Indirect printing of agm

The present invention relates to a method of applying granules of a material that absorbs moisture and converts moisture into a gel, a carrier layer in particular in training, (AGM - absorbent gelling material) for use in absorbent articles, baby diapers, pants, pants, sanitary pads and other similar. These articles usually have a carrier layer with AGM particles deposited by indirect printing together with the other layers making up the complete product.

FIELD OF THE INVENTION [0002] The term "AGM granules" as used herein includes materials capable of absorbing and retaining a large amount of liquid compared to its volume. "AGM" is an acronym for the English expression Absorbent Gelling Materials - Materials that absorb and convert moisture into a gel. These materials are made of superabsorbent polymers. In a given context, AGM materials can be granules of particles of various sizes, including powder materials or mixtures of powder materials and granules of particles of various sizes and forms (e.g. fibers).

[0003] Such AGM materials are usually deposited from melt-formed fibers or fibers in absorbent pads made by pneumatic spinning from cellulosic (or similar fibrous materials or combinations thereof) or are directly deposited on the nonwoven support layer. The present invention applies to both of these methods. This type of "absorbent article" can be used to manufacture diapers, sanitary napkins or any other liquid absorbent products.

[0004] Various methods have already been proposed for the distribution of AGM granules on a substrate with a specific pattern and thickness profile. These methods include blowing a volatile mixture of AGM granules and fibers 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 where AGM is distributed.

[0005] United States Patent 5,030,314 discloses a method and apparatus for forming composite articles with pockets for solid particles. This method is carried out through the use of apparatus consisting of an application roller having separate indentations, elements feeding solid particles to separate indents, elements rotating the application roller, elements transferring solid particles onto the receiving fabric, elements applying adhesive according to the pattern, elements moving the covering fabric through the elements applying the adhesive according to the pattern and elements connecting the receiving fabric with the covering fabric.

[0006] Particularly in the case of absorbent cores with little or no cellulose fibers, in which the AGM granules are the only liquid-retaining material, the arrangement of the AGM granules with shape and distribution accuracy is very important.

[0007] In this context, mention should be made of the possibility of using single or multi-element cores with one or more AGM layers on top of each other, overlapping or stacked side by side. This also allows the use of different types of AGM on individual layers. Therefore, the variety of obtained product is practically unlimited. However, the accuracy of granule distribution is very important.

SUMMARY OF THE INVENTION [0008] Accordingly, the present invention relates to a method of applying AGM granules to a surface, with high accuracy regarding the distribution, structure and amount of AGM material on a given surface, by indirect printing. This method of performing the process can be used to apply AGM particles that require accurate, print-like, granule or powder placement on a carrier layer. One specific method of application may be to make first the cores containing AGM / glue used in disposable diapers or to make parts of such cores.

[0009] This method of indirect printing is in accordance with patent claim 1.

[0010] The invention also relates to apparatus for carrying out the method according to the invention.

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

The present invention provides a method and apparatus that significantly increases the accuracy of AGM deposition. The standard deviation obtained so far has been reduced by about 1/4 compared to the value obtained using earlier modern technology. Therefore, diaper cores with an exact AGM distribution profile in the lateral and longitudinal direction can be obtained. The method according to the invention allows, above all, to deposit AGM granules with high accuracy on fast moving layers of the carrier at a surface speed from 1 m / sec to 3 m / sec, preferably from 5 m / sec or even 10 m / sec and most preferably up to 15 m / sec.

Due to the accuracy of the AGM granules, 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 herein includes any movable element capable of collecting granules and a thickness profile and

AGM with a predetermined shape for depositing granules without changing their configuration on the support substrate.

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

[0015] In the context of this document, the term "bulk" or "tank" means any type of granule delivery, in particular a hopper.

[0016] A "retention means" is provided so that the AGM granules taken through the recesses of the transfer device remain in these recesses during movement from the tank to the transfer position in which the granules are delivered to the carrier layer. In one preferred exemplary embodiment, the retention means is a belt that is routed along the surface of the transfer device, particularly a printing roller, from the reservoir to the transfer position. Other possible examples that are particularly recommended are vacuum methods to hold AGM granules in the cavities. It is also possible to use an electromagnetic field.

