IL23945A - Netting material in sheet form - Google Patents

Description

patents Form No, 3.

PATENTS AND DESIGNS ORDINANCE S PE C il l G AT ion netting__/ Improvement B in and relating to/ material in sheet form*, We* T.J, SMITH &J PHEW LIMITED, a British Company, of Neptune Street, Hull, Yorkshire, England, WILLIAM ALBERT SAMM0N9, of 38 , ilders, Sawbrldgeworth, Hertfordshire, England, and ALBERT NEVILLE MAY, of 5, Aoorn Street, Huns don, Hert ordshire, England, both British Subjeots, do hereby deolare the nature of this invention and in what manner the same is to be performed, to be partiou* larly desoribed and asoertalned in and by the following statemen t- v This invention relates to material in sheet form, which may have a thickness within the range of a fraction of a thousandth of an. inch up to, say, half an inch or even more, and particularly, although not exclusively, to such sheet material formed from suitable thermoplastic materials such for example as polymers of the define group including ethylene and propylene, and copolymers thereof in any suitable blend as, for example, high-density or medium-density linear polyethylene and ethylene-propylene copolymer and some of the polyester group; and has^or its object to provide such sheets as an openwork structure of desired configuration, in a simple and efficient manner.

It has previously been proposed in the Specification of United Kingdom Patent No.914489 to produce open net fabrics from films of certain thermoplastic materials with one surface at least formed as an embossed surface of small solid bosses or raised figures arranged with spaces between adjacent bosses in longitudinal and transverse rows, by first stretching the embossed film at a desired rate in one direction, termed the longitudinal direction, and then subjecting the stretched film to a stretching which is transverse to the first stretching„ which splits the film with a multiplicity of short splits through the material thereof, to leave a net-like structure in which each boss has four thinned narrow bands extending therefrom to the adjacent bosses of the two adjacent longitudinal rows when the material is expanded „ From this it will be appreciated that the longitudinal stretching and the transverse stretching take place in succession*, According to the present invention — with material solid bosses or raised figures arranged with spaces between adjacent bosses in longitudinal and transverse rows — a method for the production of an openwork sheet structure comprises subjecting such a sheet of material to stretching or stressing in two distinct directions simultaneously until the material takes a degree of permanent set and splits in various positions or zones of the thinned material located between the raised figures, to leave, upon the cessation of the stressing, bands integral with and interconnecting the various adjacent raised figures, to give a certain configuration depending to a large extent on (a) the mechanical properties of the material, (b) the arrangement of the raised figures, and (c) the shape of the raised figures 0 In order that the invention may be better understood, it will now be described with reference to the accompanying diagrammatic drawings, which are given by way of example only and in which Fig„1 is a diagrammatic plan view, to illustrate sheet material continuously travelling in a machine and subjected first to longitudinal stretch and then to transverse stretch.

