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    Home > Coatings News > Paints and Coatings Market > Outdoor low-light wood-print powder coating development and application

    Outdoor low-light wood-print powder coating development and application

    • Last Update: 2021-01-15
    • Source: Internet
    • Author: User
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    China Paint Online News Information
    article focuses on the film-forming process, coating system, coating technology, etc. of hot sublimation transfer wood grain powder and stereoscopic hand wood grain powder. It is pointed out that these two kinds of outdoor low-light wood-print powder coatings have broad application prospects in China.1,
    powder coating is a "5E" advantages of non-end application products, after more than half a century of development has been very mature. As an important one in decorative powder coatings, thermal transfer powder coatings are widely used in the field of construction, such as aluminum profiles, curtain walls, anti-theft doors and so on. Today's thermal transfer powder coatings in general industry, household appliances and other decorative applications have also been successful applications. As a heat transfer powder coating after the rise of three-dimensional feel wood-print powder coating has been quietly developed in China.
    wood-printed powder coating was originally only the most used hot sublimation transfer powder coating, has become a common name for thermal transfer powder coating. Today's wood-print powder coating is not simply the name of the thermal sublimation transfer powder coating, but also contains three-dimensional feel wood-print powder coating, wood-print powder coating connotation has been extended. Stereoscopic feel wood-print powder coating is a special kind of multi-coated powder coating. In-house application of thermal sublimation transfer powder coating technology has been very mature in China, especially the anti-theft door market development and application has created a large number of in-house (epoxy / polyester type) thermal transfer powder coating manufacturers. However, the thermal transfer powder coating technology for outdoor applications is still controlled by foreign-funded enterprises, especially outdoor low-light thermal transfer powder coatings. Domestic enterprises on the three-dimensional feel wood-print powder coating research and development is very small, let alone mass production. Therefore, so far, the development of outdoor low-gloss weather-resistant powder coating is still trapped around a large number of domestic powder-making enterprises, from the text will be outdoor low-gloss wood-print powder coating in-depth discussion.2, outdoor low-gloss heat sublimation wood powder coating comparison and selection
    In China, outdoor applications of powder coating varieties are mainly polyester / TGIC type, polyester / β-HAA type and polyester / acrylic type, foreign enterprises also have polyester / isocyanate type (commonly known as "polyurethane type"). In fact, can be used in outdoor products far more than these, this paper combined with the domestic market situation, only the above four chemical systems in the heat sublimation transfer wood-print powder coating applications to explore. The term "low gloss" here refers to the film gloss measured by the 60o gloss meter below 40%.
    polyester resins used in this study are derived from companies such as Cytec, Dixing (DSM), Anwei Shenjian, etc.; acrylic resins are derived from companies such as Dongguan Zhongtian and Ningbo Zhihua; and curing agents are taken from Degussa, Bayer, Autoba, Ningbo South China Sea and other enterprises; additives provided by Clariant, ESTRON, Ningbo Nanhai, Zhejiang Zhihua, Guangzhou Zehe, etc.; pigment selection Clariant, bus and KLORMAX and other company products, fillers for domestic enterprises.
    test selection extruder for domestic twin screw extruder, electrostitive spray gun for domestic, small shredder for domestic coffee or Chinese medicine shredder, oven for domestic electric heat heng temperature oven, heat transfer machine for domestic special hot paint machine, hot painting machine physical graphics and operation see Figure 1 and Figure 2.
    2.1 polyester/ isocyanate powder coating
    commonly known as polyurethane powder coating, mainly in the outdoor lightless to high-gloss heat sublimation transfer powder coating appeared in China's market. The resin substrates in the formulation were first made from DSM's P-6504 (medium to low hydroxy), P-1444 (high hydroxy) resins, and isocyanate curing agents were used in Degussa's BF1530 or BF1400. Now Cytec, Guangzhou Association polymer and other companies can provide the corresponding resin, Bayer also has the corresponding isocyanate curing agent products. Hydroxyl energy polyester resin with isocyanate, you can get high-gloss powder coating, the same hydroxy resin with isocyanate can also get low-gloss powder coating, heat sublimation low-light polyurethane powder coating formula as shown in Table 1.
    As can be seen from Table 1, low-gloss polyurethane powder coating formulations usually require two polyester resins with high and low hydroxy values, and adjusting the ratio of the two resins in the case of a certain amount of film-forming substances can reduce the coating gloss, with a minimum gloss of about 5%. This formula structure is obviously different from the common powder coating formulation, the system composition is more complex. The hydroxyl value of commonly used low-hydroxy resins is 25 to 35 mg KOH/g, the hydroxy value of medium-low hydroxy resins is 40 to 50 mg KOH/g, and the hydroxy value of high-hydroxy polyester resins is 280 to 320 mg KOH/g, they The formulation ratios of isocyanate crosslinkers (e.g. BF1400) are 85:15, 80:20 and 40:60, respectively, and it is clear that the higher the hydroxyl value, the more curing agents (closed isocyanates or isodone). Low hydroxy resins are represented by Cytec's CRYLCOAT®2890-0, 2891-0, 2845-0, and 2920-0, 4833-0, with resin hydroxy values of 30 to 35 mg KOH/g. The medium-low hydroxy resin is represented by CRYLCOAT ®E04060, and the resin hydroxy value is about 50mgKOH/g. The high hydroxy resin is represented by CRYLCOAT®2814-0 and E04076, and the resin hydroxy value is about 280mg KOH/g.
