Guardian (polymer)

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.

Production

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 37.5μm 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]

Properties

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]

Polymer banknotes

Guardian is used in the printing of polymer banknotes by many central banks.

It is the base material used for currencies printed by:

Country	Central bank	Currency	Banknotes
Australia[9]	Reserve Bank of Australia	Australian dollar
Bangladesh[10]	Bangladesh Bank	Bangladeshi taka
Brunei[11]	Brunei Currency and Monetary Board	Brunei dollar
Canada[12]	Bank of Canada	Canadian dollar	Frontier Series
Chile[13]	Central Bank of Chile	Chilean peso
Costa Rica[14]	Central Bank of Costa Rica	Costa Rican colón
Dominican Republic[14]	Central Bank of the Dominican Republic	Dominican peso
Guatemala[14]	Bank of Guatemala	Guatemalan quetzal
Honduras[14]	Central Bank of Honduras	Honduran lempira
Hong Kong[14]	Hong Kong Monetary Authority	Hong Kong dollar
Indonesia[15]	Bank of Indonesia	Indonesian rupiah
Israel[14]	Bank of Israel	Israeli new shekel
Malaysia[16]	Bank Negara Malaysia	Malaysian ringgit
Mauritania[14]	Central Bank of Mauritania	Mauritanian ouguiya
Mauritius[14]	Bank of Mauritius	Mauritian rupee
Mexico[17]	Bank of Mexico	Mexican peso
Mozambique[14]	Bank of Mozambique	Mozambican metical
Nepal[18]	Nepal Rastra Bank	Nepalese rupee
New Zealand[19]	Reserve Bank of New Zealand	New Zealand dollar
Nicaragua[14]	Central Bank of Nicaragua	Nicaraguan córdoba
Nigeria[14]	Central Bank of Nigeria	Nigerian naira
Papua New Guinea[20]	Bank of Papua New Guinea	Papua New Guinean kina
Paraguay[14]	Central Bank of Paraguay	Paraguayan guaraní
Romania[21]	National Bank of Romania	Romanian leu
Samoa[22]	Central Bank of Samoa	Samoan tālā
Singapore[23]	Monetary Authority of Singapore	Singapore dollar
Thailand[24]	Bank of Thailand	Thai baht
United Kingdom[14]	Bank of England	Pound Sterling
Vanuatu[14]	Reserve Bank of Vanuatu	Vanuatu vatu
Vietnam[25]	State Bank of Vietnam	Vietnamese đồng
Zambia[26]	Bank of Zambia	Zambian kwacha

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]