FI58738B - FOERFARANDE FOER ATT FRAMSTAELLA EN NAETKONSTRUKTION - Google Patents

Description

huiiliir ^ l ΓβΙ ^ ADVERTISEMENT CO οτα LBJ <11, UTUÄOGNINOSSKRIPT 3Ö738 C (45) Patent ny'innctty 10 C4 1031 ^ (51) Kv.ik.1 / Int.a.1 B 29 D 31/00, 7/24 SUO MI - Fl N LAN D (* 1) HM "« lh »k * m« «- P« t * i> t «eknJn * 3926/73 (22) H * - ** .- *** · * , 19.12.73 '* (23) Alkupllvl — Giltigh «ttd> f 19-12.73 (41) Tullut JulkiMkai - Bllvlt affmtllg 17-07-7 ^

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- · (32) (33) (31) Requested «Tuoilcaut — fegird pHoritat 16.01.73 16.01.73 USA (US) 32U028, 32U030 (Tl) Hercules Incorporated, Wilmington, Delaware 19899, USA (US) (72) Charles Whan Kim, Wilmington, Delaware, Chia-Seng Liu, Newark, Delaware, Richard MacDuff, Newark, Delaware, USA (7k) Oy Heinänen Ab (5k) Method for manufacturing a network structure - Förfarande för att framställa en nätkonstruktion to produce a mesh structure, in which parallel, elongate protrusions are formed on each side of the film of thermoplastic material so that the protrusions on different sides of the film form an angle with each other, and the film is then stretched to form openings in the regions of the bands between the protrusions.

It is known in the manufacture of mesh structures (for example from U.S. Pat. No. 3,488,415) to form continuous diagonal grooves on one side of the plastic film and continuous diagonal grooves perpendicular to the former on the other side of the film so that in stretching the film in the directions of the grooves the grooves intersect, stretch and thus open gaps, creating a reticulated structure in the film. The thickness of these mesh structures is greatest at the points where the strips between the grooves intersect, so that unobtrusive locking points are formed at these points, since no or little elongation occurs at the intersections of said strips during stretching of the grooved film. The tensile strength and tear-off properties of such a network are relatively poor because the non-stretchable and thus non-molecularly oriented thick points weaken the network, and thus the network is also not homogeneous in properties. In connection with the manufacture of yarns, it is known (from U.S. Pat. No. 3,500,627) that a yarn can be made by forming on one side of a strip of plastic material a plurality of parallel protrusions which can be formed into fibers and on the other side a series of transverse protrusions forming a sharp angle. . The molecular structure of the strip is then oriented by unidirectional stretching, after which the protrusions forming the strands are mechanically cut and a wire is provided with strands directed from it to the side.

The method of the present invention is characterized in that the protrusions on different sides of the film from which the mesh structure is formed by stretching are formed differently from each other so that the ratio of the cross-sectional areas of the main protrusions on one side and the transverse protrusions on the opposite side is at least 1.5: 1 and the ratio of the height of the main protrusions to the thickness of the bands between the protrusions is at least 3: 1.

After the main protrusions and transverse protrusions are formed in the plastic film, the plastic film is stretched in such a direction as to provide continuous and homogeneous orientation of the main protrusions, and the plastic film can be stretched in two different directions, preferably perpendicular to each other. For example, when the main protrusions are formed in the machine direction and the transverse protrusions are formed in the transverse direction to the machine direction, the mesh structure can be fabricated with a single stretch, in this case in the machine direction. Alternatively, a more open network structure can be achieved by performing successive stretches or simultaneous stretching in both the machine direction and the machine direction transverse direction. When stretching a plastic film whose main protrusions are machine direction, the first v.e, tensioning is generally transverse to the machine direction. When stretching is performed, the thinnest points of the plastic film, namely those points where the bands between the main protrusions intersect the bands between the transverse protrusions, become oriented and normally open themselves so as to create a homogeneous pattern of openings in the film. Depending on the amount of stretching, the opening of the net in certain cases does not take place in the first stretching stage, but only in the next stretching, perpendicular to the first stretching. In all cases, the opening of the net occurs spontaneously during stretching and thus there is no need to form the fibers mechanically. In this spontaneous formation of the fibers, i.e. the opening of the network, it occurs that the transverse protrusions are formed into transverse fibers and the main protrusions are formed into main fibers.

