A UV-curable crystalline powder coating resin and its preparation method

Abstract

The present application relates to the field of powder coating, and particularly relates to a UV light-cured crystalline powder coating resin and a preparation method thereof, which comprises the following raw materials in mass parts: polyol 25-35 parts, first type of polybasic acid 45-55 parts, non-organic tin catalyst 0.01-0.1 part, antioxidant 0.01-0.05 part, second type of polybasic acid, acrylic acid end-capping agent 5-10 parts, alkalization regulator 0.01-0.1 part, polymerization inhibitor 0.01-0.05 part and photoinitiator 3-5 parts; the present application uses polyol, first type of polybasic acid, second type of polybasic acid, non-organic tin catalyst, antioxidant, alkalization regulator, acrylic acid end-capping agent, polymerization inhibitor and photoinitiator in a specific ratio as main raw materials, and controls reaction temperature, reaction time and acid value to prepare a UV light-cured crystalline powder coating resin, which has high crystallinity, low Tg, high gloss, UV light-cured property and low energy consumption, and therefore has wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of powder coatings, and more particularly to a UV-curable crystalline powder coating resin and its preparation method. Background Technology

[0002] Traditional powder coatings employ a thermosetting process. Due to their high resin Tg (>60℃), they melt, flow, and cure at high temperatures of 180-200℃ to coat the surface of the device. This high curing temperature results in high energy consumption and limits their application to non-heat-sensitive substrates. Crystalline powder coating resins, on the other hand, have lower Tg and are crystalline at room temperature. They can melt, flow, and cure at relatively lower temperatures to coat the surface of the device. Traditional UV-cured coatings generally involve volatile organic compound (VOC) emissions, and even VOC-free UV-cured coatings may experience leakage of small-molecule acrylic resin.

[0003] With the development of the social economy and the improvement of environmental awareness, the coating industry requires the realization of "oil-to-powder" coating, that is, the transformation from oil-based coatings to powder coatings. However, for heat-sensitive substrates, high-temperature curing conditions are not suitable. UV curing can achieve melting and leveling at a lower temperature (90-110℃) and then curing under UV light, thus enabling powder coating of heat-sensitive substrates such as solid wood products, plastic products, metal alloys, and paper products, thereby broadening the application range of powder coatings. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a UV-curable crystalline powder coating resin and its preparation method to solve the problems in the prior art.

[0005] To achieve the above objectives, the present invention provides a UV-curable crystalline powder coating resin and its preparation method.

[0006] A UV-curable crystalline powder coating resin is prepared from the following raw materials in the indicated mass fractions: 25-35 parts of polyol, 45-55 parts of first-type polyacid, 0.01-0.1 parts of non-organotin catalyst, 0.01-0.05 parts of antioxidant, second-type polyacid, 5-10 parts of acrylic end-capping agent, 0.01-0.1 parts of alkalization regulator, 0.01-0.05 parts of polymerization inhibitor, and 3-5 parts of photoinitiator.

[0007] Preferably, the polyol is any one of ethylene glycol, neopentyl glycol, 1,4-butanediol, and hexanediol.

[0008] Preferably, the first type of polyacid is any one of succinic acid, adipic acid, and dodecyl diacid.

[0009] Preferably, the second type of polyacid is any one of phthalic acid, phthalic anhydride, and fumaric acid.

[0010] Preferably, the non-organotin catalyst is either stannous oxalate or stannous octoate.

[0011] Preferably, the antioxidant is either phosphorous acid or triphenyl phosphite.

[0012] Preferably, the polymerization inhibitor is any one of p-hydroxyanisole, hydroquinone, and 2,5-dimethylhydroquinone.

[0013] Preferably, the alkalization regulator is triethylamine.

[0014] Preferably, the acrylic end-capping agent is any one of glycidyl methacrylate and 3,4-epoxycyclohexyl methacrylate.

[0015] Preferably, the photoinitiator is any one of 1-hydroxy-cyclohexylbenzophenone, benzophenone, and diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide.

[0016] Preferably, the water content of the polyol, the first type of polyacid, the second type of polyacid, the non-organotin catalyst, the antioxidant, the alkalization regulator, the acrylic acid end-capping agent, the polymerization inhibitor and the photoinitiator are all less than 500 ppm.

