Surface Coatings International Issue 2008/6312

Alkyd resins are typically produced bythe condensation polymerisation ofnatural oils or fatty acids with

polyhydric alcohols such as pentaerythritol,glycerol or trimethylolpropane, and dibasicacids such as phthalic anhydride andisophthalic acid. Since natural oils and fattyacids are renewable raw materials andpolyhydric alcohols can be produced fullyor partly from renewable raw materials,alkyd resins represent a very ‘green’ binderselection compared with acrylic binders,whose building blocks are currently derivedfrom mineral oil.Pentaerythritol can easily be made from

renewable resources, as it is made from thealdehydes of methanol and ethanol (seeFigure 1). The main environmental problemwith alkyd resins is therefore that they aretypically used in diluted form in organicsolvents.Organic solvents can be hazardous at

many levels, both locally during themanufacture of the solvent and paint, andwhen the paint is applied and dried.Globally, volatile solvents can cause harmto the environment in the form of ozonedepletion. It is therefore very important tominimise the use of volatile content incoatings. Such a shift of technology is alsoenforced in the EU countries by theprovisions of the VOC (or ‘Decopaint’)directive. These provisions limit the amountof solvents that can be used in variousdecorative paints. The limits for differentapplications are given in Table 1.The suggested routes to VOC-compliant

coatings, high-solids resins and alkydemulsions, present a number of technicalchallenges such as drying performance,final hardness or solvent resistance. Somefindings are presented from work aimed atimproving the properties of resins for theseapplications by the use of technologiessuch as:

l molecularly tailored resins;l reactive surfactants for internal

stabilisation;l urethane alkyd emulsions;l alkyd-acrylic hybrids.

Over the years, many reactive diluentshave been proposed but have had limitedsuccess because they have not metperformance requirements or because ofenvironmental considerations. Reactivediluents based on allyl ethers, for example,are unsuitable for oxidative drying alkydsdue to the emission of acrolein.Linear polymers create viscous products

through chain entanglement, and theviscosity rises smoothly in proportion totheir molecular weight, according to theMark-Houwink equation (see Figure 2 andEquation 1).

Examples of resin formulation and paintperformance are given.

High-solids alkyds –molecular engineeringHigh-solids alkyds are reported to havebeen produced by various methods, forexample by using special molecular designand reactive diluents. The classical methodis to reduce the molecular weight and/orincrease the oil length, but this will giveinferior coating properties.

MethanolCH4O

Molecular weight 32.04

AcetaldehydeC2H4O

Molecular weight 44.05

FormaldehydeCH2O

Molecular weight 30.03

PentaerythritolC5H12O4

Molecular weight 136.15

EthanolC2H6O

Molecular weight 46.07

H H

0±± OH

OH

OHOH

OH

0OH

Fermentation

Figure 1: Biochemical route to pentaerythritol

Routes to VOC-compliant alkyd coatingsK Sörensen

Perstorp Specialty Chemicals AB, R&D, Application Development and Support, SE-284 80 Perstorp, Sweden

Table 1: Selected provisions of the EU VOC directive

Product subcategory Type Phase I (g/l) Phase II (g/l) (from 1.1.2007) (from 1.1.2010)

A Interior matt walls and ceilings WB 75 30(Gloss ≤25@60°) SB 400 30

B Interior gloss walls and ceilings WB 150 100(Gloss >25@60°) SB 400 100

C Exterior walls of mineral substrate WB 75 40SB 450 430

D Interior/exterior trim and cladding paints WB 150 130for wood and metal SB 400 300

E Interior/exterior trim varnishes and wood stains, WB 150 130including opaque wood stains SB 500 400

