A latent catalyst, its preparation method and application in ultra-low temperature curing powder materials

Abstract

The present invention discloses a latent catalyst, a preparation method thereof and an application thereof in ultra-low temperature curing powder coatings. The product comprises the following components in parts by mass: 10-20 parts of organic ammonium hydroxide; 2-8 parts of polyanhydride; 25-35 parts of polyol; 45-55 parts of polybasic acid; 0.01-0.1 part of catalyst; 0.1-1 part of antioxidant. The organic ammonium hydroxide first reacts with the polyanhydride, and then reacts with the polybasic acid and polyol through melting and high-temperature polymerization to prepare a latent catalyst for ultra-low temperature curing powder coatings with an acid value of 15-35 mgKOH / g, a viscosity of 2000-3000 mPas@175 °C, and a glass transition temperature Tg of 45-55 °C. It has good catalytic performance, enables the powder coating to have a certain operation time, and the surface leveling performance of the paint film is excellent.

Description

Technical Field

[0001] The present invention belongs to the field of synthesis of catalysts for coatings, and specifically relates to a latent catalyst, a preparation method thereof, and an application thereof in a super-low-temperature curing powder material. Background Art

[0002] Powder coatings are environmentally friendly coatings, with the "Four E" characteristics of environmental protection, economy, high efficiency, and excellent performance, and can be applied to fields such as automobiles, building materials, and household appliances, especially in the building materials and household appliance industries, which have developed rapidly. Compared with liquid coatings, powder coatings have a high solid content and no VOCs (volatile organic compounds) are generated during the curing process.

[0003] The curing temperature of conventional powder coatings is 180 - 200°C. At this temperature, the resin and the curing agent have sufficient time to first melt and level, and then crosslink and cure, forming a protective film with good mechanical properties and excellent surface effects on the substrate surface, so that the substrate meets various conventional use requirements. However, for various heat-sensitive substrates, such as various fiberboards (such as MDF), plastics, woodware, alloys, etc., when the temperature reaches 200°C, their structures are already damaged and they cannot be used anymore, so these substrates cannot use conventional powder coatings. With the development of resin technology for powder coatings, powder coatings that can be cured at lower temperatures have been developed. For example, at 130 - 160°C, by using resins with higher activity and mixing and curing them with epoxy resins, etc., coatings with qualified properties can be obtained, but the surface of such resins is poor and they can often only be used for producing textured coatings. Therefore, in order to broaden the application fields of powder coatings and meet the requirements of environmental protection and low energy consumption, it is still necessary to develop low-temperature powder coatings with good surface properties at lower temperatures.

[0004] Patent CN111630081A reports that at 80 - 130°C, through Michael addition reaction, a powder coating with excellent surface properties and cured at a lower temperature is prepared by using a methylene-containing substance A, an unsaturated double-bond-containing substance B, and a latent catalyst strong base C substance. Compared with traditional low-temperature powders, due to the lower curing temperature, about 90 - 110°C, the action time of the latent catalyst is extended, and the curing reaction proceeds gently, thus having the advantages of good surface leveling of the coating and low energy consumption.

[0005] In view of the disadvantages of the latent catalyst C substance in the above invention, such as low molecular weight, poor blending performance with high-molecular substances A and B, high latent period activity, and easy initiation of polymerization, the present invention makes the following improvements: This latent catalyst is made into a high-molecular substance through polymerization means, so that it can be perfectly blended with substances A and B, the performance during the latent period is stable, and catalysis is achieved during subsequent low-temperature baking to obtain a coating with excellent surface properties. Summary of the Invention

[0006] The object of the present invention is to provide a latent catalyst for ultra-low temperature curing powder coatings and a preparation method thereof. First, an organic ammonium hydroxide aqueous solution is reacted with a polyanhydride. After the indicators are qualified, a polyol, a polybasic acid and a catalyst are added to carry out an esterification and dehydration reaction at a high temperature. After the indicators are qualified, an acidifying agent is added for acidification capping, and finally a vacuum polycondensation reaction is carried out. The prepared latent catalyst has an acid value of 15 - 35 mgKOH / g, a viscosity of 2000 - 3000 mPas @ 175 °C, and a glass transition temperature Tg of 45 - 55 °C. The latent catalyst is added to commercially available A and B resins to prepare a powder coating, which does not agglomerate or cure after being stored at 50 °C for 14 days. The prepared powder coating is sprayed on an MDF board and has good leveling performance on the film surface and excellent mechanical properties after curing at 90 - 110 °C.

