Flawed color and defects on the surface of solvent-free composite films - Causes and rectification solutions

During solvent-free lamination production, the finished products often exhibit problems such as film surface blemishes, cloudy color differences, left and right alternating surfaces, and uneven blocky shading. The appearance is characterized by inconsistent local light transmission, dull base color, and chaotic textures. After curing, these issues cannot be naturally repaired, directly resulting in degradation of the appearance of transparent films and light-printed films. This problem is mostly caused by uneven coating, abnormal rheology of the adhesive, and mechanical accuracy deviations, and is a common and difficult defect in solvent-free mass production.

Poor coating uniformity is the core cause. The viscosity of solvent-free laminating adhesive is high and its leveling property is weak. The temperature of the coating roller is low and the adhesive temperature is insufficient, which can cause uneven leveling of the adhesive, local thickness variations, and form uneven cloud-like blemishes after curing. Inconsistent mixing of adhesives and instantaneous fluctuations in the ratio lead to inconsistent reaction speeds of the lateral adhesive layers, directly causing color differences between the left and right sides and the alternating surfaces.

 

Mechanical and process deviations will exacerbate the blemishing problem. Uneven pressure on the composite pressing rollers, slight eccentricity of the roller surface, uneven thickness of the adhesive layer, and after lamination, uneven light-dark patterns appear. Excessive machine speed, large tension fluctuations, and slight micro-jitter of the film surface cause microscopic non-uniform adhesion. In addition, unstable temperature and humidity in the workshop, accumulation of adhesive skin on the adhesive plate, and the attachment of foreign particles can also cause irregular blemishes and fog-like blemishes.

 

On-site rectification requires precise temperature control and improvement of leveling. Stabilizing the temperature of adhesive operation ensures uniform spreading. Regularly calibrate the mixing ratio of adhesives and the parallelism of the roller surface, as well as pressure balance. Match a reasonable machine speed and tension to eliminate film surface jitter and promptly clean the adhesive skin on the roller and dirt on the roller surface. By stabilizing the coating state and optimizing mechanical accuracy, the problem of blemishing and color differences in solvent-free composite can be completely solved, ensuring uniform transparency and uniformity of the film surface.