The Modified Calcium Carbonate Plays a Crucial Role In The Paper Industry

Posted: 2023-08-28

• The latest Global Calcium Carbonate Industry report, released by market research company Report Buyer in July 2020, projects that the global calcium carbonate market is expected to reach $23.8 billion in 2020 and $32.6 billion in 2027, with a compound annual growth rate of 4.6%. Furthermore, the paper calcium carbonate market is projected to expand at a compound annual growth rate of 4.7% and achieve a value of $16 billion by 2027. Due to advancements in technology and the flourishing paper industry, nano-calcium carbonate has emerged as the most promising filler for this sector. General requirements for fillers in paper production include high whiteness, excellent hiding power, low impurity content, specific particle structure of calcium carbonate, low oil absorption value, and uniform particle size distribution. By incorporating nano calcium carbonate as a filler material, papers can exhibit superior characteristics such as enhanced whiteness, improved light scattering properties, refined surface texture while maintaining high bulk density along with desirable plasticity and softness.
   
   
   
  The extensive utilization of calcium carbonate in the paper industry is based on the global transition from acidic paper processes to alkaline or neutral ones, enabling widespread substitution of previous materials such as talc and China clay with cost-effective calcium carbonate. With the advancement of the paper industry, higher demands have been imposed on white fillers. Consequently, the significance of calcium carbonate in the field of papermaking has garnered increasing attention.
   

  The Application of Calcium Carbonate In The Paper Industry is Significant

   
   
   
  The global usage of nano-calcium carbonate in paper production accounts for approximately 20% to 40% of the paper's total weight. Incorporating calcium carbonate into the paper coating can enhance its glossiness, whiteness, opacity, oil absorption capacity, smoothness, resistance to aging and bacteria. Nano calcium carbonate is an ideal filler for high-quality paper products such as feminine sanitary napkins, baby diapers, and cigarette papers. By integrating nano-calcium carbonate into the coating material, a glossy and white coated paper with robust surface strength and excellent ink absorption properties can be achieved.
   
  - Due to the small and uniform particle size, the wear on the paper machine is minimized, thus enhancing equipment durability.
   
  - The inclusion of nano-scale calcium carbonate can enhance both the whiteness and smoothness of the paper while reducing its weight. Additionally, it exhibits strong hiding power and high strength characteristics that significantly improve overall paper quality.
   
  - Different types of papers have specific requirements regarding crystal shape and particle size of calcium carbonate; presently, flake and spindle forms are commonly utilized.
   

  Modification Technology of Calcium Carbonate

  
  Although calcium carbonate is an essential filler in the paper industry, its compatibility and binding force with unmodified pulp fiber are inadequate, resulting in low retention rates. This can lead to material interface defects and a reduction in the mechanical strength of paper. Therefore, modification of calcium carbonate is necessary, with chemical coating modification and surface treatment being the main methods employed.
   

  Chemical Coating Modification

  
  The surface modification of heavy calcium carbonate in the Ca(OH)2-H2O-CO2 system results in a rough crystal cleavage surface and passivated edges and angles after nano-coating, thereby enhancing its dispersion performance. Additionally, there is an electrostatic attraction between the nano-coated GCC and fibers, leading to the formation of a network structure with strong bonding forces among paper fibers. Moreover, this improves the tensile index, filler retention rate, rupture index, tear index, and folding resistance of the filled paper.
   
  Using cationic chitosan and carboxymethyl cellulose as modifiers for light calcium carbonate PCC filler treatment based on polyelectrolyte composite principle. The deposition of polyelectrolyte composite on PCC surfaces significantly increases particle size while concentrating particle distribution and improving uniformity by 1 times specific surface area enlargement. Compared to unmodified PCC, modified PCC exhibits superior retention properties due to mechanical interception combined with colloidal adsorption that allows it to be retained as single particles or flocs on fiber surfaces and within fiber pores.
   
  By employing starch-modified calcium carbonate under starch coating effects, calcium carbonate aggregates into larger clusters resulting in slurry retention rate increase up to 87.34% and calcium carbonate retention rate up to 86.50%. Through dual actions from fiber surfaces and starch coatings, calcium carbonate particles are uniformly coated onto tobacco stem fiber surfaces forming a complex known as calcium carbonate-fiber complex. This leads to slurry retention rates reaching 90.37% along with a 90.53% calcium carbonate retention rate effectively enhancing physical properties such as tensile strength and loose thickness of the substrate.
   

