Cost-effective paint and powdercoating: coating materials

GG

386

This Good Practice Guide was produced by

Envirowise

Prepared with assistance from:

Enviros Consulting LtdMcLellan and Partners Ltd

Cost-effective paint and powdercoating: coating materials

Summary

This Good Practice Guide is one of four complementary guides providing advice on cost-effective paint and powder coating. It is aimed at paintshop and production managerswhose operations use paint and powder coating materials, as well as organic solvents.

Certain organic solvents, also known as volatile organic compounds (VOCs), can give rise toemissions which contribute to low-level air pollution and directly to global warming.

The Guide explains how a company can reduce its costs and VOC emissions by changing fromconventional coatings to coatings that apply the same coating load with less solvent. Manycompanies are now switching to low solvent content coatings rather than fit expensive VOCabatement equipment to their processes.

Alternative coatings containing less organic solvent, and hence VOCs, include:

■ water-based paints;

■ high solids paints;

■ powder coatings;

■ organic solvent-free liquid coatings.

The factors to be taken into account when switching to an alternative coating system and whatconstitutes good practice for drying/stoving are also considered in this Guide. Industry examplesillustrate the cost savings and other benefits that can be achieved by switching to low solventcontent coating systems.

This Guide highlights ideas that will:

■ save money;

■ save time;

■ use less paint and solvent.

Reducing VOC emissions through the use of low solvent content or solvent-free coating systemsmay help some companies increase capacity without needing a regulatory permit to operateunder Local Authority Integrated Pollution Prevention and Control (LA-IPPC) or Local Air PollutionPrevention and Control (LAPPC). Use of these coatings will also help companies that areregulated to meet their obligations under LA-IPPC or LAPPC in a cost-effective manner.

There are a decision chart and an action plan at the end of this Guide to help you focus on theareas that are most relevant to your company.

The other guides in the series cover materials management, surface cleaning and preparation,and application technology. All are available free of charge through the Environment and EnergyHelpline on freephone 0800 585794 or via the Envirowise website (www.envirowise.gov.uk).

This Guide builds upon GG52, first printed in 1997, and contains up-to-date legislation andindustry examples.

Contents

Section Page

1 Introduction 1

2 Regulatory requirements 22.1 Pollution prevention and control regulations 22.2 Part II of the Environmental Protection Act 1990 32.3 Special waste regulations 32.4 Solvent reduction scheme 42.5 Compliant coatings 42.6 Solvent management plan 4

3 Paint systems 53.1 Conventional paints 53.2 Two-pack paints (2K) 53.3 High solids paints 53.4 Water-based paints 63.5 Powder coatings 73.6 Electrodeposited paints 83.7 Autodeposited paints 93.8 Ultraviolet and electron beam cured coatings 93.9 Novel systems containing supercritical carbon dioxide 9

4 Considerations when changing coating systems 114.1 Coating thickness 114.2 Reducing VOC emissions 12

5 Waste/solvent recovery 135.1 The cost of waste disposal 135.2 On-site recovery 13

6 Abatement systems 156.1 Particulate abatement 156.2 VOC abatement 16

7 Drying/curing 177.1 Air drying 177.2 Stoving ovens 177.3 Infrared stoving 187.4 Ultraviolet and electron beam curing 18

8 Decision chart and action plan 20

9 Sources of further information 229.1 Trade associations 229.2 Materials suppliers 229.3 Other sources 22

Appendix Legislative controls and reduction of emissions 23

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Introduction

The four complementary guides to cost-effective paint and powder coating in thisseries are:

Cost-effective paint and powder coating: materials management (GG385)

Cost-effective paint and powder coating: coating materials (GG386)

Cost-effective paint and powder coating: application technology (GG387)

Surface cleaning and preparation: choosing the best option (GG354)

These guides and other Envirowise publications mentioned herein are available free of chargethrough the Environment and Energy Helpline on freephone 0800 585794 or via the Envirowisewebsite (www.envirowise.gov.uk).

These guides are intended to help a range of companies, including:

■ metal finishers;

■ fabricators;

■ component and assembly manufacturers for original equipment manufacturers;

■ original equipment manufacturers.

The guides are applicable to companies using paints and powders to coat in:

■ predominantly manual operations, eg degreasing baths and hand-spraybooths;

■ partially automated operations;

■ fully automated operations.

The CD-ROM Paint for profit (IT394) is designed to helpcompanies in the vehicle body repair industry reduce wasteand costs while increasing competitiveness. It provides waysof reviewing the amount of paint and solvent used, help withmeeting the legal requirements for handling solvents and thelatest tips and techniques for managing and handlingmaterials.

The booklet Finishing with a profit (EN359) contains practicaland simple ideas to help small metal finishing and surfaceengineering companies save money by reducing the waste ofchemicals, water and energy. Ideas on how to reduce wastein vapour degreasing, paint and powder processing, thermalspraying, galvanizing and heat treatment are presented andsources of more detailed information are signposted.

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Regulatory requirements

Organic solvents are widely used in UK industry for a range of processes. In the metalcoating industry, trichloroethylene can be used for cleaning and a range of organicsolvents including xylene, white spirit and butyl acetate may be part of the paintformulation, or used for thinning.

These, and other organic solvents, give rise to volatile organic compound (VOC) vapours. Currently,levels of these VOCs in the atmosphere are a subject of widespread concern and regulation. This isprimarily because of their role in the formation of low-level air pollution affecting human health,crops and natural vegetation, but also because they contribute to global warming.

The EC Solvent Emissions Directive was implemented by the Pollution Prevention and Control(Solvent Emissions Directive) (England and Wales) Direction 2002, placing strict controls on VOCemissions from industry and defining emission limit values for new and existing installations.

2.1 Pollution prevention and control regulations

Paint and powder coating processes are regulated under the Pollution Prevention and Control(PPC) Regulations. The processes described in this series of guides are included under Section 6.4of the Regulations and fall within Part A(2) for Local Authority Integrated Pollution Prevention andControl (LA-IPPC), or Part B for Local Air Pollution Prevention and Control (LAPPC). Operators ofprescribed processes must submit a detailed application for a permit to operate under LocalAuthority Air Pollution Control (LAAPC).

