Polyester resin for container powder coating as well as preparation method and application of polyester resin

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to polyester resin for a container powder coating as well as a preparation method and application of the polyester resin. The polyester resin for the container powder coating is prepared from the following raw materials: fat polyol, aromatic polyol, a hydrazide compound, polyacid, an end-capping reagent, a catalyst and a curing accelerator. The aromatic polyol and the hydrazide compound are introduced into the main chain structure of the polyester resin, so that the main chain of the polyester resin can be prevented from being broken under the conditions of high temperature, fuel gas and the like and the generation of yellowing chromophoric groups can be prevented, and the obtained polyester resin can be used for preparing the powder coating with excellent fuel gas baking resistance and temperature resistance.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and specifically relates to a polyester resin for container powder coating, its preparation method and application. Background Technology

[0002] Containers are specialized tools for international logistics and transportation, requiring them to travel back and forth from land to sea, and enduring various harsh environmental conditions during use. First-generation container coatings used solvent-based paints, resulting in significant emissions of volatile organic compounds (VOCs) and insufficient environmental friendliness. With technological advancements and increasing demands for environmental protection, container coatings have gradually shifted from traditional oil-based paints to water-based coatings, reducing VOC emissions by 80% and improving safety. However, the total residual VOC levels remain high, solid waste has not decreased, and wastewater discharge has actually increased. Powder coatings, due to their VOC-free emissions and simple application process, can completely solve the coating pollution problem in the container industry and are gradually gaining widespread application in containers.

[0003] Currently, both the interior and exterior bottom coatings of shipping containers use indoor powder coatings, while the exterior coating uses outdoor powder coatings. Powder coatings typically have high curing temperatures (180-200℃), and given the large size of shipping containers, traditional electric heating methods are energy-intensive. Gas-fired furnaces are national standard energy-saving periodic operation furnaces, offering significantly better energy savings compared to electric heating. Therefore, gas-fired furnaces are generally used for baking and curing powder coatings on shipping containers. However, substances such as nitrogen oxides in gas-fired furnaces can easily cause yellowing of the powder coating, affecting the container's appearance. Furthermore, if the container remains in an excessively hot environment for an extended period, the coating will lose its gloss and yellowing will accelerate, affecting both the protective and decorative properties of the coating.

[0004] Some studies have shown that adding antioxidant 168 and anti-yellowing agent 1300 to polyester resin can achieve the effect of fire-resistant baking, but its main application is in outdoor powder coatings with triglycidyl isocyanate curing system.

[0005] Therefore, providing a polyester resin that enables indoor powder coatings to have excellent resistance to gas baking and temperature resistance, thereby enabling the good application of indoor powder coatings in the container field, is of great significance. Summary of the Invention

[0006] The present invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial alternative. Specifically, the present invention provides a polyester resin for container powder coating, wherein the indoor powder coating prepared therefrom has excellent resistance to gas baking and temperature resistance.

[0007] The inventive concept of this invention: The raw materials for preparing the polyester resin used in container powder coatings of this invention include fatty polyols, aromatic polyols, acylhydrazine compounds, polybasic acids, end-capping agents, catalysts, and curing accelerators. By introducing aromatic polyols and acylhydrazine compounds into the main chain structure of the polyester resin, this invention can prevent the polyester resin main chain from breaking under high temperature and gas combustion conditions, and prevent the generation of chromogenic groups that cause yellowing. When applied to powder coatings, this results in powder coatings with excellent resistance to gas combustion baking and high temperature resistance.

[0008] Therefore, a first aspect of the present invention provides a polyester resin for container powder coating.

[0009] Specifically, the raw materials for preparing the polyester resin used in the container powder coating include fatty polyols, aromatic polyols, acylhydrazine compounds, polybasic acids, end-capping agents, catalysts, and curing accelerators.

[0010] Preferably, the fatty polyol includes at least one of neopentyl glycol, ethylene glycol, diethylene glycol, and 1,2-propanediol.

[0011] Preferably, the aromatic polyol includes phthalic acid.

[0012] Preferably, the acylhydrazide compound includes at least one of oxalic acid dihydrazide, isophthalic acid dihydrazide, and terephthalic acid dihydrazide.

