Coating of metal coil is a highly efficient, automated process that is used to produce long lasting, uniform coatings on metal surfaces. In coil coating operations metal coils are unwound, pre-treated, coated, cured, and rewound for shipment to fabricators. Pre-painted metals produced by coil coating are used extensively throughout the world in various applications ranging from consumer goods to construction materials.
Coil Coating Challenges
Increased global demand for pre-painted metals has put strain on coil coating operations to improve efficiency. Increasing line speed, however, often results in coating defects and coatings that do not meet appearance specifications. Coil coaters are thus faced with a two sided problem: How to increase production speed and efficiency without sacrificing performance and appearance.
Eastman CAB Improves Coil Coating Efficiency
Eastman Cellulose Acetate Butyrate (CAB) polymers are uniquely suited for improving multiple aesthetic properties of coil coatings including:
The aesthetic improvements provided to coil coatings by Eastman CAB allow for line speed to be increased without an increase in reject rate or coating imperfections.
Improving Metallic Flake Alignment
Metallic and pearlescent finishes are highly popular in coil coatings. One of the main benefits of Eastman CAB in coil coatings is it's ability to act as a viscosity control agent in coil coatings and "lock" metallic and pearlescent flakes in an orientation that maximizes the reflectivity of the flakes. This improved flake orientation means that coil coating formulators can use fewer flakes to achieve the same, or improved appearance. To demonstrate this improvement in flake / pigment alignment and "flop" the formulations below were applied to aluminum on a coil coating pilot plant line.
Once cured, the two coating formulations were compared using confocal microscopy to determine the surface roughness and a multiangled spectrophotomer was used to measure flop values. The results of this testing are below.
Standard
The coil coating formulation containing Eastman CAB-551-0.01 has a significantly smoother surface due to better pigment orientation. This improved orientation leads to a dramatic increase in flop index.
Improve Surface Consistency
Flow and leveling play a large factor in reducing surface defects and maximizing gloss. This becomes especially true when the speed of a coil coating line is increased. When added to a coil coating, Eastman CAB ensures that the coating remains smooth over the substrate after application and during curing. This in turn can remedy common surface defects that occur when coil coating line speeds are increased including:
Orange peel
Fish eyes
Craters
Pigment flooding
Crawling / Retraction
To demonstrate the improvements seen in surface consistency, two primed aluminum panels were finished with the same coil coating formulations listed above. The side by side comparion of the panels is below.
Standard
It becomes very apparent when compared side by side that the coil coating containing CAB has much better surface consistency and in turn has better reflection and gloss than the coil coating that does not contain CAB.
Improve Pigment Dispersion
Titanium dioxide and other pigments are commonly used in coil coatings and are often times the most expensive part of the formulation. Eastman CAB, when added directly into the grind stage of the pigment dispersion process significantly improves pigment dispersion. To demonstrate this improvement in pigment dispersion two pieces of aluminum were coated with the coil coating formulations below.
The coated aluminum panels were then cured and measured for Delta L and Delta B values using a spectrophotometer. The results of this testing are in the chart below.
The formulation containing 1% CAB-551-0.2 showed a drastic increase in Delta L and a decrease in Delta B. The improved dispersion of titanium oxide in this formulation resulted in a lighter, more vibrant white color.
How to Add CAB to a Formulation
Adding Eastman CAB to a pre-existing coil coating formulation is fairly simple. The most common technique is to first dissolve the CAB in a suitable coil coating solvent to make a stock solution. This stock solution of CAB and solvent can then be let down into your formulation at the addition rate you determine provides the optimal performance. The Eastman CAB used in coil coating formulations can vary depending on the desired properties of the coating and the substrate. Common grades of Eastman CAB, their function in coil coating formulations, and recommended usage rates are listed in the table below.
Chempoint specialists are standing by to help guide you to the correct combination of Eastman CAB to achieve maximum performance and efficiency for your coil coating formulation.
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