Progress in Organic Coatings 55 (2006) 316–323

Coating characteristics of electron beam cured bisphenol A diglycidyl etherdiacrylate resin containing 1,6-hexanediol diacrylate on wood surface

Virendra Kumar ∗, Yatendra Kumar Bhardwaj, Sunil SabharwalRadiation Technology Development Section, Bhabha Atomic Research Centre, Mumbai-400085, India

Received 13 June 2005; accepted 13 January 2006

Abstract

Electron beam curing of bisphenol A diglycidyl ether diacrylate resin (BDGDA) mixed with varying amount of 1,6-hexanediol diacrylatemonomer (HDDA) was investigated using low energy DC electron beam accelerator. Cured coating films were analyzed by Fourier transformedinfrared spectroscopy (FTIR), gel fraction, swelling ratio and thermogravimetric (TG) techniques. The wood surfaces cured with different coatingcompositions were tested for their end use performance properties like gloss, pencil hardness, scratch resistance, mar resistance, abrasion resistance,chemical resistance, steam resistance and cigarette burn resistance. FTIR studies indicated that the density of acrylate functionality and degree ofcuring increased with the HDDA content in the feed mixture. This observation was supported by gel fraction and swelling studies as well. Thette©

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hermal stability, pencil hardness, mar resistance, abrasion resistance and solvent resistance properties of coating were observed to improve withhe incorporation of HDDA. However, there was significant decrease in gloss and scratch resistance at higher HDDA content. The coating showedxcellent steam and stain resistance but poor resistance to cigarette burns.

2006 Elsevier B.V. All rights reserved.

eywords: Electron beam curing; Coatings; Bisphenol A diglycidyl ether diacrylate resin; 1,6-Hexanediol diacrylate; Gel fraction; Wood

. Introduction

The conventional curing processes mostly use solvent-basedhemicals formulations, which generally creates environmentalollutions by emitting large amount of volatile organic com-ounds (VOC) and other hazardous air pollutants (HAP) intohe atmosphere [1–4]. However, increased awareness regard-ng the environment, energy conservation, economics and bettererformance of products have emerged as the driving force towitch from conventional curing to radiation curing process5–9]. Radiation curing is polymerization/crosslinking reactionsnitiated by radiation energy to convert liquid chemical systemnto non-tacky solid matrix. Radiation energy include ionizingadiation like high-energy electrons, �, � or � rays from radionu-leids, X-rays and non-ionizing radiations like UV [10–13].adiation cured products have emerged as materials of choice

or specific end uses because of some unique properties [14]. Theajority of radiation curing work has been devoted to UV curing

15,16]. EB curing offers certain advantages over UV curing and

is being preferred mainly because of day-to-day advancement inEB machines, instantaneous complete curing, no requirement ofphotoinitiators, possibility of curing of thick coatings and bet-ter process control [17]. Considering these advantages of EBcuring, several groups have studied various types of EB cur-able resins including acrylates, methacrylates, vinyl esters andepoxies to develop high-performance polymer matrix compos-ites for novel applications [18]. EB curable formulations mainlyconsist of oligomer or prepolymer and reactive monomers. Theoligomer is responsible for the performance properties of thecured film but many oligomers have viscosities that are too highfor practical applications. Low viscosity reactive diluents areadded in suitable proportion to oligomers to reduce their viscos-ity [19]. The diluent needs to be judiciously chosen so that thedesired properties of the oligomer are not compromised and ifpossible it should further enhances the characteristics of coat-ing. In the recent times much attention has been paid to radiationcuring of epoxy acrylate resins for surface coating applications[20,21]. Various types of resins in combination with differentreactive diluents were cured and examined for end performanceproperties of the coatings [20–22]. Epoxy acrylate resins based

∗ Corresponding author. Tel.: +91 22 25590178/79; fax: +91 22 25505151.E-mail address: vkumar@magnum.barc.ernet.in (V. Kumar).

on diglycidyl ether of bisphenol A hold pride position in coatingindustry because of its low cost and many desirable properties

300-9440/$ – see front matter © 2006 Elsevier B.V. All rights reserved.oi:10.1016/j.porgcoat.2006.01.002

V. Kumar et al. / Progress in Organic Coatings 55 (2006) 316–323 317

Table 1Coating compositions and evaluation of film characteristics at different EB dose

Sample Oligomer BDGDA Reactive diluent HDDA Results after irradiation to doses (kGy)

210 280 350 420

X0 100 0 1 2 2 3X1 100 10 1 2 2 3X2 100 20 1 2 3 3X3 100 30 1 1 3 4X4 100 40 1 1 3 4

Ratings: 1, tacky; 2, slightly tacky; 3, non-tacky; 4, non-tacky with shrinkage.

like hardness, gloss, chemical resistance, etc. Wood coatingapplications typically demand high gloss, which can be obtainedfrom epoxy acrylate oligomers. HDDA has a very low viscosityand offers a much-appreciated combination of solvency, flex-ibility, adhesion, reactivity, toughness and outdoor stability inthe cured film [23].

