Classification of titanium dioxide

Titanium dioxide is a very important white pigment in industrial production. There are many types of it. According to the production process, it can be divided into sulfuric acid titanium dioxide and chloride titanium dioxide. According to the crystal form, it can be divided into anatase titanium dioxide and rutile titanium. White powder is divided into pigment-type titanium dioxide and special titanium dioxide according to the object of use. The following will introduce the classification of titanium dioxide for you.

(1) Titanium dioxide by sulfuric acid method and chloride method

According to different production processes, it can be divided into sulfuric acid titanium dioxide and chloride titanium dioxide. Chloride titanium dioxide is very popular in coatings because of its low impurity content, narrow particle size distribution, high whiteness, and good pigment performance.At first, the product quality of the sulfuric acid method was not as good as that of the chlorination method, but in order to compete with the chlorination method, the sulfuric acid method improved the process and strengthened process control, which greatly improved the quality.Comparing the quality of products produced by the two methods, although in some aspects (such as particle size distribution, impurity content, color, etc.), the quality of products produced by the chlorination method is indeed slightly higher than that of the sulfuric acid method.Since the operating rate of oxidation equipment is higher than that of sulfuric acid, the relative density of oxidation products in the world titanium dioxide market has exceeded that of sulfuric acid. In 1996, the production capacity of the chlorination process accounted for about 55% of the world’s total production capacity, and the sulfuric acid process accounted for 45%. At present, there is basically no rutile sulfate titanium dioxide in the US market, and the remaining sulfuric acid factories in the United States produce anatase titanium dioxide. It can be said with certainty that the rutile type titanium dioxide used in coatings has recently occupied the majority, and will continue to grow in the future due to environmental protection issues.

(2) Rutile and anatase titanium dioxide

According to the crystal form, it can be divided into rutile type and anatase type titanium dioxide. The sulfuric acid method can produce rutile titanium dioxide and anatase titanium dioxide, while the rutile titanium dioxide can only be produced by the chloride method. The rutile titanium dioxide crystal structure is dense, and the anatase crystal structure is loose. Due to the high refractive index of the rutile type, its hiding power and achromatic aberration are about 20-30% higher than that of the anatase type, and the durability of the rutile type is greater than that of the anatase type. From the perspective of whiteness and hue, at the ultraviolet end of the visible spectrum, rutile absorbs more light than anatase, so rutile tends to have a yellow phase, which is not as white as anatase, which has a blue phase. However, with the improvement of manufacturing technology, some varieties of rutile type are no different from anatase type in this respect, or even no difference. Although the price of anatase is cheaper, but because the price difference is not big, to achieve the same hiding power, anatase titanium dioxide needs to be used more than twice, resulting in increased cost and poor durability, so developed countries generally do not use anatase As a paint pigment, it is not even used as an interior paint because of its poor optical resistance. In the past, anatase titanium dioxide was used to make self-cleaning exterior wall paint and road marking paint because of its easy pulverization, but it is basically not used now. Only some paints have special requirements, such as only using a small amount of anatase Titanium dioxide can show a clean white or light blue phase.

(3) Large particle size and small particle size titanium dioxide

The particle size of titanium dioxide crystals is below 1pm, belonging to the submicron range. Generally, in order to achieve effective light scattering, produce the best hiding power and achromatism, the particle size of titanium dioxide should be equal to or slightly smaller than half of the wavelength of the scattered light. However, since human eyes are sensitive to yellow-green light, the average particle size of titanium dioxide pigment for coatings should be 0.2-0.3um. Theoretically, when the grain size of titanium dioxide is less than 0.19um, there is no hiding power. But in fact, due to the inevitable aggregation of titanium dioxide crystals, this particle size is much smaller than 0.19um. In recent years, ultra-fine titanium dioxide with a particle size of 0.01-0.05 μm has been successfully developed. It is a non-hiding, transparent titanium dioxide, which is widely used in transparent coatings of different colors and automotive topcoats.

