June 25, 2013
How Paper is Made
As promised in my last post, An Ode to Uncoated Paper, I am back to talk about the paper making process. Talking about paper, without sharing details on how it‚’ made, would feel too much like cheating you out of valuable knowledge! Besides, you’ll be amazed at what you’re about to learn.
Let‚’ keep this basic shall we?
The paper machine has four principal units‚Äö√Ñ√Æforming section, press section, drying section and machine calendaring.
Not so complicated and I bet you’re wondering if the machine calendaring is where calendars are made. It‚’ not, by the way.
Here is where the paper stock, before it becomes paper, is first diluted with water to create a special pulp consistency. It is then pumped into the headbox and the pulp is spread along the width of the machine which moves the pulp onto a finely-woven plastic belt. The water is then drained from the material leaving just the pulp behind.
Ever hear the word dandy roll? If you still work with commercial printers or design a lot of corporate identity and stationery pieces, then you may recognize the term. A dandy roll is the cylindrical frame covered with wire mesh which helps distribute the fibers and improve paper formation. This is where watermarked paper is first created. The watermark design will be on the surface of the dandy roll, which is often part of the forming section process.
Once the pulp leaves the forming section web, it is moved through the press section. The press section is one of the easiest to remember because it is here that any remaining water is pressed out of the pulp. When pulp enters this section it still contains 75-85% water. Using two rolls, the pulp sheet passes between the ¬¨‚â†rolls leaving behind approximately 65% water in the pulp.
Here the paper pulp is machine dried until only about 5% or less of water remains in the material. The dryers are steam-heated cast iron drums and arranged in tiers. The sheet is held tightly against the dryers until the water is evaporated out of the paper.
Machine calendars are actually vertical cast steel rolls that are stacked together. They have polished surfaces and are used to smooth the paper as it travels down the calendar rolls. A paper that has been calendared has been machine-finished.
Often times a paper will be‚ “supercalendered‚” which simply means the paper was passed through a stack of steel filled with cotton or synthetic rolls. This process is used for both uncoated and coated papers.