STABLE FABRICS AND REDUCED PERMEABILITY. FOR PAPER MANUFACTURERS. CONTAINING PIBRAS COM FINS DESIGNED TO DISTORT AT LOW LEVELS
STRENGTH BY HAVING A REDUCED SURFACE IN TRANSVERSAL CUT INSIDE THE FIN
BACKGROUND OF THE INVENTION In the preparation of the paper, woven and spiral woven webs are used to support the cellulose pulp fibers as they travel through the paper making process and as they are converted from a thin aqueous paste to finished paper.
It has been found that the control of the mechanical stability and permeability of these bands is a critical factor for the production of consistent, high quality paper. As they have increased the speeds of the paper manufacturing machines, the fabrics designed for use in the dryer sections of the paper manufacturing machines have seen their permeability reduced from 1515 m3 per minute per m2 with a pressure differential of 1.27 cm. of water up to 100 or less. There has also been a tendency towards the use of thinner fabric constructions to minimize the differential forces in the paper when it passes over and under the bands in certain procedural steps. For woven materials, these two requirements for fabrics used by paper manufacturers are in conflict since the common way to reduce permeability is to increase the size of the weft yarn or the number of passes per centimeter, and both factors can result in a greater thickness of the tissue. Increased weft adjustment forces are required to force the wefts in these fabric designs to achieve the contemplated products of low permeability. These high frame adjustment forces lead to damage to fibers and machine. For spiral woven fabrics, ribbons and X-shapes, threads have been developed that are inserted into the open areas of the fabric design. These designs give satisfactory permeability results, however, they require very careful control of the sizes and levels of the relatively high forces to insert the material into the tissue and prevent distortion thereof. DESCRIPTION OF THE PREVIOUS TECHNIQUE As the demand for industrial fabrics and for paper manufacturers has shifted towards thinner, reduced permeability materials, the suppliers of such fabrics have changed from the use of round monofilament wefts to the use of twisted and wired constructions of the yarn, which have a greater capacity to conform up to the interstitial spaces formed in the intersections of the warp and weft yarns. This shift has been moderately successful in terms of the production of lower permeability and improved tissue stability. Some negative results of this practice are that the smaller monofilaments used in the wired constructions are more easily damaged due to their severe exposure to environmental conditions and that the wired strands tend to be contaminated to a greater degree with the "tars" of the process in a more accelerated way than the frames based on authentic monofilaments. The supplemental stages of handling and processing required to produce these twisted and wired yarns also make their cost remarkably greater than those of the monofilament. There has also been a shift towards the use of warp yarns more like the ribbon. These warps generate an improved contact with the paper and decrease the number of interstices, resulting in a greater permeability of the fabric. The reduction in the number of interstices has had a negative impact on the stability of the tissues since in the interactions at the junctions of the fibers they block or interlock the tissue. The wear caused by the thin profile of the threads that belong to the weft and that have a ribbon shape has also been an inconvenience to a more popularized use of this concept. The stability of the fabric is improved by increasing the interaction between the warp and weft yarns. When each pass of the weft is inserted into the fabric, it is struck against the warp so that the warp assumes a ripple without ideal use. ** The weft remains relatively flat, and the distortion created at the mechanical intersection of the warp and the weft contributes remarkably to the stability of the weave. Current methods for improving stability include increasing the count of passes, the use of warps and / or multifilament wefts, the use of wired weft yarns and the application of resinous tissue treatments. Each of the methods mentioned here is acceptable in selected areas, however, they all imply a penalty for cost or performance that prevents these innovations from being acceptable at a general level. In the patent number 5,097,872, Laine et al, teaches the use of an X-shaped fiber to achieve improved stability in the fabric, however its application requires an almost complete flattening of the fiber on one side by bending forces and the Use of the described design would not contribute to an improved control of permeability. There is no mention or inferred concept of applying hinged or variable cross sections in the arms of the X. In contrast, the present patent application requires that some finned extensions have a diminished area in cross section by their length to achieve their greatest ease of bending and distortion during weaving. In the weaving process, forces are present both due to the bending and compression of the fibers during "the tapping", that is, the adjustment of the weft. When the bending or contact forces are not present, the fins will remain erect to block the interstitial spaces of the tissue. Patent number 4,633,596 Josef teaches the use of warp fibers that have a center that is thinner than the edges and that improves the dimensional stability of the fabric by a lesser distortion in the warp and weft crossings. This is in marked contrast with the use of a finned and hinged web and lining fibers running in the machine cross direction in woven and spiral fabrics. The designs shown would not be crushed or distorted easily during weaving. Neither does Josef claim or mention a relationship with spiral fabrics. The drawings and the Josef patent treaty tend to be oriented toward the production of tissue designs intended for the creation of fabrics with high permeability. In Patent No. 5,361,808, Bowen teaches the use of weft fibers with fins that flex at the warp and weft junctions, but whose fins remain extended to block the interstitial space of the tissue where there is no mechanical contact by other fibers. The length of fins and the use of plasticizers are the mechanisms described to promote flexibility.
