Description

Tecnnical Field

The present invention relates to an embossing roller that comprises a plurality of projections distri¬ buted in a given pattern over its surface, for embossing a laminar strip material such as, for example, a strip of paper, plastic, tissue paper or similar products.

The invention also relates to an embossing unit incorporating at least one embossing roller of the above type and to an associated embossing method. Lastly, the invention relates to a laminar embossed product obtained using a roller and a method according to the invention.

Background Art Embossing is a process which is often used in the paper converting industry, especially in the processing of what is known as "tissue" paper, for the production of toilet paper, tissues, kitchen roll and the like. Embossing involves deforming the laminar material by compressing it between a roller provided with projections of various shapes and a pressure roller which may be smooth or may also be provided with projections or indentations and which may be made of a rigid or yielding material. Various embossing techniques have been developed over the years, these differing both in terms of the type and number of rollers and counter- rollers used and in terms of the methods whereby the material to be treated is passed between the rollers. The strip material can consist of one or more webs that can be passed through a single nip between the embossing roller and the pressure roller. This technique is, for example, described in US-A-4,659, 608.

According to other embossing techniques, two or more webs are passed between separate pairs of embossing

rollers and pressure rollers and are then joined together using various techniques. Examples of embossing units of this type are described in US-A-2, 978, 006, US- A-3,414,459, US-A-3, 694 , 300, US-A-3, 881, 210, US-A- 5 3,556,907, US-A-4, 320, 162, US-A-4 , 483, 728 , EP-Λ- 0,370,972, WO-A-95/02089, WO-A-94/15776, and others.

Usually, the embossing roller has a plurality of projections of various shapes, for example frusto- pyramidal or frustocomcal projections (or even of more ljO complex shape) , which are distributed in a repeating geometric pattern - for example in helical alignments. In some cases, projections of different shapes and heights are present on the same embossing surface of a single embossing roller, as, for example, described in

15 US-A-4. , 320, 162. In this case, for example, the embossing roller has a series of frustopyramidal or frustocomcal projections arranged in helical alignments, but in some, geometrically distributed, areas the frustopyramidal projections are absent and are replaced with projections

20 of a different height which represent a composite design. This embossing roller gives a complex embossed effect. However, preparing the roller surface is extre¬ mely difficult since projections of varying shapes and heights need to be made in an extremely accurate

25 pattern.

Application No. FI 94 0 000067 for a multiple registered design, filed on 17 November 1994 by the same applicant, discloses a series of embossing cylinders provided with frustopyramidal projections arranged in

30 various designs. Some of these have a series of con¬ tinuous channels which run parallel to the direction of the projections and which can be produced during the same process as that in which the projections are made. There is no provision for recessed designs which are

35 discontinuous and/or not parallel to the alignments of the projections on the cylinder.

Summary of tne Invention

The invention proposes a new type of embossing roller which is inexpensive and simple to produce ana which enables embossed materials with specific aesthetic effects to be obtained. The low costs involved m preparing the roller surface mean that different rollers can be maαe inexpensively according to the specific requirements of individual users.

Basically, the roller according to the invention has an embossing surface provided with projections, on which surface a recessed design is formed which consists of one or more indentations or incisions that extend from the tops of the projections to the bases thereof and whose depth is preferably greater than the height of the said projections. Such a design can be made quite easily, for example by milling, optionally using a form milling cutter so as to avoid generating sharp edges and thereby minimize problems of wear of the pressure roller. The projections can be made m a prior process by means of one of the known systems, for example using chip-removal, chemical or plastic-deformation processes. Whereas the basic preparation of the roller surface in order to produce the projections is lengthy and expensive, producing the subsequent recessed design is a relatively simple operation. This means that embossing rollers with customized designs can be made available to various users, using a standard embossing roller - that is one provided with conventional projections - as a starting point. The recessed design may consist of incisions which are not parallel to the alignments of the projec¬ tions, or of incisions which are parallel to the align¬ ments of the projections but are not continuous, that is, for example, of lines forming rectangles or squares. Generally speaking, the design can be discontinuous and not parallel to the alignments of the projections. These options are made possible by the fact that the recessed design is not formed at the same time as the projections

are formed, but m a subsequent stage, once the roller has already been provided with the projections.

