Application and Development of Iron Oxide Pigments in Powder Coatings

Abstract: The development of environmentally friendly powder coatings and the application of iron oxide pigments in powder coatings are introduced
.
As powder coatings have higher requirements for pigment particle size, temperature resistance and other indicators, the application of ultra-fine and temperature-resistant iron oxides in powder coatings has also attracted more and more attention
.

Therefore, the focus is on the development of ultra-fine and temperature-resistant series of iron oxide pigments and the application in powder coatings.

Preface

In the past five years, domestic powder coatings have developed relatively steadily, and have gradually moved from a single level to a road of product specialization

At present, the production of foreign superfine iron oxide powder is mainly concentrated in companies such as Bayer and Huntsman.
With the continuous development of domestic iron oxide companies in recent years, Zhejiang Huayuan Pigment Co.
, Ltd.
has acquired Deqing Totian Sanfeng Pigment Co.
, Ltd.
, Got the technical support of Japan Toda Sanfeng to launch ultra-fine iron oxide powder, and reached the international leading level in powder index
.

Table 2 shows some indexes of Zhejiang Huayuan Pigment Co.

The two major requirements of powder coatings for pigments are good dispersibility of the pigment and good temperature resistance.
The temperature resistance is usually to ensure that it does not change color within 30 minutes at 180°C
.

The dispersibility of pigment powder has two meanings.
One aspect is the dispersibility of the pigment under natural conditions.
The pigment with good dispersibility does not aggregate or agglomerate;

On the other hand, it is the speed of forming the dispersion system in the solvent and the stability of the dispersion system.
The finer the particles, the greater the free energy on the surface, and the tendency to agglomerate, making it difficult to disperse
.

Under normal circumstances, the dispersibility of a pigment is related to the average particle size of the pigment.
Good dispersibility can improve the coloring power, hiding power, and color of the pigment to reduce the cost during use
.

Therefore, the ultrafine iron oxide pigment prepared by Zhejiang Huayuan Pigment Co.
, Ltd.
can be controlled in particle size, so that it can be better used in powder coatings
.

1.
2 Temperature-resistant iron oxide pigments

The temperature resistance of iron oxide pigments is an important indicator of the performance of iron oxide
.
The field of application is generally different, different test methods, the most common are the oven temperature resistance, temperature resistance and the like injection
.

Due to the different internal composition and structure of iron oxide pigments of different colors, their temperature resistance is also different.
For example, iron red has better temperature resistance, and iron yellow and iron black have poor temperature resistance.
The temperature resistance of black pigments is an important issue in the development of iron oxide pigments
.

Zhu Zenglin and Pan Guoxiang studied the topic of improving the temperature resistance of iron yellow and iron black by coating methods, and successfully developed temperature-resistant iron oxide yellow and temperature-resistant iron oxide black products, which made the oven temperature resistance of iron yellow reach 500℃ Above, the oven temperature resistance of iron black can reach above 600℃, which greatly broadens the application fields of iron yellow and iron black
.

Let's take iron oxide yellow as an example to introduce iron oxide pigment temperature-resistant products
.
2 Zhejiang Huayuan Pigment Co.
, Ltd.
iron oven temperature yellow card pictures
.

It can be seen from Figure 2 that Figures 2(a) and (b) are the paint color cards made of ordinary silicon-aluminum-coated iron oxide yellow at 240℃, 5min and 270℃, 5min temperature resistance, Figure 2(c) and (d) It is a paint color card made of slow-release coated iron oxide yellow at 240℃, 5min and 270℃, 5min temperature resistance
.

It can be seen from observation that the color difference of Figure 2 (a) and (b) is relatively obvious, while Figure 2 (c) and (d) of iron oxide yellow coated with slow release are similarly treated at 270°C for 5 min.
The color difference of the paint color card is only 1.
48 (less than 3.
0 is the allowable color difference)
.
This shows that the prepared heat-resistant yellow iron pigment powder can meet the needs of the powder coating industry
.