[0017] In the present context, "ejection element" means providing the AGM granules to the transfer position, as defined above, on the support substrate. To provide granules, the granules can be ejected by means of air streams or a magnetic field, or simply by gravity.

BRIEF DESCRIPTION OF THE DRAWINGS [0018] The above and the following features, aspects and advantages of the present invention will be better understood with reference to the following description referring to the accompanying drawings.

Fig. 1 shows one specific exemplary embodiment of the present invention;

Fig. 2 is a schematic illustration of the embodiment in Fig. 1 showing additional details;

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

Fig. 4 corresponds to Fig. 2 with a modification of one feature;

Fig. 5 again corresponds to Fig. 2 with the modification of one feature;

Fig. 6 again corresponds to Fig. 2 with the modification of one feature;

Fig. 7 shows an example of a combination of Fig. 3 and Fig. 6;

Fig. 8 shows another example embodiment of the apparatus according to the invention used to implement the methods according to the invention;

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

[0020] The printing roller (18) enters the opening (16) of 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 impossible.

[0021] The printing roller (18) has holes and recesses (22) on its surface, which are filled with AGM granules from the bottom end (20) of the tank with AGM material (12) in the hopper, while the surface of the roller (18) passes through AGM material (12) inside the hopper. The number, size and position of the wells (22) is selected so that the volume and pattern of the wells correspond to the intended pattern and thickness profile of the AGM material that will be picked up by the print roller and transferred to the carrier layer as explained below.

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

[0023] However, a preferred embodiment is a rotary printing roller.

[0024] AGM granules are received by the depressions (22) on the printing roller (18) when one of the depressions (22) of the transfer roller (18) is in the loading position. AGM granules are retained in these cavities on the road from the charging funnel (10) to a position called the "transfer or contact position" in which the print roller (18), rotating clockwise, as in Fig. 1, is in a position directly opposite the surface of the support layer (24). The carrier layer (24) rests on a rotary support shaft (25).

[0025] The support layer may, for example, be a nonwoven fabric on which AGM granules are ejected or applied (by gravity) from a printing roller. In order for the AGM granules to remain on the carrier layer (24), it is best to spray the adhesive between the printing roller (18) and the carrier layer (24), whose upward position is determined by the reference number (26) before transferring the transfer layer. Because the adhesive is applied in the upper position (26) on the support layer (24), AGM granules retain on the support layer (24). The most desirable 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 Nordson Company, Dawsonville, Georgia, USA.

[0026] It is preferred that the thrust roller (25), which alternatively can be replaced by a movable belt, also retains AGM particles on the carrier, especially by applying a pressure difference (vacuum) through the screen forming the cylindrical surface of the thrust roller (25). In another position below the transfer position, between the printing roller (18) and the carrier layer (24), which position is indicated by (28), the adhesive is - recommended, but not necessary - sprayed on AGM granules on the carrier layer (24), with it is best that the glue is a microfiber glue that, like fibers, enters between the AGM granules to hold all the deposited material together. In an alternative exemplary embodiment, an adhesive covering layer may be applied to the AGM granules.

[0027] If large amounts of adhesive are applied in positions (26) and / or (28), it is recommended to use materials for the cylindrical surface of the thrust roller that have a low or no tendency to accumulate adhesive residue. These can be Teflon ™ coated surfaces, or if a belt is used instead of a support roller, they may be silicone rubber materials. Particularly in the case of a support layer (23) exposed to a vacuum from the inside of the thrust roller, the surface of the thrust roller can be made of a screen of silicone rubber (preferably reinforced with material).

[0028] As shown in Fig. 1, in this particular embodiment, the printing roller (18) moves through the AGM material by rotating the roller counterclockwise indicated by the arrow in Fig. 1, AGM granules are taken into cavities that additional cavities , of course there is a risk, in addition to those filling from the hopper between the adjacent roller edge (22), but the AGM granules, the surface of the printing roller (18) and the bottom of the hopper will be taken. Therefore, this edge is equipped with scrapers (19), one example of which is shown in Fig. 2.

