Note: Descriptions are shown in the official language in which they were submitted.
~L~9~314
Background of the Invention
1. Field of the Invention
The present invention relates to a process for the
manufacture of organic polymer polyol dispersions having a
water content of 0.2 to 5 percent by weight by dehydration
of the reaction products of polyhydroxyl compounds and
aqueous polymer dispersions.
2. Description of the Prior Art
By mixing organic polyhydroxyl compounds with
agueous polymer dispersions having solids contents of 20 to
~5% by weight relative to the total weight in weight ratios
of 1 to 0.05 to 1 to 2, aqueous polymer polyol dispersions
having viscosities of 5 to 500~ Pas are formed. Due to the
resulting great viscosity, the complete mixing of the raw
materials is either not possible, or possible only after
long, intensive stirring re~uiring considerable energy.
Also because of decreased viscosity of the mixture, the
water only slowly diffuses to the liquid surface in order to
evaporate. In the case of non-homogeneous mixtures, the
separation of the water results in a coagulation o~ the
batch. Coagulation also is fre~uently incurred with large
batches in cor~monly used mixing vessels due to the prolonged
temperature stress.
Summary of the Invention
The purpose of this invention is to carefully
separate water from miXtures of organic polyhydroxyl com-
pounds in aqueous polymer dispersions and to ~roduce polymer
polyol dispersions in high space time yields having water
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~0~73~
contents of less than 5 percent by weight relative to the
total weight with the maximum viscosity of the mixtures
being 10 Pas.
The purpose of this invention was surprisingly met
by a process for the manufacture of organic polymer disper-
sions from polyhydroxyl compounds and aqueous polymer dis-
persions, comprising the steps of (a) mixing a polyhydroxyl
compound and an aqueous polymer dispersion in a reaction
medium containing a recycled partially dehydrated polyol
polymer dispersion wherein the weight ratio of introduced
polyhydroxyl compound to the introduced aqueous polymer
dispersion is 1:0.5 to 1:2, (b) removing water from the
mixture in an amount sufficient to provide a water content
~; of 0.2 to 5 percent by weight based on the total weight of
the mixture, (c) removing a portion of the polymér polyol
dispersion obtained, and (d) recycling the remaining portion
, ,
of the polymer polyol dispersion obtained with the weight
ratio of the recycled polyol dispersion to the removed
polyol polymer dispersion being from 40:1 to 1:2.
The discharged polymeric polyol dispersion is
preferably dehydrated to a water content of 0.01 to 0.3
percent by weight relative to the total weight in one to two
additional dehydration stages.
Surprisingly it was found that by incorporating
:.
mixtures of pslyhydroxyl compounds and aqueous polymer
: : dispersions in the above referenced quantity ratios in
; ~ already partially dehydrated polymer polyol dispersions, the
viscosities depending upon the type o~ the polyhydroxyl
.
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~0973~
compound and the aqueous polymer dispersion used is reduced
from originally 5 to 50,000 Pas to 0.2 to 10 and usually 0.5
to 5 Pas, that is by at least the factor of 10 and usually
10 to 1000.
Brief Description of the Drawing
In the accompanying drawing, the single figure
represents typical apparatus that may be used to carry out
the processes of the invention.
Description of the Preferred Embodiments
The following should be noted concerning the
polyhydroxyl compounds and aqueous polymer dispersions
useablè as starting components for the manufacture of
organic polymer polyol dispersions:
Initially it should be said that the referenced
polyhydroxyl compounds and polyols are the same compounds.
The differing definition was chosen in order to better
describe the process according to the invention where the
freshly added polyhydroxyl compound after the partial separa-
tion of the water and the resulting organic dispersion are
referred to as polyols.
Suitable polyhydroxyl compounds and/or polyols
are, for instance, polyacetals, alip~atic polycarbonates,
polyester amides, polyesters and preferably polyalkylene
;~ ethers containing linear and/or branched hydroxyl groups.
