Quality control is critical throughout the nonwovens lamination process. Without it, you risk ending up with an inferior product and wasting precious materials and resources.
You also risk losing market share at a time when the industry is extremely competitive (in 2019, the global consumption of nonwovens was over 11 million tons and was valued at $46.8 billion).
In order to achieve and maintain the quality control you need when producing your nonwovens laminates, it is important to have a deep understanding of the processes that are under your control and how to turn that to your advantage. Let’s take a look.
How to ensure the highest lamination process quality control.
There are just a handful of process characteristics that must be strictly controlled and that truly dictate the quality of your final nonwovens laminate. In particular, these are the tension, the temperature, the nip pressure and the adhesive application
When it comes to web tension, it is defined as the force applied to the web in the machine direction (MD). The importance of tension during the entire lamination process cannot be overstated. For proper web handling, the web must always be in traction with the rollers and the tension to which it is subjected must never be too much or too little.
Tension control is critical for all stages of web handling. In general, finishing applications are divided into three distinct tension zones:
Each of these tension zones must be controlled independently but must work in synergy with the others. The tension applied in each zone is not the same, but it relies specifically on the torque of the rollers. The torque must change as a roll is being unwound or wound to maintain the proper tension.
The temperature setting in nonwovens lamination is of the utmost importance in order to obtain a product of the highest quality.
When it comes to hot melt adhesive lamination there is the need to have an accurate control of the adhesive temperature and the need to cool down the laminated web in order to avoid a change of the properties of the composite material.
If we talk about the thermal lamination process instead, this requires high temperatures to take advantage of the thermoplastic properties of one or more synthetic layers in the composite. The heat, along with pressure, will melt synthetic layers just enough to bond with the nonwoven layers. However, the temperature setting must be precise. If it is too low, the bonding won’t be effective and may not hold. Viceversa, if the temperature is too high it will cause a degradation of the materials in the layers, which will affect the structural integrity of the composite.
The nip is the space between two rollers along the lamination line. When passing the web through the nip, pressure is applied to smooth out the web and the ensure uniform distribution of the adhesive. How much pressure is applied to the web as it passes through the nip can be a game changer during the lamination process.
The key to nip pressure is to keep it as minimal as possible: too much pressure can compress the web too much and even tear it. In addition, the nip pressure will help control the tension on the web. It’s also important to understand that how the web passes through the nip is affected by how the two rollers move in relation to one another. If the alignment or torque of the rollers is off, defects such as shear wrinkles can occur.
Control over adhesive application is critical to quality control. If there is too little adhesive, bonding will not be strong enough and there may be sections that are not bonded at all. If there is too much adhesive, there will be thicker, stiffer areas within the composite. This control over adhesive application is relevant regardless of what application methods are used. Application methods include:
- Coating heads – contact application that is applied to the entire substrate surface
- Sprays – non-contact application that is delivered in a variety of patterns, such as bead, meltblown or sinusoidal
It is critical to control the application of the adhesive to keep it in line with the speed at which the web layers are moving. The faster the web is moving, the faster the application needs to be to achieve the optimal coating weight for the final product. These settings must be precise.
The role of Industry 4.0 in quality control
Measuring the various settings of nonwovens lamination machinery can be tedious and human error is inevitable when adjusting the settings manually. However, Industry 4.0 has changed the game when it comes to quality control.
Industry 4.0 is regarded as the next stage of the technological revolution, one that shifts the computerization of tasks to full automation, thanks to technologies such as the cloud and the Internet of Things (IoT).
Nonwovens lamination machinery that is designed based on Industry 4.0 principles includes:
- Sensors located all along the entire production line
- A cloud connection between the machines and the main software platform
- A user-friendly dashboard that provides complete visibility into and control over the production process in real-time
The sensors located on the machines can measure settings such as temperature, pressure and torque and can detect defects in the product as they happen. Since these data are being sent in real-time, adjustments can be made during production. With artificial intelligence (AI), these adjustments can be made by the software, keeping the production flowing at optimal speed with optimal settings at all times.