In reality what provides almost the whole product absorbency is SAP. Many producers are trying to introduce a new technology to eliminate completely fluff and obtain a more efficient core from cost point of view.
Apparatus for transferring particulate material onto a web and build a fluffless absorbent core are not complex from technological point of view.
Many years ago (and even today on simpler machines) rotary drum to dose SAP and transfer it on an airlaid web was a quite widespread system used in many sanitary napkins production lines. This drum had reservoirs on the surface and number, size and position of which determining the amount and pattern of SAP granules taken up by the drum and released onto a substrate (generally a nonwoven web). It was simple and effective, reliable and cheap (the so called indirect printing process).
In diapers the profile of absorbent core, whereby certain regions of the article comprise more SAP than other regions, is the key to get the appropriate core efficiency. And the traditional systems were not able to guarantee proper SAP placements especially at high speed in particular when fine particulate material is used and/ or when small and large quantities of reservoirs are used.
It has been found that at high speeds, SAP particles are not always satisfactorily dropped (e.g. from a feeder / hopper) into the reservoirs of the drum. Reservoirs may only be partially filled, whilst at certain areas of the drum excess SAP may build up. If vacuum (in the drum) is used to aid filling of the reservoirs, then this SAP build-up may obstruct the vacuum suction and this it may further obstruct the filling of the reservoirs This thus may result in an inaccurate distribution of the SAP in the absorbent cores, or even defects in the formed absorbent cores.
A possible apparatus and method for producing, even at high speed, absorbent structures comprising SAP could have the following structure:
a)a SAP feeder for feeding particles to
b)a drum with multiple reservoirs receiving SAP and transferring it to
c)a substrate like a nonwoven web
d)with a three dimensional plate applying pressure on part of SAP and guiding it into drum reservoirs
Plate is essential to properly fill reservoirs and guarantee desired SAP profile. Plate type and design can be different and many patents have been filed to protect a specific shape or function.
Vacuum can be used to keep reservoirs filled until the very last moment SAP have to be released and positioned on the substrate.