[0013] Preferably, the polybasic acid includes at least one of terephthalic acid, isophthalic acid, succinic acid, and adipic acid.

[0014] Preferably, the capping agent includes at least one of 2-2'-biphenyldicarboxylic anhydride and trimellitic anhydride.

[0015] Preferably, the catalyst includes at least one of monobutyltin oxide, monobutyltin triisooctanoate, and titanium-based catalysts.

[0016] Preferably, the titanium-based catalyst includes at least one of phthalate chelates, tetrabutyl titanate, and tetraisopropyl titanate.

[0017] Preferably, the curing accelerator includes at least one of triphenylethylphosphine bromide, triphenylphosphine, methyldiethanolamine, and tetramethylammonium chloride.

[0018] Preferably, by mass percentage, the raw materials for preparing the polyester resin for container powder coating include 22-29% fatty polyol, 3-6% aromatic polyol, 2-5% acyl hydrazine compound, 52-60% polyacid, 7-11% end-capping agent, 0.04-0.15% catalyst and 0.3-0.6% curing accelerator.

[0019] Preferably, the glass transition temperature of the polyester resin used in the container powder coating is 58-68°C. Controlling the glass transition temperature of the polyester resin to 58-68°C is beneficial to improving the temperature resistance of the polyester resin.

[0020] Preferably, the polyester resin used for the container powder coating has an acid value of 65-75 mgKOH / g.

[0021] Preferably, the polyester resin used for the container powder coating has a melt viscosity of 2500-5500 mPa·s at 200°C.

[0022] A second aspect of the present invention provides a method for preparing the polyester resin for container powder coating described in the first aspect of the present invention.

[0023] Specifically, the preparation method of the polyester resin for container powder coating includes the following steps: The raw materials are mixed and polycondensed to obtain the polyester resin for container powder coating.

[0024] Preferably, the method for preparing the polyester resin for container powder coating includes the following steps: (1) Mix the fatty polyol, aromatic polyol, polyacid and catalyst, and heat to obtain mixture 1; (2) Cool the mixture 1 and add the acylhydrazine compound, keep warm, and obtain mixture 2; (3) Vacuum the mixture 2, then cool it down, and add the end-capping agent to react and obtain mixture 3; (4) Mix the mixture 3 and the curing accelerator, discharge, crush and granulate to obtain the polyester resin for container powder coating.

[0025] Preferably, in step (1), the fatty polyol and aromatic polyol are first mixed at a temperature below 140°C, and then the polyacid and catalyst are added in sequence.

[0026] Preferably, in step (1), the temperature after heating is 238-243℃.

[0027] Preferably, in step (1), the heat preservation time after heating is 2-5 hours.

[0028] Preferably, in step (1), the acid value of the mixture 1 is 30-40 mg KOH / g.

[0029] Preferably, in step (2), the temperature after cooling is 200-205℃.

[0030] Preferably, in step (2), the temperature of the heat preservation is 205-225℃, and the heat preservation time is 1-3h.

[0031] Preferably, in step (2), the acid value of the mixture 2 is 20-25 mg KOH / g.

[0032] Preferably, in step (3), the vacuum degree during vacuuming is -0.09 to -0.098 MPa, and the vacuuming time is 60-150 min.

[0033] Preferably, in step (3), the acid value after vacuuming is 5-10 mg KOH / g.

[0034] Preferably, in step (3), the temperature after cooling is 180-185℃.

[0035] Preferably, in step (3), the reaction temperature is 185-200℃ and the reaction time is 30-60min.

[0036] Preferably, in step (3), the acid value of the mixture 3 is 65-75 mg KOH / g, and the viscosity of the mixture 3 is 2500-5500 mPa·s.

[0037] Preferably, in step (4), the mixing is carried out by stirring for 20-40 minutes.

[0038] A third aspect of the present invention provides a powder coating for containers.

[0039] Specifically, the powder coating for containers includes the polyester resin described in the first aspect of this invention.

[0040] Preferably, the powder coating for containers is a powder coating for spraying inside the container and for coating the bottom outside the container.

