A low-cost, high-leveling polyester resin for powder coatings and preparation method thereof

Abstract

The present invention relates to a low-cost, high-leveling polyester resin for powder coatings. The polyester resin is mainly obtained by polymerization using refined kitchen waste oil, trimethylolpropane, 1,2,6-hexanetriol, triethylene glycol, isophthalic acid, brassyl acid, terephthalic acid, and adipic anhydride as main raw materials; the polyester resin chain segment finally obtained contains a large amount of C 16 ‑C 18 The product has excellent water resistance and a low softening point of 90-100°C. It also makes comprehensive use of the triglyceride components of refined kitchen waste oil, which has a low cost. In addition, the terminal carboxyl group of the polyester resin has small steric hindrance and high activity. Finally, after low-temperature curing with E-12 at 160°C / 15min, the resulting 60 / 40 polyester resin coating has an excellent leveling effect, with a leveling grade of 7 or above. It can be used in indoor coatings in areas with high requirements for leveling grades.

Description

Technical Field

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

[0002] As people's living standards improve, more and more waste oil is generated in daily life and food processing enterprises. In particular, there are floating oil discharged from food processing and tableware washing in the catering industry, waste oil from frying food, scraps of animal and plant oils, acidified oil residues, etc. The main component of these waste kitchen oils is still triglycerides, but they contain a large number of toxic molds and other ingredients that are no longer edible. If these waste oils are directly discharged into the sewer, it will not only block and corrode the pipes, but also cause huge water pollution.

[0003] Powder coatings have the characteristics of no solvent pollution, 100% film formation, and low energy consumption. They have developed rapidly in recent years. However, with the sharp rise in the price of petrochemical raw materials, the price of raw materials needed by the powder coating industry has also increased greatly. For example, the price of polyester resin and E-12 epoxy resin has increased by more than 30% on average, which has brought obvious cost pressure to downstream customers. Since the composition of E-12 epoxy resin is almost impossible to change, customers are in urgent need of low-cost polyester resin to reduce the cost of powder coatings. In the current conventional indoor coating, 60 / 40 powder coatings can perfectly achieve the balance between cost and performance, with good performance and suitable polyester and epoxy resin ratio, the highest cost performance, and large dosage. In recent years, with the development of coating technology, the requirements for high-leveling coatings for indoor furniture coatings have become higher and higher. In the current industry development, how to reduce the cost of polyester resin in 60 / 40 powder coatings and enhance the leveling ability of indoor furniture coatings are technical problems that need to be solved urgently. Summary of the invention

[0004] In view of the above problems, the present invention starts with the design and synthesis of polyester structure, and mainly uses refined kitchen waste oil, trimethylolpropane, 1,2,6-hexanetriol, triethylene glycol, isophthalic acid, brazil acid, terephthalic acid, and adipic anhydride as main raw materials for polymerization; the polyester resin chain segment finally obtained contains a large amount of C 16 -C 18 The product has esterification group, excellent water resistance, low softening point, basically at 90-100℃, and comprehensive utilization of the triglyceride component of refined kitchen waste oil, low cost, and the terminal carboxyl group of the polyester resin has small steric hindrance and high activity. Finally, the coating film of the 60 / 40 type powder coating after low-temperature curing with E-12 at 160℃ / 15min has excellent leveling effect, and the leveling grade reaches level 7 and above. It can be used in indoor coatings in fields with high requirements for leveling grade.

[0005] The invention relates to a low-cost, high-leveling polyester resin for powder coatings, which is obtained by polymerization reaction using raw materials including refined kitchen waste oil, trimethylolpropane, 1,2,6-hexanetriol, triethylene glycol, isophthalic acid, brazilic acid, terephthalic acid and adipic anhydride.

[0006] Wherein, the main component of the refined kitchen waste oil is C 16 -C 18 triglycerides, which is similar to the common vegetable oil components, by weight, of which C 16 -C 18 The triglyceride content is 92-95%, C 16 -C 18 The content of diglyceride and monoglyceride is 2-5% in total, and the moisture content is ≤3%.

[0007] The polyester resin for low-cost, high-leveling powder coating as described above, wherein the raw materials include, by weight:

[0008] 850-1300 parts of refined waste cooking oil;

[0009] 135-200 parts of trimethylolpropane;

[0010] 180-245 parts of 1,2,6-hexanetriol;

[0011] 80-130 parts of triethylene glycol;

[0012] Isophthalic acid 340-475 parts;

[0013] 120-154 parts of brazilic acid;

[0014] 100-160 parts of terephthalic acid;

[0015] Adipic anhydride 45-68 parts;

[0016] The raw materials also include catalysts and antioxidants.

