Calcium Carbonate Modification: Functions and Downstream Application Analysis

Calcium carbonate is one of the most widely used inorganic fillers in plastics, coatings, masterbatch, rubber, and other industries. It has wide sources, low cost, and high whiteness. After filling, it can effectively reduce product costs. However, natural calcium carbonate powder has a hydrophilic surface and high polarity, and has poor compatibility with organic polymer materials such as PP, PE, and PVC. Direct filling is prone to problems such as agglomeration, uneven dispersion, and weak interfacial bonding.

Especially for ultrafine powder, the specific surface area is large and the surface energy is high, making the agglomeration tendency more significant. Grinding can solve the fineness problem, but cannot solve the application adaptability problem. Surface modification is a key process for calcium carbonate to transform from an ordinary filler into a functional filler. This article analyzes the role of calcium carbonate modification and the downstream applications of modified calcium carbonate, and explains the complete line solution of Shanghai Clirik Machinery Co., Ltd. in the field of ultrafine powder grinding and surface modification.

1. Can Unmodified Calcium Carbonate Be Used Directly?

Conclusion: Unmodified calcium carbonate is not completely unusable, but it is difficult to use well, stably, and in large amounts.

1.1 Scenarios Where Unmodified Calcium Carbonate Can Be Used

Some downstream scenarios have low requirements for surface modification, and unmodified calcium carbonate can be used directly:

1. Ordinary coatings, putty powder: mainly used for filling and volume increase, with low requirements for interfacial bonding;
2. Low-end plastic products: low filling amount, low performance requirements;
3. Building materials, cement, mortar: themselves are inorganic systems, no organic/inorganic compatibility issues;
4. Some rubber products: when filled in small amounts, unmodified powder can also be used.

1.2 Scenarios Where Unmodified Calcium Carbonate Causes Problems

In the following scenarios, unmodified calcium carbonate will cause obvious quality problems:
 

Application Scenario	Problems of Unmodified Calcium Carbonate
PP woven bag filler	Ultrafine powder agglomeration, uneven dispersion, rough surface and reduced strength of finished products
Plastic masterbatch	Poor compatibility with resin, limited filling amount, unstable product performance
Ultrafine calcium carbonate filled PP/PE	Large specific surface area, high surface energy, severe agglomeration, unable to disperse uniformly
High filling system	Slightly higher filling amount, mechanical properties drop sharply
Coatings with higher requirements	Poor dispersibility, affected film flatness

The core reason is: calcium carbonate is an inorganic material, and resin is an organic material, and the interfacial compatibility between the two is poor.

1.3 Summary

Without modification, the powder can only be "filled in", not "melted in". The value of modification is to make calcium carbonate from barely usable to truly usable.

2. Core Functions of Calcium Carbonate Modification

Calcium carbonate modification usually uses modifiers such as stearic acid, titanate coupling agents, and aluminate coupling agents to form a uniform coating layer on the powder surface. Its core functions can be summarized in the following four points:

2.1 Improve Compatibility

Make the calcium carbonate surface change from hydrophilic to lipophilic, improving the bonding force with resins such as PP, PE, and PVC.

2.2 Inhibit Agglomeration

Reduce the surface energy of the powder, prevent ultrafine particles from agglomerating, and ensure uniform dispersion.

2.3 Improve Dispersibility

Make the powder uniformly distributed in the resin, ensuring stable product strength, toughness, and surface flatness.

2.4 Increase Filling Amount and Reduce Product Cost

Modified powder can achieve a higher filling ratio without significantly sacrificing mechanical properties, thereby reducing product cost.
Modification is a key link connecting powder processing and end-use applications.

3. Downstream Applications of Modified Calcium Carbonate

The applications of modified calcium carbonate are concentrated in fields requiring high filling, high dispersion, and high performance.

3.1 Plastics Industry

Typical applications: PP woven bag filler, plastic masterbatch, PE/PVC products

1. PP woven bag filler: Ultrafine limestone powder with a fineness of D98 12μm, high whiteness, and small particle size can improve the strength, toughness, and surface flatness of woven bags after filling; however, it must be surface-coated by the CLG Powder Surface Coating Machine to solve the agglomeration problem and improve compatibility with PP resin.
2. Plastic masterbatch: Requires high-purity, high-whiteness limestone. After modification, it has good compatibility with resin, uniform filling, and stable product strength.
3. PE, PVC products: Modified calcium carbonate can improve dispersibility, processing performance, and reduce raw material costs.