It has been found that very good strength properties can be achieved in a network structure in which the main fibers are larger than the transverse fibers so that the orientation at the intersections of the main fibers and the transverse fibers is concentrated in the main fibers. The transverse fibers are preferably narrower and also oriented so as to provide sufficient structural integrity of the network structure in order to keep the structure flat and prevent it from bending, whereby the main fibers remain parallel and their distances remain flat. The single-layer plastic mesh structures thus produced are dimensionally stable, self-supporting, easy to handle and have good tensile strength in the direction of the main fibers, in addition to which their tear strength in the other direction is good. Such nets are very useful as a reinforcement for paper products and nonwovens based on staple fibers and as a cover for absorbent pads.

The invention will now be described in more detail with reference to the accompanying drawings, in which

Figure 1 shows a schematic perspective view of a device for forming protrusions on both sides of a plastic film in accordance with the principle of the present invention.

Fig. 2 shows on a larger scale the film according to Fig. 1, in which protrusions have been formed.

Figure 3 also shows on a larger scale a part of the film in which the main protrusions are at a relatively long distance 4,58738 from each other, in which the bands between the main protrusions are relatively deep grooves and in which the transverse protrusions are relatively close to each other, the bands being relatively narrow.

Figure 4 also shows on a larger scale a part of another film in which the main protrusions are relatively close to each other, in which the bands between the main protrusions are narrow, and in which the transverse protrusions are relatively far apart, the bands between them being relatively deep grooves.

Fig. 5 shows an enlarged perspective view of a part of the upper surface of the network structure obtained by stretching and orienting the film according to Fig. 2 in two directions.

Fig. 6 shows an enlarged perspective view of the other side of the network structure according to Fig. 5.

Fig. 7 is a schematic perspective view similar to Fig. 1 of an apparatus for forming protrusions on both sides of a plastic film. The device differs from the device according to Fig. 1 in that here the transverse protrusions are formed discontinuously in the machine direction.

Fig. 8 shows on a larger scale the film treated with the device according to Fig. 7, seen from the side of the transverse protrusions, the figure showing the imperfection of these protrusions.

Fig. 9 is a schematic perspective view of an apparatus for forming continuous protrusions in the machine direction on one side of the plastic film and discontinuous transverse protrusions on the other side of the plastic film.

Figure 10 shows the other side of a mesh structure made by stretching the plastic film of the figures in two directions.

Figure 11 shows the other side of the network structure according to Figure 10.

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Figure 12 shows a top view of a part of a network structure whose main fibers are machine direction and the transverse fibers are transverse to the machine direction.

Figure 13 shows a top view of a part of a net structure in which the main fibers are transverse to the machine direction and the transverse impacts are machine direction.

Fig. 14 shows a top view of a part of a net structure whose main fibers form an angle with the machine direction and whose transverse fibers are machine direction.

Fig. 15 shows a top view of a part of a net structure whose main fibers form an angle with the machine direction and whose transverse fibers are perpendicular to the main fibers.

Figure 1 shows a forming roll 21 having a plurality of grooves 22 forming a plurality of transverse major protrusions 23 in a film of thermoplastic polymeric material 24 to be passed between the rolls, the protrusions 23 being interconnected by thin film-like strips 25. The second forming roll 26 having a plurality of curved or circular grooves 27 is located opposite the roll 21 and is intended to form a plurality of elongate transverse protrusions 2Θ on one side of the film 24 such that the transverse protrusions are interconnected by thinner strips 30. The shaping rollers 21 and 26 rotate in the directions indicated by the arrows. There are a number of different ways to achieve the double design described herein. One way is that a plastic film 24 still in the molten state, coming directly from the extruder, is fed between two rotating forming rollers 21 and 26, which rolls are pressed against each other by devices not shown in the drawing. From the inventive rolls, the spacing and the thickness of the film thus formed are adjusted by adjusting the thickness of the extruded film between the forming rolls and the magnitude of the compressive force between the rolls. The temperatures of the rolls are appropriately controlled from the inside and are adjusted so as to cause the molten plastic, which is shaped on both sides as desired, to solidify and solidify.

