Low-temperature curing polyester resin and powder coating

Abstract

The invention relates to the field of polyester resin materials, in particular to low-temperature curing polyester resin and powder paint.The low-temperature curing polyester resin is prepared from, by weight, 30-40 parts of neopentyl glycol, 50-60 parts of terephthalic acid, 5-10 parts of adipic acid, 0-0.1 part of organic tin catalyst, 5-10 parts of hyperbranched polyisocyanate, 5-10 parts of end-capping reagent and 0.1-1 part of auxiliaries; the hyperbranched polyisocyanate is prepared from trimethylolpropane, N, N-dihydroxyethyl-3-amino methyl propionate and alicyclic diisocyanate, the prepared powder coating can be cured at a low temperature, the coating has excellent performance, and the powder coating has wide application prospects in the fields of building material aluminum materials and engineering machinery.

Description

Technical Field

[0001] The invention relates to the field of polyester resin materials, in particular to a low-temperature curing polyester resin and a powder coating. Background Art

[0002] Powder coatings with triglycidyl isocyanurate (TGIC) as curing agent have good surface decoration, mechanical properties, weather resistance and yellowing resistance, and are widely used in the fields of building materials, aluminum materials and engineering machinery. The curing temperature of commercially available TGIC system powder coatings is relatively high, generally 190-230°C. High-temperature curing has the following main defects: The curing energy consumption is high and the coating cost is high; the use of thick workpieces and heat-sensitive substrates is limited; the workpiece cooling speed is slow and the coating efficiency is low.

[0003] In order to overcome the above defects, the powder coating industry is committed to developing TGIC system low-temperature curing powder coatings. The main technical means at present is to use highly active polyester resins, but the leveling, mechanical properties and stability of commercially available low-temperature curing polyester resins are weak. The above defects limit the application scenarios of low-temperature curing powder coatings. Summary of the invention

[0004] Purpose of the invention: In view of the above technical problems, the present invention proposes a low-temperature curing polyester resin and powder coating.

[0005] The technical solutions adopted are as follows: A low-temperature curing polyester resin is prepared from the following raw materials in parts by weight: 30-40 parts of neopentyl glycol, 50-60 parts of terephthalic acid, 5-10 parts of adipic acid, 0-0.1 parts of organotin catalyst, 5-10 parts of hyperbranched polyisocyanate, 5-10 parts of end-capping agent, and 0.1-1 parts of auxiliary agent; The preparation method of the hyperbranched polyisocyanate is as follows: Trimethylolpropane and N,N-dihydroxyethyl-3-aminopropionic acid methyl ester are first reacted to obtain a hyperbranched intermediate, and the hyperbranched intermediate is then reacted with alicyclic diisocyanate to obtain the hyperbranched polyisocyanate.

[0006] Furthermore, the low-temperature curing polyester resin is prepared from the following raw materials in parts by weight: 30-40 parts of neopentyl glycol, 50-60 parts of terephthalic acid, 5-10 parts of adipic acid, 0.001-0.1 parts of organic tin catalyst, 5-10 parts of hyperbranched polyisocyanate, 5-10 parts of end-capping agent, and 0.1-1 parts of auxiliary agent.

[0007] Furthermore, the alicyclic diisocyanate is isophorone diisocyanate and / or dicyclohexylmethane diisocyanate.

[0008] Furthermore, the molar ratio of the trimethylolpropane, N,N-dihydroxyethyl-3-aminopropionic acid methyl ester and alicyclic diisocyanate is 1:3:6.

[0009] Furthermore, the end-capping agent is a composition of fumaric acid and isophthalic acid in a mass ratio of 1-5:1-5.

[0010] Furthermore, the organic tin catalyst is at least one of monobutyltin oxide, dibutyltin oxide and stannous octoate.

[0011] Furthermore, the auxiliary agent includes an antioxidant and a curing accelerator.

[0012] Furthermore, the antioxidant is a hindered phenol antioxidant, preferably antioxidant 1010.

[0013] Furthermore, the curing accelerator is a quaternary phosphonium salt curing agent, preferably ethyl triphenylphosphonium bromide.

