Technical Theme – Chemicals

Nalco’s TULIP™ Yankee coating technology uses innovative chemistry to improve creping and softness at higher reel moistures.

In this article Nalco explains how TULIP Yankee coating technology can deliver the desired sheet softness while saving drying energy and reducing the negatives associated with low moisture creping. A TW report

To satisfy consumer demand for premium tissue products, tissue makers have moved towards creping at lower moisture in order to boost sheet attributes in terms of softness and bulk generation. Low moisture creping is beneficial for developing a very aggressive interaction between the sheet on the Yankee surface and the creping blade. This results in a more dramatic impact at the creping blade which delivers improved sheet characteristics.

However, lower moisture creping is also associated with a higher cost of operation due to increased energy demands, various machine runnability issues and a higher potential for downtime. TULIP Yankee coating technology provides a complete new offering as it is designed specifically for tissue grades, to open the creping moisture operating window and improve process efficiency. Using Nalco Yankee Coating Space™ methodology, we have created a unique platform in terms of adhesion, durability, and coating softness.

Figure 1: TULIP Yankee coating provides higher adhesion in a wider moisture range comparing noncrosslinking PAE (NX-PAE) and crosslinking PAE (X-PAE).

Nalco’s TULIP Yankee coating technology is based on proprietary and patented polymers. This new technology provides high adhesion over a wide range of creping moistures. Compared to conventional creping chemistries, the new coating tends to be more efficient, allowing for up to a 50% replacement ratio at equal or higher creping moisture. Coating uniformity and the softness of the coating are also improved.

TULIP Yankee coating technology is capable of delivering very high adhesion levels both at the suction press roll (for proper transfer) and at the creping blade (for sheet quality and sheet handling). Due to its very high wet and dry tack, TULIP can provide high adhesion within a wider moisture operating range. Laboratory testing (Figure 1) and industrial application clearly confirm this wider moisture operating range.

The following case provides an example of how TULIP Yankee coating technology has performed in the industry. In this case a tissue maker, using a virgin fibre furnish, wanted to improve sheet softness characteristics by making changes to the Yankee coating package. The goal was to improve sheet quality without negatively impacting machine productivity or reducing creping moisture. The tissue maker was interested in improving softness as much as possible and the incumbent PAE-based Yankee coating could not deliver the required improvements.

TULIP Yankee coating technology was introduced on the machine and based on the high adhesion properties of TULIP, the add-on of adhesive material was reduced by approximately 50% while the release add-on was slightly increased. An increase in stretch was observed, which allowed for an increase in reel speed, and a resulting increase in productivity.

The crepe structure during the TULIP trial was finer than with the incumbent package. The sheet softness was also improved. Based on the initial promising results, it was decided to increase creping moisture by 0.5% moisture points from 5.4% to 5.9%. To accomplish this increase in creping moisture, the TULIP coating addon was increased, but was still 35% lower than the incumbent PAE coating package. The higher sheet softness targets were maintained at this higher creping moisture throughout the blade life, as shown in Figure 2.

An improvement in relative sheet softness from 13.5 to 14.1 was observed when using TULIP coating, even at higher creping moisture. Machine runnability improved when using the TULIP coating with an increase in productivity being reported. The increase in creping moisture offers the potential for energy savings. Reduced coating add-on should also improve drying efficiency.

In summary, Nalco’s TULIP Yankee coating technology (based on proprietary and patented polymers) has demonstrated superior coating characteristics compared to the conventional PAE chemistries. TULIP Yankee coating technology allows tissue makers to achieve improved sheet properties and/or reduce manufacturing cost. Compared to traditional PAE technology, TULIP exhibits greater adhesion, improved uniformity, and a wider creping moisture operating window.

Figure 2 – Relative softness and average sheet moisture for trial conditions.

Benefits of TULIP Yankee coating technology for tissue manufacturing:

• Improved handfeel softness (due to increased adhesion)
• Reduction in the adhesive add-on by up to 50%, while maintaining the same level of adhesion
• Improved sheet quality and machine productivity due to higher tolerance of moisture variation
• Ability to substitute lower cost fibres while maintaining sheet quality targets
• Potential to crepe at higher moisture without a loss of adhesion and/or sheet quality, resulting in improved machine productivity and potential energy savings

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