WO2010010580A2

WO2010010580A2 - A device and method for embossing of packaging material like foil, paper or metalized paper

Info

Publication number: WO2010010580A2
Application number: PCT/IN2009/000413
Authority: WO
Inventors: Rakesh Nanjundiah
Original assignee: Rakesh Nanjundiah
Priority date: 2008-07-21
Filing date: 2009-07-20
Publication date: 2010-01-28
Also published as: WO2010010580A4; WO2010010580A3

Abstract

Packaging material is embossed by passing between two fine teethed rotating rolls, which are pressed against one another. Both the rolls have fine pyramidal teeth on them. The teeth are designed and manufactured such that the apex angle of the pyramids of one of the rolls is different from the apex angle of the pyramid of the other roll. This differential angle of the two pyramids will provide operational clearance for each teeth and thus reduce the friction between the two rolls and increase the flexibility of the system in the practical dynamic condition of the embossing in the packaging industry. This will also function as one or more variable parameter to vary the quality and texture of embossing.

Description

A DEVICE AND METHOD FOR EMBOSSING OF PACKAGING MATERIAL LIKE FOIL, PAPER OR METALIZED PAPER

The present invention relates to a device for embossing of packaging material like foil, paper or metalized paper placed between two rolls pressed against each other.

Background of the Invention

The embossing of packaging materials is done by passing the packing material between two rotating rolls. Both these rolls are made of steel and have fine teeth on them. One of the rolls which is rotated by an external power source is called the driving roll (or the drive roll) and the other roll which is mounted in the same plane, parallel to the driving roll, which rotates due to the engagement with the driving roll is called the driven roll. The embossing is obtained by pressing these rolls together either by a set of springs or by pneumatic pressure or other methods in fixtures known as embossing heads. The teeth on the rolls mesh with each other and therefore emboss the packaging material placed between the rolls by transferring the teeth pattern onto the material. This transfer of the embossing pattern onto the packaging material results in the increase of the effective thickness of the material and alteration of its mechanical properties, so that handling and wrapping can be achieved easily.

In the existing design both the rolls are of the same kind and have teeth of exactly the same shape and size. The type of embossing material used varies depending upon the application and the industry. With the use of biodegradable metalized paper, the rolls used for embossing are required to run under much higher pressures as these papers are much tougher when compared to the foils and other materials which were being used earlier. Thus, the load on each of the teeth will be much higher and therefore the chances of failure of the teeth due to misalignments caused due to the various internal and the external factors will also increase. In the existing design one of the rolls is mounted on a flexible system wherein the roll is allowed to move freely in the axial and radial direction, while teeth are held in such a position where the relative friction is very high and the teeth tend to get locked in this position.

US Patent No. 6,176,819 Bl discloses a technique for embossing foils between a pair of rollers having toothings of the same kind which comprise rows of pyramidal teeth extending in the axial and the circumferential directions. The heads of the teeth are flattened and the edges of the pyramids are cut. The teeth of each roller are configured to mutually engage each other via a film to be embossed, one of the rollers being fixedly supported and driven while the other being freely rotatable the arrangement being such that upon engagement of the rollers each of the teeth of one of the rollers is symmetrically enclosed between four teeth of the other roller.

Under these circumstances, the size and shape of the teeth on each of the rolls (or rollers) have to be controlled in such a way that the normal law of nature itself must position the teeth of the driven roll relative to the teeth of the driving roll in the most preferred position, so as to achieve the best embossing with minimum chances of damage to the teeth. Further, in a dynamic situation of embossing, in addition to the clearance provided to one of the rolls, each teeth has to be provided with clearances in order to eliminate the problem of interference. The present invention is a step in this direction that makes the embossing device of the present invention particularly suitable to cater to the need of high pressure embossing for bio-degradable metalized paper.

Summary of the invention

The salient feature of this invention is that the teeth on one of the rolls are made different from the teeth on the other meshing roll. That is, the geometry of the teeth of the driven roll is intentionally made different from the geometry of the teeth on the driving roll. This difference in the teeth geometry has been created to provide the rolls and the teeth the freedom to move and swivel freely in all the required directions, (within the limits of the selected design) so as to achieve smooth engagement and running in the dynamic condition. The present invention also ensures interference free running of the teeth with minimum friction and delivers good quality of embossing of the packaging material.

Accordingly, the present invention provides a device for embossing packaging material like foil, paper or metalized paper placed between the two rolls pressed against each other, the driving roll "A" being driven by external power, while the other driven roll "B" being driven by the driving roll by meshing of the two rolls, the arrangement being such that each roll has small pyramids, the pyramids of the driving roll "A" being dimensionally different from the pyramids of the driven roll "B".

