Parachute materials

It would be desirable to find a way to reduce the tendency of the film material (or article formed therefrom) to break under impact and to increase the energy absorbing properties of the article.

The present invention relates to ways of distributing the tension and other forces in a film material in order to minimize the risk of rupture.

In some cases, it would be desirable to modify in this way most of the article or even the article as a whole. For example, it may be desirable to modify the frame formed from materials. It is desirable to modify the entire surface area (or parts of the parachute frame), especially the parachute frame, to minimize the risk of breakage under impact or to reduce the impact on the load that the frame is supposed to carry or for similar reasons. total surface area) of wide cloths such as a parachute cover.

In other cases, it is desirable to modify smaller film extensions in selected areas. Thus, particular problems with bags arise as there is generally a particular zone in the bags where there is a greater tendency to start

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- break and this is referred to as the break zone. It would therefore be particularly desirable to modify the bag in the rupture zone. Once rupture begins, it tends to propagate outside the rupture zone. The rupture zone for any particular bag construction can be postulated from theoretical considerations or, in a more practical aspect, can be determined experimentally by dropping a few full bags.

The rupture zone is often associated with a seam in the bag because the film material adjacent the seam generally has a tendency to rupture more than that of the film material in the remaining areas of the bag. It appears that the act of forming the seam may adversely affect the properties of the film material in areas adjacent to the seam. However, it should be noted that the rupture zone may not extend over the entire length of the seam since in a conventional bag the rupture zone may be located primarily in the area midway between the two ends of the seam. .

When the bag is a sheathed bag having a terminal seam and comprising opposite outer faces interconnected at its side edges by side sheaths, there is a tendency for a particular break zone to occur at the junction between the side sheaths and the seam.

A bag may have more than one rupture zone. For example, if the bag is sewn at the top and bottom there will generally be a break zone associated with each seam (where there will be a tendency to break during vertical falls) and if the bag has side sheaths there will generally be a particular break zone at the junction between the side hems and the seam (where there is a tendency to rupture during horizontal falls).

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The process of subjecting the film material from which the bag is formed is certainly well known to various orientation steps and other treatments to give it optimum properties, but conventionally the film exhibits uniform properties across the whole of the film. bag, and also

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Ref: Ξ-Α-Β _4— It is well known to etch the surface of the film both for the sake of visual appearance and to facilitate stacking of the film. However, conventional global recording techniques do not yield the improvements that would be desirable.

The film orientable thermoplastic material according to the invention has at least one stretched zone in which the material has been stretched in a first direction and, adjacent to opposite sides of that zone, undrawn zones which extend substantially in said first direction and in which the material is stretched. material is substantially unstretched.

Thus, in the present invention the film material does not have uniform stretching but varying degrees of stretching so as to provide at least one stretched zone and a plurality of substantially undrawn zones. These unstretched zones have a significantly lower degree of stretch than the stretched zone, but may be slightly more stretched than the original film material prior to stretching. in the stretched area. Preferably, there are a plurality of unstretched zones, each located between a pair of zo in the stretches.

Generally, the degree of stretching in stretched zones is at least 10% and generally at least 20%, for example up to 30 or 40% or more, relative to the original film material and preferably the film material in substantially unzipped areas. The stretched lines show very little or no stretch compared to the starting film material. The initial film material should be orientable but may already have been oriented to the limit extent.

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It is therefore necessary that in each stretched zone the film material has a greater length than the non-stretched zone. adjacent row. The film material in the stretched zone may comprise a series of evenly or irregularly disposed pleats extending transversely of the length of the stretched zone. A convenient way of forming each of the stretched zones comprises providing a series of positions

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-5 extending transversely, in which the film material is stretched (i.e. the material is stretched in said first direction of the stretched zone). In particular, this object is best achieved by stretching each zone by embossing the film material therein with teeth extending transversely to said first direction. Often, the stretched zones are longitudinal and extend in the first direction.

The present invention may be applied to the entire area of ​​a sheet material in which case, as indicated, there is preferably a plurality of stretched and undrawn zones alternating with one another. Each undrawn zone may be in the form of a rib which may be straight or zigzag and which may typically be from 5 to 150% of the length of each stretched zone. Typically, each unstretched zone is at least 0.5 mm long and each stretched zone is at least 2 mm and preferably 5 mm long. When undrawn zones alternate with stretched zones, undrawn zones are generally no more than about 5 mm and sometimes 10 mm in width although they may be wider while stretched zones may often be up to 20 mm wide. mm or 30 mm or more.

The invention has particular value when applied to prevent sack rupture.

In this aspect of the invention there is provided thermoplastic tubular film material which is or may be sewn to form a closed bag having a rupture zone in which there is a tendency to rupture when the bag is subjected to rupture forces by being left fall when full and the material in peli. The area adjacent the rupture zone includes a shock absorbing zone comprising at least one stretched zone extending in a direction substantially away from the rupture zone and wherein the film material has been substantially stretched in that direction, and a plurality of substantially unstretched zones adjacent to and extending substantially in the same direction as the stretched zone or each of these zones,

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breaking forces transmitted outside the breaking zone by the unstretched zones and into the stretched zone or zones.

Tubular material according to the present invention may be a closed bag or open bag or an open tube which may be sealed to form an open bag. For example, it may be an endless pipe that can be sealed and cut to form a plurality of pipes. The material is generally extended in tubular form, but if desired, a sheet may be sealed laterally to form the tubular material.

In this aspect of the invention the rupture zone is preferably along a hot-stitched or stitched seam in the end bag and the shock absorbing zone is preferably a shock absorbing band (BAC) which is separated from the seam by an area. through which the breaking forces can be transmitted to the shock absorber band and the band comprises a plurality of ribs of substantially unstretched material extending substantially in the direction of forces acting on the seam (which will be substantially perpendicular to the seam) separated by strips of film material that have been stretched substantially in the same direction (i.e. usually substantially perpendicular to the seam). The length of each unstretched rib should, for optimal properties, depend on the particular film materials used, but is typically in the range of 5 to 150% of the length of each adjacent stretched strip. As already mentioned the direction of the forces acting on the seam is usually substantially perpendicular to the seam. An exception to this rule is seams formed by bias in hems.

Each undrawn rib preferably extends continuously through the full depth of the shock absorber band. The ribs may extend as a substantially straight line or as a zigzag line provided that the changes in direction in the zigzag line are not so large as to prevent the transfer of loading forces along the length of the line.

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When the rupture zone is the seam itself, it is desirable that the shock absorber zone be slightly displaced, for example at least 1 cm and often at least 3 cm, from the seam so that the rupture forces in or adjacent to it. can be distributed over a useful extension of the shock absorber band. Good results are generally obtained when the displacement is for example no more than 10 cm and often no more than 5 or 6 cm. The depth of the shock absorber band, that is, the distance between its adjacent edge and the furthest edge, is typically in the range of 3 to 10 cm.