Polyesters con~aining hydroxyl groups are produced
for instance from multivalent pxeferably bivalent carboxylic
acids such as adipic acid, sebacic acid, phthalic acid,
halogenated phthalic acids, maleic acids, fatty acids,
~.
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and/or their derivates such as anhydrides and esters ~ith
low molecular alcohols and multivalent alcohols such as
ethylene glycol, polyethylene glycols, propylene glycols,
polypropylene glycols, butanediol, hexanetriol, glycerine
and so forth. Preferably used, however, are hydroxyl group
containing polyethers which are obtained by reaction of one
or more alkylene oxides with two to four carbon atoms in the
alkylene radical with a starter molecule which contains at
least two active,hydrogen atoms. Suitable alkylene oxides
include tetrahydrofuran, epichlorohydrin, 1,2- and 2,3-
butylene oxide and preferably ethylene oxide and 1,2-
propylene oxide. The alkylene oxides may be used individ-
ually, alternatingly in sequence or as mixtures. Possible
starter molecules are water, phosphoric acid, amines such as
ammonium, hydrazine, ethylenediamine, hexamethylénediamine,
toluene diamine, diaminodiphenolmethane, and melamine; amino
alcohols such as mono- and diethanolamines; polycarboxylic
acids such as adipic acids, and terephthalic acid and di-
and multivalent alcohols such as ethylene glycol, propylene
glycol, diethylene glycol, glycerine, trimethylolpropane,
pentaerythritol, sorbitol and sucrose. Such hydroxyl group
containing polyethers are produced according to familiar
~; processes, for instance, analagous to the data provided in
the German publication DT-OS 2 220 723, page 4.
The hydroxy~ number of the polyhydroxyl compounds
used may vary within a wide xange. Generally the hydroxyl
- number of the polyhydroxyl compounds used in accordance with
this invention are within the range of approximately 20 and
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below up to approximately 1000 and above, preferably bet~ee~
approximately 20 to approximately 600, and particularly
between approximately 25 to approximately 450.
The hydroxyl number is defined as the number of
milligrams of potassium hydroxide which is required for the
complete hydrolysis of the completely acetylated deriva-tive
produced from one gram of polyhydroxyl compound. The
hydroxyl number can also be defined by the following equation:
OH ~= 56,1 x 1000 x f
In this e~uation:
O~ stands for the hydroxyl number of polyhydroxyl
compound
f represents the functionality that is the average
~-- number of hydroxyl groups per molecule of poly-
hydroxyl compound, and
M stands for the molecular weight of the polyhydroxyl
compound.
Which polyhydroxyl compound is used in the ~espec- -
tive case depends on the final application of the polyurethane
products to be produced from the compounds. The molecular
weight or the hydroxyl number is chosen in such a manner
that flexible, semi-flexible or rigid foams or elastomers
are obtained when the polymer polyol dispersions produced
from the polyhydroxyl compound is used for a polyurethane
foam. If the polyhydroxyl compounds are used for rigid
foams, the preferred hydroxyl number is approximately 200 to
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. . ,
73~
approximately 1000; if the compounds are used for semi-
~lexible foams, the hydroxyl number is between approximately
30 to approximately 150; and if used for the manufacture of
flexible foams, the hydroxyl number is approximately 20 to
approximately 70 or more. These limits do not at all restrict
the current invention but they are used only to explain the
large number of possible combinations of the polyhydroxyl
compounds.
The aqueous polymer dispersions to be used in
accordance with this invention have solids contents of 20 to
65 percent by weight, preferably 40 to 65 percent by weight
relative to the total weight and are produced by familiar
processes such as solution or suspension polymerization, and
preferably by emulsion polymerization.
The emulsion polymerization in aqueous media is
commonly carried out at temperatures between 30 and 100C
generally in the presence of emulsifiers such as alkali
salts, in particular sodium salts of alkyl or alkylaryl-
sulfonate, alkyl sulfates, ~atty alcohol sulfonates or fatty
acids with 10 to 30 carbon atoms with sodium salts of alkyl
sulfonates or fatty acids with 12 to 18 carbon atoms being
preferred as emulsifiers In general, the emulsifiers are
used in quantities of 0.3 to 5 and in particular from 1.0 to
2.0 percent by weight relative to ~he monomers. If required,
commonly used buffer salts such as sodium bicarbonate and
~ sodium pyrophosphates are also used.
