Indirect printing of AGM

[0001] The present invention relates to a method for applying granules of absorbent gelling material (AGM) to a carrier layer for use in an absorbent article, in particular a diaper for infants or adults, training pants, diaper pants, sanitary pads, panty liners and the like. These products usually contain a carrier layer with AGM particles deposited on it by indirect printing together with successive layers forming a complete product.

BACKGROUND OF THE INVENTION [0002] The term "AGM granules" as used herein includes materials capable of absorbing and retaining a large amount of fluid compared to its volume. "AGM" is an acronym for the English absorbing gelling material. These materials are created mainly by superabsorbent polymers. In the present context, the AGM material may be used in the form of granules of various particle sizes, including powder materials or a mixture of powder material and granules of various particle sizes or forms (e.g., fibers).

[0003] AGMs of this type are usually embedded in absorbent pads made of hot-air or cellulose fibers (or similar fibrous materials or combinations thereof) or deposited directly onto the nonwoven support layer. The present invention is applicable to both of these methods. This type of "absorbent article" can, for example, be used to produce diapers, sanitary napkins, and even any type of absorbent article.

[0004] Various methods have been proposed to achieve the distribution of AGM granules on a substrate having a predetermined pattern and thickness profile. These methods include blowing a mixture of AGM granules and fibers in the air through a tube onto a vacuum drum. These types of methods only allow limited control of the pattern and AGM thickness distribution on the surface on which the AGM is spread.

[0005] Particularly in the case of absorbent cores with or without a small amount of cellulose fibers, in which the AGM granules are the only liquid retaining material, the distribution of the AGM granules with accuracy in terms of shape and distribution is extremely important.

[0006] It should be noted in this context that it is possible to use single or multi-core cores with one AGM layer or several layers on top of each other, overlapping or stacked side by side. It also allows the use of other AGMs on individual layers. In this way, the possibilities of differentiating the obtained product are almost endless. However, the accuracy of the granule distribution is important.

SUMMARY OF THE INVENTION [0007] Accordingly, the present invention relates to a method of applying AGM granules to a surface with high accuracy with respect to the distribution, structure and amount of AGM material on a surface by indirect printing. This method of production can be used when applying AGM particles requiring an accurate, print-like arrangement of granules or powders on a carrier layer. One particular application can be the production of cores containing mainly AGM and disposable diaper glue or parts of such cores.

[0008] According to a first embodiment of the present invention, the indirect printing method according to the invention is characterized in that

- AGM granules are taken by a transfer device from the AGM granule tank,

- said transfer device has cavities on its surface, the number, size and position of which determine the quantity and pattern of AGM granules collected by the transfer device,

- the transfer device moves from the reservoir to the sliding carrier layer (transfer or contact position),

- means are provided for retaining AGM granules inside said cavities during movement of the transfer device to said contact (or transfer) position,

- means are provided for ejecting said AGM granules onto the carrier layer in said transfer position, as claimed in the document.

[0009] The invention further relates to apparatus for carrying out the method according to the invention.

[0010] US-A-5 030 314 discloses a method according to the preamble of claim 1.

[0011] Indirect printing means below transferring the AGM separated from the AGM tank before it comes into contact with the carrier layer. Direct printing means that AGM is not emitted from the AGM tank before it contacts the carrier layer. This invention is not concerned with.

[0012] The present invention discloses a method and which significantly increases the accuracy of AGM deposition. up to now the standard deviation has been reduced to the apparatus, Obtained by^kabout^Labout ^1/4 value obtained using modern state of the art. In this way, diaper cores with an exact AGM distribution profile in the transverse and longitudinal directions can be obtained. The method according to the invention allows, in particular, the deposition of AGM granules on fast-moving carrier layers at a surface speed of 1 m / s to 3 m / s, preferably up to 5 m / s or even 10 m / s, and even more preferably up to 15 m / s high accuracy. Due to the accuracy of AGM granule deposition, the invention allows the production of e.g. an absorbent core without cellulose or similarly absorbent and / or hydrophilic fibers in diapers, which leads to the fact that the core is extremely thin, and the comfort of use and fitting of the products is greater.

[0013] The term "conveying device" as used in the document includes any movable element capable of collecting AGM granules of a predetermined shape and thickness profile and depositing the granules without changing their configuration on the support substrate.