[0017] The catalyst is tetrabutyl titanate, and the dosage is 0.1-0.15% of the mass of the refined kitchen waste oil; the antioxidant is a complex of antioxidant 1010 and antioxidant 168, and the mass ratio of the two is 5-7:1; preferably, the mass ratio of the two is 6:1; the dosage of the antioxidant is 0.15-0.3% of the total mass of the raw materials.

[0018] The present invention also relates to a method for preparing a low-cost, high-leveling polyester resin for powder coatings, comprising the following steps:

[0019] A. Add the formulated amount of refined waste cooking oil, trimethylolpropane, 1,2,6-hexanetriol and a catalyst into a reaction kettle, and heat the reaction kettle to 160-170° C. to perform an ester exchange reaction;

[0020] B. Take samples for testing, and use high performance liquid chromatography to detect the content of triglycerides. When the content of triglycerides is lower than 2wt%, C 16 -C 18 Monoesterified dihydroxy compound; continue to add the formulated amount of isophthalic acid and brassyl acid, raise the temperature to 225-230℃ and continue to keep the temperature to carry out polymerization reaction;

[0021] C. Take samples to test the acid value of the reaction polymer. When the acid value is 28-35 mgKOH / g, add the formulated amount of triethylene glycol and terephthalic acid, and continue to heat and polymerize at 225-230°C;

[0022] D. Take samples to test the acid value of the reaction polymer. When the acid value is 20-25 mgKOH / g, add the formulated amount of composite antioxidant, start the vacuum system, and continue to heat up to 230-235°C for vacuum polycondensation reaction;

[0023] E. When the acid value of the polymer is reduced to 8-13 mgKOH / g, the vacuum system is turned off, adipic anhydride is added as a capping agent, and the polymerization reaction is carried out at 225-230°C;

[0024] F. When the acid value of the reactant reaches 47-54 mgKOH / g, stop the reaction, discharge the material while hot, cool the polyester resin, crush it into granules, and obtain it.

[0025] Among them, in step B, the temperature is gradually increased to 225-230°C at a heating rate of 7-9°C, and then the polymerization reaction is carried out by keeping warm; in step C, the temperature is gradually increased to 220-230°C at a heating rate of 8-10°C; in step D, the vacuum degree is maintained at -0.095Mpa to -0.097Mpa; in step F, the polyester resin is cooled by a steel belt with condensed water.

[0026] The present invention also relates to the use of the polyester resin for powder coatings with low cost and high leveling properties as described above or the polyester resin obtained by the preparation method in 60 / 40 polyester resin for powder coatings.

[0027] For example, the method for preparing the low-cost, high-leveling 60 / 40 polyester resin for powder coatings of the present invention may specifically include the following steps:

[0028] A. Add the formulated amount of refined kitchen waste oil, trimethylolpropane, 1,2,6-hexanetriol and catalyst into a reactor, and heat it to 160-170° C. to perform a sufficient transesterification reaction;

[0029] B. Take samples for testing. Use high performance liquid chromatography to detect the content of triglycerides. When the content of triglycerides is less than 2wt%, it means that the main component of triglycerides in the refined kitchen waste oil has been transesterified. 16 -C 18 Monoesterified dihydroxy compound; at this time, add the formulated amount of isophthalic acid and brassyl acid, gradually increase the temperature to 225-230℃ at a heating rate of 7-9℃, and continue to keep warm for polymerization reaction;

[0030] C. Take samples to test the acid value of the reaction polymer. When the acid value is 28-35 mgKOH / g, add the formulated amount of triethylene glycol and terephthalic acid, and continue to heat and polymerize at 225-230°C;

[0031] D. Take samples to test the acid value of the reaction polymer. When the acid value is 20-25 mgKOH / g, add the compound antioxidant in the formula amount, start the vacuum system, maintain the vacuum degree at -0.095Mpa to -0.097Mpa, and continue to raise the temperature to 230-235°C for vacuum polycondensation reaction;

[0032] E. When the acid value of the polymer is reduced to 8-13 mgKOH / g, the vacuum system is turned off, adipic anhydride is added as a capping agent, and the polymerization reaction is continued at 225-230°C;

[0033] F. When the acid value of the reactant reaches 47-54 mgKOH / g, stop the reaction, discharge the material while hot, and pass it through a steel belt to cool the polyester resin, and then crush and granulate it.

[0034] The product obtained by the above preparation method has the appearance of colorless and transparent particles, an acid value of 47-54 mgKOH / g, and a softening point of 90-100°C.

