Limestone powder can be used in the
paper industry. The limestone powder used here belongs to coating grade
calcium carbonate.
This kind of high value-added fine, superfine and active calcium carbonate is widely used in
papermaking process.
After crushing, the general particle size is
2μm≥90% for
neutral sizing papermaking process;
2μm≥50% is mainly used for
coating paper filler.
SBM Ultrafine Powder Tech will analyze the advantages and disadvantages of
heavy calcium carbonate (also named ground calcium carbonate,GCC) and
light calcium carbonate (also named precipitated calcium carbonate,PCC) in the paper industry.
Then, SBM will compare and introduce two
ultra-fine grinding mills commonly used calcium carbonate in the paper industry.
Ground calcium carbonate and precipitated calcium carbonate
1. Sources and types of calcium carbonate
Calcium carbonate is divided into
ground calcium carbonate (GCC) and
precipitated calcium carbonate (PCC).
Limestone,
calcite and
marble are natural
CaCO3, which is mechanically crushed, ground, and classified into fine particles called
ground calcium carbonate (GCC).
GCC can be used as a filler and pigment. When used in papermaking, 90% of the particle size is less than 2um, and it has a prismatic structure.
It is an irregular scones when observed under an electron microscope.
According to the particle size, GCC can be divided into three categories: ultrafine CaCO3 (UFGCC), with an average particle size of 0.5-0.9 um; fine CaCO3 (GCC), with an average particle size greater than 3 um.
The average particle size is the most important physical property of GCC, and other important properties include whiteness, oil absorption, and crystal form.
GCC processing methods include wet and dry methods, depending on the requirements of the product.
Dry grinding is relatively cheap and is often limited to the production of 2-3 um particles.
Smaller particle sizes have a tendency to aggregate, making it difficult to handle and classify. The production of ultra-fine GCC requires a wet process.
Precipitated calcium carbonate (PCC), also called light calcium carbonate, has the following three different preparation processes; lime milk carbonization method, which is the action of lime milk and Na2CO3; and the action of lime milk and ammonium chloride.
The average particle size of PCC is between 1.5-2.5 um.
The different preparation process conditions of PCC make the crystalline morphology, particle shape and surface charge of PCC have great differences, which will have different effects on the performance of the filled paper.
2. The difference in the form and application of PCC and GCC
The shapes of PCC and GCC particles are significantly different. GCC particles have a prism structure, which is a common crystal form of calcite. PCC is an unequal-sided prism, sometimes called a rosette structure. Because the fine crystals are thin and long, clustered into clusters, the particles surrounding the core have a larger specific surface area than the GCC prism, so it has a greater light scattering ability, so that the paper has a higher whiteness and opacity. However, this rose-shaped structure also makes a large number of voids in or between the particles, which affects the combination of fibers, so that when the paper can be filled with more than a certain threshold, the strength of the paper will be reduced and voids will be generated. ﹑Reduce the speed of the vehicle to become a serious problem. This problem can be overcome by mixing PCC and GCC for filling. PCC manufacturers are working hard to develop and replicate particles similar to natural prisms to compensate for the limitations of unequal prisms when PCC is filled with high loading.
In order to achieve good gloss and smoothness, high solid content of the coating is required. As mentioned above, PCC unequal prismatic particles are aggregated by a rose-shaped core and needle-shaped crystals surrounding it to make a high solid content. The strong dispersion during coating causes needle-shaped and rose-shaped nuclei fission, which leads to a decrease in optical performance and an increase in the amount of adhesive. Generally speaking, the application of PCC in coatings cannot compete with GCC. PCC is dominant in the North American paint market, while GCC is mainly used in paint formulations. Since the filling amount of PCC cannot exceed 15%, the benefit of switching to alkaline papermaking is reduced. Only GCC can operate stably at high loading rates (sometimes up to 30%).
3. Features and limitations of PCC and GCC
3.1 Advantages of PCC as a filler
(1) PCC with unequal prism shape can make the paper produce high opacity, whiteness and bulkiness.
(2) The wear number is low in the papermaking process, which reduces the wear on the equipment.
