CA1097314A - Process for the manufacture of organic polymer polyol - Google Patents

Abstract

PROCESS FOR THE MANUFACTURE OF
ORGANIC POLYMER POLYOL

Abstract of the Disclosure A process for the manufacture of partially de-hydrated organic polymer polyol dispersions from the re-action of polyhydroxyl compounds and aqueous polymer disper-sions wherein the problem of excessive viscosity is overcome by mixing the reactants with a recycled partially dehydrated polyol polymer dispersion, removing water from the reaction mixture, removing a portion of the partially dehydrated polyol polymer dispersion, and recycling the remainder.

Description

~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 ~k ~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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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, ~.

".' ~7~4 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 ~73~4 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 ; - 6 -. .

. . , 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, ~373~4 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, ~0~73~4 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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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, ~ ' ~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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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.

~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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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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~73~

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 -~973~

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 .

~ 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 ::
' :

~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).
:, ~ - 20 -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.

Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the manufacture of organic polymer dispersions from polyhydroxyl compounds and aqueous polymer dispersions comprising the steps of 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, removing water from the mixture in an amount suf-ficient to provide a water content of 0.2 to 5 percent by weight based on the total weight of the mixture, removing a portion of the polymer polyol dispersion obtained, and recycling the remaining portion of the polymer polyol dispersion obtained, with the weight ratio of the recycled polyol dis-persion to the removed polyol polymer dispersion being from 40:1 to 1:2.

2. Process for the manufacture of organic polymer polyol dispersions as defined in claim 1, wherein the mixture of partially dehydrated polymer polyol dispersion added to polyhydroxyl compound and aqueous polymer dispersion has a viscosity which is at least a factor of 10 smaller than the viscosity which would be obtained by directly mixing the polyhydroxyl compound and an aqueous polymer dispersion.

3. Process for the manufacture of organic polymer polyol dispersions as defined in claim 1, wherein the removed polymer polyol dispersion is dehydrated in at least one additional dehydration stage to a water content of 0.01 to 0.3 percent by weight.