Use Of Electrostatic Spray Techniques For The Surface .
*I-1-/I .1INTEROFFICE COMMUNICATIONMIDWEST RESEARCH INSTITUTEJ u l y 11, 1984To:P r o j e c t F i l e No. 7705-LFrom:Barbara W. D u l e t s k y pSubject:Use o f E l e c t r o s t a t i c Spray Techniques f o r t h e Surface Coating o fP l a s t i c Parts f o r Business Machines/The most common type o f c o a t i n g equipment use by f a c i l i t i e s t h a t coat p l a s t i cp a r t s f o r business machines i s m u a l a i r atomizc?spray.E l e c t r o s t a t i c spraymethods have been demonstrated t h a t appear t o achieve higher t r a n s f e r e f f i c i e n c i e sthan conventional a i r s p r a y 7 T f o s eo f t h i s memorandum i s t o present informationgained through i n d u s t r y contacts about e l e c t r o s t a t i c spray technology, and t o drawconclusions about i t s a p p l i c a b i l i t y t o t h e surface c o a t i n g o f p l a s t i c p a r t s f o rbusiness machines.ELECTROSTATIC SPRAYA.TheorvThe basic mechanism o f e l e c t r o s t a t i c spray i s the d i f f e r e n c e i n p o t e n t i a l energyo f t h e c o a t i n g and t h e p a r t t o be coated, which causes an e l e c t r o s t a t i c f o r c e t oe x i s t between them. T y p i c a l l y , t h e c o a t i n g i s given a p o s i t i v e charge a t t h e gunand p r o p e l l e d toward t h e p a r t by means o f a h i g h pressure airstream. Since t h egrounded p a r t i s o p p o s i t e l y charged, the a t t r a c t i o n o f the c o a t i n g p a r t i c l e s f o r t h ep a r t overcomes t h e momentum o f t h e p a r t i c l e s . Consequently, t h e c o a t i n g "wrapsaround" t h e p a r t r a t h e r than being l o s t as overspray. By t h i s method, t r a n s f e re f f i c i e n c y i s g r e a t l y improved over conventional a i r spray methods. I n d u s t r y contactshave estimated t r a n s f e r e f f i c i e n c y f o r e l e c t r o s t a t i c guns t o be anywhere f r o m 30 t o90 percent, depending on t h e method o f atomization ( i . e . , a i r , a i r l e s s , a i r - a s s i s t e d /airless). 1-5When t h e p a r t t o be coated i s a nonconductive substrate such as p l a s t i c , i t i snecessary t o p r o v i d e a conductive surface t h a t can bleed o f f t h e e l e c t r i c a l charger e s u l t i n g from t h e accumulation o f charged p a i n t p a r t i c l e s . This may be done byapplying a conductive s e n s i t i z e r t o t h e surface t o be coated, grounding the e l e c t r o magnetic i n t e r f e r e n c e / r a d i o frequency i n t e r f e r e n c e (EMI/RFI) s h i e l d i n g l a y e r ,grounding a conductive f i x t u r e o r image behind t h e t a r g e t , using a p l a s t i c t h a t i si t s e l f conductive, o r spraying an e l e c t r i c a l l y conductive topcoating such as awaterborne coating.1. Conductive s e n s i t i z e r . The most common method o f preparing p l a s t i c f o re l e c t r o s t a t i c spraying i s spray a p p l i c a t i o n o f a conductive s e n s i t i z e r . A t y p i c a ls e n s i t i z e r contains 1 t o 8 percent by volume h y d r o p h i l i c s a l t i n s o l u t i o n w i t h anorganic solvent o r water. I t can be a p p l i e d by spraying, m i s t i n g , hand-wiping, o rdipping. As t h e s o l v e n t evaporates, t h e s a l t expands by absorbing water molecules