[0007] The technical solution adopted by the present invention is as follows: A latent catalyst comprises the following components in parts by mass: 10 - 20 parts of organic ammonium hydroxide, 2 - 8 parts of polyanhydride, 25 - 35 parts of polyol, 45 - 55 parts of polybasic acid, 0.01 - 0.1 part of catalyst I, and 0.1 - 1 part of antioxidant.

[0008] Preferably, the organic ammonium hydroxide is one of tetrabutylammonium hydroxide, tetrapropylammonium hydroxide, and tetraethylammonium hydroxide. The polyanhydride is one of pyromellitic dianhydride and trimellitic anhydride. The polyol is one of neopentyl glycol, trimethylolpropane, diethylene glycol, ethylene glycol, and 2-methyl-1,3-propanediol or a mixture of any of them in any proportion. The polybasic acid is one of terephthalic acid, isophthalic acid, and adipic acid or a mixture of any of them in any proportion. The catalyst I is one of monobutyltin oxide, n-butyltin trioctoate, and stannous oxalate. The antioxidant is one of phosphorous acid and triphenyl phosphite.

[0009] A preparation method of a latent catalyst: First, the organic ammonium hydroxide is reacted with the polyanhydride at room temperature, then the polyol, the polybasic acid and the catalyst I are added. After melting, high-temperature esterification dehydration, vacuum polycondensation, treatment, cooling and crushing, a latent catalyst containing an organic amine salt with an acid value of 15 - 35 mgKOH / g, a viscosity of 2000 - 3000 mPas @ 175 °C, and a glass transition temperature of 45 - 55 °C can be obtained.

[0010] Preferably, take each raw material in proportion. First, add organic ammonium hydroxide and polyanhydride into a reactor and react at room temperature. After the system becomes clear and transparent, add polyol into the reaction kettle, introduce nitrogen, heat up to 100 - 120 °C for melting, add polybasic acid and a catalyst, continue to heat up to 160 - 200 °C to start the esterification reaction and distill out water. Control the heating rate so that the temperature at the top of the fractionating column does not exceed 102 °C. Heat up to 230 - 250 °C and continue the esterification reaction for 10 - 12 hours. When the acid value reaches 10 - 14 mgKOH / g, cool down to 220 - 230 °C, add an antioxidant under nitrogen protection, add polybasic acid for a secondary esterification reaction, with the reaction temperature of 230 - 250 °C. After the system becomes clear and transparent, cool down to 220 - 230 °C and carry out vacuum polycondensation, with the vacuum degree of -0.095 - -0.1 MPa and the polycondensation time of 0.5 - 2 hours. Stop the polycondensation when the acid value reaches 15 - 35 mgKOH / g and the viscosity reaches 2000 - 3000 mPas@175 °C. Finally, after discharging, cooling and crushing, a latent catalyst used in ultra-low temperature curing powder coatings is prepared.

[0011] Compared with the prior art, the present invention reacts organic ammonium hydroxide with polyanhydride to obtain an ammonium salt with carboxyl groups, and uses this as a raw material to carry out an esterification reaction with other polybasic acids and polyols to obtain a latent catalyst. The catalyst prepared by this technology has a controllable active component content and stable storage, enabling the coating to have a certain operation window and leveling time, so that the surface of the paint film has good leveling performance. Detailed implementation mode

[0012] The following clearly and completely describes the technical solutions in the embodiments of the present invention in combination with the specific content of the present invention; obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments, which does not constitute a limitation to the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

[0013] First, the following explanations are made for the terms that may be used in this article:

[0014] The term "and / or" means that either one or both of the two can be achieved. For example, X and / or Y means that it includes both the cases of "X" or "Y" and the case of "X and Y".

[0015] Descriptions using terms such as "comprising", "including", "containing", "having" or other similar semantics shall be construed as non-exclusive inclusion. For example, including a technical feature element (such as raw material, component, ingredient, carrier, dosage form, material, size, part, component, mechanism, device, step, process, method, reaction condition, processing condition, parameter, algorithm, signal, data, product or article, etc.) shall be construed as not only including the explicitly listed technical feature element, but also including other technical feature elements known to the art that are not explicitly listed.