[0035] The polyester resin is mixed with E-12 epoxy resin, titanium dioxide, barium sulfate, leveling agent, brightener, benzoin, etc. to obtain a 60 / 40 mixed powder coating. The coating preparation method is as follows: according to the formula of the 60 / 40 mixed powder coating, the materials are mixed evenly, extruded, tableted, and crushed by a twin-screw extruder, and then the tablets are crushed and sieved to obtain a powder coating; the powder coating is sprayed on the surface-treated tinplate substrate by an electrostatic spray gun, and cured at a low temperature (e.g., 160°C / 15min) to obtain a coating.

[0036] Beneficial effects of the present invention:

[0037] The present invention adopts structural design and selects specific raw materials, firstly, the main component C of refined kitchen waste oil is converted into 16 -C 18 The triglyceride of C was obtained by high temperature transesterification reaction with trimethylolpropane and 1,2,6-hexanetriol.16 -C 18 Monoesterified dihydroxy compounds, mainly C 16 -C 18 Monoglycerides, C 16 -C 18 Trimethylolpropane monoester, C 16 -C 18 1,2,6-hexanetriol monoesters, and then these C 16 -C 18 The monoesterified hydroxy compound is then polymerized with other polyacids and polyols to obtain polyester resin; the resulting polyester resin chain contains a large amount of C 16 -C 18 The product has esterification group, excellent water resistance, low softening point, basically at 90-100℃, and comprehensive utilization of the triglyceride component of refined kitchen waste oil, low cost, and the terminal carboxyl group of the polyester resin has small steric hindrance and high activity. Finally, the coating film of the 60 / 40 type powder coating after low-temperature curing with E-12 has excellent leveling effect, and the leveling grade can reach level 7 and above. It can be used in indoor coatings in areas with high requirements for leveling grade. DETAILED DESCRIPTION

[0038] To facilitate understanding of the present invention, various exemplary embodiments of the present invention are now described in detail. This detailed description should not be regarded as a specific limitation of the present invention, but should be understood as a more detailed description of certain aspects, features and embodiments of the present invention.

[0039] Among the raw materials, the main component of refined kitchen waste oil is C 16 -C 18 triglycerides, of which C 16 -C 18 The triglyceride content is 92-95wt%, C 16 -C 18 The content of diglyceride and monoglyceride in total is 2-5wt%, and the water content is ≤3wt%, which is purchased from Foshan Longao Environmental Protection Technology Co., Ltd.; the rest are commonly used commercially available raw materials.

[0040] Example 1

[0041] A low-cost, high-leveling polyester resin for powder coatings, the raw materials comprising by weight:

[0042] 900 parts of refined kitchen waste oil;

[0043] 145 parts of trimethylolpropane;

[0044] 200 parts of 1,2,6-hexanetriol;

[0045] 90 parts of triethylene glycol;

[0046] 350 parts of isophthalic acid;

[0047] 125 parts of brazil acid;

[0048] 110 parts of terephthalic acid;

[0049] Adipic anhydride 50 parts;

[0050] The catalyst is tetrabutyl titanate, and the dosage is 0.15% of the mass of refined kitchen waste oil;

[0051] The antioxidant is a complex of antioxidant 1010 and antioxidant 168, and the mass ratio of the two is 6:1; the amount of the antioxidant is 0.2% of the total mass of the raw materials.

[0052] The preparation method comprises the following steps:

[0053] A. Add the above-mentioned amount of refined kitchen waste oil, trimethylolpropane, 1,2,6-hexanetriol and catalyst into a reactor, and heat it to 165° C. to carry out a sufficient transesterification reaction;

[0054] B. Sampling for testing, using high performance liquid chromatography to detect the content of triglycerides. When the content of triglycerides is 1.5wt%, it means that the main component of triglycerides in the refined kitchen waste oil has been transesterified, and C 16 -C 18 Monoesterified dihydroxy compound; at this time, add the formulated amount of isophthalic acid and brazilic acid, gradually increase the temperature to 228°C at a heating rate of 8°C, and continue to keep warm for polymerization reaction;

[0055] C. Take samples to test the acid value of the reaction polymer. When the acid value reaches 31 mgKOH / g, add the formulated amount of triethylene glycol and terephthalic acid, and continue to heat and polymerize at 228°C.

[0056] D. Take samples to test the acid value of the reaction polymer. When the acid value reaches 22 mgKOH / g, add the compound antioxidant in the formula amount, start the vacuum system, keep the vacuum degree at -0.096 MPa, and continue to raise the temperature to 232°C for vacuum polycondensation reaction;

[0057] E. When the acid value of the polymer is reduced to 10 mgKOH / g, the vacuum system is turned off, adipic anhydride is added as a capping agent, and the polymerization reaction is continued at 228°C;

[0058] F. When the acid value of the reactant reaches the expected value, stop the reaction, discharge the material while it is hot, and pass it through a steel belt to cool the polyester resin, and then crush it into granules.

