GB2075428A - Method and apparatus for embossing foil - Google Patents

Abstract

A method for embossing foil to produce warp-free, textured packaging sheet comprises the forming of bosses in the foil 18 while firmly supporting the foil clamped on rigid lands at the perimeter of the boss to be formed. Drawing the foil between rigid male 32 and female 30 walls of a forming cavity while so held, and interposing a sheet of yieldable material 20 between the surface of the female portion of the cavity and the sheet of foil 18 produces a yieldable matrix against which the foil comes to rest. The apparatus comprises a pair of embossing rolls of different diameter. The smaller 16 bears male embossing portions 32. The larger roll 18 has female cavities 30 exactly complementary to the male portions and is preferably produced by rolling the formed and hardened male roll against a second roll. <IMAGE>

Description

SPECIFICATION Method and apparatus for embossing foil Background of the Invention Textured foil of the type to which this invention applies is used in packaging of commodities and appears most often in the make-up of retail packages. An example of this type of foil is found in packages designed for marketing of cigarettes.

The metallic part of the foil forms an excellent vapor barrier and is desired for this purpose as well as for wrapping and adding attractiveness to the appearance of a pack of cigarettes. In the operation of cigarette packaging machinery it is usual to advance a foil-paper laminate into the equipment at a rate sufficient to supply each pack of cigarettes with the amount of foil necessary to make up a given package. The foil component is combined cooperatively with other components to make up a complete cigarette pack containing a standard number of cigarettes. The package is overwrapped and sealed to make it air tight then placed in a carton.

The prior art devices for processing the foil to emboss it comprise texturing rolls which are of cooperating complementary male and female die members arranged to rotate into register for forming bosses in the foil at the nip of the forming rolls. In one such device, the pair of rolls consist of one roll made with rigid male forming plugs. This is caused to run in compressive contact along a nip line against a roll surface with a resilient polyurethane covering. The foil is pressed into the yieldable surface of the polyurethane covered roll by the male forming bosses to form bosses in the foil.

These above methods are widely used in cigarette making and packaging machinery, but an inherent problem associated with the feeding of the textured foil is caused by the tendency of the textured foil made by former methods to curl and cause it to be difficult to guide through automatic machinery. Tendency to curl requires that more highly engineered guide and control features be provided than for a foil which lies flat. A flat foil will advance a greater distance through packaging machinery without the need for excessive guiding and controlling apparatus specially made for the express purpose of keeping the foil flat while it is manipulated in automatic handling.

Summary of the Invention The present invention achieves the production of relatively curl-free textured foil by embossing the foil while localizing the effects of lateral dimensional deformation in the foil to the immediate surface area of each individual boss.

According to one preferred embodiment of the invention, in drawing the foil to produce an individual boss, the surrounding perimeter about the base of the boss is held in place, stabilised dimensionally, and is maintained so while the fina drawing of the boss takes place. A male die in contact with the foil presses against the foil to drive and draw it into a complementary rigid walled female die to form the boss.

According to a further aspect of the invention, a yieldable material is made to interlie the opposite surface of the foil and the surface of the female portion of the forming die. The yieldable material deforms uniformly along with the foil being drawn to provide a cushioned surface mating area between the surface of the foil and the walls of the female die.

The compressive characteristics of the yieldable material are such as to distribute the compressive forces uniformly over the stressed area of the foil under contact for drawing it into conformity with the general form of the walls of the individual female die cavities. Thus the foil is relatively unimpeded in its freedom to deform yet is resiliently and forgivingly supported in the desired final configuration between the forming members.

In this manner only that area of foil which is included within the perimeter of each boss is apt to be affected in lateral dimension while being drawn to form a particular boss. A minimum of curling is thus imparted to the rest of the sheet of foil as embossing action proceeds. Since the drawing action for each boss is localized, an uneven lateral distention of the bulk of the sheet of foil is held to a minimum.

Brief Description of the Drawings Figure 1 is a side view in elevation showing a pair of embossing rolls and web and foil feed bobbins.

Figure 2 is a side view in elevation showing the embossing rolls of Figure 1 and a feed bobbin of prelaminated foil.

