed to cool and then further processed. When this method is used in practice, in particular in the case of a high proportion of fibers and increasing fiber length, however, a large variation in the strength values and numerous local weak points in the shaped article are found. Owing to the high shear forces, such as those which occur in melt impregnation, fine filaments, for example comprising carbon fibers, are broken and filament damage or tearing of threads occurs in the process. A similar situation is encountered with the use of wet coating methods, i.e. of a liquid impregnating bath in which the plastic is dissolved in a solvent, in this case the difficulties associated with the evaporation of the solvent occurring in addition. [0004] In the dry coating method, the rovings to be coated are preferably moved through a fluidized bed. This fluidized bed consists as a rule of a thermoplastic polymer powder in which additives are optionally incorporated (compounded), or of a curable thermosetting plastic powder or plastic powder premix, this being absorbed onto the fibers as a coating. It is also possible to apply the individual components of the coating in the fluidized bed method uniformly and directly to the fibers in the desired composition, the individual coating components present in the fluidized bed optionally additionally being mixed in the fluidized bed so that separation of the individual components is virtually prevented. Thereafter, the coated fibers are at least partly melted, preferably in a continuous oven, for example by means of IR radiation, and then cooled again. An improved distribution of the plastic on the fiber is thus achieved. However, this dry coating method has the disadvantage that a part of the powder used for the coating falls off the fiber again after emergence from the coating unit, with the result that the powder application and hence the proportion of resin and/or the proportion of filler in the end product is limited, which adversely affects the quality of the end product. However, the coating powder also falls off in the continuous oven and decomposes in contact with the overheated oven surface, resulting in the formation of decomposition products which enter the venting unit and the environment via the waste air. In addition, these particles, in the form of dust or in the form of decomposition products, also enter other parts of the production plant, in particular the filters of the venting unit, and block the filters of the venting unit there. This in turn leads to imbalances in the operating procedure and the operating conditions, which adversely affects the quality of the coated rovings. [0005] In all cases of said coating methods, a large variation in the strength values and numerous local weak points in the thread formed and hence also in the shaped article occur in practical use, in particular in the case of a high proportion of fiber. In particular, there are also local differences in the thread diameter and in the roundness or in the degree of roundness of the fiber and in the coating thereof with plastic, which subsequently causes said disadvantages. There is therefore a need to reduce or completely eliminate these disadvantages. [0006] For the production of thin threads, in particular of saw threads for the electronics industry for cutting precise shaped articles, for example shaped articles which consist of silicon carbide, or wafers, chips and related shaped articles, or in the production of solar collectors, it is furthermore necessary for these threads to have been processed so as to be as thin as possible and very precise, i.e. of the same diameter along their entire length, the diameter of these threads being in the micron range, preferably in the range of 100-1000 microns (.mu.m), and the variation in the linear deviation of the diameter from the required value should be within only a few microns. In this context, a very exact sizing of the threads is necessary, i.e. both the diameter and the roundness of the thread along the entire thread length are exactly established and monitored within the specified dimensions. [0007] For the coating of rovings, in particular in powder coating, preferably linear unidirectional rovings are used, also in the present invention, i.e. rovings in which the filaments are arranged substantially parallel and substantially straight or plane-parallel. These rovings can be more easily fanned out and hence more uniformly coated in the coating process. [0008] It has now been found that thin plastic-coated continuous threads (consisting of a multiplicity of individual filaments) or those comprising plastic-coated fibers or rovings, consisting of substantially parallel filaments, are obtained if the rovings on which the plastic, optionally applied as powder, is present in the molten or liquid state are passed, after the coating, through a rotating device by means of which local rotation of the fibers is executed. As a result of such a local high rotation, the fibers are compressed to a high degree. In the process, the threads are twisted with one another, starting from the rotating device, backwards along the individual threads in the direction of the coating device. After passing through the rotating device, however, there are no longer any rotations or there are rotations only to a small extent, so that, after passing through the rotating device, the filaments have no spiral revolutions per meter or only a small number