2from the air and forms a continuous, conductive film on the part.described in a vendor brochure, is shown in Figure 1.6This process, asSensitizers dissolved in organic solvents such as isopropyl alcohol are beingused more frequently than waterborne sensitizers. Since isopropyl alcohol is a VOC,application of this type of conductive sensitizer is a source of VOC emissions.There are no data available on whether or not the overall VOC emissions are reducedby using a conductive sensitizer prior to electrostatic spray, but preliminaryestimates and calculations show that emissions may be reduced by as much as 63 percent.Table 1 shows the approximate tradeoff between emissions from air atomized sprayapplication of a conductive sensitizer and emission reductions achieved by usingelectrostatic spray for subsequent topcoats. A l-percent solution of sensitizer inisopropyl alcohol is assumed, since this would contain the highest expected proportionof VOC. The coverage for 1 gallon of sensitizer is assumed to be 1,500 square feet,since this represents the highest level of VOC emissions for the 1,500 to 2,000 ft2/galrange supplied by the manufacturer.2. Grounded EMI/RFI shielding. In order to attenuate EMI/RFI signals, plasticbusiness machine housings should be effectively shielded by a layer of conductivematerial. This is most commonly achieved by zinc-arc spraying or by application ofconductive coatings using conventional air atomized spray guns. Other EMI/RFIshielding techniques include electroless plating and the use of conductive plastics.For zinc-arc spraying and air atomized spraying.of conductive coatings, a layerBygrounding this layer, the exterior surface can be coated electrostatically. Althoughplastic acts as an insulating barrier between the conductive layer and the spraygun, the charged paint particles are still attracted toward the grounded E M V R F I shielded surface. Attraction may be uneven, however, depending on the uniformity ofthe shielding coating. This is a disadvantage, since a nonuniform electrostaticforce does not provide a good basis for an even surface finish.o f conductive material is applied to the interior surface of each housing.In the case of electroless plating, the part is dipped in a conductive solution,thus making both interior and exterior surfaces conductive. By grounding the metalsurface, the topcoating can be applied electrostatically.In the same way that charged paint particles can be applied electrostatically toa metal surface, they can also be applied to conductive plastics. Plastic can bemade conductive by the use of molded-in metal flakes or carbon particles. Dependingon the surface resistivity, this type of substrate can be an effective base forelectrostatic sprayi ng.3. Grounded image. A conductive fixture or image may be placed behind the partand then grounded to facilitate electrostatic spraying. Like the previous method,the plastic part does not prevent the attraction of the coating for the groundedsurface. Since the plastic part lies within the force field created by the differencein potential, the charged paint particles are deposited on the part.4. Waterborne coatings. Waterborne coatings can be charged at the gun andsprayed electrostatically onto a plastic part. Once the coating forms a continuousfilm on the grounded part, the surface is rendered conductive. As long as thecoating remains wet, it continues to bleed off the charge and maintains a differencei
4TABLE 1. EMISSIONS FROM ELECTROSTATIC SPRAY COATING (FOLLOWING APPLICATIONOF A CONDUCTIVE SENSITIZER) COMPARED TO CONVENTIONAL A I R ATOMIZED SPRAY COATINGSensitizer ApplicationVOC content o f s e n s i t i z e rVOC d e n s i t y (isopropyl a l c o h o l )S o l i d s content o f s e n s i t i z e r 99% by volume, as a p p l i e d 6.56 l b / g a l 1% by volume, as a p p l i e dCoverage a t 100% t r a n s f e r e f f i c i e n c y 1,500 f t 2 p l a s t i c p e r 1 g a l s e n s i t i z e r 0.667 gal sensitizer/1,000 f t 2 p l a s t i c 0.00667 g a l solids/1,000ft.2plasticS e n s i t i z e r usage a t 25% t r a n s f e r e f f i c i e n c y ( a i r atomized spray guns) coverage t 0.25 0.0267 g a l solids/1,000 f t 2 p l a s t i