As the demand for packaged goods increases, it is important to look at all manufacturing processes involved to improve overall performance. The coating process of the can interiors can have a dynamic impact on overall stability and consumer experience. Eastman’s resin intermediates can improve upon common flexibilizing technology and increase overall stability and resistance of the interior coating.
Why are Interior Can Coatings Important?
Metal can interiors are prepared and coated to prevent corrosion & to maintain freshness for a variety of foodstuffs and beverages. These coatings have traditionally been derived from epoxy resins, but they offer little to no chemical resistance in the final performance. Eastman’s cycloaliphatic intermediates (CHDA and CHDM) exhibit an exceptional balance of both delivered hardness and flexibility for premium protection.
When it comes down to brass tax, the numbers don't lie. The table below details several key metrics in coating performance between AD, Eastman's 1,4-CHDA and PIA in a polyester-melamine enamel (Resin:NPG/TMP/Diacid/PIA [1.97/0.30/1.00/1.00]). Learn more about Eastman's CHDA ►
AD
1,4-CHDA
PIA
Flexibility/hardness
Impact resistance
Direct, in.-lb
>160
156
76
Reverse, in.-lb
>160
96
64
Pencil hardness to mara
HB
2H
4H
Stain and chemical resistanceb
Iodine after 30 min
M
N
N
Mustard after 24 h
VS
N
N
50% NaOH after 9 h
N
N
N
50% H2SO4 after 9 h
M
N
N
Corrosion resistance
Detergent resistance after 10 days
Creepage, in. (mm)
0.75 (19.05)
0.13 (3.18)
0.06 (1.59)
% Gloss retention at 60°
30
99
96
% Gloss retention at 20°
16
90
86
Blistering
S
M
VS
Cracking
N
N
N
aPencil hardness scale from least to most hard: HB, F, H, 2H, 3H, etc. bEffects scale: N = none, VS = very slightly, S = slight, and M = moderate
Hydrolytic Stability
Coating performance can vary greatly under basic or acidic conditions, especially in regard to overall hydrolytic stability. Eastman's CHDA diester out performs a range of common cycloaliphatic intermediates like adipic acid and PIA. The chart below measures hydrolysis of an NPG glycol diester at an elevated temperature of 120°C.
