Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Vacuum Insulation Panels
The present invention relates to vacuum insulation panels having an improved
insulating effect, a gas diffusion-impermeable plastics film suitable for the
production of such vacuum insulation panels, and the use of such vacuum
insulation
panels in refrigeration equipment.
Vacuum insulation panels ("VIP"), being excellent insulating materials, have
attracted a great deal of interest in all areas of thermal insulation, but
especially in
domestic refrigeration equipment. As a rule they are superior to rigid
polyurethane
foams, which are normally used in domestic refrigeration equipment, by a
factor of
more than two as regards their insulating effect. Normally vacuum panels are
produced by a process in which microporous supporting materials are covered
with
films and welded in vacuo. The pressure in a VIP is normally less than 1 mbar,
for
only at such low pressures is the requisite insulating effect achieved. Among
present-day VIPs, in principle two types should be distinguished:
microporous precipitated silicic acid covered with plastics film corresponding
to EP
0 463 311 or DE 40 19 870 Al, EP 0 396 961 B1 and EP 0 446 A2 or DE 40 08 480,
and microcellular plastics foams covered with an aluminium composite film,
such as
are described for example in US Patent 4,669,632.
The disadvantage of VIPs based on a core layer of microporous precipitated
silicic
acid is that a pulverulent material is used as starting material and
accordingly the
VIPs have significant thickness tolerances and deviations from planarity that
complicate the incorporation in refrigeration equipment.
The disadvantage of VIPs based on a core layer of plastics foams is that
plastics
foams have only a very small absorption capacity for gases, in particular
water
vapour, with the result that the gas-tightness of the film used for the
application of
these otherwise outstandingly suitable VIP core materials is extremely
important.
Conventional barrier films of plastics materials, such as are described for
example in
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EP 0 517 026 A1, do not produce the necessary gas barrier effect. Although gas-
absorbing substances or substances that react with gases ("getter") can of
course be
added to the core layer in order to trap gases that diffuse in and thereby
maintain the
low pressure in the VIP, this measure does not always prove satisfactory. For
this
reason an aluminium composite film is preferably used as a total gas barrier
in order
to maintain the vacuum in the VIP. This aluminium composite film however
dissipates so much heat at the edges that a large part of the insulating
effect of the
VIPs is lost. Of course, this effect is detected only when measuring the
thermal
transmission in a complete refrigeration unit. The influence of the edge
effects
cannot be detected when measuring the coefficient of thermal conductivity
according to DIN 18164 Parts 1 and 2.
Nevertheless, VIPs based on a core layer of plastics foams have achieved a
significant market penetration since their dimensions can be accurately
matched to
requirements and they can be produced simply and inexpensively in the form of
very
flat (plane) sheets. However, the aforementioned disadvantage of heat
transmission
via the edges of the double-sided aluminium film restricts their further
widespread
use.
The object of the present invention was accordingly to provide VIPs that
exhibit the
advantages of VIPs based on a core layer of plastics foams, namely flat
(plane)
surfaces and dimensionally accurate processability, but avoid or substantially
reduce
the losses in insulating performance due to edge effects.
According to the invention this object was achieved by vacuum insulating
panels
(VIPs) having a microporous sheet as core layer and a covering of a highly gas
diffusion impermeable plastics film comprising at least 7 layers having the
following
layer sequence
(1) polyolefin heat-sealable layer (I)
(2) adhesive or bonding layer (II)
(3) gas barrier layer (III)
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(4) adhesive or bonding layer (II)
(5) polyolefin layer (IV)
(6) adhesive or bonding layer (II)
(7) a layer (V) consisting substantially of polyester and/or polyamide and/or
polypropylene sputtered with aluminium or SiOx or a metal oxide of the
2°d
or 3'~ main groups.
With a VIP according to the invention an oxygen diffusion of substantially
below
0.01 cm3/m2 d bar and a water vapour diffusion of substantially less than 0.02
g/mz d
can be achieved, with the result that the durability of the insulating effect
of a VIP
fabricated in this way corresponds to practical requirements. A loss of
insulating
performance due to edge effects, as occurs when using aluminium composite
films
according to the prior art, is not found.
