Background to the Invention Many granular or pulverulent materials are supplied to the end user in sacks that have been fabricated from one or more plies of sheet material. Typically, the plies are selected from paper and/or plastics materials and may include laminated sheet material.

The selection of the sheet materials will, of course, depend upon the desired characteristics of the finished sack, for example with regard to such properties as sack strength and air permeability. The sacks are assembled in such a manner as to provide an aperture through which the intended contents are charged into the sack. Although the filling aperture in certain cases may subsequently be closed or sealed by means of a gluing or crimping operation, in certain other applications, the filling aperture is provided with a valve which is intended to prevent the egress ("spillage") of contents from the sack after filling.

Cement, for example Ordinary Portland Cement (OPC), is normally supplied in multi-ply paper sacks, typically including also at least one ply of plastics sheet material, and which typically have a nominal content of 25kg cement. Filling is normally effected on a rotary packer or carousel to which the sacks are fed at a high rate, e. g. 60 sacks per minute. In the rotary packer, an air/cement mixture is supplied by means of a spout through the filling aperture and valve. To allow the filling to proceed to completion, it is necessary for air in the said air/cement mixture to escape and, accordingly, the sack is so constructed as to exhibit sufficient air permeability (porosity or"drainage") to permit egress of air.

This permits the filling of the sacks with cement at high bulk density, preferably in just one pass through the cement-packing machine. The required drainage is generally achieved by the use of a combination of plies of appropriate air permeability, e. g. the use of a perforated outer ply in the material from which the sack is constructed. Of course, for efficient filling operation, the drainage should not be so low that the sacks cannot properly be filled in one pass through a conventional cement-packing machine and, therefore, the drainage is not normally less than 5 m3/hr, typically not less than 10 m3/hr. Normally, the drainage will

not be higher than 70 m3/hr, typically no higher than 60 m3/hr. The above drainage figures are those measured, as is standard in the art, on the finished sacks. Testing the drainage of a sack may be carried out on the Permeability Tester machine manufactured by Haver & Boecker, D-59302 Oelde, Germany. See also"Determination of the Air Permeability of Paper-made Valve Bottom Sacks", Instructions 14/11/86 issued by Research Association Kraft Papers and Paper Sacks, Paper Technical Foundation (PTS), Munich, Germany. The optimum drainage range for efficient filling operations will, of course, vary for different packing machines and conventionally it has been believed that the most satisfactory filling is achieved with the highest drainages.

Conventionally, cement sacks are constructed using a standard Kraft paper as the outermost ply, which may be perforated. This may be used in conjunction with an innermost ply formed of high porosity paper and an intermediate ply formed of a high density polyethylene film that has been perforated. The perforations are generally in the form of slits and/or round holes. The basis weights (grammages) of the outermost and innermost plies will generally be in the range of 50 to 120 g/m2. Usually the outermost ply has a basis weight equal to, or up to 30 g/m2 more than, the basis weight of the innermost ply. Typical constructions use paper materials having an outermost grammage of 70-100 g/m2 and an innermost grammage of 60-70 g/m2. Slightly different sack geometries are needed for any given set of plies to cope with the differing air quantities encountered when packing a given mass of various grades of cement at various manufacturing sites.

After the filling operation, the sacks of cement are subjected to various operations such as transference to a conveyor system and loading onto pallets. The handling of the sacks during the subsequent operations can result in spillage of cement from the filled sacks through the filling valve: in current commercial practice, losses through such spillage may be in the range of from 10 to 100g per sack. Clearly, it would be beneficial to keep the loss by spillage consistent and low. The benefits that would arise would include improved workplace cleanliness, reduced cleaning needs, minimisation of environmental pollution, reduced loss of product, an improved appearance of the sacks when delivered, and reduced soiling with dust of persons who are carrying the sacks.