The parts of the seam where the breaking forces are most likely to cause breakage are those which are most inwardly displaced from the side edges of the bag in conventional bags, and therefore it may not be necessary for the shock absorber band to extend. to the outermost edges. Instead, the web may extend between external positions that are offset inwardly relative to the edges of the bag.

In a second aspect of the invention, the orientable film material is provided in the form of a bag comprising opposite outer faces interconnected at their side edges by side sheaths. In this case there is a particular rupture zone at the junction between the side sheaths and a hot-stitched or seamed end seam that tends to cause rupture when the bag is dropped onto one of its flat faces. Part or all of the side sheaths may be in the form of one or more of the previously described stretched zones formed of longitudinally stretched material while the undrawn zones may be within the sheaths, for example alternating with stretched zones or the central sheath bending, or it may be at the outer edges of the sheaths or at the edges of the outer faces of the bag or may be offset inward from the outer edges of the bag. This construction means that the load is supported by longitudinally undrawn areas in or adjacent to the sheaths but longitudinally stretched areas69 126

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-8 the sheaths absorb the shock and thus protect the joints from rupture.

The following will be discussed in more detail how to avoid breakage along a seam. The impact stress of a seam on a bag is usually one of the most critical properties of the bag. The term impact stress refers herein to drop tests performed on the bag filled with the intended powder or granules. Normally it will not be possible to produce a simple heat-bonded shell-like seam (as opposed to more complicated heat-spliced ​​seams of the trimmed type) in bags formed from relatively rigid polymers (with reference to their modulus of elasticity) such as polypropylene or polypropylene. high density polyethylene, even when the two mentioned polymers have been modified by the addition of elastomers in economical quantities. practically acceptable.

The shell stress of these heat-bonded seams, measured at the low speeds that are usual for stress testing, will usually have values ​​generally at the same level, or even higher, than a low-density polyethylene hot-stitched seam. of similar thickness, while the impact stress of polypropylene or high density polyethylene seams will be much lower than that of low density polyethylene seams.

Studying these problems it has been found that poor impact strength is linked to a phenomenon that may be equivalent to the notch effect, namely the concentration of drawing forces in a narrow linear area around the tip of the seam contact face. Additionally, there will often be a real notch effect due to imperfections in the shape of the heating rods used for forming a heat seam. Orientation will begin where the tensile forces are concentrated. If the stretching action is slow, this orientation will gradually develop away from the starting line and improve strength in this area. If, however, the speed of the stretching action exceeds a certain range

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Critically, depending on the material and parameters of the pre-heat-bond operation, the orientation progress (which is a time-dependent process) will remain confined to a very limited line zone rather than gradually extending this zone.

High energy action in an extremely limited area almost instantaneously causes the rupture.

It is believed that the different character of the orientation process when carried out below and above the critical range of drawing speeds is mainly due to the heat developed by drawing and the heat produced by friction being high when the polymer is rigid. At speeds below the critical range it is believed that there is sufficient time for heat to be conducted to adjacent portions of the film to assist the gradual and smooth development of orientation. Conversely, at speeds above the critical temperature there is not enough time for heat to be conducted out of the narrow zone under the influence of the notch effect (or the like) and the polymer will melt almost instantaneously in this zone.

The perforations caused by the seam in a stitched seam can also cause weakening and in this case the breaking strength is very speed dependent.

In the present invention it has been attempted to alter the characteristics of the bag material in a region close to the seam in order that the energy released by the bag fall is guided in order to attack another predetermined and less sensitive part of the bag construction.

It should be noted that the deficiency described in rigid, heat-seamed sternal bags is particularly pronounced if the material is oriented by stretching below its melting point. In this context it is well known that uniaxially oriented high density polyethylene or polypropylene crosslinked laminates (which may contain small portions of elastomer) with a suitable but not very strong bond established between the layers exhibit high values ​​of spread rupture and impact resistance on the film itself and the

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Glued bags (mainly valve bags) obtained from these crosslinked laminates have important commercial uses. Note that stiffness per se is a desirable property

X for sacks material. It is also known that the heat-joined seams in these crosslinked laminates exhibit good tensile strength when measured at the speeds normally used in stress testing, however the impact strength of these seams is particularly low, making them material, which would otherwise be very useful, completely useless for simple construction of seamed bags.

From studies and theoretical work on oriented film material, it has been found that the above-mentioned notch effect (or similar) is adversely complemented by loss of orientation in the area immediately adjacent to the heat-bonded area. (Orientation is of course also lost in the seam area itself, but since this area is less thick this fact seems to be irrelevant in this context). In the oriented material itself, there is a high resistance against further orientation development, which is no longer found in the non-oriented linear zone adjacent the seam. Therefore, not only the notching effect (or similar) but also the loss of orientation causes the impact action to be confined to a very narrow area. As a result, even materials much less rigid than high density polyethylene or polypropylene, but in oriented state, become useless for the seamed bag constructions which are the subject of the present invention.

US Patent No. 5. No. 4,039,364 relates to a process for producing a crosslinked laminate of a different type from the above mentioned crosslinked laminates. In this process each layer is biaxially oriented and instead of re-crossing the directions of the uniaxial orientation, a re-crossing of polymer grain is established, which grain is primarily produced during extrusion and then during the sequence of steps. stretch, is deflected to a desired zigzag course. As stated in the aforementioned patent, these crosslinked laminates are generally suitable for forming heat-joined seams,

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This may be partly explained by the shrinkability by which the heat-seamed seam and adjacent areas increase in thickness and partly also by the special zigzag configuration of the polymer grain. In spite of this, an improvement of the heat-bonded seams of these crosslinked laminates is still desirable, as the examples of the present specification will show.

In addition, as with the adverse role of material stiffness in connection with the impact strength of a seam, it should be borne in mind that what matters here is the stiffness at existing temperatures when the full bag is dropped. , internationally or accidentally. Thus, even normal low density polyethylene is relatively rigid, for example at -2D ° C, and the heat-sealing resistance of single seams of low density polyethylene bags at these temperatures has been found to be significantly lower than that established at room temperature. However, -20 ° C and even lower temperatures are in many cases normal for bag handling and therefore there is also a need to reinforce the seams of low density polyethylene bags.

A preferred bag (or tubular bag-forming material) according to the invention comprises, in combination with a seam, a pattern in embossing bars along the adjacent but spaced seam of the seam. The embossing pattern consists of rows of tooth-like cut-outs in which the film is elongated principally in the direction of forces occurring during a critical type of fall, i.e. usually mainly perpendicular to the seam, separated by ribs. substantially unchanged film material to produce a shock absorbing effect that protects the seam itself when the full bag is dropped. Embossing causes stretching.

The ribs of substantially unchanged film material should be sufficiently narrow (compared to tooth-like indentations) and the degree of local elongation produced by embossing should be sufficiently high.

