TIGHTENED SACK

Abstract: The invention relates to paper sacks and applies to the sealing of the paper sack mouth which is closed by glueing. According to the invention a cut is formed on the end flap (5), reaching from the side creasing (6) to the diagonal creasing (3), and the additional flap (11) thus formed on the side flap is folded open before the side flap is folded against the end flap. The flaps can be pressed against each other as tightly as possible also by the side fold. The invention can be utilized for both open-mouth sacks and sleeve valve bags and it can be realized with conventional sack manufacturing methods.

Description: TIGHTENED SACK FIELD OF TECHNOLOGY This invention relates to paper sacks, and applies to the sealing of a paper sack mouth which is closed by glueing. The invention can be utilized for both open- mouth sacks and sleeve valve bags, and it can be realized with conventional sack manufacturing methods. BACKGROUNDOFTHETECHNOLOGY When manufacturing paper sacks, a hose is formed of the paper web and cut into parisons ofthe desired length, and either one end or both ends are closed to form the bottom. If both ends are closed, a topping-up valve is left on the bottom between the flaps folded one upon another. The bottom is usually closed by first folding inwards the thinner end flaps and. on top of these, the wider side flaps. Before the side flaps are folded, glue sectors are formed; end glue sectors which help attache the side flaps to the end flaps, and side glue sectors which help attache the edge of one side flap to the other side flap. One of the problems with paper sacks is the tightness of the bottom. Especially the folding point between the side flap and the end flap is critical. In multi-layer sacks, tightness can be improved by forming longer inner layers to the closable end, as a result of which the layer edges overlap (so-called step-end bottom). However, for material reasons it is not advantageous to overlap the layers of two- layer sacks. A simpler solution for multi-layer sacks is a so-called semi- overlapping bottom where the inner layer is longer by the end flaps and the uppermost side flap. Often neither of these methods produces satisfactory tightness. Furthermore, directing problems may arise in the production as a result of which the machine must be run relatively slowly. Tightness can be improved also by glueing a separate sealing piece between the flaps. This, however, requires a separate unit for the machine and can therefore not be realized with production lines already in use. DESCRIPTION OF THE INVENTION General Description A paper sack according to claim 1 has now been invented. Preferred embodiments of the invention are presented in the claims. What is essential in the invention is that on the closable end of the parison, an introspective helical cut is formed on the end flap from the side creasing to the diagonal creasing of the end flap, and the additional flap thus formed is folded open before the side flap is folded against the end flap. With the help of the end glue sector, the flaps can be pressed against each other as tightly as possible also by the side fold. The invention can be realized with a bottom machine of a conventional sack production line without any additional units. Extra material is not required. Drawings The attached drawings are a part of the detailed description of the invention. Ln the drawings - Fig. 1 presents the closable mouth ofthe sack parison, with the creasings marked by dashed line, - Fig. 2 presents the mouth with the flaps partly folded and - Fig. 3 presents the mouth with the flaps completely folded. Detailed description The end of a parison cut from the paper hose is closed with a so-called bottom machine. It is used to form the diagonal creasings (3) from the parison edges (1 ) to the end (2) and a horizontal centre creasing (4), to fold the end flaps (5) of the bottom inwards along the diagonal creasings. to form the horizontal side creasings (6), to form the necessary end glue sectors (7) and side glue sectors (8) and to fold along the side creasings the side flaps (9 and 9') on top of the end flaps. (For the sake of clarity, all creasings are illustrated by dashed line in Fig. 1, even if not all of them would be formed in the early stages.) Usually a so-called bottom piece is glued on top of the bottom (not illustrated). End glueing is not formed on the valve end of a sleeve valve bag, as a result of which the space between the folded flaps remains open, forming a topping-up valve. To seal the valve it is possible to make a longer end flap on the valve end, or glue an additional flap on top of the end flap to add length. According to the invention, a cut (10) is made on the end flap (5) of the parison inwards from the end (2) of the parison and the side creasing (6), towards the longitudinal axis of the parison, reaching to the diagonal creasing (3). Sharp- pointed additional flaps (11) thus formed on the end flaps (5) are folded outwards along the diagonal creasings (3). The best way to make the cut is by the end of the side creasing (6) perpendicularly to the diagonal creasing. The end glue sector (7) is formed on the inner surface of the side flap and the exterior surface of the end flap so that it reaches from the tip of the additional flap along the exterior edge (12) of the cut, over the inner edge (13) of the cut and along the exterior edge of the end flap to the side creasing (6). The inner edge of the end glue sector is parallel with the longitudinal axis of the parison. The side glue sector (8) is formed on the inner surface of the end of the uppermost side flap (9') so that the aforesaid side flap when folded adheres to the side flap (9) underneath. When the side flaps (9) and (9') are folded and pressed against the end flap (5), the end glue sector (7) is pressed between the fold so that it seals the bottom well also by the side creasing (6) where the fold has exteπor surface against exterior surface. Furthermore, in multi-layer sacks glue pushes through the diagonal inner edge (13) of the cut sealing the layers, thus preventing the penetration of packaged material between the layers. Material between the layers decreases the strength of the sack. Additional flaps (1 1) formed on the bottom cause no disadvantages, and normally they are covered by the bottom piece. Ln fact, the additional flaps even strengthen and reinforce the sack. The strength of multi -layer sacks according to the invention can be further improved by glueing layers together at certain points. Cπtical points include especially the end edge and end angles ofthe bottom of a filled sack. Fig. 1 shows the glue sectors (14) and (15) added between the paper layers to reinforce these areas. The invention can be utilized in the manufacture of one-layer and multi-laver sacks. Preferably the sacks are two-layer sacks. If wanted, the layer ends of multi-layer sacks can be fitted to overlap as appropriate to further improve tightness. Sacks according to the invention can be manufactured with conventional sack production lines already in use. The helical cut (10) can be easily realized with conventional tools with a bottom machine in connection to creasing. The end glue sector (7) can also be easily brushed in the desired shape with conventional distributor rolls. No extra material is required in the production, and the production is not essentially slowed up.

Claims: CLAIMS 1. A sealed paper sack with a bottom closed by glueing, which has end flaps (5) folded inwards along the diagonal creasing, and side flaps (9, 9') folded on top of the end flaps along the horizontal side creasing, characterized in that the end flap has a cut (10) reaching from the side creasing (6) to the diagonal creasing (3). and that the additional flap (11 ) thus formed on the side flap (9) has been folded open before the side flap has been folded against the end flap. 2. A sack according to claim 1 , characterized in that the cut (10) reaches from the end of the side creasing (6) perpendicularly to the diagonal creasing (3). 3. A sack according to claim 1 or 2, where the side flap (9, 9') is attached to the end flap (5) with an end glue sector, characterized in that the end glue sector (7) goes from the side flap (9, 9') over the inner edge ( 13 ) of the cut to the end flap (5). 4. A method for making a sealed paper sack, the method including the forming of a hose from the paper web, the cutting of the hose into parisons. the folding of end flaps inwards along the diagonal creasing and on top of these the side flaps along the horizontal side creasing, characterized in that the cut reaching from the side creasing to the diagonal creasing is formed on the end flap, and that the additional flap thus formed is folded open before the side flap is folded against the end flap.

Inventors: RIKASSAARI PENTTI, SIEVERS VALTER, RIKASSAARI, PENTTI, SIEVERS, VALTER
Applicants: UPM KYMMENE OY, UPM-KYMMENE OY
Application year: 1996
Main classification: B65D30
IPC codes: B65D33