DE102018106629A1 - Calendering plant and method for producing perforated nonwovens for multi-layer absorbent products - Google Patents

Abstract

The invention relates to a calendering system (100) for producing perforated nonwovens (NW) for multilayer absorbent products. The plant (100) comprises a conveyor belt (110) arranged in a longitudinal direction (L) and adapted to convey a web (W) of natural and / or synthetic textile fibers, and a calender (120) which is adapted to the conveyor belt (110) is arranged in the longitudinal direction (L), wherein the calender (120) comprises a pair of motorized and counter-rotating rollers (121, 122), wherein the rollers (121, 122) are parallel to each other and define a nip (125) , With respect to a median plane (P) in the axial direction, the jacket of each roller (121, 122) comprises at least two symmetrical parts (121a, 121b, 122a, 122b), on each of which a plurality of corresponding helical grooves (126a, 126b, 127a, 127b) having the same pitch and opposite winding directions.

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the sector of multi-ply absorbent products, such as diapers, mattress pads and tampons, and more particularly to a calendering and calendering process for producing apertured nonwoven fabrics intended for these products.

GENERAL PRIOR ART

Multi-ply absorbent products, such as diapers, mattress pads and tampons and, more generally, absorbent products for use in sanitary and health care generally comprise an "outer" layer having a plurality of holes intended to contact a user's skin to come, an underlying layer for receiving and distributing liquids and a suction layer disposed below the latter and intended to retain the liquids.

As is known, an absorbent product for health use must provide appropriate comfort in contact with the skin of the user while ensuring rapid passage of a fluid flow, for example, urine or blood, to the underlying layers.

The outer layer is typically made of a nonwoven fabric of natural and / or synthetic fibers of thermoplastic material, for example polypropylene, also called "fleece" in short, in which a plurality of holes are provided which are suitable to allow the passage of a liquid flow.

The preparation of the outer layer provides for the production of a nonwoven fabric and its subsequent perforation. For the perforation of the nonwoven fabric, two main methods of processing are generally known.

A first method of operation is to calender the nonwoven fabric through a pair of counter-rotating motorized rollers which are heated to temperatures substantially equal to those which soften the polymeric material from which the nonwoven fabric is made. One of the rolls generally has a smooth shell, while the other has a shell in which multiple cuts are made. The rollers are respectively pressed against each other, forming a nip therebetween, and are rotated at various angular velocities so as to exert a pulling action on the web causing the formation of a plurality of openings or cracks. These cracks are located at the contact areas between the edges of the notches created in the mantle of one of the two rolls and the continuous surface of the other roll.

The cracks are abruptly welded and dimensionally stabilized along the circumference, thanks to the effect of local melting produced by the combined action of the pressure between the opposing rolls and their heating temperature.

This method makes it possible to obtain holes with dimensions which are suitable for guaranteeing the transport of the liquids through the outer layer so that they reach the inner layers of a multi-layered product. Moreover, this method is essentially applicable to all thermoplastic polymer materials generally used in the production of nonwovens.

The pressure from one roll to the other and their different speeds of rotation create frictional forces that result in premature wear of the roll surfaces which often require repair, with consequent costs for maintenance and production stoppage.

In addition, the holes obtained by this machining method have a rather irregular horseshoe shape, which is caused by the frictional forces applied at the points of contact between the moving rollers with respect to the point of incision of the processed nonwoven fabric.

Another problem with calendering processing is the high plasticizing effect of the polymer material from which the web is produced, which is caused by the working temperatures of the rolls, which substantially correspond to its softening temperature. This aspect causes a deterioration of the textile handle of the material, which is perceived by the user as lesser comfort.

A second processing method for punching nonwovens provides for their passage in contact with a rotatable roller, on the surface of several needles are created. The roll is heated to a temperature corresponding to the softening temperature of the polymeric material from which the processed web is made. Upon contact with the needles, the fleece is perforated and the edges of the holes become porous its dimension immediately stabilized by the effect of the working temperature of the roller.

This processing method allows to obtain holes of more regular dimensions than those obtained by calendering and is essentially applicable to all polymeric materials used in the manufacture of nonwovens.

However, the holes are substantially elliptical in shape, the extent of which is determined by the clearance angle of the needles present on the roller, which makes the dimensions of the holes absolutely dependent on the specific roller used.