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12 to ensure that the shock absorbing effect described above is in fact established and acts to retard the stretching action so that a certain orientation can develop calmly in the area just adjacent to the seam. 0 The optimum pattern design (hereinafter referred to as the choke absorber band) depends on the efficiency requirements, the characteristics of the film, the size of the bag, the material with which the bag will be filled, the degree of filling, the sewing process and the temperature at which falls are to occur. In either case, however, this design will not pose major problems for a trial and error expert.

The ribs of unchanged film material may generally be straight ribs (reference to Figures 1 and 2a) or may be generally zigzag, as by zigzag embossing (reference to Figure 3). The former makes engraving toolmaking simpler while the latter allows for a more effective shock absorbing effect, which may be necessary when the material is particularly rigid or particularly oriented.

In the above description, the invention has been described with particular regard to heat-bonded seams of the shell type. However, there is often a similar problem of low impact resistance in overlapping seams in cases where heat bonding of the material is difficult, particularly when the polymer is oriented. Similar problems may also occur with overlapping seams joined by a cast adhesive and with supersonically produced seams. 0 The invention is therefore useful in all these cases.

Furthermore, the invention is very advantageous in conjunction with a stitched seam. The strength of a stitched seam depends essentially on the tear propagation resistance of the film, which in turn critically depends on rigid and / or oriented material on the breaking speed. This is also true. for the two types of crosslinked laminates described above which both have a high resistance to rupture

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<img file="PT90306B_D0003.tif" />

It is up to a certain critical range of breaking speed, but generally poor weak breaking strength above this range. The shock absorbing band can therefore be advantageously used to absorb most of the impact action, reducing the breaking speed below the critical range.

The shock absorbing band is applicable to top and bottom seams as well as side seams. It has been found that the forces exerted near the corners of a full bag when it is dropped are always relatively small and therefore there is no need for the shock absorber band to extend even to the edges of the bag.

The present invention further relates to the process of combining the seam of a bag with embossing in the specific pattern described above for the product and the combination of sewing and embossing equipment to practice this process.

The shock absorber band may be produced prior to, simultaneously with or subsequent to the sewing process. Thus, the shock absorber band may be etched (a) on the film before tube formation or (b) on the tube before bag formation, or (c) on the bag before filling or (d) on the full bag before final seam formation or (e) after seam formation. 0 Wind also refers to bags and pre-stages of bags (e.g., form-and-fill tubes) with a shock absorbing band correctly located with respect to a seam that does not yet exist but is intended to be done later. . This will usually be the top seam or both top and bottom seams formed in conjunction with the filling process. Bag forming or filling machines using pre-formed tubes with shock absorbing bands may be provided with synchronization devices to form seams with correct locations with respect to the bands.

As mentioned earlier, a shock absorbing band for the top seam of an open bag may be formed after the filling process in combination with the seam of the bags. The stitching will usually be carried out by means of a sealing

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In conventional band or conventional sewing machine and in such cases the shock absorber band is preferably continuously produced between a pair of embossing wheels of which one may be provided with a male surface pattern. and the other with a corresponding female surface pattern. (See Figure 5a and b). In other cases, it will generally be preferable to intermittently record, for example using a hydraulic or pneumatic press, even between male and female surface standards.

If, by etching tubular films, a transverse shock absorber housing is formed, it may be difficult without special measures to open the tube for filling. Thus, it is often advantageous to form at least the shock absorbing band for the top seam of an open bag while the bag material is a flat film and then convert the flat film into a tube. In such cases, the engraving machinery may conveniently be combined and synchronized with either the printing machine or directly with the bag forming machine.

In this case, the side seam is formed after embossing the shock absorber band to the top and / or base seams and when the side seam is produced either by applying a hot melt adhesive or by heat bonding, the application heat will cause the embossing to disappear at the point where the shock absorber band intersects with the side seam. However, this has no adverse effect as long as the side seam is located very close to one of the edges of the bag, as, as mentioned above, the impact action is relatively weak near the skis on the bag.

The fact that only the unchanged ribs in the shock absorber band have to withstand the stresses perpendicular to the seam means that the elasticity coefficient in this band appears significantly reduced, so that the band acts as a rubber band and so on. time the total yield stress in the band will be reduced. These characteristics

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These features will be explained in more detail in combination with Figures 1 to 4. Reducing yield strength can lead to permanent deformation of the material within the shock absorber band even during normal bag handling or storage, but these deformations will be they are usually of little importance as they are confined to the narrow band and generally end when the protrusions are straightened. 0 Balancing the need for good fall efficiency and sufficient yield strength is an important factor to take into account in reaching the optimum standard.

If the bag is to be handled by hand and kept in shape thereafter, the shock absorber band should preferably not cross the surface of the edge bag on board, but some portions near the edges should be left untapped, such portions should be of sufficient length to prevent any substantial deformation when the full bag is raised at the corners. As mentioned above, there is no essential need for a shock absorbing effect at these locations since in any case the stretching forces will be relatively low here when the bag is dropped.

In order to achieve a sufficiently important shock absorbing effect, the engraving pattern and depth should be adapted to give no more than 15% and preferably no more than 25% critical drop height improvement for a fall cycle. The critical fall height is defined here as the fall height which is statistically the limit between success and failure when a bag with the relevant content of dust or granules is dropped 6 times in the following cycle: (1) 1 flat surface, (2) flat surface, (3) 19 edge, (4) 29 edge, (5) base, (6) top.

However, with proper selection of the pattern and engraving depth (lines for this selection are given in combination with Figures 1 to 4) the increase in critical drop height for a drop cycle can in many cases be 50 % or 100%

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-16 or even more, without causing any essential damage to the ability to resist deformation during bag handling and storage. Embossing the film material in bags is known as a means of improving the non-slip characteristics that are important for stacking bags. For this purpose, however, it is important to select a recording type that results in only a minimal reduction in the yield coefficient and yield strength (with reference to apparent values ​​as explained in greater detail in combination with Figures 1 to 5). A bag with the shock absorber band may also, in order to improve its non-slip properties, be provided with additional embossing in other selected areas or generally over the entire surface, but in such cases the pattern and depth of the engraving in the shock absorber band must be adapted to produce a substantially greater shock absorbing effect. (The basic characteristics of the shock absorbing effect are explained more quantitatively in combination with the graphs in Figures 4A and 4B).

