Printing
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Printing processes
Lithography
Printing processes, including inks and coatings, contribute to the discharge of volatile organic compounds (VOCs) and other chemical pollutants into our environment. The advent of digital technology has minimized some of this through use of computer to plate (ctp) printing and digital proofing. A re-focus on disposal and re-use of materials and elimination or reduction of solvents can also reduce the overall negative environmental impacts.
Offset Lithography is the most common printing practice in Australia. It uses a single metal plate where the image and non-image areas are on the same plane. The non-image or non-printing area is hydrophilic which means that it does not absorb the ink. A dampening solution- a mixture of water and isopropyl alcohol- is used to help the non-image area repel the ink. The image area comprises of an outline to be printed that is hydrophobic which means that it readily absorbs the ink. The image area carrying the ink is offset to a rubber covered blanket cylinder that places the image on the substrate.
Two types of inks are used in lithographic printing, heatset and non-heatset. Heat-set inks are set by hot air or a direct flame dryer evaporating the solvent. Non-heat set inks dry under ambient conditions through oxidation and polymerisation. Both types of inks are composed of high boiling point (150 degrees celsius) petroleum oils. In heat-set inks the high temperature of the dryers evaporates the majority of the solvent, leaving only to 2 - 40 per cent of the solvent in the substrate.(EA 1999)
The substrate can be either web - a continuous roll that is fed into the press and later cut up - or sheet where single sheets are fed in one at a time. Both heat-set inks and non-heat set inks can be used with a web substrate. A sheet substrate can only use non heat-set inks. The standard dampening solution in web fed lithography is 15- 30 per cent isopropyl alcohol, while the sheet fed method is 5 - 20 per cent.
Offset lithographic printers use cleaning solutions to clean the press and machine parts. These traditionally contain 90 - 100 per cent solvent.
Waterless Printing
Waterless printing is an offset lithographic process that eliminates the water or dampening solution. The printing plate is silicone rubber coated and attracts ink to the image area through a means of temperature control on the press. The process is faster and cleaner than traditional offset lithography. There is a reduction in paper waste and energy usage through reduced press time. Waterless printing is very effective at printing on uncoated papers, compared to offset lithography, which can result in a dull, blurry image. The elimination of water means the ink sits on top of the paper, giving a crisp image with vibrant colour. Waterless printing can use both web and sheet fed paper.
Solvents
Solvents are a major source of air emissions from printers due to their volatile nature. Solvents are commonly used by printers in the inks, cleaning solutions, dampening solutions and in the film and plate processing chemicals. The most significant contributor to a printer's Volatile Organic Compound (VOC) emissions are the type of inks used on the press. (Evans 1997)
Some solvents used in the printing process and their environmental effects:
- Acetone is used as a solvent in inks. It is toxic to animal and plant life.
- Toluene is used in cleaning solutions. It contributes to the formation of ozone.
- Methyl Ethyl Ketone is used as a solvent for lacquers, adhesives and inks. It is toxic to aquatic life.
- Isopropanol is used in dampening solutions. It is toxic to aquatic life. (PIAA 2000)
Volatile Organic Compounds
Volatile Organic Compounds (VOCs) is a general term that includes all organic compounds (substances made up of predominantly carbon and hydrogen) with boiling temperatures in the range of 50-260 degrees celsius; they are likely to be present as a vapour or gas in normal ambient temperatures. The term VOC generally refers to the presence of these substances as their gaseous form in polluted air. (National Pollutant Inventory Database)
Environmental Impacts
Once released in the environment VOCs react with oxides of nitrogen to produce ozone and other compounds. The most significant environmental impact of VOCs are their formation with vehicle exhaust to form photochemical smog. In its liquid form VOCs can effect water and soil quality. (Some VOCs are known to cause cancer in animals and some are suspected or known to cause cancer in humans. Build up of VOCs in indoor environments have been known to cause sick building syndrome.) (National Pollutant Inventory Database)
To reduce the overall emissions of VOCs from printing all solvent use should be minimised and substituted with other less volatile products wherever possible. Where VOC emissions are unavoidable there are a number of techniques used to prevent the VOC emissions entering our environment. These include thermal incineration (straight afterburning), catalytic incineration (afterburning at a lower temperature using a catalyst) and activated carbon absorption, where the solvent is recovered using a bed of activated carbon. This technology is normally only found in large-scale printers. (Earth Design Environment)
Inks
Printing inks have three major components:
pigments, made up organic and inorganic materials which produce the desired colour;
- a liquid vehicle which carries the pigment and evaporates on drying;
- and binders that assist the pigment locking to the substrate, which are usually composed of organic resins and polymers.
The release of VOCs from solvent based inks and the toxic nature of some heavy metals in the pigments are key environmental considerations. (Evans 1997)
The list below outlines different types of inks.