Alternatively, the previously made film can be reheated to a softening temperature of 6,58738 and then fed between two forming rollers, 21 and 26. In another method, a polymer in powder form may be used, which is passed as such between two heating rollers, not shown, so that these heating rollers cause the plastic to melt and soften and thus form a film which is then fed to two press rolls. and 26, between. According to one embodiment of the method, a previously cast flat film is passed between two rolls pressing against each other at a sufficiently high pressure so that the protrusions compress the film without the film melting or softening. It will be appreciated that many different procedures may be used to apply the principles of this invention to practice. Alternatively, without the use of press rolls to provide the desired protrusions on both sides of the film, a method of using two concentric molds moving relative to each other can be used, as described in the aforementioned U.S. Patent 3,488,415.

It has been found that the most preferred ratio of the cross-sectional areas of the main protrusions to the cross-sectional areas of the transverse protrusions is between 1.5: 1 and 100: 1, with the ratio of the height of the main protrusions to the thickness of the bands between the main protrusions being 3: 1 or greater.

This ratio allows successive drawing and orientation steps to form a raised film into a network structure having uniformly spaced major fibers that are uniformly and homogeneously oriented along their entire length and that are completely homogeneous in cross-section. As shown in Fig. 2, the cross-sectional area of the main protrusions and the cross-sectional area A2 of the transverse protrusions are each calculated so that the area extends into the film. on the opposite side as shown. Figure 2 also shows the height of the main protrusions and the thickness T2 of the bands connecting the main protrusions.

The cross-sections of the protrusions to be made may vary. They can be semicircular, rectangular, triangular, trapezoidal or of any desired shape.

In addition, the shapes of the main protrusions and the transverse protrusions may be either similar or different from each other. Similarly, the shapes and sizes of the bands separating the protrusions, | l ’j <· · · from each other are not critical.

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The lanes may be narrow, with the protrusions being close to each other, or wide, with the protrusions being farther apart. In addition, the transverse protrusions may be farther apart than the main protrusions or vice versa. The sizes of the openings in the network structure can be adjusted within certain limits by adjusting the distances between the main protrusions and the transverse protrusions.

Fig. 3 shows a part of a shaped film, indicated by the general reference numeral 11a, having a plurality of main protrusions 37 formed on one side of the film and a plurality of transverse protrusions 3Θ formed on the other side of the film and directed perpendicularly. against the 37 directions of the main protrusions. The main protrusions 37 are spaced longer than the transverse protrusions and the lanes 39 therebetween are thin. The bands between the transverse protrusions 38 are narrow grooves 40 with a smaller film thickness. It should be noted that the height 41 of the main protrusion 37 measured from the strip 39 to the top of the main protrusion 37 is much larger than the height of the transverse protrusion 38 measured from the bottom of the groove 40 to the top of the strip 38. It can be seen from Figure 4 that the shaped film 43 has a plurality of proximal major protrusions 44 on one side of the film and parallel to each other, and a plurality of spaced transverse protrusions 46 located on the other side of the film and parallel. The thin band 47 between the main protrusions 44 is very narrow in this case, while the band 48 between the transverse protrusions 46 is relatively wider. Thus, it can be said that the invention is relatively independent of the distances between the elevations and the heights of the elevations.

The direction of the main protrusions is also not critical. The main protrusions can be formed in the machine direction or transverse to the machine direction of the plastic film, i. 90 ° to the machine direction, or to any other angle. When the main protrusions are either machine direction or transverse to it, orientation of the main protrusions with respect to their longitudinal axes can be easily accomplished using either a conventional traction roller device operating at different linear speeds or a standard stretching frame. Also in the case that the protrusions obtained by shaping are diagonal to the machine direction, the orientation of these protrusions and the formation of the network can be achieved by using the same type of equipment.

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When orienting the main protrusions which form an angle with the machine direction with respect to their longitudinal axes, it is sometimes advantageous to use a linear pulling device with a long tension, whereby stretching in the machine direction the plastic film can turn downwards and the main protrusions orient in principle with respect to their longitudinal axes. When stretching in this way, it is generally advantageous to proceed in such a way that the linear stretching takes place transversely to the machine direction and is oriented by guiding the film through a stretching frame.

The direction of the transverse protrusions on the opposite side of the film must be such that it forms an angle with the main protrusions, which in many cases is preferably 90 °, but can also be of a different magnitude. Any angles between 15 ° and 90 ° between major elevations and transverse elevations are useful.

