Intelligent design of Yankee Coatings - Paper Technology International 2023 - Paper Technology International 2023 - Flipbook - Page 126

Intelligent design of Yankee Coatings - Paper Technology International 2023

PAPERTECHNOLOGYINTERNATIONAL Intelligent design of Yankee Coatings - Paper Technology International 2023
TAD - TAD machines can provide a wide range of sheet
moistures coming to the Yankee from as low as 10% to upwards
of 40%. These machines almost exclusively utilize virgin furnish
due to the high softness grades produced, as well as perceived
difficulties in efficient use of the TAD dryer with recycle furnish.
Creping moistures are typically less than 5%. For TAD machines
the adhesive needs to provide the necessary wet tack adhesion to
transfer the relatively “dry” sheet to the Yankee. Traditionally this
has been accomplished with a two-part adhesive program utilizing
polyvinyl alcohol (PVOH) for wet tack and a polyaminoamideepichlorohydrin (PAE) polymer for dry tack at the creping blade
and durability. Recently a simplified single-component advanced
adhesive has been introduced for TAD and hybrid machines
eliminating the necessity for two-part adhesive programs (reference
10). Required adhesive add-ons are high (30-60 mg/m2) to build a
thick enough coating layer to transfer the structured sheet which
will only have a contact area of 25% or less with the dryer surface.
For TAD coatings modifiers are typically used to soften and control
film build as well as to adjust the film durability. Humectants can
be used to accommodate the lack of moisture contribution to the
coating from the sheet and the low creping moistures. Phosphates
are typically beneficial in contributing to uniform films. It should also
be recognized that the release chemistry used on the TAD fabric can
also impact the Yankee coating properties.
TAD Case Study – Nalco Water’s NAVIGATORTM adhesive
products offer customers unique PAE-based adhesives in terms of
film softness and durability. Although they can be used on CWP
assets, they are particularly effective on advanced machines. Table
II provides a snapshot of a recent conversion from a competitive
PVOH/PAE adhesive program to a PVOH/Navigator program.
Improvements were observed in speed, breaks per day and blade
life resulting in a 7% production increase.
similarly, components like fabrics/belts and Yankee coatings are also
still in a dynamic phase of development. Current Yankee coating
technology tends to be a hybrid of TAD and CWP considerations.
PVOH is typically used as an adhesive component, similar to TAD,
in conjunction with a PAE. Simplified one adhesive programs are
also taking hold (reference 10). Depending on machine type, the
coating needs to accommodate both “flat” and structured sheets with
surface contact areas of essentially 100% (flat) to approximately 2560% for structured sheets. Adhesive add-on ranges tend to be in the
15-30 mg/m2 range, although extremes can be seen as low as 10
mg/m2 and as high as 70 mg/m2. Both modifiers and releases can
be used as well as humectants and phosphates.
Hybrid Case Study – In this example Nalco’s
NAVIGATORTM adhesive technology in conjunction with PVOH was
utilized to provide dependable transfer to the Yankee, more reliable
machine runnability, good adhesion at the creping blade and much
more uniform parent reel building. A before and after comparison
of reel build with the previous PVOH/PAE program to the PVOH/
Navigator program is shown in Figure 8. The combination of good
transfer and creping adhesion resulted in a flatter reel profile.
Table II: Result summary of a TAD Yankee coating conversion
from a competitive PVOH/PAE adhesive program to a PVOH/
Navigator program on a 26 gsm towel grade.
Table III: Summary of Yankee coating considerations for the
three major machine types.
Hybrid – Hybrid machines currently encompass several
branded machine types including Advantage™ NTT®, Advantage™
QRT® and Advantage™ eTAD® from Valmet and ATMOS from
Voith. The NTT, QRT and ATMOS machines can switch from
conventional to structured sheets dependent on the fabric or
belt installed. Hybrid machines can present a fairly wide sheet
moisture range at transfer to the Yankee (46-64%) and represent an
intermediate range between that of CWP and TAD. Hybrid machines
are more versatile that TAD’s with their ability to handle recycle
fiber. Creping moistures tend to be similar to TAD at less than 5%.
Hybrid machine technologies are still evolving at a rapid pace, and
126

Paperturn flipbook system