Polymers 2020 , 12 , 173
10of 14
Table2. Quality parameters of the Coating (Polycoat 38) and the release agent (Disprosol 17).
Polycoat 38 ®
Disprosol 17 ®
Parameter
Appearance
Liquid Ambar
Liquid Ambar
Color
pH
3.00–5.00 < 600 cP
6.00–8.00 < 400 cP
Viscosity
Total solids
38.00%
100%
Density
1.01–1.03 g / mL
0.80–0.90
Charge density
1800mEq / L
N / A
Dispersion
N / A
100% in water
N / A: Not applied.
The parameters shown in Table 1 provide information for industrial purposes and certain parameters such as pH must be within a range that can a ff ect the performance of the yankee. For example, the water of the tissue paper mills has a relatively neutral pH, so the mixture of both products must be maintained between 5–9 to avoid deterioration in the yankee [34]. On the other hand, other parameters such as the viscosity of the products provide information on the product itself. A high viscosity is related to a lower flexibility of the polymer which may decrease the adhesiveness of the coating [35]. The release agent may be necessary to decrease the viscosity of the final product and its smoothness to achieve a more uniform creping [5,33]. Another important property for this type of cationic polymer-based resin is the charge density. Charge density is related to the percentage of azetidine rings formed in the resin which are those that adhere to the fiber when the paper passes through the yankee [30]. A higher charge indicates greater adhesiveness and although it is a desirable property an excess may cause an excessive paper sticking causing deterioration of the coating when comes in contact with the creping blade [7]. This undesirable property is generally provided by top-charge resins such as PAEs, which have been presenting these problems despite their broad application [3]. When comparing the charge density of a PAE such as Dispro 620 ® manufactured at Disproquin S.A.S (2700 mEq / L) with Polycoat 38 ® (1800mEq / L), it was inferred that there is a bigger amount of azetidinium groups in the PAE compared to the Polycoat 38 ® . These groups are the reason of the interaction with the fiber [24] and although a good adhesion to the fiber is necessary, an excessively high charge generates a very strong adhesion, which leads to di ffi culties in the demolding and reduces the creping e ffi ciency [3–5]. For this reason, the use of a PAE was discarded and the application was done with the Polycoat 38 ® , which generated paper with desirable properties, as explained previously at Section 3.8 [36]. 3.9. Application of the Polycoat 38 Along with Disprosol 17 as Yankee Dryer Coating-Release Agent The interaction of the coating-release agents with the paper and the yankee dryer leads to a complex chemistry that has not been fully developed. In addition, this interaction is a ff ected by multiple process such as changing a felt, a blade, cleaning a mesh or modifying a pick-up pressure [13]. For this reason, measurements of the e ff ectiveness of products at the laboratory level are only approximate and are not necessarily reflected in the application [37]. Therefore, the analysis that is performed during production goes hand in hand with the experience of the operator and the process quality analyst. Thus, the application of the product was done starting at a ratio of 1:1 until reaching a dose of 7mL / min of Polycoat 38 ® and10mL / min of Disprosol 17 ® (1:1.4), which allowed an optimal profile of the paper roll in obtaining at a speed of 352 m / min. A balanced profile indicates that there are no bulges in the forming-roll caused by a poor distribution of chemicals or an unstable emulsion or a swelling in the paper. On the other hand, during the application there were no bursts of paper in formation which indicates that there is an optimal adhesiveness generated by the Polycoat 38 ® and a good relationship
Made with FlippingBook - Online catalogs