Web embossing machine

Abstract: The web embossing machine of the present invention has two embossing cylinders (3, 5) brought close to one another for combining two paper webs (N3, N5) by the pressure contact between mutually corresponding protrusions (S) on the two cylindrical surfaces. The protrusions are in rows which present a pattern inclined relative to the axes (X-X) of the respective cylindrical surfaces, i.e., in a helicoidal fashion and relative to a plane passing at right angle through said axis, and thus achieve a subsequent and progressive contact instead of a simultaneous contact throughout the row. The inclination relative to a plane passing at right angle through the cylinder axis avoids repetitive pressure actions on the pressure rollers cooperating with the embossing cylinders.

Description: The invention relates to an embossing machine for the paper converting industry, having two embossing cylinders, each with a Plurality of parallel rows of protrusions and each with a cooperating pressure roller, to emboss a pattern onto two respective paper webs, said embossing cylinders being movable close to one another for bonding the two embossed paper webs by pressure-contact between mutually corresponding protrusions of the embossing cylinder. At least one of the two paper webs is moistened after embossing between an embossing cylinder and its mating rubber-covered rolls and before mating with the other web or at the junction between the two cylinders. This obtains the stable junction with the other web between the facing protrusions of the embossings of the two webs. The protruding surfaces of the two embossing cylinders are obtained by removal of material, through mechanical or chemical procedures or others, so as to have the protrusions disposed in at least a series of rows equidistant from each other and parallel to the axis of the cylindrical surface. Preferably, the protrusions are also aligned in a second - series of rows at a right angle to the rows of the previously mentioned series and primarily according to the circumferential rows of protrusions. In the embossing units of the above mentioned and known type, drawbacks are found on the rubber covering of the pressure rollers which cooperate with the embossing cylinders. US-A-3 961 119 discloses a web embossing machine of the above mentioned type. wherein the two mutually cooperating embossing rollers are provided with rows of protrusions which are arranged according to helicoidal rows of protrusions. These rows are inclined about 45° to the axis of the relevant cylinder. This arrangement of protrusions gives rise to an alignment of protrusions which lyes in a plane that is perpendicular to the cylinder axis. This causes a concentration of wear on the rubberized pressure roller according to annular lines, since the protrusions aligned according to annular lines contact the pressure roller always in the same annular area, with consequent deformation of the rubber-covered surface in the course of time until the rubber-covered roll or the rubber covering thereof needs to be replaced. From US-A-3 738 905 there is known a further embossing machine, wherein the protrusions are in form of helicoidal channels and ribs. Also this known arrangement can have the drawback of a concentration of wear of the rubber roller, along helicoidal lines, and consequently a deformation of the roller. Moreover, due to the particular shape of these helicoidal protrusions, the glue which is applied on one of the webs before bonding thereof is distributed over a large area. This large amount of glue is unnecessary for the purpose of bonding the two webs together and negatively affects the quality of the end product. An object of the invention is that of avoiding those drawbacks due to the repetitiveness of positions of the embossing cylinder protrusions onto the rubber-covered rolls, especially where circumferential rows of protrusions of the embossing cylinders contact the rubber covering. Furthermore, the prior-art arrangement of the protrusion rows parallel to the axis causes, during operation, vibrations and concentrated and repeated stresses. This is due to the fact that one row of protrusions of one embossing cylinder contact simultaneously one row of protrusions of the other cylinder. in order to compress the two paper webs present between the opposed tips of the protrusions of the two cylinders. This causes variations of stress condition between the contact positions and non-contact positions of the protrusions of the rows which follow one after the other, and thus concentrated stresses, vibrations, and drawbacks as far as the dimensioning, maintenance and life of the various elements are concerned. This occurs also in US-A-3 961 119, since the helicoidal arrangement of the rows of protrusions generates a secondary alignment of protrusions, which is parallel to the cylinder axis. US-A-3 738 905 does not give rise to this inconvenience, since it does not provide rows of protrusions, but helicoidally arranged channels. However, this known machine is suitable only for some kinds of manufactured products and, as stated above, the helicoidal shape of the embossed ribs causes disadvantages as far as application of glue is concerned. Another object of the invention is that of avoiding these drawbacks which are known to those skilled in the art. These and other objects, which will be evident to those skilled in the art by the reading of the following description, are achieved by an embossing machine of the above mentioned kind, with the features of claim 1. Further advantageous features and embodiments of the machine of the invention are set out in the dependent claims. US-A-4 659 608 disdoses a machine with an embossing cylinder which has a first and a second series of parallel rows of protrusions. The object of this known arrangement is that of avoiding nesting of bosses when the embossed web is wound to form a roll. This known machine is, however, based on a different embossing process, since it has only one single embossing cylinder which cooperates with one single pressure roller. Embossing is performed on previously coupled plies forming the web. For the purpose of illustrating the invention, there is shown in the accompanying drawings a form thereof which is at present preferred, although it is to be understood that the various instrumentalities of which the invention consists can be variously arranged and organized, and that the invention is not limited to the precise arrangements and organizations of the instrumentalities as herein shown and described. In the drawings, wherein like reference characters indicate like parts: FIG. 1 shows very schematically an embossing unit which produces tip-to-tip embossing. FIG. 2 shows a plan view of a portion of an embossing surface with almost pyramidal-frustum protrusions in two series:of protrusions, with the rows of one series being at a right angle to those of the other series. FIG. 3 shows a local section on line III-III of FIG. 2. FIG. 4 shows examples of possible inclinations. According to the drawings within a housing 1. two embossing cylinders 3 and 5 respectively are mounted, which are disposed with their axes parallel to each other. The embossing surfaces are in contact one with the other at the tips S of embossing protrusions. Cooperating with the embossing cylinder 3 is a roll having a surface 7 which is yielding (such as rubber-coated or non-elastic) and which provides a pressure surface for cooperating with the embossing surface of cylinder 3. Numeral 9 indicates another pressure roller similar to that indicated by 7, for cooperating with the embossing cylinder 5. The two rollers 7 and 9 are mounted on arms 7A and 9A respectively, which are pivoted and resilientally urged (for example, by cylinder-piston systems 7B and 9B) to press the respective rollers 7 and 9 against the corresponding embossing cylinders. Both pressure rollers 7 and 9 may be located beneath the respective embossing cylinders or both above them. N3 and N5 indicate the two paper webs which are fed between cylinder 3 and roller 7 and respectively between cylinder 5 and roller 9 in order to be embossed. The two embossed webs are driven around cylinders 3 and 5 and are joined together at protrusions S in facing relationship on the embossed webs, through a so-called tip-to-tip combining procedure. A two-ply web N2 is thus obtained which is moved away by passing it between driving rollers 10 and 12 or in any other suitable and known way. For combining the two paper webs there is provided a suitable adhesive applicator 14, which is urged against the web N3 on the surface of cylinder 3 to apply adhesive onto the web N3 which rests on the tips of the protrusions of cylinder 3. The adhesive is transferred by web N3, as said cylinder 3 turns to the junction thereof with web N5 in the nip between the protrusions of cylinders 3 and 5. This is the so-called tip-to-tip arrangement. According to the invention, instead of having, as usual, rows of protrusions which are parallel to the axes of the two embossing cylindrical surfaces of cylinders 3 and 5, there is provided that the rows of one series of protrusions be slightly inclined with respect to the respective axis, and thus with a slightly helicoidal development according to an axis F1-F1 which forms an angle Y with respect to the axis and with respect to the projection of the axis of rotation X-X of the cylinder, as shown in Fig. 2. The protrusions which are mostly pyramid frustrum-shaped with a tip S indicated in Figs. 2 and 3, are distributed so as to be arranged not only along alignment F1-F1 (which is inclined by the angle Y with respect to axis X-X), but also along a further alignment F2-F2 which is inclined by the same angle Y with respect to a plane disposed at a right angle to the axis X-X of the cylindncal surface. This is achieved when the two series of aligned protrusion rows are perpendicular to one another in the crossing zone and are, therefore, both helicoidal and capable of being easily worked through operations of spiral turning or through chemical or other known processes. Fig. 4 shows possible examples of inclinations. Diagram A corresponds to what is illustrated in Fig. 2. Diagram B shows inclined broken lines, and diagram C shows gradually varying inclinations. By this inclined disposition of the rows of protrusions, with the mutual rotation of the embossing cylinders 3 and 5 according to the arrows of Fig. 1, there is prevented a simultaneous contact of all the protrusions of one row with the corresponding protrusions of the cooperating row of the other cylinder, which causes the above-mentioned drawbacks. With the above-mentioned inclination, there occurs a progressive contact of the protrusions of one row with those of the corresponding row of the other cylinder and, therefore, a gradual and a substantial uniform contact is obtained without concentrations of stresses and without vibrations of the type caused by the instantaneous and simultaneous contact of the tips lined up according to the axes of the embossing cylinders of traditional type. In this way, the vibrations and concentrated stresses are avoided, and there is obtained a very regular operation and a very satisfactory result in the working of the paper through an improved machine according to the invention. As the circumferential alignment of the protrusions is avoided, in any way there is avoided a repetition of contacts along circumferences on the pressure rollers which, instead, are in contact with the protrusions in such a way that the wear will be distributed all over the surface. It is understood that the drawing shows an exemplification given only as a practical demonstration of the invention, as this may vary in the forms and dispositions without. nevertheless, coming out from the scope of the idea on which the invention is based.

