Patent Description:
Machines for welding of two layers of plastic film material together are known in the art operating in generally by two different principles of welding. One is a stop-and-go principle where two layers of overlaid plastic film are moved discontinuously on top of an anvil plate and briefly halted in position, when heated welding means are pressed on top of the overlaid film to weld the two layers of film together in a pattern defined by the layout of the welding means. Another is continuous welding, where the heated welding means are situated on the periphery of a rotating welding drum and the two layers of overlaid plastic film are moved continuously past the welding drum tangential to the drum and the welding takes place during contact between the plastic films and the heated welding means. The two layers of plastic film material may be in the form of separate layers or in the form of a tubular film.

Such continuous welding is known from <CIT>, where the layers of overlaid plastic film are moved along half of the periphery of the welding drum guided and tensioned against the periphery of the drum by two web guidance rollers situated close to the rotating welding drum at opposite sides of it. The heated welding means are bars extending parallel to the axis of rotation of the drum.

An alternative continuous welding process is disclosed in <CIT> where the two layers of film are guided along a driven cylinder with a plurality of anvil bars extending on the peripheral surface parallel to the axis of rotation, and a second rotating welding device having a parallel axis of rotation comprises heated welding bars extending parallel to the anvil bars, and a heat seam is formed between the overlaid plastic films as they passes the point of contact between the welding bars and the anvil bars.

In <CIT> a heated welding drum and an anvil drum are employed for continuous welding of two overlaid layers of plastic film material, where the anvil drum is pressed against the welding drum and the welding seam is formed when the web of plastic film passes the nip between the anvil drum and the heated welding drum. Web guidance rollers are arranged to maintain the web in contact with the heated surface of the welding drum over a peripheral extend of about <NUM>° in order to preheat the web prior to the welding at the nip. During start and stop of the continuous welding process, the continuous movement of the web is halted, the anvil drum is lifted away from the heated welding drum and two or more web saver rollers are moved to lift the web of plastic film away from the heated surface of the welding drum in order to prevent the web to thermally deform or melt when the web is no longer in a continuous movement with respect to the peripheral surface of the heated welding drum.

In the continuous welding machine shown in <CIT>, a stretchable tensioning band is employed to press a web of a tubular film towards a rotating welding drum over half of the peripheral extend of the welding drum. The welding drum has a plurality of heated welding bars extending on the peripheral surface parallel to the axis of rotation, and the tensioning band ensures a sufficient tangential pressure on the web towards the welding bars for a time sufficiently long for a welded seam to be formed between the two layers of plastic film material of the tubular film.

It is also known in the art of continuous welding machines to use a rotating welding drum with a plurality of heated welding bars extending on the peripheral surface parallel to the axis of rotation, wherein the welding bars can be retracted into the drum and away from the peripheral surface in order to prevent direct contact with the web during start up and shut down of operation of the welding machine. A further welding machine is disclosed in <CIT>.

It is an objective of the present disclosure to provide a welding machine for continuous welding of two layers of plastic film material together in a welding pattern, where the switching between a production mode of operation of the welding machine and a stop of operation of the welding machine is improved.

The present invention relates to a welding machine for continuous welding of two layers of plastic film material together in a welding pattern, the machine comprising.

With continuous welding is understood that a web of the two layers of plastic film material can be fed continuously through the welding machine and past the welding means of the machine, as opposed to stop-and-go welding.

The two layers of plastic film material, i.e. the web, may comprise to separate layers of a heat-weldable plastic film material, in particular a thermoplastic film, or it may comprise a tubular film of heat-weldable plastic film material. The individual film layer is preferably of a thickness in the range of <NUM> to <NUM> microns, in particular in the range of <NUM> to <NUM> microns, where the use of a thermoplastic material as High Density Polyethylene (HDPE) allows for more sustainable air cushions at a lower film thickness than e.g. the use of Low Density Polyethylene (LDPE). Alternatively, a polyester or polypropylene film may be employed.

The welding pattern of the welding means may comprise welding bars extending in a direction parallel to the axis of the welding drum, but the present invention is more advantageous to use with a more complex welding pattern extending in both the axial direction and the peripheral direction of the cylindrical surface of the welding drum.

The heating arrangement arranged to heat the welding means to a welding temperature may comprise electrical heating means applied directly to the welding means or may include a heat transferring medium such as a heated oil that is circulated to heat the welding means.

