TECHNICAL FIELD

[0001] The invention relates to the technical field of the paper industry, with particular reference to the manufacture of paper tubes and in particular of the tubular cores on which rolled products are wound.

BACKGROUND ART

[0002] As is known, such cores are preferably made of cardboard, by means of machinery known as tube-forming machines, known per se, which spirally wind one or more bands of said cardboard around a metal spindle, so as to form a continuous tube.

[0003] In output, the tube is cut to the desired size and in particular, for the tubes used in winding rolls of tissue paper, corresponding to the width of the tissue paper reels to be wound thereon and is then fed to a rewinder which forms the rolls of the width of the paper reel.

[0004] The choice of cardboard for the manufacture of the tubular cores is due to the need to reconcile good mechanical strength with a low cost of the raw material and with the possibility of recycling the same material when the tissue paper roll has been completely used.

[0005] In WO 2006/086030, a method and related apparatus for forming cardboard tubular cores are disclosed. In this method, the cardboard is wound in a spiral so that one small edge of a turn overlaps the other small edge of a previously wound turn. Each turn therefore has at its two ends two small edges intended to overlap, i.e., two overlapping regions of very small width with respect to the overall width of the turn. An adhesive is advantageously distributed on both sides of the small edge so that the adhesion force between the small edges of two successive turns is maximum. In fact, the cardboard bands have a certain thickness and when they are wound around the spindle, a rather high force tends to make them reopen, thus it is necessary to provide layers of glue on both sides of the small edge to maximize the adhesive force. [0006] However, the use of cardboard also has other disadvantages, such as the need for correct disposal at the end of use. For this reason, tubular cores made of tissue-type paper have been proposed in the past, i.e., a paper of low weight substantially identical to the type of paper which must then be wound in a roll around the tubular core.

[0007] An anterior document PCT W02009/007551 discloses a tubular core made of tissue paper and a method for obtaining the same.

[0008] Said core consists of at least one band of tissue paper, at least locally impregnated with starch, which is spirally wound according to the conventional technique of making tubular cores in cardboard, i.e., by exactly flanking the turns to each other by virtue of which the winding pitch is exactly equal to the width of the band being wound; the starch is entrusted with the function of increasing the structural rigidity of the core itself.

[0009] In order for the tissue band which is spirally wound to have the necessary consistency and rigidity, a peculiar manufacturing method is envisaged which includes: coupling two bands of tissue paper, with one or more plies, interposing a layer of adhesive therebetween; coupling two further bands to the first two bands with one or more plies, interposing respective layers of adhesive, until the desired overall number of plies and the desired consistency and rigidity are reached.

[0010] The possibility of making tubular cores made of tissue-type paper is also known to the inventor of the present patent application. The tubular tissue core and the method for making it are protected by Italian Patent No. 102017000025090, which is characterized in that the tissue strip is spirally wound on itself with a sufficiently small helical pitch so that a number of turns are overlapped to confer the correct thickness and mechanical strength to the tubular core. The turns are glued to each other by means of adhesive distributed on the inner side on a portion with less width than that of the ply, of an entity at least equal to the helical pitch. In fact, the adhesive cannot be distributed on the portion of the strip which must go directly into contact with the winding spindle, in order not to dirty it with adhesive. Furthermore, with respect to the helical pitch, the adhesive-free zone must obviously have a greater amplitude to provide a certain safety margin in anticipation of any adhesive contact with the spindle.

[0011] The method of the invention allows to obtain tubular cores made of tissuetype paper in a very economical and highly productive manner, as it allows to use paper reels of a much wider width than was the case with the production systems of the prior art. It also allows to overcome the disadvantages deriving from the use of cardboard, simultaneously not causing increases in product cost neither in terms of raw material costs nor production process costs. However, the tissue tubular cores obtained by this method have a "peeling" defect due to the presence of the area of the width of the strip on which the adhesive is not distributed. In fact, although the various layers of fabric strip are substantially glued together well, the inner surface of the tubular core has the defect of "peeling" with a flap which tends to detach, protruding into the inner cavity of the tubular core. This disadvantage is caused by the fact that when the tube being formed exits the spindle, it has a portion of the inner surface which does not adhere to the overlying layers, as it is free of adhesive due to the safety margin kept in the width of the unglued paper section. This peeling defect does not cause structural problems for the tubular core but is such as to cause the tubular cores produced to be considered of poor quality.

