Patent Application
20240401275
The present invention relates to a packaging material consisting of an unbleached kraft paper with a Kappa number according to ISO 302:2015 between 38 and 60, preferably between 40 and 58 as the base material, wherein the kraft paper is manufactured from at least 90% primary cellulose and has a grammage according to ISO 536:2019 between 65 g/m2 and 170 g/m2, as well as a sleeve or banderole respectively, produced from such a packaging material, a method for producing the same and a sleeve manufactured from such a packaging material and a use of the packaging material.
Unbleached kraft paper is widely used as a packaging material since it has a high resistance to tearing and furthermore, it also has good stability with respect to exposure to moisture and chemicals. Kraft paper is also easy to print, regardless of whether it is bleached or unbleached, so that for a consumer of the packaged goods the necessary information printed directly on the packaging can be seen. A typical use of kraft paper and in particular unbleached kraft paper is its use in the production of bags for the packaging of a wide variety of materials, such as building materials, sharp-edged materials, food, toys or the like. In the packaging sector, however, there is not only the form of packaging in which the goods to be packaged are completely wrapped in the packaging paper, such as, for example, bags closed on all sides, but it is frequently possible to simply surround goods to be packaged or goods to be sold in bundles with a kind of loop, on which information about the contents, possibly the shelf life or the like, and frequently brand names are printed. Such loops frequently also serve to provide cohesion of a plurality of similar or different related goods to be packaged and, for example, in the clothing sector frequently several goods, such as a plurality of T-shirts, socks or the like are packaged by enclosing them with a loop or a sleeve. It is essential for the packaging material from which such a loop is made that it tightly encloses the goods to be packaged or enclosed so that the loop cannot be pulled down unintentionally and that one or more of the products enclosed by the loop cannot fall out and it is further ensured that the goods to be surrounded by the loop can be inserted into it without damage on the one hand and on the other hand, during such an insertion or a subsequent transport, handling or the like, the loop surrounding the goods does not tear or become otherwise damaged.
In the same way, it is frequently necessary to provide tubular packaging materials in which compressible or resilient objects must be packaged, as far as possible, in their most compressed form, in order on the one hand to keep the space requirement of these packages as small as possible and, on the other hand, to ensure that the packaged goods are not compressed and decompressed unnecessarily frequently during transport and thus possibly results in material fatigue. It seems particularly important in this context that the packaging material is not stressed by the tensile stress exerted by the resilient goods packaged therein beyond its stretching ability or elasticity and tears, or the tubular packaging material is damaged when the goods to be packaged are inserted. To date, plastic films or bands, which can be produced in different designs and can also be manufactured to suit the respective requirements, have been considered to be most suitable for this purpose. For environmental reasons, the aim is to replace plastic packaging as far as possible with packaging made from materials made from renewable raw materials and in particular biodegradable raw materials. Recently, there has been increased research into producing special papers, in particular kraft papers, which meet a wide range of requirements with regard to durability, elasticity, moisture resistance and the like in order to replace plastic packaging. Particularly in cases where annularly closed tubes, bands or loops have to be used as packaging materials, there is the problem that packaging consisting of paper, for example, is produced from a flat paper web, which web must be glued or closed in some way to form the ring or tube. If this closure is only closed or formed after the goods to be packaged have been inserted therein, the time required until a formed adhesive point has hardened or dried or thermoplastic material has hardened may be too long for mass production, so that by analogy with plastic packaging, it is necessary to form this tube, ring or loop before introducing the products to be surrounded thereby. In order that products can be inserted into such a tube, ring or loop or into such a band without destroying it, such packaging material or packaging paper must not only have excellent elasticity in the radial direction, i.e. in the circumferential direction of the ring or loop, but also must not tear at the edges, particularly when the objects are inserted.
The present invention therefore aims to provide a packaging material made of an unbleached, optionally coated, kraft paper, which does not tear both in the machine longitudinal direction and the machine cross direction under high loading, in particular a loading that stretches the paper, and remains sufficiently elastic or resilient over time so that the items packaged therein cannot fall out after a fairly long time due to a loss of tension or elasticity of the packaging material.
To solve this problem, the packaging material according to the invention is substantially characterized in that the kraft paper contains at least 90% primary cellulose, containing at least 80%, preferably at least 85%, in particular at least 88% cellulose with a length-weighted mean fibre length according to ISO 16065-2:2014 between 2.0 mm and 2.9 mm and less than 5%, preferably less than 4.5%, in particular less than 4.2% fillers as well as cationic starch and other process aids, that the primary cellulose is contained in the form of beaten cellulose, in particular, high-consistency beaten cellulose having a Schopper-Riegler degree of beating according to ISO 5267-1:1999 between 13° SR and 20° SR, that the packaging material has strain ratio MD/CD of the kraft paper at break according to ISO 1924-3:2005 of >1.1, a tear length in the machine direction according to ISO 1924-3:2005 of >10 km, a tear index in the cross direction of the kraft paper according to ISO 1974:2012 is >16.0 Mn·m2/g and that the kraft paper is optionally coated on at least one side with a coating material.
