Aqueous modified polyester dispersions and coatings and methods for their preparation

Abstract

The application discloses a water-based modified polyester dispersion and a coating and a preparation method thereof. The water-based modified polyester dispersion comprises the following raw material components: a polyether monoamine, an epoxy resin, dimethylbutyric acid and / or dimethylpropionic acid, tetrabutylammonium bromide, a polybasic acid, a polyhydric alcohol, a dibasic acid anhydride and an esterification catalyst. The water-based modified polyester dispersion prepared by the application has a volatile content of zero, good storage stability, and the obtained water-based coating has good water boiling resistance, impact resistance, T-bending resistance, acid and alkali resistance, and excellent comprehensive performance.

Description

Technical Field

[0001] This invention relates to the field of waterborne polyesters, and more specifically, to waterborne modified polyester dispersions and their preparation methods. Background Technology

[0002] Coil coatings are specialized coatings used to coat the surfaces of substrates such as steel and aluminum plates to create pre-coated coils. Statistics show that polyester systems are the most widely used in coil coatings, accounting for approximately 60%, with the remainder including PVC plastisol, PVDF, and silicone-modified polyester. Polyester resins cross-linked and cured with amino resins or end-capped isocyanates produce films with high hardness, good flexibility, and are the most widely used. In recent years, with increasingly stringent environmental policies, the development of UV-curable coil coatings and water-based coil coatings has flourished.

[0003] However, most of the current water-based polyester technologies involve introducing ionic groups into the polyester molecular chain to make it hydrophilic, and most of them contain 20% to 40% alcohol ether cosolvents or a certain amount of amine neutralizers (such as dimethylethanolamine), resulting in a high VOC (volatile organic compound) content. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a modified waterborne polyester dispersion and coating and a method for preparing the same, wherein the modified waterborne polyester dispersion has excellent performance and is completely free of volatiles.

[0005] The technical solution of the present invention is as follows:

[0006] A waterborne modified polyester dispersion comprising the following raw material components: polyether monoamine, epoxy resin, dimethylolbutyric acid and / or dimethylolpropionic acid, tetrabutylammonium bromide, polybasic acid, polyol, diacid anhydride and esterification catalyst.

[0007] Preferably, the molar ratio of the hydroxyl groups in the polyol to the carboxyl groups in the polyacid is 1.05 to 1.25:1, the molar amount of the diacid anhydride is 40-80% of the excess hydroxyl group molar amount, and the excess hydroxyl group molar amount is equal to the molar amount of the hydroxyl groups in the polyol minus the molar amount of the carboxyl groups in the polyacid.

[0008] Preferably, the molar ratio of the polyether monoamine, dimethylolbutyric acid and / or dimethylolpropionic acid, epoxy resin and diacid anhydride is 1:1:1:1-1.15.

[0009] Preferably, the mass of the tetrabutylammonium bromide is 0.1-0.5% of the total mass of the raw material components.

[0010] Preferably, the mass of the esterification catalyst is 0.1-0.5% of the total mass of the polyacid and the polyol.

[0011] Preferably, the aqueous modified polyester dispersion further includes an antioxidant, wherein the mass of the antioxidant is 0.1-0.5% of the total mass of the polyacid and the polyol.

[0012] Preferably, the antioxidant is selected from hypophosphite and / or triphenyl phosphite.

[0013] Preferably, the polyol is selected from one or more of neopentyl glycol, trimethylolpropane, 3-methyl-1,5-pentanediol, 1,4-cyclohexanediol, 2-ethyl-1,3-hexanediol, hexanediol, and 2-butyl-2-ethyl-1,3-propanediol.

[0014] Preferably, the polyacid is selected from one or more of the following: azelaic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic anhydride, and hexahydrophthalic anhydride.

[0015] Preferably, the catalyst is selected from one or more of dibutyltin oxide, dibutyltin dilaurate, and tetraisopropyl titanate.

[0016] Preferably, the dicarboxylic acid anhydride is selected from one or more of phthalic anhydride, maleic anhydride, tetrahydrophthalic anhydride, and hexahydrophthalic anhydride.

[0017] Preferably, the polyether monoamine has an amine value of 0.30-1.08 and / or a molecular weight of 1000-3000.

[0018] Preferably, the epoxy resin is a bisphenol A epoxy resin and / or a bisphenol F epoxy resin with an epoxy equivalent of 450 to 1700.

[0019] This invention further provides a method for preparing the above-mentioned aqueous modified polyester dispersion, comprising:

[0020] (1) The polyether monoamine and the dimethylolbutyric acid and / or dimethylolpropionic acid are reacted at 150-200°C until no more water is released and the residual solvent is removed by vacuum. Then the epoxy resin is added and reacted at 120-130°C to obtain a monoepoxy hydrophilic polymer.

