50 / 50 polyester resin for low-cost and high-hardness powder coating and preparation method of 50 / 50 polyester resin

Abstract

The invention relates to a 50 / 50 polyester resin for a low-cost and high-hardness powder coating, which is obtained by copolymerizing a pyromellitic dianhydride byproduct, triethylene glycol, 2, 5-dimethyl-2, 5-hexanediol, polypropylene glycol 1000, neopentyl glycol, terephthalic acid, adipic acid and the like. The polyester resin gives consideration to the rigidity and flexibility requirements of a polymer chain segment, a film formed after the polyester resin and E-12 epoxy resin are cured is good in impact resistance, high hardness of the film is achieved, the leveling level is high, the boiling resistance of the polyester chain segment is guaranteed, the cost of the polyester resin is reduced, the effect of reducing the cost of the 50 / 50 mixed powder coating is achieved, and the application range of the 50 / 50 mixed powder coating is widened. And a new way is developed for high-added-value comprehensive utilization of the pyromellitic dianhydride by-product.

Description

Technical Field

[0001] The invention relates to the technical field of polyester resins, and in particular to a 50 / 50 polyester resin for low-cost and high-hardness powder coatings and a preparation method thereof. Background Art

[0002] At present, as the country's supervision of VOC emissions becomes increasingly strict, the development space of solvent-based coatings such as paints is getting smaller and smaller, while environmentally friendly powder coatings with no VOC emissions are developing rapidly. Powder coatings are mainly composed of polymer resins, curing agents, additives and fillers. They have many advantages such as 100% film formation, no VOC emissions, recyclable coatings, and high cost performance. In recent years, they have developed rapidly in various indoor and outdoor coating fields. In the field of indoor coating, powder coatings are mainly divided into 50 / 50 mixed type (polyester resin and epoxy resin mass ratio is 50 / 50), 60 / 40 mixed type (polyester resin and epoxy resin mass ratio is 60 / 40), 70 / 30 mixed type (polyester resin and epoxy resin mass ratio is 70 / 30) and other powder coating varieties. Among them, the 50 / 50 mixed type has the largest amount of powder coatings due to its relatively high content of E-12 epoxy resin and excellent comprehensive performance. However, since the price of E-12 epoxy resin is generally higher than that of the matching polyester resin, the cost of 50 / 50 mixed powder coatings is higher than that of 60 / 40 mixed and 70 / 30 mixed products. How to reduce the formula cost of 50 / 50 mixed powder coatings is also the key to further expanding the market for 50 / 50 mixed powder coatings. As the main raw material of polyimide, pyromellitic anhydride has a high purity requirement, generally above 99.5%. At present, pyromellitic anhydride is basically oxidized by durene at high temperature, and then the crude product of pyromellitic anhydride is obtained, and then the required high-purity pyromellitic anhydride is finally obtained through solvent crystallization, filtration, and drying. However, the crystallized filtrate contains by-products produced in the high-temperature oxidation process, such as a mixture of various organic acids such as methylphthalic acid, trimellitic anhydride, pyromellitic acid, and pyromellitic acid monoanhydride. After removing the solvent, a solid still residue is obtained, and the acid value is generally 780-838mgKOH / g. Due to the large number of polyacid types contained, it is impossible to effectively separate, and it is mainly treated as waste material, with low added value. How to carry out high added value comprehensive utilization has always been a difficult problem in the industry.