The endless welding band is provided for applying a pressure force on the web of plastic films towards the welding means over a substantial extend of the periphery of the welding means on the welding drum, whereby the heat transfer from the welding means to the web takes place over a longer period of time, thus providing for a higher velocity of the web during production operation of the welding machine.

The first operational mode is a production mode of the welding machine, whereas the second operational mode, where the one or more separation rollers is displaced in between the welding means on the peripheral surface of the welding drum and the two layers of plastic film material to a second position where the two layers of plastic film material and the welding band are separated from the periphery of the welding drum is a transitional mode from the first operational mode to a stop of operation of the welding machine. The second operational mode can also be reversed for the welding machine to go from a stopped mode to the first operational mode.

By the present invention, it is achieved to temporarily remove the web of plastic films as well as the means for pressuring the web against the welding means of the welding drum, i.e. the welding band, in one procedure by means of moving the separation rollers. This is particularly advantageous when the the welding means are not easily retractable, such as when the welding pattern constitutes a two-dimentional welding pattern that spans at least <NUM>° of the peripheral surface of the welding drum.

It is preferred that the welding machine comprises at least two separation rollers because the machine can be constructed to be more compact of design that a welding machine comprising only one separation roller and the means for displacing the separation rollers may be formed more simple.

It is particularly preferred that the welding machine is arranged so that the two layers of plastic film material extend flush with the welding band between the two separation rollers in the second operational mode of the welding machine.

The welding pattern of the welding means extends in the transverse direction parallel to the axis of the welding drum as well as in the curved direction perpendicularly to the transverse direction, i.e. a two-dimensional welding pattern, and spans at least <NUM>°, preferably at least <NUM>° of the peripheral surface of the welding drum. Even more preferred, the welding pattern extends substantially continuously throughout the peripheral surface of the welding drum to provide a substantially continuously welding pattern to the two layers of plastic film material.

The present invention is particularly advantageous with a welding pattern of the welding means extending in the transverse direction parallel to the axis of the welding drum as well as in the curved direction perpendicularly to the transverse direction, i.e. in a two-dimensional welding pattern, because such pattern is very difficult to retract from the surface of the welding drum during stop and start of the continuous welding process and the present invention provides an alternative to such solution, where the web of layers of plastic film material can be temporarily removed from the welding means by means of the one or more separation rollers.

The welding pattern of the welding means is preferably designed to form closed pockets between the two layers of plastic film material so as to provide inflatable pockets.

In another design, the welding means is designed to form connected pockets between the two layers of plastic film material so as to provide ice cube bags.

The first application roller and the second application roller are preferably arranged to be displaceable by means of application roller displacement means controlled by the control means between a first position thereof in the first operational mode of the welding machine and a second position of the first application roller and the second application roller in the second operational mode of the welding machine to accommodate the displacement of the at least one separation roller from the first position thereof and to the second position of the at least one separation roller.

The first application roller and the second application roller are preferably arranged to apply the welding band to the welding means on the surface of the welding drum over a peripheral extend of at least <NUM>°, preferably of at least <NUM>° of the welding drum.

The welding machine preferably further comprises at least one pressure drum which is arranged to, in the first operational mode of the welding machine, provide a pressure force on the welding band towards the welding drum within the peripheral extend where the welding band is applied to the welding drum, wherein the at least one pressure drum is arranged to be displaceable by means of a pressure drum displacement means controlled by the control means, between a first position thereof in the first operational mode of the welding machine and a second position of the pressure roller in the second operational mode of the welding machine to allow for the two layers of plastic film material and the welding band to be separated from the periphery of the welding drum by means of the separation rollers. The purpose of the at least one pressure drum is to increase the pressure force on the web of plastic films towards the welding means on the welding drum, whereby the heat transfer from the welding means to the web increases at the position of the one or more pressure drums, thus providing for a higher velocity of the web during production operation of the welding machine.

The present invention furthermore relates to a method of producing a web comprising two layers of plastic film material being welded together in a two-dimensional welding pattern forming pockets between the two layers of plastic film material by use of a welding machine as disclosed herein, wherein the welding pattern of the produced web is formed by means of the welding means on the welding drum.

The pockets formed between the two layers of plastic film material are preferably closed pockets so that the produced web is an air cushion film for subsequent forming of air cushions.

In a further aspect, the present disclosure relates to a welding machine for continuous welding of two layers of plastic film material together in a welding pattern, the machine comprising.

