CA1137688A - Process for reducing the residual monomer content in vinyl chloride polymer dispersions sensitive to shear and/or temperature stresses - Google Patents
Process for reducing the residual monomer content in vinyl chloride polymer dispersions sensitive to shear and/or temperature stressesInfo
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- CA1137688A CA1137688A CA000317253A CA317253A CA1137688A CA 1137688 A CA1137688 A CA 1137688A CA 000317253 A CA000317253 A CA 000317253A CA 317253 A CA317253 A CA 317253A CA 1137688 A CA1137688 A CA 1137688A
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- dispersion
- steam
- polymer
- residual monomer
- vinyl chloride
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
- B01D3/34—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping with one or more auxiliary substances
- B01D3/38—Steam distillation
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F6/00—Post-polymerisation treatments
- C08F6/14—Treatment of polymer emulsions
- C08F6/16—Purification
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- Chemical Kinetics & Catalysis (AREA)
- Health & Medical Sciences (AREA)
- Medicinal Chemistry (AREA)
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- Organic Chemistry (AREA)
- Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
Abstract
NLJr:TW
A B S T R A C T
A process for reducing the residual monomer content in an aqueous vinyl chloride polymer dispersion sensitive to shear and/or temperature stresses, said polymer dispersion containing at least 75% by weight of polymerized vinyl chloride, polymerized in the presence of 0.001% to 1% by weight of emulsifiers, based on the solids content of the dispersion and having an average particle size of from 0.1 to 20 microns, comprising the step of treating said polymer dispersion with steam at an absolute pressure of below atmospheric pressure and a temperature of 50°C to 100°C while evacuating the degassing vessel, for a time sufficient to substantially reduce the residual monomer content, preferably to less than 40 ppm.
-A-
A B S T R A C T
A process for reducing the residual monomer content in an aqueous vinyl chloride polymer dispersion sensitive to shear and/or temperature stresses, said polymer dispersion containing at least 75% by weight of polymerized vinyl chloride, polymerized in the presence of 0.001% to 1% by weight of emulsifiers, based on the solids content of the dispersion and having an average particle size of from 0.1 to 20 microns, comprising the step of treating said polymer dispersion with steam at an absolute pressure of below atmospheric pressure and a temperature of 50°C to 100°C while evacuating the degassing vessel, for a time sufficient to substantially reduce the residual monomer content, preferably to less than 40 ppm.
-A-
Description
~13~7~88 This invention relates to a process for reducing the residual monomer content in an aqueous vinyl chloride polymer disper~ion sensitive to shear and/or temperature stresses.
Vinyl chloride polymers usually still contain monomeric vinyl chloride after the polymerization step. For the removal of this residual monomeric vinyl chloride from aqueous polymer dispersions, various processes have been described~
as, for example, in published German Patent Application DOS 26 3S~7~ wherein vinyl chloride is removed from aqueous dispersions, latexes or suspensions by blowing organic or inorganic gaseous ~ubstances and/or organic liquids in which vinyl chloride is at least moderately soluble, therethrough.
During this blow-through process, the pressure in the degassing vessel is maintained below atmo~pheric pressure. O~her applications teach carrying out the residual monomer removal at reduced pressure in the degassing vessel,with hot, saturated, or unsaturated steam~ but always with steam above atmospheric pressure.
All of the procedures that have become ~nown until now are, however 7 unsuitable for degassing polymer d~spersions which are sensitive to shear and/or temperature stresses.
Such polymer dispersions are in general those with average particle sizes between O.l and 20ju, which generally contain no protective colloids and only small quantities of emulsifiers.
It was, therefore, the object of the invention to find a process for reducing the residual monomer content of aqueous polymer dispersions which are sensitive to shear and/or temperature stresses.
Another object of the present invention is the develop-ment of a process for reducing ~he residual monomer content o~
~ 7 ~ ~
an aqueous vinyl chloride polymer dispersion sensitive koshear and/or temperature stresses, said polymer in said dis-persion ~ontaining at least 75% by weight of polymerized vinyl chloride and having an average particle size of from 0.1 to 20 ~1, said polymer dispersion having from 0.001% to 1% by weight of emulsifiers, based on the solids content of the dispersion, consisting of the steps of introducing from 0.05 to 0.25 kg of steam per liter of dispersion into said dispersion at a steam t~mperature of from 50C to 100C and a steam pressure of between 0.1 and 0.9 bar over a period of from 20 minutes to 3 hours while maintaining an internal pressure on said dispersion corresponding at most to the water vapor partial pressure at the pre~ailing dispersion temperature 3 and recovering a polymer dispersion :having a reduced residual monomer content.