As mentioned in the introduction, heat-bonded bottom and / or top seams with sheathed bags have a particular point-formed rupture zone located at or immediately adjacent to each of the intersections between the innermost folds of the sheaths. and the base or top seam joined by heat. The rupture in these zones occurs mainly when the full sac is dropped onto its flat faces. There are two reasons for the tendency to rupture at these points, one of which is the sudden change in thickness between the sheathed portion of the bag, 4th fold and the unsheathed portion, that is, 2 fold. This variation in thickness makes heat bonding particularly critical. Another reason why rupture tends to occur at these ports is that when the bag is filled and the sheath is therefore unfolded to give the bag the shape of a brick, the pull on the sheath at each corner of the bag has to be taken above all. at the narrow point where the heat-joined seam intersects the innermost fold of the sheath. Thus, when the bag is dropped onto one of its flat faces the contents are pushed against the corners of the bag and

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The resulting pull on the sheath at this corner is concentrated at the narrow intersection point. Accordingly, the sheathed bags cannot withstand flat drops from the same maximum heights but as single pillow-type bags of similar material, unless similar precautions are taken. This also applies to sheathed bags formed from soft and easily heat-bonded materials such as PELBD or LDPE.

In the art, this problem is solved by providing each sheathed corner with two extra heat-joined straight seams, each sealing one side of the sheath to the corresponding outer fold of the bag and starting each at said intersection point and extending obliquely, usually at an angle of 45 ° to the longitudinal direction of the bag. With these extra heat-joined seams, the sheath will remain unfolded in the normal manner around the corner and will give the bag a brick shape during filling, but now the forces on the sheath at the corner of the bag during a flat fall will be distributed over the full length of the bags. two extra seams joined by heat instead of concentrating on a single stitch.

A disadvantage of this known and used precaution is the relatively long time required for the special extra color joint, which necessarily includes a cooling step before the two sides of the sheath meet again, as otherwise they would merge together to form a single seam.

Therefore, the process of forming the extra seam is more conveniently, according to the present invention, replaced by applying BAC to the sheaths at the corners of the bag. This BAC should not, in essence, extend to the two outer layers of the bag, but should be confined to the sheath close to the corner (with reference to the bag structure prior to unfolding the sheath).

Ideally, undrawn areas or ribs in the BAC should all point towards the shape intersection point. pointing in the same direction as the tensions in the unfolded sheath,

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But in order to simplify the construction of the tools, the embossing pattern should be similar to that of Example 3, in which the ribs all extend in the longitudinal direction of the bag. At least the ribs closest to the innermost bend of the sheath should point mainly towards the intersection point.

As an additional advantage, the apparently high reduction in elasticity coefficient achieved by embossing the sheaths near the corners of the bag helps the contents of the bag to better fill the space in the corners and thus the brick shape becomes perfect.

Shock absorbing bands may optionally be used in combination with the embossing of the sheath described herein. Thus, the combined use of embossing of the shock absorbing sheath and band described in example 3 results in an improvement in the critical fall height by a factor of more than three. Embossing of the sheath is preferably performed on a flat film before tube formation or on a flat tube before sheathing, but may also be performed after sheathing and even after bag formation, provided that the inside of the bag is conveniently accessible.

An alternative and in some cases simple precaution, which does not really fall within the above definition of shock absorber but which uses an analogous effect, is the embossing of the innermost fold of the sheath immediately adjacent to the base seams and / or top. Thus, the sheath and adjacent faces of the bag may be considered as a special form of shock absorbing zone according to the invention, which may extend from a position at or near the junction between the seam and the sheaths. and does not need to extend substantially through the extension of the sheaths. The edges of the outer faces of the bag and / or patches within the sheath may serve as substantially undrawn areas adjacent to the stretched zone, i.e. part or all of the area within the sheaths. Embossing simul69 126

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Attaching the outer layers of the bag may not cause damage but makes the process simpler. This embossing on the sheaths should be deep enough and / or close enough to the seam to produce the effect of essentially pushing away a tension applied to the bend away from the point of intersection (where heat bonding tends, as already mentioned, to be critical) and to a part of the heat-seamed seam near the corner of the bag.

Preferably, this embossing should gradually fade toward the edge of the bag so as to distribute the forces in the innermost fold of the sheath over a wider portion of the base or top seam.

To ensure accurate location of this embossing with respect to the point of intersection between the innermost fold and the seam of the base or top, this embossing is most conveniently performed simultaneously with the formation of the heat seam and the same equipment. which may comprise devices for detecting the transverse location of the innermost fold and also for automatic transverse adjustment or for detecting the location of the embossing.

As already mentioned, the shock absorber band is very suitable for bags formed from the crosslinked laminates described in US patent n. 4,039,364. The same applies to the embossing of sheaths described above. US patent no.^s. No. 4,629,525 discloses improved crosslinked laminate compositions of this type consisting of two or more folds, each of which usually has a main layer, a laminating layer and a seaming layer. The two embossing systems according to the present invention may advantageously be used, separately or in combination, in bags formed from these compositions. Thus, a particularly preferred backing layer is formed for use in a laminated bag sheet of the invention from a mixture of high molecular weight high density polyethylene with significantly lower molecular weight low density polyethylene, the latter being preferably selected

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Among copolymers and / or branched polyethylenes having the same month. or a higher elongation at break (tested at ambient temperature under slow stretching) than high molecular weight polyethylene and having the ability to segregate distinctly, but forming a distinct microface, from high molecular weight polyethylene while cooling. a fused homogeneous mixture of components. The mixing ratio of the polyethylenes is preferably 25:75 to 75:25. Inclusion of polypropylene having a significantly lower molecular weight may also be advantageous in amounts of 0 to 70% based on the combined weight of polypropylene and both polyethylenes.

High molecular weight high density polyethylene (PADPME) preferably has a viscosity index of about 0.2 or less by condition F of ASTM D123B and low density polyethylene is preferably linear low density polyethylene (PLBD).

In the accompanying drawings:

Figure 1 shows, on a scale of about 1: 3, an open cushion type, provided with two shock absorbing bands, one near the heat-seamed seam at the bottom of the bag, and one at the top near the predetermined region for closure by either heat seam or seam bonding.

Figures 2A and B show approximately full scale details of the bag base of Figure 1, A being a horizontal view of the bag and B a vertical longitudinal section through a row of cutouts.

Figure 3 shows a modification of the shock absorber band of Figure 2A, also shown in a horizontal view and on a near real scale.

Figure 4A shows stress / resistance diagrams taken on 5 specimens of the shock absorber band zone of a bag produced according to the process described in Example 4.

Figure 4B shows comparative voltage / resistance diagrams taken on 5 specimens from the same bag but outside the

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-21 shock absorber band.

Figures 5A and 8 show different sections of a series. embossing wheels (rollers) suitable for forming the shock absorber band. Figure 5A shows a section through bb of Figure 5B and Figure 5B shows a section through aa of Figure 5A.

Figure 6 shows a perspective view, approximated to full scale, showing a corner of a sheathed bag in which the sheath is provided with an embossing to eliminate the critical tension that otherwise occurs at the intersection of the sheath. seam and innermost fold of the hem.

