The effect of slip agents on the characteristics and propertiesof epoxy-phenolic can coatings

Chao Jiang, Peter Oldring, Laurence Castle,

Paul Cooke, James T. Guthrie

� FSCT and OCCA 2008

Abstract The migration issues associated with thetransfer of chemicals from epoxy-based can coatingsinto foodstuffs have been studied in recent years. Slipagents are usually used in can coatings for ease ofmanufacture and to provide required physical resis-tance properties. Slip agents in epoxy-based cancoatings are suspected of not only performing aslubricants but also having effects on the other proper-ties of coatings, including their migration resistance.This article contains information relating to the eva-luation of the influence of selected slip agents on thecharacteristics and properties of specific epoxy-pheno-lic can coatings. These characteristics and propertiesinclude those thermal properties of the coatings thatrelate to curing characteristics, the surface appearanceof cured coating films, the wetting properties that maybe associated with migration issues, and the abrasionproperties of the cured epoxy-phenolic systems. It wasfound that three selected slip agents each affected theproperties of the specific epoxy-phenolic can coatingdifferently. One of three selected slip agents inparticular reduced the interaction (‘‘wettability’’) of

the specific coatings by test fluids and so may help toreduce chemical migration.

Keywords Epoxy-phenolic, Slip agent, Wetting,Abrasion

Introduction

Can coatings are widely used in the production ofmetallic food containers. These coatings are used toprotect metal substrates against corrosion and to avoidcontact between the metal and the foodstuffs. Epoxy-phenolic can coatings are usually used on tin-platesubstrates, and have been so used and developed sincethe 1950s.1,2

As an organic coating, epoxy-phenolic can coatingsare generally produced from reactive thermosettingresin precursors, namely epoxy resin precursors andphenolic resin precursors, which are deposited onto ametal substrate. During curing, the polymer flows toform a smooth film and, simultaneously, a crosslink-ing reaction takes place to create a continuousnetwork.1,2 Therefore, the ability to predict the curingbehavior of such can coatings is of great importance tothe coating applications.

In recent years, migration of epoxy resin componentsinto food from epoxy-based can coatings includingepoxy-phenolic can coatings has received considerableattention. The initial concern mainly surrounded orga-nosols and types of epoxy-based can coatings that insome cases exceeded the specific migration limit (SML)for bisphenol A-diglycidyl ether (BADGE), current atthe time. This standard has been revised and is thesubject of epoxy regulation (EC) No 1895/2005. Theextent of any migration between the internal cancoating and the food content has been recognized asbeing within the recommendations of food contactlegislation.1,3,4

C. Jiang, J. T. Guthrie (&)Department of Colour Science, University of Leeds,Woodhouse Lane, Leeds, West Yorkshire LS2 9JT, UKe-mail: ccdjtg@leeds.ac.uk

P. OldringValspar (UK) Ltd., Station Lane, Witney, Oxon OX28 4XR,UK

L. CastleDepartment for Environment Food and Rural Affairs,Central Science Laboratory, Sand Hutton, York YO41 1LZ,UK

P. CookeValspar Corporation, Industriestrasse 9,CH 8627 Gruningen, Switzerland

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DOI 10.1007/s11998-008-9114-8

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Bisphenol A (BPA), also known as 2,2,-bis(4-hydroxy-phenyl) propane, is an important monomer that is used inthe manufacture of epoxy resins for can coatings that areintended to be in contact with foods and beverages.5 Inrecent years, there has been increasing public concernregarding BPA migration into canned food. Low-levelmigration of BPA has been studied in canned vegeta-bles,6–8 in infant formula,9 in canned alcoholic drinks,10

and in canned fish and meat products.7

BADGE, also known as 2,2-bis(4-hydroxyphenyl)propane bis(2,3-epoxypropyl) ether, is employed as anintermediate in the manufacture of epoxy-based cancoatings.4 For over 10 years, published data in severalEuropean countries (UK, Switzerland, Germany, TheNetherlands, Austria, Italy, Denmark) have beenavailable on BADGE-derivatives and their migrationfrom can coatings into foods and food simulants acrossa range of canned foods.4,8,10–17

