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Simpler furniture finiShing

the performance of water-borne single-pack acrylic furniture finishes has con-tinually improved. modern finishes can provide fast drying and block resistance, but their solvent and stain resistance is limited. A self-crosslinking water-borne acrylic polymer gave good resistance properties in clear coats and was modi-fied to enhance performance in pigment-ed finishes.

W ater-borne one-component acrylic sys-tems have grown in popularity with fur-

niture paint applicators in recent years because of their ease of use and good cost profile. A key factor in this growth has been the increased performance of water-borne acrylic systems, in particular hardness development and improve-ments in early block resistance.One major area where further performance improvements are required is in chemical resistance, particularly in respect of solvents and highly staining chemicals. For a long time this could only be achieved with two-compo-nent or UV cross-linkable systems.A new generation of 1K resins in a well-de-

new single-pack coatings can provide high chemical resistance. By Jerome caron, guy clamen and Thom hermens, dow coating Materials.

signed formulation now makes it possible to obtain coatings with improved chemical resistance to alcohol and coffee, even in pig-mented systems. Good hardness develop-ment and early block resistance, needed for industrial coating application line speeds, are also maintained.

neW binderS Are teSted AgAinSt commerciAl productS

All the polymers tested were high-end perfor-mance market one-component water-borne acrylic reference binders particularly recom-mended for industrial furniture applications.The newly developed experimental materi-als as well as the commercial reference sys-tems were formulated in the same general formulation structure using the same raw materials. All formulations were sufficiently coalesced to ensure a film formation temper-ature normalised to ≤ 5 °C with the recom-mended coalescent package.A blend of propylene glycol n-butyl ether / dipropylene glycol n-butyl ether (1/1) was used for all internal binders and the acrylic

commercial market reference shown as R1. A blend of propylene glycol n-butyl ether / dipropylene glycol methyl ether (1/1) was used for the commercial product R2, as rec-ommended in the technical datasheet.

chemicAl And blocking reSiStAnce teSt procedureS

The chemical resistance properties were tested following an internal procedure de-rived from the EN 12720 standard using a 1 (poor) to 5 (excellent) rating scale. Wood test panels were prepared by applying two suc-cessive layers of approximately 200 µm wet film thickness (70-80 µm total DFT) either by drawdown or air assisted spray directly on spruce wood panels. Panels were then dried for two weeks at 23 °C / 50% RH before test-ing.The stackability test is used to determine the tendency of coated surfaces to stick to each other (block) when stacked or placed in con-tact with each other under pressure. 150 µm wet film thickness coatings are drawn down on aluminium plates and dried for 30 sec-

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Results at a glance

ű The performance of water-borne single-pack acrylic furniture finishes has continually improved, leading to their widespread adoption in industrial production.

ű While modern finishes can provide fast drying and early block resistance, good resistance to solvents and strong-ly staining materials such as coffee can usually only be obtained with two-pack or UV curing finishes.

ű A self-crosslinking water-borne acrylic polymer was developed which showed better solvent and stain resist-ance than standard products in clear finishes. However, stain resistance was limited in pigmented finishes, and so a modified binder was created which has chemical interactions with pigments.

ű This second binder showed im-proved performance, but care may be needed in selecting matting and other additives to allow the best resistance properties to be developed.

Figure 1: interactive binder /pigment chemistry.

Table 1: ratings for blocking test.

rating sticking tendency surface damage

5 panels do not stick at all oK (no damage) : 0%

3 panels stick together moK: < 10%

4 panels stick together slightly m (minor) : < 20%

2 Difficult to take apart mM : < 50%

1 Very difficult to take apart M (Major) : < 80%

0 panels completely stuck together MM : > 80%

Figure 2: different structures of dry paint films.