In Figures 1 to 3, (1) represent rows of tooth-like cut-outs and (2) represent unchanged (or substantially unchanged) ribs, forming (1) and (2) together the shock absorbing band (hereinafter abbreviated to BAC). ), (3) represents the heat-joined seam on the base. At the top, (4) indicates the area where the location of the closure is predetermined by either heat seam or seam joining. There are relatively long distances, and X₂, between BA-Cs and (3) and (4) respectively, the length of which will be discussed below.

At each corner of the bag preferably a free embossing zone Y is left. Zone Y should be calculated to be sufficient to avoid any essential deformation when the full bag is lifted at the corners as intended to be handled.

Edge fall is undoubtedly the most critical type of fall for cushion bags with heat-stitched or stitched top and bottom seams. (For flat sheathed bags it is more critical due to the special problem addressed in Figure 6 and for longitudinal seams the bottom or top falls are more critical). When the edge of the bag filled with dust or granules hits the floor, the contents spread very horizontally. By the time the bag hits the ground the spread of the contents is confined to take place almost entirely perpendicular to the length of the bag and, near the top and bottom, the impact on

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Flat surfaces of the bag will then cause a high longitudinal pull, which means a strong stretching action at the top and bottom seams. This stretching action has been found to be greater near the middle of the seams or near z

board that hits the ground. It is understandable that the stretching action is almost nil at the corners that do not hit the ground but it is very surprising that it is also low near the corners that hit the ground.

The improvements achieved by using BAC are best understood by observing the diagrams presented in Figures 4A and 9.

For the diagrams shown in Figure 4A, the edges of each of the 11 to 14 specimens of the invention were cut by the line. average length of two unchanged ribs (2) and each specimen comprises two rows of tooth-like indentations (1) with one unchanged rib (2) in between. In total, therefore, each specimen consists of two rows of tooth-like cut-outs (1) and two unchanged ribs (2). The length of the specimen is 22 mm. The initial distance between the two tension test equipment tongs is 50 mm and the specimen has BAC throughout this space. (The length of the BAC is also 50 mm, see example 4). The testB speed is 500 mm / min = 1000% elongation per min. In the diagrams, 10 mm on the abscissa corresponds to 20% elongation.

The comparative diagram of Figure 4B was also formed from specimens 16 to 19, 20 mm in length, cut from shock-absorbing band-free portions of the bag.

In the range from zero to deflection point Y the ribs become elastic elongated but begin to yield to Y. In this range, the comparison between the two diagrams shows that the slope of curves A is almost exactly half that of curves B, according to the fact that each rib in the BAC in this particular case (see example 4) has been formed to the same extent as each row of cutouts, so that almost precisely half of the length of the specimen is over the load. 0 slope on this

126

This range is a measure of the coefficient of elasticity - for embossed samples it is more accurate to speak of apparent elasticity coefficient - and the diagrams show how BAC makes the material more rubbery.

With the film composition used in example 4, the ratio of rib extension to division in the BAC could also have been somewhat higher than the actual 1: 2 ratio, while still providing satisfactory improvements, however, may be required. make the ratio much smaller for much stiffer compositions, for example 1:10 or even 1:20 (see example 1 in which it was necessary to use a ratio of 1:10).

Between the deflection point Y and the subsequent deflection point A, the ribs sag under tension while the indentations remain still loose. At point A, the indentations are stretched and begin to stretch as the ribs continue to sag. At the last deflection point the cutouts also begin to sag.

The percent elongation at A is essentially equal to the original stress ratio in the clipping row, in this case about 28% equaling the 1.23: 1 ratio.

An important factor for the function of the BAC is the apparent reduction in the yield and yield point discussed above, which invites impact to attack the BAC rather than shroud the seam. Another important factor is the energy absorbed by BAC from zero to deflection point B, which will be called BAC energy. It must be high enough to soothe the impact of the falling edge so that after the effect of the BAC the seam attack is not strong enough to damage it.

The indentations should preferably be as deep as possible in practice (i.e. the stretch ratio in the indentations as high as possible) so that the energy of BAC per unit length of BAC is as high as possible ( for any embossing pattern),

126 Ref: SAB

<img file="PT90306B_D0008.tif" />

however, the following practical limitations should be borne in mind:

(a) the limited stretching of the film in relation to the required high process speeds;

(b) the weakness of the teeth (friezes) of the embossing devices.

With the types of lattices described in the examples which were previously stretched in both directions prior to embossing in ratios of about 1.4: 1 to 1.6: 1, it has been found to be It is difficult to exceed 1.3: 1 or 1.4: 1 ratios in the formation of the cutouts unless the film is preheated in the areas to be embossed and the preheating should normally be avoided. not complicate the process. Stretch ratios of less than about 1.3: 1 are also applicable for forming rows provided that an improvement of at least 15% but preferably over 25% can be achieved at the critical fall height of the bag ( as defined above).

length of BAC and ratio of length of each rib to division in the optimal BAC (total length of a rib and a row of cuts) should be established by systematic or general experience and depend, as already mentioned in the summary description of the invention, the efficiency requirements, the characteristics of the film, the size of the bag, the material to be filled with the bag, the degree of filling of the bag, of the heat seaming or stitching process and the temperature at which falls are expected to occur. As far as efficiency requirements are concerned, the balance between the need for good drop efficiency and the need for bag shape stability is particularly important.

In Figures 1 to 3 the indentations are shown oblong with their longitudinal direction perpendicular to the longitudinal direction of the ribs (2). This structure will usually be advantageous, but it is also possible to replace each oblong cutout with two or more generally circular cutouts, although this requires more complicated embossing equipment.

126

Ref: SAB

<img file="PT90306B_D0009.tif" />

In some cases, when only a small BAC effect is desired, simple rows of generally circular cut-outs alternating with the ribs may be used (2).

The division of the indentations in each row should preferably be as small as possible in practice, with the lower limit determined by the possible stretching of the teeth (friezes) in the embossing equipment and the practical accuracy possible for this equipment. For bags formed from very thin films, this division may fall to about 1.5 mm, while suitable values ​​for bags formed from stronger material are generally between about 2.0 and 4.0 mm. , although somewhat higher divisions may also apply.

It has already been mentioned that the cutouts should not start immediately adjacent to the seam (ie at a distance x = 0). In this case, each rib 2 would pull almost with its full force a corresponding portion of the seam and virtually no improvement would be achieved.

To even out the seam forces, x should never generally be less than the distance between two neighboring ribs, ie the length of each row of cutouts and preferably x should sometimes be, for example, 2 to 6 times. This is the distance. 0 The value of x may also be higher, but since the stresses, when the bag hits the floor with one edge, are concentrated near the top and bottom, the entire BAC should be confined to a zone at a distance from the seam. (or predetermined location to become a seam) not exceeding 25/4 and preferably not exceeding 15% of the total length of the bag (or, in the case of BAC being made for side seam protection, bag extension) .

