Paper production technology

Preparation of paper needs vegetable substances that have long enough fibers, and which, being mixed with water, will give a uniform, plastic paper mass, the so called pulp. Semi-finished products for the paper production include:

• wood pulp or cellulose;
• cellulose of annual plants (straw, phragmites, hemp, rice, etc.);
• hemicellulose;
• recycled paper;
• rag half-stuff;
• asbestos, wool and other textile fibers (for special types of paper).

Paper manufacturing consists of the following processes:

• pulppreparation (grinding and mixing the components, sizing, and coloring content of the pulp);
• development of the pulp on a paper machine (dilution with water and cleaning of the mass of dirt, molding, pressing and drying, as well as the primary finishing);
• finishing (calendering, cutting);
• sorting and packing.

When milling the fibers are imparted the necessary thickness and physical properties. Grinding is done in devices of periodic and continuous action (roll, conical and disc mills, refiners and others). To make the paper suitable for writing and give it hydrophobic properties, the pulp is introduced with rosin glue, paraffin emulsion, alumina and other adhesion promoting substances (the so-called sizing); starch and animal glue are added to enhance the connection between the fibers and increase the mechanical strength and hardness; to increase the strength of paper in the wet state - urea formaldehyde and melamine-formaldehyde resins.

To increase brightness, smoothness, softness, and opacity, as well as improve the printability of paper mineral fillers (kaolin, chalk, talc) are injected; to color and enhance the whiteness - aniline (less mineral) dyes. Some types of paper, such as absorbing and insulating, are produced without gluing and filling.Paper made of hemp and rice paper is whiter than of wood pulp, therefore, often it requires no additional chemical bleaching fibers.

Finished pulp with concentration of 2.5-3.5% is fed by the pump from the preparatory department to the mixing pool, where from it comes to the paper machine. Before that the mass isdiluted with circulating water (at a concentration of 0.1-0.7%) and passed through sewage treatment equipment (sandboxes, vortex and centrifugal cleaners and strainers).The most common is the so-called ‘dining room’ paper machine(with a flat grid). It consists of a net, press and drying parts, calender and reel.

Paper is furnished in a continuous stream onto a moving mesh of the machine closed in the ring for sheet formation, dewatering and compaction of the paper web. Further dehydration and sealing of the web is made in the press section formed by multiple rolling presses; between their rolls the paper web is transported by a cloth serving as an elastic underlining throughout the whole process.

The final removal of water takes place in the drying section, where the paper web alternately comes in contact by its surfaces with drying cylinders heated from within by steam and arranged in a checkerboard pattern in two tiers. We obtain a smooth surface of the paper because it is pressed between the cylinders against the upper and lower felts. The resulting paper web is wound onto the reel on the rolls, which is a rotating cylinder, which is pressed against the roller with the paper wound on it.

Then the paper can be processed in a super-calender, which is a battery of 5-8 vertical metal shafts. When moving downward between the shafts the web becomes more smooth, compacted and leveled in thickness.