Patent Publication Number: US-2010119180-A1

Title: Paper valve sack with inner catch

Description:
The present invention relates to a special paper valve bag with inner panel. 
     Paper bags and in particular paper valve bags, are very well known in general and are used for receiving, transporting and storing bulk material in general, e.g. cement, gypsum, animal feed or animal litter, but in particular also for fine-grain or pulverulent contents. Conventional sizes of such bags usually have a volume of 5 kg, 10 kg but also 25 kg. Typical paper valve bags usually comprise an essentially rectangular bottom, an essentially likewise rectangular top part, located opposite the bottom, a tubular paper-bag body, which extends between the bottom and top part, and possibly a cover sheet. This cover sheet is applied to the outside of the top part and may possibly be provided with a carrying handle or be designed as such. 
     Paper valve bags typically have a tubular valve fastened in the folded bottom. Paper valve bags are usually provided with a folded bottom in the form of a cross bottom or block bottom, special bottom flaps engaging over a corner fold. The tubular valve mentioned is fastened in an interspace formed from the corner fold and the bottom flaps. The valve itself comprises a carrier material which is folded in the longitudinal direction of the bottom and has a top side and an underside which are connected to one another via longitudinal folding lines. 
     In its closed state, the valve, on account of the design, lies flat in the bottom until it is spread open within the context of the paper bag being filled from the outside, usually by way of a filling tube, and in this way it allows the interior of the bag to be filled. The valve is closed by the filling material of the bag pushing against the bottom of the same and thus pressing the underside of the valve against the top side thereof. The design means that certain losses of filling material as a result of the latter trickling out or of dust escaping are unavoidable, for which reason attempts have been made to provide the carrier material of the valve with a weldable layer and, in addition, to weld the top side of the valve to the underside of the valve. Once this additional layer has been applied, the valve can then be closed using hot air or ultrasound equipment. 
     The already described design features of paper valve bags with block bottoms or crossbottoms which are produced from paper give rise to disadvantages insofar as the flaps on the inside of the sack bottom or else of the top part, form undesirable cavities such as crevices or pockets in which in particular fine-grain pulverulent filling materials, but also granular or pasty residues of the bag contents can settle. So-called inner panels are thus adhesively bonded into the inside of the bottom or the top part of the paper valve bag, these inner panels usually being formed by rectangular sheets produced from the same material as the paper valve bag itself. The inner panels are welded or adhesively bonded to the flaps all the way round, as a result of which the cavities are closed in relation to the interior of the bag. 
     WO 95/02544 A1 discloses a method of producing special bags in which the bag material and the inner panel consist of paper coated internally with polyethylene. In this method, the inner panel is adhesively bonded, along the peripheries running parallel to the narrow-side peripheries of the bottom, to the associated bottom flaps, and parallel to the broad-side peripheries of the bottom the mutually facing coated surfaces of the inner panel and of the bottom flaps are connected to one another by continuous welds. 
     DE 20 204 015 551 A1 describes a paper sack with sheet-material overlapping for fine-grain bulk material. This paper sack has a bottom, a top part and a tubular paper-sack body. This shaping allows cost-effective transportation and, moreover, the sack body lends itself well to having printing applied to it. The relevant prior art also discloses the practice of applying to the outer region of the top side of a paper sack a cover sheet, which likewise lends itself well to having printing applied to it and is thus suitable for providing product-related and manufacturer-related information, but also for advertising purposes. It is further known to combine the cover sheet with the carrying handle, which can take place, in particular, by two parallel cuts being punched out of a cover sheet, in which case the user can form a carrying handle for the paper sack from the welded cover sheet. 
     It has already been pointed out several times that, on account of the design, paper valve bags always lose some of their contents as a result of the latter trickling out or of dust escaping. A further disadvantage is that paper valve bags are sensitive to the penetration of moisture, which can have an adverse effect overall on the contents. Attempts have therefore been made, by providing numerous variations and additional fitting features, to optimize the configuration of paper valve bags further. Improvements which have been of prime importance here, in particular, are the protection of the contents against moisture and filling-related problems along with the configuration of the paper bags. 
