Coating technology: dispersion and precipitation of pearlescent coating

Core tip: scatter The key to the performance of paint is that pigment should be well wetted and dispersed to prevent pigment aggregation The wetting process is to make the wetting agent wrap the pigment surface and separate it from air and water This process can be accomplished by electron exclusion or steric hindrance mechanism With ionic surfactant, cation or anion can be adsorbed on the surface of pigment When the polar pigment particles touch a piece, they will repel each other, so that the pigment dispersion system is stable The stabilizers used to strengthen the steric resistance should be able to attach the whole structure to the surface of the pigment to form a film to prevent the pigment from agglomerating Shenyang steel structure fireproof coating construction expert punde Building Fire Engineering Co., Ltd Recommended introduction: since its establishment, Shenyang punde Construction Fire Engineering Co., Ltd has cultivated a group of professional construction teams with excellent equipment, rich experience and serious responsibility with advanced and scientific management methods and strict engineering quality assurance and after-sales service system It has undertaken a number of fire system installation projects, which has been praised by customers Every idea and special requirement of you will be fully considered by us and fully realized in the construction technology, which will become the cornerstone of our successful long-term development We are looking forward to your invitation, to provide you with quality services and high-quality technical support! All construction coatings have passed ISO9001 Paint Home News: the key to the performance of dispersed paint is that the pigment should have good wetting and dispersion to prevent pigment aggregation The wetting process is to make the wetting agent wrap the pigment surface and separate it from air and water This process can be accomplished by electron exclusion or steric hindrance mechanism With ionic surfactant, cation or anion can be adsorbed on the surface of pigment When the polar pigment particles touch a piece, they will repel each other, so that the pigment dispersion system is stable The stabilizer used to strengthen the steric resistance should be able to attach the whole structure to the surface of the pigment to form an adsorption layer to prevent the aggregation of pigment flakes These stabilizers include polymeric dispersants, nonionic surfactants and polymeric resins Although sometimes, the use of polymer resin alone is not enough to fully wet the pigment, but they can be cross-linked with the resin in the paint system, the pigment flakes are well embedded in the paint system, so that the whole life of the paint has the best performance Based on this, we are willing to choose polymeric resin In oil system, the wetting mechanism of steric hindrance is mostly used; in water system, both electron repellent and steric hindrance are used Pearlescent pigments can be dispersed by ordinary agitators, similar to metal powders The correct mixing method should be to add the pearlite powder to a carrier which is being stirred by an axial-flow stirrer with low shear force The pigment can not be poured in all at one time, but should be poured in gradually When the first part has been fully wetted, it can be added until it is completely wetted Finally, continue to stir for 15 minutes to make the pigment disperse better It can be mixed with an axially rotating toothed stirrer (Cowles type), the amount of pigment shall be less than 25%, and the speed shall not exceed 2000 ft / min In the process of mixing, the height democracy of the mixing slurry should be changed in order to prevent unevenness of the dead angle under the mixing slurry In addition to the above methods, the pigment can be wetted in a compatible solvent, and then added to the carrier; or the pigment can be added to a part of the carrier to form a concentrated solution, and then mixed with the remaining carrier evenly In order to avoid the fragmentation of pigment flakes or the falling off of metal oxides from mica flakes, it is necessary to avoid using agitators with high shear force, such as ball mills, etc In general, pearlescent pigments should be added after the other ingredients are completely mixed The incomplete dispersion of pigment will lead to the defects of paint, such as low color fastness, poor rheological property, appearance difference, poor performance, etc Pigment dispersion in paint can be directly identified by microscope, or by measuring the settling speed and volume of pearlescent pigment With the help of a microscope, it is possible to directly detect whether the pigment chips are agglomerated In general, the concentration of pigment in paint will increase again, which hinders us from accurately observing its dispersion Therefore, we must add varnish or solvent to the paint before observation to reduce the concentration of pigment, but this will change the paint system, make the pigment x coagulate or separate, leading to wrong conclusion By sedimentation method, the paint to be tested or the modified paint without rheological modifier can be directly used After a few days of standing, slow or incomplete settlement and minimum settlement volume indicate good dispersion The soft hardness of the package should also be considered in the qualification, as it is related to redispersion Like other inorganic pigments, pearlescent pigments will settle at the bottom of the packaging tank because their specific gravity is greater than that of the carrier In the storage process, the pearlescent pigment chips will lie on the ground one by one, closely arranged together, and the carriers between the chips will be squeezed out Because the pigment chips have smooth surfaces, they can be closely contacted and bonded, and it is difficult to disperse them again People do not want the phenomenon of pigment precipitation in the finished paint, which will lead to color migration, poor color fastness and poor quality There are two ways to reduce the precipitation of pigment in the paint system: 1 As mentioned before, prevent the pigment from gathering through good wetting and dispersion; 2 Make the pigment well suspended in the carrier A good suspension force in the carrier is to make the pigment wafer independent in the carrier, providing more resistance to prevent pigment precipitation Improving the viscosity of paint is undoubtedly the easiest way to prevent sinking However, the viscosity is limited by the requirements of the application process, the adjustable range is not large, and improving the viscosity has little effect on the anti sinking of the paint stored in the hard packaging for a long time Another anti sedimentation method is to establish a three-dimensional structure net in the system if some special additives (anti sedimentation agent or thixotropic adhesive), such as silica fume or organic clay, are used in the carrier The carrier, pigment and auxiliary are connected by hydrogen bond as a framework, so as to increase the association between pigment and carrier and reduce the sedimentation tendency In addition, clay or silica gel particles will form a rhomboid structure between the pigment chips, thus forming a close aggregation between the tissue chips and the chips, so that the pigment will be quickly and easily dispersed in the carrier The effectiveness of the above additives depends on the type of solvent and resin Different additives can be selected for different systems Usually these additives should be added in the wetting and dispersing step to achieve the best effect However, some clays and silica gel need to be subject to high shear or heating treatment, so this pre grinding operation must be carried out first, and then added to the pearlescent pigment Please operate in strict accordance with the product manual Excessive use of silica gel or clay will reduce the transparency of the paint If it is used in the finishing coat, it will also reduce the DOI (image clarity) and glossiness In particular, if these additives are not properly dispersed, the negative impact will be more prominent They will also weaken the moisture resistance of the coating, so the use amount shall be determined through the test, and the minimum amount shall be controlled as far as possible It can be used in combination with coagulant The polymer dispersant is coupled with the pigment surface, and the anti settling agent provides the hydrogen bond as the skeleton The molecular structure of the dispersant has more positions to combine with the hydrogen bond than the pigment, which enhances the anti settling ability of the pigment Another type of assistant can replace hydrogen bond by forming three-dimensional colloidal structure through the interaction between van der Waals force and carrier This kind of assistant is superfine calcium carbonate which has been treated by special organic treatment The typical product is ircogel 905 from Lubrizol company One advantage of using ircogel 905 is that the additive can be added to any step in the paint production process In the OEM paint with high solid content, ircogel905 is used in combination with silica gel, which has a very good anti sinking effect on pearlescent pigment Because silica gel and ircogel 905 form the mutual force, hydrogen bond and van der Waals force, they play the left and right respectively, and have mutual bearing, so as to get a good anti sinking effect Home of coatings is specialized in coatings, diatom mud, paint coating, coating technology, fire retardant coating news and coating, diatom mud, paint coating, coating technology, fire retardant coating decoration knowledge and decoration renderings,