[0003] In view of the above problems, the present invention uses pyromellitic anhydride byproduct, triethylene glycol, 2,5-dimethyl-2,5-hexanediol, polypropylene glycol 1000 (PG-1000), neopentyl glycol, terephthalic acid, adipic acid, etc. to copolymerize to obtain the product. First, the pyromellitic anhydride byproduct is subjected to an esterification end-capping reaction with an excess of mixed diols such as triethylene glycol, 2,5-dimethyl-2,5-hexanediol and neopentyl glycol, and then a chain extension reaction is carried out with terephthalic acid and polypropylene glycol 1000 (PG-1000) to obtain the main polymer chain structure, and finally adipic acid is used to perform an end-capping reaction to obtain the product. After the polyester resin and E-12 epoxy resin are cured, the coating has good impact resistance, achieves high hardness of the coating, and has a high leveling grade, and also ensures the water boiling resistance of the polyester segment. Due to the large amount of use of the by-product of pyromellitic anhydride, the cost of the polyester resin is significantly reduced, thereby achieving the effect of reducing the cost of the 50 / 50 mixed powder coating, and also develops a new way for the high added value comprehensive utilization of the by-product of pyromellitic anhydride. Summary of the invention

[0004] A 50 / 50 polyester resin for low-cost, high-hardness powder coatings, comprising the following raw materials in parts by weight:

[0005]

[0006] The raw materials also include catalysts and antioxidants.

[0007] Preferably, the catalyst is tetrabutyl titanate, and the amount used is 0.04-0.07% of the total mass of the raw materials; the antioxidant is antioxidant 1010, and the amount used is 0.2-0.3% of the total mass of the raw materials.

[0008] The by-product of pyromellitic anhydride used is the solid residue after the filtrate after solvent crystallization is removed from the crystallization solvent when pyromellitic anhydride is refined by solvent method, the volatile matter is less than 3%, and the main component is a mixture of various organic acids including methyl phthalic acid, trimellitic anhydride, pyromellitic acid, and pyromellitic acid monoanhydride, with an acid value of 780-838 mgKOH / g, for example, it can be purchased from Yangzhou Longfei Environmental Protection New Materials Co., Ltd.; polypropylene glycol 1000 (PG-1000) is a colorless, transparent, oily, viscous liquid with a hydroxyl value of 102-125 mgKOH / g and an average molecular weight of about 1000, model PG-1000, for example, it can be purchased from Hai'an Petrochemical Plant in Jiangsu Province.

[0009] The method for preparing a low-cost, high-hardness 50 / 50 polyester resin for powder coatings as described above comprises the following steps:

[0010] A. Add the formulated amount of 2,5-dimethyl-2,5-hexanediol, triethylene glycol, neopentyl glycol and catalyst into a reaction kettle, start stirring and heat to 130-135°C, then add the formulated amount of pyromellitic anhydride by-product, stir and mix thoroughly, then gradually heat to 200-205°C, and continue to heat to carry out esterification polymerization reaction;

[0011] B. Take samples for testing. When the acid value of the polymer is reduced to 3-5 mgKOH / g, it indicates that the carboxyl group of the byproduct of pyromellitic anhydride has been completely esterified by the hydroxyl group of the diol. At this time, add the formulated amount of polypropylene glycol 1000 and terephthalic acid, and heat to 225-230°C for chain extension polymerization.

[0012] C. Take samples for testing. When the acid value of the polymer reaches 28-36 mgKOH / g, add the formulated amount of antioxidant, and then start the vacuum system to continue the vacuum polycondensation reaction at 225-230°C;

[0013] D. Take samples to detect the acid value of the polymer in the reactor. When the acid value of the polymer reaches 12-17 mgKOH / g, release the vacuum system, then add the formulated amount of adipic acid to carry out carboxyl end-capping reaction. When the acid value of the polymer reaches 65-74 mgKOH / g, stop the reaction, discharge the material while hot, cool the polymer, and then crush and granulate it to obtain polyester resin.

[0014] Further, in the method for preparing a low-cost, high-hardness 50 / 50 polyester resin for powder coating as described above, in step A, the temperature is gradually increased to 200-205°C at a heating rate of 12-15°C / h; in step C, the vacuum degree is controlled between -0.097Mpa and -0.099Mpa; in step D, the polymer is cooled with a steel belt with condensed water.

