Cette série de Questions-Réponses est basée sur les interrogations les plus fréquentes de nos clients. Nous vous livrons les réponses de Paul Machin en Anglais.

Q1.  Paul, some of the topics related to solvent inks are undoubtedly complex, so can you first ease our readers into things by telling us a little bit about how solvent inks actually work, and why certain solvent inks require coated media whilst others can print on a wide range of uncoated substrates.

A1.  In simple terms solvents are present in inks for three primary reasons. Firstly, they are needed to dissolve the film former (resin) in the ink. This is the material that is required to coat the colourants in the ink. Without the resin, the ink would be like a powder and would rub off any substrate that was printed. Different solvent types are required to dissolve the film formers. Different film formers are required depending on the substrate to be printed. A 'strong' or 'active' solvent is necessary to dissolve acrylic or PVC resins, for example a ketone such as cyclohexanone.

Secondly, the choice of solvent can control the speed of drying. Obviously fast evaporating solvents dry much quicker than slower evaporating solvents.

Thirdly, solvents can provide the key to the substrate. Adhesion to porous substrates such as paper and board is obtained by the ink soaking into the substrate. Where a non-porous substrate such as PVC or an acrylic is printed, the solvent in the ink will take an active role by dissolving the surface of the substrate. If 'passive' solvents are used on difficult substrates the ink will 'sit' on the surface and can easily be removed by scratching or gently wiping with a weak solvent such as iso-propanol alcohol (IPA). These 'passive' or weak solvents are frequently lower in odour and often are considered as being eco-solvents.

Q2.  You say 'considered as being eco-solvents', there seems to be some confusion in the market about both the legality of this term, and what it actually means, some say economical, some say environmentally friendly, what is your understanding of eco-solvent?

A2.  If an eco-solvent is perceived as being economical, that may well be the case. Passive solvents are frequently cheaper to buy than active solvents, for example aromatic hydrocarbons are substantially cheaper than ketones. Therefore since the solvent is the major constituent of the ink then the ink itself should be less expensive.
If an eco-solvent is claimed to be environmentally friendly, then I must disagree. All active solvents are harmful to the environment in some way. They have an adverse impact on the atmosphere. They have a harmful effect when discharged to the sewer. They pose major problems with disposal to land-fill. So yes, it is in fact illegal to call a solvent ink eco-friendly.

Q3.  Our own CitroSOL inks contain organic colourants, organic solvents and have been developed to ensure they are 100% free of both cyclohexanone and isophorone. There have been many adverse comments posted recently about the use of these particular chemicals in solvent inks, can you please explain what these chemicals are, why they are used and what the health and safety implications are.

A3.  Cyclohexanone and isophorone belong to the ketone group of solvents. They are frequently used because they have excellent solvency to most plastics. Both solvents have very low occupational exposure levels: isophorone 5 parts per million, cyclohexanone 10 parts per million, for an eight hour working day as they affect the respiratory system. There is some evidence that isophorone has a limited carcinogenic effect. This means that the working environment where such solvents are used will have to be controlled. This usually means localised extraction and monitoring of the atmosphere to ensure that the concentrations are not exceeded. The use of cyclohexanone is now subject to biological monitoring, i.e. blood measurements.

Q4.  There has been much speculation of late about pending legislation. When will this new legislation come into force, and what does it mean to users at different levels, for example the commercial grand format user, the high street sign shop with a wide format solvent printer, and perhaps even a user of a small solvent printer in home or office environment.

A4.  There are a number of new pieces of legislation that affect the digital printer. It has to be said at the outset that monitoring by the authorities of the compliance to this and other legislation is more likely to affect the grand format 'industrial-sized' printer than the smaller printer in the home or office. However, some of this legislation will still apply. There are three main areas of concern; pollution of the atmosphere, providing a safe working environment and correct disposal of waste.
Pollution of the environment is generally caused by the release of solvent in the atmosphere. A grand format printer can release substantial quantities and the new Government Guidance (PG6/16) applies from April 2004 and relates to all forms of printing including digital.

The provision of a safe working environment is essential. If there are 5 or more people at your place of work the enforcing authority is the Health and Safety Executive (HSE) otherwise it will be the Local Authority. There are a number of crucial issues that the HSE will be looking at if they visit your site. Have you undertaken the necessary risk assessments? Has your Control of Substances Hazardous to Health (COSHH) assessment been completed? The latter subject involves careful examination of the products you are using especially if it involves solvent based inks.

There is new legislation currently being developed to cover the safe disposal of hazardous materials. All inks, solvents, dirty ink tins and contaminated wipes are considered as being hazardous waste. The correct disposal of these materials is the responsibility of the digital printer.

Q5.  Can you tell us how stringently these regulations will be enforced, and what penalties, if any, might be incurred?

A5.  As with most breaches of the regulations, you are OK until you get caught. The HSE or Local Authority inspector has considerable discretion. If you have done nothing, this will be taken into consideration with the likelihood that the offence will be punished and that will probably include a fine. If you have attempted to undertake the necessary actions to comply, it is highly probable that the inspector will merely send you a warning by letter. The penalties can range dramatically. HSE inspectors have more powers than the police. They can enter your premises at anytime without your permission. They could, in some circumstances, put a lock and chain on your gate and forbid you from entering. The trite expression “Ignorance of the law is no defence” certainly applies.

Q6.  Paul, you mentioned previously about health and safety issues related to using solvent inks. To some this might seem quite scary, to round things off for this article could you relate these health and safety issues to a benchmark that we already know, such as use of household detergents and cleaning materials.

A6.  Every chemical should be treated with respect whether it is a household detergent, bleach, gloss paint or solvent based digital inks. The basic principle to remember is that we, as humans, are made solely from chemicals. Therefore, if a chemical will react with another chemical, such as a bleach killing germs in the toilet, it will react on humans as well.

The answer is simple. Provide a control mechanism to avoid unnecessary contact with the chemicals. Most ladies who undertake the washing-up will automatically put on rubber gloves. This will stop the household detergent from removing the natural protective skin oils. Failure to stop the removal will lead to dry skin and subsequently dermatitis.
The necessary control mechanisms for handling solvent based digital inks are; gloves to avoid skin contact, glasses to stop splashes getting into the eyes and extraction for removing the solvent fumes when large format prints are being generated. What is different from what goes on in the kitchen? In reality very little!