Unit 2 - Closures Flashcards
Who are the 3 main users of closures, and give an example of each
- Supplier closures
- Include base of steel cans and closed end of tubes
- Fillers closures
- Bottle caps and heat-seal films
- Consumer closures
- Re-closeable lids etc.
Name the 5 main types of closures
- Glued / taped
- Stitched / stapled
- Folded / twisted
- Mechanical
- Heat-sealed
What do stitched / stapled closures rely on?
Rely on tear strength of the substrate
What do folded / twisted closures rely on?
Rely on dead-fold characteristics of materials and the accuracy of cutting / creasing operations for cartons
Name the 4 ways in which mechanical closures are applied
- Threaded
- Seamed
- Clamped
- Pushed on
How are threaded closures applied and removed?
Twist on and twist off
What materials can threaded closures be made from?
Metal or plastic
Name the 3 types of machinery that can apply threaded closures
- Single head
- Linear head
- Multi-head capping machinery
Name the two types of threaded closures and describe them
- Continuous - rotation draws the threads of the cap onto the container by at least 360° to make the seal
- Interrupted - closure descends until a liner forms a seal, with typically less than 90° rotation; can also be called a lug closure
Give the 2 types of neck used with threaded closures and state what materials they are used with
- Symmetrical - designed for glass bottles
- Modified buttress - designed for plastic
Name the 3 ways to achieve a seal with a threaded closure
- Wadded closure
- Wad-less closure
- Plastisol liner
Describe a wadded closure
- The wadding conforms to the irregularities of the container top to provide a seal between the rim and the closure
- Usually made from pulpboard or expanded plastic lined with PE
- Held in place by friction fit
Describe a wad-less closure
- Seal is made between the pack and the cap, so the dimensions are critical
- Inside of the cap has a lip which fits securely over the neck of the bottle enabling the seal
Describe a Plastisol liner
- A suspension of PVC particles in a liquid plasticiser - it flows as a liquid and can be poured into a heated mould
- When heated to 177°C, the plastic and plasticiser mutually dissolve in each other, which give a flexible plastic when cooled
Describe how an induction seal is applied
- Screw threaded closure is applied to the container to a set torque and then the capped container is passed between induction coils
- The aluminium foil layer in the wad in heated via electromagnetic field transferring energy to metallic laminate and the heat seal coating on the foil is softened and adheres to the rim of the container (like a milk or condiment bottle)
- There is no contact between the sealing coils and the closure
What happens when an induction seal is opened?
On opening, the foil diaphragm remains sealed to the container, giving tamper evidence and maintaining preservation
Name and describe the two types of induction seals
- Two-piece liner - heat melts the wax, which is absorbed by the pulpboard which releases the aluminium layer to adhere to the container; the pulpboard remains in the cap
- One-piece liner - the backing remains on the foil layer
What are twist on / twist off closures made from?
Heavy gauge, lacquered or printed steel
Seals via flowed-in plastisol liner
Give 3 advantages of twist on / twist off closures
- Withstands heat processing
- Tamper-evident pop-up button
- Fast application with typically less than 90° rotation
What material are twist on / twist off closures usually applied to?
Used mainly on glass jars
What do twist on / twist off closures require to work?
Requires clean thread area
Give a disadvantage of twist on / twist off closures
Can be difficult to remove
How do twist on / twist off closures provide tamper evidence?
Filled in a steam environment to draw a vacuum, created by the steam filling the headspace then condensing creating a vacuum to give a concave lid button
Describe the composition of a press on / twist off closure
- Printed metal shell with no threads
- Flowed-in soft liner
- During heat processing, liner conforms to container threads
Give 3 advantages of press on / twist off closures
- Tamper evidence via pop-up button
- High speed
- High throughput
Describe a pry off / lever lid and one requirement
- Required the lid to fit accurately to the container body in order to be leakproof
- The rim of the container is used as a level point
Describe seamed closures and where they are used
- Formed by the mechanical folding of metal and require a sealing compound
- They are used where microbiological integrity is critical and so tolerances are very tight
Describe the composition of a crown cork closure
- Heavy gauge tinplate with preformed liner or plastisol
- Crimped glass bottle finish
- Other developments include twist off crowns which use a lighter tinplate
Describe roll on pilfer proof (ROPP) closures
- Aluminium shell, punched from printed and lacquered sheets with no threads
- Liner inserted for sealing
- Usually applied to glass bottles
- Capping machine rolls threads into sidewall of shell
Give an advantage and a disadvantage of ROPP closures
- Provides tamper evidence
- Collar can be difficult to remove
What 3 materials can push in / push on closures be made from?
- Metal
- Cork
- Plastic
What three things do push in / push on closures rely on?
- Friction fit (dimensional accuracy)
- Extensibility of materials
- Compressibility of materials
Describe heat seal closures
- Made by softening thermoplastic materials, such as PE, using heat and pressure
- Seal can be made permanent or peelable depending on materials and processing conditions
Describe how an ultrasonic seal is formed
- Uses mechanical vibration to create heat - the movement creates friction along molecular chains and contact points for both the substrate and sealing film; it is this friction which melts the materials together
- Heat is developed internally rather than by traditional conduction from external layers
- A voltage is supplied to an ultrasonic generator which converts this to a mechanical vibration; a sonotrode transmits this to the film
Give 6 advantages of ultrasonic seals
- Low thermal loads so film shrinkage can be eliminated
- No burning hazards
- Cold weld tools ensure faster cooling and increased stability of the tool
- Less cleaning
- Shorter heating and cooling phases
- Smaller sealing lines which saves packaging materials
Give 2 disadvantages of ultrasonic sealing
- High cost
- Loss of effectiveness with crystalline materials as the crystals dampen the ultrasonic pulse
Name 3 things that a good ultrasonic seal depends on and why
- Time - too long will result in slow line speed; too short will lead to a poor seal
- Temperature - too low and no seal will form; too high will result in over-melting
- Pressure - too low and no seal will form; too high and the sealing layer will be squeezed out
Give 3 things that can be designed into closures
- Tamper evidence
- Child resistance
- Dispensing and measuring
Describe 3 qualities of tamper evident closures
- Must provide visible evidence that pack has been breached
- Relies on customer recognising that something is different
- No agreed standard for tamper evidence
Describe 3 qualities of child resistant closures
- More closely regulated - international standards for single use and reusable systems; BS EN 28317
- Must be usable by adults - especially the elderly
- Usually have two features to be operated at once - for example, push and turn
Give a disadvantage of dispensing and measuring closures
How you reclose with residual product needs to be considered
