Zhang Huadong Meicheng Industrial Co.
Abstract: This article mainly discusses the selection of the boiling resistance system for aluminum powder coatings.
According to the formula design ideas of aluminum powder coatings, the formula is sorted out and related experiments are carried out.
It is concluded that the TGIC curing is better in the boiling resistance system, and the comparison is super Weather resistance, architectural superior grade, architectural grade products, experimental data are given, and corresponding reference formulas are given.
Aluminum profiles are the main structural materials for doors, windows and curtain walls today, and are widely used worldwide.
Aluminum extrusion (without surface treatment) single appearance, and prone to corrosion in a humid atmosphere, it is difficult to meet high decorative building material of claim weather and strong com" href="http://">coating line coatingol.
In order to improve the decorative effect, enhance corrosion resistance and extend the service life, aluminum profiles generally need to be surface treated.
The surface treatment technology of aluminum profiles can be divided into three categories: anodizing treatment, anodizing-electrophoresis treatment, and organic coating treatment.
Among them, the organic coating treatment includes powder spraying and fluorocarbon spraying.
The partial thickness of the powder coating should be controlled between 40~120μm.
The powder coating is strong and durable, has good chemical resistance, and is simple to produce.
It occupies a large proportion in the surface treatment of aluminum profiles.
The powder coatings in aluminum profiles are typically mixed type, polyester type, acrylic, polyurethane, fluorocarbon, etc.
At present, weather-resistant polyester powder coatings are commonly used, and most of the polyester resins used in powder coatings are saturated types.
According to the structure of its end groups, we usually can be divided into two categories: terminal shuttle bases and terminal meridian bases.
The number average molecular weight of the shuttle-terminated polyester ranges from 2000 to 80009/mol, and the acid value ranges from 2 to 100 mgKOH/g.
Among them, medium and high acid value (45~85mgKOH/g) are generally used in epoxy/polyester hybrid powder coatings, and low and medium acid value (20~45mgKOH/g) polyester triglycidyl isocyanate Vinegar (TGIC) and HAA are used as curing agents to prepare pure polyester powder coatings with excellent weatherability.
Recently, in the process of communicating with our customers, a word frequently appeared, "to be resistant to boiled water", then we have done some related experiments on our products, and obtained some formulas and data.
We hope to discuss with the colleagues from upstream and downstream related companies.
, Make progress together.
2 Design ideas for the formulation of boil-resistant aluminum powder
According to the requirements of the customer's boiling resistance, I have classified our previous products, aiming at the characteristics of the aluminum profile powder coating formulation design ideas:
(1) The weather resistance, high temperature resistance of the film-forming material and the storage stability of the finished powder coating are relatively high.
(2) Curing agent is a cross-linking reaction with polyester resin, so that the powder coating can be over-cured to form a film with certain physical and mechanical properties and chemical resistance.
At present, TGIC and HAA curing agents are commonly used.
(3) Filler: To improve the hardness, rigidity and scratch resistance of the coating film, barium sulfate is generally selected for aluminum profile powder coatings, of course, some mica powder, silica powder, glass beads, etc.
can also be added.
(4) Pigment: The aluminum profile powder needs to choose a pigment with high hiding power, weather resistance, acid and alkali resistance, and high temperature resistance.
All the experiments in this article are mainly white, and no comparison of pigments is made.
(5) Auxiliary: The general requirements of the auxiliary or auxiliary auxiliary for aluminum profile powder are good compatibility, easy dispersion, non-toxic or low-toxicity, less smoke, and anti-yellowing.
Based on the above design ideas, we prepared the following experiments.
3 Experimental part
1 Raw materials
Polyester resin (RD62310; M2311; M2341; RD6960OM; RD69811), TGIC (7 mainstream products in the market), HAA (3 mainstream products in the market), rutile powder, barium sulfate, mica powder, leveling agent, brightener, benzoin , Additives, wax powder, boil-resistant additives, etc.
2 Experimental equipment
Mixing equipment, 32 series twin screw extruder, ACM grinding system, small electrostatic spray gun, high temperature oven, film thickness meter, gloss meter, gelatinizer, beaker, experimental electric furnace, differential scanning calorimeter, etc.
