Production of parchment is carried out in the paper- and- parchment production facilities of "Troitskaya paper mill." The design capacity of the mill (for parchment 68 gsm, at the speed of the parchmentizing machine 180 m / min) is 25000 tons per year. Parchment is produced on two parchmentizing machines № 121 and № 122, supplied by the Finnish company «RAUMA-REPOLA» (now «Sunds Defibrator Loviisa») in 1989.
Vegetable parchment manufacturing is based on a process of fast (4-6 seconds) uniform swelling and partial dissolution of cellulose in sulfuric acid.
Sheet of base paper moves from tambour mounted on the pope reel into sequence of two parchmentizing bathtubs (PM) with "cold" acid and "warm" acid. Acid temperature and level in the bathtubs are kept constant by means of sensors.
Parchmentizing bathtubs are equipped with overflow devices and are made of polyethylene. For better parchmentizing of the base paper there is foreseen application of "cold" acid. In the process of freezing there occurs internal dehydration of fibers by means of pulling water from the finest pores and capillaries to the centers of water crystallization. It causes compaction of the structure and reduction of hydrophility. Ice crystals wedge and break up the fiber structure, thereby weakening the intermolecular bonds of cellulose, helping to improve its reactivity.
Time of base paper processing with sulfuric acid in parchmentizing bathtubs depends on depth of immersion of paper lead-rollers, speed of PM, density and temperature of acid in parchmentizing bathtubs.
Sulfuric acid is squeezed out of a parchment sheet by press rolls after each parchmentizing bathtub.
After parchmentizing bathtubs a parchment sheet enters acid bathtubs with countercurrent washing for to extract acid out of them. Counter-current washing consists of a sequence of twelve acid bathtubs, connected to each other with the overflow pipes in "chessboard" order. Bathtubs are made of polypropylene. Acid is squeezed out of a parchment sheet by press rolls after each parchmentizing bathtub.
After the acid bathtub the parchment sheet moves to washing area consisting of eight wash bathtubs for further cleaning acid off. Rinsing bathtubs are equipped with spray devices and interconnected with overflow pipes in the "chessboard" order. Technological water, mechanically purified, with acid residues is squeezed out of a parchment sheet by press rolls after each parchmentizing bathtub.
Washed parchment undergoes softening (plasticization) for to obtain softness and elasticity. Processing of parchment is done in a plasticization bathtub with warm glycerol solution. Glycerol out of the parchment sheet is squeezed out on press rolls after a bathtub.
After plasticization bathtub the parchment enters the dryer section of the parchmentizing machine, which consists of 26 drying cylinders and two chilling cylinders.
From the drying section the parchment sheet goes to chilling cylinders and then to the twin-shaft machine calender. After the calender the sheet goes to the pope reel through a scanning device, which defines the humidity of parchment and weight of one square meter of parchment. After the pope reel a parchment roll, after weighing on the balance, moves by a conveyor belt to the longitudinal slitting machine, where cutting of parchment into specified widths takes place.
After cutting, if it is necessary, the parchment is packaged in moisture-resistant paper or film, so that is does not absorb moisture during storage, and then it comes onto a roll-packaging line, where the rolls are packaged with cardboard.
Finished rolls are sent down to the warehouse of finished products.