In order to address these migration issues, severalfood contact factors have been addressed. The wettingresistance of the internal can coating films and thepossibility of the interactions between the internal cancoating films and the food content in the can have beenstudied. One hypothesis is that if the food content inthe can does not swell and penetrate the surface of thecoating films, migration into and out of the foodcontent will be less likely to occur.18,19

Among the factors of relevance to the behavior ofthe coating surface are the slip agents in the formula-tions of the can coatings. These have been modifiedwith the goal of achieving optimal properties (e.g.,abrasion and rub resistance, optimal friction).1,2,20,21

There are several theories (including the Bloomtheory, the Ball theory, the Cone theory, and soon)20 to explain how the slip agents that are present atthe film surface of the can coating might have asignificant influence on the migration resistance andrelated properties of the coating film.

Slip agents, both natural and synthetic, are commonlyused in surface coatings to improve surface lubricity andto impart abrasion or scratch resistance.1,2 These slipagents are sometimes referred to as internal lubricantssince they are added to the wet coating formulation andrely on migration to the surface of the coating, oncuring.1,2,4,20,21 Examples include the poly(ethylene)and polyamide wax types that are usually used in smallamounts to achieve the desired performance character-istics, e.g., lubrication, hardness, and flexibility.2,20,21

This article examines specifically the effects of theuse of three selected slip agents in coating formulationson several properties of an internal can coating.

Experimental

Materials

A generic model BPA-based epoxy-phenolic formula-tion and the relevant raw materials (including three

slip agents that were used comparatively: a mixtureof carnauba wax and lanolin wax—Slip 1; lanolinwax—Slip 2; and a polyamide wax—Slip 3) wereprovided by the Valspar Corporation (Industriestrasse9, CH 8627 Gruningen, Switzerland).

The defoamer additive used in the epoxy-phenoliccoating was a naphtha (petroleum), heavy alkylate.

The tin-plate panels (2.8/2.8) were provided by theImpress Corporation (Impress, Centre de Recherchede Crosmieres, BP109, 72206 La Fleche, France).

K bar coaters of No. 1, No. 3, and No. 5 (6, 24, and50 lm, wet deposit) were provided by R K PrintInstrument Ltd. Litlington, Royston, Herts, SG8 0QZ,UK.

Preparation of model epoxy-phenolic coatings(EPH01J, a modified and simplified commercialcan coating)

The solid BPA-based epoxy resin precursor (ERP,238.0 g) was pre-mixed with solvents of the glycol etheracetate type (261.0 g), the glycol ether type (136.0 g),and the ester type (34.0 g) on the roll mill overnight, toobtain the ERP solution.

Eight containers were prepared and identified.A total of 67.0 g of the pre-prepared ERP solutionand 21.0 g of the phenolic resin precursor solutionwere mixed well using a Heidolph mixer, type RZR1,for 5 min. Slip 1 (carnauba wax + lanolin wax, 2.5 g),defoamer (0.1 g) and a solvent of the glycol etheracetate type (11.0 g) and a solvent of the ester type(4.0 g) were assembled as a mixture. The dispersionwas then mixed for 10 min and the product wasidentified as EPHS1.

The above procedures were repeated with the use ofthe different sets of the slip agents, as shown inTable 1, to provide coatings EPHS2, EPHS3, EPHS12,EPHS13, EPHS23, EPHS123, and EPHNS, respec-tively. Here EPH denotes the epoxy-phenolic polymersystem and S denotes that slip agent is present. Thenumbers denote which slip combination was used.

