Coating knowledge: coating Literature: Construction of waterborne fire retardant coating and analysis of coating defects

Core tip: 0 Preface As a functional coating, fire retardant coating can effectively prevent or delay the spread of fire According to different fire retardant mechanism, fire retardant coatings can be divided into two categories: intumescent and non intumescent Compared with non intumescent fire retardant coating, intumescent fire retardant coating has the advantages of material saving, easy construction, beautiful surface and so on Therefore, it is widely used in occasions with high requirements for aesthetics (high standard building market), such as high-rise buildings, airport terminals, railway stations and so on The intumescent fire retardant coating can be divided into solvent type and water type according to different dispersing media 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 As a functional coating, fire retardant coating can effectively prevent or delay the spread of fire According to different fire retardant mechanism, fire retardant coatings can be divided into two categories: intumescent and non intumescent Compared with non intumescent fire retardant coating, intumescent fire retardant coating has the advantages of material saving, easy construction, beautiful surface and so on Therefore, it is widely used in occasions with high requirements for aesthetics (high standard building market), such as high-rise buildings, airport terminals, railway stations and so on According to the different dispersing media, intumescent fire-retardant coatings are divided into solvent based and water-based In recent years, with the increasing awareness of environmental protection and the continuous development of water-based fire-retardant coatings, the performance of water-based fire-retardant coatings has been widely improved, and its quality has gradually approached that of solvent-based fire-retardant coatings, for example, through the 2.5h Chinese fire-fighting commission test Interchar1120, the water-based fireproof coating of international paint, is a typical representative 1 The construction of waterborne fire retardant coating has its own characteristics, as follows: 1.1 the drying process of waterborne fire retardant coating is always accompanied by water volatilization, so moderate temperature and good ventilation are very important The surface temperature of steel should be at least 3 ℃ higher than the dew point temperature, and the drying performance of water-based fire retardant coating is the best when the temperature of atmosphere and substrate is 10-40 ℃ Humidity also has a great influence on the drying performance of fire retardant coating Most coating manufacturers suggest that the relative humidity of air should be below 80% Corresponding dehumidification devices shall be equipped in the humid and rainy areas near the sea The heating of fuel oil will produce water vapor which will affect the drying and curing of the coating Therefore, it is not recommended to use 1.2 base material treatment with good base material treatment is the premise for any coating to play a role, and water-based fireproof coating is no exception All surfaces shall be clean, dry and pollution-free The weld and corner parts shall be polished to form a smooth surface The surface defects such as welding slag and spatter shall also be polished Similar to solvent based fire retardant coating, at present, the mainstream water-based fire retardant coating manufacturers all recommend to construct a primer first, which can provide the necessary anti-corrosion performance of the whole coating system, and it should have good compatibility with fire retardant coating Different manufacturers of primer and fire retardant coating are not only prone to compatibility problems, but also difficult to define responsibilities after problems occur Therefore, coating manufacturers with one-stop service (providing fire-proof and anti-corrosion coatings at the same time) are favored by the market Large paint manufacturers such as international paint will even provide approved matching primer and finish system 1.3 the waterborne fire retardant coating for finishing coat construction is greatly affected by the water vapor in the air, and the accumulated water and long-term condensed steam will reduce its service life, even cause the coating foaming and failure It is very important to protect the fireproof coating (or "seal") with the top coat The surface of fireproof coating shall be clean, dry and have good compatibility before finishing 1.4 the mechanical mixing of construction method can ensure the uniform state of the coating Under no circumstances can manual mixing be used, but excessive mixing shall be avoided Excessive mixing will cause more air to be mixed in the coating and affect the coating quality Brush coating and roller coating are also suitable for the construction of water-based fire retardant coating, but their single film forming is relatively low, generally speaking, they are only used in small areas and repair In addition, the airless spraying pump driven by compressed air shall be modified to adapt to the coating construction For example, a filter device shall be installed to prevent external pollutants from entering the spraying pump and causing blockage; any wet end extension rubber head shall be removed and the suction pipe shall be directly connected to the coating At present, the thickness of ultra-thin fire retardant coating is about 2.0mm, so it needs multiple construction to achieve the target film thickness After the above coating construction, it is necessary to check whether the coating thickness meets the requirements 2 possible film defects and reasons any coating needs to be properly constructed Improper construction will lead to different types of film defects The film defects of waterborne fire retardant coating have their own characteristics 2.1 the cracking of the cracking water-based fire retardant coating shows that the surface is no longer flat and smooth, but has hair like small cracks Over application and construction environment are the two main factors leading to film cracking Over construction on site will easily lead to single coating construction exceeding the maximum single coating thickness At this time, the coating on the outermost layer of the coating gradually solidifies, and the surface coating becomes dense and hard; however, the solvent in the lower layer of the coating is blocked from volatilizing, so it is difficult to separate from the coating, resulting in the cracking of the coating In the corner and joint of steel structure, the coating is easy to be too thick and cracked due to over construction Too low construction temperature is also a major factor that causes the cracking of water-based