Water based inks
Printing inks can be either water based or petroleum and alcohol based. Water based inks are the most environmentally friendly option because when the water vehicle evaporates no VOC's are emitted. Gravure, flexography and screen-printing can sometimes use water-based inks, depending on the substrate. Some substrates such as plastic and glass and some types of coated papers will not allow a water-based ink to effectively bind with the substrate, thus reducing the quality of the print.
Petroleum based inks
The most commonly used inks are petroleum based, because of their quick drying time and binding nature to the substrate. The pigment is suspended in petroleum and the solvents are composed of alcohol. As the ink dries, alcohol and petroleum evaporate and VOCs are released. Petroleum based inks can emit upwards of 30 per cent VOCs.
Vegetable based inks
A popular alternative to petroleum based inks are vegetable based inks. These can be made from a variety of vegetable oils including corn, walnut, coconut, linseed, canola and soy-bean oils. There are many advantages to using vegetable based oils from both an environmental and technical design perspective.
Replacing petroleum oil with vegetable oil in printing inks utilises a renewable resource and helps conserve finite petroleum supplies. It reduces emissions from >30%VOC to as low as 2 - 4% VOCs. The printing press can be cleaned with a water-based cleaner, replacing a high solvent cleaner and further reducing VOC emissions. The printed product is easier to deink in the recycling process and results in a less hazardous sludge. (Evans 1997)
Vegetable based inks can be cleaner and brighter, and more rub resistant than petroleum inks. They are well suited to uncoated and recycled stocks because the ink doesn't spread as much. They do not cost more than petroleum based inks.
Disadvantages to using vegetable based inks are their slower drying time, particularly on uncoated paper. Pure formulation vegetable based inks cannot be used in heat-set ink processes. To achieve appropriate drying times for these processes, vegetable oil may only replace a portion of the petroleum oil. If no petroleum oil were used the print shop would increase their energy use heating and drying the ink, thus counteracting the environmental benefits of using vegetable based inks. (Minnesota Environmental Initiative)
Discuss with your printer what percentage of VOCs are emitted from the ink they use when it dries, and how this compares to other inks that are available. The amount of VOCs emitted will depend on the type of printing, ie. sheet fed or web fed. Ask for the lowest VOC content possible. Sheet fed inks should have a 1/2% to 1% content while web set inks are much higher around 18%. (Eco Online)
Toxic Colours
Metallic and fluorescent ink
Pigments create the colour in ink. Some contain metallic substances, which can be harmful to the environment and animal life, and have the potential to harm human life if ingested, inhaled or absorbed. Ink with metallic pigments will eventually enter landfill, leaching potentially toxic compounds to the water table.
Avoid using metallic and fluorescent colours as well as inks with added antimony, arsenic, barium, cadmium, chromium, lead or mercury. Alternative pigments are sometimes available which can closely match the colour you want without using heavy metals. (Minnessota Environmental Initiative)
Environmental Management of inks
Inks are expensive and can impact on our environment and health to varying degrees. Any opportunity to reduce ink usage and waste will help save money and reduce environmental impacts.
Minimising solid ink coverage, and the numbers of colours you use is a simple and effective way of reducing the environmental impacts of your job.
Dampening solution
Offset lithography utilises a dampening solution containing high levels of a solvent called isopropyl alcohol (IPA) which contributes to VOC emissions. There are dampening solutions available which are low content IPA or IPA free, such as ethylene glycol, glycol or cellusolve ethers. These alternatives can reduce the VOC emissions from dampening solutions by up to 99 per cent. Converting to a low content or IPA free dampening solution may require some operational adjustments by a printer, however this extra cost can be offset in the future by reducing the need for pollution control equipment. (PIAA 2000)
Waterless printing is an offset lithographic process that has eliminated the use of a dampening solution altogether. This results in a reduction in the overall amount of VOCs emitted in the printing process, in comparison to a lithographic printer running an IPA dampening solution.
Paper waste
The quantities of paper can be reduced by improving work practices on the press and reducing the amount of make ready (bringing job up to a high print standard) paper waste. Different printing processes operate at different speeds, with different accuracy. Generally the slower and more precise the press, the less paper waste there is.
Coatings
Coatings are available to heighten a gloss or matt finish and to protect the surface of a printed product from scuffs, scratches and fingerprints. When deciding if a coating should be used it is important to consider the application of your printed piece, its required durability and life span. The stock you are selecting will also determine if a coating is required. For many stocks, particularly uncoated papers, printing ink alone will be sufficient. It is best to discuss this with your printer.
If you decide that your job requires a coating there a different types available which impact on the environment to varying degrees.
Press Applied Varnish:
This type of varnish is applied on the press, like an extra ink colour, in both matt and gloss finishes. It can be set up to cover the entire printing area, or as a spot varnish in a particular area of the print.