Polyolefin homopolymers or polyolefin copolymers may be used as polyolefin
heat-
sealable layer (17. Preferred are linear low density polyethylene ("LLDPE"),
polybutylene ("PB"), ethylvinyl acetate ("EVA"), high density polyethylene
("HDPE"), ionomers ("I") and mixtures of these substances. According to the
invention a mufti-layer embodiment of the polyolefin heat-sealable layer (I)
produced by co-extrusion of a plurality of layers from the aforementioned
materials
is also possible. The thickness of the polyolefin heat-sealable layer (I) is
preferably
20 to 200 Vim, particularly preferably 50 to 100 pm.
As adhesive or bonding layer (II) there are preferably used commercially
available
adhesives such as in particular two-component polyurethane adhesives.
Polyolefin
adhesives, preferably of polyethylene homopolymers, ethylene/ethyl acrylate
("EAA") or ethylene/methacrylic acid ("EMMA") may however also be used. The
thickness of the adhesive layer or bonding layer (II) is preferably at most 6
p,m,
particularly preferably 2 to 6 pm.
The gas barner layer (III) preferably consists substantially of polyvinyl
alcohol
("PVOH"), ethylene/vinyl alcohol copolymer ("EVOH'~ and/or of polyamide or of
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mixtures of PA and EVOH or, in the case of a mufti-layer embodiment, of a
layer-
type combination of PA and EVOH or of mixtures of PA and EVOH, and is
preferably stretched at least monoaxially. The gas barner layer is optionally
provided with a barner lacquer coating, preferably with an acrylic lacquer.
The
thickness of the gas barner layer (III) is preferably 10 to 120 p,m, and in
the single-
layer embodiment is particularly preferably 10 to 20 ~,m.
The polyolefin layer (IV) preferably consists substantially of polyethylene,
polypropylene or polyethylene copolymers. According to the invention this
layer is
preferably 5-500 p,m, particularly preferably 50-200 p,m thick. It has been
found in
this connection that the relatively thick polyolefin layer (IV) imparts a
substantially
smoother and more uniform surface to the VTP. This is particularly
advantageous in
the bonding of the VIP when installing a refrigeration unit. In the case of a
folded
VIP the surface wetted with adhesive is generally not sufficient for an
adhesion of
the VIP.
The layer (V) of polyester and/or polyamide and/or polypropylene is preferably
sputtered, on the side remote from the remaining layers, in a conventional
manner
with aluminium, SiOx or a metal oxide of the 2"d or 3ra main groups, and may
optionally be provided on the non-sputtered side with a barrier layer
lacquering,
preferably with an acrylic lacquer. The layer (V) is preferably a layer
consisting
substantially of polyester or polypropylene that has been sputtered with
aluminium,
preferably in a thickness of 30 to 80 nm. The thickness of the layer (V) is
preferably
10 to 40 p,m, particularly preferably 10 to 20 Vim.
The at least 7-layer plastics film that is also the subject of the present
invention may
contain in one or more layers, normal amounts of conventional additives and
auxiliary agents such as for example lubricants, anti-blocking agents and
antistatic
agents.
It has been found that the unexpectedly high impermeability was achieved
specifically by a combination of a relatively thick polyolefin layer (IV)
together with
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the gas barrier layer (III) preferably of polyvinyl alcohol, and the sputtered
layer
(V). It is also important in this connection that the gas barrier layer (III)
in the
overall structure is arranged directly underneath the heat-sealable layer and
is thus
protected from moisture.
According to the invention VIPs that employ plastics foams as core layer are
preferred. The plastics foams may be polyurethane or polystyrene foams. Also
suitable are sheets produced from ground and pressed plastics foams, such as
described for example in EP 0791155 B 1.
