Opportunities for In-mould Painting at TVS Motor · PDF fileOpportunities for In-mould Painting at TVS Motor ... TVS Motor Company is the third largest manufacturer of two-wheelers

Smithers Rapra Technology, 2011
107Progress in Rubber, Plastics and Recycling Technology, Vol. 27, No. 2, 2011
Opportunities for In-mould Painting at TVS Motor Company Ltd
K. Rajendren
WMG, University of Warwick, Coventry, CV4 7AL
Summary
TVS Motor Company is the third largest manufacturer of two-wheelers in India and one of the top ten manufacturers in the world. The company manufactures 1.5 million two-wheelers for both its domestic and overseas requirements. The companys manufacturing process involves painting of plastic, metal and aluminium components to enhance their appearance and performance properties. The company currently uses a conventional post painting process for its moulded plastic panels. However the conventional post painting process causes a huge impact on the environment through flue gas emissions from baking ovens, solvent emission from paint booths and ovens, sludge generation from paint booths and wastewater generation from paint booths and pre-treatment processes. The volumes of waste and cost for part attached to the painting process for TVS Motor Company are detailed in this paper. Paint shop replacement technologies in relation to current in-mould decoration technologies such as pigmented plastics, in-mould film, co-injection moulding and in-mould spray painting (INSPIRE) are considered. Based on current specifications and requirements for painted plastic components, INSPIRE is found to be the most advantageous paint shop replacement technology for current TVS Motor Company Ltd production as it uses a thermoset, matching current specifications. A design of experiments is performed using a polyester skin and ABS substrate to optimise part coverage for a sample part. Using statistical analysis spray time and spray pressure are found to be the most important process parameters for paint coverage. Paint coverage could be greatly improved compared to that which has been previously reported.
1. INTrODuCTION
The present process used for motorcycle plastic parts finishing in TVS Motor Company Ltd (Hosur, India) is the post painting process. This involves
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108 Progress in Rubber, Plastics and Recycling Technology, Vol. 27, No. 2, 2011
K. Rajendren
electrostatic paint spraying of moulded plastics in a paint shop. This paper considers the current painting system and specifications in use and then considers optimisation of other technologies for plastic parts finishing. An optimised process should have better functional and appearance properties, lower operating cost, and less environmental concerns than the current method.
The electrostatic painting process currently used for motorcycle plastic parts finishing involves the following major steps:
Cleaningandsurfacepreparation
Primerpainting
Topcoatpainting
Curing
These are the same type of stages commonly carried out to produce automotive coatings [1,2].
The performance measurement of the resultant paint film can be carried out under two broad categories. The first category deals with measuring aesthetic properties of the paint film: the most popular test methods measure glossiness of the surface [3], distinction of image [1], orange peel [4] and colour [5]. A second category measures functional properties. The critical functional properties which are commonly measured are adhesion [6], hardness [7] and UV tolerance [8]. Any new system must match or exceed these properties, ideally at a lower operating cost and reduced environmental impact.
With the increasing awareness of the impact of global warming on the environment, the emissions from paintshops are a major cause of concern. The chemicals used in the painting process like paints, solvents, cleaning chemicals, furnace oil, diesel etc, all have a negative environmental effect. The source of this impact can be broadly classified into four categories:
Fluegasemissionfrombakingovens
Solventemissionfrompaintboothsandovens
Sludgegenerationfrompaintbooths
Wastewatergenerationfrompaintboothsandpre-treatmentprocess
Fuelgasemissionfrombakingovens
Currently plastic components are painted with polyurethane paints which are heated at 70C for 20 minutes and this is normally carried out in a heat curing oven. This process of heating normally takes place in two phases. In the first phase, the component is raised to the required temperature and in the second phase it is maintained at that temperature for the required time for full cure

