Preparation and properties of polyester/epoxy/acrylic resin low-gloss powder coatings

Lan Fenfen, Ding Ran, Tian Zhen, Zhang Hongli, Huang Yiping, Xu Govin, Bao Junjie
Anhui University School of Chemistry and Chemical Engineering
Anhui Province Green Polymer Materials Key Laboratory
Water-based Polymer Materials Anhui Engineering Technology Research Center
Summary:
legally synthesizes epoxy-containing acrylic resins using free-based polygene, and mixes the resin with epoxy resins, polyester resins, fillers, additives, etc. to prepare a low-gloss powder coating. Through infrared, molecular weight, scanning mirror, gloss, pencil hardness and other tests, the effect of the amount of trigger on the performance of synthetic acrylic resin and the effect of styrene content, different resin ratio, curing agent type on powder coating performance were studied. The results show that in the sample of acrylic resin of the mixed material, with the increase of styrene monomer content, the gloss of the coating is gradually reduced, the coating gloss of the powder coating prepared by the three resins can reach 6.6, the pencil hardness is above 6H, the adhesion is 0, and its comprehensive performance has been greatly improved .
Foreword
Powder coatings developed since the 1950s have the advantages of high utilization rate of raw materials, good decoration, hard coating, safe use, environmental protection, etc., and have been widely used in construction, leather, automotive and other fields. According to the resin classification, powder coatings can be divided into thermoplastic and thermosolytic two categories, and thermosolytic. At present, the resins commonly used in thermostate powder coatings are: epoxy resin, polyester resin, acrylic resin, polyurethane several categories. In recent years, with the improvement of people's aesthetic concept, the demand for natural elegant, good decorative low-gloss coatings is also gradually increasing.
acrylic powder coating has the advantages of good decoration, good weather resistance, and low gloss powder coating shows a larger upward trend. The main methods of de-lighting of powder coatings are: adding some anti-lighting agents, adding fillers, mixing two or more resins, and introducing a monolith with poor compatible in the resin. The use of anti-light agents may lead to a decrease in the performance of the coating film, filler lighting effect is limited. At present, more research at home and abroad is acrylic, epoxy resin, polyester and other composite anti-light resin. The addition of composite resins results in high-performance, low-gloss powder coatings while reducing coating costs while avoiding the use of detergents.
This paper synthesizes a series of epoxy acrylics, mixing them with polyester and epoxy resins, using different curing temperatures of the official energy groups between mixed resins, making the coating shrink unevenly when filmed, resulting in microscopic roughness;
Experimental Part
1.1 Reagents and Instruments
Methyl Acrylic Shrink Glycerides (GMA), Acrylates (BA), Styrene (St), Methyl Acrylates (MMA), Benzoyl Peroxide (BPO), Xylene, Titanium White Powder, Sulfate: Analysis Pure, Shanghai McLean Biotech Co., Ltd. Epoxy E-12 (epoxy value 0.129), pyridine-based polyester resin, diamine: industrial products, Huangshan Jinfeng Industrial Co., Ltd.; 2-benzene-based meth closed IPDI: laboratory homemade; resting fragrance: analytical pure, Shanghai Aladdin Biotech Co., Ltd.; outdoor matte powder coating: Yangzhou Zhongyang Powder Coating Co., Ltd.
Fourier Transform Infrared Spectrometer: IRPrecstige-21, Izu Corporation of Japan; Scanning electron microscope: S4800, FEISirion, Netherlands; Gloss instrument: JFL-B206085, Tianjin Jinfulun Technology Co., Ltd.; Lacquer film impactor: Q153-3K1, Tianjin Material Tester Factory; Paint film adhesion rower: QFH-A, Dongguan Huaguo Precision Instrument Co., Ltd.
