Application and development trend of calcium carbonate in coatings industry

Posted: 2019-07-02

• Shanghai Clirik Machinery company devote to the field of calcium carbonate powder grinding mills more than 15 years. If you have any needs, please consult online.

  
  

  Calcium carbonate is the most widely used extender pigment in paints. It fills the skeleton and substrate in the paint film and improves the performance of the paint.

  o Putty powder, 70-80% is ground calcium carbonate;
  o In the thick paint, the amount of calcium carbonate is generally above 30%; in the water-based paint, the amount of calcium carbonate is 20-60%;
  o In the topcoat, calcium carbonate is an ideal matting filler, such as matt white buttermilk wall paint containing 11.5% of heavy calcium carbonate;
  o Metal anti-rust paint, calcium carbonate has a certain anti-rust effect, the appropriate amount is about 30%;
  o Polyvinyl alcohol 106, 803 and other building interior wall coatings, generally containing light calcium carbonate 16%-20%;
  o Interior paints, such as polyester latex paints, typically contain about 10% calcium carbonate.

  

  
  Application of calcium carbonate in the coatings industry

  1. Calcium carbonate for latex paint

  The role of calcium carbonate in latex paint:
  o As a body pigment, it has a filling effect, making it fine, uniform and white.
  o Has a certain dry hiding power, generally using ultra-fine products, when the particle size is close to the particle size of titanium dioxide, it can improve the hiding effect of titanium dioxide.
  o Improve the strength, water resistance, dryness and scrub resistance of the paint film.
  o Reduce costs, using 10%-50%.

  For example, the ultra-fine heavy calcium carbonate powder(GCC) material has a significant effect on shortening the dispersing sanding time, improving the hiding power, improving the viscosity of the latex, reducing the amount of titanium dioxide and improving the polishing performance of the putty in the production process of the latex paint.

  When designing the coating formulation, the high-performance latex paint uses ultra-fine calcium carbonate, and the low-grade latex paint selects heavy calcium with relatively coarse particle size and low oil absorption.

  At present, the effect of heavy calcium carbonate powder is better in the interior latex paint, the particle size control d97<10μm, d50 is about 1.5μm, whiteness>95%, CaCO3≥98%.

  2. Calcium carbonate for automotive paint

  During the driving process, the bottom of the car and the wheel fenders are often washed by the impact of sediment, gravel and sewage. Therefore, the coating on the surface of the substrate is easily damaged, and the corrosion resistance is lost. The substrate will be very Fast rust and wear.

  In order to solve this problem, it is necessary to apply a vehicle base paint having sandstone impact resistance and corrosion resistance at these locations. PVC plastisol is one of the automotive chassis lacquers. It is mainly composed of PVC paste resin, plasticizer, filler (calcium carbonate), stabilizer, tackifier, solvent and other additives.

  The amount of calcium carbonate will be close to 30% of the total component (depending on the formula), and the addition of nano-calcium carbonate will improve the rheological properties and membrane of the system to a greater extent than ordinary calcium carbonate. Impact resistance.

  The automobile chassis paint is required to be easy to spray during the construction spraying process, has low viscosity and good fluidity, and requires high viscosity after construction to prevent dip and sag. This requires the coating to be at a high shear rate, the viscosity is significantly lower, and it is easy to spray leveling; while at low shear speed or at rest, it has a high viscosity, which prevents the coating from sinking and sag. The performance is called thixotropy, and the nano calcium carbonate product can meet this requirement well in terms of construction performance and structural properties.

  Nano-calcium carbonate for automotive chassis paint has the following characteristics:
  o has a high degree of activation;
  o has a higher yield stress;
  o has good thixotropy;
  

  
  3. Calcium carbonate for ink

  Calcium carbonate is mostly used to reduce the cost and increase the volume of filling ink. Generally, high-performance ultra-fine calcium carbonate is required. The main feature is that the particles are fine, about 0.02-1.0 μm, and the specific surface area is large, with oil absorption. Large quantity, good transparency, good brightness and good stability.

  In practical applications, nano-light calcium powder or nano-active light calcium powder is most suitable. However, the price of nano-active light calcium powder is high, so most of them use nano-light calcium powder as ink production.

  The ink body prepared with the active calcium carbonate has good bone viscosity and good adhesion, has good printing performance, is fast drying, and has no side effects. Due to its small particle size, it exhibits excellent dispersibility, transparency, excellent gloss and hiding power in ink products, as well as excellent ink absorption and dryness, resulting in fine prints and complete dots. Especially after the resin is widely used as the resin binder, the active calcium carbonate has almost replaced other fillers with its excellent stability.

  At present, most of the domestic high-grade ink fillers use ultra-fine calcium carbonate, and must be activated to form a spherical or cubic shape.

  4. Calcium carbonate for powder coating

  Fillers for powder coatings generally contain heavy metals and do not meet the international standards for heavy metals. Especially for products exported to Europe and the United States, the requirements for heavy metal content are extremely strict. Calcium carbonate is a white filler that is both inexpensive and free of heavy metal elements, and can completely replace the commonly used barium sulfate filler in powder coatings. Mainly used for the painting of toys, baby carriages, sporting goods, kitchen utensils and home appliances.