These and other objects o~ the in~ention will become more apparent a~ the description the.reof proceeds.
Th~ subject o~ ~he invention is a process for reducing the residual monomer content of aqueous polymer dispersions sensitive to shear and/or temperature stresses, which polymer contains at least 75% by weight, base~ on the polymer weight, of vinyl chloride units, and has an average particle ~ize of between 0.1 and 20 ~, sai~ polymer dispersion having been obtained in the presence of 0.001% to 1% by ~eight of emulsi-fiers, based on the solids content of the dispersion, comprising treating the polymer dispersion with skeam, characterized in that steam is introduced into th~ dispersion at a temperature of between 50 and 100C, preferably 60 to ~0C, and a pressure of between 0.1 and 0.9 bar, preferably 3o 0.2 to 0.7 bar, for a period of from 20 minutes to 3 hours ~-'\ .
~13768~3 in a quantity of 0.05 to 0.25 kg per liter of dispersion and at the same time an internal pressure, corresponding at most to the water vapor partial pressure at the degassing tempera-ture, prevails in the degassing ~essel~ that is, on the surface of said polymer dispersion.
More particularly, the present invention relates to a process ~or reducing the residual monomer content of an aqueous vinyl chloride polymer dispersion sensitive to shear and/or temperature stresses, said polymer in said dispersion containing at least 75% ~y weight of polymerized vinyl chloride and having an average particle size of from 0.1 to 20 ~, said polymer dispersion having from 0.001~ to l~o by weight of emulsifiers, based on the solids content of the dispersion, consisting of the steps of introducing from 0.05 to 0.25 kg of steam per liter of dispersion into said dispersion at a steam temperature of from 50~ to 100C and a steam pressure of between 0.1 and 0.9 bar over a period of from 20 minu~es to 3 hours while maintaining an internal pressure on said disper-sion corresponding at most to the water vapor partial pressure at the prevailing dispersion temperature, and recovering a polymer dispersion having a reduced residual monomer content.
By the process of the inven~ion polyvinyl chloride dispersions are o~tained with residual monomer contents of 40 ppm or less, when their residual monomer content after polymerization is over 200 ppm.
An advantageous procedure for reducing the mono~er content consists in supplying a greater quantity of steam per unit of ti~e toward the end of the degassing step than at the beginning. The temperature of the dispersion should not exceed ~0C during degassing; generally one operates at temperatures above 40C.
1~L376~
One or more inert gases may be added to the steam, where the sum of the partial prassures is 0.1 to 0.9, prefer-ably 0.3 to 0.7 bar.
Surprisingly, it becomes possible by the addition of saturated, unsaturated or supe~heated steam at temperatures between 50 and 100C, prefera~ly 60 to ~0C, at a pressure between 0.1 and 0.9 bar, preferably 0.2 to 0.7 bar, while applying a vacuum to the degassing vessel, to effect the monomer reduction without the occurrence of coagulation of the latices sensiti~e to shear or to tem~erature stresses.
The polymer dispersions being treated according to the invention are preferably latices which comprise solids contents of between 20~o and 6~,6 by weight. The particle diameter of these latex particles may fluctuate within wide limits, but generally stability problems are obser~ed in particular in latices having an aver~ge particle size of between 0.1 and 20,u.
The polymer component may be formed entirel~ o~ vinyl chloride units, but alternatively, it is conceivable that in addition to a minimum of 75% by weight of vinyl chloride units, other monomer units copolymerizable with vinyl chloride may be present.
Preferred as monomers copolymerizable with vinyl chloride are those which contain only one polymerizable ~roup, namely the group ~CH=CC. Example~ are the vinyl halides, such as vinyl bromide and vinylidene chloride; vinyl esters with or~anic acids, more particularly vinyl alkanoates having from 1 to 20 carbon atoms in the alkanoyl and vinyl phenylcarboxy-lates~ such as vinyl formate, ~inyl acetate and vinyl benzoate;
acrylic compounds, for example~ lower alkyl (meth)acrylates~
such as methyl acrylate and methylmethacrylate; as well as 376~8 unsaturated dicarboxylic acids, particularly alkenedioic acids havin~ from 2 to ~ carbon atoms and cycloalkenyl dicarboxylic acids, such as maleic acid, fumaric acid, methylene malonic acid, itaconic acid, citraconic acid or tetrahydrophthalic with alkanols acid; as well as the mono and di~esters of these acids/having 1 to 1~ carbon atoms, such as dimethyl maleate, diethyl maleate and di~n-butyl ~aleate, mono-(2-ethylhexyl) maleate, dimethyl fumarate, diethyl fumarate, di-n-butyl fumarate, di-(2-ethylhexyl) fumarate and dilauryl fumarate. Naturally, lQ mixtures of more than two monomers can also be used.
