Note: Descriptions are shown in the official language in which they were submitted.
Fibrous mat for hot moulding to moulded articles
The invention relates to a fibrous mat for hot
moulding to moulded articles.
Multilayer fibrous mats, particularly those with
special surface coatings are known. In particular, a
multilayer fibrous mat for producing moulded articles in
a press mould by exposing the fibrous mat to pressure
and elevated temperature and formed from cellulose,
lignocellulose or similar fibres is known, whose two
surface layers are also formed from a tangled fibre
fleece and provided with at least a proportion of
thermosetting synthetic resins. The thermoplastic
binder-containing central tangled fibre layer and the
two outer surface layers provided with thermosetting
binders are produced here by the layerwise placing of
the mat material on a conveyor belt and in the state
moulded to moulded articles are simultaneously present
in the form of a firm union or sandwich o~ said multi-
layer arrangement (P 32 33 385).
However, it has been found that the additional
gluing of the surface layers with a thermosetting
material which takes place in this known process
according to the partial flow principle during the
production of the mat and moulding is at least partly
~5 absorbed by the absorbent central layer, which is dis-
advantageous in that in such known three-layer mats, the
disadvantage thereof, i.e. the thermal and mechanical
surface treatment, is lost again through the thermoset-
ting binder used therein undesirably migrating into the
central layer. This effect can only be compensated by
the addition of larger thermosetting binder quantities
to the surface layer fibres, which would make the desi-
red end product much more expensive.
Another known process for producing insulating
plates, using mineral fibres as a basis~ can be advan-
tageously realized in that the non-woven fabric is
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applied to an also moving surface ~ibre fleece during
production, so that during compression the insulating
plate is joined to the fleece carrier (DE-OS 28 53 316).
In product-dependent manner, particular attention
has long been paid to the processing of wood fibre
materials of the present type and also non-woven fabrics
comprising natural or mineral fibres and the like to
plates or three-dimensionally shaped products~ The
nature of the surface treatment can range from the
lo simplest resin enrichment, primers or varnishes to
printing and lining with films or lamination with
plastics and the like.
The application of surface layers to supporting
central layers, either in the form of special surface
layer gluing treatments, additional lining material or
the like, generally leads to the desired improved sur-
face characteristics, but is generally also linked with
a sealing of the surface in the sense of being imperme-
able e.g. for gases or liquids, which can be disadvanta-
~ geous in many cases and particularly for the processing
of such mats to moulded articles excludes certain pro-
cedures or other technically simply performable process
steps. Reference is made in exemplified manner in this
connection to the production-favorable vacuum deep draw-
ing process for co-ordinating such moulded articles with
thermoplastic films, as well as to certain characteris-
tics of completely moulded parts, which are considered
to be more advantageous when used as linings in pas-
senger areas of motor vehicles if they ensure a certain
air permeability and moisture absorption, which can
significantly improve the climatic conditions within
such passenger areas.
The problem of the present invention is therefore
to so further develop a three-layer fibrous mat of the
aforementioned type that, in the case of minimum use of
higher-grade materials both on the fibre side and on the
binder side and with minimum manufacturing expenditure
contributes to the provision of moulded articles, whose
surface is both insensitive to wetness and breaths mois-
ture and whose thermal, chemical and physical charac-
teristics can compete with those of comparable surface-
sealing coatings or coverings.
According to one embodiment of this invention the
invention provides a fibrous mat for hot moulding to
moulding to moulded articles, comprising a central
tangled fibre layer treated with a binder and in each
case one heatproof, binder-containing tangled fibre
surface layer Oll the two surfaces of the central layer,
the surface layers forming a firm sandwich with the
central layer, characterized in that the surface layer
of at least the unmoulded mat has a higher tensile
strength than the central layer and that the surface
layer in the mat moulded to the moulded article is
constructed as a moisture-regulating membrane, the
weight per unit area of the binder-free portion of the
heatproof tangled fibres of the surface layer being
between 10 to about 100 g/m2 and the individual tangled
fibres with a proportion of about 100 to about 200% by
weight, based on this weight per unit area, are coated
in fibre-enveloping manner with a binder already pre-
~5 condensed prior to the moulding of the fibrous mat, so
that the diameter ratio between the coated and uncoated
tangled fibres of the surface layer is between 1.4 and
1.75.
