To produce all kinds of paper, any wood fiber can be used as a raw material. The properties of the finished paper depends on the breed of timber used, the method of processing chips, the type of added chemicals, and the type of equipment, which was used for paper manufacturing.
High-quality paper is made from a mixture of fibers of deciduous and coniferous species, with the addition of mineral filled core and various chemical additives. Coniferous tree are pine, fir and spruce. Softwood fibers are characterized by a much greater length and diameter as compared to hardwood fibers. These fibers give the paper more strength than hardwood fibers, and the best paper passes through the press and other treatment processes, which can expose its customers. Some types of paper, which used for bags and packages, to increase the strength can be made from 100% pine fiber.
Deciduous fiber is obtained from deciduous trees (those that lose their leaves in winter). Examples of deciduous trees are maple, oak, aspen, poplar and birch.
Production of chemical pulp.
Wood should be turned into chips, to provide a large surface area and mobility needed for the boiling process. After grinding, in order to “withstand” chips, they are stored in huge piles for a few weeks. This reduces the tendency of wood tar deposited in the boiling process, which leads to gum stains on the paper.
After “aging” in piles chips comes to sorting, where it is removed from the debris and foreign objects, and pneumatic conveyor is delivered to the pulp mill.
There are two methods of chemical processing of cellulose, which produces two different types of cellulose. Sulphite pulp. From the name itself implies that the wood is cooked in an alkaline solution (usually a mixture of sodium hydroxide and sodium sulfide). In the form of materials commonly used spruce, pine or birch. In the production of kraft pulp released pungent smell (apparently from caustic soda), which is a big disadvantage when it comes to the organization of production near the village.
Sulphite pulp is boiled in acid solution. The active ingredients here are the ions of hydrogen sulfide and metal. Raw materials are usually spruce, pine or beech.
When finished, the fiber is partially exempt from the lignin. The resulting pulp is then washed, dehydrated and pumped through a pipe to a paper mill, if it is close by, or dried, packaged and shipped to customers.
Because of the remaining lignin (its content after cooking can vary between 1.5 – 7%) sulphite pulp is usually brownish in color, while the sulfite – gray and yellow. After a multi-step process of bleaching lignin residues are removed and the pulp by a white or slightly grayish color. Previously, this process was used chlorine – is extremely harmful to the environment chemical. Today, most of the world pulp mills switched to chlorine-free bleaching process (ECF elementary chlorine free – TC – totally chlorine-free).
This sort of pulp is produced by grinding wood into special mill with the addition of water. Once the wood is transformed into pulp (cellulose), it is bleached and pumped into a nearby papermaking plant or dried, are sold on the market. Because of the lack of chemical steps of removing lignin from wood pulp, paper made from it quickly turns yellow when exposed to UV radiation. Modern technologies allow producers wood pulp change its characteristics and quality. So, in many cases, when such paper properties like strength, don’t have paramount importance, in the production of paper wood pulp is used.
Paper, made from soft wood pulp (NBSK), is much stronger, because the fibers are longer. Paper from solid hardwood (VNKR) is less robust due to the short length of its fibers. On the other hand, short fibers provide a smooth, easy-to-print paper surface.
Wood pulp of a greater amount of paper – about 97%, whereas the efficiency of chemical pulp is 55-60% for NBSK and 40-50% for VNKR. The main drawback of wood pulp is the fact that its production needs much electricity.
Paper from chemical pulp has good strength. These figures, however, may be reduced if the manufacturer, wanting to achieve greater brightness.
Paper from wood pulp has a lower density, high stiffness, absorbs ink (printing and has a good opacity. Excellent ranability makes this paper ideal for newspapers and magazines. Wood pulp disadvantage, as already mentioned, is the high content of lignin, out- for what she made of paper yellow with time.
Finished pulp is transported to the paper machine, where it makes of paper. If papermaking plant is nearby, the cellulose in the aqueous solution is pumped through the pipe just from one shop to another. Its content in such a solution is only 2-4%. If papermaking plant is located far away, dried pulp, reducing the water content of 5-10% of it, packed and sent to the recipient.