- ~ By the same token, the commonly used polymerization
initiators such as persu~fates or organic peroxides combined,
-- 7 --
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if necessary, with reducing agents may be utilized. The
weight ratio of water to monomers is preferably between 1.5
to 1 and 0.7 to 1 and the polymerization is preferably
continued until a nearly complete reaction, that is more
than 90 percent and in particular more than 96 percent of
the monomers, has been attained. The size of the latex
particles can be varied by familiar methods such as inocula-
tion, emulsifier concentration, staggered emulsifier ad-
dition, liquor ratio, emulsion feed and addition of agglom-
erating agents. The particle size (diameter) may ~e between500 and 5000 angstroms, preferably however a polymer having
a medium particle size (d50-value of mass distribution) is
used which can be determined by counting out with electron
microscopes or by altered centrifuge methods. These par-
ticles are between 1000 and 4000 angstroms. The unit measure
"d50-value" means that 50 percent of the mass of the polymer
particles have a diameter above the d50 value and correspond-
ingly 50 percent of the mass of the poIymer particles have a
diameter below the d50 value. The breadth of the mass
distribution of the dispersed polymer particles can vary
within wide limi-ts. Preferably, however, those polymer
dispersions are used where at least 20 percent of the mass
of the polymer particles have a diameter between 1000 and
4000 angstroms.
Suited for the manufacture of the aqueous polymer
dispersions are cross-linked fine particle homo- and co-
polymerizates which contain either no or preferably at least
one group which is reactive with isocyanates such as OH,
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NH2, NH, COOH, CONH2 groups or the like. These homo- and
copolymerizates are produced in a familiar manner from
corresponding polymerizable olefinic unsaturated monomers.
Possible monomers which contain groups which are
reactive with isocyanates and which serve as building com-
ponents for the homo- and copolymerizates, include unsatu-
rated polymerizable alcohols such as vinyl glycol, butene-
2-diol-1,4 butanol and allyl alcohol, esters of unsaturated
carboxylic acids~such as acrylic acid or substituted acrylic
acids, crotonic acid, fumaric acid, itaconic acid, straight
or branched chains with possibly either group containing
multivalènt alcohols particularly di- and triols with average
molecular weights of 50 to 6000, preferably 50 to 2000 where
at least one OH group of the multivalent alcohols is not
esterified, unsaturated copolymerizable polyols with average
molecular weights of 200 to 6000, preferably 500 to 2000,
- amides of unsaturated carboxylic acids such as acrylamide,
methacrylamide, or other derivates which are reactive wlth
NCO groups and/or unsaturated mono- or dicarboxylic acids
` ~ 20 such as acrylic acid, methacrylic acid, fumaric acid, among
others or their mixtures.
These moDomers containing groups which are re-
active with isocyanates can be used individually or as a
i ~ mixture with other polymerizable monomers which do not
contain these re~ctive groups to produce the homo- and
copolymerizates.
- Suitable monomers which do not contain groups
reactive with isocyanates include vinyl aromatics such as
~' :
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_ g _
~ ~ 7 31 ~
styrene, alpha-alkylated styrene such as alpha-methylstyrene,
ring substituted styrenes such as vinyl toluene, o- and
p ethyl styrene and t-butyl styrene, halogen substituted
styrenes such as o-chlorostyren , 2,4-dichlorostyrene, and
o-bromostyrene, olefinic unsaturated nitriles such as
acrylonitrile and methacrylonitrile, vinyl halides such as
vinyl chloride, vinylidene chloride and vinyl bromide, vinyl
esters of alpha or beta unsaturated carboxylic acids such as
esters of acrylic acid, methacrylic acid, crotonic acid,
maleic, fumaric, itaconic acid, containing monoalcohols with
1 to 10 carbon atoms such as methyl, e-thyl, propyl, i-propyl,
- n-butyl, i-butyl, tertiary butyl, hexyl, octyl, 2-ethylhexyl,
and lauryl acrylates and/or methacrylates. Mixtures of such
vinyl compounds are also suitable.
