Research on the Extinction Effect of Aromatic Amine and Zinc Ion Complex in Powder Coatings

Abstract: Zinc 2-mercaptobenzothiazole (ZMBT) is widely used in the extinction system of powder coatings.

1 Introduction

The powder coating matting system based on zinc 2-mercaptobenzothiazole (ZMBT) is currently the most widely used; the system has stable matting effect, strong gloss adjustment, and excellent anti-yellowing performance, but the powder coating is stable in storage Poor paint online coatingol.

Based on the above assumptions, we choose two aromatic amine epoxy curing agents: 4,4-diaminophenylmethane (DDM) and 4,4-diaminodiphenylsulfone (DDS).

2 Experimental part

2.

Zinc chloride (analytical purity), ethanol (95%), DDM, DDS, ZMBT, zinc dimethyldithiocarbamate (ZDEC, melting point 250°C), epoxy resin E-12, new Chinese method 50/ 50 polyester P5086, Anhui Shenjian 50/50 polyester SJ3#B, Yulin polyester YL5050, aluminum salt, matting barium, brightening agent, leveling agent, benzoin, carbon black, etc.

2.

Three-necked flask (500mL), oil bath heating pot with magnetic stirring, suction filter device, twin-screw extruder, high-voltage electrostatic spraying equipment, constant temperature blast oven, coating thickness gauge, gloss meter, coating impactor, metallographic microscope

2.

The synthesis process of the aromatic amine/zinc salt complex is as follows [4], add 19.

2.

Add 24.

2.

The experimental resin, curing agent filler, etc.

3 Results and discussion

3.
1 Cured epoxy resin matting

According to the data in Table 1, the four kinds of zinc ion complexes can cure epoxy resin well, and the impact performance of the coating film is good; from Figure 2, it can be seen that ZMBT, DDM/Zn2+, DDS/Zn2+ produce flat after curing For the matte surface, the microscopic surface morphology is very close, which is in line with the assumption
.

ZDEC is not a combination of epoxy resin curing agent and zinc ion, and does not conform to the "epoxy curing agent + zinc ion" structural model.
The reason why epoxy resin can be cured is due to the zinc ion in ZDEC; zinc chloride is a This kind of Lewis acid itself can promote the epoxy ring-opening reaction, but the reaction speed is too fast and should not be used alone [3].
The ligand in ZDEC changes the reactivity of zinc ions to make ZDEC curable epoxy resin; surface morphology of coating film The cause of wrinkles may be that the curing reaction speed is too fast; and the matting effect is caused by the wrinkle effect of the coating film
.

ZMBT, DDM/Zn2+, DDS/Zn2+ curing epoxy resin has a big difference in gel time, which is exactly the same as the reactivity sequence of the three ligands MBT, DDM, DDS and epoxy resin; DDS has the weakest reactivity, so DDS /Zn2+ curing epoxy has the longest gel time; MBT has the strongest reactivity, and ZMBT has the shortest gel time
.

3.
2 Extinction of the mixed system

According to the data in Table 2, ZMBT, DDM/Zn2+, DDS/Zn2+ can achieve effective extinction in the mixed system, which can reduce the gloss by about 10% and the surface is flat; it can be seen directly from the microscope photo in Figure 3; the blank group (a) The surface morphology is relatively flat, and DDM(b), ZMBT(c), DDS(d) can all change the micro-roughness of the coating film surface, resulting in denser and deeper "small holes", thereby extinction
.
Because ZDEC does not conform to the "epoxy curing agent + zinc ion" structural model, it cannot produce a matting effect in the mixed system;

Because zinc ion compound can be considered as a synergistic curing agent for epoxy resin, its melting point is higher, thereby prolonging the curing time of epoxy resin; therefore, ZMBT, DDM/Zn2+, DDS/Zn2+ are added to the mixed system formula, and the gel time is uniform.
Higher than its corresponding blank group
.
Among them, ZMBT has the weakest effect on curing time, while DDS/Zn2+ has the most obvious effect on curing time, extending from 225 s in the blank group to 300 s; the difference in gel time is caused by the reaction of MBT, DDM, DDS and epoxy groups Due to the speed difference, this may ultimately affect the compound extinction properties of the zinc ion compound
.

3.
3 Compound matting system

It can be seen from Table 3 that since DDM/Zn2+ and DDS/Zn2+ are less reactive than ZMBT and the powder coating has a longer gelling time, only the combination of ZMBT and aluminum salt can produce a significant gain matting effect.
The gloss increases instead
.

4 Conclusion

This article verifies the hypothesis that the "epoxy curing agent + zinc ion" model can be extinct from three levels
.
① Cured epoxy resin extinction; ② Mixed system extinction; ③ Compound gain extinction; 4,4-diaminophenylmethane (DDM) and 4,4-diaminodiphenylsulfone (DDS) do not conform to the third in the extinction effect Due to the different reactivity of the ligands, MBT is obviously a more "suitable" epoxy curing agent combined with zinc ions; this article verifies the feasibility of the "epoxy curing agent + zinc ion" structural model for extinction.
It is helpful to understand the extinction mechanism of ZMBT in powder coatings
.

references:

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[2] Li Defa.
Study on accelerator M (2-thiol benzothiazole) modified epoxy resin adhesive [J].
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[3] Hu Yuming, Wu Liangyi.
Curing agent [M].
Beijing: Chemical Industry Press, 2004: 377.

[4]Jaideva Singh.
L&R.
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Hemakumar Singh＆R.
Chitra.
Synthesis, spectroscopic, powder X-ray diffraction and DNA binding studies on copper(II) complexes of 4,4'-diaminodiphenyl sulfone[J].
J IRAN CHEM SOC (2012) 9:441-448.

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