[0014] The present invention also provides a powder coating, which is prepared from the following raw materials in parts by weight: 250-300 parts of low-temperature curing polyester resin, 20-30 parts of triglycidyl isocyanurate, 50-60 parts of montmorillonite, 15-20 parts of titanium dioxide, 80-100 parts of barium sulfate, 3-5 parts of leveling agent, 1-3 parts of benzoin, and 1-3 parts of brightener.

[0015] Furthermore, the montmorillonite is treated with epoxy resin intercalation modification.

[0016] Furthermore, the preparation method of the montmorillonite is as follows: Sodium montmorillonite is dispersed in water to obtain a suspension; dioctylamine is dissolved in ethanol, and hydrochloric acid is added and stirred to obtain a dioctylamine hydrochloride solution; the dioctylamine hydrochloride solution is added to the suspension, stirred and reacted at 50-70°C for 12-48 hours, the precipitate is collected, washed, and dried to obtain an organic montmorillonite, epoxy resin is dissolved in an organic solvent to obtain a solution, the organic montmorillonite is added, ultrasonic oscillation reflux reaction is performed for 1-10 hours, and finally the organic solvent is removed by reduced pressure distillation.

[0017] The present invention has the following beneficial effects: The invention adds hyperbranched polyisocyanate as one of the raw materials into the synthesis process of polyester resin. Its unique short and highly branched hyperbranched structure can significantly reduce the entanglement of molecular chains, making the molecules easier to flow, thereby reducing viscosity and improving leveling properties. In addition, a large number of terminal isocyanate groups contained in the invention can react with dibasic acids and diols to form a three-dimensional cross-linked network, thereby increasing the cross-linking density of the polyester resin, thereby increasing the hardness and impact resistance of the cured coating, and both the curing temperature and curing time are reduced, showing low-temperature curing performance. Fumaric acid has both unsaturated double bonds and dibasic acid structures. It not only participates in the polycondensation of the main chain, but also blocks the terminal hydroxyl groups by excessive addition. Using fumaric acid to block the end can improve the impact resistance and flexibility of the polyester resin, while isophthalic acid can give the polyester resin higher heat resistance and chemical resistance. The two can work together as end-capping agents to improve the comprehensive performance of the polyester resin. Montmorillonite in powder coatings can significantly improve the mechanical strength, heat resistance, weather resistance and processing performance of the coating through nano-enhancement, barrier effect and functional synergy. The present invention performs epoxy resin intercalation on the montmorillonite, adopts a cation exchange method in an aqueous medium, introduces dioctylamine between montmorillonite lamellae, replaces sodium ions, and increases the distance between montmorillonite lamellae. The epoxy resin is inserted into the montmorillonite lamellae through cross-linking with amino groups. During the curing process of the powder coating, the excess epoxy groups in the montmorillonite lamellae can participate in the cross-linking of polyester resin and triglycidyl isocyanurate, thereby improving the curing rate and curing strength of the coating.

[0018] The powder coating prepared by the invention can be cured at a relatively low temperature, and the coating has excellent performance and has broad application prospects in the fields of building materials, aluminum materials and engineering machinery. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The synthetic route of the hyperbranched polyisocyanate in Example 1 is shown in FIG. DETAILED DESCRIPTION

[0020] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially. The techniques not mentioned in the present invention are all referenced to the prior art. Unless otherwise specified, the following examples and comparative examples are parallel experiments, using the same processing steps and parameters.

[0021] Embodiment 1: A powder coating is prepared from the following raw materials in parts by weight: 280 parts of low-temperature curing polyester resin, 25 parts of triglycidyl isocyanurate, 55 parts of montmorillonite, 15 parts of titanium dioxide, 90 parts of barium sulfate, 3 parts of leveling agent BYK-360P, 2 parts of benzoin, and 2 parts of brightener XSL-701.

[0022] Wherein, the preparation method of low temperature curing polyester resin is as follows: 1 mol of trimethylolpropane, 3 mol of methyl N,N-dihydroxyethyl-3-aminopropionate and 1 g of p-toluenesulfonic acid were added to a flask connected with a water separator, a feeding funnel and a mechanical stirrer. The mixture was stirred and heated to 120°C for reaction for 5 hours and then returned to room temperature. The reaction product was washed with a saturated sodium bicarbonate solution and then dried to obtain a hyperbranched intermediate. 6 mol of isophorone diisocyanate and 2 g of catalyst DBTDL were added to the flask. The mixture was stirred and heated to 60°C and then the hyperbranched intermediate was added. The mixture was stirred and reacted for 2 hours to obtain a hyperbranched polyisocyanate.