The endless welding band is provided for applying a pressure force on the web of plastic films towards the welding means over a substantial extend of the periphery of the welding means on the welding drum, whereby the heat transfer from the welding means to the web takes place over a longer period of time, thus providing for a higher velocity of the web during production operation of the welding machine. The purpose of the at least one pressure drum is to increase the pressure force on the web of plastic films towards the welding means on the welding drum, whereby the heat transfer from the welding means to the web increases at the position of the one or more pressure drums, thus providing for a higher velocity of the web during production operation of the welding machine.

It is preferred that the at least one pressure drum is arranged to be displaceable by means of a pressure drum displacement means controlled by the control means. Also, the welding machine comprising at least two pressure drums.

Examples of the present invention are shown in the figures, of which.

The welding machine <NUM> shown in <FIG>, <FIG> and <FIG> comprises a welding drum <NUM> having heated welding means <NUM> on its peripheral surface for continuous welding of a web of two layers of plastic film material <NUM>', <NUM>" together in a welding pattern which forms closed pockets between the two layers for the production of an air cushion film for subsequent forming of air cushions. The web <NUM>', <NUM>" is guided in between the welding drum <NUM> and a welding band <NUM> by means of a web guidance roller <NUM> at the top right of the welding drum <NUM>. After the web <NUM>', <NUM>" has been welded and is exiting from between the welding drum <NUM> and the welding band <NUM>, another web guidance roller <NUM> at the top left of the welding drum <NUM> received the welded web <NUM>', <NUM>" for further handling.

The welding means <NUM> are during production heated to a temperature preferably in the range of <NUM>° to <NUM>° C, depending on the characteristics of the plastic film material, but lower as well as higher temperatures, such as in the range of <NUM>° to <NUM>° C may be employed. The welding means <NUM> are heated by means of a heated oil in a buffer tank (not shown) which is circulated to the welding means <NUM>. Alternatively, the welding means <NUM> may be heated directly by means of electrical heating elements.

The welding band <NUM> is an endless belt of a fibre reinforced silicone rubber material extending in the width of the welding means <NUM> for providing a force in the radial direction of the welding drum on the web <NUM>', <NUM>" towards the welding means <NUM> and thereby ensuring the heat transfer from the welding means <NUM> to the web <NUM>', <NUM>". The welding band <NUM> is guided by five band guidance rollers <NUM>, <NUM>, <NUM>, <NUM> of which two rollers <NUM>, <NUM> serve as application rollers to apply the welding band <NUM> to the welding means <NUM> over approximately <NUM>° of the peripheral of the welding drum during production as shown in <FIG>. A tensioning roller <NUM> is arranged to be displaceable by means of tensioning roller displacement means <NUM> in order to i. ensure the correct tensioning of the welding band <NUM> during production and thus the correct force to be provided to the web <NUM>', <NUM>". During production, the welding band <NUM> is driven at a speed about <NUM> meter per minute by means of a motor (not shown) driving one of the band guidance rollers <NUM>, and the web <NUM>', <NUM>" as well as the periphery of the welding drum <NUM> are driven at the same speed. The speed may be varied due to considerations regarding the plastic film material.

During operation of the welding machine <NUM>, a pressure drum <NUM> is provided to apply a pressure force on an outer surface of the welding band <NUM> towards the welding drum <NUM> where the web <NUM>', <NUM>" is placed between the welding band <NUM> and the welding drum <NUM> as shown in <FIG>, whereby the welding of the web <NUM>', <NUM>" by means of the heated welding means <NUM> is improved and the speed of the web <NUM>', <NUM>" through the welding machine <NUM> may be increased as compared to an otherwise identical welding machine without the pressure drum <NUM>. The pressure drum <NUM> can be displaced by means of pressure drum displacement means <NUM> in order to adjust the pressure force applied to the welding band <NUM> and to displace the pressure drum <NUM> away from the welding band <NUM> when production operation of the welding machine <NUM> is stopped as shown in <FIG> and <FIG>.

When the production operation of the welding machine <NUM> is to be stopped, the contact between the web <NUM>', <NUM>" and the heated welding means <NUM> must be interrupted in order to avoid heat damages to the web <NUM>', <NUM>". <FIG> shows the transition mode to the stop of production as shown in <FIG>. In <FIG>, the first application roller <NUM> and the second application roller <NUM> have been displaced to the sides by means of the application roller displacement means <NUM> in order to make room for the displacement of the first and second separation rollers <NUM>, <NUM>. The tensioning roller <NUM> is displaced accordingly by means of the tensioning roller displacement means <NUM> in order to keep the welding band <NUM> tensioned so as to avoid slack of the welding band <NUM>, which is still moving together with the web <NUM>', <NUM>" and the welding drum <NUM>. Slack of the welding band <NUM> while still moving could cause damaged to the welding band <NUM> as well as other parts of the welding machine 1The pressure drum <NUM> is displaced away from contact with the welding band <NUM> by means of the pressure roller displacement means <NUM> in order to accommodate the separation of the welding band <NUM> from the welding drum <NUM> by means of the separation rollers <NUM>, <NUM> as shown in <FIG>.