[0017] A method for preparing a UV-curable crystalline powder coating resin includes the following steps:

[0018] S1. Add the polyol to the reactor and melt it at 100-120℃ under a nitrogen atmosphere. Add the first type of polyacid and non-organotin catalyst, react at 160-200℃, and distill off the water. Control the temperature at the top of the fractionation column to not exceed 102℃ to obtain mixture A.

[0019] S2. Heat mixture A to 230-250℃ and react for 10-12 hours. When the acid value reaches 8-10 mg KOH / g, cool it down to 220-230℃, add antioxidant and type II polybasic acid, and heat it to 230-250℃ to react for 2-4 hours. When the acid value reaches 12-14 mg KOH / g, mixture B is obtained.

[0020] S3. Vacuum polycondensation is performed on mixture B at a vacuum degree of -0.095 to 0.1 MPa for 2-4 hours. Polycondensation is stopped when the acid value reaches 2-4 mg KOH / g and the viscosity is 1500-2000 mPa∙s at 100℃. Nitrogen gas is introduced to break the vacuum, and the temperature is lowered to 85-95℃ to obtain mixture C.

[0021] S4. Add acrylic acid end-capping agent, alkalization regulator and polymerization inhibitor to mixture C, stir for 2-3 hours, when the acid value is not greater than 0.5 mg KOH / g and the viscosity is 1500-2000 mPa∙s at 100℃, to obtain mixture D;

[0022] S5. Add a photoinitiator to mixture D and disperse for 30 minutes to obtain a UV-curable crystalline powder coating resin.

[0023] The beneficial effects of this invention are:

[0024] This invention provides a UV-curable crystalline powder coating resin and its preparation method. The method uses a specific ratio of polyol, a first-type polyacid, a second-type polyacid, a non-organotin catalyst, an antioxidant, an alkalizing regulator, an acrylic end-capping agent, a polymerization inhibitor, and a photoinitiator as main raw materials. By controlling the reaction temperature, reaction time, and acid value, a UV-curable crystalline powder coating resin is obtained. Since the first-type polyacid is a linear dicarboxylic acid, its addition in the first step allows it to polymerize with the linear diol to form a linear polyester. The second-type polyacid contains olefin bonds or benzene rings, and its addition in the second step can extend the chain of the linear polyester synthesized in the first step, forming regularly arranged crystalline regions, thereby improving the crystallinity of the resin. Therefore, this powder coating resin has high crystallinity, low Tg, high gloss, UV curability, and low energy consumption, thus having broad application prospects. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0026] Example 1: A method for preparing a UV-curable crystalline powder coating resin, comprising the following steps:

[0027] S1. Add 30g of ethylene glycol to the reaction vessel, purge with nitrogen and heat to 100℃, add 50g of adipic acid and 0.05g of stannous oxalate, continue heating to 200℃ to start the esterification reaction and distill off the water, control the heating rate so that the temperature at the top of the fractionation column does not exceed 102℃, heat to 230-250℃ and continue the esterification reaction for 10h, when the acid value reaches 8mgKOH / g, cool down to 220℃;

[0028] S2. Under nitrogen protection, add 0.02g of phosphorous acid and 8g of fumaric acid, heat to 230℃ and continue the esterification reaction for 3h. When the acid value reaches 13mgKOH / g, perform vacuum polycondensation at a vacuum degree of -0.095MPa for 3h. Stop polycondensation when the acid value reaches 4mgKOH / g and the viscosity is 1500mPa·s at 100℃.

[0029] S3. Nitrogen gas is introduced to break the vacuum, and the temperature is lowered to 85°C. Under nitrogen protection, 7g of glycidyl acrylate, 0.05g of triethylamine, and 0.05g of hydroquinone are added. After reacting for 3 hours, when the acid value reaches 0.4mgKOH / g and the viscosity is 1600mPa·s at 100°C, 3g of 1-hydroxy-cyclohexylbenzophenone is added and dispersed for 30 minutes to obtain a UV-curable crystalline powder coating resin.

