WO2021074764A1

WO2021074764A1 - A device and a method for bonding labels to sack workpieces

Info

Publication number: WO2021074764A1
Application number: PCT/IB2020/059539
Authority: WO
Inventors: Gaurav LOHIA
Original assignee: Lohia Corp Limited
Priority date: 2019-10-16
Filing date: 2020-10-11
Publication date: 2021-04-22

Abstract

During bonding process of labels and workpieces, which are made from thermoplastics, they are heated to 350+ ^oC before actual bonding. Effect of high temperature and thinness of surfaces causes thermal shock on the materials to be bonded, leading to product failure or quality issues. A device 1 to apply labels onto the sack workpieces 2 made from thermoplastics is disclosed to overcome these drawbacks. The device of the invention consists of a table platform 1A to carry cut and folded tubular pieces 2 with box ends 2A/2B of fabric. The device of the invention further consists of a label web pre-heating and conveying mechanism 1B which has at least one indirect heater 10 that pre-heats the label web strip 7 before labels 12 are formed and a conveying mechanism 11 to convey the label strip 7 and the pre-heated labels 12 for bonding with the tubular cut pieces 2. A method of bonding labels to sack work pieces by preheating the label web is also disclosed.

Description

A DEVICE AND A METHOD FOR BONDING LABELS TO SACK WORKPIECES

Field Of Invention: The invention relates to a device and a process for indirectly heating labels and for bonding them to workpieces/bag bottoms.

Background of Invention:

Nowadays, the branding on product packaging is the most important criteria for brand promotion and marketing. The packaging products made from thermo plastic web are becoming more popular due to light weight and possibilities of having high resolution printed film on surface, for enhanced branding. Generally, the woven polyolefin fabric with thermo-plastic surface coating or laminated with oriented plastic printed film are used to make suitable packaging bags, one of most popular form is block bottom type bag.

Processes and devices for bonding thermo-plastic web on tubular pieces or workpieces, which are also often made of thermo-plastic web, are known. For example, US 4589943 and US 2543220 teach a device and method for adhesive bonding of labels with workpieces. Further, US application 20020050323A, teaches an improved web material dispenser for advancing a web material to an applicator, such as a tape applicator for applying a strip of tape to form a cutting edge, a reinforcing tape, a box sealer, and the like. The system utilizes a feed roller to advance the web to a vacuum anvil roll where the web material is cut and advanced to a vacuum wheel applicator. In one aspect to a web material delivery system capable of changing the length of the web material delivered to the applicator. The layers of thermo-plastic web are bonded with each other using suitable glue or hot melt adhesive or thermal bonding techniques. The most popular technique is the thermal bonding technique.

The term “bonding” combines several different methods of joining thermo-plastic web, wherein the process temperature is a decisive factor. Usually, as stated above, the surface of at least one of the thermo-plastic webs being bonded together is treated by heating and then the thermos-plastic webs are bonded or welded under pressure.

During the bonding process, typically labels and workpieces made from thermos- plastics and which are to be bonded are brought together in a roll slit. The contact surfaces of the elements to be bonded are heated inside the roll slit typically with hot air.

However, setting the bonding temperature only by means of a suitable air stream has drawbacks. For example, as with the demand of increase in processing speed lead to increase in the hot-air temperature beyond 350°C, further, there is demand for decreasing the packing cost which has led to decrease in the total weight of thermo-plastic web and its coating. These combined effect of increase in the hot air temperature and decrease in the material weight, often cause higher thermal shock on the thermoplastic web layers to be bonded, leading to product failure or uneven surface.

Devices are also available where parts of the conveying system with which the labels or the work pieces are in direct contact are heated - in other words, a system to carry out direct heating. A drawback of these systems is that the direct contact heat applied to the labels is not easily controllable. A further drawback of these systems arises due to the increased travel speeds and reduction in thickness of coatings applied to the webs. Due to these two factors, the web/ label coating suffers abrasion and loss of integrity, as a result of which the quality of the bond formed between the two surfaces diminishes.