Fig02 is a similar view to Fig01 but showing one method of subjecting the sheet material to simultaneous longitudinal and transverse stretcho Fig«3 is a similar view to Fig02, but showing another method for subjecting the material to simultaneous stretch in two directions, i0e0, longitudinal and transverse „ Fig04- is a greatly enlarged plan view of a portion of a sheet of thermoplastic material having the upper surface with parallel rows of similar projections of regular hexagonal form in staggered relation, the lower surface of which material (not shown) is flato 12 (Fig„ )» Pig06 is a similar view to Figs0 4- and 5, but showing the material, from the condition of Figc4-, after it has been subjected to transverse stretching, that is, after it has been pulled in the direction of the arrows 13 (Fig„5) to form a net-like structure, Fig0 is a greatly enlarged plan view of a portion of a sheet of thermoplastic material having the upper surface with parallel rows of similar projections of regular hex-agonal form in staggered relation and with the lower surface flat, such as shown in but after it has been simultaneously stretched in the longitudinal and transverse directions, in accordance with the method of the present inventiono Fig08 is a greatly enlarged plan view of a portion of a sheet of thermoplastic material having parallel rows of elongated rectangular projections on one surface, in staggered relation,; Fig„9 is an enlarged end view of a portion of the sheet shown in Fig„8o FigolO is a plan view of the material shown in Figs0 8 and 9» after it has been subjected to simultaneous longitudinal and transverse stretching, in accordance with the present invention, and Figo11 shows a plan view of the material shown in Fig.7 (which material is the result of simultaneous stretching in two directions according to the invention) after it has been further simultaneously stretched in two directions, according to the invention0 Figo illustrates a known method for subjecting sheet material, which is travelling through the machine, first direction of the arrow 15<> It passes through gripping-and driving rollers 16 and 17 and then to other gripping and driving rollers 18 and 19 a desired distance from the first pair, and which have a greater linear surface speed than the rollers 16 and 17 o As a result, the material is stretched in the longitudinal direction, that is, the direction indicated by the arrow 20 ? the width of the material is also lessened, as shown,, After the longitudinal stretching and beyond the rollers 18 and 19 » the material is expanded (by any usual stentering means - not shown) in the direction of and as indicated by the arrows 21 , and then passes in the direction of the arrow 22 to a suitable take-up roller (not shown) o FigSo , 5 and 6 show sheet material in the three stages of the known old method of Fig„ 1 , and the material as shown in Fig04 passes between the rollers 16 and 17 to the first stretching0 (The "dots" on the material 14 at the left-hand side of Figure represent the hexagonal bosses of the material of Fig04, and the crossing lines to the right of the Figure represent the net-like formation shown in Fig06o) Briefly described, it should be remembered that the first stretching is in the direction of the arrows 12 (Figo 4) and is continued until the thinned material 23 between the raised figures or bosses 24, is sufficiently stretched to take a degree- of permanent set and is brought to the condition shown in Fig05 ° Upon subjecting the thus-elongated material to the second stretching operation in the direction of the arrows left of Figo 5) a multiplicity of splits 26 (indicated at the right of Fi o 5) are initiated,, When the material has been, expanded to the state shown in Fig06, a net structure has been formed and this comprises the hexagonal raised figures 24 each having four bands 2 integral therewith and extending to four adjacent raised figures„ From Fig06 it will be seen that the width of the material as shown in Fig05 has been increased o Figs0 I, 4, 5 and 6, and the method of manufacture to which these Figures relate, are as set forth in the before-mentioned earlier Specification0 FigSc 2 and 3 show two methods for the simultaneous longitudinal and transverse stretching of sheet material travelling through the machine „ In FigD 2 , the material 28 from a let-off roller (not shown) passes between gripping and driving rollers 29 , 30 to any suitable known stentering device (not shown), to stretch it transversely as represented by the arrows 31 , and until it passes between other gripping and driving rollers 32 , 33 <> As the transverse stretching (arrows 31 ) would normally longitudinally shorten the material in the stentering zone, a degree of simultaneous longitudinal stretching would be given to the material if the gripping and driving rollers 32 and 33 had the same linear surface speed as the gripping and driving rollers 29 and 300 However, to increase the amount of the longitudinal stretch, the rollers 32 and 33 can have a greater linear surface speed than the rollers 29 and 30.

The simultaneous stretching by the method indicated in -V it is kept to its own original width and the final gripping. and driving rollers 35 a d 36 have a greater linear surface speed than the first gripping and driving rollers 37 and 38 0 From this it will be appreciated that normally the material 34 , after it has been through the rollers 37 and 38 , would become narrower unless restrained" from so doingo Accordingly, by providing means to prevent the narrowing, the material is automatically transversely stressed, as represented by the arrows 39 ¾ whilst it is being longitudinally stretched (by the greater linear surface speed of the rollers 35 and 36 over the rollers 37 and 38 ) as indicated by the arrow 400 Either of the means indicated in Fig0 2 or 3? or other suitable means, can be used for the simultaneous stretching in two directions, of the material having projections on at least one surface, to carry out the method of the present invention o In one example of carrying the invention into effect, the material as indicated by Fig0 4 is subjected to simultaneous stretching in two directions by the method indicated in Fig„ 3 o This causes the material to be given a net-like formation as indicated in Fi g7 , with six thinned bands 41 proceeding from each hexagonal raised figure 42 to the six adjacent hexagonal raised figures 0 In another example according to the present invention the sheet has the formation as shown in FigSo 8 and 9 where 3 are elongated rectangular shaped projections on one surface of a suitable plastic film 44„ Although the V from rectangle to rectangle in the same row, and 0.5 mni° spacing between parallel rectangles „ The sheet material was subjected to simultaneous stretching according to the method of Fig0 and, whilst kept at the same width, it was longitudinally stretched to nearly three times its original length, with the result that the very openwork structure shown in FigdO was formed, having six arms from and integral with each of the rectangles 45, the arms also extending to and being integral with the six adjacent rectangles 45» For carrying the present invention into effect, the stretching force in one direction may be equal to, or more than, or less than, that of the other simultaneously applied force in the orthogonal direction,, Again, each simultaneously applied stretching force may be limited in its action and only remain effective to produce a certain percentage or actual elongation in the particular direction, whatever the percentage or actual elongation to be effected in the other . direction,, Still, again, the applied force of one of the two simultaneously applied forces, may be uniform or regularly or otherwise varied during its calculated continuanceo Although the simultaneous forces are in action simultaneously, in some cases one may be started more or less a short time before the other; or one may be calculated to end more or less a short time before the other0 The shape in plan of the raised figures on one or both surfaces of the sheet of material is preferably polygonal, irregular or regular - preferably the latter0 For instance, they may be triangular, square, pentagonal, hexagonal, This preference is due to the fact that the more. or less sharp angular edges of the raised figures cause substantial, differentiation in the stresses of the thinned material of the sheet in the neighbourhood of said edges, which has been found to increase the potential splitting of the material from these positions when the simultaneous stretching is effectedo As will be appreciated, within the very wide limits of the present invention a very great variety of openwork sheet structures can be produced, extending from thin films, foils or the like to relatively thick plates, according to "the dimensions of the startin material 0 The raised figures can, as already set forth, be small hexagons with adequate spaces betweeno For example, in a specific instance the film material was 0„005" thick, and the spaced raised figures in rows 60 to the inch in two directions mutually at right angles, to give some 3600 raised figures to the square inchc However, there may be rows say of 100 up to 300 or even more to an inch in two directions, as it is possible in commerce at present to procure embossing rollers having such a pitch spacing for the projections „ In other cases, the spacing of the raised figures or embossments could be relatively large, for example a quarter of an inch, and the thickness of the film could be as desired and, for example, one-sixteenth of an inch or more..