Claims: A machine for the paper converting industry, having two embossing cylinders (3, 5), each with a plurality of parallel rows of protrusions (S) and each with a cooperating pressure roller (7, 9), to emboss a patter onto two respective paper webs (N3, N5), said embossing cylinders (3, 5) being movable close to one another for bonding the two embossed paper webs by pressure-contact between mutually corresponding protrusions of the embossing cylinders, wherein said rows of protrusions are developed in a pattern such that each protrusion is aligned with each one of the adjacent protrusions according to lines which are all inclined with respect to a plane passing at right angles through the axis of each cylinder, thus to avoid or at least to reduce the repetition of pressure actions in localized circumferential zones of the pressure roller, characterized in that said protrusions are disposed also in such a way that each protrusion is aligned with each one of the adjacent protrusions according to lines which are all inclined with respect to the axis of the relevant cylinder in order to obtain a continuous and substantially uniform contact of the protrusions of one cylinder with those of the other cylinder, to avoid stress concentrations and vibrations, and that each protrusion is formed by a single protruding element. A machine according to claim 1 in which said rows of protrusions are developed in a helicoidal pattern. A machine according to claim 1 wherein the pressure rollers have a resilient surface. A machine according to any one of claims 1 to 3 in which the rows of protrusions have a development with constant angles. A machine according to any one of claims 1 to 3 in which the rows of protrusions have a brokenline development. A machine according to any one of claims 1 to 3 in which the rows have a development with continuously varying angles to the cylinder-axis.

Inventors: BIAGIOTTI GUGLIELMO, BIAGIOTTI, GUGLIELMO
Applicants: PERINI FABIO SPA, FABIO PERINI S.P.A.
Application year: 1989
Main classification: B31F1
IPC codes: B31F1