    In the case of high hydroxy polyester resin dosage is the same, formula A and formula B because of the use of low hydroxy polyester resin, the need for curing agent is less, and formula C and formula D using medium and low hydroxy polyester resin, curing agent dosage significantly increased. Experiments show that formula A and formula C have a 60o gloss of 15% to 25%, while formula B and formula D have a gloss of less than 10% (no light). Practice application also shows that the powder coating product gloss prepared without high hydroxy polyester resin is at least 60%, with the increase of coating gloss of high hydroxy resin dosing rapidly reduced, when reduced to a certain degree (bottom) after the coating gloss increased, until the formula all use high hydroxy resin coating gloss reached another peak. The mechanical properties of the coating will change with the change of the dosage of high hydroxy polyester resin, and the impact resistance and bending performance of the coating will decrease with the increase of the amount of high hydroxyl polyester resin, the hardness of the coating film will increase, and the chemical resistance of the coating film will increase.
    In recent years, with the development of polyester/isocyanate powder coatings, there have been closed isocyanate and isocyanate (internally enclosed) isocyanate curing agents on the market, as well as isocyanide-based and isocyanate-based co-existence of dual-ernogenic group curing agents (Bye Ear company CrelanVPLS2181/1, the ideal structure of the product is shown in Figure 3), by matching with epoxy-based crosslinkers (e.g. TGIC or PT910/912) can also get less than 10% gloss powder coating. As the corresponding powder coating product application has not yet appeared in China, it will not be repeated here.
    However, the mechanism by which such systems obtain the effect of light-down or lightless powder coating is very complex, and its application is not as extensive as that of a single system, and the basic requirements of the application (e.g. transportation, production reproducible, good mechanical performance, economy, etc.) cannot fully meet the requirements of traditional processes. The latest development has successfully developed an ammonia powder coating anti-lighting method that adjusts the coating gloss and has very good leveling. This is a chemical anti-light system, can obtain different gloss degrees of polyurethane powder coating, and can improve the mechanical properties of the coating film, with excellent leveling and weather resistance. This new polyurethane de-lighting system uses amorphoine hydroxy-energy polyester resins with specialty hydroxy-energy crystalline polyester resins, and the de-lighting effect is independent of crosslinker types (closed isocyanate or isosterone).
    de Gusa has launched a special crystalline resin product EP-R4030, which has been industrialized and brought to market. Designed for low-gloss, ultra-weather-resistant powder coatings, the product has a resin hydroxy value of 30 and a melting point of 110 degrees C. The addition of 35% to 45% of the total resin in the formula provides a low gloss effect and flexibility (see Figure 4). With its preparation of low gloss (5% to 25%) coating film has ultra-weather resistance and good flexibility, coating film gloss has a very excellent batch-to-batch stability.
    it is well known that the use of a mixture of non-stereotyped polyester and crystalline polyester can result in excellent leveling and mechanical properties of powder coatings. However, the typical coating appearance of these mixtures is high gloss. Using special crystalline resins (e.g. Degussa's crystalline polyester resin), a light-free polyurethane powder coating can be obtained, effectively improving the mechanical properties of the coating film and maintaining good storage stability.
    Figure 5 is a polyurethane powder coating made from crystalline polyester resin VESTATON®EPR-4030 instead of amorphoous polyester resin, which has a relationship between curing conditions and the mechanical properties of coating. The ultra-weather-resistant polyurethane is designed with a high impact resistance of 160lb.in and a glossy variation range of 10% to 90%. Curing temperature and extrusive conditions have been found to have little effect on coating gloss. Ultra-weather-resistant low-gloss powder coatings retain most of the film gloss after 3000h exposure tests.
    polyester/isocyanate powder coating de-lighting system has a very high cross-link density, thermal sublimation transfer is not sticky paper. The absorption capacity of heat sublimation ink is better, and the transfer pattern is clear. Therefore, from the transfer process and effect, polyurethane powder coating is very suitable for thermal sublimation transfer. However, due to the market isocyanate curing agent, high hydroxy polyester resin price is outrageously high, resulting in low-light polyester powder coating prices beyond the domestic market can accept the degree, so the promotion is very difficult, market share is not large. However, polyurethane powder coatings are still required in many applications for thermal transfer of powder coatings.