thereof but are arranged substantially parallel, linear and straight. Such threads can then be further processed, for example additionally coated with a suitable plastic and/or optionally with mineral particles and then hardened. [0009] In a particular embodiment of the present invention, the rotating device consists of a rotating sizing die. By means of the rotating sizing die according to the invention, the fiber composite is additionally sized and particularly highly homogenized, and at the same time compressed, the enclosed gases being forced out of the composite. Sized rovings which have been processed to have an exact diameter along their entire length and have only a small linear deviation in the desired diameter length and hence a high degree of roundness and moreover are very compact or compressed result. [0010] This gives excellent saw threads or coated rovings which have been processed exactly in the diameter or in the degree of roundness along their entire length, the variation in the linear deviation of the diameter from the required value being small. These saw threads are suitable in particular for producing shaped electronic articles, such as wafers, chips and related shaped articles. [0011] In addition, there are the advantages that the material applied during the coating of the filaments is better distributed in the roving owing to the effect of the rotating device. Consequently, no material or only very little material falls off the coated fiber on entry into the continuous oven. As a result, material losses are reduced, the material consumption is optimized and the environment is protected, which is evident in particular on heating or on hardening the coating materials. [0012] If a rotating sizing die is used, any melt cone is spun away by the rotating sizing die at its die edge and is not deposited dropwise on the thread. In accordance with the design of a sizing die, as shown below in FIG. 2a, any melt cone is spun away at the die exit. A sized thread of high density and free of air inclusions results. [0013] By means of the method according to the invention, the proportion of filler in the coating premix can be substantially increased so that products having a lower proportion of fibers and higher proportion of fillers can be produced. The bulk density and the flowability of granules produced from such threads compressed according to the invention are also substantially increased, and the formation of tufts during granulation is considerably reduced. [0014] By means of the method according to the invention, the tensile strength of the coated rovings in the production method itself is also increased to a surprisingly great extent and can readily be doubled. Thread breaks in the method, in particular in the area between the coating device and the rotating unit, are thus very substantially avoided even at high thread tension. [0015] These unexpected advantages make it possible to carry out the entire method under significantly greater thread tension, which in turn permits a more balanced procedure and increased productivity of the production plant. Surprisingly, as a result of the local rotational effect produced by the rotating device, even relatively coarse powder particles having a particle size up to 300 .mu.m remain enclosed in the composite in dry coating, so that uneconomical very fine milling of the polymers with narrow particle size spectrum can be dispensed with. [0016] The invention is defined in the patent claims. In particular, the invention relates to a method for producing compressed, plastic-coated fibers or rovings, consisting of substantially parallel filaments, starting from rovings consisting of plastic-coated filaments, characterized in that rovings, or a plurality of such rovings as a composite, consisting of substantially parallel filaments on which the plastic applied, optionally as a powder, is present in the molten or liquid state, are passed, after the coating, through a rotating device by means of which local rotation of the fibers is executed so that the individual threads in the method are twisted with one another in the form of rotations, starting from the rotating device, backward along the threads in the direction of the coating device it being the case, however, that after passing through the rotating device there are no longer any rotations or there are rotations only to a small extent, so that, after passing through the rotating device, the filaments have no spiral revolutions per meter or only a small number thereof, but are arranged substantially parallel and linear or straight. [0017] The invention also relates to a particular embodiment for producing compressed, plastic-coated fibers or rovings, consisting of substantially parallel filaments, which is characterized in that the rotating device consists of a rotating sizing die, sized and compressed threads being obtained. [0018] The roving treated in this manner or a plurality of such rovings as a composite can be subjected to further coating or subsequent coating. In this context, the invention also relates to a method which is characterized in that the rovings compressed according to the invention are subsequently coated in a subsequent coating procedure additionally with mineral powders or metal powders at temperatures above the melting point of the coating polymer, or with plastic, optionally as a mixture with mineral powders, and then hardened or allowed to solidify. [0019] The present