[0014] A preferred embodiment of the transfer device is a shaped drum or rotary roller, referred to in the present context as a "printing roller" or "transfer roller" because transferring the pattern of AGM granules can be compared to printing. Another embodiment is a movable belt having surface depressions that is moved between the AGM granule tank and the transfer position.

[0015] The term "bulk" or "tank" AGM granules in the present context refers to any type of granulate delivery, particularly a hopper.

[0016] A "retention means" is provided so that AGM granules collected by the recesses of the transfer device are held in these recesses during movement from the tank to the transfer position, when the granules are delivered to the carrier layer. In one preferred embodiment, the retention means is a belt guided along the surface of the transfer device, particularly a printing roller, between the container and the transfer position. Other possible embodiments that are particularly preferred are vacuum methods for retaining AGM granules in cavities. It is also possible to use an electrostatic field.

[0017] "Ejection element" in the present context means providing the AGM granules in the transfer position as defined above on the support substrate. For delivery

<td>granules</td><td>granules can be ejected by means of air streams</td>

<td>or field</td><td>electrostatic or just gravity. BRIEF DESCRIPTION OF THE DRAWINGS</td>

[0018] The above and the following features, aspects and advantages of the present invention will become more apparent with reference to the following description relating to the accompanying drawings.

Fig. 1 shows one embodiment of the present invention;

Fig. 2 is a schematic illustration of the embodiment of fig. 1 showing an additional detail;

<td>Lynx .</td><td>3 illustrates the modification of the embodiment in fig. 2;</td>

<td>Lynx .</td><td>4 corresponds to figure 2 with the modification of one feature;</td>

<td>Lynx.</td><td>5 again corresponds to fig. 2 with the modification of one feature;</td>

<td>Lynx.</td><td>6 again corresponds to fig. 2 with the modification of one feature;</td>

<td>Lynx .</td><td>7 illustrates a combination embodiment</td>

<td>Fig. 3 and</td><td> 6;</td>

<td>Lynx .</td><td>8 shows another embodiment of the apparatus according to</td>

of the invention and for carrying out the methods of the invention;

Fig. 9 is a cross-sectional view taken along line 9-9 of another embodiment of the invention shown in Fig. 10.

Fig. 10 is a left front view of Fig. 9.

DETAILED DESCRIPTION OF THE INVENTION [0019] Fig. 1 shows a hopper (10) filled with loose AGM (12). The hopper (10) has an inlet (14) on the upper side and an outlet (16) on the bottom. The hopper is one embodiment of the "tank" in the present context.

[0020] The printing roller (18) enters the hole (16) in the charging funnel (10) in such a way that the bottom of the charging funnel around the opening (16) exactly matches the contour of the roller (18) and accidental falling of the AGM granules is not possible.

[0021] The printing roller (18) contains holes or recesses (22) filled with AGM granules from the bottom end (20) of the AGM material tank (12) in the hopper (10), and the surface of the roller (18) passes through the AGM material (12) inside the hopper (10). The number, size and position of the wells (22) are selected so that the volume and pattern of the wells correspond to the intended pattern and thickness profile of the AGM material received by the printing roller and transferred to the carrier layer as described below.

[0022] The printing roller (18) is one embodiment of the transfer device according to the present invention. Another embodiment may, for example, be a belt having in its surface recesses for receiving AGM material.

[0023] A preferred embodiment may, however, be a rotary printing roller.

[0024] The AGM granules are taken through the recesses (22) of the printing roller (18) when one recess (22) of the transfer roller (18) is in the loading position. AGM granules are retained in these cavities (22) on the way from the charging funnel (10) to the position referred to as the "transfer or contact position", in which the printing roller (18), rotated clockwise in Fig. 1, is in the direct position opposite the surface of the carrier layer (24). The support layer (24) is supported on the rotating thrust shaft (25).

