Ink is a fluid substance in which pigment particles are uniformly dispersed in the binder and has a certain viscosity. It is an indispensable and important material in printing. And nano calcium carbonate is a kind of filling material that is widely used in printing ink, its purpose is to reduce the cost, adjust the fluidity of the ink and the color concentration of the ink.
As a special nano calcium carbonate for ink, the product performance and quality requirements are very strict. For example, in principle, the higher the gloss of nano-calcium carbonate, the better, and the color of the ink product cannot be affected after filling; the oil absorption value and fluidity must reach the standard, which is related to the compatibility of nano-calcium carbonate with resin and binder; the particle size of nano-calcium carbonate To be between 30~40nm and so on.
Therefore, in order to achieve the above-mentioned indicators of the above-mentioned series of special nano calcium carbonate for ink, the production process of calcium carbonate must be strictly controlled to ensure the controllability of product quality.
1. Carbonization process of nano calcium carbonate for ink
(1) Batch carbonization method
The limestone is burned to generate CaO and kiln gas. CaO is added to the rotary digester and digested with water to obtain Ca(OH)2 emulsion. After refining, Ca(OH)2 is obtained. The refined emulsion is sent to the carbonization reactor, and the purified kiln gas is introduced for carbonized. By controlling the temperature of Ca(OH)2 and the flow of kiln gas, the nucleation rate of calcium carbonate nuclei is effectively controlled; after carbonization to a certain number of nuclei, the control of nucleation is transformed into control of crystal growth At this time, the crystal shape regulator is added to control the growth rate of each crystal plane, so as to achieve controllable morphology; continue to carbonize to the end point, add a dispersant to adjust the surface charge of the particles, and obtain uniformly dispersed cubic nano-calcium carbonate particles.
(2) Continuous spray method
Using the spray carbonization process, the average particle size can be obtained by adjusting the concentration of calcium hydroxide suspension, the spray droplet diameter, the concentration of CO2 mixture, the air velocity, the gas-liquid ratio and the carbonization rate of the slurry during the reaction process. For calcium carbonate smaller than 100 nanometers, the reaction parameters can also be adjusted, and single ultra-fine calcium carbonate products such as cubic, chain-shaped, and spherical-like can be obtained.
For example, the three-stage carbonization method is selected, and the concentration of calcium hydroxide suspension in the carbonization process is controlled to be 0.1~10% (weight), the temperature is 1~30°C, the diameter of the droplet and the carbon dioxide gas are 10~40°C (volume), a certain Air velocity, can produce cubic calcium carbonate less than 0.1μm.
2. Quality control method of nano calcium carbonate for ink
(1) Selection of modifiers
As a surface treatment agent for ink calcium, a surface treatment agent with good compatibility with the resin base must be used, and it has a certain gloss and transparency.
(2) Control of specific surface area
As the specific surface area increases, the primary particles become smaller, the interaction force between particles increases continuously, and the transparency is good; in order to ensure the transparency of the product, the specific surface area must be controlled to be greater than 40m2/g, and the specific surface area should not be too large. Otherwise, the surface energy of the particles will increase, which will have a negative impact on the oil absorption value and flow performance of the product.
(3) Average particle size and transparency index
When formulating inks, an important indicator is fineness. When there are coarse particles in the ink, the film formation is not smooth, which affects the appearance and transparency.
The average particle size of translucent ink calcium is about 60nm, which is the most commonly used product in resin ink. It is easy to disperse, has good abrasion resistance, and can improve ink fluidity and leveling.
The average particle size of the transparent ink calcium is about 30nm. Used in resin-based glossy offset printing inks with high transparency, high gloss, excellent elasticity and excellent printability.
(4) Use of dispersant
When carbonized to pH=7, adding dispersant, such as sodium hexametaphosphate, sodium tripolyphosphate and sodium pyrophosphate, etc., and then adding surface treatment agent, can improve the dispersibility and fluidity of ink calcium.
As the amount of dispersant increases, the fineness of nano calcium carbonate decreases and the fluidity increases. By adding inorganic dispersant, the dispersibility and fluidity of ink calcium can be adjusted.
(5) Effective control of pH value
In the application of ink, because the pH of calcium carbonate is too high, it will cause instability of the ink material, and flocculation is likely to occur. After aging, secondary carbonization and addition of acid will reduce the pH value of calcium carbonate.
Epilogue
China is a major producer and consumer of calcium carbonate in the world. With the continuous development of the national economy, the demand for calcium carbonate not only increases in quantity, but also requires specialization and functionalization of product quality, especially nano-calcium carbonate with a particle size of less than 100nm. With the quantum size effect, surface effect and macroscopic quantum effect that ordinary calcium carbonate cannot have, the demand for products is increasing.
There are currently more than 30 nano-calcium carbonate manufacturers in China, with an annual output of more than 1 million tons, which are widely used in rubber, plastics, coatings, paper, ink and other industries. However, the overall level is uneven. In order to meet the needs of the rapid development of these industries, it is necessary to continuously improve the quality and grade of nano-calcium carbonate used in the production of these industries.