There is therefore a need to provide a device and a process that will obviate the above mentioned drawbacks and at the same time allow the progress of the label through the roll slit at the normal working speed of a bag-making conveyor line thereby maintaining the speed of production at least above 60 bags per minutes. There is also a need to provide device and systems that decreases the sudden thermal shock to thermo-plastic web label being bonded by hot air/thermal bonding with the workpiece moving on the conveyor.

Object of invention:

One object of the invention is to provide a device and a process that will allow the progress of the label through the roll slit at the normal working speed of a bag-making conveyor line thereby maintaining the speed of production.

Another object of the invention is to provide systems for thermoplastic web labels that work on indirect heating principle to avoid sudden thermal shock.

A further objective of invention is to provide adequate bonding strength to the label and workpiece/bag body.

Another object is to improve the packaging branding through usage of printed or laminated labels

Statement of the invention:

The present invention provides a device for applying pre-heated labels 12 onto the workpieces 2 moving on the conveyor platform which consists of a table platform 1A to carry the cut and folded tubular pieces 2 of fabric, where the ends of the tubular cut pieces are folded so as to form box ends 2A/2B and a label web pre-heating and conveying mechanism wherein the said mechanism has at least one indirect heater 10 that pre -heats the label web strip 7 and said conveying mechanism conveys the pre-heated label strip 7 and eventually the pre-heated labels 12 for bonding with the tubular cut pieces 2 followed by the actual bonding of the pre-heated labels 12 to the work pieces 2 wherein the pre heating is carried out using indirect/non-contact heating means 10/15.

Brief Description of Figures:

Figure 1 shows a schematic representation of the device of the invention Figure 1A shows the indirect heating system of the invention in a view taken along cross-section A-A indicated in Figure 1

Figure 2 shows a schematic of the bag making process showing bonding of labels to the bag

Figure 3 shows a close-up view of the bonding process using pre-heated labels

Summary of Invention:

A device 1 as shown in Figure 1 to apply labels onto the workpiece moving on the conveyor platform is disclosed. The device of the invention consists of a table platform 1A to carry the cut and folded tubular pieces 2 of fabric, where the ends 2A/2B of the tubular cut pieces 2 are folded so as to form box ends. The device of the invention further consists of a label web pre -heating and conveying mechanism IB. This mechanism has at least one indirect heater 10 that pre-heats the labels or coversheets 12 that are to be applied to prepared/folded ends of the tubular cut pieces 2, and a conveying mechanism 11 to convey the label strip 7 and the pre-heated labels 12 for bonding with the tubular cut pieces 2. The mechanism IB allows pre-heating of the continuous web of plastic 7 from which pre-heated labels 12 are made, followed by the actual bonding of the pre-heated labels 12 to the work pieces 2. In particular, the pre -heating is carried out using indirect/non-contact heating means 10. More particularly, none of the devices used for conveying of the labels 12 or work pieces 2 such as the guide rollers 8 or conveying cylinder 6 or platforms 1A, are heated directly. The invention also discloses a method of applying pre -heated labels to sack work pieces.

List of Parts:

1 - Device to apply labels to bags, 1A - table platform, IB - label web heating and conveying mechanism

2 - Tubular cut pieces or work pieces; 2 A, 2B - ends of work pieces, 2C - work piece substrate, 2D - workpiece coating

3 - Transverse slit in the table platform; 3A slit or gap between the suction and counter-pressure rollers

4 - Counter-pressure roll

5 - Suction roll

6 - Conveying cylinder; 6A - belt strip

7 - Web of plastic or label web or label web strip, 7A - label web supply station,

8 - Deflecting or guide rolls

9 - Nozzle; 9A - second nozzle for cooling of belt strip

10 - Pre-Heater or indirect pre -heating means

11 - Web label conveying means

12 - Cut pre -heated label or cut piece of heated label; 12A - label substrate, 12B - pre-heated label coating, 12C - non-bonding surface of the label

13 - Bag with label, 13A - bonded region

14 - Stacking/delivery station

15 - Additional pre-heating zone

16 - Knife mechanism or arrangement or cutting means

17 - Web aligning sensor, 17A - print mark sensor

Detailed Description of Invention:

A device 1 to apply labels onto the workpiece moving on the conveyor platform is disclosed. The device of the invention consists of a table platform 1A to carry the cut and folded tubular pieces 2 of fabric, where the ends 2A/2B of the tubular cut pieces 2 are folded so as to form box ends. In an aspect of the invention, the box ends 2A/2B are suitably provided with a valve patch. Such tubular cut pieces 2 are now ready to receive labels or cover sheets 12 so that sealed box ends are formed. The device of the invention further consists of a label web pre-heating and conveying mechanism IB. This mechanism has at least one indirect heater 10 that pre-heats the labels or coversheets 12 that are to be applied to prepared/folded ends of the tubular cut pieces 2, and a conveying mechanism 11 to convey the label strip 7 and the pre -heated labels 12 for bonding with the tubular cut pieces 2. The mechanism IB allows pre-heating of the continuous web of plastic 7 from which pre -heated labels 12 are made, followed by the actual bonding of the pre-heated labels 12 to the work pieces 2. In particular, the pre-heating is carried out using indirect/non-contact heating means 10 (refer to Figure 1A). More particularly, none of the devices used for conveying of the labels 12 or work pieces 2 such as the guide rollers 8 or platforms 1A, are heated directly.

As shown in Figure 1 , a machine frame, which is not illustrated, supports a table plate 1A, on which tubular pieces or work pieces 2 made of thermo-plastic, which are displaced continuously in the direction of the arrow A and represent raised or assembled bottoms 2A/2B, are conveyed by means of conveyors, which are not illustrated. In the case of the tubular pieces 2, conveyed so as to lie transversely to direction A at a predetermined distance from each other, the assembled bottoms (2A, 2B) or the raised bottoms are folded in the plane of the tubular pieces 2. In the machine frame, a counter-pressure roll 4 and a suction roll 5 are provided, which form together a pair of conveying rolls and whose roll slit 3A lies in the plane of the top side of the table 1, are mounted in a transverse slit 3 of the table 1. The workpiece 2, or the cut piece from which a bag is made, could be any thermoplastic packaging material body preferably bag body formed by folding of end flaps. A continuous web of plastic, or the label web 7 of pre-determined width is fed with a label web supply station 7A. It travels in the direction shown by arrow B (Figures 1 and 1A) along a label web heating and conveying mechanism IB. The label web 7 is preferably coated with suitable composition of polyolefine material at least on one side and is optionally printed on the surface that is exposed to the outside (the top surface). In another embodiment, the label web 7 is laminated with an oriented plastic/polyolefine printed (OPP) film on the one side which is visible from top end of packaging/workpiece and other bonding side has coating of thermoplastic material. It is cut into labels of the required size which then get bonded onto the formed bottoms 2A/2B of the work pieces 2.

During this process, as an inventive aspect of the device 1 to apply labels to sack pieces 1, the continuous label web strip 7 and/or the cut labels 12 are pre -heated using indirect pre-heating means 10 which may be convection heaters such as plate heaters or heaters that operate on infrared energy. There may be more than one pre-heater 10 which may be located suitably along the travel path of the label web 7. The suitable locations for these additional pre-heaters 15 are where said label web 7 is traveling between any two rollers or over any of the rollers 8 as shown in Figure 1. The temperature of the pre-heaters 10/15 may be adjustable.

The temperature of the pre -heating means 10/15 is generally set above the ambient temperature and in a temperature range up to 180°C. Figure 1A shows a view of the indirect pre -heating means 10 the invention. The distance between moving label web strip 7 and pre-heating means 10 is adjustable and kept between around 0.1 to 10 mm, depending on the linear weight of label web strip, its coating thickness and process speed.

The key object of the invention - that is pre -heating the label strip 7 or the labels 12 such that the structural integrity of the coating of the labels 12 is preserved while reducing the temperature gradient between the surfaces to be bonded to each other - is achieved by provision of indirect pre -heating means 10. The pre heated label web strip 7 is guided through web aligning sensor system 17 ensuring eventually proper alignment of each pre-heated label 12 on the sack pieces 2. The pre-heated label web strip 7 is further guided through the conveyance system which has a series of guide rollers 8 and which has further optional indirect heating means 15 for further controlled heating of moving label web strip 7.