3.2 Coatings Industry

Typical applications: Fillers for paints and coatings

1. Powder for paints usually remains unmodified, but has high requirements for particle size distribution;
2. Requires narrow particle size distribution and uniform, stable particle size to ensure smooth film and uniform dispersion;
3. Modified powder for masterbatch and unmodified powder for paints have the same basic quality requirements for raw materials, both requiring high-purity, high-whiteness limestone. The difference lies in the post-treatment process.

3.3 Masterbatch Industry

Typical applications: Filled masterbatch, functional masterbatch

1. Modified powder for masterbatch requires additional surface modification;
2. After modification, the powder has good compatibility with resin, uniform filling, and stable product strength;
3. Raw material quality determines basic performance, and modification process determines final adaptability.

3.4 Rubber, Adhesives, Sealants, and Other Industries

1. Modified calcium carbonate can improve dispersibility, reinforcement, or reduce costs;
2. There are different requirements for powder fineness, whiteness, and activation degree, and modifiers and processes should be selected according to the system.

4. Modification Process Route: Comparison of Integrated and Secondary Modification

Calcium carbonate modification is not just adding a modification machine; the choice of process route directly affects cost and quality stability.

4.1 Integrated Dry Process: HGM Ultrafine Mill + CLG Powder Surface Coating Machine

1. Utilize the residual heat generated during grinding for stearic acid coating without additional heating;
2. Integrated control from grinding to modification ensures stable and controllable quality;
3. Avoid quality fluctuations and cost losses caused by transportation, storage, and secondary processing of purchased powder;
4. More energy-saving and consumption-reducing than secondary modification of purchased powder.

For a detailed breakdown of each stage from raw material to finished powder, see our article: Complete Production Line from Limestone Raw Material to Ultrafine Modified Powder.

4.2 Key Process Control Points

1. Feed moisture control before grinding;
2. Powder temperature entering the coating machine: 85–110°C;
3. Modifier addition amount: precisely controlled by loss-in-weight feeding;
4. Moisture of material entering the coating machine: ≤0.5%;
5. Closed negative pressure dust removal for the entire production line;
6. Confirm ore purity, target particle size, and modifier parameters before production;
7. For small capacity, choose HGM; for large capacity, evaluate CLUM Vertical Roller Mill.

5. Frequently Asked Questions

Q1: Will the whiteness decrease significantly after modification?

No. Whiteness mainly depends on the quality of the raw ore and the wear degree of wear parts. When equipment selection is reasonable and wear parts are properly controlled, grinding and modification have minimal impact on whiteness.

Q2: Do unmodified powder for paints and modified powder for masterbatch have the same requirements for raw materials?

The basic quality requirements are the same, both requiring high-purity, high-whiteness limestone. The difference lies in the post-treatment process: masterbatch powder requires surface modification, while paint powder remains unmodified.

Q3: If the powder temperature is too low and enters the CLG Powder Surface Coating Machine directly, will the modification effect be affected?

Yes. Stearic acid dry coating requires the powder to maintain 85–110°C. If the temperature is too low, the modifier cannot fully melt, and the coating activation rate decreases. It is necessary to use the residual heat of the mill or equip an auxiliary heating system.

Q4: What are the main reasons for unstable modifier addition ratio and fluctuating activation degree?

Common reasons include: loss-in-weight feeding equipment failure or inaccurate calibration, powder feed flow fluctuation, unstable powder feed temperature, and wear of internal mixing components of the coating machine. It is necessary to regularly calibrate, stabilize flow, control temperature, and check blade wear.

Q5: Can two sets of HGM100L-II + CLG600 modification units operate simultaneously and adjust fineness independently?

Yes. Each unit is independently equipped with a classification system and a modification system, and fineness and modification parameters can be set and adjusted separately without interference.

Q6: What are the requirements for particle size distribution when 10-micron limestone powder is supplied to both masterbatch and paint industries?

Both industries require narrow particle size distribution and uniform, stable particle size. A high-precision classification system is needed to stably control the 10-micron fineness indicator.

6. Conclusion

The value of calcium carbonate powder lies not only in fineness and whiteness, but also in whether it can be stably, uniformly, and efficiently applied to downstream systems. Modification is a key bridge connecting powder processing and end-use applications.
Shanghai Clirik Machinery Co., Ltd. provides the integrated dry process of HGM Micro Powder Grinding Mill + CLG Powder Surface Coating Machine, using residual grinding heat for stearic acid coating. It is suitable for PP woven bag filler, plastic masterbatch, coatings, and other application scenarios. If you are planning an ultrafine calcium carbonate or limestone powder grinding and modification project, please contact us. We will provide suitable equipment selection and complete line solutions based on raw material quality, target particle size, capacity requirements, and modification needs.