The status of titanium dioxide in the ink is irreplaceable, because titanium dioxide is far superior to other white pigments in determining the quality of the ink. Such as refractive index, achromatic power, hiding power and oil absorption.

Under the same conditions, the refractive index of rutile titanium dioxide was 2.76, the refractive index of anatase titanium dioxide was 2.55, the refractive index of zinc sulfide was 2.37, the refractive index of zinc barium white was 1.84, and the refractive index of lead white was 2.00. In terms of achromatic power, titanium dioxide also shows better performance than other white pigments.

The relative value of rutile titanium dioxide achromatic power was 100, the relative value of anatase titanium dioxide achromatic power was 77, the relative value of zinc sulfide achromatic power was 40, the relative value of zinc barium dioxide, the relative value of zinc barium dioxide, and the relative value of lead white blasting power was 9. In terms of hiding power, the advantages of titanium dioxide make it difficult to match other white pigments.

The relative value of rutile titanium dioxide hiding power is 100, the relative value of anatase titanium dioxide hiding power is 78, the relative value of zinc sulfide hiding force is 39, the relative value of zinc barium white hiding force is 18, and the relative value of lead white folding hiding force is 12.

From the oil absorption per 100 grams of white pigment, the oil absorption of rutile titanium dioxide is 25 grams, the oil absorption of anatase titanium dioxide is 30 grams, the oil absorption of zinc sulfide is 15-25 grams, the oil absorption of zinc barium white is 14-16 grams, and the oil absorption of lead white is 8-15 grams, which shows that the oil absorption of titanium dioxide is also the best.

In the finished ink product, the four key properties of refractive index, achromatic power, hiding power and oil absorption support the quality of the ink, and titanium dioxide has the refractive index, achromatic power, hiding power and oil absorption that are difficult to achieve by other white pigments, so titanium dioxide as an ink additive is more suitable than other white pigments.

At present, the annual production of titanium dioxide in the world exceeds 6 million tons, most of which is used in pigments. Due to its high refractive index, good optical stability and chemical inertness, titanium dioxide is widely used in paint, rubber and plastic, paper, cosmetics and other industrial fields. In addition to conventional pigment applications, titanium dioxide is also used in other industrial sectors such as energy, pharmaceuticals, environmental and electronic materials.

    There are two industrial methods for producing the pigment titanium dioxide: the sulfuric acid method and the chlorination method.

    The sulfuric acid process was the first method for the production of anatase and rutile titanium dioxide. In this method, concentrated sulfuric acid is used to dissolve ilmenite (FeTiO3, containing 40% to 65% TiO2), titanium slag (containing 75% to 85% TiO2), or a mixture of the two in a certain proportion. Through the separation of insoluble impurities, a sulfuric acid solution of titanium is obtained. Hydrated titanium dioxide precipitation is achieved by adding suitable seed crystals and heating and boiling. The resulting precipitate is filtered and washed to remove acids and soluble impurities. Hydrated titanium dioxide is calcined at high temperature to obtain the primary pigment titanium dioxide. The chlorination process requires the use of titanium ore that is purer than the sulfuric acid process. Titanium ore first reacts with Cl2 under carbonic conditions, and the obtained titanium tetrachloride is purified by distillation. Titanium tetrachloride is oxidized at high temperature to generate titanium dioxide. The untreated pigment titanium dioxide is dispersed in water by a ball mill or sander to ensure the elimination of excessively large particles consisting of sintered aggregates. Dispersants are often used to promote the dispersion of titanium dioxide in water.

    After that, the production process usually inorganic coating of titanium dioxide particles, and then washing, filtration, drying, gas powder and other processes to produce TiO2 products.

    The production of titanium dioxide essentially extracts TiO2 from low-purity ores, mainly ilmenite: FeOTiO2. While the main impurity of ilmenite is iron, other metal impurities also contain manganese, chromium, vanadium, zinc, copper, lead, nickel, and, to a lesser extent, cadmium and mercury.

    The two production methods of titanium dioxide are to extract titanium dioxide from ore with sulfuric acid or chlorine. The sulfuric acid process typically requires the use of more than 3 tons of acid to produce 1 ton of titanium dioxide. Historically, all these acid and metal impurities have been discharged into the water. Although most of the chlorine in the chloride process is circular, the reaction impurities are excreted as metal chlorides. Both production methods have a large amount of harmful gas production.

The generation and discharge of industrial wastewater has also attracted great attention. In the past few decades, the environmental problems in titanium dioxide production have undergone very positive changes, and the environmental concept of green production has been widely accepted in Europe and the United States and other countries.