The curing behaviour and performance of the EB curablecoatings largely depends on their chemical formulations. In thepresent work, we have investigated the EB curing behaviourand end use performance properties of bisphenol A diglycidylether diacrylate (BDGDA) coating containing varying amountof reactive diluent (HDDA).

2. Experimental

2.1. Materials

The oligomer bisphenol A diglycidyl ether diacrylate (Pho-tomer 3016F) and reactive diluent 1,6-hexanediol diacrylate(Photomer 4017F) were supplied by M/s Cognis Corporation,USA and were used as received without further purification. Thechemical structures of oligomer and reactive diluent are givenbelow. The composed veneer plywood samples were purchasedfrom local suppliers.

2

2

m∼

for coating (Table 1). These formulations were applied onto glassplates and wood samples, of desired sizes using a motorized barcoater (Khushboo Scientific, India) with wire wound bar coaterno. 7. The coated samples were irradiated using an indigenous500 keV DC electron beam accelerator, under static conditionat beam current = 0.5 mA, beam energy = 370 keV, to get curedcoating film. The dosimetry of EB accelerator was carried usingnylon film dosimeter prior to irradiation. The thickness of thecured coating was found to be ∼100 �m. For FTIR studies, gelfraction determination, swelling and TG studies the chemicalformulation cured on glass plates were peeled off to conductthese studies.

2.2.2. FTIRFourier transformed infrared spectroscopy (FTIR) measure-

ments were performed on a FTIR spectrophotometer (FT/IR-660from JASCO, Japan). FTIR spectra were recorded in the rangefrom 400 to 4000 cm−1 with a resolution of 4 cm−1 and averagedover 25 scans. Cured film samples were thoroughly ground atliquid nitrogen temperature and mixed with KBr to prepare discsby compression. The uncured liquid samples were dissolved inacetone and then a drop of sample was sandwiched between twoKBr discs to record the spectra.

2.2.3. Gel fractionThe cured films of known weight were extracted for 10 h

ief

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2

atr

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2

tat

.2. Methods

.2.1. EB curing of epoxy acrylate resinOligomer (BDGDA) and reactive diluent (HDDA) were

ixed in different proportions with continuous stirring at40 ◦C to get homogeneous mixture to be used as formulations

n acetone using soxhlet extraction assembly. The films afterxtraction were dried in vacuum and weighed to estimate gelraction using following relation:

el fraction (%) =[

weight after extraction

initial weight

]× 100 (1)

.2.4. Swelling of cured film in acetoneCured films of known weight were dipped in acetone for 48 h

nd weighed after blotting the excess solvent from the surfaceo estimate the swelling ratio of the cured film using followingelation:

welling ratio = swelled weight

initial weight(2)

.2.5. Thermogravimetric analysisThermogravimetry analysis was carried out using TGA Met-

ler 3000 instrument. The thermograms were recorded in airtmosphere at a heating rate of 10 ◦C/min from room tempera-ure to 600 ◦C.

318 V. Kumar et al. / Progress in Organic Coatings 55 (2006) 316–323

2.2.6. Performance tests of cured wood panelsThe cured wood samples were tested for different end per-

formance properties, as per guidelines of standard test methodsviz. gloss at 60◦ angle (ASTM: D 523-99) [24], pencil hard-ness (ASTM: D 3363-00) [25], Taber abrasion test (ASTM: D4060-01) [26], scratch hardness resistance (BS: 3900 Part E2),stain/chemical resistance conducted for seven different stainingagents (EN 438-2: 1991), steam resistance (EN 438-2: 1991),and cigarette burn resistance (IS12823: 1990).

3. Results and discussion

3.1. Curing behaviour of coating compositions

In order to optimize the radiation dose to get non-tacky coat-ing, chemical formulations were exposed to different EB dosesin the range of 210–420 kGy. The EB curing behaviours of dif-ferent formulations are given in Table 1. It was observed that upto 350 kGy dose, formulations X1 and X2 gave tacky surface,whereas, compositions X2, X3 and X4 resulted in non-tacky uni-form films. At dose of 420 kGy all the formulations resulted innon-tacky films with some shrinkages in coating compositionscontaining higher content of HDDA (X3 and X4).