undesirable dry paint film ideal dry paint film

pigment

extender 1extender 2

emulsion

onds at room temperature before placing in an oven set at 40 °C for six minutes.At the end of the drying period, the panels are taken out of the oven and after 30 sec-onds at room temperature, the panels are placed in contact with each other (face to face laid flat) and a weight of 200 g/cm2 is applied overnight. The panels are manually taken apart in order to assess their tendency to stick together and blocking tendency. The rating scale shown in Table 1 takes into ac-count both the force needed to take apart the two panels and the surface damage.

croSSlinking And other WAyS to enhAnce reSiStAnce

Traditionally the mechanical and chemical re-sistance properties of binders can be enhanced through various crosslinking mechanisms that can be of the inorganic or organic type.Conventional crosslinking mechanisms have shown limited enhancement of the chemical resistance properties, often combined with limitations in long term emulsion polymer stability, VOC levels in the coating or aesthet-ic properties.Additional polymer developments set out to reduce the coatings’ sensitivity to stains by changing the traditional way of stabilising polymer emulsions without any surfactant/emulsifiers (as in the acrylic commercial mar-ket reference benchmarks R1 and R2 men-tioned here).

Property r1 r2 eXa1 eXa2

solids (%) 40 40 40 44

MFFt (°c) 33 15 42 36

pH 8.6 8.0 7.5 8.1

Table 2: Physical properties of binders eX a1 and eX a2 and commercial market reference benchmarks (r1, r2).

A new self-cross-linkable water-borne acryl-ic polymer (EXA1) incorporating a novel crosslinking mechanism was developed to further improve chemical resistance, par-ticularly against solvents and highly staining chemicals.It was benchmarked in clear topcoat formula-tions applied over a dark colour pigmented primer against typical one component water-borne acrylic commercial market reference benchmarks (R1, R2) recommended for this application. The physical properties of the acrylic polymers are described in Table 2.

initiAl teStS mAde in cleAr topcoAt formulAtionS

Typical clear formulations were used to formulate the polymers (an outline formu-lation is described in Table 3). It could be demonstrated (Table 4) that only the new experimental self-cross-linkable water-borne acrylic polymer with the novel cross-linking mechanism can bring the required balance of water, alcohol and early block resistance properties at low VOC levels. It outperformed commercial reference binders particularly recommended for their excellent chemical resistance properties.The chemical resistance properties obtained with the novel binder in a glossy topcoat for-mulation were checked in low-gloss flattened clear formulations (Table 5) after developing

The interactive binder interacts with the surface of the filler

interactive binder

Filler

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raw materials clear formulation

Pigmented formulation

low gloss (eXa2)

Water 10.0 4.8 6.7

Dispersing agent 1.0 1.3

Defoamer 1 0.2 0.5 0.4

tio2 pigment 19.3 19.3

extenders q.s.

polymer 77.5 56.0 q.s.

ammonia (14%) 0.2 0.2

coalescing agent 1 q.s. q.s. q.s.

coalescing agent 2 q.s. q.s. q.s.

Wetting agent 0.2 0.2 0.2

Mar aid* (wax based)

3.0

Defoamer 2 0.2 0.2

Matting agent q.s. q.s. q.s.

thickeners q.s. q.s. q.s.

Water q.s. q.s. q.s.

totaL 100.0 100.0 100.0

Weight solids % 32% 44%

Vol. solids % 32% 32%

pVc % 18

* raw material used for glossy formulations or only when silica matting agent (Matt2) was used.

Table 3: Test formulations (all in parts by weight).

Polymer eXa1 r1 r2

coffee (1h) 5 5 5

Water (24h) 5 5 4.5

ethanol 50% (1h) 5 4 3.5

Block resistance 4 m 3 mM 4 m

coalescent (g/l) 50 65 30

Table 4: resistance properties of clear topcoats.

Polymer / properties eXa1 r1 r2

Matting agent 4% Matt1 (wax based)

2% Matt2 (silica based)

Water (24h) 5 3.5 4

ethanol 50% (1h) 4 3 3.5

60° gloss 25 27 29

Table 5: Basic resistance properties of low gloss clear topcoats.

