General Description
EVA is the copolymer of ethylene and vinyl acetate and is an elastomeric polymer that produces materials which are ‘rubber like’ in softness and flexibility. The weight percent of vinyl acetate usually varies from 10 to 40%, with the remainder being ethylene. EVA is used in different applications such as craft-foam sheets, padding in sports equipment e.g., boxing gloves and in biomedical engineering applications such as a drug-delivery device.
Pre-Production
EVA will absorb less than 0.2% water in 24 hours at room temperature. This means that drying is not normally necessary. If it is, dry in a hot air oven for 8 hours at 50ºC to 60ºC or in a desiccant dryer for 3 hours at 80ºC
Low VA content e.g. 7%
Temperature ºC
Zone No.
Location
From
To
–
Hopper Throat
30
50
1
Barrel Rear (hopper end)
120
140
2
Barrel Middle
130
150
3
Barrel Middle
140
160
4
Barrel Front
150
170
5
Barrel Nozzle
160
180
6
Mould
15
30
High VA content e.g. 28%
Temperature ºC
Zone No.
Location
From
To
–
Hopper Throat
30
50
1
Barrel Rear (hopper end)
130
160
2
Barrel Middle
150
180
3
Barrel Middle
170
190
4
Barrel Front
180
210
5
Barrel Nozzle
190
220
6
Mould
15
40
Processing Notes
Mouldings required a high surface gloss and good mechanical properties are moulded using slow injection speeds.
Adjust screw speed (the rpm) to suit the moulding cycle but do not use a screw surface speed of greater than 0.5 to 0.55ms-2.
Back pressure should be kept as low as possible.
When the temperature is 235ºC then the maximum residence time in the barrel should not exceed 2 to 3 minutes.
Tool Requirements
EVA’s wide shrinkage range makes it extremely difficult to accurately predict the shrinkage value necessary to achieve the desired dimensions for a particular component.
Mould venting is essential when using EVA, as the filling pattern of the mould can be considerably altered with poor or non-existent venting.
Typical runner sizes range from 4mm to 7mm in diameter. Diameters above 7mm tend only to increase the cycle time and do not significantly assist in the filling of the mould.
Post Production
No need to purge with another material.
Portfolio:
ExxonMobil – EVA – Escorene
Total – EVA – Total EVA
