The latest research on improving the impact performance of super weather resistant powder coatings for aluminum profiles

introduction

Powder coatings began in the early 1940s.

Powder coating is easy to implement automated production, which can increase productivity.
Powder coating has become a rapidly developing new coating product and new process, and has now become a recognized coating product that conforms to Type 4E
.

Among them, polyester powder coatings are widely used in outdoor facilities such as buildings, automobiles, and traffic roads due to their excellent comprehensive properties and relatively low cost advantages.
At present, more than half of the thermosetting powder coatings are based on polyester resin.

.

With the expansion of application fields, the weather resistance of polyester powder coatings still cannot meet the needs of the market well.
Super weather resistance and high performance are very important and urgent
.

At present, the existing super weather resistant polyester powder coatings and fluorocarbon powder coatings have initially met the needs of the market in terms of weather resistance, but in terms of physical properties, they lag far behind.
The embarrassing situation of "crack"
.

This research starts from the existing super weather resistant polyester system to study and explore the factors that affect the physical properties of the super weather resistant polyester powder coating system, and initially improves the physical properties of the polyester super weather resistant powder coating, especially the impact performance
.

1.
Formula design of super weather resistant powder coating for aluminum profile

Experimental raw materials: Resin A and Resin B are super weather-resistant resins from different manufacturers
.
The additives used in the formulation are general additives for powder coatings
.

Test standard: GB 5237.

The impact height is used as the test condition for testing the impact resistance of super weather resistant powder coatings: impact height of 50cm, punching depth of (2.
5±0.
3)mm, and decreasing impact strength of 40cm and 30cm
.

After consulting relevant literature and experimental conclusions, the main ways to improve the mechanical properties of the coating film are as follows
.

1.
1 Selection of super weathering resin

Resin is the main film-forming substance of powder coatings, and the most important component that determines the properties of powder coatings and coating film performance
.

Considering the performance of the super weather-resistant coating film, the higher the crosslinking density of the coating film and the better the density of the coating film, the poorer the permeability of the chemical medium and the better the weather resistance of the coating for the same type of resin and curing system
.

Therefore, when choosing a resin, you should choose a variety with strong reactivity, many reactive groups, and high acid value
.
This resin reacts more completely with the curing agent, the crosslinking density of the film-forming material is high, and the corresponding coating has good impact performance
.

In addition, the high glass transition temperature (Tg) of the resin can increase the hardness of the coating film, but it is not conducive to the impact strength of the coating film
.

Relatively speaking, a resin with a low glass transition temperature is beneficial to the improvement of the impact strength of the coating film, but the storage stability of the powder coating is not good.
Therefore, it is necessary to select a resin with a suitable glass transition temperature
.

Table 1 lists two super weather resin wherein the acid value of the resin A moderate moderate reactivity, an acid value of greater reactivity of the resin B was larger than the resin A, the resin A resin having a low glass transition temperature than deg.
] C.
6 B
.

Table 2 shows the impact of different resins on the impact performance.
From Table 2, it can be seen that the impact resistance of the resin A coating film is better than that of the resin B coating film, indicating that the glass transition temperature of resin B is too high and the coating film is brittle
.

Try to add appropriate resin B to the resin A system to increase the crosslinking density of the coating film system and improve the impact strength of the coating film
.

1.
2 The amount of resin in the formulation system

The amount of resin is an important indicator of the coating.
It not only affects the cost of the coating, but more importantly, the amount of resin directly affects the performance of the coating
.
In addition to transparent powders, general powder coatings add pigments and fillers such as barium sulfate in order to reduce costs and improve performance
.

Generally speaking, the impact performance of a coating with a large amount of resin is better than a coating with a small amount of resin.
Therefore, appropriately reducing the mass fraction (or volume fraction) of the pigment and filler in the formulation is beneficial to improve the impact strength of the coating film
.

It can be seen from Table 3 that the resin content of 5# to 8# increased from 50% to 65%, and the impact performance difference was obvious.
The impact performance of the coating film increased with the increase of the resin content
.
9# and 10# have improved impact performance due to the addition of toughening agent
.
However, from the degree of improvement, it is obvious that the impact performance of the coating film with a high amount of resin is better
.

The experimental results show that the greater the amount of resin, the better the impact performance of the coating film, but the increase in the amount of resin will increase the cost, so this study chooses the 7# formula for further improvement

1.
3 Degree of completion of curing reaction

In powder coating formulations, the more complete the reaction between the resin and the curing agent, the better the impact strength of the coating film

In order to make the cross-linking and curing reaction of the resin and the curing agent complete under the baking conditions, a system with high reactivity between the resin and the curing agent should be selected, that is, a system with a short gel time of the powder coating should be selected

As shown in Table 4, the same group of powder selects three groups of curing conditions of 200℃/10min, 200℃/15min, and 210℃/15min for testing

200℃/10min is the grouping of curing conditions, the impact strength of the coating film is obviously worse than that under normal curing conditions; while the grouping under 210℃/15min curing conditions, the impact strength of the coating film is slightly better than that under normal curing conditions

The length of the curing time has a direct relationship with the completeness of the coating.

It can be seen from Table 5:

(1) The amount of resin is 56%: the impact performance is poor when no curing accelerator is added, and the gel time is slightly longer
.
The coating film is slightly cracked at the impact height of 30cm, and the coating film is cracked when it is more than 30cm
.

The addition of 0.
15% curing accelerator has a greater impact on the gel time and speeds up the reaction
.
The impact performance of the coating film is improved significantly, and the impact height can be over 30cm
.
The coating film is slightly cracked when it is more than 30cm;

(2) The amount of resin is 60%: when no curing accelerator is added, the gel time is shorter than that of 56% resin, the reaction speed is faster than 60% resin, and the impact performance of the coating film is better than that of 56% resin.
；

After adding the curing accelerator, the gel time is shorter, the reaction speed is faster, and the impact performance of the coating film is significantly improved, which can pass 50cm
.
When the coating film thickness is thicker, the impact performance decreases significantly
.

It can be seen from the above experimental results that the degree of completion of the coating film reaction has a great influence on the impact performance of the coating film
.
The higher the completion degree of the coating film reaction, the better the impact performance
.

The study found that measures can be taken to extend the curing time or increase the curing temperature to improve the impact performance
.

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1.
4

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6：

（2）60%：，70μm30cm ，30μm，
。80μm
。

，80～100μm 50cm
。
。

From the analysis of the experimental results, the addition of plasticizers greatly improves the impact performance of the super weather-resistant powder coating film, but the addition of plasticizers may affect other properties of the coating film
.

In summary, in order to obtain super weather resistant powder coatings with excellent comprehensive performance, the first consideration is to choose a resin with high reactivity and high crosslinking density, and secondly, to increase the amount of resin as much as possible within the controllable range of production costs;

2.
Conclusion

As the production environment attracts more and more attention, the development of powder coatings will surely become the mainstream.
Among them, super weather resistant polyester powder coatings will become more and more due to their excellent weather resistance and excellent comprehensive performance.
Perfect and mature, the system will be more
.

However, the existing super weather-resistant polyester powder coatings have limited physical properties compared with ordinary weather-resistant powder coatings, which limits their application range
.
Now that technology is changing with each passing day, the development of new technologies and new theories will surely improve its performance
.