Plants with a consumption capacity of more than 150 kg/hour or more than 200 tonnes/year ofcoating substances containing organic solvents fall within Part A(2).

Unless falling within Part A(2), processes for applying to a substrate in any period of 12 months,20 tonnes or more of paint or other coating materials which are applied in solid form, or using 5 tonnes or more of organic solvents, fall within Part B. Lower thresholds apply to activitiesinvolving the repainting or respraying of road vehicles. The quantity of organic solvents includesthat used in pretreatment (surface cleaning) processes.

All regulated coating activities must either comply with the emission limits, or alternatively usethe Solvent Reduction Scheme, as specified in the latest revision of the appropriate ProcessGuidance Note (given in the appendix). Regulated coating activities must comply fully with therequirements of the Solvent Emissions Directive by 31 October 2007.

There are transitional arrangements for existing installations, which are authorised as Part Bprocesses under the Local Air Pollution Control (LAPC) regime.

Advice about LA-IPPC, LAPPC and other legislation governing your operation is available fromthe Environment and Energy Helpline on freephone 0800 585794.

Even if your company does not use enough solvent to be regulated under the PPC Regulations,using good practice will still enable you to achieve significant cost savings. Companiesapproaching the relevant threshold may also be able to postpone or avoid regulation underLAPPC, by improving their operating practices.

The use of solvent-based coating materials, whatever the application method, gives rise topollution and waste. This is due to the organic solvent content of the paint, which has toevaporate to cure the coat.

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Although this waste is almost inevitable, being an inherent and desirable part of the process,organic solvent losses to atmosphere can be minimised - or even eliminated - by changing tomodern coating systems.

Most coating manufacturers now offer low solvent content or solvent-free systems for a widerange of industrial applications. Changing from conventional to modern coatings could helpyour company to:

■ reduce its material consumption;

■ improve production capacity or efficiency through the reduced time needed to applyalternative coatings;

■ save money and time by avoiding the need to apply for a permit to operate under LAPPC;

■ improve the health and safety of employees;

■ reduce its impact on the environment;

■ cost-effectively meet regulatory requirements.

Alternatively, operators can fit VOC abatement systems and continue to use solvent-based paints.However, this approach to regulatory compliance represents an additional cost in the form of capitalinvestment and ‘end-of-pipe’ operating costs. Most coating companies operating under LAPPC aretending to switch to other types of coating, rather than fit abatement equipment to their processes.

It may also be possible to avoid regulation under LAPPC by using more efficient applicationmethods to reduce consumption of solvents.

Cost-effective paint and powder coating: materials management (GG385) gives practical adviceon how to reduce paint and solvent consumption during coating operations.

Cost-effective paint and powder coating: application technology (GG387) gives practical adviceon how to reduce paint and solvent consumption during coating operations, with an emphasison the equipment used.

Surface cleaning and preparation: choosing the best option (GG354) describes how surfaceengineering companies can reduce operating costs, VOC emissions, solvent consumption andwaste by improving the management of their pretreatment and surface cleaning processes. Itexplains how to choose the most appropriate cleaning method to optimise performance and tocomply with key environmental, health and safety legislation such as the Solvents EmissionDirective. Good practice for mechanical, organic solvent, aqueous and biological cleaning isdescribed and a matrix to help companies evaluate alternative cleaning options is presented. TheGuide stresses the importance of adopting good practice and improving solvent managementbefore investing in alternative cleaning systems.

2.2 Part II of the Environmental Protection Act 1990

Part II of the Environmental Protection Act deals with waste on land. The Environmental Protection(Duty of Care) Regulations 1991 (SI 1991 No 2839) impose a Duty of Care on waste producers toensure that their wastes are correctly disposed of. A company is expected to ensure that:

■ any waste transported off-site is labelled adequately;

■ the waste is transported by a licensed carrier;

■ the waste is transferred to a suitably licensed transfer station or waste disposal site.

2.3 Special waste regulations

The Special Waste Regulations (SI 1996 No 9727) present the criteria for what constitutes aspecial waste and describe how the disposal of that waste is to be controlled. VOC or

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solvent-containing wastes are usually classified as special wastes due to their toxicity and/orflammability. Transport of special waste requires pre-notification to the Environment Agency. TheSpecial Waste (Amendment) (England and Wales) Regulations 2001 (SI 2001 No 3148) amendand update the 1996 Regulations.

2.4 Solvent reduction scheme

Installations subject to the PPC Regulations and the Solvent Emissions Directive have the optionof either complying with the VOC Emission Limits and Fugitive Emission Values specified in theappropriate Process Guidance Note or using the Solvent Reduction Scheme. The aim of theSolvent Reduction Scheme is to reduce emissions to a ‘Target Emission’ equivalent to that whichwould have been achieved if the specified emission limits had been applied. Note that theemission limits for those VOCs carrying risk phrases (such as trichloroethylene) are mandatory.

The operator choosing the Solvent Reduction Scheme prepares an Emission Reduction Planwhich might include the use of:

■ water-based paints (low organic solvent content);

■ high solids paints;

■ powder coatings;

■ organic solvent-free coatings;

■ more efficient application methods (see GG387).

The Target Emission is calculated from the total mass of solids in the coating materials consumed.This information is available from your coatings supplier.

Target emission values, which will be reduced in stages up to 2007, are given in the ProcessGuidance Notes.

2.5 Compliant coatings

The concept of compliant coatings was introduced under the LAPC regime.

Where compliant coatings are in use, existing activities subject to the Solvent Emissions Directivedo not have to comply with the VOC Emission Limits until 31 October 2007.

The permissible VOC contents for compliant coatings for various purposes are given in theProcess Guidance Notes.

2.6 Solvent management plan

The operators of all installations subject to the Solvent Emissions Directive must prepare a SolventManagement Plan.

An inventory of all materials consumed, output and wastes, together with their solvent contents,is required, from which the annual solvent consumption and emissions are determined. For newand substantially changed installations, which are not using the Solvent Reduction Scheme, theannual quantity of solvent lost in fugitive emissions is also calculated. The procedure for thecalculations is given in the appropriate Process Guidance Note.

