In the dry lamination production process, the insufficient initial adhesion of polyurethane laminating adhesive is a common technical drawback. The strength of the finished product is normal after aging, but the adhesive layer has weak grip immediately after the composite is completed, which easily causes relaxation during winding, membrane layer slippage, left-right deviation, inter-layer misalignment, and leads to edge curling, warping, and inconsistent winding tension, directly affecting the stability of the cutting and bag-making processes, and is a frequent hazard in lamination production.
The low working viscosity of the adhesive is the main cause of weak initial adhesion. Excessive dilution and excessive addition of ethyl acetate will significantly reduce the solid content of the adhesive solution and the coating amount, resulting in a thin adhesive layer, rapid wetting but insufficient instantaneous grip, and inability to firmly lock the two layers of substrates during the initial bonding, which is prone to relative displacement under high-speed machine speed and causes overall sheet sliding and deviation.
Incompatibility between the coating and drying conditions will exacerbate the problem. Excessive oven temperature and overly dry adhesive layer, the adhesive surface approaching the state of losing adhesion, the initial adhesion of the adhesive is significantly reduced. Excessive machine speed, insufficient effective drying distance of the oven, dry surface and slightly wet interior of the adhesive layer, unstable adhesive force after bonding. At the same time, insufficient pressure of the pressing roller, low adhesive temperature, and rapid leveling will also lead to insufficient instantaneous adhesion, causing the sheet to slide during winding.
On-site improvement requires precise control of the working viscosity, eliminating excessive dilution, ensuring that the effective coating dry amount meets the standard. Reasonably adjust the temperature gradient of the oven to avoid excessive drying of the surface layer, match an appropriate machine speed to ensure an appropriate dry-wet state of the adhesive layer. Appropriately optimize the composite pressure and adhesive surface temperature to enhance the instantaneous bonding grip. Stabilizing the initial adhesion performance can completely solve the problems of winding deviation, slippage, and inconsistent tension, improving the regularity of the sheet and the stability of subsequent processing.