3 Test method
The preparation method is to weigh the resin and curing agent, pigments and fillers, and additives according to the proportion.
The process flow is batching, premixing, crushing, sieving, and electrostatic spraying onto 0.
3mm tinplate, and the film thickness is controlled to be 60~80μm.
The final baking and curing are used to obtain the tested sample.
4 Performance testing standards for paint and film
Boiled test method: GB5237.
4-2004, 6-14-l, we boiled 2H, 4H, 6H respectively.
Glass transition temperature: GB/T 19466.
2-2004, test the glass transition temperature of polyester resin, the heating rate is 10K/min.
Impact performance: According to GB/T 1732-1993, the coating film is positively flushed and recoiled, and the cracking of the coating film is observed.
Gel time: GB/T 16995-1997, test the gel time at 180℃.
Gloss: Test the 60° gloss of the coating film according to GB/T 9754.
4 Experimental results and analysis
1 Comparison of HAA and TGIC systems for boil-resistant aluminum powder coatings
According to the experimental needs, we developed a polyester resin of RD62310, which can react with HAA or TGIC.
The specific indicators are shown in the table below.
We selected 3 mainstream HAAs from the market and TGIC from some companies.
When comparing TGIC, we use architectural superior M23ll as the main comparison polyester resin.
The index and formula of polyester resin are shown in the following table:
From the polyester resin of RD62310, comparing the TGIC and HAA systems, the boiling resistance performance of the TGIC system is obvious from the test results.
Next, we compared the TGIC curing agents from different manufacturers from the market and found that under normal circumstances, the formula is formulated to match the architectural superior grade M23ll polyester resin.
The product parameters are shown in the table.
The comparison test showed that the gloss retention rate for 6 hours of boiling resistance was more than 60%, and only one or two products were slightly inferior.
The boiling resistance of TGIC produced by Meicheng was relatively excellent.
The detailed comparison is shown in the figure below.
In short, comparing the two major systems of HAA and TGIC, we prefer to choose TGIC as the main system for the boiling-resistant formula.
2 Examples of boiling-resistant formulas for aluminum powder coatings
According to the different weather resistance grades of aluminum profile powder, we selected several resins and made corresponding tests.
For the powder formula made from the super weather-resistant polyester resin formula, the boil-resistant gloss retention rate is very good, as shown in the figure.
We have made flexible modification to the super weathering resin.
Adding 3% AD additives can produce a product with a positive and recoil of 50kg·cm, and the boiling resistance and weather resistance will not change.
It is an ideal formula in the super weathering series.
For the polyester resin of architectural superior grade, the prepared formula and we improved the compactness of the coating film surface by adding different layered fillers to achieve boiling resistance.
From the experimental results, it can be seen that it will be good at 2h to 4h.
The performance of the layered filler is basically the same when it slowly reaches 6 hours.
It can be foreseen that the layered filler has improved, but the improvement is also limited.
Of course, we also select the boiling-resistant additives on the market, adding 2% of the amount can play a certain role, and the boiling-resistant performance is relatively better.
The function of boiling-resistant additives is to increase the activity of the resin, increase the degree of curing of the coating, and increase the density of the coating, the better.
Based on the above experimental results, we have developed two more water-resistant architectural grade polyester resins RD6960OM and RD69811.
The product data is shown in the previous form.
From the experimental data, the boil-resistant formula of RD69811 achieves an 8h gloss retention rate of more than 70%, which is an ideal building-grade product.
The boiling resistance of powder coatings is related to the composition of the formulation, curing process, pigments and fillers, and pre-treatment methods.
As a key material in the formulation of powder coatings, polyester resin can appropriately increase its acid value and viscosity, which is beneficial to the water resistance of the coating film.
Powder spraying is an important trend in the development of aluminum profiles at this stage.
Many processes in powder spraying production also have many areas that need to be improved.
Manufacturers are required to continuously modify existing processes to improve the surface treatment level of domestic aluminum profiles and promote aluminum.
The profile industry is developing in a newer, deeper and higher direction to meet the requirements of consumers for higher living standards.