PRACTICAL MEASURES TO SAVE MONEY IN SCREEN PRINTING

Transcription

1 GG60 GUIDE ENVIRONMENTAL TECHNOLOGY BEST PRACTICE PROGRAMME Be Solvent Wise PRACTICAL MEASURES TO SAVE MONEY IN SCREEN PRINTING GOOD PRACTICE: Proven technology and techniques for profitable environmental improvement

2 PRACTICAL MEASURES TO SAVE MONEY IN SCREEN PRINTING This Good Practice Guide was produced by the Environmental Technology Best Practice Programme Prepared with assistance from: ch Consulting Group Crown copyright. First printed e This material may be freely reproduced except for sale or advertising purposes. Printed on paper containing 75% post-consumer waste.

3 SUMMARY Companies that use their organic solvents wisely can become more competitive and can help protect the environment by reducing their volatile organic compound (VOC) emissions. This Good Practice Guide provides screen printers with the necessary tools to make efficient and cost-effective use of their solvents. Screen printers use organic solvents in a variety of ways, but particularly for screen wash and thinning inks. In addition, some inks contain organic solvent. Those companies that take action to produce more product for the same amount of solvent used will: spend less on solvents and solvent-based inks; spend less on waste disposal; improve their company s health, safety and environmental performance. Reducing the amount of solvent used may allow companies to move below the registration threshold for authorisation under Local Air Pollution Control (LAPC), thereby saving registration fees and ongoing authorisation costs. This Guide explains, with the aid of a detailed worked example, how to analyse and control solvent consumption. The techniques commonly referred to as Measuring to Manage involve: measuring solvent consumption over a specified period of time; relating solvent consumption to a relevant production measure to define a solvent consumption standard; taking action to reduce the amount of solvent used; comparing actual consumption with standard or target consumption; detecting changes in consumption patterns; taking action to correct these changes. Industry Examples describe the savings and other benefits achieved by four screen printers through a Measuring to Manage solvent programme.

4 CONTENTS Section Page 1 How this Guide can help you save money Controls on solvent use Measuring to Manage 2 2 Solvent use in screen printing Organic solvent content of inks Solvent use for screen cleaning 5 How to carry out a Measuring to Manage programme 6.1 Step 1 - Investigate solvent use within the company 6.2 Step 2 - Decide which solvent to measure and how to measure it 7. Step - Taking production into account 9.4 Step 4 - Decide which measurement period to use 9.5 Step 5 - Gathering data 10.6 Step 6 - Analysing data and taking action to reduce solvent use 11.7 Step 7 - How to interpret CUSUM graphs 18.8 Step 8 - Measuring to Manage is ongoing 28 4 Industry examples BTP Screen Process Printers Ltd Halo Company Ltd 2 4. RH Technical Industries Ltd Walkers of Manchester Ltd 6 5 Action plan 8 Appendix Sample worksheet: data collection and analysis 41

5

6 1 HOW THIS GUIDE CAN HELP YOU SAVE MONEY By using solvents* wisely a company can become more competitive while at the same time reducing its volatile organic compound (VOC) emissions. Good Practice Guide (GG1) Cost-effective Solvent Management helps companies take a strategic approach to achieving these goals, while Good Practice Guide (GG28) Good Housekeeping Measures for Solvents describes a wide range of practical measures. Both these Guides are available free of charge through the Environmental Helpline on This Good Practice Guide provides screen printers with the necessary tools to make efficient and cost-effective use of their organic solvents. Implementing a systematic approach to controlling solvent consumption will help screen printers to: reduce the cost of buying solvents and solvent-based inks; reduce the cost of disposing of waste solvents and inks; improve the company s health, safety and environmental performance; reduce solvent use to avoid registration under the Local Air Pollution Control (LAPC) provisions of the Environmental Protection Act 1990 (EPA 1990), thus reducing both costs and difficulties. 1.1 CONTROLS ON SOLVENT USE Screen printers using a total of five tonnes or more of organic solvent per year are required to register with their local authority and obtain authorisation to operate. All sources of solvent, including the solvent content of inks, are included in this total. Authorisations are granted by local authorities if screen printers comply with the requirements of PG6/16(97) Secretary of State s Guidance Note - Printworks. A revised version of PG6/16(92) was published in ch Authorised screen printers in the UK must comply with most of these requirements by 1 e In addition to keeping VOC and dust emissions below specified levels, registration under the EPA 1990 imposes various record-keeping and reporting requirements on screen printers. Registration involves paying an initial fee and then annual charges, which entails a considerable amount of work. Anything that reduces solvent use below the five tonne threshold will help to avoid these additional costs. While unregistered screen printers are under no legal obligation to keep records of their solvent use, they may have to prove to their local authority that their solvent use is below the registration threshold. Advice on the most recent legislation regarding solvents and their use in screen printing can be obtained through the Environmental Helpline on * For the purposes of this Guide, solvent implies an organic solvent that evaporates readily at normal temperature and pressure; also known as a VOC. 1

7 1.2 MEASURING TO MANAGE Measuring to Manage is a systematic method of analysing and controlling solvent consumption, thus enabling companies to save money by producing more product for the same amount of solvent. 1 The techniques used in Measuring to Manage solvent can just as easily be applied to the management of other raw materials, packaging and utility use, eg water and energy. The essential elements of Measuring to Manage are: measuring the solvent consumption of a company, department, production line or machine over a specified period of time; relating solvent consumption to a relevant measure of production (eg production quantity, hours run and screens cleaned) and thus define a solvent consumption standard; setting targets for reduced solvent consumption; regularly comparing actual consumption with the standard or target consumption level; reporting changes in consumption and determining the reasons for the variation; taking action to correct these changes and reduce solvent consumption; continually aiming to minimise solvent consumption while maintaining product quality, production efficiency, safety, etc. Measuring to Manage requires a combination of technical and managerial skills. Measuring solvent consumption and data analysis require technical input. Correcting problems requires both technical skills, eg the repair of faulty equipment, and managerial skills such as persuading people to change their behaviour and habits, eg putting lids back on solvent containers when they are not in use. This Guide aims to give screen printers all the technical skills needed to implement a Measuring to Manage programme. Some guidance is provided on the managerial skills associated with Measuring to Manage, eg on how to achieve targets. Section explains how to: prepare to carry out Measuring to Manage; identify which solvents to measure and thus control; identify the most appropriate production measure to use; choose the best time period for measurements, eg batch, days, weeks or months; record the data; analyse the data to produce a standard consumption; report and interpret each period s data and variations. Each stage of this systematic approach to controlling solvent use is illustrated with a worked example which shows how a fictitious screen printer achieved significant savings through implementing a Measuring to Manage programme for screen wash. You are advised to start by setting up a Measuring to Manage programme for a single material or resource. Once the relevant skills have been acquired, as many programmes as necessary can be set up. 2

