Last week, with the help of the video produced by Sappi Paper, I shared a brief synopsis of how paper is manufactured, emphasizing coated paper. This week, we’ll spell out the process in more detail, and go through the process of manufacturing uncoated paper.
Uncoated paper has many names: offset; opaque, opaque offset, text, uncoated book, tag, as well as other names. Regardless of the name, uncoated paper means paper that does not go through a finishing process where a coating is applied, and the paper is calendered or “polished”. When you buy a book at Barnes & Noble, or you buy a ream of 20 lb. bond at Staples, you’ve got an uncoated sheet at your fingertips. Uncoated paper can be in either text or book weight, or cover weight. And while paper companies do manufacture specialty coated papers, like Neenah’s Environment line, we’re going to focus this post on regular uncoated paper.
Just like coated papers, the process starts with the paper mill taking wood pulp, or recycled paper products, and subjecting them to a bath that breaks down the pulp or paper to the fibers. This turns the pulp into a slurry or a paste that is placed into tanks where chemicals and additives such as clay, chalk or titanium dioxide, which all modify the properties of the slurry and help bond the fibers. The slurry is then pumped through various machines to clean and purify it.
Once the slurry hits the paper-making machine, more water is added to it, making it a thick liquid that is applied to a wire mesh via high-pressure sprayers. As this liquid is applied to the wire mesh, the moisture is removed by both gravity and suction, which causes the paper fibers to spread and become a thin mat, which closely resembles the final paper product.
The paper now is called a web, which is lifted from the wire mesh and squeezed between rollers, dropping the water content substantially. It then passes through more rollers, which are heated, and this process dries out the sheet even further. The paper then is sent through a final drying process before it is subjected to various means to even the surface. The paper is then wound onto large reels, and at this point, is either sheeted for packaging as cut sheets, or sent into the further process of coating.
I am often asked what, in particular, is the difference between an offset and an opaque offset. And what about text papers. So, let’s look at the three types and their primary differences:
- Offset – offset is a grade just slightly higher than bond. The surface is smooth, but still has texture. Ink tends to absorb easier into offset, so it’s use is best suited for textbooks and anything text-heavy, like training manuals or user manuals.
- Opaque – or opaque offset, is offset, but its surface has been polished, so that the ink sits on it better. You can use opaque offset for catalogs that have photographic images within the text.
- Text and cover – these sheets are often polished more than an opaque sheet, and often have unique properties like colors, textures, or even specs of recycled matter in them. We will actually go into text papers next week
So, next week we’ll cover how specialty papers and synthetic papers are manufactured.