SUMMARY OF THE INVENTION

[0012] Therefore, an object of the present invention is to propose a method for the production of tubular cores made of low-weight paper such as tissue, monolucid paper, tissue paper, paper for printing newspapers or the like, which allows to overcome the problems of the prior art highlighted above.

[0013] More specifically, an object of the present invention is to propose a method for the production of tubular cores made of low-weight paper which does not have the peeling defect typical of the solution of the prior art.

[0014] A further object of the present invention is to propose a machine adapted to implement the method of the invention and adapted to produce tubular cores according to the invention. [0015] According to a first aspect of the present invention, the above objects are achieved by a method for making tubular cores for rolled products which includes: unwinding at least one paper strip of a weight not exceeding 80 gr/m2 from at least one relative reel of equal width; winding said paper strip on a spindle, with such winding actuated according to a helical spiral of a pitch much less than the width of the strip such that each turn being formed overlaps the previous one by a width proportional to a sub-multiple of the overall width of the strip itself and in a certain section perpendicular to the axis of the tube at least three turns are overlapped; applying a first adhesive film on a first side of said strip, said adhesive application occurring between the aforementioned unwinding from said reel and the aforementioned winding on said spindle, said adhesive application being adapted to distribute the aforesaid adhesive film in a substantially uniform manner on a predetermined portion of the width of said strip intended to overlap the previous turn, applying a second adhesive film on the side opposite said first side of said strip, said application occurring between the aforementioned unwinding from said reel and the aforementioned winding on said spindle, said adhesive application being adapted to distribute the aforesaid adhesive film at a first edge of said strip intended to not overlap the turn previously wound around said spindle.

[0016] The application of the second adhesive film on the side of the strip opposite the application side of the first adhesive film solves the peeling problem because it adheres the part of the ply which tends to peel to the inner surface of the tube.

[0017] According to another aspect of the invention, the aforesaid objects are achieved by means of a tubular core for rolled products made with the method described above.

[0018] According to still another aspect of the present invention the objects are achieved by means of a machine for the production of paper tubes and in particular tubes used in the winding of tissue paper rolls, which comprises: a forming spindle arranged with its own horizontal longitudinal axis, said spindle having a cylindrical outer surface;

- A feed unit of a paper material in strips, comprising a first plurality of return rollers, at least one of which is motorized, said return rollers being arranged to make a feed path in an extended configuration of said paper strip material from at least one reel of said paper strip material to said spindle to wind inside said cylindrical outer surface of said spindle;

- A belt guide device comprising a second plurality of return rollers at least one of which is motorized and at least one belt stretched in a closed path between said return rollers, said spindle forming a return element of said second plurality of return rollers, at least one return roller immediately upstream of said spindle with respect to the advancement direction of said belt of said second plurality of return rollers coinciding with a return roller immediately upstream of said spindle of said first plurality of return rollers, with said paper strip material which in a portion of the path immediately upstream of said spindle advances by a portion of its width lying on said belt; at least a first adhesive distribution device arranged along the path of said paper strip material and adapted to distribute a layer of adhesive on the surface of said paper strip material opposite the surface facing said belt, at least a second adhesive distribution device arranged along the path of said paper strip material and adapted to distribute a layer of adhesive over a portion of the surface width of said paper strip material facing said belt not intended to come into contact with said belt. [0019] Further peculiar and advantageous features of the invention, as well as specific embodiments are expressed in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Features of the invention will become apparent from the following description of preferred embodiments of the invention, in accordance with what is reported in the claims and with the aid of the attached drawings, in which:

Fig. 1 illustrates products of the known art: Figures 1A and 1B show tubular cores made according to a prior art method, Fig. 1C shows a rolled product comprising a prior art core;

