Shiny acrylics - European Coatings Journal€¦ · market. New resin modified surfactant-free...
10
Quelle/Publication: Ausgabe/Issue: Seite/Page: European Coatings Journal 11/2006 24 Shiny acrylics Resin modification of dispersions improves block resistance and gloss. Though there is a continuing move from solventborne to waterborne coatings, acrylic dispersions have so far not been able to compete with alkyds in the high-gloss paint market. New resin modified surfactant-free self-crosslinking acrylic dispersions with multiphase particle morphology are shown to combine higher gloss with outstanding blocking resistance. Gregor Apitz*, Ralf Autrata, Markus Dimmers. * Corresponding author. Contact: Dr. Gregor Apitz, Alberdingk Boley GmbH, Düsseldorfer Str. 39, 47829 Krefeld-Uerdingen, Germany; [email protected] Alkyd-based paints still dominate the ultra-high gloss paint segment since they combine this property with good anti-blocking performance and low material costs. On the other hand, paint and coating formulations have been targeted by increasingly rigorous directives on environmental and health protection over the last 15 years. The resulting strong trend towards water-based low MFFT binders which allow low VOC paints and coatings to be formulated is still evolving. Water-based acrylic dispersions have found widespread use in nearly all paint and coatings application areas. They normally provide finishes with excellent appearance and overall film properties. Good weatherability and durability in particular make them suitable for interior and exterior decorative coatings as well as for high-performance industrial applications. Some factors which affect the gloss of waterborne paints are examined below, with comparisons between surfactant stabilised single-phase and multiphase acrylic dispersions and their resin modified counterparts as water-based binders for gloss paints. Multiphase dispersions enhance blocking resistance Gloss paints based on surfactant stabilised, single-phase acrylic dispersions (ie, the polymer particles consist of a homogeneous copolymer) have to be formulated carefully in order to reach gloss levels that are almost comparable with those of alkyd based paints. The formulation of low VOC or VOC-free gloss paints based on single-phase acrylic dispersions which will cure under ambient conditions requires relatively soft polymers to achieve a low MFFT. A major drawback of these soft binders is their tendency to dirt pick-up, low surface hardness and poor blocking resistance. A common strategy to enhance blocking resistance while maintaining a low film forming temperature is to employ multiphase acrylic polymer dispersions [1, 2]. Multiphase particles are derived by sequential or partially parallel feed of at least 2 different monomer mixtures (with significantly different Tg) to the polymerisation reactor [3]. This procedure creates structured polymer particles, in which the low Tg part contributes to elasticity and good film formation while the high Tg part improves blocking and hardness properties. During emulsion polymerisation, thermodynamic and kinetic factors determine the morphology of the resulting polymer particles [1, 4, 5]. The morphologies that can be achieved vary from small domains distributed inside a particle to core-shell or inverted core-shell, but can also be raspberry-like structures, or completely phase-separated morphologies. Acrylic dispersions containing these multiphase particles are able to combine conflicting requirements such as low MFFT (therefore having a low or zero requirement for film forming agents) on the one hand with high blocking resistance on the other hand. Today these 'core-shell' dispersions can be regarded as standard technology and have gained a remarkable market share in all segments that demand high levels of coating performance. Acrylic dispersions stabilised by tall oil based resinse Resin modified acrylic dispersions have been well known for a long time. They are for example employed in paints, clear coatings, as grind resins and in graphic arts applications. In these water-based binders the modifying resin functions mainly as a stabiliser to prevent the polymer particles from coagulating. From an ecological point of view, the use of renewable raw material sources for the manufacture of the modifying resins is very attractive. During industrial production of cellulose, for example, tall oil is generated as a natural by-product. This is a mixture of rosin acids and fatty acids, and can be reacted (without the need for any solvents) with all kinds of vinyl monomers and copolymerisable carboxylic acids in the presence of a polymerisation initiator and other components [6]. Emulsion polymerisation of vinyl monomers in the presence of tall oil based resins leads to an interesting class of polymer dispersions [7] with outstanding gloss performance. Due to the effective electrostatic and steric stabilisation of the polymer particles by the tall oil based resin, no further surfactants are needed during emulsion polymerisation. Sequential polymerisation of two different monomer mixtures in the presence of a tall oil based resin therefore leads to analogues containing multiphase polymer particles. In addition, this class of polymer dispersions can be provided with common cross-linking systems that are already known from conventional surfactant stabilised dispersion polymers [8-12]. Effects of tall oil based resin modification on dispersions The main aim of this work is to compare the property profiles in terms of gloss and blocking resistance of conventional, surfactant stabilised single and multiphase acrylic dispersions against those of tall oil based resin stabilised single and multiphase acrylic dispersions. Simple model acrylic dispersions were therefore synthesised without any specific optimisation. In order to ensure that gloss differences were not caused by different total monomer compositions, all samples were polymerised using exactly the same total main monomer composition. Three samples, identified as S-acrylic-4, S-acrylic-5 and R-acrylic-6 were additionally provided with a self-crosslinking system that is triggered by the evaporation of water during film formation. Because the total monomer compositions for all model dispersions employed were identical, this comparative study focuses on the effects of particle size, particle size distribution and particle morphology (resulting from the corresponding particle stabilisation technology) on gloss and blocking resistance. The multiphase particle morphology of S-acrylic-5 and R-acrylic-6 is responsible for a much lower MFFT when compared with the corresponding single-phase dispersion polymers (see Table 1). Blocking resistance can be combined with high gloss In order to provide proper film forming conditions for all Vincentz Network +++ Schiffgraben 43 +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
Transcript of Shiny acrylics - European Coatings Journal€¦ · market. New resin modified surfactant-free...