[0015] For example, the method for preparing the 50 / 50 polyester resin for low-cost, high-hardness powder coating comprises the following steps:

[0016] A. Add the formulated amount of 2,5-dimethyl-2,5-hexanediol, triethylene glycol, neopentyl glycol and catalyst into the reaction kettle, start stirring and heat to 130-135°C, then add the formulated amount of pyromellitic anhydride byproduct, stir and mix thoroughly, then gradually heat to 200-205°C at a heating rate of 12-15°C / h, and continue to heat for esterification polymerization reaction;

[0017] B. Take samples for testing. When the acid value of the polymer is reduced to 3-5 mgKOH / g, it indicates that the carboxyl group of the byproduct of pyromellitic anhydride has been completely esterified by the hydroxyl group of the diol. At this time, add the formulated amount of polypropylene glycol 1000 and terephthalic acid, and heat to 225-230°C for chain extension polymerization.

[0018] C. Take samples for testing. When the acid value of the polymer reaches 28-36 mgKOH / g, add the formulated amount of antioxidant, then start the vacuum system to continue the vacuum polycondensation reaction at 225-230°C, and control the vacuum degree between -0.097Mpa and -0.099Mpa;

[0019] D. Take samples to detect the acid value of the polymer in the reactor. When the acid value of the polymer reaches 12-17 mgKOH / g, release the vacuum system, then add the formulated amount of adipic acid to carry out carboxyl end-capping reaction. When the acid value of the polymer reaches 65-74 mgKOH / g, stop the reaction, discharge the material while hot, cool the polymer with a steel belt with condensed water, and then crush and granulate it to obtain polyester resin.

[0020] The obtained product is light yellow transparent particles, with an acid value of 65-74 mgKOH / g and a softening point of 107-116°C.

[0021] The use of the low-cost, high-hardness 50 / 50 polyester resin for powder coatings as described above or the low-cost, high-hardness 50 / 50 polyester resin for powder coatings obtained by the preparation method in 50 / 50 mixed powder coatings.

[0022] As described above, the raw materials including polyester resin, E-12 epoxy resin, titanium dioxide and barium sulfate are used, which are mixed, extruded, tableted and crushed by a twin-screw extruder, and then the tablets are crushed and sieved to form powder coating.

[0023] For example, using a general 50 / 50 mixed powder coating formulation, the formula in parts by weight is usually as follows:

[0024]

[0025] According to the above powder coating formula, the materials are mixed evenly, extruded, tableted and crushed by a twin-screw extruder, and then the tablets are crushed and sieved to form powder coating. The powder coating is sprayed on the tinplate substrate after surface treatment by an electrostatic spray gun, and after curing, the coating coating is obtained.

[0026] Beneficial effects:

[0027] The present invention adopts copolymerization of pyromellitic anhydride byproduct, triethylene glycol, 2,5-dimethyl-2,5-hexanediol, polypropylene glycol 1000 (PG-1000), neopentyl glycol, terephthalic acid, adipic acid and the like to obtain the polymer. Firstly, esterification and end-capping reaction is carried out with pyromellitic anhydride byproduct and excess mixed diols such as triethylene glycol, 2,5-dimethyl-2,5-hexanediol and neopentyl glycol, and then chain extension reaction is carried out with terephthalic acid and polypropylene glycol 1000 (PG-1000) to obtain the main polymer chain structure, and finally end-capping reaction is carried out with adipic acid to obtain the polymer. The polyester resin takes into account the rigidity and flexibility requirements of the polymer chain segment. Among them, flexible monomers such as triethylene glycol, 2,5-dimethyl-2,5-hexanediol, polypropylene glycol 1000 (PG-1000), neopentyl glycol and adipic acid fully realize the impact toughness of the high-functionality raw materials of the by-product of pyromellitic anhydride after chain extension. On the basis of fully utilizing the high-functionality by-product of pyromellitic anhydride, the coating film has good impact resistance after being cured with E-12 epoxy resin, and the high hardness of the coating film is achieved, and the leveling grade is high. In addition, monomers such as 2,5-dimethyl-2,5-hexanediol, neopentyl glycol and terephthalic acid have good water resistance, which also ensures the water boiling resistance of the polyester chain segment. Due to the large amount of use of pyromellitic anhydride by-product, the cost of the polyester resin is significantly reduced, thereby achieving the effect of reducing the cost of 50 / 50 mixed powder coatings, and also developing a new way for the high added value comprehensive utilization of pyromellitic anhydride by-products. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with embodiments. It should be noted that, in the absence of conflict, the embodiments in this application and the technical features in the embodiments can be combined with each other. It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as those generally understood by those of ordinary skill in the art to which this application belongs. The words "including" or "comprising" and the like used in the disclosure of the present invention mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0029] The raw materials described in the present invention are all commercially available. For example, the byproduct of pyromellitic anhydride used is the solid residue after the filtrate after solvent crystallization is removed from the crystallization solvent when pyromellitic anhydride is refined by solvent method, the volatile matter is less than 3%, the main component is a mixture of various organic acids including methyl phthalic acid, trimellitic anhydride, pyromellitic acid, pyromellitic acid monoanhydride, the acid value is 780-838 mgKOH / g, purchased from Yangzhou Longfei Environmental Protection New Materials Co., Ltd.; polypropylene glycol 1000 (PG-1000) is a colorless, transparent, oily and viscous liquid, the hydroxyl value is 102-125 mgKOH / g, the average molecular weight is about 1000, the model is PG-1000, purchased from Hai'an Petrochemical Plant in Jiangsu Province.

