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Security paper

PAPCEL provides complete SPLs for security paper grades. Banknotes are usually made from pulp with contents of cotton, linen and hemp fibres, alternatively supplemented with abaca and others. Banknote paper basis weights range between 80 and 90 gsm. Compared to the common paper grades, banknote paper significantly differs as for a fiber composition and subsequently a higher resistence to wear. Wearproofness is achieved by appropriately treating the furnish, and by filling the paper structure with polyvinylalcohole or gelatine further improving paper mechanical properties. A banknote average lifetime is two years. The process of manufacturing banknote papers and their admixtures is agreed between contracting authorities and papermakers and are covered by a great level of secrecy.



Security papers - basic sorting

The security paper group includes:
  • Banknote papers.
  • Stamp papers for tax, duty, fee and other government stamps, postage stamps, toll stickers, food stamps, tickets and the like.
  • Papers for stocks, shares, bills, cheques, securities, bonds and the like.
  • Document papers for government documents like passports, identity cards, school certificates, university diplomas etc.
Their properties must comply with the specific use requirements:
  • High tensile strength
  • High tearing strength
  • High opacity
  • Low air permeability
  • Excellent printability
  • Protection against forgery
  • Good runnability
This is an example of PAPCEL machinery for manufacturing banknote paper.
  • Coarse screening node, chemical pulp and linters refining node
  • PM approach flow (AF) systems for top and botom layers
  • Broke unit
  • Water treatment node
The SPLs and AF systems are always designed to ensure stock quantities sufficient for PMs. The SPL processes two furnish sorts - chemical pulp and linters - and feeds PM with stock of a required quality.

Pulping node, chemical pulp and linters refining node

Furnish is carried by a conveyer and batch pulped in a vertical LCV pulper with a ø16 mm bored screen plate. Processed stock from the pulper is pumped through an HD-cleaner to a pulped stock chest. From the chemical pulp chest stock is pumped to a cyclic refining node with a disc refiner. From the linters chest stock is pumped to a cyclic fibrillation node with conical refiners. Refined stock is then pumped to storage tanks. From the linters tank stock is pumped to another cyclic fibrillation node with conical refiners and from there to another storage tank. Due to a need of high freeness the refining nodes must be operated in a cyclic mode. As soon as the required stock pressure is reached the refiners are automatically loaded up to the set value. During the preset refining time stock circulates in the refining node until the required freeness is reached (chemical pulp from approx. 13 ºSR up to approx. 45 ºSR, linters from approx. 12 ºSR up to approx. 55 ºSR). Then a stock outflow pneumatic valve opens and a cyclical refining pneumatic valve shuts. If linters are partially cyclically refined a part of stock is automatically discharged to the further refining process. A control system operates all the valves, enables a connection to level controllers, automatically starts and stops the refining node and automatically controls a load of each refiner as per the set refining time. During the set refining period the automatics is able to change the refiners required load up to 3 times. Having been processed this way, linters and chemical pulp are pumped to a common mixing chest where also other admixtures like starch can be added. Perfectly mixed stock is then pumped at a controlled consistency of approx. 2,5% to a machine chest.

Approach flow systems

From the machine chest stock is pumped through a conical egalising refiner to a level chest. The pump is equipped with a suction tube. The level chest is equipped with a permanent safety overflow piped into the suction tube. From the level chest stock flows at a controlled throughput to a fan pump suction and from there to an LD-cleaner. Then the stock flow is divided into two pipeline branches; approx. 70% flows to a bottom layer STU-201 knotter while approx. 30% flows to a top layer STU-081 knotter.

Dilution water for the bottom headbox is pumped to be purified in an STU-081 pressure screen. Accept from the STU-081 flows to the bottom headbox, reject returns back to the water tank.

Water treatment node

White water is pumped from a white water chest with a drainage safety overflow to a flotation cell. Purified water is piped from the flotation cell to a chest with an overflow to a sewer tray drained to an effluent biological treatment plant. Purified water is then pumped to the PM and used for the SPL, AF systems and broke unit operation, dilution and consistency control purposes. 

