What is nano calcium? What is the crucial role that will be played in the manufacture of plastic products?

China is a big country in the production and consumption of plastic products. In 2006, plastic products exceeded 40 million tons.

The amount of inorganic minerals used in calcium carbonate averages about 10% of the total amount of plastic products. That is, in 2006, China's plastics processing industry used at least 4 million tons of inorganic powder materials. Calcium carbonate (including heavy calcium and light calcium) is the most widely used and largest amount of inorganic minerals. In the total amount of inorganic mineral powder materials used, calcium carbonate accounts for more than 80%, mainly calcium carbonate resources. Rich, low price, good stability, simple color, low wear, easy to dry, easy to process, non-toxic and many other advantages.

1. Basic requirements for calcium carbonate in the plastics industry

Calcium carbonate as a common split material for plastics has many advantages that other powder materials do not have, such as high whiteness, indicating planned treatment, light wear on processing equipment and molds, good fluidity in molding processing, etc. The price is low, and it has become the first choice of inorganic mineral powder materials in the plastic 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 very cheap compared to synthetic resin, it is also cheaper than any other powder material. However, due to the large number of suppliers, the company is still price sensitive and can be used. The cheaper the better.

2) The higher the whiteness, the better: the color of calcium carbonate itself is whiter than that of other inorganic mineral powder materials. It can be more than 90 degrees from the specific value. The effect of whiteness on the properties of filled plastic is not obvious. However, plastic processing companies still hope that the higher the whiteness, the better, based on the following reasons:

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

The higher the whiteness, the better the visual impression, and the higher the grade;

The higher the whiteness, the more uniform the final color with other pigments.

3) The particle size distribution should be appropriate: As a powder material, it is necessary to consider the particle size distribution of the particles themselves under the test conditions. It is necessary to consider the existence state of these particles from the practical application, whether they are agglomerated together, and processed in the filling system. Whether the agglomerates can be evenly divided in the process.

From the perspective of cost, as long as it can meet the requirements of use, Ningke uses thick, not fine;

From the viewpoint of 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;

Considering the price liquidity, under the premise of controlling the maximum particle size, it is better to write the particle size first;

The history and distribution of light calcium and then calcium carbonate sold as commodities are very different from those in the Soviet Union and its dispersed phase. If the agglomeration problem is not solved well, it will not show the advantage of small particle size.

2, common problems

1) The problem of nano calcium carbonate

Whether the particles can be uniformly and non-adherently dispersed in the plastic matrix is ​​the key to judging whether it can be called nano-plastics, because the nano-sized small size is only when the nano-scale particles are evenly distributed in the matrix plastic. Benefits, large specific surface area benefits, and quantum effects can be truly realized, resulting in a qualitative leap in material properties, rather than just getting some improvements and improvements.

It is undeniable that at this point in the production process, the particle size of calcium carbonate is indeed in the category of nanometers. However, in the subsequent dehydration and drying process, these primary particles are agglomerated by force, which is actually the product to our users. Agglomerates, using existing powder surface treatment equipment, treatment agents, and subsequent mixing equipment, are unlikely to break up the agglomerates, making it impossible to obtain true calcium carbonate modified nanoplastics.

This year, there have been a lot of research results around the use of nano-calcium carbonate for plastics and its dispersion in the collective. For example, Sichuan University introduced wet-grinding, high-speed (4000r/min) mixing, ultrasonic vibration, vibration grinding and other methods into equipment. Calcium treatment process; Baoji Yunpeng Plastics Technology Co., Ltd. has successfully developed a new type of depolymerization agent to depolymerize nano-calcium carbonate agglomerated particles in high-speed motion for surface coating, which will help partially agglomerate nano-carbonated Calcium is dispersed in the base plastic at a nanometer scale, and the performance of the filled plastic is significantly higher than that of the conventionally treated calcium carbonate, and a very valuable attempt has been made. The performance of Yunpeng's products produced by depolymerization new technology is shown in Table 1.

Table 1 Application effect of calcium carbonate filler masterbatch in mulch

Film type tensile load (N) elongation at break (%) coaching tear load (N)

Vertical / horizontal vertical / horizontal

Pure LLDPE 2.90/2.30 (reference value) 321/654 0.75/1.28 (reference value)

Add 10% masterbatch 2.93/2.33 283/617 0.78/1.20

Add 15% masterbatch 2.07/1.83 257/533 0.83/1.60

Add 20% masterbatch 2.57/1.98 275/658 0.78/1.13

Add 33% masterbatch 2.20/2.03 250/692 0.75/1.00

GB13735 excellent products 1.6/1.6 160/160 0.6/0.6

Note: 1. The content of CaCO3 in Yunpeng masterbatch is 75%; 2. The film is made in the production equipment of Gansu Tianshui Plastic Co., Ltd., and the inspection results of other inspection items are in line with the international requirements of film.

It can be seen from Table 1 that when Yunpeng's calcium carbonate filler masterbatch is added to the mulch film by 33%, although the mechanical properties of the pure resin mulch film are reduced, it can still meet the requirements of national standards. In the proportion of the mulch film, the maximum drop of the tensile load and the right-angle tear load is about 20%, and if the calcium carbonate-filled masterbatch produced by the conventional technique is used, the tensile strength of the filled PE film is 30% when the CaCO3 content is 30%. Vertical and horizontal decreases by 45% and 42%, respectively, and the right-angle tear strength decreased by 32% and 31%, respectively.

