TECHNICAL FIELD

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

BACKGROUND ART

[0002] As is known, the tubular cores for rolled products are preferably made of cardboard, by means of machinery known as tube-forming machines, known per se, which wind one or more cardboard strips of very reduced width in a helical spiral around a metal spindle, with a helical pitch substantially equal to the width of the strip so that there is no overlap between two successive turns, except for the outer turn formed with a cardboard of a slightly wider width than the bands inside the tube in which there is a minimum overlap, and thus forming a continuous tube.

[0003] In output, the tube is cut to length to be then fed to a rewinder which forms the rolls.

[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 strip material roll has been completely used.

[0005] However, this production method has the limit that the cardboard reels from which the tube is formed must have a very small width and, consequently, also the relative diameter cannot be too high, since the turns do not have to substantially overlap, so in the modern traditional tube-forming machines which work at very high speeds, it is necessary to very often resort, even every 10-15 minutes, to replacing the exhausted cardboard reels with new cardboard reels to be unwound, therefore it is necessary to have a person dedicated to the management and preparation of said reels. [0006] Furthermore, the use of cardboard has other disadvantages, such as the need for correct disposal at the end of use.

[0007] Another drawback related to the use of cardboard is the limited lifespan of the blades of the machines which cut the rolls in the production lines of tissue paper rolls.

[0008] A further disadvantage is related to the limited possibility of using the production waste of the tissue paper roll lines, which cannot be thrown back into the pulper of the continuous machine except in limited amounts and having the caution of installing very expensive and energy-consuming systems in the continuous machine.

[0009] Another disadvantage is the very low market value for cardboardcontaining waste produced in the production lines of tissue paper rolls, which can be worth even half of the waste without cardboard.

[0010] Another disadvantage lies in the complexity of handling and storing said reels.

[0011] Another disadvantage lies in the probability of injury related to the frequency with which said reels must be moved which, being very narrow with respect to their diameter, are not sufficiently stable.

[0012] Another disadvantage is the need to use cardboards of different weights to be combined with each other to produce different tubes with limited possible choices.

[0013] For these reasons, 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.

[0014] An anterior document PCT W02009/007551 discloses a tubular core made of tissue paper and a method for obtaining the same.

[0015] Said core consists of at least one strip 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 strip being wound; the starch is entrusted with the function of increasing the structural rigidity of the core itself. [0016] In order for the tissue strip which is spirally wound to have the necessary consistency and rigidity, a peculiar manufacturing method is envisaged which includes: coupling two strips of tissue paper, with one or more plies, interposing a layer of adhesive therebetween; coupling two further strips to the first two strips 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.

[0017] However, this production method only minimally solves the problem of having to very often change the reels of material which is unwound out to make the tubular core.

[0018] 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.

[0019] The method of the invention allows to obtain tubular cores made of tissuetype paper in a highly productive manner, as it allows to use paper reels of a much wider width and diameter than was the case with the production systems of the prior art. Labour costs are greatly reduced due to the fact that reel changes occur much less frequently and regardless the overall production costs remain unchanged or even increase due to the high cost of raw material. In fact, while cardboard costs around €450/T (euro/ton), tissue paper costs around €1 ,000/T. In addition, in order to achieve the necessary mechanical strength of the tissue paper tubular core, it is required that, with the same length and outer diameter, the tissue tubular core weighs more than the corresponding cardboard tubular core. From the above, it is easy to deduce that the cost of the raw material used to make tissue tubular cores is 2 to 3 times higher than the cost of the raw material necessary to make cardboard tubular cores. Although the labour costs are lower, they cannot compensate for the higher raw material cost. The tissue tubular cores are therefore uneconomical with respect to the cardboard cores and their production is therefore only convenient by increasing the sale price of the final product and by virtue of the environmental advantages linked to disposal. Since the costs of the tissue tubular cores are higher, it is extremely unlikely that these can completely replace the cardboard tubular cores. The tube-forming machines for making tissue tubular cores are conceptually different with respect to the traditional tubes and, for companies that want to adopt them, this entails the further problem that the production line should provide for the simultaneous presence of both traditional tubes and tissue tubes. In fact, the company would eventually be forced to produce both tissue tubular cores and cardboard tubular cores, keeping both machines on the production line with obvious costs due to both the use of additional machinery and the size of the space.

SUMMARY OF THE INVENTION

[0020] Therefore, an object of the present invention is to propose a method for the production of tubular cores which is able to obtain the advantages of the overlapped turns production method, in which high width and diameter starting reels can be used, without incurring an increase in the overall production costs.

[0021] Another object of the present invention is to propose a method for making tubular cores for rolled products which allows to produce tubular cores with much lower overall production costs with respect to those of the prior art.

[0022] Yet another object of the present invention is to propose a method for the production of tubular cores for rolled products which allows to produce lighter tubular cores with the same structural strength features with respect to traditional cardboard tubular cores.

[0023] The aforesaid objects and still others are achieved by a method for making tubular cores for rolled products, which conventionally includes:

- unwinding at least one strip from at least one relative reel of equal width;

- winding said 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 of said strip are overlapped;

- applying an adhesive film on a 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 turn previously wound on the spindle,

[0024] Peculiarly, according to the method of the present invention said strip is made of printing paper for printing newspapers with a weight between 18 and 80 g/m ² .

[0025] With respect to tissue, the low-weight printing paper has a significantly lower cost per ton, comparable to the cost of cardboard, and also has a significantly lower thickness thus allowing to use starting reels which, for equal volume, wrap a much longer strip. It is thus possible to use the production method with multiple overlapping turns which allows to use very wide reels of very large diameter, of 1.5 m and even more, thus reducing the need for dedicated operators in the management and preparation of the reels to be unwound for forming the tubes, and at the same time the cost of the raw material remains comparable to that of cardboard, so that it is possible to create tubular cores for rolled products with reduced overall production costs with respect to conventional cardboard tubular cores.

