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Printing Process & Techniques Year 3 > Dye printing > Flashcards

Dye printing Flashcards

1
Q

Describe the physical structure of wool fibre.

A

Outside scales with an inner cortex

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2
Q

What chemicals are wool sensitive to? What are they stable to?

A
  • sensitive to Alkalis

- stable to acids

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3
Q

What process can be carried out on wool to reduce felting?

A

Chlorination, an oxidation process

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4
Q

How does scouring effect wool?

A

-removes spinning oils and greases

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5
Q

How does chlorination effect wool?

3

A
  • improves wetting qualities
  • improves dye uptake
  • provides stronger, brighter colours
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6
Q

What are the three categories of acid dye?

A
  • acid levelling
  • acid supermilling
  • acid milling
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7
Q

What qualities does acid levelling achieve?

3

A
  • brilliant colours
  • good levelness
  • fairly weakly attracted to the fibres
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8
Q

What qualities does acid supermilling achieve?

3

A
  • strongly attracted to the fibre
  • difficulties obtaining level dyeing
  • restricted colour range
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9
Q

What qualities does acid milling achieve?

3

A
  • intermediate properties
  • there is a compromise between washfastness and levelling
  • commonly used
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10
Q

What is the typical process for acid dye?

3

A
  • print, dry
  • steam for 30 mins
  • wash off, rinse with cold water, then with hot water
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11
Q

Name 3 types of cellulosic fibres

A
  • cotton
  • linen
  • flax
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12
Q

What are the effects of singeing on cotton?

A
  • a burn-off of protruding fibres, seed husks, etc, for a cleaner surface
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13
Q

What is the effects of desizing on cottons?

A

Removal of “sizes”, e.g chemicals added to cotton to protect the yarn during weaving

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14
Q

What are the effects of scoring on cottons?

3

A
  • treatment with hot alkali
  • removes fatty materials and waxes
  • gives better wetability and absorbency
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15
Q

What are the effects of bleaching on cottons?

A
  • oxidation process using hydrogen peroxide
  • removes any natural colour
  • improves wetting and swelling ability
  • easier penetration for dye, cleaner background
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16
Q

What are 2 pros of direct dyes?

A
  • good solubility

- relatively low cost

17
Q

What are 3 cons of direct dyes?

A
  • tendency to bleed
  • dye fixing agents should be used
  • cheap but lower quality
18
Q

what are vat dyes and how do they work?

A
  • insoluble dyes
  • they are converted to a water soluble form by reduction in alkali conditions
  • oxidised back to insoluble dye when on the fibre
19
Q

What are the properties of vat dyes and what are the used for?
(3)

A
  • expensive
  • very high wet fastness and light fastness
  • used for upholstery, bedding, and curtains
20
Q

What are the 5 steps of the vat dye process?

A
  • print and dry rapidly, cool
  • steam for 15 mins at 103 degrees
  • oxidise in a bath containing hydrogen peroxide to get the dye colour back
  • add acetic acid to neutralise
  • cold rinse, followed by warm rinse, followed by boil wash with detergent
21
Q

How do reactive dyes attach to cellulosic fibres?

A

Forms a covalent bond, effectively becoming part of the fibre

22
Q

Name two pros of reactive dyes

A
  • full range of bright colours available

- excellent wash fastness

23
Q

Name to cons of reactive dyes

A
  • fairly expensive

- some environmental problems

24
Q

What conditions must there be for reactive dyes to produce a covalent bond?

A

Alkaline conditions

25
Q

What percentage of reactive dye reacts with water rather than fibre? What is it called when this happens?

A
  • 5-30%
  • hydrolysis
  • must be removed after dying
26
Q

What dye is used for polyester printing?

A

Disperse

27
Q

What are the properties of polyester?

4

A
  • synthetic
  • hydrophobic
  • more stable to chemical treatments than natural fibres
  • dyes find it hard to penetrate
28
Q

How are disperse dyes applied to polyester?

4 steps

A
  • applied as dispersion in water
  • low rate of uptake by fibre
  • requires high temp for fixation
  • reduction clearing bath removes surface dye
29
Q

The 4 components of reactive dye molecules are S C B and R. What do these stand for?

A

S- water solubilising group
C- coloured group
B- bridging group
R- reactive group

30
Q

What does the ‘reactive group’ component of a dye molecule do?

A

-forms the covalent bond with the fibre

31
Q

What kind of conditions do reactive dyes need for fixation?

A

-alkaline

32
Q

Why is it important to remove ‘sizes’ from fabric? How can they effect fabric if not removed?

A

-they can cause the reduction of dyes, losing colour

33
Q

Explain the acid dyeing process

A

-negative charges dyes are applied to wool under acid conditions, which have a positive charge (H+)

34
Q

Acid dyes have ____ with wool because of ____ forces

A
  • substantivity

- ionic

Printing Process & Techniques Year 3 (6 decks)

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