1. How to avoid the use of toxic lead chromate and lead molybdate without affecting the color of the paint?

Due to the toxicity of lead-containing pigments, countries are increasingly limiting the use of lead-containing pigments in coatings. Formulators often use organic pigments in combination with titanium dioxide to replace lead-containing pigments. However, in some applications, organic pigments combined with metal oxide mixed pigments (inorganic composite coloring pigments) exhibit better performance than titanium dioxide. The distinctive color tone, saturation and high hiding power inherent in metal oxide mixed pigments give formulators more possibilities to reduce expensive organic pigments in the formulation and reduce or even eliminate titanium dioxide.

 For organic pigments, many pigments also show very good hiding power and weather resistance, which can be used to replace lead-containing pigments. Red pigments include Pigment Red 48:4, Red 112, Red 170, Red 254, Red 255, Violet 19 and the like. Orange pigments include Pigment Orange 36 and Orange 73 and the like. Yellow pigments include Pigment Yellow 74, Yellow 109, Yellow 110, Yellow 139, Yellow 151, Yellow 154 and the like. Especially in yellow pigments, we recommend the use of bismuth vanadium molybdenum yellow (Pigment Yellow 184), which is much brighter than the metal oxide mixed pigment titanium nickel (Pigment Yellow 53), and has stronger tinting strength and more Good hiding power (even without the addition of titanium dioxide), outstanding heat and weather resistance. Finally, it is worth noting that compared to lead-containing pigments, these pigments are considered safe and non-toxic as long as they have good dedusting equipment in production (inhalation of pigment dust is harmful to human lungs).



 2. What factors affect the flocculation of pigments in the coating system?

 The following parameters have an effect on flocculation:

 Viscosity: Pigment particles are easier to move under low viscosity conditions. Therefore, reducing the viscosity of the coating system will make the flocculation group smaller and the flocculation speed will decrease. Temperature: The effect of temperature on viscosity is obvious. An increase in temperature causes a decrease in viscosity. Thereby indirectly reducing flocculation.

 Flash time (drying time, wet-on-wet coating application interval, or time required to evaporate large amounts of solvent before entering the oven): Excessive flashing time can also cause large amounts of flocculation of the pigment.

 Titanium Dioxide: Titanium dioxide without coating on the surface exhibits a great tendency to flocculate. The size of the pigment particles and the particle size distribution of the pigment particles: the pigment particles are more active in the coating system, and the possibility of collision with each other is large, and the possibility of flocculation is also increased. But this is not absolute. If the particle size of the pigment is very small, the viscosity of the entire system will increase. It reduces the movement of pigment particles and is less likely to cause flocculation.

 Pigment Concentration (Titanium Dioxide and Pigment): Increasing the pigment concentration will cause the viscosity of the system to rise and reduce the tendency to flocculate.

 Adhesives: Small binder molecules are more easily adsorbed by the pigment surface, but due to its small volume, the resulting steric hindrance between the pigment particles is small, which is more likely to cause pigment flocculation. At the same time, the chemical structure of the binder is also related to pigment flocculation.

 Solvent: Choosing the right good solvent will fully extend the polymer molecules of the binder and increase the mutual repulsion between the pigment particles. Prevent pigment flocculation. The solvent of the poor solvent shrinkage binder is agglomerated, which reduces the steric hindrance between the pigment particles and promotes the flocculation of the pigment.

 3. What types of phthalocyanine blue can be used in the coatings industry?

 Phthalocyanine blue is mainly composed of copper phthalocyanine, its chemical structure is complex, its appearance is dark blue powder, and phthalocyanine blue has many crystalline forms. There are three kinds of crystalline products, which are red light, and have the highest tinting strength. Cyanine blue (pigment blue 15); with type green light, relatively best thermodynamic stability of β-type phthalocyanine blue (pigment blue 15:3); relative to the most vivid red ε-type phthalocyanine blue (pigment blue 15: 6). In an aromatic solvent such as xylene, alpha-type phthalocyanine blue is converted to a more stable beta-phthalocyanine blue. In order to prevent this transformation, a portion of monochlorocopper phthalocyanine is usually incorporated into a solvent-stable α-phthalocyanine blue or pigment blue 15:1 during the crude phthalocyanine blue pigmentation process.

 Since the surface of the phthalocyanine blue pigment is non-polar, the interaction with the binder is weak in many coating systems, resulting in poor stability of the pigment dispersion system. Coating systems containing phthalocyanine blue pigments are more susceptible to flocculation or delamination during storage. This disadvantage is greatly improved after surface treatment and chemical modification of the solvent-stable pigment blue 15:1 molecule. The modified phthalocyanine blue pigment was designated as Pigment Blue 15:2 in the dye index.

 In the field of coatings industry, α-type phthalocyanine blue with red phase is popular with β-type phthalocyanine blue with green phase due to its bright color, strong tinting strength, easy dispersion and good fluidity. Because the occurrence of flocculation is not only related to pigments, but also has a great relationship with the binder and solvent of the coating system. It is impossible to find a phthalocyanine which can exhibit the best anti-flocculation performance in any coating system. Blue varieties, which also require paint workers to achieve the best combination of formulations through a large number of experiments for different coating systems.