For installations using the Solvent Reduction Scheme, the annual solvent emission determinedfrom the Solvent Management Plan must be less than the Target Emission to achieve compliance.

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Paint systems

Comparison of the properties of alternative coating systems with those of conventionalpaints highlights their advantages for companies seeking to reduce costs and VOCemissions.

3.1 Conventional paints

Conventional solvent-based paints consist of a surface coating material - generally a pigment,together with a binder resin - dissolved in an organic solvent. Typical conventional paints contain60 - 80% solvent (720 - 960 g of VOCs/litre of coating), ie 20 - 40% coating solids by weight.

During application and drying of the paint, solvent evaporates from the coating leaving adurable, pigmented coating on the surface of the metal. The paint is dried either by being leftto dry in ambient air or by stoving.

3.2 Two-pack paints (2K)

Two-pack paints consist of two components which, when mixed together, begin to react to formthe final coating. This coating often performs better than coats produced by conventional paintsystems because it is formed by chemical bonding. However, once the paint is mixed, it must beused within a matter of hours or it will set. The formulations include toxic isocyanates or amines,which raise health and safety issues1.

Three-pack (3K) paint systems, where the third component is usually a pigment, are also available.

The quantity of VOCs in two-pack systems depends on the thinning requirements and thechemical nature of the two components. However, generally it will be less than conventionalpaint systems, ie the solvent content will be 0 - 50%. VOC-free coatings are known as organicsolvent-free liquid (OSFL) coatings.

For medium to high volume users of coatings, mixing machines are available that mix the twocomponents together just before the spray gun. This results in much less wastage of materialthrough over-mixing or production delays. These machines are described in more detail in Cost-effective paint and powder coating: application technology (GG387).

An additional benefit of some two-pack paints is that they require less energy to cure thanconventional single-pack paints.

3.3 High solids paints

These paints contain a much higher proportion of solids (30 - 70%) than conventional paintsand, consequently, a lower proportion of solvent. VOC emissions are, therefore, lower.

The other main advantage of high solids paints is that the amount of available dry, applied coverachieved per unit volume is higher than with conventional paints. A faster build-up is, therefore,achieved and the quantity of paint needed to do the job is less. This factor should be taken intoaccount when comparing the prices of high solids paints with conventional paint systems.

1 See HSE Information Sheet EIS18 Isocyanates: health surveillance in motor vehicle repair and manufacturers’Material Safety Data Sheets. Available from HSE Books, PO Box 1999, Sudbury CO10 2WA. Website:www.hsebooks.co.uk

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Pumping and transport of high solids material is challenging. Some high solids systems, ie witha solids content of over 70%, are so viscous that to achieve paint mobility they have to beapplied using a heated spray system.

3.4 Water-based paints

Owing to the regulatory and other pressures to reduce the VOC content in coatings,considerable development work has been carried out on water-based paints.

Although water-based paints generally have the same level of solids as conventional paints, ie 20 - 40% solids, most of the solvent is water. The remainder is a compatible organic solvent.

The significantly lower organic solvent consumption achieved by using water-based paints oftenbrings companies below the threshold for regulation under LA-IPPC or LAPPC.

Fig 1 compares the solvent content of conventional, high solids and water-based paints.

Due to the higher water content of these water-based paints, they may take slightly longer todry, resulting in an increase in energy use for stoving. In some cases, the drying process can bespeeded up by preheating workpieces before they are coated.

In larger plants with pumped paint delivery systems and piped paint distribution, equipment andpipelines may have to be replaced by plastic or stainless steel units to prevent corrosion.

Water

Solvent

Solids

Conventional High solids Water-based

Perc

enta

ge

Fig 1 Solvent content of typical conventional, high solids and water-based coatings

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Some paint manufacturers are developing ‘recyclable’ water-based paints. The paint isformulated so that overspray collected in water-washed booths is circulated through anultrafiltration system. The pigments and resins are collected and concentrated, and can be madeup with water and small amounts of the appropriate solvent for use with virgin paint.

Installations already using this type of product in Europe report that operators rinse the sprayguns in the booth wash water, so that virtually all paint not deposited on the workpiece iscollected for re-use.

3.5 Powder coatings

These coating systems are completely solid - usually a thermosetting plastic or thermoplastic orresin material. No solvents are, therefore, released when powder coatings are applied to asurface.

There is a wide range of formulations available, each offering particular performancecharacteristics. Selection can be made for properties such as weatherability and corrosion,chemical or heat resistance.

Comparable transfer efficiencies (50 - 70%) to those of wet paints are achieved with similarapplication methods. However, oversprayed powder can be captured and re-used. This results inhigh material efficiencies of up to 97%. The small losses tend to be due to fines removed fromthe recovered powder. Build-up of fines in recovered powder can adversely affect the quality ofthe finish.

Komfort Office Environments plc of Crawley, Sussex, supplies custom-designed,extruded aluminium partitioning in kit form for UK and overseas markets.

In 1992, Ron Packer, Komfort’s manufacturing manager, estimated the company’sannual solvent emissions to be 76 tonnes. Fitting VOC abatement equipment to thecoating lines would have cost an estimated £68 000. With capacity set to double andthe impending need to comply with PG6/23, Komfort began to evaluate the optionsavailable to avoid having to fit abatement equipment. Komfort’s particular processrequirements - including up to 40 colour changes a day - led to the choice of water-based paints as the most suitable solution requiring the minimum technical change.

Following trials of compliant primers and water-based topcoats, an acceptable finish- in terms of quality and price - was obtained after some minor teething problems.Use of mainly water-based primers and topcoats means that annual VOC emissionsare now only 8 - 10 tonnes. This substantial reduction has been achieved eventhough the number of items sprayed has increased three-fold.

Initially, little capital investment was required because existing HVLP applicationequipment could be used. Even though the water-based paints cost more thanconventional paints, the cost per item is comparable with conventionally coateditems due to the higher coating efficiency of water-based paints. Expenditure ofbetween £68 000 and £136 000 on abatement equipment has also been avoided.

Since the changeover, new spray guns have been introduced, which give an ovalspray pattern. The transfer efficiency has improved from 60 - 65% to 80 - 85% as theresult of this change.