In order to give full play to the optical properties of titanium dioxide pigments in different types of coatings, the modern titanium dioxide industry has produced titanium dioxide with various particle sizes. Generally, 0.2-0.3um is small particle size titanium dioxide, and 0.4-0.5um is large particle size titanium dioxide. Small particle size rutile titanium dioxide has high gloss and good whiteness. Anatase titanium dioxide has a fresh tone, blue background color, and large achromatic aberration. It is mainly suitable for high-gloss coatings with low pigment volume fraction to increase incident light. The number of scattering points in the coating film to improve the covering power of the coating film is the so-called particle number effect. However, the anti-powdering degree of small particle size goldstone titanium dioxide is poor. The medium-sized rutile titanium dioxide pigment has balanced properties and good chalking resistance. It is widely used in various coatings, and some are called general-purpose titanium dioxide. There are two types of large particle titanium dioxide, one is spongy aluminum-silicon-coated titanium dioxide for flat latex paint, which has high oil and water absorption and can improve the hiding power. It is mostly used in paint formulations exceeding the critical pigment volume concentration to reduce The amount of titanium dioxide, the other is iron ink for metal cans and titanium dioxide for some home appliance coatings. Since the coating film of this type of paint is formed at one time, and most of them are very thin, in order to achieve the maximum hiding power, the pigment volume fraction of the paint must be very high. If it is large, it will inevitably lead to the aggregation of pigment particles, and some particles cannot act as scattering points because they cannot receive incident light, resulting in a decrease in light scattering efficiency, that is, the so-called particle agglomeration effect, so it is especially suitable for use at this time Titanium dioxide with large particle size, but this large particle rutile titanium dioxide is different from the hiding power titanium dioxide used in latex paint.

(4) Titanium dioxide with different degrees of anti-powdering

According to the degree of chalking resistance, titanium dioxide can be divided into non-chalking type, medium chalking resistance type and high chalking resistance type. Although there are certain differences in anti-powdering performance and durability, they are often used in combination in practical applications. Anatase and rutile titanium dioxide without surface treatment have optical activity, poor durability, are non-powdering, and can only be used internally. And some have strict requirements on the optical rotation, even if the anatase type is used inside, the optical rotation is poor. Titanium dioxide with medium powder resistance is called high powder resistance in some literatures. General titanium dioxide such as R-902, TR-92, etc. belong to this type, and most of them are suitable for low PVC, medium PVC enamel and spray paint. Some titanium dioxides used in medium to high PVC enamel, alkyd and flat latex architectural coatings also fall into this category and are surface treated. High anti-powder type, also known as ultra-durable type, has excellent durability, and is especially suitable for automotive topcoats, exterior coil coatings and long exterior wall coatings for street high-rise buildings with long repainting cycles that require durability and gloss protection.

(5) Zinc stabilized and aluminum stabilized titanium dioxide

In the production process of sulfuric acid titanium dioxide, before calcining hydrated titanium dioxide, if zinc oxide is added to make the rutile crystal more stable, it is called zinc-stabilized titanium dioxide; if aluminum oxide is added to stabilize the crystal, it is called aluminum-stabilized titanium dioxide. Zinc oxide is a rutile accelerator, which can make the crystallization conversion rate of rutile reach more than 98%, and it remains in the finished titanium dioxide, part of it enters the TiO2 crystal lattice, and part of it exists on the surface of the TiO2 crystal to form a coating layer, which can improve the quality of titanium dioxide. Therefore, rutile titanium dioxide with zinc is more suitable for oily paints, because vegetable oil-based wood has poor weather resistance, so zinc oxide can stabilize oily base materials. Modern coatings use synthetic resin as the main base material, which does not require zinc for stabilization, and can also be made of zinc-free titanium dioxide, which has high powder resistance. Zinc oxide in zinc-containing varieties will react with the acidic binder in the paint, which will affect the whiteness, dispersion and gloss of titanium dioxide, as well as the storage stability of latex paint. Therefore, some companies do not advocate the addition of zinc. For example, titanium dioxide by chloride method does not contain zinc, but some companies still advocate the addition of zinc.

