The effect of filler's physical and chemical properties on coatings

Text/Yuyuan 1, Lu Qiang 2, Zhao Wenfei 2, Yu Ningjia 1

1.

Abstract: Through the study of the physical and chemical properties of 8 commonly used fillers, the influence of the physical and chemical properties of the fillers on the coatings is analyzed mainly around the moisture, Mohs hardness, mineral form, density and oil absorption of the fillers

0 Preface

Extender pigments, also called fillers, include many compounds, mainly salts of barium, calcium, magnesium or aluminum, oxides of silicon or aluminum, or double salts derived from the first two types of substances.

Through the research, comparison and analysis of the physical and chemical properties of 8 commonly used fillers, this article will help paint workers understand the impact of fillers on coatings, and can better grasp and use them

1 The physical and chemical properties of the filler

In this paper, silica, talc, calcium carbonate, barium sulfate, wollastonite, kaolin, mica powder and bentonite are the main research objects

2 The effect of the physical and chemical properties of the filler on the coating

2.

The water content of the filler includes the water inherent in the mineral structure, as well as the water adsorbed on the mineral surface, cracks and infiltration when exposed to the air

2.

Mohs hardness is the performance of the chemical bond strength inside the filler.

2.
3 The influence of mineral forms on coatings

Mineral morphology is the appearance characteristics of mineral single crystals, regular continuous crystals and aggregates, and can usually be divided into columnar, needle-shaped, plate-shaped, fibrous, flake-shaped, granular, and so on
.
In addition, mineral fillers may have one or several forms due to the difference in the origin of mining and the method of obtaining (natural and synthetic), that is, "homogeneous polymorphism"
.

The mineral forms of the fillers studied in this paper and their effects on coatings are mainly manifested in the following four aspects
.

1) Flaky
.
The fillers belonging to the flaky structure include talc, kaolin, mica powder and bentonite, but the subtle structural differences affect their differences in application
.
For example, flake talcum powder and mica powder can be in close contact with the substrate in parallel with the substrate in the coating film, thereby forming a dense protective film, which makes the coating have better permeability resistance, and the coating film exerts good water resistance and Solvent resistance; at the same time, the flaky structure can also improve the bending strength and internal stress of the coating film, and prevent the coating film from cracking due to bending or expansion and deformation of the substrate, resulting in small cracks, thereby improving the adhesion of the coating
.
Kaolin and bentonite belong to a special flaky structure, and both are layered composite structures
.
Kaolin is a layered structural material with a composite unit structure layer composed of a tetrahedral layer and an Al［O(OH)］6 octahedral layer; the main component of bentonite is montmorillonite, which is composed of two pieces of silicate A layered silicate composed of a sheet and an aluminoxoctahedral sheet in the middle
.
The difference between the two: Since the montmorillonite that composes bentonite has negative charges between layers, it can absorb cations, water and organic polar molecules, so bentonite can attract -COOH and -OH in acrylic acid and carboxymethyl cellulose.
It is inserted between the layers to form a three-dimensional network structure, which makes the coating thixotropic and increases the viscosity of the coating; and the interlayer force of kaolin is only van der Waals force, so the interlayer adhesion is weak and the adsorption is not strong, so kaolin has no anti-settling Efficacy
.

2) Crystalline and amorphous
.
Crystalline is a regular geometric shape that can be seen under the microscope, while amorphous refers to the structure of some incomplete crystals or some amorphous solids.
Silica and calcium carbonate have both of these two forms.
Because the difference of crystal morphology not only affects the same filler material with many different physical and chemical properties at the same time, but also affects the different functions of the filler in the coating
.
For example, crystalline silica is quartz sand.
Because of its hard texture and strong abrasion resistance, it can be used in floor paint and real stone paint to improve the abrasion resistance and washing resistance of the coating film; amorphous silica due to chemical stability Good, it not only plays a skeleton role in the coating, but also has the characteristics of high melting point (1704℃) and good heat resistance.
It can also improve the heat resistance and weather resistance of the coating; and the coating industry also uses amorphous Nano-silica is used as an anti-settling agent.
The mechanism of anti-settling is due to the presence of unsaturated residual bonds and hydroxyl groups in different bonding states on the surface of the silica.
Its molecular state is a three-dimensional chain structure.
This structure gives the coating excellent thixotropy.
And dispersion stability
.
Calcium carbonate can be divided into light weight and heavy weight according to the different production process.
Because light calcium carbonate is obtained by chemical processing, and can be obtained by controlling the reaction conditions to obtain specific and regular geometric shapes, such as specific needles and flakes , Spherical or cubic, etc.
, so it belongs to the crystalline form; the heavy calcium carbonate is the minerals that are crushed and thinned by mechanical grinding, and the crystal form remains natural and diversified, which is amorphous
.
Light calcium carbonate is widely used in water-based coatings because of its small particle size, easy dispersion and good gloss; heavy calcium carbonate is ground from calcite, limestone and marble.
Due to its high density and good filling properties, it is suitable for primers It can improve the reinforcement and leveling effect of the substrate; at the same time, because the heavy calcium carbonate has suitable hardness, uniformity and fineness, and low price, it can be used together with titanium dioxide to increase the hiding power of the coating film and reduce the amount of expensive titanium dioxide
.

3) Plate shape
.
The mineral form of barium sulfate is in the form of a plate.
It is the filler with the smallest moisture content listed in this article, so it has the best dispersibility in the paint; it has the characteristics of the smallest oil absorption.
It not only has good filling performance in the paint, but also reduces the resin.
In addition, barium sulfate has good chemical stability, which is resistant to acids and alkalis and is insoluble in water.
After coating, it has a good protective effect on the long-term outdoor application of the coating film, and improves the service life and durability of the coating
.
The disadvantage is that it is dense and easy to settle.
It is mostly used in powder coatings
.

