Indirect Printing of AGM

ES 2 397 213 T3

DESCRIPTION

Indirect AGM Printing

Field of the invention

The present invention relates to a method of applying absorbent gelling material (AGM) granules on a carrier layer for use in an absorbent article, especially baby or adult diapers, diaper panties, Pull-up learning panties (panty diapers), sanitary napkins, panty liners or the like. These articles typically comprise the carrier layer with the AGM particles deposited thereon by indirect printing along with other layers to form the complete article.

Background of the invention

The term "AGM granules" herein includes materials capable of absorbing and retaining a large amount of liquid relative to their volume. "AGM" is the abbreviation for Absorbent Gelling Materials. These materials are mainly made up of superabsorbent polymers. In the present context, the AGM material can be used as granules of different particle size, including powder-like materials or a mixture of powder material and granules of different particle sizes or shapes (eg, fibers).

AGM materials of this type are usually embedded in absorbent pads of meltblown fibers or cellulose fibers (or similar fibrous materials and combinations thereof) or directly deposited on a nonwoven carrier layer. The present invention is applicable to both of these methods. This type of "absorbent article" can be used for example to make a diaper, a sanitary napkin or even an article to retain liquid of any kind.

Different methods have been proposed to obtain a distribution of AGM granules on a substrate having a predetermined pattern and thickness profile. These methods include blowing an airborne mixture of AGM granules and fibers through a conduit to a vacuum drum. Methods of this type allow only limited control of the design and thickness distribution of the AGMs over the surface on which the AGMs are distributed.

In US 5,030,314 a method and apparatus for forming composite articles having pockets of particulate material is described. The method is carried out using an apparatus comprising an applicator roll having discrete indentations, a feeding means for supplying the particulate material to the discrete indentations, a means for rolling the applicator roll, a means for conveying a receiver strip beyond the applicator roll, a means of transferring the particulate material to the receiver strip, a means of applying stamped adhesive material, a means for moving a cover band past said means for applying an embossed adhesive and a means for joining the receiving band and the cover band.

Especially in the case of absorbent cores containing little or no cellulose fiber and having AGM granules as the only liquid storage material, the precision of the shape and discretion of the AGM granule distribution is very important. .

In this context it should be mentioned that cores of one or more pieces, a layer of AGM or several layers overlapping one on top of the other or one next to the other can be used. This also allows different AGMs to be used in different layers. Therefore, the possibilities of variation of the obtained product are almost infinite. However, achieving high precision in the distribution of granules is important.

Summary of the invention

Thus, the present invention relates to a method for applying AGM granules on a surface with a high precision of distribution, design and quantity of AGM material positioned on the surface by indirect printing. This process method can be used in an AGM particle application that requires exact positioning, printing type, of granules or powders on a carrier layer. A particular application may be the preparation of cores comprising mainly AGM / glue for disposable diapers or parts of these cores.

The indirect printing method is according to claim 1.

The invention also relates to an apparatus, especially an apparatus for carrying out the method according to the invention.

Hereinafter, the term "indirect printing" means the transfer of the AGMs that are separated from the bulk storage of AGM before they come into contact with the carrier layer. "Direct printing" means that the AGMs are not separated from the AGM bulk storage prior to contacting the carrier layer. This is not included in the present invention.

ES 2 397 213 T3

The present invention provides a method and apparatus for significantly increasing AGM deposition accuracy. The standard deviation achieved so far has been reduced by approximately 1/4 of that achieved with previous advanced technology. Thus, diaper cores with an exact AGM distribution profile in the lateral direction and the longitudinal direction can be obtained. The method according to the invention especially allows the deposition of AGM granules on fast moving carrier layers at surface speeds of 1 m / s to 3 m / s, preferably up to 5 m / s, or even up to 10 m / s even more. preferably up to 15 m / s, with high precision. Thanks to the precision of the deposition of AGM granules, the invention makes it possible to manufacture, e.g. eg, an absorbent core without cellulose or similarly shaped absorbent and / or hydrophilic fibers in diapers, resulting in a very fine core and improved comfort and fit during wear of the articles.

The term "transfer device" herein includes any moving element capable of collecting AGM granules in a predetermined shape and thickness profile and depositing the granules - without modifying the configuration thereof - onto a carrier substrate.

A preferred embodiment of the transfer device is a patterned rotating drum or roller, referred to as a "print roller" or "transfer roller" in the present context because transferring an AGM granule pattern can be similar to printing. Another embodiment would be a moving belt having cavities on the surface and moving between the bulk storage of AGM granules and the transfer position.

The term "bulk" or "bulk storage" of AGM granules refers in the present context to any type of granule supply, especially a hopper.

A "retention means" is provided to hold the AGM granules that have been collected by the cavities of the transfer device within these cavities during movement from the bulk to the transfer position where the granules are supplied to the carrier layer. In a preferred embodiment, the retaining means is a strap that is guided along the surface of the transfer device, especially the printing roller, on the way from the bulk to the transfer position. Another possible embodiment, which is especially preferred, is a vacuum means to hold the AGM granules in the cavities. An electrostatic field can also be used.