In Patent No. 5,364,692, Bowen and Sith teach the use of lining yarns in the form of T, X, or V to reduce the permeability of spiral fabrics. No special form or mechanism is mentioned to produce "arms" with less rigidity than the bending forces. This application contrasts markedly as it specifies that the arms or fins of the shaped fiber contain a reduced cross-sectional area intended to promote bending at force levels that are half or less than those that would be needed if the fin had a cross section uniform. In patent number 4,381,612, Shank describes spiral fabrics containing one or more lining filaments but does not disclose any technology or intention to design the lining filaments to achieve greater ease of distortion. SUMMARY OF THE INVENTION The present invention provides thin and stable tissues of controlled permeability, for papermaking or industrial purposes, especially dryer-type fabrics that have the ability to be easily produced in traditional industrial looms or in textile manufacturing lines. spiral. A special advantage is achieved in the manufacture of designs for fabrics with permeability objectives of less than I75m3 per minute per m2 with differential pressure of 1.27 cms of water. The fabrics in which this invention is used also show improved dimensional stability compared to the level achieved by the currently common use of twisted and pleated monofilament webs in the weaving or fins, unconfined, in the weaving and in the production of spiral fabrics. Specifically, the present invention provides within a fabric for the manufacture of paper, the improvement in which some or all of the yarns contain filaments designed to flex and distort to have reduced levels of fiber to fiber forces since they possess two or more finned extensions, of which some are characterized in that they have incorporated a "hinge" area of reduced cross section and / or variable thickness from the center outwards. For the purpose of the present treatise, a yarn may consist of one or more filaments, however, the preferred embodiment of this invention will be a monofilament. A reduction in the cross-sectional area of 20% or more at any location along the fin except for the normal radius at the fin's end will be considered as a suitable property to meet the reduced specification in cross section. In view of the fact that the force required to obtain the deformation is proportional to the cube of the thickness or width of the fin, a reduction of 20% in the thickness of the fin results in a reduction of approximately 50% in the force of "knocking" or "lock adjustment", required to mold the yarn in the fabric. The advantage of the requirement of less mechanical stress can be used to increase the interlacing of the fibers while at the same time reducing the damage caused by warp tensions and the "tapping" forces, ie adjustment of the weft. In the production of spiral fabrics, an increased flexibility of these shaped or hinged fins greatly reduces the forces required to insert into the open segments of the design. When the spiral fabric shrinks in the thermal solidification, the flexible fin designs within the fabric are interlaced with minimal distortion of the tissue surface while at the same time providing the reduced, convenient air permeability. For most fabric products, the best design will be a monofilament yarn with denier between 400 and 3000, however it is possible to use multifilaments with uniform or mixed designs of the cross section. Multiple filament yarn designs can be used to achieve tissue-specific properties including permeability, thickness and stability. The filaments constituting these multifilament yarns will have a denier of more than 100, preferably 200 to 1500, and when combined into multifilaments they will usually have low levels of twist. These threads can be used in the weft, warp or filling of industrial fabrics. Any type of suitable polymer and additive package can be used to achieve yarns for fabrics used by paper or industrial type manufacturing machines. Significant economic benefits are achieved due to the reduced denier of these threads compared to other threads previously used for this service. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective cross-sectional view of the preferred embodiment for a filament having fins with a radial reduction area in cross section. Figure 2 is a perspective cross-sectional view of the preferred embodiment for a filament having the "hinged" fin concept of the invention. Figure 3 shows a fin with a reduction of the stepped area while Figure 4 shows a combination of fins with cross sections of reduced area and without them. Figures 5,6, and 7 show average hinge fins co, a reduction of the curved area and a reduction of the straight area, respectively. Figures 8 and 9 show a distortion of the cross-cut fins, hinged and reduced when they are introduced into the fabric.
