Study on boiling performance of building materials weather-resistant powder coating

Wen/Dangerous, Huang Lei, Jiang Wei
Guangdong Huacai Powder Technology Co., Ltd.
abstract: applied to the structure of aluminum profiles in the building coating film has a certain waiting grade and water-resistant cooking performance requirements, and often because the coating film water-resistant cooking performance is not up to standard in the storage or transportation process, in high temperature and humidity weather long-term contact with water vapor, and cause the coating surface color change and adhesion is not good, so to ensure that the coating has good water-resistant performance is very critical. The current building materials standard GB, AAMA, Qualicoat and so on have certain requirements for coating film resistant to boiling, and each large aluminum profile factory itself on aluminum profile coating weather resistance and boiling performance also have clear relevant standards. In this paper, according to the high-pressure boiling test method in theQualicoat standard, the influence factors and factors of water-resistant cooking performance of building materials ultra-weather-resistant two-component anti-lighting products

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1 Foreword
is the main structure of doors, windows and curtain walls and is widely used in the field of architecture. Unsophicated extruded aluminum alloy profiles have a single appearance and are susceptible to acid-base corrosion in humid atmospheres, making it difficult to meet the requirements of high decorative and strong weather resistance of building materials. In order to improve the decorative effect, enhance corrosion resistance and extend the service life, aluminum profiles are generally surface treatment. Aluminum profile surface treatment technology can be divided into anode oxidation treatment, anode oxidation-electrophoresis treatment, organic coating treatment three categories, of which, organic coating treatment includes powder spraying, fluorocarbon spraying. The local thickness of the powder coating should be controlled between 40 and 120 m, the powder coating is durable, the chemical resistance is good, the production is simple, and it occupies a large proportion in the surface treatment of aluminum profiles.
a new round of VOCs pollution prevention and control operations in China, green buildings are highly respected, the use of VOCs emission standards of architectural decoration paint is the key. Oil powder has been vigorously promoted, powder coatings as a green and environmentally friendly coatings in color and gloss long-lasting aspects of liquid coatings, in other performance tests, wear resistance, scratch resistance and durability, etc. are also significantly better than liquid coatings, zero VOC, no toxic heavy metals, reduce carbon emissions and other environmental characteristics to replace oily paint has become an inevitable trend. Powder coatings in aluminum profiles, currently commonly used in weather-resistant polyester powder coatings, powder coatings with polyester resins are mostly saturated, usually we according to its end-base structure can be divided into end-shuttle-based and end hydroxyl two categories. The average molecular weight of end-shuttle-based polyester is between 2000 and 8000g/mol, and the acid value is from 2 to 100mgKOH/g. Among them, medium and high acid value (45 to 85 mg KOH/g) is generally used in epoxy/polyester mixed powder coating, low medium acid value (20 to 45 mg KOH/g) polyester with isocyanate shrunk glycery vinegar (TGIC), hydroxyamide (HAA) as a cure for excellent weather resistance of pure polyester powder coating.
foreign methods to detect coating water boiling performance are: QUALICOAT 14th standard boiling water resistance test method: (1) boiling water normal pressure test (2h, no scratching, with tape adhesive tearing) ;(2) boiling water high pressure test (lh, no scratch, with tape adhesive tearing). Performance requirements are: after the coating has been tested with boiling water, there should be no shedding and other defects, allowing for minor color changes. There are no requirements for boiling water resistance in the AAMA standard, but are described in the adhesion test: the boiling water normal pressure test (20min, rowing, adhesive tearing with tape). Performance requirements: the coating in the rowing area should not fall off, the surface can not have bubbles. The test of coatings by two standards focuses on adhesion. At present, the domestic implementation standard is GB 5237.1-2017 "aluminum alloy building profile Part 1 powder spray profile" in the test method of boiling water performance: (1) boiling water normal pressure test (2h) ;(2) boiling water high pressure test (1h). Requirements: The coating surface should not have bubbles, wrinkles, water spots and shedding defects, but slight changes in color are allowed. The coating requirements of the national standard are reflected in the surface quality.
2 Experimental Testing section
2.1 Test method
All test standards in this article can be found in Table 2-1-1.
2.2 Experimental equipment
twin screw extruder SLJ-30D: (Yantai Donghui Powder Equipment Co., Ltd.);
: deionized water, in line with GB/T 6682 in the three-stage water requirements.