Since the packaging material contains at least 90% primary cellulose, containing at least 80%, preferably at least 85%, in particular at least 88% cellulose with an average length-weighted fibre length according to ISO 16065-2:2014 between 2.0 mm and 2.9 mm contains less than 5%, preferably less than 4.5%, in particular less than 4.2% fillers as well as cationic starch and other process aids, it is possible to provide an unbleached kraft paper with an extremely tear-resistant structure and in particular due to the narrow length distribution of the fibre lengths of the primary cellulose used, it is possible to achieve excellent homogeneous paper properties in both the machine direction and in the cross direction. Due to its durability and its ability to be (micro) creped in a Clupak system, such unbleached kraft paper can also be used safely and reliably for the packaging of sharp-edged objects or heavy materials, such as cement or beverage bottles. Since it furthermore contains less than 5%, preferably less than 4.5%, in particular less than 4.2% (the stated percentages are always to be understood as percent by weight in the context of the present invention) of fillers as well as cationic starch and process aids, it is possible, at the same time, to obtain a durable but not excessively stiff unbleached kraft paper in which high percentages of starch, in particular cationic starch, can be used due to the lignin remaining in the kraft paper and the hemicelluloses remaining in the kraft paper and the associated high numbers of negative charges. Since an unbleached kraft paper produced in this way is not excessively stiff, but is extremely elastic, it is possible, particularly when loops, bands, sleeves or tubes are made from this packaging material, to securely and reliably enclose the objects packaged therein without there being any need to fear that these will slip out of the packaging material in an unintentional manner, whereby when producing such tubes, bands or loops, care must be taken to ensure that the unbleached kraft paper has greater elasticity in the winding direction of the loop than In the cross direction of the loop. Since the packaging material is formed in such a way that the primary cellulose is contained as beaten cellulose, in particular cellulose beaten with high consistency, with a degree of beating according to Schopper-Riegler according to ISO 5267-1:1999 between 13° SR and 20° SR, it is still possible to break up existing fibre agglomerates, such as strips and splinters, whereby a uniform sheet or particularly homogeneous kraft paper can be formed, in which an optimized combination between flexibility of the fibre and tear index in the cross direction can be achieved. It is unnecessary to state that by increasing or by high- or low-consistency beating of paper, both the tear length and the air permeability of the paper can be adjusted, wherein however the latter is not important in the present case, especially when coatings are optionally applied, since a neither a rapid filling of closed bags made of the packaging material according to the present invention should be achieved nor does the air permeability in any other way bring about advantageous or negative properties for packaging made from the packaging material.
The packaging material can also consist of 100% primary cellulose. Since the packaging material, in particular the unbleached kraft paper, consists of 100% primary cellulose, it is possible to safely avoid negative influences on the end product, which originate, for example, from recycled cellulose as well as from cellulose obtained from waste paper and, in particular, a reduced strength or elongation at break of the packaging material mostly caused by waste paper or recycled cellulose can thereby be avoided. In connection with the present invention, t is essential that the elongation at break or the strain ratio, the tear length in the machine direction and the tear index in the cross direction can be kept high and as constant as possible over time in order to provide consistent material properties with which it is possible to produce tubular packaging or sleeves or loops in which heavy or sharp-edged objects can be packaged and/or wrapped and can be stored for a fairly long time without any risk that the unbleached kraft paper will tear and the packaging manufactured therewith will deteriorate.
Since the unbleached kraft paper of the packaging material has a strain ratio MD/CD according to ISO 1974:2012 of >1.1 it is ensured that its elasticity in the machine direction (MD) is greater than that in the cross direction and the packaging material is therefore not only stretchable in the MD and CD direction but can be subjected to a greater change in length in one direction than in the other without having to fear destruction, in particular tearing, of the packaging material.
The fact that the strain ratio MD/CD of the kraft paper is >1.1 in accordance with ISO 1974:2012 further ensures that even objects that do not have a homogeneous or even and smooth surface can be packaged safely and reliably in this packaging material based on unbleached, optionally coated kraft paper, since the paper substantially encloses the packaged goods on all sides after it has returned to its original shape from its expanded shape due to the insertion of the goods and is also able to securely and reliably hold goods with uneven surfaces. At the same time, the stretch is sufficiently large so that the products can be inserted into the packaging material without damaging it, in particular can be inserted into tubular sleeves shaped from this optionally coated paper or packaging material and it is furthermore ensured that after introduction of the materials and stretching of the paper, the paper is returned to its original shape and tightly encloses the packaged objects, so that there is no need to fear that packaged objects can fall out, for example, from tubular or ring-shaped packaging made from the packaging material according to the invention. Furthermore, it has been shown that if the strain ratio MD/CD of the kraft paper according to ISO 1974:2012 is >3, no further improvement in the properties of the packaging material required for packaging heavy objects can be achieved.
Since the tear length in the machine direction of the kraft paper is >10 km in accordance with ISO 1924-3:2005 it is further ensured that the machine strength in the longitudinal direction of the packaging material is so great that even if, for example, tubular or ring-shaped packaging was made therefrom, even non-flexible objects can be inserted into the interior of this packaging material thus shaped without needing to fear any unintentional tearing of the kraft paper. Since the tear index in the cross direction of the kraft paper according to ISO 1974:2012 is furthermore >16.0 MN·m2/g, it is ensured that there is no risk of tearing of a free edge of the packaging material, even in the event of unintentionally high loads on the edge of the packaging material and in particular if tubular or ring-shaped products are manufactured from this packaging material, such as loops or sleeves, there is no need to fear tearing of the packaging material and therefore destruction of the packaging when the goods to be packaged are inserted.