(3) The surface charge has a high potential, which is conducive to the distribution of particles in the paper.
3.2 The defects of PCC application in papermaking
(1) The specific surface area of the particles is large, which reduces the sizing efficiency.
(2) The small gaps between the particles affect the bonding between the fibers, thereby reducing the strength of the paper.
(3) PCC retains more water than GCC, which means that the speed of the paper machine has to be reduced.
(4) When the PCC filling amount exceeds 15%, a large number of productivity problems will occur.
(5) The unreacted AKD adsorbed on the PCC particles will cause white resin barriers after entering the white water, which will further affect the quality of the paper and the operation of the paper machine.
(6) The operation of the micro washi machine that has not been fully neutralized will have an adverse effect.
3.3 The advantages of adding GCC
(1) A higher filling volume is allowed, which can improve economic efficiency.
(2) The shape of the particles is conducive to the combination of fibers and the strength of the paper.
(3) The operability of the paper machine is better, because the retained water is less and the water filterability is better.
(4) Less impact on sizing.
(5) There is no precipitation problem.
3.4 Defects of GCC
(1) The whiteness and opacity are lower than PCC with the same filling amount.
(2) A dispersant must be added to the slurry-like GCC on the way to the user to prevent the particles from settling, thus increasing the cost.
(3) The hardness of natural CaCO3 is relatively large, and the shape of the particles makes the abrasion number relatively large, which will cause relatively large abrasion to the wire and paper machine parts.
The prerequisite for the good use of calcium carbonate fillers is the application of the medium-alkaline sizing process. Alkaline sizing has better economic and environmental benefits in application, rather than increasing production costs. The increased cost of using neutral sizing agents and retention aid filters and other chemicals should be compensated by increasing the retention rate of fillers and fine fibers, greatly increasing the ash content of the paper, and increasing the added value of the product.
Comparison of two types of mills used for limestone powder processing for papermaking
1. HGM micro powder grinding mill
HGM micro powder grinding mill also called HGM ultrafine grinding mill, HGM three-ring medium-speed mill and 21r/24r/28r grinding mill.
Discharge particle size: 150-3000 mesh, D97<2500 mesh, D50<3μm
Production capacity: 0.5-45 t/h
Advantages:1. High cost performance.
2. Low maintenance costs.
3. It can grind a wide range, from coarse powder to fine powder to ultra-fine powder.
4. It is suitable for the fine powder requirements of various industries.
Parameters:
| Model |
HGM80 |
HGM80A |
HGM90L |
HGM100L-Ⅱ |
HGM100P |
HGM125L |
HGM1680L |
| Ring Diameter(mm) |
800 |
800 |
900 |
1000 |
1000 |
1250 |
1680 |
| Ring Number (PCS) |
3 |
3 |
4 |
4 |
4 |
4 |
4 |
| Input Size (mm) |
≤10 |
≤10 |
≤10 |
≤15 |
≤15 |
≤20 |
≤20 |
| Adjustable range of finished product (mesh) |
150-3000 |
150-3000 |
150-3000 |
150-3000 |
150-3000 |
150-3000 |
150-3000 |
| Capacity (t/h) |
0.5-5.5 |
0.5-5.5 |
0.8-6.5 |
1.2-10 |
1.2-11 |
2.5-20 |
5-45 |
| Outlet Size L*W*H (mm) |
8605*4139*6050 |
10454*3393*6626 |
11735*3952*7525 |
14507*3633*7562 |
14362*4200*7562 |
19261*4406*8591 |
25067*5414*9007 |
| Main motor power (kw) |
75 |
75 |
55*2 |
132/75*2 |
132/75*2 |
185 |
315 |
2.CLUM ultrafine vertical roller grinding mill
Discharge particle size: 400-3000 mesh, D97<3000 mesh, D50<2μm
Production capacity:Advantages:1. High 2 micron powder content.