F Interior and exterior minimal build wood stains WB 150 130SB 700 700

313Surface Coatings International Issue 2008/6

[η]= K*[Mw]a Equation 1

Where η = viscosity, K is a constant andMW the molecular weight.Hyperbranched and dendritic polymers

deviate from this proportionality and havea lower viscosity than anticipated at highermolecular weights due to reducedentanglement and a low hydrodynamicvolume.The viscosity of an alkyd resin is also a

function of free volume availability. Thefree volume of a material is the sum of thespaces or holes that exist between themolecules of a material resulting from theimpact of one molecule or one moleculesegment striking another. These holes openand close as the molecule vibrates.At temperatures above the glass-

transition temperature (Tg), the holes arelarge enough and last long enough formolecules or molecular segments to moveinto them, resulting in a low viscosity. Freevolume increases as the temperatureincreases, and the rate of volume increaseis higher above the Tg or if a solvent isused.1

Alkyds made from glycerol are very linearin nature and it is difficult to build up highmolecular weights with oil lengths suitablefor decorative paints so as to provide highlevels of coating properties. This isovercome by using a higher functionalpolyalcohol such as pentaerythritol. Thesepenta alkyds have improved drying andcoating properties, but their viscosityincreases due to their higher molecularweight and broad molecular weightdistribution.One option for designing a high-solids

alkyd involves, for instance, replacingpentaerythritol with di-pentaerythritol (di-penta). Di-penta is a unique polyol with ahigh functionality, six primary hydroxylgroups, and with good heat and UVstability. The highly branched, densestructure of di-penta facilitates theformulation of alkyds with high solidscontent in combination with good dryingcharacteristics.Another option is to use the hydroxylic

acid dimethylol propionic acid (Bis-MPA)that will self-condense to producebranched structures with a lower viscosityat the same molecular weight comparedwith more linearly formulated counterparts.The example in Table 2 shows a pure

aliphatic alkyd, but partial application ofthis technique could also be considered innormal formulations. The second approach

can be taken to an even higher level toproduce hyperbranched alkyds in whichmost of the molecular weight is containedwithin the globular structure of themolecule (see Figure 3).In practice, such a hyper-branched alkyd

can be made by modifying the commercialhyperbranched product Boltorn H20 withfatty acids. Such a product is available asBoltorn U3000. In Table 2, alkydformulations are presented where di-pentaand bis-MPA replace penta and other alkydcomponents to produce high-solid alkyds.

Alkyd synthesis

Except for the standard alkyd, which wasproduced by the fusion process, the alkydsyntheses were carried out according to thestandard alkyd process at 240°C, withxylene as the azeotropic solvent, which wasultimately distilled off in a vacuum.Calculated and measured characteristics ofthe alkyds are given in Table 3. From thetable, it is clear that alkyds with very lowviscosity can be obtained by usingspeciality polymers in alkyd formulations.

Paint and paint performance

The alkyds shown in Table 3 were used indifferent white high-gloss paintformulations, as shown in Table 4. However,the di-penta alkyd has so far only beenevaluated as a clear coat. The paints werethen evaluated for drying performance andgloss. The di-penta alkyd and thehyperbranched version met the VOCrequirement for 300g/l max for trim paints.The paint performance study is also

presented in Table 4 and shows that high-gloss paints can be formulated using bis-MPA, di-penta or Boltorn alkyds. In all ofthese cases, the paints are softer than thecomparable alkyd, but gloss hold-out onweathering was better on the bis-MPA andthe Boltorn alkyds than the standard. Thedi-penta alkyd exhibited very good dryingand hardness development, closer to thestandard alkyd, although still onlymeasured as a clear coat.