The plastic industry and titanium dioxide can be described as inseparable. Among the more than 500 titanium dioxide grades in the world, more than 50 are exclusive to plastics, and the average annual growth rate of up to 6% also makes the plastic industry the fastest growing field using titanium dioxide, and "wins" the second largest user of titanium dioxide. Where there is a material application, there are naturally matching indicators, parameter considerations, particle size distribution and particle shape significantly affect the key indicators of titanium dioxide for plastics. The particle size of titanium dioxide for plastics is just within the range of laser particle size analyzer, so for the application of titanium dioxide in the plastic industry, the industry may wish to pay more attention.

   As we all know, the scientific name of titanium dioxide is titanium dioxide, with excellent white performance, high hiding power and high achromatic power, is widely used in ink, paper, coatings, paints and other industries, enjoying the reputation of "white king", which is an important reason for the application of titanium dioxide in plastic products, that is, titanium dioxide can determine the appearance of light or white plastic products. Of course, titanium dioxide has many other benefits for plastics, such as improving the heat, light and weather resistance of plastic products, protecting plastic products from UV light, and improving the mechanical and electrical properties of plastic products. Almost all thermosetting and thermoplastic plastics will use titanium dioxide, they can be mixed with resin dry powder, can also be mixed with plasticizers containing liquid, the dosage is generally about 3-5%, polyolefins (mainly low-density polyethylene), polystyrene, ABS, polyvinyl chloride, etc.

   In the plastic industry, there are four main indicators to measure the quality of titanium dioxide - hiding power, dispersion, weather resistance and whiteness. The better the hiding power of titanium white, the lighter and thinner the plastic products produced; The dispersion affects the production cost of plastic products, the better the dispersion of titanium dioxide, the higher the smoothness and brightness of plastic products; Titanium dioxide with good weather resistance is indispensable for plastic products and plastic doors and windows used outdoors.

   The last big indicator is whiteness, the so-called whiteness refers to the degree of distance from the ideal white. The factors affecting the whiteness of titanium dioxide are mainly as follows. The first point is impurities, in the titanium dioxide process, especially the sulfuric acid titanium dioxide process, most of the operation is to remove impurities in the product, because impurities seriously affect the application performance of titanium dioxide, especially whiteness. Color-developing metal oxide impurities can affect whiteness at very low content, these elements are iron, manganese, chromium, copper, etc., these impurities themselves have color, in the white titanium dioxide is very easy to color.

 

The second point is the distribution of particle size and particle size, which mainly affects its whiteness through the reflection and scattering of light by titanium dioxide particles. The smaller the particle size of titanium dioxide, the higher the whiteness value, which is mainly due to the smaller the particle size of titanium dioxide, the increase of surface area, and the enhancement of light reflection and diffuse reflection. According to the characteristics of light waves, when the particle size of the pigment particles is less than half of the light wave, the maximum scattering of the color light of the wavelength can be obtained, after analysis, the best particle size for the wavelength blue light scattering is about 0.2 μm, and the maximum particle size of the longer wavelength red light scattering is about 0.35 μm, therefore, the scattered light of the small particle size of titanium dioxide is blue phase, and the transmitted light is blue complementary color red and yellow phase, on the contrary, the scattered light of large particle size titanium dioxide is red phase, and the transmitted light is blue phase. Usually the particle size of titanium dioxide for coatings is 0.2~0.4μm, while most plastics use titanium dioxide particle size is finer, particle size is 0.15~0.3μm, because this can obtain a blue background phase, most of the resins with yellow phase or easy to yellowing resin has a shielding effect.

   In addition, particle shape, titanium content, and coating agent have a certain influence on the whiteness of titanium dioxide. Among them, the influence of particle shape on whiteness is relatively small, in general, the whiteness of layered titanium dioxide is slightly lower, and the whiteness of spherical and rod-shaped is slightly higher. The increase of titanium dioxide content, titanium dioxide whiteness value also increas

Titanium dioxide is an important white pigment, which can be divided into plate titanium type, anatase type and rutile type, plate titanium type is very unstable. Compared with traditional white pigments such as lead white, zinc white, zinc barium white, titanium dioxide has a variety of excellent properties such as high refractive index, strong achromatic power, large hiding power, and harmlessness, and is known as a good white pigment. Used in coatings, plastics, chemical fibers, ceramics and other industries. Among them, the amount of paint is very large, accounting for about 57% of the total amount of titanium dioxide. So how is titanium dioxide applied to coatings?

