A low-temperature curable polyester resin and powder coating

Abstract

The present invention relates to the field of polyester resin materials, and specifically to a low-temperature curing polyester resin and a powder coating. 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, 0-0.1 part of an organotin catalyst, 5-10 parts of a hyperbranched polyisocyanate, 5-10 parts of a blocking agent, and 0.1-1 part of an auxiliary agent; the hyperbranched polyisocyanate is prepared from trimethylolpropane, N,N-dihydroxyethyl-3-aminopropionate methyl ester, and an alicyclic diisocyanate. The powder coating prepared by the present invention can be cured at a lower temperature, and the coating has excellent properties, and has a wide application prospect in the fields of building materials aluminum and construction machinery.

Description

Technical Field

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

[0002] Powder coatings with triglycidyl isocyanurate (TGIC) as the curing agent have the characteristics of good surface decoration, mechanical properties, weather resistance and yellowing resistance, and are widely used in the fields of building materials, aluminum profiles and construction machinery. The curing temperature of commercially available TGIC-based powder coatings is relatively high, generally 190 - 230°C. High-temperature curing mainly has the following defects:

[0003] High curing energy consumption and high coating cost; limited use for thick workpieces and heat-sensitive substrates; slow cooling rate of workpieces and low coating efficiency.

[0004] In order to overcome the above defects, the powder coating industry is committed to developing TGIC-based powder coatings with low-temperature curing. Currently, the main technical means is to use highly active polyester resins, but commercially available low-temperature curing polyester resins have weak leveling properties, mechanical properties and stability, and the above defects limit the application scenarios of low-temperature curing powder coatings. Summary of the Invention

[0005] Object of the Invention: Aiming at the above technical problems, the present invention provides a low-temperature curing polyester resin and a powder coating.

[0006] The technical solution adopted is as follows:

[0007] A low-temperature curing polyester resin is prepared from the following raw materials in parts by weight:

[0008] 30 - 40 parts of neopentyl glycol, 50 - 60 parts of terephthalic acid, 5 - 10 parts of adipic acid, 0 - 0.1 part of organotin catalyst, 5 - 10 parts of hyperbranched polyisocyanate, 5 - 10 parts of capping agent, 0.1 - 1 part of auxiliary agent;

[0009] The preparation method of the hyperbranched polyisocyanate is as follows:

[0010] Trimethylolpropane reacts with N,N - dihydroxyethyl - 3 - aminopropionate methyl ester first to obtain a hyperbranched intermediate, and the hyperbranched intermediate then reacts with an alicyclic diisocyanate to obtain the hyperbranched polyisocyanate.

[0011] Further, the low-temperature curing polyester resin is prepared from the following raw materials in parts by weight:

[0012] 30 - 40 parts of neopentyl glycol, 50 - 60 parts of terephthalic acid, 5 - 10 parts of adipic acid, 0.001 - 0.1 part of organotin catalyst, 5 - 10 parts of hyperbranched polyisocyanate, 5 - 10 parts of capping agent, 0.1 - 1 part of auxiliary agent.

[0013] Further, the alicyclic diisocyanate is isophorone diisocyanate and / or dicyclohexylmethane diisocyanate.

[0014] Further, the molar ratio of trimethylolpropane, N,N - bis(2 - hydroxyethyl)-3 - aminopropionate methyl ester and alicyclic diisocyanate is 1:3:6.

[0015] Further, the capping agent is a composition of fumaric acid and isophthalic acid with a mass ratio of 1 - 5:1 - 5.

[0016] Further, the organotin catalyst is at least one of monobutyltin oxide, dibutyltin oxide, and stannous octoate.

[0017] Further, the auxiliary agent includes an antioxidant and a curing accelerator.

[0018] Furthermore, the antioxidant is a hindered phenol antioxidant, preferably antioxidant 1010.

[0019] Furthermore, the curing accelerator is a quaternary phosphonium salt curing agent, preferably ethyltriphenylphosphonium bromide.

[0020] The present invention also provides a powder coating, which is prepared from the following raw materials in parts by weight:

[0021] 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 brightening agent.

[0022] Further, the montmorillonite is treated by intercalation modification with epoxy resin.

[0023] Further, the preparation method of the montmorillonite is as follows:

[0024] Take sodium - based montmorillonite and disperse it in water to obtain a suspension; dissolve dioctylamine in ethanol, then add hydrochloric acid and stir to obtain a dioctylamine hydrochloride solution; add the dioctylamine hydrochloride solution to the suspension, stir and react at 50 - 70 °C for 12 - 48 h, collect the precipitate, wash, and dry to obtain organophilic montmorillonite. Dissolve epoxy resin in an organic solvent to obtain a solution, then add the organophilic montmorillonite, carry out ultrasonic oscillation and reflux reaction for 1 - 10 h, and finally remove the organic solvent by vacuum distillation.