As core layer there are preferably used according to the invention
microcellular,
open-pore foamed sheets, in particular of polyurethane or polystyrene. In a
further
preferred embodiment ground, closed-cell foamed materials that have optionally
been compressed under the addition of suitable binders to form sheets, serve
as core
layer for the VIPs according to the invention. In this way the production of
VIPs
according to the invention can be incorporated in the recycling process for
spent
foams.
The production of the VIPs is normally carried out by placing the microporous
sheet
serving as core layer in a bag prefabricated from the films according to the
invention
(polyolefin/hot-sealable layer (I) on the inside) and sealing the still open
edge in a
vacuum of 10'3 to 1 torr. The VIP according to the invention is obtained after
the
aeration of the vacuum chamber.
The high gas impermeability of the film according to the invention imparts a
sufficient durability to the VIP despite the low absorption capacity of the
core layer.
If nevertheless a getter is to be used in order to ensure durability of the
VIP, the
amount used may be correspondingly small. Also, even the use of small amounts
of
a substance that binds water vapour may possibly be sufficient. Examples of
suitable getters are:
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in order to bind the atmospheric constituents oxygen and nitrogen, alkali and
alkaline earth metals; to bind moisture and carbon dioxide, alkaline earth
oxides; and
in order to bind just moisture, commercially available silica gels and
molecular
sieves. Suitably formulated getters made from these materials are commercially
available.
The film according to the invention may in a special embodiment also be used
only
to produce one side of the film bag, the opposite side forming a conventional
multi-
layer film with an aluminium barrier layer, which preferably comprises an A1
layer
with a thickness of 6-20 pm and a PE layer with a thickness of 50-200 Vim. In
this
embodiment too the thermal insulation is not significantly affected by edge
effects.
The VIPs according to the invention may be widely used as high-performance
insulating materials for insulation in building and construction, industrial
insulation,
and in particular in refrigeration equipment.
When used in refrigeration equipment the VIPs usually occupy part of the
insulation
volume - refrigeration equipment is normally insulated with rigid polyurethane
foam. In this way energy savings of up to 30% can be achieved without
increasing
the wall thickness.
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Examples:
Measurement methods:
The properties of the mufti-layer film according to the present invention are
determined according to the following methods:
The oxygen, nitrogen and carbon dioxide permeability of the films is
determined
according to DIN 53380.
The water vapour permeability of the films is determined according to DIN
53122.
The coefficient of thermal conductivity ~, is determined according to DIN
18164
Part l and Part 2.
The determination of the cabinet index (heat transmission through the shell of
the
refrigeration equipment) is described in detail in Example 7.
The subject of the invention will be described in more detail hereinafter with
the aid
of the following examples:
1. Films:
The high barrier effect of the films according to the invention was
demonstrated
using the following examples of films:
Example a:
Layer I: Polyolefin heat-sealable layer of ethylene/vinyl acetate copolymer,
3.5% vinyl acetate, 50 p,m
Layer II: two-component polyurethane adhesive, 2 pm
Layer III: gas barrier layer of polyvinyl alcohol, biaxially stretched, 12 pm
Layer II: two-component polyurethane adhesive,
2 pm
Layer IV: polyethylene layer, 120 pm
Layer II: two-component polyurethane adhesive,
2 pm
Layer V; metallised biaxially stretched polyethylene terephthalate film, 12
p,m
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Example b:
Layer I: Polyolefm heat-sealable layer of ethylene/vinyl
acetate copolymer,
3.5% vinyl acetate, 50 pm
Layer II: two-component polyurethane adhesive, 2 p,m
Layer III: gas barrier layer of polyvinyl alcohol, biaxially
