A polyester powder coating and a method for its preparation

Abstract

The application discloses polyester powder coating and a preparation method thereof, and relates to the field of advanced petrochemical chemical new materials. The polyester powder coating is prepared from the following raw materials in parts by weight: 560-595 parts of carboxyl polyester resin, 70-80 parts of epoxy modified silicone resin, 30-40 parts of HAA curing agent, 0.1-0.2 parts of accelerator, 1-2 parts of blocked isocyanate, 150-180 parts of modified pigment filler, 8-12 parts of leveling agent, and 1.5-2.5 parts of degassing agent. The unblocking temperature of the blocked isocyanate is 130-150 DEG C. The modified pigment filler is prepared from a hydroxyl-terminated hyperbranched polyester, an isocyanate-based silane coupling agent and a pigment filler. The application guarantees the smoothness of the coating through cooperation of the components and reasonable proportioning of the components, the powder coating can be cured at 150 DEG C, the energy consumption is greatly reduced, and meanwhile, the application is also favorable for preventing the problems of yellowing or pinhole formation of the coating due to high temperature.

Description

Technical Field

[0001] This application relates to the field of advanced petrochemical new materials, and in particular to a polyester powder coating and its preparation method. Background Technology

[0002] Polyester powder coatings, as an environmentally friendly coating material, have been widely used in the field of metal surface protection and decoration in recent years.

[0003] Traditional polyester powder coatings are typically made from carboxyl polyester resins, triglycidyl isocyanurate, pigments, fillers, and other additives. However, their curing temperature usually needs to reach above 190℃, resulting in high energy consumption. Furthermore, prolonged baking at high temperatures can easily lead to yellowing or pinholes in the coating, affecting its appearance. In addition, conventional pigments and fillers have poor compatibility and dispersibility with the resin matrix, easily causing agglomeration and resulting in orange peel texture and poor toughness in the coating. Summary of the Invention

[0004] In order to improve the above-mentioned problems of polyester powder coatings in related technologies, this application provides a polyester powder coating and a method for preparing the same.

[0005] Firstly, the polyester powder coating provided in this application adopts the following technical solution:

[0006] A polyester powder coating is prepared from the following raw materials in parts by weight: 560-595 parts carboxylated polyester resin, 70-80 parts epoxy-modified silicone resin, 30-40 parts HAA curing agent, 0.1-0.2 parts accelerator, 1-2 parts blocked isocyanate, 150-180 parts modified pigments and fillers, 8-12 parts leveling agent, and 1.5-2.5 parts degassing agent;

[0007] The unblocking temperature of the blocked isocyanate is 130-150℃;

[0008] The modified pigments and fillers are prepared from hydroxyl-terminated hyperbranched polyester, isocyanate-based silane coupling agent, and pigments and fillers.

[0009] This application incorporates epoxy-modified silicone resin and blocked isocyanate into existing polyester powder coatings, replacing traditional pigments and fillers with modified pigments and fillers. The proportions of each component are adjusted according to the composition of this application. Specifically, the modified pigments and fillers obtained by co-modifying the pigments and fillers with terminal hydroxyl hyperbranched polyester and isocyanate silane coupling agents, replacing traditional pigments and fillers, improves the flowability of the pigments and fillers, enhances their dispersibility in carboxylated polyesters, and prevents the orange peel problem in the coating. The blocked isocyanate can react with the hydroxyl groups in the modified pigments and fillers and the carboxyl groups in the carboxylated polyester resin, improving the interfacial bonding strength and toughness between the pigments and fillers and the carboxylated polyester resin. However, it should be noted that the addition of blocked isocyanate should not be excessive, as excessive amounts can easily lead to a decrease in coating toughness. The addition of epoxy-modified silicone resin can improve the toughness of the coating. On the other hand, by utilizing the reaction between the epoxy groups in the epoxy-modified silicone resin and the carboxyl groups in the carboxyl polyester resin, the compatibility between the epoxy-modified silicone resin and the carboxyl polyester resin can be improved. This effectively enhances the high-temperature resistance of the epoxy-modified silicone resin and prevents the coating from yellowing easily at high temperatures.