Quelle/Publication:
Ausgabe/Issue:
Seite/Page:
European Coatings Journal
11/2006
24
Shiny acrylics
Resin modification of dispersions improves blockresistance and gloss.Though there is a continuing move from solventborne towaterborne coatings, acrylic dispersions have so far notbeen able to compete with alkyds in the high-gloss paintmarket. New resin modified surfactant-free self-crosslinkingacrylic dispersions with multiphase particle morphology areshown to combine higher gloss with outstanding blockingresistance.Gregor Apitz*, Ralf Autrata, Markus Dimmers.* Corresponding author. Contact: Dr. Gregor Apitz,Alberdingk Boley GmbH, Düsseldorfer Str. 39, 47829Krefeld-Uerdingen, Germany;[email protected] paints still dominate the ultra-high gloss paintsegment since they combine this property with goodanti-blocking performance and low material costs. On theother hand, paint and coating formulations have beentargeted by increasingly rigorous directives onenvironmental and health protection over the last 15 years.The resulting strong trend towards water-based low MFFTbinders which allow low VOC paints and coatings to beformulated is still evolving. Water-based acrylic dispersionshave found widespread use in nearly all paint and coatingsapplication areas. They normally provide finishes withexcellent appearance and overall film properties. Goodweatherability and durability in particular make them suitablefor interior and exterior decorative coatings as well as forhigh-performance industrial applications. Some factorswhich affect the gloss of waterborne paints are examinedbelow, with comparisons between surfactant stabilisedsingle-phase and multiphase acrylic dispersions and theirresin modified counterparts as water-based binders for glosspaints.
Multiphase dispersions enhance blocking resistanceGloss paints based on surfactant stabilised, single-phaseacrylic dispersions (ie, the polymer particles consist of ahomogeneous copolymer) have to be formulated carefully inorder to reach gloss levels that are almost comparable withthose of alkyd based paints.The formulation of low VOC or VOC-free gloss paints basedon single-phase acrylic dispersions which will cure underambient conditions requires relatively soft polymers toachieve a low MFFT. A major drawback of these softbinders is their tendency to dirt pick-up, low surfacehardness and poor blocking resistance.A common strategy to enhance blocking resistance whilemaintaining a low film forming temperature is to employmultiphase acrylic polymer dispersions [1, 2]. Multiphaseparticles are derived by sequential or partially parallel feedof at least 2 different monomer mixtures (with significantlydifferent Tg) to the polymerisation reactor [3].This procedure creates structured polymer particles, inwhich the low Tg part contributes to elasticity and good filmformation while the high Tg part improves blocking andhardness properties.During emulsion polymerisation, thermodynamic and kineticfactors determine the morphology of the resulting polymerparticles [1, 4, 5]. The morphologies that can be achievedvary from small domains distributed inside a particle tocore-shell or inverted core-shell, but can also beraspberry-like structures, or completely phase-separatedmorphologies. Acrylic dispersions containing thesemultiphase particles are able to combine conflicting
requirements such as low MFFT (therefore having a low orzero requirement for film forming agents) on the one handwith high blocking resistance on the other hand.Today these 'core-shell' dispersions can be regarded asstandard technology and have gained a remarkable marketshare in all segments that demand high levels of coatingperformance.