The thermoplastic material when employed can, if desired, include a suitable proportion of fillers and/or colouring matter, as well as stabilisers and otherwise, to produce the openwork sheet structure, it, however, being understood that only such additions and quantities thereof In some cases the sheet material when made into a net-like structure by the simultaneous stretching methods according to the invention, may, and preferably whilst subjected to a heat treatment, be again submitted to a second simultaneous stretching method according to the inventiono An example of the result of this is shown in Fig_110 This has been formed experimentally by taking the material shown in Figo79 subjecting it to a suitable softening heat and simultaneously stretching it both longitudinally and transverselyo It will be seen that the arms 41 which connected the hexagons in the horizontal rows, have been broken,, and the remaining arms 41 elongated and thinned„ However, as will be appreciated, a more openwork structure has been formed, which is desirable for some uses of the material „ It should be understood that the present invention includes not only the main method and subordinate methods as herein described, but also the finished products them-selves whenever formed by the said method or methods „ The invention is not limited to the precise forms or details herein set forth, as these may be varied to suit particular requirements «

Claims (1)

1. HAVING NOW particularly described and ascertained the nature · of our said invention and in what manner the same is to be performed*- we declare that what we claim is t xxxxxxxxxxxxxxxxxx 1 o A method for the production of openwork structures from material in sheet form and particularly, although not exclusively9 from sheet thermoplastic materials, characterised by the fact that at least one surface of the material is formed as an embossed surface of small solid bosses or raised figures arranged with spaces between adjacent bosses in longitudinal and transverse rows, and that said material is subjected to a stretching or stressing in two distinct directions simultaneously until the material takes a degree of permanent set and splits in various positions or zones of the thinned material located between the raised figures, to leave, upon the cessation of the stressing, bands integral with and interconnecting the various adjacent raised figures., to constitute the openwork structure„ 2o method for the production of openwork structures from material in sheet form, as claimed in claim 1 , in which the material is caused to pass continuously through a machine, for example from a let-off roll, in which machine the "draw" on the material effects a longitudinal stretch in the material, whilst simultaneously a transverse stretch is effected on such longitudinally stretching material by means of any suitable stentering or equivalent mechanism, the simultaneously stretched material then, in the form of the required openwork structure , being delivered, for example, to a take-up roller0 3o A method for the production of openwork structures from material in sheet form, as claimed in claim 1 or 2, V < end rows, which rows are staggered and have the rectangles, in all the rows parallel, to produce a structure in which the openings have large area compared with that of the solid material o 4 A method for the production of openwork structures from material in sheet form, as claimed in claim 1 , 2 or 3, in which the sheet material with the projections on at least one surface, after being formed into an openwork structure by simultaneous stretching in two directions, is again subjected to such simultaneous stretching in two directions, preferably while subjected to a suitable heat treatment, to produce a more openwork structure0 5o A method for the production of openwork structures from material in sheet form, as claimed in any one of the preceding claims, in which, whilst the stretching in two directions is simultaneous for the majority of the stretching time, either stretch may start before the other and, similarly, either stretch may end before the other0 6o A method for the production of openwork structures from material in sheet form, as claimed in any of the preceding claims, in which the forces applied to effect the simultaneous stretching in two directions, may be equal or unequal o » A method for the production of openwork structures from material in sheet form, as claimed in any one of the preceding claims, in which either stretch may be effected by a uniformly applied force, or by a variable force- Bo Methods for the production of openwork structures from material in sheet form, and particularly, although not exclusivel from suitable sheet thermo lastic materials 9o Openwork structures, formed from any of the materials herein described,, when produced by any of the methods, claimed in the preceding claims 0 ' Dated this Thirteenth day of July 1965