Log v

isc

Log Mw

[η]= K*[Mw]a

Linear polymers

Dendrimers

Figure 2: Viscosity of dendrimers departs from the Mark-Houwink equation at high molecular weights

Table 2: Bis-MPA, di-penta and ‘concept’ alkyd formulations

Ingredient Standard alkyd Bis-MPA alkyd Di-penta alkyd Concept alkyd

Tall oil fatty acid 62.20 69.91 62.25 75.04Phthalic anhydride 23.88 – 14.13 9.89Pentaerythritol mono grade 20.42 – –Di-pentaerythritol – – 21.84 16.62Benzoic acid – – 8.38Bis-MPA – 39.56 – 4.48Total charge 106.50 109.47 106.60 106.03Water of reaction (g) 6.50 9.47 6.60 6.03

Surface Coatings International Issue 2008/6314

High-solids alkyds –reactive diluentsThe findings above indicate that it ispossible to produce alkyds having very lowviscosity with a low solvent content. Thehyperbranched alkyds can be used asreactive diluents in a standard alkyd tomeet the VOC requirement regarding trimpaints. However, due to their aliphaticnature, they create soft films, which is whysome applications definitely requiredifferent formulations to meet therequirements. Can it be possible to designan alkyd giving fast drying, hard films and

low viscosity when mixed with a standardalkyd?One possible method of improving

hardness and physical drying might be toincorporate hard segments with areasonable Tg shielded by softer segmentsand still maintaining a high molecularweight (see Figure 4). The shielding isnecessary to provide the low viscosity,while the architecture itself must allow fora free volume sufficient to give areasonable application viscosity.One approach involves the combined use

of di-penta and bis-MPA in the same alkyd.By applying a smart molecular design and

step-by-step synthesis, where the di-pentais partly fatty acid-functionalised and thebis-MPA is used to make hard segmentsthat are primarily linearly spaced, togetherwith phthalic anhydride between the partlyfatty acid-functionalised di-pentamolecules, a low viscosity resin is producedthat is very well suited for use as a diluterfor high-solids resins. The formulation ofsuch a resin is presented as the 'conceptalkyd' in Table 2.

Alkyd synthesis

The alkyd synthesis was carried outaccording to the normal method for alkyds,with xylene as the azeotropic solvent. Forthe concept alkyd, the reaction was carriedout in three steps. In the first step, thefatty acid was reacted with the di-penta toan acid number of 3mg KOH/g at 220°C.Phthalic anhydride was added in a secondstep and reacted at 160°C, then held untilthe anhydride ring opened on the coreester.In a third step, the bis-MPA was reacted

in portions at 160°C. The alkyd was thenrun at 200 to 210°C until the desired acidnumber was reached. The low reactiontemperature was chosen to minimise thereaction of the tertiary carboxyl group ofbis-MPA. Calculated and measuredcharacteristics of the concept alkyd aregiven in Table 3. From the table, it is clearthat an alkyd with very low viscosity can beobtained.

Lacquers and lacquer performance

Lacquers were produced from the standardalkyd in Table 2 and the concept alkyd, andas a resin mix where the concept alkyd andthe standard alkyd were mixed. Thelacquers were formulated to have the sameviscosity. As shown in Table 5, the VOC ofthe diluted resin was considerably lowerthan that of the standard alkyd and metthe requirement for category D in the VOCdirective for 300g/l max.Lacquer performance is shown in Table 5,

which reveals that drying was just as goodin the diluted alkyd as in the standard. It isour belief that this concept could be usedwith many conventional alkyds and itcould, as such, act as a good tool for resinproducers for producing binders suitablefor paints that comply with therequirements for 2010.

O

O

O

O

O

O

OO

O

O

O

O O

O

O

O

O

O

O

OO

O

O

O

O

HO

O

O

O

OHHO

O

O

Boltorn

HOHO

HOHO

HO

HO HO

HO

HO

HO

HO

HO

HO

OHHO

HO

HOHO

HOHO

HO

HO

OH

HO

OH OHOH

OH

OH OH

OH

OO

O

OO O

OO

O

O O

O

O

OO

O

OO

OO

OO

O

O

OO

OO

O

O

O

O O O

OOO

OO O

OO

OO

OO

O O

OO

O

O O OO

OO

OO

O

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH OH

HO

HO

OH

OH

Pentaerythritol

HO

HO

OH

O OH

OHOH

Di-penta

OH

HO

OHOH

HO

OH

OH

OH

O

O O

O

O

Bis-MPA hyperbranched

O

Figure 3: Some molecules that will yield branching and dense structures

Alkyd emulsionsAlthough high-solids alkyds may be used tomake VOC-compliant alkyd coatings, thesewill, in most cases, still contain solvents. Aswitch from diluting with solvents todiluting with water might therefore be aneven better solution from an environmentalstandpoint. Alkyd emulsions can be madeusing no, or virtually no, solvents.A frequently recommended method for