In conventional cement sacks the filling aperture is located at a corner of the sack and leads into a filling tube formed by the interior face of the end wall that is adjacent to the said corner and a strip of material that extends, generally parallel to the said end wall, into the sack from the edge of the side wall that is adjacent the said corner. A conventional

valve that has been used in cement sacks is formed from a single ply of paper having a high basis weight ("grammage"), typically about 100g/m2, which has been folded so as to provide a flap. This valve is placed in the filling tube and secured to the interior face of the end wall by means of an adhesive such that, after the sack has been filled, movement of cement towards the filling aperture will urge the flap away from the end wall towards the extended strip of material, as a result of which the flap seals the filling tube. However, the resultant seal is not always efficient and it is not uncommon for the spillage past this valve to amount to 40g or more per sack during the post-filling handling of the sack.

Various improved valves have been proposed. For example, DE-A-2,935,971 discloses a cross-or block-bottom valved sack of paper or the like material, with a filling valve in one of its two sack bottoms which are laterally adjacent to the bottom side folding line, said valve being in the region of a valve-forming corner insert and which comprises an inner, tube-shaped valve part of flexible plastics film projecting into the interior of the sack through the valve-forming corner insert at one end and a valve part of paper which on the exterior surrounds the region of this valve part and on the interior encloses it, above which the valve layer is glued to the sack bottom, characterised in that the two valve parts are formed from two separate flat material layers of width exceeding the sack bottom width and glued over each other in the sack bottom and made up to the shape of a tube, said layers each comprising a paper sheet and film sheet connected to said paper sheet, whereby the two film sheets form the tube shaped valve part projecting into the interior of the sack and the two paper sheets are glued in the region of the valve-forming corner insert to this insert as well as to the bottom side flaps taking in their edge regions lying outside the bottom fold lines, and that the film sheet of the first glued, lower flat material layer extends beyond the transverse edge which faces the interior of the sack, of its paper layer with a free projection, while the film sheet, which, as a second, glued, upper flat material layer seals off its paper sheet essentially flush with the transverse edge facing the interior of the sack, which paper sheet itself projects beyond the valve-forming corner insert.

A similar type of valve that is currently available for placement in the filling tube of a cement sack is constructed from four pieces of paper, one pair of paper pieces (the"top" pair) being attached to the interior of the end wall and the other pair (the"bottom"pair) being attached to the strip extending from the side wall. The valve (which may be referred to as a"four-component paper valve") includes a flimsy sheet, top and bottom, the top flimsy sheet being shorter than the other. When the filling spout is withdrawn and the sack

is full, the flimsy sheets form cuffs which are offset (owing to the different lengths of the flimsy sheets): the filling of the cuffs with the cement powder causes the cuffs to seal off the filling aperture.

The valve which is the subject of DE-A-2,935,971 and the above-described four- component paper valve of the prior art are relatively complex in their construction. In International Patent Application No. PCT/GB00/02095, there is described a valve that is simpler in construction and yet which is still capable of reducing spillage from the filled sacks to a conventionally acceptable level. Nonetheless, even the low levels of spillage that may be achieved with the best of the valves currently available can still result in sacks that are soiled with cement dust. This dust is a nuisance to both the retailer, who will generally consider it necessary to stock cement sacks in an area remote from other goods in order to avoid the transfer of cement dust to the latter, and also to the purchaser, who may need to take steps to avoid or minimise the transfer of the cement dust to clothing or to the interior of the vehicle used to convey the cement sacks from the point of purchase to the point of use.

Furthermore, the conventional construction of the cements sacks, in requiring multiple plies (in order to provide the necessary strength for holding the high-density contents with minimal risk of tearing or bursting of the sack), entails a not insignificant cost in raw materials. Should any plies later require detachment for separate disposal, this is difficult to achieve as they are not only interleaved but are also usually joined to other plies during the manufacture of the sack, e. g., by glue. Moreover, the requirement for the sacks to exhibit adequate drainage for filling operations has generally meant that the sacks are not properly waterproof and merely exhibit water resistance. They are therefore stored under cover or indoors to ensure a reasonable shelf life for the product which they contain.

Plainly, improved water-tightness would be an advantage, given that cement is commonly used outdoors and the cement sacks are then vulnerable to rainy conditions.

