The Application of Calcium Carbonate Powder in PVC Processing

What’s Calcium Carbonate

Calcium carbonate is an inorganic compound, which is the main component of limestone. Its molecular formula is CaC0 and its molecular weight is 100.09. Among them, calcium oxide (CaO) accounted for 56.03%, and calcium dioxide (C02) accounted for 43.97%. Calcium carbonate widely exists in nature. Now it has been used in plastic processing industry after treatment.

Calcium Carbonate Classification

Calcium carbonate can be classified into light calcium carbonate, heavy calcium carbonate and active calcium carbonate according to different production methods.

Lightweight calcium carbonate, also known as precipitated calcium carbonate, is made by calcining limestone and other raw materials to produce lime (the main component is calcium oxide) and carbon dioxide, then digesting lime with water to produce lime milk (the main component is calcium hydroxide), and then through human carbon dioxide carbonized lime milk to produce calcium carbonate precipitation, and finally by dehydration, drying and grinding. Because the sedimentation volume of light calcium carbonate (2.4-2.8 mLg) is larger than that of heavy calcium carbonate (11-1.4 mLg), it is called light calcium carbonate.

Heavy calcium carbonate is abbreviated as heavy calcium. It is made by directly crushing natural calcite, limestone, chalk and shells by mechanical method. Because the settling volume of heavy calcium carbonate is smaller than that of light calcium carbonate, it is called heavy calcium carbonate.

Active calcium carbonate is also called modified calcium carbonate. Surface treated calcium carbonate, colloidal calcium carbonate or white Yanhua, or live calcium for short, is prepared by surface modification of light or heavy active calcium carbonate with surface modifier. Because the surface modified calcium carbonate generally has a reinforcing effect, that is, the so-called “activity”, so it is customary to call the modified calcium carbonate as active calcium carbonate.

Calcium Carbonate Uses

Research and development of plastics industry requires not ordinary light calcium carbonate, but special calcium carbonate for plastics development.

(1) with low oil absorption value and moderate price, which is best modified by activation, requires a certain fineness, and the average particle size of calcium carbonate required by plastics with better uniformity of particle size is generally within the range of 0.1gm-5um. If calcium carbonate below 0.lgm is used, surface modification must be used to improve dispersion. In the case of large filling with low requirement, it is generally advisable to use calcium carbonate with an average particle size of 5 pm~20 M. However, special attention should be paid to the fact that a small amount of large particles will seriously affect the performance of the product. In addition to considering the average particle size, it is necessary to limit the proportion of too large and too small particles.

(2) The oil absorption value of calcium carbonate which requires a certain oil absorption value is related to its particle size and crystal shape, and the oil absorption value directly affects the application of calcium carbonate in plastics. This is because plasticizers must be added in plastic processing. If the oil absorption value of calcium carbonate is high, the amount of plasticizer absorbed by calcium carbonate is also large, so the processing performance of plastics is poor. On the contrary, the oil absorption value of calcium carbonate is small, and the amount of plasticizer absorbed by calcium carbonate is small, which has little effect on the processing performance of plastics.

(3) Semi-finished products of calcium carbonate with certain dispersion are inevitably agglomerated in drying, so the actual particle size of calcium carbonate products is far larger than that of primary particles, while the mixing shear force is limited in plastic processing, and the agglomeration is not easy to disperse, so calcium carbonate is required to have a certain degree of dispersion. The dispersion of calcium carbonate modified by surface modifier is also improved because of its activity on the surface of particles.

(4) Modified cupolate calcium carbonate exhibits superior properties in plastics. The application of calcium carbonate powder has gone through three stages as a result of the requirements mentioned above.

In the first stage, because the development and application of special additives for PVC processing has just started, the existing additives in other industries are often used in the formulation design. At that time, in order to solve the problem of dispersion and enhancement of inorganic fillers in PVC resin, the concept of coupling agent or modifier in the field of composite material processing was adopted, and this work was mainly completed in the production enterprises of calcium carbonate. The products enterprises only raised their hope of reducing costs, and the calcium carbonate manufacturers came to find ways to help meet this requirement. The main characteristic of this period is that the addition of calcium carbonate is only a filler form. The main reason is that at that time, whether silane coupling agent, titanate coupling agent, stearic acid and other modifiers were single additives. Their role was also limited to coupling effect. When choosing these additives, people only considered how to introduce them between filler and resin matrix. Stronger interaction did not consider the processing formula as an integral whole.