stretched, 12 pm
Layer II: two-component polyurethane adhesive, 2 p,m
Layer IV: polyethylene layer, 120 p,m
Layer II: two-component polyurethane adhesive, 2 pm
Layer V: metallised biaxially stretched polypropylene film,
20 pm
Example c:
Layer I: Polyolefin heat-sealable layer of ethylene/vinyl acetate copolymer,
3.5% vinyl acetate, 50 p.m
Layer II: two-component polyurethane adhesive, 2 pm
Layer III: gas barrier layer of a PVOH layer lacquered on both sides with
PVDC
Layer II: two-component polyurethane adhesive, 2 p,m
Layer IV: polyethylene layer, 120 pm
Layer II: two-component polyurethane adhesive, 2 ~m
Layer V: metallised biaxially stretched polyethylene terephthalate
film, 12 pm
Example d:
Layer I: Polyolefin heat-sealable layer of ethylene/vinyl
acetate copolymer,
3.5% vinyl acetate, 50 pm
Layer II: two-component polyurethane adhesive, 2 ~m
Layer III: gas barrier layer of a co-extruded PA/EVOHIPA
layer
Layer II: two-component polyurethane adhesive, 2 pm
Layer IV: polyethylene layer, 120 pm
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Layer II: two-component polyurethane adhesive, 2 p,m
Layer V: metallised biaxially stretched polyethylene terephthalate filin, 12
p,m
Comparison example e: (Combithen PXX, according to EP 0 517 026 A1):
1 S' layer: polyolefin layer, 50 p,m
2d layer: two-component polyurethane adhesive,
2 ~m
3ra layer: polyvinyl alcohol layer, 12 p,m
4'" layer: two-component polyurethane adhesive,
2 pm
5'h layer:polyolefin layer, 120 pm
6~' layer: two-component polyurethane adhesive,
2 p,m
7'h layer: polyvinyl alcohol layer, 12 p.m
8'h layer: two-component polyurethane adhesive,
2 pm
9'h layer: polyolefin layer, 120 p,m
10'h layer:two-component polyurethane adhesive,
2 pm
11 'h layer: stretched polyethylene terephthalate
film, 12 pm
Comparison example f (Aluthen, P. Wolff Walsrode):
1 S' layer:polyolefin layer, 50 pm
2"d layer: two-component polyurethane adhesive,
2 pm
3'~ layer: stretched polyethylene terephthalate
film, 12 ~m
4~' layer: two-component polyurethane adhesive,
2 pm
5'}' layer: aluminium film, 12 p,m
6'h layer:two-component polyurethane adhesive,
2 pm
7'h layer: stretched polyethylene terephthalate
film, 12 pm
The following water vapour, oxygen, nitrogen and carbon dioxide permeabilities
were determined:
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Permeability Water Vapour Permeability
Example [cm3/m2dbar] (g/mZd~
(23C, (23C, 85% ref. humidity)
0%
ref.
humidity)
02 NZ COZ
_
a 0.01 <0.01 0.02 0.015
b 0.01 <0.01 0.03 0.02
c 0.01 <0.01 0.02 0.015
d 0.01 <0.01 0.02 0.015
Comparison Example
a 0.01 <0.01 0.03 0.1
f unmeasurably unmeasurably small
small
2.) Description of the film bag:
The film bag was produced by a three-sided welding process using 50 x SO cm
size
pieces of film. Bags were produced from the following materials:
I. Symmetrically fabricated film bag of a commercially obtainable aluminium
containing mufti-layer film (Aluthen-P from Wolff Walsrode, see Example
l.f).
II. Symmetrically fabricated film bag of a commercially obtainable metal-free
barrier layer film (Combithen PXX from Wolff Walsrode, see Example l.e).
III. Symmetrically fabricated film bag of the mufti-layer filin according to
the
invention and as disclosed in Example l.a.
IV. Asymmetrically fabricated film bag of the mufti-layer film according to
the
invention described in 2.III and the aluminium-containing mufti-layer film
described in 2.I.
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3.) Description of the core layer - sheet of recycled rigid foam
corresponding to WO 96/14207
1000 g of a PUR rigid foam flour from a refrigeration equipment recycling
plant are
uniformly mixed with 35 g of water and 100 g of a polyisocyanate mixture of
diphenylmethane diisocyanates and polyphenyl-polymethylene-polyisocyanates
(Desmodur~ VP PU 1520 A20; Bayer AG) in a Lodige-Pflugschar mixer equipped
with twin substance nozzles. A moulded part of size 40U x 400 mm is formed
from
this mixture in a mould frame, and is uniformly compacted and then compressed
to
25 mm in a laboratory press under a pressure of 5 bar and at a temperature of
120°C
for 8 minutes using a time-measurement program.
