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Environmentally Aware Printing – Types of Adhesives (continued)

admin — Mon, 15 Mar 2010 21:23:15 +0000

Environmentally Aware Printing – Types of Adhesives (continued) – 16th March 2010
Future work
In the short term in Europe emphasis will be given to approving and commissioning 100% filterable hot melts in order to minimise problems at the mill and maintain/ improve finished product quality. The only product found to meet all the requirements currently is the reactive hot melt already described.

This, of course, does not give us a truly recyclable adhesive but it allows the finished product to be recycled in a ‘safer’ fashion and at the moment this is regarded as a step forward.

Research into the area of dispersible products will continue but this work needs to take a somewhat new direction with the increasing popularity of closed loop systems and restrictive disposal legislation. A water-dispersible product must be 100% dispersed in the pulping system and be carried through to the finished paper with 100% retention on the fibres, without any detrimental effect on paper properties. In fact, the ultimate goal would be to incorporate the adhesive into the paper to give some positive benefit. The adhesive may then be considered totally recyclable. Looking at the alternative definition of recyclable given at the start if this paper, re-use of the adhesive should be investigated; not necessarily as the same adhesive as a binder or filler.

To be continued…

Peter Harrison is Joint Managing Director of The Printing House Ltd, and Print Buying Direct of Crewe, Cheshire, UK.

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Environmentally Aware Printing – Types of Adhesives (continued)
Test methods
Evaluation of the degree of stickie contamination in waste paper stock has been subject of much debate in the past and a vast array of different testing techniques exists and is used. These techniques can be generally divided into four categories:
?   Peel tests – measuring the force required to separate stickies and fibres.
?   Extraction methods – using solvents and a weight determination.
?   Hand sheet inspection methods – visual and instrumental number checks.
?   Tack tests – measuring stickie tackiness and stickie/ fibre bond strength.

Apart from physical examination of stickie entities, their effects on paper properties are also of importance, utilising tests such as strength, ash content, smoothness and density, oil and water absorbency and surface analysis (contact angle/ wettability).

Results from all these tests and others define the quality if the finished product and ultimately determine application areas and value of the product.

Environmentally Aware Printing – Types of Adhesives (continued)

admin — Wed, 10 Mar 2010 21:48:54 +0000

Environmentally Aware Printing – Types of Adhesives (continued) – 11th March 2010
d) Reactive hot melts adhesives

Undoubtedly one of the most likely technologies to have an impact in the replacement of solvent-based products and recyclability in general is that of reactive hot melt adhesives.

Conventional hot melts are made of relatively low molecular weight thermoplastic materials, to ensure melting and application at moderate temperatures. This leads to obvious limitations with heat resistance and strength which can be exploited in the high temperature, high shear repulping process giving rise to small average particle size.

To overcome this, moisture-curing polyurethane hot melts have been developed utilising a cross-linking reaction which raises heat resistance and strength to previously unattainable levels whilst maintaining flexibility and low temperature adhesion. This unusual blend of properties makes this type of product ideal for recycling purposes since the high cohesive strength and excellent flexibility allows the product to remain intact rather than deforming/ breaking down under heat and shear to be forced through screens or shattering as a hard, highly cohesive conventional hot melt might.

Laboratory work on these products suggests that the adhesive does indeed remain as a discrete film and is filtered out completely in the process. These laboratory results have been borne out in typical recycling mills where complete spines of directories/ books have been removed at the first coarse screening stage, with no trace of the adhesive further down the line.

This approach is gaining in mills from a safety viewpoint since there is little or no chance of adhesive contamination in the papermaking process. The technique obviously still involves disposal of the rejected adhesive, probably in landfill, but the amount compared with conventional hot melts is halved.

To be continued…

Peter Harrison is Joint Managing Director of The Printing House Ltd, and Print Buying Direct of Crewe, Cheshire, UK.

NEW: We now sell Large Poster Printing and Banner printing online (A1 Posters, A0 Posters etc) and Banner Stands

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Environmentally Aware Printing – Types of Adhesives – part 3

admin — Sun, 07 Mar 2010 21:32:10 +0000

Environmentally Aware Printing – Types of Adhesives – part 3 – 8th March 2010

3. Hot melts

a) EVA-based hot melts.

Hot melt adhesives based on conventional synthetic polymers such as ethylene vinyl acetate (EVA) represent a potentially significant source of contamination in the recycling process. Such adhesives generally soften and partially disintegrate but do not disperse under the influence of temperature and shear. Contamination can originate from anywhere in the adhesive composition, i.e. polymer, wax, pigment, plasticiser or resin.

These EVA-based hot melts are removed reasonably efficiently by modern mill systems, indeed in some cases relatively soft, low melting point adhesives can be used without problems due to the effectiveness of the screening, cleaning and dispersing systems.

Unfortunately, in many mills which have limited cleaning capacity and/or a high attrition pulping phase, small particles of adhesives can find their way into the high finished product already described. An interesting and somewhat disturbing thought is that less than 1kg of adhesives can totally ruin over 100 tonnes of stock unless adequate precautions are taken.