Since the packaging material is formed such that a tear index in the cross direction (CD) of the kraft paper according to ISO 1974:2012 is >16.0 MN·m2/g, the packaging material substantially consisting of unbleached, optionally coated kraft paper, can also be severely stressed at its edges without needing to fear any tearing or further tearing of the paper from the edge to the centre. Finally, it can thereby be prevented that even if a small crack is formed in the packaging material, this is not unintentionally enlarged.
In connection with the present invention, the term “packaging material” is understood to mean substantially unbleached kraft paper, which can optionally be coated on one or two sides. Furthermore, it can have one or more layers of kraft paper.
According to a further development, the packaging material can also consist of 100% primary cellulose. Since the packaging material, in particular the unbleached kraft paper, consists of 100% primary cellulose, it is possible to more reliably avoid negative influences on the end product, which originate, for example, from recycled cellulose as well as from cellulose obtained from waste paper and in particular, a reduced strength or elongation at break of the packaging material mostly caused by waste paper or recycled cellulose can be avoided. In connection with the present invention, it is essential that in particular the elongation at break or the strain ratio, the tear length in the machine direction and the tear index in the cross direction can be kept high and as constant as possible over time in order to provide consistent material properties, with which it is possible to manufacture tubular or ring-shaped packaging or sleeves in which heavy or sharp-edged objects can be packaged and/or wrapped therewith and can be stored for a fairly long time without there being any need to fear any tearing of the unbleached kraft paper and deterioration of the packaging produced therewith.
As corresponds to a further development of the invention, since the packaging material is formed such that it has a starch content of 0.5% to 2.2% of the kraft paper, in particular 0.7% to 2.0%, it is possible to keep the excellent mechanical properties of the unbleached kraft paper, the surface smoothness of at least one side of the kraft paper, high and keep the Bendtsen roughness low and thus provide excellent printability of this at least one side of the packaging material. In the present context, an attempt is made at the same time to configure only one side, in particular the side facing away from the machine or “top side” of the paper, to be correspondingly smooth in order to make the adhesion to the inside of tubular or ring-shaped packagings, i.e. the side facing away from the “top side”, made of the packaging material according to the present invention as great as possible in order to prevent as far as possible any loss of the items packaged therein due to slipping out.
According to a further development of the invention, the packaging material is configured such that the primary cellulose consists of a mixture consisting of at least 80% softwood cellulose, preferably at least 90% softwood cellulose, in particular at least 95% softwood cellulose having a length-weighted mean fibre length according to ISO 16065-2:2014 of at least 2.0 mm, preferably at least 2.2 mm and the remainder of hardwood cellulose having a length-weighted mean fibre length according to ISO 16065-2:2014 of at least 1.0 mm. Due to the predominant amount of softwood cellulose having a length-weighted mean fibre length according to ISO 16065-2:2014 of at least 2.0 mm and the remainder of hardwood cellulose having a length-weighted mean fibre length according to ISO 16065-2:2014 of at least 1.0 mm, the strength property can be positively influenced by the softwood cellulose and the smoothness of at least one side of the unbleached kraft paper can be positively influenced by the hardwood cellulose, and by means of a targeted choice of the cellulose composition, a packaging material can be provided having both excellent mechanical properties, in particular elongation at break, and also sufficient smoothness, which provides good printability. Furthermore, with such a choice of cellulose mixture, in particular the high contents of softwood cellulose, it can be ensured that an unbleached packaging material thus produced has a large tear length in the machine direction, whereby a particularly resilient packaging material can be provided, in which objects having a higher weight can also be stored can be packed with a higher weight without the packaging necessarily needing to have a bottom and/or top surface.
Since, as corresponds to a further development of the invention, the packaging material is configured so that it has a tensile strength index in the machine direction according to ISO 1924:3: 2005 of >105 Nm/g, preferably at least 115 Nm/g, a non-destructive packaging of even heavy or sharp-edged objects in the packaging material according to the present invention is ensured. Due to the tensile strength index according to the invention in the machine direction it is further ensured that when producing, for example, tubular packaging or loop-shaped or sleeve-shaped packaging from the packaging material according to the invention, it is possible to provide sufficient load-bearing capacity of the packaging material, with the result that even heavy objects can be safely fitted into such a loop or sleeve made of the packaging material and furthermore there is no need to fear tearing of the material.
In the same way, as corresponds to a further development of the invention, the packaging material has a TEA index in the machine longitudinal direction according to ISO 1924-3:2005 greater than 5.0 J/g, preferably greater than 5.5 J/g. Since the TEA index in the machine longitudinal direction is greater than 5.0 J/g, it is possible to provide a packaging material that is extremely elastic and stretchable without resulting in any tearing of the packaging material. The TEA index is understood as the tensile energy absorption index according to ISO 1924-3:2005.
In order in particular to avoid tearing or bursting of the packaging material according to the invention from the edges to the centre, the invention is further developed such that the packaging material has a bursting strength according to ISO 2758:2014 of greater than 750 kPa, preferably greater than 770 kPa, particularly preferably greater than 800 kPa. According to the invention, the bursting strength is adjusted or increased, inter alia, by a combination of the following measures: use of cellulose from softwood, a low filler content and a high proportion of, for example, cationic starch. Furthermore, beating, in particular low-consistency beating, also has a positive influence on the bursting strength.