4) Needle or fibrous
.
Wollastonite also has this kind of elongated crystal morphology
.
Acicular wollastonite has an aspect ratio of 10-20, which can act as a smoothing agent in the coating and can also improve the leveling of the coating; fibrous wollastonite helps to tighten the pigments and fillers in the coating.
Play a reinforcement role, thereby improving the mechanical strength, toughness and durability of the coating film; at the same time, the fibrous structure also helps it overlap in the coating film to improve shielding, strengthen the ability to reflect ultraviolet rays, and improve the coating film’s performance.
Weather resistance and aging resistance
.
Because of its high oil absorption, fibrous talcum powder helps to improve the rheology of the coating, prevent the sedimentation of the pigment and the sagging of the paint solution; it also helps to improve the absorption of the stretching stress of the coating film and prevent the coating from cracking.
It also has the characteristics of improving the durability of the coating film; compared with flake talc, the flatness of the coating film made of fibrous talc is slightly insufficient
.

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4 The influence of the density of the filler on the coating 

Pigment and filler volume concentration (PVC) refers to the ratio of the volume of colored pigments and extender pigments in the paint to the total volume of all non-volatile (including resin solids, pigments and fillers) in the formulation.
The calculation formula is: pigment and filler volume concentration = pigment Filler volume/(pigment filler volume + resin dry film volume)×100%
.
The above 8 kinds of fillers are calculated according to 100g, and 100g thermosetting acrylic resin emulsion (density 1.
03g/cm3) is used to prepare paint.
Since the resin emulsion uses xylene (density 0.
86g/cm3) as the diluent, it can be calculated The density of the resin dry film is 1.
19g/cm3
.
From the density of the filler in Table 1, the PVC of a single filler for acrylic paint can be calculated, as shown in Table 2
.

The comparison shows that: 1) Bentonite has the smallest density in Table 1, which is 2.
0-3.
0g/cm3, but it is the largest in PVC with a single filler of acrylic paint, at 49.
79%; among the 8 fillers, sulfuric acid has the highest density.
Barium is 4.
3-4.
5g/cm3, but it is the smallest in PVC with a single filler for acrylic paint, at 31.
57%
.
2) The density of the 8 fillers is sorted from highest to lowest: barium sulfate>mica powder>wollastonite>calcium carbonate>talc>kaolin>silica>bentonite.
Correspondingly, single filler used in acrylic paint PVC is: barium sulfate <mica powder <wollastonite <calcium carbonate <talc powder <kaolin <silica <bentonite
.
As explained above, as a single filler for acrylic paint, the greater the density of the filler, the smaller the PVC; and vice versa
.
3) The influence of the density of the above single filler on the coating is as follows: the greater the density of the filler, the smaller the PVC, the lower the volume of the filler occupies the dry film volume of the coating, the smoother the coating film, the higher the gloss, and the denserness of the coating.
The stain resistance is relatively good, the impact resistance and flexibility of the coating film are better; the lower the density of the filler, the greater the PVC, the higher the volume of the filler accounts for the dry film volume of the coating, the relatively harder the coating film, and the degree of compactness The gloss is slightly lower, the coating film is slightly rough and the stain resistance is slightly poor, but the coating film has relatively good air permeability
.

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5 The influence of oil absorption on paint

（CPVC）（PVC）
。：CPVC=100ρB/（ρB+0.
01·OA·ρP），：ρB（1.
03g/cm3）、OA、ρP
。1CPVC，3
。

：1）1，6～12g/（100g），，65～72g/（100g），10
。CPVC，36.
38%，CPVC，79.
97%，2.
2
。2）18：＞＞＞＞＞＞＞，3CPVC：＜＜＜＜＜＜＜
。：CPVC，，CPVC；
。3）23，8（），CPVC＜PVC（CPVC（）=36.
38%，PVC（）=41.
72%），：，，，；、，，，；，：、、、，，；，，
。CPVC＞PVC，，，CPVC，，
。CPVCPVC2.
53，
。

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Before preparing the coating, the matching of fillers should be determined according to the final use of the coating, and strive to choose those fillers that are convenient to obtain, with good quality and low price, diverse functions, and strong replaceability
.
Therefore, you need to pay attention to the selection of fillers:

1) Select fillers with relatively little moisture to prevent the filler from being affected by moisture and agglomeration, which will affect the dispersion and cause the coating to return to coarse; at the same time, keep the filler as dry and store as possible to avoid the moisture of the filler and the foaming of the coating, thereby affecting The quality and appearance of the coating film
.
 

2) Choosing fillers with moderate Mohs hardness will not only help improve the scratch resistance, scrub resistance and abrasion resistance of the coating, but also avoid the wear of the filler on the mechanical equipment during grinding
.

 3) Fully consider the mineral form of fillers, they play different functions and roles in coatings
.
 

4) When the density of the selected filler is smaller, the PVC will be higher, and the volume of the filler occupied by the dry film volume of the coating is relatively higher, which will reduce the mechanical properties of the coating film; and the greater the density of the filler selected, the higher the PVC will be.
Small, the resin dry film volume accounts for the highest coating dry film volume, which helps to improve the gloss, impact resistance and flexibility of the coating film
.
  

5) When designing the ratio of pigment, filler and resin, in addition to considering the density of the filler, the oil absorption of the filler should also be considered.
When the oil absorption is larger, the CPVC is relatively smaller, which will increase the amount of resin and increase the cost of coating production; The smaller the oil absorption of the filler, the larger the CPVC and the smaller the amount of resin
.