Note: Descriptions are shown in the official language in which they were submitted.
3~s~3
~ he present invention relates to an important improve-
ment obtained in -the manufacture of bloc~s of polyurethane foam.
Specifically, it relates to obtaining blocks of polyurethane foam
which do not have the densified bottom of the blocks obtained by
the usual process.
As is known, polyurethane foarn is a plastic which has
acquired increasiny importance over recent years. It is a pro-
duct of many uses in such different industrial sectors such as,
for example, the automotive industry and the textile industry.
In Spain, the distribution of consumpti.on of polyurethane foarn
is represented by the following approximate percentages:
Upholstery 40%
Mattresses 38%
Automative 14%
Textile industry 3%
Others (containers for
foods" toys, etc) 5yO
Total 100%
Polyurethane foam is basically the product of the re-
20 action of a polyol with a polyisocyanate, which are the princi- ~ -
pal ingredients. Other products are also necessary, such as
water, catalyst, activator, blowing agents, dyes, etc. As is
known to experts in -the art there is a great variety of types of
foams, which is the result of the possibility of variation in the
nature of the various components of which they are made, and in
their relative proportions. ~mong the characteristics which can
be varied, according to the selection of components and propor-
tions, are stiffness, density, resistance to degradation, tensile
strength, cell size, etc. Among the parame-ters involved, of spe-
cial importance are -the nature of the polyol and of the polyiso-
cyanate, and the ratio between polyol/polyisocyanate/water/blow-
ing agent.
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Industrially, polyurethane foam is obtained in the form
of blocks. These blocks can have a length of even more than 100
metres, their width normally bein~ 2 metres anc1 their height
varying between 80 cm and 130 cm. The shape of the cross-section
of the blocks of foam obtained by the conventional process is re-
presented in Figure 1 of the drawings, which shall be described
below on in this specification.
Independently of the type of foam produced, a serious
problem associated with the manufacture of the block is the den-
sification occurring in the bottom thereof. As a result of thisdensification it is necessary to waste an important part of the
finished material, because its density is notably greater and its
mechanical characteristics are very much inferior to those of the
rest of the block.
As experts in the art will admit, frequently the per-
centage of the densified area comes to be 5% by weight, even
reaching 7%, in relation to the total weight of the block.
The disadvantage supposed by obtaining blocks of foam
having a densified bottom is obvious, if the following fac-tors
are considered:
a) The amount of wasted raw material can be of consider-
able importance, in light of the fact that the daily production
of an average-sized polyurethane foam installation exceeds
20,000 kg.
b) There is the added cost of trimming with proper mech-
anical means, preferably saws designed specifically for this pur-
pose, the densified layer of foam which can have a length of more
than 100 metres (the length of the block~, a width of two metres
and a thickness of 10-15 mm.
c) The difficulty of marketing said trimmed densified
layer as a by-product.
d) Since an important part of the components OL the
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foam is of petrochemical origin, the need is readily seen to
economize those materials to the maximum considering the
present high cost of petroleum and its derivatives.
It is deduced from the foregoing that the object
of obtaining blocks without the lower densified area is highly
desirable for the polyurethane foam industry.
me preceding problems and inconveniences are
solved by the process of the invention which provides a block
. without the densified area, thus attaining notable utilization
10 of the raw materials and a substantial saving in manufacturing ~ -
costs.
According to the invention there is provi.ded a
: process for eliminating densification of the bottom area during
the manufacture of blocks of polyurethane foam, in which said
. blocks are produced in a foam-producing installation which
: includes a foaming tunnel, an endless conveyor belt formed of
hinged plates, said belt running through the tunnel, a mixer- ~-
feeder head for depositing a liquid mixture of reactants on ;
said endless belt at a location defining a foam upstream of
said enaless belt, and drawing means made of drawing conveyors
for drawing the polyurethane foam, characterized in that (1)
the endless conveyor belt is made to function for a period of ~ -~
;~ time of between 15 and 90 minutes, at the same time as said : -
endless belt is heated, so that the surface temperature of the
upper portion of said belt, which constitutes the floor of the ~-
tunnel, passes from room temperature to a temperature Tp of
between 60 and 80C; (2) the movement of the endless belt is
stopped, a web of material is placed on the belt to be inter- -
posed between the foam and the plates of the belt, and
immediately feeding is begun from the mixer-feeder head of the
mixture of the reactants constituting the foam upstream of said ;.
