dyeing & dyestuff Flashcards
1
Q
What is dyeing?
A
The application of color to a textile material with a degree of fastness.
2
Q
What is the difference between dyeing and printing?
A
Dyeing applies a uniform single color, while printing creates multicolored patterns.
3
Q
What are the two main types of colorants used in textiles?
A
Dyes and pigments.
4
Q
How do dyes impart color?
A
By penetrating the fiber’s internal structure on a molecular level.
5
Q
How do pigments impart color?
A
By attaching to the fiber’s outer surface, held by a binder.
6
Q
Name three historical natural dyes.
A
Indigo, madder, cochineal.
7
Q
Why are synthetic dyes more prevalent than natural dyes today?
A
Superior color depth, brightness, and colorfastness; lower cost and higher volume production.
8
Q
What was the first synthetic dye?
A
Mauveine, discovered by William Henry Perkin in 1856.
9
Q
What are the four forms in which textiles can be dyed?
A
Fiber, yarn, fabric, garment.
10
Q
What is another term for fabric dyeing?
A
Piece dyeing.
11
Q
Name two methods of dyeing fibers.
A
Stock dyeing and dope dyeing (solution dyeing).
12
Q
Describe stock dyeing.
A
Dyeing fibers in loose form, requiring special equipment.
13
Q
Describe dope dyeing.
A
Incorporating colored pigments into the polymer before fiber extrusion.
14
Q
What is a benefit of dope dyeing?
A
Excellent fastness properties.
15
Q
What is a drawback of dope dyeing?
A
Increased cost and reduced flexibility for color changes.
16
Q
What is a heather style fabric?
A
A fabric with a mixed color effect created by blending differently colored fibers.
17
Q
Name three methods of dyeing yarns.
A
Skein dyeing, package dyeing, beam dyeing.
18
Q
When is skein dyeing used?
A
For bulky yarns that shouldn’t be wound under tension.
19
Q
What is a key advantage of yarn dyeing over printing?
A
Typically produces higher color quality.
20
Q
What are dye tubes used for?
A
Winding yarn for package dyeing.
21
Q
What is critical for high-quality package dyeing?
A
Accurate control of yarn tension and package density.
22
Q
What type of dyeing is advantageous for fabrics that crease easily?
A
Beam dyeing.
23
Q
What is the most widely used dyeing technique?
A
Fabric dyeing.
24
Q
Name three fabric printing methods.
A
Engraved roller, flat screen, rotary screen.
25
Describe tie-dyeing.
A technique involving knotting fabric and dipping it in dye baths to create patterns.
26
What is a benefit of garment dyeing?
Faster response time to market color changes.
27
What is a drawback of garment dyeing?
Lower color quality and reproducibility compared to fabric dyeing.
28
What must be considered when garment dyeing?
Thread, buttons, zippers, and seams must withstand the process.
29
List the three primary objectives of the dyeing process in order of importance.
Shade matching, colorfastness, cost-effectiveness.
30
What is the largest cause of textile seconds?
Off-shade (failure to match the shade standard).
31
What organization publishes test methods for textile fastness?
AATCC (American Association of Textile Chemists and Colorists).
32
What three components are necessary for color perception?
Light source, observer, object (and its surroundings).
33
What standard light source is typically used for shade evaluation?
D-65 (artificial daylight).
34
What is ring dyeing?
Incomplete dye penetration resulting in uneven color and potential for white areas with wear.
35
What is a crucial step for good-quality dyeing?
Good fabric preparation (scouring and bleaching).
36
How should knit fabrics be handled during wet processing?
Minimize tension to reduce shrinkage.
37
What is chemical barré?
Uneven dye uptake due to varying crystalline/amorphous regions in fibers.
38
What is mechanical barré?
Streakiness in knitted fabrics caused by factors other than dyeing.
39
Name two classifications of dyeing processes based on fabric amount.
Exhaustion (batch) dyeing and continuous dyeing.
40
Describe exhaustion dyeing.
Dyeing a fixed amount of material in a bath, requiring time and agitation.
41
What is fractional exhaustion?
The ratio of dye in the fabric to the initial dye in the bath.
42
What is percent dye owf?
Percentage of dye based on the initial weight of the fiber/fabric.
43
What is liquor ratio?
The ratio of bath weight to fabric weight.
44
What is a benefit of a higher liquor ratio?
More level dyeing.
45
Describe continuous dyeing.
Dyeing a continuously moving width of fabric using a padder.
46
What is wet pickup in continuous dyeing?
The amount of dye solution absorbed by the fabric.
47
What can cause uneven dyeing in continuous dyeing?
Uneven drying after padding.
48
What is an advantage of continuous dyeing?
Higher production efficiency and lower water/energy use per yard.
49
What is a disadvantage of continuous dyeing?
High initial cost and large space requirements.
50
What promotes levelness and uniformity in dyeing?
Good preparation, agitation, high liquor ratio, gradual temperature increase.
51
Name three factors that can cause non-level dyeing.
Inadequate agitation, low liquor ratio, rapid temperature increase.
