Material: Recycled
Glass
Issue: One of the marketing advantages
the glass container industry uses to sell its
product is the perception by consumers that glass
is a higher quality package than plastic.
With glass’s perceived quality and beauty,
however, come several characteristics that are
viewed as negatives by bottlers, retailers, and
the public: weight, breakability, and limited
colors. Over
the past two decades, glass container coatings
have been under development to address these limitations.
The coatings are only now reaching the
point of economic and technical viability.
Best
Practice:
Several projects have been conducted by the glass
industry to develop practical ways to use thin
coatings to enhance the characteristics of glass
containers. Today’s
polymer coatings are photocurable and do not require
solvents. Cured
coatings are clear, thin, and durable. The process is simple, reliable, low in cost, and has high deposition
efficiency. The
strength enhancement mechanism is efficient in
film thickness from 3 to 15µm, with a uniform
5µm film being targeted as the standard by an
international collaboration of glass industry
stakeholders.
Coatings are available in an increasing
number of colors, with chemistries ranging from
alkyd to epoxy to solvent base.
Container glass coatings offer the following
potential advantages:
Weight With the extra cushioning of a thin polymer coating, glass containers
retain their aesthetics but the glass wall can
be made thinner, making the container lighter
in weight. The lighter weight means that food
producers ship more product and less package per
ton.
Breakability All facilities that process food into glass containers, ship glass
containers, or retail food in glass containers,
experience breakage regularly that is both a mess
and a safety hazard. Glass containers that bang into each other during filling, shipment,
or in retail stores have greater resilience with
coatings. Glass always fractures at a defect or scratch.
Coatings inhibit the formation of stress
concentrators that would normally result from
handling wear and tear.
Coated bottles may withstand internal pressure
loads 30% to 100% greater than uncoated bottles.
Processability Uncoated glass containers have been sprayed for years by container
manufacturers with a final wash that improves
the surface lubricity and allows glass containers
to move more easily through high-speed bottling
equipment. With
coated bottles the lubricity can be “tuned” to
the specific bottling equipment. Results of work performed at American Glass
Research (AGR International) have shown that coatings
reduce the stress of containers sliding against
each other. The
coatings reduce the coefficient of friction sufficiently
to protect the containers without reaching the
point where the bottle is too slippery for handling
or label application is inhibited.
The lower mass, and therefore lower inertia,
of the containers means the containers move more
easily and with less energy through material handling
systems.
Color The container industry has standardized on three colors of glass:
clear, amber, and green, with some blue and variations
among the colors. Coated containers can all be made with clear
glass and coated to any color with no loss of
glass’s aesthetics. This means less process changeovers for container
manufacturers and only one base color for recyclers.
Recycling Recyclers would welcome having only clear glass to sort from the
recycling stream.
The coatings are designed for single trip
containers, which are recyclable from container
to cullet to container.
The coatings are environmentally friendly
(they are organic and contain no solvents) and
can be reprocessed in any glass tank because organic
burn-off occurs before reaching glass melting
temperatures.
Implementation: The application system to apply
the coating is modular, designed to be integrated
into existing glass plants.
In the coating process, which is sometimes
similar to the printing process, the coating is
deposited from a transfer substrate on to the
container. Coatings
may also be applied using spray and waterfall
techniques. Technologies for coating glass containers are
being marketed to container manufacturers in both
the United States and Europe.
As with most new technologies, the most
difficult decision is whether and when to make
the capital investment in the new process.
Some early adopters have already modified
their plants to apply coatings on an as-needed
basis.
Benefits:
The
physical performance benefits of coatings are
clear in allowing glass containers to flow through
production lines with reduced friction, limiting
abrasions and scratches which reduce container
strength. Container coatings may be important in maintaining
or increasing the market share of glass containers,
thereby making recycled glass a consistent recyclable
stream.
Application
Sites:
Glass container manufacturing plants
Contact: For more information about this Best Practice, contact
CWC, mailto:info@cwc.org
References: Advanced Glass Treatment Systems Research and Development Program, an industry coalition, 1992. Ellsworth, Timothy F., Advanced
Glass Systems, Inc. “New Container Coating Technology
Is Developed,” Glass Industry, April 1992,
pp. 16-17. Evans, H.T., Cerdec Corp. Drakenfeld
Products. “PACKAGING 2000: A Look at the Future
of Glass Decoration,” Glass
Industry, August 1996, pp.12-13. Graham, Paul W.L. “Container
Coatings Take on Increased Importance,”
Glass Industry,
February 1992 issue, p. 10. Hamlin, Chris. Brandt Technologies,
Windsor, New York.
Issue
Date / Update: November 1996
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