Food Packaging Technology Multiple Choice Questions & Answers (MCQs) on “Surface Treatment of Glass”.
1. Temperature of hot-end treatment is glass is around ______
a) 300°C
b) 450°C
c) 250°C
d) 550°C
Answer: d
Clarification: In hot-end treatment (typically carried out while the glass container is at 550°C), vapor containing tin or titanium (generally in the form of a tetrachloride) is brought into contact with the outside of the container, forming a thin unimolecular film of metal oxide.
2. Why is hot-end treatment is done in glass?
a) To prevent surface damage
b) To ensure better adhesion and
c) To strenghthen the surface
d) To prevent surface damage, ensure better adhesion and strenghthen the surface
Answer: a
Clarification: Hot-end treatment is done in glass to prevent surface damage. This treatment is done while the container is still hot, strengthens the surface and improves the adhesion of the subsequent cold-end coating.
3. Temperature of cold-end treatment is glass is around ______
a) 200°C
b) 150°C
c) 100°C
d) 80°C
Answer: c
Clarification: Cold-end treatment (typically carried out while the glass container is at less than 100°C) is designed to protect the container surface and assist its flow through the filling line.
4. Cold-heat treatment is primarily done to increase the lubricity.
a) True
b) False
Answer: a
Clarification: The given statement is true. Typically, it involves spraying an organic material in an aqueous base containing either waxes, stearates, silicones, oleic acid or polyethylene onto the outside of the container to increase its lubricity by providing a surface with a low coefficient of friction. It is important to check the compatibility of the cold-end treatment with any adhesives used to attach labels.
5. The function of hot-end treatment and cold-heat treatment in glass is the same.
a) True
b) False
Answer: b
Clarification: The given statement is false. The function of hot-end treatment and cold-heat treatment in glass is the different. Hot-end treatment is done primarily to prevent surface damage like blurring, whereas, cold-heat treatment is done to increase the lubricity of the surface for better adesion.
6. What are shrink sleeves in glass?
a) Adhesives
b) Temperature control
c) Protective labels
d) Lubricants
Answer: c
Clarification: Shrink sleeves are protective sheets used on glass. Most shrink sleeves are made of oriented plastic films that shrink around a glass container when heat is applied. Two types of protective labels are used on glass bottles in the form of a body sleeve: one constructed from thin, foamed PS; the other is made from uniaxially oriented PVC or PS. PVC offers some thermal insulation. Whereas PS contains the glass fragments and prevents shattering of glass, if droppped.
7. Hot-end coatings are applied before the container enters the annealing oven.
a) True
b) False
Answer: a
Clarification: The given statement is true. Hot-end coatings are applied before the container enters the annealing oven (when the glass is still hot due to the previous forming process).
8. Cold-end coatings are applied before the container enters the annealing oven.
a) True
b) False
Answer: b
Clarification: The given statement is false. Cold-end coatings are applied after the container comes out of the annealing oven and cools. It is mainly applied to increase the lubricity and minimize the scratching of surfaces.
9. Which of the following is not a cold-end coating?
a) Waxes
b) Polyvinyl alcohol
c) Silicon
d) Nylon
Answer: d
Clarification: Nylon is not a cold-end coating. Cold-end coatings typically consist of lubricants such as waxes, polyethylene, polyvinyl alcohol, and silicone.
10. Which of the following is a hot-end coating?
a) Tin chloride
b) Sodium hydroxide
c) Lithium aluminium hydride
d) Boron
Answer: a
Clarification: Hot end coatings consist of tin chloride (which reacts to form tin oxide) or organo-tin. These compounds are applied in vapor form and leave a rough high-friction surface on the glass container, which provides a good adhesive surface for the cold-end coatings. They also supply hardness, fill in minor cracks, and compress the glass surface.
11. The term “birdswings” and “spikes” used in glass refers to _______
a) cold-treatment
b) heating oven
c) heat treatment
d) defects.
Answer: d
Clarification: Some 60 defects can occur in finished glass containers, ranging from critical defects such as “birdswings” and “spikes” (long, thin strands inside the container that would probably break off when the container was filled) to minor defects such as “wavy appearance” (an irregular surface on the inside).