8 1.2.1 Industry Examples Measuring to Manage solvent has already been used successfully within the UK screen printing industry to reduce the consumption and wastage of screen wash and other solvents. The cost savings and other benefits achieved by four companies are summarised in Table 1 and described in more detail in Section 4. All four companies implemented the Measuring to Manage solvent programme detailed in this Guide, with the aims of: reducing the amount of screen wash used; keeping their solvent inventory below the threshold for registration under LAPC. 1 Having achieved these initial aims, the companies intend to use Measuring to Manage to maintain these savings and to continue to improve their environmental performance. Company No. of Benefits* employees BTP Screen Process Printers Ltd 50 25% decrease in screen wash use, worth 4 000/year. Avoided registration under LAPC. Highlighted need for more operator training. Halo Company Ltd 40 50% reduction in screen wash use in the screen reclamation area, worth 450/year. Increased general awareness of solvent use. RH Technical Industries Ltd >120 22% decrease in screen wash use, worth 700/year. No need to register under LAPC. Helped to standardise cleaning procedures. Walkers of Manchester Ltd 100 Use of screen wash and solvent for thinning inks maintained at level below threshold for registration under LAPC. Highlighted opportunities for improvement. * All savings are at 1996 prices. Table 1 Industry Examples The Action Plan in Section 5 summarises what you need to do to reduce your operating costs by making your solvents go further. A sample worksheet for recording data is provided in the Appendix for you to photocopy and use as you wish. Remember: If you don t measure it, you can t manage it Use of computers This Guide describes how to carry out a Measuring to Manage programme in a simple, paper-based format. You may prefer to use computer spreadsheet programs to help record and analyse your collected data. Spreadsheet programs have the advantage of automatic graph drawing facilities. Look for these in the program manual and help library.

9 2 SOLVENT USE IN SCREEN PRINTING Screen printing is used for a wide range of applications including: 2 paper printing, eg posters, packaging and artwork; textile decoration, eg T-shirts and fabrics; consumer packaging, eg plastic bottles; precision printing onto plastic and metals, eg rulers and car dashboard instruments; glass/mirror decoration; printed circuit board manufacture; hybrid circuit board manufacture, ie electronic components built onto board by screen printing; membrane switch manufacture; ceramic transfer manufacture. Solvents are used in various aspects of the screen printing process including: cleaning screens and printing machinery, eg screen wash; thinning inks; as a component of printing inks; screen reclamation. Cleaning screens and printing machinery consumes most solvent. 2.1 ORGANIC SOLVENT CONTENT OF INKS The diversity of applications means that screen printers use a variety of inks. The typical organic solvent content of some currently used inks is given in Table 2. Ink type Organic solvent content Thin film inks 4% Ultra-thin film inks 60-70% Oxidation drying gloss inks 20% Vinyl inks 42% Two-pack catalytic inks 0% Inks for glass 2% Inks for PVC sheets/bottles 45% Textile inks 60% Water-based inks 10%* Ultraviolet (UV) curing inks (includes water-based) 0% *10% is usual, but it can be as high as 15%. Table 2 Typical solvent content of inks used in screen printing 4

10 The organic solvents used in inks include: white spirit; aromatic hydrocarbons; ethers; alcohols; ketones; acetate esters. Screen printers often add solvents to inks (10-20% by volume) to thin the ink and modify its drying properties to maintain quality. Solvent use in inks depends on: 2 the area of each print; the thickness of the ink film; the number of prints made in the run. 2.2 SOLVENT USE FOR SCREEN CLEANING When a print run is finished (either at the end of a run or at the end of the day), excess ink is recovered from the screen for subsequent use and the screen is cleaned. The cleaned screen is either held for future runs of the same job or reclaimed for re-use on another job. Screen cleaning, which involves the use of solvents such as cyclohexanone, can be carried out manually or in special screen cleaning machines. During print runs, solvents are used to: Spot clean - this is required when a speck of dirt or dry ink has to be removed from a screen. Partial clean - this is needed when the whole screen becomes contaminated with dirt or dry ink. The standard of cleaning is not as high as a full clean where the screen may be stored for re-use or sent for recovery. Solvents are also used to clean screen printing machines between runs, eg removing spills and splashes of ink. The amount of solvent used during screen cleaning depends on: The area of the screens. The operator performing the cleaning. The amount of ink removal required. Screens that are left dirtier than others or left to dry before being cleaned require more solvent Screen reclamation If the print run is complete or the screen has become damaged, screens can be reclaimed for re-use. There are many proprietary materials on the market for the removal of screen stencils, some of which contain solvents. Like screen cleaning, screen reclamation can be carried out either manually or in special screen cleaning machines. 5

11 HOW TO CARRY OUT A MEASURING TO MANAGE PROGRAMME This Section explains the eight steps involved in a Measuring to Manage solvent programme. Each of these steps is illustrated with a worked example showing the application of Measuring to Manage in a fictitious screen printing company. The systematic approach to analysing and controlling solvent use described in this Guide has already been successfully implemented by several screen printers in the UK. The Industry Examples described in Section 4 highlight the cost savings and other benefits achieved by four actual companies. The worked example involves PrintWise Ltd, a successful screen printing business, employing about 0 people and specialising in printing on vinyl. Annual solvent use is four tonnes/year. PrintWise Ltd s main reason for implementing a Measuring to Manage solvent programme is to reduce its operating costs and thus remain competitive. Although the Company s annual solvent use is below the limit for authorisation under LAPC, the managing director is worried about exceeding the registration threshold if production increases. Complaints from a nearby housing estate about odours from the factory mean that he is also under pressure to improve solvent handling..1 STEP 1 - INVESTIGATE SOLVENT USE WITHIN THE COMPANY To obtain the greatest possible savings from a Measuring to Manage programme, it is important to focus on the largest sources of waste. Although most screen printers think they know where screen wash, etc is used within their company or department, they are often unaware exactly where solvent is wasted. Step 1 of a Measuring to Manage solvent programme in a screen printing company has two stages: identify and quantify all purchases and disposals of screen wash, thinning solvents, solventcontaining inks and solvents used during screen reclamation; identify where solvent and solvent-containing materials are used and where waste is generated. Good Practice Guide (GG1) Cost-effective Solvent Management describes in detail how to investigate solvent use within a company. This Guide is available free of charge through the Environmental Helpline on The information obtained during Step 1 can be summarised on a flow diagram showing all the processes using solvents and the sources of solvent-containing wastes. Fig 1 shows an example of solvent use and costs in a fictitious screen printing company.* Having studied the flow diagram, the company might ask the following questions: Why do we waste 1% of the ink we buy? Do we need to use solvent to clean the screens before we use them? Where does all the cleaning solvent end up? Only two-thirds is sent for disposal. 6 * These amounts do not relate to the worked example used to illustrate the steps involved in a Measuring to Manage solvent programme.