Table 1: Different combinations of the slip agents in theselected epoxy-phenolic can coatings

Coatings Slip 1 (g) Slip 2 (g) Slip 3 (g)Carnauba

wax + lanolin waxLanolin

waxPolyamide

wax

EPHS1 2.5 0 0EPHS2 0 0.5 0EPHS3 0 0 0.5EPHS12 2.5 0.5 0EPHS13 2.5 0 0.5EPHS23 0 0.5 0.5EPHS123 2.5 0.5 0.5EPHNS 0 0 0

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Preparation of coated, cured tin-plate samples

In a typical situation, blank tin-plates, 13.5 · 7.8 cm,were coated. A Werner-Mathis oven (ModelKTF4099), set at 200�C, was used for the curing stagesof the study. The temperature profile was checkedusing a calibrated thermocouple (Model PICO TC-08K) at the beginning, middle, and end of the productionprocess. The wet coating was mixed well before use.Three tin-plate sheets were marked and coated withthe EPHNS coating, 6 lm wet deposit from K barcoater No. 1, which is equal to 2.4 lm when dry. Thecoated tin-plates were cured in the Werner-Mathisoven for 10 min. These procedures were repeated forcoatings EPHS1, EPHS2, EPHS3, EPHS12, EPHS13,EPHS23, and EPHS123, respectively.

The procedures were repeated for thicker coatings,obtained using K bar coater No. 3 (24 lm wet deposit)and No. 5 (50 lm wet deposit), respectively, equivalentto 6.4 and 14.2 lm dry film thicknesses.

Thermal studies

A TGA 2050 thermogravimetric analyzer and a DSC2010 differential scanning calorimeter were used toperform thermal evaluations of the formulated epoxy-phenolic coatings. The conditions for both the TGAand the DSC methods were a heating rate of 20�C/min,a temperature range from room temperature to 500�C,and an N2 flow rate of 50 cm3/min.

Surface appearance evaluations

A JEOL JSM-820 scanning electron microscope(SEM) was used to provide images at high magnifica-tions from the surfaces of the samples. The acceleratingvoltage used was in the range 5–15 kV according to therequired magnification.

Each sample was mounted on a brass stub and waspretreated by coating with a uniform gold film of30 nm using a Bio-Rad diode sputter coating unit (Bio-Rad House, Maylands Avenue, Hemel Hempstead,Hertfordshire, HP2 7TD, UK) before being subjectedto SEM.

Surface contact angle evaluations

In the present study, a contact angle meter (PearsonPanke Ltd., London), designed for measuring staticcontact angles, was used in the assessment of thesurface wetting properties of samples. The objectivewas to monitor the effect of the selected slip agents onthe surface wettability of selected coatings.

The data that are acquired from experimentation areprocessed according to the Young model21 with respectto the determination of the critical wetting tension (cc)of the cured, coated substrates. This technique involves

the plotting of the cosine of the contact angle (h),observed with drops of known fluids, of known surfacetension (cLV), placed on the coated surface, against therespective surface tensions. Fluids are chosen on thebasis of the forces that hold their molecules together(polar, dispersion, hydrogen bonding) so that a range ofinteraction types can be considered. Although theapproach usually gives a degree of spread to the cos hvs cLV relationship, it does provide relevance toeffective experimental situations in which compositesurfaces are being monitored.22

The test liquids with their known surface tensionvalues: nitromethane (36.9 mN/m), tritolyl phosphate(40.9 mN/m), poly(ethylene glycol) (44.7 mN/m), andformamide (58.2 mN/m) were used as test liquids insurface contact angle evaluations to the samples.

The procedures are as follows. The coated and curedtin-plates were cut into strips (2.5 · 7.8 cm). A sessiledrop of each test liquid was applied on the surface ofthe strip. Then the surface contact angles of each fluidon each strip were measured with respect to applyingseveral drops of test fluid at different locations of thestrip to obtain a representative result for the wholesurface of the strip.

Abrasion studies

A Wallace rubproofness testing unit (Wallace Instru-ments, Unit 4, St. Georges Ind. Est., Richmond Road,Kingston, KT2 5BQ, UK) model A7 was employed tostudy aspects of the abrasion resistance of the curedcoating systems.