The term "expelling medium" in the present context means delivering the AGM granules in the transfer position as defined above to a carrier substrate. To supply the granules, these can be expelled by air jets, by an electrostatic field or simply by gravity.

Brief description of the drawings

The foregoing and additional features, aspects, and advantages of the present invention will be better understood upon reading the following description with reference to the accompanying drawings.

Fig. 1 shows an embodiment of the present invention;

Fig. 2 is a schematic illustration of the embodiment of Fig. 1 showing further detail;

Fig. 3 shows a modification of the embodiment of Fig. 2;

Fig. 4 corresponds to Fig. 2 with a modification of a characteristic;

Fig. 5 again corresponds to Fig. 2 with a modification of a characteristic;

Fig. 6 again corresponds to Fig. 2 with a modification of a characteristic;

Fig. 7 shows an embodiment that is a combination of Figs. 3 and 6;

Fig. 8 shows another embodiment of an apparatus according to the invention for carrying out the methods according to the invention;

Detailed description of the invention

Fig. 1 shows a hopper (10) filled with a bulk of AGM material (12). The hopper (10) has a feed opening (14) on the upper face and a feed opening (16) on the bottom. The hopper forms an embodiment of what is called "bulk" in the present context.

A printing roller (18) enters the opening (16) of the hopper (10) so that the bottom of the hopper surrounding the opening (16) closely follows the contour of the roller (18) to avoid accidental spillage of AGM granules.

The printing roller (18) is provided with holes or cavities (22) on its surface which are filled with AGM granules from the lower end (20) of the bulk of AGM material (12) in the hopper (10), while the surface of the roller (18) passes through the AGM material (12) that is inside the hopper (10). The

ES 2 397 213 T3 number, size and position of the cavities (22) are selected so that the volume and design of the cavities correspond to the design and thickness profile envisaged for the AGM material to be received by the printing roller and transferred to a carrier layer, as will be explained later.

The printing roller (18) forms an embodiment of a transfer device according to the present invention. Another embodiment could, for example, be formed by a belt having cavities on the surface thereof for receiving AGM material.

However, a rotating print roller can be a preferred embodiment.

The AGM granules are collected by the cavities (22) of the printing roller (18) when one of the cavities (22) of the transfer roller (18) is in this loading position. The AGM granules are retained in these cavities on their way from the hopper (10) to a position referred to herein as the "transfer or meeting position" where the printing roller (18) rotates counterclockwise. clockwise from Fig. 1 it is in a position directly facing the surface of a carrier layer (24). The carrier layer (24) is supported by a rotating support roller (25).

The carrier layer is, for example, a web of non-woven material on which the AGM granules are ejected or placed (by gravity) from the printing roller. To retain the AGM granules in the carrier layer (24), glue is preferably sprayed onto the carrier layer (24) upstream of the transfer position between the printing roller (18) and the carrier layer (24), the upstream position designated with numerical reference (26). Since the glue is applied in this upstream position (26) on the carrier layer (24), the AGM granules are retained on the carrier layer (24). An especially preferred glue for holding the AGM granules on the carrier layer (24) is a microfiber type glue with which very fine fibers are obtained by spraying a hot melt adhesive material through fine nozzles. These nozzles are available from the Nordson Company, Dawsonville, Georgia, USA.

It is preferred that the support roll (25), which could alternatively also be provided by a moving belt, also pushes the AGM particles against the carrier, especially using a pressure differential (vacuum) across a screen that forms the cylindrical surface of the support roller (25). In another position downstream of the transfer position between the printing roller (18) and the carrier layer (24), whose position designated with (28), glue is sprayed (preferably, but optionally) on the AGM granules which are on the carrier layer (24), the glue preferably also being a microfilament glue that enters as fibers between the AGM granules to hold the entire deposit together. In an alternative embodiment, a coating layer containing glue can also be applied to the AGM granules.

When large amounts of glue are applied at positions 26 and / or 28 it is advantageous to use materials for the cylindrical surface of the backing roll which have little or no tendency to accumulate adhesive residue. These can be Teflon ™ coated surfaces or, if a belt is used instead of a support roll, silicone rubber materials. Especially in the case that the carrier layer (24) is exposed to a vacuum inside the support roll, the surface of the support roll can be made of a silicone rubber screen (preferably metal-reinforced).

As shown in Fig. 1, in this particular embodiment the printing roller (18) moves through the AGM material by rotating the roller counterclockwise, designated by the arrow in Fig.

1. Some AGM granules are collected in the cavities (22) of the roller, but logically there is a certain risk that other AGM granules located beyond those that fill the cavities are carried out of the hopper between the surface of the roller (18) and the adjacent edge of the bottom of the hopper. Therefore, a scraping means (19) is provided at this edge, an example of which is shown in Fig. 2.