Higher efficiency from water-based paints

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The payback on investment in powder recovery equipment depends on the saving in materialcosts. The economics of powder recovery may also depend on the number of colours beingsprayed. Continuing developments in powder coating systems are gradually allowing thinnerlayers to be produced.

Powder coats are quite different to wet applied coats. For example:

■ they often do not require priming coats, although appropriate surface pretreatment is required;

■ they are generally heavier than wet applied coats;

■ processing times are faster because there is no need for solvent to be flashed off before curing.

However, powder coatings have several disadvantages, including:

■ tinting and colour mixing is not possible; colours have to be ordered from the manufacturer;

■ colour changes can be time-consuming as equipment has to be cleaned thoroughly tominimise contamination;

■ finish quality is difficult to gauge until after the coat has been cured.

Application methods and equipment for powder coating are described in more detail in Cost-effective paint and powder coating: application technology (GG387).

3.6 Electrodeposited paints

When an electric current is passed through components being dipped in electrocoating paints,the coating becomes attracted to the surface of the component and bonds to it in a similar wayto electroplating. The water-based paints, which have to be able to conduct electricity, arespecially formulated for electrodeposition.

Although electrodeposition is often used for dip priming in the production of cars, the techniqueis also applicable to a wide range of products. It is more commonly found in medium to highvolume coating operations.

Electrodeposition is particularly good at coating complex shapes - providing the viscosity of thepaint is low enough to enable it to penetrate into holes and box sections.

As the coating forms on each part of the job, that part becomes insulated and the paint isattracted to non-coated parts. There is no loss of coating through overspray and, providing drag-out is minimal, material yields are excellent.

Peatey’s Coatings is one of the largest trade coaters in the north of England andapplies powder and wet paint to a wide variety of products. Peatey’s was establishedin 1947 and employs 56 people at the Leeds site. Peatey’s introduced a powdercoating process on its site in the early 1970s and powder coating commissions nowrepresent 80% of turnover as more customers recognise the benefits that powdercoating brings. The wide ranging benefits of powder coating include:

■ easy application;

■ easy and repeatable achievement of good surface finishes;

■ only a single coat (no primer) is needed to achieve a strong, durable coating;

■ greater flexibility and speed of turnover.

Time and money saved with powder coating

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When the components are removed from the dipping bath, they are usually rinsed with water,dried and cured in an oven.

3.7 Autodeposited paints

Autodeposition is based on the same basic principles as electrodeposition, but with one keydifference - components are coated without the need for an electric current to be passedthrough them.

The process is used to coat ferrous substrates using a mixture of rubber latex and carbon blackin a dilute solution of hydrofluoric acid. The resulting coating is exceptionally hard (pencilhardness 5 - 8 H) even though the stoving temperature is lower than that for electrodeposition,ie 100°C compared with 170 - 180°C.

Autodeposition can be used for applications where very hard coatings are required. The lowstoving temperature also means that composites of steel with rubber or plastic can be coatedwithout damaging the rubber or plastic. This also means that parts such as car jacks with nyloncores and bearings can be coated once they are assembled - saving time and reducing logisticalproblems.

Because autodeposition coats where it wets, it is exceptionally good at painting complex shapesand tubes. Autodeposition is also self-limiting in terms of dry film thickness, so the consistencyof surface thickness is assured.

3.8 Ultraviolet and electron beam cured coatings

Ultraviolet and electron beam (UV/EB) technology may be used in place of some conventionalpaints. It has the advantages of minimal VOC emissions and very short cure times. The need forVOC abatement plant is eliminated and the volume of ‘work in progress’ is substantially reduced.

It is based on epoxy, acrylic or urethane resins carried in a low volatility solvent which isincorporated into the coating with minimal loss to atmosphere.

The technology is established in applications for wood products and plastics and is becomingavailable for use on other substrates.

Conventional application methods can be used, high volume low pressure (HVLP) spray gunsbeing particularly suitable, although specialised curing equipment is required.

A disadvantage is that all coated surfaces have to be visible to the UV/EB sources, which limitsthe applicability to relatively simple shapes.

3.9 Novel systems containing supercritical carbondioxide

A novel development is the replacement of some of the medium to high volatility componentsin paint systems with supercritical carbon dioxide. The solvent content for a high solids coatingcontaining supercritical carbon dioxide is typically 280 g of VOCs/litre of coating compared to480 g VOCs/litre of coating for a typical high solids coating.

The carbon dioxide acts as a solvent because it is held at very high pressure (75 bar), which makesit a supercritical fluid (neither a liquid nor a gas, but with the properties of both). When the paintis sprayed, the carbon dioxide is depressurised and expands to become a gas. This also aidsatomisation.

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Compared with conventional organic solvents, carbon dioxide is relatively harmless; it dissipatesreadily in air and should not cause health problems in a normally ventilated spraybooth orpaintshop.

For these paint systems, the manufacturers claim that:

■ they can be easily retrofitted to conventional liquid spray operations;

■ any type of paint system, eg conventional, high solids, water-based or 2K, can be produced;

■ the quality of atomisation is superior to any currently available non-electrostatic liquid spraysystem;

■ finish quality is enhanced.

Although there are some industrial users of paint systems containing supercritical carbon dioxidein the USA and Europe, the system is not in industrial use in the UK at the time of writing.

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Considerations when changingcoating systems

When considering whether to change a coating system, eg from conventional paints towater-based paints, it is important for companies to decide their aims in carrying out thechange and prioritise those aims.

The prioritised aims should be matched against all available paint systems to determine the bestpossible match. Such aims might include:

■ reducing VOC emissions;

■ reducing the cost of coating materials;

■ reducing the cost of applying coatings;

■ increasing production capacity through reduced processing time;

■ maintaining or improving finish quality;

■ ensuring required coating thickness is achieved easily;

■ resolving health and safety issues;

■ meeting LAPPC compliance requirements.

Your company’s priorities may limit the number of alternative coating systems that are suitable.

4.1 Coating thickness

The thickness of the applied coat should be given special attention when considering changingcoatings.

All things being equal, eg applied coat quality, durability, hardness and adhesion, the choice ofalternative coating systems will depend on the application rate and solvent emissions from thevarious coating systems available.