cVOC emissions a t 25% t r a n s f e r e f f i c i e n c y ( a i r atomized spray guns) 0.0267 gal solids/1,000 f t 2 p l a s t i cx 99 g a l VOC/gal s o l i d sx 6.56 l b VOC/gal VOC 17.3 l b VOC/l,OOO f t 2 p l a s t i cCoating A p p l i c a t i o n 68% by volume, as a p p l i e dVOC content o f coatingVOC d e n s i t y (average)S o l i d s content o f c o a t i n g 7.36 l b / g a l 32% by volume, as a p p l i e dCoverage a t 100% t r a n s f e r e f f i c i e n c y 5 m i l x 1 ft2 s o l i d s / f t 2 p l a s t i c 720 in3 solids/1,000 f t 2 p l a s t i c 3.12 gal solids/1,000 ft2 p l a s t i cCoating usage a t 25% t r a n s f e r e f f i c i e n c y ( a i r atomized spray guns) coverage 0.25 12.5 g a l solids/1,000 f t 2 p l a s t i cVOC emissions a t 25% t r a n s f e r e f f i c i e n c y ( a i r atomized spray guns) 12.5 g a l solids/1,000f t 2 plastic'x 68 g a l VOW32 g a l s o l i d sx 7.36 1b VOC/gal VOC 196 l b VOC/l,OOO f t 2 p l a s t i c(continued)
5TABLE 1.-(continued)VOC emissions and emission reductionsa for electrostatic spray:Trans fer e ff i c i ency30507090- Coating usage (gal solids/1,000 ft2):(coverage itransfer efficiency)VOC emissions for electrostatic spray( l b VOC/l,OOO ft2):(Coating usage x 68 gal V O W 3 2 galsolids x 7.36 l b VOC/gal VOC)VOC emissions from application ofconductive sensitizer (1 b VOC/l, 000 81109124a415663163VOC emissions for electrostatic sprayfollowing application of conductivesensitizer ( l b VOC/l,OOO ft2)VOC emissions for air atomized spray( l b VOC/l,OOO ft2)Emission reductiona ( l b VOC/l,OOO ft2)Emission reductiona (percent)aEmission reduction achieved by using electrostatic spray following applicationof a conductive sensitizer instead of conventional air atomized spray.
6i n p o t e n t i a l between t h e p l a s t i c p a r t and the p a i n t p a r t i c l e s . I n a d d i t i o n t odecreasing VOC emissions and c o a t i n g consumption, t h i s method a l s o reduces t h e f i r ehazard caused by spraying h i g h volumes o f VOC.6.Applications i n I n d u s t r y1. Equipment and conductive coatings/substrates vendors. E l e c t r o s t a t i c sprayequipment and conductive coatings/substrates are r e a d i l y a v a i l a b l e through manyd i f f e r e n t vendors. Some o f these vendors were contacted f o r i n f o r m a t i o n on t h e useo f t h e i r products i n t h e surface c o a t i n g of p l a s t i c p a r t s f o r business machines.Table 2 summarizes t h e i n f o r m a t i o n gathered from these contacts.2. Surface coaters o f miscellaneous p l a s t i c p a r t s . Surface c o a t i n g i n d u s t r i e st h a t are using t h i s technique f o r p l a s t i c products such as s a f e t y helmets, automobilef a s c i a , window shutters, etc., are l i s t e d i n Table 3. The t r a n s f e r o f t h i s technology t o business machine p a r t s may n o t be made d i r e c t l y , however. The e f f e c t i v e n e s so f t h i s spray method depends, t o a l a r g e extent, on t h e s i z e and complexity o f t h ep a r t t o be coated. F o r instance, p a r t s w i t h recessed and louvred areas are p a r t i c u l a r l y d i f f i c u l t t o cover e l e c t r o s t a t i c a l l y due t o t h e "Faraday Cage'' e f f e c t . On t h eo t h e r hand, e l e c t r o s t a t i c spraying o f c o a t i n g onto a l a r g e f l a t t a r g e t would approach100-percent t r a n s f e r e f f i c i e n c y and provide complete and uniform coverage.3. Surface coaters o f p l a s t i c p a r t s f o r business machines. I t i s uncommon f o rf a c i l i t i e s t h a t surface coat p l a s t i c business machine p a r t s t o employ e l e c t r o s t a t i cspray methods. Table 4 shows t h e names o f t h e companies t h a t were contacted s p e c