3.2. FTIR studies

tswapfpamcf

Fig. 2. FTIR of coating formulation after curing at 210 kGy. (a) X0 and (b) X4.

Density of acrylate double bond in the coating compositionwill govern the irradiation parameters, e.g. total dose and coatingperformances like shrinkage, brittleness, hardness, etc. Addi-tion of HDDA in BDGDA resin should increase in the acrylatedouble bond density due to lower molecular weight of HDDAcompared to BDGDA. The characteristic optical density ratioA809/A1509 responsible for the absorption of acrylate doublebond and bisphenol A, respectively, were plotted in Fig. 3 asa function of HDDA content in the mixture. The results showedthat there is a linear increase in the ratio with the increase inHDDA content, which reflected the increase in the functionalgroup density with the addition of HDDA in the resin BDGDA.

The EB curing caused a reduction in the number of unsatu-rated acrylate functionality, reducing the intensity of the peakat 809 cm−1. The degree of cure can be therefore related to theintensity of 809 cm−1 peak; higher the degree of cure lesserintense the peak. A quantitative determination of the degree ofcure was made by comparing the reduction in the intensity ofthe peak at 809 relative to the peak at 1509 cm−1 (C H defor-

Fa

FTIR is a very good tool to characterize the coating formula-ion and to estimate the degree of curing [27–29]. The FTIRpectra of two uncured and cured coating formulations, oneith no HDDA (X0) and other with maximum HDDA (X4),

re shown in Figs. 1 and 2, respectively. Certain characteristiceaks corresponding to different functional groups present in theormulations clearly appeared in the FTIR spectra. A prominenteak at 1724 cm−1 corresponds to carbonyl group stretching ofcrylate. Peaks at 1509 and 830 cm−1 correspond to C H defor-ation vibration of bisphenol A. Peaks at 809 and 1408 cm−1

orresponds to C C deformation of acrylate group, which wereound to reduce significantly after curing.

Fig. 1. FTIR of uncured coating formulation. (a) X0 and (b) X4.

ig. 3. Optical densities ratios A809/A1509 for mixture of BDGDA and HDDAs a function of HDDA content.

V. Kumar et al. / Progress in Organic Coatings 55 (2006) 316–323 319

Fig. 4. Degree of curing (%) as a function of HDDA content in BDGDA(dose = 210 kGy, beam energy = 370 keV, beam current = 0.5 mA).

mation of bisphenol A), which was assumed to remain constantduring the curing reaction. The degree of cure was estimated bycomparing the areas of two peaks. The degree of cure, estimatedas a function of HDDA content in the formulation mix is shownin Fig. 4. The degree of curing of coating formulation was foundto increase with the increase in the HDDA content. The increasein curing with the increase in HDDA content can be attributed toreduction in the viscosity of the formulation. The lower viscos-ity of the coating composition provides enhanced mobility to theradicals formed on BDGDA as well as on HDDA to chemicallyreact and form three-dimensional crosslinked structure.

The effect of radiation dose on degree of cure of differentcoating formulations containing varying amount of HDDA wasinvestigated and the results are shown in Fig. 5. As expected,degree of curing increased with the increase in the radiationdose because at higher radiation dose the number of radicalsgenerated will be more resulting in higher crosslinking extent.It was interesting to note that the effect of dose on degree ofcuring was more prominent for pure BDGDA or formulation

F(

Fig. 6. Effect of HDDA content on properties of coating. (a) Gel fraction, (b)swelling ratio in acetone (dose = 210 kGy, beam energy = 370 keV, beam cur-rent = 0.5 mA).

containing comparatively lower concentration of HDDA. SinceHDDA monomer is multifunctional in nature, at higher HDDAconcentration, extent of curing is completed or gets saturated atvery low doses.

3.3. Gel fraction

Gel fraction estimation is an important property of any coat-ing, as it is directly a measure of extent of crosslinking of thecured film, which in turn decides the final properties of the coat-ing. The results of gel fraction measurements are shown in Fig. 6.It was found that the gel fraction increased with the HDDAcontent in the coating composition and finally gets saturated at20 phr. The gel fraction results were supported by the degree ofcuring estimated by FTIR, as discussed in the earlier section. Theincrease in the gel fraction is due to the increase in the densityof the functionality (acrylate groups) and reduction of viscosityof formulations with the addition of HDDA in BDGDA.