 

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First, the role of titanium dioxide in coatings

 

The coating is mainly composed of four parts, such as film-forming substances, pigments, solvents and additives, and the pigments in the paint have a certain hiding power, which can not only cover the original color of the painted object, but also give the coating film a bright color, and realize the decorative effect of lighting and beautification. At the same time, the pigment is closely combined with the curing agent and the substrate, and is integrated, which can enhance the mechanical strength and adhesion of the coating film, prevent cracking or falling off, and can enhance the thickness of the coating film, prevent the penetration of ultraviolet rays or moisture, improve the anti-aging and durability of the coating film, and extend the service life of the coating film and the protected object.

 

Among the pigments, the amount of white pigment is very large, and the performance requirements of the coating for white pigment: (1) good whiteness; (2) Good grinding and wettability; (3) Good weather resistance; (4) Good chemical stability; (5) Small particle size, high hiding power and achromatic power, good opacity and gloss.

 

Titanium dioxide is a white pigment used in coatings, its output accounts for more than 70% of inorganic pigments, and the consumption accounts for 95.5% of the total consumption of white pigments. At present, about 60% of the world's titanium dioxide is used to manufacture various coatings, especially rutile titanium dioxide, most of which is consumed by the coating industry. Coatings made of titanium dioxide, bright color, high hiding power, strong coloring power, saving dosage, many varieties, protect the stability of the medium, and can enhance the mechanical strength and adhesion of the paint film, prevent cracks, prevent ultraviolet rays and moisture penetration, prolong the life of the paint film, and the color matching of almost every pattern in the colorful pattern paint is inseparable from titanium dioxide.

 

Different kinds of coatings for different uses have different requirements for titanium dioxide, such as powder coatings require rutile titanium dioxide with good dispersion. Anatase titanium dioxide has low achromatic power, strong photochemical activity, used in powder coatings, and the coating film is prone to yellowing. The rutile titanium dioxide produced by the sulfuric acid method has the advantages of moderate price, good dispersion, good hiding power and achromatic power, etc., and is very suitable for indoor powder coating. In addition to good dispersion, hiding power and color elimination power, titanium dioxide for outdoor powder coating also requires good weathering, so the rutile titanium dioxide produced by the general chlorination method of titanium powder for outdoor powder coating.

 

 

Second, the impact of the main quality fluctuation of titanium dioxide on the coating

 

1 whiteness

 

Titanium dioxide as a white pigment of the coating, its whiteness is very important, is one of the key quality indicators of the coating requirements, titanium dioxide whiteness is poor, will directly affect the appearance of the coating film. The main factor affecting the whiteness of titanium dioxide is the type of harmful impurities, because titanium dioxide is very sensitive to impurities, especially rutile titanium dioxide.

 

Therefore, even trace impurities will have a significant impact on the whiteness of titanium dioxide. The whiteness of titanium dioxide produced by the chlorination process is often better than that produced by the sulfuric acid process, because the raw material titanium tetrachloride used in the chlorination process to produce titanium dioxide has been distilled and purified, and the impurity content of the raw materials used in the sulfuric acid process is high, and the impurities can only be removed by washing and bleaching and other process technologies.

 

2 Hiding power

 

The hiding force is the surface area of the coated object per square centimeter, when it is completely covered, the

In powder coating coating, there are two main reasons for poor curing of the coating film, one is that the formula design of the powder coating is unreasonable, and the coating performance does not meet the requirements; Second, the performance of the powder coating itself is not a problem, but in the coating process, the coating process control is unreasonable, resulting in the coating film performance failing to meet the technical indicators.

 

1. Consider from the aspect of powder coating formula design

If the matching of resin and curing agent is unreasonable in formula design, such as the reactivity selection of resin or the selection of the variety and dosage of curing agent is unreasonable, the mass percentage content or volume concentration of the filler is too large, etc., these problems will affect the physical and mechanical properties of the coating film, resulting in poor curing of powder coating in coating.

 

2. Consider the powder coating process

The reasons why the powder coating process affects the poor curing of the coating film are as follows:

 

(1) The baking temperature of the baking oven fails to reach the baking temperature required by the powder coating

Although the control temperature of the baking oven is easy to reach the design temperature or the baking temperature required by the powder coating when there is no load, under full load, due to the insufficient total heat supply, sometimes it is not possible to reach the design temperature or the baking temperature required by the powder coating.