Headbox and forming section.
Head box – this is the first major component of the papermaking process on the machine. Headbox is the capacity to accurately controlled pressure, designed for diluted suspension of fibers and a uniform distribution of the fibers on the machine width to achieve the profile of the canvas with a single basis weight. Pressure in the head box should be monitored to ensure that the flow rate of the suspension fiber or “jet” is as close to the speed of a moving grid, on which the fiber bed. This rate ratio “of the jet and the grid” is very important to position (orientation) fibers, uniform clearance sheet, reduce curl and improve other properties of paper.
After the free water is removed, and the canvas by 20% consists of dry fibers, it is moved to infinity, moving carpet. Then the fabric on the cloth passes through the press, which squeezes out of it even more water. Cloth wet paper web moves between two heavy rollers with a matched load to squeeze the cloth and linen. Water is pressed out of the cloth and removed by soaking the cloth. When the blade comes out of the press section, it is about 40% consists of dry matter.
Now, the canvas into the main part of the drying machine to remove the remaining water. Here, in turn, passes the canvas over and under big, steam-heated drying cylinders, the temperature of the cylinder increases sequentially, as the paper moves through the machine. The canvas is held in contact with the drying cylinders series dryer felts, which simultaneously increase the drying efficiency and support the canvas, moving through the machine. Monitoring temperature and intensity of drying fabric provide uniform drying paper without wrinkling and other defects.
Gluing of the surface.
Dried to 98% dry matter content of the paper web is fed from the main dryer section at the size press, where it passes between two large rubber covered rolls, from which it is applied on both sides of a thin film of starch. Rods with grooves across the whole width of the shaft, exactly dosed amount of starch needed to create uniform thin “film” on the shafts, from which it is transferred on both sides of the paper. The main purpose of the starch film is coating of fiber / filler paper to prevent plucking fibers or filler particles and clogging of the printing, copying, and other equipment of the customer. Besides the size press is used to adjust the final color webbing or for further processing of its surface a variety of special trains. Since starch solution also contains water, cloth, passed through a size press again must pass through a short drying part to restore the moisture content of the paper to the desired final value of 4.5 to 5.0%.
Coating is defined as the coverage of the paper surface layer of kaolin, chalk, starch, latex, and other additives to improve its print and strength properties. Each manufacturer has its own special formula of the substance, which it uses for its coated paper.
After leaving the last dryer section, the paper web passes through the calender, two polished steel cylinder with a consistent, very high load. Controlling the load of the cylinders, we squeeze the paper, adjusting the thickness and smoothness of the surface giving. Smoothness, which makes paper calender, improves printability and surface structure. Unfortunately, on the calender treatment also reduces the thickness, stiffness, and other desirable qualities of paper, so there has to compromise. After calender paper web is scanned computer, measuring its various parameters and transmits this information back to the automated control systems headbox, drying section, basis weight control, and other control systems that continuously monitor the process and adjust his regime. Then, the paper web on the reel wound into large rolls or vestibules and overhead crane moves to longitudinal slitting machine.
The paper, which went out from the paper machine, usually wound on the big wide roller (jumbo roll), or “lobby”. Tambour may have a width of 2.5m to 9m. For a more convenient transportation, cutting and printing docks cut into rolls of fixed width. The rolls may have a diameter of 1.6 meters for shitting machine, or less, in accordance with the order of the buyer. Factories are trying to link the orders so that the sum of the widths of the small roll was as close to the width of the vestibule. Otherwise, it is the so-called “satellite” non-standard format.
Rolls, which were cut to the customer’s request, immediately sent to the wrapping machine. Here they are wrapped in two layers of brown kraft paper with a plastic coating that protects the paper from moisture penetration and damage during storage. Then rolls automatically transported directly to the warehouse where they are stored prior to shipment to customers.
Rolls, designed for sheet of paper sent to shitting shop, where they are cut into sheeting machines.