Physical Properties

30 августа, 2015

Pokraskin

The main advantages ofcadmium pigments are:

• excellent temperature stability

• Insolubility in organic solvents (non-bleeding)

• light fastness and weather fastness

• chemical resistance

• non-migratory

• good dispersibility

• Polymers colored with cadmiums have good resistance to distortion and warpage

• high opacity

• can be recycled in polymers

Table 3.1: Colour index and typical properties.

Colour Index Name	Pigment Yellow 35	Pigment Orange 20	Pigment Red 108
Composition	CdS-ZnS	CdS-CdSe	CdS-CdSe
Colour Index No.	77205	77119	77 202
C. A.S. No.	8048-07-05	12656-57-4	58339-34-7
EINECS No.	232-466-8	235-758-3	261-218-1
Oil absorptionw/w	21.8	20.7	20
Specific gravity	4.6	4.8	4.8-5.1
Bulk density g/cc	0.91	0.95	0.98-1.1
Residue on 300 mesh	<0.1	<0.1	<0.1
pH extract	6.5-7.0	6.5-7.0	6.5-7.0
Water soluble salts	<0.2%	<0.2%	<0.2%

N. B. Lithopones have Colour Index names with the suffix 1. For example, Pigment Yellow 35:1 is the lithopone equivalent of Pigment Yellow 35.

Particle size measurements using electron microscopy show the primary particles to be 0.2-5 im.

A slightly larger particle size will be found if the determination is done by other methods such as disc centrifuge or sedimentation techniques (Figure 3.5), depending on how well the pigment is dispersed.

Cadmium pigments are stable to 400 °C with only minimal degradation, allowing them to be used in the majority of polymers, and also allowing colored articles to be recycled. They have limited use in some polymers, such as silicone molding compounds, acrylic molding compounds and acetals.

Chemical resistance is good, particularly to alkali, reducing agents and dilute acids. They are, however, susceptible to attack by concentrated mineral acids. Light fastness properties are also good (typically 7 by the Blue Wool Scale). In weathering tests, their performance is generally considered excellent in mass tone. However, the ability of the carrier resin to allow moisture to permeate, the presence of oxidizing agents and the presence of titanium dioxide when combined can all reduce performance. Thus, resistance to weathering in mass tone can be better than in reduced tone.

Because of the inorganic nature of the pigment, cadmiums are not soluble in organic solvents and polymers. They have therefore very low migration levels.

Much work has been done to determine levels of extractable cadmium leached from colored articles. This has been done to determine how much cadmium is likely to be released in food contact applications, and to predict cadmium release

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from waste products in landfill sites. It has been shown that in all but a few polymers insignificant levels of cadmium are leached out.