Heavy calcium carbonate is a widely used chemical raw material. As a filler and reinforcing agent, it is widely used in papermaking, plastics, coatings, rubber, ink, food, cosmetics and other industries. It can not only increase product volume, save raw materials, but also It can reduce the cost, and can improve the physical properties, printing performance and size setting of the products.
In recent years, in the production and application of heavy calcium carbonate, ultra-fine particle size and product function differentiation have become the development trend and requirements. Modified with heavy calcium carbonate.
Modification method of heavy calcium carbonate
In the traditional sense, the modification method of heavy calcium carbonate should consider its application field, processing method and blending object to select different modifiers and modification methods. However, many western countries pay more attention to the grinding-aid modification of heavy calcium carbonate when grinding it, so as to comprehensively improve the basic qualities such as the dispersibility and affinity of the powder, so that the filling effect of the modified heavy calcium carbonate can reach the best .
In general, the current modification methods of heavy calcium carbonate include the following: physical coating stearic acid modification, chemical surface modification, mechanochemical modification, surface deposition modification and high-energy surface modification.
Among them, chemical modification includes coupling agent (silane coupling agent, titanate coupling agent and aluminate coupling agent) modification, compound coupling modifier modification, polymer coating modification and organic modification and other methods.
From the perspective of practical production and application, the above methods have improved the powder dispersibility and activation effect to varying degrees, but in terms of stability and cost-effectiveness evaluation, there is no consensus in the downstream, and there is still room for improvement.
Grinding aids focus on modification when the heavy calcium carbonate particles are most active, ensuring the best coating and making the amphiphilic state lasting and stable, thus completely solving the problems of secondary agglomeration and high oil absorption of fine powders. Fundamentally improve the fluidity and dispersibility of the powder, greatly optimize the classification effect, while increasing the added value of the powder factory, it enables the downstream factory to expand the filling amount and improve the processing technology.
Features and Benefits of Grinding Aid Modification
(1) Characteristics of modification of grinding aids
The modification of grinding aid is to spray the prepared grinding aid slurry on the stone material from the feeding port of the equipment when grinding the powder. In the mill, through the environmental action of circulating air, mechanical force and high temperature, the particles are naturally formed. It can break the balance of pulverization and agglomeration during the grinding process, and at the same time reduce the polarity of the particles, so as to reduce the agglomeration, improve the lipophilicity, and improve the productivity and powder fluidity.
1. The modification scene is moved forward: from the modification machine to the mill, the prominent feature is the grasp of the time point, and at the same time, the strong wind force and the instantaneous high temperature of the classifier are used to improve the uniformity of the coating of additives Active bonding effect with particles.
2. Pure physical coating: Although there are ions and polymer matrix to form interface bonding during the coating process, the entire modification process has no chemical reaction and is purely a physical coating, which does not affect the grinding process and does not corrode equipment. , on the contrary, it has obvious lubricating effect on the whole grinding process.
(2) Advantages of modification of grinding aids
1. Eliminate the secondary agglomeration of powder from the source kinetic energy
In order to achieve the reinforcing effect of heavy calcium carbonate, the particle size is required to be as small as possible, but the small particle size of heavy calcium carbonate itself has a great specific surface area and surface energy (ie, the reverse agglomeration force relative to the crushing force), It is easy to cause agglomeration to form large particles. These large particles will become stress concentration points in the polymer matrix, which will affect the performance of the product and even cannot be processed downstream. The modification of grinding aids is different from the traditional modification methods. When the surface energy of the powder is the strongest, that is, when the powder is cyclically broken, countless layers of coating are carried out, which completely eliminates the source kinetic energy of secondary agglomeration, and is supplemented with antistatic. And temperature-resistant agent, while eliminating thermal energy and electrostatic attraction, effectively ensuring stable and durable dispersion and fluidity.
2. Fundamentally improve the lipophilicity of the powder surface
There are many hydroxyl groups on the surface of ground calcium carbonate, and water is easily absorbed, making the surface of ground calcium carbonate particles hydrophilic and oleophobic, polar, and difficult to uniformly disperse in the non-polar organic polymer matrix, and it is difficult to be dispersed with the polymer. The interface formed by the matrix has poor adhesion. Converting the polarity of hydrophilic and oleophobic to surface lipophilicity is the main goal of modified powder, and it is also the main means to solve the compatibility between powder particles and organic polymers. The advantages of grinding aid modification are mainly reflected in the grasp of time point and coating mechanism.
(1) Heavy calcium carbonate is ground from natural carbonate minerals. During the grinding process, the minerals undergo reverse dissociation, exposing unsaturated particles Ca2+ and CO32-, and the degree of unsaturation of these particles Ca2+ and CO32- It is very high and has strong activity. It can interact with the moisture attached to its surface to hydrolyze to form active points. The modification of grinding aids is to modify the particles when the particle activity on the surface of the ground calcium carbonate is the strongest. Practice has proved that this is the best time to change the hydrophilic and oleophobic properties of the powder and reduce the surface polarity, which has a significant effect on improving the dispersibility and compatibility of modified ground calcium carbonate in the matrix;
(2) The modification of grinding aid coating is similar in form to modification of physical coating with stearic acid, and it is a kind of physical action process. The molecular structure of the grinding aid is an amphiphilic structure, and part of it is a hydrophilic group (common -OH, -NH2, -NR3+, -COOH, -SO3H and other functional groups), which can pass through ionic bonds, covalent bonds, hydrogen Bonds, crushing, friction and other mechanical forces are tightly adsorbed on the surface of solid particles to prevent the desorption of grinding aids from the surface of heavy calcium carbonate; the other part is lipophilic solvation chains (such as polyester, polyacrylate, etc.) , its polymer molecular chain is very long, which can effectively prevent the re-agglomeration of heavy calcium carbonate particles, and is suitable for dispersing in different polar matrices. Compared with stearic acid coating modification, the effect is much worse than that of grinding aid. Its lipophilic group is alkyl, although the structure is similar to that of polymer, but only has 17 C atoms, which cannot be used in non-aqueous dispersion system. A sufficiently large steric hindrance effect is formed, and the stability is poor, so that the hydrophilic group is easily desorbed from the particles with low polarity or non-polarity, which leads to the re-flocculation of the dispersed ions and the formation of agglomerated particles.
Therefore, the modification of grinding aids has stronger binding force with the surface of heavy calcium carbonate particles, and almost no desorption occurs. These advantages provide excellent advantages for the wide application of heavy calcium carbonate in filled plastics, pigments, inks, coatings and other industries. Basic quality assurance.
3. Improve production efficiency
Grinding aid slurry is mostly treated by superconductor, in the state of small molecules, with high frequency penetration, under the action of wind and mechanical force, the large particles of calcium carbonate particles are accelerated and decomposed into smaller or even micron-sized and nano-sized particles. , effectively improve the mill production capacity, and at the same time, the increase of the unit output of the mill will increase the temperature of the system, increase the internal energy, enhance the chemical activity of the surface of the heavy calcium carbonate particles, and easily adhere to the modifier, making the heavy carbonic acid The internal energy of calcium particles is reduced and is in a relatively stable state.