A low density matting structure of improved transverse strength obtained by vertically laying continuous melt-spun thermoplastic macrofilaments (diameter=0.1-1.5 mm) onto a horizontally moving profiled support in overlapping rows of irregularly looped filaments to form a peak and valley three-dimensional structure undulating in its longitudinal and/or transverse directions. The matting articles consist essentially of the melt-spun filaments which are self-bonded or fused at random points of intersection without using any bonding agent or reinforcing inserts, and the resulting matting is especially distinguished by a high transverse strength per unit of surface weight of at least 2 Nm/g and preferably 4 Nm/g.
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1. A process for the production of a low density, transversely strengthened, three-dimensional, undulating peak and valley matting structure composed of a plurality of continuous melt-spun and self-bonded synthetic polymer filaments of a diameter of about 0.1 to 1.5 mm., which process comprises:
melt-spinning said plurality of filaments from a series of closely spaced spinning orifices arranged in rows on the bottom face of a spinning nozzle such that the filaments fall vertically downwardly for deposit onto a moving support intersecting the filaments substantially horizontally at a distance of about 3 to 20 cm. below said nozzle face and having projections which provide a patterned reentrant supporting surface with uppermost salient portions and downwardly opening reentrant areas therebetween; first directing said filaments onto said uppermost salient portions for support thereon to form the peaks of said matting struture, and then directing said filaments as filamentary loops both longitudinally and transversely into said reentrant areas so as to form the valleys of said matting structure, the filaments from adjacent spinning orifices overlapping and self-bonding with each other at random points of intersection; cooling and solidifying the freshly deposited and self-bonded filaments while the matting is continuously transported away from the spinning nozzle on said moving support; and finally removing the cooled and solidified matting from the moving support.
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Self-bonded matting articles are known, for example, from German laid-open application, DT-OS No. 1,810,921, which corresponds to U.S. Pat. No. 3,691,004. These known mattings are formed by extruding a polymer melt as threads or filaments with a diameter of 0.1 to 1.5 mm. from nozzle openings or spinning orifices that are equidistant from one another in at least three rows and staggered with respect to one another from row to row. The spun or extruded filaments in the form of a thread bundle with parallel rows of filaments are deposited directly onto a cooling liquid, preferably water, the spacing between portionof or transverse overlapping of filament loops and the fusing together at random points of intersection is still further increased, of course, by providing a larger number of spinning openings and/or by increasing the ratio of spinning velocity to the velocity of the moving support (transport velocity). Both of these measures, however, cause an undesired increase of the area weight and the density of the finished matting.
It has been found that with operating conditions otherwise remaining the same, i.e. so as to retain a constant area surface weight, the number of bonding or fusion points and thereby the transverse strength can be remarkably increased if the moving support is reciprocated transversely to its direction of longitudinal transporting movement. Preferably the traversing or reciprocating movement has an amplitude or stroke distance of about 3 to 10 mm and a frequency of about 80 to 300 strokes per minute. Each stroke is measured by a complete cycle back and forth, i.e. traversing the stroke distance twice in each cycle.
Such traversing or reciprocating movement when added to the normal transport speed of about 2 to 10 m/min results in a further increase in the transverse strengths per unit of surface weight by a factor of about 2 to 3. For example, in using nylon filaments, the minimum transverse strengths per unit of surface weight can be increased up to values of at least 7 Nm/g and preferably at least 10 Nm/g. Polycaprolactam filaments have been used exclusively in such mattings so as to achieve these values of the transverse strength and therefore result in especially preferred and exceptionally useful matting article articles .
Suitable apparatus for carrying out the traversing or reciprocating movement of the supported matting is shown in partly schematic form in FIG. 1a which is taken through the axis of rotation of the drum 2 located vertically below the spinning nozzle 1. The drum 2 is driven by motor M over pulley 8 which rotates the drive shaft 9 keyed to the sliding hub 10 mounted for reciprocal movement axially of shaft 9. This drive shaft is conveniently mounted in a frame 11 in the bearing supports 12 and 13. A flange 14 carries the coil spring 15 which resiliently urges the drum hub 10 to the left where a stop flange 16 can be adjustably fastened to the shaft to regulate the stroke distance or amplitude of the drum reciprocation.