Figure 3 is a schematic diagram of the iron oxide yellow surface coating process
.
The so-called coating refers to the process of adsorbing or coating one or more substances on the surface of particles to form a core-shell structure of different substances.
The formation mechanism can be roughly divided into chemical bonding, Coulomb attraction and supersaturation theory, etc.

.

At present, the commonly used coating methods include hydrothermal method, precipitation method and surface polymerization method
.
It can be seen from Figure 3 that the ultimate goal of surface coating is to coat the surface of the yellow iron oxide pigment particles with a layer of material to inhibit the elimination of the structural water of the yellow iron oxide, so that it can exist stably at high temperatures
.

At present, the temperature resistance of iron oxide pigments can meet the temperature resistance of powder coatings, but the research on hue stability and vividness of iron oxide pigments is still an important topic for better application to powder coatings
.

2 The role of pigments in powder coatings

2.
1 Composition of powder coating

The powder coating is a new, solvent-free, 100% solid powder coating with environmentally friendly characteristics, which is a general direction for the development of coatings in the future
.

The powder coating is not only in powder form, but also in powder form during use.
The process of melting into a liquid occurs only when it is baked into a film
.

In addition, powder coatings basically do not contain volatile components during use, and 100% of the film-forming materials are coatings, and the theoretical product rate is also 100%
.

At present, the classification of powder coatings can be divided into two types: thermoplastic and thermosetting based on film-forming substances.
The composition of powder coatings is usually four parts: film-forming substances, additives, pigments and functional components
.

The film-forming substance is the basis of the coating, also called the base material; the auxiliary agent is to increase the film-forming property of the powder coating and improve the defects of the powder coating; the pigment is mainly to increase the color and hiding power of the powder coating; the function of the functional component is to increase special features of powder coatings, such as corrosion, fire-retardant, antibacterial
.

In the process of use, the film-forming substance determines the main properties and uses of the powder coating
.
Therefore, suitable film-forming materials and corresponding additives should be selected to meet the requirements of powder coatings in different applications
.

2.
2 The choice of pigments for powder coatings

The use of pigments in powder coatings mainly plays a role in coloring and decorative effects
.
Commonly used are inorganic pigments and organic pigments.
Inorganic pigments have the characteristics of low cost, good light and weather resistance, good heat resistance, strong hiding power, stable hue, etc.
, but they are slightly inferior to organic pigments in the vividness of hue;

Organic pigments have the characteristics of bright color, wide adjustable range of hue, and high tinting power.
However, organic pigments often have disadvantages such as higher cost, poor heat resistance, limited light and weather resistance, and poor hiding power
.

Therefore, inorganic pigments have certain advantages in the use of powder coatings
.
Among inorganic pigments, some varieties of pigments are toxic (such as those containing cadmium, chromium, and lead)
.

Therefore, iron oxide pigments, as traditional environmentally friendly non-toxic pigments, have become the first choice for powder coatings
.
In addition, iron oxide pigments also have the characteristics of a full range of hues and a wide adjustable range of colors
.

2.
3 Requirements for pigments for powder coatings

At present, the pigments suitable for powder coatings can be divided into four categories: color pigments, metallic pigments, functional pigments, and extender pigments according to their properties and uses
.
In addition to imparting various colors to powder coatings, pigments can also improve the relative mechanical properties of powder coatings and reduce costs
.

In the process of use, the requirements of powder coatings for pigments are: pigments do not react during the preparation, storage, transportation and use of powder coatings;

Pigments should be stable and not affected by air, humidity and environment; in terms of coloring, pigments require good dispersibility, tinting power, hiding power and temperature resistance.
Normally, the best dispersion particle size is 0.
2～0.
7μm.
The temperature resistance should be above 180℃, because the general powder coating is baked at 180～200℃;

The pigment should have excellent light and weather resistance, especially in weather-resistant powder coatings, the light resistance should be 7-8 grades, and the weather resistance should also reach 5 grades or more;

Finally, the oil absorption of the pigment is required to be moderate, and the impermeability is good; in addition, it is best not to use toxic pigments, such as lead, cadmium, and chromium toxic metal pigments
.