A porous 25 mm sheet having a bulk density of 250 kg/m3 is obtained. The sheet
was heated for ca. 2 hours at 120°C in order to free it from all
volatile constituents.
4. Production of VIPs
The panels produced in 3. were placed in the film bags produced according to
2.I to
2.IV, evacuated to a pressure of 2 x 10'' torn and welded. The corresponding
VIPs
are obtained after aeration.
It was found that the VIPs produced with the thick film according to the
invention
have a substantially smoother surface than those with a thin film.
The still existing, low water vapour permeability can be determined by
measuring
the weight increase of the VIPs after a storage test. The weight increase was
determined after a storage time of 1 year and was extrapolated to 15 years. In
this
connection it was borne in mind that the core layer consisting of the rigid
polyurethane foam has a water absorption capacity of about 0.5 to 1% of its
own
weight and for this reason the pressure in the panel does not initially rise.
The
weight increase on account of the oxygen, nitrogen and carbon dioxide
permeability
can be ignored in the comparison, since it fluctuates only in the milligram
range.
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Calculated and measured weight increases from the water vapour permeability:
Weight Increase
[g]
VIP of
After 1 Year After 1 Year Extrapolation
to
Film Bag
(calculated) (measured) 15 Years
2.I 0 0.2 3
2.II 11.68 5.34 80.1
2.III 1.75 1.63 24.45
2.N 0.88 0.72 10.8
5. Measurement of the coefficient of thermal conductivity ~,
The thermal transmission was measured according to DIN 18164 Parts 1 and 2 for
the VIPs with the film structure 2.I to 2.IV produced in 4. The sheets all
have a
comparable thermal transmission of 9.0-9.1 mW/m°K.
6. Incorporation of VIPs in a refrigerator
As shown in a vertical section in Fig. 1, VIPs (reference numeral (1)) with
the film
1 S structure according to 2.I to 2.IV, but with dimensions of 60 x SO x 2.5
and 50 x 50
x 2.05, were bonded together before installation on the inside of the external
housing
(reference number 2)) in a table-top refrigerator. A further VIP was bonded to
the
inside of the door and to the rear wall (both not shown in Fig. 1). The VIPs
thus
occupied part of the insulation volume. After the installation of the internal
housing
(reference numeral 3)) the remaining insulation volume was conventionally
filled
with PUR foam (reference numeral 4)).
Four refrigerators having different film structures of the VIPs employed in
each case
were produced.
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After bonding, the VIPs formed with the preferred thick filin according to the
invention had bonded better and more permanently than VIPs produced with thin
films, such as for example according to the structure 2.I. In the latter case,
after the
foaming of the residual spatial volume, in some cases there was a lack of
bonding
between the VIP and the outer covering.
7. Measurement of the cabinet index of refrigerators produced with
different VIPs
The refrigerators produced under 6. were investigated as regards their cabinet
indices as follows: by means of an adjustable electric heating device
installed in the
interior of the refrigerator, the interior space was raised to a temperature
30°C to
40°C higher than the ambient temperature. After the internal
temperature had
reached a stationary state (as a rule after 4 days), the cabinet index Z (in
W/°K) was
determined by measuring the electrical heating effect and the mean temperature
difference between the interior and surroundings over a period of 24 hours,
the
temperature measurements in the interior being made using a total of 6
thermocouples. The following results were obtained:
_ . __ . . . .2.I _. ..._._ __.036._.i::~..
... _ _.. _ . _ ...
2.II 0.30
2.III 0.29
2.IV 0.29
As can be seen, in the case of 2.I (aluminium composite film on both sides)
the
thermal transmission is substantially greater than when using the plastics
film, and
what is more even when the plastics film is used only on one side in
combination
with an aluminium composite film (2.IV) on the other side.
