Training on Coating Matting Knowledge

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Training on Coating Matting Knowledge: Main Topics: 1. Explanation of what matting effect is. 2. Basic elements required to achieve a matte finish. 3. Major types and varieties of matting agents/matting powders. 4. Discussion on how to disperse matting agents/matting powders. 5. Parameters that affect the matting effect. 6. Summary of the most popular application areas for matte coatings. Introduction: Why is matting needed? Items with a matting effect can be found everywhere in daily life: at home, on the way to work, or in restaurants under the cover of night. Most indoor furniture features a matte finish, and the wooden panels covering the exterior of restaurants also have a matte surface. When faced with the choice between a shiny or matte finish, we are not limited merely by fashion and aesthetic considerations. Practice has shown that requirements such as ease of cleaning, brightness, and touch feel also influence our choices. When we arrive at the office, whether by car, bus, or train, we find that the interior finishes of various modes of transportation are generally matte. From a practical and safety standpoint, school blackboards feature a matte surface to prevent glare. The interior of the sedan also features this type of design; various economical and practical devices, as well as the interior decorations, are coated with a non-reflective matte paint for safety reasons. Avoiding reflection is a challenge. Skyscrapers are generally not coated with shiny paint; instead, pre-painted panels are used to cover the steel or aluminum substrate, and matte paint is always employed to prevent dangerous reflections that could irritate the eyes of pedestrians or drivers. Furthermore, cost-effectiveness is another important factor in choosing the surface condition of coatings. For example, when certain substrates are scratched, have minor dents, or become dirty, matting coatings can conceal these defects, whereas applying glossy paint makes it difficult to hide such imperfections. What is the matting effect? What is a ‘matting effect’? For example, color, whether it has a matte or glossy appearance, is a subjective impression created by our senses. Light reflects from a smooth surface into our eyes, and we classify it based on its luster. (White) To be precise, only the portion of light that hits the surface is directly reflected back; the rest enters the paint film, where it scatters internally and is absorbed by the pigments and substrate. (Black, Yellow) The reflectance intensity depends on the flatness of the surface. For example, mirrors are well known for their high reflectivity of light, with very shiny surfaces. Conversely, the microscopically rough surface of a paint film scatters light, reflecting only a portion of it. In this example, a yellow matte surface appeared. The condition for achieving a perfect extinction effect is to scatter all incident light. This also means diffusing the direct light rays falling on the substrate. Otherwise, the substrate will transmit light completely, resulting in a shiny appearance. The microscopic roughness of the paint film surface is what causes light to be scattered, thus creating a matte-effect surface. The basic elements for achieving a matte finish: Pumice powder was previously used to grind the outer surface of dried paint coats. Fine scratches are created through processing, giving the paint film a delicate and elegant matte finish. There are now more materials available for making matte surfaces. Although some processing steps are relatively complex, they are very quick. Additives based on silica, paraffin, organic materials, or even fillers can be incorporated into coatings to create a micro-rough surface on the paint film after drying. Figure 1: Formation of the matting coating. After application of the solvent-based paint, the solvent begins to evaporate immediately; as viscosity increases, applying the paint becomes increasingly difficult until it is completely dry, at which point a hard yet elastic paint film is formed. The evaporation of the solvent causes the matting agent to spread across the entire surface of the paint film, while the paint film becomes thinner. This shrinkage is the main cause of the formation of micro-roughness, or in other words, it results in a matte paint film. The figure below explains why coatings with high levels of volatile organic compounds (VOCs) tend to achieve a matting effect more easily than those with high solid content. We can draw a conclusion: the higher the resin solid content, the more difficult it is to achieve a matte surface. UV or EBN systems show almost no shrinkage, and this is precisely why it is so difficult to achieve a matte finish with these coatings. It can also be said that the thicker the paint film, the more difficult it is to achieve a matte surface. Figure 2: Cross-section of a paint film containing matting powder. III. Main types and varieties of matting agents/matting powders. All matting agents/matting powders used in the coatings industry have their own functions and characteristics. o Silica o Paraffin o Fillers o Organics. Uses of silica: There are many ways to obtain extenders