[0030] Preparation Example 1

[0031] A 50 / 50 polyester resin for low-cost, high-hardness powder coatings, comprising the following raw materials in parts by weight:

[0032]

[0033]

[0034] The catalyst is tetrabutyl titanate, and the amount used is 0.04% of the total mass of the raw materials;

[0035] The antioxidant is antioxidant 1010, and the dosage is 0.2% of the total weight of the raw materials.

[0036] The method for preparing a low-cost, high-hardness 50 / 50 polyester resin for powder coatings comprises the following steps:

[0037] A. Add the formulated amount of 2,5-dimethyl-2,5-hexanediol, triethylene glycol, neopentyl glycol and catalyst into the reaction kettle, start stirring and heat to 135°C, then add the formulated amount of pyromellitic anhydride by-product, stir and mix thoroughly, then gradually heat to 205°C at a heating rate of 15°C / h, and continue to heat and carry out esterification polymerization reaction;

[0038] B. Take samples for testing. When the acid value of the polymer is reduced to 3-5 mgKOH / g, it means that the carboxyl group of the by-product of pyromellitic anhydride has been completely esterified by the hydroxyl group of the diol. At this time, add the formulated amount of polypropylene glycol 1000 and terephthalic acid, and heat to 230°C for chain extension polymerization.

[0039] C. Take samples for testing. When the acid value of the polymer reaches 28-36 mgKOH / g, add the formulated amount of antioxidant, then start the vacuum system to continue the vacuum polycondensation reaction at 230°C, and control the vacuum degree at -0.099Mpa;

[0040] D. Take samples to detect the acid value of the polymer in the reactor. When the acid value of the polymer reaches 12-17 mgKOH / g, release the vacuum system, then add the formulated amount of adipic acid to carry out carboxyl end-capping reaction. When the acid value of the polymer reaches the expected value, stop the reaction, discharge the material while hot, cool the polymer with a steel belt with condensed water, and then crush and granulate it to obtain polyester resin.

[0041] The obtained product is light yellow transparent particles, with an acid value of 66 mgKOH / g and a softening point of 115°C.

[0042] Preparation Example 2

[0043] A 50 / 50 polyester resin for low-cost, high-hardness powder coatings, comprising the following raw materials in parts by weight:

[0044]

[0045] The catalyst is tetrabutyl titanate, and the amount used is 0.07% of the total mass of the raw materials;

[0046] The antioxidant is antioxidant 1010, and the dosage is 0.3% of the total weight of the raw materials.

[0047] The preparation method is the same as that of Preparation Example 1.