52
Why are dye classes fiber-specific?
Different fibers have different chemical structures and affinities for different dyes.
53
Name four common dye classes.
Direct, reactive, acid, disperse.
54
What is a key consideration when choosing dyes besides shade and fastness?
Toxicity to workers and the environment.
55
Where can information on dyestuffs be found?
AATCC Buyer's Guide and Colour Index International online.
56
What is a fishbone diagram used for?
Identifying causes of problems in a manufacturing process.
57
What are the four 'M's in a typical manufacturing process?
Materials, Machines, Manpower, Methods.
58
What are the main categories in the shade reproduction fishbone diagram?
Materials, Equipment, Human Factors, Processes, Controls, Logistics.
59
How many dye classes are used to dye cotton and other cellulosics?
Five: Direct, Naphthols, Reactives, Sulfurs, Vats.
60
What is the most widely used dye class for cellulosics?
Reactive dyes.
61
Which fibers are typically dyed with disperse dyes?
Almost all synthetic fibers, particularly polyester.
62
Which fibers are primarily dyed with acid dyes?
Nylon, wool, silk.
63
Which fibers are dyed with basic dyes?
Acrylic fibers and cationic-dyeable polyester.
64
How are polypropylene and polyethylene fibers dyed?
Solution dyeing or pigment/binder systems.
65
Describe mechanical entrapment in dye retention.
Dye molecules are physically trapped inside the fiber.
66
Describe ionic bonding in dye retention.
Oppositely charged dye and fiber form a strong bond.
67
Describe covalent bonding in dye retention.
Dye chemically reacts with the fiber to form a bond.
68
Describe preferential absorption in dye retention.
Dye is attracted to the fiber due to chemical similarities.
69
Name three commercially important dye classes for cellulosics.
Direct, reactive, vat.
70
Describe the dye retention mechanism of direct dyes on cellulose.
Preferential absorption via hydrogen bonding and Van der Waals forces.
71
Why is salt added to direct dye baths?
To neutralize the negative charge on the fiber and overcome dye repulsion.
72
How can washfastness of direct dyes be improved?
Aftertreatments like cationic fixing agents or formaldehyde.
73
Describe the dye retention mechanism of reactive dyes on cellulose.
Covalent bonding through chemical reaction.
74
What is a problem with reactive dyes?
Competing reaction with water, leading to dye inactivation and loss.
75
Describe the dye retention mechanism of vat dyes on cellulose.
Mechanical entrapment after solubilization, application, and insolubilization.
76
What chemical are most vat dyes based on?
Anthraquinone.
77
Describe the application of disperse dyes on polyester.
Dispersed in water with a surfactant, penetration enhanced by carriers or pressure dyeing.
78
What is a carrier in disperse dyeing?
An organic chemical that swells the fiber to allow dye penetration.
79
What is the Thermosol process?
A continuous dyeing process using disperse dye sublimation at high temperatures.
80
Describe the dye retention mechanism of acid dyes.
Strong ionic bonding with amines in the fiber.
81
What are pre-metallized acid dyes?
Acid dyes containing chrome or cobalt to improve fastness.
82
Name three classes of acid dyes.
Leveling, milling, neutral (super milling).
83
What is a retarder in dyeing?
A chemical that slows the dyeing rate to promote levelness.
84
Describe the dye retention mechanism of basic dyes.
Strong ionic bonding with negatively charged fibers.
85
What is the glass transition temperature of acrylic fibers?
Approximately 180°F.
86
How are basic dyes categorized?
By exhaustion rate (K values).
87
What is a general relationship between ease of application and washfastness of dyes?
Easy-on, easy-off; easy application often means poor washfastness.
88
What are the advantages of pigment coloration?
Economical, applicable to all fibers, extensive color range, high lightfastness, satisfactory washfastness.
89
What are the disadvantages of pigment coloration?
Poor crockfastness (especially heavy shades), binder stiffness, potential for pad roll build-up, migration issues.
90
What is union dyeing?
Achieving a uniform shade on a blended fabric.
91
What is cross-dyeing?
Dyeing each fiber component of a blend a different shade.
92
What is reserve dyeing?
Leaving at least one fiber component undyed.
93
What is tone-on-tone dyeing?
Dyeing fibers in a blend with the same dye class but to different shade depths.
94
What is multi-level dyeing?
Dyeing multifilament yarns with different filament types having different dye uptake capabilities.
95
What is staining in blend dyeing?
One fiber being stained by the dye intended for the other fiber, resulting in poor fastness.
96
What is the purpose of dyeing machinery in batch dyeing?
To move dye liquor through the goods, or goods through the dye liquor, promoting level dyeing.
97
What is the purpose of dyeing machinery in continuous dyeing?
Even, uniform dye application with thorough penetration.
98
What is a key feature of jet dyeing machines?
Fabric propelled by pressurized jets of dye bath liquid.
99
Describe a dye jig.
A machine with rollers holding fabric in open width, moving it back and forth through the dye bath.
100
Describe a dye beck.
An atmospheric machine with an elliptical roller propelling fabric in rope form through the dye bath.