Both methods of processing also result in the formation of small crusts along the edges of the holes resulting from the welding of the synthetic textile fibers after punching. While essential to stabilizing the hole dimensions, these crusts impart a degree of roughness to the finished nonwoven fabrics that the end user perceives as an inferior textile feel.

Another disadvantage of the known punching methods described above is that the production speed, typically of the order of 35-40 meters per minute, is considered rather low by those skilled in the art.

Recently, another method of fleece punching was offered, the subject of the Italian patent 102014902243741 on behalf of the applicant.

According to this method, a web of synthetic textile fibers in looser form is fed on a conveyor belt, at one end of which a calender is arranged, comprising a pair of motorized rollers parallel and opposite to each other and forming a nip between them. The rolls are heated to the softening temperature of the material from which the synthetic textile fibers are made and pressed against each other. On the mantles of both rolls several grooves are created with a spiral course.

During processing, in the region of the nip, thermal welding takes place simultaneously between the synthetic fibers and the formation of the holes in the web thus obtained, which is at the working temperature of the rolls which is close to the softening temperature of the material or the separation effect and / or Section of the fibers resulting from the respective movements between the edges of the spiral grooves, which are present on both rollers, which rotate at the same angular velocity or at different angular velocities.

The processing method can be equally implemented when starting from a web that has already undergone thermocompression in an oven.

This method of producing perforated nonwoven fabrics is extremely advantageous compared to the previously known ones because it enables to obtain very regularly shaped holes whose edges have crusts of smaller dimensions than those achievable by the methods already known, to the advantage the handle of the nonwoven fabric produced is.

The provision of spiral grooves on both rollers of the calender also makes it possible to reduce the contact pressure between them, whereby the wear of the mantle surfaces of the counter-rotating rollers can be restricted.

However, when the counter-rotating rollers are actuated at different angular speeds, movement of the material being rolled is observed in a direction transverse to the loading direction, that is, "drifting" due to the occurrence of entrainment forces generated by the helical grooves that are created on the reels themselves. The movement in the transverse direction is more pronounced the greater the difference between the angular velocities of the counter-rotating rollers and the inclination of their spiral grooves.

BRIEF SUMMARY OF THE INVENTION

There is therefore a need for improvement in the calendering equipment for producing apertured nonwoven fabrics for multi-layer absorbent products, which is an object of the present invention.

This object is achieved by a calendering plant the main features of which are set forth in claim 1 and also by a calendering process whose main features are set forth in claim 6, while the remaining features are set forth in the remaining claims.

A solution idea on which the present invention is based is to produce a calendering machine for producing perforated nonwovens from natural and / or synthetic fibers, which comprises a calender in which, analogously to Italian patent 102014902243741 , on in coats of counter-rotating motorized rollers several spiral grooves are created. According to the invention, the shell of each roll has at least two symmetrical parts with respect to a plane of symmetry in the axial direction, which have helical grooves with the same pitch and an opposite winding direction.

This configuration makes it possible to prevent the drifting effect caused by the difference between the rotational speeds of the rollers and the inclination of the helical grooves on their sheaths, because the helical grooves in the opposite direction on the web of natural and / or synthetic textile fibers in the Passage through the nip to produce equal and opposite thrusts in the axial direction.

According to one embodiment of the invention, the symmetrical parts of the shell of each roll can be advantageously separated by a circumferential shell part without grooves, for example a gutter. This configuration offers the advantage of allowing the production of a slit nonwoven comprising at least a portion completely without slits, which is suitable as an indication of cutting the web into strips.

Like in Italian patent 102014902243741 In the name of the Applicant, the calendering system according to the invention is also suitable for the production of perforated or slotted webs starting from webs of carded fibers, which are arranged in a loose form on a conveyor belt which feeds the calender. This offers the advantage that it is not necessary to use a furnace for carrying out the thermo-cohesion of the textile fibers. The latter takes place directly during the passage of the carded fibers through the nip defined by the rollers of the calender.

The particular configuration of the motorized and counter-rotating rollers of the calender of the plant according to the invention allows their use not only for the production of perforated or slotted webs of natural and / or synthetic fibers, which are intended for absorbent products, but also advantageously for the production of perforated or slotted sheets of polymeric material for various uses.

