The diapers on the market are all kinds of products, but they are mainly composed of skin-friendly surface layer, diversion layer, absorption core, back layer of these four parts.
Among them, the absorption core is the most important structural component in diapers. As the main absorption layer, it is required to absorb urine quickly and spread urine to the whole absorption core by the use of diversion and core absorption. Then, the absorbent resin (SAP) can quickly absorb and lock urine, and make it non-reverse osmosis.

• Absorption core development process
  

1. In 1960, Procter & Gamble incorporated nonwoven materials and fluff pulp into diapers as absorbent core, which made diapers have certain applications
   
2. In 1980, Unica added SAP on the basis of the original absorbent core, which made the diapers have certain liquid absorption and retention properties. It was called the first generation absorbent core.
   
3. However, there is neither stratification nor partition inside the absorption core, and the problem of lumps will appear after the absorption, which will lead to the obstruction of urine transverse diffusion, and the excessive amount of liquid absorption in a certain area will affect the reverse osmosis performance of diapers. The absorption core of the second generation is divided on the basis of the first generation, which can fix the villus pulp and SAP to a certain extent, and reduce the problem of clumping after the diaper suction.
4. With the development of dry papermaking technology, namely dust-free paper technology, the third generation of absorbent core, namely composite absorbent core, was born by combining dust-free paper with porous fluffy nonwovens and SAP.
   The absorbent core is bonded between each layer of material by hot-melt adhesive, and the diaper becomes thinner.
   The absorbent core contains a large amount of SAP, and the absorbent volume of the diaper becomes larger.
   In addition, the mesh structure of porous fluffy nonwovens can fix SAP well, absorb fluid evenly from the core, and expand vertically and horizontally into the whole body after absorbing fluid, making the surface of diapers smoother.
   At present, most domestic diapers use the third generation of absorption core.
5. The fourth-generation absorption core is further divided in the interior of the third-generation absorption core, and each layer is better fixed. The absorption core becomes thinner and lighter, but the technology is still being improved.
   

• Absorption core structure analysis
  

• Traditional villi pulp absorption core
  

The cladding layer is made of tissue paper or non-woven materials or multi-layer composite materials. The upper cladding layer usually has the functions of diversion and ventilation, while the lower cladding layer usually has the functions of anti-seepage and barrier.

Villus pulp ( fluff pulp) can fix SAP to a certain extent, prevent SAP from moving and piling up, and keep the surface of diapers smooth and soft.
In addition, the core-suction effect of fluff pulp can solve the problem of gel blockage after SAP suction, weaken the phenomenon that diapers are prone to glop after SAP suction, and improve the feeling of wearing comfort.
But, in this kind of diapers, the wearer should avoid large mobile slip or flip in SAP, and caused the uneven distribution, SAP distribution areas more quickly and expansion and hinder the spread of urine, eventually lead to faults, tuo, influence of diapers fluid absorption for many times, more severe cases can cause surface film tear, urine leakage, stimulate the wearer of the skin.

It is usually coated with dust-free paper and porous fluffy nonwovens, then spread SAP between porous fluffy nonwovens, and then use hot melt glue to bond each layer.

Ultra-thin composite absorbent cores generally have the defect that the absorbent speed is faster at the first time and then decreases seriously, while the traditional villous slurry absorbent core has a more balanced absorbent speed.
With complex structure and many layers, it has lower production speed and higher production cost compared with the traditional villous pulp absorption core.

With the continuous improvement of people's requirements for lightweight, breathable, liquid absorbent, hygienic and non-stimulating diaper products, the diaper absorption core will develop towards the direction of diversified and comprehensive functions, and the structure of the absorption core will be continuously improved.
Among them, the research on the structure of composite absorption core will bring new breakthroughs to the field of sanitary products, which is conducive to grasping the needs of consumers, developing better new products, giving play to the potential of China's diaper market, improving market penetration and expanding market share.