Common sense of coating: the reason of affecting the curing speed of coating

Core tip: the main factors affecting the curing speed are coating type, coating thickness, curing method, curing conditions, curing equipment and specific curing procedures, etc (1) Type of coating Under the same curing condition, the curing speed of the coating varies greatly with the type of coating Generally speaking, volatile paint curing fast, oil paint curing slow The situation of polymeric paints is very different The curing speed of photosensitive paint is the fastest, while other polymer paint is mostly between volatile paint and oil paint When mechanical assembly line is used for coating, volatile paint and acid cured amino alkyd paint are commonly used (2) coating Paint agent, top 10 Chinese wall paint brands Recommended introduction: interior wall paint and exterior wall paint can achieve beautiful, clean and pleasant effects, but the effects in different environments are different, so the color of the paint will be different There are ten brands of Chinese paint, ten brands of global paint, ten brands of Chinese wall paint, and ten brands of Chinese paint, Famous trademark of Chinese paint and coating In private rooms, most of us choose according to our own personality, personal hobbies and living habits The younger generation will choose the interior wall paint with rich colors and bright colors, while the older ones will have some working experience Home of coatings: the main factors affecting the curing speed are coating type, coating thickness, curing method, curing conditions, curing equipment and specific curing procedures (1) under the same curing conditions, the types of coating are different, and the curing speed is very different Generally speaking, volatile paint curing fast, oil paint curing slow The situation of polymeric paints is very different The curing speed of photosensitive paint is the fastest, while other polymer paint is mostly between volatile paint and oil paint When mechanical assembly line is used for coating, volatile paint and acid cured amino alkyd paint are commonly used (2) In the process of coating thickness, the coating is not formed in one time basically, and the method of multiple thin coating is usually adopted (for example, the oil paint is generally about 35 μ m at one time, the nitrocellulose paint is about 15 μ m, etc.) Under the same curing conditions, when the thin coating is cured, the internal stress is small, resulting in less coating defects; when the coating is too thick, the internal stress is large, prone to wrinkle and other defects; at the same time, due to the evaporation of solvent, coating shrinkage, resulting in uneven luster, internal non solidification, etc It has been proved by practice that the physical properties of the paint film formed by multiple finishing are better than that of the same thickness paint film formed by one finishing, except polyester paint (3) Curing condition 1 - curing temperature curing temperature plays a decisive role in the curing rate of most coatings When the curing temperature is too low, the solvent volatilization and chemical reaction are slow, and the coating is difficult to cure The increase of temperature can accelerate the evaporation of solvent and water, accelerate the oxidation reaction and thermochemical reaction of the coating, and accelerate the curing speed of the coating However, the temperature cannot be increased indefinitely, because the temperature is not directly proportional to the curing speed When the curing temperature is too high, the curing speed does not increase obviously, but it will make the paint film yellow or dark Not only that, the temperature also affects the substrate during the coating curing process When the base material is heated, the moisture content changes, and the base material shrinks and deforms, even warps and cracks When the curing temperature of volatile paint is over 60 ℃, the solvent volatilizes violently and the surface layer dries quickly When the internal solvent vapor reaches the surface layer, it is easy to produce bubbles Therefore, when artificial curing method is adopted, the surface temperature is generally not more than 60 ℃ 2-air humidity air humidity should be appropriate If the temperature is too high, the evaporation rate of water in the coating will decrease, and the evaporation rate of solvent will slow down, so the curing rate of the coating will be slowed down Most of the coatings are suitable for curing in air with relative humidity of 45% - 60% If the air in the drying and curing place is moist, not only the curing process is slow, but also the film formed is hazy and has other defects When the relative humidity is high, the coating is easy to produce the phenomenon of "whitening" Because of the oily paint, when the relative humidity is more than 70%, the effect on the curing rate of the coating is more significant than that of the temperature During the curing process, the internal stress of the coating is related to its relative humidity Table 5-1 shows the shrinkage stress of various coatings after curing under different relative humidity 3 - ventilation conditions when the coating is cured, corresponding ventilation measures shall be taken to make the coating surface have appropriate air circulation Timely exhaust of solvent vapor and increase of air circulation can reduce the curing time, improve the curing efficiency and ensure the curing quality a Air velocity Air circulation is beneficial to the self curing of paint film In the closed environment with high concentration of solvent vapor, the film solidifies slowly or even does not dry Ventilation is conducive to the volatilization of paint film solvent and the removal of solvent vapor, and can ensure the safety of natural curing place Forced air drying chamber is to produce circulating hot air by ventilation, and its drying and curing effect depends on air flow speed to a great extent The higher the air speed, the better the heat transfer effect The better the heat transfer effect is, the lower the air flow rate is usually used for hot air drying, generally 0.5-5m / s, and the temperature is 30-50 ℃ b Direction of air flow The direction of air flow is also very important The direction of air flow and coating has two forms: parallel and vertical According to the experiment, the hot air drying with vertical air supply is better than that with parallel air supply 4-The external conditions are used to polymerize and solidify the coating, which is a complex chemical reaction process The curing rate is related to the properties of the resin, the amount of curing agent and catalyst And the external conditions, such as temperature, infrared, ultraviolet, electron ray, etc., can often accelerate this reaction The effect of external conditions depends on the degree of compatibility between external conditions and coating properties For example, the UV curing coating can be cured into a film in just a few seconds If infrared or other heating methods are used, it is difficult to cure or even not For example, the coating cured by electron ray is faster than that cured by photosensitive paint under the irradiation of electron ray emitted by electron accelerator, while the reaction of other coatings to electron beam is not strong Therefore, the curing method of the coating should be reasonably selected according to the nature of the coating used In the second quarter of Shenzhen, 7 batches of defective coatings were found in the spot check of coating product quality Shenzhen recently released the results of the spot check of coating product quality in the second quarter of 2009 Harmful substances were detected in a batch of products produced by Shenzhen Chuangyuan Chemical Co., Ltd This time, 63 batches of coating products produced by 36 enterprises in Shenzhen were inspected, 56 batches were qualified, and the sampling qualification rate was 88.9% The spot check is based on the compulsory national standards GB18581-2001, the limit of harmful substances in solvent based wood coatings for interior decoration materials, GB18582-2008, the limit of harmful substances in interior wall coatings for interior decoration materials and other standards as well as the product standards expressly stated by the enterprise The volatile organic compounds, free formaldehyde, heavy metals, benzene, toluene, ethylbenzene, xylene and other 17 items of the coating samples were tested The main problems found in the spot check are as follows: first, TDI is not qualified, TDI is a highly toxic inhalation poison, which has a strong irritant effect on the eye and respiratory system A batch of "Pu Jingang yellow resistant transparent light oil" produced by Shenzhen Chuangyuan Chemical Co., Ltd is not qualified Second, VOC is unqualified, which brings harm to the health of coating construction personnel and the air quality of construction environment A batch of "coating" NC transparent varnish produced by Shenzhen Far East chemical coating Co., Ltd is unqualified Third, the free formaldehyde is unqualified, mainly because the indicated value is inconsistent with the actual content The Quality Supervision Department explained that the main reason for the unqualified products is that the production enterprises do not have the quality inspection ability of key projects, nor send the products to the third-party testing agency for testing, which leads to the lax control of formula design and production control It is reported that Shenzhen Municipal Bureau of quality supervision has dealt with the unqualified production enterprises in accordance with the provisions of the product quality law and other relevant laws and regulations, and made rectification within a time limit And will continue to increase the supervision and random inspection of coating products, and earnestly focus on the quality from the source, to promote the overall level of the quality of coating products in our city Home of 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