Functionalization of colloidal silica nanoparticles and their application in coatings

Abstract:
the chemical properties of surface-modified nano-silicon dioxide and its application in coatings. The research status of water-phase silicone sol dispersion system is introduced. The chemical properties of alkyl silica and its reaction to the surface of nano-silicon dioxide are summarized, and the

. The different methods of characterizing surface modified nano-silica and their properties with unalmed nano-silicon dioxide were presented. Product characteristics studied include charge density, collosium stability in salt, gel stability after freezing and thawing, and surface stress. The effect of surface-modified nano-silicon dioxide on some important properties in coatings is proved. For example, by adding surface-modified nano-silicon dioxide can improve the water resistance, hardness, scratch resistance, cover and stain resistance of coatings and coatings.
Keywords: Silane, surface modified, silica nanoparticles, collogenic silica, water-based
silane modified silica nanoparticles in coatings and paints
This section discusses different methods for using silicon dioxide dispersions in coatings and paints. The aim is to show how this new technology can be used to improve the performance of coatings and paints. Examples of the application of silane modified silica dispersions in transparent coatings and silicate coatings are given, and how they can be used for dispersion of inorganic pigments. In addition, examples are provided of how the addition of modified silica dispersions improves the product performance of acrylic and aolate resin coatings.
the role of silicon dioxide dispersants modified by silicone alkyl in transparent coatings
silica-modified silica dispersions can be used in transparent coating (CC) formulations. Formulation technology is a difficult field for beginners to enter, as most of the knowledge in this area is a trade secret developed as a formulation for coating companies. Therefore, it is not possible to provide general information on how to add new ingredients, such as modified silica dispersions in complex formulations. In order to study the application effect of silane modified silicon dioxide dispersion in coating formulation, a formula design scheme for polyurethane dispersion is proposed.
table 1 shows the different ingredients in the recommended formulation for transparent coatings based on Alberdingk®U 9150 (polyurethane dispersion). The table lists the product number, product type, quantity, and vendor. The addition of silicon-based modified silica dispersions is approximately 10 wt of the total amount in the formulation, equivalent to a transparent coating formula containing 3wt% of silicon dioxide.
Figure 1 shows the effect of different amounts of silane modified silica dispersion on Persoz hardness by adding 10wt% and 20wt% to the resin solid. Figure 1 uses a two-part (2-k) system with a total solid content of 35wt%.
the relationship between pasteur hardness and coating composition and drying time (d) at room temperature in Figure 1. In the Pasteur hardness test, the hardness of the coating was measured by measuring the damping time of the swing pendulum, compared to the resin content, the amount of silicon dioxide was 10wt% and 20wt%
respectively. This is placed on the coated surface with two stainless steel balls. When the pendulum begins to move, the stainless steel ball rolls over the surface and exerts pressure on the coating. The amplitude of the swing decreases over time. Record the time, in seconds, when the swing is reduced from 12 degrees to 4 degrees. The harder the coating, the longer the damping time.
can be known from Figure 1, the addition of silane modified silica dispersion has a significant effect on pasteur hardness. This effect is also enhanced as the amount of silicon dioxide dispersion added to the silane-modified coating formulation increases. Obviously, the coating takes time to improve its hardness after application. In a transparent coating formulation containing a 20 wt% silane modified silica dispersion, maximum pasteurization can be achieved after 7 days. However, when the addition is less modified silica dispersion (approximately 10 wt), it takes 30 days to reach the maximum pasteur hardness. In addition, after 30 days, the transparent coating containing 20% silane modified silica dispersion has a pasteury hardness of approximately 240 seconds, without adding any silicon dispersion with a pasteur hardness of approximately 160 seconds. When a modified silica dispersion is added to the transparent coating formulation, the modified silica particles form a network structure of silica in the coating, which acts as a skeleton enhancement. This explains the significant increase in pasteur hardness shown in Figure 1.
2 shows the results of a water-based two-part polyurethane coating that does not contain any silicon dioxide and is formulated to contain traces of a resin-containing 10% silicone-modified silica dispersion. It is clear from the figure that the coating without silica in the formulation is much more damaged than the coating containing 10% silane modified silica dispersion.
