Common knowledge of coating: principle and application of coating extinction

Core tip: semi gloss or matte powder coatings are sometimes required depending on the application In order to reduce the gloss of the coating, the commonly used matting agents are ultrafine silica, talcum powder, aluminum stearate, calcium stearate, low molecular thermoplastic resin, etc To obtain the extinction effect, the following methods can be used: a When the powder coatings with different curing speed are mixed by dry mixing method, the gloss of the obtained coatings will obviously decrease and play a role of extinction Due to the rapid curing of powder coating with high reactive activity, the resin with slow curing of continuous phase and reaction are blocked, and finally solidified 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: according to the use sometimes need half light or matte powder coating In order to reduce the gloss of the coating, the commonly used matting agents are ultrafine silica, talcum powder, aluminum stearate, calcium stearate, low molecular thermoplastic resin, etc In order to obtain the extinction effect, the following methods can be used: A mix the powder coating with different curing speed with dry mixing method, then the gloss of the obtained coating film will obviously decrease, which plays a extinction role Due to the rapid curing of powder coating with high reactive activity, the resin with slow curing of continuous phase and reaction are hindered, and finally the cured film loses luster Although this method is effective, it increases the manufacturing process and cost b Add thermoplastic resin The extinction powder coating can be obtained by adding cellulose acetate to epoxy powder coating, fine powder low molecular weight polyethylene and polypropylene resin to polyester powder coating The gloss of the film is affected by the manufacturing conditions Because the addition of thermoplastic resin will affect the storage stability of powder coating, the addition amount is limited to 2-3% of the resin amount c Special curing agent with extinction effect d Add filler with extinction effect Adding ultra-fine silica, talc and other fillers can reduce the luster significantly Especially the particle size of the filler has a great influence on the gloss of the film The larger the particle size, the lower the luster We should pay attention to increasing the amount of filler, which will reduce the smoothness and mechanical strength of the film In the epoxy powder coating, the effect of calcium carbonate particle size on the gloss of the coating is shown in the table Adding ultra-fine silica and kaolin to acrylic acid and polyester powder coating can get the extinction coating In addition, the addition of polyethylene paraffin, hydrogenated castor oil and other waxes can also get the extinction coating In recent years, with the continuous improvement of people's living standards, on the one hand, consumers feel that the reflection of high gloss bright paint film is more serious, which is harmful to people's eyes; on the other hand, consumers' aesthetic concept is more and more inclined to leisure, fashion and personalization Coupled with the booming demand of China's automobile and home appliance industry These factors lead to a sharp increase in the demand for low gloss coatings with soft appearance At the same time, how to produce the coatings with extinction performance has become a problem that coating designers must consider The measurement of gloss and gloss the reflection of light on the surface of an object occurs when light is projected onto it The reflection of light on the surface of an object is called gloss The luster of different object surface is different It is called glossiness to measure the reflection ability of object surface to light Gloss is expressed as a percentage The higher the glossiness of an object's surface, the stronger its ability to reflect light, and the higher its brightness The glossiness was measured by photoelectric glossmeter According to the glossiness, the coating can be divided into bright, matte and matte The classification of gloss of coatings (taking 60 ° reflected gloss (i.e the incident angle of light is 60 °) as an example): Matt coatings: gloss < 10%; matt coatings: gloss 15-60%; bright coatings: gloss > 60% 2 The factors that affect the gloss ① the roughness of the coating surface the gloss of the object surface is closely related to the roughness of the object surface When light hits the surface of an object, some of it will be absorbed by the object, some of it will be reflected and scattered, and some of it will be refracted The smaller the roughness of the object surface, the more light is reflected and the higher the glossiness is On the contrary, if the surface of the object is uneven, the scattered light will increase, which will reduce the glossiness The roughness (H) of the surface of the bright object which can be felt by human vision can be calculated according to the formula: H = λ / cos α, in which the wavelength of the light emitted by human and α is the angle of incidence For example, when the angle of human radiation is 60 °, it can be calculated that h = 1.1 μ M when the surface roughness h of the object is greater than 1.1 μ m, it will be uneven and the glossiness will be reduced ② In the film forming process, after the coating is applied on the surface of the object, the film is solidified by the volatilization of the solvent (for solvent based coating) The formation process of coating film is very important to the surface roughness and gloss of coating film In the wet film stage, the evaporation rate of the solvent is controlled by the diffusion of the solvent on the surface of the film When the evaporation rate of each component of the solvent is not very different, it is possible to obtain a high gloss surface; on the contrary, when the evaporation rate of each component of the solvent is different in the wet film stage, it will make the polymer molecules tend to form curls, or even precipitate into particles or clusters of different sizes, The coating surface is uneven In the dry film stage, the volatilization rate of solvent is