If required, the homo- and copolymerizates can be
~ partially cross-linked and may have a gel content of more
- than 5 percent, preferably of 30 to 100 percen-t. The gel
content is calculated as follows from that part of a poly-
merizate which is insoluble in a solvent such as cyclo-
hexanone or methylethylketone:
Weight of undissolved substance
Gel Content (%~ ~ (dried) x 100
To~al weight of the pol~merizate
~rosslinking of the product can be facilitated by adding up
to approximately 20 pexcent by weight of a cross-linking
agent during the poLymerizatio~ of the monomer. As an
alternative to this process, the cross-linking can be carried
out following the manufacture of the polymerizate by heating,
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~73~4
adding peroxides or other cross-linking agents, or by ir-
radiation. Suitable cross-linking agents which are poly-
merized together with the simple olefinic unsaturated
monomers include divinyl benzene, diallylmaleate, diallyl-
fumarate, diallyladipate, allylacrylate, allylmethacrylate,
diacrylate and dimethylacrylate of polyhydroxy alcohols such
as ethylene glycol, dimethylacrylate, and other multiple
olefinic unsaturated monomers.
In order to improve the carrying capacity of
foamed polyurethanes, the composition of the homo- and
copolymerizates is for instance chosen in such a manner that
its glass temperature is at least at 40C or above.
In order to obtain particular properties, for
instance, the applications which re~uire high elasticity and
- simultaneously improve carrying capacity even at low tempera-
ture, graft polymerizates with two glass temperatures are
used, the one glass temperature being below -20C and the
other being above +40.
The mixed graft polymerizates ar~ produced by
polymerizing graft monomers in the presence of the pre~ormed
graft base generally according to traditional gra~t polymeri-
zation methods. In the case o~ such graft polymerization
reactions, the monomers are generally added to the pre-
produced rubber base and this mixture is polymerized in
order to at least chemically bind or gra~t part of the mixed
polymerizate to the rubber base.
The weight ratio of the graft base to the graft~d
monomers can vary between 90 to 10 to 10 to 90, preferably
~ betweFn 80 to 20 to 40 to 60
73~
Various crosslinkable rubbers to which the mixed
polymerizate can be grafted are suitable as base for the
grafted mixed polymerizate. These include the diene rubbers,
acrylate rubbers, polyisoprene rubbers and mixtures thereof~
The preferred rubbers are diene rubbers or mixtures
of diene rubbers, that is, all rubber-like polymerizates
(that is, polymerizates with freezing temperatures of not
more than -20C in accordance with ASTM test D-746-52 T) of
one or more conjugated 1,3-dienes such as butadiene, iso-
prene, piperylene, chloroprene, and the like. Such rubbersinclude homopolymerizates and mixed polymerizates of con-
jugated 1,3-dienes with up to an equal amount by weight of
one or more mixed polymerizable monoethylenically unsaturated
monomers.
The already quoted monomers which by themsel~es
result in pol~merizates having a glass temperature of above
+40C can be used as graft monomers.
For particular applicatlons, it is very definitely
possible to also use mixtures of graft polymerizates and
homo- or copolymerizates having a glass temperature o~ about
40C. Appropriately, the graft polymerizates to be used
have a gel content of pre~erably above 30 percent.
Other aqueous polymer dispersions to be used in
accordance with this invention are, for instance, described
~ in the German Offenlegungschriften 24 57 727 and 25 08 582.
; ~ The aqueous polymer dispersions are used in quanti-
ties of 5 to 200, preferably in quantities from 20 to 100
percent by weight rela~ive to the polyhydroxyl compound.