The frequency of reciprocation can be preset or regulated in any number of ways using conventional camming or piston/cylinder devices to move the relatively light weight drum and the matting being formed. As shown in FIG. 1a, for example, two cams 17 can be synchronously rotated by motor M' at variably adjusted speeds for back and forth movement of their respective cam followers 18 which can be mounted as a bar or rod 19 in suitable bearing sleeves with small wheels or rollers at each end to reduce friction as much as possible. One wheel 20 runs on the cam 17 while the opposite wheel 21 can ride in a concave ring around the base rim 22 of the drum which also carries the triangular prisms 4 mounted thereon. The rim 22 is connected to the hub 10 by means of the spokes 23 in a sturdy but light construction.
In place of cam operated means to reciprocate the drum in a transverse direction, i.e., on its axis of rotation, one can also attach a piston rod (not shown) to an axially slidable flange 16 and then move the piston rod by hydraulic or pneumatic force at the desired frequency. Other variations will be obvious to a skilled mechanic.
The moving support found to be most useful according to the invention is one with a large number of individual projections, protrusions, protuberances, or similar upright members, which are preferably uniformly distributed in rows and files in an aligned or staggered pattern and removably fastened to the underlying base support of a roller, drum, conveyor belt or the like. These projections can extend upwardly or outwardly from the base support for a height of from 2 to 100 mm, for example, depending on the intended purpose or utility of the matting. The preferred height of the projections is about 5 to 70 mm. The projections can be the truncated pyramids of FIG. 3, nails with more or less pronounced flat heads of FIG. 4, the semispheres of FIG. 5, or the truncated cones of FIG. 6. One may also use screws, bolts, or other arbitrarily formed elements which are easily fastened in the supporting base of the roller, drum, conveyor belts or the like, provided that there are upper salient portions first receiving the downwardly spun filaments.
The valley spacing between adjacent projections, e.g. pyramids, should be sufficiently great so that the filaments hang down in loops between the peaks insofar as possible to the surface of the roller, drum or belt support so that they can also form points of fusion or bonding even at the lowest regions of the valleys. It is especially advantageous for the number of projections per unit area of the support to be within a range of about 16 to 150 projections per square decimeter. With matting thicknesses of 10, 15 and 25 mm, an especially successful distribution of the projections has been found to be a number of about 120, 65 and 50 projections per square decimeter, respectively.
Referring again to FIG. 2, it is possible to easily produce this preferred set of projections by providing the roller, drum, conveyor belt or the like with an adherent layer or plate into which a network of V-shaped grooves are formed by cutting, milling or the like. In this way, one obtains the preferred projections consisting of four-sided truncated pyramids. The matting produced with such projections has a waffle-like undulating three-dimensional structure.
The height ratio of height to mean distance between these pyramids h:d as illustrated by FIG. 2 is usually within limits of about 6:1 to 1:3 and preferably 4:1 to 1:2. However, these proportions can be widely varied while still gaining at least some improvement in transverse strength per unit of surface weight.
A somewhat less desirable moving support is that illustrated by FIGS. 7, 7a and 9 in the form of a grid or lattice structure supported on a drum or a conveyor belt, the lest desirable support being the screen band or belt shown in schematic form in FIG. 8. Such drum or belts are useful, however, as transporting means and in either case can be reciprocated in a transverse direction where required. When used as the moving support for the present invention, e.g., as mounted on the drum 2', by means of radial support members 24 fastened to the rim 3', the grid or lattice supporting surface can be formed by rods or tubing 25 and 26 composed of wood, rubber or other suitable material, including non-adherent plastic or ceramic elements, arranged on a drum 2' as shown in FIG. 7a, or as a screen belt as shown in FIG. 9 with the longitudinal rods 25' and transverse or cross rods 26'.
