Guardian (polymer)

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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 37.5µm 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 µm 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]

Polymer banknotes[edit]

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.[27] In 1998, the Bank Negara Malaysia issued a commemorative RM50 banknote,[27] and the Central Bank of Sri Lanka issued a commemorative Rs200 banknote.[28] In 1999, the Northern Bank of Northern Ireland issued a commemorative £5 banknote,[29] and the Central Bank of the Republic of China in Taiwan issued a commemorative NT$50 banknote.[30][27] In 2000, the Central Bank of Brazil issued a commemorative R$10 banknote[31] and the People's Bank of China issued a commemorative ¥100 banknote.[27] In 2001, the Central Bank of Solomon Islands issued a commemorative SI$2 banknote.[32] In 2009, the Bank of Mexico issued a commemorative $100 banknote.[27]



Further reading[edit]