[0041] Specifically, the main chain structure of the polyester resin of the present invention incorporates aromatic polyols and hydrazide compounds, which can prevent the polyester resin main chain from breaking under conditions such as high temperature and gas combustion, and prevent the generation of chromogenic groups that cause yellowing, thereby enabling the prepared powder coating to have excellent gas combustion baking resistance and temperature resistance.

[0042] Preferably, the powder coating for containers further includes epoxy resin, fillers, additives, benzoin, and pigments.

[0043] Preferably, the filler comprises at least one of titanium dioxide and barium sulfate; more preferably, the filler comprises titanium dioxide and barium sulfate.

[0044] Preferably, the barium sulfate comprises matting barium sulfate.

[0045] Preferably, the additive includes at least one of a leveling agent and a wetting accelerator; more preferably, the additive includes a leveling agent and a wetting accelerator.

[0046] Preferably, the pigment includes at least one of carbon black and iron yellow; more preferably, the pigment includes both carbon black and iron yellow.

[0047] Preferably, the powder coating for containers comprises, by weight, 125-175 parts polyester resin, 125-175 parts epoxy resin, 167-207 parts filler, 5-10 parts additives, 2-4 parts benzoin, and 1-3 parts pigment.

[0048] More preferably, by weight, the powder coating for containers comprises 125-175 parts polyester resin, 125-175 parts epoxy resin, 80-100 parts titanium dioxide, 87-107 parts barium sulfate, 3-6 parts leveling agent, 2-4 parts wetting accelerator, 2-4 parts benzoin, 0.5-1.5 parts carbon black, and 0.5-1.5 parts iron oxide yellow.

[0049] Preferably, the epoxy resin includes E-12 epoxy resin.

[0050] Preferably, the method for preparing the powder coating for containers includes the following steps: The raw material components of the powder coating for containers are mixed, melted and extruded, and then processed through tableting, crushing and sieving to obtain the powder coating for containers.

[0051] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows: (1) The present invention introduces aromatic polyols and hydrazide compounds into the main chain structure of polyester resin, which can prevent the polyester resin main chain from breaking under high temperature, gas and other conditions and prevent the generation of chromogenic groups that cause yellowing. The resulting polyester resin can be used to prepare powder coatings with excellent gas baking resistance and temperature resistance.

[0052] (2) The preparation process of this invention is simple and easy to promote and apply in industrial applications. Detailed Implementation

[0053] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0054] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0055] The raw material composition and dosage of polyester resin in Examples 1-4 of the present invention are shown in Table 1, and the raw material composition and dosage of polyester resin in Comparative Examples 1-2 are shown in Table 2.

[0056] Table 1: Raw material composition and dosage (g) of polyester resin in Examples 1-4

[0057] Table 2: Raw material composition and dosage (g) of polyester resin in Comparative Examples 1-2

[0058] Example 1 The raw material composition and dosage of polyester resin in Example 1 are shown in Table 1.

[0059] Example 1: A method for preparing polyester resin, comprising the following steps: (1) Add fatty polyol and aromatic polyol to the reaction vessel and stir and mix them evenly at a temperature below 140°C to obtain a mixture; (2) Add polybasic acid and catalyst to the mixture in step (1), slowly heat to 243°C, and then keep warm for 4 hours until the acid value reaches 38 mg KOH / g; (3) Cool the material after step (2) to 201℃, add hydrazide compound, keep warm at 213℃ for 2h, and the acid value reaches 24mgKOH / g; (4) The material after step (3) was vacuumed for 125 minutes under a vacuum degree of -0.095MPa until the acid value reached 7mgKOH / g; (5) Cool the material after step (4) to 180°C, then add the end-capping agent and react at 200°C for 60 min; (6) Add curing accelerator to the material after step (5), stir for 25 minutes, then discharge, crush and granulate to obtain polyester resin for container powder coating.

[0060] Example 2 The raw material composition and dosage of polyester resin in Example 2 are shown in Table 1.