In Figures 5A and B, both wheels (5) and (6) are driven at the same radial speed and the surfaces of both are formed as teeth and circular notches, the teeth of one wheel fitting into the notches of the other, leaving space in the means for the material of the bag so that when passing between the teeth in69 126

Ref: SAB

<img file="PT90306B_D0010.tif" />

The penetrants are stretched perpendicular to the direction of advance. While the teeth in (5) are continuously circular, the teeth in (6) even have the shape of teeth as shown. All corners and edges that come in contact with the bag are carefully rounded and polished to prevent perforation of the material.

The bag is passed through the embossing device and carried in a direction parallel to the top or bottom seam, thus forming the top or bottom BAC shown in Figure 1. Both BACs can, of course, be formed simultaneously by the use of Two pairs of embossing wheels.

The inlet, and equipment is preferably provided with guide wheels (rollers) which act to keep the bag straight while counteracting the dragging of it into the middle of the wheels (not shown).

The pair of wheels is preferably mounted open and close to prevent embossing near each corner.

Bag feeding to the device and opening and closing of the wheels can be done manually, semi-automatically or automatically. Just prior to embossing and working in line with the wheels, a preheating device can be provided which selectively heats the vicinity of the approaching BAC. This device may, for example, be a device similar to that which produces heat band bonding, but operated at a temperature at which such bonding does not occur. After embossing there may be a calendering step for volume reduction.

The device described here is the simplest and most economical equipment for BAC production. Alternatively, a press may be used, having better interpenetrating teeth but of course with a straight rather than circular arrangement. This will be the equipment normally used if the process is performed prior to bag formation.

Referring to Figure 6, which illustrates the appearance of a sa

126

Ref: SAB

With the sheath according to the invention, the location (7) where the heat-joined seam (8) intersects the innermost fold (9) of the sheath is extremely critical when the bag is dropped onto one of its larger surfaces ( flat fall). As the contents of the bag spread horizontally, the material of the flange adjacent to (9) is under a particularly high tension that tends to start breaking along the seam at point (7).

This problem was solved by stretching a portion (10) of the sheath in a direction parallel to the longitudinal direction of the bag. This stretching is carried out by embossing between mutually interpenetrating teeth more conveniently prior to sheath formation. This recording is confined to the layers (11) and (12) forming the sheath, the outer layers (13) and (14) are not recorded. This localized stretch is referred to as the Sheath Embossing. This stretching eliminates or reduces the stresses at (7) and can therefore, in case the bag material is a relatively rigid film or an oriented film, increase the critical drop height by a factor of 2 or 3 or even more ( see example 3).

□ drawing shows Sheath Embossing as a number of cutouts rather than as a pattern, such as BAC, in which rows of cutouts alternate with unchanged ribs. However, this alternate pattern is also useful, but not required, for Sheath Embossing.

Hitherto the invention has been described almost entirely with a view to its application in bags, where the need is to provide shock absorbing properties to a selected area next to a seam. However, it was briefly mentioned that there may also be a need to modify a substantial proportion or even the entire article, especially with regard to parachute production. This applies in partj. operate the economic parachute and marketed for

X in materials such as vehicles or containers. It is generally desirable that the opening of the parachute be as delayed as possible, but the impact forces on the cargo and the parachute itself when unfolding set the time limit for its parachute opening.

126

Ref: SA —Β

-28opening.

Thus, parachutes are often fitted with shock absorbers. The present invention, however, allows for the achievement of a particular shock absorbing effect; effective by simple and economic means. Thus, the frame can be made of film material (preferably consisting of several layers which can be loosely joined only) which over an appropriate length is provided with a pattern of stretched and undrawn areas according to the invention. Alternatively, the parachute cover may be formed of polymeric material provided with a pattern of stretched and undrawn areas according to the invention, over an essential part of its area, which may be almost the whole of its area.

The direction of substantially undrawn areas in this pattern should preferably be mainly parallel to the local directions of force when the parachute unfolds and should preferably be in the form of a plurality of ribs.

It is well known that orientable polymers, especially highly crystalline and rigid polymers such as high density polyethylene or polypropylene, exhibit high yield points and at the same time, if stretched slowly, a high elongation at breakpoint (up to about 10 times) and a high final voltage. Thus, energy absorption up to the breaking point is also very high when the polymers are slowly drawn, but during very fast drawing they can rupture almost without permanent deformation. By application of the present wind, the physical characteristics can be significantly impaired so that even under the worst impact conditions permanent deformation can be initiated even at a near zero stress which progresses predetermined under increasing stress. strength up to a high degree of elongation and up to a force close to the final tensile force obtained during slow stretching.

Especially for these uses, the substantially unstretched ribs should preferably be very narrow and the degree of stretch in the individual film etching. you will see it vary very gradually between zero at the nerve border69

Ref: SAB

<img file="PT90306B_D0011.tif" />

<img file="PT90306B_D0012.tif" />

-29ra is the maximum value near the center of the recording between two ribs.

A very suitable material for such a frame is high density polyethylene and polypropylene, both of which can be used without mixing. For the parachute cloth (or cover) biaxially oriented cross-linked laminates may be used and in general similar compositions as the bag material used. Examples 3 and 4. In addition, the blends may contain polypropylene.

Example 1

This example demonstrates the improvements achieved with a polypropylene based heat-seamed cushioning bag shock absorber band obtained from biaxially crosslinked 03C oriented laminates. At this temperature, the heat-seamed seam will have such a weak action without a BAC that this material cannot be used for sturdy single-seam heat-resistant sacks.

A polypropile based crosslinked laminate was produced. in the gas phase type, equivalent to that described in Example 2 of UK Patent no. 1,526,722 and corresponding US patent no.^s. 4 039 364 but with the following differences:

(a) 4 pleats instead of 3, with the main steering angles: + 45SC, +303, -303, -45 °, (b) 90 gn gauge instead of 72 g 2, (c) the added mixture the polypropylene in the middle layer of the coextruded film was 20% linear low density polyethylene (LDPE) instead of 14% EVA, (d) the surface layers of the coextruded film were polypropylene and dimer rubber mixtures. ethylene propylene (DMEP) instead of the USA.

The crosslinked laminate was formulated as a tube using an extruded cast adhesive for the side seam and the tube was cut into pieces of about 1.0 m

126

Ref: SAB &lt;* I ·: i / v

<img file="PT90306B_D0013.tif" />

length. Flat width 500 mm. The side seam was positioned very close to the edge. The base seams for the open bags were produced manually by pulse sealing. In order to allow for size reduction in the heat-seamed seam and consequently to increase its thickness, the cooling period in the heat-bonding process was established in. zero, so that all cooling would take place after pressure release on the tongs.

