Development of Polyester for High-solid Coil Coating

Pre-coated metal coils are organic/metal composite sheets that are sold in rolls or sheets after coating or pasting a polymer film. It can be machined directly into various parts or products, assembled or installed as the finished product, without the need to re-coat, greatly simplifying the total production process of sheet metal to make the finished product.
pre-coating process because of its energy-saving, environmental protection, high efficiency, good coating quality and other advantages, so since the 1980s Wuhan Iron and Steel Company officially introduced China's first pre-coated metal coil production line, to 2015, the number of production lines rapidly developed to more than 500 . The amount of coil coatings used is also growing rapidly, according to incomplete statistics, the domestic coil coating usage in 2018 is about 350,000 t, is expected to reach 500,000 t by 2025.
pre-coated metal coil production process, the exhaust gas of organic solvents produced in the baking process can be collected and burned into thermal energy reuse, more energy-saving and environmentally friendly, but its VOC content in the construction state can not meet the requirements of less than 420g/L (inclusive). Under the premise that the coil production line is not easy to adjust, it is a feasible route to develop high solid coil coating to meet environmental protection requirements.
the key to the development of high solid sub-roll coating is to develop high solid sub-resin, the experiment shows that only the use of high-solid and low-stick polyester resin, the construction of the paint solid parts can meet the requirements. Industry research on high-solid low-stick polyester resin has many years of history, Changzhou Coating Institute in the 1990s in cooperation with Wugang developed a solid divided into 75%, viscosity of 2000mPa.s line polyester, the polyester in large quantities The application of HPP alcohol monosome, it has a high relative molecular quality and better regulation, it can be introduced into the formulation can effectively reduce the viscosity of the resin, improve the regulation of the resin, and can effectively reduce the resin relative to the lower molecular quality and produce damage to the final paint film performance of small molecular resin. However, the cost of the product is too high, and the cross-linking speed can not meet the requirements of the increase in coil wire speed and was eliminated. With the improvement of coil wire speed, the researchers abandoned the wire structure and branched it in the structural design of high-solid content resin. Some researchers used trihydroxymethyl propane, neo-glycol, and the use of diacid, benzene, isoprene, laurel acid and other acids by esterification to achieve a relative molecular mass between 850 to 2000 polyester polyols, A high solid coating with a solid content of 75.6% was prepared with hexa-oxygen methyl melamine curing, and the hardness of the paint film pencil obtained by curing at 177 degrees C/15min was HB-2H. The introduction of tylitol can improve cross-linking to a certain extent, but the introduction of flexible and high monochloric acid reduces the hardness of the paint film. The technical ideas adopted in this paper are as follows: First, the introduction can obviously reduce the sticky sclerate shrink glyceride monomer, and secondly, in the synthesis process to take step-by-step poly-legal, this poly-legal than the original one-step synthesis method can significantly reduce the same relative molecular quality of the resin viscosity, effectively improve the mechanical properties and resistance of the resin, so as to develop a product that meets the requirements.
1 Experimental part
1.1 high solid polyester resin synthesis principle
the traditional polyester synthesis process to synthesize low relative molecular quality low viscosity resin is not difficult, but its mechanical properties and resistance are poor, can not meet the market for coil coating performance requirements. In order to solve this problem, this paper adopts the following technical ideas: in the process of resin synthesis, the introduction of shrinking glyceride monomer, because of its structural characteristics, its introduction can effectively reduce the viscosity of the same relative molecular mass resin; The advantages of this process are: first, to effectively avoid the traditional process synthesis of ring-shaped internal esters (the substance greatly destroyed the performance of the final product); The technical idea is adopted in order to synthesize the high solidity and low viscosity of various high performance polyester resins, and as a base material, and finally prepare the construction state VOC content of less than 420g/L (including) high solid sub-roll coating. The resin synthesis process is shown in type (1).
1.2 Raw materials and instruments
hetdiacids (AA): industrial grade, Rodia; methyl propylene glycol (MPD): industrial grade, Rhiand; heteahydrobenzene (HHPA): industrial grade, Aladdin; Benzene (PA): Industrial-grade, Changzhou Xuanming Chemical Co., Ltd.; butyl oxide: esterification catalyst, industrial-grade, imported commercial sale; xylene: industrial-grade, domestic commercially available; Schocarbonate shrinking glycerides (E-10): Industrial Grade, Shell; TMP: Industrial Grade, Pastor; Mixed Solvents: Made from S-150, DBE, propylene Glycol Methyl Ether Acetate mixed with the same quality, Industrial Grade, CNOOC Changzhou Environmental Protection Coatings Co., Ltd.; Amino resin: industrial grade, imported commercial sales; Additives: industrial grade, imported commercial sales; Catalyst: industrial grade, imported commercial sales; Titanium white: industrial grade, pan titanium; pale yellow primer: CHANGZHOU Environmental Protection Coatings Co., Ltd., CNOOC.