[0025] The support layer is, for example, a non-woven fabric onto which AGM granules are ejected or applied (by gravity) from a printing roller. In order to hold the AGM granules on the carrier layer (24), adhesive is sprayed onto the carrier layer (24) prior to the transfer position between the printing roller (18) and the carrier layer (24), whose upward position is determined by reference number (26). Because the adhesive is applied in this upper position (26) to the carrier layer (24), the AGM granules are retained on the carrier layer (24). A particularly preferred binder or adhesive for retaining AGM granules on the support layer (24) is a microfiber adhesive containing very thin fibers formed by spraying hot melt adhesive material through appropriately thin nozzles. Such nozzles are commercially available from the Nordson Company, Dawsonville, Georgia, USA. Methods of combining AGM with a carrier by a binder, in particular by hot melt adhesive, are described in US Patent No. 5,560,878, issued October 1, 1996 to Dragoo et al. Methods for combining hot melt adhesives with AGM or other particles are further described in US 5560878.

[0026] Preferably, the thrust roller (25), which optionally can also be a movable belt, also presses the AGM particles against the carrier, particularly by applying a pressure difference (vacuum) through the screen forming the cylindrical surface of the thrust roller (25). In a different position after the transfer position between the printing roller (18) and the carrier layer (24), which location has been marked (28), the adhesive is sprayed on the AGM granules on the carrier layer (24), which adhesive is also preferably a microfiber adhesive, which, like fibers, enters between AGM granules and holds together all deposited material. In an alternative embodiment, it is also possible to apply an adhesive covering layer to the AGM granules.

[⁰⁰²7] Je^SLI in half^fromen^andac^h (²⁶) ^and (^lat^b) (2Ó) nakkda p^uta large amount of glue, it is preferable to use materials on the cylindrical surface of the thrust roller that have little or no adhesive residue accumulation. These can be Teflon ™ coated surfaces or if a silicon roller is used instead of a support roller. Particularly, a belt, rubber materials, if the carrier layer (24) is exposed to a vacuum from the inside of the thrust roller, the surface of the thrust roller can be made of a silicone rubber screen (preferably reinforced with metal).

[0028] As shown in Fig. 1, in this particular embodiment, the printing roller (18) moves through the AGM material by turning the roller anti-clockwise as shown by the arrow in Fig. 1; AGM granules are taken through the cavities (22) of the roller, but there is of course some risk that additional AGM granules in addition to the filling cavities will be taken from the hopper between the surface of the printing roller (18) and the adjacent bottom edge of the hopper. Therefore, there are scrapers (19) on this edge, one example of which is shown in Fig. 2.

[0029] In Fig. 2, those elements or parts which were previously described in connection with Fig. 1 are designated with the same reference numbers.

[0030] The scrapers (19) in Fig. 2 are formed by a scraping bar (30) having a scraping edge (32) in close contact with the surface of the printing roller (18). The distance between the scraper bar (30) and the printing roller (18) should be above 0 mm, so that there is no excessive pressure and damage to the device and AGM particles. The mixture of particle sizes is one of the factors to consider when choosing the scraper edge distance. Eg. very large AGM particles with an average diameter of 900 microns and more require a gap of less than 900 microns. The upper limit of the useful distance should be about 1 mm, with a preferred distance of 0.01 to 0.5 mm, more preferably 0.03 to 0.1 mm, to ensure proper scraping for longer production runs.

[0031] Fig. 3 shows an embodiment corresponding to the embodiment of Fig. 2, but additionally shows a retaining element for retaining AGM granules in cavities (not shown) made in the surface of the printing roller (18) on the path from the hopper (10) to transfer position.

[0032] One possibility of holding the AGM granules in the cavities is to create a vacuum from the inside of the printing roller (18) in combination with the suction holes (not shown) at the bottom of the cavities. Another embodiment of the stopping element is shown in fig. 3; it is formed by an endless belt (34) moved along with the rotation of the printing roller (18) along its surface from the position immediately behind the scraper bar to the position immediately before the transfer position, where the granules are transferred to the carrier layer (24), not shown in Fig. 3 . The belt is driven by the upper and lower guide rollers (36, 38) in the upper and lower position of the belt track at the printing roller (18) and around the third guide roller distant from the surface of the printing roller, forming a triangle with the other guide rollers (36, 38). The belt (34) can be driven by driving one of these three rollers so that the belt (34) moves in the direction of the arrows. Alternatively, the belt may not have a drive and may move due to contact with the surface of the printing roller (18).