[0010] Furthermore, through the combination of various components and their reasonable proportions, this application enables the molten material to have good fluidity, promotes the smooth discharge of gas in the molten material, and ensures the smoothness, flatness, and toughness of the coating. In addition, the curing agent used in this application is HAA curing agent, which enables the powder coating to be cured at 150°C. Compared with the traditional curing at 190°C or above, this greatly reduces energy consumption and also helps to prevent the coating from yellowing or developing pinholes due to high temperature.

[0011] In some specific embodiments, the weight ratio of the terminal hydroxyl hyperbranched polyester, isocyanate-based silane coupling agent, and pigments / fillers is (15-20):(0.25-0.5):10.

[0012] In this application, the preferred weight ratio of the controlled-end hydroxyl hyperbranched polyester, isocyanate-based silane coupling agent, and pigments and fillers is in the range of (15-20):(0.25-0.5):10. This can improve the dispersibility of the modified pigments and fillers while utilizing the reaction between the residual hydroxyl groups in the modified pigments and fillers and the unblocked isocyanate, thereby enhancing the interfacial bonding strength and toughness between the pigments and fillers and the carboxyl polyester resin.

[0013] In some specific embodiments, the hydroxyl-terminated hyperbranched polyester has a hydroxyl value of 80-100 mgKOH / g and a number-average molecular weight of 6000-10000 g / mol.

[0014] In this application, the preferred hydroxyl-terminated hyperbranched polyester has a hydroxyl value and number-average molecular weight within the above-mentioned range, which is beneficial to further improve the toughness of the coating.

[0015] In some specific embodiments, the pigments and fillers include titanium dioxide, nano-silica and nano-calcium carbonate, and the weight ratio of titanium dioxide, nano-silica and nano-calcium carbonate is (3-4):(2-3):(3-5).

[0016] In some specific embodiments, the modified pigments and fillers are prepared by the following methods:

[0017] Isocyanate-based silane coupling agent is dissolved in solvent, pigments and fillers are added, and the mixture is stirred at 50-65℃ for 1-2 hours. Then, the mixture is filtered, and the filter residue is washed and dried to obtain organosilicon-modified pigments and fillers.

[0018] Hydroxyl-terminated hyperbranched polyester was added to the organosilicon-modified pigments and fillers, and the mixture was ball-milled at 40-60℃ for 20-60 min to obtain the modified pigments and fillers.

[0019] In this application, the modified pigments and fillers are prepared using the above method, which is beneficial to improving the modification effect of the pigments and fillers and promoting the uniform dispersion of the modified pigments and fillers in carboxylated polyester resin.

[0020] In some specific embodiments, the solvent is at least one of diethylene glycol dimethyl ether and ethylene glycol dimethyl ether.

[0021] In some specific embodiments, the epoxy value of the epoxy-modified silicone resin is 0.02-0.16 eq / 100g.

[0022] In this application, the epoxy value of the epoxy-modified silicone resin is preferably 0.02-0.16 eq / 100g, which can prevent the coating toughness reduction problem caused by excessively high epoxy value.

[0023] In some specific embodiments, the blocked isocyanate is at least one of blocked HDI, blocked IPDI, and blocked TDI.

[0024] In some specific embodiments, the accelerator is at least one of ethyltriphenylphosphine bromide and 2-thiol benzothiazole zinc salt, the leveling agent is at least one of organosilicon leveling agent, phosphate ester modified acrylic leveling agent or fluorine modified acrylic leveling agent, and the degassing agent is benzoin.