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7;3~
To manufacture the organic polymer polyol disper-
sions, the polyhydroxyl compound and the aqueous polymer
dispersions are fed into a partially dehydrated circulated
polymer polyol dispersion via separated feed lines and
intensively mixed with the polymer polyol dispersion. The
~ecycled circulating polymer polyol dispersion has a water
content of 0.2 to 5 percent by weight, preferably of 0.2 to
2 percent by weight relative to the total weight. The
weight ratio of in-troduced polyhydroxyl compound to intro-
duced agueous polymer dispersion can be varied within thelimits of 1 to 0.5 to 1 to 2, preferably 1 to 0.2 to 1 to 1.
The obtained reaction mixture is heated to the dehydration
temperature of appro~imately 40 to 90C, preferably 60 to
85C with the aid of heat exchangers. The water is separated
under reduced pressure at approximately 5 to 150 millibarj
preferably 20 to 75 millibar in commonly used equipment such
as falling film or thin film evaporators.
The discharged polymer dispersion is dehydrated to
a water content of 0.01 to 0.3 percent by weight, preferably
of 0.04 to 0.1 percent by weight relati~e to the total
weight, and preferably at least 1, preferably l to 2 in
additional dehydration areas at a temperature of approxi-
mately ~0 to 90C, preferably of 60 to 85~C and a pressure
of 0.1 to 25 millibar, preferably of 1 to 10 millibar with
the aid of commonly used eguipment such as falling film or
thin film evaporators.
A preferred model of the manufacturing process
according to this invention is again explained in detail
using the drawing.
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~g73~4
The drawing figures stand for:
1. Heating medium feed line.
2. Heating medium drain line.
3. Circulation for partially dehydrated polymer
polyol dispersion.
4. Feed line for polyhydroxyl compound.
5. Feed line for aqueous polymer dispersion.
6. Drain line for partially dehydrated polymer polyol
dispersion.
7. Drain line for polymer polyol dispersion.
8. Discharge for water vapor and vacuum connection.
9. Metering pump for polyhydroxyl compound.
lO. Metering pump for a~ueous polymer dispersion.
11. Heat exchanger.
12. Mixing aggregate which may be heatabIe.
I3. Pressure~regulator.
14. Falling film-evaporator.
15. Vapor separator.
16. Discharge pump for partially dehydrated polymer
polyol dispersion.
17. Discharge pump for regulating the circulating and
discharge ~uantity of-partially dehydrated polymer
polyol dispersions.
18. Falling film or thin film evaporator.
19. Vapor separator.
20. Dlschaxge pump.
21. Cooler.
, -
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, ,
,
; ~
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.,
3~
Via feed line ~4) and meteriny pump (9), the polyhydroxyl
compound is introduced into the circulation (3) of recircu-
lated partially dehydrated polymer polyol dispersion and the
mixture is heated to approximately 80C in the heat exchanger
(11). Vacuum steam, for instance, is suitable heating
medium. The heated mixture passes through a possibly heat-
able mixing aggregate (12) in which aqueous polymer dis-
persion is introduced via feed line (5) and metering pump
(lO). At this point, the viscosity of the mix~ure increases
from 300 to 3000 mPas to a maximum of 500 to 5000 mPas as
the reaction takes place. In order to prevent water from
evaporating in the mixing unit (12) - this might result in
coagulation of the dispersion a pressure regulator (13) is
inserted which is adjusted to a pressure equal to or greater
than the water vapor pressure at the mixing température, for
instance, to a pressure of 0.5 to 1.5 bar at 80C. A mixture
consisting of recycled polymer polyol dispersion, freshly
added polyhydroxyl compound and freshly added a~ueous polymer
dispersion is released into the falling film evaporator (14)
which is under a partial vacuum. The resulting liquid vapor
mixture flows into the vapor separator (15) from where the
water vapor is removed vla separating line (~. The par~
tially dehydrated polymer polyol dispersion having a water
,~ content o~ 0.2 to 5 percent by weight relative to the total
weight and a viscosity of 300 to 3000 mPas at 70C is dis-
charged by means of *he discharge pump ~16~ from the vapor
separator (15) which is under partial vacuum, and with the
aid of discharge pwmp (17) is separated into the circulating
.