Further advantages, features and application modalities of the present invention will become apparent from the following detailed description of some embodiments thereof, given by way of example and not of limitation.

list of figures

• - 1 eine seitliche Ansicht ist, die eine Anlage zur Produktion von gelochten Vliesen gemäß der vorliegenden Erfindung schematisch darstellt;
• - 2 eine Vorderansicht der gegenläufigen motorisierten Walzen eines Kalanders der Anlage von 1 schematisch darstellt;
• - 3 eine Vorderansicht der gegenläufigen motorisierten Walzen eines Kalanders der Anlage von 1 gemäß einer alternativen Ausführungsform der Erfindung schematisch darstellt;
• - 4 eine Vorderansicht der gegenläufigen motorisierten gegenläufigen Walzen eines Kalanders der Anlage von 1 gemäß einer weiteren Ausführungsform der Erfindung schematisch darstellt.

Reference is made to the figures of the accompanying drawings, in which:

• - 1 Fig. 3 is a side view schematically illustrating an apparatus for producing perforated nonwovens according to the present invention;
• - 2 a front view of the counter-rotating motorized rollers of a calender of the plant of 1 schematically represents;
• - 3 a front view of the counter-rotating motorized rollers of a calender of the plant of 1 schematically according to an alternative embodiment of the invention;
• - 4 a front view of the counter-rotating motorized counter-rotating rollers of a calender of the plant of 1 schematically according to another embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

1 illustrates in an extremely schematic manner a calendering machine according to the invention for producing perforated nonwovens for absorbent products 100 indicated calendering system extends in a longitudinal direction L and comprises a conveyor belt 110 formed to convey a web W of natural and / or synthetic textile fibers in loosely-formed or synthetic textile fibers previously thermobonded in a furnace.

The attachment 100 also includes a calender 120 , after the conveyor belt 110 is arranged in the longitudinal direction L, that of the conveyor belt 110 supplied web W of textile fibers absorbs to turn it into a perforated nonwoven NW, as will be described in detail below.

For example, in the case of using natural and / or synthetic textile fibers in a looser form, they may be replaced by a carding machine 130 the plant 100 treated bales are fed to the end of the conveyor belt 110 is disposed opposite to where the calender 120 is arranged, that is in front of the conveyor belt 110 with respect to the longitudinal direction L. Alternatively, the natural and / or synthetic textile fibers may be fed continuously from a spinning machine (not shown), also in front of the conveyor belt 110 with respect to the longitudinal direction L is arranged. In this case, the system is located 100 arranged in series with the spinning machine.

With reference to 2 includes the calender 120 a pair of motorized opposing rollers 121 . 122 which are parallel to each other and both provided with a plurality of spiral grooves. The rollers 121 . 122 are on respective waves 123 . 124 attached and define a nip 125 suitable for enabling the passage of the web W formed from the natural and / or synthetic textile fibers to form a perforated nonwoven web NW. The waves 123 . 124 are operative with (not shown) actuating means of calendering 100 connected, the respective geared motors and universal joints include.

In an operating condition of the plant 100 become the rollers 121 . 122 by respective actuators (not shown) of the system 100 pressed against each other and heated by known means to a temperature generally between 100 ° C and 150 ° C, for example, equal to that at which softens the polymeric material from which the web W is formed. As is known, allows this operating state, the pressure force and the high temperature of the rollers 121 . 122 synergetically to create in the web W openings in the region of the contact zones between the crests of their grooved profiles.

The rollers 121 . 122 be from a (not shown) control system of the plant 100 controlled and can rotate at the same angular velocity or at different angular velocities.

Also with reference to 2 includes the coat of each roller 121 . 122 with respect to a median plane P in the axial direction at least two symmetrical parts 121 . 121b . 122a . 122b on which respective spiral grooves 126a . 126b . 127a . 127b are created, which have the same pitch, but opposite winding directions.

In other words, the spiral grooves return 126a . 126b . 127a . 127b that roll on each 121 . 122 are created, their winding direction at its center plane P in the axial direction.

If the motorized counter-rotating rollers 121 . 122 operated at different angular velocities, create the spiral grooves created on their coats 126a . 126b . 127a . 127b thanks to this configuration equal and opposite forces in the axial direction, whereby the drift of the web W when passing through the nip 125 is prevented.