When using such screens or grids on a drum or endless band, it is desirable to provide sufficiently large reentrant openings and sufficiently narrow rods or grid members so that the filaments are deposited, ordinarily with a traversing or reciprocating movement of the grid support, to drape over the rods from side to side as well as in the longitudinal direction. In this manner, the filaments form sagging loops in a random overlapping fashion to again achieve an essentially three-dimensional peak and valley matting structure with both transverse and longitudinal undulations. Once this matting is solidified without adhering to the screen or grid support, preferably with the aid of cooling air as indicated in FIG. 7, it is withdrawn over a guide roller 27 without passage through a cooling bath and without any addition of bonding agents, impregnants, or the like. The finished matting can be wound up or deposited in any suitable manner for storage.
Care must be taken in using a screen or grid to avoid its entrapment or attachment to the matting due to encirclement of individual rods or grid members by even a single filament. Depending upon the particular filaments being spun, these problems can be avoided by taking certain precautions, e.g. using rods or grid members of a diameter substantially greater than the individual filaments and maintaining a horizontal support for some extra distance after vertical deposit of the filaments.
It is important that the projections, regardless of their particular form or construction, offer an upper salient portion or surface-whether in a horizontal plane as in the case of truncated pyramids or cones or by the selection of a structural material with a rough surface onto which the impinging filaments are directed vertically with sufficient surface resistance so that a part of the filaments remains deposited on top of the projections, i.e. on or over the individual peaks.
The material forming the projections should not adhere to the hot spun filaments, at least after they have been cooled and solidified just prior to removal from the moving support. Suitable materials for making the projections include especially wood and rubber, although highly polished metals may also be used and can be coated if necessary with lubricants or anti-stick agents. Ceramic or other special materials can also be used e.g. polytetrafluoroethylene (Teflon) coated members or the like. Wood or rubber projections are especially easy to fabricate and attach to a base support and can be easily cleaned or replaced as individual projections or segments of a profiled surface. This ensures a three-dimensional matting structure with an especially high void or hollow space and correspondingly low density.
While known mattings produced from synthetic polymer macrofilaments of about 0.1 to 1.5 mm in diameter have a hollow space or proportion of voids reaching a maximum of about 91 to 92%, mattings produced according to this invention achieve a hollow space of more than 95%, i.e. with reference to the total volume of the matting. Correspondingly, the mattings of this invention are distinguished from previous mattings of this type by a very low weight per unit volume, i.e. a density or measure of its solid content which can be expressed as the surface weight per unit thickness. This surface weight of the matting per unit of its thickness, as obtained by the process of the invention, is less than 50,000 g/m3 and preferably less than 40,000 g/m3, while in the known mattings, this value lies far above 70,000 g/m3. When these weights per unit volume are multiplied by 10-6, one can obtain a density measurement in units of grams per cubic centimeter (g/cm3). The extremely low density values according to the invention are thus calculated as less than 0.05 and preferably less than 0.04 g/cm3.
The most significant difference of the matting of the invention from the known mattings resides in its high transverse strength of at least 600 N/m, preferably of at least 1,000 N/m. When combined with the low surface weight and low density of the matting, this strength for a given weight or density represents a highly advantageous improvement.
Finally, the matting of the invention also exhibits a higher polymer density compared to mattings spun into a bath, this higher density being due to a partially crystalline molecular structure of the polymer. For example, in polycaprolactam mattings produced according to the invention, there were determined average densities of the polymer itself of about 1.14 g/cm3, while filaments spun directly into a water bath are in an amorphous state and exhibit an average density of only about 1.12 g/cm3. The formation of crystalline regions or so-called crystallites in the polymer is most evident in polymers having short repeating monomeric units and symmetrical structures, especially the usual fiber-forming thermoplastic polymers. Gradual cooling of the matting also helps to increase the formation of a more crystalline structure. Therefore, once the matting has been laid, it is preferably maintained at a temperature substantially below its melting point (Tm) but still above the second order transition temperature, sometimes referred to as the "glass transition temperature" (Tg). These temperatures are well known for conventional fibre-forming polymers such as polyesters, polyamides or the like. In particular, for the production of mattings that are to be stored or exposed to a wide range of environmental conditions, e.g. as soil retention mats or turf mats, UV-stabilizers can be added such as 0.2 to 1.0% by weight of carbon black, thereby preventing a loss of transverse strength even after relatively long exposure to sunlight.
