Rigid polyurethane foam for refrigerated vehicles and containers

Rigid polyurethane foam
for refrigerated vehicles and containers
Dr. Rainer Welte
Helmuth Wittekopf
Page 1 of 6
File No.: PU21019-0410 en
Issue 2004-10-11
Insulation
Technical Information

Rigid polyurethane foam
for refrigerated vehicles and
containers
Summary
Food and other highly perishable, temperaturesensitive
merchandise such as electronic devices,
pharmaceuticals and fine chemicals are shipped or
transported over land in specially insulated containers
or refrigerated vehicles. Containers insulated
with rigid polyurethane foam are used almost exclusively
nowadays on account of the excellent properties
of this material. Polyurethane is also being
used more and more as a core material for sandwich
panels for refrigerated vehicles.
Contents
Page 2 of 6
File No.: PU21019-0410 en
Issue 2004-10-11
Page
1. Perfect protection for 2
sensitive goods
2. Insulation for the most 4
demanding applications
3. New-generation blowing agents 5
1. Perfect protection for sensitive
goods
Food and other highly perishable, temperaturesensitive
merchandise such as electronic devices,
pharmaceuticals and fine chemicals are shipped or
transported over land in specially insulated containers
or refrigerated vehicles.
To allow efficient transportation without damaging
the merchandise, refrigeration or freezing temperatures
have to be kept constant even when external
temperatures vary markedly, so features such as a
high insulation value and hygiene are just as critical
as light weight, a high loading capacity and ease of
unloading. Containers insulated with rigid polyurethane
foam are used almost exclusively nowadays
in international shipping on account of the excellent
properties of this material. Polyurethane is also
being used more and more as a core material for
sandwich panels for refrigerated vehicles. High
mechanical strength, high insulating efficiency and
economical production are combined in this core
material.
Global refrigerated transport
Polyurethane-insulated containers are transported
on special container ships with a large loading capacity
of up to 7,500 TEU (TEU stands for 20 ft
equivalent unit). At present, there are about
800,000 refrigerated containers throughout the
world, most of which are insulated with rigid polyurethane
foam.
Refrigerated containers are invariably used for
shipping temperature-sensitive goods, while vehicles
with diverse refrigerated superstructures can
be used in addition to actual containers for land
transport. Semi-trailers up to 16 m in length are
used for bulk transportation while smaller refrigerated
vehicles are involved in regional distribution.
The increase in the number of refrigerated containers
and vehicles reflects the growth of international
trade in highly perishable goods. Success in this
growing sector of the transport industry relies on
adaptation to different market requirements. Refrigerated
vehicle manufacturers normally cater for
regional markets, whereas refrigerated containers
are produced and sold internationally.
Insulation
Technical Information

160
140
120
100
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40
20
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File No.: PU21019-0410 en
Issue 2004-10-11
0
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Production of reefer containers 1991 - 2006 (2004 - 2006 predicted, in 1,000 TEU)
Bayer MaterialScience AG is a powerful ally for
manufacturers as it is represented internationally in
the polyurethanes sector. By no means all other
manufacturers of polyurethane raw materials for
1400
1200
1000
800
600
400
200
0
refrigerated transport have the expertise which
Bayer has gained through its extensive knowledge
of international and national market trends.
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Worldwide reefer container fleet (2004 - 2006 predicted, in 1,000 TEU)
Insulation
Technical Information

2. Insulation for the most demanding
applications
Refrigerated containers and vehicles are generally
run under conditions which demand both optimum
thermal insulation and high mechanical strength.
These properties have to be maintained throughout
the service life of the product, which often exceeds
15 years. The specific requirements of shipping
lines, leasing companies, etc., which result from a
number of different influences, are also an important
factor and include:
• type of freight transported
• loading and unloading conditions
• quality of handling in different areas
• requirements of the International Standards
Organization (ISO regulations)
• personal preferences and company policy
• national transport legislation.
In addition, production costs, durability, corrosion
resistance, low repair and maintenance costs (lifecycle
costs) have to be taken into consideration
when producing refrigerated containers and vehicles.
Bayer MaterialScience AG works in close cooperation
with its customers here: all our polyurethane
raw materials are subjected to a lengthy internal
quality assurance procedure in compliance
with strict DIN EN ISO 9001/2000 standards.
A typical refrigerated container
Page 4 of 6
File No.: PU21019-0410 en
Issue 2004-10-11
Reinforcing sandwich panels
The design of the frame, the floor and the roof of
insulated containers and vehicles is critical, the
strength of the structure being dependent on the
mechanical properties of the reinforcing sandwich
panels. These panels consist of a rigid polyurethane
foam core with metal facings which are
bonded over the entire surface of the polyurethane
core layer to strengthen the container. The constant
vibrations and shocks encountered during road
transportation make long-term stability an essential
requirement, and one which the elasticity of the
rigid polyurethane foam satisfies.
In addition to the mechanical requirements, the
original high insulation value of the rigid polyurethane
foam has to be maintained over long periods
to avoid aging. This is achieved by using facings
which prevent the diffusion of water even at internal
temperatures below - 25 °C. The insulation thickness
ranges from 50 to 200 mm at densities of between
45 and 100 kg/m³. However, if internal temperatures
are only 0 °C to 5 °C, thinner insulating
layers down to a minimum of 20 mm are used.
The facings can consist of aluminum, steel,
stainless steel or glass fiber reinforced plastics
laminates and are from 0.4 to 2.0 mm thick. The
sandwich panels are produced in lengths of 3 to
16 m using specially designed temperaturecontrolled
foam presses and are either welded or
riveted to the frame, depending on the materials
used and the frame construction.
Insulation
Technical Information

