Silanol Emulsions as Additives for Latex Coatings: Innovative Material and Technology

TAGS:  Architectural Coatings     Acrylic Coatings     Sustainability / Natural Coatings    

This is a sponsored article by DyStar.

The chemistry and reaction of alkoxysilanes have been well-studied in solventless or solvent-borne coatings. However, the use of hydrolyzable silanes in waterborne systems has been relatively slow to develop. Depending on the alkoxysilane type and reaction conditions, the reactions could be difficult to control.

DyStar has developed several silanol emulsions that can be used as additives in latex coatings. They can be a valuable option to enhance block resistance and lower surface energy without deleterious effects on other coating applications or performance properties.

This article provides a summary of the structure, function, and processing conditions of these multifunctional silanol emulsions. A more detailed look at the performance benefits of these additives in an acrylic latex paint formulation is provided here. As several multifunctional additives are under development, DyStar has invited customer interaction on new applications.

Explore more about the new multifunctional silonal emulsions by DyStar in detail.

Meeting Industry Needs

The coatings industry is one of the most heavily regulated industries in the world, so producers have been forced to adopt low-VOC technologies. Consumer preferences have driven the industry to more environmentally friendly products with low minimum film forming temperatures (MFFT).

Durability is also a rising need attributed to the growing demand for products that last longer, maintain a higher performance, and keep their appearance for longer with less maintenance. Unfortunately, in many cases these trends have had negative consequences:

• Tackiness and resulting blocking problems and dirt pick-up
• Reduced wash, scrub, and stain resistance
• Longer open times
• Exterior gloss loss and reduced durability
• Interfacial problems (adhesion, wettability)
• Flow and leveling problems

Additives can help in correcting the issues noted above, but they can be expensive, incompatible, or too narrowly focused. Changes in legislation (reduction of aromatic solvents, VOC regulations, replacement of alkylphenol ethoxylates) also make new additives necessary.

DyStar interviewed players in the architectural paint market to identify the most important problems when it comes to semigloss and high gloss paints (Figure 1). They then decided to focus on developing an additive that could affect block/tack, imprinting (e.g., fingerprints), and dirt pickup since these attributes are often interrelated and have high satisfaction gaps. A common issue with performance in low VOC paint systems is the tackiness and “green feel”. ^[1]

Silanol Emulsions as Latex Paint Additives: Function and Mechanisms

Silanols have been shown to self-crosslink, improve adhesion to substrates, and depending on functionality, increase coupling to the base resin. These features can help solve the problems indicated above. However, silanols are difficult molecules to incorporate into a water-based paint system and remain stable and effective.

Alkoxysilanes will react with water to generate silanol (Figure 2). In this illustration:

• Si (silicone) is the center of the molecule,
• R is a non-hydrolyzable organofunctional group, and
• -OCH₃ is a functional alkoxy that is hydrolyzable.

The critical condensation step provides the desired reactive silanol. Once the silanol is formed it can readily react with itself, with a functional resin, or with a substrate. Catalysts and/or heat are often used for reaction with other resins and substrates.



Figure 3 shows condensation onto a substrate having hydroxyl surface groups. The silanols ultimately form an oxane bond with the inorganic substrate (Si – O – Metal).



Figures 4 and 5 illustrate a condensation reaction of a silane with an -OH functional polymer and a condensation reaction of a silane with itself.




Depending on the reaction conditions, the hydrolyzed silanol can quickly crosslink with itself to form a silane network. Conditions such as pH, temperature, presence of catalyst, amount of functionality within the silane, and other functional groups can all impact the stability of the hydrolyzed silane. What is desired, but difficult to achieve, is a reactive waterborne silanol emulsion that has long-term stability in a latex system.

By modifying molecular weight, branching and functionality, DyStar has been able to develop silanol emulsions that not only have aqueous stability but also have the required stability when added to waterborne resins and fully formulated paints and inks.