When a shaped film having a pattern of continuous main protrusions on one side and a pattern of continuous transverse protrusions on the other side is stretched, the thin portions of the film, namely those where the strips 25 and 30 intersect, tear by themselves to form openings. When the second stretching is performed, a mesh structure similar to that shown in Figs. 5 and 5 is obtained. The main protrusions 23 of the shaped film shown in Figures 1 and 2 have separated into main fibers 53 which are homogeneously and continuously oriented. The transverse protrusions 28 have also become separated from each other and oriented as transverse fibers 54 which join the main fibers 53 and keep them homogeneously evenly spaced apart. Fig. 6 shows the other side of the network structure according to Fig. 5, from which it can be seen that the transverse fibers 54 can be oriented continuously and without interruption across the main fibers 53.

Alternatively, the transverse fibers 54 may be discontinuous at the points where they intersect the major fibers 53, which can be achieved either by adjusting the pattern to provide a "splitting effect" or by using a roll that forms transverse protrusions as discontinuous.

As shown in Fig. 1, the adjusted pattern can be obtained by using grooved forming rollers 55 and 56, which are 9,58738 similar to rollers 21 and 26 in Fig. 1. The distribution of plastic between the main riser roll 55 and the transverse riser 56 can be varied by adjusting the melting temperature, pattern roll temperature , the contact time of the patterned film with the roll and the thickness of the film as it enters the nip between the shaped rolls. A certain controlled variation in the distribution of the polymer can also be achieved by selecting which roll the molten sheet first contacts. Shrinkage of the plastic during the cooling phase can also affect the good results obtained by the method.

The formation of discontinuities in transverse ridges can be promoted by using thin plastic films, keeping the molten polymer relatively cold before contacting the forming roll, keeping the plastic film in contact with one roll, preferably with larger grooves, some distance before the film enters the nip between the rolls with the roll, preferably with larger grooves, some distance after it has left the nip between the rolls. The degree of penetration of the polymer into the grooves of the roll with a finer pattern and the shrinkage of the polymer as it cools after patterning at the compression point between the rolls are undoubtedly factors which contribute to the excellent results obtained by the process of the invention. Especially in the case where the film is relatively thin, at the points where the grooves 57 of the main protruding roll 55 intersect with the grooves 58 of the transverse protruding roll 55, there is not enough plastic to fill both the relatively narrow grooves 58 and the relatively wide grooves 57 because the available plastic fills wider grooves 57. This is because the polymer tends to flow along the path of least resistance, namely towards the large grooves. The same phenomenon also occurs with thicker membranes when the pressure is low. At low molding temperatures, due to the higher flow resistance of the polymer, there is a greater tendency for discontinuous transverse bumps to occur. As a result, in such a mode of operation, the rough grooves 57 of the forming roll 55 are evenly filled with polymer, but the fine grooves 56 of the forming roll 56 are not completely filled. As a result, the shaped transverse protrusions occur discontinuously, as shown in Fig. 8, because an insufficient amount of polymer has been able to flow to provide the transverse protrusions 59 completely at the points 60 where they intersect the main protrusions 61, resulting in strong and costly crosslinking. in addition to other advantages, there is then a higher relative amount of polymer in the main protrusions than can be obtained with other working methods. Furthermore, the discontinuous transverse protrusions 59 are also advantageous in that they allow the main protrusions 61 to be complete and uniformly oriented, since then the main protrusions 61 and the transverse protrusions 59 do not pass transversely.

Discontinuities can be formed in the transverse protrusions by using continuous main protrusions forming rollers 62 and discontinuous transverse protrusions forming rolls 63, as shown in Fig. 9, whereby the main protrusions are made in the machine direction of the plastic film. The main embossing roll 62 has a plurality of parallel groove-like grooves 64 formed therein to form main protrusions 65 in the film 70. The transverse embossing roll 63 has a plurality of discontinuous grooves 66 formed parallel thereto with the longitudinal axis of the roll 67. . In each row of grooves 66 surrounding the forming roll 63, each groove 66 is closed with respect to an adjacent groove by a closure portion 6Θ in the roll 63.

