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talc

[huá shí fěn]

Fine non sandy powder

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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Talcum powder is a kind of industrial product , is a magnesium silicate mineral talc group, which is mainly composed of hydrous magnesium silicate. After being crushed hydrochloric acid Treatment, water washing, dry And become.

It is commonly used as filler for plastic and paper products, rubber filler and anti sticking agent for rubber products, advanced paint and coating, etc.^[1]

On October 27, 2017, world health organization International Agency for Research on Cancer Published Carcinogen For preliminary arrangement of the list, talcum powder without asbestos or asbestos like fibers is included in the list of Class 3 carcinogens.^[2]

Chinese name: talc
Foreign name: Talcum powder^[1]
Alias: talc^[1]

Color: White or off white
Smell: Odorless and tasteless
Water solubility: Insoluble
CAS No: 14807-96-6

catalog

Molecular Structure Diagram

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The molecular structure of talcum powder is as follows:

Molecular Structure Diagram

component

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The main component of talc is magnesium silicate containing water in talc, and the molecular formula is Mg three [Si four O ten ](OH) two 。 Talc Monoclinic system 。 The crystals are pseudohexagonal or rhombic flakes, occasionally seen. It is usually in dense block, leaf, radial Fibrous aggregate 。 Colorless, transparent or white, but light green, light yellow, light brown or even light red due to a small amount of impurities; The cleavage surface is pearly. hardness 1. Specific gravity 2.7~2.8.

characteristic

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It has excellent physical and chemical properties such as lubricity, fire resistance, acid resistance, insulation, high melting point, chemical inactivity, good hiding power, softness, good gloss, strong adsorption power, etc. Since the crystalline structure of talc is layered, it has the tendency of splitting into scales and special lubricity.^[1]

It is relatively stable under normal conditions, without obvious side effects, but long-term large intake is carcinogenic. GB 9685-2008 stipulates that the maximum amount of paint used is 2.0%; Plastic (PE PP、PS、AS、ABS、PA、 PET、PC)、 Rubber and paper shall be used appropriately according to production needs.^[1]

physical property

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name	talc	Grade	Superior products
fineness	1250 (mesh)	country of origin	Hebei
Silicon dioxide content	60（%）	Allowable error	±0.01（kg）
Magnesium oxide content	30（%）	Whiteness	ninety-three

Specification of talcum powder

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200 mesh, 325 mesh, 500 mesh, 600 mesh, 800 mesh, 1250-8000 mesh, etc.

industrial production

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talc

The mined talc (raw material of talc powder) is directly used after selecting excellent talc Raymond Mill Or other high pressure mills can be directly crushed and directly used Woven bag (50kg, or 25kg woven bags) can be sold after packaging. In terms of mining methods, due to the extremely unstable ores and unstable surrounding rocks, the occurrence of ore bodies is mostly inclined and steeply inclined thick and extra thick ore bodies. The shape and thickness of ore bodies vary greatly, and there are many inclusions in the ore bodies. In the past, horizontal slicing separation and filling were used Mining method (At present, some mines still use this method).

Type of talcum powder

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Chemical grade

Purpose: for rubber 、 Plastic 、 paint And other chemical industries as strengthening and upgrading Filler 。 Features: increase the stability of product shape, increase the tensile strength, shear strength, flexural strength, pressure strength, reduce deformation, elongation, Coefficient of thermal expansion It is characterized by high whiteness, uniform particle size and strong dispersion.

Ceramic grade

Application: It is used to manufacture high-frequency porcelain, wireless porcelain, various industrial ceramics, architectural ceramics, household ceramics and ceramic glaze. Features: no color change at high temperature, whiteness enhanced after calcination, uniform density, good gloss and smooth surface.

Cosmetic grade

Use: It is a high-quality filler in the cosmetics industry. Features: It contains a lot of silicon. It has the function of blocking infrared rays, thus enhancing the sunscreen and anti infrared properties of cosmetics.

Pharmaceutical food grade

Use: for pharmaceutical and food industries additive 。 Features: non-toxic, tasteless, high whiteness, good compatibility, strong gloss, soft taste, strong smoothness. PH value is 7-9, which will not degrade the characteristics of the original product.

Paper grade

Application: It is used for various high and low grade paper making products. Features: Paper powder has the characteristics of high whiteness, stable particle size and low abrasion. The paper made with this powder can achieve smoothness and delicacy, save raw materials and improve the service life of the paper.

Brucite powder

Application: It is used to manufacture electric porcelain, wireless electric porcelain, various industrial ceramics, architectural ceramics, household ceramics and ceramic glaze. Features: no color change at high temperature, whiteness enhanced after calcination, uniform density, good gloss, smooth surface.

Product classification

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According to the physical and chemical properties, each variety of talcum powder can be divided into three quality grades: superior, first-class and qualified.