In other words, allows the special shape of the coats of the rollers 121 . 122 of the calender 120 , the problem of transverse movements of the web W, which occur at the plant, which is the subject of Italian patent 102014902243741 in the name of the Applicant to solve at the root, while maintaining the same operational advantages.

Another technical effect that arises from the removal of the drift effects of the web W of textile fibers is that the full effectiveness of the method for forming the openings in the produced nonwoven fabric NW is guaranteed, which is to the advantage of its final quality.

It is understood that the particular configuration of motorized and counter-rotating rollers 121 . 122 of the calender 120 the plant of the invention 100 their use not only for the production of perforated or slotted webs of natural and / or synthetic fibers intended for absorbent products, but also for the perforation of films of polymeric material, which serve for various uses.

The openings formed in the web W during the processing of the web NW have a substantially square shape when the rolls 121 . 122 rotate at the same angular velocity, or the shape of a rhombus with the larger diagonal aligned in the longitudinal direction L, that is in the pulling direction when the rollers 121 . 122 be rotated at different angular velocities.

For example, in the illustrated embodiment, the helical grooves provided on the symmetrical parts of each roller have a 45 ° inclination which is convergent to the center plane P. However, different inclinations may be provided.

In addition, in the illustrated embodiment, the spiral grooves of each part meet each other at the median plane P, but it is to be understood that the spiral grooves may also be offset in the circumferential direction.

With reference to FIG 3 According to one embodiment of the invention, the symmetrical parts 121 . 121b . 122a . 122b the mantle of each roller 121 . 122 advantageously by a rotating part 128 of the jacket itself, which is completely free of spiral grooves. In this case, the slit nonwoven comprises NW with the calendering equipment 100 is produced, a part completely free of slots between the two symmetrical slotted parts, which is suitable to serve as a guide for cutting the web into strips.

The rotating part 128 For example, it may be a gutter, which offers the advantage of having contact pressure between the sheaths of the rolls 121 . 122 and thus to reduce the wear of the surfaces locally.

4 represents a further embodiment of the invention, in which the shell of each roll 121 . 122 with respect to the median plane P in the axial direction an even number of symmetrical parts 121a ' . 121b ' . 122a ' . 122b ' , 121a ", 121b", 122a ", 122b", for example, four, and in which the adjacent parts have a plurality of corresponding spiral grooves 126a ' . 126b ' . 127a ' . 127b ' , 126a ", 126b", 127a ", 127b" having the same pitch and different winding directions.

Also in this case, the symmetrical grooved parts of the mantle 121a ' . 121b ' . 122a ' . 122b ' , 121a ", 121b", 122a ", 122b" of each roller 121 . 122 advantageously from a respective rotating part 128 . 128 ' . 128 ' of the jacket, which is completely free of spiral grooves, thereby enabling the cutting of the produced perforated web into several parallel strips.

As mentioned earlier, the calendering machine according to the invention is 100 suitable for the production of perforated or slotted webs NW, even when starting from webs of carded fibers, in loose form on the conveyor belt 110 are arranged, which is the calender 120 which offers the advantage that no oven has to be used to thermocover the textile fibers. The latter takes place directly during the passage of the carded fibers through the nip 125 passing through the rollers 121 . 122 of the calender 120 is defined.

According to one embodiment of the invention, for this purpose advantageously first polypropylene textile fibers and second polypropylene-polyethylene textile fibers may be used, in which the polypropylene forms the core, while the polyethylene forms the outer shell.

The second textile fibers of polypropylene and polyethylene are preferably present in an amount between 10% and 20% by weight.

During operation of the system 100 become the rollers 121 . 122 of the calender 120 maintained at temperatures between 100 and 110 ° C, that is substantially at the softening temperature of the polyethylene. Since polyethylene generally has a lower softening temperature than polypropylene, they melt on contact with the rolls 121 . 122 of the calender 120 only the polyethylene fibers and create a kind of adhesive between the polypropylene fibers, which retain their mechanical function as chain links. As a result, the finished web NW comprises a relatively limited amount of molten material, which helps to increase the fluffiness of the product, which is perceived by the end user as an even more comfortable textile feel.

