Mono Ammonium Phosphate usage in the tissue industry

By Nick Mike, NGM Tissue Consulting, LLC

THE PROBLEM:

1. The Yankee coating is not forming a continuous film, picking, and streaky
or

2. The Yankee coating appears to be over releasing, not developing and the sheet is weaving.
Both scenario's can be related to the over use or under use of Mono Ammounium Phosphate or MAP.

The correct addition of MAP by the tissue maker can offer the difference between a well running machine or haying all day. Tissue makers should be aware of the effect of MAP and how best to utilize this product.

DISCUSSION:

The addition of Mono Ammonium Sulfate to the Yankee spray shower, can help create a very stable and workable yankee coating. Many tissue makers do not have a working gasp of what this additive is or how it works. In this article we will cover MAP's function and benefits and why it can be a key component in any yankee coating program.

Uniformity Of Yankee Coating: MAP creates a uniform bonding surface on the yankee dryer to accept the organic coating much like paint primer is to paint. MAP was originally used in the metal plating industry to prep the metal surfaces to accept the plating metals. MAP does the same for yankee coating. It allows the organic yankee coating to more readily adhere to the yankee surface and in a uniform film.

Protection: MAP also forms a hard, micro surface on cast iron yankees that will create a harder micro-surface. Cast iron has a Rockwell hardness of 23. When continuously exposed to MAP, Rockwell hardness increases to 35. This harder surface, protects the yankee from the doctor blade.

Improved Yankee Coating: MAP not only spreads the coating uniformly it also helps to accelerate the cross linking of the organic polymer used to adhere the sheet to the cylinder.

Corrosion Protection: MAP will help prevent corrosion by interfering with electron transfer across the water phase and the yankee surface. This is especially important in mills susceptible to Yankee cylinder edge crevasse buildup.

Surface Smoothing and Void Filling: As cast iron cylinders age, they become more porous. MAP will tend to help fill these voids and allow a smoother yankee surface to accept the sheet. The result is fewer picks breaks and a delay in the further degradation of the yankee.

However, too much MAP, will allow the desirable, hard, oxide surface, created by the phosphate, to start forming a flakey, unstable substrate. This type of surface will not allow a stable base for yankee coating application. The sheet will no longer adhere to the yankee. Its like trying to apply a yankee coating to a surface coated with talc.

CONCLUSION: MAP can be very beneficial in protecting the yankee surface and establishing a good yankee organic coating. Scratch and porosity filling as well as corrosion resistance are other benefits of MAP. However, MAP can be problematic if overused as the surface formed by too much MAP can be flakey and non-stable. The correct MAP addition is essential to a well running tissue machine.

Nick Mike of NGM Tissue Consulting, LLC can be reached by calling 603-616-8931, or by email at nmike03580@yahoo.com.