Epoxidized polyester resin and preparation method and application thereof
Technical Field
The invention belongs to the technical field of powder coatings, and particularly relates to an epoxidized polyester resin, and further discloses a preparation method and application thereof in preparation of the powder coating.
Background
The powder coating is 100% solid powder without organic solvent, which is different from oil-based coating and water-based coating, and the powder coating is a novel environment-friendly coating which does not use solvent or water as a dispersion medium but uses air as a dispersion medium, is uniformly coated on the surface of a workpiece and forms a coating film with special purpose after being heated. The powder coating has the advantages of no VOC, environmental protection, energy conservation, high construction efficiency, wide application range and the like, and gradually replaces organic solvent type coatings with the advantages of economy, environmental protection, high efficiency, excellent performance and the like, thereby becoming an important development direction in the coating industry and keeping a faster growth rate all the time. The polyester powder coating is widely applied to the coating field due to the characteristics of excellent durability, decoration, processing formability and the like.
The traditional polyester for powder coating is carboxyl polyester resin or hydroxyl polyester resin mostly, but the polyester of the system can not realize self-curing of the polyester system, and all the polyester needs to be cured by adding a corresponding curing agent. For example, in the case of indoor powder coatings, E-12 epoxy resins are often used in combination with carboxyl polyester resins. However, in the conventional powder coating system, as the E-12 epoxy resin needs to use epichlorohydrin and sodium hydroxide as raw materials in the synthesis process, the E-12 epoxy resin contains a certain amount of sodium chloride and sodium hydroxide, which have certain adverse effects on the boiling resistance of the finally prepared powder coating; meanwhile, the existence of chloride ions also has certain corrosion effect on the metal base material; furthermore, the cost of the E-12 epoxy resin itself is relatively high. These all affect and limit to some extent the properties and stability of the powder coatings.
Disclosure of Invention
Therefore, the technical problem to be solved by the invention is to provide an epoxidized polyester resin and further disclose a preparation method thereof;
the second technical problem solved by the present invention is to provide the use of an epoxidized polyester resin for the preparation of powder coatings.
In order to solve the technical problems, the epoxidized polyester resin comprises the following raw material components in mol percent based on the total amount of the epoxidized polyester resin:
preferably, the epoxidized polyester resin comprises the following raw material components in mol percent based on the total amount of the epoxidized polyester resin:
the epoxidized polyester resin also comprises an esterification catalyst, and the molar amount of the esterification catalyst accounts for 0.05-0.25 mol% of the total molar amount of the raw material components.
The esterification catalyst comprises di-tert-butyltin dichloride.
The epoxidized polyester resin also comprises an antioxidant, and the molar amount of the antioxidant accounts for 0.1-0.3 mol% of the total molar amount of the raw material components.
The antioxidant comprises antioxidant 300, namely 4,4' -thiobis (6-tert-butyl-m-cresol).
The invention also discloses a method for preparing the epoxidized polyester resin, which comprises the following steps:
(1) mixing selected amounts of diethyl terephthalate, mercaptosuccinic acid and 12-hydroxystearic acid, and heating and melting at a temperature below 130 ℃;
(2) adding a selected amount of dihydroxy-1-phenyl ethane, 2, 5-dimethyl-2, 5-hexanediol and neopentyl glycol into the mixed material, adding a selected amount of catalyst, gradually heating to 180 ℃ under the protection of nitrogen, adding a selected amount of glutamic acid, uniformly mixing, and slowly heating until no obvious distillate is evaporated out and the acid value of the reactant is less than 25 mgKOH/g;
(3) adding a selected amount of antioxidant, maintaining the vacuum degree of 40-60mmHg for 2-4h to promote the formation of polyester resin, and stopping the reaction when the acid value is reduced to below 12 mgKOH/g;
(4) cooling the materials to 140 ℃ and 150 ℃, adding a selected amount of resorcinol diglycidyl ether, carrying out heat preservation reaction for 1-3h, stopping the reaction when the acid value of the reactant is less than 2mgKOH/g, discharging at high temperature while the reactant is hot, cooling, crushing and granulating to obtain the resorcinol diglycidyl ether.
In the step (2), the reaction temperature is not more than 235 ℃.