[0023] Add 35g of neopentyl glycol, 55g of terephthalic acid, 10g of adipic acid and 0.05g of monobutyltin oxide into a reactor, heat to 240°C under nitrogen protection, keep warm for reaction for 3h, control the acid value at 12-16mgKOH / g, take samples to measure the acid value, cool to 220°C, add 8g of hyperbranched polyisocyanate and continue to react for 1h, then add 6g of a capping agent composed of fumaric acid and isophthalic acid in a mass ratio of 1:1, heat to 240°C, continue to react for 2h, control the acid value at 47-50mgKOH / g, start vacuuming, the pressure is at -0.095Mpa, until the acid value is 30-36mgKOH / g, add 0.5g of antioxidant 1010 and 0.1g of ethyltriphenylphosphonium bromide, stir evenly, cool to 200°C and discharge.

[0024] The preparation method of montmorillonite is as follows: 100 g of sodium montmorillonite was dispersed in 500 ml of deionized water to obtain a suspension, 20 g of dioctylamine was dissolved in 100 ml of ethanol, and 15 ml of concentrated hydrochloric acid was added dropwise, and the mixture was stirred thoroughly to obtain a dioctylamine hydrochloride solution. The dioctylamine hydrochloride solution was slowly added dropwise to the suspension, and the mixture was stirred and reacted at 60° C. for 24 hours. After the mixture was restored to room temperature, the precipitate was collected by filtration, washed with ethanol and deionized water, and dried to obtain an organic montmorillonite. 10 g of flexible epoxy resin DER 732 was dissolved in 500 ml of xylene to obtain a solution, and the above-mentioned organic montmorillonite was added thereto, and the mixture was heated to reflux, and ultrasonically oscillated to react for 5 hours. Finally, the xylene was removed by reduced pressure distillation.

[0025] The preparation method of the above powder coating is as follows: The raw materials are mixed evenly according to the formula amount and then added into a twin-screw extruder for mixing and extrusion, cooling, crushing, grinding and sieving.

[0026] Embodiment 2: A powder coating is prepared from the following raw materials in parts by weight: 300 parts of low-temperature curing polyester resin, 30 parts of triglycidyl isocyanurate, 60 parts of montmorillonite, 20 parts of titanium dioxide, 100 parts of barium sulfate, 5 parts of leveling agent BYK-360P, 3 parts of benzoin, and 3 parts of brightener XSL-701.

[0027] Wherein, the preparation method of the low temperature curing polyester resin and montmorillonite is the same as that of Example 1; The preparation method of the above powder coating is as follows: The raw materials are mixed evenly according to the formula amount and then added into a twin-screw extruder for mixing and extrusion, cooling, crushing, grinding and sieving.

[0028] Embodiment 3: A powder coating is prepared from the following raw materials in parts by weight: 250 parts of low-temperature curing polyester resin, 20 parts of triglycidyl isocyanurate, 50 parts of montmorillonite, 15 parts of titanium dioxide, 80 parts of barium sulfate, 3 parts of leveling agent BYK-360P, 1 part of benzoin, and 1 part of brightener XSL-701.

[0029] Wherein, the preparation method of the low temperature curing polyester resin and montmorillonite is the same as that of Example 1; The preparation method of the above powder coating is as follows: The raw materials are mixed evenly according to the formula amount and then added into a twin-screw extruder for mixing and extrusion, cooling, crushing, grinding and sieving.