Ionic and~or non-ionic emulsifiers and/or protective colloids may be used as dispersing agents. Preferably anion-active emulsifiers are employed. These are, ~or example, alka~i metal and~ in particular, ammo~.ium salts of fatty acids such as lauric or palmitic acid, o~ acid phosphoric acid alkyl esters such as sodium diethylhexylphosphate, of acid fatty alcohol sulfuric acid esters~ of paraffin sulfonic acids, of alkyl naphthalene sulfonic acids and of sulfosu~cinic acid dialkyl esters Also very suitable are the alkali m~tal and ammonium salts of fatty acids containing epoxy groups, such as ammonium epoxystearate, or, respectively, the alkali metal and a~monium salts of the products obtainable by reaction of per acids~ such as peracetic acid, with unsaturated fatty acids such as oleic or linoleic acid, with formation Or dihydroxy-stearic acid and hydroxyacetoxystearic acid, for instance;
as well as the alkali metal and ammonium salts of the r~actlon products of per acids with unsaturated hydroxy-fatty acids such as ricinoleic acid. Alternatively, cation-active e~ulsi-fiers, such as lauryl pyridinium hydrochloride5 may be used.
As examples of non-ionic emulsifiers, the following 1~376~
may be named: partial fatty acid esters of polyhydric alcohols~ snch as ~lycerin monoskearate, sorbital monolaurate or palmitate: partial fa~ty alcohol ethers of polyhydric alcohols- polyethoxylates of fatty alcohols or aro~atic hydroxy compoun~s~ as well as the known polypropylene oxide-polyethylene oxide condensation products.
The total quantity of ionic or non-ionic emulsifiers is usually about 0.001% to 1~ by weight, based on the weight o~
the monomer or monomers.
The protective colloids which may optionally be present as dispersin~ agents, are ~he natural or synthetic polymers which are normally employed as protective colloids in suspension ~olymerization. These are1 for example, polyvinyl alcohol, possibly also containing up to 40 mol /~o of acetyl groups;
gelatines and cellulose ether derivatives, such as water-~ . ._ soluble methyl cellulose, carboxymethyl cellulose and hydroxy-- ethyl~ellulose; as wellas copolymers of maleicacid ortheirhslf esters with styrene ortheir salts. The pro~ectivé colloids are used in quantities of 0.1% to 3% by weight, preferably 0.3~ to 2~ by weight~ based on the weight of the monomer or monomers.
Polymerization is effected in the usual manner, with the aid of monomer-soluble free-radical-forming catalysts.
Examples of these monomer-soluble ca-talysts are benzoyl peroxide, lauroyl peroxide, 2,4-dichlorobenzoyl peroxide, azo-isobvtyric acid dinitrile~ dialkyl peroxy-dicarbonates, as well as acetyl-cyclohexane-sulfonyl peroxide. These monomer-solllble catalysts are emplo~yed preferably in quantities of from 0.01% to ~% by wei~ht, advanta~eously 0 05% to 1% by wei~ht based on the weight of the monomer or monomers.
~ 3 ~ 8 ~
The usual polymerization aids other than those named above, such as parti~le and molecular size regulators, can be employed as well The quantity ratio of water to monomer to be polymerized is not c~itical~
The pH value of the polymerization batch is preferably ~ to 10 and the polymerization temperature preferably about 30 to ~0C. Since, ~enerally, polymer dispersions susceptible to shear are involved, overly vigorous agitation during poly-merizat,ion is to be a~oid~d~
The polymer dispersions to be degassed are transferred to a degassing vessel after completion of the polymerization.
Thereafter, a vacuum is created in the gas space above the polymer latex by using vacuum pumps. In so doing, an internal pressure is created which adjusts to correspond to the water vapor part~al pressure at the temperature of the dispersîon.