[0048] The obtained product is light yellow transparent particles with an acid value of 74 mgKOH / g and a softening point of 108°C.

[0049] Preparation Example 3

[0050] A 50 / 50 polyester resin for low-cost, high-hardness powder coatings, comprising the following raw materials in parts by weight:

[0051]

[0052] The catalyst is tetrabutyl titanate, and the amount used is 0.07% of the total mass of the raw materials;

[0053] The antioxidant is antioxidant 1010, and the dosage is 0.2% of the total weight of the raw materials.

[0054] The preparation method is the same as that of Preparation Example 1.

[0055] The obtained product is light yellow transparent particles with an acid value of 69 mgKOH / g and a softening point of 112°C.

[0056] Preparation Example 4

[0057] A 50 / 50 polyester resin for low-cost, high-hardness powder coatings, comprising the following raw materials in parts by weight:

[0058]

[0059] The catalyst is tetrabutyl titanate, and the amount used is 0.07% of the total mass of the raw materials;

[0060] The antioxidant is antioxidant 1010, and the dosage is 0.3% of the total weight of the raw materials.

[0061] The preparation method is the same as that of Preparation Example 1.

[0062] The obtained product is light yellow transparent particles with an acid value of 71 mgKOH / g and a softening point of 110°C.

[0063] Comparative Preparation Example 1: Using commercially available general-purpose 50 / 50 polyester resin, acid value 68 mgKOH / g, softening point 114°C, model SJ3C, Anhui Shenjian New Materials Co., Ltd.;

[0064] Examples 1-4 and Comparative Example 1 (obtained using the polyester resins in the above Preparation Examples 1-4 and Comparative Preparation Example 1, respectively):

[0065] The general purpose 50 / 50 mixed powder coating formula is as follows in parts by weight:

[0066]

[0067]

[0068] Preparation of coating: Mix all materials according to the above powder coating formula, extrude, tablet and crush with a twin-screw extruder, and then crush the tablets and sieve (160-180 mesh) to make powder coating. The powder coating is sprayed on the surface treated tinplate substrate with an electrostatic spray gun, with a film thickness of about 80μm, and cured at 180℃ / 15min to obtain the coating.

[0069] Performance comparison

[0070] The coating index test is based on GB / T 21776-2008 "Standard Guide for Testing of Powder Coatings and Their Coatings". The pencil hardness test is based on GB / T 6739-2006 "Determination of Film Hardness by Pencil Method for Paints and Varnishes". The pencil hardness parameters are 2B-B-HB-FH-2H-3H-4H. From left to right, the hardness level gradually increases. The leveling level is determined by the PCI grading method, 0-10, and the larger the number, the better the leveling.

[0071] The polyester resins prepared in the above examples and comparative examples were used to prepare coatings according to the coating formulations provided by the present invention, and the coating properties were tested as shown in Table 1 below.

[0072] Table 1 Properties of powder coating films

[0073]

[0074] As can be seen from Table 1, the product prepared by the present invention adopts a specific formula and process, fully utilizes the high functionality of the byproduct of pyromellitic anhydride, obtains a low-cost, high-hardness 50 / 50 polyester resin for powder coatings through the step-by-step polymerization of flexible monomers, and finally solidifies with E-12 epoxy resin. The coating surface is smooth and flat, and there is no cracking phenomenon in terms of impact resistance. The coating gloss is basically above 93%, and the coating hardness reaches 2H, and the leveling grade is basically 5 and above, which is significantly higher than the hardness and leveling grade of the coating prepared by the ordinary commercial 50 / 50 polyester resin (Comparative Example 1), and there is no change in the surface after boiling in boiling water for 2h. The product of the present invention comprehensively utilizes the byproduct of pyromellitic anhydride, not only reduces the cost of polyester resin, but also provides a method for the high added value utilization of the byproduct of pyromellitic anhydride.

