Brighter Brights and Whiter Whites

I was thinking about something the other day, and I thought I'd share it with you.  It seems like there's always a competition between paper companies to see who can make the brightest/whitest sheet.  The conventional method is by adding optical brightening agents (OBAs) or optical whitening agents (OWAs) at the wetend of the machine.  This seems to work fine but you can only brighten or whiten so much before you lose the effectiveness of the OBA or OWA.

So what else can you do?  Well you can innovate and make a better OBA or OWA.  This would require some collaboration with a chemical company and could take years to develop.  So I started thinking about this and here's what I came up with.

Since the OBAs and OWAs are added at the wetend they have a limited dwell time.  I wonder if increasing this dwell time would allow the OBAs and OWAs to achieve greater brightness and greater whiteness.  If nothing else it could improve OBA/OWA efficiency, get more brightness or whiteness with less chemicals.  So now the question is where can you add it?  How far back can you go? 

What about the pulp mill?  Why can't it be added back there?  It's definitely worth a trial right?  I am not a pulp mill guy though so you should talk with your pulp mill manager to gain insight into where some good addition points might be.  Also remember that if you are going from a grade the requires OBAs or OWAs to a grade that doesn't require OBAs or OWAs that it might take a little while to get all the OBAs or OWAs out of the system.  Ideally you would want to try this at a mill that makes OBA/OWA required paper most or all of the time.

So the concept is to base-load the chemicals in the pulp mill and add as necessary in the wetend to reach your target brightness/whiteness.

Start-up Checklists

I know most people hate checklists, especially operators.  They have a checklist they go through when they start-up, but usually it's in their head.  Implementing formal checklists for each operator is a good way to avoid costly mistakes. 

Start-ups after an outage are very hectic.  Everyone has been working for a long time.  They're tired and ready to go home.  Having a checklist helps the operators go through the necessary steps, it also keeps the operators accountable. 

So how do you go about implementing these checklist?  The first step is to develop the checklist.  The operators should be involved in this process so that they take some ownership of the checklist.  Once the checklist is finalized, it must be determined who will actually carryout the checklist.  For example a supervisor can go through the checklist with the operator to make sure that the proper steps have been taken.  Simply giving the checklist for the operator to go through by themselves is not a great way to implement this tedious task.  Operators would soon discard the use of the checklist and go back to their old ways.  Having senior operators be responsible for the checklist would be a good way to provide some accountability.

The checklist should be turned in and kept for at least the next two outages.  They should also be revised from time-to-time as new equipment is installed or modifications are made to current piping and equipment.

This is a fairly simple way to improve start-up efficiencies.  Remember it's all in the way you implement the checklist.  Once it is executed poorly, it will be difficult for operators to buy into the program.

Troubleshooting Tip: Ring Crush Test

The ring crush test is a method for measuring the edgewise crush resistance by forming the paper into a cylinder and applying a crushing force to the edge. For more information refer to TAPPI T818.

Linerboard products are subjected to crushing forces in handling, storage and shipment. Knowledge of the edgewise compression strength is useful in controlling the manufacturing process, and in providing an indication of the compression resistance to be expected in the finished product.

Here is a list of actions that may improve Ring:

1.Rush the sheet more or drag the sheet less.
2.Optimize refining. There should a sweet spot for ring crush. There may be times when the fiber is over refined.
3.Dry up the sheet more if possible.
4.Increase basis weight.

Realize if you dry up the sheet to improve ring crush, it may reduce your tensile strength, or burst strength. Also, increasing basis weight will increase the cost of production. However, it is better than producing broke, or reject paper.  The best method for optimizing refiners is to talk to your senior stock prep operators. If they've been around for a while, they generally have a pretty good idea where to start based off refiner plate wear and the grade of paper. When adjusting the rush/drag, be sure to get your machine tenders' input. Also make sure to pay attention to the draws as this can have an effect on them, you don't want to have a break due to lack of attention to detail.

Troubleshooting Tip: Cobb Test

Paper is composed of a randomly felted layer of fiber, its structure has a varying degree of porosity.  Therefore, the ability of fluids, both liquid and gaseous, to penetrate the structure of paper becomes a property that is very significant in the use of paper.  The need to limit the spreading of ink resulted in "sizing" the paper with gelatinous vegetable materials, which had the effect of sealing or filling the surface pores.  The term "sizing" was later applied to the treatment of paper stock prior to the formation of the sheet, with water-repellent materials such as rosin or wax.  Resistance towards the penetration of aqueous solution / water is measured by Sizing or Cobb values.

The Cobb Test measures surface water absorption over 60 seconds, expressed in g/m2.  The procedural Standards are explained in TAPPI T 441.

There are several actions you can take to improve Cobb Test numbers.  An increase in refining can help close the sheet, which would improve Cobb results.  A change in furnish can also help.  You would increase broke content if possible and/or increase hardwood content.  These fibers are smaller and can fill the holes or pores in the sheet.  If you have alum at your disposal, increasing the addition rate could help.   Also increasing pH can help close up the sheet.  Be careful when carrying out any of these actions.  You increase the risk of sealing the sheet by closing up the sheet.