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Yuan Lei Small Classroom | Application of Calcium Carbonate in Paper Mill

Release time:

2024-01-29 09:38

 

Yuan Lei Small Classroom | Application of Calcium Carbonate in Paper Mill

 

With the development of neutral papermaking and coating processing technology, calcium carbonate has been widely used as a filler and pigment in North America and Europe. Add FillCaco3Significantly improves the durability of the paper. In our country, talc powder is mainly used as filler and pigment, but with the development of medium alkaline papermaking,Calcium carbonateThe application will continue to grow.Calcium carbonateInph6The following is easy to decompose and can only be used as a filler in medium alkaline papermaking.

 

Calcium carbonateSources and types

Calcium carbonate is divided into ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC). Limestone and marble are natural CaCO3, which are mechanically crushed, ground and classified to make fine particles called GCC. GCC can be used as filler and pigment. When used in papermaking, 90% of the particle size is less than 2um. It is a prismatic structure and is an irregular scone type observed under 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 of more than 3 um. The average particle size is the most important physical property of GCC. Other important properties include whiteness, oil absorption and crystal form. GCC processing methods are wet and dry, according to the requirements of the product. Dry grinding is cheaper and is often limited to the production of 2-3 um particles. Smaller particle sizes have a tendency to aggregate, making handling and classification difficult. The production of ultra-fine GCC requires a wet process. Precipitated calcium carbonate (PCC), also known as light calcium carbonate, has the following three different preparation processes: lime milk carbonization method, that is, lime milk and Na2CO3; lime milk and ammonium chloride. The average particle size of the PCC ranges between 1.5 and 2.5 μm. The different preparation process conditions of PCC make the crystal morphology, particle shape and surface charge have great differences, which have different effects on the performance of the filling paper.

 

PCCand GCC in terms of morphology and application differences

The shape of PCC and GCC particles are significantly different. GCC particles are of a prismatic structure, which is a common crystalline form of calcite. The PCC is a non-equilateral prism, sometimes referred to as a rose-shaped structure. Because the fine crystals are thin and long, aggregated into clusters, the core particles have a larger specific surface area than the GCC prisms, and therefore have greater light scattering ability, making the paper sheet have higher whiteness and opacity. However, this rose-shaped structure also makes there are a large number of voids in the particles or between the particles, which affects the combination of fibers. When the paper can be filled with more than a certain threshold, the strength of the paper is reduced, voids are generated, and the speed of the paper is reduced. This problem can be overcome by adding a mixture of PCC and GCC. PCC producers are working to develop particles that replicate natural-like prisms to compensate for the limitations of high PCC loadings of unequal prisms. In order to obtain good gloss and smoothness, the solid content of the coating is required to be high. As mentioned above, PCC unequal prism particles are formed by the aggregation of a rose-shaped nucleus and needle-shaped crystals around it. When the coating is made of high solid content, strong dispersion causes needle-shaped and rose-shaped nuclei to split, resulting in reduced optical properties and increased adhesive dosage. In general, the application of PCC in coatings cannot compete with GCC. PCC dominates the paint market in North America, while GCC is mainly used in paint formulations. Since the loading of PCC cannot exceed 15%, the benefit of switching to alkaline papermaking is reduced. Only GCC can operate stably at high filling levels (sometimes up to 30%).

 

PCCand GCC features and limitations

 

3.1 PCCAdvantages as a filler

1) in the form of unequal edgesPCCCan produce high opacity, whiteness and bulk of the paper sheet.

22) The abrasion number is low in the process of copying and manufacturing, so as to reduce the abrasion of the equipment.

3) The potential of surface charge is high, which is conducive to the distribution of particles in the paper.

 

32  PCCDefects in papermaking applications

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 sheet.

3PCCthanGCCMore moisture is retained, which means that the speed of the paper machine is reduced.

4) WhenPCCFill more15%There are a lot of productivity problems.

5) adsorption inPCCUnreacted on the particlesAKDAfter entering the white water, a white resin barrier will be generated, which will further affect the quality of the paper sheet and the operation of the paper machine.

6) Trace amounts that are not sufficiently neutralized have an adverse effect on the operation of the paper machine.

 

3.3  Add FillGCChas the advantage

1) Allows a higher amount of filling, which can improve economic efficiency.

2) The morphology of the particles is conducive to the combination of fibers and the strength of the paper sheet.

3) The paper machine has better runability because it has less water retention and better water filtration.

4) has little effect on sizing.

5) No precipitation problem occurs.

 

3.4  GCCthe defect

1Whiteness and opacity lower than the same amount of fillingPCC.

21) MudGCCOn the way to the user, a dispersant is added to prevent the particles from settling, thus increasing the cost.

3) NaturalCaCO3The hardness is larger, the form of the particles makes the wear number larger, the net part, the paper machine parts have greater wear.

 

Good use of calcium carbonate filler is the premise of the application of good alkaline sizing process. The application of alkaline sizing has better economic and environmental benefits, rather than increasing production costs. The increased cost of using chemicals such as neutral sizing agent and retention aid filter agent should be compensated by improving the retention rate of fillers and fine fibers, greatly increasing the ash content of paper pages, and increasing the added value of products.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Paper mill, pcc,gcc, granule, fill, calcium carbonate, particle size, produce, filler, effect

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