[0025] Secondly, the preparation method of polyester powder coating provided in this application adopts the following technical solution:

[0026] A method for preparing a polyester powder coating includes the following steps:

[0027] The carboxylated polyester resin, epoxy-modified silicone resin, HAA curing agent, accelerator, blocked isocyanate, modified pigments and fillers, leveling agent, and degassing agent are mixed evenly in the specified proportions to obtain a premix.

[0028] The premix is ​​fed into a twin-screw extruder with a vent, and melted in an environment with a temperature of 100-110℃ and a speed of 150-180rpm. Then it is extruded, sheeted, crushed and ground to obtain polyester powder coating.

[0029] This application proposes to mix the raw materials to obtain a premix before melting and extruding it. This process helps to promote uniform dispersion of the raw materials. By controlling the appropriate temperature, the problem of premature cross-linking of polyester powder coatings, which leads to difficulty in extrusion, can be prevented, thereby improving the product stability of polyester powder coatings.

[0030] In summary, this application includes at least the following beneficial technical effects:

[0031] (1) This application uses the combination of each component and the reasonable proportion of each component to make the molten material have good fluidity, promote the smooth discharge of gas in the molten material, and ensure the smoothness, flatness and toughness of the coating. In addition, the curing agent of this application is HAA curing agent, which can cure the powder coating at 150℃. Compared with the traditional curing at 190℃ or above, it greatly reduces energy consumption. At the same time, it is also conducive to preventing the coating from yellowing or producing pinholes due to high temperature.

[0032] (2) In this application, the weight ratio of the controlled-end hydroxyl hyperbranched polyester, isocyanate-based silane coupling agent and pigments and fillers is preferably in the range of (15-20):(0.25-0.5):10. This can improve the dispersibility of the modified pigments and fillers while utilizing the residual hydroxyl groups in the modified pigments and fillers to react with the unblocked isocyanate, thereby enhancing the interfacial bonding strength and toughness between the pigments and fillers and the carboxyl polyester resin.

[0033] (3) In this application, the preferred end-hydroxyl hyperbranched polyester has a hydroxyl value of 80-100 mgKOH / g and a number average molecular weight of 6000-10000 g / mol, which is beneficial to further improve the toughness of the coating. Detailed Implementation

[0034] The following section provides further explanation of this application in conjunction with specific experiments.

[0035] Preparation Example

[0036]

Preparation Example 1

[0037] A modified pigment and filler is prepared from raw materials including 15 kg of hydroxyl-terminated hyperbranched polyester (hydroxyl value of 100 mg KOH / g, number average molecular weight of 6000 g / mol), 0.25 kg of propyltriethoxysilane isocyanate, 10 kg of pigment and filler, and 15 kg of diethylene glycol dimethyl ether. The pigment and filler are composed of titanium dioxide, nano-silica, and nano-calcium carbonate, with a weight ratio of 3:2:5.

[0038] The preparation method of the modified pigments and fillers is as follows:

[0039] S1. Dissolve propyltriethoxysilane isocyanate in diethylene glycol dimethyl ether, add titanium dioxide, nano silica and nano calcium carbonate, stir and react at 50°C for 2 hours, then filter, take the filter residue, wash and dry to obtain organosilicon modified pigments and fillers.

[0040] S2. Add hydroxyl-terminated hyperbranched polyester to organosilicon-modified pigments and fillers, and ball mill at 40℃ for 60 min. The ball-to-material ratio is 5:1. Use zirconia balls with a diameter of 4-6 mm for grinding, and the ball mill speed is 20-25 rpm to obtain modified pigments and fillers.

[0041]

Preparation Example 2

[0042] A modified pigment and filler is prepared from raw materials including 20 kg of hydroxyl-terminated hyperbranched polyester (hydroxyl value of 80 mg KOH / g, number average molecular weight of 10000 g / mol), 0.5 kg of propyltriethoxysilane isocyanate, 10 kg of pigment and filler, and 15 kg of diethylene glycol dimethyl ether. The pigment and filler are composed of titanium dioxide, nano-silica, and nano-calcium carbonate, with a weight ratio of 4:3:3.

