General knowledge of coating: application analysis of titanium dioxide in coating

Core tip: 0 Introduction Titanium dioxide, the scientific name of titanium dioxide, is an important white pigment Compared with traditional white pigments such as lead white, zinc white and lithopone, titanium dioxide has many excellent properties such as high refractive index, strong achromatic power, large covering power, good dispersion, good whiteness and non-toxic It is known as the king of white pigments and widely used in coating, plastic, ink, paper making, chemical fiber, ceramics and other industries 。 Among them, the amount of coating is the largest, accounting for 57% of the total titanium dioxide Paint, commonly known as "paint", is a kind of coating on the surface of objects through different construction processes Paint agent, top 10 Chinese wall paint brands Recommended introduction: interior wall paint and exterior wall paint can achieve beautiful, clean and pleasant effects, but the effects in different environments are different, so the color of the paint will be different There are ten brands of Chinese paint, ten brands of global paint, ten brands of Chinese wall paint, and ten brands of Chinese paint, Famous trademark of Chinese paint and coating In private rooms, most of us choose according to our own personality, personal hobbies and living habits The younger generation will choose the interior wall paint with rich colors and bright colors, while the older ones will have some working experience Titanium dioxide is an important white pigment Compared with traditional white pigments such as lead white, zinc white and lithopone, titanium dioxide has many excellent properties, such as high refractive index, strong achromatic power, large covering power, good dispersion, good whiteness and non-toxic It is called the king of white pigment and widely used in coatings and plastics , ink, paper, chemical fiber, ceramics and other industries Among them, the amount of coating is the largest, accounting for 57% of the total titanium dioxide Paint, commonly known as "paint", is a kind of continuous solid-state film material which can be coated on the surface of objects through different construction processes to form a solid adhesion with a certain strength, and can play a role in protecting, decorating and characteristic functions of objects Coating has many advantages ① coating has a wide range of applications and can be widely used on various material surfaces, such as metal, wood, cement products, plastic products, leather, paper products, textiles (2) there are many kinds of coatings, which can meet the requirements of different properties, and can produce coatings with different properties according to the needs; (3) the coating is easy to use, and can be constructed on the surface of the object to be coated with relatively simple methods and equipment; (4) it is easy to maintain and update, and the coating film on the object The old can be scrubbed or recoated, some of the damage can be repaired, or the appearance of the coating can be changed according to the needs, and the new coating can be obtained frequently without large investment It has been widely used and developed for a long time because of its advantages and its role in human society In this paper, the performance of titanium dioxide, the role of titanium dioxide in coatings and its application status, the influence of the main quality fluctuation of titanium dioxide on coatings are summarized, and some suggestions on the development of titanium dioxide for coatings are put forward, which provides reference for the application of titanium dioxide in coatings Titanium dioxide can be divided into plate titanium type, anatase type and rutile type according to the crystal form The plate titanium type is very unstable When the temperature is higher than 650 ℃, it will be directly converted to rutile type, which has no practical industrial value At present, only anatase type and rutile type titanium dioxide are used in industry However, the crystal structure of anatase type is not as dense as rutile type, and its refractive index is lower than rutile type, so its hiding power and fading power are 20-30% lower than rutile type, and its durability is also far lower than rutile type Therefore, rutile type titanium dioxide is mainly used in coating industry Titanium dioxide is nontoxic and stable in chemical properties It hardly reacts with other substances at room temperature However, titanium dioxide itself has some lattice defects, and there are many photo activation points on its surface Under the action of light, titanium dioxide can undergo continuous oxidation-reduction reaction, which has photochemical activity Therefore, titanium dioxide for coating now has to undergo surface treatment The refractive index of pigment is the primary factor that dominates the optical properties of pigment, and it is also the basis of other properties The optical properties and pigment properties are inseparable The pigment properties are the specific forms of optical properties Table 1 lists the optical properties and corresponding pigment properties of titanium dioxide and other common white pigments It can be seen from table 1 that the refractive index of titanium dioxide is the highest, Other pigment performance index is also the best, so titanium dioxide is essential, the most dosage of white pigment Comparison of optical properties between titanium dioxide and other white pigments The particle size has a great influence on the optical properties and pigment properties of titanium dioxide In the visible light range, the most suitable particle size range of titanium dioxide is 0.15-0.35 μ m, which is equivalent to half of the wavelength of the scattered visible light The titanium dioxide with the particle size in this range has the highest scattering power, and the whiteness, covering power, achromatic power and glossiness are also the best Dispersion refers to the dispersion ability of pigment in the colored medium Under certain conditions, the dispersion degree of pigment particles in the base material medium within a certain time, or the dispersion time required to reach a certain dispersion degree in the system under certain dispersion conditions Dispersion is also called abrasive dispersion or abrasive wettability When water is used as the dispersion medium, it is also called water dispersion Sex Dispersibility is an important application performance index of titanium dioxide pigment, which directly affects its achromatic power, covering power, surface luster, oil absorption and other indexes When it is used in paint, its dispersibility in paint affects the storage