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~uantity and the discharge quantity. Via discharge pump
(17) in drain line (63, the discharge quantity is trans-
ported into a storage vessel or in discharge line (6') to a
falling film evaporator (18) with vapor separator (19) which
is operated on a flow-through basis. At this point, at a
temperature of approximately 80C and a pressure of 1 to 10
millibar, the water content of the polymer polyol dispersion
is reduced to a value smaller than 0.3 percent by weight
relative to the ~otal weight. The resulting water vapor is
separated via the off-line for water vapor and the vacuum
connection (8) via line (7) and the discharge pump (20).
The polymer polyol dispersion is discharged from the vapor
; separator (19) which is under partial vacuum and is cooled
to room temperature in cooler (21).
The polymer polyol dispersions produced according
to this invention have a water content of 0.2 to 5 percent
by weight rela-tive to the total weight and viscosities of
300 to 3000 mPas at 70C depending on the type of the applied
polyhydroxyl compound and the aqueous polymer dispersion.
The produc~s are very well suited for the manu-
facture of polyurethane foams particularly flexible foams
with a high compression factor such as automobile seats,
~ upholstered furnitur~ and so forth.
; The process according to this invention is ex-
plained further by the following examples. The parts given
in th- examples are by weight unless otherwise indicated.
. ~
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Example 1
The process arrangement utilized is shown in the
drawing.
13 Kilograms per hour of an organic polyhydroxyl
compound having an average molecular weight of 4800 and a
hydroxyl number of 35 are added to 50 kilograms per hour of
a partially dehydrated polymer polyol dispersion which is
being recycled. The mixture is heated to 70C and is mixed
with 6.5 kilograms per hour of a 50 percent by weight aqueous
dispersion relative to the total weight of a copolymerizate
produced from 95 parts of styrene, 5 parts of hydroxypropyl
. . acrylate and 2 parts of divinyl benzene having a particle
size of 150 nm with the aid of a mixing unit (12) at 1.4
bar. Ahead of the heated falling film evaporator (14), the
pressure of the mlxture is reduced to 30 millibar. This
causes the water content of the polymer polyol dispersion to
drop from 5.4 percent by weight to 0.3 percent by weight -
relative to the total weight and the viscosity (measured in
~ the rotation viscosimeter at a shear rate of D=0.1 seconds
; 20 1) at 70nC from 4000 to 2500 mPas. 16.3 Kilograms of
partially dehydrated polymer polyol dispersions are removed
from the circulation via discharge pump (17) while 50 kilo-
~:~ grams per hour circulate (ratio of circulating to discharge
quantity 3.1 to 1). 3.2 Kilograms per hour of water vapor
are removed from the vapor separator (15).
The discharged polymer polyol dispersions having a
water content of 0.3 percent by weight is heated to 77C in
the falling film evaporator (18) and is dehydrated to a
,
.
~ - 17 -
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water content of 0.08 percent by weight relative to the
total weight at a reduced pressure of 4 millibar. The water
vapor removed via discharge line (8) from the vapor separa-
tor (19) is condensed in a steam jet unit. The dehydrated
polymer polyol dispersion is discharged via drain line (7),
discharge pump (20) into cooler (21).
The maximum viscosity of 4000 mPas resulting
during the reaction is hardly above the viscosity of the end
product of 2500 mPas and far below the value of 50,000 mPas
which results from the direct mixing of the polyhydroxyl
compound and aqueous polymer dispersion at 70C.
Example 2
9 Kilograms per hour of the polyhydroxyl compound
described in Example 1 are added to 250 kilograms per hour
of a partially dehydrated polymer polyol dispersion which is
being recycled, the mixture is heated to 70C and is mixed
with 5.6 kilograms per hour of a 40 percent by weight aqueous
dispersion relative to the total weight of a copolymerizate
manufactured from 55 parts of acrylonitrile and 45 parts
styrene having a particle size of 160 nm at 1 bar. Subse-
quently and ahead of the heated falling film evaporator
(14), the pressure of the mixture is reduced to 20 millibar.