The present invention also provides a method of embossing packaging material like foil, paper or metalized paper, the method comprising the steps of passing said packaging material between pyramidal teeth of a driving roll "A" and driven roll "B" of an embossing device, wherein said pyramidal teeth of the driving roll and driven roll are dimensionally different and configured to mesh freely and emboss a pattern on said packaging material when pressed together, pressing said packaging material between the pyramidal teeth of the driving and driven rolls with the driving roll set into motion thereby embossing the packaging material with the pattern provided by the pyramidal teeth meshing from two sides of the packaging material and withdrawing the embossed packaging material out of the embossing device.

Brief Description of the Accompanying Drawings

Figure Ia shows the pictorial view of the two rolls in the meshed condition. The two views of the rolls in the meshed condition are shown in figures Ib and Ic. In the figures Ib and Ic, the teeth of the driving roll "A" is seen meshing with the teeth of the driven roll "B". Here the rolls have different apex angles.

Figure 2 shows meshing of the two rolls in Figs. Ib and Ic with the packaging material in between them.

Figures 3a and 3b show that the teeth of the one of the rolls are truncated, while the teeth of the other are not. The apex angles of the pyramids in the two rolls are different.

Figure 4a and 4b shows meshing of the two rolls shown in Figures 3a and 3b with the packaging material in between them.

Figures 5a and 5b show two views of the rolls in which the teeth of both the rolls are truncated and are having different apex angles. Figures 6a and 6b shows the two views of the meshing of the two rolls in Figures 5a and 5b with the packaging material in between them.

Figure 7 shows the pictorial view of the teeth of the two rolls with truncated tips and rounded edges in the working condition. In this the pyramid of one of the rolls is located in between four pyramids of the other roll.

Figures 8a, 8b and 8c show the point of contact of the teeth of the two rolls, when both the rolls have full (un-truncated) teeth.

Figures 9a, 9b and 9c show the points of contact of the teeth of the two roll when one of the rolls have truncated teeth while the other have full pyramidal teeth.

Figures 10a, 10b and 10c indicate the points of contact of the teeth of the two rolls, when the teeth of both the rolls are truncated.

Figures 11a and lib show the points of contact of the teeth when one of the rolls is shifted by half the pitch.

Figures 12a and 12b show the points of contact of the teeth when the teeth of one of the rolls are partially shifted.

Detailed Description of the invention

The embossing of the material is achieved by passing the material to be embossed between two embossing rolls pressed together by springs or pneumatic pressure. During this process the pattern on the rolls will get transferred to the material and the effective thickness of the material increases, thus, increasing its stiffness and other properties of the material in addition to giving it a matte finish. Such embossed materials are used for packing many items including cigarettes.

To give this effect to the material, teeth of each of these rolls will be of the shape of small pyramids with a square or rectangular base. In a typical roll the full pyramids have square base of side about 0.400 mm and a height of about 0.150 mm. To get the best embossing, when the two rolls mesh, each pyramid of the roll is expected to locate itself at the gap between four pyramids of the other roll, thus pressing the material in this recess to give a matte finish to the material. In the existing process, both the rolls namely the driving and the driven have the teeth of the same kind.

This invention envisages making the teeth of the driven roll different from the teeth of the driving roll. The two teeth can be made different in many ways. One of the methods is to make the size of the teeth different from one another. According to this invention, the size of bases of the pyramids in both the rolls are maintained same, so that the basic structure of embossing is not altered, while the apex angles of the pyramids of the two rolls are altered. The apex angle of the pyramids of the driving roll is kept different from the apex angle of the pyramid in the driven roll according to the invention. This difference in the angle provides a natural clearance to the teeth and makes the entry of teeth in between the teeth of the other roll smooth.

The engagements of the teeth where in both the rolls have full un-truncated teeth, as seen in the axial and radial direction is shown in Figures Ib and Ic. In these figures the teeth of the driving roll "A" is seen meshing with the teeth of the driven roll "B". The apex angle of the pyramids in the driving roll "A" in the cylindrical direction is X and the apex angle in the axial direction is Y. The apex angle of the pyramids in the driven roll "B" in the cylindrical direction is P and in the axial .direction is Q. As per this invention, angle P is made different to angle X and angle Q is different angle Y. The angle P is less or more than angle X and angle Q is less or more than angle Y, but never equal.

The value of the angle (X-P) is independent of the angle (Y-Q) and the same can be altered to achieve the best results. In a much simpler situation X-P = Y-Q, which means that clearance in the cylindrical and the axial direction are the same. While X is not equal to Y and P is not equal to Q, the base of the teeth of both the rolls are rectangular. Also when X = Y and P = Q, the pyramids are symmetrical and have a square base. It is essential that the circumferential distance between two rows of pyramids in the axial direction is maintained same in both the rolls. Moreover, the linear distance between two circular bands of pyramids in both the rolls is also maintained same.