[0030] Embodiment 4: The method is basically the same as Example 1, except that the preparation method of the low temperature curing polyester resin is as follows: 1 mol of trimethylolpropane, 3 mol of methyl N,N-dihydroxyethyl-3-aminopropionate and 1 g of p-toluenesulfonic acid were added to a flask connected with a water separator, a feeding funnel and a mechanical stirrer. The mixture was stirred and heated to 120°C for reaction for 5 hours and then returned to room temperature. The reaction product was washed with a saturated sodium bicarbonate solution and then dried to obtain a hyperbranched intermediate. 6 mol of isophorone diisocyanate and 2 g of catalyst DBTDL were added to the flask. The mixture was stirred and heated to 60°C and then the hyperbranched intermediate was added. The mixture was stirred and reacted for 2 hours to obtain a hyperbranched polyisocyanate.

[0031] Add 30g of neopentyl glycol, 50g of terephthalic acid, 5g of adipic acid and 0.001g of monobutyltin oxide into a reactor, heat to 240°C under nitrogen protection, keep warm for 3h, control the acid value at 12-16mgKOH / g, take samples to measure the acid value, cool to 220°C, add 5g of hyperbranched polyisocyanate and continue to react for 1h, then add 5g of a capping agent composed of fumaric acid and isophthalic acid in a mass ratio of 1:1, heat to 240°C, continue to react for 2h, control the acid value at 47-50mgKOH / g, start vacuuming, the pressure is at -0.095Mpa, until the acid value is 30-36mgKOH / g, add 0.05g of antioxidant 1010 and 0.05g of ethyltriphenylphosphonium bromide, stir evenly, cool to 200°C and discharge.

[0032] Embodiment 5:

[0033] The method is basically the same as Example 1, except that the preparation method of the low temperature curing polyester resin is as follows: 1 mol of trimethylolpropane, 3 mol of methyl N,N-dihydroxyethyl-3-aminopropionate and 1 g of p-toluenesulfonic acid were added to a flask connected with a water separator, a feeding funnel and a mechanical stirrer. The mixture was stirred and heated to 120°C for reaction for 5 hours and then returned to room temperature. The reaction product was washed with a saturated sodium bicarbonate solution and then dried to obtain a hyperbranched intermediate. 6 mol of isophorone diisocyanate and 2 g of catalyst DBTDL were added to the flask. The mixture was stirred and heated to 60°C and then the hyperbranched intermediate was added. The mixture was stirred and reacted for 2 hours to obtain a hyperbranched polyisocyanate.

[0034] 40g of neopentyl glycol, 60g of terephthalic acid, 10g of adipic acid and 0.1g of monobutyltin oxide are added to the reactor, heated to 240°C under nitrogen protection, kept warm for reaction for 3h, the acid value is controlled at 12-16mgKOH / g, sampled to measure the acid value, cooled to 220°C, 10g of hyperbranched polyisocyanate is added and the reaction is continued for 1h, then 10g of a capping agent composed of fumaric acid and isophthalic acid in a mass ratio of 1:1 is added, the temperature is raised to 240°C, the reaction is continued for 2h, the acid value is controlled at 47-50mgKOH / g, vacuuming is started, the pressure is at -0.095Mpa, until the acid value is 30-36mgKOH / g, 0.5g of antioxidant 1010 and 0.5g of ethyltriphenylphosphonium bromide are added, stirred evenly, the temperature is lowered to 200°C and the material is discharged.

[0035] Comparative Example 1: The method is basically the same as Example 1, except that a commercially available polyester resin (Synthomer Albester 5148) is used instead of the homemade low-temperature curing polyester resin.

[0036] Comparative Example 2: The method is basically the same as Example 1, except that no hyperbranched polyisocyanate is added during the preparation of the low-temperature curing polyester resin.

[0037] The preparation method of low temperature curing polyester resin is as follows: Add 35g of neopentyl glycol, 55g of terephthalic acid, 3g of adipic acid and 0.05g of monobutyltin oxide into the reactor, heat to 240℃ under nitrogen protection, keep warm for 3h, control the acid value at 12-16mgKOH / g, take samples to measure the acid value, cool to 220℃, add 6g of end-capping agent composed of fumaric acid and isophthalic acid in a mass ratio of 1:1, heat to 240℃, continue to react for 2h, control the acid value at 47-50mgKOH / g, start vacuuming, the pressure is at -0.095Mpa, until the acid value is 30-36mgKOH / g, add 0.5g of antioxidant 1010 and 0.1g of curing accelerator TBAB, stir evenly and then cool to 200℃ for discharge.