non-zinc flower hot galvanized steel plate: Shandong Guanzhou Co., Ltd.; Scraper Rod (RDS3, RDS10, RDS24): Onkell Shanghai International Trade Co., Ltd.; Blow drying box (DHG-9146A) ): Shanghai Jinghong Experimental Equipment Co., Ltd.; High temperature oven: EcEFast Australia; Electronic balance: Meitler-Tolido; High-speed dispersion machine (GFJ-1100/U): Shanghai Modern Environmental Engineering Technology Co., Ltd.; Laboratory small sander: Shanghai Saijie Chemical Equipment Co., Ltd.; Scraper fine meter (QXD type): Tianjin material tester factory; Magnetic thickness meter: MikrotestVI., Bickgartner Company; T bend tester: domestic; paint film pencil scratch hardness meter (QH) Q type: Tianjin material test machine factory; scratch knife: the former Ministry of Aeronautics and Astronautics Wuhan instrument factory; lacquer film impact tester: Changzhou City Wealy coating machinery factory; Q-UVB artificial acceleration aging: Q-Lab company; gel penetration chromatography: Waters company. Digital viscosity meter (NDJ-8S): Shanghai Pingxuan Scientific Instruments Co., Ltd.
1.3 Synthesis of polyester resin step
(1): Binary acid, methyl propylene glycol, esterification catalyst and xylene are added to the reaction bottle equipped with agitator, thermometer, water splittor, fractional column, inert gas inlet, while passing on the inert gas. Slowly heating up at the rate of 10 degrees C/h, after the material melts, start stirring, to 140 degrees C reflow reaction, insulation at 200 degrees C 1 to 2h, and then slowly heat up to 230 degrees C insulation reaction to the measured acid value stable, cooling linear end-to-end pyrethroide pre-polyester.
step (2): Continue to inject methyl propylene glycol, xylene, trihydroxymethyl propane, and serotonin shrink glycerides in the above reaction bottles on the basis of step (1), while passing on the inert gas. Slowly heating up at a rate of 10 degrees C/h, after the material melts, start stirring, insulation at 200 degrees C 1 to 2h, and then slowly heat up to 230 degrees C insulation reaction to the measured acid value of less than 5mgKOH/g, cooling to less than 180 degrees C, vacuum removal of residual water and small molecular alcohol. Continue to cool down to about 150 degrees C, add mixed solvent, add the amount to the thin to solid content of 80%, during the full stirring, filtration, the resulting filter is a high solid polyester resin.
1.4 paint and plate making process
in a clean container will be made of high solid polyester resin, dispersant, mixed solvent high-speed dispersion stirring uniform, add titanium dioxide, with high-speed dispersion stirring uniform, poured into the laboratory with a small grinder, and add a moderate amount of beads, grinding dispersed to fine <25 m, the material, to get dispersed white pulp. Add the remaining paint resin, amino resin, additives, catalysts and mixed solvents to the above-mentioned white pulp, and mix well with high-speed dispersion to obtain the white finish.
8.0cm×15.0cm×0.5mm hot galvanized steel plate with waterless ethanol wiped clean, with RDS3 shaving rod scraping pre-coating liquid, baked in an oven at 140 degrees C 40 to 60s, dry film thickness: 1 to 2 m, cooling. Then use RSD10 to scrape the light yellow primer, bake at 280 degrees C 30 to 50s, dry film thickness: 5 to 6 m, cooling. Finally, the above-made finish is scraped with RDS24, baked at 280 degrees C 30 to 50s, dry film thickness: 15 to 16 m, remove, cool, test the performance of the coating film.
1.5 performance test
resin acid value: by GB /T2895-2008 test, resin solid content: by GB/T1725-2007 test, resin viscosity: by GB/T7193-2008 test, resin number relative to molecular mass by gel penetration chromatography measured.
high solid finish properties are tested in accordance with Table 1.
Table 1 High Solid Part Face Paint Performance and Its Test Method
2 Results and Discussion
2.1 Effect of Binary Acids on Resin and Paint Film Performance
Acids, aromatic benzene and lipid ring hehydrobenzene and three compound binary acids to synthesize polyester resin, and respectively, the preparation of white coil paint paint paint paint, to investigate the effect of binary acid type opposite the paint performance, the results are shown in Table 2.