Ilmenite Ilmenite, which is used in sulfuric acid to produce titanium dioxide, sometimes contains a certain amount of pentavalent niobium, which enters the titanium dioxide lattice when calcined. Since titanium has four electrons and niobium has five electrons, the extra electrons can increase the semiconducting properties of titanium dioxide crystals, produce light absorption, and affect the whiteness of titanium dioxide, which is a serious problem for rutile titanium dioxide. In order to overcome the adverse effects of niobium, trivalent aluminum should be added when calcining hydrated titanium dioxide to compensate the fifth electron of niobium and make titanium dioxide electrically neutral, which is called aluminum-stabilized titanium dioxide. At this time, it is formed in the titanium dioxide and enters the crystal lattice called acid insoluble aluminum. At present, there are much more titanium dioxide stabilized by aluminum than zinc stabilized.

(6) Titanium dioxide with inorganic coating and organic coating

The vast majority of modern titanium dioxide pigments, especially the rutile type, require surface treatment to improve dispersibility, hiding power, decolorizing power, durability and other properties. According to the coating material, it can be divided into titanium dioxide treated with inorganic surface coating and organic surface coating.

The inorganic coating is mainly oxides or hydrated oxides of metals such as aluminum, silicon, titanium, zirconium, etc., which can be treated with a single treatment agent, or more commonly treated with several treatment agents to produce a synergistic effect. For most of the small particle size titanium dioxide, in order to make it have a high gloss, it is often only treated with aluminum, while the high anti-powdering type titanium dioxide is often treated with silicon, aluminum, titanium, zirconium and other joint treatments. Of equal importance to the properties of titanium dioxide is its dispersibility in film-forming substances. In order to improve the dispersion, organic surface treatment was developed abroad in the late 1960s and early 1970s. Organic treatment agents include polyols, triethanolamine, diisopropanolamine, esterified styrene-maleic anhydride copolymer, polymethylsiloxane, etc. Foreign companies widely use organic coating treatment process.

(7) Titanium dioxide with light coating and heavy coating

Before the emergence of latex paint and special titanium dioxide, the TiO2 content in titanium dioxide pigments was mostly 95 to 96%, and the amount of inorganic coating was roughly 3 to 4%. This kind of titanium dioxide with a small amount of coating is called light coating. Titanium dioxide. Now, the minimum content of TiO2 is 89%, and the dosage of inorganic treatment is less than 10%, also known as light-coated titanium dioxide. The content of titanium dioxide in flat latex paint is low. In order to make the coating film have proper hiding power, it is necessary to rely on the help of dry hiding power. Therefore, titanium dioxide for latex paint with high aluminum and silicon processing capacity is designed. In order to produce dry hiding power of this kind of titanium dioxide, the dosage of surface treatment should be increased, and the particle surface should be rough and porous. The titanium dioxide content of this pigment is as low as 80-85%, and the titanium dioxide with an inorganic coating amount of more than 15% is called heavy coated titanium dioxide. Titanium dioxide for water-based latex paint is used in a large amount in the world, so various titanium dioxide companies in the world produce this heavy-coated titanium dioxide in large quantities to meet the needs of architectural coatings.

