Note: Descriptions are shown in the official language in which they were submitted.
Mo-2993
LeA 24,844
A PROCESS FOR THE PRODUCTION OF MOLDINGS OF
DIFFERENT ELASTICITY OR HARDNESS FROM AT
LEAST TWO 5 LIQUID, FOAM-FORMING REACTION MI~TURES
BACKGROUND OF THE INVENTION
The present invention relates to a process for
the production of moldings and more especially cushions
of different elasticity or hardness from at least two
liquid foam-forming reaction mixtures, more especially
polyurethane foam reaction mixtures. A first and at
least a second reaction mixture are introduced into a
mold cavity and left to react to form a molding having
zones of different elasticity or hardness before the
molding is removed from the mold.
The production of moldings, particularly
cushions, by in-mold foaming is gaining in popularity
over the method of cutting to size because it i8
efficient and involves virtually no losses. The
cushions can be subsequently provided with a fabric
covering. Alternatively, the covering can be placed in
a deep-draw die and directly back-foamed.
Various processes have been proposed for the
production of moldings having zones of different
hardness. According to EP-Bl-68,820, a second foam
mixture is directly introduced onto a first foam mixture
at a time corresponding to an expansion in volume of the
first mixture of ~100% to ~2300%. One or more
relatively hard zones are thus formed within a
relatively sot foam. In this process, the second
reaction mixture cannot be introduced until the first
reaction mixture has undergone the necessary expansion
in volume. The cycle times of the foaming process are
thus undesirably lengthened. In addition, the actual
objective, namely covering relatively hard zones with a
layer of soft foam to increase comfort, is di~ficult to
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achieve because the expansion of the soft layer remains
limited in certain zones to only narrow thicknesses
which only inadequately impart the desired properties.
In addition, difficulties also arise with regard to the
5 reproducibility of these coverings.
In another process (U.S. Patent 4,190,697), a
mixture forming a relatively hard foam is fi~st
introduced into the mold where it is allowed to begin
foaming. Afterwards, a second mixture forming so~ter
10 foam is introduced when the first mixture has reached 10
to 80% o its full foaming capacity. The second mixture
permeates the first mixture during introduction and
causes it to swell. Both mixtures then react and form a
polyurethane foam article having zones of different
15 density. The disadvantage of this process is that the
permeation and underflow of the first reaction mixture
is irregular so that the properties (and, primarily the
indentation hardness) of the moldings obtained are not
sufficiently reproducible.
Accordingly, the object of the present
invention was to provide a process which makes shorter
cycle times possible for good reproducibility in the
development of the zones of different hardness or
elasticity.
BRIEF DESCRIPTION OF THE DRAWINGS
Figures 1 and 2 illustrate the production of a
seat cushion.
Figure 3 shows the finished seat cushion.
Figures 4 to 10 show further embodiments of
30 seat cushions with side webs which can be produced by
the new process.
Figure 11 is a longitudinal section through a
seat cushion having foam zones of three dif~erent
hardnesses.
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DESCRIPTION OF THE INVENTION
According to the invention, the above object is
achieved in that, on introduction into the mold, the
second reac~ion mixture is allowed to cream up to such
5 an extent that, by the time it comes into contact with
~he first reaction mixture, it already has a lower
density than the first reaction mixture. The second or
further reaction mixture(s) is introduced onto and/or
next to the layer(s) formed by the first or further
10 reaction mixture(s).
More particularly, the present invention is
directed to a process for the production of a molding
from at least two different liquid foam-forming reaction
mixtures comprising:5 (i) introducing a first foam-forming reaction
mix~ure into a mold,
(ii) introducing a second foam-forming reaction
mixture onto and/or next to the layer formed
by said first reaction mixture, the
introduction of said second mixture being
such that said second mixture is so advanced
in its expansion that by the time it contacts
said first mixture, said second mixture
already has a lower density than said first
mixture,
(iii) allowing said reaction mixture to react to
form a molding having zones of different
elasticity or hardeness, and
(iv) removing said molding from said mold.
In this way, any formulation may be used for
the first reaction mixture which opens up new
applications because, through the introduction of the
second or further reaction mixture(s) with correspond-
ingly lower density, the course of the process is made
35 largely independent of the state of the first reaction
mixture at the moment it is contacted by the second.
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Another effect is that 9 on contact with the first
mixture by overflowing from the side or by direct
application to the layer of the first mixture, no
turbulence is generated so long as the force of impact
5 is not too great. In other words, the introduc~ion of
~he second mixture has to be carried out with some care.
On the other hand, even the mixing units widely in use
today guarantee sufficiently low discharge rates to
avoid turbulence of the various reaction mixtures.