Figure 10 shows a special fin design in the form of a "ball". Figures 11 and 12 show fiber designs with 2 and 8 fins to indicate some variants that can be produced with this concept. Figures 13, 14 and 15 show designs of spiral fabrics that demonstrate the concept of the hinged flap. Figures 16 and 17 show designs of arched and half-moon filaments that would be particularly useful in spiral fabrics but could also be used in woven products. In Figures 1, 2 and 4, the thickness of the fin in TI and T2 are those measurements where the proportion of the reduction in thickness would typically be calculated. If T2 divided by TI is less than 0.8, the flap would fall within the specification of the present invention. It is specifically noted that the normal rounding or radio effect of such a fin is not considered a reduction
"manufactured" except for a design such as that of the fin in the form of "ball". For a special case like this one, the maximum radius will be used as the denominator in the calculation of the reduction of the cross-sectional area of the fin. DETAILED DESCRIPTION OF THE INVENTION The finned filaments used in accordance with the present invention can be prepared from a variety of thermoplastic materials. Polyethylene terphthalate, polyphenylene sulfide and 1,4-polydicyclohexanol terphthalate are currently used to a high degree, but they are not the only materials that could be chosen. To obtain the desired flexibility in the fins, these new yarn designs often require the addition of polymer-specific plasticizing agents during the filament extrusion process. The use of traditional additive recipes that may include heat stabilizers and polyhydrolysis, contaminant releasing agents and other processing aids of this type common to a production of papermaking yarns is considered a standard method. Modifications are needed in the usual techniques for the production of filaments in order to achieve an acceptable smoothness and uniformity in the filaments for these new yarn forms. This is caused by the general ratio of the width of a filament to the thickness of a fin, necessary to obtain flexibility without fracture. In this aspect the concept of fins in hinged or variable cross section is superior to the prior art. The conical shape or the hinge results in a more flexible fin that reduces the need to make excessive use of plasticizing agents or extra long fins. If the shape factor can be characterized by the ratio of the overall diameter of the filament divided by the average thickness of a fin, then filaments with a form factor of 3.5 to 20 can be used for these fabrics. The average thickness of the fin can be be calculated by usual techniques of mathematics. An example is presented in Figure 1 in which TAVG = (TI + T2) / 2. R divided by TAVG is the form factor considered for the purpose of this invention it is convenient to have the lowest possible form factor to reduce the surface to volume ratio of the fiber to thereby reduce the damage caused by the degradation procedures controlled by diffusion. For practical reasons, the number of fins will vary from 2 to 12. The fabrics are woven from these new yarns with variable fin cross-section, in the same way, in the case of round fiber constructions, in the form of tape, twisted and pleated, currently in common use. In Figures 8 and 9 the yarn of the warp is shown as 1 and the weft yarn as 2. The curving of the weft fins is shown by the warp during weaving. Figure 8 shows a cross section of the fabric showing the use of weft yarns with fins that are all hinged. He An important concept here is that the deformable fins are easily shaped to fill the available volume between the warp yarns and during this operation the interlacing of the woven structure is achieved to dramatically reduce the open character of the fabric. Frames that contain less than 4 finned extensions often turn out to be sensitive to the light twist inserted in the weft when it is fed to the process above the sprinkler coils. This twist insert results in small irregularities in surfaces and permeability, phenomena that can be important in the critical areas of the product. The X design, as found, closely matches the open, rectangular or rhombic area, common to most fabric designs and also constitutes a very good compromise to achieve material savings and ease of water removal during spinning. The use of more than 4 lobes reduces the importance of the orientation of the weft thread in the fabric, but makes it more difficult to extrude the monofilament. The physical size of the fiber filament design will be determined by the selected cross-sectional shape, the flexibility designed in the fins, the thickness of the tissue sought and the size of the selected partner, ie the weft or the warp. Figure 9 shows a fabric design similar to Figure 8 but containing a weft yarn with a cross section that is gradually reduced instead of carrying hinged weft yarns. The formation of large numbers of small fin distortions per cm of width during tissue production provides remarkable lateral stability and stiffness in products containing these fibers with flexible fins. Filaments of this type can be used in the warp, but their advantages are now more easily achieved in applications in frames or in the lining thread. The warp rows with fins located on one side of the yarn so that the fins would bend towards the interior of the woven fabric, would constitute an example of a design that would be suitable for this patent concept. Figure 13 shows a hinged liner thread inserted in the previously open area of a spiral woven design. The size of the yarn is carefully controlled so that it can be easily inserted into the open areas of the fabric before the thermal fixation. Figures 14 and 15 show preferred embodiments of the concept for spiral fabrics. A crescent lining yarn has been inserted into the open area of the fabric design and has been compressed on the upper and lower face during thermal fixation when the shrinkage of the spirals under tension flattens the fabric, distorts the fins and interlacing the fabric. If the fins are easily distorted, the surface of the fabric will remain smooth and flat. The permeability control can be achieved by inserting these special liner yarns in selected open areas or for another example, achieving an alternation between the yarns of this invention and other types of yarn. For a saving in production and material, the most preferred embodiment is the use of arched or half-moon designs with hinged areas, to achieve, in accordance with the present invention, spiral-shaped products. Summing up it can be said that the fibers of the invention will preferably be made monofilaments with a denier between 400 and 3000, having from 2 to 12 fin-type extensions, of which some have a variable cross-sectional area, designed to promote bending with a force reduced in relation to the force that would have been required if the cross section of the fin were uniform. In order to make this strength reduction important, the design criteria were to choose a tolerance in order to obtain a 50% reduction in force, with a reduction in width in the cross section of more than 20%. Multifilament fiber designs can be used, with the filaments aletiated with such designs having a denier between 200 and 1500 and in which some of the filaments contain fins with variable areas designed to promote bending. The fibers can be used either in the warp, in the weft or in the filling of the tissues intended for the manufacture of paper or for other industrial purposes, which can be woven fabrics or spiral designs.