Property Comparison of DyStar Silanol Emulsions

Masil® Ultra MF 8200, Masil® Ultra MF 8201, and Masil® Ultra MF 8219 are self-curing multifunctional silanol emulsions. As additives in latex paints, they impart enhanced properties. The emulsions provide a shelf life of 12 months in unopened sealed containers without extreme heat exposure. When added to various latex and paint systems, they show no signs of “kick-out” or separation when aged for six months. The properties of the three emulsions are shown in Table 1.

Property	Masil® Ultra MF 8200	Masil® Ultra MF 8219	Masil® Ultra MF 8201
Appearance	Milky white liquid, homogeneous	Milky white liquid, homogeneous	Milky white liquid, homogeneous
Solids, %	49.4	47.8	~45-50
Viscosity, mPa.s @ 25°C	75	40	50
Density, kg/l @ 25°C	1.001	1.001	1
pH	6.0	6.1	4.0
Flash Point	None	None	>93°C

Table 1: Properties of DyStar Silanol Emulsions

When the water in the emulsion is evaporated, the materials cure and form films. However, the current target for these materials is as an additive to latex paint systems to improve properties as well as film-forming characteristics. Table 2 offers a comparison of the three products.

	Masil® Ultra MF 8200	Masil® Ultra MF 8219	Masil® Ultra MF 8201
Type	Water based emulsion	Water based emulsion	Water based emulsion
Chemical functionality as silanol	Lower, film forming	Lower, film forming	Higher, film forming
Particle size	1-2 micron	<1 micron	<1 micron
Stability	6-12 months	12 months	12 months
Odor	Minimal	Minimal	Moderate
Major latex film enhancement	Block resistance, scrub resistance, water repellency	Dirt pick-up resistance, flow and leveling, water repellency	Adhesion, pencil hardness, water repellency
Recommended concentration (a ladder study is suggested)	1-3%	1-3%	1-3%

Table 2: Comparison of DyStar Silanol Emulsion Latex Paint Additives

Due to their reactivity, these additives are chemically locked into the cured paint film. No additional catalyst or heat is required for curing, although curing can be accelerated with heat. Simple mixing easily incorporates these products into non-ionic and anionic water-based systems. At the recommended concentration levels, there is no paint instability.

There are two main categories of Masil® MF silanol emulsion products. Two products namely – (Masil® Ultra MF 8200 and Masil® Ultra MF 8219) have lower functionality, and one (Masil® Ultra MF 8201) has higher functionality. These additives enhance film properties at the substrate interface and in the body of the paint film as illustrated in Figure 6.

Value of Silanol Emulsions as an Additive in Latex Paint

In order to determine the aqueous stability of Masil® additives, the additives were blended into acrylic latex at concentrations of 0.5 to 3 percent. The resulting paint systems show no significant changes in wet properties with the increase in silanol.

In order to determine the performance properties of Masil® Ultra MF 8200 and Masil® Ultra MF 8219 additives in dried paint films, a starting point formulation as shown in Table 3 was employed. The additives were incorporated to achieve concentrations of 1, 2 & 3%. The basic processing steps are provided in Table 4.

Function	~1% Additive	~2% Additive	~3% Additive
For Grind:
Water	13.8	13.80	13.80
Coalescing aid	1.56	1.56	1.56
Biocide	0.20	0.20	0.20
Antifoam - FOAM BLAST® 4205	0.20	0.20	0.20
Dispersing agent	0.20	0.20	0.20
Pigment	23.40	23.40	23.40
Rheology thickener	0.49	0.49	0.49
Water	1.66	1.66	1.66
Rheology thickener	0.20	0.20	0.20
For Pre-Letdown:
Water	2.93	2.93	2.93
Binder	45.90	44.92	43.95
Masil® Ultra MF Additive	0.98	1.95	2.93
Water	2.34	2.34	2.34
For Letdown:
Antifoam - FOAM BLAST® 4205	0.15	0.15	0.15
Water	3.91	3.91	3.91
Rheology thickener	2.00	2.00	2.00
pH adjustment	0.10	0.10	0.10

Table 3: Starting Formulation of Semi-Gloss White Paint with Masil® Ultra MF 8200 and MF 8219 additive.