Depending on the actual situation, it is possible to vary these angles and arrive at the angles to achieve the best embossing. It has been found from trials that keeping the apex angles of the pyramids of the driving roll, (namely X and Y) more than the apex angles of the driven roll (namely P and Q) yields best results.

Any system would always take the path of least resistance. At the time of initial engagement, the teeth may engage in many different positions. Once the rolls start rotating under pressure, the teeth will settle at the point of minimum center distance of the two rolls and point of minimum resistance that is the point of maximum clearance, which will be the most stable working position.

Due to the difference in angles of the pyramids of the two rolls, the clearance between one teeth of the driving roll and the corresponding four engaging teeth of the driven roll is much higher in the device of this invention than in the conventional system. Thus, the gap created in between the four pyramids being the place of maximum clearance and therefore minimum resistance, the tips of the pyramids of the other rolls would naturally get guided into this space and will always try to remain in this position itself.

The novelty of this invention is that, in all working positions of the rolls and in all the variants of the pyramidal teeth, the resistance between the rolls in this new design is the minimum.

NON TRUNCATED PYRAMIDS: The two rolls with non-truncated (full) teeth in the engaged condition is shown in Figs Ib and Ic. The three views of the meshing teeth of the two rolls with full non- truncated pyramids on each of the rolls as per the new design in the most stable working position is as shown in Figures 8a, 8b and 8c. In these figures, the apex angle of the pyramids of the driving roll is more than the apex angle of pyramids of the driver roll. Due to the differential angles of the teeth of the two rolls, the heights of the pyramids of the two rolls are different. It can be seen that the tip of the pyramids of the driven roll are in contact with the root of the pyramids of the drive roll. This means that there will be a single point contact for every set of teeth. ONE OF THE PYRAMIDS TRUNCATED: The rolls in the engaged condition, wherein the driving roll having non-truncated teeth and the driven roll with truncated teeth with different apex angles, is as shown in figures 3a and 3b. The same roll in these figures with the packaging material in between them is shown Figures 4a and 4b. The three views of the meshing of the teeth in the most stable working position are shown in figures 9a, 9b and 9c. It can be observed that the contact takes place on four corner points of the truncated crust of the pyramid, which is truncated.

BOTH THE PYRAMIDS TRUNCATED: The two views of the meshing rolls when both the rolls have truncated teeth with different apex angles are shown in Figures 5a and 5b. The same roll with the packaging material between them hem is shown in Figs. 6a and 6b. In the figure, the apex angle of the pyramids of driving roll is more than the apex angle of the pyramids of the driven roll. Three views of the meshing of these teeth in the most stable position of working are as shown in figures 10a, 10b and 10c. In this situation, the point of contact will be the four corner points of the truncated crust of the pyramid of the driven roll.

Even when the rolls are not working in the most stable position, that is, when the teeth of the driven roll is not exactly in between four teeth of the driving roll or when the teeth are axially or radially shifted, the actual contact will be on a line. The two views of the teeth in this condition, wherein the teeth if shifted by half the pitch, is as shown in Figures 11a and lib.

The two views of the teeth in meshed condition, when the shift is not exactly equal to half the pitch (i.e. less or more than half the pitch), is as shown in Figures 12a and 12b. Even in this condition the actual contact will be on a line, but the length of the line being less than shown in Figures 11a and l ib. The length of the line of contact depends on the amount of shift and the extent of truncation of the two teeth.

In contrast, in the existing design, wherein the apex angle of both the pyramids are equal to each other, in the most stable position of working, all the four inclined edges of the pyramid are fully in contact with the inclined edges recess of the other roll, resulting in high friction and tendency of the teeth to get locked in this position. When the rolls are not working in the most stable position, that is when the teeth of the driven roll is in between four teeth of the driving roll but are axially or radially shifted from the most stable position, there will be a surface contact of the inclined surfaces of the pyramids, and thus maximum friction.

Thus, in the teeth design made as per this new invention, the contact is always on points in the most stable working position of the teeth. This is true for all variants of the pyramids. Naturally, this is the position of minimum friction. Even while the teeth are shifted, for all variants of the pyramid, the maximum contact is on two lines, thus resulting in substantially lesser friction than the existing design.

In practical situations of the shop floor, the rolls will have to function in situations where we have dusty environment, bearings with clearances, system with out of roundness, manufacturing inaccuracies, uneven wear, partial clogging of rolls, to name a few. The best of manufacturing and operational methods can reduce each one of them, but cannot completely eliminate them. Each one of these and any combination of these will give rise to dynamic forces in the system in various directions.

Thus, any system, especially dynamic systems should have some flexibility built into them so that these dynamic forces are eliminated, or at least, reduced. This has to be done at the teeth level by providing clearances for each of the teeth, so that the teeth are free to move, align and adjust themselves, possibly many times every minute, for the smooth functioning of the system.

