The attitude of ink makers varies when the subject of environmentally friendly inks is raised – from ‘boring’ to ‘it’s the basis of our entire company’s activity’. The response tends to depend on the degree to which the ink maker is involved in the mainland European market. Those with overseas connections report that there is a lot more interest in environmentally friendly inks by printers in Northern continental Europe than in the UK. The question that needs to be asked is: what exactly does ‘environmentally friendly’ mean?
The starting point with sheet-fed litho inks is that they are traditionally the most environmentally friendly class of inks. The varnish is made up of resins dissolved in a mixture of vegetable oil and petroleum distillate. The resins most commonly used in conventional sheet-fed litho inks are produced by chemical modification of naturally occurring resins and vegetable oils. They are renewal resources and as environmentally friendly as is expected.
Petroleum Distillates
The area of most attention is the petroleum distillate content which can be up to 35-40% of an average ink (most of which is in the varnish). It is argued that this is a non-renewable raw material and is potentially a VOC (volatile organic compound) that can have an adverse effect on the atmosphere. The amount of feed stocks, in the form of petroleum distillate, used in sheet-fed litho inks is so tiny by comparison to that consumed by cars and other transport vehicles that non-renewability is a weak argument for change. The other suggestion is that the distillate represents a potential VOC. In fact, the distillates used have boiling ranges of 260-320C, are not defined as VOCs in legislation and are absorbed into the body of the paper not evaporated into the atmosphere.
Vegetable Oil Based Inks
Nevertheless, the trend is to reduce the petroleum distillate content and replace it with vegetable oil. This change first became possible as a result of developments in resin technology that allow the proportion of vegetable oil to be increased without detriment to the performance properties of the ink. Fully vegetable oil based inks are available and have been for many years for use on non-absorbent substrates and as laser proof inks for business stationery. Unfortunately, fully vegetable oil based inks are generally too slow for most modern high speed litho presses. The interesting exception is the four-back-four multicolour presses.
These presses require an ink that sets at exactly the right speed. If it sets too slowly there will be a transfer of wet ink from the first side printed to the blankets of the second four colours. If the ink sets too fast, the tack rise that takes place during setting will cause transfer of semi-dried ink to the blankets of the second four colours. It happens that fully vegetable oil based inks can give just the right speed of setting as well as being environmentally friendly.
Most of the vegetable oil inks are based on vegetable oil esters rather than the original vegetable oil. Vegetable oil esters are manufactured from by-products of a chemical reaction that is carried out on vegetable oils to produce glycerol. These by-products are subsequently reacted with alcohol to produce the esters. They are of lower viscosity and more powerful solvents than the original vegetable oils so that they overcome the problems described above for traditional inks. As a result, an increasing proportion of sheet-fed litho inks are free from petroleum distillates. As the use of colour has increased in newspapers, the quality of inks has increased with the move towards vegetable oil based inks and the development of inks with much higher colour strength. Most success has been achieved with newspaper colours. Apart from potential environmental benefits, there are technical advantages of better litho properties such as: cleaner printing, brighter colours, sharper printing, better transference and better mileage. Rub resistance is also improved and although there is some argument about the degree there is no significant side-effect on de-inking. However, this trend has been reversed more recently, even in the USA, as problems have been encountered with speed of drying on some grades of newsprint.