[0061] Example 2: A method for preparing polyester resin, comprising the following steps: (1) Add the amount of fatty polyol and aromatic polyol according to Table 1 into the reaction vessel, stir and mix evenly at below 140°C to obtain the mixture; (2) Add polybasic acid and catalyst to the mixture in step (1), slowly heat to 240℃, keep warm for 3.5h, and the acid value reaches 35mgKOH / g; (3) Cool the material after step (2) to 200°C, add hydrazide compound, keep warm at 205°C for 1.5h, and the acid value reaches 23mgKOH / g; (4) The material after step (3) was vacuumed for 140 min under a vacuum degree of -0.095 MPa until the acid value reached 6 mg KOH / g; (5) Cool the material after step (4) to 180°C, then add the end-capping agent and react at 200°C for 60 min; (6) Add curing accelerator to the material after step (5), stir for 40 minutes, then discharge, crush and granulate to obtain polyester resin for container powder coating.

[0062] Example 3 The raw material composition and dosage of polyester resin in Example 3 are shown in Table 1.

[0063] Example 3: A method for preparing polyester resin, comprising the following steps: (1) Add fatty polyol and aromatic polyol to the reaction vessel and stir and mix them evenly at a temperature below 140°C to obtain a mixture; (2) Add polybasic acid and catalyst to the mixture in step (1), slowly heat to 238℃, keep warm for 2 hours, and the acid value reaches 31mgKOH / g; (3) Cool the material after step (2) to 205°C, add hydrazide compound, keep warm at 215°C for 2 hours, and the acid value reaches 20mgKOH / g; (4) The material after step (3) is vacuumed for 100 min under a vacuum degree of -0.095MPa until the acid value reaches 5mgKOH / g; (5) Cool the material after step (4) to 184°C, then add the end-capping agent and react at 200°C for 40 min; (6) Add curing accelerator to the material after step (5), stir for 30 minutes, then discharge, crush and granulate to obtain polyester resin for container powder coating.

[0064] Example 4 The raw material composition and dosage of polyester resin in Example 4 are shown in Table 1.

[0065] Example 4: A method for preparing polyester resin, comprising the following steps: (1) Add fatty polyol and aromatic polyol to the reaction vessel and stir and mix them evenly at a temperature below 140°C to obtain a mixture; (2) Add the polyacid and catalyst to the mixture in step (1), slowly heat to 241°C, keep warm for 3 hours, and the acid value reaches 36 mg KOH / g; (3) Cool the material after step (2) to 205°C, add hydrazide compound, keep warm at 225°C for 2 hours, and the acid value reaches 23 mg KOH / g; (4) The material after step (3) was vacuumed for 80 minutes under a vacuum degree of -0.095MPa until the acid value reached 9mgKOH / g; (5) Cool the material after step (4) to 184°C, then add the end-capping agent and react at 200°C for 50 min; (6) Add curing accelerator to the material after step (5), stir for 30 minutes, then discharge, crush and granulate to obtain polyester resin for container powder coating.

[0066] Comparative Example 1 The raw material composition and dosage of the polyester resin in Comparative Example 1 are shown in Table 2.

[0067] Comparative Example 1: The preparation method of polyester resin includes the following steps: (1) Add fatty polyol and aromatic polyol to the reaction vessel and stir and mix them evenly at a temperature below 140°C to obtain a mixture; (2) Add polybasic acid and catalyst to the mixture in step (1), slowly heat to 243℃, keep warm for 4 hours, and the acid value reaches 33mgKOH / g; (3) The material after step (2) was vacuumed for 150 min under a vacuum degree of -0.095 MPa until the acid value reached 10 mg KOH / g; (4) Cool the material after step (3) to 185°C, then add the end-capping agent and react at 190°C for 30 min; (5) Add curing accelerator to the material after step (4), stir for 30 minutes, then discharge, crush and granulate to obtain polyester resin for powder coating.

[0068] Comparative Example 2 The raw material composition and dosage of the polyester resin in Comparative Example 2 are shown in Table 2.

[0069] Comparative Example 2: The preparation method of polyester resin includes the following steps: (1) Add the fatty polyol to the reactor and stir and mix it evenly at a temperature below 140°C to obtain a mixture. (2) Add polybasic acid and catalyst to the mixture in step (1), slowly heat to 241°C, keep warm for 3 hours, and the acid value reaches 30 mg KOH / g; (3) The material after step (2) was vacuumed for 150 min under a vacuum degree of -0.095 MPa until the acid value reached 8 mg KOH / g; (4) Cool the material after step (3) to 185°C, then add the end-capping agent and react at 190°C for 30 min; (5) Add curing accelerator to the material after step (4), stir for 30 minutes, then discharge, crush and granulate to obtain polyester resin for powder coating.