The reason for placing the side seam too close to one of the edges is that the intersection between the heat seam and the side seam was found to be one of the most prone points to initiate breakage along the heat seam (at the board fall). Rather, the weak zone is not in the side seam itself, but immediately adjacent to it. at the point where the union is inadequate. It has been hypothetically assumed that the fall of the edge causes only small stretching forces near the ground edge, compared to the stretching forces felt in the middle of the seam - and of course the stretching forces will be practically near the other edge - so it was also assumed that the highest critical fall height is reached with the side seam near one of the edges. The proof of what has been exposed here is presented in Example 2.

Each bag was filled with 25 kg of polyethylene granules and a top piece was cut to leave about 11 to 12 cm of free space above the content level (standing bag, larger bag faces folded over the content level). , measurement of this form of free space). The bag was closed several times with a reinforced tape. In terms of production in practice the bag should be closed by either heat or seam joining and a top BAC should also be provided but it was thought that the effect of the BAC per se would be better determined by investigating only the seams, heat-bonded or sewn, formed prior to bag filling.

drop test was performed at room temperature of OSC and the contents of the bags (the polyethylene granules) were pre-prepared.

126

Ref: SAB

<img file="PT90306B_D0014.tif" />

cooled to this temperature.

In a series of initial attempts, the ratios applicable between unchanged rib extensions and cut fibers were determined as follows. A primitive laboratory press was prepared for embossing only one row of cutouts consisting of 15 single cutouts, each 10 mm long, with row division (distance between the top of two neighboring cutouts) of 3 .0 mm. BAC was formed from edge to edge by repeating row-by-row embossing. The ribs were kept to a constant extent in each bag but different rib extensions were tried. The stretch ratio, corresponding to the embossing depth, is believed to have been 1.20: 1 and was the same for all embossings. BAC was started 30 mm from the heat-seamed seam.

It was found that the extent of the ribs had to be decreased to about 2 mm to give significant improvement and the optimal value was estimated at 1 mm.

An embossing apparatus was constructed as shown in Figures 5A and B to provide a rib length of 1 mm, row length 10 mm, row length (= BAC length) 50 mm, division of each row 3. mm and 17 in each row. BAC start 30 mm from heat-seamed seam. Increased bag extension.

The embossing was performed at room temperature with the wheel teeth practically in full adjustment (exactly the same adjustment in all experiments) which is believed to have corresponded to a draw ratio of 1.2: 1.

The heat resistance of the seam with and without relaying was determined as the critical fall height which statistically represents the limit between success and failure when a bag with the relevant content is dropped 6 times in the next cycle (l ) 1st flat surface, (2) 2? flat surface (3) 1st edge, (4) 23 edge, (5) base, (6) top.

However, to simplify the test work for sa69 126

Ref: SAB

And the cushion-type with heat-stitched seams, the determination has been modified to have a single drop per bag, more precisely a lip fall, over the nearest lateral edge. The justification for this simplification lies in the experiment (confined to the type of biaxial crosslinked laminates. that when a bag has been dropped, the disoriented and weak line adjacent the heat-joined seam will be reinforced by an orientation caused by the fall. Thus, subsequent falls from the same height would in any case give rise to positive results and are therefore unnecessary. Furthermore, the falls (1) and (2) of the above-mentioned cycle (the flat falls) have generally been found not to weaken or strengthen the heat-seamed seam of a cushioning bag. This simplification of the test procedure does not apply to sheathed or sewn bags.

A table of results is given below, indicating for each attempt the failure height - F.

of fall in cm and success - P or

Without BAC

<td>Bag NS</td><td>Height of fall</td><td>Result</td>

<td> 1</td><td> 160</td><td>F</td>

<td> 4</td><td> 140</td><td>P</td>

<td> 5</td><td> 140</td><td>F</td>

<td> 12</td><td> 120</td><td>F</td>

<td> 13</td><td> 120</td><td>F</td>

<td> 14</td><td> 120</td><td>F</td>

<td> 18</td><td> 100</td><td>F</td>

<td> 19</td><td> 100</td><td>F</td>

With BAC

<td>Bag N2</td><td>Height of fall</td><td>Result</td>

<td> 3</td><td> 250</td><td>F</td>

<td> 15</td><td> 240</td><td>P</td>

<td> 17</td><td> 240</td><td>P</td>

<td> 16</td><td> 240</td><td>F</td>

<td> 6</td><td> 220</td><td>F</td>

<td> 7</td><td> 200</td><td>P</td>

<td> 8</td><td> 200</td><td>P</td>

<td> 9</td><td> 200</td><td>P</td>

<td> 10</td><td> 200</td><td>F</td>

<td> 11</td><td> 200</td><td>P</td>

<td> 2</td><td> 190</td><td>P</td>

126

Ref: 5-AB

-33 Since only one of the bags without SAC passed no tests, more precisely nS. 4 of 140 cm, while 3 bags of 120 cm and 2 of 100 cm failed, it is believed that nS. 4 was not in fact a board fall and should be rejected. The critical edge drop value will therefore be less than 100 cm for the bag without BAC while it is estimated to be around 220 cm for the bag with BAC.

Example 2 The purpose of this example is an elaborate drop-resistance comparison at room temperature between BAC-free and BAC-free heat-seamed bags formed from biaxially oriented cross-linked laminates of two different compositions, one based on polypropylene and the other on polyethylene. In each case, the comparison of drop tests is also made between bags having the side seam at 15 cm from one edge and bags with the side seam adjacent to one edge. 0 The polypropylene-based crosslinked laminate was a 4-ply laminate as in Example 1, except that the addition to the polypropylene in the middle layer of the coextruded film was now done with 10% DMEP. 0 90 g. The polyethylene crosslinked laminate used was a combination of high molecular weight high density polyethylene (PADPME) and low density linear polyethylene (PLBD), more precisely the 2-ply crosslinked laminate referred to as R3 in Example 3 of US Pat. 4,629,525.

The tube and bag formation was carried out as in example 1. The bag extension was 490 mm for polypropylene based bags and 560 mm for polyethylene based bags.

BAC standard, its distance from the heat-seamed seam, the embossing equipment and the fit between the teeth of the latter were exactly the same as in Example 1. BAC increased the bag extension. The stretch ratio is believed to be about 1.20: 1.

The bags were filled with 50 kg of PUC granules and sand and the top closure was formed with a reinforced adhesive tape as

126

Ref: SAB · /

-34-; . ····· '' in Example 1.

Clearance 11-12 cm, as in Example 1.

The critical fall height was determined in the same simplified manner as described in Example 1.

In the table below:

Type A film is polypropylene 90 g m2 Type B film is polyethylene 70 gm ^ Type S bag is a BAC-free bag with side seam at 15 cm from edge Type C bag is a bag similar to Ξ but with side seam around the corner the Type C + BAC bag is a C-like bag but with BAC the Type C + 2BAC bag is a C-like bag but with

2BAC in the on-board drop tests, the fall height, success P or failure F, semi failure (F) with a division below 10 mm or division in the BAC probably due to perforation during embossing (F^X).