2.3 Main raw materials
Ultra-resistant high and low acid resins (Allnex); HAA curing agents (EMS); TEPIC (Nissan), leveling agents (Estron); sabbaths (winning); wax powders (US3 Leaf); TiO2 (Komu); carbon black (Evonik); anti-light sulphate (Huajia); modified cladding sulphate, etc.
2.4 formulation design
according to building materials weather-resistant two-part de-lighting principle design.
2.5 Preparation of weather-resistant powder coatings
According to the design list of polyester resins, curing agents, additives and pigments, the material is mixed evenly, added to the twin screw extruder mixing extruder extruded, cooled after it is broken, ground through the sieve. Mix the powder coating of the high and low acid parts made separately, spray the mixed powder evenly on the aluminum phosphate plate with the electrostitive spraying equipment, then bake it in an oven at 200 degrees C for 15min and remove to cool to room temperature.
2.6 High-pressure water boiling test
inject 2/3 volume of deionized water into the pressure cooker, put the made model into the pressure cooker, the model and the model should have a certain interval, and can not be in contact with the wall of the pressure cooker, to ensure that the test sample length of at least 2/3 soaked in water, set the pressure cooker pressure control at 0.1 Mpa, when the pressure meter rises to 0.1Mpa time, time test 1 hour. After the test is complete, remove, immediately rinse the surface with running water, and then use filter paper to absorb moisture from the surface.
3 results and the impact of
3.1 polyester resins are discussed
different resins have different water-resistant properties, such as epoxy polyurethane and acrylic resins, which are generally better than polyester resins. Polyester resin due to its own structural unit contains ester bonds, lack of sufficient benzene ring structure, and curing agent reaction will contain residual hydroxyl, more easily combined with water molecules, resulting in coating damage.
weather-resistant end pyrethroid polyester resin is widely used in outdoor building materials, is the current mainstream powder coating film-forming substances, film-forming principle is polyester resin niobyl and curing agent provided by epoxy or hydroxyl cross-linking reaction, the formation of thermo-solid paint film. In this reaction process, polyester resin residual hydroxyl and curing agent (TGIC or HAA) in the epoxy base is difficult to add reaction to ether, and polyester resin medium pyrethroid is easy to react with epoxy into esters, so the end of the hydroxyl polyester in the powder coating curing into a membrane process remains.
By comparing several different hydroxyl polyester resins, to study the effect of residual hydroxyl amount in polyester resin on the water-resistant boiling performance of the coating film, Figure 3-1 shows that with the increase of the residual hydroxyl content of polyester, the resistance of its powder coating coating film to boiling water began to decrease, because after hydroxyl adsorption of water molecules, these water molecules at high temperatures can hydrolyze their proximity to the ester bonds, resulting in large molecule fracture chain, paint coating gloss. Resin viscosity increased its water after boiling preservation rate is also on the rise, because when the acid value of a certain time, the viscosity increased resin molecular weight increased, ester bonds more difficult to hydrolysate;
in construction applications, the weather resistance of powder coatings is very important, and it is generally required that coatings guarantee ultra-weather resistance of 10 years or more. The main factors leading to film powdering are: ultraviolet rays can destroy the resin structure of the coating surface, will form a white powder-like substance, the use of artificial accelerated weather resistance test, simulation of the application of the coating in the outdoor environment, can be obtained in a relatively short period of time equivalent to long-term weather resistance test results. The weather resistance performance of the coating film and the resistance to boiling also have a certain relationship, choose a, b, c three weather-resistant resins, its weather resistance rating is a by Table 3-1-2 and Figure 3-1 can be seen that the coating water cooking performance and coating resistance is positively related. The size of the resin acid value fundamentally determines the cross-link density of the coating, the higher the acid value represents that the coating can form a higher cross-link density of the coating, the corresponding coating water resistance will be better, so the choice of high acid value resin, or improve the cross-link density of the reaction coating film will have a better water-resistant cooking effect.
