Finishing Stage of Disposable Diapers
Assembly of the components
At this point in the process, there are still three separate components, the absorbent pad, the top sheet, and the backing sheet. These three components are in long strips and must be joined together and cut into diaper-sized units. This is accomplished by feeding the absorbent pad onto a conveyor with the polyethene bottom sheet.
The polypropylene top sheet is then fed into place, and the compiled sheets are joined by glueing heating, or ultrasonic welding. The assembled diaper may have other attachments, such as strips of tape or Velcro™, which act as closures.
The long roll is then cut into individual diapers, folded, and packaged for shipping.
Quality Control
The main activity of the quality control is to check products absorbency which should be within the set international norms.
One key is to make sure the polymer/ fibre ratio in the absorbent pad is correct. Too much variation will impact the diaper’s ability to soak up moisture. Industry trial and error has shown that for optimal performance and cost, the fibre to particle ratio should be about 75:25 to 90:10. Even more critical than these ratios are the size and distribution of these particles.
It has been established that particles with a mass median particle size greater than or equal to about 400 microns work very well with the fibres to enhance the rate at which the fluid is transported away from the body. If the particles very much outside this range, gel blocking may occur.
There are several standard tests the industry uses to establish diaper absorbency. One is referred to as Demand Wettability or Gravimetric Absorbance. These tests evaluate what is are commonly referred to as Absorbance Under Load (AUL). AUL is defined as the amount of 0.9% saline solution absorbed by the polymers while being subjected to pressure equivalent to 21,000 dynes, or about 0.30 lb/sq in (0.021 kg/sq cm). This test simulates the effect of a baby sitting on a wet diaper. If the diaper has an absorbency of at least 24 ml/g after one hour, the quality is considered acceptable.
Other quality control factors besides absorbency are related to the diaper’s fit and comfort. This is an essential parameter check and Particular attention must be paid to the melt characteristics of the nonwoven fabrics used to form the diaper’s shell. If materials with different melting points are used, the material that melts the quickest may become too soft and stick to the assembly apparatus. When the fabric is pulled off it may be left with a rough surface that is uncomfortable to the user. Finally, the alignment of the components must be carefully checked or leakage may result.
Disposable baby diapers sold in the EU/USA must comply with the European/USA General Product Safety Directive and where they contain lotions and fragrances, must also comply with the requirements of the European/USA Cosmetics Directive. Our industry does more than simply comply with the legal framework to ensure that our products are
Disposable diaper manufacture is a high technology field which has consistently shown innovation over the last few decades. Nonetheless, there are still a number of areas which require additional improvement. One such area is that of leakage reduction. It is likely that the manufacturers have developed 3D leak guard with elastic bands to hold the waist more tightly without causing chafing or leakage or discomfort. It is also likely that current concern regarding the role of disposable diapers in landfills will impact manufacturing and formulation. This concern may lead to the development of diapers which are less bulky and more biodegradable.