i f i c a l l y about t h e i r use o f t h i s method. O f t h e 19 companies surveyed, 5 have usede l e c t r o s t a t i c spraying on a production basis, and 4 others have experimented o ri n t e n d t o experiment w i t h it. While t h e companies t h a t use t h i s method i n productionb e l i e v e t h a t t r a n s f e r e f f i c i e n c y has been improved, o n l y one was able t o provides p e c i f i c supporting data. 30Many contacts o f f e r e d p o s s i b l e reasons f o r t h e i n f r e q u e n t use o f t h i s method i nthe industry. A major f a c t o r i s t h e i n i t i a l c a p i t a l c o s t o f t h e equipment. Ane l e c t r o s t a t i c hand-held gun costs 2,000, which i s 10 times t h e c o s t o f a conventionala i r atomizing gun.17 Although t h e vendors a d v e r t i s e a s h o r t payback p e r i o d due t ot h e savings i n c o a t i n g consumption, most coaters would n o t r e a l i z e t h i s savingsw i t h o u t i n c u r r i n g p r i o r losses common t o i n c o r p o r a t i n g new equipment. Many o fthe small j o b shops do n o t have t h e resources a v a i l a b l e t o experiment w i t h t h i stechnology. Even i f t h e i n i t i a l c a p i t a l investment were n o t a b a r r i e r , they wouldn o t have t h e p l a n t c a p a c i t y t o maintain t h e i r production r a t e w h i l e r e t r a i n i n g t h espray gun operators.I n a d d i t i o n t o manual spray guns, a u t o m a t i c a l l y c o n t r o l l e d systems are a v a i l a b l efrom various equipment vendors. The c a p i t a l c o s t of an automated system i s muchgreater than t h a t o f manual guns, b u t t h e c o n s i s t e n t and e f f i c i e n t spraying i tAutomation i s p a r t i c u provides has the p o t e n t i a l t o improve t r a n s f e r e f f i c i e n c y .l a r l y b e n e f i c i a l f o r f a c i l i t i e s t h a t coat l a r g e q u a n t i t i e s o f s i m i l a r parts. Oncethe c o a t i n g l i n e has been programmed t o spray a c e r t a i n rack o f p a r t s , largeq u a n t i t i e s can be coated w i t h l i t t l e o r no adjustments t o t h e c o n t r o l s . Advantagesof t h i s technique i n c l u d e improved t r a n s f e r e f f i c i e n c y , increased production r a t e ,and consistency i n q u a l i t y o f t h e f i n a l products. Improved t r a n s f e r e f f i c i e n c y has
TABLE 2.Company, addressELECTROSTATIC SPRAY (ES) COATING--EQUIPMENT AND CONDUCTIVE COATING/SUBSTRATE VENDORS- - - . -- - - ----- - -Product- .- . -.IMethod of ES coatingEMVRFIAdvanced Chemicals and CoatingssTemple City, Calif.CoatingsGroundedCelanese Corp.Charlotte, N.CCarbon fibersConductive carbon fibermeshDeft. Inc.'OIrvine. Calif.ChemicalsConductive coatingsComments- withGrounding the EMI/RFI shielding has been usedpolyurethane topcoat applications.- FordMotor Co. had been involved in ES usingnonwoven veil of conductive carbon fibers.- wovenInternational Paper Co. manufacturers the nonaesh.*Electro-Cote Chemicals, 1nc.I'Noblesville, Ind.Chemicals (conductivesensitizer)Conductive sensitizer*Electro Kinetic Systems, Inc. l 2Wilmington. Oel.EM1 shielding coatingsGrounded EHI/RFI-Enshield@ EMI/RFIshielding processSpray equipmentGraco, Inc.'Minneapolis, Minn.Grounded EMI/RFI*No surface pretreatmentSensitizers are in isopropyl alcohol solution.Effectiveness increases with humidity. Up tofour top coats can be applied by ES.IBM and A m c o are involved i n ES coating usingconductive sensitizers.Ransburg and Air Power manufacture ES equipment.- EM1shielding can be sprayed onto exteriorcoating.surfaces and used as a base for*Enthone. Inc.Bridgeview. 1 1 1 .Deft sells mostly to aerospace industry, butthey are working with Beckman Instruments todevelop coatings with ES potential.Business machine coaters may not have the resources to experiment with costly new technologies such as ES.