powder coating fluidity

1, powder coating mobility and its detection

The fluidity of the powder is the degree of air flow in the fluidized bed, which is an important basis for evaluating the performance of the powder coating. The quality of powder coating flow can usually rest angle or mobility coefficient to measure. The repose angle is the direct detection method of powder flow, the smaller the angle of repose, the better the fluidity. There are two kinds of commonly used detection methods:

1.1 standard funnel method

(Holzer flow meter)

GB/T1482-2010

This method is mainly used to detect the flow of metal powder, metal powder through the measurement of 50g standard size hole of the funnel the time required per s/50g, with longer, said flow worse, and better liquidity.

1.2 natural accumulation angle

(angle of repose, powder angle)

Let the powder through a set of screen flow down and accumulate in the diameter of 1 inch flat plate, when the plate filled with powder, powder cone angle is called the angle of repose angle or pile of powder. The greater the stacking angle, the worse the mobility of the powder, and the better the mobility of the powder.

2, the factors affecting the flow performance

Powder mobility is the basic property of the powder, which is the difficulty of the flow of powder. The performance of powder flow is related to many factors, such as size, shape, roughness, dry humidity and so on. Generally speaking, increasing the friction coefficient between particles can make the powder flow difficult. It is generally the best particle flow of spherical particles, and the particle shape is irregular, small size, rough surface of the powder, its mobility is poor.

In addition, powder flow affected the adhesion of particles, particle surface adsorption, gas or water if adding forming agent will reduce the fluidity of powder, powder flow directly affects the mixing uniformity, liquidity is poor, easy adhesion, while mixing cannot be mixed together.

The glass transition temperature of powder coating determines the flow properties and storage stability of powder coating. The glass temperature of T polymer is improved, the stability of powder is improved, the agglomerate property is decreased, and the fluidity of powder coating is improved. The glass temperature increases with the increase of molecular weight, when the molecular weight increases to a certain degree, the glass temperature of the polymer is not changed obviously. The glass temperature is too high, the number average molecular weight of the resin, melt viscosity, poor mobility, the mechanical properties of the powder coating film decreased. In the production, the molecular weight of the resin is 5000 ~ 2000, and the glass temperature control is more suitable than the range of 50 ~ 65.

3, the effect of flow properties on powder coating

3.1 influence on coating construction

In the process of powder electrostatic spraying, good fluidity powder, like boiling water, looked very fluffy, with flowing water effect, from powder supply barrels to spray powder transmitted light, good atomization powder from the nozzle, overcome the powder coating pellet caused by spraying gun or "spit powder" production abnormal phenomenon. The poor mobility of the powder in the powder barrel, which leads to the low efficiency of powder coating.

3.2 the impact of the process of production and storage

Powder coating has a direct effect on the storage stability of the product. In the process of producing the product, the powder will start to agglomerate. With the push of the time and the storage process of extrusion, powder began to harden. Texture powder coating after loss of texture effect, matt powder also appeared deterioration.

4. Improvement of the flow property of powder coating

The flow of powder coating and storage stability is closely related to the storage stability of powder mainly depends on the resin and curing agent of glass transition temperature, they occupy a large proportion in the formula design, so to play a more important role. Although the amount of curing agent is little, it has a significant effect on the storage property of powder coating. In the case of ensuring the appearance of the film, as far as possible to select a high glass temperature of the resin and curing agent.

In the powder coating formulation, the mass fraction of pigments and fillers have obvious effect on the fluidity, powder coating pigments and fillers is mainly to improve the rigidity of the coloring and the mass fraction of fillers is too high resin is relatively less, the flow performance of powder coating is worse. At the same time in the design process, as far as possible to add or do not affect the glass temperature and storage stability of additives, such as less fluid leveling agent, wax type extinction agent and accelerator, etc.

In addition method improved loose osteoporosis agent powder coating, powder coating decreased angle of repose, the powder is not easy to agglomerate, add after adjustment between the powder coating film of affinity and cohesion, can improve the anti caking temperature of powder coating, powder coating improved storage stability, improve the performance of the powder flow; in addition electrostatic powder spraying, the powder coating is not easy to plug the spray gun, avoiding caking and wall sticking phenomenon. Hubei new material Chemical Co Ltd, dry flow agent 445 belong to this class of additives.

By way of adding extra large specific surface area, strong moisture absorption ability of fumed silica and alumina and other additives, the interlayer formed between particles of powder coating, powder coating to reduce the particle collision and coagulation of opportunities, reduce the attraction and friction between the powder particles and prevent contact between the particles and the powder paint easy to agglomerate. Hubei, an anti caking agent is 466, with inorganic minerals as the main auxiliary organic surface active agent, crushing and processing by air, anti caking