CA1105650A - Process for reducing the monomer content in expandable beads of thermoplastic materials - Google Patents
Process for reducing the monomer content in expandable beads of thermoplastic materialsInfo
- Publication number
- CA1105650A CA1105650A CA329,252A CA329252A CA1105650A CA 1105650 A CA1105650 A CA 1105650A CA 329252 A CA329252 A CA 329252A CA 1105650 A CA1105650 A CA 1105650A
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- CA
- Canada
- Prior art keywords
- beads
- water
- monomers
- monomer
- vessel
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- 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
- C08F6/006—Removal of residual monomers by chemical reaction, e.g. scavenging
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/22—After-treatment of expandable particles; Forming foamed products
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- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Organic Chemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
- Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
- Polymerisation Methods In General (AREA)
Abstract
ABSTRACT OF THE INVENTION
The invention relates to a process for reducing the monomer content in expandable thermoplastic beads which are produced by poylmerizing an ethylenically unsaturated monomer or a mixture of such monomers in aqueous suspension in the presence of a blowing agent. The residual monomers in both the beads and the process water are reduced by treatment of the slurry of beads and water obtained after polymerization in a vessel at a temper-ature above 65°C in the presence of at least one water soluble initiator.
In order to avoid the expansion of the beads the vessel is kept completely filled with a liquid, preferably water, during the temperature treatment.
The invention relates to a process for reducing the monomer content in expandable thermoplastic beads which are produced by poylmerizing an ethylenically unsaturated monomer or a mixture of such monomers in aqueous suspension in the presence of a blowing agent. The residual monomers in both the beads and the process water are reduced by treatment of the slurry of beads and water obtained after polymerization in a vessel at a temper-ature above 65°C in the presence of at least one water soluble initiator.
In order to avoid the expansion of the beads the vessel is kept completely filled with a liquid, preferably water, during the temperature treatment.
Description
This invention relates to a process for production of expandable thermo-plastic beads with a low residual monomer content.
E.xpandable thermoplastic beads, e.g. poly(vinylidene chloride - acrylo-nitrile), polystyrene or poly(styrene-acrylonitrile) beads, are produced com-mercially in a suspension polymerization process where the liquid monomer is dispersed in an aqueous medium containing one or several suspension agents, a hydrocarbon blowing agent and a polymerization initiator.
In the initial stage of the polymerization the monomers and the blowing agent form a droplet with only one phase. In a later stage of the polymer-10 ization the blowing agent is not soluble in the polymer phase and builds aseparate phase in form of small inclusions in the polymer droplet.
The obtained beads comprise polymer shells containing the liquid, vola-tile blowing agent. The beads expand by being heated to a temperature above the boiling point of the blowing agent and above the softening point of the polymer, e.g. at about 70C for poly(vinylidene chloride-acrylonitrile) - beads. The beads can be used for production of cellular ma~erial, which find many uses in e.g. the insulation industry or packaging industry.
A serious problem in all polymerization technique is the residual mono-- mer content. The monomers are more or less poisonous and as the polymeri-zation can never be conducted to a 100 per cent conversion, both the result-ing polymerizate and process water is contaminated with residual monomers.
I~is problem is especially accentuated in the polymerization of expandable beads as these also contain a third phase, i.e. the blowing agent, in which monomers may be dissolved.
'! Large amounts of acrylonitrlle in copolymers, e.g. poly(vinylidene chloride-acrylonitrile) and poly(styrene-acrylonitrile), drastically restrict the area of applications and the market for them, as free acrylonitrile in the process water as residual acrylonitrile in the beads increase the r ': ,,, : ~,.. ... ... .
: . ' : . : ::::. . .. :, . ' - :
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health hazards for the people handling the beads.
In recent years numerous methods for purifying polymeri~ates from residual monomer have been suggested, so called stripping, especially in the polyvinyl chloride technology. The most common methods relate to the use of elevated temperatures in order to cause diffusion of the monomers from the polymer phase. The elevated temperature increases the mobility of the monomer molecules and plasticises the polymer and both these factors in-creases the rate of stripping.
Today the most commonly used method for stripping vinyl chloride from polyvinyl chloride is to treat the resulting polymer and process water with steam at temperatures within the range of 80-125C at ambient pressure. In certain processes the stripping is conducted at reduced pressure. Such a process is descr:ibed in e.g. DT-OS 25 21 780.