Using an embossing roller of this type in a conventional embossing unit produces an embossed strip material with a traditional pattern, for example with frustocomcal or frustopyramidal points, over whicn a relief design corresponding to the recessed design formed on the embossing roller is superimposed. The design is particularly sharp and prominent when the density of the projections is fairly high, for example between 30 and 50 projections per cm ² or higher. However, the possibility of forming the same design on rollers with a lower projection density, for example of between 5 and 100 or, preferably, of between 10 and 60 projections per cm", is not excluded.

The embossing unit can be of the type comprising a single embossing roller and an associated pressure roller, between which one or more webs forming the strip material are passed. In this case a relief design will be formed on one face of the material, while a corresponding recessed design will be produced on the other face. The material will then be packaged m such a way that the relief design will be on show.

On the other hand, the embossing unit can also be of the type with two embossing rollers, each of which is provided with an associated pressure roller. In this case the webs forming the strip material are embossed separately and then joined together. It is thus possible to obtain various web combinations, as will be described in greater detail below.

Further advantageous features of the embossing roller, embossing unit, method of preparation and strip material according to the invention are given in the appended claims, which form an integral part of the present description.

Brief description of the drawings

A better understanding of the invention will be gained from the description and appended drawing, which

shows a practical and non-limiting example of the said invention. In the drawing:

Fig. 1 shows an embossing unit into which the present invention can be incorporated; Fig. 2 shows a greatly enlargeα diagrammatic cross-section of the embossing zone;

Fig. 3 shows a planar development of a portion of the embossing roller of Fig. 1;

Fig. 4 shows a planar development of a portion of strip material embossed by the roller portion of Fig. 3;

Fig. 5 shows a more complex embossing unit into which the present invention can be incorporated;

Fig. 6 shows a diagrammatic enlargement of the lamination zone of the embossing unit of Fig. 5 in a first embodiment;

Fig. 7 shows an enlarged cross-section of a laminar material as it comes out of the embossing unit of Fig. 5 in a first embodiment; Fig. 8 shows a diagrammatic enlargement of the lamination zone of the embossing unit of Fig. 5 in a second embodiment;

Fig. 9 shows an enlarged and diagrammatic cross- section of the strip material as it comes out of the emoossing unit of the second embodiment;

Fig. 10 shows a diagrammatic enlargement of a portion of strip material embossed according to a third embodiment; and

Figs 11 and 12 show a planar development of a portion of an embossing roller and a local section through the said roller respectively, m a further embodiment .

Detailed description of the invention Referring initially to Figs 1 to 4 , a first embodiment of the invention will initially be described.

Fig. 1 shows a particularly simple embossing unit comprising an embossing roller 1 working m con _j unction with a pressure roller 3. The two rollers 1

and 3 are pressed against each otner and a strip material N to be embossed, for example made of tissue paper, is passed through the nip formed between them. The rollers 1 and 3 rotate in opposite directions, as indicated by the arrows in the drawing, while the strip material advances between them.

The embossing roller 1 is provided with a plura¬ lity of projections or protuberances 5 on its active surface, while the pressure roller 3 has a smooth exter- nal cylindrical cover made of an elastically yielding material which deforms under the pressure of the pro _j ec¬ tions 5, as diagrammatically illustrated in Fig. 2. The projections 5 have a top 5E and a base 5B, with the distance - measured in a radial direction - between t _h e base and the top defining the height H of the pro _j ec¬ tions .

The strip material N can consist of a single web or a plurality of webs which, as they pass between the rollers 1 and 3, are joined together and embossed. In addition to the projections 5, the surface of the embossing roller 1 has a recessed design formed by a plurality of channels or indentations 7 which can be seen in the planar development (Fig. 3) of a portion of the active surface of the roller 3. The channels or indentations 7 form a design which is chosen by the user employing the machines and is reproduced on the strip material N in the form of a relief design D (Fig. 4) on one -face and a recessed design on the other face.

The depth of the channels 7 (in the example illustrated) is greater than the height H (Fig. 2) of the projections 5 on the roller 1, so that the design D is particularly well defined on the material N.

In a modified embodiment, one or more non- embossed webs can be joined to the embossed material coming out from the pair of rollers 1 and 3, these webs being applied to the rear surface - that is the surface in contact with the pressure roller. The embossed web or webs can be joined to the smooth web by applying a glue and with the aid of a smooth counter-roller which, for

example, works in conjunction with the saiα embossing roller 1.