Specifications

The ground talcum powder is divided into the following two specifications according to its fineness and screen passing rate:

a. Fineness 45 μ m to pass screen mesh Expressed as a percentage of product weight;

b. Fineness 75 μ m to pass screen mesh Is expressed as a percentage of the product weight.

Fine talcum powder Particle size distribution and Grain size composition , expressed as the cumulative percentage content of products less than 20, 10, 5 and 2 μ m.

Product mark

The product mark of talcum powder is shown as follows:

Tag example

Example 1: paint grade talcum powder with whiteness of 75% and fineness of 45 μ m and passing rate of 98%

Talc TL75-45-98GB

Example 2: Fine talcum powder with whiteness of 80% and particle size of less than 20 μ m and cumulative percentage of more than 85%

Talc powder WF80-20-85GB

Example 3: rubber grade talcum powder with fineness of 75 μ m and passing rate of 99.9%

Talc powder AJ75-99.9GB

Technical requirements for cable grade talc

The physical and chemical properties of cable grade talc shall comply with the provisions in the following table.

Physical and chemical performance index of cable grade talc%
Physical and chemical properties	Premium	First Grade	Qualified products
Acid insoluble matter ≥	ninety	eighty-seven	eighty-five
Acid soluble iron (as Fe two O three ) ≤	zero point zero two	zero point zero five	one
Loss on ignition (1000 ℃) ≤	six	eight	ten
Magnet suction ≤	zero point zero four	zero point zero seven	zero point zero one

Events related to green tea, black tea, melon seeds added with industrial talcum powder illegally and completely faded after soaking for 20 seconds

On February 18, 2013, many media reported that many melon seed processing plants used industrial grade talc powder to make low-quality melon seeds smooth and bright. Industrial talc powder generally contains asbestos, which is a strong carcinogen. The survey found that in order to pursue a better appearance, alum 、 Sodium metabisulfite Such substances harmful to human body are overused in the production process of fried goods. Many melon seed processing plants also add vanillin 、 Saccharin sodium Wait more than ten kinds food additives The workers grasp it freely, depending on their feelings. The black tea melon seeds and green tea melon seeds produced in this way flow into the market in large quantities, and their prices are more expensive than ordinary original melon seeds.

Scope of application

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(1) Cosmetic grade (HZ): used for all kinds of moisturizing powder, beauty powder Talcum powder Etc.

(2) Pharmaceutical food grade (YS): pharmaceutical tablets, pharmaceutical powders (such as Acafen powder ）Icing a powder for prickly heat And traditional Chinese medicine prescriptions, food additives Isolating agent Etc.

(3) Paint grade (TL): used for white constitutional pigments and various water-based, oil-based, resin industrial coatings, primers, protective paints, etc.

(4) Papermaking grade (ZZ): used as filler for all kinds of paper and paperboard, wood asphalt control agent.

(5) Plastic grade (SL): for polypropylene 、 nylon 、 polyvinyl chloride 、 polyethylene 、 polystyrene And polyester and other plastic fillers.

(6) Rubber grade (AJ): used as rubber filler and anti sticking agent for rubber products.

(7) Cable grade (DL): used for cable rubber additive and cable isolating agent.

(8) Ceramic grade (TC): used to manufacture electric porcelain, wireless porcelain, various industrial ceramics, architectural ceramics, household ceramics and enamel.

(9) Waterproof material grade (FS): used for waterproof roll, waterproof coating, waterproof ointment, etc.

(10) Fine talcum powder: used for advanced paint, plastics, cable rubber, cosmetics Copper plate paper Coatings, textile lubricants, etc.

Effect of Talc Powder on Micro foamed Polypropylene Composites

Polypropylene (PP)/talcum powder is widely used in automotive plastics because of its low price and excellent mechanical properties. However, the material still has some shortcomings, such as high density, which is not conducive to the lightweight of vehicles. Micro foamed PP/talc material not only has excellent properties of composites, but also reduces density and weight.

1. Sample preparation

（1）PP/ Talc master batch

Adopt the same direction Double screw extruder Extrusion granulation, process parameters: screw speed 140r/min, feeding rate 1.2-1.5r/min, extrusion heating zone temperature 160-188 ℃.

(2) Micro foamed PP/talc composites

PP/talc master batch Foaming agent master batch The dumbbell spline that meets the test standard is prepared by secondary opening molding in the injection molding machine. The injection temperature is 175 ℃, the injection rate is 95%, and the injection pressure is 500kPa.

2. Effect of talc powder on mechanical properties of microcellular composites

Specific strength is an important index to measure the light weight and high strength of materials. Compared with pure PP, the specific tensile strength of unfoamed PP with 5% talcum powder decreased, the specific flexural strength increased, and the specific impact strength remained unchanged; With the further increase of talc content, the specific tensile strength, specific flexural strength and specific impact strength of the material decreased.

Compared with pure PP, the specific tensile strength and specific bending strength of PP foamed with 5% talcum powder increased, and the specific impact strength slightly decreased; The specific tensile strength, specific flexural strength and specific impact strength of foamed materials decreased with the increase of talc content. For the same material, the specific strength of foamed material is lower than that of non foamed material.