[0021] (2) The polyacid and polyol are heated to 145-155℃ under an inert atmosphere, the esterification catalyst is added, the temperature is raised to 180-220℃ and the reaction continues until the acid value reaches 2-10 mgKOH / g, the temperature is lowered to 140-160℃ and the diacid anhydride is added, the reaction continues for 1-1.5h, the monoepoxy hydrophilic polymer and tetrabutylammonium bromide are added, the reaction continues at 140-160℃ until the acid value no longer decreases, and the modified polyester resin is obtained;

[0022] (3) The modified polyester resin is dissolved in deionized water at 70-90°C to obtain the water-based modified polyester dispersion.

[0023] Preferably, step (2) further includes heating the antioxidant and the polyacid and polyol to 145-155°C under an inert atmosphere.

[0024] Based on the above water-based modified polyester dispersion, the present invention can further obtain a water-based coating with zero volatile matter, which has excellent environmental performance, and is also resistant to boiling water, impact, T-bending, acid and alkali, and methyl ethyl ketone (MEK) wiping.

[0025] In the aqueous modified polyester dispersion and its preparation method of the present invention, a hydrophilic mono-epoxy hydrophilic polymer with excellent hydrophilicity can be obtained by reacting the primary amino group of polyether monoamine with the carboxyl group of dimethylolbutyric acid and / or dimethylolpropionic acid, and by reacting the secondary amino group with epoxy resin. Furthermore, polybasic acid and polyol can synthesize hydroxyl-terminated polyester resin, and diacid anhydride can react with hydroxyl groups to obtain carboxyl-terminated polyester. Finally, the carboxyl-terminated group of polyester resin is grafted with the mono-epoxy hydrophilic polymer, and hydrophilization is achieved through the nonionic hydrophilic segments on the mono-epoxy hydrophilic polymer. The synthesis does not require the addition of cosolvents and amine neutralizers, thus achieving a completely volatile-free preparation. At the same time, in each raw material component, epoxy resin, dimethylolbutyric acid and / or dimethylolpropionic acid can introduce more highly active hydroxyl groups, increase the crosslinking density after the material reacts with amino resin, and improve its hardness and toughness. Meanwhile, the polyether segments of polyether monoamine can provide flexibility, achieving a balance between hardness and toughness, and obtaining an aqueous modified polyester dispersion with excellent performance and storage stability. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0027] Example 1

[0028] The aqueous modified polyester dispersion was prepared by the following steps:

[0029] (1) 83.4g of polyether monoamine with a molecular weight of 1000 and 12.4g of dimethylolbutyric acid were refluxed at 180-190℃ until no more water was released. The reflux solvent was removed by vacuum, and then 32.7g of epoxy resin E51 was added. The mixture was reacted at 120-130℃ until the active hydrogen was completely reacted to obtain monoepoxy hydrophilic polymer B.

[0030] (2) 40g adipic acid, 70g isophthalic acid, 71.3g 3-methyl-1,5-pentanediol, 37.3g 1,4-cyclohexanediol and 0.5g triphenyl phosphite were heated to 150℃ under nitrogen protection. 0.4g dibutyltin oxide was added and the temperature was raised to 195-205℃. The reaction was carried out until the acid value was 2-5mgKOH / g. The temperature was lowered to 140-150℃ and 12.4g phthalic anhydride was added. The reaction was carried out for 1.5h. Then polymer B and 0.2g tetrabutylammonium bromide were added for end-capping reaction. The reaction was carried out at 150-160℃ until the acid value no longer decreased. The temperature was lowered to obtain modified polyester resin A.

[0031] (3) Heat 539g of deionized water to 75-85℃, add modified polyester resin A while stirring to dissolve, and obtain a zero-VOC waterborne modified polyester dispersion.

[0032] Example 2

[0033] The aqueous modified polyester dispersion was prepared by the following steps:

[0034] (1) 65.4g of polyether monoamine with a molecular weight of 2000 and 4.4g of dimethylolpropionic acid were refluxed at 190-200℃. After the reaction was stopped, the reflux solvent was removed by vacuum, and then 14.9g of epoxy resin E44 was added. The reaction was carried out at 120-130℃ until the active hydrogen was completely reacted to obtain monoepoxy hydrophilic polymer B.

[0035] (2) 40g of hexahydrophthalic anhydride, 70g of isophthalic acid, 61.1g of 2-butyl-2-ethyl-1,3-propanediol, 45.1g of 3-methyl-1,5-pentanediol and 0.3g of triphenyl phosphite were heated to 150℃ under nitrogen protection. 0.4g of dibutyltin oxide was added and the temperature was raised to 195-205℃. The reaction was continued until the acid value was 2-5mgKOH / g. The temperature was lowered to 150-160℃ and 3.2g of maleic anhydride was added. The reaction was carried out for 1h. Then, polymer B obtained above in S1 and 0.2g of tetrabutylammonium bromide were added for end-capping reaction. The reaction was carried out at 150-160℃ until the acid value no longer decreased. The temperature was lowered to obtain modified polyester resin A.