[0070] Application examples The raw material composition and dosage of the powder coatings used in Application Examples 1-4 and Comparative Application Example 1-2 are shown in Table 3.

[0071] Table 3: Raw material composition and dosage (g) of powder coatings in Application Examples 1-4 and Comparative Application Examples 1-2

[0072] In Table 3, "-" indicates that no addition was made.

[0073] The raw material composition and dosage of the powder coating in Application Example 1 are shown in Table 3.

[0074] The method for preparing powder coatings as described in Example 1 includes the following steps: The raw material components are mixed evenly, melted and extruded using a twin-screw extruder, then pressed into sheets and crushed. The sheets are then pulverized and sieved to obtain powder coating.

[0075] The raw material composition and dosage of powder coatings in Application Examples 2-4 and Comparative Application Examples 1-2 are shown in Table 3.

[0076] Application Example 2-4 and Comparative Application Example 1-2: The preparation method of powder coating is the same as that of Application Example 1.

[0077] Performance testing 1. The acid value, melt viscosity, and glass transition temperature of the polyester resins in Examples 1-4 and Comparative Examples 1-2 were tested using the following methods: Acid value: Tested according to GB / T6743-2008; Melt viscosity: ICI cone-plate viscosity was determined at 200°C according to ASTM D4287-88; Glass transition temperature (Tg): Tested according to GB / T 19466.2.

[0078] The acid value, melt viscosity, and glass transition temperature of the polyester resins in Examples 1-4 and Comparative Examples 1-2 are shown in Table 4.

[0079] Table 4: Test results of acid value, melt viscosity, and glass transition temperature of polyester resins in Examples 1-4 and Comparative Examples 1-2

[0080] 2. Performance tests were conducted on the powder coatings prepared in Application Examples 1-4 and 1-2, respectively. The test items and methods are as follows: Coating gloss: Tested according to GB / T 9754-2007; Coating impact: Measured according to ASTM D2794 standard; Gas-fired baking resistance: The powder coatings prepared in Application Examples 1-4 and Comparative Application Examples 1-2 were applied to the surface of a 1.6 mm thick cold-rolled sheet using electrostatic spraying. The sheets were cured by electric heating (180℃ / 15 min) and gas-fired baking (180℃ / 30 min), respectively, with the sheet cured by electric heating (180℃ / 15 min) serving as the standard sheet. The color difference ΔE between the gas-fired baked coating and the electric-fired baked coating was measured using a colorimeter. The smaller the color difference ΔE, the better the gas-fired baking resistance of the coating. Heat resistance: The powder coatings prepared in Application Examples 1-4 and Comparative Application Examples 1-2 were applied to the surface of a 1.6 mm thick cold-rolled sheet using electrostatic spraying. The sheet was then cured by electric heating (180℃ / 15 min) to obtain a test plate. The gloss was measured using a gloss meter to obtain the gloss before baking, and the L, a, and b values ​​were measured using a colorimeter. The test plate was then placed in a 230℃ oven for 3 hours. After baking, the gloss was measured again using a gloss meter to obtain the gloss after baking, and the L, a, and b values ​​were measured using a colorimeter. The gloss retention rate and color difference ΔE were calculated. Gloss retention rate = gloss after baking / gloss before baking × 100%; color difference ΔE is obtained by calculating the changes in L, a, b values ​​before and after baking. The larger the color difference ΔE, the greater the color change of the coating before and after baking. The higher the gloss retention rate and the smaller the color difference ΔE, the better the heat resistance of the coating.

[0081] The performance test results of the powder coatings in Application Examples 1-4 and Comparative Application Example 1-2 are shown in Table 5.

[0082] Table 5: Performance test results of powder coatings in Application Examples 1-4 and Comparative Application Example 1-2

[0083] As can be seen from Table 5, the powder coating prepared by the polyester resin of the present invention has a small color difference under gas baking, and has good gas baking resistance. The gloss retention rate of the coating after electric baking at 230℃ / 3h is above 98%, and the color difference is below 0.3, which shows good heat resistance. At the same time, it also has good mechanical properties and gloss.