[0016] The term "consisting of" means excluding any technical feature element that is not explicitly listed. If this term is used in a claim, it will make the claim a closed type, so that it does not include technical feature elements other than the explicitly listed ones, except for the related conventional impurities. If this term only appears in a sub-clause of a claim, then it only limits the elements explicitly listed in that sub-clause, and the elements recorded in other sub-clauses are not excluded from the overall claim.

[0017] The term "parts by mass" represents the mass ratio relationship between multiple components. For example, if it is described that component X is x parts by mass and component Y is y parts by mass, then it means the mass ratio of component X to component Y is x:y; 1 part by mass can represent any mass. For example, 1 part by mass can be expressed as 1 kg or 3.1415926 kg, etc. The sum of the parts by mass of all components is not necessarily 100 parts, and can be greater than 100 parts, less than 100 parts or equal to 100 parts. Unless otherwise specified, the parts, ratios and percentages described herein are by mass.

[0018] When a concentration, temperature, pressure, size or other parameter is expressed in the form of a numerical range, this numerical range should be understood as specifically disclosing all ranges formed by the pairing of any upper limit value, lower limit value and preferred value within this numerical range, regardless of whether this range is explicitly recorded. For example, if the numerical range "2 - 8" is recorded, then this numerical range should be construed as including ranges such as "2 - 7", "2 - 6", "5 - 7", "3 - 4 and 6 - 7", "3 - 5 and 7", "2 and 5 - 7", etc. Unless otherwise specified, the numerical ranges recorded herein include both their end values and all integers and fractions within this numerical range.

[0019] The latent catalyst for ultra-low temperature curing powder coating resin provided by the present invention and its preparation method will be described in detail below. The content not described in detail in the embodiments of the present invention belongs to the prior art well-known to those skilled in the art. For those conditions not specified in the embodiments of the present invention, they are carried out according to the conventional conditions in the art or the conditions recommended by the manufacturer. For the reagents or instruments not specified in the manufacturer in the embodiments of the present invention, they are all conventional products that can be obtained through commercial purchase. Example 1

[0020] This example provides a latent catalyst for ultra-low temperature curing powder coatings, and its preparation method includes:

[0021] Take each raw material according to the following mass parts: the mass parts of tetrabutylammonium hydroxide, pyromellitic dianhydride, neopentyl glycol, diethylene glycol, terephthalic acid, isophthalic acid, monobutyltin oxide, and phosphorous acid are respectively: 15:5:29:5:40:5:0.08:0.92;

[0022] First, add pyromellitic dianhydride and tetrabutylammonium hydroxide to the reaction kettle, stir and react at room temperature until it is clear and transparent. Then add neopentyl glycol and diethylene glycol to the reaction kettle, heat to 100°C to melt it, and introduce nitrogen for protection. Then add terephthalic acid and the catalyst monobutyltin oxide, and raise the temperature under nitrogen protection. When the temperature rises to 180°C, start to esterify and remove water, turn on the cooling water of the fractionating column, control the top temperature of the column not to exceed 102°C, continue to raise the temperature to 245°C, and continue the esterification reaction. After reacting for 12 hours, take a sample to measure the acid value. When the acid value reaches 12mgKOH / g, the first-step esterification reaction ends;

[0023] Cool down to 220°C, add phosphorous acid and isophthalic acid under nitrogen protection, then raise the temperature to 240 - 250°C and continue to react. Wait until the system is clear and transparent, and the second-step esterification reaction ends.

[0024] Cool down to 220°C, start vacuum polycondensation, the vacuum degree is -0.098MPa, the polycondensation time is 3 hours, take a sample to measure the acid value. When the acid value reaches 15 - 35mgKOH / g and the viscosity is 2650mPas@175°C, the vacuum polycondensation ends;

[0025] After breaking the vacuum with nitrogen, discharge, cool, crush and package to obtain a latent catalyst for ultra-low temperature curing powder coatings, and its glass transition temperature Tg is 50°C. Example 2

[0026] This example provides a latent catalyst for ultra-low temperature curing powder coatings, and its preparation method includes:

[0027] Take each raw material according to the following mass parts: the mass parts of tetrabutylammonium hydroxide, pyromellitic dianhydride, neopentyl glycol, terephthalic acid, isophthalic acid, adipic acid, stannous oxalate, and triphenyl phosphite are respectively: 15:5:34:38:5:2:0.08:0.92;