Fig. 2 illustrates tubular cores according to the present invention during their forming process: Fig. 2A shows an embodiment of a single wrapped strip, Fig. 2B shows an embodiment variant with two partially overlapped strips; Fig. 3 illustrates, in a highly enlarged scale, a detailed view to highlight the overlapping of the turns of tissue paper on the spindle;

Fig. 3 schematically illustrates, in side view, the main elements of a tubeforming machine usable for actuating the method of the invention;

Fig. 4 schematically illustrates, in plan, the machine of Fig. 3;

Fig. 5 shows in a schematic side view of greater detail the machine of Fig. 3, in which further components necessary for the actuation of the method of the invention are visible;

Fig. 6 shows in a schematic side view a belt guide device of the machine of Fig.

3;

Fig. 7 shows a schematic sectional view according to the section line V-V of Fig.

6;

Fig. 8 shows a detail of Fig. 7;

Fig. 9 illustrates in a view similar to Fig. 7, the belt guide device in a different operating configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS [0021] In figure 1A, a tubular core made according to the prior art method described in Italian patent no. 102017000025090, to which reference is made, is indicated as a whole with A.

[0022] The tubular core A consists of a paper strip 10 with one or more spirally wound plies, so that the pitch of the winding helix is proportional to a sub-multiple of the width of the strip 10 itself so that in a generic section perpendicular to the axis of said tubular core A at least three turns and in any case a number of turns S of said paper are overlapped depending on the value of the width of the strip 10 and the value of the helical pitch.

[0023] An adhesive film 2 is interposed between each pair of successive turns S, distributed substantially uniformly over almost the entire portion of the width which is overlapped.

[0024] In an embodiment shown in fig. 1B, a tubular core A' is made by winding two strips 10, 10' with each strip spirally wound according to a helical pitch proportional to a sub-multiple of its width.

[0025] Advantageously, each strip 10 is wound on the previous one so that the relative turns S are staggered along the longitudinal axis of said tubular core A' by a predetermined amount.

[0026] On the inner surface of each strip 10', 10", where inner is more precisely meant as the surface intended to become the inner surface of the wound turns, that facing the spindle, a relative adhesive film 2, 2' is applied in an appropriate position. As can be seen in Fig. 1B, the adhesive 2' is distributed over the entire width of the inner surface of the innermost strip 10', as this strip does not come into contact with the spindle and therefore does not risk dirtying it, while on the outermost strip 10 the adhesive is distributed for a width equal to the portion of the width which overlaps the previous turn and which consequently does not come into contact with the spindle M. In reality, to avoid dirtying the spindle a certain safety margin must be included so that the unglued flap, 3, will be larger than what is theoretically envisaged above.

[0027] With reference to Fig. 1 C, the tubular core A, A' removed from the forming spindle is used for forming rolled products, R. When the wound roll is cut into a plurality of rolls of smaller width, as is usually the case in the production of toilet paper, paper towels or the like, the unglued flap 3 can internally detach due to the so-called peeling problem, causing a poor-quality product.

[0028] To avoid this problem, as shown in figure 2A in which a tubular core 1 according to the present invention is visible during the forming process, the method of the present invention includes: unwinding a strip 10 of paper of a weight not exceeding 60gr/m ² from at least one relative reel B of equal width; winding said paper strip 10 on a spindle M, with such winding actuated according to a helical spiral of a pitch much less than the width of the strip 10 such that each turn S being formed overlaps the previous one by a width proportional to a sub-multiple of the overall width of the strip 10 itself and in a certain section perpendicular to the axis of the tube at least three turns are overlapped; applying a first adhesive film 2 on a first side of said strip 10, said adhesive application occurring between the aforementioned unwinding from said reel B and the aforementioned winding on said spindle M, said adhesive application being adapted to distribute the aforesaid adhesive film 2 in a substantially uniform manner on a predetermined portion of the width of said strip 10 intended to overlap the previous turn; applying a second adhesive film 4 on the side opposite said first side of said strip 10, said application occurring between the aforementioned unwinding from said reel R and the aforementioned winding on said spindle M, said adhesive application being adapted to distribute the aforesaid adhesive film 2 at a first edge 5 of said strip 10 intended to not overlap the turn S1 previously wound around said spindle M.