from silica, and they can be mainly divided into two categories based on their manufacturing processes. One is the gel method, and the other is the precipitation method of manufacture. Both types of products after treatment can be made into standard silica matting agents. The treatment process refers to the modification of the silica surface to a certain extent using organic (paraffin) or inorganic materials. Treated silica has different particle sizes, particle size distributions, and pore volumes. Silica has a relatively strong light-attenuating effect, and its use in large quantities may lead to an increase in viscosity. There is a tendency for precipitation during storage, especially with untreated silica. Synthesized aluminum silicate can partially replace titanium dioxide as a high-quality extender and can be used in emulsion primers. This product provides a balanced matting effect in dry emulsion paint films. It can be used as a matting agent in long-oil alkyd resin systems, but it must be dispersed together with pigments and fillers. Apart from in powder coating systems, silica matting agents can be used in all types of coatings. Uses of paraffin Wax: Nowadays, there are a variety of different paraffin wax products available on the market. Wax products based on polyethylene, polypropylene, and Brazilian wax are most commonly used in coatings and inks. Wax products based on polytetrafluoroethylene (PTFE) can also be used as matting agents. Compared to silica, paraffin modifies the paint film by floating on the outermost surface. This will also affect the following properties: extinction/gloss ； Anti-slip and anti-stain properties ； Anti-adhesion and anti-wear properties, as well as anti-settling and anti-surface-tension properties. Most of these products have been micronized, allowing them to be used within a wide concentration range in wax-emulsion-based coatings. Its dispersibility varies depending on the particle size and particle size distribution. Uses of fillers: By using specific fillers, we can significantly increase the pigment volume concentration of coatings, and this can have an impact on various aspects. This is why the concept of lightfastness is limited only to colored paints and to inexpensive, low-quality coating systems. The particle size distribution of the filler is very narrow, so it must be dispersed together with the pigment. To adjust the desired gloss level, silica is usually added at the end of the coating manufacturing process and mixed in. Organic materials: Through modern grinding techniques, we can grind plastics based on polymethylurea resin. The product has little effect on viscosity; its thermal stability reaches 200°C. It also exhibits good solvent resistance and is easy to disperse. IV. How to disperse matting agents/powders. By studying matting agents, we can classify them into two types: (i) those that are mixed together with the paint, and (ii) those that are dispersed along with pigments and fillers. The second process is easy to implement. Good dispersion can be achieved together with pigments and fillers by using appropriate equipment (high-speed dispersers, ball mills, etc.). Figure 1: When dispersing silica, paraffin, or organic substances as matting agents, three different methods can be employed: the concentration method (chromophore technique) ； Dispersion is carried out directly during paint manufacturing ； Or, as requested by the user, it can be carried out in the final stage of coating application, so as to allow for easy adjustment of the matte finish. Concentration methods have advantages and disadvantages. The advantage is that the concentrate is easily available, and mixing can be achieved through low-speed stirring with a mixer. The downside is that, first, the concentration of the matting agent is not high, and second, the solvent evaporates from the surface of the concentrate, resulting in reduced stability of the paste form of the matting agent during storage. And they accumulate to form semi-dry lumps, which are difficult to disperse when added to coatings. Finally, if the slurry concentrate contains resin, it is difficult to achieve wide application. A consideration when producing coatings is the common mixing methods used to add matting agents. A mixer or dissolver can be used to mix the soft matting agent with the low-viscosity adhesive. Most extenders are easy to disperse. For example, using a ball mill can **reduce the particle size and achieve higher gloss; thus, using a higher dosage of matting agent can adjust the desired degree of matting.