Broke unit

Stock from a couch pulper is pumped to a thickener OK-500. Thickened stock is piped to a chest at a consistency of approx. 3%. Fibres separated in the flotation cell are piped to the same chest from where stock is pumped to the pulp and linters mixing chest.

Banknote paper is manufactured by paper machines with cylinder moulds at low work speeds, mostly at a deckle of up to 3 m and with several special modifications above all regarding the security features.

Banknote paper is made from 100% cotton chemical pulp (so called cotton paper) at basis weights of 80 to 90 gsm. Generally cotton paper compared to a common one is much more resistant to tearing and wear, it is opaquer and does not contain common chemicals making paper luminiscent in the ultraviolet light.

Concept of the PAPCEL paper machines making security papers

With regards to the required capacities of the concerned paper grade production the PMs are usually made with a deckle of up to 3 m and regarding a watermark with a speed range of 20 to 90 m/min, no more than 120 m/min. Dominant elements of such paper machines are cylinder moulds. Stock pumped to a cylinder mould vat reaches a level determining basis weight of the respective layer. Stock is carried by the cylinder mould upwards and then picked up by a pick-up screen. At the same time the cylinder mould performs a role of a dandy roll to make the watermark of the manufactured paper grade. Changing a paper grade, another cylinder mould assigned for the respective banknote paper grade must be used.

Press part

A press part of the PM making double-layer banknote papers usually consists of a single double-nip (combi) press, in certain cases with a single-felt press added. It is designed by the properties of the manufactured paper grades range with regards to the used safety elements. Also the used linear pressures are lower due to slow pressing process dewatering. Due to the latter fact the final dryness after the press part usually ranges from 39 to 42 %.  

The first press part variant is a combi press including a triple-chamber pick-up press roll, a smooth central roll with a double oscillating doctor and a top press roll with a separate felt. Another less common variant is an assembly comprising again a triple-chamber pick-up press roll, a central triple-chamber suction roll and a top smooth press roll. And finally the third press part variant is composed of two presses. The first press is of a combi type where the central press roll serves also as a pick-up roll. It has 5 chambers, with a pick-up, two keeping and two pressing chambers. The bottom press roll has a felt, the top one is smooth. The combi press is followed by a straight press with a bottom felt. The combi press linear pressures are 40 and 60 kN/m, the same in the second press is 70 kN/m.

Drying part

The drying part of the banknote paper machine is of a standard double tier configuration. The drive of the drying sections is of a multi-engine type by means of closed gearboxes - each gearbox drives all the dryers in the respective section. The drying part is divided into a pre-drying section and an after-drying section due to required quality of the manufactured paper grades.

Surface treatment unit - size press, film press

A surface treatment unit enabling a needful surface quality treatment is a necessary part of the banknote PM.

Soft calender

A soft calender is another machine unit used to treat banknote paper during its manufacture on the PM. The banknote properties require calendering both sides.

Reeling

As well as most PMs, the machines making banknote papers end with a reeler.

Rewinding

Banknote papers are rewound on two-drum winders with metallized drum surface coating. Rolls wound on paper cores of required diameters must meet all the requirements of the subsequent converting operations.

Other equipment of banknote PMs

The other machinery needed to complete banknote PMs is entirely comparable to the same of PMs making other paper grades. They only respect required performance and size parameters. Multi-engine drives, scanners, QCS and DCS control systems, hydraulic and lubrication devices, vacuum systems and others are part of this auxiliary systems.

Paper machine manufacturing sacurity papers (except banknote papers)

With a fourdrinier wire and a dandy roll, a surface treatment unit (size press, film press) in a drying part and a soft calender, a design of the PM manufacturing security (except banknote) papers is very similar to the same of single-wire paper machines making printing and writing or special paper grades.

The security papers are the main production program of slow paper machines with a deckle of less than 3 m. For the PMs wide up to 5 m working at medium speeds (600 to 800 m/min) the safety papers are only a supplementary part of their main production program.