fire retardant coating At the same time, when the construction is carried out in windy weather, the coating is more likely to crack When the temperature is too low, the curing speed of the coating film decreases, the hard drying time and coating interval extend, and the evaporation of water vapor inside the coating slows down However, the surface water volatilizes too fast in windy weather, which also causes the solvent volatilization to be blocked and causes cracking In addition, the paint system does not match will also lead to the film cracking For example, if the surface of the elastic fire retardant coating is painted with the general non elastic fire retardant coating, it is easy to cause the crack and bulge of the finish paint In case of paint cracking, generally polish the film with defects to fresh coating or primer, and then spray again According to the coating manufacturer's construction suggestions, adjust the spray gun pressure, nozzle size and the distance between the spray gun and the base material At the same time, use the wet film card to measure the film thickness regularly to prevent the coating from being too thick And we should gradually master the construction skills of different manufacturers in the continuous construction to avoid the recurrence of problems In case of strong wind, appropriate measures shall be taken to prevent the effect of strong wind on film curing 2.2 the flow of the water-based fire retardant coating is characterized by strip bulge on the surface of the coating and obvious traces of liquid flow Like other types of coatings, waterborne fire-retardant coatings have the limitation of maximum construction film thickness, and overspray over the film thickness will cause film sagging Sagging usually occurs in the corner, corner and other areas of steel This part of the area is easy to lead to the accumulation of coating film and produce too thick coating film In addition, poor construction technology (the nozzle is too close to the steel plate) or excessive dilution will also lead to this phenomenon Adding too much diluent will affect the viscosity of the coating, reduce the viscosity of the coating, and enhance the fluidity of the coating, so it is more prone to sagging In general, power tools are used to polish and remove the sagging coating in the area where sagging occurs, and the parts where the film thickness is not up to the standard need to be repainted In order to be beautiful, it can be smothered and leveled For the workers with poor construction technology, construction training shall be carried out to master reasonable construction skills; the steel corners shall be pre coated; at the same time, the opinions of the coating manufacturer shall be followed to dilute with appropriate proportion to avoid over dilution 2.3 the film slide caused by the oil stain on the surface is generally shown as the overall downward slide of some areas relative to other film areas, and the obvious slide boundary will be generated after the film slide This phenomenon is usually caused by the greasy dirt on the surface of the substrate When there is oil pollution on the surface, it will lead to the change of the film tension of the water-based coating, so the film will slide down on the surface of the oil pollution The size and status of the sliding area and the status quo are consistent with the size and status quo of the oil pollution area In this case, the damaged coating shall be removed and the base material shall be repaired after oil removal At the same time, find out the pollution source on site and take corresponding measures to isolate the pollution source 2.4 the foaming performance of the film foaming water-based fire retardant coating is the same as that of the common coating, and the surface of the coating bulges or even cracks, so you can use tools to pick up the bubbles At the same time, the adhesion of the film becomes poor, and there is block shedding But the foaming of water-based fire retardant coating has its unique characteristics The chemical expansion system of water-based fire retardant coating is generally composed of catalyst, charring agent and foaming agent The catalyst is generally ammonium polyphosphate (APP) with medium and low polymerization degree The charring agent is mostly pentaerythritol, while the foaming agent is melamine They have certain hygroscopicity Taking ammonium polyphosphate as an example, because of its high content of phosphorus and nitrogen, good thermal stability, it can be called a strong dehydrating agent when heated, which makes many polymers generate carbides, and at the same time generates oxygen in the ammonia gas to isolate and dilute the air, which plays a role of flame retardant and fire prevention, so it is widely used as an important flame retardant in waterborne fire retardant coatings However, there are some problems that are difficult to overcome in the use of app at present, such as poor resistance to dialysis, easy to separate from the polymer surface, easy to absorb moisture and hydrolyze after separation, thus affecting the performance of fire retardant coating The higher the polymerization degree of app, the stronger its water resistance When the polymerization degree of app is 200-400, the water resistance of the coating is poor, and the components of the coating are prone to phase separation and precipitation, resulting in the decrease of stability The choice of app with high polymerization degree is beneficial to enhance the water resistance of fire retardant coating, but at present, the market is still dominated by app with low polymerization degree, which results in the poor resistance of water-borne fire retardant coating to still water and running water Generally speaking, during and after the construction of water-based fire retardant coating without topcoat protection, external high humidity water vapor and rain are likely to cause fatal impact on the coating Blistering and falling off of fire retardant coating on site is caused by water or rain washing After coating construction, it will be washed by rain or gathered by water without finishing coat protection, resulting in blistering Due to the formulation of water-based fire-retardant coating system, the construction should also pay attention to the influence of weather The construction temperature should be 10-40 ℃, the maximum relative humidity is less than 80%, and the substrate temperature is higher than the dew point temperature by more than 3 ℃ During the actual construction, when the weather conditions continue to deteriorate, such as when the temperature drops below 10 ℃, the construction shall be stopped, otherwise there will be a risk of condensation of water vapor If possible, it is recommended to turn on the environmental control device in case of severe weather conditions