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How to increase the performance of weather resistance

Views:0     Author:Jia Hua Aluminium Co., Ltd     Publish Time: 2019-11-09      Origin:Site

How to increase the performance of weather resistance

Powder coating aluminum profiles is widely used in the construction due to its good performance of weather resistance and environmental. But some buildings will be built near the sea. So they will need the high requirement of the powder coating aluminum profiles. Powder coatings are mainly composed of resin, curing agent, auxiliary agent, pigment and filler, etc.The powder on the surface of the aluminum profiles with the time pass will have a phenomenon in which performance is gradually reduced.  Then to prevent this phenomenon it needs weather resistance. The weather resistance of the powder coating aluminum profiles is a important key which influence the life time. So how to improve the weather resistance of aluminum profiles?

 

There are a lots of element which will influence the performance of weather resistance.The below is kinds of reason.

 

Raw materials

Powder coatings are mainly composed of resins, curing agents, additives, pigments and other materials. The weather resistance of these materials basically determines the weather resistance of the coating. Therefore, in order to improve the weather resistance of powder coatings, firstly, raw materials whose weather resistance is required to meet the requirements of the aluminum profile industry should be selected, and these weather-resistant raw materials should also satisfy other properties of the coating film. When the performance of the coating film conflicts with each other, it can be focused on a certain performance according to the customer's requirements, but the results of the artificial accelerated aging test should meet the requirements of accelerated weathering in GB 5237.4-2008.


Resin

Since resin is the main film-forming substance of powder coatings and is the main component determining the properties of powder coatings and film properties, the choice of resin is crucial. The powder coating polyester resin for aluminum profiles commonly used by large manufacturers in the market was selected, and the 300-hour aging resistance test and the appearance of the coating film were respectively prepared by the same formulation structure and the same manufacturing process, and the results are shown in Table 1.

 

ResinABCDEF
GH
Guaranteed light rate(%)

59

58546354665859
Color difference1.491.231.281.401.341.59

1.19

1.39
Coating appearanceFlat BadFlat BadFlatBadFlatBad

(Accelerated aging conditions are 8 hours light, 4 hours condensation cycle; UVB-313EL lamp, irradiance 0.65W/m2, light temperature 60 °C; condensation temperature 50 °C)


It can be seen from the test results that the resins D, F and H have good weather resistance in a series of resins, but the disadvantage of this resin is that the molecular weight is large and the melt viscosity is high. If applied in the plane powder, the film flow will eventually be caused. Poor flat performance. Therefore, by using a resin with good weather resistance in the powder coating formulation to improve the weather resistance of the plane powder, it must be considered whether the leveling of the coating film will be deteriorated, and whether the customer can accept it after the deterioration.


Curing agent

Although the environmentally friendly type of curing agent of HAA system is well known, its disadvantage is that the curing reaction has the formation of by-products, and the disadvantages such as pinholes and pig pores are easily generated during thick spraying. The film is over-baked and resistant to yellowing and durability is inferior to TGIC system. . [1] The aluminum profile industry is currently difficult to accept these drawbacks of the HAA system, or most powder manufacturers have not solved these drawbacks, so the powder coating for aluminum profiles is still based on the TGIC system. The curing agent TGIC also has a certain influence on the weather resistance of powder coatings.

After aging resistance tests were conducted on TGICs of the top three manufacturers in China, it was found that their aging resistance was basically the same, and there was no major difference. Therefore, it does not make much sense to improve the weatherability of the powder coating by the selection of the curing agent TGIC.

 

The production process

The powder coating production process mainly includes four stages of premixing, melt extrusion, tablet crushing and fractional crushing. The two processes of premixing and melt extrusion have great influence on the weather resistance of the powder coating. The role of premixing is to make the various raw material compositions in the powder coating formulation evenly dispersed, laying a good foundation for melt extrusion. In order to improve the weather resistance, in the pre-mixing stage, the raw materials must be fed in a certain order, and the amount of feed is controlled to be 20%-80% of the mixing tank capacity, and the mixing time is appropriately extended.

Melt extrusion is to homogenize the various components of the powder coating composition, that is, to achieve the composition of each particle in the finished powder coating. In order to improve the weather resistance, in the melt extrusion stage, under the premise of no gelatinized particles, the extruder temperature is appropriately increased (especially in the case of low temperature), and the resin is melted into a fluid to ensure that the pigment can have Good wetting and *large shearing force are beneficial to the high dispersion of pigments and the like, so that the components become a uniform system; while ensuring the production schedule, the extrusion speed can be appropriately reduced to ensure sufficient materials. Melt mixing time; thereby improving the mixing effect, so that the pigment filler in the powder coating is fully coated by the resin, and the particles of various raw material components are uniformly dispersed, especially the curing agent and the resin can be uniformly mixed according to the formula ratio, and when solidified The coating film can be fully cured, thereby increasing the surface compactness of the coating film, and finally improving the weatherability of the powder coating layer.


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