From another point of view, the interaction of technological improvement in this period was often carried out between PVC products enterprises and calcium carbonate enterprises. The production enterprises of additives did not take much initiative to participate in the design of this modified formula. The purpose of adding calcium carbonate is simply to reduce the cost, but due to technical limitations, in addition, the use of coupling agent also has a relatively complex operating procedure, and many modification enterprises of calcium carbonate do not understand, or do not fully comply with, so the level of industry development is uneven. At this time, the low limit of adding calcium carbonate as filler is only whether it is moulded or not, which has little effect on the properties of the material after moulding.

In order to increase the amount of cheap filler calcium carbonate to reduce the cost, various additives need to be added, and various additives need to have a reasonable proportion to meet the coupling, dispersion, lubrication and strengthening functions. In this form, the voice of the compounding of coupling agents and other additives is increasing, which also attracts the second development of additives for PVC processing. The exhibition stage is the special modifier stage for PVC processing. At this time, calcium carbonate powder really entered the PVC processing.

In this way, it not only serves as a medium filler, but also as a modifier. In order to help polyvinyl chloride products manufacturers simplify the difficulty of formulation design and make more advanced processing formulation technology more effective in promoting and applying, in line with the concept of “improving quality and reducing cost”, on the basis of fully absorbing the experience of Nanjing University’s coupling agent and plastic processing, Xiehe Company innovated the traditional concept and took the lead in putting forward the concept of “plastic processing modifier”. The first generation of modification agent XH-CR11 for PVC processing in China has been developed and industrialized rapidly.

As a result of the previous two stages of technological development, functional powders have begun to emerge. Around 2003, in order to endow the product with better performance and improve the valuable opinions feedback from XH-CR1 customers, Huang Yannutu took the lead in putting forward the concept of “functional modifier”, and gradually popularized the concept of “compounding, functionalization and specialization” of modifier in the industry. The newly introduced products of XH-CA and XH-CB series of functional modifiers not only have the original XH-CA products, but also have the original XH-CB series of functional modifiers. – CRI1 products have all the properties, and because it uses imported high-performance polymer additives, it has the function of promoting the plasticization of the system without affecting the heat resistance and mechanical properties of the products. At the same time, CRI1 products are strip-shaped and more convenient to use. As soon as it is launched, it has received the positive response and wide adoption of customers.

Generally, the fineness of calcium carbonate used in the modification of PVC is between 5 micron and 20 micron. This kind of finished material can be milled by XZM series ultrafine mill of ZENITH. The market prospects of processing calcium carbonate for PVC in India and Pakistan are also relatively broad. Usually when it is used to process calcium carbonate, micro-grinding not only meets the production requirements of environmental protection, but also has its own matters needing attention in use. Here is an introduction to the use of micro-grinding for the majority of users.

1. In order to make the micro-grinding normal, we should establish the equipment “equipment maintenance and safe operation system” to ensure the long-term safe operation of micro-grinding, at the same time, we should have the necessary maintenance tools, grease and corresponding accessories.
2. When the micro-grinding roller device is used for more than 500 hours to replace the roller, the rolling bearings in the roller sleeve must be cleaned, the damaged parts should be replaced in time, and the refueling tools can be used by manual refueling pump and butter gun.
3. During the use of micro-grinding, fixed personnel should be responsible for the supervision, and operators must have a certain technical level. Before installation, the operators must be trained to understand the principle and performance of micro-grinding and to be familiar with the operation rules.
4. The micro-grinding should be repaired after a period of use.
At the same time, repairing and replacing the vulnerable parts such as roller grinding ring spade cutter, etc. The connecting bolts and nuts should be carefully checked before and after the roller grinding device is used to see whether there is loosening phenomenon and whether there is enough lubricating grease.

Common faults and troubleshooting methods of micro-grinding, and faults occurring during the use of ultra-micro-grinding, can be handled according to the following table:

1. Low yield without or without flour.
(1) The powder locker has not been adjusted properly and the seal is not tight, resulting in powder inversion.
(2) The shovel knife is worn out and the material cannot be shoveled.
(3) Blockage of airway
(4) The leakage seal of the pipeline is not good.
(1) Check and adjust the seal of the powder lock, and find that the blade should be shoveled at the leak.
(2) Replace the new spade.
(3) After cleaning up the material in the air duct, the material will be re-discharged.
(4) Sealed pipeline.
2. The finished powder is too coarse or too fine.
(1) The blades of the analyzer are worn seriously and cannot be classified.
(2) The air volume of the fan is inappropriate.
(3) Changing the blade length properly and closing the air intake of the small fan to solve the problem of excessive coarseness.

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