[0075] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that, for those skilled in the art, the described embodiments can be modified in various ways without departing from the spirit and scope of the present invention. Therefore, the above description is illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A low-cost, high-hardness 50 / 50 polyester resin for powder coatings, It is characterized in that The invention comprises the following raw materials in parts by weight: The raw materials also include catalysts and antioxidants.

2. A 50 / 50 polyester resin for low-cost, high-hardness powder coating as claimed in claim 1, It is characterized in that The by-product of pyromellitic anhydride used is a solid residue obtained by removing the crystallization solvent from the filtrate after solvent crystallization when pyromellitic anhydride is purified by solvent method, the volatile matter is less than 3wt%, the composition is a mixture of organic acids including methylphthalic acid, trimellitic anhydride, pyromellitic acid and pyromellitic acid monoanhydride, and the acid value is 780-838mgKOH / g.

3. A 50 / 50 polyester resin for low-cost, high-hardness powder coating as claimed in claim 1, It is characterized in that The catalyst is tetrabutyl titanate, and the amount used is 0.04-0.07% of the total mass of the raw materials.

4. A 50 / 50 polyester resin for low-cost, high-hardness powder coating as claimed in claim 1, It is characterized in that The antioxidant is antioxidant 1010, and the dosage is 0.2-0.3% of the total weight of the raw materials.

5. A 50 / 50 polyester resin for low-cost, high-hardness powder coating as claimed in claim 1, It is characterized in that Polypropylene glycol 1000 is a colorless, transparent, oily, viscous liquid with a hydroxyl value of 102-125 mgKOH / g and an average molecular weight of 1000.

6. A method for preparing a low-cost, high-hardness 50 / 50 polyester resin for powder coatings as claimed in any one of claims 1 to 5, It is characterized in that The following steps are involved: A. Add the formulated amount of 2,5-dimethyl-2,5-hexanediol, triethylene glycol, neopentyl glycol and catalyst into a reaction kettle, start stirring and heat to 130-135°C, then add the formulated amount of pyromellitic anhydride by-product, stir and mix thoroughly, then gradually heat to 200-205°C, and continue to heat to carry out esterification polymerization reaction; B. Take samples for testing. When the acid value of the polymer is reduced to 3-5 mgKOH / g, add the formulated amount of polypropylene glycol 1000 and terephthalic acid, and heat to 225-230°C for chain extension polymerization. C. Take samples for testing. When the acid value of the polymer reaches 28-36 mgKOH / g, add the formulated amount of antioxidant, and then start the vacuum system to continue the vacuum polycondensation reaction at 225-230°C; D. Take samples to detect the acid value of the polymer in the reactor. When the acid value of the polymer reaches 12-17 mgKOH / g, release the vacuum system, then add the formulated amount of adipic acid to carry out carboxyl end-capping reaction. When the acid value of the polymer reaches 65-74 mgKOH / g, stop the reaction, discharge the material while hot, cool the polymer, and then crush and granulate it to obtain polyester resin.

7. A method for preparing a low-cost, high-hardness 50 / 50 polyester resin for powder coatings as claimed in claim 6, It is characterized in that In step A, the temperature is gradually increased to 200-205° C. at a heating rate of 12-15° C. / h.

8. A method for preparing a low-cost, high-hardness 50 / 50 polyester resin for powder coatings as claimed in claim 6, It is characterized in that In step C, the vacuum degree is controlled between -0.097 MPa and -0.099 MPa; in step D, the polymer is cooled by a steel belt with condensed water.

9. Use of a low-cost, high-hardness 50 / 50 polyester resin for powder coatings according to any one of claims 1 to 4 or a low-cost, high-hardness 50 / 50 polyester resin for powder coatings obtained by the preparation method according to any one of claims 5 to 8 in 50 / 50 mixed powder coatings.

10. The use as claimed in claim 9, which uses raw materials including polyester resin, E-12 epoxy resin, titanium dioxide, and barium sulfate, which are mixed, extruded, tableted, and crushed using a twin-screw extruder, and then the tablets are crushed and sieved to form a powder coating.

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