One article to understand the application of titanium dioxide performance in coatings

I.

Titanium dioxide is an inorganic white pigment whose main component is titanium dioxide.

Regardless of solvent-based or water-based coatings, if titanium dioxide is used, its role is not only to cover and decorate, but also to improve the physical and chemical properties of the coating, enhance chemical stability, and even improve hiding power, color reduction power, and corrosion resistance.

2.

The different shapes and sizes of titanium dioxide particles have very different degrees of light scattering, which is a key factor affecting the hiding power of titanium dioxide

In the coating system, if the film-forming material is not enough to completely cover the titanium dioxide particles, it will make the titanium dioxide particles contact and agglomerate each other, which is equivalent to an increase in the particle size of the titanium dioxide, which makes the coating hiding power Down

3.

In the field of coatings, the degree of dispersion of powder particles determines product performance to a large extent

 Titanium dioxide in a stable suspension state in the coating will increase the hiding power of the coating.

Fourth, the influence of the amount of dispersant on the hiding power of the coating

 When titanium dioxide is dispersed, the particles tend to agglomerate due to the smaller particles relative to the filler.

5.

Titanium dioxide, as a highly efficient light-scattering pigment, provides excellent whiteness and hiding power for the coating film

Constraints on resources, energy consumption, and the environment brought about by this have become more and more prominent

In addition to the need to promote the development of new titanium dioxide production processes and new technologies, coating manufacturers also need to actively explore how to improve the use efficiency of titanium dioxide, or seek new alternatives to reduce the amount of titanium dioxide used
.

1.
Improve the use efficiency of titanium dioxide

In practical applications, the agglomeration or flocculation of titanium dioxide results in the failure to obtain ideal coverage even when the content of titanium dioxide is relatively high
.
Therefore, improving the light scattering efficiency of titanium dioxide has become a hot topic of research
.
Michael combined the Monte Carlo simulation method to explain that when the equal volume of fine filler is used in the coating formulation to replace the coarse filler, more space barriers will be obtained between the titanium dioxide particles, thereby effectively improving the hiding power of the coating film
.

As the particle size of the filler decreases, the titanium dioxide pigment is better separated, and the light scattering efficiency of the titanium dioxide is improved
.
This means that to obtain the same hiding power, the amount of titanium dioxide used will be reduced
.
The space barrier of this kind of titanium dioxide is also known as the "pigment dilution" effect
.
However, the diluted titanium dioxide particles also have the possibility of re-aggregation
.
In 2013, Dow Chemical won the US Presidential Green Chemistry Challenge Award for successfully developing EVOQUE pre-composite polymer technology
.

If the distance between ordinary coating titanium dioxide particles is too close, the light scattering area will overlap, which will reduce the efficiency
.
The pre-composite polymer is fixed on the surface of the titanium dioxide particles in the coating to form an effective space barrier, thereby improving the distribution of the titanium dioxide particles in the coating and the light scattering efficiency, increasing the hiding power of the coating film, and enabling the coating formulation The amount of medium titanium dioxide is reduced by 20%, and the same or even better covering effect can be achieved with less cost
.

In addition, the addition of pre-polymerized compound also helps to improve the stain resistance and corrosion resistance of the coating
.
The application of this technology can significantly reduce energy consumption
.
According to the results of the third-party verified life cycle assessment (LCA), EVOQUE pre-composite polymer can reduce the carbon emissions of coating products by more than 22% and the water consumption by 30%
.

In 1997, Virtanen proposed a titanium dioxide particle embedded technology, which uses titanium dioxide particles as the core and externally wrapped calcium carbonate as the shell to form a functional pigment with a core-shell structure
.

The calcium carbonate in the outer layer provides an effective space barrier between the titanium dioxide particles and improves the light scattering efficiency
.
The carbon footprint is about 70% lower than that of ordinary titanium dioxide, and partial replacement of titanium dioxide can be achieved
.
This pigment has been commercialized in FP pigments company
.
Similarly, Kemu has developed a surface-treated titanium dioxide TS-6300
.
Conventional surface treatment is often for reducing the photocatalytic activity of titanium dioxide and improving dispersibility
.
The advanced processing technology in TS-6300 creates additional barrier space between the titanium dioxide particles, reduces the agglomeration effect between the titanium dioxide, and improves the light scattering efficiency
.
Moreover, this surface treatment increases the oil absorption of the titanium dioxide particles and reduces the level of CPVC, so that the presence of air in the coating film can be used to improve the light scattering efficiency in the case of lower PVC
.

2.
Introduce air

The presence of air in the coating film can reduce the refractive index of the resin/air mixture, thereby increasing the refractive index difference with the titanium dioxide pigment and improving the light scattering ability of the coating film
.
In coatings, there are usually three types of voids that help to improve coverage, namely the air in the resin, the air in the filler particles, and the air at the interface between the resin and the pigment
.