[0043] The preparation method of the modified pigments and fillers is as follows:

[0044] S1. Dissolve propyltriethoxysilane isocyanate in diethylene glycol dimethyl ether, add titanium dioxide, nano silica and nano calcium carbonate, stir and react at 50°C for 2 hours, then filter, take the filter residue, wash and dry to obtain organosilicon modified pigments and fillers.

[0045] S2. Add hydroxyl-terminated hyperbranched polyester to organosilicon-modified pigments and fillers, and ball mill at 60℃ for 20 min. The ball-to-material ratio is 5:1. Use zirconia balls with a diameter of 4-6 mm for grinding, and the ball mill speed is 20-25 rpm to obtain modified pigments and fillers.

[0046]

Preparation Example 3

[0047] A modified pigment / filler differs from that in Preparation Example 1 in that the hydroxyl-terminated hyperbranched polyester has a hydroxyl value of 60 mg KOH / g and a number-average molecular weight of 15000 g / mol. In this preparation example, the molar amount of hydroxyl groups in the hydroxyl-terminated hyperbranched polyester is the same as in Preparation Example 1.

[0048]

Preparation Example 4

[0049] A modified pigment / filler differs from that in Preparation Example 1 in that the hydroxyl-terminated hyperbranched polyester has a hydroxyl value of 120 mg KOH / g and a number-average molecular weight of 3500 g / mol. In this preparation example, the molar amount of hydroxyl groups in the hydroxyl-terminated hyperbranched polyester is the same as in Preparation Example 1.

[0050] Example

[0051]

Example 1

[0052] A polyester powder coating is prepared from 560 kg of carboxylated polyester resin, 70 kg of epoxy-modified silicone resin, 30 kg of HAA curing agent, 0.1 kg of accelerator, 1 kg of blocked isocyanate, 150 kg of modified pigments and fillers, 8 kg of leveling agent, and 1.5 kg of degassing agent.

[0053] Among them, the carboxylated polyester resin has an acid value of 80 mg KOH / g, a number-average molecular weight of 5000, and a glass transition temperature of 50℃;

[0054] The epoxy value of the epoxy-modified silicone resin is 0.02-0.07 eq / 100g, specifically the product of Longsheng Sihai with brand name SH-023;

[0055] The accelerator used is ethyltriphenylphosphine bromide;

[0056] The blocked isocyanate uses blocked HDI, specifically Asahi Kasei's MF-B60X product, with a desealing temperature of 120℃.

[0057] The modified pigments and fillers used were those prepared according to [Preparation Example 1];

[0058] The leveling agent used is organosilicon leveling agent ZY-1603;

[0059] Benzoin is used as the degassing agent.

[0060] In this embodiment, the preparation method of the polyester powder coating is as follows:

[0061] The carboxylated polyester resin, epoxy-modified silicone resin, HAA curing agent, accelerator, blocked isocyanate, modified pigments and fillers, leveling agent, and degassing agent are mixed evenly in the specified proportions to obtain a premix.

[0062] The premix is ​​fed into a twin-screw extruder with a vent, and melted in an environment with a temperature of 100-110℃ and a rotation speed of 150rpm. Then it is extruded, sheeted, crushed and ground to obtain polyester powder coating.

[0063]

Example 2

[0064] A polyester powder coating is prepared from 595 kg of carboxylated polyester resin, 80 kg of epoxy-modified silicone resin, 40 kg of HAA curing agent, 0.2 kg of accelerator, 2 kg of blocked isocyanate, 180 kg of modified pigments and fillers, 12 kg of leveling agent, and 2.5 kg of degassing agent.

[0065] Among them, the acid value of the carboxylated polyester resin is 60 mg KOH / g, the number average molecular weight is 10000, and the glass transition temperature is 70℃.