[0059] The acid value of the polyester resin finally prepared was 49 mgKOH / g and the softening point was 94°C.

[0060] Example 2

[0061] A low-cost, high-leveling polyester resin for powder coatings, the raw materials comprising by weight:

[0062] 1250 parts of refined waste cooking oil;

[0063] 195 parts of trimethylolpropane;

[0064] 240 parts of 1,2,6-hexanetriol;

[0065] 120 parts of triethylene glycol;

[0066] 460 parts of isophthalic acid;

[0067] 150 parts of brazil acid;

[0068] 150 parts of terephthalic acid;

[0069] Adipic anhydride 65 parts;

[0070] The catalyst is tetrabutyl titanate, and the dosage is 0.1% of the mass of refined kitchen waste oil;

[0071] The antioxidant is a complex of antioxidant 1010 and antioxidant 168, and the mass ratio of the two is 6:1; the amount of the antioxidant is 0.3% of the total mass of the raw materials.

[0072] The preparation method is the same as above.

[0073] The acid value of the polyester resin finally prepared was 53 mgKOH / g and the softening point was 98°C.

[0074] Example 3

[0075] A low-cost, high-leveling polyester resin for powder coatings, the raw materials comprising by weight:

[0076] 1000 portions of refined waste cooking oil;

[0077] 170 parts of trimethylolpropane;

[0078] 220 parts of 1,2,6-hexanetriol;

[0079] 100 parts of triethylene glycol;

[0080] 420 parts of isophthalic acid;

[0081] 140 parts of brazil acid;

[0082] 130 parts of terephthalic acid;

[0083] Adipic anhydride 56 parts;

[0084] The catalyst is tetrabutyl titanate, and the dosage is 0.15% of the mass of refined kitchen waste oil;

[0085] The antioxidant is a complex of antioxidant 1010 and antioxidant 168, and the mass ratio of the two is 6:1; the amount of the antioxidant is 0.15% of the total mass of the raw materials.

[0086] The preparation method is the same as above.

[0087] The acid value of the polyester resin finally prepared was 51 mgKOH / g and the softening point was 96°C.

[0088] Example 4

[0089] A low-cost, high-leveling polyester resin for powder coatings, the raw materials comprising by weight:

[0090] 1,100 portions of refined waste cooking oil;

[0091] 178 parts of trimethylolpropane;

[0092] 230 parts of 1,2,6-hexanetriol;

[0093] 110 parts of triethylene glycol;

[0094] 400 parts of isophthalic acid;

[0095] 130 parts of brazil acid;

[0096] 120 parts of terephthalic acid;

[0097] Adipic anhydride 53 parts;

[0098] The catalyst is tetrabutyl titanate, and the dosage is 0.1% of the mass of refined kitchen waste oil;

[0099] The antioxidant is a complex of antioxidant 1010 and antioxidant 168, and the mass ratio of the two is 6:1; the amount of the antioxidant is 0.15% of the total mass of the raw materials.

[0100] The preparation method is the same as above.

[0101] The acid value of the polyester resin finally prepared is 50 mgKOH / g and the softening point is 95°C.

[0102] Comparative Example 1

[0103] Commercially available ordinary 60 / 40 polyester resin, with an acid value of 53 mgKOH / g and a softening point of 116°C, was purchased from Anhui Shenjian New Materials Co., Ltd., model SJ5CT.

[0104] Comparative Example 2

[0105] The other conditions were the same as those in Comparative Example 1, except that the solid condition was changed from 160°C / 15min to 180°C / 15min.

[0106] Application Examples

[0107] According to the formula of 60 / 40 mixed powder coating, the formula in parts by weight is usually as follows:

[0108] 360 parts of the polyester resin obtained in the above examples and comparative examples;

[0109] 240 parts of E-12 epoxy resin;

[0110] 160 parts of titanium dioxide;

[0111] Barium sulfate 180 parts;

[0112] 8 parts of leveling agent;

[0113] Brightener 8 parts;

[0114] 4 parts of benzoin.

[0115] Preparation of coating: Mix all materials according to the formula of 60 / 40 mixed powder coating, extrude, tablet and crush with twin screw extruder, and then crush and sieve the tablets to make powder coating. The powder coating is sprayed on the tinplate substrate after surface treatment with electrostatic spray gun, and cured at 160℃ / 15min to obtain coating.

