How We Make White Top Linerboard
See the process details.
Containerboard is one of the largest paper markets in North America. Almost everything that is manufactured and sent to market is packed and shipped in containerboard — from oranges to computers. Containerboard is the paper that goes into making corrugated cartons. Corrugated has two sheets of linerboard sandwiching a corrugated medium. This construction protects the contents of the boxes, but also gives the boxes stacking strength.
Catalyst markets a containerboard product called white top linerboard. White top is what is used on the outside of boxes for advertising products with colourful graphics. In today's big-box retail stores such as Costco and Sams, products are put on shelves in their original shipping containers. Now the corrugated cartons have to not only get the products from the factories to the stores' shelves, they must also catch the potential buyers' eyes and convey information about the contents.
Our Silverliner™ white top linerboard is strong to protect the goods inside the boxes and acts as a graphic paper that prints and accept inks well.
To produce Silverliner™, we combine two layers of pulp on our kraft paper machine at Elk Falls Division. We make the base layer from unbleached kraft long-fibre pulp. This base layer is where the strength of the paper comes from. We apply a bleached short-fibre kraft pulp top layer to the brown kraft base that makes the paper look white on one side and creates a good printing surface. We then press and dry the two layers in the machine and roll them into jumbo reels of paper.
Depending on customers' needs, we will vary the thickness of pulp that we use to make a stronger, thicker paper or a thinner, more economical paper. In all cases customers are looking for a good white paper that prints well.
Process Details
1. Wood chips
This is where the kraft paper-making process begins. Silverliner™ needs to be both strong and smooth, so the process starts with a combination of different types of wood chips. For the brown base sheet, we use northern softwood chips. These chips make a very strong pulp, providing a linerboard with excellent ring crush and burst characteristics. For the top of the paper, we use a short fibre chip, which is bleached in the process. These wood chips give us the smooth white surface that is needed for high graphic printing.
2. Head boxes
Because Silverliner™ is white on one side and brown on the other, we use two pulp streams and two head boxes. The first head box creates the strong brown base. The second head box applies the layer of bleached pulp. Both streams of pulp are mostly water when the formation begins.
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3. Fourdrinier
During the next step, we remove the majority of the water in the fourdrinier using a combination of gravity, vacuum and centrifugal force. At the contact point between the top and the bottom layers of white and brown pulps, the layers bind to form one strong sheet.
4. Press and dry
We remove more water in these stages by squeezing water out on a press. The sheet then passes over and around dozens of steam-filled drums. By the time the sheet emerges, moisture content has been reduced to less than 10 per cent.
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5. Calender stack
At this stage, we iron the now-dry paper between polished steel rolls, giving the paper a smooth finish and a precise and uniform thickness that reflects the customer's stated specifications. What began as watery pulp in the head box is now finished paper. The entire process takes less than a minute.
6. Reels and rolls
In the final step we wind the paper tightly onto a large reel that's as wide as a city street and weighs as much as 30 tonnes. We then cut the paper to customer-specified widths, wind it onto small rolls and envelop it in a vapour-barrier wrap for storage and shipping. Each roll can hold up to 20 kilometres of papers.