According to the above analysis of material specific strength, after foaming, the specific strength of PP material with 5% talcum powder is the highest. Continue to increase the mass fraction of talcum powder, but reduce the specific strength of the material. Therefore, a small amount of talc filling is conducive to improving the mechanical properties of PP after foaming.

Asbestos composition

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Talc is one of minerals. It is buried underground together with serpentine containing asbestos, so it often contains asbestos in natural form. The National Toxicology Program of the United States and the Occupational Safety and Health Administration (OSHA) did not list talc powder as a known or possible carcinogen, so there is no way to say that asbestos in talc causes cancer; The American Association of Governmental Industrial Hygienists (ACGIH) also listed talc as "not classified as a human carcinogen". Talc talcum powder is still used in the United States. according to International Cancer Research Center (IARC) lists "talc containing asbestos" as carcinogen.

Application of Talc Powder

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Application in paint

Talc powder has good suspension and dispersibility, and low corrosivity. In the coating, talc powder as a filler can play a skeleton role, reduce manufacturing costs and improve the film hardness of the coating. It also has the characteristics of improving the stability of product shape, increasing tensile strength, shear strength, pressure strength, reducing deformation, elongation, thermal expansion coefficient, high whiteness, uniform particle size and strong dispersion. Talc powder with lamellar particle structure can make the coating film have high water resistance and impermeability of enamel paint. Talc powder with fibrous particle structure can improve the rheological and leveling properties of the coating and improve the weather resistance of the coating.^[3]

Talc powder is mainly used in primer and intermediate paint. Talc powder is preferred for many products, flash drying primer and paint for transportation vehicles. The primer for steel structure can use talc powder in whole or in part to improve the sedimentation of the coating, the mechanical force of the coating film and the recoating ability.^[3]

Application in plastics

Inorganic filler plays an important role in the modification of plastics and becomes an indispensable modifier. Talc powder with white flake structure is an effective reinforcing material in plastics. It can give plastics high rigidity, creep resistance and good solid luster no matter at room temperature or high temperature. The addition of talcum powder can change various properties of plastics, such as Molding shrinkage Surface hardness, bending modulus, tensile strength, impact strength, thermal deformation temperature, molding process and product dimensional stability. Adding talcum powder to polyethylene and polypropylene plastics can effectively improve the surface hardness and scratch resistance of products. It is known that the price of talcum powder is 10%~20% of that of plastics, so the application of talcum powder to plastics can not only improve the performance, but also effectively reduce the cost of materials and improve the Economic benefits of enterprises 。^[3]

Application in Papermaking

Talc powder has unique properties such as layered structure, softness, hydrophobicity, etc. It has significant advantages when applied to the paper industry: (1) it helps to improve filler retention and paper opacity, smoothness, and printability, giving paper high ink absorption; (2) Stable chemical properties, not only suitable for paper making in acid conditions, but also can be used with calcium carbonate in neutral conditions; (3) Its surface is hydrophobic (lipophilic), and organics are easily adsorbed on its layered surface. The addition of talc powder reduces the consumption of dyes and effectively saves costs. In addition, its lipophilicity makes it available as resin, adhesive inhibitor and waste paper deinking agent; (4) It can combine well with sizing agent to improve sizing agent retention, reduce the absorption of paper pages, and prevent printing ink from penetrating the paper pages; (5) Talc powder has low friction coefficient, which can make the coating surface smooth and smooth, reduce the coating fracture, reduce the printing pressure, etc; (6) As a coating pigment with high morphological ratio, talcum powder has excellent fiber coverage and good printing effect, and can also improve intaglio printing quality; (7) Talcum powder has special lubricity, and the coated paper made of talcum powder can obtain high finishing degree on the calender, and can reduce the use of lubricant in the coating.^[3]

Food application

The edible talc powder is used as an additive in the pharmaceutical and food industries. It is non-toxic, tasteless, soft and smooth, so it can be eaten, but it is carcinogenic if used excessively or for a long time.

According to the national standard GB2760-2011, the maximum amount of talc used in cold fruits and medicinal products (liquorice products) is 20.0g/kg.

Human hazard

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Talc is closely related to asbestos, a strong carcinogen. Talc particles have been proved to be the cause of ovarian and lung tumors in cancer patients. In the past 30 years, scientists have been closely examining talc particles and found the danger similar to asbestos. In 1973, the US Food and Drug Administration (FDA) responded to the evidence in this regard by drafting a resolution to limit the amount of asbestos fibers in cosmetics grade talcum powder. However, no official decision has been made, and cosmetic grade talcum powder is still not controlled by the federal government. This kind of idleness ignored the report of the National Toxicology Project in 1993, which found that the cosmetics grade talcum powder without any asbestos fiber caused tumors in animal research objects. Obviously, cosmetic grade talc with or without asbestos fiber is a carcinogen.

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