PLASTIC WOVEN LAMINATE, BAG MADE THEREFROM, METHOD OF MAKING SAME

Abstract

A plastic laminate has a plastic fabric formed from woven-together film strips of a plastic containing an additive that increases the absorption of laser radiation and an outer film bonded to the fabric and having at least one first film layer formed of a plastic that is free of laser-absorbing additive.

Claims

1. A plastic laminate comprising: a plastic fabric formed from woven-together film strips of a plastic containing an additive that increases the absorption of laser radiation; and an outer film bonded to the fabric and having at least one first film layer formed of a plastic that is free of laser-absorbing additive.

2. The plastic laminate defined in claim 1, wherein the film strips contain the laser-absorbing additive over their total thickness.

3. The plastic laminate defined in claim 1, wherein the film strips each have a multilayer structure, the laser-absorbing additive being in only some of the layers of the film strips.

4. The plastic laminate defined in claim 3, wherein each of the film strips is comprised of at least: a core layer containing the laser-absorbing additive; and two outer cover layers that are free of the laser-absorbing additive and that sandwich the core layer.

5. The plastic laminate defined in claim 4, wherein the strip fabric is severed completely along a score line and one of the cover layers is intact.

6. The plastic laminate defined in claim 1, further comprising between the outer film and the strip fabric: an extrusion laminated intermediate layer directly connected to the strip fabric between same and the outer layer.

7. The plastic laminate defined in claim 6, wherein a score line completely severs the strip fabric and ends in the intermediate layer.

8. The plastic laminate defined in claim 1, wherein the one first film layer and the strip fabric are formed from polypropylene.

9. The plastic laminate defined in claim 1, wherein the outer film is on one face of the strip fabric, the laminate further comprising: an inner film has a sealing layer on its side opposite the strip fabric on ab opposite second face of the strip fabric.

10. The plastic laminate defined in claim 1, wherein the laser-absorbing additive contains talc or layered silicates.

11. A packaging bag of the woven plastic laminate according to claim 1, wherein the outer film is on an outer surface of the bag.

12. A method of making a woven plastic laminate comprising the steps of: polypropylene containing a laser-absorbing additive is extruded to form a polypropylene film; orienting the polypropylene film and cutting it into film strips; weaving the film strips to form a strip fabric sheet; laminating the strip fabric sheet by extrusion with an outer film sheet comprising at least one first film layer that is free of laser-absorbing additive to form a woven plastic laminate sheet; and forming a score line by radiation using a laser such that the strip fabric sheet is at least partially destroyed along the score line.

13. The method defined in claim 12, wherein the score line is formed as a tear line such that it extends transversely between opposing edges over the entire width of the woven plastic laminate sheet.

14. The method defined in claim 12, wherein the score line is formed to extend transversely between opposing edges only over a portion of a width of the woven plastic laminate sheet.

15. The method defined in claim 12, wherein the score line is formed with a CO.sub.2 laser.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0042] 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:

[0043] FIG. 1 is a perspective schematic sectional view of a woven plastic laminate for bags;

[0044] FIG. 2 is a section through a laminate according to the invention with a score line;

[0045] FIG. 3 is a view like FIG. 2 of an alternative embodiment of the invention;

[0046] FIG. 4 is a view of a woven plastic laminate sheet to form a side fold bag with different score lines; and

[0047] FIG. 5 shows an unfilled flat side fold bag according to the invention.

SPECIFIC DESCRIPTION OF THE INVENTION

[0048] As seen in FIG. 1 a woven plastic laminate for woven plastic laminate bags is formed of a strip fabric 2 formed from intersecting film strips 1 and an outer film 3. The strip fabric 2 and the outer film 3 laminated together by extrusion between them of an intermediate bonding layer 4 that directly engages both the strip fabric 2 and the outer film 3. As shown in FIG. 2, the outer film 3 is provided on its back face in contact with the intermediate layer 4 with an imprint 5 visible through the at least partially transparent outer film 3.

[0049] The individual film strips 1 forming the strip fabric 2 are made of oriented polypropylene (O-PP) to give the laminate a particularly high strength. Even in the event of local damage to the woven plastic laminate, tear propagation is prevented by the individual film strips 1.

[0050] Due to the combination with the outer film 3, the result is especially advantageous properties of the woven plastic laminate. The outer film 3 forms a smooth high-quality surface with the imprint 5 being optimally protected. Furthermore despite the woven structure of the strip fabric 2, an imperviousness of the woven plastic laminate is ensured by the outer film 3.

[0051] In practice there is the need when making woven plastic laminate bags to provide the woven plastic laminate with at least one score line 6 (see FIG. 2 below) in order to be able to tear the woven plastic laminate in a controlled manner in the production process or to expose an opening through which the bag's contents can be accessed or poured.

[0052] The problem is that this strip fabric 2 has an especially great stability. Furthermore as seen in FIG. 1 the strip fabric 2 is not flat. Instead the individual film strips 1 are interwoven so that there are local differences in layering. Whereas two film strips 1 are one above the other over most of the service area in the thickness direction, sometimes there is only one or even no layer of the strip fabric 2 at the transitions 7 and at corners or points of intersection 8 between the strips 1.

[0053] Whereas the woven plastic laminate can easily be punched through or cut completely, partial punching or cutting of the woven plastic laminate to produce a score line 6 not pass all the way through the workpiece is difficult. The score line 6 must be created in such a way that preferably the entire strip fabric 2 is severed or at least scored uniformly without excessive damage to the outer film 3 at the transitions 7 and points of intersection 8.

