This article from UV curing specialist, GEW’s Jennifer Heathcote, delves into the current state of mercury regulation. Jennifer explains where major legislating bodies currently stand on this topic and discusses how it affects UV curing for the printing market.
Governments and non-governmental organizations (NGOs) establish and periodically update policies stipulating that the most dangerous and most toxic materials must be substituted with alternatives when identified. Harmful materials meant for replacement are commonly referred to as substances of very high concern (SVHC). An SVHC designation drives regulation that defines the circumstances under which the material is banned from use and specifies how allowable materials must be obtained, sold, transported, imported, exported and disposed. When no viable alternatives to SVHCs exist, exemptions or phaseout timelines are often established.
Mercury in UV Curing Lamps
Mercury (Hg) is an example of an SVHC – you can watch Jennifer’s webinar on Mercury Regulation here. Regulation of mercury directly impacts manufacturers and users of UV curing since UV lamps contain a small amount of elemental mercury. The physics of elemental mercury results in broadband emissions of ultraviolet, visible and infrared energy when mercury is vaporized into a high-temperature plasma within a sealed quartz tube containing inert gas under medium pressure. Without mercury, UV lamps do not function. During transport, storage and use, mercury inside UV lamps exists in liquid, gas and plasma states. For lamps sourced from reputable suppliers, mercury in all three states is safely contained within the lamp’s sealed quartz tube.
Since the 1940s, UV curable chemistry has been formulated to react to the broad-spectrum output generated only by vaporized elemental mercury. This applies to standard mercury arc and microwave lamps as well as additive, doped and metal halide lamps that contain small amounts of metal in addition to mercury. Examples of metals used in additive lamps include iron, gallium, indium, and tin. The addition of metal shifts the spectral distribution within the UV band and facilitates optimal cure in some formulations.
The amount of elemental mercury inside UV curing lamps varies across designs and lamp lengths; however, it is typically between 10 and 100 mg per lamp. UN Environment references an average of 25 mg per lamp for global inventory estimates. For context, a single mercury amalgam dental filling, also known as a silver filling, contains an average of 800 mg of mercury. This means there is often more mercury in a person’s mouth than is contained in all the UV lamps of a typical printing press or converting line.
Mercury Safety Concerns
While mercury is a dangerous neurotoxin, it is generally safe from direct human exposure and environmental harm when naturally bound within the Earth, permanently disposed or properly secured in sealed products and storage containers above ground. Mercury becomes potentially harmful to humans and animals when released from its confines and dispersed within the global ecosystem or biosphere. Mercury enters the biosphere as gas and vapour emissions to air and direct and indirect releases to water. Once free, mercury migrates easily, readily changes form and potentially exposes all organisms with which it makes contact.
Mercury Regulation
Policies enacted within the European Union under RoHS2 and within the United States under the Lautenberg Act3 as well as by regulatory bodies such as the European Commission (EC), the EPA4, UN Environment Programme (UNEP)5, and the international Minamata Convention on Mercury6 are meant to reduce or eliminate anthropogenic mercury use. Anthropogenic refers to mercury that is directly or indirectly emitted to air or released to water by human activity. While complete elimination of anthropogenic mercury is not possible today, restrictions and enforcement are expected to increase over the coming decade.
It is important to emphasize that there are currently no policies or legislation in the UK, the EU, the US or in any other country worldwide that specifically ban mercury UV curing lamps from production, use, export, import or general shipment. In addition, no new restrictions specifically addressing mercury vapour UV curing lamps are anticipated in the near term. Regulation, however, is ongoing, and it is important to periodically review regulatory trends and changes to legislation.
European Union – RoHS
Globally, the most active mercury legislation applicable to UV curing systems is the European Commission’s Directive on the Restriction of Hazardous Substances (RoHS). RoHS regulates the use of hazardous substances in electrical and electronic equipment (EEE) as well as the subsequent waste stream of electrical and electronic equipment (WEEE). RoHS applies to all items manufactured for use in the EU and items manufactured elsewhere and imported to the EU. There are currently ten SVHCs that RoHS restricts. One of them is mercury.
There have been two versions of the RoHS Directive as well as several amendments. RoHS was initially legislated in 2003 with RoHS 2 replacing the original in 2011. The categories of EEE covered under RoHS are provided in Annex I of the Directive. Medium-pressure mercury arc lamps are classified in Annex I as Category 5 Lighting Equipment.39 Detailed in Annex III of RoHS 2 are all applications and products exempted from restriction.
Annex III has historically granted mercury UV curing lamps renewable five-year exemptions. The exemption adopted in 2016 was due to expire in 2021 but was renewed through early 2027. During 2026 or early 2027, the European Commission will reassess the state of the UV curing market and the current viability of alternative technologies. A decision will be made whether to renew the broad exemption for UV curing lamps another five years, narrow the exemption for certain applications with proven alternatives or eliminate the exemption altogether.
Regardless of mercury’s exemption status, RoHS contains a scope carve-out that excludes large-scale stationary industrial tools (LSSITs) and large-scale fixed installations (LSFIs). For the UV curing industry, the scope carve-out is widely interpreted to include printing presses, industrial curing chambers and tunnels and converting lines among other industrial and commercial installations. As a result, the use of mercury UV curing systems in most production applications is generally understood to be exempt from RoHS restrictions indefinitely due to scope regardless of any specific ban on mercury UV curing lamps or exemptions listed in Annex III. Spare parts and upgrades to existing UV curing equipment installed prior to any imposed bans are also allowed indefinitely.
