Note: Descriptions are shown in the official language in which they were submitted.
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HEAT INSULATING VACUUM PANEL
BACKGROUND OF THE INVENTION
It is already known how to manufacture heat insulating vacuum
- panels from porous materials, and a film sheet covering the porous
material. The "hollow space" of the porous material is made air-tight by
evacuation. The porous material can consist of either porous bulk
material or of rigid foam material. The film sheet normally consists of a
combination of several layers, whereby different functions such as
diffusion resistance against various gases and medhanical hardening are
performed by using the various layers. The most frequently sold vacuum
panels have a core of porous bulk material, usually based on silicates.
The use of rigid polyurethane foam as a filling material for a
vacuum panel is described in U.S. Patent 4,668,555 (corresponding to
European Patent 188,806). The challenge of this process is to achieve
the required open-cells through precise recipe selection, and meeting -
certain prooess parameters. Rigid polyurethane foam materials are
primarily dosed-cell by nature. Another problem is the diffusion of volaffle
components such as amines, blowing agents, and also monomers when
using rigid polyurethane foam materials as carrier matefials for vacuum
panels. An advantage of rigid polyurethane foam materials in comparison
with porous bulk materials, is their precise dimensioning as a finished
vacuum panel, as well as their size accuracy. -
British Patent 1,308,468 describes a process for irreversibly
~ncreasing the volume of foams by swelling the foam and thereafler
rendering the swelling permanent by treating the foam with one or more
reagents which react to produce solids in the cells of the foam.
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DESCRIPTION OF THE INVENTION
Surprisingly, it has now been discovered that an excellent carrier
material for vacuum panels can be produced efficiently with a method by
curing an open-cell synthetic foam material with polyisocyanates. In this
approach, use is made of the process described in British Patent
1,308,468 (corresponding to German Auslegeschrift 1,911,645).
The open-cell synthetic foam material serves, in effect, only as a
mold since it does not require any strength. The strength is achieved -
through impregnation and subsequent curing of the polyisocyanate used -
according to the present invention.
me invention is therefore directed to a heat insulating vacuum
panel, consisting of: -
a) an open-cell rigid synthetic foam material which is obtained
through impregnation of an open-cell synthetic foam
material with a polyisocyanate and subsequent curing of
said polyisocyanate, and
b) afilm-sheetcovering the rigid syntheticfoam material,
whereby the film sheet containing the foam material is evacuated and
then hermetically sealed.
According to the invention, it is preferred that
1) the syntheUc foam material be a polyurethane foam
material,
2) the synthetic foam material be an open-cell foam produced
by pressing and calendaring prior to the impregnation with
the polyisocyanate,
3) the synthetic foam material be impregnated with
polyisocyanate using calendaring,
4) the synthetic foam material have a cell size between 0.01
mm and ~ mm,
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5) the polyisocyanate-saturated synthetic foam material be
freed from volatile components by tempering at
temperatures between 50 - 250C, preferably 120 - 200C,
at low pressure if necessary, prior to covering with the film
sheet, and
6) a mulU-layer film sheet be used as the covering film sheet, ; ~
preferably a polyethylenelaluminum sheet or polyethylene/ ~ -
polyvinylalcohol sheet.
All known film sheets; for example, laminated sheets can be
10 considered for the vacuum panel herein since they are also used for the
manufacture of commercial vacuum panels. Laminations of polyethylene -~
sheet with polyvinyl alcohol sheet or polyethylene sheet with aluminum
sheet are particularly preferred.
All synthetic foam materials can be consldered for the foam
15 material of the present invention. Since the required strength is achieved
through a subsequent impregnation and polymefization of the isocyanab
- ~ to be used based on the invention, no requirements are imposed on the
mechanical strength of the foam material itself. However, it is important
that the foam materials used have a fine cell structure for the heat
.
20 insulaUng characterisUcs of the vacuum panels. Therefore, foam
materials with a cell size of smaller than O.1 mm are preferred.
The polyisocyanates mentioned in British Patent 1,308,468 (the
disclosure which Is hereby incorporated by reference) are suibble as the
polyisocyanate. The teaching of British Patent 1,308,468 is preferably
25 followed dur~ng ~he ~mpregnation of the foam and the curing of the
polyisocyanate therein.
Another advantage of the vacuum panels herein is that the foam
materjal can be ta~lored prior to or after the impregnation. Thus, the foam
material can be manufactured at a location (both in space and Ume) `
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remot~ from the site where the vacuum panels are finally produced.
The vacuum panels obtained based on ~he invention can be used
in all applications for insulating materials. Preferred is their application in
cooling appliances and refrigerators, where there are especially high
5 requirements imposed on the insulation capability.
The invention is further illustrated but is not intended to be limited
by the following examples in which all parts and percentages are by
weight unless otherwise specified.
EXAMPLE
100 weight parts of a polypropylene glycol ether, in which
trimethylpropane and 1,2 propylene glycol (1:1) were used as the starter
(OH-number 47), were mixed with 2.7 weight parts of water, 0.8 weight
parts of silicone stabilizer, 0.1 weight part permethylated diethylene-
triamine and 0.23 weight parts of a tin salt of 2-ethylcaproic acid. 45.9
weight parts of isomer mixture consisting of 80 weight parts 1-methyl-
benzene-2,4-diisocyanate and 20 weight parts 1-methylbenzene-2,6-
diisocyanate were added to this mixture and mixed well with a high-
speed mixer. The white elastic foam material showed an extensive open-
cell structure, and had a volume of about 35 kg/m3.
The foam material was impregnated and cured with a
polyisocyanate (TDI) according to the process of example 44 of British Patent
1,308,468. The rigid foam material thus obtained was heated to 120-C
for 2 hours in order to remove all volatile components. The foam material
was then covered by a film sheet. This film sheet consisted of three
layers (polyester, aluminum, and polyethylene). The mold was evacuated
for 35 minutes until the pressure in the foam was 0.001 mm Hg, and
thereafter i~ was hermetically sealed.
The resultant vacuum panel has a heat conductivity of 0.009
W/Km (at 24-C).
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Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be understood that such
detail is solely for that purpose and that variations can be made therein
by those skilled in the art without departing from the spirit and scope of
5 the invention except as it may be limited by the claims.
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