Feasibility study of a HAA system extinction scheme

Text/Wu Ge Qian Xudong Zhu Qiming Li Tong
Anhui Jingcheng New Materials Co.
, Ltd.

Abstract: This article mainly introduces a matting scheme of β-hydroxyalkylamide (HAA) system—M-80 and its use method and coating performance.
Through the weather resistance, boiling water resistance, and neutral salt resistance of the matting coating Test research on haze, acid and alkali resistance, etc.
, found that M-80 can obtain 5% (60°) gloss while taking into account the excellent comprehensive performance.
It is a feasible HAA system matting solution
.

1 Introduction

The coating of the paint not only protects the substrate, but also has the effect of maintaining the beauty.
In order to achieve the desired appearance effect, the gloss of the coating is a very important indicator in the powder coating
.
It is customary to divide powder coatings into high gloss (≥85%), gloss (70%～85%), semi gloss (30%～70%), and matte (10%～30%) according to the gloss of the coating.
), matt (≤10%) coating online coatingol.
com
.
The country does not have uniform regulations on this, and different countries have different classification methods
.

The powder coatings for indoor applications are mostly polyester/epoxy systems, while the powder coatings for outdoor applications are mainly triglycidyl isocyanurate (TGIC) cured polyester systems or β-hydroxyalkylamide (HAA) cured polyesters According to the system, TGIC produces pollution and damages the human body during the production process.
The European Union has banned the use of TGIC, and the domestic control of TGIC will gradually become stricter
.
In the future market, based on higher curing efficiency and no irritation to the environment and human body, HAA curing polyester system will have better development potential in powder coatings for outdoor applications
.

 

However, it is difficult to achieve satisfactory matting effect for HAA cured polyester system coatings on the market.
Even if some HAA cured polyester matting systems reach low gloss, they will have many defects such as poor leveling, or need to match specific polyesters.
, So its application is greatly restricted
.

1.
1 HAA curing reaction mechanism

HAA is a polyhydroxy compound.

Generally, the esterification reaction of fatty alcohol can be carried out at a high temperature above 225°C or by using a catalyst, but due to the presence of amide groups, β-hydroxyalkylamide can be carried out at 150°C through an intermediate containing an oxazolidine structure The esterification reaction does not require a catalyst, as shown in Figure 2
.
In powder coatings, the hydroxyl group of β-hydroxyalkylamide undergoes an esterification reaction with the end carboxyl group of the polyester resin at a certain temperature to increase the crosslink density of the polyester to achieve the effect of a curing agent
.

1.
2 HAA system extinction solution-M80
 

Anhui Jingcheng is committed to improving industry efficiency and reducing industry costs, focusing on the research and development of powder coating matting agents and other auxiliary products used in different systems
.
In response to the current market demand, Anhui Jingcheng launched the M80 matting product suitable for HAA curing polyester system.
Through the mechanism of different reactivity of high acid value polyester and low acid value polyester in the curing process, the surface of the coating film shrinks uniformly.
To achieve the effect of matting
.

 

This article introduces the application method and coating performance test of M-80.
M80 matting product is a carboxyl-terminated polymer, which needs to consume a certain amount of HAA curing agent, which can match most of the universal acid values ​​on the market with 30 mgKOH/g The polyester of the left and right can obtain a gloss of 5 degrees when the coating film is leveled well
.
The coating weather resistance, salt spray resistance, boiling water resistance, acid and alkali resistance, etc.
can meet industrial needs, so M-80 is a feasible HAA system matting solution
.

2 M-80 preparation method of paint coating

2.
1 Main raw materials and equipment

The main raw materials and experimental instruments used by M-80 to prepare paint coatings are shown in Table 1 and Table 2
.

2.
2 Sample preparation method

2.
2.
1 Ingredients
 

Weigh M-80, polyester, fillers, curing agents, pigments, additives, etc.
according to the formula, and pre-mix them evenly
.

2.
2.
2 Mixing and tableting

Put the pre-mixed raw materials into the twin-screw extruder.
The working principle of the extruder is shown in Figure 3
.
Through the shearing force of the screw extrusion, the raw materials are in a uniformly dispersed molten state at an appropriate screw temperature
.

After the screw is extruded, the raw material in the molten state is compressed through the double drums with cooling water to be in the state of flakes, and then cooled by the fan, and the flakes are taken and coarsely crushed
.

2.

The coarsely crushed flakes are pulverized in a multifunctional pulverizer to form fine powder particles, which are sieved through a 180-mesh inspection sieve to obtain fine-grained powders, which are used as powder coatings for experimental testing

2.

Pour the prepared powder coating into the electrostatic spray gun, and select the pretreated clean tinplate.

M-80 matting products mainly have the characteristics of low gloss and high degree of general matching in the market.

 3.

In order to verify whether the M-80 product can be combined with the commonly used outdoor polyester with an acid value of 28~34mgKOH/g on the market to achieve a universal matching matting effect, we selected polyesters of different brands from multiple manufacturers and used the first group in Table 3.

It can be seen that M-80 can match most common polyesters with an acid value of 28~34mgKOH/g in the market.

3.

3.
4 Factors affecting the surface morphology of coatings prepared by M-80

The paint coating prepared by using M-80 has a certain difference in surface morphology according to the matched oligoester, but the overall leveling meets actual requirements.
As shown in Figure 4, the thickness of the coating film is more than 70μm.
Achieve a smooth and fine leveling morphology
.
In the HAA cured polyester system, there are many other factors that affect the surface morphology of the coating
.