invention also relates to the use of the rovings compressed according to the invention, or a plurality of such rovings as a composite, for producing saw threads which are suitable, for example, for producing shaped electronic articles, preferably wafers, chips and related shaped articles, and for producing tapes and prepregs, fiber-reinforced plastic granules and fiber-reinforced shaped articles or fiber-reinforced pultruded or extruded profiles. Included therein are also fabrics which are woven from coated rovings and optionally then pressed. Tapes also comprise continuously produced fiber-reinforced tapes. Prepregs comprise unidirectional and fabric-reinforced prepregs. [0020] The present invention also relates to the threads, saw threads, tapes, prepregs, fiber-reinforced plastic granules, fiber-reinforced shaped articles, fiber-reinforced pultruded or extruded profiles produced in this manner. The present invention furthermore relates to a device for carrying out the method according to the invention. [0021] Said coated individual filaments or individual rovings as a composite may have been coated in the melt coating method, in the wet coating method and/or in the dry coating method, preferably in the dry coating method. The compression of the individual filaments or of the individual rovings as a composite is carried out in such a way that, after the coating process, the coated, individual filaments or individual rovings as a composite are passed through at least one rotating device, preferably a device which simultaneously sizes and compresses, such as, for example, a rotating sizing die, with the result that these filaments or the individual rovings as a composite are compressed on passing through or are simultaneously both sized and compressed by the rotating sizing die. [0022] A suitable rotating device as indicated in FIG. 1 and shown more exactly in FIG. 2 may consist, for example, of two cooled shafts provided with V-grooves, which are arranged one behind the other at an angle of less than 90.degree. (<90.degree.), preferably at an angle in the range from 5.degree. to 20.degree.. Preferably, the 1st shaft is arranged at an angle of more than or less than 90.degree. to the thread direction, preferably at an angle of at least 91.degree. or 89.degree. (>1.degree.), preferably at an angle in the range from 600 to 120.degree.. The second grooved shaft is arranged at right angles to the thread running direction. The coated roving runs through, for example, above the first shaft and below the second shaft, i.e. the rovings are passed over the first shaft and then under the second shaft, in each case in the V-grooves thereof. In this case, the first shaft rotates counterclockwise and the second shaft clockwise. The V-groove of the first shaft is laterally offset in the thread axis by at least 1 mm, preferably at least 5 mm, so that the thread runs laterally over the oblique flanks of the first shaft. The thread is pressed against the V-flanks as a result of the angular arrangement of the shafts and as a result of the offset of the grooves and is rotated by the component acting perpendicularly to the thread axis, so that a clockwise or counterclockwise rotation of the thread results. The number of rotations (stated as rotations per meter) is determined primarily by the angle opening of the 1st shaft. The rotation of the grooved shafts is achieved by the friction with the coated rovings or additionally by an external drive. The number of rotations per meter is product-dependent and is determined by optimizing the angular arrangement and the friction of the coated roving in the V-grooves, which presents no problem for the person skilled in the art. [0023] The rotating shafts are preferably mounted or installed after the first or optionally after a further continuous oven. The rotation acts uniformly, as already described above, over the entire length of the roving or rovings, back to the location where the roving leaves the coating device or, for the present example, the first rotating shafts. After passing through the rotating device, the rotations cease again and give the thread according to the invention with substantially parallel fibers, which have no rotations per meter or only a few thereof. [0024] If a sizing die is used, it rotates at such a high speed that the individual filaments or individual rovings as a composite are compressed and also sized. All excess coating material which forms as a melt cone at the die exit is spun away during the sizing. The diameter of the sizing die is set so that the desired thread diameter is obtained. As already mentioned, the threads in the method are rotated from the rotating sizing die in each case along the thread backward in the direction of the coating device. After passing through the rotating sizing die, there are, however, no longer any rotations in the forward direction or only a part of the rotations persist, so that, after passing through the rotating sizing die, the threads (filaments) have no spiral revolutions per meter or only a small defined number thereof. Continue reading about Method for producing compressed, plastic-coated rovings... Full patent description for Method for producing compressed, plastic-coated rovings Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method for producing compressed, plastic-coated rovings patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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