How To Choose Pilot Coating Machine For New Adhesive Formula Test

In roll-to-roll coating production, paper and plastic film are two of the most widely-used substrates. Although processed on similar coating machines, paper coating and film coating bring completely different challenges in material property, parameter setting, drying requirement and final product performance. Understanding their differences is essential for equipment selection, formula adjustment and stable mass production.

Paper is a porous, hygroscopic substrate made of plant fiber. During paper coating, part of coating liquid will penetrate into paper fiber gaps besides staying on the surface. Operators need to balance penetration and surface covering. Too much penetration causes excessive absorption, resulting in thin coating layer, poor barrier performance and paper curling. Typical paper-coating products include heat-sealable food-grade paper, thermal paper, coated printing paper and release paper. For paper processing, tension has relatively wide tolerance. However, drying temperature and air volume must be well controlled to avoid paper shrinkage, wrinkling or deformation caused by moisture change.

By contrast, plastic film such as PET, BOPP and PE is non-porous and non-absorptive. All coating materials stay on the substrate surface without permeation. The biggest difficulty for film coating lies in surface adhesion. Most films have low surface energy. Without proper pre-treatment such as corona treatment, coatings tend to peel off or form pinholes. Film substrates are highly sensitive to tension. Excessive tension will produce permanent stretching and web distortion, which directly ruins coating thickness uniformity. Common film-coating outputs are protective film, adhesive tape, optical functional film and release film.

Corresponding equipment and process parameters also vary greatly. For paper coating, blade coating and reverse roll coating are frequently adopted, with focus on controlling penetration and drying shrinkage. For film coating, slot-die coating and comma-bar coating are popular, requiring high-precision tension control and surface pre-treatment devices. Even using the same coating machine, operators need to adjust web tension, drying curve, coating viscosity and web speed when switching between paper and film production.

Many manufacturers intend to use one coating line for both paper and film. It is feasible only when the machine is equipped with high-precision tension control system, adjustable drying unit and optional corona station. Simple retrofitting of paper-oriented machines cannot meet stable film-coating demands.

To sum up, paper coating deals with porous and moisture-absorbing material, focusing on penetration control and anti-shrinkage. Film coating targets non-absorptive smooth substrate, putting emphasis on surface adhesion and precise tension management. Clarifying these distinctions helps manufacturers reduce trial-and-error costs and improve finished-product yield for flexible packaging, adhesive and new-material industries worldwide.

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