Different coating systems used to apply a similar thickness of coat will:

■ apply at different rates, depending largely on solids content;

■ emit different amounts of solvent.

Therefore, applying the same weight of solids to an item can require differing amounts of paintand lead to the emission of differing amounts of solvent. Fig 2 shows the comparative solvent,and hence VOC emissions, from different coating systems.

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4.2 Reducing VOC emissions

Switching paint types can have a significant effect on VOC emissions by reducing the amount ofsolvent used or even eliminating the use of solvents entirely.

For example, consider a typical paintshop using topcoats, which normally contain about 840 gof solvent/litre of paint, ie 30% solids. If this were a high solids paint containing 350 g ofsolvent/litre of paint, ie 68% solids, then just under half the normal volume of paint would berequired to build up the same surface coating.

Total solvent reduction associated with using topcoat would be just over 50%. For a typicalpaintshop with half its paint use involving topcoats (with no change of primers), this wouldreduce total solvent consumption by around 25%.

Even greater reductions can be made by changing to water-based topcoats, which typicallycontain 10% solvents, 60% water and 30% solids. Although the volume used would be similarto a conventional topcoat, solvent emissions would be 85% less. For a paintshop with half itspaint use involving topcoats (with no change of primers), this would reduce its total solventconsumption by around 43%.

If you combine changing to a lower solvent coating system with the use of high transferefficiency application methods, eg high volume low pressure (HVLP) spray guns, you will reducesolvent consumption even further. This may mean that your company’s use of solvents remainsbelow the threshold for regulation under LAPPC or enables it to comply cost-effectively with theconditions of its permit to operate. You can find out more about HVLP spray guns in Cost-effective paint and powder coating: application technology (GG387).

When considering changing to low solvent or solvent-free coatings, you should always considerthe cost and the amount of solvent emitted per job. This is because the amount of the new paintneeded to do the same job may also be less. This is certainly the case with high solids paints.Many sprayers using water-based paints also report a better build-up of coating and, as aconsequence, paint savings.

Low solvent coatings have the disadvantage that they require much cleaner surfaces to promoteadherence than high solvent coatings. Equipment cleaning can be more difficult, particularlywith high solids paints.

Water-based

Powder coating

High solids

Conventional

0 100 200 300 400 500 600

Grams

WaterSolventCoating

Fig 2 Solvent emissions from typical coatings applied to an identical thickness

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Waste/solvent recovery

5.1 The cost of waste disposal

Waste disposal regulations require your company to ensure that all your wastes are correctlydisposed of. This means that all wastes containing solvents, eg spent cleaning fluids, wastepaints and thinners and dirty gunwash, have to be sent to registered specialist waste disposalcompanies that can either recover the solvent or dispose of it in a proper manner, eg byincineration or blending it into a waste-derived fuel.

This can be a costly exercise - in both time and money as companies need to undertakeadditional activities including:

■ segregating and storing solvent wastes;

■ spending time filling in formal documentation as required by the legislation;

■ paying the waste disposal company to take away the solvent waste;

■ paying for replacement solvent.

Contact the Environment and Energy Helpline on freephone 0800 585794 for free advice on thelatest waste disposal and other regulations affecting your operations.

5.2 On-site recovery

There is an alternative to using a waste disposal company to take away solvent waste -recovering the solvent on-site, which may need authorisation. A number of small solventrecovery machines are available. The solvent waste is put into the machine’s waste tank and themachine switched on. The machine heats the waste, boils off the solvent and collects the cooledvapours in a separate tank. These distillation machines are automatic; they can be set runningand left to get on with the job. They typically take 12 or 25 litres of waste solvent at a time andneed about eight hours to treat one batch of waste. Larger units can be made to order.

The recovered solvent is not high quality, but can often be used as gunwash or as a low-gradecleaning solvent. A small amount of residue is left in the waste tank. This is often solid and can bedisposed of with other solid waste in the appropriate manner. If the residue is liquid, it may haveto be stored and sent for specialist disposal - however, the volume will be much smaller than before.

Using a solvent distillation machine could save your company time and money because:

■ recovered solvent can be used as gunwash or as a low-grade cleaning solvent, significantlyreducing the amount spent on these raw materials;

■ waste disposal charges are substantially lower, as up to 90% of the solvent is recovered;

■ storage of solvent wastes is no longer a significant problem (some waste may have to bestored, depending on particular circumstances);

■ there is much less need for reliance on a specialist waste disposal company and fewer time-consuming forms to fill in.

If you are considering carrying out your own solvent recovery, you will need to:

■ work out how much solvent waste your company produces or is likely to produce;

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■ decide what size of machine would be needed to treat this amount of waste;

■ balance the machine’s capital and operating costs against the cost of disposing of yoursolvent waste and the amount spent on low-grade cleaning solvents.

Running costs for solvent distillation machines are very low. A typical 25 litre unit costs 75 pence,ie 3 pence/litre, to process one batch of solvent.

Before buying a solvent recovery unit, it is important to carry out trials using typical paint andthinners residues, to assess whether the resulting reclaimed solvent is suitable for use in youroperations.

You should ensure that the machine:

■ is certified as safe for treating flammable solvents;

■ is ‘explosion proof’;

■ has safety features that prevent the machine being opened when hot.

Flight Refuelling Ltd, a specialist aerospace company, operates a wide range of metaltreatment processes from plating, passivation and anodising, through to heattreatment, degreasing and organic coating.

The paintshop uses large quantities of low-grade solvents for wipe degreasing andgunwashing. A solvent distillation unit was, therefore, installed to reclaim solventfrom dirty gunwash, waste paints and thinners. After the first six months, solventpurchases had fallen by 60%. Recycled solvent now accounts for nearly 90% of thepaintshop’s requirements for low-grade solvent.

Waste solvent recovery has reduced both solvent purchase and disposal costs. Theresidues in the distillation unit are safer to dispose of and are present in much lowerquantities than previously, hence disposal costs are lower. The payback period on theinvestment in the recovery unit was just over six months.

Solvent recovery reduces purchase and disposal costs

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Abatement systems

Some industrial coating users may need to use abatement systems to minimise emissionsof dust to the atmosphere. Those companies that do not or cannot use compliantcoating materials may also be required to install VOC abatement equipment.