[0025] The present invention has the following beneficial effects:

[0026] The present invention adds hyperbranched polyisocyanate as one of the raw materials to 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 more fluid, thereby reducing viscosity and improving the leveling property. Moreover, a large number of terminal isocyanate groups contained can react with dibasic acids and diols to form a three-dimensional crosslinked network, increasing the crosslinking density of the polyester resin, and further improving the hardness and impact resistance of the cured coating. Both the curing temperature and curing time are reduced, showing low-temperature curing performance;

[0027] Fumaric acid has both unsaturated double bonds and a dibasic acid structure. It participates in the main chain polycondensation and also improves the impact resistance and flexibility of the polyester resin by adding an excessive amount of blocked terminal hydroxyl groups. Using fumaric acid as the end-capping agent can improve the impact resistance and flexibility of the polyester resin. Isophthalic acid can endow the polyester resin with higher heat resistance and chemical resistance. The two cooperate as end-capping agents to improve the comprehensive performance of the polyester resin;

[0028] Montmorillonite significantly improves the mechanical strength, heat resistance, weather resistance and processing performance of the coating through nano-reinforcement, barrier effect and functional synergy in powder coatings. In the present invention, it is intercalated with epoxy resin. By using the method of cation exchange in an aqueous medium, dioctylamine is introduced into the interlayer of montmorillonite to displace sodium ions, increasing the interlayer spacing of montmorillonite. Epoxy resin is inserted into the montmorillonite interlayer through crosslinking with amino groups. During the curing process of the powder coating, the excess epoxy groups in the montmorillonite interlayer can participate in the crosslinking of the polyester resin and triglycidyl isocyanurate, improving the curing rate and curing strength of the coating.

[0029] The powder coating prepared by the present invention can be cured at a lower temperature, and the coating has excellent properties, showing broad application prospects in the fields of building materials aluminum and construction machinery. Description of the Drawings

[0030] Figure 1 It is the synthesis route diagram of hyperbranched polyisocyanate in Example 1. Detailed Description of the Invention

[0031] For those not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase. Technologies not mentioned in the present invention refer to the prior art. Unless otherwise specified, the following examples and comparative examples are parallel tests and adopt the same treatment steps and parameters.

[0032] Example 1:

[0033] A powder coating is prepared from the following raw materials in parts by weight:

[0034] 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.

[0035] Wherein, the preparation method of low temperature curing polyester resin is as follows:

[0036] 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.

[0037] 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.

[0038] The preparation method of montmorillonite is as follows:

[0039] 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.

[0040] The preparation method of the above powder coating is as follows:

[0041] 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.

[0042] Example 2:

[0043] A powder coating is prepared from the following raw materials in parts by weight:

[0044] 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 brightening agent XSL-701.

[0045] Among them, the preparation methods of the low-temperature curing polyester resin and montmorillonite are the same as those in Example 1;

[0046] The preparation method of the above powder coating is as follows:

[0047] Mix the raw materials evenly according to the formula amount, then add them to a twin-screw extruder for mixing and extrusion, cool, crush, grind into powder, and sieve.

[0048] Example 3:

[0049] A powder coating is prepared from the following raw materials in parts by weight:

[0050] 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 brightening agent XSL-701.

[0051] Among them, the preparation methods of the low-temperature curing polyester resin and montmorillonite are the same as those in Example 1;

[0052] The preparation method of the above powder coating is as follows:

[0053] Mix the raw materials evenly according to the formula amount, then add them to a twin-screw extruder for mixing and extrusion, cool, crush, grind into powder, and sieve.

[0054] Example 4:

[0055] It is basically the same as Example 1, except that the preparation method of the low-temperature curing polyester resin is as follows:

[0056] Add 1 mol of trimethylolpropane, 3 mol of N,N-dihydroxyethyl-3-aminopropionate methyl ester, and 1 g of p-toluenesulfonic acid into a flask equipped with a water separator, a feeding funnel, and mechanical stirring. Stir and heat to 120 °C for 5 h, then restore to room temperature. Wash the reaction product with saturated sodium bicarbonate solution and dry to obtain a hyperbranched intermediate. Add 6 mol of isophorone diisocyanate and 2 g of catalyst DBTDL into the flask, stir and heat to 60 °C, then add the hyperbranched intermediate, and stir and react for 2 h to obtain a hyperbranched polyisocyanate.