Circles of 11.50 cm in diameter were cut from agrade 120 abrasion sheet obtained from the 3MCompany (3M United Kingdom PLC, 3M Centre, CainRoad, Bracknell, RG12 8HT, UK). The circular abra-sive sheet was mounted onto the bottom disc. A sample(2.5 · 2.5 cm) of coated tin-plate was weighed beforebeing stuck to the top disc via its uncoated side.

The sample on the top disc, with the coated surfacefacing downwards, was lowered until just touching theabrasive sheet. A known load was applied onto the topdisc.

The bottom disc along with the abrasive sheet wasmade to rotate for 10 rotations. After 10 rotations, theunit was stopped. The coated sample was removed andweighed. This procedure was repeated after 30, 50, 100,and 200 rotations.

The abraded material was removed carefully and itsmass was measured. A new circular abrasive sheet wasapplied for the testing of each coated sample.

Results and discussions

Thermal studies

Most of the components of a coating formulation willhave a role in affecting the curing/drying processes.

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Based on this consideration, TGA and DSC analysismethods were used to study the effect of the slip agentson thermally induced changes of the coatings thatoccurred.

The TGA profiles of EPHNS, EPHS1, EPHS2, andEPHS3 coatings were considered. It is appropriate todivide the curing/drying processes into four stages: rapidsolvent(s) evaporation, slow solvent(s) evaporation/filmformation, film network development, and the thermaldecomposition of the formed film. As an example, theTGA profile of EPHNS coating is presented in Fig. 1.Four framed areas in Fig. 1 represent four stages of thecuring/drying processes. Thus, the results from theTGA profiles of EPHNS, EPHS1, EPHS2, and EPHS3coatings can be described in Table 2.

EPHNS, EPHS1, EPHS2, and EPHS3 have verysimilar weight loss profiles (Table 2). A continuousrate of mass (solvent) loss is seen up to approximately100�C (most volatile solvent). A slower loss in mass(more bound solvent being removed) and coating filmformation follows up to around 210�C. Further filmformation and network development shows up from�210–370�C. Then, the plateau region is followed bymass loss due to decomposition, from about 370�C.

The structured coating film starts to form between�100 and �210�C depending on the formulations usedand on the curing conditions applied, as a second stageof the drying process, identified in Table 2. During thisstage, the mass loss of the coating is slower.

The DSC results in Figs. 2–5 show that in thetemperature range from 100 to 210�C the thermallyinduced changes are specific, if complex. This is true forthe EPHS1 and EPHS2 systems. For EPHS3 (poly-amide wax), the thermal process is less well defined.

During the film network development process, in thetemperature range of �210–370�C, the mass loss of thecoating slows continuously.

The thermal decomposition process is the fourthstage of the drying process—the period from �370 to500�C, as shown in Fig. 1. In this period, the weight loss

100

80

60

40

20

00 200100 300 400 500

Wei

ght (

%)

Temperature (°c)

120.99°C 51.64%

360.19°C 34.30%

Residue: 7.966%(1.840 mg)

Fig. 1: TGA profile of EPHNS (no slip) at heating rate20�C min–1 from �30 to 500�C

Table 2: Descriptions of curing/drying profiles of different epoxy-phenolic can coatings

Coating Rapid solvent(s)evaporation (�C)

Slow solvent(s) evaporation/film formation (�C)

Film networkdevelopment (�C)

Decomposition offormed film

EPHNS (no slip) �30–100 �100–210 �210–370 Onsets at �370�CEPHS1 (carnauba

wax + lanolin wax)�30–100 �100–210 �210–375 Onsets at �375�C

EPHS2 (lanolin wax) �30–100 �100–210 �210–390 Onsets at �390�CEPHS3 (polyamide wax) �30–100 �100–215 �215–400 Onsets at �400�C

0.0

–0.5

–1.0

–1.5

–2.0

–2.5

Hea

t flo

w (

W/g

)

0 400 500200 300100

Temperature (°c)

89.30°C

160.88°C

Fig. 2: DSC profile of EPHNS (no slip) at heating rate 20�Cmin–1 from �30 to 500�C