3.2 Effects of pigments
The varieties of fillers commonly used in powder coatings include palladium sulfate (heavy crystalline powder, precipitated palladium sulfate) calcium carbonate, talcum powder, mica and kaolin. The weather resistance and water resistance of radon sulfate are better than calcium carbonate, and mica due to phosphorus flaky crystal structure can improve the tightness of the coating, prevent water infiltration, can greatly improve the weather resistance of the coating film, water-resistant performance. Several fillers are water resistant: mica, kaolin> sulphate, talc powder> calcium carbonate.
outdoor weather-resistant two-group products are generally used to eliminate pure sulphate A, high weather resistance level requirements can use aluminum hydroxide or table bread cover treated with vanadium sulfate B. By comparing the effects of the two types of molyphidium sulfate on the water-resistant properties of the coating film, the test results were as shown in Table 3-2-1.
can be seen from Table 3-2-1 and Figure 3-2, the surface and preservation rate of the coating film with nicotospheric sulfate B is significantly better than that of nicotospheric acid A. Because the general precipitated sulphate on the market is --- kinds of hydromassive inorderable salts, and the main film material of powder coating is resin, so the precipitation of sulphate and resin is equivalent to a physical mixture, poor compatible, the formation of the resin and precipitation of radon sulfate binding point becomes the weak point of the coating film, easy to enter, especially at high temperature water molecules more easily penetrate, resulting in coating damage failure. Due to the hydrophobicity of precipitation of sulphate, it will lead to a decrease in the water-resistant boiling resistance of the coating film, and we selected the sulphate B for the surface bread cover treatment, can float on the surface of the water, with good hydrophobicity.
generally 100% pure pigments will not have a significant impact on the water resistance of the coating. Some pigments are treated with surface treatment agents, which can greatly reduce the water resistance of coatings if they are hydroactive surfactants. For example, some acetic pigments themselves are less resistant to boiling water, and if they contain hydrophobic surface treatment agents, their effect on the coating will be greater when boiled. In addition to the effects of hydro-hydrolytic treatment agents on pigment surfaces, there are some pigments, if the molecules are low, especially the molecular structure asymmetry of low-molecular compound pigments, the coating resistance to boiling will also be relatively large.
3.3 Effect of Additives
When there is a problem with the water-resistant performance of the coating film, adding the appropriate amount of water-resistant cooking aids to the powder coating formulation will improve the water-resistant performance of the coating film. The workings of water-resistant cooking aids include increasing the cross-link density of the coating, enhancing the adhesion of the coating, and providing a better hydrophobic surface to improve the coating's water-resistant cooking performance. The principle of the action of water-resistant cooking additives is slightly different from that of different manufacturers, but water-resistant additives can only play their due role if the boiling performance needs to be slightly improved. When the coating is cured by polyester or curing agent, it does not have the effect of fundamentally improving the boiling performance.
building materials products in order to improve the coating film resistance to boiling performance, will generally add a small number of closed isocyanate or GMA acrylic resin to increase the reaction cross-link density, isocyanate can and the system residual hydroxyl reaction, increase the density of the coating film, which not only helps the coating film weather resistance, but also can increase the coating resistance to water cooking. The effect on film weather resistance and boiling performance was analyzed.
From Figure 3-3, it can be seen that, with the increase of GMA acrylic resin or closed diocyanate in the formulation system, the water-resistant cooking performance of the coating film will be improved to a certain degree, when reached a certain amount after stabilization, after 1 hour of high-pressure boiling, the preservation rate is very good, the coating surface has no significant change. When the system to add GMA acrylic coating surface looks more rough, but after boiling after boiling surface becomes smooth and delicate, gloss but there is a certain improvement, GMA acrylic resin than isocyanate to improve the performance of water-resistant cooking is more obvious.
this paper, the effects of different raw materials in the formulation of weather-resistant powder coating on the coating film resistance to high-pressure boiling, as well as the method guidance for increasing the resistance of the coating film to water-resistant boiling performance.
increases the cross-link density of the system reaction, improves the surface density of the coating film, can effectively improve the water resistance of the coating film, and when the resin reacts with the curing agent, the greater the cross-link density of the coating film, the better the water-resistant cooking performance. The higher the viscosity and branching of the resin with the appropriate acid value, the better the water-resistant cooking properties of the coating film. Selecting a hydrophobic sulphate filler that has been treated with table bread cover can effectively prevent water molecules from entering the coating film through the coating surface gap at high temperature and high pressure, and improve the water-resistant boiling performance of the coating film.
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