Then saturated, unsaturated, or superheated steam is introduced, at temperatures of between 50 and 90C, pr~erably 60 to ~0C, and a pressure between 0,1 and 0.~ bar, preferably 0.2 to 0.7 bar Naturally~ it is possible to draw the steam supplied for monomer removal into khe degassing vessel only if the internal pressure in the degassing vessel has a pressure at least lower than the steam to be drawn in. Steam of the aforementiQned specification can be produced, for example, by steam converters ~rom steam which is hotter and/or under higher pressure.
The treatment, according to the invention, of the polymer latices with steam of the aforementioned specification in degassin~ vessels whose internal pressure is lower than atmospheric pressure, ext~nds over a period of time of from 20 minutes to 3 hours. After this period~ any residual monomeric vinyl chloride is generally reduced to values below ~76 ~0 ppm For thls de~assing step~ steam quantities of 0.05 to 0.25 kg of steam per liter of dispersion are necessary~ The introduction of steam can be e~fected so tha-t generally no, or only a slight, volume increase of the polymer dispersion occurs. When proceeding according to the invention, the degassing process can be controlled so that heating of the dispersion to temperatures beyond gOC does not occur.
Nor~ally, howev~r, one operates at temperatures above 40C, as the degassing step would othe~ise take too long. The te~peratures of the pol-ymer dispersion can be established by the quantity and temperature of the admitted steam and the vacuum applied on the dispersion surface.
In another form of executing the process, regulation o~ the temperature of the polymer latex is effected externally, by supplylng or remo~ing hea~, so as to be able to Yary within . wide limits the quanti~y of admitted steam, whlch substantially influences the efficiency of the process.
The following examples are illustrative of khe process of the invention without belng limitative in any respect.
After the polymerization step, 4 liters o~ a vinyl chloride polymerizate dispersion,obtained by micro-suspension polymerization, were charged into a temperature-controllable cylindrical Yessel of 150 mm diameter and 400 mm height, which was also equipped with a propeller agitator. The dispersion was adjusted toan absolute pressure o~ 150 Torr and 60C. In the course of 2 hours, 0.10 kg of steam per liter of latex was passed through. The steam had a temperature of 63C and a pressure of 170 Torr. During the entire ~egassing time, the absolute pressure o~ 150 Torr was maintained in the degassing ves~el.
~ ~i7~ ~ ~
The initial monomer content of 1,360 ppm was reduced after one hour to lO~o and after two hours to below 40 ppm.
Coagulation did not oc¢ur.
EXAMPL~ 2 (Comparative Example) The process of Example 1 was repeated, but with a reduction of the quantity of steam to 0.045 kg of steam per liter of latex. The initial monomer content of 1,090 ppm was reduced, in thi~ case~ to ~9% after one hour and to 3~% after 10 two hours.
EXAMPL~_~
(Comparative Example~
The pro¢ess of Example 1 was repeated, but without : passage of steam~ The initial monomer content of 1,160 ppm was reduced after one hour to only ~2% and after two hours to only 6~% of the initial moncmer content.
The preceding speci~ic embodiments are illustrative of the practice of the in~ention. It is to be understood, however~
that other expedients known to those skilled in the art or disclosed herein, may be employed without departing from the spirit of the in~ention or the scope of the appended claims.
Vinyl chloride polymers usually still contain monomeric vinyl chloride after the polymerization step. For the removal of this residual monomeric vinyl chloride from aqueous polymer dispersions, various processes have been described~
as, for example, in published German Patent Application DOS 26 3S~7~ wherein vinyl chloride is removed from aqueous dispersions, latexes or suspensions by blowing organic or inorganic gaseous ~ubstances and/or organic liquids in which vinyl chloride is at least moderately soluble, therethrough.
During this blow-through process, the pressure in the degassing vessel is maintained below atmo~pheric pressure. O~her applications teach carrying out the residual monomer removal at reduced pressure in the degassing vessel,with hot, saturated, or unsaturated steam~ but always with steam above atmospheric pressure.
All of the procedures that have become ~nown until now are, however 7 unsuitable for degassing polymer d~spersions which are sensitive to shear and/or temperature stresses.
Such polymer dispersions are in general those with average particle sizes between O.l and 20ju, which generally contain no protective colloids and only small quantities of emulsifiers.