0.0

–0.5

–1.0

–1.5

–2.0

–2.5

–3.0

Hea

t flo

w (

W/g

)

0 400 500200 300100

Temperature (°c)

108.39°C

131.65°C

148.35°C

187.72°C

Fig. 3: DSC profile of EPHS1 (carnauba slip + lanolin slip)at heating rate 20�C min–1 from �30 to 500�C

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increases sharply. Different percentages of the residueswere obtained. EPHNS and EPHS2 gave a similarvalue at �8% of residue, EPHS1 gave a value at�12%, and EPHS3 had a value at �15%.

The results in Figs. 1–5 and in Table 2 show that theeffects of slip agents on the curing behavior and on thecuring decomposition can be significant. The presenceof a slip agent in the coating changes the thermalprofiles in the earlier stages and in the later decompo-sition phases. It is concluded that Slip 1 and Slip 2 donot influence greatly the solvent evaporation processes.However, combinations with Slip 3 showed more rapiddrying.

The surface appearance characteristics

Micrographs of the cured epoxy-phenolic coatingswere taken at a 100· magnification. An example isshown in Fig. 6 for the EPHNS coating.

On comparing the SEM micrographs of the curedcoatings from EPHS1, EPHS2, and EPHS3 with that ofEPHNS, it became clear that the presence of Slip 1 inthe selected epoxy-phenolic coating makes the surface

of the coating smoother after the curing process. Slip 2gave a poorer surface appearance. Slip 3 gave a roughsurface to the coating after curing.

Surface contact angle evaluations

The formulations containing the three selected slipagents, deposited at three thicknesses, were studied.The results are given in Fig. 7. Here, ‘‘1’’ indicates thegreater wetting resistance of the coating films by testfluids and ‘‘2’’ indicates the lesser interaction betweenthe coating films and the test fluids. Three dry filmthicknesses (2.4, 6.4, and 14.2 lm) were used on thebasis that if more coating was applied to the tin-plates,more slip agent could migrate to the surface of thecoating films during and after curing, giving greaterwetting resistance to the coating.

The results from the relationships of contact anglesof different cured coatings at three film thicknesses andthe surface tensions show that cc changes on varyingthe film thicknesses (2.4–14.2 lm) of the coating.

Compared to results for EPHNS, the presence ofSlip 1 in the coating decreases the cc value from �31 to�21 mN/m, indicating that the surface of coating film isless readily wetted. The steeper slope of EPHS1compared to the slope of EPHNS indicates that the

Fig. 6: SEM micrograph of the tin-plate coated with EPHNScoating

0.0

0.5

–0.5

–1.0

–1.5

–2.0

Hea

t flo

w (

W/g

)

0 400 500200 300100

Temperature (°c)

115.55°C

438.86°C

Fig. 5: DSC profile of EPHS3 (polyamide slip) at heatingrate 20�C min–1 from �30 to 500�C

0

0.2

0.4

0.6

0.8

1

0 10 20 30 40 50 60 70

cos

q

2.4 µm

6.4 µm

14.2 µm“2”

γc

Surface tension (mN/m)γLV

“1”

Fig. 7: Cos h vs surface tension for cured EPHNS (No slip)at three film thicknesses (2.4, 6.4, and 14.2 lm)

0.0

–0.5

–1.0

–1.5

–2.0

–2.5

–3.0

Hea

t flo

w (

W/g

)

0 400 500200 300100

Temperature (°c)

107.19°C

119.72°C

147.76°C

Fig. 4: DSC profile of EPHS2 (lanolin slip) at heating rate20�C min–1 from �30 to 500�C

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ability to interact with the surface of the coating filmwould be reduced, particularly by fluids of highersurface tension, such as some aqueous dispersionfoods.

The trends relating to the slopes provided bysamples of EPHS2 and EPHS3 are similar to those ofEPHNS (Fig. 7). However, the resulting cc valuesdiffer, as shown in Table 3.