12 /litre Cost Inks Thinning solvent /litre Cost Ink mixing Screen preparation Cleaning solvent /litre Cost Printing Ink recovery Printer cleaning Fig 1 Solvent use and costs in an example screen printing process /litre for disposal Cost /litre Waste ink Cost Cleaning solvent Cleaning solvent /litre Cost 120 Screen cleaning Waste solvent /litre for disposal Cost Solvent use Although PrintWise Ltd uses a small amount of solvent to thin inks, most solvent is used as screen wash. The investigation has also revealed that top quality solvent was being used routinely as screen wash. A few years earlier, lower quality cleaning solvent had been banned from the factory, as a temporary measure, after a quality problem was blamed on operators mistakenly using the solvent to thin inks. The intention had been to devise a method of segregating the two types of solvent but this had been forgotten and the temporary ban had become permanent. Purchasing cheaper, lower quality screen wash in a different coloured drum to the more expensive top quality thinning solvent will allow the operators to distinguish between the two types of solvent. This measure is expected to save substantial amounts of money each year..2 STEP 2 - DECIDE WHICH SOLVENT TO MEASURE AND HOW TO MEASURE IT Step 1 should provide a realistic picture of the main uses and wastage of solvent within the company. The next step is to decide which material use or waste to minimise first. Companies should also decide their objectives from a Measuring to Manage programme. If the aim is to reduce costs, then you should measure the most expensive solvent-containing material by cost. If the aim is to minimise solvent use, then you should measure the largest solvent use or waste stream by volume or weight, eg screen wash. It is best to start with: a solvent that is used regularly and in large quantities; a solvent application that involves a direct, easy-to-measure use of solvent, eg cleaning screens or equipment, rather than an indirect use of solvents such as in ink. Once the skills needed for Measuring to Manage have been acquired, then the programme can be extended to other solvents. 7

13 Which solvent to measure? As most of the solvent is used to clean screens, the managing director of PrintWise Ltd decides to concentrate on reducing the cost of screen wash. The printing machines use three different size screens (0.2 m 2, 0.4 m 2 and 0.8 m 2 ), which are cleaned manually in a ventilated booth..2.1 Be consistent When measuring solvent consumption, it is important to be consistent rather than concentrating on obtaining an accurate reading every time. The method used should be standardised and the results repeatable. For example, if a jug is used to measure out screen wash from a drum, then that jug or a similar jug (the same size, make, etc) should be used throughout the process and throughout the programme. A measurement standard should also be set, eg each jug is to be filled to a standard height. Solvent use can then be measured in units of a standard jug. Using calibrated containers, eg jugs, bottles, beakers, cylinders or buckets, to obtain accurate measurements is even better. A measurement standard should still be set, eg measuring screen wash to the nearest hundred millilitre. More thought may be needed if solvent is piped to machinery. In-line meters are best, but expensive to install. Measuring the solvent volume in either the machinery reservoir/tank or the solvent store (or both) before and after solvent transfer is another way of determining transferred solvent volumes. The chosen solvent may be used for only one process. If so, then solvent consumption can be measured from stocktake and delivery figures..2.2 Measuring and recording solvent use There are two basic methods of measuring solvent use - direct measurement and indirect measurement. The choice of method depends on the solvent being studied. If a solvent has only one application in the process, it can be measured by either method. However, if a solvent has many areas of application and its consumption is being measured in only one area, then direct measurement is best. Direct measurement This method involves setting up a system that can collect the data at the time they are produced. These data can then be grouped into the required time period - weeks or print runs. Every time that the chosen solvent is used, the volume or weight used is recorded. For example, ask the operator to count the litres, gallons or number of drums/jugs of screen wash used each day/shift/week. A good way of doing this is to set up a procedure which requires operators to sign and date a form each time they use solvent. Indirect measurement Solvent use in the process can be measured by performing a stocktake at the end of each period, for example, every week. Accurate monitoring of deliveries is also necessary to determine consumption. The stocktaking process must also be consistent and accurate for the collected data to reflect solvent consumption. Solvent consumption = Previous stocktake - Current stocktake + Deliveries during period 8

14 How to measure solvent use? The screens are cleaned by two operators, who fetch screen wash from the stores in a small bucket, as required, and apply it with the brush used to scrub the screens clean. The two operators also use their supply of screen wash to clean the printing machines at the end of print runs and for spot cleaning during print runs. The managing director therefore asks the operators to fill their bucket to the nearest litre mark and keep a tally at the stores of how many buckets of screen wash they use each week. He asks them to record whether they fill the bucket to the 1, 2 or litre mark.. STEP - TAKING PRODUCTION INTO ACCOUNT Solvent measurements have limited value unless they can be linked to production throughput over the same period of time. Step involves deciding on an appropriate production measure. Although the choice of production measure - direct or indirect - depends on how the solvent is used, it should also reflect the change in solvent consumption. The chosen production measure must be measured over the same time period as solvent consumption...1 Direct measures of production A direct measure of production relates to the level of activity in the process that is being observed. For example, if screen wash is being measured, then possible direct measures of production include: number of screens washed/week; area of screens washed/week...2 Indirect measures of production An indirect measure of production provides a good indication of the activity of the production process. The measure should vary in relation to the material being monitored. For example, if the ink used in printing is being measured, then possible indirect measures of production include: number of operating hours/week; number of production hours/week; value of production in a batch. Which production measure? As the larger screens require more screen wash, the managing director chooses the area of screens cleaned each week as the production measure rather than the number of screens cleaned..4 STEP 4 - DECIDE WHICH MEASUREMENT PERIOD TO USE The time period chosen depends to a certain extent on the production measure. The choice is usually between: batch, eg print run; daily; weekly; monthly. 9

15 If solvent use in the process is directly related to the number of batches or print runs, then it may be sensible to collect data on solvent use and production measure by batch. Data collection by day, week or month depends on the volume of production and how much time is available to carry out the work associated with Measuring to Manage. Weekly monitoring is recommended because it allows meaningful data to be collected within a time scale that is short enough for changes to be remembered. The effects of any variations in procedure on the amount of solvent used can also be observed. For example, if the normal operator is away and the amount of screen wash increases, this could be due to several factors. However, the most obvious are: the operator is using more screen wash on each screen because there are no instructions for screen cleaning; more screen wash is being used because the instructions do not indicate exact solvent volumes. Measuring solvent and production on a daily basis is time-consuming and may not yield any more information than weekly monitoring. However, there are occasions when this level of investigation, for a short period, may help to resolve particular problems with individual equipment. Monthly monitoring is the least time-consuming period to choose but it has the major drawback of being too long a period; the reasons for poor performance at the beginning of a month are forgotten by the end of the month..5 STEP 5 - GATHERING DATA Before starting to gather information, it is helpful to make it clear to everyone involved in the Measuring to Manage programme what the aims are and what is going to happen to the information they collect. It is also important to make sure everyone is clear about the practical aspects of the programme, eg: what to measure; when and how to measure it; where and how to record the measurement; who to give the measurement records to. Process operators and others should be urged to continue working as usual. If people perform better than normal during the initial stages of the programme, a true picture of performance will not emerge immediately. As they slip back into their traditional ways, performance may get worse before it gets better (as action is taken to eliminate these traditional ways). It is better to start off with all the bad habits out in the open. Collection of good quality data for at least six weeks is recommended before any attempt is made to analyse these data..5.1 Recording data Subsequent data analysis will be easier if the data for actual production and solvent use during each time period are collated in adjacent columns of a table similar to the sample worksheet in the Appendix. Please feel free to photocopy this worksheet for your own use. 10