endless belt, the temperature during this stopped period
decreasing from the value Tp to a value TR; ~3) at the
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moment the value TR is attained the endless belt is again put
into motion, operation is started of devices for supplying and
taking up the web of material which covers the surface of said
endless belt, controlling at the same time the temperature of
the surface of the upper portion o:E the belt forming the floor
of the tunnel so that in a first reaction area situated upstream
on said endless belt it acquires a constant value TR, and in a
second consolidation area another constant value T~, said
temperature values being constant for each type of foam, and
in that the time said temperature is maintained for each type
of foam is determined by the ratio tT = tR ~ tc~ tT being the
total time of permanence of the foam in the reaction tunnel, tR
being the time .it takes a foam element to traverse the reaction
area, said tR being fixed for each type of foam, and tc being
the time it takes a foam element to traverse the consolidation
area, and (4) after leaving the foaming tunnel the block in
. formation undergoes, in at least one area located either before
the drawing conveyors, between them or after the last of said
conveyors which constitute the drawing means, drying in the
~ 20 lower part of the block in a drying area which is held at a
: constant temperature TS higher than TR and Tc, after the passing
of which removal is made of the web of material, thus obtaining
a block of polyurethane foam having no densified bottom and a -
. ~miform surface which does not require final trimming.
In order that the invention may be better understood,
drawings are accompanied in which:
Figure 1 illustrates the cross-section of a block
of foam as obtained by the conventional processO
Figure 2 is a schematic side view of the
installation for producing polyurethane foam blocks in which the
invention is carried out' and finally
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Figure 3 is a graph showing temperature in C
on the vertical axis, and time on the horizontal axis. m e
horizon-tal length CO' represents the time during which, with
the endless conveyor belt of the foaming tunnel in operation
without any feeding of the components of the foam, a hinged
element thereof passes from ambient temperature to a value Tp.
The length o tOI~ represents the time during which said endless
belt remains stopped. The length O"B' represents the time it
takes an element of said belt, upon which foam is being formed,
to pass through the foaming tunnel. Finally, the length B'G'
represents the time it takes an element of the block of foam
to travel the distance between the end of the foaming tunnel
and the end of the drying area.
With reference to Figure 2, the following is a
; description of the conventional process for manufacturing blocks
f l?oly-
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urethane foam. The fundamental parts of the installation are:
A foaming tunnel constituted by an inclined conveyor belt 1,
formed by hinged plates P, the upper or conveying run of said
belt constituting the floor of the foaming tunnel. The rest of
said tunnel is formed by walls 5 and the roof T, in which as may
be seen in the Figure there are three conduits for evacuating the
gases which are formed and/or released during the reaction, such
as C02 and the blowing agent. In the upstream par~ of the foam~
ing tunnel there is a mixer-feeder head MA, in which the various
components of the foam are mixed in the proper proportions and
then fed to the endless belt.
Situated beyond the endless conveyor belt, -the upper
or conveying run of which constitutes the floor of the foaming
tunnel, are several drawing conveyors, represented as 2 and 3 in
Figure 2, which draw the foam formed in the foaming tunnel to an
arrangement of idle rollers 6, from which the bloc~ of foam E is
then cut and stored.
A web, which moves over the surfaces of the conveyors
1, 2 and 3 and has the same width as said conveyors, is inter-
posed between the mass of foam E and said surface of the convey-
- ors. Said web, fed from a supply reel 4, moves a-t the same speed
; as conveyors 1, 2 and 3, and is removed by a take-up reel 4'.