Grind Instructions	Pre-Letdown Instructions	Letdown Instructions
Add all the components of the grind into a beaker. Mix for 15 minutes at 2000 rpm Check the grind. It should be a 6 Hegman or higher	Add all the components of the pre-letdown into a second beaker.                                      Once the grind is off the mixer, put the pre-letdown on the mixer Add the grind to the pre-letdown. Mix for 15 minutes at 1000 rpm	Once the grind and pre-letdown are done mixing, add the letdown components into the pre-letdown beaker Mix for 15 minutes at 1000 rpm

Table 4: Basic Processing Steps Used for Starting Formulations

Handling Precautions

Air introduction during the handling of the paint systems may lead to a pH drift and cause separation over time. A nitrogen blanket is recommended after each use due to the moisture sensitivity of the wet emulsion surfaces.

Viscosity

As can be seen from the viscosity data in Figure 7, there is a viscosity decrease as more of the silanol additive is used. The additive may be acting as a dispersing aid in the paint formula since there is no significant viscosity trend in the control formulation. The use of HEUR rheology additive provides a viscosity improvement.

Increased Contact Angle: Dirt Pick-Up and Scrub Resistance

Silanol additives provide a degree of hydrophobicity due to their low surface energy. This characteristic is generally determined by contact angle measurement with water. The contact angle was determined for a water droplet onto an aluminum substrate that was coated with the modified formulations and then dried for 7 days at room temperature. Higher contact angles (lower surface tension) were observed as the concentration of silanol increased (Table 5).

Additive	Percent by Weight	Contact Angle, Degrees
None (control)	0	78.1
Masil® Ultra MF 8200	1	80.1
	2	85.4
	3	82.1
Masil® UltraMF 8219	1	81.1
	2	88.3
	3	93.1

Table 5: Contact Angle for Water Droplets on Dried Paint Film

On wood substrates, the low surface energy prevents water penetration while still allowing the passing of moisture vapor. The lower surface energy can also provide improved dirt pick-up resistance, stain resistance, and anti-graffiti characteristic (hydrophobicity) of the paint films.

Dirt pick-up testing was performed by pouring a mixture of carbon black and black iron oxide powder onto a section of a coated Leneta substrate. The test piece was then exposed to 50°C for 1 hr and then cooled to room temperature. The sample was then rinsed with water and wiped off with a damp cloth. An observable enhancement in dirt pick-up resistance was achieved with the incorporation of the Masil® Ultra MF 8200 silanol additives. The improvement is most significant at the 1% level.

Scrub testing was performed per ASTM D2486, Method A (cycles to failure) to determine the erosion resistance of the silanol-modified paint systems. The greater the ease of soil removal with a minimum of film erosion, the greater will be the useful service life of the coating. The ASTM test method primarily evaluates the scrub resistance of interior wall paint. The results of these tests are shown in Table 6. The improved scrub resistance is believed to be due to the silanol additive. Since the Masil® additives provide internal crosslinking, they are anti-migratory and repeated exposures continue to show improvement.

Control (No Additive)	1% Masil® Ultra MF 8200	1% Masil® Ultra MF 8219	2% Masil® Ultra MF 8200	2% Masil® Ultra MF 8219
1691	1794	1746	1940	1845

Table 6: Scrub Resistance Testing, ASTM D2486 Cycles to Failure

Blocking Resistance

The block resistance of the modified paint films increases with increasing the amount of Masil® Ultra MF 8200. Film hardness decreases slightly at the highest loading levels. Figure 8 illustrates the anti-block improvement using test parameters of 1000 gm load applied for 30 min at 40°C and then cooling for 30 min before testing. There was no film removal at an additive level of 2%.


The increase in blocking resistance will also provide the paint film with resistance to imprint that occurs due to fingerprints or dirt particles. These enhancements are due primarily to the silanol additive.

Adhesion

Cross-hatch adhesion tests were performed per ASTM 3359 on aluminum and cold-rolled steel substrates. Figure 9 shows the effect of silanol additives on paint adhesion. There is no adhesion drop-off at additive levels of 0-1% on CRS and a slight improvement in adhesion was noticed on aluminum substrates. Increased adhesion is expected on substrates that have surface hydroxyl groups for reasons that are described above.