[0030] Example 2: A method for preparing a UV-curable crystalline powder coating resin, comprising the following steps:

[0031] S1. Add 35g of neopentyl glycol to the reactor, purge with nitrogen and heat to 100℃, add 55g of dodecyl dicarboxylic acid and 0.05g of stannous oxalate, continue heating to 220℃ to start the esterification reaction and distill off the water, control the heating rate so that the temperature at the top of the fractionation column does not exceed 102℃, heat to 230-250℃ and continue the esterification reaction for 11h, when the acid value reaches 9mgKOH / g, cool down to 220℃;

[0032] S2. Under nitrogen protection, add 0.05g of triphenyl phosphite and 6g of phthalic acid, heat to 230℃ and continue the esterification reaction for 4h. When the acid value reaches 14mgKOH / g, perform vacuum polycondensation at a vacuum degree of -0.095MPa for 3h. Stop polycondensation when the acid value reaches 4mgKOH / g and the viscosity is 1800mPa·s at 100℃.

[0033] S3. Nitrogen gas is introduced to break the vacuum, and the temperature is lowered to 90°C. Under nitrogen protection, 7g of glycidyl acrylate, 0.05g of triethylamine, and 0.05g of hydroquinone are added and reacted for 3 hours. When the acid value reaches 0.3mgKOH / g and the viscosity is 1900mPa·s at 100°C, 3g of 1-hydroxy-cyclohexylbenzophenone is added and dispersed for 30 minutes to obtain a UV-curable crystalline powder coating resin.

[0034] Example 3: A method for preparing a UV-curable crystalline powder coating resin, comprising the following steps:

[0035] S1. Add 32g of 1,4-butanediol to the reactor, purge with nitrogen and heat to 100℃, add 55g of dodecyl dicarboxylic acid and 0.05g of stannous oxalate, continue heating to 220℃ to start the esterification reaction and distill off the water, control the heating rate so that the temperature at the top of the fractionation column does not exceed 102℃, heat to 230-250℃ and continue the esterification reaction for 10h, when the acid value reaches 8mgKOH / g, cool down to 220℃;

[0036] S2. Under nitrogen protection, add 0.04g of triphenyl phosphite and 5g of phthalic anhydride, heat to 230℃ and continue the esterification reaction for 3h. When the acid value reaches 12mgKOH / g, perform vacuum polycondensation at a vacuum degree of -0.095MPa for 2h. Stop polycondensation when the acid value reaches 3mgKOH / g and the viscosity is 1500mPa·s at 199℃.

[0037] S3. Nitrogen gas is introduced to break the vacuum, and the temperature is lowered to 90°C. Under nitrogen protection, 6g of glycidyl acrylate, 0.04g of triethylamine, and 0.05g of hydroquinone are added. After reacting for 3 hours, when the acid value reaches 0.2mgKOH / g and the viscosity is 1600mPa·s at 100°C, 3g of 1-hydroxy-cyclohexylbenzophenone is added and dispersed for 30 minutes to obtain a UV-curable crystalline powder coating resin.

[0038] Comparative Example 1:

[0039] This comparative example uses conventional outdoor powdered polyester resin, model RPCOAT W203, as a control.

[0040] Performance testing

[0041] The UV-curable crystalline powder coating resins obtained in Examples 1-3 of this invention and the powdered polyester resin in Comparative Example 1 were tested:

[0042] Test method: The products obtained in Examples 1-3 and the powdered polyester resin in Comparative Example 1 were cooled and crushed with a steel belt, pulverized with a grinding mill, and finally sieved with a sieve to obtain UV-curable powder coatings. The UV-curable powder coatings were electrostatically sprayed onto MDF boards, baked at 100°C for 10 minutes, and then UV-cured. The test results are shown in Table 1 below:

[0043] Table 1. Performance test results of Examples 1-3 and comparative examples.