 

Especially in the northern region, the temperature of the workshop in winter is low, if the insulation conditions of the baking oven are poor, the temperature before the coated object enters the baking oven is low, and the coated material has thick walls and large heat capacity, this problem is more likely to occur.

 

When the oven temperature cannot reach the baking and curing temperature of powder coating, the temperature standard problem can be solved by increasing the heating power; In addition, the curing purpose can also be achieved by extending the baking curing time!

 

(2) In the baking oven, the baking curing time does not meet the baking time required by the powder coating

In the baking conditions of powder coatings, the baking time refers to the baking time calculated after the coated object reaches the baking temperature, not the time that begins to be calculated after the coated object is placed in the baking oven.

 

When the thicker the coated material and the more parts are hung, the greater the heat capacity of the coated object, and the longer it takes for the coated object to heat up to the control temperature.

 

In ovens of a certain length, the shorter the effective baking time when the speed of the conveyor chain remains constant. If the effective baking time is not enough, the curing of the coating film is incomplete, and the physical and mechanical properties of the coating film cannot meet the requirements.

 

Therefore, in powder coating, it is best to use a furnace temperature tracking tester to determine the temperature change of the coated object in the baking oven under full load conditions to determine the reasonable baking and curing temperature and time, so as to ensure the complete curing of the coating film, and also ensure the physical and mechanical properties of the coating film.

 

(3) The surface treatment of the coated object is not good

If the oil on the surface of the coated object is not cleaned, the oxide scale or rust is not cleaned, or the quality of the phosphating film is not good, and many phosphating liquid residues are stained on the surface, the adhesion between the coating film and the substrate will be affected after powder coating.

 

At the same time, it will also lead to poor impact resistance of the coating film, which must be solved by improving the surface treatment quality of the coated object.

 

(4) In terms of film performance inspection, it should be carried out in strict accordance with the test temperature and coating thickness specified in the product standard

Generally speaking, the thickness of the coating film is thicker than specified; When the temperature of the test chamber is lower than the specified temperature, the impact strength, flexibility, cupping test and adhesion of the coating film are poor, and it is not easy to pass;

 

When the coating film thickness is thin and the test temperature is higher than the specified temperature, these physical and mechanical properties are easy to pass. From the perspective of ensuring product quality, try to test the performance indicators of the coating film under more demanding conditions in order to ensure the quality of the coating product without fail.

 

In addition, it is also necessary to consider that when the baking curing temperature is too high and the baking time is too long, the color of the coating film changes due to the heat agi

3. Influence on ink coloring strength The tinting strength of titanium dioxide depends on the scattering ability of titanium dioxide to visible light, and it has a direct impact on the tinting strength of the ink, the larger the scattering coefficient, the stronger the coloring force; The higher the refractive index of titanium dioxide, the stronger the coloring strength. Titanium dioxide is the product with the highest refractive index among white pigments, and the refractive index of rutile titanium dioxide is higher than that of anatase titanium dioxide. Therefore, the selection of titanium dioxide should choose titanium dioxide with strong scattering ability and high refractive index.

4. The influence on the dispersion performance of titanium dioxide particles and whether the light reflection is uniform, directly affect the dispersion performance of titanium dioxide. If the surface of titanium dioxide particles is smooth and uniformly reflected, its dispersion is good, and the gloss and whiteness of the prepared white ink are also good; On the contrary, the surface of the particles is rough and the diffuse reflection increases, which will greatly reduce the gloss and poor dispersion, which directly affects the whiteness and transfer performance of white ink. For this purpose, titanium dioxide must be treated before it can be used.

 

In addition, the factors affecting ink are as follows:

 

Good light and weather resistance: If it is a long-term outdoor print, it is necessary to ensure that titanium dioxide has good light and weather resistance, otherwise the ink will turn yellow and chalking. Good heat resistance: For baked iron ink, the baking temperature of the printing process reaches about 180°, and the time is up to 2 hours. Such printing conditions require that the titanium dioxide in the ink has excellent heat resistance, otherwise the white ink will turn yellow at high temperatures, lose its luster, and even make the printed matter scrapped. Oil absorption: With the improvement of printing speed and technology, inks that need to reduce viscosity are required, and the oil absorption of titanium dioxide has become the key. Under the condition that the color concentration remains unchanged, the oil absorption should be reduced as much as possible, which is conducive to improving the formulation of viscosity inks.

