Barrier coated plastic containers and coating methods therefor

Details Barrier coated plastic containers and coating methods therefor Barrier coated plastic containers and coating methods therefor

2001-04-27

2003-07-29

Meeks, Timothy (Department: 1762)

Coating processes

Direct application of electrical, magnetic, wave, or...

Polymerization of coating utilizing direct application of...

C427S491000, C427S577000, C427S579000, C427S596000, C427S249150, C427S249170, C427S255310, C427S255500, C427S255600

Reexamination Certificate

active

06599584

ABSTRACT:

TECHNICAL FIELD
This invention relates to plastic containers, such as beverage containers, that include a barrier coating to reduce gas permeation therethrough, wherein the barrier coating has enhanced resistance to loss of barrier properties caused by handling abuses and expansion of container walls.
BACKGROUND OF THE INVENTION
Plastic containers comprise a large and growing segment of the food and beverage industry. Plastic containers offer a number of advantages over traditional metal and glass containers. They are lightweight, inexpensive, nonbreakable, transparent, and easily manufactured and handled. However, plastic containers have at least one significant drawback that has limited their universal acceptance, especially in the more demanding food applications. That drawback is that all plastic containers are more or less permeable to water, oxygen, carbon dioxide, and other gases and vapors. In a number of applications, the permeation rates of affordable plastics are great enough to significantly limit the shelf-life of the contained food or beverage, or prevent the use of plastic containers altogether.
It is known that a container structure that combines the best features of plastic containers and more traditional containers could be obtained by applying a glass-like or metal-like layer to a plastic container, and metallized plastic containers. For example, metallized potato chip bags have been commercially available for some time. However, in applications where the clarity of the package is of significant importance, metallized coatings are not acceptable. Obtaining durable glass-like coatings on plastic containers without changing the appearance of the container has proven to be much more difficult.
A number of processes have been developed to apply glass-like coatings onto plastic films, where the films subsequently are formed into flexible plastic containers. However, relatively few processes have been developed that allow the application of a glass-like coating onto a preformed, relatively rigid plastic container such as the polyethylene terephthalate (PET) bottles commonly used in the U.S. for carbonated beverages, and heretofore no process has been developed to provide application of a glass-like coating onto the external surface of a plastic container that is sufficiently durable to withstand the effect of pressurization of the container, that retains an enhanced barrier to gases and vapors subsequent to said pressurization, and that does not affect the recyclability of the containers. Pressurized beverage containers currently comprise a very large market world-wide, and currently affordable plastics have sufficiently high permeation rates to limit the use of plastic containers in a number of the markets served.
Such pressurized containers include plastic bottles for both carbonated and non-carbonated beverages. Plastic bottles have been constructed from various polymers, predominantly PET, particularly for carbonated beverages. All of these polymers, however, exhibit various degrees of permeability to gases and vapors, which have limited the shelf life of the beverages contained within them. For example, carbonated beverage bottles have a shelf-life which is limited by loss of CO
2
. (Shelf-life is typically defined as the time needed for a loss of seventeen percent of the initial carbonation of a beverage.) Because of the effect of surface to volume ratio, the rate of loss becomes greater as the size of the bottle is reduced. Small containers are needed for many market applications, and this severely limits the use of plastic bottles in such cases. Therefore, it is desirable to have a container with improved carbonation retention properties.
For non-carbonated beverages, similar limitations apply due to oxygen and/or water-vapor diffusion, again with increasing importance as the bottle size is reduced. Diffusion means both ingress and egress (diffusion and infusion) to and from the bottle or container. The degree of impermeability (described herein as “gas barrier”) to CO
2
diffusion and to the diffusion of oxygen, water vapor, and other gases, grows in importance in conditions of high ambient temperature. An outer coating with high gas barrier can improve the quality of beverages packed in plastic bottles and increase the shelf life of such bottles, making small bottles a more feasible alternative, which presents many advantages in reduced distribution costs and a more flexible marketing mix.
It is also desirable that plastic containers such as PET bottles be recyclable. Known barrier enhanced coatings, however, are often organic and relatively thick and therefore can contaminate a recycled plastic product. Organic coating materials incorporated into recycled plastic make unsuitable containers for beverage or food items because the beverage or food items can contact the organic coating material and become contaminated. In addition, relatively thick coatings form relatively large particles during recycling of plastic material and can damage the appearance and properties of a resulting recycled plastic product. In particular, relatively large coating particles in recycled plastic can make otherwise clear plastic hazy. Hazy plastic is often undesirable for containers such as beverage and food containers.
Additionally, the cost of applying a coating to the outside of a bottle must not add significant cost to the basic package. This holds even when the coating is a gas barrier that significantly increases the shelf-life of beverage contained in that bottle, significantly reduces product spoilage of beverage contained in that bottle, significantly reduces product spoilage due to UV radiation, virtually eliminates environmental stress cracking, and/or provides a specific color. This criterion eliminates many processes for high gas barrier coatings, because plastic bottles are themselves a very low cost, mass produced article. Affordability implies in practice that the cost of the coating must add minimal or no increase to the cost of the whole package and in fact, the cost can be less.
A coating on the outside of plastic bottles must be capable of flexing. When bottles are used for pressurized containers, the coating preferably should be able to biaxially stretch whenever the plastic substrate stretches. It also is preferable that the coating be continuous over the majority of the container surface. Adhesion is particularly important in the case of carbonated beverages, since CO
2
within the bottle exerts some or all of its in-bottle pressure on the coating. This pressure can rise to exceed 6 bar, exerting considerable forces on the coating/plastic interface. The coating must also resist scuffing, normal handling, weathering (e.g., exposure to rain, sun, and temperature fluctuations), and the coating must maintain its gas barrier throughout the bottle's useful life.
There are several plasma-enhanced processes which apply an external, inorganic coating to a range of articles, which in some cases includes bottles. Many of the processes are targeted to provide coating properties which are quite different, and far less onerous than high gas barrier bottle coatings. Such processes target, for example, abrasion resistance, where the coating continuity is not a major factor, since the coating can protect the microscopic interstices. Other processes target cosmetic or light-reflection properties and some processes have a pure handling protection role. Often the substrate does not flex or stretch, and the article itself is higher priced than plastic bottles so that cost is not a benefit of the design. In some cases, the substrate allows far higher coating temperatures than those allowed by PET, the most common plastic-bottle material. Such processes generally do not provide the coating continuity, adhesion, and flexibility needed for high gas barrier coatings, nor do they provide a solution to the other problems associated with high gas barrier coatings described above.
PCT WO 98/40531, which addresses the foregoing deficiencies and problems, describes an electric a

Affiliated with

Also associated with

Rating

Barrier coated plastic containers and coating methods therefor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Barrier coated plastic containers and coating methods therefor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Barrier coated plastic containers and coating methods therefor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3078885