The results from EPHS12, EPHS13, EPH23, andEPH123 show again that variation in the film thick-nesses (2.4–14.2 lm) of the coating has little or noeffect on cc (see Table 3); cc is affected mainly by theslip agents used in the coating containing Slip 1 givingvalues reduced from �32 mN/m (for no slip situation)to �23 mN/m (for the presence of Slip 1). Coatingsthat contain mixtures of slip agents that include Slip 1give a significantly steeper slope to those that do notinclude Slip 1.

Two clear families of the curves can be seen inFig. 8. ‘‘Family 1’’ represents the cured epoxy-phenoliccoatings that do not contain Slip 1. ‘‘Family 2’’indicates the cured epoxy-phenolic coatings that con-tain the Slip 1 system.

The data in Table 3 show that the cc of the‘‘Family 1’’ is in the range of 31–33 mN/m and thatof the ‘‘Family 2’’ is between 21 and 24 mN/m. The

presence of Slip 1 in the ‘‘Family 2’’ system caused thedifference in cc relative to specimens noted in ‘‘Family1.’’ Therefore, of the systems studied, Slip 1 wouldappear to be the best slip agent system for reducing cc.This study is based on a hypothesis that if the wettingability of cured coating film is reduced, then themigration into or out of the coating films would also bereduced.

It should be recalled that the theme of the currentarticle relates to the consequences (beneficial orotherwise) of incorporating slip agents into coatingsthat are designed to be internal lacquers for food andbeverage containment. Thus, interaction between thecontents and the coating needs to be minimal.Evidence of such reduced interaction, as seen inreduced cc values, is of considerable relevance as itindicates lesser prospects for swelling of the internalcan coating and potential for consequential reducedmigration phenomena.

Abrasion studies

Here, the effect of the presence of the different slipagents in the coating systems on the abrasion resistanceof cured coatings is considered. The procedureadopted, coupled with the associated topic, wasthat described by Hosseinpour and by Hosseinpouret al.22,23

Eight different coating samples were preparedwhereby the three slip agents were used individuallyand in combination, in the epoxy-phenolic coatingformulation. These were cured as described earlier.

Figure 9 shows the weight loss of the coatings thatcontained different combinations of the three slipagents after different numbers of rotation, for thesame load (280 g). As the number of the rotationsincreased, the extent of the weight loss by abrasionalso increased. This extent varied with the resistanceof the coating surface, dominated by the differentcombinations of slip agents. The tin-plate sample

0

0.2

0.4

0.6

0.8

1

cos

q

EPHS1

EPHS2

EPHS3

EPHS12

EPHS13

EPHS23

EPHS123

EPHNS

“1”

“2”

γLV Surface tension (mN/m)

γc0 10 20 30 40 50 60 70

Fig. 8: Cos h vs surface tension for cured epoxy-phenoliccoatings at film thickness (2.4 lm)

0.0000

0.0050

0.0100

0.0150

0.0200

0.0250

0.0300

250

Number of rotations

Wei

ght

loss

(g)

EPHNS

EPHS1

EPHS2

EPHS3

EPHS12

EPHS13

EPHS23

EPHS123

0 50 100 150 200

Fig. 9: Weight loss under abrasion for the cured epoxy-phenolic coatings containing different combinations of theslip agents (load of 280 g)

Table 3: Summary of cc of cured epoxy-phenoliccoatings at three film thicknesses

Coating Film thicknesses (lm)/cc (mN/m)

2.4 4.6 14.2

EPHNS 31.6 ± 1.0 31.9 ± 1.0 32.0 ± 1.0EPHS2 33.2 ± 1.0 32.4 ± 1.0 32.8 ± 1.0EPHS3 31.6 ± 1.0 31.8 ± 1.0 31.4 ± 1.0EPHS23 33.0 ± 1.0 32.5 ± 1.0 32.4 ± 1.0EPHS1 21.5 ± 1.0 22.2 ± 1.0 22.7 ± 1.0EPHS12 24.3 ± 1.0 24.7 ± 1.0 24.3 ± 1.0EPHS13 22.2 ± 1.0 23.4 ± 1.0 23.0 ± 1.0EPHS123 23.2 ± 1.0 23.6 ± 1.0 23.3 ± 1.0