[0029] Applying a thin band of adhesive at the edge 5, on the outer side of the strip 10, allows the portion of strip to adhere to the subsequent turns, thus avoiding the peeling problem.

[0030] Furthermore, with respect to the prior art, the method of the present invention includes the use of a paper strip of a type other than tissue, as long as its weight is sufficiently small, in particular not exceeding 80 g/m ² . This allows the use of low-cost paper and the low weight allows the necessary deformation to avoid a conical diameter increase of the tubular core caused by overlapping turns.

[0031] In the method of the invention, the first adhesive film 2 is applied to the side of the aforesaid strip 10 intended to become the inner surface of a relative turn S wound on said spindle M so that the adhesive is distributed substantially uniformly over a predetermined portion of the width of the strip less than the portion which overlaps the previous turn S, while the second adhesive film 4 is applied to the opposite side of the strip near the first edge 5. It should be noted that the second adhesive film does not necessarily have to affect the entire width not affected by the first adhesive film 2, but it is sufficient that it extends from the first edge 5 for a section of reduced width. Advantageously, the second adhesive film 4 is applied at said first edge 5 for an overall width of about 1 cm or a little more.

[0032] In the embodiment variant shown in Fig. 2B, the method includes the simultaneous unwinding of two strips, 10, 10' from corresponding reels and the simultaneous winding of said strips 10, 10' on the aforementioned spindle M, according to respective helical spirals having the same pitch but staggered from each other by a predetermined amount along the longitudinal axis of said tubular core 1 , less than the width of the strips. In this case the second adhesive film is applied only to a first strip 10 arranged to be the innermost strip wound on said spindle M.

[0033] The method described above can advantageously be actuated by means of a tube-forming machine according to the present invention for making tubular cores for rolled products, a preferred embodiment of which will be described below with reference to figures 3 to 9.

[0034] The tube-forming machine, indicated as a whole with 20, is provided with a support structure, 21 , which supports a forming spindle, M, arranged with its own horizontal longitudinal axis. The spindle M has the structure of a rod with an outer surface, SM, substantially cylindrical or with a slight conicity around which the strip material is wound in a spiral. [0035] A feed assembly, 30, feeds a paper strip material, 10, 10', from two reels, B, B', of said paper strip material to the spindle M to wind around the relative cylindrical outer surface SM. The feed assembly 30 comprises a first plurality of return rollers 31 , at least one of which is motorized, said return rollers being arranged to make a feed path in an extended configuration of said paper strip material 10, 10'. In figures 3 and 4 the machine 20 is schematically shown to highlight a possible arrangement of the return rollers 31 suitable for unwinding the strips 10, 10' from the relative reels B, B' and leading them towards the spindle M. The return rollers 31 will comprise one or more motorized rollers to allow the unwinding of the strip 10, 10' from the relative reel B, B', tensioning assemblies and other elements not shown in detail nor described as being of the prior art. In Fig. 4 the representation is even more schematic in that only return rollers 31 suitable for defining the path of the strips 10, 10' are shown so that from two reels B, B' arranged coaxially side by side, the strip 10' is deflected out of the relative unwinding plane by rollers, 31a, arranged with a ninth axis orthogonal to the unwinding plane to bring the strip 10' to partially overlap the strip 10, as in the configuration shown in Fig. 2B.