The web can be of paper, polyethylene film or any other material ~ -
which has the necessary properties of strength, stiffness and
; resistance to rupture. The need for said web, which for conve-
nience will hereafter be called "paper web", is because as has
already been said, the moving conveyor does not have a continuous
surface but rather is formed by a plurality of hinged plates ~
having a space between them. Thus the indispensable need for a ~ `
web of paper or of other material is easily understood if it is
borne in mind that the foam ingredients deposited at the start of
the tunnel are liquid at the moment of mixture in the mixer-
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.. ~ ~. . , : .: .
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feeder head, 90 that without the paper web said mixed liquidwould pass into the hinges o-f the endless conveyor belt.
With respect to Figure 2 just briefly described, it
must be noted that:
1) it represents merely a schematic representation and
does not include all elements such as reactant tanks, pumps, con-
veyor drive motors, etc.
!
2) in the installation in which the conventional pro-
cess is carried out there are no elements as are represented here
by Sl, S2 and S3, which constitute an aspect of the present in-
vention which will be described farther on in this descrip-tive
specification. This means that conveyors 1, 2 and 3, as well as
the arrangement of idle rollers 6, are contiguous and do not have
the separations or spaces between said conveyors as shown in
Figure 2.
In the said installation, once operation commences at
'~ the progxammed speed, conveyors 1, 2 and 3 as well as the devices
for supply 4 and take-up ~' of the web, the li~uid mixture of
~
reactants is fed at the proper flow rate from the mixer-feeder
head MA. and the liquid mixture of reactants is deposited at the
upstream end of the foaming tunnel at A, upon the web of material
which moves along with the floor of said foaming tunnel. At the
moment of its deposit the reactant mixture is a viscous liquid
which progressively reacts exothermically, increasing its volume
and forming the block of foam. This phase of formation of the
foam is represented in ~igure 2 by an ascending curve the position
of which varies from one type of foam to another. so that point C
of the tunnel surface, which corresponds to the projection of the
end of said ascending curve, can be moved to the right or to the
left of its position in Figure 2, depending upon the reactivity
of the formulation. After attaining its maximum height the formed
block grows progressively in length, being drawn by the movement
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of conveyors 1, 2 and 3. Upon passing the last of the drawing
conveyors, represented by 3 in the Figure, and the paper web
having been removed, the block is cut into pieces of varying size
and after a curing period of 24 hours is stored.
The cross-section of sa:id block is represented in Fig-
ure 1, in which can be seen the densified bottom area F whose
undersurface is not smooth. Therefore said densified bottom F
must be trimmed to remove the densification and surface irregula-
rities, with the inconveniences this supposes as explained above.
The improved process of the invention comprises, as a
first step, running the endless conveyor belt of the foaming tun-
nel without any feeding of the components of the foam, and rais-
ing the temperature of the enclosure of said endless conveyor
belt. The result of this heating is that the temperature of the
upper portion of the belt forming the floor of the cited foaming
tunnel passes, in a period of time ranging between 0 and 90 min-
utes, from room temperature (Ta) to a temperature tTp) of about
80C, This temperature variation is represented in the left part
~1 of Figure 3.
,~ 20 The movement of the endless conveyor belt is then stop-
ped for a proper period of time, the paper web is placed on the
' belt to be interposed between the plates of the belt and the
-, block of foam, and in the upstream part of the said foaming
tunnel the mixture of the reactants which create the foam begins --
1 to be fed through the mixer-feeder head onto the paper web. Du-
ring this period when the belt is stopped the temperature drops
from Tp to a value called reaction temperature TR, fixed for each
j type of foam, at which moment (point A of Figures 2 and 3) move-
ment of the endless belt is resumed, and simultaneously the
'!1 30 devices for feeding and taking up the paper web are activated.
Commencing from this moment, the temperatu~ of the sur-
face of the upper portion of the endless belt of the foaming
3~
tunnel - which is substantially the same as that of the conti-
nuous paper web and consequently substantially equal to that of
the bottom part of the block of foam in formation which rests
upon said paper web - is r~gulated so that in a first area called
the reaction area the aforesaid value TR is maintained, and in a
~ second area downstream of the first, called the consolidation-~ area. a value superior to TR is maintained, hereafter called Tc.
In at least one area downstream of the foaming tunnel,
i the bottom of the consolidated moving block is sub~ected to a10 drying temperature called TS as it passes through a drying area.
