Note: Descriptions are shown in the official language in which they were submitted.
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HONEYCOMB CORE OF A MOISTURE SEALING ~ATERIAL
The present invention relates to a honeycomb core, built
up of strips made with a material, such as cellulose
material, the strength and/or the shape of which is sensi-
tive to the action of moisture, and to a honeycomb panel
in the form of a sandwich construction, comprising such a
honeycomb core and two cover plates which define panel
faces, between which the core is glued.
For many uses, for example in pallets or in interior parts
for cars it is desirable that such a honeycomb core or
such a honeycomb panel is moisture-proo~ and particularly
water-proof. Moisture resistance can be achieved by using
a plastic instead of the moisture-sensitive material. Most
plastics, however, have a much lower temperature stability
than cellulose material such as, for instance paper, and
they are in most cases more expensive. Moreover, plastics
have the disadvantage that an environmentally harmful
product is obtained, and that the conventional manfactu-
ring methods which are geared to paper processing, in
particular the cutting and glueing thereof, will have to
be completely revised.
Apart from this, moisture resistance can be achieved by
impregnating the paper with a moisture-repellant means.
The usual method ~or recovering paper ~or recycling is,
however, stirring the paper to pulp in water in a so-
called pulper. Since the water cannot penetrate the im-
pregnated, moisture-repellant paper, this method is not
usable for impregnated paper. Consequently, the paper can
no longer be recovered ~rom that.
The invention aims at providing a material for the honey-
comb core and the honeycomb panel which is moisture-resis-
tant, easily workable in the usual paper processing pro-
duction processes and furthermore easily recoverable for
re-use.
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-- 2
For this purpose the honeycomb core according to the
invention is characterized in that the strips are built up
in layers and comprise a layer of plastic, and the honey-
comb panel according to the invention is characterized in
that at least one of the cover plates is moisture-proof.
The core and the panel according to the invention are
characterized in that the strips are built up in layers
and comprise a layer of plastic, and the panel according
to the invention is characterized in that at least one of
the cover plates is moisture-proof.
The core and the panel according to the invention a-e thus
provided with moisture-sealed layers. Moisture, and in
particular water, can only affect the exposed outer surfa-
ce of the core or the panel, and cannot reach the material
which is closed in, for instance by further processing and
mounting of the material. Apart from that the moisture-
sensitive material can be recovered for re-use.
All the strips of the honeycomb core comprise the plastic
layer so that the core or the panel can be cut to an
arbitrary size and still remain moisture-proof.
If both cover plates of the panel are thus moisture-proof,
these will cooperate with the moisture-sealing layers of
the honeycomb core, so that the honeycomb cells are sepa-
rated from the outside and from each other. If the panel
is now damaged locally and a moisture sealing layer is
broken there, the moisture can indeed penetrate the cell
there, and moisten the paper layers inside it, but the
moisture cannot spread any further, because the cell in
question is isolated from its surroundings by moisture-
sealing layers. The moisture impairment in local damage is
thus localised.
The cover plates of the honeycomb panel can also be manu-
-
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factured with a material such as cellulose material, the
strength and/or the form of which is sensitive to the
action of moisture. In that case it is preferable that at
least one of the cover plates is built up in layers and
comprises a layer of plastic. The material of the cover
plates of such a panel, for example paper, can also be
recovered for re-use.
The cover plates can, however, be made of another material
which is or is made moisture-proof, such as, for instance,
wood, metal, plastic, coated paper or laminates thereof,
if this material is inherently moisture-resistant. For the
purpose of re-use the paper should be separable from these
materials.
Preferably the plastic layer of the honeycomb core is to
be found between two layers of the moisture-sensitive
material of the strips, and is thus integrated with it. If
the plastic layer is built in in that way in the moisture-
sensitive material of the core strips, the surface thereofretains the character of moisture-sensitive material. In
the case of paper the strips can be processed in the usual
ways as paper, for example by trimming, cutting and glu-
eing, for the production of the honeycomb core and with
that the honeycomb panel.
Preferably the cover plate concerned of the honeycomb
panel comprises two layers of the moisture-sensitive
material, between which the plastic layer thereof is
located, which is integral with that. By building in the
plastic layer here as well, the cover plate surfaces
retain the character of the moisture-sensitive material,
and the cover plates can be cut, glued and processed
further in the usual ways for producing honeycomb panels.
The principal faces of the produced panels then also
retain the character of the moisture-sensitive material
(for example paper) so that these panels can then be cut
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in the usual m~nne~ to size, and so that for example paper
honeycomb blocks or honeycomb panel parts can be glued
against them, with the usual glueing methods. Common
products such as pallets and interior parts for cars can
be made without radical production changes.