As a part of the label web heating and conveying mechanism IB, a conveying cylinder 6 provided with a knife arrangement 16 is mounted above the suction cylinder 5 in the machine frame. The pre-heated label strip 7 is pressed against said knife 16 and conveying cylinder 6 by means of a belt which runs over a set of guide rolls or deflecting rolls 8. The knife 16 and conveying cylinder 6 is provided in the usual manner with the knife 16 running along a line on the surface of the label web 7. To facilitate the cutting process, and also to secure the cut pre-heated label 12 onto the conveying cylinder 6, the cut label 12 is gripped onto the conveying cylinder 6 with the help of a belt strip 6A. Overall synchronous motion control of all drive or guide rollers 8 is controlled through centralized electronic controller (not shown in figures). In another embodiment, the endless belts 6A are cooled by blowing pneumatic air through a second nozzle 9 A provided for that purpose. Further, the activation of cutting device/knife 16 is controlled by print-mark sensor 17A provided on label web conveying system IB so that the labels 12 are cut from the label web 7 in view of the prints marked on the label web 7.

The labels 12 which are cut to size from the pre-heated label web 7 are delivered from the conveying cylinder 6 onto the suction cylinder 5, from where they are placed in a correct position onto the sack workpieces 2 travelling through the slit gap 3A between the suction cylinder 5 and the counter-pressure roller 4. The suction cylinder (or roller) 5 is provided with adequate number of suction holes through which suction is applied to the pre-heated and cut pieces of labels 12 such that the labels 12 adhere to the suction roller 5 until they are deposited onto the sack work pieces 2. The suction roller 5 is also provided with an optional cooling system which aids easy deposition of the cut piece of labels onto the sack work pieces.

As shown in Figure 3, hot air is blown at controlled temperature, pressure and time through nozzle 9 into the slit or gap 3A that is provided between the suction cylinder 5 and the counter-pressure roller 4, in which the pre -heated cut labels 12 and the workpiece 2 are located. Said hot air further softens the coating of the already pre -heated labels 12 and the coating of the material of the box ends 2A/2B of the work pieces 2 in such a manner that the heated labels 12 bond to the workpieces 2 firmly to form a strong and durable bond under pressure exerted by the counter-pressure roller 4. As shown in Figure 3, the tubular fabric from which the sacks are made, and the label web comprise of a substrate - workpiece substrate 2C and label substrate 12A - on which coating (workpiece coating 2D and label coating 12B) is applied. Non-bonding surface 12C of the pre -heated label 12 (which may be coated or uncoated) does not receive direct blow of hot air. Coating may be applied on one or both sides of the respective substrates 2C/12A. The surfaces of the sack and the labels that are bonded together are the coated surfaces, such that after their passage through the gap 3A, there forms a bonded region 13A made from the fused coated surfaces of the sack and the label.

To achieve co-ordination between the pre -heated cut label piece 12 and the work piece 2 so that they arrive at the gap 3 A between the suction roller 5 and the counter pressure roller 4, a sensing system comprising a work piece location sensor (not shown) is provided. As soon as the work piece reaches to its pre determined location sensor senses the presence of the work piece 2 at a predetermined location on the conveying table 1A, the conveyor roller/cylinder 6 is rotated at the necessary speed through a drive system controller by main controller (not shown in figures) such that a predetermined length is cut from the pre-heated label web 7 using the knife mechanism 16 or cutting means 16. The pre-heated cut piece of label 12 is then deposited onto the suction cylinder 5, from where they are placed in a correct position onto the sack workpieces 2 travelling through the gap 3A between the suction cylinder 5 and the counter pressure roller 4. A gap 3 is also provided in the table platform 1A with which the gap 3A is aligned.

