Coated Paper and Board

Even surface structure and good printability are the key requirements for both coated papers and paperboard. Furthermore coated paper has to deliver these attributes while being produced at ever higher machine speeds. Coated board is facing the challenging demands of the consumer packaging sector, recyclability and other end of life considerations. This drives the industry for higher manufacturing efficiency and continuous technology innovation.

New Discoveries for the Wet End.

The wet end is a complex dynamic system that is gaining increased attention as an area for improving efficiency, reducing effluent load and improving paper machine profitability. CALEXIS® Strength Agent is an additive designed to provide improvements in strength to allow paper and board producers multiple ways to improve economics, machine performance and end product benefits.

Improving Paper Strength

Through proprietary manufacturing techniques, CALEXIS improves paper strength by the following mechanisms.

  • CALEXIS increases the bonded area by forming bonds between fibers and other chemicals. The CALEXIS molecules set on the fiber surface, increasing the amount of active groups available.
  • CALEXIS disperses the micro fibrils increasing the specific bonding areas.
  • CALEXIS disperses and lubricates fibers, which leads to reduced frictional forces between the fibers. This leads to reduced floc size and therefore a better formation can be achieved.

The degree of effectiveness, however, depends upon correct CALEXIS product choice, which is dependent upon the individual paper and board making process, and the use of CP Kelco’s Wet End Analysis Tool.

Controlling Charge Balance

Due to its anionic nature, CALEXIS provides possibility for more efficient charge balance control.

Saving Refining Energy

When added before refining CALEXIS protects and dispersed the fibers improving the strength and uniformity of the refining result. Desired strength levels can be reached with less refining, as less damaged fibers provide better strength.

On-Machine and Quality Benefits

  • Savings in refining energy
  • Improved retention of cationic additives
  • Maximized filler levels
  • Incorporation of weaker or cheaper fibers
  • Control charge balance to achieve desired runnability
  • Retention adjustment
  • Improved runnability
  • Less foaming (especially in the presence of PAE)

Established Benefits to Coating.

Coating performance is a combination of various machine parameters and quality trade offs. The operating framework is set by different process conditions, formulation requirements and economics. FINNFIX® CMC plays an important role by influencing the key parameters such as rheology, material retention and the efficient carrying of whitening agents and/or optical brighteners. FINNFIX is used effectively in a wide variety of coating formulations, and is flexible enough to adapt to all coater and pigment configurations.

Rheology describes the flow behavior of the coating color at different shear conditions. In the coating process the coating color is exposed to different shear conditions like pumping, mixing, screening and metering. It is very important to adjust the rheological properties in order to maintain trouble-free runnability. The inherent shear thinning behavior combined with good blade lubrication makes FINNFIX an excellent solution at various speeds and solid contents.

FINNFIX is mechanically stable in high shear conditions and compatible with all common types of coating materials. The effect of FINNFIX is dependent on the pigment system. In clay-based systems, FINNFIX is partly adsorbed to the pigment surface and forms a network structure with the clay and the non-adsorbed FINNFIX. In contrast to this behavior, a weaker physical structure is formed with calcium carbonate systems. FINNFIX’s flexibility allows for a wide operating window as a rheology modifier, since it allows adjustment of rheological properties to individual formulation design and manufacturing needs.

Material Retentiongraph-retention
When coating color is applied on the paper the aqueous phase acts as a vehicle not only for the binder, but also for the other components in the aqueous phase. If this water or material penetration is not controlled, there will be excessive material shift from the coating color toward the surfaces, before immobilization will stop this migration. This can result in poor machine runnability, unstable system and uneven coating layer, impacting the final paper quality.

In circulation all coating colors undergo a change before reaching a steady state. Material retention control enable papermakers to reduce the time and magnitude of change before the steady state is reached. As illustrated in the figure, Color 2 has better material retention control and shorter change zone, therefore it changes less compared to the fresh coating color.

Both conventional FINNFIX grades and specially designed FINNFIX grades enable paper and board producers to optimize their coating color design resulting to a controlled material retention.

The effective control of the material retention of the coating colors enables to achieve good coating coverage. Good coverage will ensure excellent surface and optical properties for the end product and enables the coat weight optimization and that way provides additional cost benefits.

Whitening Agent Carrier (FWA/OBA)
The whiteness of high quality papers and paperboard is very important and is increasing continuously. Despite the use of pigments with high brightness, Fluorescent Whitening Agents (FWA) / Optical Brightening Agents (OBA) are used to reach and boost the finished sheet whiteness. The maximum effect of FWA/OBA can only be reached when they are well supported by a carrier.

It is a well-known fact that FINNFIX is one of the most efficient carriers available on the market today. FINNFIX enhances the FWA/OBA thus achieving the full fluorescence yield along with a high level of paper whiteness.

The carrier efficiency is identical for all FINNFIX products. FINNFIX consistently provides a high whiteness-level and imparts the best light fastness. To get the maximum support for the FWA/OBA, it is important to add a sufficient amount of carrier.