16 Keeping simple records As well as keeping a tally in the stores of the number of buckets of screen wash used each week, the managing director asks the two operators to keep a record of the numbers of each size screen they clean on a weekly tally sheet (see Fig 2) stuck on the outside of the cleaning booth. Week ending: Screen Cleaning Record Screen size Small (0.2 m 2 ) Medium (0.4 m 2 ) Large (0.8 m 2 ) Total Area Total area = m m m m2 Fig 2 Weekly tally sheet used to record production measure.6 STEP 6 - ANALYSING DATA AND TAKING ACTION TO REDUCE SOLVENT USE The first stage of the data analysis involves drawing a scatter graph of solvent use against the production measure. However, before starting to plot the first data sets (a minimum of six is recommended), consider the following questions: Has this been a typical period of production? For example, just before Christmas is often a bad time to start. Is the range of solvent use as expected, ie are the lowest and highest values typical? Is the range of production measurement typical? If the answer to any of these three questions is NO, more data are needed before the scatter graph is drawn. Going ahead at this stage could mean having to redraw the graph because the scales are wrong. 11

17 .6.1 Drawing a scatter graph First select an appropriate scale for both axes of the graph with: the production measure across the bottom of the scatter graph (the x-axis); the measurement of solvent use up the left hand side of the graph (the y-axis). If the scale of the graph is based on the minimum and maximum values from the initial data, problems will arise if subsequent measurements fall outside this range. This is quite likely as the aim is to use solvent more efficiently. The production measure can then be plotted against the relevant solvent consumption for each time period. The standard line The straight line that provides the best indication of the general slope of the points - the line of best fit - gives an estimate of the average or standard for solvent use against production. This standard line can be used to predict how much solvent should be used, given current performance, for any production level. The minimum number of data sets to which a standard line can be fitted is usually six - the more points, the better. Please contact the Environmental Helpline on if you require further information on this topic. Plotting a scatter graph At the end of the first six weeks of data collection, the managing director produces a data table (Table ). Week ending Screen area cleaned (m 2 ) Screen wash used (litres) 5/4/ /4/ /4/ /4/ /5/ /5/ Table Initial data Fig shows the managing director s scatter graph, with a line of best fit drawn through these data by eye. y Screen wash (litres) 80 v t s u Screen area cleaned (m 2 ) x Fig Scatter graph of initial data 12

18 .6.2 Using the scatter graph to identify opportunities to use solvent more efficiently The scatter graph provides an indication of solvent consumption relative to the chosen production measure. The spread of points around the standard line shows the variation in the process (see Fig ). Points above the standard line show that the process is using more solvent than the amount predicted by the standard. Points below the standard line show that the process is using less solvent than the amount predicted by the standard. The aim of Measuring to Manage is to control solvent consumption so that solvent is used as efficiently as possible. The next step is to find out what was different between the time periods and which difference(s) caused the variation in solvent use. When each week s data are added to the scatter graph, it is important to identify what made solvent use better or worse than standard for that week and to take action to: prevent the reason for the poor performance happening again; ensure good performance becomes normal performance. Solvent use is now being managed more effectively..6. Taking action to reduce solvent consumption and waste To use solvent more efficiently, the causes of excessive solvent use and waste must be investigated. These include: solvent leaks; equipment malfunction; poor housekeeping; poor operator practices; lack of operator instructions; poor maintenance practices; poor equipment design; excessive fume extraction; inadequate production planning. Good Practice Guide (GG28) Good Housekeeping Measures for Solvents describes practical measures to make solvents go further and reduce wastage. This Guide is available free of charge through the Environmental Helpline on Take action to eliminate possible causes of solvent waste one at a time. 1

19 Taking action to reduce solvent use The managing director s scatter graph (see Fig ) shows that better use is made of screen wash in some weeks than in others. His immediate aim is to bring solvent use at least to the standard, and preferably below it, every week. When the operators show him how they clean the screens, he realises that there are significant differences in their work practices, eg: Operator A always puts a lid on the bucket of screen wash when it is not being used, operator B does not. When production demands allow, operator A leaves the screens to soak for 15 minutes in the cleaning booth trough. Operator A puts a makeshift cardboard lid on the trough during the soaking period. Operator B uses a separate brush for final rinsing of the clean screen. Operator B also takes the final rinse from the bucket of clean screen wash rather than emptying the trough, cleaning it and using a whole bucketful of screen wash to refill the trough. The managing director agrees new working practices with the two operators that will use the least amount of screen wash and help to reduce evaporation. He explains that leaving buckets and troughs of screen wash open to the air leads to excessive evaporation. After four more weeks, the managing director starts to see a real improvement. He adds four more weeks data to his table (see Table 4). When he plots the new data on his scatter graph (see Fig 4), he realises that he is on target because the new points - the triangles in Fig 4 - all fall below the standard line. Week ending Screen area cleaned (m 2 ) Screen wash used (litres) 5/4/ /4/ /4/ /4/ /5/ /5/ /5/ /5/ /5/ /6/ Table 4 Data before and after taking action Screen wash (litres) y Before no-cost measures After no-cost measures Screen area cleaned (m 2 ) x 14 Fig 4 Scatter graph after implementing no-cost measures

20 .6.4 Using the scatter graph to obtain other information The standard line - or line of best fit - on the scatter graph also indicates: the baseload of solvent use, ie the volume of solvent required to start production; unit consumption, ie solvent use/production unit. When the minimum scale point on the x-axis is zero, the baseload of solvent use is indicated by the point at which the standard line crosses the y-axis of the scatter graph, ie zero production (see Fig 5). y m = S = Solvent use P Production unit Standard line Solvent use P S c Baseload 0 Production measure x Fig 5 Determining baseload solvent use and unit consumption The baseload solvent use can be calculated from the equation of the standard line, ie: where: S = (m x P) + c S = the value for the standard solvent use for that period of production m = solvent use/production unit P = the recorded production measure c = baseload solvent use Solvent use/production unit (m) is given by the gradient or slope of the standard line (see Fig 5). This value indicates how much solvent is required to carry out each unit of production on the process in question. The gradient of the standard line (m) can be calculated from the y and x co-ordinates of a point at the upper end of the standard line (v,u) (see Fig ) and a point at the lower end of the line (t,s), ie: m = (v - t) (u - s) The baseload is then calculated using the equation of the standard line (y = mx + c) and the coordinates of a point on the standard line (say, v,u): v = (m x u) + c c = v - (m x u) 15