[0044] performance Example 1 Example 2 Example 3 Comparative Example 1 Viscosity (100℃) / mPa·s 1600 1900 1600 4800 Melt curing temperature / °C 100 100 100 180 <![CDATA[UV curing energy / mJ / cm 2 > 350 350 350 / Curing time / s 1 1 1 900 Tg / ℃ 43 50 45 67 Pencil hardness H H H H Gloss (60° angle) 100° 99° 101° 100° Positive and negative impact ±50cm pass pass pass pass Adhesion 5B 5B 5B 5B

[0045] Data Analysis:

[0046] As can be seen from Table 1 above, the UV-curable crystalline powder coating resins prepared in Examples 1 to 3 of the present invention have extremely low melting and curing temperatures, low viscosity and low Tg, which greatly saves curing time. Moreover, their hardness, gloss and adhesion are no less than those of Comparative Example 1, and they can better reduce energy consumption.

[0047] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in the details for the sake of brevity.

[0048] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A UV light-cured crystalline powder coating resin, characterized in that, Prepared from the following raw materials by mass fraction: polyol 25-35 parts, first type of polybasic acid 45-55 parts, non-organic tin catalyst 0.01-0.1 parts, antioxidant 0.01-0.05 parts, second type of polybasic acid, acrylic acid end-capping agent 5-10 parts, alkalization regulator 0.01-0.1 parts, polymerization inhibitor 0.01-0.05 parts and photoinitiator 3-5 parts; The first type of polybasic acid is any one of succinic acid, adipic acid and dodecanedioic acid; The second type of polybasic acid is any one of phthalic acid, phthalic anhydride and fumaric acid; the polyol is any one of ethylene glycol, neopentyl glycol, 1,4-butanediol and hexanediol; the acrylic acid end-capping agent is any one of glycidyl methacrylate and 3,4-epoxycyclohexyl methacrylate.

2. The UV light-cured crystalline powder coating resin according to claim 1, characterized in that, The non-organic tin catalyst is stannous oxalate.

3. The UV light-cured crystalline powder coating resin according to claim 1, characterized in that, The antioxidant is any one of phosphorous acid and triphenyl phosphite.

4. The UV light-cured crystalline powder coating resin according to claim 1, characterized in that, The polymerization inhibitor is any one of p-hydroxyanisole, hydroquinone and 2,5-dimethyl hydroquinone.

5. The UV light-cured crystalline powder coating resin according to claim 1, wherein, The alkalization regulator is triethylamine.

6. The UV light-cured crystalline powder coating resin according to claim 1, wherein, The photoinitiator is any one of 1-hydroxy-cyclohexyl phenyl ketone, benzophenone and diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide.

7. The UV light-cured crystalline powder coating resin according to claim 1, wherein, The water content of the polyol, first type of polybasic acid, second type of polybasic acid, non-organic tin catalyst, antioxidant, alkalization regulator, acrylic acid end-capping agent, polymerization inhibitor and photoinitiator is all less than 500 ppm.

8. A method of producing a UV light-cured crystalline powder coating resin according to any one of claims 1 to 7, characterized in that, Comprising the following steps: S1. The polyol is added into a reaction kettle, melted at 100-120℃ under nitrogen atmosphere, the first type of polybasic acid and non-organic tin catalyst are added, reacted and distilled water at 160-200℃, the top temperature of the fractionating column is controlled to be no more than 102℃, to obtain mixed material A; S2. The mixed material A is heated to 230-250℃ and reacted for 10-12h, when the acid value reaches 8-10mgKOH / g, it is cooled to 220-230℃, the antioxidant, second type of polybasic acid are added, heated to 230-250℃ and reacted for 2-4h, when the acid value reaches 12-14mgKOH / g, to obtain mixed material B; S3. The mixed material B is subjected to vacuum polycondensation, the vacuum degree is -0.095--0.1MPa, the polycondensation time is 2-4h, when the acid value reaches 2-4mgKOH / g and the viscosity at 100℃ is 1500-2000mPa·s, the polycondensation is stopped, nitrogen is introduced to break the vacuum, and it is cooled to 85-95℃, to obtain mixed material C; S4. The acrylic acid end-capping agent, alkalization regulator and polymerization inhibitor are added into the mixed material C, stirred for 2-3h, when the acid value is no more than 0.5mgKOH / g and the viscosity at 100℃ is 1500-2000mPa·s, to obtain mixed material D; S5. The photoinitiator is added into the mixed material D, dispersed for 30min, to obtain UV light-cured crystalline type powder coating resin.