 4. What method can be used to quickly judge the dispersion properties of a pigment?

 We have many direct or indirect methods to evaluate the dispersion of pigments. For example, direct methods include fine plate method, optical and electron microscopy.

 Fineness plate method: The Hegman grinding fineness test method (Hegman) is a simple and quick method for detecting the fineness of the liquid system. The Hai's fineness plate is a rectangular stainless steel material with two shallow grooves on the surface. The shallow groove is slowly processed from 100 micron depth to 0 micron, and a small amount of abrasive material is added to the deepest part of the groove. The blade scraper scrapes the entire surface at a uniform speed to the end of the groove depth of zero. The scale is equidistantly marked next to the groove, and is uniformly decremented from the zero mark at the deepest point of the groove to the scale 8 or 10 of the horizontal surface of the fineness plate. It is observed that the sample first appears densely packed with particles, that is, the scale of the pigment particles which clearly protrudes from the surface of the abrasive material is clearly observed as an index for judging the degree of dispersion. Usually at least 7 scales are considered to have been effectively dispersed.

 Fineness test: The use of an optical microscope provides a fast, intuitive method for detecting the fineness of the pigment size. And the coloring power of the pigment can also be observed.

 In addition to this, the morphology, size and distribution of the pigment particles and the flocculation of the pigments can be observed. The specific experimental method is to drop a small drop of abrasive material on a glass slide and then cover it with a cover glass. Note that when covering the coverslip, do not use excessive force to prevent the material to be observed from being separated and affecting the inspection. The main disadvantage of optical microscopy is that the rate of discrimination is too low and the minimum resolution is only about 2 microns.

 Electron microscopy fineness test: The high resolution of the electron microscope is a bright spot. It can visually observe the particle size of the pigment, and it is the pigment particle size that is transparent to the coating, and the fluidity and color are equal. Have a decisive influence.

 The shortcomings of the electron microscope fineness test method are mainly that the equipment is expensive and the test time is long. It is necessary for an experienced technician to analyze and interpret the test data. In addition, the sample must be dried before the measurement can be performed.

 5. What is the meaning of pigment solvent resistance?

 In the production of paints, we must uniformly and stably disperse the pigments in most organic binders (composed of resins and solvents), which means that the pigments must be surrounded by organic solvents. In addition, most paints are pigmented and inevitably contacted with organic solvents (cleaners, gasoline, lubricants, etc.) during the useful life. Therefore, it is required that the pigment be as insoluble as possible in the organic solvent. If it is not insoluble, we should be aware that the addition of pigments in various organic solvents is limited. Exceeding this tolerance will result in staining caused by the dissolution of the pigment in the solvent. The solvent resistance of the pigment is essentially the ability of the pigment to resist the dissolution of the solvent and cause staining. Inorganic pigments (determined by their own chemical structural properties) and some structurally complex organic synthetic pigments generally have good solvent resistance. However, some lower grade organic pigments and surface treated pigments have poor solvent resistance. Solvents used to determine the solvent resistance of the pigment include water, pine perfume, toluene, xylene, methyl ethyl ketone, ethanol, ethyl acetate, diethylene glycol and trichloroethylene.

 6. What is the difference between the light fastness and weather resistance of pigments?

 Many coatings that use pigments (or dyes) as colorants need to maintain a constant color in their application. We define the lightfastness of a pigment as a quality specification for the exposure of the pigment to daylight. Among the compositions of sunlight, the most destructive part of the light resistance of the pigment is ultraviolet light (UV). In the lightfastness of the pigments we discussed, we only evaluated the quality specifications of the pigment's tolerance to the light environment in the external environment. In fact, it is difficult to make an accurate definition of the weather conditions. From a certain perspective, the pigment lightfastness index, which excludes other external environmental factors, may help us to give a meaningful and reproducible objective evaluation of the field stability of the coating. Pigment weatherability indicators are affected by a variety of external environmental factors, including daylight exposure, high-energy UV radiation, temperature, humidity, and erosion of various impurities in the atmosphere. Pigment weatherability indicators can be measured by outdoor exposure experiments or indoors by artificial atmospheric aging equipment to simulate the field environment. Outdoor exposure experiments usually select specific locations as experimental sites, which are often areas with very harsh climatic conditions (strong sun exposure, heavily polluted industrial atmosphere, etc.). The most famous outdoor exposure test site is Florida, USA. . The test sample is generally placed in the direction of 5 degrees in the south and subjected to outdoor exposure for 12 months or more.

