Anti-fog coating
- Condensation problems defined
- Convenient, healthy eating
- Refrigeration unit types
- Produce package types
- Not just produce packaging
- Not all refrigerated packages require anti-fog coatings
- Anti-fog coating applications and formulations
- Conclusion and review
CONDENSATION PROBLEMS DEFINED
Whenever a sealed high-humidity environment is placed through a temperature gradient, moisture condensation will occur. This condensation will materialize as small beads of water droplets forming on the inside of the package. The droplets will begin to vaporize and then form a fog on the inside of the package and transform a clear package into an opaque one and thus conceal the contents from the consumer. Most manufactures want the consumer to see their product. This is normally achieved either by packaging the product in a clear film or by printing a pictorial of the product on the outside of the package. Therefore, it is obvious that when a manufacturer packages a product in a clear package, they expect that it will remain clear. The produce manufacturer wants the consumers to see the multicolor mixture of the green lettuce, orange carrots, red cabbage, and radishes.
CONVENIENT, HEALTHY EATING
In order to attract more consumers, produce manufactures are marketing the convenience of prewashed produce. These packages are an attractive way of quickly preparing a healthy meal. Today, there are literally dozens of different salad and vegetable blends sold in the produce department in the grocery store. These packages are sealed in a plastic bag and the produce contains a relatively large amount of moisture.
REFRIGERATION UNIT TYPES
There are two different classification of refrigeration units used in the produce section of the grocery store. They are either vertical or horizontal. Because cold air is denser than warm air, the horizontal refrigeration units allow for the entire package to maintain a consistent temperature and therefore will not produce a great amount of condensation. The main drawback of the horizontal unit is that it conceals the packages from consumers as they navigate through the produce section. Because of this, the horizontal unit is not used very often any more. The vertical unit, when positioned properly in the store, can allow consumers to see products from virtually across the produce section of the store. The largest problem with the vertical unit is that it allows the refrigerated package to be in direct contact with the warm ambient air in the store. This configuration is a perfect design to allow the outside of the package, the side facing the consumer, to be exposed to a rather drastic temperature gradient. Thus vertical units create a perfect environment for the generation of a great amount of moisture condensation. In the vertical refrigeration unit, only the most outside package will experience condensation. Therefore, the greater the popularity of the product, the less time any one package will set on the outside of the unit. Ironically, the less popular the product, the more the package will require an anti-fog coating.
PRODUCE PACKAGE TYPES
Produce packages fall into two different categories. First is the ‘‘pillow’’ pouch. These pouches are made from soft, subtle films that will contain loose packaged produce. This is the most popular package for produce. Lettuce and cole slaw blends as well as baby carrots and small pieces of vegetables such as broccoli flowerets are usually packaged in the pillow pouch. These pouches have very little rigidity and thus the package will contain many wrinkles to allow for the water droplets to collect. The second type of produce packages are vertical stand-up packages. These vertical packages are made from very rigid films and will not allow any wrinkles to form. These packages usually contain more rigid produce like romaine lettuce or celery stalks. In order to work properly, these packages will utilize different types of anti-fog coatings. The rigid packages will be printed with an anti-fog that will cause the condensation to bead up and then gravity will draw the water beads to the bottom the pouch where they will do no harm. The pillow pouch will use an anti-fog that will allow the water vapor to easily wet out the wrapper. This way the moisture will not gather and will not create any fogging. This type of anti-fog is required for the pillow pouch because the wrinkles will cause the water beads to gather and will eventually cause fogging. The coatings for rigid pouches are designed to produce a dried coating that will have a very low surface energy, while the coatings for the pillow pouches are designed to have a very high surface energy.
NOT JUST PRODUCE PACKAGING
Anti-fog coatings are used not only in produce packaging, but often also in raw and prepared meat and poultry packaging. For example, meat may be packaged in rigid trays using modified atmosphere packaging (MAP), where the trays are flushed with an optimum composition of O2/N2 and then sealed with a shrink film. These packages allow a greatly increased shelf life when compared to the old-fashioned meat wrappers. However, these packages can easily experience condensation and will often need an anti-fog coating on the inside of the shrink film. Preprepared meats have become very popular at grocery stores. Rotisserie chickens are available at most grocery stores. These chickens are placed in an opaque rigid tray and then covered with a clear rigid bubble. The inside of the clear bubble will often contain an anti-fog coating.
NOT ALL REFRIGERATED PACKAGES REQUIRE ANTI-FOG COATINGS
Any package where the film is in direct contact with the product does not require an anti-fog coating no matter how much moisture the package contains. When the film is in direct contact with the product, no matter how the structure of the refrigeration unit, there is no area of air space that will allow the formation of condensation. For example, an unwashed head of lettuce with a film that is tightly wrapped around the lettuce will never experience condensation and therefore will not require the use of an anti-fog coating. Another example of a package that will not contain an anti-fog coatings are meat wrappers that are in direct contact with the meat. For example, the old-fashioned styrofoam meat trays that are tightly wrapped with a flexible film do not require an antifog coating.
ANTI-FOG COATING APPLICATIONS AND FORMULATIONS
Since anti-fog coatings are designed to deter condensation formation on the inside of the package, these coatings are always applied to the inside of the wrapper. Therefore, all anti-fogs at a minimum have two things in common. They must be FDA compliant for direct food contact and must be designed to print and adhere to the untreated side of the film. Since the inks are applied to outside of the film, the treated side is always on the outside of the package. These coatings are normally applied with at a very low coating weight, resulting in a very thin film of o1mm. Anti-fog coatings are tested for smudge resistance, block resistance, and offset (transferring to the back side of the film) resistance.
Some anti-fog coatings will affect packaging seal bond strengths, while other will not. The coatings that do interfere with seal bonds must be patterned out of the heat seal areas. Anti-fog coatings can be difficult to reach correct register because they are absolutely clear. Therefore, the coatings that do not interfere with heat seal bonds are more popular. The problem with these coatings is that they are much more prone to offsetting, so achieving the correct film weight is essential with either coating. Excessive coating applications can greatly interfere with heat seals, while a lack of coating will not allow the coating to reach its anti-fog potential.
Anti-fog coatings for flexible films are normally applied using the flexographic process; coatings for rigid dome lids for the precooked poultry are normally spray applied.
CONCLUSION AND REVIEW
Some flexible substrates are manufactured with anti-fog agents added to them. These films will only provide marginal anti-fog properties because the active agents are diffused throughout the entire thickness of the film, while the coatings are concentrated on the surface. Therefore, the use of anti-fog coatings are typically required for high-performance applications.
There is far more to anti-fog coatings than immediately meets the eye. Whether a package receives an anti-fog coating is always the decision of the manufacturer. This decision is based on the type of the product, the type of refrigeration unit, and the turnaround time of the product. The requirements for the correct type of anti-fog are mostly dependent on the type of product and package. The purpose of anti-fog coating is to allow the clear film to remain clear so that the consumer can easily see the colorful and wholesome product that the package contains. The main use of anti-fog coatings is a matter of manufacturers wanting to increase market share and product differentiation.