BOTTOM SACK

Abstract: This application introduces a paper sack with a sheath consisting of at least two paper layers, at least one of the ends of the sheath closed to form a rectangular plane bottom which bottom may have a filling valve on one gable. At the area of the gable side, at least two of the layers of the sheath are adhered together with a line of adhesive (5) or, if there is a filling valve on one gable of the bottom, at least two sheath layers are adhered together with a line of adhesive at the area of the point of contact of the edge side and the diagonal crease.

Description: Bottom Sack Field of the technology This invention relates to multi layer paper sacks which have plane bottoms closed by adhesion. Particularly the invention concerns the reinforcing of the bottom. Background to the technology It is known to manufacture paper sacks so that the mouth of a blank cut from a multi layer paper tube is folded as a rectangular bottom and the overlapping edges of the fold are adhered together. When making sleeve valve bags, both ends are closed and a filling valve is left between the folded paper layers on one gable of the bottom. Usually a separate bottom flap is further adhered on top of the bottom. Description of the invention A multi layer paper sack according to claim 1 has now been invented. Some of the preferred embodiments of the invention are presented in the other claims. According to one embodiment of the invention, at least two sack layers are adhered together at the area of the gable side of the bottom. According to a further embodiment of the invention, the sack layers are adhered together at the area of the valve corner of a sleeve valve bag. According to the invention sack durability can be essentially improved without addition of paper. Some of the embodiments of the invention are described in more detail in the following. In the drawings of the description, figure 1 represents a flattened sleeve valve bag according to the invention, figure 2 shows the manufacture of a sack according to the invention, and figure 3 shows the reinforcing of the valve of a sleeve valve bag according to the invention. A sack according to figure 1 is made of two or more paper webs by folding and adhering the edges together to form a tube. The tube is cut into pieces and both ends are closed to form a rectangular bottom with shorter gable sides 1 and longer edge sides 2. The bottoms are closed by adhesion so that the sheath is first folded inwards along the gable sides and then on top of these folds along the edge sides and the folds of the edge sides are adhered together. Also the folds are adhered together except on one corner of the bottom where a filling valve opening 3 is left. Furthermore, on top of the bottom a bottom thread 4 / 4' is adhered. Finally the bottoms are folded from the middle against the sack sheath in the direction of the long side and the sheath is flattened. Furthermore, along the gable sides 1 of the bottoms at least two paper layers of the sheath are adhered together with seams 5. The width of the seams is, e. g., 1 - 3 cm. An adhesive seam thus located is known to essentially reinforce the sack. Sacks according to the invention can be manufactured on conventional sack production lines. Figure 2 shows the manufacture of a three-layer sack using a conventional line printing machine of a production line. The inner layer is formed from web 6, the middle layer from web 7 and the outer layer from web 8. The webs are run on top of each other and then taken to a sack machine where a tube is formed by adhering the edges together, then the tube is cut into pieces and the ends are closed to form plane bottoms. The inner layer web is run through a brush roll 9, an upper creasing roll 10 and a control roll 11. On the surface of the brush roll is a plate 12 which is used for applying transverse lines of adhesive on the outer surface of the web at regular intervals in the area where the gable edges of the bottoms will be. To the brush roll the adhesive is brought from a basin 13 with the help of a lift roll 14 and a wipe roll 15. Instead of using the entire roll, the adhesive may naturally be applied by using only a rotating segment of a roll. The adhesive is applied on the surface of web 6 without pressing essentially so that it does not penetrate the paper. The creasing roll 10 can be moved which enables the adjusting of web tension and its angle against the brush roll 9. This way the pressing can always be carried out optimally. The applying of adhesive as described can be carried out in a so called line printing unit conventionally used in sack lines. However, when the printing unit is used conventionally for printing, roll 1 1 is pressed against roll 9. Such a printing unit 16 is also included in the equipment according to figure 2. It is used for printing a desired pattern of one colour on the outer layer web. The equipment also comprises a third printing unit 17 which is used for printing another colour. If wanted, this unit can also be transformed into a unit for applying the adhesive enabling the adhesion of the outer layer and the middle layer together as well. The adhesion units are naturally synchronized with the sack machine so that the line of adhesive is always placed synchronized on the area of seaming and cutting. Adhesion according to the invention can also be carried out in a transversal adhesion unit of a tube extrusion machine. Sacks according to the invention can be made using thinner paper or fewer layers (e.g. 2 * 80 g / m^) which will reduce material costs. In some filling machines, the sacks hang on the filling spout so that they lean either entirely or partially against the valve corner during filling, which easily results in the breaking of the valve. According to the present invention, also the valve structure can be reinforced. This is achieved by adhering the paper layers together in the valve gable of the bottom at the point of contact of the bottom crease and the diagonal crease. Figure 3 represents a tube on which a valve reinforcing adhesive 18 has been applied. The adhesive is located at the point of contact of the bottom crease 19 and the diagonal crease 20. The size of the line of adhesive is approx. 4 * 4 cm. Example 1 For the purposes of the research, two-layer sleeve valve bags according to the invention (measures: I 44 * 38 * 10 and II 62 * 50 * 10 cm) were manufactured from sack paper (basis weight of papers 70 g / m^). Along the gable sides of the bottom, the paper layers of the sack were adhered together with a starch adhesive. The sacks were filled with cement (21 and 44 kg) and their durability was tested by dropping them on their flat sides. For comparison, the same drop test was carried out with conventional sacks made of the same paper without adhesion of the gable sides of the bottom. The following table shows how many drops the sacks on the average (5 sacks) could endure when dropped from different heights. Sack Dropping height / cm Average number of drops Invention I 1 10 23.4 130 21.2 160 1 1.0 Invention II 130 28.8 Comparison I 1 10 7.0 130 6.0 160 2.6 Comparison II 130 7.8 It can be noticed that when the paper layers were adhered together the durability of the sack was essentially improved. When the sacks according to the invention are dropped on their flat side, the maximum tension forms on the corner areas of the sacks. Example 2 For the purposes of the research, two-layer sleeve valve bags (measures: 62 * 50 * 10 cm, filled weight approx. 50 kg) were manufactured from sack paper (basis weight of papers 90 g / m^). The paper layers were adhered together at the point of contact of the bottom crease and the diagonal crease on the valve gable of the bottom. The sacks were hung from the valve on the filling spout of a filling machine, and the loading capacity of the sacks was tested to see how much load the sack could endure before the valve corner was broken. The sacks according to the invention tolerated an average 130 kg. Conventional, unadhered sacks tolerated 40 kg.