Summary of the Invention The present invention, in one aspect, provides a sack that is suitable for containing particulate material, which sack has a filling aperture through which particulate material may be charged into the sack and, preferably, a valve located within the sack and which is arranged to inhibit egress of the particulate material through the filling aperture,

characterised in that the sack is provided with a closure member which seals the mouth of the filling aperture.

The present invention also provides, in a further aspect, a container system suitable for containing particulate material, which container system comprises a sack having a filling aperture through which particulate material may be charged into the sack and, preferably, a sealing member arranged to inhibit egress of particulate material through the filling aperture, characterised in that the sack is at least partially encapsulated.

The invention also provides a process for sealing and/or encapsulating a sack that has been filled with a particulate material.

Brief description of the drawings Exemplary embodiments of the present invention are illustrated in the accompanying drawings, which are purely diagrammatic and in which like parts are indicated by like numerals.

Figure 1 is a perspective view of a corner of a sack for cement, showing the filling aperture and filling tube.

Figure 2 is a vertical section of the sack shown in Figure 1 along the line II-II.

Figure 3 is a perspective view of a corner of the sack shown in Figures 1 and 2, after emplacement of a closure member in accordance with this invention.

Figure 4 is a perspective view of a corner of a sack, the filling aperture of which is sealed using means additional to the means shown in the embodiment of Figures 1-3.

Figure 5 is a vertical section of the sack shown in Figure 4 along the line V-V.

Figure 6 is a perspective view of a corner of a sack in which the closure member is different from the closure member shown in either Figures 1-3 or Figures 4-5.

Figure 7 is a perspective view of a corner of a sack in which the closure member is different from the closure member shown in any of Figures 1-3, Figures 4-5 or Figure 6.

Description of exemplary embodiments The present invention will be described with reference to sacks for cement. It will be understood, however, that the invention may also be applied to valves for use in sacks intended to contain other granular materials or powders. Furthermore, the term"sack" should be understood to include bags and like receptacles and containers.

The sack may be of any shape and dimensions consistent with the intended use.

Normally, however, the sack will be in the form essentially of a hexahedron having a body portion that is of substantially rectangular cross-section bounded by four walls, there being

a top wall at one end and bottom wall at the other. Usually, the cross-section is oblong, the body portion being bounded by two opposed walls separated by two opposed narrow side walls. The top wall and the bottom wall may each be formed by overlapping flaps of the material from which the sack is fabricated, the flaps being joined together, adhesively or otherwise. Either or both of the top and bottom walls may be overlaid with an outer strip (or"capping strip") of material, which is secured in place, normally by means of an adhesive (which term herein also includes glues, gums, adhesive pastes and the like).

Normally, the filling aperture will be situated at or adjacent to a corner formed by the top wall and a side wall. Normally, a strip, ledge or fold of material extends from the mouth of the filling aperture into the interior of the sack for a short distance and defines, together with the opposing portion of the interior face of the top wall, a filling tube which is arranged to receive the filling spout during the filling operation. Normally, the filling tube will be provided with or associated with a valve which will permit the ingress of particulate material into the sack during the filling operation but which will inhibit, and preferably substantially prevent, the egress of material once the sack has been filled and the filling spout has been withdrawn. The valve may be of any suitable construction, for example one of the constructions mentioned above in the Background to the Invention.

However, in view of the additional sealing afforded by the closure member that is provided in accordance with the present invention, the valve, if such is provided, can be of a simple construction; for example, it could be formed from a single flap of material. The resultant simplification of the sack-manufacturing process is plainly advantageous.

The body of the sack may be of conventional construction: for example, the sack may be constructed from a multi-ply material as described in the Background to the Invention. Such a construction may, for instance, involve an inner ply of high-porosity paper, an intermediate ply of perforated plastics film and an outer ply of optionally perforated Kraft paper. However, in certain preferred embodiments, as will be described hereinafter, the sack may be constructed from a double ply material (for instance, with one ply of paper with high air permeability coupled with an outer layer of optionally perforated Kraft paper having a higher grammage) or even a single-ply material (e. g. a conventional Kraft paper, which need not even be perforated). The use of a high-porosity paper as the outer ply in a multi-ply, e. g. two-ply or three-ply, material, or even as the sole ply in a single-ply material, also comes into consideration.