The width of the closure portion 68 is preferably equal to or slightly smaller than the width of the groove 64 of the main protrusions forming roll 62. It should be noted that the transverse protrusions are not continuous in the shaped film but are continuous only from the main protrusion 65 to the adjacent main protrusion, the point of discontinuity being denoted by 69. By shaping the film 70 in this way and then stretching it in two directions, the main protrusions can be oriented continuously and homogeneously .

Figures 10 and 11 show the upper and lower surfaces in a mesh structure obtained by stretching a film formed according to Figure 10 both in the machine direction and in a direction transverse to the machine direction. It should be noted that the main fibers 71 taper somewhat outwardly as can be seen from the drawings and that the transverse fibers 72 keep the main fibers at a certain distance from each other 71. The transverse fibers 72 join the main fibers 71 at their ends, as shown in Figure 11, and do not extend across the main fibers 71.

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When stretching a formed film, the preferred stretch ratio depends on such factors as the quality of the plastic used, the shaping pattern used, and the desired degree of separation of the major fibers in the final mesh structure. Usually, the first stretching, or orientation step, comprises stretching the shaped film generally in a direction transverse to the direction of the main protrusions, in which case the elongation is achieved. orientation of the thinner points of the plastic material between the main protrusions. For example, the patterned film shown in Figure 2, in which the main protrusions 23 are formed in a direction transverse to the machine direction, would normally (but not necessarily) be first stretched in the machine direction. This stretching can be performed using a conventional linear stretching roller device with different linear speeds of the rolls.

This orientation, which is usually 1.5 times or more, usually results in the formation of latent or real gaps between the main protrusions, forming small transverse fibers which connect the main orientations, i.e. the main fibers, which are not yet oriented. Stretching the film more than 5 times its original size at this stage is generally disadvantageous, as this can lead to transverse orientation of the plastic at the points where the main protrusions and the transverse protrusions intersect. This could interfere with the desired uniform orientation of the main fibers in subsequent stretching steps.

Alternatively, it may be advantageous to carry out, for example, a first stretch in which the film stretches twice as long in the direction of the main protrusions, and only then a stretch transverse to this direction. This orients and reinforces the main protrusions and tends to prevent all possible deformations of the shapes, i.e. the transverse orientations of the polymer in the transverse direction with respect to the longitudinal direction when performing transverse stretching.

The second orientation step is normally performed in a direction corresponding to the sunt of the main elevations. In this case, in the case according to Fig. 2, a second orientation in the direction transverse to the machine direction is performed. This transverse stretching step can be performed using a conventional stretching ring. The transverse stretching results in the orientation of the main protrusions with respect to their longitudinal axes and the separation of the small transverse fibers connecting them. The degree of stretching determines the strength and dimensions of the main fibers obtained. The degree of stretching can range from a small value of silicon than one and a half times to ten times or even greater. The maximum elongation depends on the orientation properties of the 12,58738 plastic used, among other factors. The temperatures used for stretching vary depending on the quality of the polymer used, but are generally slightly lower than those used to orient smooth films of the same polymer. The first and second successive drawing steps have been discussed above, but if desired, these two stretches can also be performed simultaneously.

The mesh structures made by the above methods include, if desired, longitudinal, transverse or obliquely oriented main fibers, which are usually joined together by smaller cross-sectional, oriented transverse fibers, whereby the orientation of the main fibers is continuous along their entire length. Examples of different models of mesh structures are shown in Figures 12 and 13. Figure 12 shows a mesh structure in which the main fibers 73 are machine direction oriented by an arrow and the transverse fibers 74 form an angle of 90 ° with the machine direction. In Fig. 13, the main fibers 75 are formed transverse to the machine direction, which is also shown by the arrow, and the transverse fibers 76 are parallel to the machine direction. In Fig. 14, the main fibers 77 form an angle with the machine direction, the direction of which is again shown by the arrow, and the transverse fibers 78 are parallel to the machine direction. Alternatively, the transverse fibers 78 may be formed transverse to the machine direction or perpendicular to the main fibers, as shown in Figure 15. When the main fibers 77 form an angle of 75 ° or less with the machine direction, it is often preferred to orient these fibers. stretching the product in the machine direction, whereby the network structure changes, i.e. bends. Usually, when making such a structure, stretching in the transverse direction to the machine direction is first performed using a stretching frame, and then stretching in the machine direction is performed, whereby the mesh structure is formed. It will be appreciated that a wide variety of other mesh structures may also be made in accordance with the principles of the present invention, in which the main fibers form any desired angle when maximum tensile strength is desired and the local fibers form an angle relative to the main fibers.