[0057] Add 30 g of neopentyl glycol, 50 g of terephthalic acid, 5 g of adipic acid and 0.001 g of monobutyltin oxide into a reaction kettle, heat to 240 °C under nitrogen protection, keep the temperature for reaction for 3 h, control the acid value at 12 - 16 mgKOH / g. After sampling to measure the acid value, cool down to 220 °C, add 5 g of hyperbranched polyisocyanate and continue to react for 1 h, then add 5 g of a capping agent composed of fumaric acid and isophthalic acid with a mass ratio of 1:1, raise the temperature to 240 °C, continue to react for 2 h, control the acid value at 47 - 50 mgKOH / g, start to evacuate, the pressure is -0.095 Mpa until the acid value is 30 - 36 mgKOH / g, add 0.05 g of antioxidant 1010 and 0.05 g of ethyltriphenylphosphonium bromide, stir evenly and then cool down to 200 °C to discharge.

[0058] Example 5:

[0059] It is basically the same as Example 1, the difference is that the preparation method of the low-temperature curing polyester resin is as follows:

[0060] Add 1 mol of trimethylolpropane, 3 mol of N,N-dihydroxyethyl-3-aminopropionate methyl ester and 1 g of p-toluenesulfonic acid into a flask equipped with a water separator, a feeding funnel and a mechanical stirrer, stir and heat to 120 °C for reaction for 5 h, then restore to room temperature. The reaction product is washed with saturated sodium bicarbonate solution and dried to obtain a hyperbranched intermediate. Add 6 mol of isophorone diisocyanate and 2 g of catalyst DBTDL into the flask, stir and heat to 60 °C, then add the hyperbranched intermediate, and stir and react for 2 h to obtain a hyperbranched polyisocyanate.

[0061] Add 40 g of neopentyl glycol, 60 g of terephthalic acid, 10 g of adipic acid and 0.1 g of monobutyltin oxide into a reaction kettle, heat to 240 °C under nitrogen protection, keep the temperature for reaction for 3 h, control the acid value at 12 - 16 mgKOH / g. After sampling to measure the acid value, cool down to 220 °C, add 10 g of hyperbranched polyisocyanate and continue to react for 1 h, then add 10 g of a capping agent composed of fumaric acid and isophthalic acid with a mass ratio of 1:1, raise the temperature to 240 °C, continue to react for 2 h, control the acid value at 47 - 50 mgKOH / g, start to evacuate, the pressure is -0.095 Mpa until the acid value is 30 - 36 mgKOH / g, add 0.5 g of antioxidant 1010 and 0.5 g of ethyltriphenylphosphonium bromide, stir evenly and then cool down to 200 °C to discharge.

[0062] Comparative Example 1:

[0063] It is basically the same as Example 1, the difference is that a commercially available polyester resin (Synthomer Albester 5148) is used instead of the self-made low-temperature curing polyester resin.

[0064] Comparative Example 2:

[0065] It is basically the same as Example 1, except that hyperbranched polyisocyanate is not added during the preparation of the low-temperature curing polyester resin.

[0066] The preparation method of the low-temperature curing polyester resin is as follows:

[0067] Add 35 g of neopentyl glycol, 55 g of terephthalic acid, 3 g of adipic acid, and 0.05 g of monobutyltin oxide to the reaction kettle, heat to 240 °C under nitrogen protection, hold the reaction for 3 h, control the acid value at 12 - 16 mgKOH / g. After sampling and measuring the acid value, cool down to 220 °C, add 6 g of a capping agent composed of fumaric acid and isophthalic acid with a mass ratio of 1:1, heat up to 240 °C, and continue the reaction for 2 h. Control the acid value at 47 - 50 mgKOH / g, start to evacuate, with the pressure at -0.095 Mpa until the acid value is 30 - 36 mgKOH / g. Add 0.5 g of antioxidant 1010 and 0.1 g of curing accelerator TBAB, stir evenly, and then cool down to 200 °C for discharging.

[0068] Comparative Example 3:

[0069] It is basically the same as Example 1, except that sodium-based montmorillonite is used instead of the self-made montmorillonite.

[0070] Performance Test

[0071] Spray the powder coatings in Examples 1 - 5 and Comparative Examples 1 - 3 evenly onto the degreased and derusted cold-rolled steel plates with an electrostatic spray gun. After baking at 150 °C for 15 min, cool naturally to room temperature to obtain the coatings.

[0072] The impact resistance of the coating is measured according to GB / T 1732 - 2020;

[0073] The hardness of the coating is measured according to GB / T 6739 - 2006;

[0074] The gelling time is tested according to HG / T 2006 - 2022;

[0075] The inclined fluidity is tested according to GB / T 28861 - 2012;

[0076] The adhesion is tested according to the standard GB / T 9286 - 2021;

[0077] The test results are shown in Table 1 below:

[0078] Table 1:

[0079]

[0080] 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 properties;

[0081] 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;

[0082] From the comparison between Example 1 and Comparative Example 2, it can be seen that the addition of hyperbranched polyisocyanate has greatly improved the performance of the powder coating;

[0083] 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.

[0084] The above examples are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing examples, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various 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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