'rhese methods are not possibLe to use in stripping monomers from ex-pandable beads, as these are very sensitive to heat and pressure. At higher temperatures, as well as at lower pressure, the beads will expand depending on the blowing agent. Another problem is that the monomers in expandable beads, and especially acrylonitrile, are more water soluble than vinyl chlor-ide, thus being more difficult to remove from the water phase. Moreover, many of the commonly used monomers in the production of expandable beads have a high boiling point which makes them difficult to remove from the water phase by raising the temperature. Thus acrylonitrile has a boiling point of 77~C, styrene 145C and vinylidene chloride 32C while vinyl chlor-ide has a boiling point of -14C.
The high concentration of blowing agent inside the beads and the high temperature at stripping produce a considerable pressure inside the beads and they expand in the unfilled or gas-filled part of the stripping device.
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-;
The pre-expanded beads constitute a problem and increase the cost oE
production, as they have to be separated by filtration or by other means from unexpanded beads, and ~he pre-expanded beads increase the amount of waste.
Attempts have been made to avoid the pre-expansion of the beads by appl~ing a high pressure, e.g. 500-1500 kPa of an insert gas, e.g. nitrogen, during stripping. However, this does not eliminate the pre-expanded beads.
The gas does not actually apply a higher pressure on the outside of the beads.
An equilibrium between the gas inside the beads and the gas in the "free volume" in the stripping device is established. The beads continue to ex-- pand because of the "free volume" and the high pressure of hydrocarbon in-side the beads.
According to the present invention a stripping process Eor expandable beads is provided, in which the pre-expansion of the beads is reduced to a considerable extent. The process also reduces the monomer content of the process water.
According to the invention there is provided a process for reducing the ~' monomer content in expandable thermoplastic beads produced by polymerizing an ethylenically unsaturated monomer or mixture of monomers in aqueous sus-pension in the presence of a blowing agent, wherein at least a part of an obtained slurry of expandable beads and water, in the presence of a water ; soluble initiator for ethylenically unsaturated monomers, is warmed to atemperature above 65C in a vessel which is completely filled with liquid medium, until an essential part of the monomer content is reduced.
By using a vessel completely filled with liquid media during the heat treatment of the expandable beads, the liquid applies a pressure on the surfaces of the beads which prevents them from expanding during the strip-ping process. The residual monomers in the expandable beads are in an . .
:. . ,.,. ................ , ~ . .: ,., : .. -., , . , . ~
~S6~i~
equilibrium with the monomers in the water phase. When the monomers are eliminated in the water phase by polymerization caused by the water sol-uble initiator it is believed that further monomer diffuse from the beads and the blowing agent in to the water phase, and the process performs as a stripping process. The diffusion is fairly rapid because of the rela-tively high temperature.
Preferably the vessel used is the polymerizing autoclave, but any suitable vessel could be used. By connecting e.g. the autoclave to an ex-ternal liquid pressure source, such as a water pipe or an expansion tank, which is partly filled with liquid media and which has suitable means for applying pressure to the water surface, the autoclave could easily be filled up during the temperature treatment of the slurry of beads. Suit-ably the vessel is kept filled by the addition of water. ~lowever, any suit-able liqu:id could be used~ such as, e.g. when stripping is conducted in a vessel separate from the autoclave, process water from a polymerization autoclave for expandable beads. If a vessel, separate from the autoclave, is used for the stripping process it is of course within the scope of the invention to add more liquid medium, e.g. water, in order to fill the vessel, or to subject part of the slurry of beads and water obtained after polymer-ization to the stripping process.
The temperature range for the treatment of the slurry can be varied within wide limits, and higher temperatures give a more efficient stripping.
The temperature should exceed 65C and the upper limit depends very much on the economical aspect and could be set to 150C. Good results are obtained when the temperature exceeds the glass transition temperature of the polymer in question. Suitably the range is within the interval of 70-120C~ and preferably 75-95C. ~le rate of stripping also depends on the time the slurry is subjected to the temperature treatment and e.g. at a temperature *
,,, , ~ .
, .: , ' , .,: ' ' ' . ~
s~
of 75C a suitable time for acrylonitrile/polyvinylidene chloride beads is 15 minutes up to 8 hours. At higher temperatures the time could be re-duced and at a stripping temperature of 95C a time of one hour gives a sufficient reduc~ion of the monomer content of the beads and the process water.