 3.
4.
1 Effect of curing agent

Relatively speaking, the hydrophilic and oil-repellent properties of HAA will cause the curing agent to be unevenly dispersed in the polyester, so it is best to choose a well-dispersed HAA curing agent such as KC552 (Anhui Jingcheng), etc.
, to avoid HAA agglomeration.
And in the pre-mixing stage, try to make HAA and polyester mixed evenly
.
As shown in Table 6, with the same raw materials and formula, when undispersed β-hydroxyalkylamide is used as the curing agent, the curing agent cannot be dispersed well during the curing process, which will cause orange peel to form on the surface of the coating, which will affect The coating is beautiful
.

3.
4.
2 The influence of coating film thickness
 

The powder coating rate of HAA cured polyester system is very high.
It is best to ensure uniform spraying during spraying and ensure that the thickness of the coating film is above 60μm.
Excessive thickness differences and partial thin coatings will cause poor appearance
.

3.
4.
3 Impact of film spraying equipment

An electrostatic spray gun with good spray atomization state should be used for spraying.
A spray gun with poor spray atomization effect will agglomerate the powder during the spraying process, causing the powder sprayed on the iron plate to fail to flow during curing to form a smooth coating film
.

3.
4.
4 The effect of pinholes in the HAA cured polyester system

Since water is generated during the curing process of HAA, when the coating film is thick, the water vapor generated during the curing process cannot be discharged from the inside of the coating
.
After cooling, the surface of the coating collapses to form pinholes .
This kind of defect can be solved well by using wax or defoamer surface additives, and at the same time, it can also achieve the effect of auxiliary leveling
.

3.
4.
5 The effect of yellowing of HAA cured polyester system
 

Since HAA itself contains an amide group, and there will be some free hydrogen protons in the carboxyl-terminated polyester, the amino group in the amide group and the active hydrogen will easily form an azo chromophore under the environment of heat, light, and ultraviolet light, which absorbs Visible light of a certain wavelength appears yellow to the outside
.
During the heating and curing process, there will be enough heat, and water will be generated during the reaction, creating conditions for yellowing
.
Therefore, adding some hindered phenol and phosphite antioxidants will improve the yellowing
.

3.
4.
6 The influence of twin screw extruder process parameters

The melt extrusion process is the core of powder coating preparation management and control, and the extruder is the main equipment of the process, so it is particularly critical to set the appropriate operating parameters of the extruder, which has an important impact on the quality of the powder coating coating
.
As shown in Table 7, the process parameters of twin-screw extrusion have little effect on the surface morphology of the coating, and M80 has strong applicability to different production line equipment
.

3.
5 Weather resistance of coatings prepared by M-80
 

Adopt ASTM G154-2006 "Operation Standard of Fluorescent UV Exposure Equipment for Non-metallic Materials", select UVB-313 fluorescent lamp and CYCLE 7, respectively to test the powder coating coating prepared by M-80 and the powder coating coating of TGIC system, and compare For the experiment, the experimental steps are shown in Table 8
.

The test results are shown in Table 9.
Compared with the TGIC system, HAA cured M-80 polyester with matching acid value of 28~34mgKOH/g has an advantage in both gloss retention and color difference after UV aging test
.

3.
6 Storage stability of M-80 prepared paint coating

Adopt GB/T 21782.
8-2008 "Powder Coatings.
Part 8: Evaluation of Storage Stability of Thermosetting Powders", and test the storage stability at a temperature of 40℃, as shown in Table 10
.
It can be seen that under normal storage temperature, the HAA cured polyester system will not undergo catalytic reaction and has excellent storage stability
.

3.
7 M-80 prepares paint coating boiling water resistance

Adopt GB/T 1733-93 "Determination of Water Resistance of Paint Films" and GB/T 9286-1998 "Crossing Tests of Paints and Varnish Films" to measure the performance of the coatings prepared by M-80 after boiling
.
As shown in Table 11, the changes in gloss and color difference are within the normal range, and the 0.
1MPa boiling water resistance test coating has a slight shedding, which is an unavoidable defect of the HAA system
.

3.
8 M-80 preparation of paint coating acid and alkali resistance
 

Adopt GB/T 9274-1988 "Determination of the resistance of paints and varnishes to liquid media", respectively configure 3% HCl solution and 5% NaOH aqueous solution for testing, as shown in Table 12, fully meet the requirements of outdoor coatings
.

3.
9 Neutral salt spray resistance of M-80 preparation coating

Adopt GB/T 1771-2007 "Determination of Resistance to Neutral Salt Spray of Paints and Varnishes", the test substrate is an iron plate, and two crossing diagonal lines are drawn on the time plate, and the scratches are as deep as the substrate
.
It can be seen from Table 13 that the matting coating prepared by M-80 has excellent neutral salt spray resistance and can meet the application requirements of aluminum profiles and other industries
.

4 Conclusion
 

In summary, in the HAA curing system, M-80 can provide a more complete solution, which can well match the common polyester with an acid value of 28~34mgKOH/g on the market, while ensuring that the matting coating is different Excellent mechanics, optics, weather resistance and other properties
.
Under the general trend that TGIC is gradually restricted in use, products such as M-80 that can meet market demand in the HAA curing system will surely occupy a place
.