Judging whether talcum powder is good or bad, "degree" will help you

Talc has a significant reinforcing effect on molecular compound plastics, but not all talc products have a reinforcing effect. The enhancement effect is very different depending on the product grade. It is difficult to come up with uniform, specific standards for talc used in the plastics industry. The general principle of plastic properties is: try to use pure talc products with uniform particle size, the product is not as fine as possible, and should be selected according to product requirements and characteristics. The source of the talc raw material must be stable at the ore point, the grade of the product, especially the particle size distribution, and the wet whiteness and hue must be stable and continuous. In view of the diversity of talc mines, the best technical results of the products still require technical support from the manufacturer. When selecting a product, at least the "four degrees" of the talc itself should be considered, namely: purity, whiteness, molecular shape structure (ie, slice), fineness, or particle size.

In general, to evaluate the pros and cons of a talc product, at least consider the above four factors. Judging the quality with only one indicator is one-sided and incomplete. If someone only judges the quality of talc powder products by average particle size, this is a very inaccurate statement.

First, purity

Purity refers to the amount of talc in the product. In natural and industrial production, talc contains impurities, and 100% pure talc products in the industry are impossible. There is no doubt that the higher the purity of talc, the better its reinforcement and other specific effects. Studies have shown that the content of certain impurities in talc not only reduces its purity, but also has a significant effect on the performance of the final product. Carbonate, metal iron and heavy metals in talc have a very bad influence on the aging resistance and thermal stability of molecular compound plastics. The chlorite content has little effect on aging and thermal stability. China's white talc belongs to the carbonate-talc type. Therefore, the carbonate should be removed as much as possible during the beneficiation process. The talc raw material with low iron and low heavy metal content should be used to produce the molecular compound plastic grade talc. The main talc deposits in Liaoning, Shandong and Guangxi have relatively high purity. After screening, the purity can reach 96-98%. It is the world's most suitable talc raw material for modifying molecular compound plastics. However, carbonates, metal irons and heavy metals in different regions and products of different manufacturers in the same region are still very different. At present, most of this high-purity minerals are exported, and there are fewer domestic demand except for some joint ventures and wholly-owned or large private enterprises. The content of pure talc in talc products in the domestic market fluctuates between 20-98%. Products with low talc content have a very limited reinforcing effect on molecular compound plastics, mainly from the filling of general fillers. However, if the content of carbonate and iron and heavy metals is high, the aging resistance of the molecular compound plastic product may be caused, and the thermal stability is poor, thereby affecting the durability of the plastic.

For the discrimination of talc purity, it is recommended to use XRD+ phase analysis for scientific research with a deviation of less than 5%. In the production, the purity of talc can be estimated by detecting the loss on ignition (except for chlorite-talc type). Generally speaking, products with a loss on ignition of less than 8.0% are more suitable for use as reinforcing fillers in molecular compound plastics, and preferably have a loss on ignition of less than 5%.

Second, whiteness

The whiteness in the talc test is narrow and broad. The narrow whiteness is the general definition of whiteness, which can be expressed by blue lightness R457, Y, L*, Ganz plastic characteristic whiteness, and Hunter whiteness. There are no less than one hundred formulas for calculating whiteness in the world, and the formulas often used in the non-metallic mineral light industry are no less than ten. Using different instruments, the results obtained by different calculation methods will be different. The national standard GB/T 5950 delineates the measurement method and calculation formula of talc whiteness. This standard adopts the International Lighting Commission (CIE) 1964 supplementary standard color system and standard illuminant D65 delimited by GB3977, and calculates the whiteness with the three usual stimulation values ​​and chromaticity coordinates; adopts the CIE LAB uniform color space delimited by GB7921 to The brightness index and chromaticity index calculations represent hue, chroma, and chromatic aberration. The method is as follows: when the ideal full reflection diffuser with a spectral reflectance ratio of 1 has a whiteness of 100 and the absolute black body whiteness of the spectral reflectance is zero, the sample is determined according to the conditions delineated by this standard. The three constant stimulus values ​​are then calculated using the formula defined, and the hue angle, chroma, and color difference between the samples can be calculated.

Generalized whiteness includes dry whiteness, wet whiteness, and hue. The degree of wetness referred to herein is the whiteness measured after the talc powder powder is added to a suitable amount of DMP (dimethyl phthalate).

For the same raw material, the finer the particle size, the higher the whiteness. The higher the moisture, the lower the whiteness. Although the degree of whiteness has no effect on the physical properties of the product, it is important to maintain the pure whitening of the color for light-colored products. One disadvantage of talc is that the color of the molecular compound plastic is more or less darkened after mixing, which is an important factor limiting the wide application of talc in molecular compound plastics. By measuring and contrasting the dryness and the wetness, the talc can be qualitatively reacted to darken the molecular compound plastic article. Products with low wet whiteness make the molecular compound plastic darker. It is worth noting that the whiteness of talc with high dryness is not necessarily high. Generally speaking, only the talc with high purity and high whiteness has high wet whiteness, that is, the degree of darkening of the molecular compound plastic product is small. The talc powder used in the molecular compound plastics industry mainly has wet whiteness and hue. Y and L* should be as high as possible, and the absolute values ​​of a* and b* should be as small as possible.