producing alkyd emulsions is the inversionprocess in which water is added to thealkyd until a critical volume concentrationof water is reached, and a phase transferfrom a water-in-oil emulsion to an oil-in-water emulsion takes place (see Figure 5).In the emulsification processes, the alkyd

droplets formed have to be stabilised bysome means. This can typically be achievedusing external emulsifiers (surfactants) orincorporating internal stabilising groups inthe polymer chain. Examples of these arepolyethylene oxide chains or ionisablegroups such as carboxyl groups fromtrimellitic anhydride (TMA) or dimethylolpropionic acid (bis-MPA). A combination ofnon-ionic polyethylene chains and anionicstabilising moieties is also possible.All techniques have their benefits and

drawbacks. When using externalemulsifiers, there is a risk of surfactantmigration within the finished film, causingsurface defects such as poor gloss,tackiness or whitening due to waterabsorption. Migration of molecules can bereduced or avoided by choosing toincorporate internal stabilising groups, butthis type of stabilisation requires extrasteps during alkyd synthesis.It has been explained elsewhere how such

an internally stabilised alkyd emulsion canbe produced to make high-gloss paints byfirst creating an adduct between TMA andMPEG.2 These paints were rather soft dueto the relatively high number ofhydrophilic ethoxylate chains needed toprovide the emulsion stability. Althoughhaving high water resistance, they did nothave a high chemical resistance, which iswhy some applications could be moredifficult to address with such resins. It istherefore of interest to show howinternally stabilised alkyd emulsions can beimproved in respect of their hardness andchemical resistance.In solvent-borne alkyd coatings, small

quantities of isocyanates are often used toimprove the chemical and outdoorresistance of the alkyd. This kind of

modification can also be applied to analkyd emulsion, although the highviscosities of these resins make thesynthesis and emulsification of the resinssomewhat tricky.Another way to improve alkyd emulsions

may involve the addition of smallquantities of acrylic dispersions to producephysical blends. This modification will

affect properties such as hardness anddrying speed in particular.

Emulsifiable alkyd resinsIn Table 6, the alkyd formulations of twointernally stabilised alkyds are given: onewithout urethane modification and one

Table 4: Paint compositions and basic properties of bis-MPA, di-penta and Boltorn alkyds

Ingredients and test Standard alkyd Bis-MPA alkyd Di-Penta alkyd Boltorn alkydprocedures

Standard alkyd 60% 57.36 – – –Bis-MPA alkyd 100% – 51.04 – –Di-penta alkyd 100% – – 71.21 –Boltorn alkyd – – – 50.54TiO2 26.90 41.47 – 40.42Zr-Octoate, 12% 0.84 1.05 1.45 1.05Co-octoate, 12% 0.24 0.3 0.35 0.30Ca-octoate, 10% 0.40 0.84 0.70 0.27Exkin 2 0.30 0.27 0.09 –Fungicide 0.30 1.38 – –White spirit 13.66 – – –Exxsol D40 – 3.65 26.20 7.42Total 100 100 – 100

PVC 17% 16% 0% 17%Viscosity, cone and plate 350 380 500 350(25°C) (mPas s)Viscosity (23°C) DIN-cup 4 (sec) – – – –Calculated VOC (g/l) 430 74 265 119