As shown in Figure 2, hot air is blown from a nozzle 9 onto the heated cut label piece 12 and the workpiece 2, particularly aimed at the areas where they are bonded to each other. The temperature and pressure of the air blown from the nozzle 9 is controlled. One key advantage of the invention is that when the pre heated cut piece of label 12 enters the high temperature zone created by the nozzle air, it doesn’t suffer a thermal shock. This is because the cut label piece 12 is already pre-heated before it enters the high temperature thermal zone whereby the temperature gradient between the pre-heated label 12 and the nozzle hot air is reduced

It is important to note that both the workpiece/bag body 2 and label web strip 7 are made from thermoplastic film, or woven or non-woven thermoplastic material or their combination, which must be coated on at least one side and optionally laminated with oriented plastic printed film.

The device 1 of the invention may be used for bonding of any size of web strip 7 onto the general surface of the workpiece 2 at required position while the workpiece travels on conveyor platform 1A. In another embodiment, the device 1 maybe portable. The various processing parameters like temperature, heating duration, hot air temperature, air velocity and pressure, process speed, rotational speed of rollers, label web cut length can be pre-determined and informed to controller through standard human machine interface (HMI).

As shown in figure 3, in one embodiment of the invention, at least the bonding surfaces of said pre -heated label 12 and sack work piece 2 are coated. In a further embodiment, the non-bonding surface 12C of pre -heated label 12 carries printed material. In a still further embodiment, the non-bonding surface of pre -heated label 12 is laminated with oriented plastic printed film. In a still further embodiment, at least some portion of workpiece 2 is laminated with oriented plastic printed film.

Experimental Results:

Results of the experiments carried out using the device of the invention, for bonding label web having coating thickness around 20 micron to 500 mm width workpiece having web substrate of around 50 gsm with coating thickness of around 18 micron, at process speed of 100 bags/minute by pre -heating the label web shows a significant increase in the bonding strength with workpiece/bag by around 3 to 10% as compared to conventional system without any pre -heating device. Further, an improved production rate of around 80 to 180 bags/ minute, for bag making system was possible depending on the bag/workpiece properties and length.

The pre -heated label 12 cut from the label web strip 7 is thermally bonded with the moving workpiece 2 using the pressure generated by counter-pressure roller 4 and is conveyed onto the stacking/delivery region 14 as shown in Figure 3.

The bag making machine can have more than one labelling device 1 of the invention positioned as per the requirement of packaging bag form. As shown in Figure 2, at each bag end 2A/2B, a device of the invention may be provided. The invention also discloses a method to apply labels 12 to tubular sack pieces 2. More specifically, the method begins with providing the device comprising a work piece conveyance platform 1A for sack work pieces and a mechanism IB for heating label web 7 and conveying it. The method comprises the steps of: a. supplying tubular sack pieces 2 along said conveying platform 1A, b. supplying label web 7 along the mechanism IB for pre -heating label web 7 and conveying it, c. pre -heating said label web 7 using the non-contact heating means 10 and/or 15, d. conveying said pre-heated label web 7 onto the conveying cylinder 6, e. cutting a label 12 of predetermined size on the conveying cylinder (6) and conveying it onto a suction roller 5, f. synchronizing the travel of said tubular sack work pieces 2 and said pre-heated label 12 so that they arrive at the gap 3 A between the suction roller 5 and the counter-pressure roller 4, g. directing hot air using a nozzle 9 towards the gap 3A onto the pre heated label 12 and the tubular sack work piece 2, h. passing the pre-heated label 12 and the tubular sack work piece 2 through the gap 3A so that their coated facing surfaces are bonded with each other to form a bonded zone 13 A.

The key aspect of the method of invention is that the step of heating is carried out using indirect/non-contact heating techniques such as convection heaters placed at a distance from the label web, or heaters that work on infrared energy.

With the device/apparatus and method of applying labels to sack work pieces disclosed here, the label strips are applied to the bag body of virtually continuous succession at a high rate of production (up to 180 bags/minute, for given bag dimension) in a fault-free operation. The overall structure and operational method are advantageously simple and with possibilities of rapid changes and rectifications to adapt required bag dimensions and various type of branding labels. It is to be understood that invention is not limited to the features and embodiments given hereinabove specifications but may be carried out in other ways without departing from its basic concept or soul of the invention.