21 Calculating the parameters of the standard line The managing director calculates the values of the slope m and the baseload c for his standard line. From Fig, he reads off: (v,u) = (80,90) (t,s) = (56,50) m = (v - t) = = 24 = 0.6 litres/m 2 (u - s) c = v - (m x u) = 80 - (0.6 x 90) = 26 litres These values tell the managing director that the weekly baseload use of screen wash is 26 litres and unit consumption is 0.6 litres/m Setting targets to reduce solvent consumption and waste The values of m and c determined from the scatter graph can be used to set targets to reduce the amount of solvent used (see Fig 6). Targets may include: reduction or elimination of the baseload of solvent use on the process(es); reduction in the solvent use/production unit. y Solvent use Reduce solvent use/production unit Reduce baseload 0 Production measure x Fig 6 Using the scatter graph to set targets to reduce solvent consumption There are no hard and fast rules for taking action. Every company and each process within a company have different problems, and present different opportunities for minimising wastage. If the baseload of solvent use is higher than expected or desired - say 25% or more of the maximum solvent use in any one period - then target this first. Alternatively, if the solvent use/production unit is higher than expected or desired, then target that first. Comparing the value of baseload solvent use and the cost of solvent use/production unit with other operating costs may facilitate this decision. 16

22 .6.6 Identifying trends by drawing a CUSUM graph Using the scatter graph, it is possible to check that taking action has made a difference, ie do the new data points fall below the standard line? By adding up the changes between the standard and actual measurements of solvent use over a number of periods (eg weeks), a measure of the success of the Measuring to Manage programme in achieving more efficient use of solvent can be obtained. Plotting this cumulative sum of changes on a graph shows how much solvent has been saved and the degree of control over the process that consumes the solvent. This graph is called a CUmulative SUM or CUSUM graph. This graph tracks the variations in solvent use from a standard solvent use (predicted by the standard equation). If savings are achieved, this change will be negative as the process is using less solvent. The CUSUM graph can also be used to check that waste reduction projects are on course. Calculating changes from the standard The difference between actual and standard solvent use for a particular week s production shows how good or bad performance was in that week. This information is useful when deciding whether or not to take action. In general, large changes are worthy of action, small changes are not. The change in solvent use from the standard for a particular level of production can be calculated from the equation of the standard line drawn from the first six weeks measurements, ie: S = (m x P) + c The value for the standard solvent use (S) for that period of production can be calculated by inserting the recorded production measure (P). The change in solvent use is the difference between the actual solvent use (A) and the standard solvent use (S) for a particular period. Calculating CUSUM For the first period of time, eg a week: For every subsequent time period: CUSUM = the change (A - S) for that week CUSUM = change + previous CUSUM Like change, CUSUM can be either negative or positive; a negative value shows that solvent savings are being consistently achieved. 17

23 Calculating CUSUM The managing director calculates CUSUM for the first ten weeks. For the week ending 5 il 1996: Production measure (P) = 67 m 2 Standard solvent use (S) =(m x P) + c = (0.6 x 67) + 26 = 66 litres Actual solvent use (A) Change (A - S) CUSUM = 69 litres = = litres = litres For the following week where change = -9 litres, CUSUM = + (-9) = -6 litres. He continues his calculations and produces Table 5. Week Screen area Standard solvent Actual screen Change CUSUM ending cleaned (m 2 ) use (litres) wash used (litres) (litres) (litres) P S A A - S 5/4/ /4/ /4/ /4/ /5/ /5/ /5/ /5/ /5/ /6/ Table 5 CUSUM data for the first ten weeks of data collection Plotting CUSUM Plotting the CUSUM values on a graph helps to monitor and maintain actions to reduce solvent use. These graphs are drawn by plotting the CUSUM values against the time period. Positive CUSUM values go above the horizontal zero line, negative CUSUM values below. It is advisable to join up the points on the graph as they are plotted..7 STEP 7 - HOW TO INTERPRET CUSUM GRAPHS The CUSUM graph enables trends and small, but persistent, changes in data to be detected. The CUSUM graph provides: an indication of the level of control over the process; a method of monitoring the effects of actions taken to reduce solvent consumption. The slope of the graph signifies the change. When interpreting a CUSUM graph, three basic rules apply: a downward sloping line means continued solvent savings are being made; 18

24 a line which levels out means that solvent savings are not being maintained; an upward sloping line means excessive solvent is being used. The typical CUSUM graph shown in Fig 7 demonstrates the type of information and warnings that CUSUM can provide. CUSUM (litres) Jan 29 Jan 26 Feb Aug 9 Sep 7 Oct Fig 7 Typical CUSUM graph.7.1 The line oscillates around the zero line Fig 8 shows that actual solvent use can be predicted from the standard equation with some degree of accuracy. The process is therefore under some form of control, but still needs to be monitored to detect any excursions from the standard consumption. CUSUM (litres) Jan 29 Jan 26 Feb Aug 9 Sep 7 Oct Fig 8 Process under some form of control.7.2 The slope of the graph is negative Fig 9 shows that the amount of solvent used by the process is less than that predicted from the standard equation. Action should be taken to maintain the good work practices and procedures that have achieved this improvement. 19

25 The slope also indicates a constant saving from an action taken to control solvent use. Provided the change to procedure is maintained, this trend should continue until the standard line is reset. CUSUM (litres) Jan 29 Jan 26 Feb Aug 9 Sep 7 Oct Fig 9 Savings are being achieved.7. The graph stabilises below the zero control line Fig 10 indicates that an action has taken place that produced a one-off saving in solvent use. No further or continued saving will result from this action. CUSUM (litres) Jan 29 Jan 26 Feb Aug 9 Sep 7 Oct Fig 10 Action producing a one-off saving.7.4 The slope of the CUSUM line changes from negative or zero to positive Fig 11 indicates that a major change in procedures or operation has occurred. This may be due to one of several reasons. Check that the original procedures for solvent use are being followed correctly. Is the change a sudden one independent of production levels? This may indicate the need to train the operator(s) using the solvent. 20

26 Have there been any major operating changes, eg has another machine been brought on-line to cope with an increase in production? If so, the standard line needs to be reset. CUSUM (litres) Jan 29 Jan 26 Feb Aug 9 Sep 7 Oct Fig 11 The effects of a major change in procedure or operation.7.5 The slope of the graph is positive Fig 12 shows that the amount of solvent used in the process is, on average, greater than predicted from the standard equation. Action should be taken to identify the reasons for this overuse. CUSUM (litres) Jan 29 Jan 26 Feb Aug 9 Sep 7 Oct Fig 12 Excessive solvent consumption.7.6 The graph stabilises above the zero control line Fig 1 indicates that some incident has occurred, or action taken, to produce a one-off loss of material. The line has levelled out again showing that there is no further loss resulting from the incident or action that produced the change. This type of change could be caused by a leak in a tank or drum. When the leak is fixed, the change levels out. Another possible cause is an increase in solvent stock within a process. 21