The necessary pressure on the filled vessel is a ~unction of both temp-erature and type of blowing agent and can easily be determined by simple tests. A blowing agent with a low boiling point naturally demands a higher pressure, otherwise the beads will expand and the pressure in the vessel will move some of the liquid medium back into the expansion tank. Accord-ingly, the minimum pressure in the expansion tank for a certain blowing agent should be so high that no liquid medium will be moved back into the ;
tank. The necessary pressure for e.g. polystyrene beads having pentane as blowing agent is within the range of 500-2000 kPa at temperatures of 75-95C, while isobutane, having a boiling point of about -12C, requires a pressure within the range of 1000-2500 kPa at the same temperatures.
As examples of suitable water soluble initiators for ethylenically unsaturated monomers well known inorganic, free radical initiators, such po~~.~ t~
as hydrogen-peroxide and ~&~iXffl or ammonium persulfates, or organic, free radical initiators, such as hydroperoxides, cyclohexanonperoxide or methyl isobutyl ketone peroxide could be mentioned. It is also within the scope of the invention to add a mixture of water soluble initiators or a combin-ation of a water soluble and a monomer soluble initiator, such as peroxides, e.g. Iauroylperoxide, peroxidicarbonates, e.g. cetylperoxidicarbonate or a~o compounds. The amount of water soluble initiator can be within the interval of 0.01-5% and preferably 0.1-2%, counted on the weight of the charged monomer.
. , : .: ;..... . . . : :
: : ' :
Suitable liquid volatile blowing agents are: petroleum ether, pentane, isopentane, neo-pentane, hexane, heptane, cyclopentane, cyclohexane, iso-butylene, n-butane and iso-butane. The blowing agents are in a known manner used in amounts of 2-95, preferably 5-40 per cent by weight based on the monomers.
The process of the invention is applicable to all ethylenically un-- saturated monomers or mixtures of such monomers capable of forming polymer ~ beads containing blowing agents. As examples of such monomers can be men-rnet~h~ l ;c tioned styrene, vinylidene chloride, acrylic esters ~ *~e~ e esters, acrylonitrile and methacrylonitrile.
The process is preferably used for expandable beads of styrene and up to 40~ of its weight of copolymerizable ethylenically ~msaturated monomers, especially copolymerization of styrene with up to 40 per cent by weight of acrylonitrile, based on the styrene, or copolymerization of vinylidene chloride and up to 40 per cent by weight of acrylonitrile or vinyl chloride, based on the vinylidene chloride, expecially copolymerization of 65-90 per cent by weight of vinylidene chloride and 35-10 per cent by weight of acrylonitrile. Most preferably the beads are produced by copolymerization, one co-monomer being acrylonitrile or methacrylonitrile.
The essential feature of the process is the use of a vessel which is com-pletely filled with liquid medium during the temperature treatment. It will be obvious that all known polymerization recipes for producing of expand-able beads from the above monomers are applicable.
It is of course possible to keep the reactor filled up during the poly-merization, or the final part of ~he polymerization, by connecting the re-actor to an external pressure source or expansion tank which is partly filled with water, and which has suitable means for applying pressure to the water surface. According to one embodiment the polymerization of the beads is - .
. , , -~
.:
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lnterrupted after 70% conversion~ preferably 95%, whereafter the water soluble initiator is charged and the autoclave is filled and the temp-erature is raised according to the invention during the final polymerization.
Example 1 (comparing test) The polymerization experiment was performed in a 13 1 reactor equip-ped with a stirrer and a mantle for heating and cooling ~he reaction medium.
The reactor was connected to an external tank which was also used for charg-ing the monomer mixture to the reactor.
- The following recipe was used to evaluate the system:
Vinylidene chloride/acrylonitrile ratio 70:30 100.0 parts Blowing agent, pentane 10.0 parts Suspension agent, polyvinyl alcohol1.0 part Suspensiorl agent, colloid oE silica type 0.5 parts ; Initiator, lau*yl peroxide 1.0 part Water 400.0 parts The water, 8.0 1, with the suspension agents was charged to the re-actor, and the reactor was evacuated for 900 s. The vinylidene chloride, --acrylonitrile, pentane and initiator (totally 2.9 1) was charged to the re-actor from the external tank. The temperature was raised to 55C and kept for 12 hours. The reactor was disconnected to the external tank during the polymerization and under these conditions the pressure rose to about 500 kPa.