It was, therefore, the object of the invention to find a process for reducing the residual monomer content of aqueous polymer dispersions which are sensitive to shear and/or temperature stresses.
Another object of the present invention is the develop-ment of a process for reducing ~he residual monomer content o~
~ 7 ~ ~
an aqueous vinyl chloride polymer dispersion sensitive koshear and/or temperature stresses, said polymer in said dis-persion ~ontaining at least 75% by weight of polymerized vinyl chloride and having an average particle size of from 0.1 to 20 ~1, said polymer dispersion having from 0.001% to 1% by weight of emulsifiers, based on the solids content of the dispersion, consisting of the steps of introducing from 0.05 to 0.25 kg of steam per liter of dispersion into said dispersion at a steam t~mperature of from 50C to 100C and a steam pressure of between 0.1 and 0.9 bar over a period of from 20 minutes to 3 hours while maintaining an internal pressure on said dispersion corresponding at most to the water vapor partial pressure at the pre~ailing dispersion temperature 3 and recovering a polymer dispersion :having a reduced residual monomer content.
These and other objects o~ the in~ention will become more apparent a~ the description the.reof proceeds.
Th~ subject o~ ~he invention is a process for reducing the residual monomer content of aqueous polymer dispersions sensitive to shear and/or temperature stresses, which polymer contains at least 75% by weight, base~ on the polymer weight, of vinyl chloride units, and has an average particle ~ize of between 0.1 and 20 ~, sai~ polymer dispersion having been obtained in the presence of 0.001% to 1% by ~eight of emulsi-fiers, based on the solids content of the dispersion, comprising treating the polymer dispersion with skeam, characterized in that steam is introduced into th~ dispersion at a temperature of between 50 and 100C, preferably 60 to ~0C, and a pressure of between 0.1 and 0.9 bar, preferably 3o 0.2 to 0.7 bar, for a period of from 20 minutes to 3 hours ~-'\ .
~13768~3 in a quantity of 0.05 to 0.25 kg per liter of dispersion and at the same time an internal pressure, corresponding at most to the water vapor partial pressure at the degassing tempera-ture, prevails in the degassing ~essel~ that is, on the surface of said polymer dispersion.
More particularly, the present invention relates to a process ~or reducing the residual monomer content of an aqueous vinyl chloride polymer dispersion sensitive to shear and/or temperature stresses, said polymer in said dispersion containing at least 75% ~y weight of polymerized vinyl chloride and having an average particle size of from 0.1 to 20 ~, said polymer dispersion having from 0.001~ to l~o by weight of emulsifiers, based on the solids content of the dispersion, consisting of the steps of introducing from 0.05 to 0.25 kg of steam per liter of dispersion into said dispersion at a steam temperature of from 50~ to 100C and a steam pressure of between 0.1 and 0.9 bar over a period of from 20 minu~es to 3 hours while maintaining an internal pressure on said disper-sion corresponding at most to the water vapor partial pressure at the prevailing dispersion temperature, and recovering a polymer dispersion having a reduced residual monomer content.
By the process of the inven~ion polyvinyl chloride dispersions are o~tained with residual monomer contents of 40 ppm or less, when their residual monomer content after polymerization is over 200 ppm.
An advantageous procedure for reducing the mono~er content consists in supplying a greater quantity of steam per unit of ti~e toward the end of the degassing step than at the beginning. The temperature of the dispersion should not exceed ~0C during degassing; generally one operates at temperatures above 40C.
1~L376~
One or more inert gases may be added to the steam, where the sum of the partial prassures is 0.1 to 0.9, prefer-ably 0.3 to 0.7 bar.
Surprisingly, it becomes possible by the addition of saturated, unsaturated or supe~heated steam at temperatures between 50 and 100C, prefera~ly 60 to ~0C, at a pressure between 0.1 and 0.9 bar, preferably 0.2 to 0.7 bar, while applying a vacuum to the degassing vessel, to effect the monomer reduction without the occurrence of coagulation of the latices sensiti~e to shear or to tem~erature stresses.
The polymer dispersions being treated according to the invention are preferably latices which comprise solids contents of between 20~o and 6~,6 by weight. The particle diameter of these latex particles may fluctuate within wide limits, but generally stability problems are obser~ed in particular in latices having an aver~ge particle size of between 0.1 and 20,u.
The polymer component may be formed entirel~ o~ vinyl chloride units, but alternatively, it is conceivable that in addition to a minimum of 75% by weight of vinyl chloride units, other monomer units copolymerizable with vinyl chloride may be present.
