Effects of Silane on Emulsion Stability and Film Properties

By Michael K.

When the silane reacts with the resin or is added to the resin solution as an adjuvant, it has been demonstrated that the film properties of the resin system can be improved

Structure and chemical properties of alkoxysilanes

The chemistry and reactivity of alkoxysilanes has been well studied

Alkoxysilanes have been used in solvent-borne systems for some time, and they can be reacted into or mixed into solvent-borne resins with relative ease

 Structural and chemical interactions with substrates

Once formed, silanols readily react with themselves, with functional resins or substrates, and each possible reaction requires different conditions to proceed

The condensation reaction is a critical step that provides (1) adhesion/adhesion to the substrate, and (2) intermolecular crosslinking within the paint film to enhance the paint film properties

water dispersion

Much industrial research continues to prepare stable dispersions of alkoxysilanes in aqueous solutions

As shown in the previous content, the success of dispersion of alkoxysilanes in water is enhanced by conversion to the corresponding silanols, which has been done at various pH conditions, but usually in the pH range of 4-7, using appropriate The surfactants of silane are also beneficial to the dispersion and stabilization of aqueous solutions, and even under these controlled conditions, there are limitations in the stability of aqueous solutions of silanes with more functional groups and larger molecular weights

Effect of Process Conditions on Emulsion Dispersions

Various process conditions were tested to optimize the stability of the incorporation of the aqueous dispersion into the latex, and three conditions including the temperature, stirring speed and addition time of the silanol solution were investigated

The first set of conditions tested was to simulate adding to the emulsion during production

The second set of conditions was used to simulate the addition in a paint or ink formulation with a temperature of about 25°C, a mixing speed of 1000-2000rpm (Cowles paddles), and rapid addition of silanols to the vortex, which represents During high shear mixing, both compounds appeared to mix well and no significant particle formation was observed in the formulation container or paint filter

Overall, compound 2 was easily incorporated into the emulsion under both standard application procedures and maintained its stability over time

Latex Precautions

Two types of emulsions were used in this study

Emulsion testing,
physical properties of clear paint film solutions

Using a 100% acrylic resin with a silanol base premixed into the emulsion on our clear and paint films, we conducted a ladder study to test the effect of varying levels of silanol
.
Table 2 shows the wettability results for these mixtures, with no significant change in wettability with increasing silanol content
.

Clear paint film test results

All samples in Table 2 were applied to Leneta cardboard, aluminum-based panels, and cold rolled steel (CRS) panels at a wet film thickness of 6 mils.
Physical data were collected after 7 days in a controlled environmental chamber.
The graph below shows this.
An important finding of this work, 0% of the data points are for the emulsion without adjuvant, the reference sample for comparison
.

Figure 5 shows the gloss results at 20° and 60°
.
With the increase of the amount of silanol added, the gloss showed a downward trend, and the decrease trend was the most significant with the addition of 2% compared with the reference sample
.

Figure 6 shows the increase in anti-sticking performance when the additive is added at 1%, after 1% we see that the anti-blocking performance slowly returns to the level of the reference sample, with the addition of 1% silane, it can be improved The anti-stick properties, however, appear to soften above 1%
.

Figure 7 on the previous page shows the drop in surface energy with the addition of silane, as expected
.
This predicts its improvement in stain resistance
.

Figures 8-10 show the hardness test, we tested the pencil hardness and Koenig hardness of the samples, and the pencil hardness of the aluminum-based paint film increased at a lower silanol content
.
On cold rolled steel we see hardness comparable to the reference until the silanol content is added to higher levels
.
The Koenig hardness was similar to the results on the cold rolled steel, and the hardness was similar to that of the reference before higher levels of silanols were added
.

Figures 11 and 12 show the effect of silane on adhesion
.
We did see that higher additions of silane reduced the adhesion of the paint film on aluminum, however, there was no effect on the adhesion on steel
.

Effects on coatings
Physical properties of coatings

We formulated a high-quality custom white semi-gloss paint and used it as a base for various concentrations of silane additives, using the paint formulations shown in Table 3
.
Note that the 1.
5% silane containing emulsion was not used for paint testing
.
Table 4 lists the wetting properties of these formulations
.

 As shown by the RVT and KU viscosity data in Table 4, the viscosity decreased as the amount of silanol additive was increased
.
Figure 13 shows the viscosity trend of Brookfield viscosity.
Since the emulsion does not have a significant viscosity change, silanol additives can be used as dispersing aids in coating formulations
.
More work is needed to understand this trend change
.

Paint film test results

All samples in Table 3 were applied to Leneta cardboard, aluminum substrates, and CRS substrates at a wet film thickness of 6 mils.
Data were collected after 7 days in a controlled environment chamber.
The graph below shows the key findings of this work
.

Figure 14 shows the gloss results for 20° and 60°, we see a slight decrease in gloss with increasing silanol additions, but the changes shown at these additions appear to be less pronounced
.

Figure 15 shows the improvement in stick-back resistance, which is improved even at an addition level of only 0.
23%, with every addition of silanol, the stick-back resistance continues to improve compared to the reference
.
At the highest addition level, the paint film was not damaged, as shown in Figure 16
.
These results are based on a single test, and we plan to use other colors of paint for further testing
.

Figure 17 shows that as the amount of silane added increases, the surface energy decreases, as expected, which predicts an improvement in the stain resistance of the coating
.

Figure 18-20 shows the hardness test of the coating, we tested the pencil hardness and Koenig hardness of the sample, we saw that the pencil hardness of the aluminum substrate was similar to the reference sample, and then when the addition amount increased to 0.
94%, the hardness dropped
.
On cold rolled steel we see hardness similar to the reference for all additions
.
The Koenig hardness showed an upward trend, and when it increased to 0.
94%, the hardness began to decrease
.
This study shows that at higher addition levels, the paint film produces a softening effect
.

Figures 21 and 22 show the effect of silane on adhesion
.
We did not detect a decrease in adhesion on either aluminum-based or CRS substrates when the silane content in the coating was higher
.
The scribe line adhesion image in Figure 23 shows the results of the test on an aluminum substrate
.

We conducted a stain resistance test by pouring a mixture of carbon black and black iron oxide over a portion of coated Leneta card stock
.
Next, we brushed the powder on this part, baked at 50°C for 1 hour, cooled for 1 hour, rinsed the powder with water and wiped with a damp cloth
.

We found that with the addition of silanol additives, the stain resistance was significantly improved
.
As shown in Fig.
24, the improvement is most significant at the addition amount of 0.
94%
.
This study is qualitative and we will optimize the stain resistance test using a spectrophotometer to obtain quantitative results in future trials
.

in conclusion

The goal of this study was to improve coating performance by adding highly branched/functional silanols, which have been shown to improve substrate adhesion and, depending on functionality, increase the coupling to the resin, which It can improve other properties of the paint film, such as chemical resistance, stain resistance and corrosion resistance, etc.
Silanol can also self-crosslink, providing another method for improving the performance of the paint film.
In theory, low molecular weight, Highly branched functional silanes provide the best improvements in film properties, however, these molecules are the least soluble in aqueous solutions and remain compatible in resin/coating systems
.

Our work shows that high molecular weight, highly branched/functional silanes can be prepared as stable silanols in aqueous solution, and the structure and functional level of the silane can determine the stability of aqueous silanols in emulsions and ultimately Its stability in coatings
.
When a stable silanol solution is formed, it can be added at the low shear mixing stage of emulsion production or at the stage of high shear coating formulation production, and once the optimum addition is added to the emulsion and/or coating, better performance
.