A typical example of improving the coverage of air in the resin is the hollow polymer microspheres first developed by Kowalski et al.
in 1984 and commercialized by Rohm and Haas Company under the name ROPAQUE
.

The latex particles containing carboxylic acid groups are used to polymerize with hard monomers such as styrene to obtain latex particles wrapped in a polymer hard shell with a high glass transition temperature (Tg)
.
Then increase the temperature of the system to above the Tg of the shell layer, and then use alkali to neutralize and dissolve the carboxyl groups in the core to expand the core, and then cool down to set the shell shape and produce water-filled microspheres
.
During the drying process of the coating film, the water evaporates through the shell of the polymer and is gradually replaced by air
.
In order to compare the effect of hollow polymer on wet and dry coverage, experiments show that coatings containing only titanium dioxide have a higher initial wet coverage, which gradually decreases with the increase of drying time until it reaches a stable state of dry coverage
.

At the same time, the coatings containing titanium dioxide and hollow polymer have similar initial wet covering, and then the covering power gradually decreases during the drying process, and after reaching the lowest point, the covering power is gradually increased due to the volatilization of the moisture in the hollow polymer To a stable state
.

When the content of titanium dioxide is reduced in the coating and the hollow polymer is used, the initial wet covering is poor, but after the coating film is dried, the same dry covering ability as the coating film containing only titanium dioxide can be obtained
.
Therefore, hollow polymers can be used to partially replace titanium dioxide, and can be used as an effective space barrier like ultrafine fillers to improve the efficiency of titanium dioxide
.
In addition, the hollow polymer can also improve the stain resistance, stain resistance, and scrub resistance of the coating film, as well as provide excellent outdoor color retention
.
Similar to the hollow polymer, the air inside the filler also helps to cover the coating film
.
The focused particle beam image at the cross section of the microporous kaolin particles produced by Omiya Company contains many micropores in the structure
.
The kaolin containing closed micropores is prepared by a rapid calcination process
.

In the traditional kaolin calcination process, natural hydrated aluminum silicate is slowly heated to 1,000°C in 30 minutes, so that the flaky clay particles form irregularly shaped agglomerates
.
The heating process of this calcined kaolin containing closed micropores only takes a few seconds
.
The hydroxyl groups in natural aluminum silicate dissociate when the temperature reaches 500°C and are released in the form of steam
.
Because the heating speed is too fast and the steam is too late to release, the pressure inside the particles increases and expands, eventually forming a lot of micropores
.
The void volume in the particles accounts for about 20%, which reduces the density of kaolin from 2.
60 to 2.
06
.

The enclosed air in the microporous kaolin completely resists the penetration of resin, solvent or water in the liquid coating, so these voids help to improve the wet and dry coverage of the coating at the same time
.
And when it is lower or higher than the paint CPVC, it can provide high hiding power to the coating film, and can save up to 20% of the use of titanium dioxide
.

Among them, in the formula lower than CPVC, set the initial point as the volume content of titanium dioxide is 20%, and does not contain any other pigments and fillers, and then increase the three contrast substances with a gradient of 5% PVC, that is, PVC from 20% Gradually increase to 45%, and keep the volume content of titanium dioxide unchanged by replacing the resin with equal volume during the whole process
.
It can be seen that the traditional calcined kaolin has very little effect on the hiding power of the coating film, because its refractive index is not much different from that of the resin
.
The two substances containing closed pores, microporous kaolin and hollow polymer, greatly improve the hiding power of the coating film
.
Although the two have similar contributions to the hiding power of the coating film, they have different effects on gloss
.
Microporous kaolin has a matte effect due to the micro-rough structure of its surface, and the hollow polymer helps to improve the gloss of the coating film
.

In the formula higher than CPVC, the starting point is 75% PVC, which contains 10% PVC titanium dioxide and 65% PVC calcium carbonate with an average particle size of 4 µm
.
Then replace the calcium carbonate with a 5% PVC gradient, and keep the total PVC and volume solid content unchanged
.

Above CPVC, microporous polymers are superior to hollow polymers and traditional calcined kaolin
.
This is due to the simultaneous effect of the voids inside and outside the microporous kaolin particles
.
And because the oil absorption of microporous kaolin is lower than that of traditional calcined kaolin, it will not adversely affect the scrubbing resistance
.
In addition, Nguyen et al.
synthesized a composite nano-sandwich of polymer and titanium dioxide by free radical emulsion polymerization technology
.

In this structure, the titanium dioxide particles are first embedded in a water-swellable hydrophilic inner layer polymer, and then coated with a hydrophobic outer layer, and finally the inner hydrophilic polymer layer is swelled in an alkaline solution.
, Forming a sandwich structure containing air and titanium dioxide particles
.

This structure provides coverage in three ways: one is titanium dioxide particles; the other is air; and the third is the space barrier provided by the outer layer
.

To sum up, in the coating formulation, for different performance requirements, by reducing the agglomeration of titanium dioxide to increase its light scattering efficiency, or by introducing air to increase additional light scattering, both can make the coating film obtain better hiding power.
Realize the partial replacement of titanium dioxide, reduce carbon emissions, and improve the sustainable development ability of titanium dioxide
.

