Addressing the ‘safe’, ‘eco-friendly’ and ‘water wash’ myth in flexographic polymer plate-type printmaking and finding safe working methods
a photopolymer print by Henrik Boegh (Cambodia)
During processing Photopolymer Printing Plates may emit: Vinyl chloride gas / styrene gas / phosgene gas / benzene / acid…
DANGER: This method is suspected to involve undeclared and poorly detectable harmful and carcinogenic emissions! Artists are advised to not use this process without full and adequate protective measures, especially during final plate scrubbing, perhaps working in a chemistry-department type fume hood.
For about twenty years there have been recurring anecdotal suggestions from regular users of photopolymer printing plates (Flexo / Solarplate / Letterpress Photo-polymer Plates with a hard metal or polyester base) who believe they may have got sick from this common plate making process that is popular and widespread in artist’s intaglio and letterpress printmaking, and in the printed packaging flexographic industry (for printing on cardboard boxes).
Despite the anecdotal hazard and sickness reports — and extensive advice from public safety experts — there was little published information about possible exposure mechanisms that could be a likely cause, and the process seems at first glance ‘waterbased’, ‘water-washable’, and of low hazard. But there were early warning signs: Significantly, the flexographic printing industry has long had significant numbers of law suites related to cancer in workers working in flexographic plate making; with vinyl chloride and asbestos poisoning as a likely cause; and some law firms specialize in that area.
NOTE: the dry photopolymer films from the circuit board and IT industry differ greatly from photopolymer plates; the polymer chemistry of dry film is more modern (it is not PVC based, but acrylates based) and has better safety credentials than flexographic plates
Product literature for photopolymer printing plates makes little reference to such hazards, and instead suggests user friendliness because of the ‘water wash’ processing method. In polymer plates artists are using an industrial product that is designed for fully enclosed machine processing (known as closed circuit polymerization) with appropriate extraction systems in the packaging and printing industries.
Professional industrial facilities that process these PVC / Nylon type polymers in the rubber, tire and printing industries have long avoided open tray ‘hand processing’ that involves VOC emissions, and replaced it with fully automated machine processing which is essential for safety. Polymerization chemistry is kept away from the workers.
We strongly advise artists against the regular use of hand processing of any type of photopolymer (flexo-type) plates, unless a full organic respirator and ventilation are consistently employed during all steps of this particularly hazardous and insidious process, which may seem quite safe when it probably isn’t safe if used without full protection!
a photopolymer plate processing machine. the ‘treatment’ section needs to be connected to a fume extraction system that vents to the outside.
Print shops and institutions are advised to purchase professional, fully enclosed, and automated plate processing machines with full extraction systems in order to ensure a safe plate making processes.
In studio tests we found evidence that water wash photopolymer plates may emit significant amounts of poorly detectable VOCs or SVOCs, (semi volatile compounds such as vinyl chloride), as well as possible acid / alkaline vapors all at once, mainly during the final ‘scrubbing’ phase once the plate is in contact with air, following the tray development in water. These fumes are hard to detect but may have a sweet smell which indicates the presence of airborne vinyl chloride or styrene monomer, both of which are known and powerful carcinogens.
photopolymer plate sample products:
Toray
(https://www.printingsystem.toray/products/resolucia/)
Toyobo
(https://en.toyobo-mc.jp/products/printight/)
DuPont
(https://www.markandy.com/supplies/flexo-printing-supplies/flexoplatemaking-and-processing-equipment/)
Speculatively, this may be the exposure mechanism at play: Heavy and semi volatile fumes can concentrate above the plate surface during scrubbing and rinsing, exposing artists to significant amounts of toxins without ever noticing it. Unknowingly, regular users of this popular photo-intaglio plate making process may expose themselves to invisible and cumulative hazardous emissions that may increase the likelihood of ill health or cancers after a few years of working with this method / quick bursts of acid / alkaline emissions during scrubbing may exacerbate the impact of solvent exposure, and create pathways into the body.
Although flexo plate manufacturers do not typically disclose the patented composition of their resins or their plates, — and do not list processing emissions in ssd sheets — it is widely known that some key monomeric components of flexographic plates (from various manufacturers) may be polyvinyl chloride (PVC), and sometimes Nylon, in combination with a small amount of acrylates (for instance MMA or Ethyl Acrylate).
Styrene-butadiene-styrene (SBS) block copolymers are commonly used as a primary binder or a component in the resin formulations for some types of photopolymer flexo printing plates.
SBS is a thermoplastic elastomer that provides the necessary flexibility, elasticity, and mechanical properties required for a flexographic printing plate. The complete photopolymerizable composition typically also includes ethylenically unsaturated monomers, a plasticizer, and a photoinitiator.