Cavities remaining after the panels have been fixed
are filled with foam to provide uniform insulation
with excellent physical properties. About 300 kg of
rigid polyurethane foam are required to insulate a
standard refrigerated container. The formulations
used and the methods of production have been
continuously developed and improved in recent
years. This guarantees that the polyurethane sandwich
panels produced have uniformly high strength
and elasticity as well as optimum insulating values.
3. New-generation blowing agents
Up until the end of 2003, the use of the HCFCbased
blowing agent R141b in the production of
rigid polyurethane foam in the transport sector was
still sanctioned under the Kyoto Protocol. Nowadays,
however, blowing agents having a GWP
(global warming potential) > 0 must be used. New
foam systems based on alternative blowing agents
have accordingly been developed.
The most promising alternatives
Since the early 1990s, Bayer has been researching
new R11-free polyurethane foams to replace the
former systems. Numerous chemical and physical
tests yielded three alternative foam systems with
the blowing agents R141b, cyclopentane and carbon
dioxide. The Kyoto Protocol states that an alternative
must now also be found for the blowing
agent R141b. Meanwhile, cyclopentane, isopentane,
n-pentane and mixtures of these have
enjoyed much success with European polyurethane
manufacturers, and there is also the new generation
of HFC blowing agents, 365mfc and 245fa.
The mechanical properties of all the foams tested
easily surpassed the minimum requirements for
such applications. The production parameters could
also largely be adapted to previous values, resulting
in minimal production changes.
Proven insulation efficiency
The insulation value of rigid polyurethane foam is
also important in refrigerated containers. The heat
transmission capacity of an insulated container, that
is the total energy required to maintain a constant
internal temperature against defined external temperatures,
determines the power requirement of the
refrigerating unit.
Page 5 of 6
File No.: PU21019-0410 en
Issue 2004-10-11
Heat losses through rigid polyurethane foam can be
calculated purely theoretically on the basis of its
γ value. On the other hand, data relating to the
complete container can only be determined by testing
the finished article.
The thermal properties of the rigid polyurethane
foam as well as any thermal bridges resulting from
structure-related factors or insufficient integrity are
critical. These parameters were investigated by
subjecting a batch of 20 containers to 12-hour tests
in a refrigeration chamber with substantially constant
temperature variations and air speeds, to determine
heat transmission. Each type of container
was examined by measuring five identical containers
in succession to provide statistically accurate
results.
Test results
When measured, the diathermancy of the HFC
blowing agents 245fa and 365mfc/227ea 94/6 was
approx. 9.5 % higher than that of R141b.
The insulating effect of the foams blown by the representatives
of the pentane family was reduced by
approx. 8 % in the case of cyclopentane, approx.
11 % in the case of 70/30 cyclopentane/isopentane,
and approx. 14 % in the case of iso-pentane and npentane,
compared with R141b-blown foam.
Cyclopentane or the 70/30 c/i-pentane mixture currently
looks set to establish itself in Europe as the
norm for large-scale production. The 94/6 HFC
365mfc/227ea mixture will for the time being retain
its place in the market as an alternative for smallscale
or specialized production. Bayer Material-
Science AG has fully-developed systems to cover
all of these developments. The loss in insulating
efficiency compared to HCFC R141b will, however,
have to be compensated by an increase in insulation
thicknesses and possibly by improved construction
and refrigeration units.
Insulation
Technical Information

This information and our technical advice – whether verbal, in writing or by way of trials – are given in good faith but without warranty, and
this also applies where proprietary rights of third parties are involved. Our advice does not release you from the obligation to verify the information
currently provided - especially that contained in our safety data and technical information sheets - and to test our products as to
their suitability for the intended processes and uses. The application, use and processing of our products and the products manufactured by
you on the basis of our technical advice are beyond our control and, therefore, entirely your own responsibility. Our products are sold in
accordance with the current version of our General Conditions of Sale and Delivery.
The methods described in this publication for testing the fire performance of polyurethane‚ and the results quoted‚ do not permit direct conclusions
to be drawn regarding every possible fire risk there may be under service conditions.
Publisher: Business Development – Insulation
Bayer MaterialScience AG,
D-51368 Leverkusen
www.bayermaterialscience.com
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File No.: PU21019-0410 en
Issue 2004-10-11
Insulation
Technical Information