Polymer eXa1 r1 r2 eXa2

ethanol 50% (1h) 4 2 2 4

coffee (1h) 2 4 3 4

Block resistance 4 moK 3 m - 3 m

coalescent (g/l) 50 76 42 76

Table 6: Properties of pigmented formulations.

Matting agent / properties

MaTT1(wax based)

MaTT1 / MaTT2MaTT2

(silica based)

oil absorption Low High

Level (%) 3 1.5 / 0.75 1.5

coalescent (g/l) 76 76 76

ethanol 50% (1h)

4 3.5 2.5

coffee (1h) 4 4 4

Table 7: effects of matting agent on chemical resistance.

extender -- eXT1 eXT2 eXT3 eXT4 eXT5

pVc tio2 18 18 18 18 18 18

pVc eXt - 7 7 7 7 7

coalescent (g/l) 87 81 81 81 81 81

gloss 20 15 15 14 16 17

alcohol 50% (1h) 5 1 1.5 4 4 4

coffee (1h) 4 4 4 4 4 4

Table 8: impact of extenders on properties.

Polymer eXa2 eXa2 r1 r1 r2 r2

pVc tio2 18 18 18 18 18 18

pVc eXt2 - 4 - 4 - 4

pVc eXt3 - 4 - 4 - 4

Matt1 3% 1% 3% 1% 3% 1%

coales-cent (g/l)

76 68 76 68 42 42

alcohol 50% (1h)

4 3.5 2.5 2 2 2

coffee (1h)

4 4 4 3 3 2

Table 9: impact of extenders on properties compared to commercial market reference systems.

Type of additive Wetting agent Thickener

additive Wetting 1 Wetting 2 Wetting 3 rM1 rM2

chemistry acety-lenic diol

alcohols ethoxylated & propoxy-

lated

polyether modified siloxane

Heur new tech. Heur

Level (% active ingredient) :

0.4 0.2 0.2 0.2 0.2

ethanol 50% (1h)

= / - = = / - = =

coffee (1h) = = = = / - =

* “=” indicates no impact of additive on performance;

“= / -” indicates a slight reduction when the additive is present.

Table 10: Wetting agents and rheology modifier testing.

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an appropriate matting agent package bet-ter suited to this new technology. These low-gloss finishes represent a major portion of furniture topcoats.

interActive chemiStry improveS pigmented finiSheS

Following a similar approach the chemical (alcohol) and stain (coffee) resistance proper-ties of experimental polymer EXA1 were then evaluated in pigmented applications. For this purpose a typical low gloss pigmented for-mulation (a formulation outline is described in Table 3) was used.In that evaluation the experimental acrylic polymer EXA1 still demonstrated good al-cohol resistance properties and early block resistance properties but limited stain re-sistance properties, especially to coffee. This showed that even with polymers which devel-op good chemical resistance for a clear appli-cation, the objective of getting good alcohol and coffee resistance at the same time could still be very challenging.This triggered the development of a second experimental acrylic binder (EXA2) more spe-cifically addressing the need for improved coffee resistance properties in pigmented applications (Table 6). The physical properties of EXA2 are described in Table 2.This new acrylic incorporates an interactive binder / pigment chemistry based on the strong affinity of the polymeric network (Fig-ure 1) to the inorganic pigment via specific polymer backbone functionalities. This leads to the formation of an inorganic/organic composite delivering optimised film integrity compared to conventional polymers (Figure 2) with improved stain resistance properties.With an appropriate film formation process it is then possible to deliver a much tighter film with improved barrier properties and stain resistance. However, even a slight reduction in coalescent (from 76 to 67 g/l), led to a less efficient film formation process and reduced the resistance rating for coffee staining from 4 to 3.Therefore raw materials which can influence the film formation process and the coalesc-ing effect need to be appropriately selected to keep the outstanding stain resistance properties of this new acrylic.

