Quality control is crucial in the nonwoven lamination process. Without it, it may end up with inferior products and waste of precious materials and resources, and in an era of extreme competition in this industry (in 2019, global nonwoven consumption exceeded 11 million tons, valued at 46.8 billion US dollars), will face the loss of market share risk.
In order to achieve and maintain the required quality control when producing nonwoven composites, it is critical to have a deep understanding of the control process and turn it into an advantage. Let's take a look. How to ensure the highest quality control of the nonwoven lamination process?
There are only a few processes that really determine the quality of the final non-woven composite material, which must be strictly controlled, mainly the application of tension, temperature, line pressure and adhesive.
Web tension is the force exerted on the web in the machine direction. Tension is extremely important throughout the lamination process. When properly handling the web, the web must always be pulled by the rollers, and it must not be under too much or too little tension.
Tension control is critical at all stages of web processing. In general, post-processing is divided into three distinct tension zones: unwinding, handling, and rewinding.
Each tension zone must be controlled independently, but must work in tandem with the other zones. The tension applied in each zone is different, depending on the torque of the rollers. The torque must be changed as the nonwoven fabric roll is unwound or unwound to maintain proper tension.
The temperature setting of the nonwoven lamination is critical to obtain a top quality product.
During hot melt adhesive compounding, the temperature of the adhesive layer needs to be precisely controlled, and the composite material needs to be cooled to avoid changing the properties of the composite material.
The thermal composite process requires high temperatures to exploit the thermoplasticity of one or more composite layers in the composite. The high temperature and pressure will melt the synthetic fiber layer enough to bond with the nonwoven fiber layer. However, the temperature setting must be precise. If the temperature is too low, it will not glue and it will not last. Conversely, if the temperature is too high, it can lead to the degradation of the material in the cloth layer, thereby affecting the structural integrity of the composite material.
The nip is the gap between the two rolls along the composite line. When the cloth surface passes through the pressing line, apply pressure to make the cloth flat and ensure the uniform distribution of the adhesive. The amount of pressure applied in the lamination process can be a game-changer as the web passes through the crimping line.
The key to controlling the line pressure is to make it as small as possible, too much pressure will press the non-woven polyethylene fabric too tightly or even tear the fabric. In addition, line pressure helps control web tension. It is also important to understand how the relationship between the two rolls is affected as the web passes through the nip. Defects such as cut-off wrinkles can occur if the positioning or torque of the composite roll is not correct.
Controlling the use of adhesives is the key to quality control. If there is too little adhesive, the bond will not be strong enough, and there may be parts that are not bonded at all. If there is too much adhesive, thick, hard areas will appear inside the nonwoven composite. Regardless of the gluing method used, the control of gluing is relevant.