If companies are forced to consider VOC abatement equipment, taking action to minimise VOCemissions can reduce the capital cost and running costs of this equipment.

Companies implementing a waste minimisation programme to limit waste and VOC emissionsshould already be considering ways of reducing the operating costs of the existing abatementequipment. This could involve saving on maintenance of water-wash spraybooths by reducingoverspray, leaving less sludge for disposal. Contact the Environment and Energy Helpline onfreephone 0800 585794 for advice and to obtain copies of Solvent capture for recovery and re-use from solvent-laden gas streams (GG12), Cost-effective solvent management (GG13) andGood housekeeping measures for solvents (GG28).

Abatement costs are ‘end-of-pipe’ costs and do not add any direct value to products. This addedcost can be considerable - the best approach is to reduce emissions at source.

6.1 Particulate abatement

The water-wash spraybooth is the most widely used form of abatement equipment for dustemissions from paint spraying, particularly for medium to high volume users.

Water-wash spraybooths substantially reduce particulate overspray from spraying operations byscrubbing it into the booth water. However, it is important to clean the booth water regularly toprevent paint solids from building up and blocking pumps and pipework.

Cleaning is generally carried out by pumping out the contents of the booth for sending to alicensed waste disposal operator. The potential presence of water-soluble solvents and metaloxides means that booth water should not normally be disposed of to drain.

Sludge removal from the spraybooth can be time-consuming and delay production. A numberof systems are available for the treatment of water from water-wash booths, which functionduring normal spraying operations. Such systems produce a sludge with a high solids content,while recycling cleaned water to the booth. This saves water, time and disposal costs.

A variety of proprietary booth water treatment systems with different methods of operation areavailable; some are more suitable for use with solvent-based paints, whilst others are designedfor water-based paints. Treatment systems are generally based on coagulation of the suspendedpaint matter, followed by flocculation. The resulting flocs are either:

■ allowed to settle out and decanted;

■ centrifuged out;

■ floated to the surface of the water (or made to float using compressed air bubbles), fromwhere they are skimmed off, as a sludge, or automatically filtered off.

The payback period for such systems is often less than one year, as the sum of the capital cost,annual sludge disposal costs, together with the cost of the chemical agents is less than theannual labour costs, waste disposal costs and plant downtime for previous cleaning operations.

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All of these costs should be considered when developing a cost-benefit case for the purchase ofa spraybooth water treatment system.

Some large-volume painting operations are also able to make use of systems to dry the paintsludge. This offers the possibility of the sludge being used for other purposes, such as an inertfiller in sound-deadening material, thereby reducing waste disposal costs.

Particulate emissions are sometimes removed - particularly in smaller operations - using a simple,disposable solid filter.

6.2 VOC abatement

The preferred methods of minimising and preventing VOC emissions are the use of low solventcontent or solvent-free coating systems. Where changes to coating systems cannot achieveemission reductions to less than the Target Emissions as defined in PG6/23, VOC abatementplant is required.

There are two main methods of VOC abatement - both of which incur capital and operatingcosts.

6.2.1 Destructive techniques for VOC abatement

Incineration is the most common destructive method, the VOCs being oxidised to carbon dioxideand water. The operating costs of thermal systems such as incinerators are high, especially withthe low concentrations of VOCs typical of spraybooth emissions. Particulate removal prior toincineration of the VOC-containing waste stream may also be necessary. Running costs can bereduced by using heat recovery or catalysts to reduce energy consumption.

Microbial methods of destroying VOCs have yet to be used on spraybooths.

6.2.2 Capture techniques for VOC abatement

Capture techniques rely on being able to remove solvent vapours from the exhaust air streamand return them to the liquid state. For example:

■ by direct cooling of the air stream to condense the vapours;

■ by using an agent such as activated charcoal to adsorb the VOCs.

The capture and recovery of the mixed, relatively low-value solvents commonly found inpaintshops are not currently cost-effective, but may offer potential benefits in comparison to theother VOC abatement options.

Solvent capture for recovery and re-use from solvent-laden gas streams (GG12) describes VOCcapture in more detail.

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Drying/curing

7.1 Air drying

Many of the paints used by industry - particularly by small volume users - are air-drying and donot need to be heated for them to dry. Parts are often left on jigs or on stands in the vicinity ofthe booth until they have dried.

Good practice in air drying involves providing a clean, dry and well-ventilated area to allow thepaint to dry properly and to prevent surface contamination, eg extraction equipment should beprovided and used to prevent fumes from any neighbouring welding operations reaching dryingparts. Additional ventilation may also be needed to prevent unacceptable solvent exposure topersonnel working nearby.

7.2 Stoving ovens

The other main method of paint drying is to use stoving ovens to provide heat to drive offsolvents and/or to effect a proper cure of the coating.

Time and temperature must be correct to obtain the required finish. These two factors areinterdependent; a coating supplier normally specifies the time needed at a specific temperature.This specified temperature is that at which the substrate surface must reach for the paint to cureproperly.

Stoving ovens are usually air re-circulating, heated by gas or electricity.

Paying attention to a number of aspects of oven operation will save money and help to maintainproduct quality.

■ When setting oven cycles, ensure that the paint surface reaches the specified temperature.The air temperature may need to be higher than the specified cure temperature tocompensate for heat transfer by the substrate away from the surface. This is especiallyimportant when high weight components are being stoved.

■ Use timers with audible or visual alarms to:

- ensure parts receive sufficient curing;

- prevent unnecessary overheating.

■ Check the operation of the stoving oven regularly to ensure that:

- air is circulating correctly;

- burners or heating elements are working efficiently.

■ Make sure that air extraction rates during stoving are sufficient to prevent a dangerous build-up of flammable gases, particularly during the first part of stoving.

■ Save energy by reducing air extraction rates once flammable gases have been driven off, butconsult the oven makers first to ensure that this can be done safely, ie without raising solvent-in-air levels to a dangerous point.

Reducing the extraction flow rate reduces the amount of heat energy needed to keep the ovenat the correct temperature. Energy savings can also be made by using a variable speed drive tocontrol the oven fan.