  Application of calcium carbonate in powder coatings:
  o can be used as a filler for high gloss coating products;
  o Semi-gloss coating products, generally can be directly added to calcium carbonate preparation, no need to add matting agent, saving cost;
  o It is a white inorganic pigment that can be used in combination with titanium dioxide to reduce costs;
  o Compared with other fillers, calcium carbonate is most suitable for some environmentally friendly products requiring low levels of heavy metals, such as children's toys, baby carriages, etc.
  o can increase the powder rate and spray area of ​​the paint, especially in the mixed powder.

  For example, ultrafine active calcium carbonate has similar oil absorption and light refractive index to barium sulfate, but the density is much smaller than that of barium sulfate. In the case of the same amount of filler, the density of the powder coating can be lowered, thereby increasing the spray area. At the same time, due to the good charging performance, the powdering rate of the powder coating can be improved. In addition, the edge coverage of the powder coating, the hardness of the coating film, and the properties of loose anti-caking will also be improved to some extent.

  
  Development trend of calcium carbonate in the coatings industry

  1. Nanocrystallization

  In the coatings industry, nano-calcium carbonate has a steric effect, can prevent sedimentation in the coating formulation, and can add whiteness and gloss without affecting the hiding power, which can significantly improve the storage stability of the coating.

  By using the "blue shift" phenomenon, adding it to the latex can form a shielding effect on the coating to achieve the purpose of resisting ultraviolet aging and heat aging, and increasing the heat insulation of the coating. Nano-calcium carbonate as a filler, filled into the coating can greatly improve its flexibility, hardness, leveling, film deposition and permeability.

  Exterior wall coating: Applying nano-calcium carbonate to exterior wall coatings, the coating exhibits strong "hydrophobicity" and the coating's crack resistance and stain resistance are enhanced.

  Water-based latex paint: In general latex paint formulations, all contain a certain amount of rigid particles, and some formulations are quite large. The presence of these rigid particles can cause excessive stress in the coating film, causing cracks in the resin, and nano-calcium carbonate. It is introduced to create more contact chances with the resin, generate more microcracks and cause elastic deformation, and convert more impact energy into heat energy to absorb, thereby improving toughness.

  By adding 2%-5% of the special polymer surface treated nano calcium carbonate to the traditional latex paint, it is found that not only the rheology and the can opening effect of the coating are improved, but also the water resistance and resistance are more surprising. Both the scrubbing property and the hardness are greatly improved, and the increase in the scrub resistance is an increase in the geometric progression.

  At present, nano-calcium carbonate produced by companies such as Shiraishi and Siem of Japan are mainly used to modify the performance of water-based latex coatings.

  Due to its nano-size effect, the large specific surface area, the surface atoms are highly activated and have a high interfacial interaction with the polymer. When added to the coating, the coating obtains a special modification function. Nano-CaCO3 is used in automotive chassis anti-stone coatings and topcoats due to its good thixotropy.

  2. Functionalization

  With the continuous improvement of technology research and development and quality of life, consumers have higher requirements for product functions, and high performance and multi-functionality have become the development trend of the coating industry.

  Adding nano-calcium carbonate, nano-ZnO, etc. to the coating system can make the coating have antibacterial and anti-mildew effects, improve the weather resistance of the coating film, and greatly improve the overall quality of the coating.

  In recent years, some coatings manufacturers and research institutes at home and abroad have begun to study the use of non-metallic minerals and deep processing products to improve or impart new functions to coatings. This field has become a new hot spot in the architectural coatings industry. 

  3. Surface modification

  In recent years, the application of nano-calcium carbonate in coatings to improve coating performance is one of the hot topics in the coatings industry. Nano-calcium carbonate is directly used in coatings, and has the following defects:
  o The surface energy of the particles is high, in a thermodynamically unstable state, and it is easy to agglomerate;
  o Calcium carbonate surface is hydrophilic and oleophobic, has high polarity, is difficult to disperse in organic medium, and has poor adhesion to the base material, easily forming interface defects, resulting in a decrease in coating film performance.

  The application of nanometer calcium carbonate particles in coatings involves the compatibility of nanomaterials with binders. The film-forming binders of coatings and polymers, rubbers and other polymers are significantly different in terms of the type and quantity of functional groups and relative molecular mass. This in turn leads to a difference in the surface polarity of the polymer and the way it interacts with the pigment and filler. In order for nanometer calcium carbonate to be successfully applied to coatings, it is necessary to surface modify the nano calcium carbonate. 

  In addition, with the development of the calcium carbonate industry, a number of special coatings of calcium carbonate have emerged. Some have a specific crystal shape, some have a particle size of less than 0.1, some are not easy to settle, some have high gloss, some are easy to disperse, and more and more high-end manufacturers are looking for calcium carbonate for coatings.

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