The next step is shown in <FIG>, where the operation of the welding machine <NUM> has been stopped. The two separation rollers <NUM>, <NUM> have been displaced in between the welding band <NUM> and the web <NUM>', <NUM>" on one side and the welding drum <NUM> on the other side so as to separate the web <NUM>', <NUM>" from the heated welding means <NUM> of the welding drum <NUM>, and the movement of the web <NUM>', <NUM>", the welding band <NUM> and the rotation of the welding drum <NUM> is halted. The web <NUM>', <NUM>" is flush with the welding band <NUM> between the two separation rollers <NUM>, <NUM> in order to avoid any slack of the web <NUM>', <NUM>" in order for it to be ready to resume production operation of the welding machine <NUM>.

In order to transition the welding machine <NUM> from the stop of production shown in <FIG> and back to production mode as shown in <FIG>, the movement of the welding band <NUM> and the web <NUM>', <NUM>" is resumed and the welding drum <NUM> is rotated to an operational speed, where after the separation rollers <NUM>, <NUM> are retracted by means of the separation roller displacement means <NUM>. The pressure roller <NUM> is moved back into contact with the outer side of the welding band <NUM> and the production mode of the welding machine <NUM> as shown in <FIG> is resumed.

By providing the welding machine with two separation rollers <NUM>, <NUM> and by providing the welding machine with application roller displacement means <NUM> as shown in <FIG>, a simple and linear displacement path of the two separation rollers <NUM>, <NUM> may be obtained.

A second embodiment of the welding machine <NUM> is shown in <FIG> in the stopped position, where only one separation roller <NUM> is provided. This is also sufficient for the separation of the welding band <NUM> and the web <NUM>', <NUM>" from the peripheral surface of the welding drum <NUM>, but it requires a more complex displacement path of the separation roller <NUM> than in the first embodiment shown in <FIG>.

Claim 1:
Welding machine (<NUM>) for continuous welding of two layers of plastic film material (<NUM>', <NUM>") together in a welding pattern, the machine comprising
a welding drum (<NUM>) which is arranged to be rotated around its axis,
welding means (<NUM>) arranged on the peripheral surface of the welding drum (<NUM>) and exhibiting the welding pattern,
heating arrangement arranged to heat the welding means (<NUM>) to a welding temperature,
an endless welding band (<NUM>),
a set of band guidance rollers (<NUM>, <NUM>, <NUM>, <NUM>) comprising a first application roller (<NUM>) and a second application roller (<NUM>) arranged to apply the welding band (<NUM>) to the welding means (<NUM>) on the surface of the welding drum (<NUM>) over a peripheral extend of at least <NUM>°, preferably at least <NUM>° of the welding drum (<NUM>) with a force radial to the welding drum (<NUM>) in a first operational mode of the welding machine (<NUM>), the set of band guidance rollers comprising at least one displaceable tensioning (<NUM>) roller for maintaining a tension of the welding band (<NUM>),
a web guidance arrangement (<NUM>, <NUM>) for guiding the two layers of plastic film material (<NUM>', <NUM>") in between the welding drum (<NUM>) and the welding band (<NUM>), and
control means for controlling the operation of the welding machine (<NUM>), characterized in that
the machine comprises one or more separation rollers (<NUM>, <NUM>), and is arranged in a second operational mode of the welding machine (<NUM>) to displace the one or more separation rollers (<NUM>, <NUM>) by means of separation roller displacement means (<NUM>) controlled by the control means, from a first position thereof and in between the welding means (<NUM>) on the peripheral surface of the welding drum (<NUM>) and the two layers of plastic film material (<NUM>', <NUM>") to a second position of the one or more separation rollers (<NUM>, <NUM>) where the two layers of plastic film material (<NUM>', <NUM>") and the welding band (<NUM>) are separated from the periphery of the welding drum (<NUM>) by means of the separation rollers (<NUM>, <NUM>).