In accordance with the present invention, closure of the filling aperture may be achieved by means of (as a closure member) an adhesive applied to surfaces within the filling tube, which filling tube is then flattened or collapsed in order to close it, the filling tube being held closed by the adhesive. However, it is preferred that the filling aperture be sealed, in accordance with the present invention, by means of a closure member that is applied to the exterior of the sack and/or that has a structure; preferably, the closure member is in the form of a lamina.

The term"lamina"as used herein is to be construed broadly to include any layer, leaf, foil, film, plate, ply, sheet or sheet-like element. The term"lamina"herein also includes multi-ply materials (e. g. laminates in the sense of two or more superposed plies or layers, bonded one to another). The closure member may be of any suitable shape and size: in certain embodiments the closure member is a substantially rectangular, e. g. oblong, sheet. In certain embodiments the closure member may be rigid and of preformed configuration, or it may be flexible and designed to acquire the necessary configuration to seal filling aperture when the closure member is put in place: for example, a sheet of material may be applied to a sack such that it curves over a corner of the sack and across the filling aperture.

In certain embodiments, the lamina closure member may be constituted by an extension or projection of the capping strip adjacent to the filling aperture, which extension or projection is placed (after the filling operation and withdrawal of the filling spout) such that it extends across the filling aperture and is then secured in place, as by means of a lamina adhesively or otherwise secured to the extension or projection and to part of the sack. Preferably, however, the closure member is a separate or discrete lamina which is so placed as to extend across the filling aperture and which is thereafter secured in place, for example by means of an adhesive. To improve the seal, the action of emplacing the closure member may be simultaneous with, or preceded by, the flattening or collapsing of the filling tube so as at least partially to close it.

The closure member may be of any suitable material, for example paper (e. g. Kraft paper), a plastics material, a textile material or a non-woven material. The closure member may be, for example, a single-ply material, a multi-ply material (e. g. a laminate in the sense of two or more superposed plies or layers, bonded one to another), or a coated material.

Amongst the synthetic materials, polyolefins, especially polyethylene or polypropylene, are preferred.

Any suitable adhesive may be used for securing the closure member in place, for example a wet glue, an impact adhesive, an ultrasonically activated adhesive, a heat-curable adhesive or a radiation-curable (e. g. RF, UV or IR-curable) adhesive. The adhesive may be pre-applied to the seal, or may be applied during application by any of several procedures, such as a wet glue application to a strip of material prior to separation into discrete sealing elements or closure members, or a'mono-web'system (where no backing film is employed). Preferably, the closure member is a self-adhesive member and in certain embodiments the adhesive will be of the re-sealable kind.

It will be understood that a freshly filled sack may be hot: for example, a freshly filled cement sack may typically have a temperature of from 80° to 90°C, and the temperature may even rise intermittently to 120°C. If the closure member is to be applied while the sack is still hot, an adhesive should be selected that will perform well under such conditions: an acrylic-based adhesive may then come into consideration. It is, of course, possible to apply the closure member after the sack has cooled, when other adhesives, e. g. hotmelt adhesives, will also come into consideration.

The closure member may constitute a label, which may bear appropriate indicia or information of some kind. The label may be pre-printed or may be printed in situ with appropriate information, bar-coding or the like. The use of real-time printing of the label can be used to differentiate one sack from another, which is an advantage over conventional sacks, which are fabricated from reels containing as many as 2500 pre-printed sack blanks.

The closure lamina or other closure member may be of any convenient size but will preferably be large enough to fully cover the filling aperture and to provide sufficient area adjacent to the exterior of the sack so as to ensure that it is firmly secured in place.

Advantageously, the closure member can be applied to the sack without the necessity of removing the sack from the production line or stopping the production line.

Thus, the closure member or seal may be applied to the sack after the take-off belt of the filling machine but before the sack is placed upon a pallet for further transport. Normally, after removal from the take-off belt the sacks are passed through a cleaning station (which generally involves blowing air onto the sack followed by vacuum extraction of the dust) in order to remove spillage that may have occurred during removal of the sack from the filling machine. Conveniently, the seal or closure member may be applied after the cleaning station and this will help to inhibit or prevent any further spillage during subsequent transport, that might otherwise have shed more dust onto the sacks. Additional bag-

cleaning equipment may be employed if appropriate, as may bag-cooling equipment and/or bag-pressing equipment, the latter being useful to express air from the bags (the less air that is present, the easier in general the process).