[0028] First, add pyromellitic dianhydride and tetrabutylammonium hydroxide into the reaction kettle, stir and react at room temperature until it becomes clear and transparent. Then add neopentyl glycol into the reaction kettle, heat it to 100 °C to make it melt, and introduce nitrogen for protection. Then add terephthalic acid and adipic acid, and stannous oxalate as the catalyst, and raise the temperature under nitrogen protection. When the temperature rises to 180 °C, start to esterify and remove water, turn on the cooling water of the fractionating column, control the top temperature of the column not to exceed 102 °C, continue to raise the temperature to 245 °C, and continue the esterification reaction. After reacting for 12 hours, take a sample to measure the acid value. When the acid value reaches 12 mgKOH / g, the first-step esterification reaction ends;

[0029] Cool down to 220 °C, add triphenyl phosphite and isophthalic acid under nitrogen protection, then raise the temperature to 240 - 250 °C and continue to react. When the system becomes clear and transparent, the second-step esterification reaction ends.

[0030] Cool down to 220 °C, start vacuum polycondensation, the vacuum degree is -0.098 MPa, the polycondensation time is 3 hours, take a sample to measure the acid value. When the acid value reaches 15 - 35 mgKOH / g and the viscosity is 2350 mPas@175 °C, the vacuum polycondensation ends;

[0031] After breaking the vacuum with nitrogen, discharge the material, cool it, crush it and package it, then the latent catalyst for ultra-low temperature curable powder coatings is obtained, and its glass transition temperature Tg is 51 °C. Example 3

[0032] This example provides a latent catalyst for ultra-low temperature curable powder coatings, and its preparation method includes:

[0033] Take each raw material according to the following mass parts: the mass parts of tetrapropylammonium hydroxide, pyromellitic dianhydride, neopentyl glycol, terephthalic acid, isophthalic acid, adipic acid, stannous oxalate, and triphenyl phosphite are respectively: 17:5:32:38:5:2:0.08:0.92;

[0034] First, add pyromellitic dianhydride and tetrapropylammonium hydroxide into the reaction kettle, stir and react at room temperature until it becomes clear and transparent. Then add neopentyl glycol into the reaction kettle, heat it to 100 °C to make it melt, and introduce nitrogen for protection. Then add terephthalic acid and adipic acid, and stannous oxalate as the catalyst, and raise the temperature under nitrogen protection. When the temperature rises to 180 °C, start to esterify and remove water, turn on the cooling water of the fractionating column, control the top temperature of the column not to exceed 102 °C, continue to raise the temperature to 245 °C, and continue the esterification reaction. After reacting for 12 hours, take a sample to measure the acid value. When the acid value reaches 12 mgKOH / g, the first-step esterification reaction ends;

[0035] Cool down to 220 °C, add triphenyl phosphite and isophthalic acid under nitrogen protection, then raise the temperature to 240 - 250 °C and continue to react. When the system becomes clear and transparent, the second-step esterification reaction ends.

[0036] Cool down to 220 °C and start vacuum polycondensation. The vacuum degree is -0.098 MPa, the polycondensation time is 3 hours. Take samples to measure the acid value. When the acid value reaches 15 - 35 mgKOH / g and the viscosity is 2400 mPas @ 175 °C, the vacuum polycondensation ends;

[0037] After breaking the vacuum with nitrogen, discharge the material, cool it, crush it and package it to obtain the latent catalyst for ultra-low temperature curable powder coatings, whose glass transition temperature Tg is 50 °C. Example 4

[0038] This example provides a latent catalyst for ultra-low temperature curable powder coatings, and its preparation method includes:

[0039] Take each raw material according to the following mass parts: the mass parts of tetrapropylammonium hydroxide, pyromellitic dianhydride, neopentyl glycol, ethylene glycol, terephthalic acid, isophthalic acid, stannous oxalate, and triphenyl phosphite are respectively: 15:5:29:5:40:5:0.08:0.92;

