Key Points to Consider Before Obtaining a Slitter Rewinder from a Supplier

The Impact of Materials

You may be experiencing some difficulties in your flexographic printing business, such as some jobs failing to wind into good quality finished rolls. The solution may lie in making a comparison between the ink formulations and printing designs of the successful jobs and the unsuccessful ones.

Marginal increases in the general thickness occur on printed regions when you deposit certain inks on a flexible web. In cases where the design has large printed or unprinted regions of the material, this unnoticeable increase in thickness multiplies over several stacked layers as the diameter of the winding roll increases.

These regions may take the form of “gauge bands” across the surface of the roll on the printed areas. Once wound, applying lay-on nip loading and web tension in the course of the winding function may lead to lasting deformities at the localized areas. These damaged regions appear as web bagginess during unwinding of the roll, and this can damage the slitter rewinder.

It is therefore important to carefully consider the layout of the printed areas in order to reduce the occurrence of this effect. However, a variation in the caliper to a certain extent of severity is inevitable. Review your sample materials and printing designs with the supplier of your machine to ensure that it is prepared correctly and includes all the necessary features.

The slitter/rewinder design requirements can also be affected by the coating properties. To ensure that processing is effective, special winding solutions and web handling is required for coatings that have low coefficients of friction (COF). For instance, when operating speeds are high, you need lay-on rollers for materials with low COF to decrease trapped air between layers as winding is done. This ensures that a roll is wound with sufficient tightness.

To achieve the right levels of nip loads for individual slit packages, it is usually necessary to use individual lay-on rollers, depending on the caliper variation level. The cost and sophistication level of web handling systems and lay-on roller that the machine requires is dependent on two main factors: the substrate COF and the cumulative print coverage.

Sensitivity of the Substrate to Wrinkling or Scratching

As a flexographer, you wouldn’t want the coated/printed material to be damaged by the machine. You must therefore carefully consider the construction and coverings of the roller. This is especially important in high-speed printing where inertia of the roller can impede the ability of the web to make the rollers go faster or slower. In such a case, there is motion between the surfaces of the roller and the web.

Web tracking errors or scratches may result from this motion and abruptly ruin the web. It is therefore worth emphasizing the importance of paying close attention to detail in order that the slitting operation is not wasteful.

In conclusion, taking these two points of consideration into account before obtaining a slitter/rewinder from a supplier, rather than only considering dimensions and speed, is in your best interest as a flexographer.