3.4. Swelling study

Coating formulations containing varying amount of HDDAwere investigated for swelling in acetone for 48 h. The results ofswelling experiments are given in Fig. 6. It could be seen that theswelling ratio of cured films decreased with the increase in theHtHstts

3

bT

ig. 5. Degree of curing (%) of coating formulations as a function of EB dose.a) X0, (b) X1, (c) X2, (d) X3, and (e) X4.

DDA content in BDGDA resin, which was again supported byhe gel fraction results showing enhanced crosslinking with theDDA content in the formulation. The reason for decrease in the

welling with the increase of HDDA content is due to increase inhe gel fraction and crosslink density of the coating. Therefore,he coatings with higher crosslinking density are expected tohow better swelling resistance against chemicals or solvents.

.5. Thermogravimetric (TG) analysis

Thermal stability of the cured coatings was investigatedy thermogravimetric analysis of the EB cured coating film.he thermograms of pure resin and resin containing differ-

320 V. Kumar et al. / Progress in Organic Coatings 55 (2006) 316–323

Fig. 7. Thermal decomposition of EB cured BDGDA coatings containing dif-ferent amount of HDDA. Inset: derivative curve of thermograms for differentformulations (dose = 210 kGy, beam energy = 370 keV, beam current = 0.5 mA).

ent extent of HDDA are given in Fig. 7. The patterns of thethermogravimetric curve of the BDGDA resin containing HDDAare similar to that of pure BDGDA. It can be seen that the curedBDGDA matrix was stable up to ∼300 ◦C. The cured matrixshowed weight loss in two steps; first major weight loss in thetemperature range of 300–450 ◦C was due to thermal decompo-sition of organic coating and second weight loss in temperaturerange 450–550 ◦C was referred to the oxidation of the resid-ual formed from the thermal decomposition of coating. It canbe seen from the derivative curve (Fig. 7, inset) that both theweight loss zones shifted to higher temperatures by ∼20 ◦C inthe presence of HDDA in BDGDA. The detailed TGA data forall coating compositions are presented in Table 2, showing thetemperatures for different % weight losses (10, 50 and 90%)of the different coatings containing varying amount of HDDA.The TG analysis indicated that the thermal stability of BDGDAcoating increased significantly with introduction of HDDA inthe matrix.

3.6. Gloss

Gloss is a measure of the coated surface to reflect light andit is an important property of coating when the purpose is toprovide aesthetic or decorative look to the surface. Gloss of

TTw

S

XXXXX

Fig. 8. Effect of HDDA content in BDGDA oligomer on the gloss of theEB cured wood samples (dose = 420 kGy, beam energy = 370 keV, beam cur-rent = 0.5 mA).

the cured samples was measured at 60◦ angle of reflectanceusing a digital mini gloss meter (Khushboo Scientific, India)calibrated against internal standard of known refractive index(BYK Gardner) and the results are reported in gloss unit (GU).The gloss values of cured surfaces are plotted as a function ofHDDA content in Fig. 8. It could be seen that the gloss of theveneer plywood surface is enhanced by more than 30 times aftercuring with BDGDA resin. The gloss of the coating decreasedgradually with the increase in the HDDA content, which maybe attributed to micro distortions such as waviness caused byshrinkage generated on the coating at higher content of HDDAdue to higher crosslinking caused by HDDA. The micro distor-tions in the coating surface scatter the reflected light in otherdirection and resulted in low gloss values at 60◦ angles.

3.7. Scratch resistance

Among the mechanical properties required for a coating tofulfill its protective role, scratch resistance in one of the mostimportant one. The damage caused by scratch on cured surfacemay be simple that causes change in the glossy look of coatingor it may be as severe that may cause deformation and finallyinduce crack of coating. The deformation is understood to con-sist of three components: elastic, ductile and brittle [12]. Theductile deformation is made of an elastic component, which canrbTh(isoatuttw

able 2hermogravimetric analysis: decomposition temperature at certain percentageeight loss of different coating films cured at 210 kGy dose

ample no. Temperature (◦C)