Sixth, the application of titanium dioxide

 Titanium dioxide is widely used in coatings, plastics, rubber, ink, paper, chemical fiber, ceramics, daily chemicals, medicine, food and other industries
.

The coating industry is the largest user of titanium dioxide, especially rutile titanium dioxide, most of which is consumed by the coating industry
.
The paint made of titanium dioxide has bright colors, high hiding power, strong tinting power, low dosage, and many varieties.
It can protect the stability of the medium, and can enhance the mechanical strength and adhesion of the paint film to prevent cracks.
Prevent the penetration of ultraviolet rays and moisture, and extend the life of the paint film
.

 The plastics industry is the second largest user.
Adding titanium dioxide to plastics can improve the heat resistance, light resistance, and weather resistance of plastic products, improve the physical and chemical properties of plastic products, enhance the mechanical strength of the products, and extend the service life
.

The paper industry is the third largest user of titanium dioxide.
As a paper filler, it is mainly used in high-grade paper and thin paper
.
Adding titanium dioxide to the paper can make the paper have better whiteness, good gloss, high strength, thin and smooth, no penetration during printing, and light weight
.
Titanium dioxide for papermaking generally uses anatase titanium dioxide without surface treatment, which can act as a fluorescent whitening agent and increase the whiteness of paper
.
However, laminated paper requires the use of surface-treated rutile titanium dioxide to meet the requirements of light resistance and heat resistance
.

Titanium dioxide is also an indispensable white pigment in advanced inks
.
The ink containing titanium dioxide is durable and does not change color, has good surface wettability and is easy to disperse
.
The titanium dioxide used in the ink industry has rutile type and anatase type
.

The textile and chemical fiber industry is another important application field of titanium dioxide
.
Titanium dioxide for chemical fiber is mainly used as a matting agent
.
Since the anatase type is softer than the gold red type, anatase type is generally used
.
Titanium dioxide for chemical fiber generally does not require surface treatment, but in order to reduce the photochemical effect of titanium dioxide and prevent the fiber from degrading under the action of titanium dioxide photocatalysis, surface treatment is required for some special varieties
.

The enamel industry is an important application field of titanium dioxide.
The enamel grade titanium dioxide has high purity, good whiteness, fresh color, uniform particle size, strong refractive index and high color reducing power, and has strong turbidity and Opacity, make the coating thin, smooth and strong acid resistance after enamelling.
It can be evenly mixed with other materials in the enamel manufacturing process, does not agglomerate, and is easy to melt
.

The ceramic industry is also an important application field of titanium dioxide.
Ceramic grade titanium dioxide has the characteristics of high purity, uniform particle size, high refractive index, excellent high temperature resistance, and no ash when kept at a high temperature of 1200°C for 1 hour
.
High opacity, thin coating, light weight, widely used in ceramics, construction, decoration and other materials
.

China's titanium dioxide industry began in the mid-1950s
.
With the continuous development of the titanium dioxide industry, more and more brands are recognized by mankind.
Data shows that China’s total titanium dioxide production capacity accounts for 30% of the world’s 2.
6 million tons
.
In addition, China has also become the world’s largest consumer of titanium dioxide.
From 1999 to 2011, China’s consumption of titanium dioxide increased from 248,000 tons/year to 1.
65 million tons/year, with a compound annual growth rate of 17.
11%, far exceeding GDP growth.
Speed
.

There are more than 50 titanium dioxide manufacturers in China, which are distributed all over the country.
A large number of small and medium-sized enterprises are concentrated in the eastern region lacking resource advantages
.
However, China's titanium ore resources are mainly concentrated in the southwest region, and the entire industry is still in a period of relatively fragmented development
.

Our country has changed from sulfuric acid anatase titanium dioxide to rutile titanium dioxide in the past.
The production capacity of rutile titanium dioxide has exceeded 70%, and this proportion is still increasing, but the products are still concentrated in the middle and low grades.
High-end titanium dioxide still relies on a large amount of imports, and the domestic product quality is obviously superior to several large titanium dioxide companies
.
In addition, there are only 30,000 tons of chlorinated titanium dioxide products nationwide, which is insignificant in the total amount of 1.
47 million tons.
In the next step, four or five companies plan to develop chlorinated titanium dioxide business, with a planned production capacity of more than 600,000 tons.
The period is a critical period for transforming product structure, upgrading China's technological level, introducing technology, and digesting and accepting it
.

Seven, conclusion

With the increasingly serious problems of the ecological environment and the increase of people's awareness of environmental protection, the titanium dioxide industry with high pollution and high energy consumption is facing huge challenges and tests
.
Titanium dioxide is a very important white pigment in coatings.
Improving its use efficiency, reducing its usage, and developing new materials to achieve partial replacement are necessary measures to achieve its sustainable development
.