How Is Paper Made?
This Inquiring Mind Wanted to Know.
Do you know how paper is made? If you are like most, you are probably aware that machinery, water, and of course trees are involved, but that may be the extent of your paper making knowledge. Recognizing that this was the limited extent of mine, I went out in pursuit of more information.
To learn more about the paper making process, I recently took a trip to Monadnock Paper Mills, located on the banks of the Contoocook River in Bennington, New Hampshire. Monadnock is a small, family run mill which places exceptional emphasis on environmental stewardship, community involvement, and on the production of premium high performance papers – and it shows. From its well groomed, picturesque grounds; to its impressive eco-friendly manufacturing process; to the consistently beautiful, high quality card stock papers it produces, Monadnock sets a prime example, and was an excellent environment in which to learn how paper is made.
It turns out there is much more to paper than water and trees, and the paper making process is quite interesting, in fact. If you’re interested in learning just how paper is made, read on.
What Is Paper Made Of?
The Basic Components.
To understand how paper is made, you must first understand what it’s made of. Though the paper-making process is fairly complex, the basic components that go into paper are fairly simple.
- Hardwood: Hardwood provides paper formation, contributing to the printability, appearance, and feel of the sheet.
- Softwood: Softwood provides paper strength. As an example, paper bags, which need mostly to be strong, not to nicely print, are made mostly of softwood. As a comparison, printing paper is generally made with a two to one ratio of hardwood to softwood for proper formation and a bit of strength.
- Fillers: Mineral fillers contribute to paper opacity, brightness, printability, and overall appearance.
- Lots of Water: Water is a key ingredient in the paper making process, which is why most paper mills are located on a source of water.
Where Does The Paper Making Process Begin?
The paper-making process begins in the hydrapulper, which is a large blender, or mixing bowl if you will. This large, stainless steel bowl measures approximately ten feet wide and fifteen feet deep and has large blades at the bottom. To begin the process of preparing fiber for paper making, the correct ratio of fibers, fillers, additives, dyes, brighteners and water are blended together for about forty-five minutes. The end result is a thick, wet mixture that resembles a giant bowl of oatmeal.
That Pulp Needs More Water!
Into the Machine Chest.
Before the fiber blend gets to the paper machine, it will be 99% water, 1% fiber, and will look like cloudy, white water. Leaving the hydrapulper, the oatmeal-like blend is nowhere near this viscosity, so the fiber will have to hit a few more stops before it gets to the paper machine. The next step is to dump the fiber into the machine chest – a large holding tank where the blend will get further diluted with water.
Up into the Refiners.
Next, the fiber is pumped from the machine chest up into the refiners. In a nutshell, refiners are a series of plates that turn against each other, forcing individual hardwood and softwood fibers between them. Refiners work to split and cut fibers to length, creating more contact points along the individual fibers so that they can easily stick together and form a cohesive mat of paper when they get to the paper machine.
The refining process plays an important role in paper making, because it prepares fibers specifically for the kind of paper being made and its properties.
Last Stop Until the Paper Making Machine
Before hitting the paper machine, the fiber blend undergoes a centrifugal cleaning process – a very simple process to eliminate dirt, sand, and other foreign debris from the blend.
This simple process works by passing the fiber blend through a series of rotating cones. Wood fiber is very light, much lighter than dirt, sand, etc. Through centrifugal force, light wood fiber rotates up and out of the cone, and heavy dirt drops out of the bottom, leaving a clean fiber blend that is now fully prepared to be made into paper.
Into The Fourdrinier Machine – Making Fiber into Paper Since 1799.
Beginning at the Head Box.
The watery fiber blend is turned into paper using a Fourdrinier Machine, a machine that was invented in France in 1799. This machine consists of an endless, revolving and oscillating porous screen (imagine a very large treadmill) called a wire; a series of suction, roller, and steam heat dryers; and a variety of calender(roller) presses for formation & finish. The machine’s two main purposes are to:
- Form a large, continuous sheet (a web) of paper
- Dry this sheet
Before being made into paper, the watery blend sits at the front of the machine in a large, stainless steel cylindrical tank called a head box. At the very bottom of the head box there is an adjustable opening that allows a varying amount of fiber blend to flow out onto the wire. A limited fiber flow creates a thinner sheet of paper, a larger flow creates a thicker sheet, or card stock/cover stock.