This causes the water content of the polymer polyol dis-
perison to drop from 1.8 percent by weight to 0.6 percent by
weight relative to the total weight and the viscosity at
70C from 1600 to 400 mPas. 11.3 Kilograms per hour of
partially dehydrated polymer polyol dispersion are discharged
while 250 kilograms per hour are being recycled (ratio of
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~ 73~4
recycle to discharge quantity being 22 to 1). 3.3 Kilograms
per hour of water vapor is removed from the vapor separator
(15) via drain line (8) and is precipitated in a condenser.
The discharged polymer polyol dispersion is de-
hydrated at 74C and at 2.5 millibar in a falling film
evaporator (18) and vapor separator (19) to a water content
of 0.25 percent by weight relative to the total weight.
The maximum viscosity of 1600 mPas obtained during
reaction is hardly above the viscosity of the final product
of 400 mPas and far below the value of 100,000 mPas which
would result from directly mixing the polyhydroxyl compound
and the aqueous polymer dispersion at 70C.
8 Kilograms per hour of an organic polyhydroxyl
compound having an average molecular weight of 4000 and a
hydroxyl number of 28 is added to 50 kilograms per hour of a
partially dehydrated polymer polyol dispersion which is
being recycled and the mixture is heated to 80C and mixed
with 4 kilograms per hour of an aqueous polymer dispersion
according to Example 1 at 1 bar. Subsequently and ahead of
the heated falling film evaporator (14), the pressure of the
mixture is reduced to 17 millibar. This causes the water
content of the polymer polyol dispersion to drop from 3.5 to
~ ~ 0.25 percent by weight relative to the total weight while
,; .
the viscosity of 1300 mPas at 80C remains constant. 10
Kilograms per hour of partially dehydrated polymer polyol
dispersion is discharged whereas 50 kilograms per hour is
recycled ~ratio of circulating to discharged quantity is 5
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~973~4
to 1). 2 Kilograms per hour of ~ater vapor is removed from
the vapor separator (15).
The discharged polymer polyol dispersion is de-
hydrated at 84C and 1.5 millibar in the falling film evapor-
ator (18) and vapor separator (19~ to a water content of 0.1
percent by weight relative to the total weight.
The incurred maximum viscosity of 1300 mPas cor-
responds with the viscosity of the end part product and is
far below the va~ue of 3,500,000 mPas which results from
directly mlxing the polyhydroxyl compound and the aqueous
polymer dispersion at 80C.
Example 4
12 Kilograms per hour of an organic polyhydroxyl
compound having an average molecular weight of 6500 and a
hydroxyl number of 26 are added to 50 kiloyrams per hour of
partially dehydrated polymer polyo-l dispersion, the mixture
is heated to 73C and is mixed with 6 kilograms per hour of
an aqueous polymer dispersion according to Example 1 at 1.3
bar. Subsequently and ahead of~the heated ~alling film
evaporator (14~, the pressure of the mixture is reduced to
23 millibar. This causes the water content of the polymer
polyol dispersion to drop from 4.8 to 0.5 percent by weight
~, , - .
relative to the total weight and the viscosity ~rom 5000 to
,; 1200 mPas at 73C. 15 Kilograms per hour oE partially
; dehydrated polymer polyol dispersion is discharged while 50
kilograms per hour is recycled (ratio of circulating to
discharged quantity is 3.3 to 1), 3 kilograms per hour of
water vapor is removed from the vapor separator (15).
:,
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3~973~4
The discharged polymer polyol dispersion is de-
hydrated to a water content of 0.06 percent by weight rela-
tive to the total weight at 80C and 5 millibar in the
falling film evaporator (18) and vapor separator (19).
The incurred maximum viscosity of 5000 mPas is
hardly above the viscosity of the final product of 1200 mPas
and is far below the value of 4,500,000 mPas which results
from directly mixing the polyhydroxyl compound and the
aqueous polymer dispersion at 73C.
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