10 Where a third or further reaction mix~ure(s) is/are
introduced, this/these mixture(s) hasthave to be
balanced in regard to its/their creamy consistency in
such a way that, at the moment of contact with one of
the other reaction mixtures, it ~eets the lower density
15 requirement.
The second or further reaction mixture(s) may
be introduced at the same time as or after the first or
other reaction mixture, depending on requirements.
Simultaneous introduction is advisable in particular
20 when the various reaction mixtures are introduced into
various regions. In this connection, it is quite
possible to charge two regions separated for example by
a third region with the same reaction mixture while the
region lying in between is charged with another reaction
25 mixture. If it is desired to in~roduce another reaction
mixture directly onto a first reaction mixture, it is
best to do this after an appropriate time interval so
that the mixture previously introduced has already
spread out extensively over the region in question.
Where and when the softer or the harder
foam-forming reaction mixture is introduced first or
whether the two are introduced at the same time depends
on various factors, but primarily on where in the mold
cavity the corresponding zones of different hardness are
35 to form.
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In particular, it is possible by the new
process to obtain rigid zones covered on one side or all
sides with layers of any thickness of flexible foam or
vice versa. Since the second reaction mixture, through
5 its creamy consistency, may have reached its maximum
degree of foaming before the first reaction mixture
(providing appropriate activators are used), it is
possible for the still relatively liquid first reaction
mixture to be laterally forced upwards at least to a
10 certain level or even completely to surround the foam
formed by the second reaction mixture. Such partial or
complete coverage in any desired thickness may readily
be determined by tests and depends largely on the
geometry of the molding or mold cavity and on ~he
15 quantities involved.
Suitable raw materials for the production of
the moldings in question are, in particular, any of the
usual polyurethane foam systems (cf. also Kunststoff-
Handbuch, Vol. VII, Polyurethane, by Vieweg and
20 Hochtlen, ~arl-Hanser-Verlag, Munchen 1966, in
particular pp. 440-503 and 569-571). The differences in
hardness between the individual reaction mixtures are
generally adjustable through index variation and/or
through the formulations, for example through the filler
25 content, crosslinker variation, gross density ratio, and
the like. The rapid creaming of the second mixture is
obtained by adding to this formulation additives which,
when the components are mixed, spontaneously evo~ve CO2
or any other compound gaseous under the reaction
30 conditions. The amine-carbon dioxide adducts described
in EP-A-121,850 are preferably used. However, it is
also possible to produce a froth foam. The creaming can
also be effected or accelerated by loading one o~ the
reaction components with gas, and in particular with an
35 inert gas such as CO2 or N2. The component can be
charged with gas at various gas pressures by
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substantially any dissolving or dispersing means.
Another possibility is to prepare the second reaction
mix~ure correspondingly early, i.e. to introduce it with
delay so that it has already acquired the necessary
5 lower density by the time it comes into contact with the
first mixture. In this sense, the second reaction
mixture may be prepared even earlier than the first so
that it may be introduced, for example, at the same time
or immediately after the first mixture has spread out to
10 form a layer.
The process according to the invention is
particularly suitable for the production of vehicle seat
cushions having side webs. The novel aspect of this
particular application is that a first foam-forming
15 reaction mixture is poured into those parts of the mold
cavity corresponding to the webs and onto that part
corresponding to the seat surface, followed by at least
a second foam-forming reaction mixture so advance in its
expansion that, by the time it comes into contact with
20 the layers of the first reaction mixture, it has already
acquired a lower density than the first reaction mixture
so that, at best, it sinks in but does not permeate the
first layer. In this way, it is possible to produce
both uncovered seat cushions and also those having
! 25 back-foamed coverings. Through the use of several
mixing heads for preparing the same reaction mixture or
different reaction mixtures, the new process may be
varied very widely in its application.
The new process is illustrated by a practical
30 example of its application for the production of a
cushion for vehicle seats in conjunction with the
drawin~s.
The new process can be used to produce a seat
cushion of the type shown in Figure 3 with side webs 1,
35 2 and seat section 3. The outer zones 4, 5 of the side
webs consist of a relatively hard ~oam, e.g., one having
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a density of 50 kg/dm3 and a compression hardness
according to DIN 53 577 of 7.3 kPa. The seat section 3
is separated from the side webs 1, 2 by grooves 6, 7. A
zone 8 of relati~ely soft foam, e.g., one having a
5 density of 50 kg/dm3 and a compression hardness of 3.3
kPa, extends over the seat section 3 beyond the grooves
6, 7 into the side webs 1, 2 and forms a firm, but
clearly defined union with the zones 4, 5. The to~al
volume of the seat cushion is, e.g., 32 dm3 of which,
10 e.g.,
25 dm3 is occupied by the softer foam corresponding to
the zone 8.