Claims: Claims 1. A paper sack with a sheath consisting of at least two paper layers, at least one end of which sheath is closed as a rectangular plane bottom with shorter gable sides and longer edge sides, which bottom may have a filling valve on one gable, characterized in that at the area of the gable side at least two of the sheath layers are adhered together with a line of adhesive (5) or that, if there is a filling valve on one gable of the bottom, at least two sheath layers are adhered together with a line of adhesive (18) at the area of the point of contact of the edge side and the diagonal crease. 2. A method for making a paper sack, in which method a sheath consisting of at least two paper layers is formed and into the sheath a rectangular plane bottom with shorter gable sides and longer edge sides, and on one gable of the said bottom a filling valve may be formed, characterized in that at least two sheath layers are adhered together at the area of the gable side of the bottom or that, if a filling valve is formed on one gable of the bottom, at least two sheath layers are adhered together at the area of the point of contact of the edge side and the diagonal crease. 3. A method according to claim 2, in which method a sheath is formed of at least two paper webs which are run on top of each other and arranged and joined from their edges together to form a tube, characterized in that to adhere the layers a line of adhesive is applied to the desired location on at least one paper web on that surface which will be placed against another paper web so that the adhesive remains on the surface of the web and does not penetrate the paper. 4. A method according to claim 3, characterized in that the line of adhesive is applied with a rotating roll.

Inventors: RIKASSAARI PENTTI, SIEVERS VALTER, RIKASSAARI, PENTTI, SIEVERS, VALTER
Applicants: UPM KYMMENE OY, UPM-KYMMENE OY
Application year: 1996
Main classification: B31B39
IPC codes: B31B39, B65D30