[0038] Comparative Example 3: The method is basically the same as Example 1, except that sodium-montmorillonite is used instead of homemade montmorillonite.

[0039] Performance Testing The powder coatings in Examples 1-5 and Comparative Examples 1-3 were respectively sprayed uniformly onto the degreased and derusted cold-rolled steel plates using an electrostatic spray gun, baked at 150° C. for 15 min, and naturally cooled to room temperature to obtain coatings.

[0040] The impact resistance of the coating is determined according to GB / T 1732-2020; The coating hardness is measured according to GB / T 6739-2006; The gel time is tested according to HG / T 2006-2022; Tilt fluidity is tested according to GB / T 28861-2012; Adhesion is tested according to standard GB / T 9286-2021; The test results are shown in Table 1 below: Table 1:

[0041] As can be seen from Table 1 above, the powder coating prepared by the present invention can be cured at a relatively low temperature (150°C, 15 min), and the coating has excellent performance; From the comparison between Example 1 and Comparative Example 1, it can be seen that the low-temperature curing polyester resin in the powder coating of the present invention has better low-temperature curing performance than the commercially available polyester resin; From the comparison between Example 1 and Comparative Example 2, it can be seen that the addition of hyperbranched polyisocyanate greatly improves the performance of the powder coating; From the comparison between Example 1 and Comparative Example 3, it can be seen that the montmorillonite intercalated with epoxy resin has a greater improvement in the performance of the powder coating.

[0042] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low temperature curing polyester resin, characterized in that: It is prepared from the following raw materials in parts by weight: 30-40 parts of neopentyl glycol, 50-60 parts of terephthalic acid, 5-10 parts of adipic acid, 0-0.1 parts of organotin catalyst, 5-10 parts of hyperbranched polyisocyanate, 5-10 parts of end-capping agent, and 0.1-1 parts of auxiliary agent; The preparation method of the hyperbranched polyisocyanate is as follows: Trimethylolpropane and N,N-dihydroxyethyl-3-aminopropionic acid methyl ester are first reacted to obtain a hyperbranched intermediate, and the hyperbranched intermediate is then reacted with alicyclic diisocyanate to obtain the hyperbranched polyisocyanate.

2. The low temperature curing polyester resin according to claim 1, characterized in that The alicyclic diisocyanate is isophorone diisocyanate and / or dicyclohexylmethane diisocyanate.

3. The low temperature curing polyester resin according to claim 1, characterized in that The molar ratio of the trimethylolpropane, N,N-dihydroxyethyl-3-aminopropionic acid methyl ester and alicyclic diisocyanate is 1:3:

6.

4. The low temperature curing polyester resin according to claim 1, characterized in that The end-capping agent is a composition of fumaric acid and isophthalic acid in a mass ratio of 1-5:1-5.

5. The low temperature curing polyester resin according to claim 1, characterized in that The auxiliary agents include antioxidants and curing accelerators.

6. A powder coating, characterized in that: It is prepared from the following raw materials in parts by weight: 250-300 parts of the low-temperature curing polyester resin according to any one of claims 1 to 5, 20-30 parts of triglycidyl isocyanurate, 50-60 parts of montmorillonite, 15-20 parts of titanium dioxide, 80-100 parts of barium sulfate, 3-5 parts of leveling agent, 1-3 parts of benzoin, and 1-3 parts of brightener.

7. The powder coating according to claim 6, characterized in that The montmorillonite is modified by epoxy resin intercalation.

8. The powder coating according to claim 7, characterized in that The preparation method of the montmorillonite is as follows: Sodium montmorillonite is dispersed in water to obtain a suspension; dioctylamine is dissolved in ethanol, and hydrochloric acid is added and stirred to obtain a dioctylamine hydrochloride solution; the dioctylamine hydrochloride solution is added to the suspension, stirred and reacted at 50-70°C for 12-48 hours, the precipitate is collected, washed, and dried to obtain an organic montmorillonite, epoxy resin is dissolved in an organic solvent to obtain a solution, the organic montmorillonite is added, ultrasonic oscillation reflux reaction is performed for 1-10 hours, and finally the organic solvent is removed by reduced pressure distillation.

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