The seat cushion is produced as shown in
Figures 1 and 2. The mold 11 has a cavity 12 which
15 represents the seat cushion upside down, as also shown
in Figure 3. The regions 13, 14 correspond to the side
webs 1, 2, the region 15 to the seat section 3 and the
dividers 16, 17 to the grooves 6, 7 of the seat cushion.
By means of two mixing heads 18, 19 (Figure 1), the
20 reaction mixture forming the softer foam is introduced
into each of the two side web regions 13, 14 in a
quantity of e.g., 180 g. Thereafter (Figure 2), the
mixing heads 18, 19 are placed over the seat region 15
where the same reaction mixture is introduced in a
25 quantity of, e.g., 1150 g. The dividers 16, 17 prevent
the reaction mixture from flowing off into the side web
regions 13, 14. By means of two mixing heads 20, 21,
the reaction mixture forming the harder foam is
introduced ont the first reaction mixture already
30 present in the side web regions 13, 14 at the same time
as the seat region 15 i8 being filled by the mixing
heads 18, 19. The density of the first reaction mixture
at the moment of contact with the second reaction
mixture is, e.g., 0.8 kg/dm3 while the second reaction
35 mixture is introduced in such a creamed statè that it
has a lower density of, e.g., 0.3 kg/dm3, at the moment
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of contact with the first reaction mixture~ The time
delay between the ~eginning of introduction of the first
reaction mixtùre and contact by the second is in the
case of the numbers exemplified abo~e 7 seconds. After
5 closure of the mold 11, the reaction mixtures foam
completely to form the seat cushion shown in Figure 3.
In the case of ~arious numbers exemplified
above, the first reaction mixture forming the softer
foam had the following formulation (pbw = parts by
10 weight):
Component A
100 pbw of a polyether obtained by addition of
propylene oxide and then ethylene oxide to
trimethylol propane, having a functionality of 3,
a primary OH content of about 80% by weight and
an OH number of about 30;
3.1 pbw water;
0.2 pbw bis-dimethylaminoethylether;
0.4 pbw of a commercial foam stabilizer consisting of
a mixture of low molecular weight siloxanes
(Stabilisator KS 43, a product of BAYER AG,
Leverkusen, Fed. Rep. of Germany);
0.8 pbw triethylene diamine (33Z in dipropylene
glycol).
25 Component B
45.3 pbw of an isocyanate containing approx. 65Z by
weight 4,4'-dimethylmethane diisocyanate and
approx. 20% by weight 2,4'-diphenyl methane
diisocyanate and approx. 15Z by weight polymeric
MDI; NCO content approx. 32.5Z. Components A and
B were mixed at an NCO index of 85.
The second reaction mixture forming the harder
foam had the following formulation:
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Component A
100 pbw of a polyether obtained by addition of
propylene oxide and then ethylene oxide to
trimethylol propane, having a functionality of 3,
a primary OH content of about 80% by weight and
an OH number of about 30;
3.1 pbw water;
0.2 pbw bis-dimethylaminoethylether;
0.4 pbw commercial foam stabilizPr consisting of a
mixture of low molecular weight siloxanes
(Stabilisator KS 43, a product of Bayer AG,
Leverkusen, Fed. Rep. of Germany);
0.8 pbw triethylenediamine (33Z in dipropylene
glycol);
15 4.0 pbw of the adduct of C02 with N-methyl
ethanolamine.
Component B
70.6 pbw of an isocyanate containing approx. 65% by
weight 4,4'-diphenylmethane diisocyanate and
approx. 20% by weight 2,4'-diphenylmethane
diisocyanate and approx. 15~ by weight polymeric
MDI for an NCO content of approx. 32.5Z.
Components A and B were mixed at an NCO index of
110 .
In the other embodiments of seat cushions
produced by the new process which are shown in Figures 4
to 10 (in section in the normal position), the zones of
softer foam are hatched at broad intervals while the
zones of harder foam are hatched at narrow intervals.
In Figure 11, the seat section consis~s of a
ioam of medium hardness (which i8 also at the back of
the knees). On the underneath of the seat cushion,
however, there is a very soft zone. The third zone is
the hardest.
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Although the invention has been described in
detail in the foregoing for the purpose of illustration,
it is to be understood that such detail is solely for
that purpose and that variations can be made therein by
5 those skilled in the art without departing from the
spirit and scope of the invention except as it may be
limited by the claims.
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