(8) Special-purpose and general-purpose titanium dioxide

Titanium dioxide specially designed for certain purposes is called special-purpose titanium dioxide, which is characterized by certain properties related to specific applications are designed to be very high, so it has advantages in application performance and cost,because it can maximize the performance potential of titanium dioxide in this regard. There are many special-purpose titanium dioxides in modern times. The large particle size and heavy-coated titanium dioxide used in architectural latex paints is a special-purpose titanium dioxide. On the contrary, titanium dioxide with a wider range of applications and a more balanced performance is called general-purpose titanium dioxide. Its characteristic is that various performances are taken care of. Therefore, it can replace the special type under certain conditions.Its advantage is that it is versatile and can reduce the user’s titanium dioxide inventory. Its disadvantage is that it cannot meet the performance required by the user to the maximum extent, and the user will waste some performance that they do not use.

Therefore, there may be some deficiencies in performance and/or cost.
For many years, almost all the rutile titanium dioxide used in my country’s coating industry is general-purpose, and only in recent years has a small amount of special-purpose titanium dioxide been used. This is because there are many paint manufacturers in our country, each of which produces very little paint, but has a complete range of varieties. Therefore, only general-purpose titanium dioxide can cope with this situation.

(9) Lipophilic, hydrophilic and amphiphilic titanium dioxide

According to the affinity of titanium dioxide to the base material in the application system, it can be divided into lipophilic, hydrophilic and amphiphilic titanium dioxide.
Titanium dioxide without surface treatment is essentially hydrophilic and oleophobic due to the large number of hydrophilic groups on the surface, such as surface hydroxyl groups, etc., but in order to make it sufficiently hydrophilic,hydrophilic treatment (surface treatment) must also be carried out, and an appropriate amount of anionic dispersant must be added to the application system, so modern titanium dioxide varieties that can be applied to water-based systems all have dispersants that require this technical indicator. Lipophilic titanium dioxide is generally not subjected to surface treatment. The crystalline hydrated iron oxide coating can improve the lipophilicity of titanium dioxide, because it facilitates the adsorption of the polymer matrix and produces steric hindrance in the application system. Most organic surface treatments can improve the lipophilicity of titanium dioxide. Modern titanium dioxide pigments are all amphiphilic, and they are suitable for both oily (solvent-based) and water-based systems.

(10) Water slurry, oil slurry and dry powder titanium dioxide

According to the existing status of titanium dioxide products, it can be divided into water slurry titanium dioxide, oil slurry titanium dioxide and dry powder titanium dioxide. At present, the largest supply is still dry powder titanium dioxide.
In the early 1970s, in order to reduce the grinding and dispersing operations of users, water-based titanium dioxide products were put on the market. It is stable in dispersion and can be pumped. It is suitable for users of water-based slurry with a relatively large amount of the same brand.Especially for manufacturers of paper and water-based architectural coatings.In addition to saving dispersion time and power consumption, Lichuan water slurry titanium dioxide can also reduce the loss of titanium dioxide, eliminate dust flying and do not need to deal with packaging bags, and users can easily realize production automation. The titanium dioxide in the slurry can be either anatase or rutile. The slurry contains about 60-80% titanium dioxide pigment, depending on the type of titanium dioxide pigment. The water slurry also contains dispersants, pH regulators, preservatives, bactericides, etc. Water slurry titanium dioxide is widely used in North America, and all major titanium dioxide manufacturers in North America are producing in large quantities without exception. Oil slurry titanium dioxide is also a pre-dispersed product, which is used to prepare small batches of coating products. Most of the oil slurry titanium dioxide is produced by non-titanium dioxide producers, so it is completely different from the water slurry titanium dioxide.

(11) Composite titanium dioxide

In order to save the amount of titanium dioxide, when the titanium dioxide market is tight, there will always be some composite titanium dioxide on the market. The titanium dioxide originally produced by the sulfuric acid method is a calcium sulfate titanium dioxide composite pigment. It was once very popular and has been used for decades. Recently, it has disappeared from the vast majority of the market.
The performance of this so-called titanium-calcium composite pigment is relatively good in solvent-based coatings, but it is not suitable for water-based systems, because calcium sulfate crystals will grow in water,And trace amounts of calcium ions and sulfate ions will cause flocculation of latex paint.