Due to the natural clearance created in each of the intersection of the pyramids by this novel invention, the rolls will be able to move independent of the other in all the directions and will also be able to effect a small amount of rotation relative to one other. This dynamic flexible system will automatically reduce the dynamic load on each of the teeth and increase the life of the teeth without compromising the quality of embossing.

It is important to note that embossing is a dynamic phenomenon. Even during working, due to various reasons like clogging of few of the gaps between the pyramids of the rolls, the rolls will be temporarily forced away from each other at that particular point, while in all the other points on the roll tends to remain in the engaged position. When a clean gap is reached during rolling, the teeth will have to be guided in to the space between the pyramids. Even during this dynamic situation, the additional clearance created by the differential angle will make the pyramids take the most desired position.

Whenever teeth of the same type roll on one another, there is interference. For the same reason while designing a gear, the flanks of the teeth will be designed as a part of an involute or cycloid to achieve pure rolling motion. During embossing, only one roll, namely the driving roll is rotated by an external source, and the driven roll is rotated due to the meshing of the teeth, making the meshing situation similar to that seen in gears. By providing different angle to the teeth of the two rolls as per this invention, clearance is automatically available to each teeth and this completely eliminates the chances of interference of the teeth, thus, resulting in smooth running of the rolls. Also that the clearance will automatically prevent the locking of the teeth, even when accidentally run with out packaging material.

With this invention, one more variable is now available in addition to pitch and truncation of the pyramids, which can alter the quality and texture of embossing. By varying the angles of the pyramids of the two rolls, it is possible to get different depths even when the extent of truncation is maintained at the same level. In other words, it is also possible to get the same depth with different extents of truncation of the teeth and different apex angles pyramids of the teeth. Thus, embossing of different textures can the achieved by changing the angles and the extent of truncation independently.

Practical experimentation has shown that best of the results can be obtained when the apex angles of the pyramids of the driven roll is maintained 6 to 12 degrees less than the apex angle of the pyramids of the driving roll. This has been found true irrespective of the extent of truncation of the teeth.

In all the above deliberations the pyramids considered have sharp edges on all the corners and at the plane of truncation. The rolls are used embossing packaging material which is very sensitive and may puncher the packaging material. It has been found that rounding of all the sharp edges, as shown in Figure 7, by a suitable radius will completely eliminate the chances of puncturing. This will also improve the performance of the rolls and also eliminate the chances of chipping of the edges of the pyramidal teeth.

Claims

I CLAIM

1. A device for embossing packaging material like foil, paper or metalized paper placed between the two rolls pressed against each other, the driving roll "A" being driven by external power, while the other driven roll "B" being driven by the driving roll by meshing of the two rolls, the arrangement being such that each roll has small pyramids, the pyramids of the driving roll "A" being dimensionally different from the pyramids of the driven roll "B".

2. The device of claim 1, wherein the pyramids present on the driving roll "A" have an apex angle different for the apex angle of the pyramids on the driven roll "B".

3. The device of claim 1, wherein the pyramids have rectangular or square base.

4. The device of any preceding claim, wherein the apex angle of the pyramid present on each of the rolls in the circumferential direction and the axial direction are different to provide varying clearances in the two directions.

5. The device of any of claims 2 or 3, wherein the said apex angle in the axial and the cylindrical direction are same so that the clearances in the axial and the cylindrical direction are equal.

6. The device of any preceding claim, wherein the apex angles of the pyramids on the driven roll "B" is lesser than the apex angles of the pyramids on the driving roll "A".

7. The device of any preceding claim, wherein the pyramids of both the rolls are full pyramids.

8. The device of any preceding claim, wherein one roll has full pyramids and the other roll has truncated pyramids.

9. The device of any preceding claim, wherein both the rolls have truncated pyramids.

10. The device of claim 9, wherein the extent of truncation of the pyramids in the two rolls are same.

11. The device of claim 9, wherein the extent of truncation of the pyramids in the two rolls are different.

12. The devices of any of claims 1 to 11, wherein a difference of 6 to 12 degrees is maintained between the apex angles of the two rolls.

13. A method of embossing packaging material like foil, paper or metalized paper, said method comprising the steps of: passing said packaging material between pyramidal teeth of a driving roll "A" and driven roll "B" of an embossing device, wherein said pyramidal teeth of the driving roll and driven roll are dimensionally different and configured to mesh freely and emboss a pattern on said packaging material when pressed together; pressing said packaging material between the pyramidal teeth of the driving and driven rolls with the driving roll set into motion thereby embossing the packaging material with the pattern provided by the pyramidal teeth meshing from two sides of the packaging material; and withdrawing the embossed packaging material out of the embossing device.

14. A device for embossing packaging material, substantially as described herein, particularly with reference to and as illustrated in the accompanying drawings.

15. A method of embossing packaging material, substantially as described herein, particularly with reference to the preceding description. x