** When adding a matting agent to adjust the final lightfastness, stirring is required; the matting agent should also disperse easily, and the stirring device must be simple. It is essential to ensure that there is enough space inside the container for the extender to be poured in from the top, and to guarantee that the container is airtight to prevent dust accumulation – these are all necessary conditions in the production process. Critical rate m/sec Rate min-1 Diameter of dissolver disk mm Circumference mm 1000 1500 2000 2500 5000 Critical rate m/sec 30 94 1.5 2.4 3.1 3.9 7.9 40 126 2.1 3.1 4.2 5.2 10.5 60 189 3.1 4.7 6.3 7.9 15.7 80 251 4.2 6.3 8.4 10.5 20.9 100 314 5.2 7.9 10.5 13.1 26.2 How to control the dispersion quality of the light-stopper? When a light-extinguishing agent is used, it is necessary to measure the fineness of the coating or its Hegmann value in order to obtain information on the degree of dispersion. Furthermore, we can also control the gloss within a 60° range. From the main parameters mentioned above, it is clear that the glossiness of the product’s finish must be under control. Furthermore, measuring the gloss at 60° and 85° is also essential for us to further understand extinction. Since there is no rule for comparing with common coating systems, particle size values can sometimes also be defined as an acceptable method. The fineness can usually be greater than 25 micrometers, such as in the case of silica matting agents. Reducing the particle size value lowers the matting effect and increases luster. Viscosity and transparency (for varnishes and photosensitive coatings) also must be kept within a relative standard range. V. Parameters affecting the matting effect There are two aspects to the factors that influence the matting effect: the properties of the product and the characteristic parameters of the coating. * Concentration of matting agent * Performance of matting agent * Coating system. Concentration of matting agent: Users usually test various quality parameters of the matting agent. They will evaluate the products, various chemical components, manufacturing and concentration techniques, and gain an understanding of the products through blending as well as learn about the differences in dispersion properties. Figure 1 shows the effect of the average particle size of the matting agent and the effect of concentration on gloss. Figure 1: Gloss parameters. Figure 2: Paraffin parameters. Performance of matting agents: The smaller the average particle size of a matting agent, the better the matting effect isn’t necessarily guaranteed; however, the resulting paint film will be smooth. Conversely, larger particle sizes result in stronger extinction effects, but the paint film is not smooth. During the storage of varnish, if the particle size of the matting agent is large, there is a tendency for separation and deposition. In particular, untreated silica and fillers must be used in combination with anti-settling agents or fine paraffin particles to avoid this phenomenon. Fine paraffin particles and easily dispersible hydrophobic silica can be recommended, as they have a refractive index similar to that of those additives. The commonly used silica, paraffin, and organic matting agents have the same refractive index as resins, which is one of the reasons for their widespread use. Substrates such as wood, film, and leather (natural or synthetic) must be coated with a transparent paint. When using a matting agent, its impact on the transparency of the coating must be minimal; the selected resin and matting agent should also have the same ‘refractive index’, as this helps to increase the transparency of the coating. The amount of matting agent in the paint film also affects transparency. More efficient light-extinguishing agents require less addition and can achieve better transparency. Coating system: Typical factors that affect the coating system include (i) the binder system, (ii) the application area of the coating, (iii) the coating thickness, and (iv) the drying conditions. The figure below shows the matting effect of different adhesive systems. Figure 1: Effect of different applications on the matting effect. The figure below shows the impact of various construction methods on the matting effect. Figure 2: Effect of manufacturing process on glossiness. Sometimes, coatings can dry under different conditions; for example, after forced drying for a week, they may be dried in air. The result is different degrees of extinction. Applying multiple layers of the same paint film can enhance the same level of gloss. Figure 3: Figure 4: The above figure shows these effects. Popular application areas The following lists the most common applications of extenders in coatings. It explains why matting coatings are so popular in these fields. Decorative coatings, varnishes, solvent-based paints; decorative coatings, colored paints, solvent-based paints; coloring of wood; emulsion paints; water-based decorative coatings, mainly used for surface finishing; floor finishing; for aesthetic purposes, as well as to prevent reflection and ensure slip resistance; industrial coating applications, including heat curing, air curing, and isocyanate curing; coating of metals and plastics; for anti-reflective effects, as well as for aesthetic and stylish purposes; electrophoretic coatings; silica used as a high-performance filler; coatings for rolls and containers; furniture coatings, varnishes, and colored paints ； UV curing systems; topcoats for carved wood floors – stylish and fashionable appearance, anti-reflective properties, non-slip surface. Wall paper and metal foil coatings – stylish and fashionable appearance, anti-reflective properties, non-slip surface. Leather and synthetic leather – fashionable appearance, anti-reflective properties, pleasant touch feel. Matting topcoats; offset printing inks; used as flow agents in powder coatings. Anti-reflective properties