The invention also discloses the application of the epoxidized polyester resin in preparing powder coating.
The powder coating is 60: type 40 polyester powder coating.
The epoxidized polyester resin is formed by copolymerizing diethyl terephthalate, glutamic acid, mercaptosuccinic acid, 12-hydroxystearic acid, dihydroxy-1-phenylethane, 2, 5-dimethyl-2, 5-hexanediol, neopentyl glycol, resorcinol diglycidyl ether and other raw materials, the acid value of the finally obtained polyester resin is lower than 2mgKOH/g, the epoxy equivalent is 900g/mol, the softening point is 85-105 ℃, the epoxy resin can be used for replacing E-12 epoxy resin and commercially available carboxyl polyester with a high acid value (the acid value is 48-52mgKOH/g) to be cured, a coating film can completely meet the requirements of powder coatings, and the prepared powder coatings have better stability and boiling resistance.
The epoxy chloropropane and alkali are not used in the preparation process of the epoxidized polyester resin, so that the final product almost has no chloride residue, the coating performance of the powder coating and the metal substrate are not influenced, and the cost of the powder coating is effectively reduced.
Detailed Description
Example 1
The epoxidized polyester resin described in this embodiment includes the following raw material components in mol percentage based on the total amount of the epoxidized polyester resin:
the preparation method of the epoxidized polyester resin according to the embodiment includes the following steps:
(1) adding selected amounts of diethyl terephthalate, mercaptosuccinic acid and 12-hydroxystearic acid into a mixer, and heating and melting at a temperature of lower than 130 ℃;
(2) adding a selected amount of dihydroxy-1-phenyl ethane, 2, 5-dimethyl-2, 5-hexanediol and neopentyl glycol into the mixed material, adding a selected amount of catalyst, gradually heating to 180 ℃ under the protection of nitrogen, adding a selected amount of glutamic acid, uniformly mixing, and slowly heating until no obvious distillate is evaporated out and the acid value of the reactant is less than 25 mgKOH/g; and controlling the reaction temperature in the whole process not to exceed 235 ℃;
(3) adding a selected amount of antioxidant 300, maintaining the vacuum degree of 40-60mmHg for 2-4h to promote the formation of polyester resin, and stopping the reaction when the acid value is reduced to below 12 mgKOH/g;
(4) cooling the materials to 140 ℃ and 150 ℃, adding a selected amount of resorcinol diglycidyl ether, carrying out heat preservation reaction for 1-3h, stopping the reaction when the acid value of the reactant is less than 2mgKOH/g, discharging at high temperature while the reactant is hot, cooling, crushing and granulating to obtain the resorcinol diglycidyl ether.
As a result of detection, the epoxidized polyester resin obtained in this example had an acid value of 0.7mgKOH/g, an epoxy equivalent of 829g/mol and a softening point of 98 ℃.
Example 2
The epoxidized polyester resin described in this embodiment includes the following raw material components in mol percentage based on the total amount of the epoxidized polyester resin:
the preparation method of the epoxidized polyester resin described in this example is the same as that of example 1.
The epoxidized polyester resin obtained in this example was found to have an acid value of 0.9mgKOH/g, an epoxy equivalent of 842g/mol and a softening point of 101 ℃.
Example 3
The epoxidized polyester resin described in this embodiment includes the following raw material components in mol percentage based on the total amount of the epoxidized polyester resin:
the preparation method of the epoxidized polyester resin described in this example is the same as that of example 1.
The epoxidized polyester resin obtained in this example was found to have an acid value of 0.5mgKOH/g, an epoxy equivalent of 870g/mol and a softening point of 98 ℃.
Example 4
The epoxidized polyester resin described in this embodiment includes the following raw material components in mol percentage based on the total amount of the epoxidized polyester resin:
the preparation method of the epoxidized polyester resin described in this example is the same as that of example 1.
The epoxidized polyester resin obtained in this example was found to have an acid value of 0.8mgKOH/g, an epoxy equivalent of 810g/mol and a softening point of 95 ℃.
Example 5
The epoxidized polyester resin described in this embodiment includes the following raw material components in mol percentage based on the total amount of the epoxidized polyester resin:
the preparation method of the epoxidized polyester resin described in this example is the same as that of example 1.
