FIELD OF INVENTION

The embossing of packaging materials is done by passing the packing material between rotating rolls. All these rolls are made of steel and have fine teeth on them. The roll which is rotated by an external power source is called the drive roll. The two or more rolls which are mounted with their axes parallel to the drive roll, which rotate due to their engagement with the drive roll are called the driven rolls.

The embossing is obtained by passing the material to be embossed between the drive roll and the set driven rolls. These driven rolls are pressed against the drive roll, either by a set of springs or by pneumatic pressure or other methods in the fixture known as embossing head.

All the driven rolls can be mounted on a common frame, which can be pressed against the drive roll or alternatively each of the rolls can be independently pressed against the drive roll. Here the teeth on the rolls meshing with the other roll, will drive the driven roll and also emboss the packaging material placed between the rolls by transferring the teeth pattern to the material. This results in transfer of the embossing pattern to the packaging material resulting in the increase of the effective thickness of the material and alteration of its mechanical properties, so that the handling and wrapping can be done easily. This will also change the appearance of the packaging material by making a portion of the packaging material to be left without embossing or making it to undergo partial embossing, together with the completely embossed packaging material, various logos, designs etc are generated. These designs, in addition to giving a good appearance to the packaging material, can also form a security seal for the material, being unique in its texture and design. BACKGROUND OF THE ART

The following documents have been found to be relevant prior art documents in respect of the present invention.

US patent no. 6, 176,819 B l discloses the process of embossing with two meshing rolls with teeth of the same kind. US patent no. US- 671541 1 B l discloses the process of embossing of 3 or more roll system where in " all the rolls have the tooting of the same kind and same dimension", so that the 3 ^rd roll etc. does re-embossing of the paper embossed by the first set of rolls.

Indian patent no. 283456 of the same inventor, deals with embossing with two meshing rolls, wherein the teeth of one roll being different from the teeth of meshing roll.

European patent EP 2 313 263 B l (US patent 8494900) also has three rolls in the system where in one of the driven rolls is having only cylindrical grooves or helical grooves. As per this invention the angle and the depth of teeth of the drive roll are different in axial and cylindrical directions. The invention claims to achieve differential strengths of the teeth in the axial and the cylindrical direction.

US patent 7, 147,453 B2 (Indian Patent 223042) envisages the use of three rolls for embossing. In this patent, all the three rolls do not have pyramidal teeth at all. One of the driven rolls does not have pyramidal teeth, but comprises of rings or longitudinal ribs or is smooth (a plain roll).

US patent application no. US 2008/01 16610 A l discloses two and three roller system, wherein at least one of the rolls has the teeth structure which is not pyramidal in shape. DESCRIPTION OF TERMINOLOGY

The explanation for some of the terminologies used in this application is as below.

Apex angle is the angle subtended between the two inclined surfaces of the pyramid. The apex angle of the pyramid measured in the circumferential direction of the roll is called the angle in the "cylindrical direction" and the apex angle of the pyramid measured along the axis of the embossing roll is called the angle in "axial direction". When some material is removed from the tip of the pyramid, the pyramid is said to be truncated.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS

Figure l a & lb shows the meshing of the drive roll A with the driven rolls B & C. The driven rolls B & C being pressed against the drive roll A.

Figure 2a indicates the meshing of the teeth of the drive roll A with driven roll B. Figure 2b shows the position of the teeth being in contact in the cylindrical direction while the figure 2c shows the teeth of roll A and roll B in contact in the axial direction. A l is the apex angle of the pyramid in the cylindrical direction and A2 is the apex angle of the pyramid in the axial direction. In the figures 2b & 2c, B l is the apex angle of the pyramid in the cylindrical direction and B2 is the apex angle of the pyramid in the axial direction.

Figure 3a indicates the meshing of the teeth of the drive roll A with driven roll C. Figure 3b shows the teeth being in contact in the cylindrical direction while the figure 3c shows the teeth of roll A and roll C in contact in the axial direction. A l is the apex angle of the pyramid in the cylindrical direction and A2 is the apex angle of the pyramid in the axial direction. In the same figures 3b & 3c, C I is the apex angle of the pyramid in the cylindrical direction and C2 is the apex angle of the pyramid in the axial direction. Figure 4a indicates meshing of drive roll A with driven roll C where in the pyramidal teeth when both the drive roll and driven rolls are truncated. In the figure 4b, angle A3 is the apex angle of the truncated pyramid of the drive roll A in the cylindrical direction and A5 is the width of the truncated pyramid in the cylindrical direction. In the same figure 4b, angle C3 is the apex angle of the truncated pyramid of the driven roll C in the cylindrical direction and C5 is the width of the truncated pyramid in the cylindrical direction. In the figure 4c, angle A4 is the apex angle of the truncated pyramid of the drive roll A in the axial direction and A6 is the width of the truncated pyramid in the axial direction. In the same figure 4c, angle C4 is the apex angle of the truncated pyramid of the driven roll C in the axial direction and C6 is the width of the truncated pyramid in the axial direction.

Embossing caused by rolls A & B has been termed as first stage embossing, embossing by A & C has been termed as second stage embossing and so on.

