Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
The present invention relates to a process for
producing foamed material from waste paper and similar materials.
Paper, cardboard, waste cardboard or materials with similar properties
are usable as raw materials in the same way, either sorted according
to type or as a raw material mixture. The invention is intended to
preferably make a contribution to environmental protection by the
recovery and treatment of secondary raw materials that are available
in substantial quantities.
It is possible by the process according to the
invention to produce different final products, in particular
construction elements for thermal insulation and for sound damping, as
well as elements for vibration absorption and shock absorption. Other
final products include roof covering panels or wall lining panels,
composite boards, and other shaped bodies for use as filler material
for insulation and packing purposes. Special treatments to the final
product are possible by adding, for example, hydrophobic agents,
fireproofing agents, rot-inhibiting agents or reaction aids.
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The above enumerations are to be understood as given by
way of example.
In the state of the art it is known that several
processes for the manufacture of such products are already known.
Furthermore, suitable devices for carrying out such processes for and
producing the final product itself can be found in the documented
state of the art. With respect to the state of the art, reference is
made to the following listed documents:
DE 31 14 527; DE 33 07 736; DE 34 20 195; DE 34 44 264; DE 35 10 214;
DE 35 22 395; DE 36 24 164; DE 36 41 464; DE 37 04 309; DE 37 18 545;
DE 39 00 289; DE 40 25 694; DE 41 35 069; DE 92 00 066; DE 92 16 620;
DE 93 03 498.
An important known process step is the preparation of a
liquid or aqueous pulp from these raw materials, which is referred to
below as the "paper pulp", including the steps of cutting up and
mixing of the components.
These preparatory measures are not the subject matter
of the invention, but are only made use of. Of special importance is
the heat treatment of the paper pulp made available.
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The known technical solutions for the heat treatment of
the paper pulp are, without exception, based on conventional
processes, devices or installations.
The term "conventional" is understood to mean the
following:
- the expansion of the mass is achieved through
the introduction of heat at temperatures from 120°C to 140°C;
- the heat treatment at temperatures above
200°C with water vapor saturation in an autoclave;
- the thermal and mechanical introduction of
energy in the extruder; upon exiting from the extruder, the mass foams
up due to the drop in temperature and pressure;
- heating under pressure application in
general; and
- treatment with hot air and steam.
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All of these processes are characterized by high energy
requirement, which often is associated with considerable financial
expenditure in terms of equipment, which in turn results from the
large number of process steps. These processes predominantly work
discontinuously because the large amounts of energy required cannot be
introduced within the shortest possible time. The evaporation of
liquid is characterized by a certain time delay and inertia. For this
reason, the prior art efficiency is adequate only for a limited number
of applications.
The after-treatment and special treatments, if any,
are, like the preparation of the paper pulp, not the subject matter of
the process according to the invention. In this regard, tested means
and methods are used.
SUMMARY OF THE INVENTION
It is an object of the present invention to reduce the
time required to carry out the known processes, which is a
precondition for permitting the process to be carried out
continuously, and for permitting a reduction in the financial
expenditure for equipment and for a reduction in any heat losses.
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According to the present invention, the above object is
achieved as follows:
It is known that a paper pulp mixed with liquid foams
up during treatment with thermal energy, when the liquid starts to
evaporate. The foaming effect can be increased by further additions
of thermal energy.
This process is based on the fact that the change of
state of a liquid into the gaseous phase is associated with a
considerable increase in volume. The vapor flowing off from the paper
pulp creates the number of flow paths that are required to enable the
vapor to escape. The solidification of the paper pulp begins upon the
withdrawal of the liquid therefrom and permits the flow paths to
remain preserved as hollow spaces.
The solution of the prior art problems according to the
present invention starts at this point.
According to the invention, the paper pulp is subjected
to microwave radiation instead of being subjected to the conventional
heat treatment, with such microwave radiation preferably being in the
range of 915 MHz and 2.45 GHz.
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The advantages of this method for introducing energy
are based on the fact that with microwaves, as opposed to heat
radiation, it is possible to realize very high energy densities. In
addition, the energy acts on the paper pulp not merely at the surface,
but also penetrates into the paper pulp and directly heats the liquid,
causing the latter to evaporate. With a suitable high energy density,
the heat treatment takes place with such violence that the resulting
vapor, by creating paths for its expulsion from the volume of the
paper pulp exposed to this penetrating radiation, leads to an
expansion of the paper pulp mass, which creates porosity within the
mass.
Since this process, due to the evaporation of the
liquid, is simultaneously a drying process, a solidification of the
material starts as the volume of the paper pulp increases, with such
solidification stabilizing the hollow spaces and porosity created in
the paper pulp. The process can be supplemented by adding foaming
agents and stabilizing agents.
The process of the invention is based upon the
following physical characteristics, the technical implementation of
which is the subject matter of the invention.
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Microwave radiation is capable of penetrating through
materials with a suitable dielectric constant, for example such as
glass or paper, without loss of energy. Other materials absorb
microwave radiation, i.e., such materials consume the energy of the
microwaves. This process is also referred to as coupling to the
microwaves. This takes place in the molecular range and is manifest
by a heating of the material activated by the microwaves. Such
material includes, for example, water in the liquid state.
Accordingly, in a water-containing paper pulp, the energy made
available by the microwaves is directly and only transmitted to the
water molecules. The heat is generated in the volume subjected to the
penetrating through radiation. Thus in the interior of the body, heat
is dissipated, and does not have to be transmitted from the outside to
the inside as with a heat transfer using a temperature difference as
the propelling force. For this reason, a body is uniformly heated
under microwave radiation throughout the entire volume irradiated.
Due to heat losses at the surface of the body, the volume-specific
amount of heat stored can be even greater in the interior of the body
than near its surface. With suitable energy density leading to
evaporation of the water, an excess pressure is generated in the
interior of the through-irradiated body volume, such excess pressure
leading to expulsion of the water vapor in the direction of the
surface of the body.
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If the irradiated body is dimensionally unstable, as it
is the case with the paper pulp considered here, flow paths are
created in the body in the form of hollow spaces by the steam being
expelled. The body takes on a porous structure and breaks up
considerably. Its volume increases. Since a hardening process starts
in this stage at the same time due to drying of the material, such
voluminous and porous structure remains preserved.
Certain additions such as binding agents or foaming
agents promote this process.
This means a substantial simplification of the after-
treatment in terms of process engineering. If necessary, after-
treatment process steps are eliminated.
A technical procedure for the implementation of this
process for the manufacture of foamed material, particularly of shaped
bodies, depends on the desired result of the production, and it can be
carried out both batch-wise (discontinuously) and continuously. This
depends upon the shape of the mold.
In terms of equipment, it is necessary to make sure
that a largely unobstructed irradiation with microwaves is possible,
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taking into account the increase in volume of the paper pulp, and that
the water vapor can be expelled from the mold unhindered at the same
time.
Further treatment steps can be used in the process for
producing a foamed material product according to the invention. For
example, there can be a vacuuming off of the vapor of the liquid
generated due to the introduction of microwave radiation. This is
followed by condensing the vapor back to a liquid; and then recycling
and reusing the liquid again for the treatment of the paper pulp.
While several embodiments of the present invention have
been shown and described, it is to be understood that many changes and
modifications may be made thereunto without departing from the spirit
and scope of the invention as defined in the appended claims.
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