From Table 2 can be seen, although the flexibility of hexadiacids is good, but because of methylene, poor adhesion, in it dominates, although the flexibility of the paint film is better, but the resistance to tape adhesion is poor, the resistance of the paint film MEK performance is also poor; Compared with benzene, white paint with polyester resin prepared with hetehydrobenzene and hendic acid has an absolute advantage in weather resistance. These results can be attributed to: (1) under the action of solvents, polymer chain segments dissolved, the fat family chain segments will be entangled with each other, the macro performance of the resin system viscosity increased. Therefore, in the case of hydroxyl value, solid fixed, aromatic, lipid ring synthetic polyester resin than fat family polyester resin has a lower viscosity; The sex is superior, and does not contain large π key, will not appear because of the absorption of ultraviolet light and make the paint film seriously lost light, aging phenomenon, compared with the fat family binary acid, because of its ring structure, hardness is better than the latter, can provide a certain rigidity for the resin. Therefore, the use of lipid ring family monosome in the formula is a better choice, but because the price of lipid ring family monosome is much more expensive than benzene and hetic acid, in practice, comprehensive consideration, the lipid ring family acid monosome with benzene, hetic acid used together.
Table
2
Effects of different types of binary acids on resin and paint film performance
2.2 effects of relative molecular mass on resin and paint film properties
and the size of relative molecular mass is one of the key factors determining resin properties. The effect of relative molecular mass on resin viscosity is very important, and the relative molecular mass is directly related to polymer viscosity under certain molecular structure and thinner dosage. The relative molecular mass of the end hydroxyl polyester resin due to its shrink reaction can be controlled by the formulation design. This is mainly related to monolith structure, ratio and acid price of the target product, and in a certain acid price range, the relative molecular mass is related to the type and quality of the monolith. In this experiment, by determining the ratio of the first step of acid oversized (the ratio of polyic acids to polyol substances in synthetic polyester resins), the acid over-amounts in this paper are .n (-COOH)/n(-OH)-1), and the effect of different acid oversized amounts (30%, 40%, 50%) on the relative molecular mass and viscosity of the final resin is examined. The above resins were separately prepared with white coil paint coatings to investigate the effect of acid over-the-top paint performance, and the results were shown in Table 3.
Table
3
Effect of acid oversized on resin and paint film performance
From Table 3, it can be seen that the relative molecular mass of the resin is basically positively related to the viscosity, and its viscosity increases at an accelerated rate as the relative molecular mass increases. As can be seen from Table 3, the smaller the acid oversized, the greater the final relative molecular mass of the resin, the better the performance after the film, because it can give the paint film a denser structure and better adhesion; However, the increase of free small molecules, but lead to the final paint film cross-link density is insufficient, thereby affecting the paint RESISTANCE MEK performance, and the stability of the coating is poor, susceptible to ultraviolet light, resulting in molecular chain break bonds, making the paint film weather resistance is not good. Comprehensive balance results, acid over-control at 40%, resin relative molecular mass range between 1500 to 2000 is the most appropriate.
2.3 Effects of the addition of glycerides on resin and lacquer film performance
The introduction of e-ecyclycerides (E-10) by using hydroxyl polyester in the synthesis of hydroxyl polyester, such asymmetric structures can improve the chemical resistance, dirt resistance and hydrolysis stability of the resin, and can significantly reduce resin viscosity and improve the solubility of the resin. Under the premise that other experimental conditions remain unchanged, the experiment selects different E-10 dosing to prepare polyester resin, and separately prepares white coil paint coating to investigate the effect of the opposite paint performance of E-10 dosing, the results are shown in Table 4.
table
4 E-10
dosing on resin and paint film performance
The anti-aging performance promotes obviously, when the dosing is too much, due to the increase of irregular small molecules in the resin, affecting the density of the final paint film, mechanical performance and aging performance are reduced, E-10 dosing is 15% of the total amount of solid resin when the comprehensive performance of the paint film is better.
2.4 Effects of different feeding methods on resin and paint film performance
Select the best formula for the above experiment, and use step-by-step poly-legal and step-by-step synthetic polyester resins under the same polyic acid, polyol, E-10 monomer dosing ratio conditions, respectively, the synthetic formula as shown in Table 5, and the preparation of coatings, comparing its performance, the results are shown in Table 6.
molecular structure has a greater impact on the performance of the resin for hydroxyl polyester resins with slightly branched degrees. As can be known from Table 6, pick.