[0066] The epoxy value of the epoxy-modified silicone resin is 0.02-0.07 eq / 100g, specifically the product of Longsheng Sihai with brand name SH-023; the accelerator used is ethyltriphenylphosphine bromide;

[0067] The blocked isocyanate uses blocked HDI, specifically Asahi Kasei's MF-B60X product, with a desealing temperature of 120℃.

[0068] The modified pigments and fillers used were those prepared in Preparation Example 2;

[0069] The leveling agent used is organosilicon leveling agent ZY-1603;

[0070] Benzoin is used as the degassing agent.

[0071] In this embodiment, the preparation method of the polyester powder coating is as follows:

[0072] The carboxylated polyester resin, epoxy-modified silicone resin, HAA curing agent, accelerator, blocked isocyanate, modified pigments and fillers, leveling agent, and degassing agent are mixed evenly in the specified proportions to obtain a premix.

[0073] The premix is ​​fed into a twin-screw extruder with a vent, and melted in an environment with a temperature of 100-110℃ and a rotation speed of 180rpm. Then it is extruded, sheeted, crushed and ground to obtain polyester powder coating.

[0074]

Example 3

[0075] A polyester powder coating differs from [Example 1] in that the modified pigments and fillers used are those prepared in [Preparation Example 3].

[0076]

Example 4

[0077] A polyester powder coating differs from [Example 1] in that the modified pigments and fillers used are those prepared in [Preparation Example 4].

[0078] Comparative Example

[0079] Comparative Example 1

[0080] A polyester powder coating differs from [Example 1] in that the modified pigments and fillers are replaced with an equal amount of the organosilicon modified pigments and fillers obtained in step S1 of [Preparation Example 1].

[0081] Comparative Example 2

[0082] A polyester powder coating differs from [Example 1] in that: in this comparative example, no blocked isocyanate was added to the polyester powder coating.

[0083] Comparative Example 3

[0084] A polyester powder coating differs from [Example 1] in that: in this comparative example, the amount of blocked isocyanate in the polyester powder coating is 8 kg.

[0085] Comparative Example 4

[0086] A polyester powder coating differs from [Example 1] in that: in this comparative example, the epoxy-modified silicone resin is replaced by an equal mass of bisphenol A type epoxy resin E44.

[0087] Performance testing sample preparation: The powder coatings prepared in each example and comparative example were sprayed onto the glass substrate. The thickness of the powder coating was 5 μm. Then, the coatings were cured at 150°C for 20 min to obtain the test samples.

[0088] 1. Appearance: Observe whether the coating formed by different powder coatings has defects such as orange peel, pinholes, yellowing, etc. If they appear, it is unqualified; if there are no such defects, it is qualified.

[0089] (2) Impact resistance: Tested in accordance with GB / T 1732-2020.

[0090] (3) High temperature resistance: Place the sample in an environment at 200℃ for 2 hours, take it out, and test the yellowing index of the sample after heat treatment in accordance with GB / T 39822.

[0091] Table 1

[0092]

[0093] Based on the test data in Example 1 and Comparative Example 1 of this application and Table 1, it can be seen that when the modified pigments and fillers are obtained by modifying the pigments and fillers with isocyanate silane coupling agents alone, the coating is prone to orange peel or pinhole problems, which is not conducive to the uniform dispersion of pigments and fillers.

[0094] Based on the test data in Example 1 and Comparative Examples 2-3 of this application and Table 1, it can be seen that neither adding blocked isocyanate nor adding excessive blocked isocyanate to polyester powder coatings is conducive to obtaining a coating that has a satisfactory appearance, an impact strength greater than 30 KJ·cm, and high temperature resistance. This indicates that the addition of an appropriate amount of blocked isocyanate can ensure a suitable degree of crosslinking, thereby enabling the coating to have both toughness and high temperature resistance.