[0033] Fig. 4 shows an alternative embodiment of the scrapers (19) of Figs. 2 and 3. The reference numbers of Figs. 2 and 3 are also used in Fig. 4 for the relevant parts. Instead of the scraper bar of Figs. 2 and 3, the embodiment of Fig. 4 includes an air nozzle (40), positioned in the position of the scraper bar (30) of Figs. 2 and 3 and ejecting air under pressure in the opposite direction to the movement of the printing roller surface (18), shown in Fig. 4 to keep the AGM granules out of the gap between the air nozzle and the surface of the printing roller (18).

[0034] The embodiment of Fig. 5, which again essentially corresponds to the above embodiments of Figures 2 to 4, shows another modification of the scraper (19), which in this case forms the rotary brush (42) in the position of the scraper bar referred to above which prevents the AGM granules from falling out of the hopper 10 by turning to the left.

[0035] Fig. 6 again shows another embodiment of the scraper (19), which in this case forms a movable belt moving around the lower and upper guide rollers (46, 48), one of which can be driven by a suitable drive (not shown) . The belt (44) moves from the side of the AGM materials vertically upwards, as the arrow shows, and returns down from the outside of the hopper (10).

[0036] The belt (44) lifts the AGM material on the inside of the hopper (10), which prevents the AGM material from falling out of the hopper by a gap between the surface of the printing roller and the belt (44).

[0037] Fig. 7 shows an embodiment which essentially combines the embodiments of Figs. 3 and 6, comprising a belt (34) for holding the AGM granules in the recesses of the printing roller and a second belt (44) acting as a scraper discussed in connection with the Fig. 6.

[0038] Fig. 8 shows an embodiment of a hopper (50) that forms a fluidized bed for holding AGM granules in a suspended state. In this case, the printing roller marked (18) rotates in granules in suspension, which are taken up by recesses in the surface of the printing roller (18).

[0039] AGM granules that are outside of the recesses (or adjacent to the surface of the printing roller (18) outside the recesses are scraped from the printing roller by a scraper (54) acting as a scraper, set in the position immediately before the contact marked (55), in this case when the printing roller is positioned directly opposite the carrier layer (24) held by the lying drum. In positions (26.28) before and after contact, there are glue position heads (56, 58) for applying glue to the carrier layer (24) in position (26) and the deposited granules

AGM in position (28) applied to the carrier layer. In this case, the printing roller is submerged in the AGM tank from above.

[0040] In a preferred embodiment, the system shown in Fig. 8 further comprises a system for circulating air suspended particles (51, 52, 57). In this arrangement, the particles are transported from the place near the contact position (55) by tubes (51, 52) in the direction of the arrow (53) to the end of the return tube (57). In this way, sticking or embedding of particles in the contact area (55) is prevented due to reduced mixing in this area of ​​the fluidized bed. The particle circulation system can usually be supplied with an air stream in the pipe transporting the particles through the conduits.

[0041] Fig. 9 shows an intermediate particle printing station comprising an AGM feeder (70, 72, 74) connected to the stator housing (68), the axis (80) of the centrifugal shaft (60) being along a horizontal line from left to right in Fig. 9. Fig. 9 is a cross-sectional view along line 9 in Fig. 10, which shows a side view of the station for printing particles from Fig. 9. In Fig. 10 shows the carrier on which AGM is mounted on a transport cylinder, also referred to as a thrust shaft (25, shown partially). The centrifugal shaft (60) is the central part (62) of the cylindrical form and the two inlet elements (64, 66) in the shape of a truncated cone on both sides in the axial direction. The inlet elements (64, 66) are connected to the AGM delivery system (68) formed by the feed pipe (70) branching into two side pipes (72, 74) connected

64, 66) a centrifugal roller. stator (68), with centrifugal inlet elements (60) at their axial ends. In this way, the AGM is supplied through the feed pipe (70) to the side pipes (72, 74) and transported to the inlet elements (64, 66) by force and finally to the central part (62) of the shaft. In this position, the AGM leaves the centrifugal shaft and , still due to the pressure created due to centrifugal force, is pressed against the inside of the screen printing roller (82), which is partly covered from the outside with a belt (86).

[0042] This printing roller is provided with holes (not shown) in the perimeter wall forming a pattern of the appropriate shape and size through which, with each rotation of the centrifugal roller, the AGM granules leave the printing station and are deposited without contact on the carrier layer (24) ( as shown in Fig. 10).