In order to have better clarity of the meshing of teeth and the points of contact, in all the above drawings the material to be embossed has not been shown in between the rolls and the teeth.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for embossing packaging material like foil, paper or metallized paper or other material on system having one drive roll "A" and driven rolls (B, C, D etc.), being pressed against the drive roll "A", as shown in Fig l a, & l b.This inventions applies to systems with at least 2 driven rolls. The salient feature of this invention is that all the rolls used in embossing, namely one drive roll "A" and all the driven rolls (B, C, D etc.) (there will be two driven rolls in a three roll system, three in a four roll system and so on) will necessarily have pyramidal teeth on their periphery. The base of these pyramids will be trapezoidal, rectangular or square.

The other salient feature of this invention is that the geometry of the teeth of each of the driven rolls (B, C, D etc.) will be different from the geometry of the teeth of the drive roll

"A".

This difference in geometry is due to the apex angle of the pyramidal teeth of all the driven rolls being different from the apex angle of the pyramidal teeth of the drive roll.

As per this invention, wherein three or more rolls are used to do the embossing, while roll A will be the drive roll and rolls B, C, D etc. will be the driven rolls meshing with the drive roll A. Each of these rolls A, B, C, D etc. will be having pyramidal teeth on their periphery.

Angle B l is always different from angle A l and angle B2 is always different from angle A2. Again in this case where additional rolls like C, D etc. are meshing with roll A, angle C I will be different from angle A l and angle C2 will be different from angle A2 and so on for the rolls D etc.

In one embodiment, the apex angle of the pyramidal teeth of the first driven roll "B" (B l & B2) will not only be different from the apex angle of the pyramidal teeth the drive roll "A" (A l & A2) as already explained, but also be different from the apex angle of the pyramidal teeth of the second driven roll "C" (B l will be different from C I and B2 will be different from C2) and so on. In another embodiment, the apex angles of the pyramidal teeth of various driven rolls (B,C etc.) will be equal to each other (ie. B 1 =C 1 , B2=C2 etc), but different from the apex angle of the pyramidal teeth of the drive roll "A" (A l & A2). In yet another embodiment, each of the rolls A, B, C etc., the apex angle of the pyramids in the cylindrical direction will be equal to the apex angle of the pyramids in the axial direction (i.e., B 1 =B2, C 1 =C2 etc) or alternatively the apex angles in the cylindrical and axial direction in each of the rolls will be different (i.e., B l not equal to B2, C I not equal to C2 etc.)

Most important feature of this invention is that, in all the cases, whatever may be the number of meshing rolls, the pyramidal teeth are designed and manufactured such that there is an angular clearance between all pairs of meshing surfaces (of the drive and the driven rolls), in both the axial direction and the cylindrical direction. This is referred as the "angular clearance between the meshing teeth "or" angular clearance" in short.

This "angular clearance" has to be maintained, when the teeth are pyramids with square base or with rectangular base or with trapezoidal base.

Also in the embodiment wherein any of the rolls or all the rolls have full pyramids, the "angular clearance" has to be necessarily present.

Also in the embodiment wherein any of the rolls or all the rolls have truncated pyramids, the "angular clearance" between the teeth has to be necessarily present.

Embossing causes deformation of the material which is pressed between the rolls. At each stage of meshing, between pair of rolls, some deformation is imparted on the material. By proper choice of the apex angle of the pyramids of the drive roll and the driven rolls and the extent of truncation of the teeth various rolls A, B, C etc., as explained herein, the extent of deformation at each stage of embossing can be predetermined and that the extent of deformation can be increased in each subsequent stages of embossing (like second, third stage etc), in addition to having the angular clearance between the set of meshing teeth at every stage. By having differential angles in the cylindrical and axial direction, controlled deformation can be had in both cylindrical and axial directions. This is called the progressive embossing as the extent of embossing is progressively increased in every stage of embossing. This progressive embossing is achieved by the specific design and manufacture of the rolls in such a way, that a combination of the this differential angles at meshing and the extent of truncation of the pyramids of the teeth of the roll will decide the exact point of contact of each pair of teeth, thus predetermining the extent of deformation achieved at each of meshing of teeth so as to give as give this progressive embossing. In contrast to the prior art, the present invention, wherein three rolls consisting of drive roll A and driven rolls B & C are considered, the following variables are available in the pyramidal teeth design, namely,

i) "Angular clearance" in the cylindrical direction, between A & B ii) "Angular clearance" in the axial direction, between A & B iii) "Angular clearance" in the cylindrical direction, between A & C iv) "Angular clearance" in the axial direction, between A & C v) "Angular clearance" in the between A & B, together with truncation of the teeth of roll A and/or B. vi) "Angular clearance" in the between A & C, together with truncation of the teeth of roll A and/or C. A combination of differential pyramidal angles of the teeth of various rolls, differential pyramidal angles in cylindrical and axial directions, different angular clearances together with different truncations and having more than one driven roll will result in many new variations of the embossing systems, which will result in the following advantages. a) Progressive embossing, that is to have a controlled embossing at every stage of embossing (i.e., at the meshing of each pair of embossing rolls) b) Progressive embossing in each of the axial and cylindrical directions c) Different patterns in embossing by having controlled embossing at every stage and direction of embossing d) Controlled teeth strengths of each of the rolls in both cylindrical and axial directions. e) Controlled sharpness of the monograms giving different shadow effects. Controlling the texture of the monogram in monograms with shadow effect. g) With this new design of the teeth pattern, one can exactly pre-determine the actual point of contact of the teeth at each stage of meshing and thus pre-designate the area of wear on the teeth, at each of the set of meshing teeth. This has been utilized to increase the life of the rolls.