Stock material or miscellaneous articles – Sheet including cover or casing – Filled with gas other than air; or under vacuum
Reexamination Certificate
1999-12-18
2001-11-27
Thomas, Alexander S. (Department: 1772)
Stock material or miscellaneous articles
Sheet including cover or casing
Filled with gas other than air; or under vacuum
C428S076000, C428S071000
Reexamination Certificate
active
06322869
ABSTRACT:
This invention relates to a combined vacuum insulating panel consisting of slabs of polyurethane and polystyrene, and the use thereof in the production of insulating elements of the type used, for example, as external walls in refrigeration equipment.
It is known that vacuum insulating panels are produced from a porous material and a gas-tight film covering it on all sides, with evacuation of the “cavity” formed by the porous material. The porous material may consist either of a porous bulky substance or else of a rigid foam. The film usually consists of combinations of several layers, the various layers fulfilling different tasks, such as a diffusion barrier to various gases and mechanical strengthening.
Vacuum insulating panels are of great interest as insulating material, particularly in the refrigeration industry.
Of particular interest as vacuum insulating panels are open-pored foams such as, for example, polyurethane foam and polystyrene foam as well as their comminuted products bound together to form a slab, such as are described, for example, in WO 96/14207.
Usually the vacuum insulating panels are combined with rigid polyurethane foam in such a way that the vacuum insulating panels are attached on one side to a cover, for example, the external metal sheet of a refrigerator, and the remaining cavity is foamed with rigid polyurethane foam (cf. FIG.
1
).
Here—in particular at large foam thicknesses—temperatures of up to 180° C. occur. On the side of the vacuum insulating panel nearer to the foam, temperatures of up to 150° C. can occur. Such temperatures are above the heat distortion temperature of the covering films used; even polystyrene foam used as filler for vacuum insulating panels melts at such temperatures. But it is especially the open-pored, microcellular polystyrene foam which is of particular interest in insulation technology as filler for vacuum insulating panels.
Accordingly, the object of the present invention was to render possible the use of temperature-sensitive polystyrene slabs in combination with polyurethane foam as insulating material.
Surprisingly, it has now been found that combination vacuum insulating panels which are stable at the foaming temperature are obtained when the open-pored polystyrene foam is covered with a layer of open-pored polyurethane foam and then covered with film, evacuated and sealed. If this combination element is constructed so that the polystyrene side is nearer to the external cover and the polyurethane side is nearer to the foam filling out the remaining cavity, then it survives the foaming process during the production of an insulating element regardless.
It is particularly surprising that the surface temperature of the vacuum insulating panel is also lowered on the side being foamed when a polyurethane foam having a density of more than 50 kg/m
2
, or a slab made of comminuted rigid foam bound together, as disclosed in WO 96/14207, is used in the vacuum insulating panel.
The present invention accordingly provides a vacuum insulating panel consisting of
a) two foam slabs laid flat on top of one another, one slab consisting of open-pored polystyrene foam and the other slab consisting of open-pored polyurethane foam,
b) a film covering both slabs, which has been evacuated and sealed with a gas-tight seal.
The two slabs are usually only laid loosely on top of one another during the production, because the mechanical stability of the vacuum insulating panel according to the invention is provided by the covering of film and subsequent evacuation, so that it is unnecessary to bond the two slabs together. But they may be bonded together or attached to one another at certain points or along strips.
The polystyrene slab consists of open-cell, for example, extruded polystyrene foam having a density of 20 to 60 kg/m
3
, preferably 25 to 45 kg/m
3
. The average cell size is preferably ≦50 &mgr;m.
The polyurethane slab may consist of an open-cell, preferably microcellular, polyurethane foam having a density of >50 kg/m
3
, preferably >80 kg/m
3
, for example, 80 to 200 kg/m
3
.
Preferably a slab made of particles of rigid polyurethane foam bound together, such as is described, for example, in WO 96/14207, is used as polyurethane slab. Here the density of the polyurethane slab is from 100 to 350 kg/m
3
, preferably 150 to 250 kg/m
3
. Where a slab made of particles of rigid polyurethane foam bound together is used, it is also preferred that
the particulate rigid polyurethane foam be a recycled material, preferably a particulate rigid polyurethane foam from the recycling of old refrigerators,
the polyurethane foam powder or flakes have a particle size of from 0.01 to 5 mm, preferably 0.1 to 2 mm, particularly preferably 0.1 to 1 mm,
the binder used to produce the polyurethane slab be a diisocyanate or polyisocyanate (preferably mixtures of diphenylmethane diisocyanates and polyphenyl polymethylene polyisocyanates).
All known gas-tight films, for example, combination films, of the type also used for the production of commercially available vacuum panels of existing prior art, are suitable for the vacuum panel produced according to the invention. Examples which may be mentioned are: a combination of polyethylene film with polyvinyl alcohol film, polyethylene film with aluminium foil and optionally polyester film or polyester-amide film. Multilayered films wherein one layer is an aluminium foil are preferred. The most preferred thickness of the aluminium foils is between 5 and 9 &mgr;m.
Prior to their being covered with film and evacuated, the foam slabs can be cut, or appropriate indentations can be cut out for the installation of switches, wiring or ducts.
The invention also provides the use of the vacuum insulating panels described above for the production of insulating elements made of polyurethane plastics, such as are used, for example, as structural elements for refrigeration equipment, in particular refrigerators or freezers. Here the vacuum insulating panel is incorporated into the insulating element in such a way that the polystyrene side is nearer to the outside and the polyurethane side is nearer to the polyurethane foam which is contained in the insulating element and fills out the remainder of the insulating volume. For the purpose of clarification, such an arrangement is illustrated in FIG.
2
.
The following Examples are intended to explain the invention in more detail, but not thereby to limit its scope.
REFERENCES:
patent: 5273801 (1993-12-01), Barry et al.
Bayer Aktiengesellschaft
Gil Joseph C.
Thomas Alexander S.
Whalen Lyndanne M.
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