*ESSolvents In EM1 and top coat must be compatiblefor a good surface finish.Leida Finishing may be using this method of EScoating.Most peo le use two-component urethanes over theEnshielde electroless plating.Coaters hat may be doing ES coating over theEnshielplating: Genron, Furniture City, E/MLubricants.8ES centrifugual atomizer, CA-1000, can achievetransfer efficiencies of 85% on conductive ornonconductive substrates.Also manufacture automatic and manual ES airspray guns. (continued)4
.-i'TABLE 2. .---(continued)ProductMethod o f ES c o a t i n gKremlin, l n c . ' 'Addison, Ill.Spray equipmentGrounded metal hangersLeaRonal, I n c . I sFreeport, N.Y.Vest',vapor e t c hs h i e l d i n g technologyGrounded EHI/RFINordson Corp. l 6Matthews, N.C.Spray equipmentConductive s e n s i t i z e r-Uneven coverage since p a i n t i s a t t r a c t e d unevenly.ES gets 38%b e t t e r t r a n s f e r e f f i c i e n c y than air-atomized ES.On metal, a i r - a s s i s t e d / a i r l e s s-Shielding process involves vapor e t c h i n gby e l e c t r o p l a t i n g .followf!dThe surface may be conductive enough a f t e r vapore t c h i n g f o r ES coating.The p l a t i n g i s a good base f o r ES coating.Xerox has experimented w i t h t h i s technique.Conductive p l a s t i c sGeneral* Cost i n h i b i t s most small coaters from usingGrounded metal rackGrounded EMI/RFISpray equipmentCmentsRendered nonconductive i f heat i s applied.Otherwise a good method.* Not as e f f e c t i v e as using a conductivesensitizer.* Coating i s a t t r a c t e d o n l y t o p o i n t s o f contactw i t h metal.* Causes uneven a t t r a c t i o n due t o nonuniformshielding.C a l l Eastnan or Celanese f o r more information.Grounded imageNordson Corp.Amherst, OhioConductive s e n s i t i z e r- A i r ESTransmet Corp.I9Columbus, OhioAluminum f i l l e r f o rconductive p l a s t i c sConductive p l a s t i c s*U d y l i t e P l a t i n g Systems2"Warren, Hich.A t tenup 1ate' EM1/RF Is h i e l d i n g processGrounded E M I / R F I-A r v i d C. Walberg & C O . 'Oowrier ' s Grove, I 11.Spray equipmentWaterborne coatings* -03ES.Hewlett-Packard i n the San Francisco area i sspraying waterborne coatings by ES.Spray equipmentRansburg Corp.Indianapolis,-- Company, addressInd.--Ransburg manufactures manual and automatic ESguns achieve 50-75 percent t r a n s f e refficiency.-.-* H i g h l y u n l i k e l y t h a t p a r t s could be coated byE S , since most o f the aluminum i s concentratednear the center and the surface i s r e s i n - r i c h .eAttenuplate process can be used as a base f o r E Scoating, although i t provides surfaces w i t h muchhigher c o n d u c t i v i t y than needed by ES.E/M Lubricants r a y be involved w i t h ES c o a t i n gby t h i s method.Walberg manufactures b o t h automatic and handh e l d ES equipment.Waterborne coatings are conductive, so nos e n s i t i z e r i s needed.Hetamora t o . i s using a Walberg system.r-P- . - I
-.-TABLE 3.ELECTROSTATIC SPRAY (ES) COATING-MISCELLANOUSType o fexperienceMethod o f ES c o a t i n gProduct coatedArthur Fulmer C O . *Miami. F l aProductionConductive p l a s t i c sSafety helmetsDavidson Rubber Co.Dover, N HProductionGrounded image,conductive s e n s i t i z e rPlastic parts forautomobilesFord Motor Co.’ProductionCarbon f i b e r meshAutomobile hoodscoopsGuide D i v i s i o n o f GM2ProductionGrounded aluminumf i x t u r e behind p a r tAutomobilefasciasCompany. addressProductionMetallic layerMiscel laneousMetamora Products Corp.24Metamora, Mich.ProductionWaterborne coatingsWindow shutters-- - -Comments**Jay P l a s t i c s 2 3Mansfield, OhioP L A S T I C COATERS--*Conductive