The dimensions of the sack may vary widely, according to the intended use. A sack for cement will typically be designed to hold, when full, an amount of cement in the range of from 5 to 70 kg, e. g. from 10 to 50 kg, the current commercial preference being for sacks of a nominal cement content of 25 kg.

In Figure 1, there is illustrated a top corner of a conventional cement sack, which cement sack has a body portion that is of substantially rectangular cross section and bounded by two opposed broad walls (one of which is visible in the figure and is marked 2) separated by two opposed narrow side walls (one of which is visible in the figure and is marked 4). The material from which the sack is fabricated is folded at the bottom of the sack and at the top to form overlapping flaps at each of those locations, which flaps are joined together adhesively (and may in each case be overlaid with an outer strip (or "capping strip") of material, e. g. paper, which is secured adhesively) so as to provide a sealed bottom wall and a top wall 6 which is sealed except for the filling aperture 8. The filling aperture 8 is defined by the corner edge 10 of the top-wall 6 and also by the corner edge 12 of the narrow side-wall 4. A strip, fold or ledge of material 14 extends from the edge 12 into the interior of the sack for a short distance, as can be seen clearly in Figure 2.

The strip 14 and the interior face 16 of the top wall 6 define a filling tube 18. As can be seen in Figure 1, the filling tube 18 may have a somewhat"flattened"cross-section, and the strip or ledge 14 and the interior face 16 form, as it were, the floor and the ceiling of the filling tube, respectively.

In Figures 1 and 2, there is shown a closure member in the form of a lamina 20 which may be a sheet of paper, of generally rectangular shape having an upper surface 22 and a lower surface 24. In the illustrated embodiment, the lamina 20 has an elongate (or oblong or strip-like) configuration, the opposed narrower edges being marked 26 and 28.

In order to close the filling aperture 8, the closure member 20 is brought into contact with the sack such that the lower surface 24 in the region of the edge 26 abuts the top wall 6 whereas the lower surface 24 adjacent the edge 28 abuts the side wall 4 of the sack. It would be possible first to fold the lamina along a line parallel to the edges 26,28 so as to form a generally bracket-shaped member which may then be brought into abutment with the comer of the sack where the filling aperture is located. However, it is currently

preferred to apply the end of the lamina 20 adjacent the edge 26 to the top wall 6 and then to fold the rest of the lamina 20 over the filling aperture and down the side wall 4 of the sack; this may be effected by means of a device such as a roller, guide or brush.

The lamina 20 may be secured to the sack by means of an adhesive. The adhesive may be applied either to the relevant portions of the top wall 6 and side wall 4 or to the lower surface 24 of the lamina 20 or to both the said portions of the sack walls and the said surface of the lamina 20. Preferably, the adhesive is applied beforehand to the surface 24 of the lamina and, more preferably, the said lamina constitutes a self-adhesive closure member. Figure 3 shows the lamina closure member 20 secured over the filling aperture of the sack. Prior to emplacement of the closure member 20 or simultaneously therewith, pressure may be applied to the top wall 6 so as to bring the interior face 16 into contact with the strip, fold or ledge 14, thereby at least partially closing the filling tube 18. Such pressure may be applied, for example, by the roller, guide, brush or other device used to fold the closure member 20 over the corner of the sack. Thus, in the embodiment shown in Figure 3, the filling tube has been at least partially collapsed with the result that the edges 10,12 have also been squeezed closer together, thereby at least partially closing the filling aperture 8.

The width of the closure member 20 (i. e. the dimension parallel to the edges 26,28) may, as shown in Figure 3, be substantially the same as the width of the narrow side wall 4 of the sack, so that the filling aperture 8 of the sack is effectively sealed. It is, however, possible to employ a closure member 20 that is narrower than the width of the sack since this may still give adequate sealing in practice, especially if the filling tube has been flattened or collapsed.