1. Influence on ink whiteness

 

(1) The effect of impurities in titanium dioxide on the whiteness of ink. The ink made of titanium dioxide with good whiteness is durable and does not yellow, which can keep the color of the print bright and bright in various environments. Generally speaking, if there are trace amounts of iron, chromium, cobalt, copper and other impurities mixed into titanium dioxide, the prepared ink will produce color cast and reduce whiteness. This is caused by the impurity ions in titanium dioxide, especially metal ions, which distort the crystal structure of titanium dioxide and lose symmetry. Rutile titanium dioxide is more sensitive to impurities, such as iron oxide in rutile titanium dioxide content greater than 0.003% will show color, and its content in anatase titanium dioxide greater than 0.009% will produce color reaction. Therefore, it is very important to choose fine, impurity-free titanium dioxide.

(2) The influence of the shape, size and distribution of titanium dioxide particles on whiteness. High-quality titanium dioxide particles have a smooth shape and no edges, and if the use of titanium dioxide with angular edges on the surface of the particles, it will greatly weaken the reflection of light and reduce the whiteness of the ink. The size of titanium dioxide particles should be controlled at 0.2~0.4μm, that is, equivalent to about 1/2 of the wavelength of visible light, so that high scattering ability can be obtained and its color appears whiter. When the particle size is less than 0.1 μm, the crystal is transparent, if the particle size exceeds 0.5 μm, it will reduce the scattering ability of the pigment to light and affect the whiteness of the ink. For this reason, the particle size of titanium dioxide is required to be suitable and evenly distributed to show good whiteness. Practice has proved that rutile titanium dioxide has better hiding power than anatase titanium dioxide, so it is more widely used in ink production.

 

2. The effect on the ink hiding power

(1) The refractive index of titanium dioxide crystals will directly affect the size of ink hiding power. In the process of gravure composite film ink printing, in order to make the print get a bright and beautiful effect, it is necessary to use white ink as a base, and then color printing. This requires titanium dioxide to have good coloring power and hiding power, otherwise the effect will be poor. Generally, the refractive index of titanium dioxide is the best in white pigments, and when preparing white ink, more titanium dioxide with high refractive index should be selected to enhance the hiding power of white ink.

 

(2) The effect of particle size, particle structure and dispersion of titanium dioxide on the hiding power of white ink. Generally, in the range of greater than 1/2 of the wavelength of visible light, the smaller the particle size, the smoother the particle surface, the better the dispersion of titanium dioxide in the resin binder, and the stronger its hiding power. Because titanium dioxide itself has an obvious crystal structure, its refractive index is larger than that of the color spreading agent, and the greater the difference in refractive index between the two, the stronger the hiding power of the titanium dioxide used. Practice has confirmed that rutile titanium dioxide has better hiding power than anatase titanium dioxide, so it is more widely used in ink manufacturing.

1. Particle and particle size distribution of titanium dioxide

 

The particle size requirements of titanium dioxide used in plastic profiles are much finer than those used in other fields. Usually coatings and other industries require a particle size of 0.2-0.4 microns, and the particle size of titanium dioxide of plastic profiles is required to be 0.15-0.3 microns, so that the blue bottom phase can be obtained, because in the blue bottom phase, from the principle of vision and pigment colorimetry, it will feel whiter.From the process of plastic profiles, this can play a role in shading the light yellow of resin raw materials and the yellow of other raw materials , unconventional large particles are almost non-existent. Titanium dioxide particles are in the optimal size range, and incident light in the visible spectrum can be scattered most efficiently.

 

2. The hiding power of titanium dioxide

 

The hiding power of titanium dioxide is expressed in opacity in the profile industry. The higher the opacity of titanium dioxide, the higher the whiteness of the plastic profile after coloring, and the hiding power of titanium dioxide is mainly affected by the particle size distribution, particle size and crystal form of the pigment.

 

3. Dispersion of titanium dioxide

 

The dispersion of titanium dioxide has a great influence on the production of plastic profiles, and is an important application performance index in the plastic profile industry. The profile obtained by titanium dioxide with good dispersion has uniform appearance color, no yellowing, and good whiteness. The main factors affecting the dispersion of titanium dioxide are: particle size distribution, specific surface area, surface potential, pH value, etc.

 

The qualitative characterization method of titanium dioxide dispersion is the electron microscope method, and the quantitative method is generally the particle size distributor measurement method, and now most of the R & D and production units of the dispersion mainly use application tests to verify its effect, so as to obtain the advantages and disadvantages of dispersion.

 

4. Optical properties of titanium dioxide

 

Plastic profiles of various substrates, optical performance indicators are mainly the brightness and hue of titanium dioxide, the main source of these two indicators is the instrument method measurement of lab test results.