10% wt. loss 50% wt. loss 90% wt. loss

0 337 402 5221 348 421 5392 355 421 5413 359 420 5384 360 422 540

ecover with time and a plastic component not recoverable. Therittle deformation introduces cracks at a certain critical load.he scratch resistance property of the EB cured wood samplesas been determined using an automatic scratch hardness testerKhushboo Scientific, India) having a hardened steel hemispher-cal point of 1 mm diameter as a scratching needle. The testamples were moved at a fixed speed of 3 cm/s beneath the pointf scratching needle. The scratch resistance and mar resistancere given as the weights on the stylus to tear off the coating ando give a visible mar on the coating respectively. This test sim-lates scratching by sharp objects. Results of scratch and marest are given in Fig. 9. It was seen that for oligomer BDGDA,here is an initial increase in scratch resistance and then decreaseith the increase in the HDDA content. The results showed that

V. Kumar et al. / Progress in Organic Coatings 55 (2006) 316–323 321

Fig. 9. Effect of HDDA content in BDGDA oligomer on the scratch resistanceand mar resistance properties of the EB cured wood samples (dose = 420 kGy,beam energy = 370 keV, beam current = 0.5 mA).

coating formulation containing 10 phr HDDA are the best amongthe various composition tried indicating higher concentration ofHDDA induce brittleness with hardness in the coating. How-ever, there was increase in mar resistance with the increase incontent of HDDA, because increase in diluent content increaseshardness and requires higher load to mar.

3.8. Pencil hardness

Pencil hardness property of coating was determined usingpencil hardness tester (BYK Gardner) with a calibrated set ofdrawing leads (Mars Lumograph, Germany) ranging from 6B(the softest) to 6H (the hardest). The sharpened pencil with cir-cular flat lead end was fixed to the pencil hardness tester andpushed away in a 6.5 mm stroke on to the coated surface. Theprocess was started with the hardest pencil and continued downthe scale of hardness to the two end points: one, the pencil thatwill not scratch the film reported as “pencil scratch hardness”,and, two, the pencil that will not cut into or gouge the filmreported as “pencil gouge hardness”.

Results of pencil hardness test of cured surfaces are shown inFig. 10. It was observed that the pencil scratch hardness of thepure BDGDA coating was 2H. Although, HDDA content up to20 phr did not improve the scratch hardness of the coating, above20 phr, the scratch hardness of coating improved by one hardnessst

3

aTafa(

Fig. 10. Effect of HDDA content in BDGDA oligomer on the pencil scratchhardness and pencil gouge hardness properties of the EB cured wood samples(dose = 420 kGy, beam energy = 370 keV, beam current = 0.5 mA). Rating forpencil hardness: 1, HB; 2, F; 3, H; 4, 2H; 5, 3H; 6, 4H; 7, 5H; 8, 6H.

The results are reported in terms of wear index defined as

Wear index =[

(Wi − Wf)

C

]× 1000 (3)

where Wi, is the weight of test specimen before abrasion (mg),Wf, the weight of test specimen after abrasion (mg) and C isthe number of cycles of abrasion recorded The results of abra-sion test are given in Fig. 11. It was found that the wear indexdecreases monotonically with the increase in the HDDA con-tent in the coating formulation, which showed that the abrasionresistance property of BDGDA improved in presence of HDDA.Improvement in abrasion resistance property of the coating withincrease in HDDA content is attributed to the increase in thehardness of coating due to the increased crosslink density.

3.10. Chemical resistance

The cured coatings were tested for their chemical resistanceby rubbing an acetone soaked soft cotton cloth for 200 doublerubs. The results of this test are given in Fig. 12. The figureshows that after 200 acetone double rubs, all the formulationperformed well except the pure BDGDA formulation. White

Fpb

cale to 3H. The pencil gouge hardness of cured surfaces of allhe coating formulations was greater than 6H hardness.

.9. Abrasion test

Abrasion resistance is one of the complex properties tochieve, as it is both a surface as well as sub-surface property.aber abrasion relates to the ability of the coating to resist thebrasion caused by abrasive wheels. Cured samples were testedor abrasion resistance property using automated Taber rotarybrasion tester (Khushboo Scientific, India) with abrasive paper150 Grit) under fixed load of 500 g on each wheel for 500 cycles.

ig. 11. Effect of HDDA content in BDGDA oligomer on the abrasion resistanceroperty of the EB cured wood samples (dose = 420 kGy, beam energy = 370 keV,eam current = 0.5 mA).

