Guardian is the trademark name of a polymer originally manufactured by Securency International, [1] a joint venture between the Reserve Bank of Australia and Innovia Films Ltd. The latter completed acquisition of the former's stake in 2013.
Its production involves gravity feeding a molten polymer, composed of extruded polypropylene and other polyolefins, through a four-storey chamber. This creates sheets of the substrate used as the base material by many central banks in the printing of polymer banknotes.
Polypropylene is processed to create pellets. [2] These pellets are extruded from a core extruder in conjunction with polyolefin pellets from two "skin layer" extruders, and are combined into a molten polymer. [2] [3] [4] This consists of a 37.5 μm thick polypropylene sheet sandwiched between two 0.1 μm polyolefin sheets, [4] [3] creating a thin film 37.7 μm thick.
The molten polymer undergoes snap cooling as it passes by gravity feeding through a brass mandrel, which imparts on the thin film many properties, including its transparency. [2] The cast tube material is then reheated and blown into a large bubble using air pressure and temperature. [2] At the base of the four-storey chamber convergence rollers collapse the tube into a flat sheet consisting of two layers of the thin film. [4] [2] This creates the base biaxially-oriented polypropylene substrate of 75.4 μm thickness, called ClarityC by Innovia Films. [3] [5]
The base substrate is slit as it exits the convergence rollers. [2] [4] Four 3-micrometre (0.00012 in) thick layers of (usually white) opacifier are applied to the substrate, two on the upper surface and two on the lower surface. [3] [4] A mask prevents the deposition of the opacifier on parts of the substrate that are intended to remain transparent. [6] These overcoat layers protect the substrate from soiling and impart on it its characteristic texture, [7] and increase the overall thickness to 87.5 μm. The resulting product is the Guardian substrate. [4]
The opacifier conversion phase involves the use of resin and solvents, creating volatile organic compounds (VOCs) as by-products that are combusted in a thermal oxidizer. [5] The resulting polymer substrate then passes through a rotary printing press using chrome-plated copper cylinders. [5] After printing, the holographic security foil is incorporated into the base substrate. [5] This is then cut into sheets and transported to the banknote printing companies in wooden boxes as a secure shipment. [5] [8]
Guardian is a non-porous and non-fibrous substrate. [2] Because of this, it is "impervious to water and other liquids", and so remains clean for longer than a paper substrate. [2] It is difficult to initiate a tear on the substrate, which has higher tear initiation resistance than paper. [2]
Guardian is used in the printing of polymer banknotes by many central banks.
It is the base material used for currencies printed by:
In 1993, the Bank of Indonesia issued a commemorative Rp 50,000 banknote and the Central Bank of Kuwait issued a د.ك1 banknote. [4] In 1998, the Bank Negara Malaysia issued a commemorative RM50 banknote, [4] and the Central Bank of Sri Lanka issued a commemorative Rs200 banknote. [27] In 1999, the Northern Bank of Northern Ireland issued a commemorative £5 banknote, [28] and the Central Bank of the Republic of China in Taiwan issued a commemorative NT$50 banknote. [29] [4] In 2000, the Central Bank of Brazil issued a commemorative R$10 banknote [30] and the People's Bank of China issued a commemorative ¥100 banknote. [4] In 2001, the Central Bank of Solomon Islands issued a commemorative SI$2 banknote. [31] In 2009, the Bank of Mexico issued a commemorative $100 banknote. [4]
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