Valve Bag

Abstract

The invention relates to a vented bag comprising a tubular vent that is secured in a folded base. Said vent comprises an upper face (4) that lies flat on a lower face (2) and consists of a base material that is provided with a weldable layer. The aim of the invention is to obtain a stable connection between the base material and the weldable layer. To achieve this, the weldable layer consists of a polyvinyl alcohol with a saponification degree ≧75%, which is applied to the base material in the form of an aqueous emulsion and is then dried.

Description

The invention relates to a valve bag with a tubular valve fastened in a folded bottom with an upper side lying flat on a lower side and comprised of a base material provided with a weldable layer.

Valve bags are conventionally fabricated with a folded bottom, for example a star seal bottom, wherein bottom flaps extend over a turned-in corner. In the interspace formed between the turned-in corner and the bottom flaps a valve is fastened, which is conventionally comprised of a base material folded in the longitudinal direction of the bottom, the valve having an upper side and a lower side connected via longitudinal fold lines. In the closed state the valve consequently lies flat in the bottom until the bag is filled, for example by means of a filling tube, when it is spread apart from the outside of the bag and thus permits the filling of the interior of the bag. The valve effect of the valve results from the fact that the filling material of the bag pushes against the bottom and thereby presses the lower side of the valve against the upper side of the valve such that the valve is closed.

Since it is possible for some of the material to trickle out or escape in the form of dust while it is being filled into the bag, it is known to provide the base material of the valve with a weldable layer and to weld the upper side to the lower side of the valve through thermal, ultrasound or electromagnetic high-frequency effect. The application of the weldable layer onto the base material routinely takes place by adhering or melting on a sheet of a weldable material. For this purpose a sheet of polyvinyl alcohol can also be utilized. However, the problem is encountered that the connection between the sheet and the base material, most often comprised of paper, does not withstand all loadings, such that under high loading the sheet becomes detached from the base material and cancels the effect of the welding.

The invention addresses the problem of improving the closure of a valve bag with a valve such that the closure is capable of withstanding even high loadings.

For the solution of this problem, a valve bag of the above described type is characterized according to the invention in that the weldable layer is comprised of a polyvinyl alcohol with a degree of saponification ≧75%, applied in the form of an aqueous emulsion onto the base material and dried.

According to the present invention, as the weldable layer a polyvinyl alcohol is utilized, which, however, is not applied in the form of a sheet onto the base layer, but rather as an aqueous solution resulting in good anchorage of the polyvinyl alcohol layer formed during the drying on the base material, preferably formed by paper, which even in the case of kraft paper is routinely stronger than the cohesion of the base material. Attempts at separating the polyvinyl alcohol layer from the base material consequently leads to the tearing of the base material. A preferred degree of saponification of the polyvinyl alcohol utilized according to the invention, is >85%. The saponification degrees of the polyvinyl alcohol according to the invention are thus markedly higher than that of the polyvinyl alcohol sheets previously used for the production of a weldable layer.

When utilizing the invented weldable layer formed by drying of the polyvinyl alcohol emulsion, it should be noted that the weldable layer becomes emulsifiable again if exposed to water, such that the layer becomes adhesive again and can bring about the unintended connection with the corresponding opposing layer or the opposing base material. If, due to exposure to moisture, this risk exists, it is advisable to insert a protective sheet between the upper side and lower side of the valve. This protective sheet is preferably removable before the valve bag is filled, for example manually through an actuation extension or a handling grip.

In a preferred embodiment the protective sheet is comprised of two layers with a folding directed toward the inside of the bag, the two layers of the protective sheet at their free ends directed away from the folding, thus oriented toward the outside of the bag, being fastened on the upper side or the lower side of the valve. Adhesion over a small adhesion area is sufficient for this purpose. Such a protective sheet is detached from the valve by the tip of the filling tube, if such a filling tube is utilized for filling the valve bag, and the protective sheet is pushed into the interior of the bag so that the valve is open for filling the valve bag.