mainly controlled by the diffusion of solvent in the whole coating, and also affects the roughness of the coating surface In addition, in the process of film formation, with the volatilization of solvent, the film will become thinner and shrink, and some suspended heavy particles in the coating will rearrange on the surface of the film, resulting in the uneven surface of the film ③ Particle size and distribution of pigment and fine material particle size and distribution of pigment (filler) in coating is one of the important factors affecting the gloss of coating It was found in the research that when the diameter of pigment particles is less than 0.3 μ m, a high gloss coating can be obtained The reasons are as follows: after the pigment particles dispersed in the coating are made into a certain thickness of the coating and dried, only the top layer of the pigment particles locally protrudes, and the surface roughness of the coating caused by the pigment ions whose particle diameter is less than 0.3 μ m will not exceed 0.1 μ M When the average particle diameter of the pigment is between 3-5 μ m, the film with good extinction effect can be obtained In addition to the above three factors, the volume concentration of pigment (PVC), the dispersion of pigment, the surface structure and surface reflection characteristics of the film can also affect the gloss of the film surface Among them, with the increase of PVC pigment, the glossiness of the coating surface first decreases, and a minimum value appears at the limit volume concentration (CPVC) of pigment, and then increases with the increase of PVC When the type and amount of pigment are determined, the better the dispersion, the higher the glossiness of the coating surface Two coating extinction problem is to use a certain method to reduce the glossiness of the coating surface 1 The principle of extinction combines the mechanism of the surface gloss of the film and the factors affecting the gloss It is believed that extinction is to use various means to destroy the smoothness of the film, increase the surface micro roughness of the film, and reduce the reflection of the film surface on the light It can be divided into physical extinction and chemical extinction The principle of physical extinction is as follows: adding an extinction agent to make the surface of the coating uneven during the film forming process, increasing the light scattering and reducing the reflection Chemical extinction is to obtain low gloss by introducing some light absorbing structures or groups, such as polypropylene grafted materials 2 Extinction method ① in today's coating industry, people generally use the method of adding extinction agent There are mainly the following categories: (1) metal soap metal soap is a kind of matting agent commonly used by early people, it is mainly some metal stearates, such as aluminum stearate, zinc stearate, calcium stearate, magnesium stearate and so on Aluminum stearate is the most widely used The extinction principle of metal soap is based on its incompatibility with the paint ingredients It is suspended in the paint with very fine particles and distributed on the surface of the film when the film is formed, which makes the surface of the film produce micro roughness and reduces the reflection of the surface light of the film to achieve the purpose of extinction (2) Wax wax is an earlier widely used matting agent, which belongs to organic suspension matting agent After the coating construction, with the volatilization of the solvent, the wax in the coating will be separated out and suspended on the surface of the coating with fine crystals, forming a rough surface scattering light, which plays a role in extinction Wax, as a matting agent, is easy to use, and can give the film a good hand feel, water resistance, damp heat resistance and stain resistance However, the formation of wax layer on the surface of the film will also prevent the volatilization of solvent and the infiltration of oxygen, which will affect the drying and recoating of the film The development trend in the future is to synthesize polymer wax and silica, so as to obtain the best extinction effect (3) Functional fine pigment, such as diatomite, kaolin, fumed silica and so on, is a kind of special functional fine pigment for matting agent, which belongs to inorganic filling matting agent When the film is dry, their tiny particles will form a micro rough surface on the surface of the film, reducing the reflection of light to obtain a extinction appearance The extinction effect of this kind of extinction agent is restricted by many factors Taking silica as an example, when it is used as a matting agent, the pore volume, average particle size and particle size distribution, dry film thickness and whether the surface of the particles has been treated will affect its matting effect The results show that silica with larger pore volume, uniform particle size distribution and particle size matching with dry film thickness has better extinction performance In addition to the above three commonly used matting agents, some dry oils, such as tung oil, can also be used as matting agents in coatings It mainly uses the high reactive activity of the double bond of tung oil to make the surface of the film uneven and achieve the extinction effect In order to obtain low gloss, matting agent plays an irreplaceable role However, there are still many defects to be improved in its use, such as the selection and application conditions of the matting agent are relatively strict; the price of the matting agent is on the high side, most of the matting agents used in China need to be imported from abroad, such as sy-l01d, ed40 and Ed30 of Grace company in the United States, js-100, tk-900 and hk-125 of Degussa company in Germany, gasil and hp340 of crossfield company in the United Kingdom, etc As a result, the price of low gloss coatings also rises; domestic matting agents contain more cyclophosphamide, so the obtained coatings are prone to yellowing and poor baking resistance How to produce high performance and moderate price matting agent is still one of the problems that coating workers need to solve 3 extinction tree