The back sheet must be soft.
But it also must be bonded strongly. That is the challenge. Our hot melt adhesive liquid is made for bonding the back sheet of diapers and pads. It bonds soft nonwoven to PE breathable back sheet. The bond must be strong. No delamination. No leaks. But the back sheet must stay soft. No hardness. No stiffness. The finished product must feel comfortable against the skin. A lot of customers ask us, "How do I bond the back sheet without making it hard?" This is the answer.
We use a low-modulus SIS and polyolefin blend.
The glue stays at a very low elastic modulus after setting. That means it is soft. The working temperature is 140-160°C. At 150°C, the melt viscosity is 2500-4500 mPa·s. Works on all coating methods. Dot spray. Fiber spray. Slot coating. Strip coating. The softening point is 80-95°C. No flow. No oil leak. The plasticizer has very good compatibility with the base. The glue layer stays soft during long use.
Here is the softness and strength data.
Dry 180° peel strength on nonwoven and PE film is 6-10 N/25mm. Wet strength retention after 24 hours in simulated urine is over 75%.
|
Parameter |
Value |
|
180° Peel Strength (Dry) |
6 - 10 N/25mm |
|
Wet Strength Retention |
> 75% |
|
Viscosity (150°C) |
2500 - 4500 mPa·s |
|
MVTR Loss |
< 10% |
|
Safety |
FDA, HG/T 3948-2025 |
Even when the diaper is full, the back sheet stays bonded. No delamination. No bubbles. No leaks. The glue has a Shore A hardness below 30 after setting. Very soft. The MVTR loss of the PE film is below 10%. Breathability is not affected. That helps prevent diaper rash. In our 70°C/72 hour heat aging test, color change (ΔE) is less than 2. No skin. No carbon. That is our hot melt adhesive liquid.
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