2, the anti-scratching of controls and hybrid systems was evaluated. This test is carried out in accordance with ISO 1518 Paint and Varnish-Scratch Test standards. This standard specifies a test method for determining the permeability resistance of a single-coated or multi-coated system for paints, varnishes or related products under specified conditions when scratched with a hemetric needle. Scratch resistance has been defined as the minimum load (in grams) required to cut the film up to the substrate. (Image from Céline de Lame, CoRI).
table 2, scratch resistance is quantified according to the maximum load (in grams), which can be applied to the needle without cutting the coating film. Add 10wt% silane modified silica dispersion to the transparent formula to improve scratch resistance by at least 300 g. This is equivalent to a 20% increase in scratch resistance.
table 2 does not contain scratch resistance (g) for three transparent coating coatings containing 10 wt% Levasil CC301. The maximum load applied to the needle is 2000 g without cutting through the coating film.
inorganic pigment dispersant
silica modified silica dispersant can be used as a dispersant for inorganic pigments. Silane-modified silica particles are in the range of 5-10nm, while pigment particles are usually in the size range of 1-10m. Since modified silica particles are about three orders of magnitude smaller than pigment particles, they can be adsorbed to the surface of pigment particles and form thin layers. The surface chemistry of modified silica particles is compatible with most inorganic pigments, which are encased in hydroxyl. In addition, silane-modified silica particles are insensitive to high concentrations of salts that may be released when preparing high concentrations of inorganic pigment water dispersions.
dioxide is the main white pigment used in coatings because of its high refractive index. However, the available resources for this metal oxide are scarce, so titanium dioxide particles must be dispersed as much as possible in order to maximize their masking capacity and reculsion coefficient.
3 release rate (%) relative to titanium dioxide content, 300 nm-700 nm. The pigment slurry of the coating is dispersed with modified collegial silicon dioxide (pigment slurry No. 1) and Dispex N-040 (pigment slurry No. 10), respectively.
3 shows how the refractive index depends on the amount of titanium dioxide pigment added to the acrylic coating. Two different dispersants were used in the trial. In the experiment, the water-based acrylic copolymer sodium salt dispersant Dispenser Dispenser Dispenser Dispenser Dispenser Dispex N-40 was used as a reference. The other dispersant is Lepasil CC 151, a modified silica dispersion with a particle size of approximately 5nm silica content of 15%. The relationship between the refringing curves of the two coatings and the content of titanium dioxide clearly shows that it is beneficial to use modified silica dispersions as dispersants.
4 shows two images of transmission electron microscopes (TEMs) scattered with titanium-white pigment particles, scattered with modified silica and Dispex N-40 above. TEM photographs of titanium dioxide pigment particles dispersed with modified silica show that titanium dioxide particles absorb a thin layer of silica nanoparticles. Titanium dioxide particles dispersed with DISPEX N-40 show sharper edges. Physical separation/interval of titanium dioxide pigment particles is possible by adsorption of a modified layer of silicon dioxide nanoparticles, which explains slightly better dispersion, resulting in higher refraction, as shown in Figure 3.
Figure 4 a) TEM microscopic photo: Titanium dioxide pigment dispersed by modified silica dispersion; b) TEM microscopic photo: Titanium dioxide pigment dispersed by acrylic copolymer sodium dispensing Dispex N-40;
since the dispersion of titanium dioxide pigment particles can be improved by using modified silica dispersants as dispersants, more concentrated long-term stable pigment dispersions can be made. In addition, by replacing surfactants with silica-modified silicon dioxide dispersants, there are no components that interact with other components in the formulation in an adverse manner. As a result, bubble problems can be reduced and coating resistance can be improved.
is the most commonly used binder
in silicate coatings, the co-adhesive in silicate coatings. By replacing some potassium silicate with modified silica dispersions, it is possible to obtain better performance silicate coatings, for example, reduced contamination resistance and stress during drying (better film-forming). By reducing the amount of potassium silicate in silicate coating formulations, the alkalinity of the coating is reduced. As a result of the reduction of alkali content, the solubility and water absorption of the coating is reduced, thus improving weather resistance.