27 CUSUM (litres) Jan 29 Jan 26 Feb Aug 9 Sep 7 Oct Fig 1 One-off loss of material The effects of taking action A CUSUM plot of the first six weeks data did not provide the managing director with much information. However, with ten weeks data, the effects of the new working practices, introduced at no-cost, are clear (see Fig 14). This graph tells the managing director that about 17 litres of screen wash have so far been saved compared to the standard. CUSUM (litres) Aug 1996 Fig 14 CUSUM graph after implementing no-cost measures Low-cost measures implemented The success indicated by the CUSUM graph encourages the managing director to implement some low-cost measures. A permanent lid is installed on the cleaning booth trough and the operators are provided with purpose-made solvent cans fitted with lids and pouring spouts. The controls on the cleaning booth trough extraction fan are also altered so that the fan is on only when the lid is open. Six weeks later, the managing director sees the difference these actions have made when he adds the new data to his scatter graph (see Fig 15) and calculates CUSUM (see Table 6). The 22

28 scatter plot (see Fig 15) shows good performance; all the new data (plotted as diamonds) fall on target below the standard line. Screen wash (litres) y Before no-cost measures After no-cost measures After low-cost measures Screen area cleaned (m 2 ) Fig 15 Scatter graph after implementing low-cost measures x Week Screen area Standard solvent Actual screen Change CUSUM ending cleaned (m 2 ) use (litres) wash used (litres) (litres) (litres) P S A A - S 14/6/ /6/ /6/ /7/ /7/ /7/ Table 6 Data table after implementing low-cost measures The CUSUM graph (see Fig 16) shows that the consistent savings have been achieved. The steeper CUSUM means that more screen wash has been saved week-on-week in the last six weeks than before. CUSUM (litres) Aug 1996 Fig 16 CUSUM graph after implementing low-cost measures 2

29 The CUSUM graph indicates a problem When he adds the data for the week ending 26 y, the managing director is surprised to find that performance has suddenly deteriorated. This is not immediately apparent from the table (see Table 7) and the circle on the scatter plot (see Fig 17), but the CUSUM line has flattened out, indicating a problem (see Fig 18). Week Screen area Standard solvent Actual screen Change CUSUM ending cleaned (m 2 ) use (litres) wash used (litres) (litres) (litres) P S A A - S 12/7/ /7/ /7/ Screen wash (litres) y Table 7 Data table after the week ending 26 y Before no-cost measures After no-cost measures After low-cost measures Problem week Screen area cleaned (m 2 ) x Fig 17 Scatter graph showing addition of data for problem week CUSUM (litres) Aug 1996 Fig 18 Problem highlighted by CUSUM graph 24

30 The managing director discovers that both operators had been away and that their replacement had not been told about the new working practices. Once training had been given and the other operators return, performance improves again (see Fig 19). CUSUM (litres) Aug 9 Aug 16 Aug Fig 19 Improvement continues once the problem is resolved What has Measuring to Manage achieved? Fig 19 also shows that about 100 litres of screen wash have been saved in ten weeks. Provided these savings can be maintained through continued Measuring to Manage, the company expects to save half a tonne of screen wash each year. In addition to the cost savings, this 12.5% reduction in solvent consumption will allow the factory to increase production without breaching the threshold for LAPC registration. Using CUSUM to determine the degree of control The size of CUSUM provides an indication of the degree of control being achieved, ie: low CUSUM values (positive or negative) indicate good control of the process; high CUSUM values (positive or negative) indicate poor control of the process. The boundary between small and large CUSUM values can be arbitrarily set at around 10% of the solvent consumption in any one period. Table 8 shows the effect of applying this rule to a process with widely fluctuating CUSUM values. For Example A, the CUSUM percentage is greater than 10% of the solvent consumption and the process could be said to be out of control. However, for Example B, the higher solvent consumption figures mean that the process could be said to be under control. Example A Example B CUSUM Solvent use CUSUM Solvent use CUSUM (litres) percentage (litres) percentage Week % % Week % % Week % % Week % % Week % % Week % % Table 8 Using CUSUM to decide whether a process is in control 25

31 .7.7 Trend analysis This simple alternative to scatter plots can often yield useful information about a process. The technique involves drawing a graph showing how solvent use changes with time (see Fig 20) Solvent use (litres) Feb 12 Feb 19 Feb 26 Feb Fig 20 Changes in solvent use with time The way in which solvent use varies with time provides considerable information about a process. Examples include: Regular variations (see Fig 21) These are usually caused by factors external to the process, such as different shift/operator practices, regular changes in production, etc Solvent use (litres) Feb 12 Feb 19 Feb 26 Feb Fig 21 Regular variations Seasonal variations (see Fig 22) External temperatures and humidity can have a marked effect on printing processes, drying times, solvent evaporation, etc. 26

32 Solvent use (litres) Jan Feb e y Aug Sep Oct Nov Dec 1996 Fig 22 Seasonal variations Periodic variations (see Fig 2) Like regular variations, these are usually caused by factors external to the process. However, they can also be caused by internal factors, such as critical parts wearing at a regular time interval. For example, after a certain number of running hours, a pump seal may start to leak causing a solvent loss Solvent use (litres) Feb 19 Feb Fig 2 Periodic variations Random variations (see Fig 24) By their very nature, apparently random variations are difficult to interpret. Use of a scatter graph may help to identify the cause Solvent use (litres) Feb 19 Feb Fig 24 Random variations 27

33 Performance evaluation Trend analysis can also be used to compare similar processes, eg solvent use on two identical screen cleaning machines. Fig 25 shows that one machine consumes more solvent than the other. The reason for this difference in performance should be investigated by the plant manager. Reasons for this type of difference include: differences in operator practice; equipment malfunction; solvent leaks; product mix effects Machine Machine 1 Solvent use (litres) Feb 19 Feb Fig 25 Comparing similar processes.8 STEP 8 - MEASURING TO MANAGE IS ONGOING A Measuring to Manage programme is like a never-ending journey - making more efficient use of solvent in one area of the factory will highlight wastage in other areas. But, while attention is given to this new problem, it is important to maintain the good performance that has already been achieved through Measuring to Manage. The best way to maintain projects to use solvent efficiently is to continue checking performance. This is easily achieved by using the CUSUM graph as a control chart..8.1 Resetting the CUSUM graph If the CUSUM graph shows a constant negative slope after several weeks or months, then this indicates that solvent use has been brought under greater control than for the standard line, ie a change in procedure has reduced solvent use. If this procedural change becomes routine, then solvent will continue to be used more efficiently. At this point, the standard line can be reset so that future performance can be tracked more easily. Resetting the CUSUM graph involves: plotting a new scatter graph using the most recent data for solvent use and production measurement - say ten weeks worth; drawing the line of best fit to these new data and calculating the equation of this line (the new standard of solvent use); redrawing the CUSUM graph (possibly with a new scale). 28 The line on the new CUSUM graph should oscillate around zero, indicating that solvent use is near the new standard and under control.

