WELDING HEAD AND WELDING DEVICE

Abstract

The present invention relates to a welding head (10) for fastening an element made of plastic material to one or more flexible webs (2, 3) made of plastic material, of which a flexible container (1) is composed. The head (10) includes a body made of electrically and/or thermally conductive material having a work surface (15) that is provided for being pressed, during the welding operation, against an element of the unit to be joined. The invention is characterized in that the work surface (15) includes a series of grooves or concave formations (16) that are essentially uniformly distributed on the surface of the work surface (15).

Claims

1. A welding head for fastening an element made of plastic material to one or more flexible webs made of plastic material, of which a flexible container is composed, wherein the head comprises: a body made of electrically and/or thermally conductive material having a work surface that is provided for being pressed, during the welding operation, against an element of the unit to be joined, wherein the work surface includes a series of grooves or concave formations that are essentially uniformly distributed on the surface of the work surface.

2. The welding head according to the preceding claim, wherein the grooves or the concave formations have a maximum depth that is greater than or equal to the thickness of the web made of plastic material.

3. The welding head according to claim 1, wherein the grooves or the concave formations have a maximum depth that corresponds to the material thickness of the fastening collar, in particular between 0.5 mm and 1.5 mm.

4. The welding head according to claim 1, wherein the concave formations have a tetrahedral shape.

5. The welding head according to claim 1, wherein the body is made of metal, preferably copper or a copper-containing alloy, more preferably brass.

6. The welding head according to claim 1, wherein the welding head for welding a neck is adapted to the web made of plastic material, and the work surface has an open ring shape in its center.

7. (canceled)

8. A method for joining, by welding, a flexible web made of plastic material of which a container wall is composed, to a further element made of plastic material, in which the web and the further element are pressed together in the area of a joining zone between a hot work surface of a welding head and a contact surface of a counterhead, with heating of at least the joining zone to a temperature that is sufficient to ensure the weld, wherein the method is characterized in that at least the work surface of the welding head includes a series of grooves or concave formations that are essentially uniformly distributed on the surface of the work surface, so that the flow of molten plastic material out of the joining zone during the welding operation is prevented.

9. The joining method according to claim 8, wherein the further element is a neck that includes an annular connecting collar, and the work surface of the welding head has a ring shape that is essentially identical to that of the connecting collar of the neck.

10. A container that is flexible, at least in part, and that is formed by the joining by welding of elements that include at least one flexible web made of plastic material, wherein at least one welding zone has an essentially regular pattern that is formed by the alternation of concave and convex and/or light and dark regions.

11. The container according to claim 10, further including a neck made of plastic material that is welded to the flexible web via an annular collar, wherein the welding zone of the collar has an essentially regular pattern on the flexible web that is formed by the alternation of concave and convex and/or light and dark regions, and that at the flexible web is free of ridges on the outer side of the welding zone of the collar.

12. The container according to claim 11, wherein the container is a flexible tubular bag for storing in particular liquid, semiliquid, or powdered products.

13. The welding head according to claim 1, wherein the welding head is linked to a heat generator in an area of a welding zone that generates heat in the area of the work surface of the welding head.

Description

[0018] Furthermore, various additional characteristics of the invention arise from the appended description with reference to the drawings, which illustrate a nonrestrictive exemplary embodiment and application examples of the invention.

[0019] FIG. 1 shows a schematic perspective of a flexible container according to the invention which forms a tubular bag,

[0020] FIG. 2 shows a schematic exploded view of a web of which the container illustrated in FIG. 1 is composed, together with a neck,

[0021] FIG. 3 shows a schematic view of a device according to the invention for welding a neck made of plastic material to a flexible web made of plastic material,

[0022] FIG. 4 shows a perspective view of a welding head according to the invention,

[0023] FIG. 5 shows a top view of the welding head according to FIG. 4, and

[0024] FIGS. 6 and 7 show a sealtight weld produced using the welding head according to the invention, and the light and dark regions in the welding zone.