    2.2 polyester/acrylic powder coating
    with polyester resin and GMA acrylic resin (with epoxy base) with a light-resistant outdoor powder coating, the technology has been very mature in China. The T-308 added in Dongguan and the AR607 in Ningbo Zhihua are among these acrylic resins (see Table 2). With this kind of GMA acrylic resin preparation lightless powder coating of the carpenole polyester resin is mainly acid value 33 to 38mg KOH/g (medium low acid value) and 24 to 26mg KOH/g (low acid value) resin, acid value 16 to 24mg KOH/g polyester resin is generally not recommended for use. The ratio of acrylic resin to pyrethroide polyester resin in the formula is 1:3 to 1:4.
    GMA acrylic resin is a copolymer containing shrinking glycelaglycerides, the reactive group is epoxy-based, the chemical structure is shown in Figure 6.
    This GMA acrylic resin is seriously incompatible with polyester resins, and despite the epoxy-based and niobium-based reactions in the product system, the final coating has a very low gloss (less than 2%), resulting in an outdoor ultra-light powder coating system. Not all products in practice require such a low gloss, and people adjust the coating gloss by adding pyrethroids or alkylamides (i.e. DDDA, TGIC or HAA), as seen in Table 3.
    test and application results show that the ratio of end-to-steride polyester to acrylic resin is best with 3:1 to 4:1, with a small amount of β-HAA, TGIC, DDDA (twelve double acids), B31 and other reaction regulators to control coating gloss and physical mechanical properties. By adjusting the formulation structure and matching ratio can achieve 3% to 30% coating gloss changes, the appearance of the coating smooth and delicate. It is undeniable that so far there are still many problems in this system, such as in the 10% to 30% gloss range, whether it is powdering or coating construction are more or less luster instability. Acrylic resin has some selectivity to polyester resin, if the variety is not selected properly can not achieve a smooth and greasy surface. In addition, the surface resistance of the light-eliminating system is poor, easy to produce scratches. Therefore, such products are currently only recommended for general industrial product coating, not for construction aluminum and other high comprehensive performance requirements of powder coating products.
    In view of the polyester/acrylic anti-lighting system there are the above problems, the foreign powder raw materials market has introduced a double-reactive activity hydroxyl and pyrethroid group of hydroxyl reactive reactive hydrometric reassignment ester resin, they react with isocyanate and anti-light acrylic resin, respectively, by adding acid reaction regulators (e.g. TGIC, PT910/912, etc.) to adjust the coating gloss. Other improvements include the use of high-gloss acrylic and anti-light acrylic resins to adjust the coating gloss, or the use of a multi-curing system containing dual-active hydrogenic reunification ester resins and dual-active hydrogenic group (epoxy and hydroxyl) acrylic resins, or the use of isocyanate cross-linked polyester resins in hydroxy and acrylic resins, through the system at the same time a variety of cross-curing reactions to achieve the purpose of de-lighting.
    optimization and improvement of the polyester/acrylic de-lighting system has undoubtedly promoted the expansion of the system from a lightless system to a light-free system, improved the stability of powder and coating production, and greatly improved the performance of powder coatings. The negative impact is that product formulation is more complex and some coatings or coatings are reduced or lost.
    powder coatings have good bending resistance, impact resistance, weather resistance, heat resistance and yellow degeneration. However, this kind of powder coating can only do low gloss coating film, coating film gloss adjustable range is narrow, usually not greater than 10% (60o gloss meter).
    2.3 Polyester/TGIC powder coating
    polyester/acrylic de-lighting system can undoubtedly replace polyester/isocyanate low-light (less than 10%) thermal transfer powder coating, so that less than 10% of the cost of low-light heat sublimation transfer powder coating significantly reduced, effectively promoting the application of thermal transfer powder coating in China. However, for the gloss 10% to 40% range of thermal transfer powder coating almost became a blind spot, formulaters can do nothing about it. We used Dry-blend technology in compound powder coatings to conduct experimental research, and finally established the formulation design and application. The test formulation for this type of product is shown in Table 4.
    Table 4 lists the best powder coating formulations in the 10% to 30% range of coating gloss. The key to wax powder de-lighting formula is resin selection and wax powder addition, coating film gloss can be adjusted in a wide range of 10% to 60%, but anti-light wax powder on polyester resin has a certain selectivity, powder coating extrusion process and equipment has certain requirements, with the increase in the amount of anti-light wax powder, powder dry powder flow and storage stability decreased. The advantage of wax powder de-lighting formula is that the appearance of the coating is smooth and smooth, and fillers with high oil absorption should be selected, such as anti-light sulphate.
    solution I formula is a traditional TGIC dry mixing system formula. Scheme IA and IB formula resin acid value is relatively close, cross-curing speed difference is small, so if not wax-based anti-lighting agent coating gloss up to about 30%;
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