Coating extinction knowledge

Why do we need to extinction?

Items with a matting effect can be seen everywhere in daily life: at home, on the way to work, or in restaurants under the night
.
The interior furniture mostly adopts matt surface, and the wooden panels covering the exterior of the restaurant are basically matted
.

When faced with the choice of gloss or matte effect, we are not limited to fashion and appearance needs coating online coatingol.

1.

What is the'matting effect'? For example, color, whether it is matte or bright appearance, is a subjective impression formed by our sense organs

To be precise, only part of the light irradiated on the surface is directly reflected back, and the rest enters the paint film, scatters inside, and is absorbed by the pigment and the substrate

The intensity of the reflection depends on the flatness of the surface

The condition to obtain a perfect extinction effect is to scatter all the incident light

The micro-roughness of the surface of the paint film is the cause of the light scattering, thus forming a matt-effect surface

2.

Pumice powder was used in the past to polish the outer surface of dry paint films

Figure 1: Formation of matte coating

After the solvent-based paint is applied, the solvent starts to volatilize immediately.

The figure below explains why coatings with high volatile organic compounds (VOC) content are more likely to have a matting effect than coatings with high solids content

It can also be said that the thicker the paint film, the more difficult it is to obtain a matte surface

Figure 2: Paint film slices with matting powder

3.

All matting agents/matting powders used in coatings have their functions and characteristics
.

3.
1, silica

There are many ways to obtain matting agents from silica, which can be divided into two categories according to the manufacturing process
.
One is the gel method, and the other is the precipitation method
.
After treatment, both types of products can be made into standard silica matting agents
.
The treatment process refers to the use of organic (paraffin) or inorganic materials to modify the surface of silica to a certain extent
.
The treated silica has different particle size, particle size distribution and pore volume
.

The matting effect of silica is relatively strong, and the viscosity may increase when used in large amounts
.
There is a tendency to precipitate during storage, especially untreated silica
.

Synthetic aluminum silicate can partially replace titanium dioxide as a high-quality extender and can be used in emulsion primers
.
The product can show a balanced matting effect in the dried emulsion paint film
.
It can be used as a matting agent in long oil alkyd resin system, but it must be dispersed together with pigments and fillers
.
Except in powder coating systems, silica matting agents can be applied to all coatings
.

3.
2 Paraffin

Now, there are many different paraffin wax products on the market
.
Wax products based on polyethylene, polypropylene and Brazilian wax are most commonly used in coatings and inks
.
Wax products based on polytetrafluoroethylene (PTFE) can also be used as matting agents
.

Compared with silica, paraffin wax modifies the paint film by floating on the outermost surface
.
This also affects the following properties: extinction/gloss; anti-slip and anti-fouling properties; anti-blocking and abrasion resistance, anti-settling properties and surface tension resistance
.

Most of these products are micronized, so that they can be used in a wide range of concentrations in wax emulsion-based coatings
.
The dispersibility varies depending on the particle size and particle size distribution
.

3.
3, filler

By using specific fillers, we can significantly increase the pigment volume concentration of the paint, and can affect all aspects
.
This is why the concept of matting is limited to paints, economical low-grade coating systems
.

The particle size distribution range of the filler is very narrow, so it must be dispersed together with the pigment
.
In order to adjust the required glossiness, the silica is usually added and stirred at the end of the coating manufacturing process
.

3, 4 organic materials

Through modern grinding technology, we can grind and process plastics with polymethylurea resin as the base material
.
The product has little effect on viscosity, thermal stability up to 200°C, good solvent resistance, and easy dispersion
.

4.
How to disperse matting agent//matting powder

By studying matting agents, we can divide them into two types: (i) stir and mix with paint, and (ii) disperse with pigments and fillers
.
The second process is easy to implement
.
It can be well dispersed together with pigments and fillers by using appropriate equipment (high-speed disperser, ball mill, etc.
.
.
)
.

figure 1 :

When silica, paraffin or organic matter is used as a matting agent to disperse, there are three different methods that can be used: concentration (color concentrate technology) method; direct dispersion during paint manufacturing; or according to user requirements, in the final stage of paint construction So that the extinction degree can be easily adjusted
.

