1 The important role of calcium carbonate in plastics

 

China has become a big country in the production and consumption of plastic products. In 2006, the output of plastic products has exceeded 40 million tons, ranking second in the world, and has maintained a double-digit annual growth rate for more than 20 years. It is foreseeable that with the increase in domestic consumer demand and the increase in the number of exports to the international market as a world-wide manufacturing base, the annual output of China's plastic products will continue to grow rapidly for a long period of time.

 

In addition to synthetic resin as the basic raw material in the plastic processing process, it is unobjectionable to use various additives and additives scientifically, correctly and reasonably. Among them, inorganic mineral powder materials are one of the most important additives. As we all know, the addition of inorganic mineral powder materials to plastics can play an important role in reducing raw material costs, improving performance and imparting new functions. In recent years, it has been further discovered that the use of inorganic mineral powder materials can alleviate white pollution and protect The environmental protection effect of the environment, in today's emphasis on the implementation of circular economy, building a resource-energy-saving, environment-friendly society, highlights the significance of the application of inorganic mineral powder materials in plastics.

 

Not all plastic materials and products must be added with inorganic mineral powder materials, nor are they all added with the same amount. When the amount of inorganic mineral powder materials used in statistical plastics is usually 10 according to the total output of plastic materials and products. % calculation, that is, at least 4 million tons of inorganic powder materials are used annually in China's plastics processing industry. Calcium carbonate (including heavy calcium and light calcium) is the most widely used and most widely used inorganic mineral powder material. Among the total amount of inorganic mineral powder materials used, calcium carbonate accounts for more than 70%, not only because of carbonic acid. Rich in calcium resources, low in price, good stability of calcium carbonate, simple color, low abrasion, easy to dry, easy to process, non-toxic and many other advantages are also an important reason for widespread use.

 

Looking at the history of the use of calcium carbonate in the plastics industry, it can be considered that since the beginning of China's plastics industry in the 1960s, the application of calcium carbonate has been accompanied by the development of the plastics processing industry. The original idea of ​​the application of calcium carbonate in plastics has benefited from the application of light calcium carbonate in rubber materials and products, which is why the use of light calcium is earlier than heavy calcium, and it continues to this day. Beginning in the 1980s, with the gradual deepening of China's reform and opening up, the processing and application of heavy calcium carbonate, which is characterized by resource economy, has rapidly emerged. The historical period of heavy use of heavy calcium carbonate represented by filling masterbatch advent. By the mid-1990s, the processing of heavy calcium had leapfrogged, and ultra-fine calcium with a particle size below 10 μm began to enter the market. Heavy calcium and light calcium were used together, and the third stage of heavy calcium in different thickness ranges began. By 2015, nano-calcium carbonate will be industrialized, opening up a new world for the application of calcium carbonate in plastics.

 

Calcium carbonate as a powder material commonly used in plastics has many advantages that other powder materials do not have, such as high whiteness, easy surface organic treatment, light wear on processing equipment and molds, good fluidity in molding processing, etc., plus resources Rich in quality and low in price, it has become the first choice of inorganic mineral powder materials in the plastics processing industry. According to the current thinking and experience of plastic processing enterprises, the factors considered in the selection of calcium carbonate constitute the basic requirements for calcium carbonate.

 

(1) low price

 

Although calcium carbonate is relatively inexpensive compared to synthetic resins, it is also relatively inexpensive compared to any other powder material. However, due to the large number of suppliers, the company is still price sensitive, and the cheaper it is, the better it can be used.

 

(2) The higher the whiteness, the better

 

The color of calcium carbonate itself is whiter than other inorganic mineral powder materials. It can be 90 degrees in terms of specific values. The effect of whiteness on the properties of filled plastics is not significant, but plastic processing enterprises still hope that the whiteness is more High is better based on

 

For the following reasons:

 

1 Higher whiteness indicates higher purity and lower content of other mineral components of non-calcium carbonate.

 

Calcium powder indicates that there may be free carbon, yellowing indicates that there may be more iron compounds, and darkening indicates that the silicon content is high. High levels of impurities can sometimes affect the color, appearance, and heavy wear of processing equipment and molds during processing.

 

2 The higher the whiteness, the better the visual impression, and the higher the grade.

 

3 The higher the whiteness, the more positive and stable the uniform color after matching with other pigments.

 

(3) The particle size and its distribution should be appropriate

 

As a kind of powder material, one should consider the particle size of the particle itself and the proportion of particles in a certain size range under the test conditions. The second is to consider the existence state of these particles from the practical application, whether it is agglomerated. Together, can the agglomerates disperse during the processing of the filling system, like the large and small islands in the sea, scattered in the “ocean” of the base plastic?

 

1 From the cost point of view, as long as it can meet the requirements of use, it is better to use coarse, not fine. For example, the heavy calcium used for the production of flat yarn for polypropylene woven bags (cloth) can be 400 mesh. If a finer calcium powder is used, not only the price itself is significantly increased, but also when the filler masterbatch is produced. Consumption of more auxiliaries and carrier resins is not worth the candle.

 

2 From the performance of the filled plastic, it is better to use a finer particle size on the premise that the cost can be appropriately increased. Table 4 lists the effect of different particle sizes of heavy calcium on the properties of polyethylene (PE) plastic films under the same filling conditions.

 

3 From the perspective of processing fluidity, under the premise of controlling the maximum particle size, the average particle size is larger.

 

For calcium carbonate products of the same particle size, the particle size distribution may vary widely, which is reflected in the average particle size. For plastic products requiring good processing fluidity (such as injection molded products, cast PE film, etc.), it is not possible to use calcium powder with an average particle size too small. If possible, it is best to control the maximum particle size. Under the premise, the particles of small particle size are separated. This is because the more particles having a small particle size, the worse the processing fluidity of the filling system.