Since, as corresponds to a further development of the invention, the packaging material is designed such that it has a wet strength index according to ISO 3781:2011 in the machine direction of the kraft paper of at least 14.0 Nm/g, in particular 14.5 Nm/g, particularly preferably at least 15.0 Nm/g, it is possible to provide in particular tubular or ring-shaped packaging with the packaging material, which is also suitable for use in moist environments. Particularly if, for example, food packagings or loops that enclose and hold together a plurality of foods or foodstuffs are manufactured from the packaging material, contact with condensation, moisture or a damp environment cannot be avoided, so that a high wet strength or a high wet strength index is desirable, but without permanent wet strength agents or large quantities thereof, needing to be used in the production of the packaging material substantially consisting of unbleached kraft paper. The wet strength index according to ISO 3781:2011 in the machine direction can be further improved by providing a coating on one or both sides of the packaging material.
Surprisingly, such a high wet strength can also be achieved with a high dry basic strength with the packaging material according to the present invention. In order to achieve high wet strength, larger amounts of auxiliary materials, such as wet strength agents, usually have to be used, which in turn cause problems when recycling the packaging material to be produced, which substantially consists of unbleached kraft paper. Since in the packaging material according to the invention, which substantially consists of unbleached kraft paper, the dry strength expressed by the tensile strength index in the machine direction is >105 Nm/g, sufficient wet strength can surprisingly be achieved very resource-efficiently without or by only adding very small amounts of wet strength agents.
In the present case, wet strength agents are understood to mean water-miscible polymer solutions in the processing state, which are primarily produced from polyamines and epichlorohydrin derivatives. Furthermore, products based on urea-formaldehyde or melamine-formaldehyde are conceivable, but are preferably no longer used for reasons of avoiding health risks. When the wet strength agents react with cellulose fibres, cross-links form between the fibres, which lead to an increased water resistance of the corresponding paper thus produced. However, the hydrophobic chain thus formed prevents easy or successful recycling of a paper treated with these wet strength agents. Returning used packaging paper to a cellulose cycle is therefore not possible or can only be achieved to a limited extent by using high temperatures and/or additional chemicals and additives. It is therefore desirable to keep the amount of wet strength agents used as low as possible, which surprisingly can be achieved with kraft paper or packaging material according to the invention.
According to a further development of the invention, the packaging material is designed such that a coating material selected from a polyolefin, in an amount corresponding to 1/15 to ⅙ of the grammage of the kraft paper, is applied to at least one side. By applying to at least one side of the packaging material a coating material selected from a polyolefin or polylactic acid (PLA), in an amount corresponding to 1/15 to ⅙ of the grammage of the kraft paper contained in or forming the packaging material, it is possible, on the one hand, to further improve the wet strength of the packaging material without the excellent mechanical properties deteriorating. On the other hand, by applying such small amounts of a coating material to at least one side of the packaging material, it can be ensured that loops, rings, tubes, sleeves or the like can be formed from the packaging material by superimposing free end regions of the packaging material and a closed ring can be formed by heat sealing the at least one thermoplastic polyolefin layer or the polylactic acid layer.
Finally, by applying an amount corresponding to 1/15 to ⅙ of the grammage of the kraft paper to a polyolefin coating material or polylactic acid coating material, it can be ensured that a packaging material thus produced is both decomposable and, due to the small amount of polymer, is not harmful to the environment.
By selecting, as corresponds to a further development of the invention, the polyolefin from high-density polyethylene (HDPE), low-density polyethylene (LDPE) or polypropylene (PP), coatings which are both stable and do not impair the mechanical properties of the kraft paper forming the basis of the packaging material can be formed.
Polyolefin coating materials having densities in the range of 900 to 950 kg/m3 as well as softening or melting temperatures between 125 and 150° C. have proven to be particularly suitable.
According to a further development of the invention, the packaging material is further developed such that a laminate consisting of several layers of kraft paper and several layers of coating material is formed. By forming a laminate from several layers of kraft paper and several layers of coating material, it is possible to provide both resilient and extremely durable packaging materials. Such packaging materials can be used, for example, as packaging bands, in particular as a replacement for plastic bands surrounding packets, packages or similar. Furthermore, such laminates can not only be used on existing industrial packaging machines, but due to the particularly high tear strength of the laminate, these can also be stapled without there being any need to fear any tearing out of the staples or tearing of the laminate due to the material weakening that has taken place.
Since, as corresponds to a further development of the invention, the laminate has at most 5 layers of the kraft paper, such as 4 layers for example, more favourably 3 layers, preferably 2 layers of the kraft paper and at most 6 layers of the coating material, such as 5 layers, for example, more favourably 4 layers, preferably 3 layers of the coating material, on the one hand, it is possible to produce laminates that are optimally adapted to the thickness requirements of industrial packaging machines. On the other hand, by using a single grammage of the kraft paper, a large number of different bands, sleeves, loops or the like can be produced from the laminate, which in particular reduces downtimes and necessary adjustments to the paper machine. As a result, the kraft paper forming the basis of the packaging material can be produced more economically.
