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Cellulose Acetate Butyrate Additives for Can Coatings

Metal cans are a mainstay in the packaging industry for many food and beverage items. They provide excellent protection to goods, are more easily recycled, and contain higher recycled content than other types of packaging, such as plastic bottles. Can coatings often need to be applied internally and externally to protect both the can and the food or beverage contained.

External can coatings protect the visual appearance and integrity of the metal against abrasion, which may easily occur during processes of canning or transport. Internal can coatings prevent possible interaction and corrosion of the metal from food.  

Good flow, leveling, and adhesion properties are required or both internal and external can coatings to prevent coverage defects and maximize the protective qualities of the coating. Good clarity, smoothness, gloss, and anti-blocking properties are necessary for external can coatings to highlight and preserve the aesthetics and integrity of the can.  

Eastman’s Cellulose Acetate Butyrate (CAB) 

Eastman’s Cellulose Acetate Butyrates (CABs) are naturally derived, sustainably sourced organic acid esters of cellulose. CAB-551-0.01 and Solus™ 2100 are two low–molecular weight CAB polymers used as additives to provide a variety of performance benefits in can coatings. They exhibit excellent solubility in a wide range of organic solvents, are compatible with many resins and plasticizers in coating formulations, and are food-contact-approved.

CAB-551-0.01 and Solus™ 2100 specifically benefit can coating formulations by forming films that have:
 

  • Better gloss, smoothness, and distinctness of image 
  • Great clarity and nonyellowing properties 
  • Reduced tack and enhanced antiblocking properties 
  • High flexibility with good abrasion resistance 
  • Increased adhesion and faster solvent release


Through these qualities, Eastman CAB-551-0.01 and Solus™ 2100 improve the effectiveness and appearance of can coatings.  

Performance Testing with CAB-551-0.01 Solus™ 2100 in Solvent-Based Can Coatings 

Tests were made using two coating formulations, presented in the next section; one was a clear coat formulation, and the other was a white-colored coating pigmented with titanium dioxide. These tests were made to quantify some of the improvements that CAB-551-0.01 and Solus™ 2100 provide to can coatings. Performance comparisons were made using these coatings with and without flow and leveling coating additives, which included CAB-551-0.01, Solus™ 2100, and a polyacrylate additive. 
 

Exterior Clear Coat Formulation
Specific gravity of formulation is 0.99 kg/L 
aNovaresine bINEOS cExxonMobil Chemical dBASF eEastman Chemical Company

Exterior White Coat Formulation

Specific gravity of formulations with no additive, 1% CAB-551-0.01, and 1% polyacrylate is 0.94 kg/L 
Specific gravity of formulation with Solus™ 2100 is 0.93 kg/L 
aNovaresine  bINEOS  cChemours dExxonMobil Chemical  eEvonik  fBASF  gEastman Chemical Company 


The test results in the following sections were exclusively from tests applying these formulations externally onto cans. However, similar test results are expected if the formulations are applied internally.  

Flow, Leveling, Blocking, and Surface Defects Test 

The first test evaluated the additives to reduce blocking and surface defects while increasing flow and leveling properties. Blocking reduction is critical to resist detrimental adhesion and ensure that coatings remain bonded to their original substrates, even when they are put in contact with another surface and pressure is applied. Improving flow and leveling allows for easier application and better coverage of can coatings. This also helps to eliminate common surface defects, such as orange peel, cratering, and fish eyes.  


Both the clear and white-pigmented coating formulations were applied to precoated metal panel substrates, then tested for block rating via ASTM D3003-01 (2006). They were also evaluated for flow, leveling, and surface defects through examination of smoothness and visual imperfections. The higher numbers below are indicative of better coating performance.  

Clear Coat Formulations 

Legend
The results show that nonpigmented can coatings generally benefit from being formulated with an additive to improve block resistance, flow, leveling, and a number of surface defects. However, when it comes to pigmented can coatings, both the Eastman CAB-551-0.01 and Solus™ 2100 demonstrated better surface-defect reduction than polyacrylate additives. 

Gloss Test

The same clear and white-pigmented coating formulations were then tested for gloss improvements from the additives. Gloss units were measured at an angle of 60°.

Clear Coat Formulations

White-Pigmented Coat Formulations

As the results indicate, the Eastman additives enhanced gloss in both the clear and white can coatings. This is compared to the polyacrylate additive, which decreased gloss in both coatings. As gloss is often desired by food and beverage manufacturers and their consumers for aesthetic purposes, CAB-551-0.01 and Solus™ 2100 provide a notable advantage to overall can appearance. 

Distinctness of Image Test and Clarity of Formulations

The outcome of the gloss test supports the results obtained for the distinctness of image (DOI) test that came next, which was made using the clear coat formulation. DOI is determined by measuring gloss close to the angle of reflection on the substrate. 

For many metal coating applications, DOI is an important attribute tied to the perception of the quality of the coated object. Higher DOI values indicate a sharper image reflected from the coated substrate. The result of the DOI test using the clear coat formulation is below.

As in the gloss test, the polyacrylate additive negatively impacted coating quality. In this case, the polyacrylate significantly decreased DOI and also created a hazy appearance within the coating. Comparatively, CAB-551-0.01 and Solus™ 2100 preserved DOI, indicating that using these additives for functionality enhancements will not compromise the visual quality of can coatings.


To better observe the haziness that occurred with the polyacrylate additive, the image below shows the clear coat with and without the additives examined in these tests. The haze caused by the polyacrylate additive can be plainly seen even after all formulations were left standing for 24 hours after being shaken.

Summary


Both internal and external coatings for metal cans are essential to protect the can and its food or beverage contents. These coatings must have good, even coverage onto metal substrates while maintaining good aesthetics. Eastman CAB-551-0.01 and Solus™ 2100 coating additives reduce surface defects of can coatings while providing excellent gloss, smoothness, distinctness of image, antiblocking, and flow and leveling properties. These all contribute to the formulation of high-quality can coatings.  If you’re interested in learning more about how Eastman cellulose esters perform in other metal coating applications, please also check out this article. To discuss your application with us and request a quote or sample of CAB-551-0.01 and Solus™ 2100, click below. 

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