Three of the following are film forming binders. Which is the odd one out?
Answer: A
China clay is an inert filler that forms no film of its own and merely occupies space in the coating. The other three all become the continuous phase of the dried film, and each cures by a different mechanism. Recognising which is which decides how the paint must be applied.
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A varnish differs from a paint in that it
Answer: B
Correct answer: contains no pigment
A varnish is binder and solvent with no pigment, so it dries to a transparent film that protects while leaving the substrate visible. That is the only necessary difference - varnishes may be air-drying or baked, and the same resin systems are used in both varnishes and paints.
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Consider the following statements about water based emulsion paints.
1. The binder is present as fine particles dispersed in water.
2. Film formation requires the particles to coalesce as the water leaves.
3. The binder is dissolved in the water.
Answer: C
Correct answer: 1 and 2 only
Statements 1 and 2 describe an emulsion paint correctly: the binder is a dispersion of polymer particles in water, and the film forms when the water evaporates and the particles are pressed together and coalesce into a continuous layer. Statement 3 is wrong, and it is the essential point - the polymer is not dissolved, which is why the paint can be thinned with water before drying and is water resistant afterwards.
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Assertion (A): An emulsion paint has a minimum temperature below which it will not form a proper film.
Reason (R): The dispersed polymer particles must be soft enough to coalesce as the water evaporates.
Answer: D
Both are true and the reason gives the mechanism: coalescing solvents are added to lower that temperature, which is why painting in cold weather is warned against on the tin. The particles must fuse into a continuous film.
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High solids and powder coatings have been developed principally to
Answer: A
Correct answer: reduce emissions of organic solvent
High solids paints carry less solvent per unit of film delivered and powder coatings carry none at all, so both cut volatile organic compound emissions - which is what environmental regulation has demanded of the industry for decades. Water based paints answer the same requirement by a different route, and none of the three was developed for cost, colour or brushability.
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Consider the following statements about powder coating.
1. The powder is applied electrostatically and then fused in an oven.
2. It emits essentially no solvent.
3. It is well suited to heat sensitive substrates such as wood.
Answer: B
The first two are correct. The third is the process's main limitation, since the article must be heated to fuse and cure the powder, which rules out many substrates although low temperature systems have narrowed the gap.
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A paint is 45 per cent solids by volume. What dry film thickness results from applying a wet film of 100 micrometres?
Answer: C
The solvent leaves, so the dry thickness is the wet thickness times the volume solids. This is the calculation a specifier uses to decide how many coats a protective system needs. Wet film gauges are used to check it as applied.
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