Dye & Pigments Flashcards
What is the primary difference between dyes and pigments?
Dyes are soluble substances that impart color through absorption, while pigments are insoluble and rely on dispersion within a binder to provide color.
- Dyes are colored substances that can be applied in solution or dispersion to a substrate, giving it colour appearance.
What distinguishes natural dyes from synthetic dyes?
Natural dyes are derived from organic or inorganic materials, such as plants and minerals.
Synthetic dyes are man-made, created using chemical processes, offering a broader color range and lower costs.
What is the defining characteristic of reactive dyes?
Reactive dyes chemically bond with fibers to form covalent bonds, ensuring good fastness due to direct reaction eith fibres..
On which types of fibers are reactive dyes primarily used?
Reactive dyes are commonly used for cellulosic fibers such as wool, silk and rayon.
What are the advantages of using reactive dyes?
A complete color range.
Good fastness properties, especially wash and light fastness.
Simple application.
Cheapest
What challenges are associated with reactive dyes?
They have a low affinity for cellulose, requiring large amounts of salt to aid absorption.
They cannot be used on synthetic fibers or fabrics treated with resin or drip-dry finishes.
What are direct dyes, and why are they widely used?
Direct dyes are water-soluble anionic dyes that are easily applied to cellulosic fibers like cotton and rayon. They are widely used because of their economical cost and simple application process
What materials are suitable for dyeing with direct dyes?
Direct dyes are primarily used for cellulosic fibers such as cotton and rayon but can also be applied to wool, silk, and nylon.
What are the advantages of direct dyes?
Simpler application
They are cost-effective
provide a full color range.
Moderate color fastness can be improved with post-treatment, such as using cationic fixing agents or copper salts.
What are the weaknesses of direct dyes?
Some shades have poor fastness, especially medium and heavy colors.
They are not suitable for applications requiring high durability or exposure to extreme conditions.
What makes direct dyes unique compared to reactive dyes?
Unlike reactive dyes, direct dyes do not form covalent bonds with fibers. They rely on adsorption and have a simpler application process.
What are vat dyes, and why are they unique?
Vat dyes are insoluble dyes that must be chemically reduced to a soluble form before application. They are known for their excellent fastness properties and are commonly used for high-quality cotton goods like denim.
Which dye type offers the best all-around fastness?
Vat dyes provide the best all-around fastness, especially for wash, light, and chlorine resistance.
Why are mordant dyes less commonly used today?
Mordant dyes require complex application processes involving pre-treatment with a mordant, making them less practical compared to modern dyes like reactive and direct dyes.