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coated with EPHS13 gave the greatest weight loss.The introduction of the Slip 2 blend into the epoxy-phenolic coating had a positive effect, with thecoating becoming more resistant to abrasion. Thepresence of the combination of Slip 1 or Slip 3 inthe coating formulations reduced the abrasion resis-tance of the cured coatings. Slip system 3 was worsethan the Slip system 1 in this respect.

The effect of the load on the amount of mate-rial that was abraded was studied, in the range of280–1080 g.

Figures 10–12 show the effect of increased load forthe samples that contained Slip 1, Slip 2, and Slip 3,respectively. The greater the load applied, the greaterwas the coating material that was abraded from thesample for the different numbers of rotations. Theresults in Fig. 9 confirm that the presence of Slip 2 inthe epoxy-phenolic coating makes the coating moreresistant to abrasion. Slip system 3 is worse than theSlip system 1 and Slip system 2 in this respect. Conclusions

Slip agents are commonly used in commercial epoxy-phenolic can coatings for different purposes. The slipcombination of carnauba wax and lanolin wax en-hances the hardness of such coating formulations.Lanolin wax can play a lubricant role in the manufac-ture of cans. Polyamide waxes give improvement ofcoating wear from coating tools (e.g., roll coating). Theresults from this study show that these three slip agentsalso influence other characteristics and properties ofepoxy-phenolic can coatings.

It is clear that all of the three slip agents have animpact on the thermal properties of coatings. The TGAresults show differences in the decomposition causedby the different slip agents. The polyamide wax has thegreatest influence on the decomposition of the coating.The three slip agents also affected the solvent(s)evaporation, the film formation, film network devel-opment, and formed film decomposition processes forthe curing coatings. The use of the slip agents delayssolvent evaporation.

The use of the carnauba-lanolin mixtures, in theepoxy-phenolic coating formulation, improves thesurface appearance after curing. Lanolin wax andpolyamide wax cause the development of a poorsurface appearance for the same coating formulation.

The use of the carnauba-lanolin mixtures in thecoatings reduces the wetting ability of cured coatingsurface and would provide less opportunity for thecured coating film to interact with fluid materials. Thiscombination plays an important role in protecting thecured coating surface from wetting by foodstuffs.

These results provide some justification for theemployment of the carnauba-lanolin combination inthe manufacture of the cans and can componentscoated with epoxy-phenolic can coatings.

Acknowledgments The work was carried out as apart of a Defra LINK project FQS45 New technologiesand chemistries for food can coatings. Funding by

0.0000

0.0050

0.0100

0.0150

0.0200

0.0250

0.0300

0.0350

Number of rotations

Wei

ght

loss

(g)

280 g

480 g

680 g

880 g

1080 g

2500 50 100 150 200

Fig. 10: Weight loss under abrasion for the cured epoxy-phenolic coatings containing Slip system 1 under differentloads

0.0000

0.0050

0.0100

0.0150

0.0200

0.0250

0.0300

0.0350

Number of rotations

Wei

ght

loss

(g)

280 g

480 g

680 g

880 g

1080 g

2500 50 100 150 200

Fig. 12: Weight loss under abrasion for the cured epoxy-phenolic coatings containing Slip system 3 under differentloads

0.0000

0.0050

0.0100

0.0150

0.0200

0.0250

0.0300

0.0350

Number of rotations

Wei

ght

loss

(g)

280 g

480 g

680 g

880 g

1080 g

2500 50 100 150 200

Fig. 11: Weight loss under abrasion for the cured epoxy-phenolic coatings containing Slip system 2 under differentloads

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Defra and matching funds in kind from ValsparCorporation, Impress Group, and H.J. Heinz aregratefully acknowledged.

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