The mesh structures described herein have good tensile strength in the direction of the main fibers, · 'as a result of the amount and uniformity of orientation of these fibers in the longitudinal direction. This strength is lower in the opposite direction to the fireplace, due to the smaller cross-sectional area of the transverse fibers connecting the main fibers. The tear strength is greatest in the transverse direction to the main fibers due to the strength of the main fibers. It should be noted that in the mesh structures of Figures 5,6,10 and 11, the transverse fibers are either continuous or discontinuous without, in either case, creating nodes at the intersections of the main and transverse fibers typical of many mesh structures fabricated by conventional methods. Such nodes, i.e. thickenings at intersections, cause the net to easily tear in either direction.

The network structures according to the invention can be used not only as single-layer networks but also very advantageously as multilayer network structures. Among the many uses of the mesh structures according to the invention, either as single-layer or multi-layer fabrics, mention may be made of medical cloths, sanitary napkins, menstrual pads, tampons, surgical textiles, surgical sponges, burn wounds and woven fabrics for paper and paper products, films and other nonwovens. For example, the mesh structure can be used as a covering reinforcing covering layer, which provides it with better tensile strength and abrasion resistance properties. In the case of nonwovens made of paper and staple fibers, mesh structures in which the main fibers are transverse to the machine direction are very advantageous. This is because in the manufacture of nonwovens made of paper or staple fibers, the fibers in them are usually oriented in the machine direction, which would require increased strength transverse to the machine direction and increased tear strength relative to the machine direction. In addition, thermoplastic mesh structures can be used as a binder to join other materials together using transducer pressure. Mesh structures are also useful as liners for shirts and the like, in addition to which they can be used instead of cheese fabrics in the manufacture and maturation of cheeses.

Although attention has been paid above to the good tensile strength and high tear strength of the mesh structures of the invention, it is, of course, clear that these mesh structures can be made in accordance with the principle of the present invention using lower main fiber stretching, lower mesh strength and tear resistance. In this case, they are suitable for use for purposes in which the said properties are not important. In certain applications, texture and smoothness may be more important than strength. An example of such applications is the use of a mesh structure as a cover for medical wipes, which is very advantageous in that the mesh structure has a soft and smooth surface which prevents skin irritation and is highly permeable so that liquids can pass through it and be absorbed into the wound absorbent wound. the inner material.

The mesh structures of the invention are very smooth because they do not have a thick layer of pulp at the intersections of the main fibers and the transverse fibers. Such smoothness makes the mesh structure soft to handle or makes it advantageous for many purposes when skin irritation of its handler or user is an important factor. In addition, these network structures can be pulled in such a way as to provide relatively flat structures, i. structures that are uniform in thickness as measured in a plane perpendicular to the plane of the network structure. This can be an important factor when using a mesh as a binder that binds two layers of material together to form a laminate or bonded fabric of uniform thickness.

The foregoing description of molding methods has involved cases in which one molding roll uses another molding roll, with molten material or film passing through them and both rolls rotating at the same speed. However, when using plastics that are relatively difficult to tear spontaneously, such as polyesters, polyamides and vinyl polymers, forming rollers rotating at different speeds can be used so that the tearing of the polymers starts latent already at the molding stage. Different speeds mean that the main lift. the circumferential speed of the roll forming the nucleus is different, from a small difference to up to 50% and either faster or slower than the circumferential speed of the roll which produces the transverse bumps. By using the rollers forming the main protrusions and the transverse protrusions at different speeds, it is possible to cause the thin parts of the shaped film to tear during the shaping step. This facilitates tearing in the next stretching step, i.e. opening into a uniform mesh structure.