[0036] The tube-forming machine 20 further comprises a belt guide device, 40 shown in detail in figures 6 to 9, which includes a second plurality of return rollers, 41 , at least one of which is motorized and at least one belt, 42 stretched in a closed path between the return rollers 41. The spindle M also forms a return element of said second plurality of return rollers 41. At least one return roller, 41b, of the belt guide device 40 which is located immediately upstream of the spindle M with respect to the advancement direction of the belt coincides with at least one return roller 31b immediately upstream of the spindle M of said feed assembly 30, so that in a portion of the path immediately upstream of said spindle M, i.e. , from the first of the coinciding return rollers 31b, 41b, it advances lying on the belt 42. More precisely, as visible in the detailed view of Fig. 8, the dimensions and position of the belt 42 are such that the strip 10 is not resting on the belt for its entire width but for a portion of the width. In the embodiment depicted, the strip 10 protrudes from the edge of the belt by a certain amount. The purpose of this portion not lying on the belt is to allow the application of adhesive, as will be described below. In this sense, it will be understandable how other embodiments are possible, for example by including a belt 42 consisting of several stripes side by side at a certain distance from each other.

[0037] The belt guide device 40 comprises a first roller support unit 50 oscillating about a horizontal axis and a second roller support unit 60 oscillating about a horizontal axis.

[0038] The first roller support unit 50 comprises at least one return roller 41b arranged upstream of said spindle M and the oscillation axis is horizontal, orthogonal to the axis of the spindle M and lying in the main lying plane, P, of the belt guide device 40, so that the oscillation of said first roller support assembly 50 determines an inclination with respect to the horizontal lying of the axis of said upstream return roller 41b. Thereby, the belt 42 and the strip 10, 10' reach the spindle M with an inclination angle which determines the helical pitch with which said paper material in strips 10, 10' winds around the spindle M. The belt is instead returned by the spindle M and leaves the same while maintaining the inclination angle.

[0039] The second roller support unit 60 comprises at least two return rollers 41 arranged downstream of said spindle M and the oscillation axis is horizontal, orthogonal to the axis of the spindle M and lying in the main lying plane, P. The inclination angle of the second roller support unit 60 determines the inclination of the axes of said at least two downstream rollers 41 and is coordinated with the inclination angle of said first roller support assembly 50 with the oscillation axis arranged at the output return roller 41 of the belt from the aforesaid unit 60 so that the belt is again centred in the lying plane P at the output from the second roller support unit 60.

[0040] As shown in figures 7 and 9, adjusting the inclination angle of the first and second roller support units allows to adjust the helical winding pitch of the strip 10, 10' on the spindle and thus the number of overlapping turns S.

[0041] With reference to Fig. 5, the tube-forming machine 20 comprises two first adhesive distribution devices 70, 70' arranged along the path of said paper material in strips 10, 10' and adapted to distribute a layer of adhesive on the surface of the paper material in strips 10, 10' opposite the surface facing said belt 42. Each of the first adhesive distribution devices 70, 70' is arranged along the feed path of the relative strip 10, 10', before it reaches the belt guide device 40. In the embodiment shown, the first adhesive distribution devices 70, 70' comprise a collection tray, a pick-up roller and an applicator roller and are not described in greater detail as they are known in the prior art. Obviously, other embodiments can be envisaged.

[0042] With reference also to Fig. 8, a second adhesive distribution device 80 is arranged along the path of said paper strip material 10, 10' and is adapted to distribute a layer of adhesive on a free portion, 11 , of the width of the surface of said paper strip material 10 facing said belt 42 not intended to come into contact with said belt 42. The second adhesive distribution device 80 is advantageously arranged immediately upstream of the spindle, M, preferably in the section of the path between the spindle and the return roller 41b immediately upstream thereof. Also in this case the second adhesive distribution device 80 is depicted as comprising an adhesive tray, pick-up rollers and an applicator roller, however it can be made with other known or newly conceived technologies.

[0043] The above description of a tube-forming machine 20 according to the present invention and the related figures refer to an embodiment of the invention which envisages the use of two strips 10, 10', however it will be immediately understandable that the structure of the tube-forming machine 20 will be substantially identical if a single strip 10 is used.

[0044] As is the case in other tube-forming machines of the known art, the tubular core which is continuously formed by winding in a spiral around the spindle M is then cut to length.

[0045] It is understood, however, that the foregoing is of exemplary and nonlimiting value, therefore any variations of detail which may become necessary for technical and/or functional reasons in the paper tube and/or performing the described steps, are considered from now on to fall within the same protective scope defined by the following claims.