Fig. 5 shows a different type of eiruoossing unit, known in the art, into which the present invention can be incorporated. This embossing unit has two embossing rollers 13, 15, each of which is provided with a plura¬ lity of projections 13P, 15P arranged in identical, symmetrical or different positions or the two rollers 13, 15, as is known per se. Each embossing roller works in conjunction with an associated pressure roller 16, 17 covered with a cover 16A, 17A made of elastically yielding material. The reference 19 indicates a glue- applying unit.

A first web VI of a strip material N is passed Detween the two rollers 13, 16 and embossed between the said two rollers, while a second web V2 is embossed between the rollers 15 and 17. The two embossing rollers 13, 15 are positioned next to each other and are pressed against each other in a contact and lamination zone m which the two, separately embossed, webs VI and V2 are joined together. The glue-applying unit 19 applies glue to those portions of the web V2 located on the projec¬ tions of the embossing roller 15 so that the two webs VI, V2 can be securely joined together in the lamination zone.

According to the invention, at least one of, or both the embossing rollers 13, 15 have an inciseα recessed design similar to the design formed by the cnannels 7 m the roller 1 of the embossing unit shown in Fig. 1.

When both the embossing rollers have a recessed design, the said designs can be the same or different. Furthermore, in either case, these designs can be in phase or staggered. In the former case, two relief designs - matching on both faces - will be produced on the embossed strip material, while in the latter case the relief designs will not match.

Fig. b diagrammatically shows a cross-section through a planar development of the lamination zone

between the two embossing rollers 13, 15 with the two previously embossed webs VI, V2 being joined together at the point where the projections 13P, 15P of the two rollers 13, 15 meet. The references 13C ana 15C aenote the channels formed in the surfaces of the two rollers 13, 15, the depth of which is greater than the height of the projections 13P, 15P, and which correspond to the channels 7 in the example of Figs 1 to 4.

Fig. 7 shows a diagrammatic and greatly enlarged local cross-section of a portion of strip material N produced using the embossing unit of Fig. 5. VI and V2 denote the two webs forming the material N, which have been joined together by means of the glue C in the zones embossed by the projections 13P, 15P. Dl and D2 denote the sections of the relief designs which are produced by the recessed designs formed in the two embossing rollers 13, 15. The two designs Dl and D2 may or may not coincide .

Fig. 8 shows an embodiment in which only the roller 15 is provided with a recessed design, defined by channels 15C, while the embossing roller 13 is provided only with projections 13P. Using this pair of embossing rollers produces a strip material - illustrated in the diagrammatic, enlarged cross-section of Fig. 9 - with one embossed web V2 having a relief design D2, while the web VI is only embossed with a pattern of projections reproducing the projections 13P on the embossing roller 13 and has no relief design.

A further type of product is obtained by passing one of the two webs, for example the web V2, only through the lamination zone between the two embossing rollers 13, 15, without previously passing it between an embossing roller and a pressure roller. This alternative route is shown in dashed lines in Fig. 5. In this case, a strip material is produced - shown in enlarged local cross-section in Fig. 10 - m which the web V2 is embossed with a design reproducing the projections on the embossing roller 13 in negative form and the relief

design Dl m positive form, and is joined by means of gluing to a non-embossed web VI .

Figs 11 and 12 show a specific form of incision in the embossing roller 13. In this case tne design, of which a portion can be seen in planar development in Fig. 11, is defined by pairs of essentially parallel mcxsion lines 13C, 13C' ¹ . Some projections 13P remain between the two lines 13C and 13C ', as can be seen quite clearly in the section of Fig. 12. A specific aesthetic effect can be produced in this way.

When the strip material consists of a plurality of webs which are joined together by means of gluing, it is possible to use a coloured glue so as to give an additional aesthetic effect. This is a technique known per se and is employed in embossing units of the pomt- to-point type having the structure illustrated Fig. 5. Nevertheless, the use of this technique m conjunction with an embossing roller having a recessed design pro¬ duces novel, high quality results and an unexpected aesthetic effect on account of the fact that that area of the strip material which is in relief, corresponding to the recessed design on the roller, will not be coloured because the entire design area D does not receive any glue. The result is a two-tone product in which the background, defined by the embossing produced by the projections 13P, 15P, is coloured as a result of the application of pigmented glue, whereas the relief design is the same colour as the original material - for example white. It should be understood that the drawing shows only one example, given solely by way of a practical demonstration of the invention, it being possible for the forms and arrangements of the latter to vary without thereby departing from the scope of the concept underly- ing the said invention. Any reference numerals appearing in the appended claims have the purpose of facilitating reading of the claims with reference to the description and the drawing, and do not limit the scope of the protection represented by the claims .