In Figure 2 three drying areas are represented as Sl, S2 and S3.
Following the drying process, the paper web is -taken up
and wound onto the take-up device 4', and adhered -to it can be
w seen a thin uniform layer of foam. The block passing to the idle
rollers has a bottom with no densification and a smooth and uni-
form aspect which does not re~uire trim~ming, an indispensable
, operation in the process of the prior art.
The foam in formation runs through the first area, the
reaction area situated upstream o the bel-t, in a previously de-
s, 20 termined time which varies from one foam to another. As has beenindicated, in this area the surface of the endless belt is held -
at a constant temperature TR. which also varies from one foam to
another. ~ ;
The time it takes the foam to traverse the consollda-
tion area depends on the predetermined time in the reaction area.
' The fundamental parameters constituting the object of
;, the invention are defined as follows:
TR = Surface temperature of the reaction area.
C = Surface temperature of the consolidation area.
30 TS = Surface temperature of the drying area.
tR = The time it takes an element of the endless belt, or -the
bottom part of the paper-lined block which rests on it to tra-
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verse the reaction area, that is, from point A to point C repre-
- sented in Figures 2 and 3 of the drawings.
; tC = The time it -takes the aforesaid element to traverse the con-
solidation area; that is, from point C to point B shown in Fig-
ures 2 and 3 of the drawings.
tT = The time it takes the mentioned element to traverse the
~; floor of the foaming tunnel, that is, from point A to point B
shown in Figures 2 and 3 of the clrawings.
If it is borne in mind that the floor of the foaming
tunnel traverses the reaction and consolidation areas, it is rea-
dily seen that
., tT = tR + tC (1 )
and since the value of tR is predetermined for each type of foam,
it is deduced that
tC = tT ~ tR (2)
While the values tR and TR are fixed for a given foam,
they vary from~one foam to another, since as experts in the art
will understand the exothermicity of the reaction of polyurethane
formation varies according to the nature of the principal ingre-
dients, and of the ratio between them. As was indicated pre-
!~ viously, the principal ingredients are polyol and polyisocyanate.
However, the percentage of water in the mixture has an important
role.
fundamental characteristic of the improvements ob-
tained with the present invention is that the surface temperatures
of the three areas fulfil the condition
C ~ TS
, In general, the difference TC - TR - ~ T ranges from
between 10 and 15C, about 10C being preferable. A temp-
ature inside the foaming tunnel in the reaction area above a maxi-
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mum limit can cause cracking of the foarn. and even its combustion.
Keeping in mind that this cracking temperature varies from one
formulation to another, between approximately 45 and 80C, we
have
TR ~ C ~ 80C
The temperature of the drying area TS can attain appa-
rently high values, ranging between 100 and 250C, in very short
periods of time. This is not in contradiction with what was said
; above with respect to cracking and/or combustion, if it is kept
in mind that said surface drying temperature is produced in an
area outside the foaming tunnel, which is traversed by the block
in a very short time.
Although in the foregoing only one drying area has
been mentioned, the invention is not necessarily limited to only
one area of this type and several can exist, although practical
reasons limit this number to three. Nevertheless, a single dry~
ing area is the most preferable.
As a consequence of the difference in the mentioned
three thermic levels, once the drying area is passed and the paper
web is removed, a block is obtained having no densified bottom
and a smooth and uniform surface, a thin and uniform layer of foam
of a density similar to that of the rest of the block having re-
mained adhered to the paper web.
;, The length of the belt 1 which constitutes the reaction ;~
area is represented by AC, CB being the longitudinal edge of the
" consolidation area. From the foregoing it will be seen that the
location of point C, although fixed for a given type of foam,
varies from one foam to another and can be to the right or to the
left of the position shown in the Fiyure.
Beyond the foaming tunnel itself three drying areas can
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be seen in Flgure 2, represented by Sl, S2 and S3. Said drying
areas are generally narrower in wid-th than the other -two areas,
the width (or what is the same thing, the time it takes a certain
element of the consolidated block to pass said drying area) being
related with the temperature in inverse ratio. That is, a rela-
tively narrow drying area (or its equivalent, a short time in
passing that area) will require a high temperature and vice versa.
