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Paper Manufacturing





Tissue Machines

"Tissue Machines are very similar to paper machines in over-all process, but they are much smaller in size and have a different kind of dryer section. Tissue is what is used to make toilet paper, paper towels, napkins, etc. Like paper, tissue is made from a pulp material, but is more often recycled and much lower quality materials. It is made in large rolls and later in a separate process "converted" to its final product."

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Learn About Paper - Glossary

Pulping Processes:

There are three main types of puling processes: Groundwood pulp; Chemical; and Chemi-mechanical.

The groundwood pulping process grinds wood into pulp. Usually this involves taking a log and pressing it against a rotating surface to grind off small pieces. Typically a grinder is about 4 feet long. The groundwood pulp is then often cooked to soften it.

The chemical process involved cooking chips from a log in a hot bath of boiling caustic.

The chemi-mechanical process is a combination of the groundwood and chemical processes.

Stock:

Stock is a mixture of water and paper fiber. It can be made of wood pulp, cloth fiber, or a mixture of any cellulose and fibrous material. Most paper is made from wood pulp.

The first materials used to separate the layers of pulp slurry were made of very thin Tevlar, which is currently used in bullet-proof vests. This enabled a more precise movement of flexible separaters to create specific pressure differences in order to control the basis weight of each layer.

(*What's Tevlar made out of?)

Coating:

Bill blade coating refers to a way of coating paper and making that coating even and consistent Coated paper cannot come in contact with any cylinders, so it must be dried by hot air on the surface using a high speed air flow. This initially formed ripples on the surface. Excess was sometimes wiped off by a blade, skimming and smoothing the surface.

Tandem coating refers to a two stage process that coats both sides of the paper sheet.

Coaters:

Coaters apply separate coatings to paper after the paper sheet has been formed and dried.

Coatings are substances put on a finished sheet of paper. They are made in what is called color kitchens. Coaters can make a paper protected or shining, like magazine paper.

More than one coater can be used. Sometimes an initial coat needs to be put on to prepare the paper for a second coat, usually when the paper is porous and the final coat is an expensive substance... then an initial coat is used to prepare the paper so that less of the expensive coat is necessary.

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(*They're coating the paper on both sides and probablly the rollers are being coated, the paper is absorbing the * from the rollers, too?)

Rheology:

Rheology is the science of studying the friction between liquids. In papermaking, it is mainly used in studying the behavior of coatings.

Some of the questions rheology helps to answer are: Will the coating adhere or fall off? Will the coating be absorbed by the paper, requiring the paper to be precoated with another material? Will the coating spread or dry in the necessary time? Will one coating react with another coating in an unwanted way?

Secondary Paper:

Secondary paper refers to any recycled fibers, waste papers, or other sources of pulp and fiber that come from a previously created product or process.

Clarifiers:

Clarifiers remove unwanted material. Sometimes these materials are reused in a different part of the process, sometimes they are discarded.

There are two main types of clarifiers: flotation and sedimentary Flotation clarifiers often use very small bubbles, making the water milky, driving unwanted materials upward with the bubbles. Sedimentary clarifiers either decant the clear material off the top or they remove the heavier unwanted materials in a centrifuge.

Crystallography:

This is science of analyzing crystalline structure of materials. In the paper industry, it usually refers to the study of cellulose, which can have up to a 20-40% crystalline structure.

High crystalline structure means less swelling of the fibers.

Converting:

The converting process is the step in papermaking that takes the sheet as it comes off of the end of the paper machine and changes it into useable paper items. Through rewinding, cutting, creping, embossing, printing, coating and other process, the sheet is transformed into napkins, facial tissue, placemats, packaging, etc."