     DE 10 2004 043 446 U1 discloses, for example, a paper valve sack with a special valve configuration. DE 20 2005 003 539 U1 describes an easily fillable paper valve sack with improved water-vapour impermeability. 
     Since, as far as the configuration of paper valve bags for in particular fine-grain and pulverulent contents is concerned, the handling comfort for the user of the contents is also becoming more and more important of late, a number of solution approaches have also already been proposed in this respect. The carrying handle combined with the cover sheet and punched therein (see above) is described, for example, in DE 20 2006 006 436 U1. In this case, the cover sheet, which is adhesively bonded over its surface area, serves for sealing the folding region of the end of the paper valve bag and also for having information printed on it and as a carrying handle. 
     The prior art also discloses a variant of a paper valve bag which has a so-called peel-back cover sheet. In contrast to the bottom cover sheet, but also to a cover sheet which is located on the outside of the top part and is adhesively bonded over its surface area, the peel-back cover sheet is adhesively bonded only over part of its surface area, and this can take place via spots of adhesive or peripheral adhesive bonding. This makes it possible for the paper valve bag to be opened without any tools being required, and the peel-back cover sheet can therefore simply be pulled off manually. In the case of conventional paper valve bags with a cover sheet adhesively bonded over the surface area, the bag has to be opened, for removal or emptying of the contents, using a tool, e.g. a knife, scissors or a trowel, and a situation where, in dependence on the respective contents, there is an undesirable development of dust cannot be ruled out altogether. Moreover, the situation where the severing and tearing open of the paper sheet material results in constituent parts of the sheet material and bits of paper getting undesirably into the contents, and contaminating the latter, cannot be avoided completely. The indisputable advantages of a paper valve bag with a peel-back cover sheet reside in the fact that no tools are required for opening purposes, in which case more handling comfort is made possible, and that moreover, it is not possible for any packaging material to get into the contents when the bag is opened. 
     The disadvantage with this configuration of a paper valve bag with a peel-back cover sheet, however, is that satisfactory closure of the bag cannot be achieved. This is because the unobtrusive gluing of the paper folds which is required in this region constitutes a significant weak point: the vibrations which occur when the filled paper valve bags are transported unavoidably result in particular in pulverulent material escaping from the bag interior into the folding region, which, at the latest when the bag is opened by virtue of the peel-back cover sheet being pulled off, inevitably results in the formation of dust. Likewise disadvantageous is the fact that the contents escape in dust form when the sack is still closed, since the fine-grain or pulverulent contents can flow outwards through those regions of the peel-back cover sheet which are folded and have not been adhesively bonded. 
     In order to overcome this problem of dust escaping and, at the same time, to improve handling, a paper valve bag which has a tear-open thread fitted on its bottom cover sheet has been available for some time now. This results in an increased sealing capacity and allows easy opening without any tools being required (see www.dy-pack.de; product: Ripit™). Such sacks are used, in particular, for animal feed or cat litter. However, it is also the case here that the situation where the contents escape in dust form, in particular during transportation, cannot be prevented altogether. 
     Paper valve bags which fully prevent the contents from escaping in dust form are likewise known from the prior art. Conventional paper valve bags which may have a bottom cover sheet or peel-back cover sheet are additionally closed with the aid of a so-called inner panel as has already been described in more detail above. The inner panel serves for sealing the folding region or the paper folds, such that the filling material is reliably prevented from escaping in dust form. DE 195 22 619 A1 describes a method of producing flat-bottom bags with an inner panel adhesively bonded therein. Such bag or sack configurations, however, have the disadvantage that, once again, tools are required in order to open them, such tools involving further, already described disadvantages. 