1.2 Synthesis of acrylic anti-light resin
said to take a certain amount of xylene added to a four-mouthed can of thermometer, agitator, condensate tube, heated to 135 degrees C after insulation 0.5h, take the formula amount of methamphetamine Acrylic shrinkage glycerides, acrylates, refined benzoyl peroxide (accounting for 4% of all monobody mass), methyl acrylates, styrene, xylene as a solvent, the mixture added to the constant pressure drip funnel, 2.5h drop finished. Then insulation reaction 2h, the remaining trigger is added twice, each interval of 1h, after the addition of the trigger, and then insulation reaction 1h. After the reaction, the acrylic anti-light resin powder can be desolated, discharged, cooled and crushed. The synthetic formula is found in Table 1.
1.3 Preparation of the anti-light coating film
samples are taken in dispersion tanks according to formula quantity, ball mill grinding 1h (speed 300r/min), oversieve (200 mesh). Apply the powder coating to the iron sheet of the horse mouth after wiping with acetone, curing 15min at 190 degrees C.
1.4 Test and Symptoms
1.4.1 Infrared Spectroscopy (FTIR) Test
with Fourier Transform Infrared Spectrometer, the product epoxy acrylates after grinding in a vacuum oven at 50 degrees C dry, the resulting powder with potassium bromide pressure sheet test, test range 400 to 4000 cm-1, scan times 32 times, resolution 2cm1.
1.4.2 Molecular Weight (GPC) Test
Using a gel permeable chromatography to test the molecular weight of acrylic resin, take 0.005g samples in a 5mL centrifuge tube, with chromatography-grade tethydrofuran as a solvent, flow rate of 1mL/min, mass concentration of 1.5mg/mL, injection with a syringe of 0.2 sm.
1.4.3 Scan Electron Mirror (SEM) Test
A scanning electron microscope is used to observe the surface shape of the coating at 5.0kV acceleration voltage, secure the sample to the conductive adhesive, and then place the sample column into the scanning electron mirror for micromorphological analysis.
1.4.4 coating gloss test
the 60 degree gloss of the film by GB/T9754-2007. Each sample is tested 3 times to average.
1.4.5 Other performance tests
pencil hardness, adhesion, impact resistance according to GB/T6739-1996, GB/T17473.4-2008, GB/T1732-1993 test.
results and discussion
2.1 infrared spectral characterification of acrylic resin
as can be seen from Figure 1, the peaks of the positions of 2995cm-1 and 2950cm-1 are C-H asymmetrical telescopic vibration peaks in CH3, CH2, and the peaks at 1721cm-1 are esters in acrylic tree esters (C C-based The characteristic telescopic vibration peaks, 1447cm-1 and 1383cm-1 are the curved vibration absorption peaks of C-H in CH3 and CH2, 1141cm-1 position is the absorption peak of ester-based C-O-C, and the vibration absorption peaks at 906cm-1 are cyclooxygenated from methyl acrylic shrink glycerides.
2.2 Effect of the amount of the trigger on the molecular weight of the acrylic resin
Figure 2 is the effect of the amount of the trigger BPO on the relative molecular weight of acrylic. As can be seen from the figure, with the increase of BPO dosing, the relative molecular weight of acrylic anti-light resin gradually decreases. The trigger is one of the main factors affecting the polymer polymerization rate and molecular weight, and in theory the relative molecular mass of the polymer is inversely related to the amount of the trigger. In the process of synthetic acrylic resin, if the molecular weight is too large, the melting viscosity of the resin is also larger, not conducive to processing, the resulting coating film flatness is poor; Therefore, the average molecular weight of the expected anti-light resin is controlled in the range of 5000 to 9000, which provides good conditions for the preparation of the coating film of the late low gloss powder coating.
2.3 Effect of styrene content on powder coating performance
Table 2 is a powder coating consisting of acrylates containing different quality styrenes (synthetic see Table 1) and epoxy resins, polyester resins, fillers, etc. Table 3 is the performance of the coating prepared under table 2 formulation. From the data in Table 3, it can be seen that with the increase of styrene content, the gloss of the coating is reduced from 9.6 to 6.6 at an angle of 60 degrees, gradually decreasing. This may be due to the poor compatible of styrene with other resins, so that the coating in the film process, destroy the continuity of the coating, the formation of a microscopic rough surface, play a de-lighting effect. And acrylic anti-light resin added, by the three resins mixed preparation of the powder coating, pencil hardness of more than 6H, with good adhesion and impact resistance, excellent performance of the coating. However, the content of styrene over the General Assembly affects the weather resistance of the coating film, so the appropriate content of styrene is 10.5g. The powder coating consisting of it has the best overall performance.
