Chapter 7 - Paint fundamental

Question 1

What is a varnish

Answer 1

Is a clear unpigmented coatings applied over metallic surface

Question 2

Pigmented varnish are called, and the differences between them

Answer 2

Enamel or lacquer

Enamel - are usually thermosetting

Lacquer are usually thermoplastic

Question 3

What is Primer surfacer

Answer 3

combination of primer and surfacer

Question 4

What are fillers and what it is used for

Answer 4

Fillers are materials of high solid content that are used to fill holes and deeper irregularity

Question 5

What are primers and what is it used for

Answer 5

Primer is a coating applied to fill unfilled surface and to promote adhesion

E.g. give out corrossion resistance over metals

Question 6

What are Surfacers and undercoats, what are they used for

Answer 6

Are coating of highly pigmented materials and large quantities of extender, theh must stick well to primers and topcoat

Question 7

What is a sealer

Answer 7

Sealer is a clear or pigmented coatings that are applied thin to prevent the contact of two coatings or substrates

Question 8

What are pigments

Answer 8

any fine solid particles that do not dissolve in the varnish

Question 9

Methods of application

Answer 9

• Spraying
• Roller
• Brushes
• Dipping
• Electrodeposition

Question 10

what are solids in paint

Answer 10

the weight percentage of involatile materials found in paint

Question 11

what is Thixotrophic

Answer 11

is a property of materials that when it is agitated it lowers its viscosity but once the agitation stops, it slowly gain the viscosity lost over a period of time

Question 12

Dry film properties requirements - Adhesion

Question 13

What is the optimal intermolecular attractions operate on short distances and how to get the molecules within that range

Answer 13

the optimal intermolecular attractions operate on short distances like around less than 10 nanomicron, to get the molecules within that range, the paint must wet the surface.

Question 13

what is a critical surface tension and how do you wet the substrate

Answer 13

the critical surface tenson of a substrate is ease of difficulty of wetting it.
to wet the substrate, the paint needs to have surface tension equal or lower surface tension than critical surface tension of that substrate.

Question 14

What Standard practice before applying paint

Answer 14

the practice of rubbing undercoats with abrasive paper to level the surface for the next coat and to clean the surface removing materials difficult to wet or poor in cohesion

Question 15

adhesion when the condition of the surface is not porous

Answer 15

The adhesion depends on the strength of intermolecular attractions between paint and substrate

carboxyl groups promote adhesion to metal

Question 16

Hardness, toughness and durability films property, usually what films possess such quality

Answer 16

usually crosslinked films possess hardness toughness and durable. higher molecular weight linear polymer do possess that but it can be brittle

Question 17

Flexibility properties in a film

Answer 17

flexibility is introduced into crosslinked films by spacing out the crosslinks so the structure becomes looser. smaller molecules that are separated by large polymer chains, reducing attractive forces between them

Question 18

Weathering will cause the loss of some properties, name that properties and the cause of that

Answer 18

Gloss will diminish
surface becoming powdery - chalking
color fade or darken - pigment

cause - uv rays, water and oxygen

Question 19

Chalking mainly happens because

Answer 19

high PVC and it caused the binder / polymer not able to hold the pigment particles

Question 20

what requirements needs to met when polishing

Answer 20

to polish well, the surface needs to be capable of being softened by the heat generated, so that it will partially flow, evening out irregularities

Question 21

what is pulling over process

Answer 21

pulling over is the process of leveling up the surface of the polymer film by rubbing a pad of soaked solvent mixture that will just dissolve the polymer and it is usually used in furniture industry

Question 22

Badly damaged for 1k and for 2k paint

Answer 22

for 1k paint - the paint film must be patched, this is done by spraying the in damage area with the same paint - but the consequences is that this may increase the paint thickness

for 2k paint - the polymer needs to be completely rubbed down as it will not redissolve into old area

Question 23

two ways of how paint dry

Answer 23

drying without chemical reaction - usually chemical reaction between paint and something outside the paint like oxygen will attack unsaturated polymers within drying oils and it will produce free radicals and cause chain growth polymerization

drying with chemical reaction - 2k paint, usually the reactions between component A - polymer with hydroxyl groups with component B - polymer with isocyanate groups

Question 24

What is pot life

Answer 24

is a limited period of time, where the paint is still usable after mixing with component a and B

Question 25

Choosing between crosslinked or non crosslinked which is better

Answer 25

of course crosslinked is superior in terms of durability, toughness and solvent resistant, the higher solid, the better. and for non crosslink to match with crosslink performance, you need to use high molecular weight