    
    
     Taking the outlined prior art as the departure point, it is an object of the present invention to provide a paper valve bag with an inner panel ( 1 ), the inner panel being located at the paper-bag end ( 3 ) which is located opposite the paper-bag end with valve ( 2 ). This new type of paper valve bag is intended to prevent in particular fine-grain or pulverulent contents, or such fine-particle content fractions, from escaping in dust form during transportation and/or during use and, moreover, is intended to allow opening and access to the contents in convenient fashion without the aid of a tool. 
     This object has been achieved in that, on its surface which is directed toward the bag interior, the inner panel ( 1 ) has an opening aid ( 4 ) which has a higher modulus of elasticity and/or a higher tensile strength than the inner panel ( 1 ). 
     The object has been solved in full insofar as it is made possible for the opening aid ( 4 ) to open the inner panel reliably and conveniently, possibly once the cover sheet or the peel-back cover sheet has been pulled off, without any tools being used. Moreover, it is further possible to make use of the advantages of an inner panel and thus to prevent completely the escape of contents in dust form. Experience with the numerous variants of paper valve bag known meant that the straightforward achievement of the aim in this way was unexpected. Moreover, the higher modulus of elasticity of the opening aid ( 4 ) has proven to be advantageous insofar as the paper valve bags can now be handled better overall with the opening aid, which is essential to the invention. This is because the opening aids ( 4 ) may be configured such that they can be gripped to good effect and thus make it easier for the filled paper valve bags to be transported manually. 
     An essential feature of the paper valve bag according to the invention consists in the opening aid ( 4 ) having a higher modulus of elasticity and/or a higher tensile strength than the inner panel ( 1 ), on which the opening aid ( 4 ) is fastened: the modulus of elasticity is usually understood to be that level of tensile stressing at which a tensile-test bar made of the material which is to be tested doubles in length. This doubling, however, is an ideal state which does not occur for any material in reality. The modulus of elasticity is given in mega-pascals (MPa) and depends on various ambient conditions, e.g. temperature, moisture or the speed of deformation. Moduli of elasticity are usually measured at 20° C. and specified for this temperature range, that is to say for room temperature. A further criterion may be the tensile strength of the opening aid ( 4 ) in relation to the inner panel ( 1 ), the tensile strength (R m ) of the material which is to be tested bearing no relationship to the modulus of elasticity. Both parameters, that is to say the modulus of elasticity and also the tensile strength, are criteria for evaluating the deformation properties of the defined material, that is to say for the elastic behaviour thereof. Tensile strength is understood to be the level of stressing which is calculated in the tensile test from the maximum force achieved, in relation to the original cross section of the material sample. As with the modulus of elasticity, the unit is mega-pascals; force per unit surface area is defined as the dimension-related unit of the tensile strength. 
     According to the invention, the opening aid ( 4 ) thus has a higher modulus of elasticity and/or a higher tensile strength than the inner panel ( 1 ). This ensures that the inner-panel material always yields to tensile stressing or expansion at an earlier point in time than the material of the opening aid. Only thus is it ensured that the opening aid ( 4 ) can be used for tearing open the inner panel ( 1 ). 
     It has proven to be particularly advantageous if, at at least one surface-area end ( 5 ) and at most two opposite surface-area ends of the inner panel ( 1 ) the opening aid ( 4 ) extends beyond ( 6 ) the extent of the surface of the inner panel ( 1 ). At the same time, or as an alternative, the opening aid ( 4 ) is fitted parallel to the longitudinal extent of the inner-panel surface, and preferably in the centre of the latter, which is likewise covered by the present invention. 
     For production-related reasons and also from the point of view of better handling, it has proven to be advantageous if the opening aid ( 4 ) is a tear-open strip or a tear-open thread. 