[0025] A flexible tubular bag made of plastic material for storing various products, as illustrated in FIG. 1 and denoted overall by reference numeral 1, is generally formed by joining two flexible webs 2, 3 made of plastic material, which are welded at their circumference. The flexible tubular bag 1 also includes a neck 4 that allows filling of the tubular bag and fitting of a spigot for tapping the contents. According to the illustrated example, the neck 4 is welded sealtight to the upper web 3, of which the tubular bag 1 is composed.

[0026] The operation for joining the neck 4 to the web 3 generally takes place before the two webs 2, 3 are joined together. To allow this connection, the neck 4, which has a tubular shaft with a generally cylindrical shape 5, as shown in FIG. 2, includes an annular connecting collar 6 at its base, having a bottom surface that is provided for being welded to the flexible web 3.

[0027] A welding device D schematically illustrated in FIG. 3 is used to establish the connection of the neck 4 to the web 3. The welding device includes a head 10 and a counterhead 17 which are adapted so that, in cooperation with one another, they press the collar 6 and the web 3 in the area of a welding zone 12. The head 10 and the counterhead 17 are also connected to means M, for example electrical high-frequency generators or ultrasonic generators, for generating heat in the welding zone. The heat generation means allow activation of the welding zone 12 to bring about melting of at least a surface thickness of the collar 6, thus ensuring a sealtight weld of the neck 5 to the web 3. The devices that are used to ensure either thermal or high-frequency welding or ultrasonic welding are well known to those skilled in the art, and therefore do not require a more detailed description.

[0028] As shown in FIGS. 4 and 5, the welding head 10 includes a cylindrical hollow body 11 made of electrically and/or thermally conductive material. In the present case, the body 11 is made of electrically and thermally conductive material, namely, a copper alloy such as brass or bronze.

[0029] The body 11 has a ring-shaped work surface 15 that is open in its center, and that includes grooves or concave formations 16 that are essentially uniformly distributed on the surface of the work surface, corresponding to a fundamental characteristic of the invention. These concave formations 16 have essentially the shape of tetrahedrons, for example, that originate from corrugation of the work surface. Of course, the concave formations may have some other design, and, for example, may include an essentially regular grid made up of intersecting furrows.

[0030] The concave formations 16 preferably, but not exclusively, have a maximum depth that is greater than or equal to the thickness of the flexible web 3. According to the illustrated example, the concave formations have a maximum depth in the range of 0.5 mm to 1.5 mm.

[0031] Once it is adapted to the welding device D, the welding head 10 according to the invention is used as follows, corresponding to the method according to the invention.

[0032] The web or webs 3 and the neck 4 are pressed together in the area of the welding zone by means of the head 10 and the counterhead 17, the heat generation means M being activated to generate heat in order to ensure melting of at least the surface thickness of the welding collar at the point of contact with the flexible web 3.

[0033] The concave formations of the work surface of the welding head advantageously allow the flow of melting plastic material to be retained in the welding zone, so that neither a ridge nor an overflow of plastic material from the welding zone results.

[0034] After cooling, the welding zone, which is discernible on the side of the flexible web, has a series of convex and concave zones and, if the web is transparent or translucent, has alternating light and dark zones.

[0035] Furthermore, it has surprisingly and advantageously been found that the use of a welding head having a textured work surface does not impair either the mechanical durability of the weld or the sealtightness thereof, so that the quality of a container that includes a welded neck corresponding to the invention is even further improved, in particular due to the absence of ridges. In addition, the stability of the weld with the welding head is essentially independent of the welding temperature, which allows welding at higher temperatures and in less time, thus increasing the production output.

[0036] According to the above-described example, the work surface of the welding head has a ring shape. However, such a formation is not necessary for the design of a welding head according to the invention. Thus, the work surface of the welding head, in particular for carrying out the circumferential welding of a flexible container according to the invention, could in particular be linear.

[0037] Of course, various other variants of the invention may be considered within the scope of the appended claims.