According to a further development of the invention, each layer of coating material located between two layers of kraft paper has an amount that corresponds to 1/15 to 1/9 of the grammage of the kraft paper, and a layer of coating material forming an outer side of the laminate has an amount which corresponds to 1/11 to ⅙ of the grammage of the kraft paper. With such a design, the amount of coating material used can be minimized, since each layer of coating material located between two layers of kraft paper only has to ensure that the two layers of kraft paper hold together and can therefore be formed from a smaller amount of the coating material. In contrast, each outer layer of the coating material must be configured to be sufficiently thick that it must ensure a secure and durable heat seal of, for example, two ends of the packaging material.
The invention further aims to design or provide a sleeve from the packaging material according to the present invention, with which sleeve it is possible to package or enclose a plurality of heavy, unconnected products and to transport them without there being any need to fear any tearing of the packaging material.
In order to achieve this object, according to the invention, a sleeve is provided from the packaging material of the present invention, which is configured such that it is formed from an optionally coated, at least single-layer web of the packaging material which is closed in the cross direction, in particular crimped, glued, preferably double-glued, welded, stapled, sewn or riveted in the cross direction, substantially made of unbleached kraft paper, and that a machine direction of the paper web in the packaging material forms a circumferential direction of the sleeve. Due to the fact that this sleeve is formed from the optionally coated, at least single-layer web of packaging material which is closed in the cross direction, in particular crimped, glued, preferably double-glued, welded, stapled, sewn or riveted, substantially made of unbleached kraft paper, it is possible to provide the greater elongation that the unbleached kraft paper has in the machine direction in the circumferential direction of the sleeve, the band, the loop or the tubular packaging, so that due to the excellent elasticity of the packaging material in the machine direction, a plurality of objects when inserted into the sleeve or into the packaging material glued into a ring does not tear or further tear the packaging material. Since it is thereby possible to enclose a plurality of objects with the sleeve, several objects that are similar or different from one another can naturally be enclosed and held together without having to provide packaging that completely surrounds the objects.
By arranging the packaging material in the finished sleeve in such a way that a machine direction of the packaging material forms a circumferential direction of the sleeve, the stretch properties in the machine direction introduced by the manufacturing process of the packaging material can be used to ensure that the objects to be packaged or enclosed can be inserted into a sleeve that has already been glued into a ring using the stretch properties of the packaging material, without there being any need to fear tearing of the sleeve and can be held firmly in this ring after they have been inserted due to the resilience of the packaging material. Furthermore, a band formed from this packaging material, in particular a laminate made from this packaging material, can also be used instead of plastic bands, which are used, for example, to close packages, to secure objects from loss and the like.
By connecting the packaging material thus to form a ring or a loop or sleeve such that it encloses a plurality of objects in the machine direction of the paper web, it is furthermore possible to insert the plurality of objects into such a sleeve without there being any fear that the band will tear in both the cross direction and longitudinal directions, even at the edges of the sleeve. It is also unnecessary to point out that such a sleeve constitutes an extremely paper-saving type of packaging with which objects can be packaged and held together safely and reliably.
Since the sleeve encloses at least two objects that are the same or different from one another, it is ensured that containers of any size can be formed, which at the same time due to the strain ratio MD/CD of the optionally coated kraft paper in accordance with ISO 1924-3:2005 of >1.1 to about 3 as well as the tear index in the cross direction according to ISO 1974:2012 of >16.0 MN·m2/g can be reliably inserted into the sleeve or the tubular product without there being any fear of tearing or tearing-out of the edges of the paper. Objects that are heavy or have a large length or height compared to the width of the sleeve can also be packaged in such a sleeve without there being any fear of tipping or subsequent tearing of the sleeve. This is because, due to the material properties of the packaging material, the objects can be tightly enclosed and therefore, even if one or more objects tip, there is no need to fear any tearing and subsequent tearing-through of the sleeve. Such a sleeve can also be used to close, for example, a box or the like.
The sleeve can be configured such that the plurality of objects are arranged in several rows, in a circle or to form a dense package in the sleeve. With such an arrangement of the enclosed objects, for example, conventional beverage packs comprising two, six or even twelve bottles can be surrounded by a band according to the invention or, for example, food products such as courgettes or bananas can be arranged in a sleeve or even, for example, several foam elements that are identical to one another, such as foam cushions or rods made of metal or wood, can be arranged inside such a sleeve.
According to a further development of the invention, the sleeve is configured so that it is subjected to tensile loading by the enclosed objects, in particular with a tensile stress that is smaller than an elongation at break in the machine direction (MD) measured according to ISO 1924-3:2005 of the optionally coated paper web. Due to the tensile loading or tensile stressing of the objects packaged inside such a sleeve, it is ensured that an object does not accidentally fall out of the sleeve, with the result that subsequently the hold of the remaining products could no longer be ensured.
In order to provide sufficient elasticity of the packaging material or to be able to provide sufficient resilience of the same, the packaging material is substantially configured such that the elongation at break in the machine direction (MD), measured according to ISO 1924-3:2005, of the paper web is >8%. Kraft papers, which have an elongation at break of the paper web of >8% in the machine direction, have proven themselves in standard packaging materials, such as heavy-duty bags and the like, which are subjected to severe loading in the MD direction, and surprisingly it has been shown that sleeves made from such material are able to hold products packaged therein safely and reliably due to the excellent resilience of this material, without there being any fear of the products slipping or falling out of the sleeve or tearing or there being any fear of tearing of the sleeve when inserting the products.