to be achieved [1]. The first phase is normally carried out using IR heating lamps which heats the part rapidly within 2-4 minutes. The second phase is carried out in oil fired indirectly heated thermal curing ovens. The burning of furnace oil releases carbon-dioxide which is released to the atmosphere.
1.2 Solvent Emission from Paint Booths and Ovens
The polyurethane paint used for painting plastic parts is a mixture of binders, pigments, solvents and additives. The main purpose of solvents is to maintain the paint in a liquid form, so that it can be used easily for spraying through air-assisted guns. The paint received from the paint manufacturers will normally haveviscosityintherangeof4050secondswhenmeasuredusingFordB4Viscosity measurement cup [9]. The viscosity of these paints will be reduced to the application range of 20-25 seconds by mixing with thinner which in turn consists of solvents like Xylene, Toluene etc. The solvents present in both paint and thinner evaporate after application both in the booths and oven and are released into the atmosphere through exhausts and pollute the environment. The typical thinner usage in a paint shop is shown in Figure 1.
Figure 1. Typical thinner usage in a paint shop (TVS Motor Company Ltd)

110 Progress in Rubber, Plastics and Recycling Technology, Vol. 27, No. 2, 2011
K. Rajendren
This data is sourced from TVS Motor Company Ltd which has three separate paint shops within the same plant for both plastics and metals and consumes 1.18 kL of thinner per day, out of which 0.38 kL is released into atmosphere and 0.81 kL, is sent to bunkers as scrap. The plant has got a thinner recycling unit which receives 0.24 kL of waste thinner from paint shops for recycling and returns 0.11 kL for fresh usage.
1.3 Sludge Generation from Paint Booths
The transfer efficiency of the electrostatic paint process for painting the plastic parts of a motorcycle in TVS Motor Company Ltd lies in the range of 4045%.Thismeansthat4045%ofthesprayedpaintgetsdepositedon the plastic components and the remaining quantity of paint along with the solvent is carried away by the flowing water in the paint booth in the form of sludge to the sludge pit. On average 400 L of paint per day is used by the plastic painting line in TVS Motor Company Ltd, which results in the generation of 60 kgs of sludge which is sent to bunkers. The calculation for sludge generated is as shown below:
Total Volume of paint used = 400 L/day
Transfer efficiency of painting process = 40%
Total volume of paint wasted = 400 * (100-40)/100 = 240 L/day
Volume solids of paint = 40%
Total sludge generated = 96 L/day~60 kgs/day~22 Tons/yr
Therefore, from a paint shop manufacturing 1000 sets of plastic parts, the approximate amount of sludge generated is estimated to be 22 T/year.
1.4 Waste Water Generation from Paint Booths and Pre-Treatment Process
The painting process uses water in two major areas, one in paint booths to carry the sludge to sludge pit, and the other in the pre-treatment process, where the plastic parts are cleaned before painting to remove dust and other foreign particles. Both these areas generate waste water which has to be sent to effluent treatment plants for treatment and is again sent for re-usage. On average, in a paint shop manufacturing 1000 sets of motorcycle plastic parts per day, 10 kL of water is being consumed which is later sent for recycling. The process of water treatment involves chemicals like sodium hypo-chloride and bleaching powder, which in turn affects the environment.

It can be seen that a change to an efficient in-mould painting process would offer a considerable improvement in terms of environmental impact for TVS Motor Company Ltd.
1.5 Cost of Current Painting Process
The cost incurred for a painting process can be classified into two distinct categories:
Directcost - Paint cost
Indirectcost - Power and fuel cost (plant running cost) - Labour cost (direct and indirect labour) - Maintenance cost - Consumables cost (pre-treatment chemical, sludge chemical, water
treatment chemicals, gloves, nose guards etc)
For the calculation of cost, a motorcycle model produced by TVS Motor Company is used as a reference. This model TVS Apache RTR is chosen due to its high manufacturing volumes; black colour paint is used for calculation. This paint is commercially termed as PU Special Black and is supplied by Kansai Nerolac Paints (Mumbai, India). The costing details of the painting process are shown in Indian currency in Table 1.
Table 1. Costing details of the painting processPaint consumed per set 0.3 litreCost of PU special black per litre 200 INRPaint cost of plastic parts per set =0.3 *200 = 60 INRDirect cost of painting process per set 60 INRPower and fuel cost

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Opportunities for In-mould Painting at TVS Motor · PDF fileOpportunities for In-mould Painting at TVS Motor ... TVS Motor Company is the third largest manufacturer of two-wheelers