The reactor was cooled from 55C to about 25C. The produced bead suspension did not contain pre-expanded beads and the amount of waste col-lected on a screen DIN 60 was about 15 g per 1000 g charged monomer.
The amounts of residual monomers in the beads were: Acrylonitrile 3200 mg/kg and vinylidene chloride 29000 mg/kg. The amount of acrylo-nitrile monomer in the process water was 1~10 mg/kg.
'' ~' '' ', "' ' ' .` : ~
56~ ;
Example ? ~comparing test) The polymerization was performed with the same recipe and the same procedure as in example l. ~lowever, after 12 hours of pol~llerization, 1.0 part of potassium persulphate in a water solution was charged to the reactor and the temperature raised to 75C and kept for 4 hours. The amount of waste was more than 100 g per 1000 g charged monomer.
The amounts of residual monomers in the beads were: Acrylonitrile 50 mg/kg and vinylidene chloride 1500 mg/kg and the amount of acrylo-nitrile in the process water was 30 mg/kg. As can be seen from this example the monomer content in the beads and the process water was considerably reduced, but the amount of pre-expanded beads was unacceptabLy high.
~xample 3 The polymerization was performed with the same recipe and the same pro-cedure as in example 1. However, after 12 hours of polymerization, 1.0 part of potassium persulphate in a water solution was charged to the reactor.
The reactor was connected to the external tank and was kept completely filled up with water from the tank at a pressure of 850 kPa. The temperature was raised to 75C and kept for 4 hours.
The amount of waste was 15 g per 1000 g charged monomer. The amount of residual monomer in the beads was: Acrylonitrile 50 mg/kg and vinylidene chloride 1450 mg/kg. The amount of acrylonitrile in the process water was 25 mg/kg.
By keeping the reactor completely filled with water according to the invention the monomer content in the beads and the process water could be considerably reduced and the amount of pre-expanded beads could be kept at a minimum.
E.xpandable thermoplastic beads, e.g. poly(vinylidene chloride - acrylo-nitrile), polystyrene or poly(styrene-acrylonitrile) beads, are produced com-mercially in a suspension polymerization process where the liquid monomer is dispersed in an aqueous medium containing one or several suspension agents, a hydrocarbon blowing agent and a polymerization initiator.
In the initial stage of the polymerization the monomers and the blowing agent form a droplet with only one phase. In a later stage of the polymer-10 ization the blowing agent is not soluble in the polymer phase and builds aseparate phase in form of small inclusions in the polymer droplet.
The obtained beads comprise polymer shells containing the liquid, vola-tile blowing agent. The beads expand by being heated to a temperature above the boiling point of the blowing agent and above the softening point of the polymer, e.g. at about 70C for poly(vinylidene chloride-acrylonitrile) - beads. The beads can be used for production of cellular ma~erial, which find many uses in e.g. the insulation industry or packaging industry.
A serious problem in all polymerization technique is the residual mono-- mer content. The monomers are more or less poisonous and as the polymeri-zation can never be conducted to a 100 per cent conversion, both the result-ing polymerizate and process water is contaminated with residual monomers.
I~is problem is especially accentuated in the polymerization of expandable beads as these also contain a third phase, i.e. the blowing agent, in which monomers may be dissolved.
'! Large amounts of acrylonitrlle in copolymers, e.g. poly(vinylidene chloride-acrylonitrile) and poly(styrene-acrylonitrile), drastically restrict the area of applications and the market for them, as free acrylonitrile in the process water as residual acrylonitrile in the beads increase the r ': ,,, : ~,.. ... ... .
: . ' : . : ::::. . .. :, . ' - :
il65~
health hazards for the people handling the beads.
In recent years numerous methods for purifying polymeri~ates from residual monomer have been suggested, so called stripping, especially in the polyvinyl chloride technology. The most common methods relate to the use of elevated temperatures in order to cause diffusion of the monomers from the polymer phase. The elevated temperature increases the mobility of the monomer molecules and plasticises the polymer and both these factors in-creases the rate of stripping.
Today the most commonly used method for stripping vinyl chloride from polyvinyl chloride is to treat the resulting polymer and process water with steam at temperatures within the range of 80-125C at ambient pressure. In certain processes the stripping is conducted at reduced pressure. Such a process is descr:ibed in e.g. DT-OS 25 21 780.