Comparison to Benchmark Additives

Certain additives have historically been used to provide enhanced adhesion, block resistance, and hydrophilicity. However, they can be expensive, and their compatibility with paint formulations is narrowly focused.

For example, fluorinated additives will provide the highest contact angles and the best block resistance as a benchmark additive, but fluorinated additives provide poor adhesion to metal substrates, especially aluminum, and are environmentally suspect due to their migration potential. The use of certain ester-based coalescing aids has also shown poor adhesion to metal, and certain adhesion promoters have shown gloss reduction effects.

Download Technical Paper: Formulating Masil® Ultra MF 8200 with different rheology & adhesion promoters »

Potential Applications of Masil® Additives

DyStar has evaluated the Masil® additives in a number of proof-of-concept paint applications. Through this work and observations, some information about the potential use of these additives in several different coating types can be developed (Table 7). Further discussions are encouraged and should be made with the DyStar team prior to using these additives.

Coating Type	Coating Chemistry	Potential Value
Protective / Marine	Waterborne acrylic	MF 8201 could enhance corrosion protection due to better adhesion, while MF 8200 or MF 8219 could help coating to reduce drag and fouling due to low surface energy
Traffic paint	Waterborne acrylics, some alkyd	MF 8201 could improve adhesion to road substrates and enhance water resistance for long service life
General industrial	Direct to metal latices, low solvent and solventless epoxy	MF 8201 could improve dirt resistance and adhesion of these aerosols, maintenance coatings, and roof coatings
Wood flat stock	Waterborne acrylic, UV curable	MF 8219 has small particle size that could be an alternative to waxes in filler-sealers, base coats, stains, varnishes, inks and topcoats
Packaging	Waterborne epoxy, acrylic, overprint varnish	MF 8200 could improve flexibility, COF and water resistance of for packaging materials, labels, metal containers, and inks
Digital / inkjet	Waterborne acrylic, radiation curable systems	MF 8219 has small particle size that could run through drop on demand inkjet heads without fear of clogging
Architectural paints – interior	Waterborne latex	MF 8200 and MF 8219 can provide Ultra-low VOC flat and gloss paints extra scrub, dirt pickup, and blocking resistance
Architectural paints – exterior	Waterborne latex	MF 8200, MF 8219 and MF 8201 can all provide water resistance and are UV stable
Architecture primers	Waterborne vinyl acrylic	MF 8200, MF 8219 and MF 8201 can help with water resistance, yet do not interfere with intercoat adhesion
Architectural stains, varnishes	Latex emulsions (highly pigmented), waterborne urethanes	MF 8200, MF 8219 and MF 8201 could all provide Decks, fences, interior wood stains enhanced water resistance in place of other additives that might migrate

Table 7: DyStar Estimation of Masil® Additives Potential Fit to Various Coating Applications

Watch this quick video presentation to gain insights on DyStar's new sustainable Masil® Ultra Multifunctional Additives for waterborne coatings. See performance data and formulation tips to help you select the right type of additive per your application.

Conclusion

DyStar has developed a set of self-curing, multifunctional silanol emulsions, Masil® Ultra MF 8200, 8219, and 8201, for use in latex paints and clear sealers. This represents a significant advancement of silicone additive technology where these emulsion-based additives show exceptional stability by themselves or when added to latex paints. The additives are designed for easy incorporation in various water-based systems.

The products are PFA-free, APEO-free, and ultra-low VOC. These properties should make them highly attractive to coatings formulators looking for sustainable solutions.

When used as an additive in a wide range of latex coatings, the Masil® additives enhance block resistance, lower surface energy (hydrophobicity), dirt pick-up resistance, and scrub resistance at concentration levels of 0.1 to 3 percent. The overall gloss, hardness, and adhesion characteristics are comparable to the control acrylic latex.

Since the release of Masil® Ultra MF series for architectural paint formulations, the DyStar development team has been building a knowledge base of potential interactions with common paint additives. DyStar will gladly host discussions with customers concerning the use of these additives in specific paint systems and applications and share information developed since the publication of this article.

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