In a preferred form of the fibrous mat, the mat is
characterized in that between the heatproof, binder-
containing tangled fibre surface layer on the surfaces
of the central tangled fiber layer for the firm reci-
procal sandwich of the layers is provided a heat-resis-
tant coupling agent in point, line, grid or grating-like
distribution, the sandwich surface portions not subject
to the action of the coupling agent being more than 15%
of the total surface.
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Thus, according to one preferred embodiment of this
invention, the invention is based on surface layers
fibres which can be substantially of a random nature,
e.g. can be in the form of organic or inorganic fibres
and have a natural or synthetic origin, whereby no
requirements are made with respect to their moisture
absorptivity or sensitivity to other environmental
influences. In addition, they need not be inexpensive
to manufacture, because only small amounts are used
compared with the supporting central layer (weight per
unit area of the total mat, as a function of applica-
tion, 1000 to 2000 g/m2).
The presently required, high-grade surface seallng,
particularly with respect to high thermal stability, is
ensured by coating the adequate length of the present
individual fibres of the tangled fibre surface layers,
preferably in the form of staple fibres, with a thermo-
setting binder in a given ratio of the fibre diameter to
the binder coating. Simultaneously it is possible to
ensure gas permeability and a moisture permeability
determinable by the surface density of the surface layer
on the finished moulding, because the individual fibres
coated with a thermosetting binder within the tangled
fibre fleece give between them homogeneously distribu-
ted, screen-like passages. Due to the fact that the
fibre-enveloping binder is partly precondensed, there is
no migration of binder into the central, relatively
absorbent tangled fibre layer, which is subject to the
action of the thermoplastic binder, so that there is no
need to thin the same in the surface area and its posi-
tive characteristics have their full effect.
As a result of precondensing, the viscosity of the
thermosetting binder in the surface layers can also be
previously defined for the moulding process. The quasi-
moisture absorption possibility of the central tangled
fibre layer through the surface layers acting in
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membrane-like manner can be precisely "dosed'1 and adjus-
ted in optimum manner to the individual application.
The heat-resistant enveloping of the surface layer
~ibres only seals the individual fibres in moisture-
tight manner, but not the tangled fibre fleece formed
therefrom. During molding, the fibres are not partly
dissolved again and do not come into direct contact with
the hot surface of the mould parts. They retain their
predetermined strength characteristics substantially
lo independently of the parameters for optimum moulding.
The precondensed binders used for enveloping the indi-
vidual fibres of the surface layers have a viscosity
such that there is not a complete sealing of the tangled
fibre layer, such as is the case with film linings. The
moisture-regulating membrane action of the surface
layers equals out high temperature fluctuations and
moisture changes within the passenger area of cars lined
with moulded articles made from such multilayer mats in
a manner pleasant for the occupants. It has surpris-
ingly been found in this connection that even if with
prolonged wetness action, moisture absorption in the
central layer, e.g. of lignocellulose fibres, has taken
place to a relatively high extent, the thickness swel-
ling of the moulded article is approximately one decimal
power lower than with comparable moulded articles which,
in place of the membrane-like surface layers, either
carry film seals or are otherwise completely air and
moisture-tight as a result of binders or coatings.
The moisture-regulating membrane, even if the
fibres of the central layer are sensitive to moisture,
makes it possible to so regulate and keep low the
moisture absorption or characteristics of the moulded
article, that there are no dimensional changes due to
swelling if moisture occurs in superfluity on the moul-
ded article. Due to the fact that the original charac-
teristics of the individual, completely sealed fibres of
O~
the surface layer fleeces are fully retained and in par-
ticular due to the fact that the high-grade thermoset-
ting gluing of said surface layers remains almost com-
pletely therein and does not partly diffuse into the
central layer, the moulded articles have excellent
strength characteristics and in particular a high impact
strength, as well as bending strength and bursting limit
values, which are otherwise only attainable with much
higher thermosetting binder proportions.