It is preferable that the built-in plastic layers are
melted together with the paper layers resting against
them. A paper product melted in that way can easily be
used as initial material in the usual production processes
for the honeycomb core and the honeycomb panel based on
paper.
The paper layers of the core material can have a surface
density between 50 and 125 g/m2, and preferably have a
surface density of about 70 g/m2, whereas the cover plates
of the honeycomb panel have a total surface density of
between 150 and 750 g/m2. In that way an optimal balance
between weight and strength of the material is attained.
It is preferable that the plastic layers used are made o~
polyethene. This material can be melted easily with paper.
The polyethene layers have a surface density between 5 and
50 g/m2 and preferably have a surface density of about 12
g/m2. Layer densities like this melt well with paper and
are not penetrable by moisture.
The honeycomb core can be built up by glueing the strips
together with a moisture-resistant glue, and the cover
plates of the honeycomb panel can be glued together with
the honeycomb core thereof with a moisture-resistant glue.
In this way the structure of the core or the panel remains
intact when becoming moist and local moisture damage to
the panel is fixed and located in an effective manner. A
suitable moisture-resistant glue is, for example, polyvi-
nyl acetate glue.
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Preferably a glue is selected which impregnates the strips
and the cover plates at the glue locations. Then the strip
and cover plate material cannot absorb any moisture at the
glueing sites. In this way, moisture migration between
adjacent honeycomb cells, parallel to the glueing bonds
and the moisture-sealing layers right through the materi-
al, is blocked in an effective way.
Polyethene and similar polymers, just as glue residues and
small paper fractions impregnated with water-resistant
glue, can easily be separated from the paper in a pulper,
by scooping it out of the pulp slurry. The separated pulp
can thus easily be recovered for re-use in paper products.
The invention will be elucidated below with reference to
an exemplary embodiment which is illustrated in the accom-
panying drawings, in which:
figure 1 is a perspective view of a honeycomb panel provi-
ded with a honeycomb core;
figure 2 is a top view of a honeycomb core in a folded-up
position;
figure 3 is a top view of a honeycomb core in a partially
drawn out position;
figure 4 is a top view of a honeycomb core in fully drawn
out position; and
figure 5 is a cross sectional view of one of the paper
strips of which the honeycomb core according to the inven-
tion is built up.
Figure 1 shows a honeycomb panel 1 which comprises a
honeycomb core 2 and cover plates 3 and 4 glued to it.
The honeycomb core 2 is built up of trapezoid-shaped
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corrugated strips 5 which consist for the most part of
paper. Instead of a light or heavy paper quality (card-
board) another cellulose material can be used.
t
In the figures 2, 3 and 4 top views of the honeycomb core
are shown in folded-up and partially and fully drawn out
positions. The strips 5 extend in longitudinal direction
along each other, and parts 6 thereof are glued at least
in part along their longitudinal direction, alternately to
the adjacent strips on both sides, for example with poly-
vinyl acetate glue (PVAC glue), the parts 7, of approxi-
mately the same length, located between the glued parts 6,
re~;n;ng unglued. If the honeycomb core is drawn o~t in a
direction perpendicular to the plane of the strips 5
(figure 3), a grid of more or less regular hexagonal cells
8 is formed, with approximately the same cell diameter D,
the cell sides of which being formed by the glued parts 6
and the intermediate parts 7 (figure 4). The cells can,
for instance, be 13 mm in diameter D and 50 mm in height
(strip width).
The strips 5 form the walls 9 of the cells 8 of the
hexagonal grid and can be folded at their ends and be
turned back for forming the adjacent strip. After stret-
ching the honeycomb core a honeycomb panel can be formedwith it by glueing (for example with PVAC glue) the cover
plates 3 and 4 to the upper and lower edges of the cell
walls 9 (figure 1). It is, however, also possible to
provide a honeycomb panel with a honeycomb core 2 accor-
ding to the invention, in which a cover plate 3 is gluedto only one side of the core 2.
The cells of the honeycomb panel 1 can be empty or filled
with an insulating material. The panel can be manufactured
cheaply of inherently flexurally slack material, but has
as a whole a high resistance to compression in a direction
perpendicular to the principal plane and has a high
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flexural stiffness.
