GB2138353A

GB2138353A - Production of bags from an elongate web

Info

Publication number: GB2138353A
Application number: GB08410389A
Authority: GB
Inventors: David Cecil Mills
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-04-21
Filing date: 1984-04-24
Publication date: 1984-10-24
Also published as: GB8410389D0

Abstract

A web travels, preferably intermittently, along a web path via at least two treatment stations (14,16,18) and around variable diverter means (26,28) which are arranged intermediate adjacent stations, for diverting the web so that the distance it travels between two stations can be adjusted. The stations may comprise welding stations, and a cutting station (30) may also be provided. Welding bars (22) at the welding stations operate on the web simultaneously. The diverter means may comprise rolls which may be linked or independently movable. The variable diverter means permits adjustment of the length of the bags produced from the web. <IMAGE>

Description

SPECIFICATION Production of bags and the like from an elongate web The present invention relates to a method and apparatus for producing articles, particularly bags, from an elongate web. It particularly relates to the production of bags from a web of thermoplastic material.

In a known way of forming bags, a continuous elongate web in the form of a flattened tube of thermoplastic material is moved in steps along a production line having a melting station spaced from a cutting station by a distance related to the size of the steps. After each step, a weld line is formed transversely across the web at the melting station.

Simultaneously, the web is cut at the cutting station.

Thus after the next step, the web is cut adjacent the previously formed weld to produce a discrete bag.

Generally, the speed of the process is limited by the welding step. Variation of the length of the bags being produced is possible by changing the spacing of the melting and cutting stations, but this is a relatively complex operation.

According to the present invention in a first aspect, there is provided apparatus for intermittent treatment of a web comprising means for causing a web to travel, preferably intermittently, along a web path; at least two treatment stations along said path; and variable diverter means intermediate adjacent stations for diverting the web so that the distance it travels between two stations is variable. The variable diverter may comprise a dancing roll. The stations may comprise a welding station, and a cutting station. All of the stations may be arranged to operate on the web simultaneously. There may be a plurality of welding stations, with variable diverter means between each adjacent pair. Thus a plurality of welds can be formed simultaneously.The diverter means may be independently movable, so that the different welding stations can be producing articles with different repeat lengths.

The welding stations may perform other operations in addition to welding, e.g. gluing or printing.

Indeed, some or all of the stations may not effect welding.

After the welding (or other) station or stations, the web may be indexed through a cutting station (or some alternative, e.g. to form tearable lines). Instead of direct on-line cutting, one or more treatment stations may apply indicia to the web, e.g. in the form of dots adjacent weld lines. The web may then be allowed to collect and it may subsequently be fed through a cutter (and/or other treatment stations) having means (e.g. a photoelectric eye) to detect the indicia. Thus the cutting (or other treatment) is effected at the correct positions without this being dependent on accurate indexing of the web. It can be performed at a rate limited only by the speed of operation of the cutting of the cutting station.

In another aspect the present invention provides a process for intermittent treatment of a web comprising: causing said web to travel generally along a path, which path takes the web to at least two treatment stations; diverting the web to a variable extent between said two stations so as to control the length of web between them; and treating said web simultaneously at both said stations.

Some preferred embodiments of the invention will now be described in greater detail with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view of a first embodiment of the invention; and Figure 2 is a diagrammatic view of a second embodiment.

The two illustrated embodiments have much in common with one another. Each employs a web in the form of a flattened tube of a thermoplastic material as is conventionally used in plastic bags. As shown, the web W is unwound from a reel 10 of pre-formed web. Of course, the extrusion and flattening of the tube could be arranged to happen on-line. The web W is fed intermittently in the direction indicated by arrows 12 by means including a stepping motor (not shown). The web W is passed through three welding stations 14,16,18. Each of these has a pair of transverse rollers 20, which are spaced from another, and which extend transversely beneath the web W. Above the web at each welding station there is a heated welding bar 22, which is displaceable downwardly to contact the web W.The three bars 22 may be mounted on a common beam 24, which is displaceable so that all of the bars 22 move synchronously.

Between the welding stations 14 and 16 there is a dancing roll 26 located generally beneath the rollers 20. Its distance beneath them is variable. Similarly, there is a dancing roll 28 between stations 16 and 18.

The two dancing rolls 26,28 may be displaceable independently, or for simplicity (but with some loss of versatility) they may be linked.

In the first embodiment, (shown in Figure 1) there is a cutting station 30 downstream of the last welding station 18. In operation, the three welding bars 22 are lowered to form three weld lines across the web W. The web W is then indexed so that the bag defined byte weld produced at station 18 is positioned so that it can be cut off by the cutting station 30. A second indexing step enables the bag produced by a welding at station 16 to be cut off. A third indexing step enables the bag produced by the welding station 14 to be cut off. There is now a fresh length of web extending across the three welding stations, and the welding step is repeated.It will be appreciated that the sizes of the bags produced are determined by the positions of the dancing rolls 26, 28 and by the distance between the welding station 18 and the cutting station 30. (There could be a dancing roll interposed therebetween). It is simple to displace the dancing rolls to alter the bag sizes. They can be at different heights so that the different stations produce bags of different sizes during the same process.

There could be a set of three cutting (or etc.) stations arranged analogously to the three welding stations, possibly with corresponding dancing rolls coupled together.

The second embodiment, shown in Figure 2, differs from the first embodiment in that there is a collecting basket 32 interposed between the last welding station 18 and the cutting station 30'.

Furthermore, each cutting station 14,16,18 includes an indicia applying head 34, and the cutting station 30' includes detecting means for detecting the indicia. The operation is substantially the same as for the first embodiment. However, in the welding step, indicia are applied adjacent the welds. After the welding step, the web W is indexed approximately three times as far as for the first embodiment, so that a completely new length of web extends through all of the welding stations, and the welded length collects in the collecting basket 32. Thus welding steps can be performed about three times asfrequently as for the first embodiment. Independently of the indexing of the web W through the welding stations, the welded web is fed from the basket 32 through the cutting station 30' which operates in response to its detection of the indicia. Of course, the cutting station 30' need not be associated with the rest of the plant as shown.

Claims

1. Apparatus for intermittent treatment of a web comprising means for causing a web to travel, preferably intermittently, along a web path; at least two treatment stations along said path; and variable diverter means intermediate adjacent stations for diverting the web so that the distance it travels between two stations is variable.

2. Process for intermittent treatment of a web comprising: causing said web to travel generally along a path, which path takes the web to at least two treatment stations; diverting the web to a variable extent between said two stations so as to control the length of web between them; and treating said web simultaneously at both said stations.

3. Any apparatus or process or inventive feature thereof disclosed herein.