Preferred as monomers copolymerizable with vinyl chloride are those which contain only one polymerizable ~roup, namely the group ~CH=CC. Example~ are the vinyl halides, such as vinyl bromide and vinylidene chloride; vinyl esters with or~anic acids, more particularly vinyl alkanoates having from 1 to 20 carbon atoms in the alkanoyl and vinyl phenylcarboxy-lates~ such as vinyl formate, ~inyl acetate and vinyl benzoate;
acrylic compounds, for example~ lower alkyl (meth)acrylates~
such as methyl acrylate and methylmethacrylate; as well as 376~8 unsaturated dicarboxylic acids, particularly alkenedioic acids havin~ from 2 to ~ carbon atoms and cycloalkenyl dicarboxylic acids, such as maleic acid, fumaric acid, methylene malonic acid, itaconic acid, citraconic acid or tetrahydrophthalic with alkanols acid; as well as the mono and di~esters of these acids/having 1 to 1~ carbon atoms, such as dimethyl maleate, diethyl maleate and di~n-butyl ~aleate, mono-(2-ethylhexyl) maleate, dimethyl fumarate, diethyl fumarate, di-n-butyl fumarate, di-(2-ethylhexyl) fumarate and dilauryl fumarate. Naturally, lQ mixtures of more than two monomers can also be used.
Ionic and~or non-ionic emulsifiers and/or protective colloids may be used as dispersing agents. Preferably anion-active emulsifiers are employed. These are, ~or example, alka~i metal and~ in particular, ammo~.ium salts of fatty acids such as lauric or palmitic acid, o~ acid phosphoric acid alkyl esters such as sodium diethylhexylphosphate, of acid fatty alcohol sulfuric acid esters~ of paraffin sulfonic acids, of alkyl naphthalene sulfonic acids and of sulfosu~cinic acid dialkyl esters Also very suitable are the alkali m~tal and ammonium salts of fatty acids containing epoxy groups, such as ammonium epoxystearate, or, respectively, the alkali metal and a~monium salts of the products obtainable by reaction of per acids~ such as peracetic acid, with unsaturated fatty acids such as oleic or linoleic acid, with formation Or dihydroxy-stearic acid and hydroxyacetoxystearic acid, for instance;
as well as the alkali metal and ammonium salts of the r~actlon products of per acids with unsaturated hydroxy-fatty acids such as ricinoleic acid. Alternatively, cation-active e~ulsi-fiers, such as lauryl pyridinium hydrochloride5 may be used.
As examples of non-ionic emulsifiers, the following 1~376~
may be named: partial fatty acid esters of polyhydric alcohols~ snch as ~lycerin monoskearate, sorbital monolaurate or palmitate: partial fa~ty alcohol ethers of polyhydric alcohols- polyethoxylates of fatty alcohols or aro~atic hydroxy compoun~s~ as well as the known polypropylene oxide-polyethylene oxide condensation products.
The total quantity of ionic or non-ionic emulsifiers is usually about 0.001% to 1~ by weight, based on the weight o~
the monomer or monomers.
The protective colloids which may optionally be present as dispersin~ agents, are ~he natural or synthetic polymers which are normally employed as protective colloids in suspension ~olymerization. These are1 for example, polyvinyl alcohol, possibly also containing up to 40 mol /~o of acetyl groups;
gelatines and cellulose ether derivatives, such as water-~ . ._ soluble methyl cellulose, carboxymethyl cellulose and hydroxy-- ethyl~ellulose; as wellas copolymers of maleicacid ortheirhslf esters with styrene ortheir salts. The pro~ectivé colloids are used in quantities of 0.1% to 3% by weight, preferably 0.3~ to 2~ by weight~ based on the weight of the monomer or monomers.
Polymerization is effected in the usual manner, with the aid of monomer-soluble free-radical-forming catalysts.
Examples of these monomer-soluble ca-talysts are benzoyl peroxide, lauroyl peroxide, 2,4-dichlorobenzoyl peroxide, azo-isobvtyric acid dinitrile~ dialkyl peroxy-dicarbonates, as well as acetyl-cyclohexane-sulfonyl peroxide. These monomer-solllble catalysts are emplo~yed preferably in quantities of from 0.01% to ~% by wei~ht, advanta~eously 0 05% to 1% by wei~ht based on the weight of the monomer or monomers.