According to a further development of the invention, the sleeve, band or the like is configured such that it consists of a laminate consisting of several layers of kraft paper and several layers of coating material, such as at most 5 layers of kraft paper, for example 4 layers, more favourably 3 layers, preferably 2 layers of the kraft paper and at most 6 layers of the coating material, such as 5 layers, more favourably 4 layers, preferably 3 layers of the coating material. By using a laminate, the sleeve, band or loop can be used as a replacement for conventional plastic bands without there being any need to fear tearing of the laminate. Unintentional loosening of a connection point of two ends of the laminate is also reliably prevented and this is regardless of whether the band or the sleeve is heat-sealed, stapled, crimped or connected to one another in any other way.
A further aim of the present invention is to provide a method for forming a sleeve from the packaging material according to the invention, whereby, due to the conventional manufacturing processes, the problem essentially lies in the fact that as a result of corresponding treatments, in principle a paper web has greater stretching properties in the machine direction than in the cross direction. It is true that isotropic papers are already known which have the same properties in the longitudinal and cross directions, these can only be produced to a limited extent on large paper machines and in particular these papers usually have at least slightly inferior properties in the cross direction.
In order to be able to optimally utilize the favourable properties of the packaging material according to the invention in a sleeve, the method according to the invention is formed such that a length of the packaging material slightly exceeding a circumference of the sleeve to be formed is cut from a web of the packaging material substantially consisting of unbleached kraft paper which is unrolled in the machine longitudinal direction, the cut length of the packaging material is pivoted through 90°, those two free edges of the cut length, which run in the cross-machine direction when the web of packaging material is unrolled, are folded over one another and closed into a tube and that a plurality of sleeves are separated from the closed tube or prepared for separation, in particular perforated, scratched or marked. Due to the non-existent possibility or economic senselessness of performing cuts or a large number of cuts in the paper in the machine longitudinal direction in a running paper web on a paper machine, the process is essentially carried out such that only a length of the packaging material is cut off from an unrolling web of the packaging material, which length substantially corresponds to the circumference of the sleeve to be produced. Naturally, a certain excess length can be provided here, which must be present as an overlap of the material during a subsequent closure of the layer of packaging material to form a tube or possibly to form a single sleeve. After cutting off the corresponding length, a tube can either be formed directly from the cut length, wherein the paper is then folded such that in principle the cross direction, i.e. the width of the web of packaging material, forms the circumferential length of the tube, or however, the cut piece of packaging material can be directly turned by 90° and subsequently glued, crimped, riveted, sewn or similar into a tube. In a final step, it is now necessary to separate corresponding pieces, which correspond to the width of the sleeve, from the tube thus formed. The separation can be done by cutting, punching, tearing off and the like, wherein perforations, marking lines, pre-punched areas or the like can be carried out for this purpose either beforehand, in which case this is either carried out directly or at the end customer, depending on the intended use and final use of the sleeve. It makes sense that those pieces that form a large number of sleeves are not separated in advance, since, for example, printing is in principle easier if larger areas can be printed accordingly at the same time.
According to a further development of the method according to the invention, the method can be carried out such that the pivoting of the cut length of the packaging material by 90° is carried out before or after folding over and closing those two free edges of the cut length that run in the cross-machine direction during unrolling of the web of packaging material. Here, as stated, it is irrelevant whether the pivoting of the cut length of the packaging material by 90° is carried out before or after folding over one another to close the two free bands of the cut length.
The packaging material according to the invention can, as corresponds to a further development of the invention, be used as a sleeve or as a band, in which case it should not go unmentioned that conventional sacks and the like can naturally also be made from this packaging material which however, only seems meaningful for high-performance products due to the special material properties.
The invention is further explained hereinafter using exemplary embodiments and drawings. In the figures:
In detail,
With such a packaging material, which is in particular configured as a loop or sleeve, it is therefore possible to hold a plurality of objects of the same or different design by the sleeve 1, without having to use, for example, an additional plastic packaging that extends over the entire package of objects. The area of the connection 4 can have any type of connection, such as for example, flat adhesive bonding (see
In
With such sleeves 1, it is now possible to captively pack a wide variety of objects together and, in particular, to ensure that, even when heavy objects, such as metal rods or the like, are packed, any tearing of the packaging material 8 is avoided. If such a sleeve 1 is pulled over objects to be packaged, in particular heavy or hard objects, it is possible to ensure that as a result of the resilience of the unbleached kraft paper forming it, in particular due to the elongation at break, tensile strength or even the tear resistance index, if a small tear should be formed in the packaging material 8 forming the sleeve 1, this does not tear any further and, moreover, the sleeve 1 thus formed contracts to such an extent after stretching that any slipping out of the objects packaged therein after the packaging has been completed can be prevented. In addition, due to the special configuration of the packaging material 8, a certain static friction can also be exerted on the objects packaged therein, which ensures that the objects are immovably accommodated inside the sleeve 1 and that any slipping out of one or more of the objects is safely prevented. The static friction mentioned here can be exerted not only by the sleeve 1, but also, for example, by the surface of the objects packaged therein.