The wet whiteness of some products of the main talc deposits in Liaoning, Shandong and Guangxi in China can reach more than 70%. In the past, the minerals produced in these places were mainly exported, and the domestic demand was not large. The current situation has changed. White talc is of course good, but the price is also high. In recent years, China’s white talc has risen rapidly because of its short supply. With the further increase in the demand for talc in the molecular compound plastics industry, the situation of short supply will further intensify. Due to the non-renewability of resources, the scarcity of white talc in the world is not temporary, and the shortage of supply will be a long-term situation in the future, and there is no possibility of reversal. Therefore, whenever possible, low-whiteness talc should be used to preserve quality resources. In fact, in many applications, white talc is not needed, so the use of white talc is actually a luxury. For example, in high molecular compound plastics, there is no difference between using high whiteness talc and low whiteness talc. Tests have shown that for every 1 degree increase in wet whiteness of talc, the plastic whiteness of the final product is improved by only 0.2-0.3 degrees. One-sided pursuit of talc whiteness does not make sense. In the past, because the price of high-grade white talc in China was too low, many users did not consider using the appropriate grade white talc, but the whiter the better. With the further increase in the price of white talc, everyone began to change the thinking and views of China's extravagance, so as to choose the talc products at their own cost.

Third, the molecular shape structure (ie, the degree)

The remarkable strengthening effect of talc on molecular compound plastic products is mainly due to its peculiar microscopic sheet structure. The more complete the flaky structure of talcum powder, the more obvious its reinforcing effect. The two main factors affecting the product sheet are:

1, the purity of talc

2. Processing technology and technology of powder

The impurities in the talc do not have a sheet structure. The purer the talc, the less the impurities, the better the sheet structure. In the process of miniaturizing talc, different processing methods are adopted, and the sheet structure of the product is maintained differently. Unsuitable processing methods and processing techniques can even destroy the sheet structure. At present, the fine talcum powder mainly adopts the airflow pulverization technology, and has two processing techniques of a hedging method and a swirling method. There are many production methods for the coarse number, but it is not suitable for the application of the high-end plastics industry.

Fourth, fineness

Micronization and nanocrystallization are the development trends of talc products. The finer the product, the better the strengthening effect, but at the same time, the surface energy of the particles increases, it is easy to agglomerate, the separation is difficult, and the price is high. Therefore, it is necessary to select the appropriate fineness of the product according to its own technical level and actual needs, and it is not necessary to be as fine as possible. The trend of fineness of talc powder used in the molecular compound plastics industry is as follows:

In the 1980s, the molecular compound plastics industry used 325-800 mesh products;

2. In the 1990s, 800-1500 mesh products were used;

3. After 2000, the main products are 1250-3000 mesh;

4. At present, 3000-6000 mesh products have been produced and used.

Evaluating the granularity of a talc product cannot be based on an average particle size. In fact, to evaluate the pros and cons of a talc product, at least the following two indicators may be referenced.

1, D50

2, D97 (or D100)

These two indicators are indispensable. At the same time as the products become finer and finer, people have put forward higher requirements on the microscopic shape and particle size distribution (PSD) of the fine-grained talc. The main indicators for evaluating PSD changed from the previous D50 to D97, D98 to the current D100. At the same time, the reproducibility of DSP is more stringent. When evaluating a product, the average particle size should not only meet the requirements, but more importantly, the particle size distribution should be as narrow as possible, and the large particles should be as small as possible. The product should try to achieve the same particle size distribution for each batch, which is very difficult in production practice. In the high-end products of talcum powder, controlling the particle size distribution, the number of coarse particles is a very critical technology, which requires high efficiency, high precision, reliable grading equipment, and rich operational experience and equipment. Maintenance capacity. There are only 6-7 companies that have relatively mature granular control technology in China. It is conceivable that although the seemingly simple talc production, the real test is equipment and operation technology.

The particle size distribution can be measured by a particle size distribution analyzer, and there are a laser method and a sedimentation method. However, most of the production practices use sieving to detect the amount of coarse particles.

Because of its own sheet-like structure, talc has a large specific surface area and a small bulk density. The body density of 325 mesh talcum powder is 0.8-0.9, but the 1250 mesh talcum powder is reduced to 0.25-0.3, and the 4000 mesh is only 0.12. This makes the dust pollution in production, the mixing difficult, the cost increase, and the production efficiency lower. And the transportation costs for long distance delivery are very high.

In response to the above problems, the talc powder compression technology and granulation technology have been developed abroad. The volume density of talc powder is greatly improved by compression. For example, the bulk density of 1250 mesh products reaches 0.8-0.9; granulation is the conversion of powdered talc powder. In the form of granules, the bulk density is further increased, so that the production process is free of dust, and the transportation and packaging costs are reduced, which is advantageous for storage. After the talc processing will be developed in the direction of miniaturization, the market needs finer properties of talcum powder. The role of compression and granulation technology in reducing product transportation costs, reducing environmental pollution, and improving downstream product production efficiency is also growing. Therefore, with the development of science and technology, there are more and more powerful and innovative production enterprises in China to invest in the environmental protection production, storage and transportation of talcum powder.

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