Method of making a woven plastic bag

Abstract

A woven plastic bag is made by longitudinally feeding flat-lying fabric web having a layer of woven-together plastic strips on a first face, opposite longitudinal edge regions spaced transversely from each other and each extending over about 10% of a transverse width of the fabric web, and a middle section between the longitudinal edge regions. A pattern is applied the first face of the fabric web in a pattern that repeats along the production direction only locally with a coating in the form of a film or in the form of a liquid plastic of a width or shape that varies transversely, and the fabric web is shaped into a fabric tube. In order to form individual woven plastic bags, the fabric tube is cut transversely into pieces of the fabric tube suitable for subsequent filling and sealing.

Claims

1. A method of making a woven plastic bag, the method comprising the steps of: feeding in a longitudinal production direction a flat-lying fabric web having a layer of woven-together plastic attachment strips on a first face, opposite longitudinal edge regions spaced from each other perpendicular to the production direction along a transverse direction and each extending over only part of a transverse width of the fabric web, and a middle section between the longitudinal edge regions; applying to the first face of the fabric web a pattern that repeats along the production direction only locally with a coating in the form of a film or in the form of a liquid plastic of a width or shape that varies in a transverse direction; shaping the fabric web into a fabric tube; in order to form individual woven plastic bags, cutting the fabric tube transversely into pieces of the fabric tube suitable for subsequent filling and sealing; connecting together mutually opposite surfaces of the bag wall with the coating along at least one joint seam that extends transversely; and forming the joint seam with at least one step in the transverse direction such that a dimension of the joint seam determined in a longitudinal direction changes at the step.

2. The method defined in claim 1, wherein the coating is applied as a first section and a second section adjacent thereto along the transverse direction, the first section having a first dimension in the production direction and the second section having a greater second dimension.

3. The method defined in claim 1, wherein the coating is applied at least in sections at an acute angle with respect to the production direction and the transverse direction.

4. The method defined in claim 1, further comprising the step, after shaping of the web into the fabric tube, of: fusing the coating to form a connection within the fabric tube between superimposed layers of the fabric web.

5. The method defined in claim 1, wherein the web is shaped into a side-gusset tube.

6. The method defined in claim 1, wherein the coating is applied in a liquid state with the pattern.

7. The method defined in claim 1, further comprising the step of: imparting to the joint seam a first dimension in the longitudinal direction at a first joint seam section starting from one of the lateral bag edges extending in the longitudinal direction and a greater dimension at a second joint seam section adjacent thereto at the step.

8. The method defined in claim 7, further comprising the step of: orienting the first joint seam section at an acute angle with respect to longitudinal and transverse directions of the wall or forming it with a bend.

9. The method defined in claim 1, wherein the fabric tube into which the fabric web is shaped has a front panel, a back panel, and first and second side gussets that connect the front panel and the back panel.

10. The method defined in claim 1, wherein the fabric tube into which the fabric web is shaped has a front panel, a back panel, and first and second side gussets that connect the front panel and the back panel and the step is on an edge of the first side gusset sandwiched between the front panel and the back panel.

11. The method defined in claim 10, wherein the first side gusset projects at a head region past the front and back panels.

12. The method defined in claim 11, further comprising the step of: forming a hand hole on the head region.

13. The method defined in claim 10, further comprising the step of: forming a notch in the front and back panels adjacent the first side gusset.

14. The method defined in claim 1, wherein an entire surface of the coating forms the joint seam.

15. The method defined in claim 1, wherein the joint seam is only extended into a portion of the coating.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

(2) FIG. 1 is an top elevational view of a flat-lying fabric web provided only locally with coatings;

(3) FIGS. 2 to 4 are views like FIG. 1 of embodiments of the coatings;

(4) FIG. 5 is an elevational view of a woven plastic bag that has been laid flat;

(5) FIG. 5A is a large scale view of the detail of FIG. 5 indicated at VA; and

(6) FIGS. 6 and 7 show optional embodiments of details of the woven plastic bag shown in FIG. 5.