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It is unnecessary to note that the second step of the process of turning the packaging material 8 by 90° can also take place after forming the tube. In any case, the packaging material 8 must be connected to one another along the edges 2, 3 in order to have the favourable material properties, which result from the machine direction of the production of the kraft paper, available in the circumferential direction of a finished sleeve 1.
With regard to the optional process steps, such as printing, perforating or the like, it should be noted that these can be carried out before or after each step following separation of the web of packaging material 8 from the reel. Thus, it can be favourable to print immediately on the separated piece of packaging material and only then form a tube from the packaging material 8.
The sleeve or loop 1 can not only be designed in one colour, but can also be printed in multiple colours, provided with company names, logos and the like, and it can also have a one-sided or two-sided coating in order, for example, to improve the moisture resistance of the packaging material 8. Finally, it can also have more than one layer of unbleached kraft paper. A laminate can thus be formed consisting of more than one layer of the kraft paper, with respectively one layer of the coating material between the individual kraft paper layers and an outer layer of the coating material in each case. The grammages of the individual coating material layers and also the grammages of the individual kraft paper layers can also differ from one another. In this case, it should be noted that the essential properties of the sleeve 1 must not be changed and neither the elongation at break, the bursting strength, the tear length, etc. are changed compared to an optionally coated single-layer paper sleeve.
Finally, it is unnecessary to point out that with a sleeve 1 according to the invention not only heavy and hard objects or plastic containers can be held together, but also, for example, socks can be surrounded, foods such as bananas, courgettes, cucumbers or the like can be connected to one another or boxes can be closed. Also, for example, goods packaged in cans or food, boxes and the like can be connected to each other to form containers.
Furthermore, the invention is explained in more detail hereinafter by reference to exemplary embodiments.
An unbleached cellulose consisting of 100% primary cellulose from softwood (mixture of spruce and pine) with a Kappa number of 51 was first subjected to high-consistency beating with a beating capacity of 230 to 240 kWh/t, wherein a degree of beating of the cellulose after high-consistency beating was 17° SR. This cellulose was then subjected to low-consistency beating with a beating capacity of 90 to 100 kWh/t. The following auxiliary materials were added to the constant part of the paper machine. Here the pH was adjusted to a pH of 6.8 to 7.0 with aluminium sulphate, cationic starch having a degree of cationization DS of 0.03 was added absolutely dry in an amount of 17 kg/t paper, alkenyl succinic anhydride in an amount of 0.8 kg/t dry kraft paper was added as sizing agent and 10 kg/t PAAE was used as wet strength agent. Furthermore, no fillers were added. The consistency of the cellulose at the headbox was 0.19%. The dewatering was carried out on a Foudrinier wire section and with a press section with three nips, wherein one of the presses can be a shoe press, wherein the line pressure at the three nips was 60 kN/m, 90 kN/m and 500 kN/m respectively (in the shoe press). Before the still wet paper was fed to the Clupak system, it was subjected to contact drying, conventional drying using hot air at 167° C., then pre-dried in a slalom drying section and treated in a Clupak system with a differential speed of −7.9% and finally dried to a final residual moisture content of 7.5%.
The kraft paper can be used as such for the production of bands, loops or sleeves and the paper properties described in the following table were measured in this kraft paper.
The kraft paper thus produced would have the following properties:
An unbleached cellulose consisting of 95% primary cellulose from softwood with a Kappa number of 41 and 5% primary cellulose from hardwood with a Kappa number of 40 was first subjected to high consistency beating with a beating capacity of 190 to 210 kWh/t, wherein the degree of beating of the cellulose after high-consistency beating was 19° SR and this cellulose was then subjected to low-consistency beating with a beating capacity of 70 to 80 kWh/t. The auxiliary materials were added into the constant part of the paper machine. The pH was adjusted to a pH of 6.8 to 7.0 with aluminium sulphate, cationic starch having a degree of cationization DS of 0.03 was added absolutely dry in an amount of 14 kg/t of paper and alkenyl succinic anhydrides were used as the sizing agent in an amount of 0.8 kg/t kraft paper absolutely dry. Glyoxalated PAM with 10 kg/t absolutely dry kraft paper was used as the wet strength agent. Furthermore, no fillers were added. The consistency of the cellulose at the headbox was 0.23%. The dewatering was carried out on a Foudrinier wire section and with a press section with three nips, wherein one of these can be a shoe press, wherein the line pressure at the three nips is 60 kN/m, 90 kN/m and 500 kN/m (in the shoe press). The kraft paper is pre-dried and then treated in a Clupak system with a differential speed of −8.6% and finally dried to an ultimate final moisture content of 7.5%
The kraft paper can be used as such and the paper properties described in the following table were measured with this paper.