Press applied varnish is typically solvent based and thus emits VOCs. These emissions can be reduced by selecting a press applied varnish in a vegetable based formulation, or by selecting an aqueous / water based vanish.
Aqueous Varnish:
Aqueous varnish is a mixture of polymers and water, available in a high gloss and matt finish that is applied on press with special equipment. It is often the most economical and environmentally preferable coating choice. It emits fewer VOCs on press and clean up does not require solvent based / toxic cleaning detergents nor high temperatures. Paper with an aqueous varnish can be recycled and re-pulped, without emitting any harmful by-products in the process. (Minnessota Environmental Initiative)
'Some aqueous varnishes contain a catalyst that allows the varnish to dry quickly without curing.' Avoid using these catalytic cures water based coatings because formaldehyde is emitted in this process. (Evans 1997; Minnessota Environmental Initiative)
UV cured varnish:
Ultraviolet cured coatings produce the most durable and glossy finish of all the varnishes. The varnish is applied with roller coaters or by screen printing and is cured through a tunnel that emanates ultraviolet radiation. (Evans 1997) The process is high in energy due to the UV lamps and air conditioners and strict environmental, health and safety measures must be maintained for the process to be safe for workers. A printed product with UV cured varnish will be non-deinkable and non-recyclable by most recyclers, and will ultimately end up in landfill, where it will take a long time to break down.
Post press finishes
After printing there are a range of standard post press operations that take your job from a sheet to a finished product. These can include folding, collating, guillotining, stitching, perfect binding, padding, creasing, drilling, packing and assembly. There are some extra post-press options available, such as embossing, thermography, foil stamping and die cutting that may be used as an added marketing element. If you are considering using one of these it is important to understand their environmental implications.
Embossing
Embossing is the creation of a raised image on paper. A die of the image to be embossed is usually made out of zinc, brass or copper and pressed into the paper. It works beautifully on uncoated paper and is more pronounced on heavier sheet weights. Embossing is a good environmental imprinting alternative because the process uses no chemicals or inks and the die can be stored and reused for other applications. (Evans 1997)
Thermography
Thermography creates a raised dull or glossy image on paper. It involves coating a slow drying rubber or oil based ink with resinous powder while it is still wet. The sheet is passed through a heat tunnel and the powder melts and fuses with the ink, resulting in a raised image. The heat tunnel in thermography requires a large amount of energy to maintain the high temperature. The heat set resins on paper printed with thermography are not easily recycled, and if they undergo de-inking, they contribute highly to the formation of toxic sludge. (Evans 1997)
Foil Stamping
Foil stamping imprints paper with a coating of polyester film that is usually shiny and metallic looking. A metal die of the image to be imprinted is created out of zinc, brass or copper and pressed onto the paper. This process does not involve many resources or toxic chemicals and the die can be reused. However, paper with foil stamping is virtually non-recyclable, because the polyester film is almost impossible to remove from the pulp. (Evans 1997)
Die Cutting
Die cutting involves cutting a specific shape or image into paper. A die is manufactured from zinc, brass or copper and acts a 'cookie cutter'. Die cutting is a relatively environmentally friendly imprinting option because it uses no chemicals or inks and the die can be reused. The trimmed paper that is often treated as waste, can potentially be designed as an extra design element. (Evans 1997)
Adhesives for binding and labels
The glue used in binding is often a petroleum based rubber glue that emits high amounts of VOCs and is difficult to remove in the de-inking process. Water based glues that emit no VOCs and dissolve in the de-inking process during recycling are available.
Printing checklist
For the most eco-friendly printing options:
- check that the printer has an environmental management system in place
- check the VOC emission ratings from the printing process - inks, coatings, cleaning solutions, dampening solutions, glues - select minimal or no VOC emissions where possible
- check that the printer can do digital to plate printing - eliminating film
- choose vegetable inks with uncoated paper where possible
- avoid metallic and fluorescent inks as these contain heavy metals
- choose aqueous varnish over UV coatings and plastic laminates
- choose water based glues
- check how the printer recycles and separates solid waste - paper off-cuts, cardboard, printing plates, ink containers, cleaning rags, palettes, screens and metals
References
EA (1999) Emissions Estimation Technique Manual for Aggregated Emissions from Printing and Graphic Arts Environment Australia
Evans, P. (1997) The Complete Guide to Eco-friendly Design North Light Books, Ohio, USA
PIAA (2000) Environmental Management Manual Printing Industry Association of Australia, Dames & Moore, VIC, Australia
National Pollutant Inventory Database
Earth Design, Environment
Minnessota Environmental Initiative, Environmental Policy Print Buyer Guide
Eco Online, Ten Ideas for Environmentally Sound Print Production
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