[0036] (3) Heat 456g of deionized water to 75-85℃, add modified polyester resin A while stirring to dissolve, and obtain a zero-VOC waterborne modified polyester dispersion.

[0037] Example 3

[0038] The aqueous modified polyester dispersion was prepared by the following steps:

[0039] (1) 15.8g of polyether monoamine with a molecular weight of 1000, 47.5g of polyether monoamine with a molecular weight of 3000 and 4.7g of dimethylolbutyric acid were refluxed at 180-190℃. After the reaction was stopped, the reflux solvent was removed by vacuum. Then 31.6g of epoxy resin E20 was added and the reaction was carried out at 120-130℃ until the active hydrogen was completely reacted to obtain monoepoxy hydrophilic polymer B.

[0040] (2) 50g adipic acid, 60g isophthalic acid, 39.9g neopentyl glycol, 90.6g 3-methyl-1,5-pentanediol and 0.3g triphenyl phosphite were heated to 150℃ under nitrogen protection. 0.5g dibutyltin oxide was added and the temperature was raised to 210-220℃. The reaction was continued until the acid value was 4-7mgKOH / g. The temperature was lowered to 140-150℃ and 3.1g maleic anhydride was added. The reaction was carried out for 1.5h. Then polymer B and 0.2g tetrabutylammonium bromide were added for end-capping reaction. The reaction was carried out at 145-155℃ until the acid value no longer decreased. The temperature was lowered to obtain modified polyester resin A.

[0041] (3) Heat 531g of deionized water to 70-80℃, add modified polyester resin A while stirring to dissolve, and obtain a zero-VOC waterborne modified polyester dispersion.

[0042] Example 4

[0043] The aqueous modified polyester dispersion was prepared by the following steps:

[0044] (1) 6.5g of polyether monoamine with a molecular weight of 1000, 45.7g of polyether monoamine with a molecular weight of 3000 and 3.2g of dimethylolbutyric acid were refluxed at 175-185℃. After the reaction was stopped, the reflux solvent was removed by vacuum. Then 21.8g of epoxy resin E20 was added and the reaction was carried out at 120-130℃ until the active hydrogen was completely reacted to obtain monoepoxy hydrophilic polymer B.

[0045] (2) 30g adipic acid, 80g 1,4-cyclohexanedicarboxylic acid, 56.4g 2-butyl-2-ethyl-1,3-propanediol, 41.6g 3-methyl-1,5-pentanediol and 0.3g hypophosphoric acid were heated to 150℃ under nitrogen protection. 0.6g dibutyltin dilaurate was added and the temperature was raised to 210-220℃. The reaction was carried out until the acid value was 4-7mgKOH / . The temperature was lowered to 150-160℃ and 3.3g tetrahydrophthalic anhydride was added. The reaction was carried out for 1h. Then polymer B and 0.3g tetrabutylammonium bromide were added for end-capping reaction. The reaction was carried out at 145-155℃ until the acid value no longer decreased. The temperature was lowered to obtain modified polyester resin A.

[0046] (3) Heat 439g of deionized water to 70-80℃, add modified polyester resin A while stirring to dissolve, and obtain a zero-VOC waterborne modified polyester dispersion.

[0047] Comparative Example 1

[0048] Aqueous modified polyester dispersions were prepared using a process similar to that in Example 1, except that: in step (1), 58.4 g of polyether monoamine with a molecular weight of 1000, 8.7 g of dimethylolbutyric acid, and 58.4 g of epoxy resin E20 were used; and in step (3), 529 g of deionized water was used.

[0049] Comparative Example 2

[0050] Aqueous modified polyester dispersions were prepared using a process similar to that in Example 2, except that: in step (1), 130.7 g of polyether monoamine with a molecular weight of 2000, 8.8 g of dimethylolpropionic acid, and 29.7 g of epoxy resin E44 were used; and in step (3), 587.6 g of deionized water was used.

[0051] Comparative Example 3

[0052] The aqueous modified polyester dispersion was prepared using a process similar to that in Example 2, except that: in step (2), 73.6 g of 2-butyl-2-ethyl-1,3-propanediol, 54.3 g of 3-methyl-1,5-pentanediol, and 11.7 g of maleic anhydride were used; and in step (3), 741.1 g of deionized water was used.