[0040] First, add pyromellitic dianhydride and tetrapropylammonium hydroxide into the reaction kettle, stir and react at room temperature until it becomes clear and transparent. Then add neopentyl glycol and ethylene glycol into the reaction kettle, heat it to 100 °C to make it melt, and introduce nitrogen for protection. Then add terephthalic acid and the catalyst stannous oxalate, and raise the temperature under nitrogen protection. When the temperature rises to 180 °C, start to esterify and remove water, turn on the cooling water of the fractionating column, control the top temperature of the column not to exceed 102 °C, continue to raise the temperature to 245 °C, and continue the esterification reaction. After reacting for 12 hours, take samples to measure the acid value. When the acid value reaches 12 mgKOH / g, the first-step esterification reaction ends;

[0041] Cool down to 220 °C, add triphenyl phosphite and isophthalic acid under nitrogen protection, then raise the temperature to 240 - 250 °C and continue to react. Wait until the system becomes clear and transparent, and the second-step esterification reaction ends.

[0042] Cool down to 220 °C and start vacuum polycondensation. The vacuum degree is -0.098 MPa, the polycondensation time is 3 hours. Take samples to measure the acid value. When the acid value reaches 15 - 35 mgKOH / g and the viscosity is 2400 mPas @ 175 °C, the vacuum polycondensation ends;

[0043] After breaking the vacuum with nitrogen, discharge the material, cool it, crush it and package it to obtain the latent catalyst for ultra-low temperature curable powder coatings, whose glass transition temperature Tg is 52 °C.

[0044] The latent catalyst for the ultra-low temperature curable powder coating prepared above has good catalytic performance, controllable operating time and good leveling performance on the paint film surface. When catalyzing the commercially available A / B resin components, a powder coating is prepared, which does not agglomerate or cure after being stored at 50 °C for 14 days. The prepared powder coating is sprayed on an MDF board, and after curing at 90-110 °C, the paint film surface has good leveling performance and excellent mechanical properties.

Claims

1. A latent catalyst, characterized in that, Comprising the following components by mass parts: Organic ammonium hydroxide 10 - 20 parts Polybasic anhydride 2 - 8 parts Polyol 25 - 35 parts Polybasic acid 45 - 55 parts Catalyst I 0.01 - 0.1 part Antioxidant 0.1 - 1 part; Wherein, the organic ammonium hydroxide is one of tetrabutylammonium hydroxide, tetrapropylammonium hydroxide, tetraethylammonium hydroxide; The polybasic anhydride is one of pyromellitic dianhydride, trimellitic anhydride; The polyol is one of neopentyl glycol, trimethylolpropane, diethylene glycol, ethylene glycol, 2 - methyl - 1,3 - propanediol or a mixture of any proportion of several of them; The polybasic acid is one of terephthalic acid, isophthalic acid, adipic acid or a mixture of any proportion of several of them; The specific steps for the preparation method of the latent catalyst are as follows: Take each raw material in proportion. First, add the organic ammonium hydroxide and the polybasic anhydride into the reactor and react at room temperature. After the system becomes clear and transparent, add the polyol into the reaction kettle, introduce nitrogen and heat up to 100 - 120 °C for melting. Then add the polybasic acid and the catalyst, continue to heat up to 160 - 200 °C to start the esterification reaction and distill out water. Control the heating rate so that the temperature at the top of the fractionating column does not exceed 102 °C. Heat up to 230 - 250 °C and continue the esterification reaction for 10 - 12 hours. When the acid value reaches 10 - 14 mgKOH / g, cool down to 220 - 230 °C. Under nitrogen protection, add the antioxidant and then add the polybasic acid for a secondary esterification reaction at a reaction temperature of 230 - 250 °C. After the system becomes clear and transparent, cool down to 220 - 230 °C and carry out vacuum polycondensation. The vacuum degree is - 0.095 - - 0.1 MPa, and the polycondensation time is 0.5 - 2 hours. When the acid value reaches 15 - 35 mgKOH / g and the viscosity reaches 2000 - 3000 mPas@175 °C, stop the polycondensation; finally, after discharging, cooling and crushing, the latent catalyst is obtained.

2. The latent catalyst according to claim 1, characterized in that, The catalyst I is one of monobutyltin oxide, n - butyltin trioctoate, stannous oxalate.

3. A latent catalyst according to claim 1, characterized in that, The antioxidant is one of phosphorous acid, triphenyl phosphite.

4. A latent catalyst according to any one of claims 1-3, characterized in that, Used in ultra - low temperature curing powder coatings.