Thermo-cohesion of the first and second textile fibers occurs by thermal conduction when they come into direct contact with the sheaths of the rolls, or by thermal convection when they are in the spaces between their grooves.

The pressure of one roller on the other causes the formation of the web NW and simultaneously the localized separation or a proper cut of the first and second textile fibers in the region of the contact points between the grooves, which are provided in the sheaths of the rolls, resulting in the formation of Openings in the web NW results.

The present invention has been described herein with reference to preferred embodiments. It is understood that other embodiments may exist that pertain to the same inventive core as defined in the scope of the claims set forth below.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• IT 102014902243741 [0017, 0026, 0029, 0042]

Claims (9)

A calendering machine (100) for producing apertured nonwoven fabrics (NW) for multi-layer absorbent products, the apparatus (100) comprising: i) a conveyor belt (110) arranged in a longitudinal direction (L) and adapted to form a web (10) W) from natural and / or synthetic textile fibers to convey; ii) a calender (120) disposed after the conveyor belt (110) in the longitudinal direction (L), the calender (120) comprising a pair of motorized and counter-rotating rollers (121, 122), the rollers (121, 122) parallel to each other and define a nip (125) in the longitudinal direction (L), characterized in that the jacket of each roller (121, 122) with respect to a median plane (P) in the axial direction at least two symmetrical parts (121a, 121b, 122a , 122b), and in each case a plurality of helical grooves (126a, 126b, 127a, 127b) having the same pitch and opposite winding directions are arranged on each of the symmetrical parts (121a, 121b, 122a, 122b). Annex (100) to Claim 1 wherein the mantle of each roller (121, 122) with respect to a median plane (P) in the axial direction is an even number of symmetrical parts (121a ', 121b', 122a ', 122b', 121a ", 121b", 122a ", 122b ") and wherein the adjacent parts in the axial direction each comprise a plurality of spiral grooves (126a ', 126b', 127a ', 127b', 126a", 126b ", 127a", 127b ") having the same pitch and opposite winding directions. Annex (100) to Claim 2 or 3 wherein the adjacent symmetrical parts (121a, 121b, 122a, 122b; 121a ', 121b', 122a ', 122b', 121a ", 121b", 122a ", 122b") of the shell of each roll (121, 122) are separated by a circumferential part (128, 128 ', 128 ") of the same shell are separated, wherein the peripheral part (128, 128', 128") is completely free of spiral grooves. Annex (100) to Claim 3 wherein the peripheral part (128, 128 ', 128 ") of the shell without helical grooves is a gutter. Appendix (100) according to one of the preceding Claims 1 to 4 further comprising a carding machine (130), the carding machine (130) being disposed at the end of the conveyor belt (110) opposite to the end where the calender (120) is located, the carding machine (130) being formed for feeding a web (W) of textile fibers in a loose form to the conveyor belt (110). A calendering process for producing apertured nonwoven fabrics (NW) for multi-layer absorbent products, the process comprising the steps of: i) arranging a conveyor belt (110) in a longitudinal direction (L); ii) arranging a calender (120) at one end of the conveyor belt (110), the calender (120) comprising a pair of motorized and counter-rotating rollers (121, 122) parallel to one another and a longitudinal nip (125) define); iii) heating the rollers (121, 122) to a predetermined temperature; iv) pressing the rollers (121, 122) against each other; v) dislocation of the rolls (121, 122) in rotation and feeding of a web (W) of synthetic and / or natural textile fibers to the nip (125) by a conveyor belt (110); wherein the shell of each roller (121, 122) comprises at least two symmetrical parts (121a, 121b, 122a, 122b) with respect to a median plane (P) in the axial direction, and on each of the symmetrical parts (121a, 121b, 122a, 122b) are each a plurality of spiral grooves (126a, 126b, 127a, 127b) are arranged, which have the same pitch and opposite winding directions. Method according to Claim 6 wherein the web (W) of textile fibers comprises first textile fibers of polypropylene and second textile fibers of polypropylene-polyethylene, wherein polypropylene forms the core of the second textile fibers, while the polyethylene forms the outer shell of the second textile fibers. Method according to Claim 7 in which the amount of the second textile fibers is between 10% and 20% by weight. Method according to Claim 7 or 8th in which the first and second textile fibers are fed in a loose form from a carding machine (130).

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