[0053] The basic properties of the waterborne modified polyester dispersions obtained in Examples 1-4 and Comparative Examples 1-3 were tested, and the results are shown in Table 1 below:

[0054] Table 1. Test results of basic indicators of waterborne modified polyester dispersions

[0055]

[0056]

[0057] The method for testing the storage stability at 50℃ is as follows: the dispersion is placed in a 500ml container, sealed tightly, and stored in a 50℃ constant temperature oven. After cooling at room temperature for 3 hours, the dispersion is observed to see if it separates into layers or produces coarse particles. If no separation or coarse particles are produced, the storage is considered stable.

[0058] Furthermore, the obtained water-based modified polyester dispersion was added to the coating, and the film performance was tested using the following method:

[0059] (1) Mix 50 parts by weight of water-based modified polyester dispersion, 9 parts by weight of amino resin (303), 0.2 parts by weight of wetting agent Tego-4100, 0.2 parts by weight of defoamer, 0.3 parts by weight of anti-flash rust agent, 0.3 parts by weight of adhesion promoter, 0.2 parts by weight of acid catalyst, 30 parts by weight of resin-free white water slurry, and 10 parts by weight of deionized water evenly to obtain a coating.

[0060] (2) Apply the prepared coating onto the degreased aluminum substrate using a scraper, bake at 235℃ for 100-120s, and test the film performance according to the test method in HG / T3830-2022. The test results are shown in Table 2 below:

[0061] Table 2 Results of Coating Film Performance Tests

[0062]

[0063]

[0064] It can be seen that the coating film performance of Examples 1-4 is better than that of Comparative Examples 2 and 3.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an aqueous modified polyester dispersion, characterized in that, It includes: (1) Polyether monoamine and dimethylolbutyric acid and / or dimethylolpropionic acid are reacted at 150-200℃ until no more water is released and the residual solvent is removed by vacuum. Then epoxy resin is added and reacted at 120-130℃ to obtain a monoepoxy hydrophilic polymer. (2) The polyacid and polyol are heated to 145-155℃ under an inert atmosphere, an esterification catalyst is added, the temperature is raised to 180-220℃ and the reaction continues until the acid value reaches 2-10 mgKOH / g. The temperature is lowered to 140-160℃ and a diacid anhydride is added. The reaction continues for 1-1.5 h. Then the monoepoxy hydrophilic polymer and tetrabutylammonium bromide are added and the reaction continues at 140-160℃ until the acid value no longer decreases, thus obtaining the modified polyester resin. (3) The modified polyester resin is dissolved in deionized water at 70-90°C to obtain the aqueous modified polyester dispersion. Wherein, the polyol is selected from one or more of neopentyl glycol, trimethylolpropane, 3-methyl-1,5-pentanediol, 1,4-cyclohexanediol, 2-ethyl-1,3-hexanediol, hexanediol, and 2-butyl-2-ethyl-1,3-propanediol; the polyacid is selected from one or more of picric acid, azelaic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic anhydride, and hexahydrophthalic anhydride; the esterification catalyst is selected from one or more of dibutyltin oxide, dibutyltin dilaurate, and tetraisopropyl titanate; the diacid anhydride is selected from one or more of phthalic anhydride, maleic anhydride, tetrahydrophthalic anhydride, and hexahydrophthalic anhydride; the molar ratio of the hydroxyl group in the polyol to the carboxyl group in the polyacid is 1.05–1.25:

1. The molar amount of the diacid anhydride is 40-80% of the molar amount of excess alcohol hydroxyl groups, wherein the molar amount of excess alcohol hydroxyl groups is equal to the molar amount of hydroxyl groups in the polyol minus the molar amount of carboxyl groups in the polyacid; the molar ratio of the polyether monoamine, the dimethylolbutyric acid and / or dimethylolpropionic acid, the epoxy resin and the diacid anhydride is 1:1:1:1-1.15; the mass of the tetrabutylammonium bromide is 0.1-0.5% of the total mass of the raw material components; the mass of the esterification catalyst is 0.1-0.5% of the total mass of the polyacid and the polyol; the amine value of the polyether monoamine is 0.30-1.08 and / or its molecular weight is 1000-3000; the epoxy resin is selected from one or more of epoxy resin E51, epoxy resin E44, and epoxy resin E20.

2. The preparation method according to claim 1, characterized in that, Step (2) also includes heating the antioxidant and the polyacid and polyol to 145-155°C under an inert atmosphere.

3. The preparation method according to claim 2, characterized in that, The antioxidant is 0.1-0.5% of the total mass of the polyacid and the polyol.

4. The preparation method according to claim 3, characterized in that, The antioxidant is selected from hypophosphite and / or triphenyl phosphite.

5. The aqueous modified polyester dispersion prepared by the method according to any one of claims 1-4.

6. A zero-volatile waterborne coating comprising the waterborne modified polyester dispersion of claim 5 and an amino resin.

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