Acceptability standards for conventional hot melts vary widely in different countries and within different mills. This is related to be varying mill systems and wide range of difficult test employed. Requirements and standards also differ depending on whether paper recycling or board recycling is the issue.

Higher cohesive strength EVA-based hot melts are available which optimise the strength/ flexibility balance in order to maximise filterability and minimise risk of stickie contamination but these will only really be effective in low attrition systems.

b) Acrylic/ pressure sensitive adhesive systems

As previously stated, the term ‘stickies’ was originally used to refer to pressure sensitive adhesives in the papermaking process. In one sense these types of materials have the potential to cause significant problems in that they are likely to be permanently tacky (if they remain intact) and do not need heat reactivation. Having said this, most of the methods described for removal of conventional EVA hot melts can also be applied to pressure sensitive adhesives (PSA), i.e. chemical and/ or mechanical treatment.

Work has shown that if the PSA product has the right balance of cohesive strength and flexibility, then screening is relatively simple, as with EVA based products. Both high-cohesive, cross-linked (by radiation curing) and water-dispersible PSA products have been developed which are potentially beneficial to the recycling process.

Peter Harrison is Joint Managing Director of The Printing House Ltd, and Print Buying Direct of Crewe, Cheshire, UK.

NEW: We now sell Large Poster Printing and Banner printing online (A1 Posters, A0 Posters etc) and Banner Stands

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Environmentally Aware Printing – Dealing with the stickies problem Part 4

admin — Tue, 02 Mar 2010 23:00:51 +0000

Environmentally Aware Printing – Dealing with the stickies problem Part 4 – 3rd March 2010

If removal of stickies by one of the above techniques is not practical or economical then chemical techniques can be utilised. This exploits the chemical differences between stickies and fibres. This can lead to either dispersion of the stickies to a very fine particle of such a size that problems are not evident or passivation of the stickies. This second approach basically de-activates the stickie particles so that they can be incorporated into the finished product undetected.

A wide range of treatments has been researched and is being used for this purpose. Common ones include talc, alum, polypropylene/ polyethylene fibrils, ethoxylated alkylphenols, zirconium, salts, ionic dispersants/ stabilisers and solvents.

In some mills a failsafe mechanism is employed in the form of a high shear, high temperature dispersing unit. The aim of this is to break down any contraries which reach the end of the cycle, into a very small particle size. This facilitates even distribution of finely divided and hopefully undetectable particles throughout the finished product.

Whilst all these techniques are useful in controlling recycling efficiency and product quality, there is a cost involved. Eventual removal and disposal of contraries can also be a costly business. Most recycling mills now build this into their calculations as they ‘Cost of Quality’. The question which remains is ‘Can this cost be minimised or possibly removed by technological development in the adhesives field?’

Peter Harrison is Joint Managing Director of The Printing House Ltd, and Print Buying Direct of Crewe, Cheshire, UK.

NEW: We now sell Large Poster Printing and Banner printing online (A1 Posters, A0 Posters etc) and Banner Stands

Print Buying Direct is the online division and a Trading Name of The Printing House Ltd. One of the UK’s leading quality printing companies for short run, long run and large format colour printing. Based in Crewe, Cheshire (Cheshire Printers), in the North West of England – delivering to customers across the UK and Ireland.

Also see our other websites The Printing House, Print Buying Direct, Prospectus printing, Golf Club Centenary Books

Environmental printers – Environmental Issues and Printing – Introduction

admin — Mon, 21 Dec 2009 09:57:20 +0000

Environmental printers – Environmental Issues and Printing – Introduction

21st December 2009

Environmental issues are becoming more and more important in people eyes, as the effects of an increasing world population, its method of behaviour and in particular its industries, are becoming obvious.

This is affecting printers in two main ways: legislation is increasing – both in extent and strictness – and customers are considering environmental issues when deciding which printer to use, and what materials should be used in the job.

Gone are the days when a print firm can put what it likes down the drain, into the air or onto the local rubbish tip. Gone also are the days when it could annoy local residents with its noise or smell; the Environmental Protection Act of 1990, Local Authority Inspectors and representatives of the Water Authorities will see to that. Fines for transgressions are rocketing, and even imprisonment may face the persistent or deliberate offender.

Customer purchasing power has also started to play its part; increasingly would-be suppliers are being asked to provide company environmental statements or other formal evidence of their commitment to the environment. Some customers are also becoming more knowledgeable about the environmental-friendliness of papers and boards, inks and glues. Many more are confused by the often conflicting stories they hear, or cannot differentiate between what is environmentally important or not. All of them will be looking to printers for information and advice, and the one who can provide it will stand a better chance of getting the custom.

To these two compulsive reasons for action should be added a third- the economic (as well as environmental) benefits to be gained by reducing the quantities of materials and energy used. Paper is generally the largest single slice of company’s costs and even a small reduction in waste can bring considerable bottom-line rewards.

While the printing industry in general is not a larger user of energy, in most firms it is often relatively easy to save some of it. In particular, firms employing flexo, gravure and heat-set web offset processes with their attendant dryers, will benefit from assessing their energy use carefully. The abatement devices necessary to prevent emissions of volatile organic compounds to the air, only now being fitted by some firms, will increase the use of energy, making it even more essential to use the right methods.

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