34 A downwards move away from zero indicates that solvent is being used even more efficiently. A consistent movement upwards from zero - say for three or four weeks - indicates that control is being lost and corrective action is required. Fig 26 shows an example of such a change CUSUM (litres) Oct 11 Nov Dec Action taken to bring process under control 6 Jan Feb Fig 26 Example of reset CUSUM graph showing indication of change Possible reasons for this change include: a solvent-saving project has hit problems; a process characteristic has changed due to a change in production levels; the process has altered physically due to maintenance, damage, modifications, etc; the personnel operating the process have changed and introduced new bad habits. The Measuring to Manage programme may need to be run again to re-optimise the process. CUSUM is reset The CUSUM line has been a constant downwards slope for over ten weeks and the managing director decides the process has improved as much as possible. He therefore resets the standard line so that the CUSUM graph can be used to manage screen wash consumption at the current level. He uses the ten weeks data from 2 August 1996 to produce a new scatter graph and calculates the equation of the new standard line. When this is compared with the original equation, the managing director concludes that the weekly solvent baseload has fallen significantly from 26 litres to 16.8 litres. Unit consumption has decreased slightly from 0.6 litres/m 2 to 0.58 litres/m 2. The new CUSUM graph (see Fig 27) has a smaller range on the y- axis because the managing director intends to use the graph to identify problems. CUSUM (litres) Aug 16 Aug 0 Aug 1 Sep 27 Sep 11 Oct 25 Oct 8 Nov 22 Nov 6 Dec 20 Dec Jan 17 Jan 1 Jan 14 Feb 28 Feb Fig 27 Reset CUSUM graph 29

35 4 INDUSTRY EXAMPLES These Industry Examples describe how four screen printing companies tackled Measuring to Manage solvent and achieved cost savings and other benefits. 4.1 BTP SCREEN PROCESS PRINTERS LTD BTP Screen Process Printers (BTP) uses a flat sheet process to produce a wide range of products, including self-adhesive vinyls, water slide transfers and point-of-sale advertising. The Company employs 50 people at its Coventry site. 4 BTP used around five tonnes of solvent a year and would have had to register for authorisation under LAPC unless steps were taken to reduce solvent consumption. The Company uses solvents mainly for thinning inks, spot washing screens and screen wash. Solvents are also used by the printer for cleaning on the press. The printer s assistant uses screen wash for cleaning screens and squeegees off the press on an adjacent working surface at the end of a print run. BTP believed that it could reduce its total solvent consumption significantly if: the amount of screen wash used was reduced; the use of solvent for spot washing was controlled more effectively. However, BTP decided to wait until results from a Measuring to Manage trial were available before committing the Company to a course of action to reduce solvent consumption. BTP wanted a simple approach to Measuring to Manage solvent, so it was decided to monitor screen wash consumption on two / 4 automatic printing lines (machine 5 and machine 16). The volume of screen wash used by each line was used as the solvent measure and the number of screens cleaned as the production measure. As the screens are all roughly the same size, results from the two lines could be compared without calculating the surface area of screens cleaned. For the period of the trial, each line operated a different cleaning operation; the printer s assistant cleaned the screens for machine 5 on the press and the screens for machine 16 off the press. Fig 28 shows the scatter plot of the initial trial data. The initial audit revealed that the volume of screen wash used on the two lines was different. Fig 28 shows that the variation in the volume of screen wash used on machine 16 did not always depend on the number of screens cleaned. The printer s assistant used an average of 0.2 litres of screen wash/screen on machine 5, whereas on machine 16, an average of 0.56 litres of screen wash/screen was used. The trial indicated that more screen wash was being used to clean screens off the press. This result came as a surprise to Mike Charlton, BTP s Managing Director. Mike said, I expected that less solvent would be used to clean screens off the press. The difference in screen wash use between the two machines highlights a need for more training. 0

36 Screen wash (litres) y Machine 5 (on press) Machine 16 (off press) Number of screens cleaned x Fig 28 Initial trial data from BTP BTP has now decided to take action to reduce its solvent consumption by: Training. Using dip cans on benches to dispense solvent for spot cleans. Buying a screen washing booth. The booth will circulate and filter screen wash which will be applied to the screens using a brush. Re-using solvent will reduce the volume of solvent used to clean screens and give knock-on savings in the purchasing and cleaning of rags. 4 Mike Charlton said, Solvent consumption is the most important environmental issue to me at the moment. Measuring to Manage solvent has helped me focus my attention on solvent use in the factory. Measuring to Manage solvent fits in with our ISO environmental management system. I intend to use it on all the printing presses to give us a better idea of the variation in solvent consumption throughout the factory. BTP expects to save 4 000/year by using Measuring to Manage solvent to reduce screen wash use by around one tonne/year (25% of current consumption). The Company will also avoid having to register under LAPC saving an application fee of and an annual subsistence cost of 625 ( prices). 1

37 4.2 HALO COMPANY LTD Halo, a small screen printer in Sussex employing 40 people, specialises in printing on vinyl and plastic. The Company s products include high-visibility signs for emergency vehicles and public transport livery decorations. Before beginning its Measuring to Manage solvent programme, Halo admitted to having little knowledge of its solvent use in printing or cleaning. Management received several surprises as a result of the initial study of solvent use. This study revealed that Halo used nearly 000 litres of solvent/year, of which 900 litres were used for screen washing. 4 Although enthusiastic about the idea of Measuring to Manage solvent, Halo wanted to try out the method before spending too much time on it. The Company had little information about how much screen wash was being used either on the printing benches to wash screens between print runs or to clean screens before they were reclaimed for re-use on other jobs. Halo decided to trial Measuring to Manage solvent in the screen reclamation area and set up a system to record: the number of screens of various sizes cleaned in any week; the amount of screen wash taken from the solvent store into the screen reclamation area. As a number of people worked in the screen reclamation area, it was necessary to make them all aware of the information they had to record when using screen wash solvents to reclaim screens. The initial six-week trial highlighted a problem in the data gathering method. It became apparent that the actual amount of screen wash used in a week was not being measured, ie screen wash withdrawn from the stores was being carried forward from one week to the next. For example, the data indicated that, in week six, nearly 20 m 2 of screen were cleaned without any screen wash being drawn from stores. Halo therefore modified the method used to measure screen wash use to take screen wash stock into account. The data for the week with no apparent screen wash use was added to the previous week s data. Considerable variation in screen wash use was also observed. 2