König pendulum hardness 1 day 24 43 22 437 days 56 23 35 421 to 6 months 104 23 69 35Initial gloss at 60° 90 87 NA 82Dry film thickness (µm) 25 25 25 45

Table 3: Characterisation of the bis-MPA, di-Penta, Boltorn and ‘concept’ alkyds

Standard Bis-MPA Di-Penta Boltorn Conceptalkyd alkyd alkyd alkyd alkyd

CalculatedOil length 65 73 65 75 78.4Acid number (mg KOH/g) 9 7 8 10 15 (15.7*)Hydroxyl number (mg KOH/g) 43 36 30 15 32 (35*)Mw (g/mole) 20422 8016 20739 6500 3945

MeasuredViscosity (23°C) 100% by wt (mPas) – 780 42000 1200 2690Viscosity (23°C) 60% by wt 5200 – – –(white spirit) (mPas)Colour (Gardner) 6 8 9 7 8* Experimentally determined value

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with. In both alkyds, an adduct oftrimellitic anhydride (TMA) and mono-methyl ether of a polyethylene glycol(MPEG 750) are used to incorporatependant MPEG chains into the alkyd resin.

Adduct and alkyd synthesis

The adduct was prepared by reacting TMAand MPEG 750 in a molar ratio of 1.05:1 at170°C for five hours, purely to open theanhydride ring. GPC (gel permeationchromatography) characterisations of theresulting adduct show that single MPEG750 substitution on the TMA molecule wasthe most frequent substitution. Triplesubstitution was not observed.The alkyd synthesis of the internally

stabilised alkyd was performed by a fusionprocess. All step one components wereadded to the reactor and condensationtook place at 230 to 240°C. When the acidnumber reached around 30mg KOH/g, thereactor was cooled to 180°C prior toadding the dispersing adduct, which wasreacted into the resins at 215°C.In the case of the unmodified alkyd, the

reactor was maintained at 215°C until thedesired acid number of 20mg KOH/g wasreached. In the case of the urethane alkyd,the resin was reacted to an acid numberbelow 5mg KOH/g prior to cooling it to80°C. At that temperature, the isocyanatewas added drop-wise and the reactor wasmaintained at 80°C until titration of theurethane content showed that the reaction

Table 5: Lacquer formulations and basic properties, including ‘concept alkyd’

Lacquer formulation Standard alkyd Diluted alkyd Concept alkyd

Standard alkyd resin, 75% in white spirit 100 60 –Concept alkyd, 100% – 40 100Co-octoate, 10% 0.46 0.52 0.6Zr-Octoate, 12% 1.56 1.78 2.08Ca-octoate, 10% 0.76 0.86 1Exkin 2 0.14 0.12 0.12Aromatic-free white spirit 29.8 22.08 20.38

Lacquer characteristicsNon-volatile content, % 56.9 68.11 80.4Viscosity, 25°C, mPas 480 480 490Calculated VOC, g/l 391 295 178

König pendulum hardness1 day 14 20 187 days 33 42 2014 days 53 54 2828 days 74 65 3149 days 88 74 40Dry film thickness (µm) 40 40 40

Table 6: Formulations of alkyds for emulsification

Ingredients Internally Internallystabilised stabilisedalkyd urethane

alkyd

Step oneBenzoic acid 3.4 3.69Pentaerythritol 21 23.36Phthalic anhydride 23.46 12.5Tall oil fatty acid 58.19 65.16Acid number (mg KOH/g) 30 30OH-value (mg KOH/g) 69.1 177Calculated Mw (g/mol) 2024 709

Step twoDispersing adduct 11.26 10Acid number (mg KOH/g) 20 <5OH-value (mg KOH/g) 43.7 124Calculated Mw (g/mol) 4648 1406

Step threeIsophorone diisocyanate – 11.04

High Tgsegment

Low Tg

O

O

O

O

O

O

O

O

O O O O O

OH OH

HO OO

O O

OO

O OH

OH

Figure 4: Concept of using a reactive diluent to combine high and low Tg segments in a molecule

was finished. Characteristics of the alkydsare shown in Table 7.