g e l i s molded-in w i t h f i b e r g l a s s andthen coatings are a p p l i e d by Ransburg ES r e c i p r o c a t i n g disc.Research w i t h e l e c t r o s t a t i c b e l l s t o determinestandard t e s t for t r a n s f e r e f f i c i e n c y .Experimented w i t h several types o f ES primers.Doing research i n v o l v i n g c o l a n i n a t i o n o f nonwovenv e i l o f carbon f i b e r nesh, followed by ES coating.Six Graco ES guns i n each booth t r i g g e r e d autonatically.System i s computer c o n t r o l l e d and TE 60 t o 70%.A f t e r base coat, products receive s p u t t e r i n ga p p l i c a t i o n o f a decorative m e t a l l i c layer.Outer c o a t i n g i s sprayed automatically w i t hRansburg ES guns.Using Walberg system for ES coating.About t o i n s t a l l DeVilbiss system.
TABLE 4.-.ELECTROSTATIC SPRAY (ES) COATING--SURFACE COATERS OF PLASTIC PARTS FOR BUSINESS MACHINES-. -- .- --- -Company, addressType of experi
The basic mechanism of electrostatic spray is the difference in potential energy of the coating and the part to be coated, which causes an electrostatic force to exist between them. and propelled toward the part by means of a high pressure airstream. . larly difficult to cover electrostatically due to the "Faraday Cage'' effect.
Spray finishing can be conducted in a spray booth, spray room, or spray area. Tuesday, February 14, 2017 Definitions Tuesday, February 14, 2017 Spray room: A spray room is a room in which spray-finishing operations not conducted in a spray booth are performed separately from other areas. 1910.94(c)(1)(iii)
Introduction to Thermal Spray Processing / 5 Thermal Spray Processes and Techniques Members of the thermal spray family of processes are typically grouped into three major categories: flame spray, electric arc spray, and plasma arc spray, with a number of subsets falling under each category. (Cold spray is a recent addition to the familyFile Size: 793KB
generator has used a mechanical force. On the contrary, This body is called the charge carrier. the new electrostatic generator uses an electrostatic . The most popular electrostatic generator is the Van de Graaff type electrostatic generator [1]. This was invented by Dr. Van de Graaff in 1931 in the USA.
a properly selected spray angle, will tend to make more effective use of the spray as well as help minimize the dis-turbance effects of wind/draft condi-tions on the water spray patterns. Spray Patterns. The Design Spray Profiles for the nozzle spray angles of 65 to 180 degrees
coverage of spray patterns as calculated from the included spray angle of the spray and the distance from the nozzle orifice. Values are based on the assumption that the spray angle remains the same throughout the entire spray distance. In actual practice, the tabulated spray angle
spray generation, spray rate and the distance between the spray nozzle and the substrate. With resists such as the AZ 4999 or the TI spray, there are some ready-to-use spray resists suitable for most applications. Adjustments to the solvent composition for an optimisation of the coating
Compliant Spray Equipment High volume low pressure guns – Can be used in areas where current usage of conventional spray is used Air-assisted airless electrostatic guns – More versatility than regular electrostatic guns to spray areas where Faraday cage effect is of concern
Cambridge IGCSE Accounting is accepted by universites and employers as proof of an understanding of the theory and concepts of accounting, and the ways in which accounting is used in a variety of modern economic and business contexts. Learners focus on the skills of recording, reporting, presenting and interpreting inancial information; these form an ideal foundation for further study, and for .