The properties of iron oxide pigments basically meet the characteristics described above, and they have great potential for use in powder coatings
.
Faced with the problem of poor color vividness of iron oxide pigments, organic pigments and iron oxide pigments are usually mixed to color to achieve the desired hue
.

2.
4 Development of functional powder coatings

With the continuous development of powder coatings, functional powder coatings have become a research hotspot in powder coatings
.
In addition to the decorative and protective effects of traditional powder coatings, functional powder coatings also have certain special functions
.

At present, the research of functional powder coatings mainly includes the fields of insulation, heat resistance, flame retardant, electrical conductivity, anti-corrosion, antibacterial, and radiation protection
.

The preparation method of functional powder coatings is mainly prepared by optimizing and improving traditional powder coatings, including production process optimization, new substance doping, surface treatment and other methods
.

Due to the wide range of uses of functional powder coatings, the huge potential in the application field, and the development of domestic functional powder coatings is in its infancy, there is huge room for development of functional powder coatings in China
.

3 Application analysis of iron oxide pigments in powder coatings

3.
1 Analysis of ordinary iron oxide pigments

Table 3 is the preparation table of common iron oxide red and iron yellow powder coatings
.
The experimental pigments used ordinary iron yellow (NO313) and ordinary iron oxide red (190) from Zhejiang Huayuan Pigment Co.
, Ltd.
, and the comparative pigments were ordinary inorganic red and inorganic yellow commonly used in the market.
The specific formula is shown in Table 3
.

，：Ⅰ/Ⅱ，100℃/120℃；，3000r/m，2min；

；180；3mm，，80μm
。

4，，(NO313)(190)
。

，200℃、10min，(NO313)ΔE0.
06，240℃、25min，ΔE0.
58；240℃、25minΔE1.
58
。

(NO313)
。，(190)
。

(NO313)(190)、，、
。

3.
2

(980T)，5
。

，(980T)12，34，1∶1
。

，：Ⅰ/Ⅱ，100℃/120℃；，3000r/min，2min；

；180；3mm，，80μm
。

Table 6 is an analysis table of the experimental data of temperature-resistant iron oxide yellow
.
Through the analysis, it can be known that the pattern of the heat-resistant iron oxide yellow (980T) on the final application of aluminum profile transfer products has been kept clear, which has obvious advantages compared with the ordinary heat-resistant iron yellow on the market
.

Nowadays, environmental protection is prevalent, and various industries are transforming to green.
All-aluminum furniture is emerging with the demand of the market.
Due to its environmental friendliness, light weight, corrosion resistance, long service life, recyclability, etc.
, it has given the society It has brought huge benefits and has been recognized and used by more and more families.
The entire furniture industry has begun to transform to the direction of all-aluminum thermal transfer wood grain powder
.

At present, domestic pigment companies are closely following the development trend of the powder coatings market and have carried out relevant research on the temperature-resistant series of powders
.

4 Conclusion

With the gradual tightening of environmental protection policies, powder coatings, as environmentally friendly coatings, have great development potential
.
At the same time, powder coatings will also pay more attention to the performance and environmental friendliness of raw materials in the selection of raw materials
.

As a traditional inorganic pigment, iron oxide pigments are widely used because of their environmental friendliness and various hues
.

At present, iron oxide is also constantly developing towards high-end.
Among them, the ultra-fine series and the temperature-resistant series have been improved on the traditional powder, and the temperature resistance and dispersibility of the powder have been improved, which can better meet the needs of powder coatings.
Development
.

The development of powder coatings is gradually developing from traditional to functional powder coatings
.
Functional powder coatings have great potential in domestic applications
.
At the same time, with the development of functional powder coatings, it is also a big challenge to optimize the preparation process and improve the performance indicators of raw materials
.
 

Source: Cai Shuai 1, Li Huiyang 2, Li Hao 2; 1.
Zhejiang Huayuan Pigment Co.
, Ltd.
; 2.
Guangzhou Caihongtu Environmental Protection New Material Co.
, Ltd.