criticAl formulAtion iSSueS With the neW binder

In order to develop the EXA2 experimental binder and demonstrate its improved chemi-cal resistance in pigmented applications, a typical low gloss pigmented formulation (see Table 3) was used to formulate the polymers.The results in Table 7 demonstrate again how film formation quality is critical for developing

the best properties. It shows the impact on the chemical resistance of two types of mat-ting agent (MATT1 and MATT2) with different oil absorption values. MATT2 has a higher oil absorption than MATT1 and demonstrated a lower chemical resistance.Extenders are widely used in this type of coating application to reduce the formula-tion cost as well as improve some specific properties such as sandability and blocking resistance. It is also well known that stain re-sistance may be reduced by the use of ex-tenders, as shown in Table 8.

NECOWELTM binders for paints and coatings offer you more:

FlexibilityThanks to customized product modifi cations and refi nements

Product quality Thanks to high-performance alkyd resins

SustainabilityThanks to a high content of renewable raw materials

Environmental and health protectionThanks to VOC and solvent-free binders

ASK Chemicals GmbH | Reisholzstraße 16 – 18 | 40721 Hilden , Germany | Phone: +49 211 71 103-0 | info@ask-chemicals.com

RESINS FOR PAINTS AND COATINGS.

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However, it could be demonstrated that, thanks to its specific film formation properties, the new acrylic was more robust than market commer-cial benchmarks in delivering more consistent performance across various pigment / extender combinations as shown in Table 9.Some other additives used for fine tuning the surface properties were tested to evaluate their impact on properties (Tables 10 and 11). This evaluation showed that for similar types of additives, the selection should be made care-fully to keep the best overall performance of the polymer.

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“The filler nature can significantly influence the chemical and stain

resistance. “

Jerome caronscientistDow coating Mater ials jcaron @ dow.com

3 questions to Jerome caron

What must be considered when adding additives in order to avoid negative impacts on the chemical resistance? One should avoid additive types which can influence the film formation by absorption of the coalescents and one should avoid additives which are highly hydrophilic.

In how far can the choice of fillers influence the stain resistance? The filler nature can significantly influence the chemical and stain resistance. Fillers with high oil absorbtion and high specific surface area are worse in general. The quantity of filler and the total PVC of the formulation significantly affect stain resistance. High PVC is worse in general.

Can the stain resistance also be improved regarding substances other than coffee and alcohol? The improved barrier performance allows a better resistance to domestic stains (example green or black tea). The migration of stains from substrates has also been seen to be reduced by this technology (tighter films).

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Learn more about single-pack coatings at European Coatings Live

on 22 March 2016, 15.00 CET at www.european-coatings.com/live

additive add1 add2 add3 add4 add5

chemistry HDpe wax

emul-sion

silanol func-tional,

silicone disper-

sion

alkox-ysilane

emulsion

organic modified siloxane

poly-ether

siloxane

Level (% active ingredient)

0.9 0.3 2 0.3 1

ethanol 50% (1h) = = / - = = = / -

coffee (1h) = / - = + = -

Block resistance = / - = - =/ - = / +

* “=” no impact of additive on performance;

“= / -” slight reduction when additive is present

“= / +” slight improvement when additive is present

“-” reduction when additive is present

“+” improvement when additive is present

Table 11: Testing of different surface additives.

cAreful formulAtion yieldS high performAnce

This study showed that a one-component water-borne acrylic poly-mer with an appropriate crosslinking technology can demonstrate ex-cellent chemical resistance properties in low-VOC industrial furniture clear topcoats.In pigmented applications, an interactive binder / pigment technology now makes it possible to obtain coatings with improved chemical re-sistance to alcohol and coffee. This technology can create highly filled high PVC formulations with good block resistance while maintaining chemical resistance.

Wetting agents, surface additives, rheology modifiers etc. need to be selected very carefully to avoid adversely impacting the chemical re-sistance that can be achieved with this technology.

literAture

Hermens T., Caron J., Clamen G., one component waterborne coating system developments for industrial furniture applications, european coating conference, 2014.

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