The kraft paper thus produced had the following properties:
An unbleached cellulose consisting of 95% primary cellulose from softwood with a Kappa number of 41 and 5% primary cellulose from hardwood with a Kappa number of 40 was firstly subjected to high-consistency beating with a beating capacity of 190 to 210 kWh/t, wherein a degree of beating of the cellulose after high-consistency beating was 19° SR and then this cellulose was subjected to low-consistency beating with a beating capacity of 70 to 80 kWh/t. The auxiliary materials were added into the constant part of the paper machine. The pH was adjusted to a pH of 6.8 to 7.0 with aluminium sulphate, cationic starch with a degree of cationization DS of 0.03 was added absolutely dry in an amount of 14 kg/t of paper and alkenyl succinic anhydrides were used as the sizing agent in an amount of 0.8 kg/t kraft paper absolutely dry. Glyoxalated PAM with 10 kg/t absolutely dry kraft paper was used as the wet strength agent. Furthermore, no fillers were added. The consistency of the cellulose at the headbox was 0.23%. The dewatering was carried out on a Foudrinier wire section and with a press section having three nips, wherein one of which can be a shoe press, wherein the line pressure at the three nips was 60 KN/m, 90 kN/m and 500 kN/m (in the shoe press). The kraft paper is pre-dried and then treated in a Clupak system with a differential speed of −8.6% and finally dried to an ultimate final moisture content of 7.5%.
The kraft paper can be used as such and the paper properties described in the following table were measured with this paper.
The kraft paper thus produced had the following properties:
An unbleached cellulose consisting of 100% primary cellulose from softwood with a Kappa number of 46 was first subjected to high-consistency beating with a beating capacity of 210 to 220 kWh/t, wherein a degree of beating of the cellulose after high-consistency beating was 18° SR and this cellulose was then subjected to low-consistency beating with a beating capacity of 70 to 85 kWh/t. The auxiliary materials were added into the constant part of the paper machine. The pH was adjusted to a pH of 6.8 to 7.0 with aluminium sulphate, cationic starch with a degree of cationization DS of 0.05 was added in an amount of 12 kg/t of kraft paper absolutely dry and alkenyl succinic anhydrides were used as sizing agent in an amount of 0.8 kg/t of kraft paper absolutely dry. Furthermore, talc was added as a filler in an amount of 2 kg/t of kraft paper absolutely dry. The consistency of the cellulose at the headbox was 0.25%. The dewatering was carried out on a Foudrinier wire section, such as a press section with three nips, wherein the line pressure at the three nips was 60 kN/m, 80 kN/m and 80 kN/m, respectively. The kraft paper was pre-dried, then fed to the Clupak system and subjected to a differential speed of −10.9%, then finally dried to a final residual moisture content of 8%.
The kraft paper can be used as such and the paper properties described in the following table were measured with this kraft paper.
The paper thus produced had the following properties:
It is needless to say that the kraft papers according to the invention can additionally be calendered, for example in a soft nip or long nip calender, or in particular can also be subjected to a coating treatment, such as a dispersion coating treatment with a thermoplastic material, such as HDPE, LDPE, PLA or PP. With such further treatments, however, the essential properties of the packaging material, such as elongation at break, Bendtsen roughness, tear length, tear index, tensile strength index, are not changed, in particular do not deteriorate. If there is a loop or sleeve further manufactured from the packaging material, care must be taken to ensure that the packaging material is arranged such that the original machine direction is arranged such that an increase in diameter or stretching of up to 20% of the sleeve or loop is possible in the event of a stretching stressing of the sleeve. By means of a coating optionally applied on one or both sides of the sleeve, the way in which the free ends of the packaging material forming the loop or sleeve are connected, can be changed. In particular, in such a case, a thermal sealing of the free ends is carried out. Without a coating, the free ends can be connected by gluing, clipping, crimping or even sewing or the like. In the case of a packaging material that is coated on one side, a connection using hot glue, hot melts or the like can also be provided. In the case of packaging materials coated on both sides, a direct connection of two coating layers is in particular provided, which can be achieved with an extremely small expenditure of time.
Multi-layer packaging materials are preferably formed as laminates consisting of at least one kraft paper layer, preferably several kraft paper layers and at least two coating layers consisting of a polyolefin, in particular HDPE, LDPE or PP or PLA.
Example 5 shows a laminate consisting of an unbleached kraft paper layer (KP) with a grammage of 120 g/m2 and an outer coating layer made of HDPE with a grammage of 15 g/m2 on both surfaces of the base paper. The kraft paper was produced as described in Example 3. An extrusion coating process was used as the coating process. The laminate formed therefore has the following structure: 15 g/m2 HDPE/120 g/m2 KP/12 g/m2 HDPE.
The laminate thus produced had the properties described in the following table.
Example 6 shows a laminate consisting of 3 kraft paper layers (KP), each having a grammage of 120 g/m2 and both an outer coating layer made of LDPE with a grammage of 15 g/m2 and an LDPE coating between two kraft paper layers with a grammage of 12 g/m2. The kraft paper was produced as described in Example 3. An extrusion coating process was used as the coating process. The laminate formed therefore has the following structure:
The laminate thus produced had the properties described in the following table.
Furthermore, it is possible to replace one or all of the polyolefin or polylactic acid layers arranged between two layers of paper with a glue and thereby create a firm cohesion of the individual layers forming the laminate. In this case, however, it is essential that the two outer coating layers are made of a polyolefin or PLA.
A band produced from such a laminate could, on the one hand, be used on conventional strapping machines and, above all, heavy and bulky objects can be held together or packaged therewith without fear of the band tearing. A band produced from such a laminate could therefore be used as a replacement for a conventional strapping band manufactured entirely of plastic.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21202532.4 | Oct 2021 | EP | regional |
| GM50152/2022 | Sep 2022 | AT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/078524 | 10/13/2022 | WO |
