Application research of high-efficiency electrostatic discharge powder coating

Abstract: Polyester/epoxy hybrid system is used as the main film-forming material, and conductive carbon fiber is used as a conductive material component to be added to the basic powder coating formula to prepare a powder coating that efficiently discharges static electricity
.

The conductive carbon fiber has excellent electrical conductivity, so its addition in the formula of this research is small.
Compared with the traditional antistatic powder coating, the cost of the product made by this research has been greatly reduced, and it has a higher cost performance
.

introduction

Anti-static powder coating is environmentally friendly, high safety performance, relatively low cost, easy painting and other characteristics, but also has anti-static this additional special features, has been increasingly widely used in electronic information, chemical safety, coal explosion-proof areas such as paint Online coatingol.

Anti-static powder coatings are also very suitable for household appliances, small household appliances, power distribution cabinets and other civilian fields due to their aesthetics and simplicity
.

Conventional anti-static powder coatings are usually composed of 35%~55% film-forming resin, 10%~30% conductive materials, 15%~30% fillers and 1%~5% additives.

The conductive material is usually added in the production process of the powder coating, which not only makes the utilization efficiency of the conductive material inefficient, but also has a great impact on the basic performance of the final coating due to the high oil absorption value of the conductive material.

.

Traditional conductive materials for anti-static powder coatings are mainly carbon black and metal materials
.
Carbon black is not only polluting and troublesome to operate, but also because of its high addition, it will greatly reduce the impact strength, adhesion and wear resistance of the powder coating itself
.

Not only that, powder coatings using carbon black as a conductive material cannot be toned (only black), which greatly reduces the decorative effect of the coating;

When metal materials are used as conductive materials to be added to antistatic powder coatings, although they can provide richer colors, their relative density is relatively high and the price is high, which greatly increases the production cost of the coatings
.

In this research, a polyester/epoxy hybrid system is used as the main film-forming material, and conductive carbon fiber is used as a conductive material component to be added to the basic powder coating formula to prepare a powder coating that efficiently discharges static electricity
.

Conductive carbon fiber has excellent electrical conductivity, so its addition amount in the product formula of this research is less.
Compared with traditional antistatic powder coatings, the cost of the product in this research has been greatly reduced, and it has a better cost performance
.

1.
Test part
1.

The experimental raw materials and basic formula are shown in Table 1
.

1.
2 Test equipment

Test equipment: mixer, extruder, pulverizer, electrostatic spray gun, oven, salt spray test box, gloss meter, thickness gauge, microscope, surface resistance tester
.

1.
3 Test method

The raw materials weighed according to the test formulas of each group are initially mixed uniformly by a mixer, and then melted, mixed and uniformly extruded by a single-screw extruder.
After the tablet is cooled and crushed, it is crushed by a high-speed mill.
Use a 180-mesh standard sieve to sieve to obtain a powder coating with uniform particle size
.

The powder coating is electrostatically sprayed on the substrate, placed in an oven, and cured into a film under the conditions of 180~200℃/20~10min.
After taking it out, it is naturally cooled to room temperature for testing various properties of the coating
.

2.
Experimental results and discussion
2.

According to previous researches, there are three main theories about the principle of electrostatic discharge of powder coatings, infinite network chain theory, thermodynamic theory and competition theory

(1) The infinite network chain theory was proposed by F.
Butch in 1972.
Its main point is: when the concentration of metal particles in the polymer system reaches a certain critical value, the metal particles will act like a bridge, making Free electron carriers "queue" from one end of the polymer to the other end, turning the insulator into a semiconductor or conductor.
The quality of the conductive network chain composed of conductive particles in the coating determines its ability to discharge static electricity
.

(2) The competition theory believes that the conductive mechanism of conductive powder coatings is the result of competition among three mechanisms: conductive channel, tunneling effect, and field emission
.

Because part of the conductive particles in the coating can contact each other to form a chain-shaped conductive channel, this is the mechanism of the conductive channel;

The tunneling effect and field emission mechanism believes that the coating conduction is not caused by the direct contact of electric particles, but because of thermal vibration or internal electric field, electrons migrate between particles to form an electric current;

Under the condition that the content of conductive material is low and the applied voltage is low, the spacing of conductive particles is larger, and the probability of forming chain-shaped conductive channels is small.
At this time, the tunneling effect plays the main role
.

Under the conditions of low conductive material content and high applied voltage, the internal electric field between conductive particles is very strong, and electrons will have a great opportunity to fly to the interface layer of the film-forming substance and jump to the adjacent conductive particles to generate current.
At this time, the field The emission mechanism plays a major role
.

There are many factors that affect the electrostatic discharge performance of doped electrostatic discharge powder coatings, mainly three factors:

The first is the type and characteristics of the main body of the film, such as the degree of crystallinity, structure type, relative molecular mass, surface tension, and viscosity;

The second is the types and properties of conductive materials, such as the size, dosage, quality stability, and micro-surface characteristics of conductive particles;

Third, the impact produced during the preparation of the powder coating process, such as extruder type, the production temperature, melt-mixing effects
.

(3) Thermodynamic theory believes that the interfacial effect formed between the main body of the coating and the conductive filler has a great influence on the formation of conductive loops in the doped system;

In the process of preparing electrostatic discharge powder coatings, the free surface of conductive filler particles becomes a wetting interface, and an interface layer is formed between the matrix and the filler, and the system produces excess interfacial energy.
As the conductive filler increases, the critical concentration is A parameter related to the interface energy of the system;

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At the same time, due to the excellent conductivity of conductive carbon fiber, the addition amount in the product formulation is small, which overcomes the disadvantages of troublesome production and high cost caused by the high proportion of conductive materials used in the production and preparation process of traditional anti-static powder coatings
.
Compared with traditional antistatic powder coatings, the powder coating products in this study have better cost performance
.