A textile backsheet is a composite material made using the process of nonwovens lamination. It is made from a nonwoven fabric and a polyethylene film that are bonded together with the use of a hot melt adhesive.
The backsheet 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 offer many other benefits, making the products:
- Soft to the touch
It is critical that the final product is of the highest quality, particularly since these products are often worn next to the skin. For this reason, defects that occur during production must be discovered and eliminated so they do not affect final product quality.
With this in mind, what follows is a discussion about three process challenges that can affect the quality of the textile backsheet you produce.
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 ensuring that the coating head consistently has an even distribution of adhesive.
When the adhesive is not evenly distributed across the coating head, it cannot be evenly applied to the substrate. This can result in areas where there is no adhesive, causing the textile backsheet to be loose and leaky in certain places, and areas where there is too much adhesive, causing some parts of the textile backsheet to become bulky and stiff.
Unfortunately, the adhesive is clear, making it difficult to see whether there is uneven distribution.
Solution – To solve the challenge of uniform adhesive distribution, 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 do so. This will give you a view of the thickness of the adhesive application, identifying the areas that are bare (devoid of adhesive). This provides a non-invasive method for monitoring the application of the hot melt adhesive quickly so that adjustments can be made to its flow to ensure it is steady and applied evenly.
When an adhesive is applied, whether with an even distribution or another type of distribution, there is the potential for it to bleed through the nonwoven. There are three main ways bleed-through can present itself:
- Strike through – when the adhesive bleeds through during production and gets on machine parts, 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
Solution – There are steps you can take with each of these challenges to minimize or eliminate bleed through, as follows:
- Strike through – adjust the amount of adhesive or the pressure to ensure it isn’t so high it will pass the adhesive through the nonwoven fabric
- Exposed adhesive – ensure perfect alignment of the textile backsheet layers so the adhesive can properly bond across the entire surface of both layers
- Migration – this happens to pressure-sensitive adhesives, so to avoid the migration of cooled adhesive, use adhesives that are less pressure sensitive and/or reduce the pressure on the product as the adhesive cools
Keep in mind that bleed through can also happen when:
- Machine settings are not consistent with the original equipment manufacturer’s (OEM) recommendations – make sure compression is not too high and that there is 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. Hot melt 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 control the temperature of the adhesive such that it doesn’t go so high that it degrades, burns, or affects 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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