[UPDATED ON SEPTEMBER 2023]
A textile backsheet is a composite material made using the lamination process, i.e. by bonding a nonwoven fabric and a polyethylene film with the use of hot melt adhesives. This composite is used in the construction of many types of products such as disposable diapers and adult incontinence products.
Textile backsheets are design to maximize the comfort of the users and to make the products:
- Soft to the touch
- Printable
- Waterproof/leakproof
- Breathable
Since these products are often in contact with the skin, it is essential that the end product is of the highest quality. For this reason, defects that occur during production must be discovered and eliminated.
In this article, we will focus on three critical challenges in the nonwoven lamination process that can influence the quality of the resulting textile backsheet.
Textile backsheet key process challenges & how to solve them
1. Adhesive Distribution Across the Coating Head
Some textile backsheets require full adhesive coverage. In these cases, the adhesive is applied with the use of a coating head designed to evenly apply the adhesive across the substrate.
One of the main challenges during the production of the textile backsheet is to ensure that the adhesive is evenly distributed on this coating head. If this is not done, there could be areas where no adhesive is present (where the textile backsheet is unglued and prone to leakage) and other areas where there is too much adhesive (and where, consequently, the composite is bulky and stiff). Unfortunately, the adhesive is transparent, and this makes it difficult to verify a possible uneven distribution.
Solution – To solve this issue, you need to be able to “see” the adhesive as it is being applied. By using a florescent formulation for the adhesive and a special UV light for optical inspection, you will be able to verify the thickness of the adhesive application, identifying areas left uncovered. This non-invasive method makes it possible to quickly monitor the application of hot melt adhesive and make adjustments to ensure that the flow of adhesive is constant and that it is evenly applied.
2. Bleed Through
During adhesive application, it is possible for leakage to occur through the textile backsheet. There are three main ways bleed through can present itself:
- Strike through: when the adhesive bleeds through during production and seeps between machine components, potentially contaminating the entire production line;
- Exposed adhesive: when there are areas of the textile backsheet that are open because the adhesive didn’t have a surface to bond to;
- Migration: when the adhesive still seeps into the nonwoven fibers even after it has reached room temperature. This problem can occur when working with pressure sensitive adhesives.
Solution – There are steps that can be taken to solve the above problems, namely:
- Strike through: adjust the amount of adhesive or pressure to ensure the latter is not so high that the adhesive passes through the nonwoven fabric.
- Exposed adhesive: ensure perfect alignment of the textile backsheet layers so that the adhesive can adhere properly over the entire surface of both layers.
- Migration: use less pressure sensitive adhesives and/or reduce the pressure exerted on the product as the adhesive cools.
Keep in mind that bleed through can also happen when:
- Machine settings do not follow the recommendations of the original equipment manufacturer (OEM); make sure compression is not too high and that there is an alignment between the web and the adhesive coating paths;
- Hot melt application equipment settings are incorrect, causing too much adhesive to be applied at once. Ensure the add-on rate for the adhesive is properly adjusted.
3. Adhesive Degradation
The degradation of the hot melt adhesive during application on textile backsheets can occur under certain circumstances. These types of adhesives are designed to melt to a low viscosity when they reach their melting point. If the adhesive is heated to too high a temperature, it will degrade faster.
Solution – It is important to monitor the temperature of the adhesive, making sure that it does not rise so high that it does not rise to such an extent that it causes the adhesive to degrade and burn or jeopardizes the operating conditions of the machinery. The heat stability will depend on the adhesive polymer used, so be sure you are familiar with the requirements of the specific adhesives you are using.
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