United States of America – Environmental Protection Agency
The U.S. Environmental Protection Agency (EPA) was given full authority by the legislative branch of the U.S. government to regulate toxic substances and chemicals through the 2016 Lautenberg Act. Today, the EPA does not ban UVcuring lamps. It is currently focused on identifying where mercury-added products are used domestically as well as the total inventory of mercury in products produced within the U.S. and imported to the U.S. Through ongoing evaluation and data collection, the EPA intends to eventually make recommendations to manufacturers on feasible mercury-free alternatives in order to facilitate a shift away from mercury.
Minamata Convention on Mercury
Another policy making body is the Minamata Convention on Mercury. This is an international treaty that entered into force August 16, 2017 and has been ratified by 139 countries including the United Kingdom, countries belonging to the European Union and the United States. The goal of Minamata is to eliminate all mercury from manufactured goods and processes.
Over the coming decades, regulatory policy will increasingly be driven by this treaty. It is important to note that compliance of international treaties such as Minamata can only be implemented and enforced within territorial borders by the respective ruling government. As a result, mercury legislation has the potential to vary by country and may not always be clear. While Minamata does not presently require a ban of mercury vapour UV curing lamps, it does require all Parties to phase-out or take measures to reduce mercury when possible. In the EU, Minamata compliance will be legislated through RoHS amendments. In the U.S., compliance will be implemented through rules published by the EPA.
The 4th meeting of the Conference of the Parties (COP) for the Minamata Convention on Mercury was held March 21 – 25, 2022 in Indonesia. No new regulations or phase-out timelines were announced for mercury vapour UV curing lamps during the meeting. However, an amendment was passed to end use of mercury dental amalgam in deciduous teeth of children under the age of 15 and in pregnant and breastfeeding women by Dec 2023. Implementation and enforcement of this amendment is the individual responsibility of each of the 139 ratifying parties. The 5th COP meeting is scheduled for October 30 – November 3, 2023 in Switzerland.
Mercury Regulation on Lamp Disposal
Since emissions to air and releases to water from mercury-added products primarily occur during waste disposal, mercury vapour lamps should never be discarded with bulk trash collection. When discarded with general trash, mercury enters the biosphere when lamps are crushed and then incinerated or buried. Fortunately, mercury pollution from UV curing lamps is avoidable by recycling lamps through facilities that ensure lamp components are separated and spent mercury is safely and securely captured. Reclaimed mercury from recycled lamps goes into long-term secure storage or permanent disposal or is processed through established protocols that safely re-introduce elemental mercury into permissible manufacturing channels.
UV LED Curing Systems
A promising mercury-free alternative to arc and microwave curing lamps are UV LED curing systems. Examples of GEW air and water-cooled UV LED curing lampheads are shown in Figure 2. While conventional lamps emit UVC, UVB, UVA, visible and infrared wavelengths, UV LED curing systems emit more intense output over a very narrow range of UVA wavelengths.
Figure 2: UV LED lampheads are available in a range of lengths and form factors and are cooled with either water circulation or forced air.
UV LED technology was introduced to the curing industry in the mid-2000s. Both LED curing systems and applicable chemistry have been evolving ever since. UV curing applications presently able to utilize LED systems include many but not all aspects of digital inkjet, screen, rotary screen, flexo, letterpress, gravure, pad, litho and dry offset printing as well as 3D printing and additive manufacturing. Other applications that are viable for LED include cold foil adhesives, laminating adhesives, cast and cure coatings, and some varnishes. It should be noted that as of mid-2023, there are still no commercially utilized LED formulations for silicone release coatings, hotmelt adhesives, and industrial hardcoats, topcoats, and clearcoats.
As confidence and experience builds and more applications become viable for UV LED, more users and markets will convert. The growing shift to LED is occurring independent of regulatory involvement due to the strong business case and increasing preference of end users for the technology. A more recent driver of UV LED curing adoption is the technology’s ability to mitigate rising energy costs for manufacturers that set inks, coatings, adhesives, and extrusions in production processes.
Conclusion
While there are no laws in the UK, the EU, the US or in any other country worldwide specifically banning mercury UV curing lamps from production, use, export, import or general shipment, the threat of regulation is creating awareness and pressure to expedite change. When change is technically, economically and practically viable for the vast majority of UV curing applications, regulatory policy will hold the market accountable and drive legislative change. Until then, users of UV curing are encouraged to educate themselves on LED technology, install UV LED systems where viable, actively engage in process development and recycle all mercury vapor lamps at end of useful life.
1Pepitone, J. (2007, June 11). Compact Fluorescent Bulbs and Mercury: Reality Check. Popular Mechanics. www.popularmechanics.com/home/reviews/a1733/4217864/
2Restriction of Hazardous Substances in Electrical and Electronic Equipment (RoHS). https://environment.ec.europa.eu/topics/waste-and-recycling/rohs-directive_en
3Frank R. Lautenberg Chemical Safety Act for the 21st Century Act, Public Law 114–182. (2016). Retrieved 2020 December 17, from www.congress.gov/114/plaws/publ182/PLAW-114publ182.pdf
4United States Environmental Protection Agency (U.S. EPA). www.epa.gov/assessing-and-managing-chemicals-under-tsca/frank-r-lautenberg-chemical-safety-21st-century-act
5UN Environment Programme (UNEP). www.unep.org/explore-topics/chemicals-waste/what-we-do/mercury
6Minamata Convention on Mercury. www.mercuryconvention.org