The Water That Went Into The Paper, Must Come Out.
Flow onto the Wire.
As mentioned above, the wire is a large, porous, revolving and oscillating screen. Fiber and water – remember, 99% water at this stage- flow out onto the moving wire. As the fiber gets carried along, excess water falls through the screen as a cohesive fiber mat forms above. The oscillation of the wire ensures that some of the fibers will cross over one another, rather than lining up in one direction. Without fiber cross over, a very weak sheet would result.
About three quarters of the way down the wire, vacuum assist pressure is used to pull water from the fiber, rather than just gravity.
Through the Dandy Roll to Squeeze Water Out Of The Paper
After gravity and vacuum assist, water is then squeezed from the paper using a roller called a dandy roll. The dandy roll not only aids in paper drying, but with compression and formation as well.
Note: Water marks are also created with the dandy roll; a logo or text water mark template placed on the roll displaces fiber in the shape of a logo or text without harming the strength of the paper.
No More Wire Support.
Paper Moves onto First Press Section.
After passing under the dandy roll, the paper, which is now 40-50% water, leaves the support of the wire and heads to the felt press section. Here, the sheet passes between two pressurized felt rollers, helping to form and compress the sheet, as well as squeeze more water from it.
Note: Since the paper is a malleable 40-50% water while passing through this first felt press section, it is here where any patterns would be applied to the paper. This would be done by covering the press with the desired pattern.
The Longest Part Of The Paper Making Machine – The Steam Dryer Section.
Fiber goes into the machine at 99% water, and leaves at 5%. Although gravity, vacuum, and the felt press work to dry the sheet out, they can not do the full job; hence the longest section of the paper making machine, the steam dryer section. Here, the sheet is guided through a series of large, steam heated cans.
Why is steam used to dry paper? Steam is an ideal method because it’s the best of both worlds – it drives excess moisture out of the sheet, while at the same time, allowing the sheet to retain a small amount so that it doesn’t get brittle.
Roll into the Sizing Press.
(That’s Sizing as in White Starchy Coating, Not Length & Width)
After drying, the sheet rolls into the sizing press. Sizing is a starch based liquid surface coating that is sprayed onto printing papers. This coating prevents individual fibers from piquing off papers during the printing process. Sizing also works to improve overall smoothness and consistency, making it a better surface in which to work with. Note that paper also includes internal sizing.
In Paper Making The Paper Gets Dried Again
Since more moisture was introduced to the paper during the sizing process, the paper now goes through a second set of dryers.
Ready to Apply a Paper Finish.
Before leaving the paper machine, the sheet goes through a final set of roller presses which are responsible for its finish. This section consists of two highly polished stainless steel rollers that sit one on top of the other. The rollers are backed by varying amounts of hydraulic pressure, different amounts of pressure creating different finishes.
To gain an understanding of how finish is applied to paper, imagine the similar process of rolling out dough with a rolling pin. The harder you press on the rolling pin (the more hydraulic pressure that is applied to the rollers), the thinner and smoother your dough (your paper) will be. Conversely, if you just lightly roll over your dough (apply less hydraulic pressure to the rollers) you will end up with dough (paper) that is thicker, rougher, and more porous than the batch that was pressed with more force. In the end, it’s the same dough (paper), made with the same ingredients (fiber blend); but the different amounts of pressure created two very different pie crusts (papers).
Getting back to a paper sense; sheets that pass through two lightly pressurized rollers will be thicker, more porous, and more toothy than their highly pressure treated counterparts. In a nutshell, if you have two identical sheets:
- Sheets treated with less pressure end up thicker, and with a toothy, absorbent, eggshell-like vellum finish.
- Sheets treated with a lot of pressure end up thinner, and with a silky smooth finish.
The Paper Is Finished
Roll it Up Onto the Core.
After the paper is finished, it gets wound up onto a core – a giant roll of paper towel, if you will. Paper keeps wrapping around the core until it is about four feet wide, at which point it comes off of the machine.
From headbox to four foot wide core, the whole paper making process takes forty to fifty minutes, on average.