because the modified silica dispersion of neutral pH is very alkaline, the pH of the formula will be slightly lower in the formulation of silicate coatings that replace a significant portion of potassium silicate. In a typical single-member (1-k) silicate coating formulation, two-thirds of potassium silicate is replaced by modified silica dispersions with a pH of about 11.2. The corresponding pH of silicate coatings with potassium silicate as the sole binder is generally around 11.7. Silicate coatings with a pH of more than 11.5 are usually classified and marked as irritants. Adding a certain amount of potassium silicate to the binder can have good coating properties, because the collosus silicon dioxide itself can not form a film. In addition, high pH enables silicate to react with calcium to produce calcium silicate, which is almost insoluble in water, thereby increasing the water resistance of silicate coatings.
to determine the absorption rate of silicate coatings is a method to show the properties of silicate coatings. Table 3 shows the absorbent nature of silicate coatings, where the coating formulation contains 20% silicate adhesives. Four different silicate adhesives were tested. The first as a reference contains only potassium silicate, while the other three formulations contain different amounts of modified silica dispersions and potassium silicate. The results showed that replacing 1/3 of potassium silicate binders with modified silica dispersions (containing 30wt%SiO2) could reduce water absorption by 10 times. Other water absorption systems containing modified silica dispersion systems have similar values, as seen in Table 3.
table 3 four different silicate coatings absorb water after 6 hours, which contain different amounts of modified silica dispersions.
by replacing a certain percentage of potassium silicate with modified silica dispersions, the performance of another product of silicate coatings is improved by anti-fouling (DPU). Figure 5 shows a stain-resistant image of four different silicate coatings, using carbon-black water slurry to simulate hydrophobic dirt. As can be clearly seen in Figure 5, the addition of modified silica dispersions to silicate binders greatly improves stain resistance. Formula 2 contains the highest proportion of modified silica dispersions in the binder, with a significant low suction rate.
image of the surface of the silicate coating, coated with carbon-black dirt, and then rinsed with water (provided, Céline de Lame, CorI). (a) Reference-potassium silicate binder; (b) 2/3 potassium silicate replaced (modified silica dispersion, SiO2 content 30%) ;( 1/2 potassium silicate replaced (modified silica dispersion, SiO2 content 30%) ;(d) 1/3 potassium silicate replaced (modified silica dispersion, SiO20%);
table 4 shows the corresponding stain-resistant numbers for four different formulations. Replacing half or one-third of potassium silicate with a silane-modified silica dispersion improves stain resistance.
table 4 is resistant to contamination of silicate coatings after coating charcoal black water slurry. The substates in these silicate coating formulations contain different amounts of silane modified silica (see Table 3).
when replacing two-thirds of potassium silicate, contamination resistance improved significantly. The reason may be that at the nanoscale, a minimum number of silicon dioxide nanoparticles is required to effectively cover the surface of pigments and fillers in modified silicate coatings, i.e. micron-scale particles. Unless the silicate coating film is completely protected by a modified layer of silicon dioxide nanoparticles, dirt particles can be attached to the unprotected portion of the silicate coating surface. In addition, the stress of the mixing system during coating drying is significantly lower than that of pure silicate coatings. Lower stress facilitates film forming and enhances coating performance.
improved product performance of colored acrylic and aliclicic acid coatings
Two important product characteristics of colored acrylic and aliclicic acid coatings are described in detail here. Adding modified silica dispersions to the binder formulation can improve the performance of both products.
Table 5 shows the formula for adding different amounts of silane-modified silica dispersion (Levasil CC 301) to the water-based acrylic paint in the substation (i.e., the paint portion) (FP2019/1). Table 5 of the raw materials 9-13 constitutes the paint part of the coating formula, while the raw material 1-8 constitutes the abrasive base of the coating formula. The reference formula paint section in Table 5 does not contain any silane modified silica dispersions.
use a brush to apply different formulations of paint (see Table 5) to the fiber cement substrate, two ways. The two-layer film coating interval is 24 h dry at room temperature. After two weeks of drying at room temperature, contamination of different coating surfaces with two different standard dirt dispersions. The dirt dispersion contains 1wt% iron oxide or 1wt% carbon black. Two dirt dispersions are applied by spraying. After spraying, the contaminated coating film will be dried 24 h at room temperature. Iron oxide is a hydrophobic pollutant used to simulate inorganic dust, while carbon black is a hydrophobic pollutant used to simulate organic particles such as diesel soot.
dry the contaminated surface by 24h, the surface is cleaned in two different ways. One method of cleaning is to gently wash under water with a soft towel, simulating rain. In the second cleaning method, a soapy water solution is used instead of artificial.