With the lamina 20 in place, as shown in Figure 3, the lower surface 24 becomes the inner surface of the closure member and the upper surface 22 becomes the outer surface of the closure member. As shown diagrammatically, the outer surface of the lamina 20 may bear printed matter. If required, the outer face 22 of the closure member 20 may be pre- printed, or printed in situ, with any appropriate indicia and/or information, such as an indication of the manufacturer, weight and nature of the particulate material contained within the sack, price,"use by"date and so on. Since the information can be printed on in situ, the invention affords the facility for indicating a precise weight for the contents, rather than the nominal contents weight which has been conventional hitherto.

In the embodiment illustrated in Figures 4 and 5, the top wall of the sack comprises a capping strip 6 which has an end portion 30 which extends or projects beyond the edge 10 of the top wall, the edge 10 defining in part the filling aperture 8. The length of the extension or projection 30 will generally be chosen so as to ensure a positive seal without use of superfluous material: for a sack intended to contain 25 kg of cement the length of the extension or projection 30 may be, for example, from 1 to 10 cm, for instance from 2 to 5 cm. Of course other lengths may come into consideration. In the closed sack, as can be seen in Figures 4 and 5, the extension or projection 30 is folded down over the aperture 8 defined by the edges 10 and 12 and is held in place by a closure member 20 which is adhered to part of the capping strip 6, to the extension or projection 30 and to part of the side wall 4. Thus, the closure member 20 secures the extension or projection 20 over the mouth of the filling aperture 8, which is thereby sealed. The closure member 20 may be applied in the manner described above with reference to Figures 1-3, preferably such that the interior surface 16 is brought into contact with the strip 14, thereby at least partially closing the filling tube and preferably bringing the edges 10,12 close together, thereby at least partially closing the mouth of the filling aperture 8.

In the embodiment shown in Figure 6, the top wall is provided with a capping strip 6 having an extension or projection 30 that is folded over the mouth of the filling aperture 8 in a manner analogous to that described with reference to Figures 4 and 5. In this embodiment, however, the closure member 20 is so dimensioned and situated such that it adheres only to at least part of the outer face of the projection or extension 30 and to part of the side wall 4. In this embodiment, therefore, the mouth of the filling aperture is covered only by the extension or projection 30 of the capping strip. The embodiment of Figure 7 is similar to that shown in Figure 6 but the closure member 20 is provided with end portions 32 that adhere to parts of respective broad walls 2.

It is regarded as surprising that an external closure member can be applied successfully to seal, at least partially, a sack that may be hot and/or dusty following the filling opertion.

As indicated above, the present invention also provides a container system in which a sack containing particulate material is at least partially encapsulated. In certain embodiments, the body of the sack may be encapsulated with one or both of the ends of the sack left unencapsulated. However, it is normally preferred that the sack be fully

encapsulated, that is to say the body and both ends thereof are enclosed within an outer container, skin, mantle, coating, membrane, wrapper or other covering.

The sack may be encapsulated within a rigid or semi-rigid container, for example of a plastics material, paperboard, cardboard or the like. In other embodiments, the encapsulation is effected by means of a flexible or semi-flexible material such as paper or, more preferably, a plastics film material. Preferably, the material used for encapsulation is made up of a stretchable material. The (semi) flexible encapsulating material may be a preformed bag, sack or the like, or the covering may be formed in situ. For example, a plastics skin or the like might be applied as a shrink wrap, stretch wrap, shrink sleeve or flow wrap, or as an extruded or blown film which is wrapped around the sack.

