Chemical bonding or sometimes referred to as adhesion bonding methods involve applying adhesive binders to webs by saturating, coating or spraying, printing (as in print bonding) or foaming technics. Print bonding is used when specific patterns are required and where it is necessary to have the majority of fibers free of binder for functional reasons. The use of chemical binders remains one of the most versatile and useful ways of manufacturing nonwoven webs. There are many different classes of chemical binders to choose from which allows the manufacturer to tailor make a nonwoven web to meet the desired performance characteristics. Because of this, chemical bonding is used to make nonwoven webs for a variety of applications.
In solvent bonding fiber surfaces are softened or partially solvated with chemicals to provide self or autogeneously bonded fibers at the crossover points. Latex emulsion is added to the dilute fiber suspension prior to feeding into the forming wire. When the web is dried, the latex binder particles form cross-links or glue points and stable bonds between the fibers.
For over four decades, almost all nonwovens required a chemical binder to provide structural integrity and numerous other properties to achieve effective performance of the nonwoven fabric. In general it was the binder that limited the overall performance of a nonwoven compared to regular fabrics since the fibers were essentially the same used for both nonwoven and fabrics.
Common complaints regarding nonwovens was:
- Not enough strength;
- Too stiff;
- Inadequate absorbency;
- Poor laundering ability; and
- It doesn't feel like a textile fabric.
Over the years a great deal of effort was spent in the development and improvement of chemical binders. This led to better binders and steady improvements of performance in nonwovens. Since the early stages binders have moved from natural resins and glues, to synthetic binders, and to what is widely used today or acrylic-based latex binders. Acrylic-latex binders contributed greatly to improved softness properties with adequate strength, and other properties, despite a higher cost.