Chapter 8 - Pigmentation: pigments and paint making

Question 1

General Formula of paint

Answer 1

Resin + Thinner / Solvent + additive + Pigment / Filler (Optional)

Question 2

Purpose of pigment in any surface coating and purpose of fillers below / what do they contribute in paint formulation
Pearlescent
Aluminum Silicate
Silane
Barium Sulfate
Mica
Iron Oxide / Zinc Phosphate
Silica / Quartz
Fumed Silica
Bentonite Clay
Organic Clay

Answer 2

1. Provide colour
2. Provide special effects
   –> like flip flop / chameleon effect (Interference or pearlescent pigment)
   –> Sparkle (Pearlescent pigment)
3. Obliterate previous color / underneath color
4. to improve adhesion of paint (Silane)
5. improve the durability and weathering properties (mica)
6. To increase the protection against corrossion (iron oxide, zinc phosphate)
7. to reduce gloss (silica / quartz powder)
8. Modify flow and properties (fumed silica for anti sagging, bentonite clay to control visco and prevent settling, organic clay to improve dispersion)
9. Improve density (Barium Sulfate)

Question 3

Properties that you need to know when selecting a pigment

Answer 3

Tinting Strength
Lightfastness
Refractive Index
Particle Size
Particle Shape
Bleeding Characteristics
Chemical Reactivity
Thermal Stability Temperature

Question 4

What is a tinting strength and the formula of finding an unknown tinting strength of an unknown pigment

Answer 4

tinting strength is the strength of a pigment to alter another pigment’s color shade, the less altering pigment required to achieve the desired shade, the stronger is the tinting strength of the altering pigment

the formula of finding an unknown tinting strength of an unknown pigmnet is

Tinting strength of unknown = Amount of Unknown / (Amount of Altering pigment x tinting strength of altering pigment)

Question 5

What is a bleeding characteristics

Answer 5

Bleeding characteristics is the solubility of a pigment in a solvent usually organic pigment is prone to bleeding

Question 6

What is Hiding power and what 3 things that determine the hiding power of a pigment?

Answer 6

is the ability of a pigment to absorb light or to scatter light so it stops the light from passsing through,

it depends on refractive index, particle size and particle shape

Question 7

what is a refractive index

Answer 7

is the parameter on how much the path of light is bent or refracted when entering a material.

if the film formers and pigment have similar RI it will appear transparent

Question 8

Optimum diameter of particle in maximum scattering light

Answer 8

around 0.2 - 0.4 nanomicrons about half the wavelength of light in air,
below 0.2 nanomicrons, the particle loses its scattering power.
above 0.4 nanomicrons, the particle will lose its hiding power due to number of interfaces in a given weight of pigment (interfaces - a point where the two subjects interact)

Question 9

What is oil absorptions in pigment

Answer 9

is the amount of oil required to turn pigment into paste

Question 10

what is agglomerates

Answer 10

is a state where two or more particles are packed together with air in between the individual particles

Question 11

what is the most important part of a pigment

Answer 11

the surface of a pigment, because it determines whether the groups has any attractions to parts of varnish molecules or not, if there is it is not desireable because they are not free to move and if the attractions comes from an additive it can render additive useless.

depending on the strength of the attractions, it could lead to clustering which resist wetting and dispersion - flocculation

Question 12

Particle Shape of pigments does contributes to the hiding power, can you give examples of each type of particle shape that a pigment has

Answer 12

particle shapes of a pigment can be spherical, cubic, nodular (rounded irregular shape), acicular (needle), lamellar (plate like), rod shape

Question 13

Rod and lamellar particle shape benefit

Answer 13

rod shape can reinforce paint films, while lamellar shape or platelike shape like mica and aluminum tend to overlap one another making it difficult for water to penetrate.

Aluminum and specially treated mica pigments also reflect light from their polished flat faces in metallic paints

Question 14

Specific Gravity in a pigment

Answer 14

gram/cm3, the lower specific gravity of a pigment the more it takes space and the less dense it is. expensive pigment may prove economical if its specific gravity is low.

Question 15

Chemical Reactivity, can make some pigments are unsuitable for some purposes, for example what and why does zinc oxide should not be used in a resin

Answer 15

zinc oxide should not be used as a white pigment with resin containing high portions of acid groups because zinc oxide is amphoteric, which can react with acid and base.

Question 16

what is a thermal stability in a pigment

Answer 16

is temperature at which the pigment decomposes and alters its nature

Question 17

Pigment types can be

Answer 17

organic and inorganic, natural and synthetic

Question 18

what is the weakness of natural pigment

Answer 18

they can be contaminated by some impurity such as silica

Question 19

Which one is more superior in these category
Brilliance and clarity of hue -
White and black Paints -
Non Bleeding -
Lightfastness -
Heat Stability -
Anti Corrossive -
Reflective Effects -

Answer 19

Brilliance and clarity of hue - Organic
White and black Paints - Inorganic
Non Bleeding - Inorganic
Lightfastness - Inorganic
Heat Stability - Inorganic
Anti Corrossive - Inorganic
Reflective Effects - Inorganic

Question 20

Resin to disperse

Answer 20

resin to disperse pigment usually contains polar group which provide attraction to pigment surface molecules

Question 21

Pigment selection guideline

Answer 21

First, you need to examine a pattern of the color to be produced in paint. estimate the number of hues that will have to be blended to provide the colour
Secondly, you need to define the properties required from the pigments,
thirdly, you need to select a suitable pigment in each hue by following guidelines from
–> general paint and pigment literature
–> colour index. the properties of pigments are given

Question 22

what is comminution

Answer 22

is where the attrition or rubbing forces to reduce the size of particles to liberate the particles from the agglomerates

Question 23

Types of mill

Answer 23

Bead mill - usually used for carbon black
sand mill -
and roller mill - usually used in ink production

Question 24

Duration for
High speed dispenser
sand mill
let down and tint stage

Answer 24

High speed dispenser and sand mill around 10 min to 48 hours

for let down and tint stage around 2 hours

Question 25

Rough guide for amount of pigment

Answer 25

1/3 of binder weight

Question 26

Procedure for colour matching and how it can be speeded up

Answer 26

the main hue and the undertones are observed using the principles of substractive mixing each pigment are dispersed separately and each of them is converted to a paint, each containing only one pigment. This is colour solutions colour solutions are blended until the desired colour is obtained, the proportions of the blend are recorded the final paint can be made through 2 process --> blending colour solution --> cogrinding and if the colour is slightly off shade. it is adjusted by additions of colour solution / concentrated pigment disperseion. By using spectrophotometers/colorimeters + computer it can speed up the process