Figure 3 is a view in elevation showing an enlarged detail of the embossing rolls of Figures 1 and 2.

Figure 4 is an enlargement of a single pair of embossing dies with foil in place.

Description of the Preferred Embodiments Referring now more particularly to the drawings and specifically to Figures 1-4 thereof, the apparatus of Figure 1 includes rotatable supply rolls or coils 10 and 12 commonly referred to as bobbins in cigarette manufacturing nomenclature.

Roll 12 carries a supply of a metallic foil 18, such as aluminum foil, in strip form of a width suitable to a pre-selected use, and roll 10 carries a supply of resilient or deformable buffer material 20, such as paper or plastic sheet material. The metallic foil may be of a range in thickness of from .0001" to .030" and of a surface quality preselected to produce a desired effect after embossing. The thickness of the buffer material 20 may vary in thickness of up to ten times the thickness of the foil as is found to be best by experiment for a particular foil thickness.

While the present invention will be described as being applied to embossing of metallic foil, and particularly for cigarette packaging, it will be understood that the material to be embossed may be used for any purpose and may be made of any ferrous or nonferrous metal or combinations thereof. Plastic or paper materials to which a metallic coating has been applied may also be used. It is also contemplated that the present invention may be practiced in connection with the use of heat applied directly to the foil by suitable means, not shown, to facilitate and enhance means not shown to facilitate and enhance embossing action. Heat may be applied directly to the material as stated above or by heating of the embossing rolls 14 and 16 in some conventional fashion of heating, not shown herein.

The foil material 18 to be embossed is shown as coiled in Figure 1 on roll 12 from which it is fed layered with the resilient buffer material 20 from roll 10 into the nip of a pair of tangential embossing die rollers 14 and 16, the impression roller 14, and the embossing roller 16. Both rollers are made of relatively hard material. The rollers 14 and 16 are driven by suitable means, not shown, to rotate in the direction of the arrows shown in the drawings. The foil 18 and the buffer material 20 pass between the rollers 14 and 16 to pressure-form the foil 18. Take-up rollers 24 and 22 receive and store the embossed foil 28 and the spent buffer material 26 respectively.

As best seen in Figure 3 and 4, the foil 18 is extruded or drawn into the female cavity 30 of the female impression roller 14 by the raised boss portion 32 of the male embossing roll 1 6.

The depressed portions are made of the configuration designed to result in the particular decorative and structural effect intended for a particular purpose.

Particular care is taken in preparing the embossing rolls to guarantee that a non-curling foil is produced at their nip. In order to achieve this, it is critical that very accurate register is had between the individual bosses and their complementary female recesses.

The embossing rolls are made of different diameters with the male projections on the smaller roll. The use of a roll of smaller diameter to carry the male die portions is found to achieve improved results over rolls having equal diameters.

In preparing a pair of rolls, first a steel roll, preferably the smaller roll, is machined or etched with the desired pattern as represented in multiple arrangements of male bosses which protrude from the surface uniformly about the periphery of the roll 16. The smaller roll is then hardened and tempered. A second roll 14 of larger diameter is prepared with a uniformly ground smooth surface.

The rolls are then mounted with their axes in a common plane and means, not shown, are provided for causing the two rolls to meet at the nip under pressure. The two rolls are rotated under controlled pressure contact until the pattern of male protrusions on the smaller roll is duplicated in complementary recesses impressed in the surface of the larger roll.

In order to guarantee continued perfect register, registration constancy zones, not shown, which act like gear drive teeth are provided about the roll peripheries for a short distance inwardly from the ends of the rolls. These consist of areas of repetitively duplicated bosses and recesses which provide the equivalent of a gear toothed drive and which resemble an embossing pattern but which are individually much larger than the bosses and recesses of the embossing pattern.

They act as a very fine toothed drive mechanism in which back-lash is practically eliminated, and driving noise and vibration are held to a minimum.

Extreme care is exercised in transferring the patterns on the embossing and driving male roll to the surface of the female roll. The relative diameters of the rolls are calculated to insure that the circumferences of the separate rolls are such that the male and female portions match evenly with no gaps or improper matching and registration of any set of recesses.

