Coating technologies – broad-based expertise and in-depth understanding make the difference
Innovation and cross-cutting multidisciplinary expertise have long been BTG’s bywords when it comes to improving coating performance to meet the needs of an increasingly diverse and demanding market.
Figure 1:
Paper coating - a complex science
What makes BTG blades different? We like to think it’s our commitment to constant innovation combined with our comprehensive coating process knowledge and multidisciplinary approach to identifying solutions that exactly respond to our customers’ real-life needs.
No other blade manufacturer bases the design and development of new products on such a thorough scientific understanding of the highly complex physical forces and chemical processes that characterize coating systems. And no other manufacturer works so closely with its customers to test and trial new technologies to ensure they deliver on their promises when it comes to improved performance, higher productivity and lower costs.
Our teams’ long experience working alongside coated paper manufacturers convinced us that delivering real added value meant developing a range of customized blade tip designs with specific behaviors depending on the particular application.
Our innovation efforts have been focused on relieving papermakers’ chronic pain points – PPS level and stability, microline patterns, streaks, run-in time, blade adaptability and edge wear, to name just a few – with the ultimate aim of improving paper quality while delivering longer, stabilized operation times.
In-depth process expertise
The introduction of cermet (ceramic-metal compounds) blade tip materials a few years ago allowed for very high final coated paper surface qualities and longer blade lifetimes. Specific customer requirements subsequently led BTG to develop several new types of Duroblade® ceramic and cermet blades, coated with different high-performance tip materials and sporting innovative designs.
One example is the use of different cermet-tipped coating blades on both pre-coat (Duroblade-XXL™) and topcoat (Duroblade-Silkoat™) in board applications. Conditions on these two coating stations are dramatically different: coating color formulations, color abrasiveness and rheological behavior. This leads to different wear conditions, wear patterns and coating color flow under the blade tips.
Our understanding of the typical differences in surface tension of different coating colors allowed us to develop new materials to reduce chemical interaction between blade tip material and coating color components and optimize wear rate and topology. Synchronous blade changes on different positions allow for constant optimized quality during the full period of operation, while blades designed in accordance with coater head- and position specificities deliver vastly better results.
Paper temperatures and moisture profiles are also slightly different from one coater head to another, which makes backing roll hardness vary more or less quickly on different positions. The resulting coatweight and fiber coverage can evolve quickly and with clear control difficulties. We studied how to master the blade tip pressure with a variation in backing roll hardness between regrindings, and implemented our findings by customizing the blade tip shape and material – yet another example of our innovative approach.
Making contact
It’s critical to understand that the blade tip is the last contact surface between the coating color and the blade, and that any aspheric or chemical interrelations between the two can exert a major influence on both coated paper quality and process stability. The evolution of blade contact conditions, in terms of both wear patterns and angles and surfaces, can drastically change depending on paper grade, type of furnish, coating color formulation and machine speed.
Thanks to BTG’s in-depth technical approach, the LWC market now has its own specialized high-performance blade – Duroblade-Energy™.
That’s why, over the past few years, the main challenge has been to obtain a contact surface that’s as stable as possible. By optimizing the blade tip design with longer or shorter initial surfaces, higher or lower initial angles, and in combination with a tip material that keeps its topography during the full operation time, stable color flow under the blade can be obtained – ensuring constant output quality.
BTG’s innovative materials and designs are now helping papermakers realize improvements of up to 15% in gloss and PPS values, with an increase in potential blade lifetime of up to 300%. In many cases, such improvements have also paved the way to the use of coarser and cheaper pigments as well as higher solids contents – further boosting manufacturers’ productivity and profitability.
A brand new Duroblade for the LWC market
Figure 2:
Duroblade-Energy™
Duroblade-Energy™ is the latest star performer on the coating scene, delivering dramatic improvements in lightweight coated paper production.
With the LWC market already extremely competitive because of chronic overcapacity, papermakers in this segment are highly cost-sensitive. At the same time, the manufacture of LWC paper presents significant technical challenges due to machine runnability and quality specificities. With grades from 39 - 80 gsm and furnishes composed of 50 - 70% mechanical pulp, ground wood pulp or thermo-mechanical pulp, the abrasiveness of the base paper, the rheological behavior of the coating color and the interrelation between base and color dewatering are all key issues in understanding the LWC production process and designing effective solutions.
The newest generation of ceramic/cermet blades designed specifically for LWC applications, Duroblade-Energy delivers great performance, improved operation of both coaters and paper machines, and significantly better coated paper quality.
A host of advantages
LWC producers who choose Duroblade-Energy benefit from excellent cross-direction coatweight profiles, very short blade run-in times and continuous machine-direction coatweight control. Based around a brand new ceramic-type material, this innovative blade offers an exceptional balance between wear-resistance and adaptability, while an advanced blade design (material, contact surface, steel caliper) combined with fine-tuned automatic profiler systems delivers excellent coatweight distribution.
Duroblade-Energy also allows manufacturers to cut down coatweight more easily than steel blades. In practice, that means that for the same coatweight target, blade pressure can be reduced by 20 - 40%. The ability to precisely control coatweight at a lower pressure allows for compensation of tube pressure loss by an increase in solids content of 2 - 3% – a benefit that’s much appreciated by papermakers because of the related reduction in energy costs in the drying section. On top of that, reduced pressure on the web has the advantage of reducing the risk of web breaks at the coater – one of the main limitations of LWC machine efficiency.
Smoother running, lower costs
The ceramic material used in Duroblade-Energy insulates against heat transfer. This increased thermal resistance allows papermakers to run blades on the fastest on-line coaters without any limitations due to dry-friction during start-up, web breaks or machine stops. And when jet applicator plug occurs during a run, ceramic blades give operators more time to react, helping avoid the risk of permanent damage.
Improved edge behavior is another important benefit: in this paper segment, cost justification can only be achieved when blades can be restarted after web breaks and machine stops. While the average lifetime of standard steel blades is around 10 hours, Duroblade-Energy can deliver as much as 30 hours’ blade life, thanks to the ultra-high wear-resistance of the Energy tip material. For on-line coaters, this directly impacts the volume produced by reducing the number of machine stops for blade changes. Edges stay cleaner than with steel blades, and run-in time when restarting with the same blade after a break or a stop is virtually eliminated, since the automatic profiler and the blade have already adapted to the base paper and backing-roll.
Duroblade-Energy boosts PPS, gloss and heliotest values to levels never before achievable with any ceramic blade. Because the coater opens less often, the risk of web breaks is considerably reduced, and since the pressure on the blade is lower and the edges are cleaner, the coater is less sensitive to small paper defects, which helps improve machine efficiency.
Outstanding results
At BTG, our innovations always target not just performance enhancements and quality improvements, but cost reduction. The advanced design of Duroblade-Energy allows the coating layer to be leveled in a smoother way than with steel. Pigment distribution is improved, thanks to a more gentle specific pressure distribution under the blade tip, while higher solids content helps keep pigments on top of fibers for improved fiber coverage. Typical advantages of Duroblade-Energy blades against conventional steel blades for LWC rotogravure applications include:
- PPS: improved/reduced by 0-10%
- Gloss: +5% to +10%
- Heliotest: +10% to +20% improvement.
Duroblade-Energy is the product of our efforts to better understand the complex physics of wear pattern phenomena and chemical interactions associated with coating color formulations, to identify the materials and designs that best fit each application. Another example, in fact of BTG innovation at work to help you raise your productivity.