Suitable plastics materials include polyolefins, for example, polypropylene or polyethylene. A polyolefin co-extruded with another synthetic plastics material may alternatively be used, as may other suitable polymeric and co-polymeric materials, e. g. polyesters and the like. The plastics materials may be monolayers or, for example, laminates, e. g. with a polyester substrate and polypropylene for the outer layer. When the encapsulation material comprises two or more components, as in the case of co-extrusions, copolymers or laminates, the weight ratio of the components may be selected from those used conventionally, depending upon the intended characteristics of the encapsulation material. Thus, for example, where the material comprises two components, the weight ratio may be from 1: 99 to 99: 1, e. g. from 10: 90 to 90: 10. Preferred plastics materials are in sheet form, preferably of 25 to 150 microns (pm) thickness, more preferably 35 to 100 microns and most preferably 60 to 90 microns. Thicker encapsulating materials may be used but this will entail an increased cost. When using encapsulation materials having a thickness of less than 60 microns, it may be beneficial to fabricate the sack to be encapsulated from a material that is comparatively thick and/or that has a comparatively high grammage. The encapsulating material may be clear or opaque and may be of any selected colour or even metallised. The outer surface of the encapsulating material may be printed, either beforehand or in situ, with any appropriate indicia and/or other information.

This permits the use of high-quality printing in order to improve consumer acceptability.

Nonetheless, e. g. where cheaper wares are concerned, it may also be possible to print the indicia and/or information on the inner sack, which is encapsulated in a transparent wrapper or other covering.

Analogously to the application of the closure member in the production of sacks according to the first aspect of this invention, the encapsulation in accordance with the second aspect of this invention may be effected in-line and without the need to stop the production line, thereby affording the opportunity to maintain production speeds.

The encapsulation may be applied at any appropriate point in the production line following the filling of the sack. Thus, the encapsulation may be applied after the take-off belt but, preferably, will be applied after the cleaning station. It has been found beneficial to express air from the sack before the encapsulation material is applied. Preferably, at least 90% of the air within the sack is removed, ideally 100%.

The sack may be of conventional, multi-ply construction, and the sealing member may be a conventional filling valve. However, as is well known, forming sacks from plies of several materials is a relatively complex procedure. With this invention, despite the high throughputs of sacks and materials typical of the cement industry, it is possible to employ a double-ply or even a single-ply material since the sack need only withstand the stresses placed upon it during the filling operation and the removal from the filling machine ; the strength required to stand the rigours of subsequent transport may be imparted by the encapsulation. The use of a simpler inner-sack construction may, of course, give savings in production costs which will either render the final product less expensive or which will allow the producer to improve or upgrade other aspects of the final packaged product without any overall increase in cost to the consumer. Furthermore, it may not be necessary to perforate any ply from which the inner sack is made, since a double ply or a single ply material may have sufficient drainage as it is in order to allow efficient filling of the sack.

A single ply high porosity Kraft sack can have sufficient porosity to allow drainage of the different air quantities associated with the filling of a range of cement products without changes to its geometry as is needed when using conventional designs. In certain preferred embodiments, therefore, the inner sack may be formed from a single ply of fully extensible, high-porosity Kraft paper having a basis weight or grammage of 80 to 120 g/m2, preferably 95 to 105 typically about 100 g/m2. The drainage of the sack material should be such as to achieve egress of as much as possible of the air introduced therein, generally over 90% and preferably above 95%, so as to provide high-density filling of the sack.

A further advantage resides in the fact that there is no need to provide the inner sack with water resistance (although this is not precluded), since the required degree of water resistance may be provided by means of the encapsulation material. Indeed, it is difficult

by conventional means to achieve a high level of water resistance (substantial waterproofness) owing to the need for the sack materials to exhibit sufficient drainage or permeability to allow efficient filling with the particulate material. However, since the encapsulation according to the present invention is applied after the inner sack has been filled, a material may be selected which imparts a high degree of water resistance or even waterproofness to the final packaged product. The encapsulation is preferably detachable so that if required, during or after use of a filled sack, the outer encapsulation layer can be detached from the inner permeable sack for separate disposal.

Furthermore, since the encapsulation may be applied shortly after the filling operation and conveniently after the cleaning station and since the encapsulation may fully enclose the filling aperture, the final product may be substantially free on its outer surfaces from dust due to spillage of contents, which will render the packaged product more acceptable to both the retailer and the end user who will no longer need to take special measures to avoid soiling of other goods, of clothing or of transport vehicles due to the transfer of cement dust or the like. However, it need not be essential for the encapsulation to be applied on the production line. For example, the inner sacks after filling may be stored until required, at which later time the sacks can be encapsulated, for example in a wrapper, sack, bag, box, carton, tub or the like.