~ 3 ~ 8 ~
The usual polymerization aids other than those named above, such as parti~le and molecular size regulators, can be employed as well The quantity ratio of water to monomer to be polymerized is not c~itical~
The pH value of the polymerization batch is preferably ~ to 10 and the polymerization temperature preferably about 30 to ~0C. Since, ~enerally, polymer dispersions susceptible to shear are involved, overly vigorous agitation during poly-merizat,ion is to be a~oid~d~
The polymer dispersions to be degassed are transferred to a degassing vessel after completion of the polymerization.
Thereafter, a vacuum is created in the gas space above the polymer latex by using vacuum pumps. In so doing, an internal pressure is created which adjusts to correspond to the water vapor part~al pressure at the temperature of the dispersîon.
Then saturated, unsaturated, or superheated steam is introduced, at temperatures of between 50 and 90C, pr~erably 60 to ~0C, and a pressure between 0,1 and 0.~ bar, preferably 0.2 to 0.7 bar Naturally~ it is possible to draw the steam supplied for monomer removal into khe degassing vessel only if the internal pressure in the degassing vessel has a pressure at least lower than the steam to be drawn in. Steam of the aforementiQned specification can be produced, for example, by steam converters ~rom steam which is hotter and/or under higher pressure.
The treatment, according to the invention, of the polymer latices with steam of the aforementioned specification in degassin~ vessels whose internal pressure is lower than atmospheric pressure, ext~nds over a period of time of from 20 minutes to 3 hours. After this period~ any residual monomeric vinyl chloride is generally reduced to values below ~76 ~0 ppm For thls de~assing step~ steam quantities of 0.05 to 0.25 kg of steam per liter of dispersion are necessary~ The introduction of steam can be e~fected so tha-t generally no, or only a slight, volume increase of the polymer dispersion occurs. When proceeding according to the invention, the degassing process can be controlled so that heating of the dispersion to temperatures beyond gOC does not occur.
Nor~ally, howev~r, one operates at temperatures above 40C, as the degassing step would othe~ise take too long. The te~peratures of the pol-ymer dispersion can be established by the quantity and temperature of the admitted steam and the vacuum applied on the dispersion surface.
In another form of executing the process, regulation o~ the temperature of the polymer latex is effected externally, by supplylng or remo~ing hea~, so as to be able to Yary within . wide limits the quanti~y of admitted steam, whlch substantially influences the efficiency of the process.
The following examples are illustrative of khe process of the invention without belng limitative in any respect.
After the polymerization step, 4 liters o~ a vinyl chloride polymerizate dispersion,obtained by micro-suspension polymerization, were charged into a temperature-controllable cylindrical Yessel of 150 mm diameter and 400 mm height, which was also equipped with a propeller agitator. The dispersion was adjusted toan absolute pressure o~ 150 Torr and 60C. In the course of 2 hours, 0.10 kg of steam per liter of latex was passed through. The steam had a temperature of 63C and a pressure of 170 Torr. During the entire ~egassing time, the absolute pressure o~ 150 Torr was maintained in the degassing ves~el.
~ ~i7~ ~ ~
The initial monomer content of 1,360 ppm was reduced after one hour to lO~o and after two hours to below 40 ppm.
Coagulation did not oc¢ur.
EXAMPL~ 2 (Comparative Example) The process of Example 1 was repeated, but with a reduction of the quantity of steam to 0.045 kg of steam per liter of latex. The initial monomer content of 1,090 ppm was reduced, in thi~ case~ to ~9% after one hour and to 3~% after 10 two hours.
EXAMPL~_~
(Comparative Example~
The pro¢ess of Example 1 was repeated, but without : passage of steam~ The initial monomer content of 1,160 ppm was reduced after one hour to only ~2% and after two hours to only 6~% of the initial moncmer content.
The preceding speci~ic embodiments are illustrative of the practice of the in~ention. It is to be understood, however~
that other expedients known to those skilled in the art or disclosed herein, may be employed without departing from the spirit of the in~ention or the scope of the appended claims.