[0054] Against this background, according to the invention the strips 1 of the fabric 2 contain a laser-absorbing additive that increases the absorption of laser radiation whereas the outer film 3 includes at least one first film layer 9 that is free of such laser-absorbing additives. If the woven plastic laminate illustrated in FIG. 1 is then impinged with a laser beam of the appropriate wavelength, then only the strip fabric 2 is scored and preferably severed selectively without any damage at all to the first film layer 9 of the outer film 3. In particular, with regard to the creation of the score line, there is also no significant difference whether two layers of the strip fabric 2 are present locally or whether only one film strip 1 or no film strip 1 at all is present at a transition 7 or at a point of intersection 8.

[0055] According to a preferred embodiment of the invention, the woven plastic laminate is formed of polypropylene. The outer film 3 may consist only of the first film layer 9 of, for example, biaxially oriented polypropylene (BO-PP). For example, the layer thickness of the outer film may be between 15 and 80 m, and a comparatively low thickness of 18 m, for example, is sufficient in particular in forming the outer film 3 made of BO-PP.

[0056] The intermediate bonding layer introduced in the extrusion lamination may also be formed of polypropylene, for example, and will typically have a thickness between 15 m and 45 m. Alternatively, for better adaptation to the materials used, extrusion lamination may be performed by coextrusion, in which case then the total thickness of the jointly extruded layers may readily also be within the stated range of 15 m to 40 m. The resultant typical surface weight or grammage of the strip fabric 2 is between 50 and 70 g/m.sup.2.

[0057] FIG. 2 shows a woven plastic laminate with the strip fabric 2 and an outer film 3 provided with the back-face or reverse imprint 5 turned toward the strip fabric 2. In FIG. 2, extrusion lamination is performed by coextrusion, and the intermediate layer 4 is connected directly to the strip fabric 2 with an additional bonding layer 10 provided over the printing on the back or inner face of the outer film 3. The bonding layer 10 may be formed from a terpolymer as the adhesive, for example.

[0058] FIG. 2 shows a preferred embodiment of the invention, where a score line 6 is created by a laser. The score line 6 can easily be created in this strip fabric 2 because of the laser-absorbing additive in the film strips 1. The directly adjacent intermediate layer 4 is also heated by thermal heating of the strip fabric 2 and is easily notched. However, the score line 6 ends within the intermediate layer 4, that is does not cut all the way through it.

[0059] FIG. 3 shows an alternative embodiment of the woven plastic laminate, in which a multilayer inner film 11 that includes a sealing layer 12 is provided in addition to an outer film 3. The sealing layer 12 is on the outer face of the inner film 11 opposite the strip fabric 2 and forms an outer surface of the woven plastic laminate. In the illustrated embodiment, the inner film 11 includes not only the sealing layer 12 but also a barrier layer 13 that may be made of EVOH or polyamide (PA), for example. The barrier layer 13 is connected to the sealing layer 12 by an adhesive layer 14, such that the inner film may be formed by coextrusion, in particular blow film coextrusion.

[0060] To join the outer film 3 on the one hand and the inner film 11 on the other hand to the strip fabric 2, extrusion lamination by coextrusion is provided. First an intermediate layer 4 and then a bonding layer 10 are connected on both sides of the strip fabric 2.

[0061] FIG. 3 additionally shows a score line 6 that sores the strip fabric 2 and preferably even severs or cuts all the way through it. The score line 6 ends in the intermediate layers 4 sandwiching the fabric 2. Depending on the material, however, individual layers may also be furnished with a laser-absorbing additive if the woven plastic laminate is no longer tearable to a sufficient extent. At least the barrier layer 13 based on EVOH or PA has a greater absorption capacity in comparison with a conventional polyolefin such as polypropylene in particular at the wavelength of a CO.sub.2 laser so that the barrier layer 13 as well is also scored by a corresponding bombardment at least to a certain extent.

[0062] According to FIG. 4, the score line 6 is provided only in the strip fabric 2 and extends only into the intermediate layers 4 directly adjacent to it.

[0063] Within the scope of the invention, it is important that the outer film 3 includes at least the one first film layer 9 that is free of the laser-absorbing additive and that remains intact when impinged by a laser beam.

[0064] However, the possibility cannot be ruled out that a film layer is severed over the entire inner film 11 when the inner film 11 is merely optional within the scope of the invention.

[0065] FIG. 4 shows as an example a woven plastic laminate sheet used to subsequently produce a side-fold tubing from which individual blanks of side-fold bags can then be cut (cf. FIG. 5). In this context, FIG. 4 illustrates that different types of score lines 6 can be formed. Whereas one type of score line 6 extends over the entire width of the woven plastic laminate sheet to form a graduated tear line allowing individual bags to be separated from one another, a second type of score line 6 extends along the transverse direction between the opposing edges of the woven plastic laminate sheet to be able to form an opening in a packaging bag. In concrete terms, the corresponding score line 6 borders a finished area that can be cut out of the packaging bag and behind that there may be reclosable strip fastener, for example.

[0066] FIG. 5 shows, purely as an example, a flat packaging bag that is formed of the woven plastic laminate according to FIG. 4 and has not yet been filled, individual pieces being torn away along the score lines provided as tear lines after folding and closing the bag at the circumference