Concentration methods have advantages and disadvantages
.
The advantage is that the concentrate is easy to obtain and can also be mixed by low-speed agitation with a stirrer
.
The downside is that, firstly, the degree of concentration of the matting agent is not high, and secondly, the solvent will volatilize from the surface of the concentrate, resulting in a decrease in the stability of the paste-like matting agent during storage
.
And it will accumulate to form semi-dry agglomerates, which are difficult to disperse when added to paint
.
Finally, if the slurry concentrate contains resin, it is difficult to be widely used
.

The problem to be considered in the production of coatings is the commonly used mixing method for adding matting agents
.
Use a stirrer or dissolver to mix the soft matting agent with the low-viscosity adhesive
.
Most matting agents are easy to disperse
.
For example, the use of a ball mill can greatly reduce its particle size and obtain a higher gloss.
Therefore, the use of a higher dose of matting agent can adjust the required matting degree
.
When adding a matting agent to adjust the final extinction degree, it needs to be stirred.
The matting agent should also be easily dispersed, and the stirring device should also be simple
.
To ensure that there is enough space in the container, so that the matting agent can be poured from the top, to ensure that the container can be sealed to avoid dust, these are necessary conditions in the production
.

Critical speed m/sec

5.
How to control the dispersion quality of matting agent?

When a matting agent is used, it is necessary to measure the fineness or Hegmann value of the paint to obtain information on the degree of dispersion
.
Furthermore, we can also control the gloss in the 60° range
.

From the main parameters mentioned above, we can see that the gloss of the product must be controlled
.
In addition, measuring 60° and 85° gloss is also very necessary for us to further understand the extinction
.
Since there is no rule for comparison with commonly used coating systems, as an acceptable method, the particle size value can sometimes be defined
.
The fineness can usually be greater than 25 microns, such as silica matting agents
.
Decreasing the particle size value will reduce the matting effect and increase the gloss
.
Viscosity and transparency (used in varnishes and photosensitive coatings) must also be controlled within a relatively standard range
.

6.
Parameters that affect the extinction effect

There are two factors that change the matting effect: the characteristics of the product and the characteristic parameters of the coating
.

   * Concentration of matting agent

   * The performance of matting agent

   * Coating system

6.
1 Concentration of matting agent

Users usually test multiple quality indicators of matting agents
.
They will evaluate the product, different chemical components, manufacturing and concentration technology, and understand the product through blending and understand the difference in dispersion performance
.
Figure 1 shows the effect of an average particle diameter of the matting agent concentration and the degree of influence on gloss
.

6.
2 Performance of matting agent

The smaller the average particle size of the matting agent is, the matting effect is not necessarily better, but the obtained paint film is smooth
.
On the contrary, the larger the particle size, the stronger the matting effect, but the paint film is not smooth
.

In the storage process of varnish, if the particle size of the matting agent is large, there will be a tendency of separation and deposition
.
In particular, untreated silica and fillers must be used in combination with anti-settling agents or fine paraffin wax particles to avoid this phenomenon
.
Fine paraffin wax particles and easily dispersed hydrophobic silica can be recommended because they have a similar refractive index to those additives
.

Commonly used silica, paraffin wax and organic matting agents have the same refractive index as resins, which is one of the reasons why they can be widely used
.
Substrates such as wood, film and leather (natural or man-made) must be covered with clear paint
.
When using a matting agent, the impact on the transparency of the coating must be small.
The selected resin and the matting agent should also have the same'refractive index', because this can increase the transparency of the coating
.
The amount of matting agent in the paint film also affects transparency
.
The more efficient matting agent requires a small amount of addition and can obtain better transparency
.

6.
3, coating system

The typical factors that affect the coating system are (i) the adhesive system, (ii) the application of the coating , (iii) the thickness of the coating, and (iv) the drying conditions
.
The figure below shows the matting effect of different adhesive systems
.

The following figure shows the influence of different construction techniques on the matting effect
.

Sometimes the paint can be dried under different conditions, for example, air drying after a week of forced drying
.
The result is a different degree of extinction
.
The same gloss effect can be increased by applying multiple layers of the same paint film
.

Seven, application areas

The most popular application areas of matting agents in coatings are listed below
.
Explain why matte coatings are so popular in these areas
.