Claims (5)
1. A process for reducing the residual monomer content of an aqueous vinyl cyloride polymer dispersion sensi-tive to shear stresses, temperature stresses and mixed shear and temperature stresses produced by micro-suspension polymer-ization, without coagulation, said polymer in said dispersion containing at least 75% by weight of polymerized vinyl chloride units and having an average particle size of from 0.1 to 20 µ, said polymer dispersion having from 0.001% to 1% by weight of emulsifiers, based on the solids content of the dispersion, and being polymerized in the presence of monomer-soluble poly-merization catalysts, consisting of the steps of introducing from 0.05 to 0.25 kg of steam per liter of dispersion into said dispersion at a maximum dispersion temperature of 80°C
and at a steam temperature of from 60°C to 80°C and a steam pressure of between 0.2 to 0.7 bar over a period of from 20 minutes to 3 hours and passing said steam through said dis-persion while maintaining an internal pressure on said dis-persion corresponding at most to the water vapor partial pressure at the prevailing dispersion temperature, and recover-ing a polymer dispersion having a reduced residual monomer content with only a slight volume increase.
and at a steam temperature of from 60°C to 80°C and a steam pressure of between 0.2 to 0.7 bar over a period of from 20 minutes to 3 hours and passing said steam through said dis-persion while maintaining an internal pressure on said dis-persion corresponding at most to the water vapor partial pressure at the prevailing dispersion temperature, and recover-ing a polymer dispersion having a reduced residual monomer content with only a slight volume increase.
2. The process of claim 1 wherein the amount of steam being introduced per unit of time is greater toward the end of the introducing step than at the beginning of said introducing step.
3. The process of claim 1 wherein the initial residual monomer content in said dispersion is over 200 ppm and said polymer dispersion is recovered with a residual monomer content of under 40 ppm.
4. The process of claim 1 wherein said dispersion has a solids content of from 20% to 60% by weight.
5. The process of claim 1 wherein said aqueous vinyl chloride polymer dispersion is polymerized in the absence of protective colloids.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP2757168.2 | 1977-12-22 | ||
| DE19772757168 DE2757168A1 (en) | 1977-12-22 | 1977-12-22 | PROCESS FOR REDUCING THE MONOMER CONTENT IN SHEAR-SENSITIVE AND / OR TEMPERATURE-SENSITIVE POLYMER DISPERSIONS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1137688A true CA1137688A (en) | 1982-12-14 |
Family
ID=6026805
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000317253A Expired CA1137688A (en) | 1977-12-22 | 1978-12-01 | Process for reducing the residual monomer content in vinyl chloride polymer dispersions sensitive to shear and/or temperature stresses |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0002820B1 (en) |
| CA (1) | CA1137688A (en) |
| DE (2) | DE2757168A1 (en) |
| IT (1) | IT1111378B (en) |
| NO (1) | NO784319L (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2911333A1 (en) * | 1979-03-22 | 1980-10-02 | Wacker Chemie Gmbh | METHOD FOR POLYMERIZING VINYL CHLORIDE BY THE MICROSUSPENSION METHOD |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NO752264L (en) * | 1974-08-29 | 1976-03-02 | Huels Chemische Werke Ag | |
| DE2509937C3 (en) * | 1975-03-07 | 1981-04-16 | Hoechst Ag, 6000 Frankfurt | Device for the aftertreatment of homo- and copolymers of vinyl chloride |
| JPS51127187A (en) * | 1975-04-26 | 1976-11-05 | Kureha Chem Ind Co Ltd | A process and an apparatus for recovering monomers |
| BE829834A (en) * | 1975-06-04 | 1975-10-01 | PROCESS FOR THE ELIMINATION OF RESIDUAL VINYLIDENE CHLORIDE IN POLYMERS OF VINYLIDENE CHLORIDE |
-
1977
- 1977-12-22 DE DE19772757168 patent/DE2757168A1/en not_active Withdrawn
-
1978
- 1978-12-01 CA CA000317253A patent/CA1137688A/en not_active Expired
- 1978-12-20 IT IT52373/78A patent/IT1111378B/en active
- 1978-12-21 NO NO784319A patent/NO784319L/en unknown
- 1978-12-22 EP EP78101822A patent/EP0002820B1/en not_active Expired
- 1978-12-22 DE DE7878101822T patent/DE2861870D1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| EP0002820A1 (en) | 1979-07-11 |
| NO784319L (en) | 1979-06-25 |
| IT7852373A0 (en) | 1978-12-20 |
| DE2861870D1 (en) | 1982-07-15 |
| IT1111378B (en) | 1986-01-13 |
| DE2757168A1 (en) | 1979-07-05 |
| EP0002820B1 (en) | 1982-05-26 |
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