In practice, the foil laminate is fed into the nip of the rolls at high speed and is driven through while receiving the desired impression of the pattern as designed. As stated above, a suitable set of apparatus of conventional design for applying spring pressure, not shown, is provided for maintaining adjustably a range of desired pressures for urging the rolls into contact at the nip.

Referring now to Figure 3, it will be seen that the laminate 18 is advanced in the direction of the arrow to interlie the bosses and recesses of the nip of the rolls 14 and 16. The inner wall of the recess 30 is shown as receiving the yieldable portion 20 of the laminate 34 which is compressed within the nip provided at the line of greatest proximity of the boss 32.

The progressive action of positive perimeter clamping and subsequent drawing of the foil while being advanced through the nip between the circumferentially disposed lands of the rolls between the recesses, together with the localized drawing action on the foil by the constantly reducing separation of the dies as rotation proceeds, limits the deformation of the foil area to the local area of the individual bosses.

As stated, this yieldable clamping and drawing action results in localized deformation of the foil.

In effect this establishes the raised pattern without substantially aberrating the uniformity of over-sI I lateral displacement of the sheet of foil area-wise during the drawing of the individual bosses therein. The foil is thus protected against undue non-uniform stress area-wise and physical damage at each boss by presence of the yieldable layer 20 which cushions and protects the foil against harsh compressive massaging of a damaging sort.

In this fashion, a relatively curl-free sheet is produced which can more accurately and conveniently be fed through package forming machinery with a minimum of problems which normally are associated with curling of the foil.

In Figure 1 of the drawings, there is shown an alternative method of foil embossing wherein the foil and yieldable material can feed separately into the rolls to meet at the nip and thereafter separate to produce a sheet of embossed foil-in similar fashion to the method of the present invention last above described.

Having described the preferred mode of carrying out my invention and bearing in mind that this description is to be considered for illustrative purposes without limiting the scope of my invention to the disclosure made herein.

Claims (12)

1. A method of embossing sheets of metallic foil between a pair of complementary embossing dies characterized in that the foil is held against lateral movement adjacent to the perimeters of individual die portions while the foil within such perimeters is pressed to form individual bosses.

2. A method according to claim 1 characterized in that the foil is passed between at least one pair of embossing rolls having complementary male and female die portions, and that the relative surface speeds of the rolls is regulated to cause accurate registration of the male die portions with respective female die portions.

3. A method according to claim 2 characterized in that the foil is clamped between lands on the respective rolls at the periphery of the individual male and female portions and locally drawn within the periphery of such portions by pressure of the male portions.

4. A method according to claim 2 or 3 characterized in that the roll with the male die portions is of smaller diameter than that with the female die portions.

5. A method according to any preceding claim characterized in that a sheet or layer of yieldable non-metallic material is passed between the embossing dies along with the foil.

6. A method according to claim 5 characterized in that the layer of foil is laminated and bonded to the sheet or layer of yieldable material.

7. A method according to claim 5 characterized in that the metallic foil is a coating on a surface of the sheet of yieldable material.

8. A method according to claim 5, 6 or 7 characterized in that the yieldable material is a paper or plastic sheet.

9. A method according to any of claims 5 to 8 characterized in that the metallic foil is brought into contact with the male embossing die.

10. A method of embossing sheets of metallic foil between a pair of complementary embossing dies, characterized in that a sheet of compressible material is placed between the dies along with the foil.

1 1. Apparatus for embossing sheets of metallic foil comprising at least one pair of complementary embossing rolls, characterized in that a first roll has female embossing cavities in its surface and a second roll of smaller diameter than the first has male bosses on its surface, the bosses being complementary to the female cavities and so arranged as to meet in register therewith.

12. A method of making a pair of embossing rolls for embossing metallic foil characterized in that a first embossing roll is formed with male bosses on its circumferential surface, and the hardened first roll is brought into contact with a second roll and rolled thereagainst to produce in said second roll an exactly complementary set of female cavities.