Core System Basics: A Better Understanding Starts Here

Cores are a hot topic in the disposable hygiene industry. Leak prevention. Performance and integrity. How thin should it be? Channels or no channels? 

Staying up to date on the latest industry trends and discussions is the only way to remain competitive in today’s market. A good foundation in the basics can be essential. That is why our experts at Bostik have compiled this overview of the traditional core system, as well as the channel and pre-compound cores. Included are the various components and the key role adhesives play in helping hold everything together.

Adhesives

Hot-melt adhesives promote core integrity by bonding components together. They are essential to preventing shifting, supporting absorbency, and providing structure. In doing so, they help ensure the core and its components can function as intended.

Topsheet

This layer of the core system makes direct contact with the wearer’s skin and enables the acquisition of fluid. Adhesives help prevent the core from shifting, which could compromise absorbency and core integrity.

Acquisition Distribution Layer (ADL)

The ADL is designed to improve fluid management. It pulls liquid quickly away from the topsheet and distributes it for better absorption. This helps keep skin dry and minimise leaks during rewet. Adhesives help anchor the ADL to the topsheet and core matrix.

Channel core

In channel core designs, specific adhesives are used to create channels free of absorbent material. The SAP and fluff are located in the tube-like areas created by adhering the top and bottom sheets, and may be stabilised with adhesive.

Compound/pre-compound core

Compound and pre-compound cores utilise layers of tissue, fluffy nonwoven, and SAP, bonded with adhesive. Pre-compound indicates that the core is made off the diaper production line, usually by a third party. Compound indicates that the core is created inline. Adhesive may be used to help minimise loss or shifting of SAP.

Core Wrap

The primary function of the core wrap is to maintain core integrity during processing by containing the fluff/SAP matrix. Adhesives are used to seal the core wrap, bond adjacent materials, and prevent shifting.

Fluff

Traditionally, fluff is found at the centre of the core. It is typically composed of cellulose from trees and helps with rapid absorption and distribution of fluid. Fluff also assists with core integrity and improves core matrix stability. The amount of fluff used may be indicated by the ratio of fluff to SAP, such as 50/50 or 30/70. Adhesives are used to stabilise the fluff/SAP matrix.

Superabsorbent polymer (SAP)

In traditional core design, this polymer is combined with fluff (cellulose or synthetic) to create the core matrix. It can also be used alone in newer, fluff-free core designs. While SAP absorbs and wicks fluid slowly, it can retain large volumes of liquid relative to weight, even under pressure. Adhesives are needed stabilise the SAP when less fluff is used.

Backsheet

The backsheet is a barrier that can be breathable or non-breathable. Adhesives may be applied to the backsheet to help prevent core shifting and leakage during use.

Wetness Indicator

Typically applied to the diaper backsheet in the crotch area, the wetness indicator is a functional adhesive that changes colour when wet. It is a common feature in many of today’s disposable diapers and some products for adult incontinence, especially those intended for institutional use.

Learn more about the purpose and functions of the disposable hygiene core when you read our article, ‘Core Needs in Disposable Hygiene’.