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It is particularly important to reduce the air extraction rate if water-based paints or powdercoatings are being used, as lower levels of flammable gases will be given off.

Where water-based paints are used, some extraction is still needed to prevent the oven airbecoming saturated with water vapour.

Larger volume users often find that the longer stoving times usually needed for conveyoroperations mean that this process step limits plant capacity. This problem can be overcome by:

■ building longer ovens;

■ using multi-pass systems (where space is limited);

■ using a quicker method of stoving, eg infrared methods.

7.3 Infrared stoving

There are two main types of infrared system:

■ Electrically powered, using an element to generate infrared (like a light bulb).

■ Gas powered, using combustion of gas to generate infrared. These systems are often referredto as radiant heaters.

The coating and substrate are heated through the absorption of infrared energy. Radiant gasheaters also have a convective heating ability, due to the release of heated products ofcombustion.

Although initial heating of the components is by infrared and is, therefore, ‘line-of-sight’, heatis also conducted to other parts of the workpiece by the substrate. Careful angling of infraredsources can promote a better cure.

Energy costs can be reduced, if the size of workpieces varies, allowing smaller components to becured, whilst switching off some of the panels of radiant systems or the elements of electricsystems. This facility is not available with conventional ovens.

The use of infrared heating can reduce stoving times considerably. This allows smaller ovens tobe used on conveyorised systems and alleviates a possible bottle-neck in the finishing process.

Retrofitting a small infrared heater before a conventional oven can also reduce stoving times andhence increase capacity.

7.4 Ultraviolet and electron beam curing

The coatings are cured almost instantaneously when irradicated with ultraviolet light or anelectron beam. The speed of curing means that space requirements are much reduced comparedwith that required for a stoving oven. The capital investment is high (particularly for electron beamcuring), but is offset by the savings in energy that would be consumed by a conventional oven.

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Wellington Garage is a medium-sized independent car repair bodyshop based inGreater Manchester, and employs 22 people. In late 1999, the company decided toreplace two drying ovens in its repair centre as these were old and uneconomic.Initially, the company obtained quotes for the direct replacement of the existingovens that were used with solvent-based coatings, but as legislation surroundingVOC emissions was due to change, the company also decided to investigate thepossibility of switching to water-based paints where possible.

Various investigations led to the conclusion that water-based primers and basecoatsshould be adopted, although the company concluded that it would still have to usesolvent-based clearcoats. This decision had implications for the ovens and hence thecompany decided to identify equipment that would dry water-based coatingsefficiently.

The chosen units are fully enclosed and airtight. Spraying is carried out within thebooth/ovens under slight positive pressure to eliminate the possibility of dust ingress.Finished jobs are baked in the ovens for typically 20 to 30 minutes. Overspray iscarried away and trapped in filters which are occasionally replaced. The booths havea very high, recirculating airflow and incorporate a heat exchanger system that helpsto recover heat from the extracted air and hence reduce gas consumption. The wallsare double-skinned and insulated. The units are fully galvanized to protect thesteelwork from corrosion, often a problem with humid airflows. The ovens alsoincorporate a lighting management system that switches off unnecessary lights.

The quotation for replacing the original drying ovens like-for-like was £22 000, whilethe chosen ovens increased the capital cost to £50 000, a £28 000 additional cost. Gasusage has been monitored and has dropped by around 18%, saving £420/year,despite an increase in vehicle throughput of 12%, a specific energy consumptiondrop of over 27%. This has added £74 000/year to the turnover of the business.

Gains from fitting improved ovens

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Decision chart and action plan

If you use solvent-based coatings, the decision chart shown in Fig 3 will help you toidentify the actions necessary. The actions required under the regulations are:

1. Prepare an inventory of all materials used, with their solvent content.

2. Using the information from (1), determine whether your activities fall within the scope of thePPC Regulations or the Solvent Emissions Directive.

3. If the answer to (2) is yes, obtain measurements of VOC emission concentrations and preparea Solvent Management Plan.

4. If the Solvent Reduction Scheme is to be used, calculate the Target Emission and prepare anEmission Reduction Plan to achieve the Target Emission. The plan might include:

- alternative low solvent content or solvent-free coating systems;

- capture and destruction or recovery of solvent emissions.

Not regulated*

VOC emissionlimits do notapply until 2007

Not regulated ifbelow threshold*

Complies with regulatoryrequirements

Will comply with regulatoryrequirements

Yes

Yes

Yes

Yes

Yes

No

Are compliant coatings in use?

No

Can annual solvent consumptionbe reduced to less than 5* tonnes

by changing coating systems or using more efficient application methods?

No

Are measured VOC emissionconcentrations less than

emission limits?

No

Can VOC emissions be reduced toless than the Target Emission by using

low solvent content or solvent-freecoating systems?

Change coatingsystems to

achieveTarget Emission

Change coatingsystems orapplication

methods

VOC abatement equipmentmust be installed

* Lower solvent consumption thresholds apply to the repainting or respraying of road vehicles.

No

Is annual solvent consumptiongreater than 5* tonnes?

Fig 3 Decision chart for users of solvent-based coating materials

Note: Annual solvent consumption includes that used in pretreatment (surface cleaning) processes.

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Other actions which could reduce VOC emissions and costs include:

■ Reducing wastage through improved housekeeping.

■ Considering installing a solvent recovery machine.

■ Performing air-drying in a clean environment.

■ Ensuring your stoving oven is operating efficiently:

- using the correct temperature and stoving time;

- fitting an audible or visual alarm to prevent overheating;

- checking the operation of the oven regularly;

- reducing air extraction rates once flammable gases have been driven off.

■ Reducing stoving time by installing infrared driers prior to the oven.

Contact the Environment and Energy Helpline on freephone 0800 585794 to obtain free copiesof the Envirowise publications mentioned in this Guide or visit the Envirowise website(www.envirowise.gov.uk).