2.4 SEM Analysis of Low Gloss Powder Coatings
to further verify the relationship between the gloss of the coating and the surface structure, its surface appearance was observed through a scanning microscope.
3 is a powder coating prepared from acrylic resins added and unopened styrene monosylene. In the magnification of 620 times the observation can be found that polyester, epoxy resin mixed with acrylic resin, the coating is different size of the bulge structure, the surface is relatively rough. Comparing the two diagrams, it was found that the powder coating prepared with acrylic resin containing styrene monosylene was rougher and the folds more obvious. As can be known from Table 3, with the increase of styrene content, the coating surface is rougher and the gloss is gradually reduced. This is due to the addition of styrene monolith acrylic resin and other resins less compatible, coating film curing surface pressure contraction is not uniform, forming a microscopic rough surface. The change of coating surface appearance corresponds to gloss and conforms to the principle of de-lighting.
2.5 Effect of different resin mixing ratios on coating performance
Table 4 is a powder coating composed of two and more resins in epoxy, polyester, and acrylic resins. Table 5 is the performance of the coating prepared under the Formula 4. From Table 5 data, it can be seen that by epoxy resin, polyester resin, acrylic in the two resins mixed powder coating, its preparation of coating gloss is more than 10%, although the matte requirements, but the matte effect is not very good; This is due to the different curing temperature between the resins, successive curing results in uneven film shrinkage, reducing gloss. When polyester is not mixed with epoxy resin, the adhesion and impact resistance of the coating film is poor. This is because the polyester resin in the carboxyl and epoxy resin in the epoxy base can not occur curing reaction, and the pure epoxy resin itself is brittle, so that the film adhesion and impact resistance is reduced, the mechanical performance of the coating film is reduced; Therefore, when the three resins are mixed together, the coating film is cured more fully and the combined performance of the powder coating is excellent.
2.6 Effects of different curing agents on coating properties
Table 6 is a formulation of powder coatings mixed with the same polyester, epoxy, acrylic resin and different types of curing agents. Table 7 is the coating performance obtained under this formula. From table 7 data can be seen, in the same mixed resin system and different curing promoter preparation of powder coating, a certain amount of curing promoter on the coating of the pencil hardness, adhesion almost no effect, the gloss of the coating film also has no obvious law, the impact on the coating has a greater impact. This is because the structure of different promoters is different, the effect of promoting resin curing reaction is different, the melting flow of the coating is also different. The curing agent can not only meet the reaction activity of the powder coating, improve the curing rate of the coating film, but also adjust the melting fluidity level of the powder coating, so that the performance of the coating coating can meet the application requirements. In addition, it was found that the powder coating prepared after the addition of the promoter showed yellowing. The reason may be that the promoter contains a amine substance, which contains raw color groups, making the coating prepared by the promoter prone to yellowing. Therefore, the selection of the right promoter is also the key to the preparation of powder coatings.
conclusion
the test of infrared spectroscopy, molecular weight, etc. shows that polyacrylates can be synthesized for curing epoxy polyester powders. From the above analysis, it can be found that when the glass transition temperature of synthetic acrylic anti-light resin is controlled at 60 to 70 degrees C and the molecular weight is in the range of 6000 to 9000, a low gloss powder coating with excellent performance can be prepared. And with the increase of styrene content, the gloss of the coating gradually decreases. When the content of styrene is 10.5g, the lowest gloss is 6.6, the hardness of the pencil is above 6H, the adhesion reaches 0, and the impact resistance is 50kg cm. Through experiments, it is found that the combined performance of powder coatings prepared by mixing three resins is superior to that of two resins. By utilizing the difference in curing temperature between resins and the incompatibness of styrene monoliths, the de-lighting effect of the coating can be significantly enhanced.
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