Figure 3 illustrates the temperature variation o a sur-
face element of the foam block bottom with respect to time. In
said Figure Oo' is the operation time of the belt of the foaming
tunnel without any feeding of the components of the foam and
O'O" is the stopping time of said belt, TR, TC and tR~ tc and Tt
having the previously indicated meanings.
It can be easily seen that the transition of the temper-
ature between the reaction and consolidation areas is not sudden
and thus the inclined length of Figure 3 e~ists, point C being at
a temperature which can be considered as intermediate between TR
and Tc. Once the plate element of reference has reached the
point of return, the part of the block bottom in contact with
said plate of reference undergoes, if the drying area Sl exists,
a rise in temperature until the value TSl is reached. If the
drying area lies downstream, for example at S2 or S3, the -temper-
ature of the block commences to diminish, tending to equal that
of the atmosphere. The dotted line represented by BF would be
the variation of the temperature with respect to time if there -
were no drying areas. ~t is also seen that the farther away the
foaming tunnel, the higher the temperature will have to be in
the drying area to counteract the decrease of the consolidation
temperature. Naturally, once past the drying area the temperature
of the block surface will diminish from points D, E or G of Fig-
ure 3 to ambient temperature.
The removal of the paper web being one of the important
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: aspects of the improvements obtained with this invention, it must
be noted that while in the foregoing reference has been made to
paper as the most common material used for the web inserted be-
tween the block of foam in formation and the rectangular hinged
plates which form the endless conveyor belt, any other weblike
material can be used which fulfils the same function.
The following is an e~ample of how commercial polyure-
thane foam can be obtained in accordance with the improved pro-
cess of this invention. This example is given only for the pur-
pose of illustration, and in no case must be considered limita-
tive.
Feeding is made from the mixing head, in an operation
as previously described, of a composition constituted by the fol-
lowing materials in the amounts as indicated in parts by weight:
` Polyol 100
Toluenediisocyanate 51.3
Water 4.1
-~ Dimethylaminoethanol 0.4
~~ Silicone
.,
Freon-ll ~trade mark) 6.5
i Tin octoate 0.2 `
Dye 0.3
The temperature of the reaction area is maintained at a ~~
value TR = 41.5 + 1C and the temperature of the consolidation
area at a value TC - 51.5 + 1C, with a time tR = 2 to 3 min-
utes in the reaction area and a time tc = 3 to 2 minutes of per-
' manence in the consolidation area. A block is obtained which
` after being subjected to a temperature of 120C in the drying
area, and the continuous paper web having been removed from the
bottom, has a substantially uniform density throughout its vol-
ume of 20 kg/m3, that is, without any densification in the bottom
and without irregularities, and which does not need trimming.
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The following shows, by simple calculation, the econom~
ic advantages of the process of the invention.
An average-sized plant produces foam 200 days of the
year and in each foaming produces a continuous block of 20 Tm, or
in other words its yearly production is ~0 x ~00 = ~,000 Tm =
4,000,000 Kg. Operating in accordance with the conventional pro-
cess and supposing an average value of 4.5% in weight for the
densified bottom, we have:
Yearly production of dense foam
~,000,000 X 0.045 = 180,000 Kg.
Yearly production of foam of uniform density
4,000,000 - 180,000 = 3,820,000 Kg.
A plant of the same size working with the process of
the present invention, and estimating as 0.5% the percentage in
weight of the thin layer of foam adhered to the paper web, would
have a yearly pxoduction of foam of uniform density of:
~ 4,000,000 - (4,000,000 x 0.005) = 3,980,000 KgO
This means that with the process of the invention year-
ly output would increase:
3,980,000 - 3,820,000 = 160,000 kg/year
It is deduced from this that the advantage of the sys-
tem consists of manufacturing 160,000 kg of foam without any
cost of raw materials. Added to this saving would be the cost
of power, labor, etc. necessitated by the trimming, storage and
sale of the dense foam.
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