Note: Descriptions are shown in the official language in which they were submitted.
CA 022176~8 1997-10-07
W O96/31339 PCT~L96/00150
A method for m~k; n~ expanded paper honeycomb core material
moi~ture- or waterproof, and the thus obt~; ne~ honeycomb
core material.
The invention relates to a method for making expanded
paper honeycomb core material moisture- or waterproof, as
well as the honeycomb core material obtained by using this
method.
Paper honeycomb core material is often used as a stiff and
light construction material. In a number of applications
it is necessary for the paper honeycomb core material to
be moisture- or waterproof, as for example in construction
panels for outside use, for use in transport and for use
in floors and such like. In these cases, the honeycomb
core material is usually delivered in moisture- and
waterproof condition, after which the user himself
provides one or both sides of the honeycomb core material
with a cover layer of plastic or metal, for example.
Paper honeycomb core material is obtained by glueing a
number of strips of paper onto each other at certain
places, and, after the glue has dried, expanding this
parcel of paper by pulling the outer strips of paper apart
laterally, thus obtaining the hexagonal cellular struc-
ture. After the expanded shape has been stabilized, the
honeycomb core material is cut into slices of the desired
thickness, which are ~urther used as honeycomb core in
honeycomb panels, for example.
It is known to make the paper honeycomb core material
moisture- and waterproof after expansion by impregnating
the paper. Impregnation is e~fected by immersing the ex-
panded honeycomb core material in a solution of formal-
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W O 96/31339 PCT~L96/00150
-- 2
dehyde and water. In the known processes immersion usually
takes place a number of times in order to apply the
desired amount of resin. After immersion, the impregnated
honeycomb core material must be dried with the aid of a
5 drying facility in order to remove the surplus of water
from the honeycomb core material.
This way of making paper honeycomb core material moisture-
and waterproof has a number of disadvantages. Formaldehyde
10 is a poisonous substance that makes recycling or dumping
di~icult. Owing to the ~act that immersion has to take
place a number of times, the treatment is time-consuming
and elaborate, which results in high process costs.
Drying, at the end of the process, is an extra step in
15 which the solvent with formaldehydefumes must be disposed
of in a safe manner.
It is an aim o~ the invention to provide a method ~or
making expanded paper honeycomb core material moisture- or
20 waterproof which overcomes these disadvantages.
According to the invention, this aim is achieved by the
measure that the honeycomb core material is provided with
a coating after expansion.
This brings about, that the paper honeycomb core material
is provided with a sealing layer that offers an effective
protection against moisture and water. The coating can be
applied in one layer, so that repeated immersions are not
30 necessary. Nor does ~ormaldehyde have to be used any more.
By applying the coating a coating-paper-coating-sandwich
is obtained, which produces a lighter and stronger t
construction as compared to impregnated paper. This method
is cheaper than the one in which strips o~ paper are
35 provided with a coating before they are glued to one
another and expanded, as less coating material is needed,
that is not on the glued areas, and as the usual glues may
CA 022l76~8 l997-lO-07
W O96/31339 PCT~L96/001~0
-- 3
be used. In addition, expenses are saved because spoilage
of honeycomb core material during production has not yet
been provided with the cost price raising coating.
The coating is preferably applied as a powder of a polymer
material, as, in this way, it is possible to apply a
coating of essentially equal thickness across the entire
length of the honeycomb cells within a short time.
In an advantageous embodiment of the method, powder is
applied by providing the paper honeycomb core material and
the powder with an opposed electric charge, as a result of
which a predetermined amount of powder can be applied to
the honeycomb core material simply and quickly, by al-
lowing the honeycomb core material to attract the powderelectrically.
In this case it is advantageous to moisten the paper
honeycomb core material with water before the powder is
applied, as this makes it easier to give the paper
honeycomb core material a suitable electric charge.
Moistening is pre~erably carried out by sprinkling with
water, preferably such an amount of water being used, that
a degree of humidity equal to 15-30 percentage by weight
of the honeycomb paper is obtained. By sprinkling, the
paper easily and quickly acquires an even, suitable degree
of humidity. It has been established that the stated
degree o~ humidity achieves good results in practice.
For the polymer powder, a thermosetting polyester or epoxy
_ is preferably used, since a strong moisture- and
waterproof coating can be made from a thermosetting
polyester or epoxy or a mixture of the two.
In an advantageous manner the honeycomb core material is
heated a~ter the thermosetting powder has been applied, in
CA 022176~8 1997-10-07
W O 96/31339 PCT~L96/00150
order to let the powder turn into a hard and thick coating
and to stabilize the coated honeycomb core material in the
expanded state, in which the heating is pre~erably carried
out by means of hot air or by in~rared radiation in order
to obtain quick and even heating.
r~
The invention also relates to the paper honeycomb core
material that is obtained with the method described above.