Alkyd emulsification

Alkyd emulsions were prepared using thephase inversion process in which water isadded progressively to the molten resincontaining emulsifiers. A water-in-oilemulsion is formed initially which, at acritical solids content, will phase reverseforming an oil-in-water emulsion. Theformulations for the alkyd emulsionsproduced are presented in Table 8.Some external anionic emulsifiers were

added to both emulsions because theywould otherwise rely only on non-ionicstabilisation. It is generally accepted thatanionic and non-ionic stabilisation shouldbe combined for best overall performance.The alkyd emulsion characteristics are alsoindicated in Table 8, showing good stability,low viscosity and a reasonably low dropletsize.

Lacquer performance

To the alkyd emulsions was added 1.5% byweight of the combination drier AdditolVXW. Coatings were drawn down on glassusing a 150µm applicator, and hardnessdevelopment and covered spot resistancewere tested. The hardness developmentshown in Table 8 reveals that the urethane-modified coating developed hardness muchfaster than the unmodified coating, and itsultimate hardness was also higher.

Water and chemical resistance weremeasured by covered spot testing on filmsapplied to glass panels after four weeks at23°C, 50% relative humidity, and for a dryfilm thickness of approximately 50µm. InTable 8 the resistance values are alsopresented, using the following grading scale:

5 = no visible change;4 = minor variation in gloss or barely

visible marks;3 = weak mark;2 = substantial mark;

1 = the structure of the surface has changedor has been partly or complete removed.

From the table it is clear that the urethanemodification gave better ethanol resistanceand it may be of interest to find a furtherapplication for this improved chemicalresistance.

Alkyd-acrylic hybridsAcrylic emulsions are widely used incoatings due to properties such as highhardness, fast drying and good gloss hold-

Table 8: Alkyd emulsion lacquer formulations and characteristics

Formulation Internally stabilised Internally stabilised alkyd – emulsion urethane alkyd – emulsion

Alkyd 49.6 49Anionic surfactant 0.3 1Defoamer 0.5 –Water 49.6 50Total 100 100

Storage stability, 1 week at 50°C OK OKDroplet size D(0.5) (µm) 0.8 1.1Viscosity (23°C) (mPa s) 49 85

König pendulum hardness 1 day 11 117 days 13 1714 days 15 2421 days 17 3828 days 18 47

Spot testing resistanceWater 6 hours 4 4Water 6 hours, recovered 5 5EtOH (48%), 30 min 1 3EtOH (48%), 30 min, recovered 5 5

Table 7: Characterisation of the alkyds preparedfor emulsification

Properties Internally Internallystabilised stabilisedalkyd urethane

alkyd

Calculated propertiesOil length (%) 55 57Acid number (mg KOH/g) 20 0Hydroxyl number 44 66(mg KOH/g)Mw (g/mole) 4649 4369

Measured propertiesAcid Number (mg KOH/g) 20.4 3.1OH-value (mg KOH/g) 44 70Mw 16756 12500Mn 2221 3289Polydispersity 7.54 3.8Viscosity (125°C) 460 894100% by wt (mPas)Colour (Gardner) 7.0 7.6

A = alkyd

Fraction of water (% by weight)Vis

cosit

y

A

DC

B

B = water droplets in oil (alkyd)C = coalescing water dropletsD = oil−in−water emulsion