Acrylic dispersions stabilised by tall oil based resinseResin modified acrylic dispersions have been well known fora long time. They are for example employed in paints, clearcoatings, as grind resins and in graphic arts applications. Inthese water-based binders the modifying resin functionsmainly as a stabiliser to prevent the polymer particles fromcoagulating. From an ecological point of view, the use ofrenewable raw material sources for the manufacture of themodifying resins is very attractive.During industrial production of cellulose, for example, tall oilis generated as a natural by-product. This is a mixture ofrosin acids and fatty acids, and can be reacted (without theneed for any solvents) with all kinds of vinyl monomers andcopolymerisable carboxylic acids in the presence of apolymerisation initiator and other components [6].Emulsion polymerisation of vinyl monomers in the presenceof tall oil based resins leads to an interesting class ofpolymer dispersions [7] with outstanding gloss performance.Due to the effective electrostatic and steric stabilisation ofthe polymer particles by the tall oil based resin, no furthersurfactants are needed during emulsion polymerisation.Sequential polymerisation of two different monomermixtures in the presence of a tall oil based resin thereforeleads to analogues containing multiphase polymer particles.In addition, this class of polymer dispersions can beprovided with common cross-linking systems that arealready known from conventional surfactant stabiliseddispersion polymers [8-12].
Effects of tall oil based resin modification ondispersionsThe main aim of this work is to compare the property profilesin terms of gloss and blocking resistance of conventional,surfactant stabilised single and multiphase acrylicdispersions against those of tall oil based resin stabilisedsingle and multiphase acrylic dispersions.Simple model acrylic dispersions were therefore synthesisedwithout any specific optimisation. In order to ensure thatgloss differences were not caused by different totalmonomer compositions, all samples were polymerised usingexactly the same total main monomer composition. Threesamples, identified as S-acrylic-4, S-acrylic-5 andR-acrylic-6 were additionally provided with aself-crosslinking system that is triggered by the evaporationof water during film formation.Because the total monomer compositions for all modeldispersions employed were identical, this comparative studyfocuses on the effects of particle size, particle sizedistribution and particle morphology (resulting from thecorresponding particle stabilisation technology) on gloss andblocking resistance.The multiphase particle morphology of S-acrylic-5 andR-acrylic-6 is responsible for a much lower MFFT whencompared with the corresponding single-phase dispersionpolymers (see Table 1).
Blocking resistance can be combined with high glossIn order to provide proper film forming conditions for all
Vincentz Network +++ Schiffgraben 43 +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
Quelle/Publication:
Ausgabe/Issue:
Seite/Page:
European Coatings Journal
11/2006
24
model binders (where the MFFT ranges from 0 to 32°C),clear coats were formulated according to the guideformulation shown in Table 2.These clear coats were cast on small test panels using a 50µm wire bar coater. After drying for 1 hour at 50°C followedby 24 hours under standard climate conditions (23°C and50% RH) the panels were stacked face to face (film to film)and blocked for 1 hour at 50°C (load = 240 g/cm2). Blockingresistance was then determined as the force necessary todeblock each pair of panels (lower values = higher blockingresistance). Testing was carried out in triplicate for eachclear coat.As expected, and although the MFFTs are much lower, theblocking resistance of the films derived from multiphaseacrylic dispersions is far better than that of the single-phaseacrylic dispersion films (see Figure 1). Further studies on themechanical film properties, and the fact that no driers wereused to enhance film curing of the tall oil resin based clearcoats, have shown that there is no contribution of anypossible cross-linking through oxidative curing of rosin fattyacid groups [13, 14].Gloss performance of the synthesised model dispersionswas compared with a commercially available solventbornealkyd paint using the guide formulation in Table 2. As can beseen in Figure 2, the tall oil resin modified single-phaseacrylic dispersion is able to achieve the same ultra-highgloss as the control, which is a solventborne alkyd.The gloss drops dramatically in changing from aconventional single-phase acrylic dispersion to thecorresponding multiphase acrylic dispersion. This is a wellknown phenomenon that is not restricted to the modeldispersions presented here. The tall oil resin modifiedmultiphase acrylic dispersion on the other hand showsapproximately the same high gloss level as the surfactantstabilised single-phase acrylic dispersion.