[0095] Based on the test data in Example 1 and Comparative Example 4 of this application and Table 1, it can be seen that when bisphenol A type epoxy resin is used instead of epoxy modified silicone resin, the coating is prone to orange peel or pinhole problems, which is not conducive to the uniform dispersion of pigments and fillers. At the same time, the toughness of the coating decreases.

[0096] Based on the test data in Examples 1 and 3-4 of this application and Table 1, it can be seen that in this application, the preferred hydroxyl-terminated hyperbranched polyester has a hydroxyl value of 80-100 mgKOH / g and a number-average molecular weight of 6000-10000 g / mol, which is beneficial to further improve the toughness of the coating.

[0097] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this specific embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A polyester powder coating, characterized in that, It is prepared from the following raw materials in parts by weight: 560-595 parts carboxylated polyester resin, 70-80 parts epoxy modified silicone resin, 30-40 parts HAA curing agent, 0.1-0.2 parts accelerator, 1-2 parts blocked isocyanate, 150-180 parts modified pigments and fillers, 8-12 parts leveling agent, and 1.5-2.5 parts degassing agent; The unblocking temperature of the blocked isocyanate is 130-150℃; The modified pigments and fillers are prepared from hydroxyl-terminated hyperbranched polyester, isocyanate-based silane coupling agent, and pigments and fillers. The weight ratio of the hydroxyl-terminated hyperbranched polyester, isocyanate-based silane coupling agent, and pigments / fillers is (15-20):(0.25-0.5):10; The hydroxyl-terminated hyperbranched polyester has a hydroxyl value of 80-100 mgKOH / g and a number-average molecular weight of 6000-10000 g / mol.

2. The polyester powder coating according to claim 1, characterized in that, The pigments and fillers include titanium dioxide, nano-silica and nano-calcium carbonate, and the weight ratio of titanium dioxide, nano-silica and nano-calcium carbonate is (3-4):(2-3):(3-5).

3. A polyester powder coating according to any one of claims 1-2, characterized in that, The modified pigments and fillers are prepared by the following method: Isocyanate-based silane coupling agent is dissolved in solvent, pigments and fillers are added, and the mixture is stirred at 50-65℃ for 1-2 hours. Then, the mixture is filtered, and the filter residue is washed and dried to obtain organosilicon-modified pigments and fillers. Hydroxyl-terminated hyperbranched polyester was added to the organosilicon-modified pigments and fillers, and the mixture was ball-milled at 40-60℃ for 20-60 min to obtain the modified pigments and fillers.

4. A polyester powder coating according to any one of claims 1-2, characterized in that, The carboxylated polyester resin has an acid value of 60-80 mgKOH / g, a number-average molecular weight of 5000-10000, and a glass transition temperature of 50-70℃.

5. A polyester powder coating according to any one of claims 1-2, characterized in that, The epoxy value of the epoxy-modified silicone resin is 0.02-0.16 eq / 100g.

6. A polyester powder coating according to any one of claims 1-2, characterized in that, The blocked isocyanate is at least one of blocked HDI, blocked IPDI, and blocked TDI.

7. A polyester powder coating according to any one of claims 1-2, characterized in that, The accelerator is at least one of ethyltriphenylphosphine bromide and 2-thiol benzothiazole zinc salt; the leveling agent is at least one of organosilicon leveling agent, phosphate ester modified acrylic leveling agent or fluorine modified acrylic leveling agent; and the degassing agent is benzoin.

8. A method for preparing a polyester powder coating according to any one of claims 1-7, characterized in that, Includes the following steps: Carboxylated polyester resin, epoxy modified silicone resin, HAA curing agent, accelerator, blocked isocyanate, modified pigments and fillers, leveling agent and degassing agent are mixed evenly according to the formula to obtain a premix. The premix is ​​fed into a twin-screw extruder with a vent, and melted at a temperature of 100-110℃ and a speed of 150-180rpm. Then it is extruded, sheeted, crushed, and ground to obtain polyester powder coating.

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