SPECIFIC DESCRIPTION OF THE INVENTION

(7) As seen in FIG. 1 a fabric web 1 for making a woven plastic bag moves in a production direction P and has an upper face covered with an initially free and exposed layer 2 formed by woven-together plastic strips. The fabric web 1 is provided with strips or spots of localized coatings 3 on the woven layer 2.

(8) The coatings 3 can for example be formed by pieces of adhered film or a plastic applied in liquid form. Especially preferably, the coatings 3 are applied as a molten liquid plastic that can be extruded in a viscous state or applied by a transfer roller.

(9) Subsequently, the fabric web 1 and its coatings 3 are reshaped in a known manner into a tube. According to the illustrated embodiment, a side-gusset tube for forming side-gusset bags is made from the tubular fabric web 1 by folding along lines 4 and 4′ in the still flat-lying fabric web 1. The first fold lines 4 form the transitions from front or back panel 5a or 5b to side gussets 6a and 6b, and the two side gussets 6a and 6b are each folded onto themselves at respective second fold lines 4′. During manufacture, a fin weld is formed at the edges of the fabric web 1, for which reason another thermoplastic coating can also be provided there.

(10) FIG. 1 shows that the coating 3 also changes in the transverse direction Q outside of the edge regions in a middle section of the fabric web 1. Specifically, the coating 3 is subdivided into strips or segments 7 spaced apart in the transverse direction Q, the segments 7 extending over somewhat more than 50% of a width of the fabric web 1 in the transverse direction Q. If the fabric web 1 is reshaped along the fold lines 4 and 4′ into a side-gusset tube, surfaces then oppose each other at the level of the coating 3 over the entire width of the side-gusset tube, at least one of which is provided with a coating 3, so that a tight weld can be achieved by fusing together the coatings 3.

(11) The coatings 3 thus fulfill the purpose of an adhesive that is present in only a single layer and then connects faces to be joined of the woven layer 2. The illustrated embodiment therefore differs from an embodiment in which, according to the prior art, a continuous strip is provided as a coating that is then connected only to itself.

(12) FIG. 1 shows a cutoff line 8 running in the transverse direction Q at which individual pieces are then separated from the fabric tube. When the fabric tube is separated at the cutoff line 8, a head seam or a bottom seam can be produced on successive woven plastic bags with the coating 3 that is severed at that point.

(13) FIG. 1 shows the surface of the web 2 that forms the inner face of the finished bag. Thus side gussets are formed by first raising the web 1 at the side gusset seams 4′ to fold the regions 6a an 6b up and over onto the middle region 451, whereupon the outer regions 5b of the back panel are folded over on to the middle region and the folded together gusset regions 6a and 6b. The segments 7 thus allow a complete closure of the tube at both longitudinal ends at the cutoff lines 8, it being presumed that the longitudinal edges are welded together in the normal manner.

(14) FIG. 2 shows an alternative embodiment for the sake of example in which the coatings form different structures. In addition to a transversely continuous strip 7′ forming a bottom seam and embodied according to the prior art, an additional strip 7″ formed with steps 10 is provided to form a joint seam 9 (FIG. 5) at a head region of the woven plastic bag. The extension of the coating 3 along the production direction P, which also corresponds to a longitudinal direction L of the woven plastic bag in the embodiment, changes at the steps 10. In other words, the corresponding strip 7″ has a region along its course that has, at the side gussets, a lesser strip width and also runs at an acute angle. As will also be described below in relation to FIG. 5, this ensures that the section with a lesser strip width can easily be pulled open at the first side gusset 6a.

(15) Furthermore, FIG. 2 shows that other shapes, such as oblique shapes, for example, can also be formed with the coating 3 applied only in sections at which joint seams 9′ are subsequently formed in the form of corner joints.

(16) Finally, FIG. 3 shows a combination of the features of FIGS. 1 and 2 according to which the coating 3 is a segmented strip 7′″ that has gaps and also changes shape along the production direction P and thus also along the longitudinal direction L of the woven plastic bag to be produced. Here the strip 7′″ is of maximum thickness over most of the region corresponding to the face panel and one of the side gussets, but is divided into a medium-width strip and a parallel minimum-width strip in the other side gusset, flanking the cut line 8. The resultant bag therefore is solidly and continuously sealed closed at a bottom edge, but at a top edge is only lightly secured together by the minimum-width strip so it can be pulled apart and the bag's contents can be poured out of a spout formed by the pulled-out and separated gusset.