[0029] In Fig. 2, the elements and parts described earlier with reference to Fig. 1 are designated with the same reference numbers.

[0030] The scrapers (19) in Fig. 2 are formed by a scraping bar (20) 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 greater than 0 mm to prevent excessive pressure and damage to AGM equipment and particles. The mixture of particle sizes is one factor that is taken into account when choosing the scraping edge distance. For example, very large AGM particles with an average diameter of 900 microns and above require a gap of less than 900 microns. The upper limit of the usable distance should be around 1 mm, with the preferred distance between 0.01 mm and 0.05 mm, and preferably between 0.03 mm and 0.1 mm, to ensure good scraping for longer production runs.

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

[0032] One possibility of retaining AGM granules in the cavities is to create a vacuum from the inside of the printing roller (18) in combination with suction holes (not shown) at the bottom of the cavities. Another exemplary embodiment of the stopping element is shown in Fig. 3 and it is created by an endless belt (34) moved along with the rotation of the printing roller (18) along the surface of the same belt 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), which it is 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 print roller belt path (18) adjacent to the belt and around the third guide roller, separated by free space from the print roller and forming a triangle with the other guide rollers ( 36, 38). The belt (34) can be driven by driving one of these three rollers, thanks to which the belt (34) moves in the direction of the arrows. Alternatively, the belt may not be powered and move due to contact with the surface of the printing roller (18).

[0033] Fig. 4 shows an alternative embodiment of the scrapers (19) in Fig. 2 and 3. The reference numbers in Fig. 2 and 3 mean the same parts in Fig. 4. Instead of the collecting bar shown in Figs. 2 and 3, examples the embodiment in Fig. 4 has an air nozzle (40) located in the position of the scraper bar (30) in Fig. 2 and 3, which nozzle as shown in Fig. 4, ejects air under pressure in the opposite direction to the surface of the printing roller (18) in order to keep the AGM granules away from the gap between the air nozzle and the surface of the printing roller (18).

[0034] The exemplary embodiment in Fig. 5, which again essentially corresponds to the embodiments z shows another modification of the scrapers (19) of the case in the form of a rotary brush (42), in the position of the previously described scraping strip and preventing the AGM granules from falling out of the hopper 10 , thanks to counterclockwise rotation.

Fig. 2 to 4, which in this [0035] Fig. 6 again shows another example embodiment of scrapers (19), which in this case form a movable belt rotating around the lower and upper guide rollers (46, 48), one of which may be driven by a suitable drive, not shown here. The belt (44) moves from the side of the AGM materials substantially vertically upwards, as shown by the arrow, and returns downwards from the outside of the hopper (10).

[0036] The belt (44) lifts the AGM material on the inside of the hopper (10) to stop the AGM material from falling out of the hopper through the gap between the surface of the printing roller and the belt (44).

[0037] Fig. 7 shows an exemplary embodiment that is essentially a combination of the exemplary embodiments of Figs. 3 and 6, comprising a belt (34) for retaining AGM granules in the recesses of a printing roller and another belt (44) which has been discussed in relation to 6, acting as a scraper.

[0038] Fig. 8 shows an exemplary 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 by (18) rotates in granules in suspension, which are taken up in cavities in the surface of the printing roller (18).

[0039] In this case, the AGM granules, which are outside the recesses or adhering to the surface of the printing roller (18) outside the recesses, are scraped by a scraping bar (54), acting as a scraper, set in the position immediately before the contact position marked by (55), when the print roller is set against 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 to embedded AGM granules in position (28) applied to the layer media. In this case, the printing roller is immersed from above in the AGM tank.

[0040] In the preferred exemplary embodiment, the system shown in Fig. 8 additionally consists of a system for circulating air suspended particles (51, 52, 57). In this system, the particles are transported by pipes (51, 52) from a position near the contact position (55) in the direction of the arrow (53) to the end of the return pipe (57). In this way, sticking or deposition of particles in the contact position area (53) is prevented due to reduced mixing of the fluidized bed in this area. The particle circulation system can usually be controlled by means of an air stream in the pipe transporting the particles along the pipes.