Gloss levels are correlated with film morphologyAnalysis of the particle size distribution of the surfactantstabilised single and multiphase dispersions by means ofdynamic light scattering shows almost identical particlessizes (60-70 nm) and particle size distributions (see Figure3, left). In this case, therefore, particle size cannot be usedto explain the obvious difference in gloss.The comparison of the multiphase acrylic dispersions(Figure 3, right) shows significant differences in particle sizeand particle size distribution. The surfactant stabilisedmultiphase dispersion shows a narrow distribution centredon approximately 70 nm whereas the resin modifiedanalogue shows a relatively broad particle size distributioncentred on 50 nm.The comparison of this small particle size with relativelybroad distribution with the coarser particle size and narrowerdistribution of S-Acrylic-4 cannot explain why both bindersachieve the same gloss levels.AFM is now a well established and powerful method toobtain detailed information about the surface morphology offilms derived from polymer dispersions. Although the particlesize distribution of the single- and multi-phase modeldispersions are practically identical, the comparison of the3-D topographic AFM-images reveals major differences, asshown in Figure 4.In contrast to the single-phase dispersion the surface of themultiphase version shows a remarkably higher surfaceroughness. This microscopic surface property correlatesperfectly with the macroscopic gloss development of thepolymer film. This surface roughness can be explained bythe different mechanical properties of the polymer domainsinvolved: as described earlier, the soft, low Tg part of thepolymer particles is responsible for film formation whereas
the hard, high Tg part of the polymer particles does not flowout during film formation and therefore creates surfaceroughness. It is this roughness of hard polymer domains thatis responsible for high blocking resistance.The AFM non-destructive tapping mode combined withphase imaging allows differences to be identified betweenpolymers of different mechanical behaviour on a nanometrescale [15, 16]. The light areas represent hard polymericmaterial whereas the darker areas represent soft andtherefore film-forming material.As can be seen from Figure 5, the tall oil resin modifiedmultiphase dispersion (right) shows a significantly finerdistribution of the hard polymer phase than thecorresponding surfactant stabilised multiphase material(left). This is due to the differences in particle size andparticle size distribution (see Figure 3) which explains themacroscopic gloss development perfectly.
Resin modification improves many desirable propertiesThis comparative study shows that tall oil resin modifiedwaterborne acrylic dispersions offer an interesting propertyprofile:- Ultra fine particle size (in-can-clarity) leading to smooth filmsurfaces;- Lower molecular weight, which results in outstanding woodwarming appearance ("Anfeuerung");- Low foaming tendency due to the absence of surfactants;- Better penetration into substrates such as wood;- Enhanced film formation.In order to achieve higher gloss levels with multi-phase talloil resin modified acrylics and to optimise their waterresistance, current studies are continuing, with an emphasison the chemical composition and quantity of the modifyingresin, the design of the different polymer phases andpolymerisation technology.
ACKNOWLEDGEMENTSThe authors would like to thank Mike Litzenburger and MikeUnger for their skilful synthesis of the acrylic polymerdispersions as well as Martina Weinrich for applicationtesting of polymer films and gloss paints.
REFERENCES[1] J. E. Jönsson, H. Hassander, B. Tornell,Macromolecules, 27, (1994) p 1932-1937[2] M. J. Devon, J. L. Gardon, G. Roberts, A. Rudin, J. Appl.Pol. Sc., Vol. 39, (1990) p. 2119[3] D. I. Lee, Makromol. Chem., Makromol. Symp., 33,(1990) p. 117[4] J. E. Jönsson, H. Hassander, L. H. Jansson, B. Tornell,Macromolecules, 24, (1991) p. 126[5] C. L. Winzor, D. C. Sundberg, Polymer, Vol. 33, No. 18(1992) p. 3797[6] WestVaco Corporation, EP 0 994 123 B1, (2000)[7] This technology is protected by patents owned byWestVaco Corporation / Alberdingk Boley Inc. (EP 1 215221 B1, (2002))[8] J. R. Grawe, G. Bufkin, J. Coat. Techn. Vol. 50, (1978) p.41[9] M. Ooka, H. Ozawa, Prog. In Org. Coat. Vol. 23, (1994)p. 325[10] T. R. Bourne, B. G. Bufkin, G. C. Wildman, J. R. Grawe,J. Coat. Techn. Vol. 54, No. 684, (1982)[11] J. Feng et al, J. Coat. Techn. Vol. 70, No. 881, (1998)[12] R. J. Esser, J. E. Devona, D. E. Setzke, L. Wagemans,Prog. Org. Coat. 36 (1999) p. 45[13] F. B. Chen, B. G. Bufkin, J. Appl Polymer. Sc., Vol. 30,(1985) p. 4551[14] P. Pulin, D. A. Raval, V. M. Mannari, J. Coat. Techn.