322 V. Kumar et al. / Progress in Organic Coatings 55 (2006) 316–323

Fig. 12. Effect of HDDA content in BDGDA oligomer on the chemicalresistance property (acetone double rub) of the EB cured wood samples(dose = 420 kGy, beam energy = 370 keV, beam current = 0.5 mA).

patches appeared on coating of pure BDGDA resin as early asafter 50 double rubs, which may be due to diffusion of ace-tone into the cured product, as discussed earlier that the pureBDGDA matrix does not undergo significant extent of crosslink-ing on irradiation and FTIR studies also established that thecoating X0 had lower degree of curing as compared to othercompositions irradiated at same radiation dose. However, otherformulations containing HDDA did not show any visible discol-oration or patch even after 200 double rubs of acetone.

3.11. Stain resistance

As the stain resistance of the coating is vital in protectingthe wood from liquid spills and stains, stain resistance testingwas conducted as per EN 438-2: 1991. The coated and uncoatedsamples were tested for seven staining chemicals list of theseand the performance of different coatings is provided in Table 3.Drops of staining agents were pipetted out onto the coating sur-faces and covered with glass cup to prevent evaporation. Afterspecified time of contact, the staining agent was wiped off withtissue paper and cleaned with water and then coating surfacewas examined for discoloration or change in appearance if any.It was found that all coating composition showed excellent stainresistance against the staining agents taken for the test.

TS

R

232B1TC

Ta

Table 4Steam resistance and cigarette burn test of EB cured coating on wood

Property Sample no.

Control X0 X1 X2 X3 X4

Resistance to steam 4 4 4 4 4 4Resistance to cigarettea burn 1 2 2 3 2 2

The rating for steam resistance test and cigarettes burn test: 1, sample charredwith surface damaged, black coloration; 2, blisters with severe mark with blackcolor in the core and brown at periphery; 3, moderate brown stain with no blisters;4, no visible change.

a Benson & Hedges.

3.12. Steam resistance

Steam resistance test was conducted as per EN 438-2: 1991.The samples were exposed to steam for 1 h and then the sampleswere examined for any visible changes on the coating surfacesdue to steam. The results are reported in Table 4, which indi-cated that the all coating compositions showed excellent steamresistance property.

3.13. Cigarette burn test

This test was conducted as per IS12823: 1990. A lit cigarettewas placed horizontally on the specimen for 1 min. The testedarea was cleaned with water and suitable solvent and then exam-ined. From results of the cigarette burn test given in Table 4, itwas found that all the coating formulations did not perform sat-isfactorily against cigarette burns and suitable additives have toidentified and incorporated in formulations to provide cigaretteburn resistance to coatings.

4. Conclusion

From the present study it could be established that a lowenergy DC accelerator can be effectively used to cure BDGDAresin in presence of suitable amounts of HDDA at optimum radi-ation dose. The properties of the cured product were a functionoilrtoaatt

A

S5SMf

able 3tain resistance test of EB cured coating on wood

eagents Time ofcontact

Sample no.

Control X0 X1 X2 X3 X4

5% NaOH 10 min 3 6 6 6 6 60% AcOH 10 min 5 6 6 6 6 60% H2O2 10 min 6 6 6 6 6 6oric acid 10 min 4 6 6 6 6 60% ammonia 16 h 3 6 6 6 6 6ea (Taj Mahal) 16 h 2 6 6 6 6 6offee (Nescafe) 16 h 1 6 6 6 6 6

he ratings for stain test: 1, dark brown stain; 2, light brown stain; 3, absorbedt surface, yellow stain; 4, white rim; 5, faint rim; 6, no effect.

f amount of reactive diluent incorporated and the total dosemparted. Presence of HDDA improved properties of coatingsike crosslinking density, thermal stability, pencil hardness, maresistance, abrasion resistance, and solvent resistance proper-ies. However, higher HDDA content results in micro distortionsn the coating surfaces and induces brittleness that adverselyffects gloss and scratch resistance properties of the coating. Themount of reactive diluent to be added to the parent oligomer,herefore, needs to be optimized for EB curing keeping in viewhe end use requirement of cured product.

cknowledgements

Authors wish to thank Dr. R.C. Sethi, Mr. S. Acharya and P.C.aroj, APPD, BARC for helping in irradiation of samples with00 keV EB accelerator. Also, Authors wish to thank Mr. K.S.S.arma, Mr. M. Assadullah, Mr. S.A. Khader, RTDS, BARC andr. Nitin Jadhav, UICT, Mumbai for technical support and fruit-

ul discussion.

V. Kumar et al. / Progress in Organic Coatings 55 (2006) 316–323 323

Appendix A. Supplementary data

Supplementary data associated with this article can be found,in the online version, at 10.1016/j.porgcoat.2006.01.002.

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