Other types of resin chemistry can include:
• Styrene-isoprene-styrene (SIS) block copolymers• Copolymers of butadiene and acrylonitrile• Acrylated polyurethanes & nbsp
NOTE: 1,3-Butadiene: Known carcinogen (EPA) and probable human carcinogen (IARC Group 2A). Exposure linked to leukemia, reproductive/developmental issues in animals, and respiratory irritation.
essentially, flexographic plates and processes typically entail similar toxic hazards and occupational sickness profiles as are common in the car tire industries and synthetic rubber manufacturing
Rubber Printing Plates may be composed of up to 50% PVC
The PVC content in these plates may be at a percentage of up to 50% to provide flexibility as well durability of the UV sensitive printing plate (quoted from: Sun Chemical).
Treatment of Washing Water: Photopolymer Plate Making produces large amounts of monomeric plastics, heavy metals, and solvents that enter the washing out water during processing. Do not discard this effluent down the drain, but use a flocculation method to break down this sludge into safe components that can be filtered and discarded. See page:
POSSIBLE ROUTES OF EXPOSURE
POSSIBLE ROUTES OF EXPOSURE – Key manufacturers of flexographic plates stress the ‘safe’ and environmentally friendly characteristics of their ‘water wash’ plate products. SDS sheets are incomplete and monomeric ingredients are not known due to patents. However, over the decades, there are continuing reports of legal cases from workers, printers and artists who got sick from supposedly ‘safe’ products and processes related to flexographic photopolymer printing. Caution is advised! Protective measures are essential to safely enjoy the benefits of this unique artistic process.
Multiple users of common flexographic plates reported a varying degree of VOC fume emissions that may occur during the final stages of manual plate making. For example, one print studio stresses that completing the polymerization process by re-exposing the plates to UV light is essential to prevent the off-gassing of VOC emissions (Zea Mays Research). As a plate is lifted out of the bath of wash-out water it is exposed to air, and then there appears to be a strong smelling oxidization reaction during scrubbing outside of the bath. (Some users notice this more than others).
It would appear that for safe and best practice users need to be aware of this, and wear a mask with carbon filter (with organic+acid protection!) especially during that final plate making stage until the plate is fully rinsed and dried. Also, good ventilation/extraction would seem essential throughout the process. A dry, warm environment during plate curing (or working in the sun!) will aid polymerization and may prevent excessive release of fumes. Some flexographic plates are known to emit carcinogenic VOCs such as vinyl chloride, formaldehyde, styrene or benzene, but each manufacturer have their own proprietary process, formula and toxicity. Often the plate chemistry is based on a PVC/Nylon mix (over 50%) with acrylate additions. Caution is always advised when using this process, and the cheapest plates are known to be the most hazardous. The flexographic printing industry themselves voice internal concerns over chemical reactions that may occur on the plate emulsion due to oxidization and contact with air.
REACTIVITY EXPLAINED: flexographic plates contain large quantities of monomer which needs to be activated for curing and made light sensitive through a large amount of powerful photo-sensitizing agents.
Types of chemistry used for photopolymers include styrenic polymers, nitrile rubber and acrylated polyurethanes. Vinyl chloride -based plates may contain traces of mercury.
(https://photopolymer.com/printing-plates/flexography)
The most powerful photo initiators used are the highly reactive and dangerous ‘free radical’ type (phosphoryl or fluoride-based; also: benzene derived).
Possible Routes of Exposure during Plate Scrubbing / Wash out, and Example:
The combination of exposure to ambient light, carcinogenic reactive monomers with free radical photo initiators, scrubbing pressure, water and oxygen from ambient air, during the final plate processing stage may create opportunity for the release of highly toxic vapors and mists as the unexposed plate emulsion is scrubbed, stripped away and dissolved; these fumes may be very hard to detect.
The combination of exposure to ambient light, carcinogenic reactive monomers with free radical photo initiators, scrubbing pressure, water and oxygen from ambient air, during the final plate processing stage may create opportunity for the release of highly toxic vapors and mists as the unexposed plate emulsion is scrubbed, stripped away and dissolved; these fumes may be very hard to detect.
Also of interest may be the fact that industry sometimes employs ‘photoacid generators’ (PAGs) embedded in the photopolymer that may become active as an emulsion stripping agent during the final stage of processing. Only experts know the exact mechanics and hazards connected to this highly complex chemistry, and formulations change frequently. Caution!
3 HAZARDS IDENTIFICATION (from an older sds sheet): Most Important Hazards Eye contact or skin contact with the material may cause some irritation.
Dermatitis may occur in some serious case.
The material contains small amount of hazardous ingredients or the ingredients of insufficient investigation of hazards.
Inflammable with the existence of ignition sources
Specific Hazards Prolonged inhalation of fumes or gases generated from the material during the processing operations may cause headache, respiratory irritation. Main Symptoms Dizziness, Headache, Irritation to eyes and skin
always check current SDS information prior to use, or consult with a chemist or industrial hygienist. See below for professional plate processing equipment with extraction.