  Surface Modification

  
  Surface modification can be categorized into three main types: coupling agent modification (such as silane, titanate, and aluminate coupling agents), compound coupling modifier modification (which combines a coupling agent with other processing modifiers, surface treatment agents, and crosslinking agents), and organic modification (using stearic acid, stearate, and phosphate ester). In this study, γ-methacryloxypropyl trimethoxysilane (KH570) was used to modify nano-calcium carbonate. The hydrolysis of KH570 resulted in the formation of SI-OH groups which then condensed with the hydroxyl groups on the surface of nano-calcium carbonate to form CA-O-Si bonds. This achieved stable and effective chemical grafting. After the modification process, the layer spacing of the nano-calcium carbonate surface crystals increased while polarity decreased.
   
  Additionally, surface energy reduced while lipophilicity enhanced leading to improved dispersion properties. Coating paper with this modified material improved optical properties while increasing paper strength and hydrophobicity. Organic modification using sodium stearate also proved successful in reducing powder surface energy and particle agglomeration while improving powder dispersion and resin binding properties for CaCO3 powder. The modified nano CaCO3 was blended with waterborne polyurethane before being uniformly coated on paper surfaces after cooling resulting in non-slip paper exhibiting better frictional and mechanical properties suitable for preparing non-slip liners or trays for transport packaging.
   

  Calcium Carbonate Grinding Mill

   
   
   

  HGM Ultrafine Grinding Mill

  
  Capacity: 0.2-45 t/h
  Feed Size: ≤20 mm
  Powder Fineness: 325-3000 mesh
   
  Mill Advantages
   
  1. 1.The yield is 40% higher than that of other mills, indicating a significantly greater output capacity compared to its counterparts. This not only enhances productivity but also enables more efficient utilization of resources.
   
  2. 2.With a high wear material utilization rate lasting between 2-5 years, this mill ensures long-lasting performance and reduces the frequency of replacements or repairs. As a result, it saves time and money while minimizing downtime and disruptions in production processes.
   
  3. 3.The adjustable particle size range from 325 to 3000 mesh offers flexibility in meeting diverse requirements for various applications. Whether fine grinding or coarse milling is needed, this mill can easily adapt to different needs which makes it suitable for a wide range of industries such as mining, chemical engineering, and construction materials.
   
  4. 4.High safety and reliability are inherent features of this mill due to its rigorous design, which eliminates the risk of screw loosening that could potentially damage the machine. Operators can work with peace of mind, knowing they are using equipment built to withstand heavy-duty operations without compromising on safety standards.
   
  5. 5.Being a closed system makes this mill an environmentally friendly choice as it prevents any emissions or leakage during operation. This not only contributes to reducing air pollution but also helps protect workers' health by minimizing exposure to harmful particles or dust generated during the milling process.
   
   
   
   

  CLUM Ultrafine Vertical Grinding Mill

  
  Capacity: 1-20 t/h
  Feed Size: ＜20 mm
  Powder Fineness: 300-3000 mesh
   
  Mill Advantages
   
  1. 1.The vertical mill is designed with a unique grinding mechanism that enables it to achieve high grinding efficiency, resulting in the ability to grind more materials in less time compared to the ball mill. This not only conserves energy but also reduces production costs.
   
  2. 2.The vertical mill has a strong drying capacity, making it suitable for dry grinding of raw materials with water content up to 15%. This feature ensures that the final product has low moisture content and is free from any impurities.
   
  3. 3.One of the major advantages of using a vertical mill is its low noise level and minimal dust emission during operation. Unlike traditional mills where metal impact causes loud noises, the roller in a vertical mill does not come into direct contact with the material being ground, resulting in reduced noise levels by 20~25 dB.
   
  4. 4.Another advantage of using a vertical mill is its low wear rate and minimal metal pollution during operation. Its metal wear rate is only 5-10g/t, which means there are fewer chances of contamination due to metallic particles getting mixed with the final product.
   
  5. 5.Vertical mills are versatile machines that can be used for various applications such as cement production, mineral processing, coal preparation, and many others. They offer greater flexibility than traditional mills because they can handle different types of materials without requiring significant changes in their design or configuration.
   
  6. 6.Easy maintenance: Vertical mills require minimal maintenance compared to other types of milling equipment because they have fewer moving parts and do not require frequent lubrication or replacement of worn-out components.

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