[0116] Performance comparison

[0117] The coating index test is based on: GB / T 21776-2008 "Testing Standard Guide for Powder Coatings and Their Coatings". The leveling performance adopts the PCI leveling grade, 1-10, the larger the number, the better the leveling.

[0118] The polyester resins prepared in the above examples and comparative examples were used to prepare coatings according to the coating formulation provided by the present invention, and then the coating properties were tested. The results are shown in Table 1 below.

[0119] Table 1 Coating properties of powder coatings

[0120]

[0121] As can be seen from Table 1, the polyester resin synthesized by the present invention can be fully cured with E-12 epoxy resin under low-temperature curing conditions such as 160°C / 15min due to the small steric hindrance of the terminal carboxyl group and high activity. The obtained coating film is flat and smooth, has excellent impact resistance, and the leveling grade is basically 7 or above. The gloss is also relatively high, basically above 93%. In addition, the high added value comprehensive utilization of waste kitchen oil is achieved, which has significant value of industrial circular economy. The ordinary commercially available 60 / 40 polyester resin product in Comparative Example 1 is end-capped with trimellitic acid, has large steric hindrance and high melt viscosity, which leads to its inability to fully cure at 160°C / 15min, resulting in the impact resistance, gloss and flow leveling failing to meet the requirements; Comparative Example 2 improves the curing conditions to the conventional curing conditions of 180°C / 15min, and can be fully cured, and the appearance, impact resistance and leveling grade of the coating film basically meet the application requirements. However, due to the high softening point and high melt viscosity, the leveling grade of the coating film after curing can only reach Grade 6, and the gloss is slightly low, which cannot achieve the high leveling effect of the present invention; while the corresponding embodiment of the present invention has a good low-temperature curing effect.

[0122] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A method for preparing a low-cost, high-leveling polyester resin for powder coatings, characterized in that: The steps include: A. Add the formulated amount of refined kitchen waste oil, trimethylolpropane, 1,2,6-hexanetriol and catalyst into a reaction kettle, and heat it to 160-170° C. to carry out transesterification reaction; B. Sampling for testing, using high performance liquid chromatography to detect the content of triglyceride, when the content of triglyceride is less than 2wt%, a monoesterified dihydroxy compound is obtained; continue to add the formula amount of isophthalic acid and brassyl acid, raise the temperature to 225-230°C and continue to keep warm for polymerization reaction; C. Take samples to test the acid value of the reaction polymer. When the acid value is 28-35 mgKOH / g, add the formulated amount of triethylene glycol and terephthalic acid, and continue to heat and polymerize at 225-230°C; D. Take samples to test the acid value of the reaction polymer. When the acid value is 20-25 mgKOH / g, add the formulated amount of composite antioxidant, start the vacuum system, and continue to heat up to 230-235°C for vacuum polycondensation reaction; E. When the acid value of the polymer is reduced to 8-13 mgKOH / g, the vacuum system is turned off, adipic anhydride is added as a capping agent, and the polymerization reaction is carried out at 225-230°C; F. When the acid value of the reactant reaches 47-54 mgKOH / g, stop the reaction, discharge the material while hot, cool the polyester resin, crush it into granules, and obtain; The raw materials are prepared in the following proportions by weight: 850-1300 parts of refined waste cooking oil; Trimethylolpropane 135-200 parts; 180-245 parts of 1,2,6-hexanetriol; 80-130 parts of triethylene glycol; Isophthalic acid 340-475 parts; 120-154 parts of brazilic acid; 100-160 parts of terephthalic acid; Adipic anhydride 45-68 parts; The main component of the refined kitchen waste oil is C 16 -C 18 Triglycerides, C 16 -C 18 The triglyceride content is 92-95wt%.

2. The method for preparing a polyester resin according to claim 1, characterized in that: The catalyst is tetrabutyl titanate, and the dosage is 0.1-0.15% of the mass of refined waste cooking oil.

3. The method for preparing a polyester resin according to claim 1, characterized in that: The composite antioxidant is a composite of antioxidant 1010 and antioxidant 168, with a mass ratio of 5-7:1; the amount of the antioxidant is 0.15-0.3% of the total mass of the raw materials.

4. The method for preparing a polyester resin according to claim 1, characterized in that: In step B, the temperature is gradually increased to 225-230° C. at a heating rate of 7-9° C., and then kept at this temperature for polymerization reaction.

5. The method for preparing a polyester resin according to claim 1, characterized in that: In step D, the vacuum degree is maintained at -0.095 MPa to -0.097 MPa; in step F, the polyester resin is cooled by a steel belt with condensed water.

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