In the following the invention will be described in further detail in conjunction with an embodiment example shown in the drawing. Therein depict:

FIG. 1 a perspective view of a valve foldable into a tubular form with a double-layered protective sheet,

FIG. 2 a schematic illustration of the valve according to FIG. 1 set into a valve bag and its use when filling the bag with a filling tube.

FIG. 1 shows a sheet of which a valve 1 is folded, in that from a lower side 2 via two longitudinal fold lines 3 two flaps forming the upper side 4 are folded over onto the lower side 2 in such manner that they slightly overlap one another. The faces of lower side 2 and upper side 4 visible in FIG. 1, which, after they are folded over, are opposing one another, are coated with a layer of polyvinyl alcohol. The coating takes place with an aqueous emulsion of the polyvinyl alcohol with a saponification degree of 88%.

The emulsion has a solids content of 30%, a pH value of 6±1 and a viscosity of 2500±500 (Brookfield method).

After the emulsion has dried, the application quantity of polyvinyl alcohol amounts to 40 g/m². The dried layer is elastic and clear and can be welded in the conventional manner, thus with hot air, heated welding gun, with ultrasound, etc. The welding is also possible with moisture and brief pressing. The coating can be re-emulsified without residue and thereby makes the material suitable for recycling without encountering any problems.

In FIG. 1 a protective sheet 5 inserted into valve 1 is evident, which is formed of two layers, and has a lower layer 6 and an upper layer 7 connected with one another via a fold line 8 directed toward the interior of the bag transversely to the longitudinal direction of valve 1, such that the layers 6, 7 have two free edges 9, 10, directed toward the opening of valve 1 oriented toward the exterior of the bag.

FIG. 2 elucidates a valve 1 set into a bag wall 11, which valve is opened through opposite curving of lower side 2 and upper side 4 and in this state makes possible the introduction of a filling tube 12. The filling tube 12 is provided at its end with an encircling swelling hose 13, through a sealing which can be established between the filling tube 12 and the valve 1 for the filling process in order to prevent the filling material from escaping in the form of dust from valve 1.

In FIG. 2 is evident that the protective sheet 5 closed with the folding line 8 toward the interior of the bag wall 11 is fixed in place with the free front ends 9, 10 on the upper side 4 or lower side 2 of valve 1. This fastening is released through the introduction of the filling tube 12 into valve 1, since the front tip of the filling tube 12 abuts the protective sheet 5 closed via the fold line 8 and pushes it into the interior of the bag during the further introduction of the filling tube 12 into the valve 1. Consequently, the protective sheet 5 is removed for the filling process and thus does not interfere during the filling nor during the subsequent welding of upper side 4 and lower side 2 with one another.

If no double-layered protective sheet 5, such as is depicted in the drawing, is utilized, a simple protective sheet also enables the protective function against the unintended adhering of lower side 2 and upper side 4 of valve 1, if the protective sheet 5 is provided with a suitable handling grip or a suitable extension which projects from the valve 1 and makes possible pulling the protective sheet 5 out of the valve 1 before the bag is filled.

Claims

1. Valve bag with a tubular valve (1) fastened in a folded bottom, with an upper side (4) lying flat on a lower side (2) and comprised of a base material provided with a weldable layer, wherein the weldable layer is comprised of a polyvinyl alcohol with a saponification degree ≧75% applied in the form of an aqueous emulsion onto the base material and dried.

2. Valve bag as claimed in claim 1, wherein between upper side (4) and lower side (2) a protective sheet (5) is inserted.

3. Valve bag as claimed in claim 2, wherein the protective sheet (5) is comprised of two layers provided with a folding (8) directed toward the interior of the bag, and that the two layers (6, 7) of the protective sheet (5) are fastened on their free ends (9, 10) facing away from the folding (8) on the upper side (4) or the lower side (2) of the valve (1).

4. Valve bag as claimed in claim 1 wherein the base material is paper.

5. Valve bag as claimed in claim 1 wherein the saponification degree of the polyvinyl alcohol is ≧85%.

6. Valve bag as claimed in claim 5, wherein the saponification degree of the polyvinyl alcohol is 88%.