It is particularly preferred that the inner sack that is encapsulated according to the second aspect of the present invention be a sack that is provided with a closure member in accordance with the first aspect of the present invention. The prevention, or at least further inhibition, of spillage afforded by the closure member is advantageous for example, in the above-mentioned embodiments wherein the sacks are stored for a period of time before the encapsulation is applied. In such embodiments, the sealing member required according to the second aspect of the invention may be constituted, for example, by the said closure member, e. g. a label secured across the filling aperture, and/or by a filling valve within, or associated with, the filling tube.

In certain preferred embodiments the encapsulation material has carrying handles or the like attached to it, in order to facilitate handling by the consumer. Furthermore, the encapsulation may be employed to bundle together two or more sacks as a single package.

Whether the package contains just one inner sack or a plurality of sacks, the encapsulation may be provided, in certain embodiments, with a resealable closure means.

The present invention is further illustrated in and by the following Examples.

In the following Examples, the lamina or label used as the closure member was applied by means of an applicator on the top wall of the sack, leaving a trailing edge of the closure member hanging over the corner and side where the filling aperture was located.

The trailing edge was then wiped down the side of the sack, sealing the filling aperture. It will be understood, however, that the closure member could alternatively be placed over the side of the sack and the trailing edge then wiped down onto the top wall of the sack, again resulting in closure of the filling aperture or valve. As a further alternative, the closure member could be brought down onto the corner of the sack so as to place the closure member fully over the sack valve area. Various arrangements are, of course, possible: the applicator is conveniently placed above the conveyor line but could be placed to the side or even under the conveyor line.

Example 1 A sack was constructed from brown kraft paper having a basis weight of 80 gsm (80 g/m2) as the outer ply, paper having a grammage of 60 gsm as the inner ply and a membrane of high density polyethylene having a thickness of 13 microns as the intermediate membrane. The sack was filled with ordinary Portland cement ("OPC"), the dimensions of the sack being such as to provide a nominal filled weight of 25 kg. The filled sack was sealed by means of a self-adhesive rectangular label made of polyethylene, having an acrylic-based adhesive on one side thereof. The label was presented on a carrier and was supplied pre-cut. The label was placed on the sack by automatic means, at a location after the first bag cleaner on the production line. The label was applied over the filling aperture and sack valve area in the manner shown in Figures 1-3.

Example 2 A sack was constructed from the materials specified in Example 1 but the capping strip was provided with an extension in the valve area. The sack was filled and a label was applied in a manner analogous to that described in Example 1, except that the filling aperture was closed by means of the capping-strip extension and the applied label, in the manner illustrated in Figures 4 and 5.

Example 3 A sack was produced, filled and sealed in essentially the manner described in Example 1, but in this case the sack was constructed of a dyed kraft paper having a grammage of 90 gsm as the outer ply, kraft paper having a grammage of 70 gsm as the inner ply and a membrane of high density polyethylene having a thickness of 13 microns as

the intermediate ply. Also, the sack was filled with Mastercrete (trade name) cement produced by Blue Circle Industries PLC, at a nominal content of 25 kg.

Example 4 A sack was produced, filled and sealed in substantially the manner described in Example 2, except that the sack was constructed from the materials recited in Example 3, the capping strip of the sack in the valve area being provided with an extension, which was folded over and secured in place with the label, as in Example 2.

Example 5 Examples 1 and 3 were repeated with sacks formed of a single ply material, namely brown kraft paper having (a) a basis weight of 100 gsm and, in further trials, (b) brown kraft paper having a basis weight of 110 gsm.

Example 6 Sacks were produced, filled with OPC and sealed as described in Example 5. The label used to seal the valve area was a polyethylene label having a thickness of 100 microns, which label was adhered to the sack by means of an acrylic adhesive. Air was removed from the sacks using bag pressing equipment, whereafter the sacks were encapsulated with a high density polyethylene film having a thickness of 80 microns.

It will, of course, be understood that the present invention has been described above purely by way of example and that modifications of detail can be made within the scope of the invention.