2.2 Weight gain problem

Since the true density of the non-metallic mineral is much larger than the resin, the density of the filler material increases significantly as the amount of addition increases, for example, heavy calcium carbonate having a density of 2.7 g/cm3 is added to the HDPE, and the weight percentage thereof At 50%, the density of the plastic-filled injection molding material reached 1.6 g/cm3, and when the weight percentage reached 80%, the density of the filled HDPE reached 2.0 g/cm3. Increase in density For plastic products that are valuable in terms of length, area, and number of parts, there is a possibility that the length, area, or number of parts are reduced due to the increase in density, which not only offsets the use of inexpensive mineral powder materials. The interests of the company may not be worth the candle.

It should be pointed out that some plastic products are not sensitive to the negative effects of dense bulk publication materials, such as unidirectionally stretched woven bag flat yarn, packing tape, tear film and the like. During the processing of polyethylene plastic film, the bubble is subjected to longitudinal stretching and radial blowing. Since the stretching ratio and the blowing ratio are much lower than the stretching ratio of the uniaxially stretched product, the addition of the filler still causes the density of the plastic film. It is increased, but compared with the injection molded products, since the stretching and blowing increase also bring gaps between the macromolecules and the macromolecules and the filler, the increase in density is much shorter than that of the injection molded article. For example, a HDPE film incorporating 30% ground calcium carbonate has a density of not more than 1.1 g/cm3, and an injection molded article of the same formulation has a density of 1.3 g/cm3.

Following this line of thinking, some companies and technicians have already made some explorations, such as using different types of fillers, or pre-processing the filler particles to foam with the matrix plastic, and taking special processes in injection molding. The method has achieved certain effects. It can be considered that the breakthrough in weight gain and can be used in actual production will bring revolutionary impact to the development of modified plastics, which is worthy of our efforts.

2.3 Molding processing dimensional shrinkage problem

In the replacement of traditional plastic materials with more cost-effective modified plastics, such as filling PP with mineral powder material instead of aBS, in addition to the performance and appearance should meet the expected requirements, the dimensional shrinkage of molding processing is an important issue that cannot be ignored. .

The change in dimensional shrinkage of the molding process affects the geometry and size of the molded article. The injection molding die for pure PP or PE is designed according to the material shrinkage rate of 1.5-2.0% (in the above research work, the molding shrinkage of pure PP under the same conditions is 1.7%), if it is filled with calcium carbonate, molding processing As the dimensional shrinkage ratio becomes smaller, problems such as locking, surface scratching, and deformation occur in articles that are released by cooling shrinkage. However, if a special material of PP or PE plastic filled with calcium carbonate is used instead of aBS resin, the dimensional shrinkage of aBS is only 0.5%. The problem of difficulty in demolding or shape change also occurs. Plastics processing companies are often reluctant to modify or re-mold molds because of the replacement of raw materials, and it is possible to use modified materials.

2.4 surface treatment problems

2.4.1 Surface treatment agent

There are many kinds of surface treatment agents, but the most widely used commercial surface treatment agents are mainly stearic acid, titanate coupling agent and aluminate coupling agent, in addition to silane coupling agent and phosphoric acid. Ester coupling agent and the like.

1) Selection of calcium carbonate surface treatment agent

Stearic acid is the cheapest and is more suitable for polyvinyl chloride plastics, because stearic acid can be used as an external lubricant for polyvinyl chloride in addition to the surface of calcium carbonate. For polyolefin plastics. Stearic acid can also be used to treat calcium carbonate, but the amount is large, and only the coating effect is caused by no chemical reaction, so the overall effect is not as good as the coupling agent.

Several coupling agents can be used for the surface treatment of calcium carbonate, but each has its own characteristics. The titanate coupling agent is mostly liquid and easy to distribute, but it is usually darker in color and is not suitable in products requiring high whiteness; Aluminate is cheaper than titanate, white or light yellow, which is good for white products, but usually solid wax, which requires sufficient time for melting and dispersing; silane coupling agent is very expensive, and due to molecular structure flexibility The carbon chain is small and short, which has an effect on the processing fluidity of the filled plastic.

When selecting a surface treatment agent, it is necessary to consider both the price and the effect, and in particular, to deal with which plastic product the heavy calcium will be used for.

2) Use of coupling agent

The most critical problem with the use of coupling agents is to get it to the fastest of each particle of calcium carbonate and chemically react to form a chemical bond. This requires that on the one hand it should be dispersed under high-speed motion, on the other hand, it should have a suitable temperature to facilitate the chemical reaction. In addition, there is a problem of the source of hydrogen proton (H). If the moisture content of calcium carbonate is high, the coupling agent may react with water first, instead of reacting with the hydroxyl group on the surface of calcium carbonate, then the purpose of surface treatment cannot be achieved. . Therefore, it is necessary to ensure the three conditions of rapid distribution, suitable temperature and no moisture, in order to play the role of the coupling agent. As to whether it should be dissolved in the solvent first, whether it must be added to the processing equipment in the form of spray, it must be divided into batches, and it is not important to pass the surface.

2.4.2 Surface treatment equipment

The high-speed mixer currently in use is not originally designed for the surface treatment of powder materials, but is designed and manufactured for the pre-plasticization of polyvinyl chloride resin, so it is not a device that is naturally suitable for powder surface treatment. It is even less suitable for powder materials with smaller particle sizes including ultrafine heavy calcium carbonate. In recent years, plastic processing equipment manufacturers have made major changes according to our requirements, so when purchasing high-speed mixers, it must be declared for powder surface treatment.

For modified plastics processing enterprises, the surface treatment of calcium carbonate is often carried out by themselves. First, the formula can be flexibly mastered. Secondly, the surface treatment of calcium carbonate can be connected in series with the downstream process. Therefore, their focus is on transforming the existing high-speed mixer. To make it more suitable for its own process requirements, and for the production of large quantities of active calcium carbonate, it is necessary to consider

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