     In respect of its configuration but also of the material of which it consists or from which it has been produced, the opening aid ( 4 ) is not subjected to any further-reaching limitations. The only essential factor is for its modulus of elasticity to be higher than that of the inner panel ( 1 ), on which it is fastened. It is thus possible for the opening aid ( 4 ) according to the present invention to consist of modified natural products such as wool, cotton or cellulose; also possible, however, are all plastics such as polymers based on the following monomers: ethylene, styrene, vinyl acetate, vinyl chloride, propylene and polyurethane. Of course, a mix of materials is also possible, in order thus to be able to meet the wide and varying requirements to which the opening aid ( 4 ) is subject. 
     The opening aid ( 4 ) can also be varied within a wide range in respect of its dimensioning: in dependence on the size and the filling volume and also the type of filling material, however, it is recommended for the width or the diameter of the opening aid ( 4 ) to be selected such that these are between 0.1 mm and 5 mm, preferably between 0.2 mm and 3 mm and particularly preferably between 0.5 mm and 2 mm. In respect of its fastening method, the present invention provides for the opening aid ( 4 ) to be adhesively bonded and/or welded to the inner panel ( 1 ). 
     As has already been discussed in general terms, so-called cover sheets or peel-back cover sheets have additional advantages, which additionally broaden the range of use of paper valve bags. For this reason, the present invention also takes account of a variant of the paper valve bag according to the invention in which the paper-bag end with the inner panel has, in the direction of the exterior surroundings, a peel-back cover sheet and/or in which the bottom has a cover sheet which is adhesively bonded or welded over the surface area. In respect of the sealing and the markings the paper valve bag according to the invention thus has additional and indisputable advantages. 
     To summarize, in respect of the opening aid ( 4 ), which is essential to the invention, it may be said that this can be fitted on the inner panel ( 1 ) in the form of a tear-open thread or tear-open strip such that its entire length runs longitudinally or else transversely in relation to the direction of the inner panel and, at least on one side, extends beyond the surface area of the inner panel ( 1 ). That part of the opening aid ( 4 ) which extends beyond the inner panel is guided, when the base and/or top part of the bag are/is folded and adhesively bonded, such that this part of the opening aid extends beyond the inner-panel fold and is thus easily accessible from the outside at all times. The opening aid ( 4 ) is preferably fixed on the inner panel ( 1 ) by adhesive bonding and fitted in the longitudinal direction in relation to the same. By virtue of the opening aid ( 4 ) being pulled manually, or else mechanically, the inner panel ( 1 ) is torn all the way along its centre, this allowing access to the contents and also making it possible for the contents to emptied without any unnecessary formation of dust. 
     The inner panel ( 1 ), on which the opening aid ( 4 ) is fastened, may consist of the same material as the paper valve bag. This material may be constituted by known paper materials in one or more layers or else also by a multi-layered material made of paper and additional barrier layers. These barrier layers consist of materials which slow down or block water vapour, e.g. metals (aluminium) or plastics (polyethylene). In respect of the paper-bag materials, three layers located one above the other are particularly suitable, the two outer layers consisting of special paper or special papers and the inner layer, in turn, consisting of a barrier layer, for example of aluminium or polyethylene. 
     In addition to the paper valve bag itself, the present invention also covers the use of the same. It relates, in particular, to a variant concerned with the packaging, the transportation and the storage of fine-grain, pulverulent and/or free-flowing materials and the mixtures thereof. The materials here have in particular particle sizes between 0.05 μm and 2 mm and lie particularly preferably in the micro-scale and nano-scale ranges. 
     The materials which are packaged as filling material in the paper valve bags, for transportation or storage purposes, have a preferred particle-size distribution between 0.1 μm and 1.0 mm, preferably between 1.0 μm and 500 μm and particularly preferably between 10 μm and 100 μm. 
     These materials are, in particular, inorganic, organic and/or metal pure and mixed substances, preferably (mixed) oxides, carbides, sulphides, hydroxides, salts, hydrocarbons and monomers and polymers of natural or synthetic origin and the mixtures thereof. 
     In respect of the filling materials, the paper valve bags according to the invention are used in particular for hydraulically setting materials and in particular for ready-to-use mortar.