In general, the mattings of the invention can be made with surface weights of about 100 g/m3 g/m2 or more, especially good results being achieved in the range of 200 to 1000 g/m2.
Higher surface weights or mattings of especially great thickness can be achieved with the apparatus suggested by FIGS. 10 and 10a, i.e. using a second spinning nozzle arranged at a distance from the first nozzle 1 so that the matting initially formed on the profiled belt support 28 is already substantially cooled, and spinning and depositing onto this preformed matting a second layer of self-bonding synthetic polymer filaments which are preferably laid in a random pattern by the traversing movement of the second endless belt 29 so as to fuse or weld firmly with one another at their points of intersection. Adhesion to the underlying layer of preformed matting is not as strong as the fused or welded filaments, but transverse strength remains very high.
The prism projections 30 of the first belt 28, as illustrated in FIGS. 10 and 10a, can be made of wood or other suitable material for non-adhering contact with the spun filaments. These prisms are easily attached by the pin connections 31 to the metal base plates 32 which in turn are cemented or otherwise firmly attached to the rubber belt 33 in a manner similar to tank treads. These prisms have been omitted from the second belt 29 in FIG. 10 since the preformed matting can be simply transported on any suitable conveyor belt for passage under the second spinning nozzle.
Especially heavy or thick mats as well as wider mats can also be produced in a preferred manner as illustrated in FIG. 11 by bringing together two prefinished or preformed mattings of the invention in a side-by-side parallel relationship on a common moving suport, being separated by a gap or spacing therebetween of several centimeters, e.g. anywhere from about 0.5 to 8 cm, and melt-spinning at least one self-binding macrofilament of a diameter of more than 0.2 mm into the gap and both transversely and longitudinally of the gap to overlap and form a seam between opposing parallel sides or edges of the two mattings, whereby the two mattings are joined securely with one another. The two preformed mattings 34 and 35 of FIG. 11 are typical of those produced on a truncated prism type of projection so as to undulate in both transverse and longitudinal directions. A guide rail 36 can be used to guide each matting from its own single width conveyor belt onto a common double width conveyor 37 to bring the two mattings together with the gap space 38 running directly under a reciprocating spinning nozzle 39 flexibly coupled to an extruder by line 40 to supply the molten polymer used to form the self-bonding seam holding the mattings together. The additional weight of this narrow seam is minimal so as to retain a high transverse strength per unit surface weight of the combined matting structure.
FIG. 12 indicates transversely corrugated or undulated matting with good flexibility for winding, e.g. as produced on the triangular prisms of FIGS. 1, 1a, 10 and 10a. Longitudinal corrugations or undulations are also feasible as illustrated in FIG. 12a if the matting is formed on a correspondingly ribbed drum or a set of wood prisms mounted on each base plate as in FIG. 10a, but turned by 90°, and aligned from plate to plate.
The mattings of the invention, through a suitable selection of the profiled support or projections and a desirably low surface weight, can have the most diverse handle or surface texture. For example, the mattings may be flexible with a soft handle or else boardlike with a very hard surface. For most purposes, especially to permit rolling the mattings for storage, a moderately flexible matting is preferred.
The matting of the invention independently of other operating conditions, e.g. the spinning speed, the desired surface weight, the type of polymer, etc., can generally be produced with a draw-off or transport speed of about 2 to 10 m/min. The matting is removed from the continuously moving support when it has cooled off sufficiently to avoid any serious deformation of the desired matting structure. As a rule, it does not need to be actively cooled, because the heat is generally dissipated sufficiently rapidly to the surrounding air and in some instances to the profile or projection. If desired, however, an active cooling can be carried for example by blowing with air or by the use of an internally cooled drum or similar heat transfer means.