38 Halo continued recording weekly data for a further six weeks using the improved method of measuring screen wash use. These data confirmed Halo s initial finding that there was no discernible trend in screen wash use and therefore a standard line could not be drawn. Halo therefore decided to use average screen wash consumption as a standard. This is shown on Fig 29 as a horizontal line. The data from the second six weeks (shown as triangles in Fig 29) indicate that screen wash use is below average in some weeks and above in others. The variation is about 50%. Screen wash (litres) y Weeks 1-6 Weeks Screen area cleaned (m 2 ) x 4 Fig 29 Halo s scatter graph after 12 weeks data collection Looking at the data again, Halo realised that the cleaning of large 2.4 m x 1.2 m (8 ft x 4 ft) screens could be the cause of the higher-than-average screen wash use. Works Manager Mick Hellen said, The larger screens are a real problem to clean. They don t fit in the cleaning trough properly and we often have to wash them twice with solvent to reclaim them. This second solvent wash is carried out in the jet wash area and the solvent is discharged as waste. Halo is planning to: increase the size of its cleaning trough; replace the obsolete solvent recycling equipment attached to the trough; ensure that any second solvent washes are carried out in the solvent cleaning trough. According to Mick Hellen, Measuring to Manage solvent has helped to raise the general awareness of solvent use in the Company. The printers are now far more careful with the way they dispense solvent onto rags. We also expect to see use of wash solvent fall substantially as we move over to using dip cans. Halo s Managing Director Peter Low commented, I am very pleased with the heightened awareness of solvents in the company which Measuring to Manage solvent has created. The potential for reducing our screen wash use is small, but the time taken to identify problems and solve them has also been small. Any savings we make go directly to the bottom line - that is profit. I am expecting to see greater improvements in ink waste in the future. Measuring to Manage has shown that Halo uses about 500 litres/year of screen wash for screen reclamation. The Company expects the planned improvements to the screen cleaning process to reduce screen wash consumption by up to 50%, saving 450/year.

39 4. RH TECHNICAL INDUSTRIES LTD RH Technical Industries Limited (RHTI), a member of Laird Group plc, prints a wide range of products from simple name-plates to complex membrane switches and fascias. Although the Company can print on almost any substrate, it works mainly with metal and plastics. RHTI s production department is split into production cells where similar machines are used or similar products are processed. RHTI employs over 120 people at Andover in Hampshire. Managing Director Chris Hills says, RHTI has been close to the LAPC registration threshold of five tonnes annual solvent use for the past couple of years. Measuring to Manage solvent has already helped us to avoid registration for the foreseeable future; the simple act of measuring solvent use in the workplace raises workforce awareness of solvent consumption and reduces consumption. 4 In 1994/5, RHTI used 175 kg of screen wash. At the outset of the Measuring to Manage solvent programme, weekly average consumption was comparable with this annual use. Despite production levels staying relatively constant, total screen wash consumption fell week by week. After ten weeks of working with Measuring to Manage solvent, RHTI s projected annual use fell to kg - a reduction of almost 700 kg/year. RHTI has also started to look at the performance of the different production cells and individual operators within each cell. For example, cell 2 uses three printing presses, all printing similar work. The overall cell performance is shown in Fig 0. When RHTI examined the performance of individual operators within the cell, differences emerged (see Fig 1). Operator A works days only, while operators B/C and operators D/E share printing benches on shifts. Fig 1 shows that operators B and C use far more solvent than the others. RHTI is now working to identify the reasons for this difference in performance. 4

40 Chris Hills said, Similarly all the other production cells show differences in operator performance. I expect to reduce solvent use by another 20% through standardising screen cleaning throughout the Company. Solvent use (litres) y Number of screens cleaned x Fig 0 Overall performance of cell 2 at RHTI y Solvent use (litres) Operator A Operators B/C Operators D/E Number of screens cleaned x Fig 1 Individual performances within cell 2 at RHTI RHTI already uses dip cans to dispense solvent, but has a number of other ideas for reducing solvent use in screen cleaning, including: using a dry cloth to clean excess ink off the screen before using solvent; folding cleaning tissues to get the most use out of tissues and solvent, ie using a small area of a tissue to clean a, then folding the tissue to expose a clean surface to continue the cleaning process; reducing solvent evaporation by storing solvent-wet tissues between use in a re-sealable vessel (like a breadbin); using garden-type plastic spray-bottles to dispense solvent onto screens for cleaning. RHTI also plans to set a factory standard for solvent use/screen cleaned to allow printers to compare their own performance. Measuring to Manage solvent has achieved savings of around 700/year in screen wash. More importantly, in the view of RHTI s Managing Director, this reduction means that RHTI will not have to register under LAPC for some time thus saving the initial fee and annual authorisation costs. Registration would have been a time-consuming burden that I am glad to be able to avoid. 5

41 4.4 WALKERS OF MANCHESTER LTD Walkers specialises in screen printing point-of-sale display materials for retailers and manufacturers of consumer goods. Walkers prints onto all substrates including plastic, metal and wood, using solvent-based conventional inks and water-based or solvent-based ultraviolet (UV) inks in four colour printing processes. The Company employs 100 people at its site in east Manchester. Walkers already uses less than five tonnes of solvent/year, thus avoiding registration under LAPC. However, the Company is keen to keep below this level and aims to move to water-based inks to eliminate the need to use solvents. Walkers decided to try out Measuring to Manage solvent on solvent use in screen cleaning because it was easier than measuring solvent use in the solvent-based inks. High-quality thinning solvent is used by the printers to clean screens on Walkers printing presses because of quality problems with poorly cleaned screens in the past. Solvents are not used for screen reclamation because the screens are cleaned thoroughly before being removed from the printing press. 4 From the outset of the Measuring to Manage solvent programme, Walkers realised that it would be necessary to measure solvent use during three distinct types of screen cleaning activity, ie spot cleaning, partial clean-ups and complete clean-ups. Solvent use was measured on the basis of the amount of solvent drawn by each printer from the stores. Three printers were chosen to carry out a trial. After the six weeks initial period, scatter graphs of solvent use against screen area cleaned were drawn for each printer (see Fig 2). The screen area cleaned was calculated by assuming that a spot clean cleaned 1% of the area of a screen, a partial clean covered 50% of the screen and a full clean 100% of the screen. Fig 2 shows that each printer s performance was slightly different; printer C being consistently the most efficient and printer B the least. However, the performance of all three also varied from week to week. Walkers decided, as an initial goal, to help printer A and printer B improve their performance to match that of printer C. Solvent use (litres) y Printer A Printer B Printer C Fig shows printer A s performance both before and after training. Four out of the six weeks x Area cleaned (m 2 ) Fig 2 Initial data collection from three printers at Walkers of Manchester 6