Shrink Tunnels FAQ

Q. People sometimes use the terms “shrink tunnels” and “steam tunnels”
interchangeably. What’s the difference?

A. Steam tunnels are one of the 3 major types of shrink tunnels. The others are hot air
convection and radiant infrared.

Q. So what are some factors to consider in choosing one vs. the other?

A. For tamper evident applications, a hot air convection tunnel produces exceptional results.
When neckbands are very dark in color, radiant infrared is the optimum choice. Convection
and radiant shrink tunnels are often combined to produce best-possible results for some
applications. Steam is the best option among the shrink tunnels for full body labels.

Q. Which is the better choice when graphics, and registration, are critical?

A. Steam shrink tunnels are best for products where high quality, distortion-free graphics
are most important. Because steam shrink tunnels provide more uniform heat impingement than
air systems, steam tunnels provide more precise label registration and shape conformance.

Q. What type of shrink tunnels are recommended for applications
involving volatile products?

A. Steam tunnels are the best choice for containers that are under pressure,
or when a low flash point or flammability is a factor.

Q. What films can be used for processing in shrink tunnels?

A. There are several main types, and new varieties of each type being developed all
the time. PVC is the most common and least costly. It’s also easiest to control during
the shrink. PVC films can be ordered in a pasteurizable or a steam grade. PETG films
have the highest shrink percentage. They, too, can be pasteurized, and are recyclable.

PETG films are very versatile, and can also be ordered with special attributes such as
a matte finish, or velvety texture. Other PETG films provide light barrier protection,
or are available in freezer grades. OPS film has the lowest vertical shrink and produces
the most consistent results, particularly on squeeze bottles.

PLA films are a plant-based alternative to petroleum-based shrink films. They’re strong
and dimensionally stable, and their high water transmission rate (WVTR) prevents moisture
from being trapped between the container and the label when containers are steam shrinked.

The most important thing, though, is to have an equipment partner who understands
the various options, including the newest ones, and can work with you to specify a type,
grade and gauge that delivers the best shelf appeal, and the most effective shrink curves.

Q. How do shrink curves impact results?

A. Shrink curves chart the percentage of shrink that occurs at specific temperatures
over specific time periods, when measured in a controlled environment. The path of
the curve indicates at what temperature threshold a material starts to shrink, the rate it
shrinks, and when it achieves maximum shrink percentage.

Q. Is there an “average” shrink percentage?

A. Standard materials shrink up to 55% in the transverse (horizontal) direction;
high shrink materials, about 70%. Films also have machine direction shrinkage
(3-7%) which must be calculated and managed to insure best results.

Q. What is the value of adding a pre or post-shrink module to shrink tunnels?

A. These modules finish off critical areas at the base or top of the sleeve in the most
energy-efficient manner. They are self-contained industrial heat guns, sometimes used
in pairs, and often with nozzles to focus the heat. Power usually comes through the
application equipment. Air flow is paused while the machine waits for product,
and only turned on when product is present.

Q. We’ll need culinary grade steam. What level of filtration is available to
remove impurities from the steam?

A. PDC steam shrink tunnels have filters that clean steam to .1 micron for culinary
grade performance.

Q. Are aerosols compatible with shrink tunnels for packaging?

A. Yes, steam tunnels are an excellent alternative for aerosol containers and
other packaging programs where low flash point or flammability is a factor.

Q. How can we reduce the risks involved with changing from printed labels
to full-body sleeves cured in shrink tunnels?

A. PDC’s Shrink Lab is equipped with a range of shrink tunnels for product testing.
We have many models and types of tunnels, and test using customer containers and
different sleeve films. It’s critical to understand every factor that can impact your
end result, including the fact that clear or lightly printed films act very differently than
films with 100% or 200% ink coverage – particularly when they are running at 200
containers per hour. Our technicians work with you to fully understand your package
concept and identify the best possible materials and shrink tunnels configuration to
achieve best-possible results.


	Contact PDC for shrink tunnels machinery to suit your products, facility and budget.