Titanium dioxide is relatively large in the production of various types of inks, ranging from 25% to 50%, and some even larger. Therefore, titanium dioxide plays a vital role in the quality of ink. There are three kinds of crystalline titanium dioxide in nature, namely rutile type, anatase type and plate titanium type. Because the titanium plate-type titanium dioxide crystal form is extremely unstable, the titanium white powder suitable for ink production is only rutile type and anatase type, and both are tetragonal crystal forms. They have stable physical and chemical functions, and are pure in color, fine in particle size and high in refractive index. In the production of inks, different types of ink products have different quality requirements for titanium dioxide. Practice has proved that rutile titanium dioxide has a good function of use and can be widely used in various types of ink production. From the comparison of the two titanium dioxide functional indexes, whether it is crystal shape, refractive index, color strength, fluorescence index, rutile titanium dioxide is superior to anatase titanium dioxide, so rutile titanium dioxide in ink production Widely used. With the rapid progress of packaging and book printing industry at home and abroad, the demand for ink shopping malls will increase day by day. As a very important white pigment in ink, many functions and effects of titanium dioxide cannot be replaced by any other materials.
Regarding the baking type printing iron white ink, the post-press baking temperature is about 180 ° C, and the baking time is as long as about 120 minutes. Therefore, it is necessary for the titanium white powder in the white ink to have excellent heat resistance. Otherwise, the white ink will turn yellow during high-temperature baking, and the gloss will be lost, and the printing will be invalidated when severe. Therefore, according to different types of inks and different printability requirements, the rational use of titanium dioxide is the key to making excellent white inks. To summarize the quality requirements for titanium dioxide for inks, the main points are as follows:
1. The whiteness is good, the durability is not yellow, and the color of the printed product can be kept bright and bright in various environments;
2. Good moisture, easy to grind;
3. Small particles, easy to spread evenly in the ink connecting material;
4. Strong hiding power, good coloring;
5. Weather resistance, heat resistance, chemical stability;
6. Good water resistance.
1. Influence on ink hiding power
(1) The irregularity of the refractive index of the titanium dioxide crystal itself directly affects the thickness of the ink hiding power. Generally, the refractive index of titanium dioxide is the best among white pigments. When preparing white ink, titanium dioxide with high refractive index should be selected to enhance the hiding power of white ink.
(2) The influence of the particle size, particle structure and dispersibility of titanium dioxide on the hiding power of white ink.
Generally, in the range of 1/2 of the wavelength of visible light, the smaller the particle size, the more lubricious the surface of the particle, and the better the dispersibility of the titanium dioxide in the resin binder, the stronger the hiding power. Since titanium dioxide itself has a remarkable crystal structure, its refractive index is larger than that of the vehicle, and the greater the difference in refractive index between the two, the stronger the hiding power of the titanium dioxide used. 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 color.
The color power of titanium dioxide depends on the scattering ability of titanium dioxide to visible light, and it has a direct influence on the coloring power of the ink. The larger the scattering coefficient, the stronger the coloring power; the higher the refractive index of titanium dioxide, the more the coloring power Strong. Titanium dioxide is the highest refractive index of white pigments, and rutile titanium dioxide has a higher refractive index than anatase titanium dioxide. Therefore, titanium white powder should be selected to select titanium dioxide with high scattering and high refractive index.
3. The impact on the function of sputum.
The shape and light reflection of titanium dioxide particles are uniform and directly affect the dispersing function of titanium dioxide. It is believed that the surface of titanium dioxide particles is smooth and evenly reflected, and its dispersibility is good. The prepared white ink has good gloss and whiteness. Conversely, if the surface of the particles is rough and diffuse reflection is added, the gloss will be greatly reduced and the dispersibility will be poor. It directly affects the whiteness and transfer function of white ink. For this reason, titanium dioxide is necessary for processing before it can be used.
In addition, in the ink production process, it is necessary to select titanium dioxide with different functions according to the detailed characteristics and requirements of various inks.
(1) Offset printing is based on the principle of oil and water repelling. Therefore, in addition to the excellent anti-emulsification function, the resin binder used in offset inks must have excellent water repellency. Otherwise, offset white ink is easy to emulsify; The offset white ink used in the printing of the field requires the titanium dioxide to have excellent light resistance and weather resistance, otherwise the white ink will turn yellow or chalk.
(2) Regarding the gravure composite film ink, in order to make the printed product bright and beautiful, the white ink is first used, and then the colorful printing is performed. For this reason, titanium dioxide is required to have excellent coloring power and hiding power.
4. Effect on ink whiteness
(1) The influence of the shape, the size, and the whiteness of the titanium dioxide particles.
The excellent titanium dioxide particles are lubricated and have no sharp edges. If the titanium dioxide powder with sharp edges on the surface of the particles is used, the reflection effect on the light will be greatly weakened and the whiteness of the ink will be lowered. The size of the titanium dioxide particles should be controlled at 0.2 to 0.4 μm, which is equivalent to about 1/2 of the wavelength of visible light, so that high scattering ability can be obtained, making the color appear whiter. When the particle size is less than 0.1 μm, the crystal is clear. If the particle size exceeds 0.5 μm, the scattering of the pigment by light is lowered, and the whiteness of the ink is affected. For this reason, it is required that the particles of titanium dioxide are suitable in size and uniform in distribution to exhibit excellent whiteness.
(2) Effect of impurities in titanium dioxide on ink whiteness.
Generally speaking, if a trace amount of iron, chromium, cobalt, copper or the like is mixed into the titanium white powder, the prepared ink may undergo color shift and whiteness will decrease. This is because impurity ions in titanium dioxide, especially metal ions, cause the crystal structure of titanium dioxide to be distorted and lose symmetry. Rutile titanium dioxide is more sensitive to impurities. For example, when iron oxide is more than 0.003% in rutile titanium dioxide, it will show color, and when it is more than 0.009% in anatase titanium dioxide, it will appear. Color reaction. Therefore, it is very important to select a precise, impurity-free titanium dioxide.
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