In Fig. 2 those elements that have already been described for Fig. 1 are designated with the same reference numbers.

The scraping means (19) of Fig. 2 is formed by a Doctor Blade (30) having a scraping edge (32) in close contact with the surface of the printing roller (18). The distance between the Doctor Blade (30) and the impression roller (18) should be greater than 0 mm to avoid excessive pressure and damage to the equipment and AGM particles. The mix of particle sizes is one of the factors to consider when selecting the distance from the doctor blade. Thus, p. For example, very large AGM particles with a mean diameter of 900 microns or greater would require a spacing of less than 900 microns. The useful upper separation limit should be about 1mm with a preferred gap between 0.01mm and 0.5mm, more preferably between 0.03mm and 0.1mm, to ensure good scraping over long production runs .

Fig. 3 shows an embodiment that corresponds to the embodiment of Fig. 2 but also shows a retention means for holding the AGM granules in the cavities (not shown) provided on the surface of the printing roller (18). on the way from the hopper (10) to the transfer position.

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One possibility for holding the AGM granules in the cavities can be a vacuum applied to the inner face of the printing roller (18) together with suction holes (not shown) at the bottom of the cavities. Another embodiment of a retention means as shown in Fig. 3 It is formed by an endless belt (34) that moves together with the rotation of the printing roller (18) together with the surface thereof from a position immediately downstream of the Doctor Blade to a position immediately upstream of the transfer position in which the granules are transferred to the carrier layer (24) not shown in Fig. 3. The belt is driven around an upper and lower guide roller (36,38) in the upper and lower position of the belt passage adjacent to the printing roller (18) and around a third guide roller spaced relative to the surface of the printing roller and forming a triangle with the other guide roller (36,38). The belt (34) can be driven by causing one of these three rollers to move the belt (34) in the direction marked by the arrows. Alternatively, the belt may idle and move in contact with the surface of the print roller (18).

Fig. 4 shows an alternative embodiment of the scraper means (19) of Figs. 2 and 3. Reference numerals in Figs. 2 and 3 are also used in Fig. 4 for corresponding parts. Instead of the Doctor Blade of Figs. 2 and 3, the embodiment of Fig. 4 is provided with an air jet box (40) which is disposed at the position of the Doctor Blade (30) of Figs. 2 and 3 and that expels air under pressure against the direction of movement of the surface of the printing roller (18), as shown in Fig. 4, to keep the AGM granules away from the gap between the air jet box. and the surface of the printing roller (18).

The embodiment of Fig. 5, which again basically corresponds to the previous embodiments of Figs. 2-4, shows another modification of the scraping means (19) which in this case is formed by a rotating brush (42) in the position of the Doctor Blade mentioned above to prevent the AGM granules from spinning out of the hopper 10 counterclockwise.

Fig. 6 again shows another embodiment of the scraping means (19), which in this case is formed by a mobile belt that moves around two rollers (46,48) of lower guide and upper guide, one of the which can be actuated by a suitable actuation not shown. The belt (44) travels on the side of the AGM materials practically in an upward vertical direction, as shown by the arrow, and then goes back down the outer side of the hopper (10).

The belt (44) lifts the AGM material on the inside of the hopper (10) to prevent the AGM material from leaving the hopper through the gap between the surface of the print roller and the belt (44).

Fig. 7 shows an embodiment that is practically a combination of the embodiments of Figs. 3 and 6, comprising a belt (34) to hold the AGM granules in the cavities of the printing roller and another belt (44) which has the function of a scraping means, as described in Fig. 6.

Fig. 8 shows an embodiment whose hopper (50) is shaped as a fluid bed to keep the AGM granules in a floating state. The printing roller designated with (18) in this case rotates through the fluidized granules which are collected by the cavities on the surface of the printing roller (18).

The AGM granules that extend beyond the cavities or that adhere to the surface of the impression roller (18) outside the cavities are detached from the impression roller by a Doctor Blade (54) that acts as a means of scraped and is arranged in a position immediately upstream of the meeting position designated by (55) in this case where the printing roller is positioned immediately opposite the carrier layer (24) supported by the horizontal drum. In positions (26,28) upstream and downstream of the meeting position there are position gluing heads (56,58) for applying glue on the carrier layer (24) at position (26) and on the granules of AGM deposited in position (28) applied on the carrier layer. In this case, the print roller is dipped into the AGM bulk storage from the top.

In a preferred embodiment, the system shown in Fig. 8 further comprises a cyclic system (51, 52, 57) of airborne particles. In this system the particles are transported from a location near the meeting position (55) along lines (51, 52) in the direction of arrow (53) to one end (57) of a return line. This prevents the particles from agglomerating or precipitating in the area of ​​the meeting position (55) due to a reduction in agitation in this area of ​​the fluid bed. The cyclic particle system can usually be operated by a stream of air in the line that carries the particles along the lines.