Claims

We claim:

1. A device for bonding labels 12 to sack work pieces 2, said device comprising a work piece conveyance platform 1A for work pieces and a conveying mechanism IB for conveying label web strip 7 and conveying cylinder 6 with cutting means 16 to cut the label web strip 7 into label piece 12; pair of suction cylinder 5 and counter-pressure roller 4 characterized in that said conveying mechanism IB for pre -heating label web strip and conveying it to predetermined location of bonding with sack or work piece (2) comprises: a non-contact heating means 10, 15 to indirectly heat label web strip 7, a conveying means 11 to convey the label web 7, said conveying means 11 further comprises: o a set of guide rollers 8 on which the pre-heated label web 7 travels, o a gap 3A provided between said suction cylinder 5 and a counter-pressure roller 4; said counter pressure roller 4 being placed on the other side of said work piece conveyance platform 1A. o a hot air nozzle 3, for directing thermal heat in said gap 3A, for sealing workpiece end 2A/2B with cut pre-heated label 12.

2. The device as claimed in claim 1, wherein said heating means 10, 15 are convection heaters.

3. The device as claimed in claim 1, wherein said heating means 10, 15 operate on infrared energy.

4. The device as claimed in claims 2 and 3 wherein said label web strip 7 and said sack work piece 2 are made from thermoplastic film, or woven or non-woven thermoplastic material, or their combination.

5. The device as claimed in claim 4 wherein at least the bonding surfaces of said pre -heated label 12 and sack work piece 2 are coated.

6. The device as claimed in claim 5 wherein the non-bonding surface of pre heated label 12 is printed.

7. The device as claimed in claim 5 wherein the non-bonding surface 12C of pre -heated label 12 is printed on or laminated with oriented plastic printed film.

8. The device as claimed in claim 7 wherein the at least some portion of workpiece 2 is laminated with oriented plastic printed film.

9. The device as claimed in claim 8, wherein said heating means 10/15 are provided at locations where said label web 7 is traveling between any two rollers 8.

10. The device as claimed in claim 8, wherein said heating means 10/15 are provided at locations where said label web 7 is traveling over guide rollers 8.

11. A method for bonding labels 12 to sack work pieces 2 using the device as claimed in claims 1 to 10, comprising the steps of a. supplying tubular sack pieces 2 along said conveying platform 1 A, b. supplying label web 7 along the mechanism IB for pre -heating label web 7 and conveying it, c. heating said label web 7 using the indirect heating means 10, 15, d. conveying said pre -heated label web 7 onto the conveying cylinder 6, e. cutting a label 12 of predetermined size from said pre -heated label web 7 on the conveying cylinder 6 and conveying it onto a suction roller 5, f. synchronizing the travel of said tubular sack work pieces 2 and said pre-heated label 12 so that they arrive at the gap 3 A between the suction roller and the counter-pressure roller, g. directing hot air using a nozzle towards the gap 3A onto the pre heated label 12 and the tubular sack work piece 2A/2B, h. passing the pre -heated label 12 and the tubular sack work piece through the gap 3A so that their coated facing surfaces are bonded with each other,

12. The method as claimed in claim 11, wherein said indirect heating technique uses convection heaters.

13. The method as claimed in claim 11, wherein said heating means 10, 15 operate on infrared energy.

14. The method as claimed in claims 12 and 13, wherein at least the bonding surfaces of said pre-heated label 12 and sack work piece 2 are coated and optionally is printed on or laminated with oriented plastic printed film.

15. The method as claimed in claims 12 and 13, wherein said label and said sack work piece are made from thermoplastic film, or woven or non- woven thermoplastic material or their combination.

16. The method as claimed in claim 15, wherein said heating means 10 and/or 15 are provided at locations where said label web 7 is traveling between any two rollers 8.

17. The method as claimed in claim 15, wherein said heating means 10 and/or 15 are provided at locations where said label web 7 is traveling over guide rollers 8.