The structure of the material of the strip 5 is shown
schematically in figure 5. The strips 5 are layered and
consist of two layers of paper 10 and 11 (another cellulo-
se material is also possible), between which there is a
layer of polyethene 12, which is melted together with the
paper layers. Of course another plastic, in particular a
polymer, can be used. The polyethene layer 12 has a surfa-
ce density between 5 and 50 g/m2 and preferably has a
density of approximately 12 g/m2. The paper layers 10 and
11 have surface densities betweeen 50 and 125 g/m2 and
preferably have a surface density of 70 g/m2.
The polyethene layer 12 is not moisture-penetrable and the
strips 5 are therefore moisture-sealed. If the material of
the strips 5 is exposed on one side to moisture, only the
paper layer 10 or 11 on that side will get wet and the
other paper layer will stay dry.
If a honeycomb panel is built up of a honeycomb core of
the moisture-sealed paper described, against which on one
or both panel sides a cover plate is glued, then at least
one of the cover plates can have the same structure as
that of the strips 5 according to figure 5. The polyethene
layer 12 can then have the same surface density as that of
the strips 5, whereas the paper layers 10 and 11 of the
cover plates can have a surface density such that the
total surface density of each cover plate is between 150
and 750 g/m2.
In a honeycomb panel according to figure 1 in which the
strips 5 of the core 2 as well as both the cover plates 3
and 4 are provided with a moisture-sealed polyethene layer
12 built into the paper as described above, the cells 8 of
the hexagonal grid are separated by moisture-sealed poly-
ethene layers 12 from each other and from the outside.
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Thus moisture cannot penetrate through the panel surfaces
or through the cell walls 9 at one of the circumferential
edges of the panel, and can only moisten a paper layer on
an outer side o~ the panel. I~ the panel is damaged local-
ly, and the moisture-sealed polyethene layer 12 is broken
there, moisture can penetrate into the respective cell or
cells 8 and moisten the paper layers exposed therein.
However, the other moisture-sealed polyethene layers 12 of
those cells 8 prevent the moisture from spreading ~urther
in the panel 1, thus limiting the moisture damage to the
damaged cells 8.
A water-resistant glue is used ~or glueing, which impreg-
~ ~ nates the paper. The relatively slow migration of moisture
through the paper, parallel to a glueing bond and the
moisture-sealed layers, or in between two strips, or
across a strip edge through the paper o~ a cover plate, to
an adjacent, undamaged cell, is ef~ectively blocked by the
local paper impregnations.
Honeycomb panels 1 according to the invention can, for
instance, be used in pallets, which are almost completely
made up of paper, with decks and foot blocks formed from
honeycomb panels according to the invention. Such pallets
can stand in a puddle of water without any problem, since
they are not sensitive to weakening by the penetration of
moisture therein.
Honeycomb panels according to the invention can, in addi-
tion, be used as ~illing material in car doors, ~or insu-
lating and ~or cushioning the impact in sideward collisi-
ons. For that purpose suitable packs of such honeycomb
panels 1 are formed, which are arranged vertically in the
car door. Because o~ ~luctuations in the relative air
humidity and the temperature, water can condense in the
inside of the door, as a result of which the panel pack
will get wet through direct condensation thereon or indi-
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rectly. Moreover, on account of ageing of the rubber seals
o~ the door window, rain water can leak into the inside of
the door, so that the panel pack, initially the edges
thereof, will get wet. The polyethene layers 12 in the
strips 5 of the honeycomb core 2 and also those in the
cover plates 3 and 4 provide an effective seal against
this moisture.
By building in the moisture-sealing polyethene layer 12 in
the paper, the material retains the character of paper.
The material can be processed using the usual methods and
materials in the production process for honeycomb cores
and honeycomb panels (and further for pallets and car door
fillings), among others by the usual cutting and glueing
actions. In addition, the material has the thermal stabi-
lity and the mechanical strength of paper, that is to say,
for example, that at 150~ C it retains its shape and
strength which is not the case with a material built up
entirely of polyethene, polypropene or another cheap
plastic.
The material o~ the honeycomb core and the honeycomb panel
according to the invention can easily be recovered for re-
use by shredding it and stirring it into water in a so-
called pulper. The water then penetrates the paper andbecause of the stirring the paper is mechanically separa-
ted from the polyethene, so that a paper slurry, the pulp,
is formed. The polyethene can then be scooped out of the
paper slurry after which the latter can be reused for
producing paper products. This method ~or recovery does
not work in the case of impregnated paper, in view of the
fact that the water cannot penetrate it. Water-resistant
glue residues and small paper fractions impregnated with
water-resistant glue can, however, also be easily scooped
up out of the paper slurry.