Following the moulding of the surface layers,
together with the tangled fibre layer to give moulded
articles, said surface layers have a microporosity
which, in per se contradictory manner and despite a
relatively high absorption capaclty for moisture within
the moulded article, ensures the aforementioned highly
stable accuracy to size of the moulded article.
The precondensed, thermosetting binder of the sur-
face layer joins the fibres thereof at their crossing
points, so that the surface layer in
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2g
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the unmoulded state can be given a higher tensile strength than the
central layer. Thus, during the moulding of the mat to the moulded
article, the shaping or deforming process i9 stabili~ed, particularly
if, such as e.g. is the case with wood fibre mats, the mat is plast-
icized by evaporation during which the thermoplastically bound fibresof the central layer largely lose their binding, whereas the binding
characteristics of the precondensate of the surface layers is largely
retained. The permeability of the surface layer makes it posslble,
to retain conventional technology for wood fibre mats and namely in
10 the case of extended shaping possibilities, improved moulded article
characteristics and due to the stabiliæing action of the surface
layers on the shaping process even with reduced wastage.
It is advantageous to use plastic fibres for the surface layer fibres
which have a softening point above 200 C~ Unlike many mineral fibres,
such fibres have high lateral strength characteristics and are not
brittle, even at low temperatures, so that moulded articles with high
impact strength in a very wide temperature range are obtained. If
increased demands are made on the strength and bending resistance of
the parts, it may be appropriate for the surface layers to be at least
partly formed from glass fibres, apart from ceramic fibres.
The bending strength and impact strength of the moulded articles can
also be improved if at least part of the fibres of the surface layer
are natural fibres. As natural fibres generally have an increased
moisture absorption during storage, it is appropriate to pretreat them
with hydrophobing agents prior to binder addition and precondensation
thereof. Improved strength characteristics of the moulded articles
can in particular be obtained if the fibres forming the tangled fibre
fleeces of the surface layers, are on a~erage longer than 20 mm.
On moulding the fibrous mats to moulded articles, the tangled fibres
of the surface layers are further bound and strengthened by the precon-
densed resin at the fibre crossing points to the extent that this has
not taken place through the precondensation and are consequently able
to absorb tensile forces to an even greater extent and optionally
~ 3~30~3
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improve the mechanical characteristics of the moulded articlesO
Yirtually all known fibre types can be used for producing the central
layers, if the temperature at which the fibrous mat is moulded to
moulded articles can be borne by the fibres without suffering damage
~his also applies with respect to the binders used in the central
layer. Generally lower demands are made on the quality of the fibres
and binder of the central layer than for comparable known fibrous mats,
particularly because the moisture-regulating characteristics of the
surface layers also permit the use of more moisture sensitive fibres.
The increased viscosity of the fibre-enveloping binder during final
moulding not only produces the desired microporosity, but also a fibre
diameter-corresponding surface roughness which, in conjunction with
the microporosity, ensures a better adhesion of surface finishes and
laminating adhesives.
lS Particularly if heat-resistant, crosslinked coupling agents are used
between the surface layers and the central fibrous fleece mat, the des-
ired gas permeability can suffer. This can be obviated in that said
coupling agent is applied in the form of point, line, screen or grating-
like patterns, the surface proportion not wetted by the coupling agent
`_20 being greater than 15%. This makes it possible to achie~e a satisfactory
gas permeability of the coupling agent layer, without the heat-resistant,
surface adhesion of the surface layers being impaired. Thus, tensile
forces during shaping can be transEerred between the surface layers and
the central fibrous fleece mat. The pattern-like coating with coupling
agent can e.g. be carried out without difficulty by perse known pressure
rollers or other prior art means, such as pressure screens and the like.
The "lattice constants" of the adhesive pattern can be between a few
milLimetres and a few centimetres, as a function of the fibre type,
length and deformation problem.
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