[0026] Furthermore, the low-weight printing paper allows to create a tube structure which provides the same strength as cardboard using much less paper by virtue of the many overlapping turns; tests carried out have found a weight reduction of even 30 to 45%, depending on the type of tube, without noticing any problem in the production of rolls using these tubes as a support.

[0027] Further peculiar and advantageous features of the invention, as well as specific embodiments are expressed in the dependent claims. DESCRIPTION OF THE DRAWINGS

[0028] 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 tubular cores according to the present invention during their forming process: Fig. 1A shows an embodiment of a single wrapped strip, Fig. 1 B shows an embodiment variant with two partially overlapped strips.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Figures 1A and 1B overall show 1 tubular cores according to the present invention made, with regard to the winding steps, according to the embodiment of the known art disclosed in Italian patent no. 102017000025090 to which reference is made.

[0030] The tubular core 1 consists of a strip 10 spirally wound around a winding spindle M, so that the pitch of the winding helix is several times less than the width of the strip, in particular 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 1 at least three turns and in any case a number of turns S are overlapped depending on the value of the width of the strip 10 and the value of the helical pitch.

[0031] An adhesive film 2 is interposed between each pair of successive turns S, distributed in a substantially uniform manner exclusively on the portion of the width of the strip which overlaps the previously wound turn.

[0032] In the embodiment variant shown in fig. 1B, the tubular core 1 is made by winding two strips 10, 10', each of which is spirally wound with a helical pitch several times less than the width of the strip, as previously disclosed and with the two strips being fed with the same inclination (same helical pitch) and longitudinally staggered with respect to the axis of the winding spindle M.

[0033] The method of the invention includes: - unwinding the strip 10 from a relative reel, B, of a width equal to the width of the strip;

- winding the strip 10 on a spindle M, with such winding being actuated according to a helical spiral with a pitch several times 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 at least three turns S are overlapped in a certain section perpendicular to the axis of the spindle M;

- applying an adhesive film 2 on one side of the strip 10, said adhesive application occurring through adhesive application means, A, between the aforementioned unwinding from the reel B and the aforementioned winding on the 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 the strip 10 intended to overlap the previous turn, so that a portion 11 of the width of the strip 10 equal to or greater than the aforesaid helical pitch is not covered with adhesive, said portion 11 comprising the portion in width of the strip intended to come into direct contact with the spindle M.

[0034] The peculiar aspect of the method of the invention disclosed above is that the strip 10 consists of printing paper of a weight between 18 g/m ² and 80 g/m ² .

[0035] Advantageously, the aforesaid printing paper is in particular uncoated, opaque newsprint paper, with a weight between 25 g/m ² and 60 g/ m ² , produced with at least 70% recycled raw material.

[0036] A newsprint, in particular with the features defined above, has a very low cost, substantially equal to that of cardboard, i.e., about 450 €/T (euro per ton) and even less and has excellent tensile strength as it is known that newsprint is produced to withstand the high speeds of offset or flexographic rotary printing machines.

[0037] The good structural features allow to produce tubular cores for rolled products which, with the same outer diameter and length, have a weight ranging from 30 to 45% less with respect to that of conventional tubular cores in cardboard. This results in a lower cost of tubular cores with respect to those in cardboard due to the lower amount of raw material contained.

[0038] The aforesaid feature also entails greater environmental sustainability because less raw material is used, less energy is used to produce the paper needed to make the tubes and less CO2 is released into the environment during transport, all in proportion to the weight reduction obtainable with this type of tube.

[0039] Furthermore, there are lower production costs with respect to the cardboard tubular cores, as the method for making multiple overlapping turns allows to use tubes on which high width and diameter reels B are mounted which have a much longer duration between one reel change and the next and consequent possibility of not employing a dedicated operator with consequent lower personnel cost. In fact, depending on the types of tubes to be made, one of these reels can also last a whole work shift, effectively eliminating the need for an operator dedicated to preparing and changing the reels necessary for the traditional tube-making machines which use cardboard.

[0040] The management of the tubular cores made is also more economical, as few large reels are more easily manageable than many reels of little weight and reduced size such as those of cardboard.

[0041] In addition to the aforesaid, the use of newsprint has further significant advantages. Firstly, almost all newsprint is produced with recycled raw materials, with significant advantages for the environment.

[0042] Another advantage lies in the smaller surface area required for the storage of the reels and greater safety in handling and in their use.

[0043] Furthermore, cleaner waste of a higher value is generated with this type of paper in the case of sale or, alternatively, the waste has the possibility of being returned directly to the pulper of the continuous machine without limitations of any kind.

[0044] Another advantage is the ability to produce purer tubes which increase the life of the blades of the machines which cut the rolls in the tissue paper processing lines. [0045] Another advantage is the possibility of using the same paper for any type of tube to be produced, being able to modify the features of the tubular core which is produced in a very fine way simply by changing the angle of the winding helix.

[0046] Moreover, with the advent of the digital age, the sale of newspapers and paper newspapers is rapidly decreasing and with it the demand for newsprint. The method of the present invention instead offers a new way for using newsprint which allows to continue to use existing newsprint production facilities at full capacity.

[0047] It is understood, however, that what is described above has exemplary and non-limiting value. For example, the terms "printing paper" and "newsprint", although they do not define the type of paper in terms of chemical or mechanical features, will be sufficiently clear to the technicians in the field who will easily identify which types of paper fall within the scope of protection defined by the following claims. 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.