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The materials from which the aforementioned mesh structures, fabrics and yarns can be made include all thermoplastic fiber-forming polymers. These include polyethylene, polypropylene hornopo 1 γ-mer, various copolymers of polypropylene containing up to 10% other olefins, block polymers containing up to 25% other olefins, block polymers, nylon-6, nylon-66 , polyethylene terephthalate, other high molecular weight thermoplastic polyesters and vinyl polymers such as polyvinyl chloride. Conjugated, i.e., two-component, plastic films in which two or more different polymers are co-extruded together to form a film having layers of different polymers can also be used. For example, two-layer mesh structures in which each has a portion made of a relatively high melting point polymer, while the remaining portion is made of a lower melting point polymer, can be joined together by placing the lower melting point polymers together in each layer and heating. Alternatively, a mesh structure having a higher melting point polymer combined with a mesh structure made of a lower melting point polymer can be prepared. In addition, a mesh structure having a portion made of a relatively high melting point polymer while the remainder is made of a lower melting point polymer can be joined to another mesh structure made only of a higher melting point polymer. Highly preferred are conjugated plastics in which a component with a higher melting point, such as nylon or polyester, forms the major part of the main fibers. This allows the two layers to be laminated without a binder by joining the layers together using heat and pressure or fluffing by heating the mesh structure or yarns made from such structures. Different. mixtures of polymers, i.e. combinations, can also be used.

Various embodiments of the present invention are set forth in the following examples, which are intended to illustrate the invention and not to limit the scope of the invention in any way.

Example 1

Propylene homopolymer having a melt flow index of 7.5; and a copolymer of propylene and ethylene containing 2.5% of 1B 58738 ethylene and having the same flow rate as the mouthpiece 1.1 together with a slit nozzle at 240 ° C to form a composite film in which the homopolymer comprised 75% film thickness. The slit nozzle was 25 cm long and had a gap size of 0.3 mm. The molten film was passed to a nip between two chrome-plated steel forming rolls, one of which had a diameter of 10 cm and the other 7.5 cm, and the length of each roll was 33 cm. The 10 cmtn roll had a shaping pattern comprising a series of grooves located on the circumference of the roll so that there were 19 grooves per centimeter. This roll was internally cooled to a temperature of 70 ° C. The second 7.5 cm roll was provided with a pattern of straight grooves parallel to the longitudinal axis of the roll, with 44 grooves evenly per centimeter. This 7.5 cm roll was not cooled and had a temperature of about 60 ° C. The molten film was passed between the two rolls at a speed of 5 meters per minute and rotated around a roll having 19 grooves per centimeter so that the contact angle was 180 °. The homopolymer side of the composite sheet was in contact with the roll having 19 grooves per centimeter. The patterned film contained 19 main protrusions per centimeter longitudinally on one side of the film, with the protrusions separated by 0.25 mm wide bands. On the other side of the film, transverse protrusions of 40 per centimeter were formed, the transverse protrusions being separated by bands 0.13 mm wide. The maximum film thickness was 0.38 mm. The ratio of the cross-sectional area of the main protrusions across the transverse protrusions1 to the non-cross-sectional area was 2: 1 and the ratio of the height of the main protrusions to the thickness of the bands between the main protrusions was 8: 1. The patterned film was fed into a stretching frame heated to a temperature of 110 ° C with circulating air at a flow rate of 6 meters per minute, and here it was stretched to twice its width. At this stage of the work, it was opened so that a uniform network structure was created, whereby the lanes between the main protrusions were opened, i.e. the apertures were created when the transverse protrusions were oriented so that the main protrusions now came about 0.76 mm apart. The film was then drawn longitudinally by subjecting it to abrasive contact with a series of 11 steel rolls having a temperature of 120 ° C, and the film moved forward in the series of rolls at a continuously increasing speed. The film was fed to the roll set at a speed of 5 meters per minute and removed at a speed of 31.5 meters per minute, as a result of which it was stretched to 7,587,738 times its length in the machine direction of the nipple. The basis weight of the obtained mesh structure was 11 g / m. The uniformly oriented main fibers were about 45 denier in size. The tensile strength of this mesh structure was 200 g / mm and the elongation was 12% in the machine direction. Its transverse strength in the machine direction was about 30 g / mm and the elongation was 12%. The net was very resistant to tearing in the transverse direction to the machine direction, with a tear strength value of 13.3 kp as determined by the Finch edge tear method, ASTM 0-827.