2. Good sphericity of the produced powder.
3. High whiteness of calcium carbonate powder.
4. High efficiency: production of ultra-fine powder of the same fineness, less power consumption, higher output.
5. Stable performance.stable equipment.
6. High profit.
7. It is suitable for industries that require high powder whiteness and particle size.
Parameters:
| ModelItem |
CLUM1425 |
CLUM1632 |
CLUM1736 |
| Working Diameters（mm） |
1400 |
1600 |
1700 |
| Number of rollers（pieces） |
3 |
3 |
3 |
| Number of classifier（pieces） |
6 |
6 |
8 |
| Power of classifier（Kw） |
6X15 |
6X22 |
8X22 |
| Main unit power （Kw） |
220-250 |
315-355 |
355-410 |
| Blower power（Kw） |
180-200 |
250-280 |
325-355 |
| Feed size （mm） |
＜10mm |
＜10mm |
＜10mm |
| Moisture of feeding material |
＜3% |
＜3% |
＜3% |
| Less than 2μm=30% output（t/h） |
9-12 |
12-16 |
14-18 |
| Less than 2μm=45% output（t/h） |
5.5-7.5 |
7-9 |
10-12 |
| Less than 2μm=60% output（t/h） |
3-4 |
/ |
/ |
Material: base on calcite
Particle size distribution: measured by microlayer diffraction particle size analyzer in British Malvern 3000 instruments
CLUM1425 TECHNICAL PARAMETER
Output (t/h)
Item |
10.0-12.0 |
7.5-9.5 |
6.0-8.0 |
4.5-6.5 |
3.0-4.0 |
| specific surface area(cm²/g) |
11000±500 |
13500±500 |
15000±500 |
17000±500 |
19000±1000 |
| 325mesh remaining amount (%) |
0.015 |
0.015 |
0.01 |
0 |
0 |
| less than 2μm powder content (%) |
30 |
40 |
45 |
50 |
60 |
| Median particle diameter D50 (um) |
5.2 |
3.0 |
2.5 |
2 |
1.4 |
| General name(mesh) |
600 |
800 |
1250 |
2000 |
2500 |
| Particle size distribution D97 (um) |
30 |
25 |
20 |
15 |
9 |
| Particle size cut point D100 (um) |
80 |
48 |
38 |
28 |
18 |
| Moisture content (%) |
<0.3% |
<0.3% |
<0.3% |
<0.3% |
<0.3% |
| Energy consumption (KW/T) |
38-40 |
40-50 |
47-53 |
50-53 |
110-125 |
CLUM1632 TECHNICAL PARAMETER
Output (t/h)
Item |
12.5-14.5 |
9.5-11.5 |
7.5-9.5 |
6.0-8.0 |
| specific surface area(cm²/g) |
11000±500 |
13500±500 |
15000±500 |
17000±500 |
| 325mesh remaining amount (%) |
0.015 |
0.015 |
0.01 |
0 |
| less than 2μm powder content (%) |
30 |
40 |
45 |
50 |
| Median particle diameter D50 (um) |
5.2 |
3.0 |
2.5 |
2.0 |
| General name(mesh) |
600 |
800 |
1250 |
2000 |
| Particle size distribution D97 (um) |
30 |
25 |
20 |
15 |
| Particle size cut point D100 (um) |
80 |
48 |
38 |
28 |
| Moisture content (%) |
<0.3% |
<0.3% |
<0.3% |
<0.3% |
| Energy consumption (KW/T) |
38-40 |
40-50 |
47-53 |
50-53 |
CLUM1736 TECHNICAL PARAMETER
Output (t/h)
Item |
15.0-18.0 |
11.5-13.5 |
9.0-11.0 |
| specific surface area(cm²/g) |
11000±500 |
13500±500 |
15000±500 |
| 325mesh remaining amount (%) |
0.015 |
0.015 |
0.01 |
| less than 2μm powder content (%) |
30 |
40 |
45 |
| Median particle diameter D50 (um) |
5.2 |
3.0 |
2.5 |
| General name(mesh) |
600 |
800 |
1250 |
| Particle size distribution D97 (um) |
30 |
25 |
20 |
| Particle size cut point D100 (um) |
80 |
48 |
38 |
| Moisture content (%) |
<0.3% |
<0.3% |
<0.3% |
| Energy consumption (KW/T) |
38-40 |
40-50 |
47-53 |