Vincentz Network +++ Schiffgraben 43 +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
Quelle/Publication:
Ausgabe/Issue:
Seite/Page:
European Coatings Journal
11/2006
24
Vol. 70, No. 883, (1998)[15] Q. Zhong, D. Innis, K. Kjoller, V. B. Elings, Surf. Sci.,290, L688 (1993)[16] F. Sommer, T. Duc, R. Pirri, G. Meunier, C. Quet,Langmuir, 11 (1995) 440
Results at a glance- Although waterborne acrylic dispersions combine manydesirable properties, it is difficult to achieve high glosswithout disadvantages such as poor blocking resistance.- Multiphase waterborne acrylics can offer even bettertechnical properties, but the change of particle structure(with the same polymer composition) dramatically lowers thegloss due to higher surface roughness.- Tall oil resin modified single-phase acrylic dispersions offergloss levels comparable to those of alkyds, while multiphaseversions still offer significantly higher gloss than theirsurfactant stabilised analogues.- Due to the absence of surfactants, tall oil resin modifiedacrylics show a lower foaming tendency during formulationof paints and coatings.- Because of their lower MW, tall oil resin modified acrylicsshow a significantly improved wood warming effect or"Anfeuerung".
The authors:-> Dr. Gregor Apitz received his PhD in organic chemistryfrom the University of Bonn. He has worked in research anddevelopment of emulsion polymers for Hoechst, Clariant andCelanese Emulsions. In 2006 he joined Alberdingk Boley asR&D group manager for polymer dispersions.-> Ralf Autrata has been active in chemical R&D since 1980.In 1985 he received his degree as a chemical technicianfrom the Fachschule Krefeld. In 1987 he joined AlberdingkBoley and, as research manager, is currently responsible forthe development of acrylic dispersions.-> Markus Dimmers joined Alberdingk Boley in 1990. He iscurrently head of Technical Marketing for coatings,polyurethane- and acrylate dispersions.
Vincentz Network +++ Schiffgraben 43 +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
Quelle/Publication:
Ausgabe/Issue:
Seite/Page:
European Coatings Journal
11/2006
24
Figure 1: Blocking resistance of clear coat films (low value = good blocking resistance) .
Figure 2: 20° Gloss of white gloss paints (200µm wet film on glass / BYKMicro-Tri-Gloss).
.
Vincentz Network +++ Schiffgraben 43 +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
Quelle/Publication:
Ausgabe/Issue:
Seite/Page:
European Coatings Journal
11/2006
24
Figure 3a-b: Particle size distributions. a): surfactant stabilised resins S-Acrylic-4(green), S-Acrylic-5 (blue); b): Multiphase resins S-Acrylic-5 (blue), R-Acrylic-6 (red)
(instrument: ALV, measuring angle: 90°) .
Vincentz Network +++ Schiffgraben 43 +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
Quelle/Publication:
Ausgabe/Issue:
Seite/Page:
European Coatings Journal
11/2006
24
Figure 4: AFM topographic 3-D image of S-Acrylic-4 (left) and S-Acrylic-5 (right).
Vincentz Network +++ Schiffgraben 43 +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
Quelle/Publication:
Ausgabe/Issue:
Seite/Page:
European Coatings Journal
11/2006
24
Figure 5: AFM image (phase contrast in tapping mode) of S-Acrylic-5 (left) andR-Acrylic-6 (right).
Vincentz Network +++ Schiffgraben 43 +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
Quelle/Publication:
Ausgabe/Issue:
Seite/Page:
European Coatings Journal
11/2006
24
.
Vincentz Network +++ Schiffgraben 43 +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
Quelle/Publication:
Ausgabe/Issue:
Seite/Page:
European Coatings Journal
11/2006
24
.
Vincentz Network +++ Schiffgraben 43 +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
Quelle/Publication:
Ausgabe/Issue:
Seite/Page:
European Coatings Journal
11/2006
24
.
Vincentz Network +++ Schiffgraben 43 +++ D-30175 Hannover +++ Tel.:+49(511)9910-000