Example 2

A propylene homopolymer having a melt flow index of 7 was extruded at 204 ° C through the slit nozzle described in Example 1. The molten sheet was formed between two rolls, one of which was the same as used in Example 1 and had 44 grooves per cm parallel to the longitudinal axis of the roll. The second roll had 14 annular grooves per cm and were located on the circumference of the roll. pääkohoutumien generated on one side of the film suddenly poi lei kkausaLan ratio of the generated second half of the transverse cross-sectional area of projections in the finished shaped plastic film was 13: 1 and the ratio of the height of pääkohoutumien bands, connecting the protrusions to one another, to a thickness of 5: 1. The patterned film was then stretched to twice its width using a stretching ring at 80 ° C, during which time regular openings, i.e. holes, were created between the main protrusions.

The film was then stretched linearly 9.2 times its length by passing it with a series of rollers whose rolls rotated at different circumferential speeds and were heated to 120 ° C. The mesh structure thus prepared had a basis weight of 15 g / m 2. The size of the homogeneously oriented main fibers was about 160 denier. The tensile strength of this mesh structure was 0.39 kp / mm in the machine direction and the elongation was 12%. The transverse strength in the machine direction was 14 g / mm and the elongation was 22%. It was highly tear-resistant in the machine direction, with a tear strength value of 23 kp when tested by the Finch edge tear method.

Example 3

High density polyethylene having a melt index of 10 was extruded at 232 ° C through a slit die having a length of 41 cm and an orifice size of 0.38 mm. The molten plate was passed between two crimping points of a chrome-plated steel forming roll, one of which had a diameter of 10 cm and the other 15 cm, with lengths of 38 cm and 51 cm, respectively. The 10 cm roll was formed with a pattern having a number of discrete grooves running around the roll of 30 per cm, these grooves forming an angle of 45 ° with the roll relative to the longitudinal axis of the roll. The 15 cm roll had an embossing with a number of grooves around the roll, of which there were 100 per cm, and the grooves on the roll still formed an angle of 45 ° with the longitudinal axis of the roll. The temperatures of these rolls were adjusted internally and maintained at 65 ° C. The molten film was then fed between two rolls at a speed of 6 meters per minute and the thickness of the film was 0.13 mm. The film was patterned so that it had 30 main protrusions per 1 cm obliquely to the other side of the film, which main protrusions were separated by bands 0.13 mm wide. Transverse protrusions formed on the other side of the film so that there were 100 protrusions per cm, with a band 0.025 mm wide between each pair of protrusions. The ratio of the cross-sectional area of the main protrusions to the same value of the transverse protrusions was about 13 and the ratio of the height of the main protrusions to the thickness of the bands between the main protrusions was 3.5: 1. The patterned film was fed to a linear drawing roll maintained at 120 ° C at a rate of 15 meters per minute and stretched to three times its length. The film was then fed to a stretch frame which was kept heated by circulating air at a temperature of 110 ° C at a feed rate of 45 meters per minute, and here the product was stretched 3.0 times its width.

At this stage, it opened into a homogeneous network structure, whereby the bands between the main protrusions formed openings through which the oriented transverse fibers passed so that the main fibers were now 0.38 mm apart. The film was then subjected to another longitudinal stretching treatment by passing it in frictional contact through a series of eleven steel rollers maintained at 120 ° C and rotating at a continuously increasing circumferential speed. The film was fed into this at a speed of 35 meters per minute and removed at a speed of 45 meters per minute, so that it was stretched 1.3 times its original length in the machine direction. The basis weight of the obtained network structure was 32 g / m. The size of the uniformly oriented main fibers was about 90 denier.

Claims (3)

19 58738 A method of making a mesh structure, comprising forming parallel, elongate protrusions (23, 28) on each side of a film (24) of thermoplastic material such that the protrusions on different sides of the film form an angle with each other, and the film is then stretched so that the protrusions openings are formed in the regions of the strips (25, 30), characterized in that the protrusions on different sides of the film (24) are formed differently from each other so that the ratio of the cross-sectional areas of the main protrusions (23) on the other side and the transverse protrusions (28) on the opposite side is at least 1.5: 1 and the ratio of the height of the main protrusions (23) to the thickness of the bands (25) between the protrusions is at least 3: 1. Method according to Claim 1, characterized in that the transverse projections (28) are formed continuously along their entire length. Method according to Claim 1, characterized in that the transverse projections (28) are formed discontinuously.