stability, fluidity, leveling, coating gloss, weather resistance and so on of the paint, and also directly affects the grinding dispersion time in the paint production process Therefore, in order to improve the dispersion of titanium dioxide, the manufacturers usually modify the surface of titanium dioxide, add organic or inorganic surfactants, in order to enhance its affinity in different developer, so as to improve the dispersion and dispersion stability of titanium dioxide Weather resistance refers to the ability of titanium dioxide coating to resist the action of sunlight and atmosphere and avoid discoloration, pulverization and loss of light when exposed to outdoor climate There are many factors that affect the weather resistance, and the photochemical activity of titanium dioxide pigment is the main factor that affects the weather resistance Due to the lattice defects of titanium dioxide itself, there are many light activation points on its surface, which slightly absorb the visible UV spectrum Under the UV light irradiation, if there is water and other catalysts, titanium dioxide can have continuous redox reaction Therefore, hydroxyl and peroxy hydroxyl radicals are generated, which have high activity, can oxidize the organic polymer in the film, break and degrade the polymer chain, destroy the continuity of the film, and reduce the weatherability of the film In order to improve the weatherability of titanium dioxide, a small amount of salt treatment agent is usually added before the calcination of metatitanic acid or the titanium dioxide is inorganic coated Adding salt treatment agent can fill up the lattice defect of titanium dioxide itself and reduce its photochemical activity The inorganic coating is a "film" on the surface of titanium dioxide particles, which can prevent the direct irradiation of ultraviolet light on titanium dioxide, or Avoid the direct contact between titanium dioxide and coating organic matter, reduce the destructive force of photochemistry, and improve the weatherability of coating The function of titanium dioxide in coatings and its application status the coatings are mainly composed of film-forming substances, pigments, solvents and auxiliaries The pigments in the coatings have a certain covering power, which can not only cover the original colors of the coated objects, but also give the bright colors to the coating film, so as to achieve the decorative effect of brightening and beautifying At the same time, the pigment and the curing agent and substrate are closely integrated, and can enhance the mechanical strength and adhesion of the coating, prevent cracking or falling off, and enhance the thickness of the coating, prevent the penetration of ultraviolet or moisture, improve the aging and durability of the coating, and prolong the service life of the coating and the protected object Among the pigments, the amount of white pigment is the largest, and the performance requirements of the paint for white pigment are as follows: ① good whiteness; ② good grinding wettability; ③ good weather resistance; ④ good chemical stability; ⑤ small particle size, high hiding power and achromatic power, and good opacity and glossiness Titanium dioxide is one of the most widely used white pigments in coatings Its output accounts for more than 70% of inorganic pigments, and its consumption accounts for 95.5% of the total consumption of white pigments At present, about 60% of the world's titanium dioxide is used in the manufacture of various coatings, especially rutile titanium dioxide, most of which is consumed by the coating industry The paint made of titanium dioxide has bright colors, high covering power, strong coloring power, low consumption and many varieties, which can protect the stability of the medium, enhance the mechanical strength and adhesion of the paint film, prevent cracks, prevent the penetration of ultraviolet and water, and prolong the life of the paint film The color matching of almost every pattern in the colorful pattern paint cannot be separated from titanium dioxide Different kinds of coatings with different uses have different requirements for titanium dioxide For example, the powder coating requires rutile titanium dioxide with good dispersion Anatase titanium dioxide has low achromatic power and strong photochemical activity When it is used in powder coatings, the coating tends to turn yellow The rutile titanium dioxide produced by sulfuric acid method has the advantages of moderate price, good dispersibility, good covering power and achromatic power, which is very suitable for indoor powder coating, while the titanium dioxide for outdoor powder coating requires good dispersibility, covering power and achromatic power as well as good weather resistance Therefore, the titanium dioxide for outdoor powder coating is generally golden red produced by chlorination method Stone titanium dioxide Waterborne coatings refer to the coatings in which most of the volatile substances are water With the enhancement of people's awareness of environmental protection and the increasingly strict environmental protection laws and regulations, waterborne coatings have been widely used As solvent based coatings, titanium dioxide is required to have good whiteness and dispersion, high hiding power, achromatic power and weather resistance, and low impurity content At present, most of titanium dioxide in the market are general-purpose titanium dioxide, which can be used in both solvent-based coatings and water-based coatings However, after all, there are essential differences between water-based coatings and solvent-based coatings, and the dispersion effect of these general-purpose titanium dioxide in water-based coatings is not very good Therefore, in order to make titanium dioxide disperse well in water-based coatings, it is necessary to have a specific target Choose titanium dioxide surface treatment Architectural coating requires acid, alkali, water and moisture resistance, and good adhesion on rough or smooth base surface In addition to the good optical and pigment properties mentioned above, titanium dioxide used in architectural coatings is required to have high weather resistance and strong resistance to pulverization, especially for exterior wall architectural coatings General purpose titanium dioxide, such as r-902, r-930, rcl-575, tr-92 and so on, belongs to the middle anti powdered titanium dioxide High resistance to powdering, also known as super weather resistant, is especially suitable for the exterior wall coating of high-rise buildings with long recoating period The main varieties are r-960, r-960-hg, r-960vhg produced by DuPont, tr-63 and tr-61 produced by Huntsman, and those produced by Kronos