 7. What can the oil absorption tell us?

 Wetting is a very important part of the entire dispersion process. The effectiveness of the wetting effect depends to a large extent on the degree of affinity of the dispersion medium and the surface morphology of the pigment and the spatial interaction of the molecular morphology of the dispersion medium and the structure of the pigment agglomerate. Simply put, the oil absorption is actually the minimum amount of oil required to wet the surface of the pigment particles and fill the gaps between the particles. A specifically quantified method means that the minimum amount of pure linseed oil that can be absorbed per 100 grams of pigment is the oil absorption of the pigment. Everyone pays attention to the absorption mentioned here. It is artificially blended with a knife by adding linseed oil with a burette. The final mixture of pigment and linseed oil reaches a thick slurry state.

 For example, the oil absorption of 30 g / 100 g means that 30 parts of oil is blended into 100 parts of the test pigment in the above-mentioned manner to reach the experimentally required thick slurry state. The oil absorption reflects the specific surface area of a particular pigment to some extent. The lower the specific surface area, the lower the oil absorption and the better the wettability of the pigment, and vice versa.

 8. What measures can I use to improve the hiding power of the coating system?

 For most coating applications, opacity is a fundamental and primary performance requirement. This is fully reflected in the yellow paint, because the yellow pigment absorbs light poorly, and the hiding power can only be achieved by scattering light. This is also the reason why the bright yellow organic yellow pigments in the industry have been poorly covered. Therefore, in the case where only a single pigment can be selected, the formulator often chooses a chrome yellow with higher hiding power (the refractive index of the inorganic pigment is about 2.5) and abandons the organic yellow pigment (refraction of the organic pigment) The rate is about 1.6). Of course, in the case where the pigment can be compounded, the formulator can add a higher hiding power and coloring power to the organic pigment by adding a high hiding power inorganic pigment (titanium white, iron oxide pigment). Adding titanium dioxide to improve system hiding power is probably the most widely used method at present. However, we should not forget that there are also ways to improve the hiding power by increasing the absorption of light, for example, a little carbon that the system can tolerate. Black will greatly enhance the hiding power of organic red. The almost all absorption of light by carbon black compensates for the lack of relative absorption and the hiding power of organic pigments with poor scattering ability. However, it must be emphasized that the less pigment in the formulation, the better the color saturation, and the addition of inorganic pigments that are highly absorbing to sunlight must be within the formula.

 9. What happens to the separation of different pigments in the coating?

 In the coatings industry, it is very common to separate the pigments from the coating, especially if there are two or more pigments in the formulation. Pigment separation can result in uneven distribution of surface pigments after the coating is dried. If it is due to the difference in the concentration of the pigment on the surface of the coating film, the phenomenon of the pigment is too much local, we call it hair. The hair buds are actually the vertical dispersion of the pigment mixture, which separates the components of the pigment mixture from each other. The pigment concentration in the vertical direction with the paint film is the same, the color is the same, the concentration in the horizontal direction is different, the color is different, and the appearance of the paint film is uneven in color of the mesh and the stripes.

 If the pigment has the same concentration on the surface of the coating film and the concentration inside the coating film is different, we call it a floating color. Floating color is a horizontal dispersion of a mixture of pigments. In the horizontal direction, the pigment concentration is the same, the color is the same, but the color is inconsistent with the lower layer color, and the pigment concentration is different. When the coating was applied to a glass plate, we observed a floating phenomenon. Pigment separation is largely related to the different mobility of different pigments in the formulation. Dispersants can improve such paint problems.

 10. What is the indicator of paint hiding power?

 The light passes through the transparent medium and passes directly without any change, and then is reflected on the surface of the substrate. Light can't penetrate when it encounters opaque media, it can only be absorbed or reflected. When discussing the optical properties of pigments, we cannot simply describe them with transparency or opacity.

 Hiding power refers to the ability of a pigment to cover the surface of the surface of a surface when it is uniformly applied to the surface of the object in a particular coating system. Paints achieve opacity indicators in two ways. These two methods refer to the absorption and scattering of light. For example, black pigments absorb light of any wavelength and have a strong hiding power; The selective absorption of light of different wavelengths reaches the hiding power; the white pigment does not absorb any light, and the hiding power is mainly reflected by the strong scattering effect.

 11. What are the technical elements in the pigment dispersion process?

 The pigment dispersion referred to in the production of paint generally means that the pigment is stably and uniformly dispersed in a specific medium in a solid state. It is mainly divided into four steps: a. Wetting of the surface of the pigment. b. Open the aggregate of the pigment. c. Uniform distribution of pigment particles in the coating. d. Long-term stability of the entire dispersion system.

 Wetting: In fact, wetting is divided into two separate processes. The air is initially distributed by the dispersion medium (solvent or water) on the surface of the pigment powder, and then the aggregate of the pigment is softened with the aid of a wetting agent.

 Open the aggregate of the pigment and spread it evenly:

 The aggregate of pigments is opened with the aid of a dispersing device. After this stage is completed, the pigment is uniformly dispersed in the dispersion medium in the state of the primary ions.

 The success of the pigment depolymerization process depends mainly on the high-speed shearing, collision and friction of the dispersing equipment to achieve the best dispersion state and efficiency. The shear or friction force must reach a maximum. And choosing the right dispersion equipment (determined by the chemical properties and viscosity of the dispersion medium) is ideal for this