Don’t forget to ask for the three other guides in the series on cost-effective paint and powdercoating, if they relate to your operation:

Cost-effective paint and powder coating: materials management (GG385)

Cost-effective paint and powder coating: application technology (GG387)

Surface cleaning and preparation: choosing the best option (GG354)

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Sources of further information

9.1 Trade associations

British Coatings Federation (BCF)James House, Bridge Street, Leatherhead, Surrey KT22 7EPTel: 01372 360660 www.coatings.org.uk

The BCF offers a number of publications giving more detailed information on environmental andregulatory aspects, health and safety, and particular coating systems.

Surface Engineering Association and Paint and Powder Finishing AssociationFederation House, 20 Vyse Street, Birmingham B18 6LTTel: 0121 237 1123 www.sea.org.uk and www.finishes.org.uk

The latter website includes a comprehensive buyer’s guide.

Paint Research Association (PRA)8 Waldegrove Road, Teddington, Middlesex TW11 8LDTel: 020 8614 4800 www.pra.org.uk

The PRA offers a number of periodicals and publications giving detailed information on coatingsystems.

9.2 Materials suppliers

The list is not exhaustive and has been compiled from information currently available toEnvirowise. The listing of an organisation should not be regarded as an endorsement of itsservices or products by Envirowise. Similarly, Envirowise makes no claim for the competence orotherwise of any organisation not listed.

AKZO Nobel www.akzonobel.com www.interpon.comA comprehensive guide to powder coating is available on the Interpon website.

Carrs Paints Limited www.carrspaints.comDetails of a wide range of coating systems.

ICI www.icipaints.comIncludes an informative introduction to paints and paint chemistry.

LVH Coatings www.lvh-coatings.co.ukDetails of specialist electrocoating systems.

Ameron (Croda) www.ameron-bv.comInformation on a range of coating systems.

PPG www.ppg.comInformation on a range of paint systems.

DuPont www.dupont.com/coatingsDetails of a wide range of coating systems.

9.3 Other sources

BIO-WISE www.dti.gov.uk/biowiseInformation on industrial biotechnology applications for metal finishing and VOC abatement.

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Legislative controls and reductionof emissions

The Pollution Prevention and Control (Solvent Emissions Directive) (England and Wales)Direction 2002 came into force on 22 March 2002. It places strict controls on VOCemissions from certain sectors of industry and defines emission limit values for new andexisting installations.

The Pollution Prevention and Control Regulations, made by the Secretary of State under Section2 of the Pollution Prevention and Control Act 1999, require the operators of prescribed processesto submit a detailed application to the regulator for a permit to operate. Most paint and powderprocesses fall within Part A(2) for Local Authority Integrated Pollution Prevention and Control(LA-IPPC) or Part B for Local Air Pollution Prevention and Control (LAPPC).

There are transitional arrangements for existing installations, authorised under the former LocalAir Pollution Control (LAPC) regime.

Some smaller operations, whose annual consumption of organic solvents is less than the relevantthreshold, are exempt from the PPC Regulations. However, other regulations may be applicable,for example, the Water Resources Act preventing unauthorised discharges to controlled watersand the Water Industry Act preventing unauthorised discharges to foul sewers.

The LAPPC Process Guidance Notes for metal coating in the general industrial sector are:

PG6/23 Coating of metal and plasticPG6/31 Powder coatingPG6/34 Re-spraying of road vehicles and PG6/40 Aerospace coatingsPG2/9 Metal decontamination processes - applies in the case of heat applied to jigs using aburner with more than 0.2 MW thermal input

PG6/23 also applies to (a) metal and plastic coating and (b) degreasing processes, where theseare carried out as part of a coating process.

The Process Guidance Notes were first published by the former Department of the Environmentfor use under the LAPC regime and subsequently revised for use under the LAPPC regime. Copiesof PG6/23 and all other Process Guidance Notes are available from The Stationery Office.

Separate guidance will be issued for LA-IPPC.

Emission controlsThe LAPPC Process Guidance Notes give specified emission limits for VOCs expressed as 30minute mean concentrations.

The VOC limits are normally exceeded during spraying when standard paints, guns and boothsare used. However, the emission limit values do not apply to installations using the SolventReduction Scheme.

Any company using compliant coatings, under the former LAPC regime, does not have to complywith the VOC emission limits until 31 October 2007.

VOCs with risk phrases R45 (which includes trichloroethylene), R46, R49, R60 and R61 aresubject to very stringent emission limits and should only be used under contained conditions.

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Emission reduction schemeAlternatively, an operator may choose to use the Solvent Reduction Scheme to achieve emissionreductions to a Target Emission, equivalent to that which would have been achieved if thespecified emission concentration limits had been applied. Under the Solvent Reduction Scheme,the operator prepares an Emission Reduction Plan which includes, in particular:

■ the use of coating materials with a reduced organic solvent content;

■ increased efficiency in the use of solids to achieve a reduction of the total emissions.

The procedure for calculating the Target Emission is given in Schedule 3 of the PollutionPrevention and Control (Solvent Emissions Directive) (England and Wales) Direction 2002.

If you need further advice about this legislation or any other regulations governingyour operation, please contact the Environment and Energy Helpline on freephone0800 585794.

Envirowise - Practical Environmental Advice for Business - is a Government programmethat offers free, independent and practical advice to UK businesses to reduce waste atsource and increase profits. It is managed by Momenta, an operating division of AEATechnology plc, and Technology Transfer and Innovation Ltd.

Envirowise offers a range of free services including:

Free advice from Envirowise experts through the Environment and EnergyHelpline.

A variety of publications that provide up-to-date information on wasteminimisation issues, methods and successes.

Free, on-site waste reviews from Envirowise advisors, called FastTrack visits, thathelp businesses identify and realise savings.

Guidance on waste minimisation clubs across the UK that provide a chance forlocal companies to meet regularly and share best practices in waste minimisation.

Best practice seminars and practical workshops that offer an ideal way toexamine waste minimisation issues and discuss opportunities and methodologies.

For further informationplease contact the

Environmentand EnergyHelpline0800 585794© Crown copyright. First printed September 2003. Printed on paper containing a minimum of 75% post-consumer waste.

This material may be freely reproduced in its original form except for sale or advertising purposes.

Harwell International Business Centre | Didcot | Oxfordshire | OX11 0QJE-mail: helpline@envirowise.gov.uk Internet: www.envirowise.gov.uk

Practical Environmental Advice for Business