The seam is formed by a Star Impulse Sealer selecting the required Bonding Time and Heating Speed, except for the two series sealed with a Doboy Band Sealer.

As can be seen from the table, the side seam movement to the edge generally leads to an improvement of about 50% at the critical fall height and the use of BAC further leads to an additional improvement of about 50%. The use of a second BAC close to the first does not lead to extra significant improvement.

126

Ref: SAB

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<td>ASS</td><td></td><td>CM</td><td>CM</td><td></td><td></td><td></td><td></td><td></td><td>CM</td><td>CM</td><td>CM</td><td>CM</td><td>CM</td><td>CM</td><td>CM</td>

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Example 3 The purpose of this example is to investigate the improvements in efficiency when sheathed bags are dropped by using Sheath Engraving alone or in combination with BAC. The material used for the bags investigated was the Rg crosslinked laminate also used in example 2, except that the example 2 PELBD was the polyethylene octene copolymer and in this example it was its butene copolymer. The gauge of the crosslinked laminate has now been gsm. The tube formation was carried out as in example 1, the tube width being 56 cm before the formation of the sheath. A 50 mm wide sheath was folded by hand and bags with heat-joined seams were formed using pulse sealing. The sealing conditions were optimized and no cooling period was applied. The sealing conditions were the same for all bags tested.

Embossing of the sheath was performed on the tube prior to sheathing, while the BAC pattern was embossed on the laminate after sheathing.

For both types of sheathing, the same engraving wheels and the same pattern as in examples 1 and 2 were used with the modification that the wheels are now tightly clamped together to increase the stretch ratio. An engraving depth corresponding to a draw ratio of 1.30: 1 was measured. The heat-stitched seam was formed about 20 cm from the beginning of the Embossing of the Sheath, and the BAC that buys, ends the sheath and the outer faces of the bag was embossed at a location immediately adjacent to the Embossing of the Sheath at the side of the latter, as opposed to the heat-seamed seam.

It should be noted (see example 1) that the width of the unchanged ribs was 1.0 mm, the width of the rows of 10 mm and the width of the BAC (and now also the Embossing of the Sheath) 50 mm.

The bags were filled with 50 kg of salt (sodium chloride). At the top, the sheath was straightened to give the bag its full width of 56 cm and the bag was closed with an adhesive tape.

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-37 reinforced. The free space on the content level was 10 cm.

The following test cycle was applied: (1) fall on one flat side, (2) fall on the other flat side, (3) fall on one edge, (4) fall on the other edge. It was considered unnecessary to perform base and top drop tests as these would neither cause nor further develop the breakages.

first bag tested was a bag without any embossing, neither Sheath Embossing nor BAC. The bag was dropped onto one of its flat surfaces from a height of 90 cm and the first fall produced a slit of about 10 cm in length at each of its critical locations (see (7) in Figure 6). The fall cycle was interrupted after this first fall.

The second bag tested was a Sheath Embossing and BAC bag and was tested in the above 4-drop cycle from a height of 400 cm. After the first two falls on the two flat surfaces very small ruptures were observed at the two critical locations and after the two subsequent edge falls the length of the rupture was measured at 10 mm and 12 mm.

A third bag, also with Sheath Embossing and BAC, was tested in the same four-drop cycle but 300 cm. No breakdown occurred.

It is therefore noted that Sheath Embossing and BAC together improved the effectiveness of the bag by a factor of more than four.

A fourth Sheath Embossing bag without BAC was produced and tested in a single drop on a flat surface from 400 cm. A tear of 5 mm at one and 8 mm at the other of the two critical locations was observed, which in any case is less than the damage of the bag. 1 tested from just 90 cm and also only in one flat fall.

With interesting additional feature of bags with

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-33- oh

Embossed Sheath Embossing, the filled bag was observed to have a block shape at the base, clearly superior to that of the sheathed bags without the Embossed Embossing.

Example 4 The purpose of this example is to demonstrate the improvements that BAC provides in a bag with stitched top and / or bottom seams.

The bags were formed from the biaxially oriented crosslinked laminate, which is designated R2 in Example 3 of US Patent No. 2. 4,629,525. This rigid is stiffer than the R 2 used in examples 2 and 3 and related to this higher rigidity exhibits greater resistance to breakage propagation. For further improvements in stitch strength, the 452 spiral cutting angle used in the aforementioned US patent example has been replaced by a 302 spiral cutting angle. □ Stretching and lamination of the pleats was performed by the improved method described in Example 3 of. PCT / GB38 / 00027. Stretch ratios were 1.40: 1 in both directions and caliber 70 g. m?

Tube formation was performed as in example 1 to give a bag width of 56 cm. The side seam was positioned 6-7 cm from the edge, which was the smallest distance that could be continuously formed in the tubes used. The bottom of the bag was sewn using an overfold of the bag material at the seam and tapping lightly with crepe paper. The distance between the points was 3 mm.

The BAC was embossed in the pattern and with the equipment described in example 1, except that the pattern was modified so that the width of the rib equals the length of the cut, however giving the same, more accurately total 11. mm (the division of the BAC) and the BAC was still 50 mm wide. This embossing pattern change was made not particularly because the sewing process should be applied, but because the other pattern, which was developed for a polypropylene composition, was considered less suitable for the composition of polyethylene.

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The stress / strain diagrams taken at 3-AC are shown in Figure 4A and the equivalent diagrams for the non-embossed crosslinked laminate in Figure 4B. The comparison between these diagrams and the explanation of their meaning is presented in the description of these Figures. As already mentioned, it is apparent from Figure 4A that the draw ratio in the rows was 1.28: 1, a value which is also approximated from the observed shape and measured dimensions for the cuts.

The bags were filled with 20 kg of polyethylene granules and closed with several turns of reinforced adhesive tape. The clearance between the top of the level and the closure, measured as indicated in example 1, was 11-12 cm.

Four bags with and four bags without BAC were tested to fall around the values ​​that were initially believed to be their critical drop heights. The same test cycle was used. than the example 3. With these experiments it was estimated for bags without BAC a critical drop height of 120 cm and for bags with BAC 250 cm.

If the bags are under particularly high pressure in a stack, the BAC may become stretched such that the embossing disappears, but it will somehow resume its initial appearance when the pressure is released. In addition, the pressure stretch will have oriented the disoriented weak line adjacent to the heat-seamed seam (in the case of heat-seamed bags) so that in which case the seam is reinforced. With dimensions properly selected for BAC deformation when embossing will not be serious for stacking quality. Thus, in all examples the full force for eliminating the recording in rebound will cause only 20-30% elongation in a 5 cm wide BAC, or with a top and bottom BAC, a total elongation of about, or less than 3 cm. Since the normal length for a 50 kg bag is about 1.0 m or slightly lower, the total elongation of the bag caused by stretching

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The maximum of the two BACs will be about 3-4 maximum, provided that the need for the effect of the BAC does not exceed the improvements shown by these examples.

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