Always Toward Better

Higher Productivity, Lower Costs, Improved Process Reliability, Better Quality: There are numerous reasons for manufacturers of printing inks and other suspensions to review their current production concepts or reconsider the grinding technologies they use. The two practical examples outlined below demonstrate the advantages of optimizing wet grinding processes. High-quality inks and functional coatings are today produced using wet grinding technology with bead mills. During this process, a rotor and stator system containing many small grinding beads that partially interact with one another is used to create effective grinding action. Due to constant physical friction between the beads, particle agglomerates of color pigments are separated from each other. Large particles are reduced in size, creating a more effective wetting effect and achieving homogeneous distribution in the medium. Quality requirements in such suspensions have increased significantly in recent years. The best example of this is the increased need for very high color strength and gloss in printing inks used for food packaging. Another factor is the continuous increase in cost pressure. For this reason, many production facilities want to redesign their existing production areas to increase efficiency or improve production processes. Additionally, manufacturers seeking to differentiate themselves through quality end products are making considerable efforts in occupational health and safety matters when working with products bearing hazard statements. Motivation varies as much as applications. In this article, real examples are included to allow detailed examination of how each manufacturer achieved its objectives.

1. Higher Productivity in Packaging Ink Production

With rising demand for individually packaged food products, the need for packaging ink also increases daily. One packaging ink manufacturer decided to turn this upward trend into an opportunity. Since the existing production area was limited, procurement of new production equipment was not possible, so the decision was made to improve the current production. Additionally, particle size variations in raw materials and contamination issues frequently caused blockages in bead mills. Shutdowns resulting from the tedious and time-consuming process of mill cleaning negatively affected the cost of the final product. The manufacturer was using a conventional high-speed mixing tank system for pre-dispersion. As a solution, a circulation-based pre-dispersion unit was integrated into the process in place of simple mixing. This enabled effective particle size reduction in the pre-dispersion stage. By eliminating large-sized particles, a relatively narrow particle size distribution was achieved (Figure 1). Compared to a mixing system, the process also requires less energy, contributing positively to unit cost. This development also produces positive results for fine grinding. Since large-sized particles can be effectively reduced in pre-dispersion, it becomes possible to use smaller 0.3 mm beads instead of 0.8 mm beads during fine grinding (Figure 2). This means the number of beads per unit volume will be approximately 10 times higher. This signifies that the grinding operation in the bead mill will work more efficiently. With 40% less specific energy input, productivity increased by 75%. With this method, production of packaging printing ink is possible at approximately twice the rate compared to conventional production using a mixing system and larger grinding beads. Since large particles are pre-eliminated in this system, even though smaller beads are used in the mill, the risk of encountering blockage problems is minimized.

2. Higher Profitability in Sublimation Printing Ink Production for the Textile Sector

Sublimation printing ink, due to the method in which it is produced, is a product that may contain foreign materials such as fibers or rubber particles. These foreign materials cannot be reduced in size during wet grinding, so during bead production they can cause contamination or color inconsistencies in the product. This is a problem frequently encountered by the manufacturer. The manufacturer produces with 0.3 mm diameter beads and must completely clean the equipment after each batch. An operation requiring approximately 4 to 5 hours is performed to discharge the beads, separate foreign materials, clean the sieve, and disassemble the mill. Since the foreign material is nearly the same size as the color particles, simple filtration after mixing is not very feasible.

Figure 1: Particle size testing using a compression gauge

The solution was envisioned as incorporating a pre-grinding stage into the process. In this application, the pre-grinding process continued until solid particles in the suspension were reduced to smaller than 100 micrometers. Since only color pigments are broken down and reduced in size rather than foreign materials, the particle size difference enables the foreign material to be filtered after the grinding process. Subsequently, the suspension continues with fine grinding in the bead mill as in routine production. Since this prevents clogging that could occur on the filtration screen, it significantly increases uninterrupted production profitability. Additionally, the expensive 0.5 micrometer filtration step previously used for the final product in the production process has been eliminated, as all contamination is removed during pre-dispersion.

Summary

• Quality expectations for printing inks and functional coatings continue to increase. • Many manufacturers want to increase facility productivity or structure their processes more efficiently. • Use of a pre-grinding unit can increase fine grinding efficiency by up to 50%. Norbert Kern Head of Grinding & Dispersion Product Management and Process Engineering Department Bühler AG.   Mehmet Sarıkatipoğlu Industrial Engineer Grinding & Dispersion Turkey Technical Sales Manager Bühler AG.  

Figure 2: 0.8 mm diameter yttrium stabilized ZrO2 bead