Paper making is a process which involves a number of steps to successfully produce a variety of papers which have different uses. Probably, half of the fiber used to make papers today is obtained from harvested wood. With this in mind, coniferous trees e.g. spruce and fir are mostly preferred in paper-making process because they have long cellulose fibers that result in manufacture of a strong paper. However, the remaining half of raw materials are obtained from recycled paper, recycled cloth and some vegetable matter. The following is the process of paper making:
Making pulp
Mainly, there are two processes which are used to convert logs into wood pulp i.e. mechanical and chemical processes.
In the mechanical process, harvested logs are first tumbled in drums to remove the barks and then sent to grinders which breakdown the wood into pulp through the use of revolving slabs. Later, the pulp is then filtered to remove any foreign materials to facilitate processing of a high quality paper.
To use the chemical process in making pulp, the logs are first de-barked for subsequent stages. Later, the de-barked logs are then cooked using a chemical solution in a digester. In the digester, the wooden chips are boiled at high pressure in a mixture of sodium hydroxide and sodium sulfide solutions which facilitate the chips to dissolve into pulp. Before filtering to remove unwanted materials, a bleaching agent or coloring maybe added depending on the type of wood used or the type of paper being manufactured.
Beating process
This is the second stage in paper making. Here, the pulp obtained in stage one is subjected to the effects of machine beaters with subsequent addition of filler materials e.g. chalks, clay or chemical substances such as titanium Oxide. These filler additives influences the opacity among other qualities of the paper and hence they are important in paper making. Also, depending on the type of paper being manufactured, sizings are added at this stage. There are different types of sizings and hence they are used appropriately because they are very vital as they affect the way paper reacts with different inks during the manufacturing process.
Pulp to paper
In order to turn pulp into paper, it is fed into big automated machines which squeeze the pulp through a series of rollers. These rollers have suction devices which are located below the belt to aid in draining off the water which may be found in the pulp. However, if water marks are supposed to be added on the paper, a device known as the dandy moves across the pulp of sheet to press a design on it.
Later, this sheet of pulp gets to the press section of the machine where it’s pressed between rollers of wool felt to produce the final paper. To remove the remaining water, manufactured paper is passed over a series of steam heated cylinders as the final stage of paper making.
Finishing
Here, the dried paper is wound into large reels waiting for further processing depending on the use of the paper. As a finishing up process, the paper is smoothed and further compacted by passing it through metal rollers known as calendars. Also, the paper may get a coating which could either be brushed or rolled on. The coating is important because it adds pigments or chemicals to the surface of the paper to supplement its sizings and fillers applied earlier during processing. Finally, manufactured paper is run through extremely smooth calendar rollers (supercalendering process) and then later cut into desired sizes for use.