Figure 5: Schematic representation of the emulsion inversion process

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out on weathering. However, acrylicscannot always match the performance ofalkyds in terms of open time, self-primingand the chemical resistance deriving fromthe oxidative cross-linking of the fatty acidcomponent in the alkyd. Cost is also afactor, the alkyd being typically cheaperthan the acrylics.Alkyds and acrylics can be combined to

make so-called hybrids. There are severalways to make these hybrids such aspolymerising the acrylic in the alkydemulsion, emulsifying the alkyd in theacrylic, or by simply blending the acryliclatex with an alkyd emulsion. The last willbe presented here to see what synergisticfeatures are available.Table 9 shows some alkyd acrylic

formulations. Both pure acrylic and styreneacrylic dispersions were tested. The physicalblends are produced simply by mixing theacrylic latex into the internally stabilisedalkyd emulsion at low shear and slow rateof addition. A suitable amount ofcoalescent agent has to be added in orderto ensure a good film formation. Theblends are very stable over time and do notvary in terms of either pH or viscosity.A combination drier was added to the

hybrids and the alkyd emulsion to obtainclearcoat formulations for evaluation.Clearcoats were applied to glass using a200µm applicator bar and coatingperformance was evaluated.Table 9 also shows the hardness

development of the coatings, revealing thatthe hardness of the hybrids is higher thanthat of the pure alkyd emulsion. The dryingtimes recorded by a Beck-Koller dryingrecorder also show that the small additionof acrylic or styrene-acrylic latex to thealkyd emulsion results in faster surfacedrying. The gloss on coated black glass at20° and 60° is very good for the pure alkydemulsion, whereas the hybrids both havesomewhat lower gloss. This could possiblybe due to a slightly excessive amount ofacrylic as too high an amount may give riseto compatibility problems.

Acrylic and styrene acrylic dispersions canthus be used to modify the coatingproperties of alkyd emulsions to addressissues such as hardness or drying time. Thestyrene-acrylic hybrid has a much betterappearance than the acrylic hybrid, and itis believed that upon film formation, thearomatic nature of the phthalic anhydrideof the alkyd and of the styrene acrylichelps to produce a good blend at a

molecular level. This statement, however,requires further evidence.

ConclusionsHigh-solid alkyds, diluent resins, alkydemulsions and hybrids have been described,all giving coatings with VOC levels belowthe limits stipulated in the VOC legislationfor 2010. Thus, environmentally-friendlycoatings can be produced by adapting thewell-established alkyd resin technology indifferent ways. Alkyd resin technology isvery versatile, and when combining it withother chemistry, the possible combinationsto be tested are limited only by theimagination of the developer.

AcknowledgmentsThis work would not have been possiblewithout the assistance of my co-workers,Anders Clausson, Olivia Karlsson, RebeckaLiedholm, Marie Westerblad and JosefinZackrisson in Perstorp Specialty ChemicalsAB in Sweden, and Vrijesh Singh and SRamakrishnan at Perstorp India, whosecontributions are gratefully acknowledged.

References

1. Manea M, A Clausson, S Stigsson

and K Sörensen, ‘High-solids alkyd

strategy’, Paint and CoatingsIndustry, 28–36, August 2007

2. Ziegler G, R Liedholm, G Ziegler, C

Skoog, M Westerblad and K

Sörensen, ‘Different stabilizing

technologies for alkyd emulsions

and their effect on coating proper-

ties’, Proceedings from the Water-

borne and High-solids Coatings

Conference, Brussels, March

2006

Table 9: Hybrid coating formulations anddevelopment of their physical properties overtime. Drying on glass panels at 23°C and 50%relative humidity

Formulation and Alkyd Acrylic Styrene test procedures emulsion hybrid acrylic

hybrid

Alkyd emulsion 100 90 90Acrylic – 10 –Styrene acrylic – – 10Coalescing agent – 0.7 1

König pendulum hardness1 day 11 10 97 days 13 16 1614 days 15 30 2621 days 17 34 3128 days 18 41 33

Beck-Koller drying times, hoursDust free 1 0.5 0.5Tack free 3 1 2Through dry 9 2 4Hard dry 22 6 11

Gloss at 20°1 day 84 72 837 days 84 67 8214 days 81 71 7921 days 82 69 77

Gloss at 60°1 day 91 88 927 days 91 87 9214 days 91 88 9021 days 91 87 90