The epoxidized polyester resin obtained in this example was found to have an acid value of 1.5mgKOH/g, an epoxy equivalent of 892g/mol and a softening point of 89 ℃.
Example 6
The epoxidized polyester resin described in this embodiment includes the following raw material components in mol percentage based on the total amount of the epoxidized polyester resin:
the preparation method of the epoxidized polyester resin described in this example is the same as that of example 1.
The epoxidized polyester resin obtained in this example was found to have an acid value of 1.2mgKOH/g, an epoxy equivalent of 884g/mol and a softening point of 86 ℃.
Comparative example 1
The polyester resin of this comparative example was prepared from the same starting materials as in example 1, except that diethyl terephthalate was not contained.
The acid value of the obtained epoxidized polyester resin is 0.9mgKOH/g, the epoxy equivalent is 819g/mol, and the softening point is 75 ℃.
Comparative example 2
The polyester resin of this comparative example was prepared from the same starting materials as in example 1, except that glutamic acid was not contained.
The acid value of the obtained epoxidized polyester resin was determined to be 1.1mgKOH/g, the epoxy equivalent to be 836g/mol, and the softening point to be 79 ℃.
Comparative example 3
The polyester resin of this comparative example was prepared from the same starting materials as in example 1, except that mercaptosuccinic acid was not included.
The acid value of the obtained epoxidized polyester resin was determined to be 0.8mgKOH/g, the epoxy equivalent weight was determined to be 830g/mol, and the softening point was determined to be 106 ℃.
Comparative example 4
The polyester resin of this comparative example was prepared from the same starting materials as in example 1, except that 12-hydroxystearic acid was not contained.
The acid value of the obtained epoxidized polyester resin is 0.9mgKOH/g, the epoxy equivalent is 839g/mol, and the softening point is 113 ℃ through detection.
Comparative example 5
The polyester resin of this comparative example was prepared from the same starting materials as in example 1, except that dihydroxy-1-phenylethane was not included.
The acid value of the obtained epoxidized polyester resin is 0.7mgKOH/g, the epoxy equivalent is 833g/mol, and the softening point is 90 ℃.
Comparative example 6
The polyester resin of this comparative example was prepared from the same starting materials as in example 1, except that 2, 5-dimethyl-2, 5-hexanediol was not included.
The detection shows that the acid value of the obtained epoxidized polyester resin is 15mgKOH/g, the epoxy equivalent is 846g/mol, and the softening point is 120 ℃.
Comparative example 7
The polyester resin of this comparative example was prepared from the same starting materials as in example 1 except that neopentyl glycol was not contained.
The acid value of the obtained epoxidized polyester resin is 0.7mgKOH/g, the epoxy equivalent is 834g/mol, and the softening point is 88 ℃.
Comparative example 8
The polyester resin of this comparative example was prepared from the same starting materials as in example 1, except that resorcinol diglycidyl ether was not included.
The detection shows that the acid value of the obtained epoxidized polyester resin is 10mgKOH/g, the epoxy equivalent is more than 10000g/mol, and the softening point is 109 ℃.
Examples of the experiments
The polyester resins obtained in examples 1 to 6 of the present invention and comparative examples 1 to 8 were respectively prepared according to the following composition 60: preparation of type 40 polyester powder coating:
and E-12 epoxy resin (acid value less than 1mgKOH/g, epoxy equivalent 846g/mol, softening point 94 ℃ C.) conventionally used in the prior art was used in place of the epoxidized polyester resin of the present invention as comparative example 9.
According to the following steps of 60: 40 the polyester powder coating is prepared by mixing the materials, extruding, tabletting and crushing by a double-screw extruder, and then crushing and sieving the tablets. And spraying the obtained powder coating on the galvanized iron substrate subjected to surface treatment by using an electrostatic spray gun, and curing at 180 ℃/15min to obtain a coating layer.
The detection criteria of the coating index are GB/T21776 2008 'Standard guide for powder coating and coating thereof', and the detection data are recorded in the following table 1.
TABLE 1 powder coating Performance test data
From the above table data, it can be seen that the epoxidized polyester resin of the present invention can be compared with the current 60: the 40-type carboxyl polyester resin is cured and used in indoor powder coating, and has good comprehensive performance.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.