(17) In the embodiments according to FIGS. 1 to 3, it is possible to form joint seams 9 and 9′ (FIG. 5) on the coatings at the bottom of the side gussets to create a bag that can stand up.

(18) It is also possible, however, to apply a coating 3 over a greater surface and to then establish the shape of the joint seam 9 or 9′ subsequently according to the shape of a thermal welding tool or the like.

(19) According to FIG. 4, the coating 3 is thus formed on the woven layer 2 in the form of a rectangular spot, the oblique joint seams 9′ that are to be formed only later being indicated.

(20) The production of joint seams 9 and 9′ in only a portion of the coating 3 can also be provided without restriction in the head region of a woven plastic bag. For instance, starting from FIG. 2, a provision can be made that the coating 3 is applied as a wide strip running in the transverse direction Q, in which case the structures indicated in FIG. 2 are formed subsequently only by the shape of a thermal welding tool that has a narrower width than the coating it is applied to.

(21) Finally, FIG. 5 shows a woven plastic bag with a bag wall that has a plastic woven layer 2 as described above that is partially exposed at an inner surface of the woven plastic bag and partially covered by coatings 3 of plastic, and opposite surfaces of the bag wall are connected to each other with the coatings 3 along several joint seams 9, 9′.

(22) A joint seam 9 seals the woven plastic bag in the transverse direction Q. The joint seam 9 has a step 10 in the transverse direction Q, the height of the joint seam 9 determined along the longitudinal direction L changing at the step 10. Specifically, the joint seam 9 has a first dimension l.sub.1 in a longitudinal direction L at a first joint seam section 9a starting from a lateral bag edge 11 running in the longitudinal direction L and a larger longitudinal dimension l.sub.2 at a second joint seam section 9b adjacent thereto at the step 10. In other words, the width of the joint seam 9 changes at the step 10 along the transverse extent of the joint seam 9.

(23) Moreover, it can be seen that the first, narrower joint seam section 9a runs at an acute angle and is also provided with a bend 12. Due to the lesser width of the first joint seam section 9a, it can be pulled open by a user, whereas the second joint seam section 9b ensures a secure closure of the woven plastic bag. In order to pull the first joint seam section 9a open, a user can grip the first side gusset 6a and pull it outward.

(24) FIG. 5 also shows that the woven plastic bag can also have a hand hole 13 on its upper bag edge, the coating 3 optionally being omitted at the hand hole 13 but otherwise forming the seam 9.

(25) FIG. 5 also shows joint seams 9′ in the form of angle welds at the ends of the side gussets.

(26) Within the scope of the invention, the coating 3 can also be applied on the faces to be coated in an openwork coating pattern 14 as indicated in FIG. 5 formed by crossing but spaced lines of the coating.

(27) With regard to the structure of the joint seams 9 and 9′ illustrated in FIG. 5, it should be noted that this structure can be precisely established on application of the coating, particularly if a joint seam 9 or 9′ or several joint seams 9 and 9′ are formed on the entire surface of the coating 3.

(28) It is also possible, however, for the joint seams 9 and 9′ to be produced on only a portion of the coating 3. This then results in the advantage that somewhat larger regions can be coated during application of the coating without having to pay special attention to precision. As regards the shape of the joint seams 9 and 9′, several possible variations generally also exist in relation to such an approach.

(29) In order to make it easier to grip the first side gusset 6a in an embodiment according to FIG. 5, it can also be embodied according to FIG. 6 such that it extends beyond the front and rear panels 5a and 5b or at least the region of the front and rear panels 5a and 5b adjacent the first side gusset 6a.

(30) In addition, or alternatively, a notch 15 can also be provided in the front and rear panels 5a and 5b adjacent the first side gusset 6a in order to make the side gusset 6a easier to grip.