It is possible to further modify the matting of the invention in a wide variety of known adaptations. Thus, the matting can be spun for example onto a grid or screen reinforcement such as a wire fabric having the same distribution of peaks and valleys as the profile or projections of the moving support. One can also line the matting with foils, fleece webs or the like, on one or both sides, depending upon the intended utility.
The improved transverse strength of the matting according to the present invention is believed to result from several factors. First of all the self-bonding or fusion of the still hot and relatively fluid filaments as they are laid in loops on the moving support create a much stronger bond than when the filaments are first quenched. A slower cooling and the appearance of crystalline regions also contributes to an increased strength. Moreover, by directing more loops in a transverse direction as the filaments are laid over the profiles or projections and into the valleys therebetween, there arises a larger number of bonding points transversely of the matting. The resulting peak and valley structure of the finished matting increases the total voids or hollow spaces even as the transverse strength is increased.
The invention is further explained by but not limited to the following examples.
Using a conventional spinning head as indicated in FIG. 1 wherein the spinning nozzle contains 188 spinning openings (diameter=0.35 mm), molten polyethylene terephthalate was spun onto a roller arranged with its uppermost surfaces at an interval of 9 to 16 cm below the bottom of the spinning nozzle. The projections on the roller consisted of a series of truncated four-sided pyramids as indicated in FIGS. 2 and 2a, arranged uniformly to provide 126 such projecting pyramids per square decimeter of roller surface. As the roller rotated to receive the vertically spun filaments and to advance the matting being formed, it was also reciprocated back and forth on its axis over a distance of 6 mm and at a frequency of 150 times per minute. The resulting sheet or band of the matting was 10 mm thick and 270 mm wide with the properties shown in Table 1 which also gives the roller speed and the distance of the roller from the spinning nozzle.
| TABLE I |
| ______________________________________ |
| Example No. 1 2 3 |
| ______________________________________ |
| A. Surface speed of |
| 4.0 2.7 4.0 |
| the roller |
| (m/min): |
| B. Distance of the roller |
| 9 9 16 |
| from the spinning nozzel |
| (cm): |
| C. Matting surface |
| 500 750 500 |
| weight |
| (g/m2): |
| D. Transverse strength |
| 1,480 3,990 1,750 |
| (N/m): |
| E. Transverse strength |
| 2.96 5.32 3.5 |
| per unit surface |
| weight (Nm/g): |
| F. Surface weight per |
| 50,000 75,000 50,000 |
| unit thickness |
| (g/m3): |
| G. Density of matting |
| 0.05 0.075 0.05 |
| (g/cm3): |
| ______________________________________ |
Using the conventional spinning head of the first three examples having a spinning nozzle with 114 spinning openings (diameter=0.40 or 0.25 mm), polypropylene was spun down onto the same roller spaced 10 cm below the nozzle openings, the roller being rotated and also reciprocated axially over a 6 mm distance at a frequency of 150 times per minute. The same four-side four-sided truncated pyramids were again employed to provide projections on the roller. The operating conditions and properties of the matting after withdrawal from the roller are shown in the following Table II.
| TABLE II |
| ______________________________________ |
| Example No. 4 5 6 |
| ______________________________________ |
| A. Nozzel opening 0.40 0.40 0.25 |
| diameter (mm): |
| B. Feed of polypropylene |
| 342 342 604 |
| melt (g/min): |
| C. Surface speed 3.3 3.0 2.1 |
| of the matting |
| (m/min): |
| D. Number of projections/ |
| 126 66 66 |
| dm2 : |
| E. Matting Surface |
| 305 325 533 |
| weight (g/m2): |
| F. Transverse 1,163 1,244 1,460 |
| strength (N/m): |
| G. Transverse strength |
| 3.81 3.83 2.84 |
| per unit surface |
| weight (Nm/g): |
| H. Matting thickness |
| 10 14.5 14.6 |
| (mm): |
| I. Surface weight per |
| 30,500 20,200 36,500 |
| unit thickness |
| (g/m3): |
| J. Density of 0.0305 0.0202 0.0365 |
| matting (g/cm3): |
| ______________________________________ |
Using different spinning nozzles, polycaprolactam filaments were spun onto the same profiled roller used in the preceding examples, spaced 9 cm. below the spinning nozzle, rotated at a peripheral surface of 4 m/min and reciprocated axially over a distance of 6 mm at a rate of 150 times per minute. The operating conditions and properties of the matting product are given in Table III.