[0084] In summary, the present invention introduces aromatic polyols and hydrazide compounds into the main chain structure of polyester resin, which can prevent the polyester resin main chain from breaking under high temperature, gas combustion and other conditions and prevent the generation of chromogenic groups that cause yellowing. The resulting polyester resin can be used to prepare powder coatings with excellent gas combustion resistance and temperature resistance.

[0085] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A polyester resin, characterized in that, The raw materials for preparing the polyester resin include fatty polyols, aromatic polyols, acylhydrazine compounds, polyacids, end-capping agents, catalysts, and curing accelerators.

2. The polyester resin according to claim 1, characterized in that, The fatty polyols include at least one of neopentyl glycol, ethylene glycol, diethylene glycol, and 1,2-propanediol; And / or, the aromatic polyol includes phthalic acid; And / or, the acylhydrazide compound includes at least one of oxalic acid diacid hydrazide, isophthalic acid hydrazide, and terephthalic acid hydrazide; And / or, the polyacid includes at least one of terephthalic acid, isophthalic acid, succinic acid, and adipic acid; And / or, the capping agent includes at least one of 2-2'-biphenyldicarboxylic anhydride and trimellitic anhydride.

3. The polyester resin according to any one of claims 1-2, characterized in that, The raw materials for preparing the polyester resin, by mass percentage, include 22-29% fatty polyol, 3-6% aromatic polyol, 2-5% acyl hydrazine compound, 52-60% polyacid, 7-11% end-capping agent, 0.04-0.15% catalyst, and 0.3-0.6% curing accelerator.

4. The polyester resin according to any one of claims 1-2, characterized in that, The glass transition temperature of the polyester resin is 58-68℃; And / or, the acid value of the polyester resin is 65-75 mg KOH / g; And / or, the polyester resin has a melt viscosity of 2500-5500 mPa·s at 200°C.

5. The method for preparing the polyester resin according to any one of claims 1-4, characterized in that, The preparation method includes the following steps: The raw materials are mixed and subjected to polycondensation to obtain the polyester resin.

6. The preparation method according to claim 5, characterized in that, The method for preparing the polyester resin includes the following steps: (1) Mix the fatty polyol, aromatic polyol, polyacid and catalyst, and heat to obtain mixture 1; (2) Cool the mixture 1 and add the acylhydrazine compound, keep warm, and obtain mixture 2; (3) Vacuum the mixture 2, then cool it down, and add the end-capping agent to react and obtain mixture 3; (4) Mix the mixture 3 and the curing accelerator, discharge, crush and granulate to obtain the polyester resin.

7. The preparation method according to claim 6, characterized in that, In step (1), the fatty polyol and aromatic polyol are first mixed at a temperature below 140°C, and then the polyacid and catalyst are added in sequence. And / or, in step (1), the temperature after heating is 238-243℃; And / or, in step (1), the heat preservation time after heating is 2-5 hours; And / or, in step (1), the acid value of the mixture 1 is 30-40 mg KOH / g.

8. The preparation method according to claim 6, characterized in that, In step (2), the temperature after cooling is 200-205℃; And / or, in step (2), the temperature of the heat preservation is 205-225℃, and the heat preservation time is 1-3h; And / or, in step (2), the acid value of the mixture 2 is 20-25 mg KOH / g.

9. The preparation method according to claim 6, characterized in that, In step (3), the vacuum degree during evacuation is -0.09 to -0.098 MPa, and the evacuation time is 60-150 min; And / or, in step (3), the acid value after vacuuming is 5-10 mg KOH / g; And / or, in step (3), the temperature after cooling is 180-185℃; And / or, in step (3), the temperature of the reaction is 185-200℃ and the reaction time is 30-60min; And / or, in step (3), the acid value of the mixture 3 is 65-75 mg KOH / g, and the viscosity of the mixture 3 is 2500-5500 mPa·s.

10. A powder coating for containers, characterized in that, Includes the polyester resin according to any one of claims 1-4.

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