Guardian (polymer)

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Guardian is the trademark name of a polymer manufactured by Innovia Films Ltd. 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.[1] 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.[1][2][3] This consists of a 37.5µm thick polypropylene sheet sandwiched between two 0.1 µm polyolefin sheets,[3][2] 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.[1] The cast tube material is then reheated and blown into a large bubble using air pressure and temperature.[1] 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.[3][1] This creates the base biaxially-oriented polypropylene substrate of 75.4 µm thickness, called ClarityC by Innovia Films.[2][4]

The base substrate is slit as it exits the convergence rollers.[1][3] 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.[2][3] A mask prevents the deposition of the opacifier on parts of the substrate that are intended to remain transparent.[5] These overcoat layers protect the substrate from soiling and impart on it its characteristic texture,[6] and increase the overall thickness to 87.5 µm. The resulting product is the Guardian substrate.[3]

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.[4] The resulting polymer substrate then passes through a rotary printing press using chrome-plated copper cylinders.[4] After printing, the holographic security foil is incorporated into the base substrate.[4] This is then cut into sheets and transported to the banknote printing companies in wooden boxes as a secure shipment.[4][7]


Guardian is a non-porous and non-fibrous substrate.[1] Because of this, it is "impervious to water and other liquids", and so remains clean for longer than a paper substrate.[1] It is difficult to initiate a tear on the substrate, which has higher tear initiation resistance than paper.[1]

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[8] Reserve Bank of Australia Australian dollar
Bangladesh[9] Bangladesh Bank Bangladeshi taka
Brunei[10] Brunei Currency and Monetary Board Brunei dollar
Canada[11] Bank of Canada Canadian dollar Frontier Series
Chile[12] Central Bank of Chile Chilean peso
Costa Rica[13] Central Bank of Costa Rica Costa Rican colón
Dominican Republic[13] Central Bank of the Dominican Republic Dominican peso
Guatemala[13] Bank of Guatemala Guatemalan quetzal
Honduras[13] Central Bank of Honduras Honduran lempira
Hong Kong[13] Hong Kong Monetary Authority Hong Kong dollar
Indonesia[14] Bank of Indonesia Indonesian rupiah
Israel[13] Bank of Israel Israeli new shekel
Malaysia[15] Bank Negara Malaysia Malaysian ringgit
Mauritius[13] Bank of Mauritius Mauritian rupee
Mexico[16] Bank of Mexico Mexican peso
Mozambique[13] Bank of Mozambique Mozambican metical
Nepal[17] Nepal Rastra Bank Nepalese rupee
New Zealand[18] Reserve Bank of New Zealand New Zealand dollar
Nicaragua[13] Central Bank of Nicaragua Nicaraguan córdoba
Nigeria[13] Central Bank of Nigeria Nigerian naira
Papua New Guinea[19] Bank of Papua New Guinea Papua New Guinean kina
Paraguay[13] Central Bank of Paraguay Paraguayan guaraní
Romania[20] National Bank of Romania Romanian leu
Samoa[21] Central Bank of Samoa Samoan tālā
Singapore[22] Monetary Authority of Singapore Singapore dollar
Thailand[23] Bank of Thailand Thai baht
Vanuatu[13] Reserve Bank of Vanuatu Vanuatu vatu
Vietnam[24] State Bank of Vietnam Vietnamese đồng
Zambia[25] 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.[13] In 1998, the Bank Negara Malaysia issued a commemorative RM50 banknote,[13] and the Central Bank of Sri Lanka issued a commemorative Rs200 banknote.[26] In 1999, the Northern Bank of Northern Ireland issued a commemorative GB£5 banknote,[27] and the Central Bank of the Republic of China in Taiwan issued a commemorative NT$50 banknote.[28][13] In 2000, the Central Bank of Brazil issued a commemorative R$10 banknote[29] and the People's Bank of China issued a commemorative ¥100 banknote.[13] In 2001, the Central Bank of Solomon Islands issued a commemorative SI$2 banknote.[30] In 2009, the Bank of Mexico issued a commemorative $100 banknote.[13]



Further reading[edit]