| TABLE III |
| ______________________________________ |
| Example No. 7 8 9 10 |
| ______________________________________ |
| A. Number of spinning |
| 164 164 270 229 |
| openings: |
| B. Spinning opening |
| 0.25 0.25 0.25 0.25 |
| diameter (mm): |
| C. Feed of polymer |
| 261 415 415 415 |
| melt (g/min): |
| D. Matting surface |
| 220 340 340 340 |
| weight (g/m2): |
| E. Transverse strength |
| 840 1,430 1,850 2,030 |
| (N/m): |
| F. Transverse strength |
| 3.82 4.21 5.44 5.99 |
| per unit surface |
| weight (Nm/g): |
| G. Matting thickness |
| 10 10 10 10 |
| (mm): |
| H. Surface weight per |
| 22,000 34,000 34,000 |
| 34,000 |
| unit thickness |
| (g/m3): |
| I. Density of 0.022 0.034 0.034 0.034 |
| matting (g/cm3): |
| ______________________________________ |
Using a spinning nozzle with 270 spinning openings (diameter=0.25 mm), polycaprolactam filaments were spun to fall freely over a vertical distance of 12 cm directly onto the profiled roller (as described above using four-sided pyramids which are truncated), the roller being rotated at a peripheral surface speed of 4 m/min. There was no axial reciprocation or traversing movement of the roller in this instance. The operating conditions and final results exhibited by the matting are shown in Table IV.
| TABLE IV |
| ______________________________________ |
| Example No. 11 12 13 |
| ______________________________________ |
| A. Number of pro- |
| 126 66 66 |
| jections/dm2 : |
| B. Matting surface |
| 300 400 500 |
| weight (g/m2): |
| C. Transverse strength |
| 850 2,010 3,070 |
| (N/m): |
| D. Transverse strength |
| 2.83 5.03 6.15 |
| per unit surface |
| weight (Nm/g): |
| E. Matting thickness |
| 10 15 15 |
| (mm): |
| F. Surface weight per |
| 30,000 26,700 33,400 |
| unit thickness |
| (g/m3): |
| G. Density of matting |
| 0.0300 0.0267 0.0334 |
| (g/cm3): |
| ______________________________________ |
Examples 11 to 13 were repeated except that the profiled roller in this instance was reciprocated or traversed axially over a distance of 6 mm at a rate of 150 times per minute. The properties of the matting are shown in Table V.
| TABLE V |
| ______________________________________ |
| Example No. 14 15 16 |
| ______________________________________ |
| Matting surface 300 400 500 |
| weight (g/m2): |
| Transverse strength |
| 2,480 5,130 6,170 |
| (N/m): |
| Transverse strength |
| 8.27 12.82 12.35 |
| per unit surface |
| weight (Nm/g): |
| ______________________________________ |
From this comparison, it will be readily seen that a reciprocation or traversing movement of the profiled roller in a direction axially of the roller, i.e. at right angles to the direction of travel of the matting on the roller, leads to an increase of the transverse strength by a factor of 2X to 3X.
One cannot measure the strength of each bonding point, and the transverse strength (N/m) of the matting by itself is not a distinguishing characteristic since it can be increased simply by adding more filaments in a given surface area or volume. However, the transverse strength per unit of surface weight of at least 2 and preferably 4 Nm/g or more is a significant value since it requires a comparison of transverse strengths for the same surface weight of different mattings. With the provision of lower density mattings of still greater transverse strengths, the finished products of the invention are less expensive while offering a much wider area of utility.
Rasen, Alfred, Vollbrecht, Rolf, Schenesse, Klemens
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