'rhese methods are not possibLe to use in stripping monomers from ex-pandable beads, as these are very sensitive to heat and pressure. At higher temperatures, as well as at lower pressure, the beads will expand depending on the blowing agent. Another problem is that the monomers in expandable beads, and especially acrylonitrile, are more water soluble than vinyl chlor-ide, thus being more difficult to remove from the water phase. Moreover, many of the commonly used monomers in the production of expandable beads have a high boiling point which makes them difficult to remove from the water phase by raising the temperature. Thus acrylonitrile has a boiling point of 77~C, styrene 145C and vinylidene chloride 32C while vinyl chlor-ide has a boiling point of -14C.
The high concentration of blowing agent inside the beads and the high temperature at stripping produce a considerable pressure inside the beads and they expand in the unfilled or gas-filled part of the stripping device.
-i , . ~ .
-;
The pre-expanded beads constitute a problem and increase the cost oE
production, as they have to be separated by filtration or by other means from unexpanded beads, and ~he pre-expanded beads increase the amount of waste.
Attempts have been made to avoid the pre-expansion of the beads by appl~ing a high pressure, e.g. 500-1500 kPa of an insert gas, e.g. nitrogen, during stripping. However, this does not eliminate the pre-expanded beads.
The gas does not actually apply a higher pressure on the outside of the beads.
An equilibrium between the gas inside the beads and the gas in the "free volume" in the stripping device is established. The beads continue to ex-- pand because of the "free volume" and the high pressure of hydrocarbon in-side the beads.
According to the present invention a stripping process Eor expandable beads is provided, in which the pre-expansion of the beads is reduced to a considerable extent. The process also reduces the monomer content of the process water.
According to the invention there is provided a process for reducing the ~' monomer content in expandable thermoplastic beads produced by polymerizing an ethylenically unsaturated monomer or mixture of monomers in aqueous sus-pension in the presence of a blowing agent, wherein at least a part of an obtained slurry of expandable beads and water, in the presence of a water ; soluble initiator for ethylenically unsaturated monomers, is warmed to atemperature above 65C in a vessel which is completely filled with liquid medium, until an essential part of the monomer content is reduced.
By using a vessel completely filled with liquid media during the heat treatment of the expandable beads, the liquid applies a pressure on the surfaces of the beads which prevents them from expanding during the strip-ping process. The residual monomers in the expandable beads are in an . .
:. . ,.,. ................ , ~ . .: ,., : .. -., , . , . ~
~S6~i~
equilibrium with the monomers in the water phase. When the monomers are eliminated in the water phase by polymerization caused by the water sol-uble initiator it is believed that further monomer diffuse from the beads and the blowing agent in to the water phase, and the process performs as a stripping process. The diffusion is fairly rapid because of the rela-tively high temperature.
Preferably the vessel used is the polymerizing autoclave, but any suitable vessel could be used. By connecting e.g. the autoclave to an ex-ternal liquid pressure source, such as a water pipe or an expansion tank, which is partly filled with liquid media and which has suitable means for applying pressure to the water surface, the autoclave could easily be filled up during the temperature treatment of the slurry of beads. Suit-ably the vessel is kept filled by the addition of water. ~lowever, any suit-able liqu:id could be used~ such as, e.g. when stripping is conducted in a vessel separate from the autoclave, process water from a polymerization autoclave for expandable beads. If a vessel, separate from the autoclave, is used for the stripping process it is of course within the scope of the invention to add more liquid medium, e.g. water, in order to fill the vessel, or to subject part of the slurry of beads and water obtained after polymer-ization to the stripping process.
The temperature range for the treatment of the slurry can be varied within wide limits, and higher temperatures give a more efficient stripping.
The temperature should exceed 65C and the upper limit depends very much on the economical aspect and could be set to 150C. Good results are obtained when the temperature exceeds the glass transition temperature of the polymer in question. Suitably the range is within the interval of 70-120C~ and preferably 75-95C. ~le rate of stripping also depends on the time the slurry is subjected to the temperature treatment and e.g. at a temperature *
,,, , ~ .
, .: , ' , .,: ' ' ' . ~
s~
of 75C a suitable time for acrylonitrile/polyvinylidene chloride beads is 15 minutes up to 8 hours. At higher temperatures the time could be re-duced and at a stripping temperature of 95C a time of one hour gives a sufficient reduc~ion of the monomer content of the beads and the process water.
The necessary pressure on the filled vessel is a ~unction of both temp-erature and type of blowing agent and can easily be determined by simple tests. A blowing agent with a low boiling point naturally demands a higher pressure, otherwise the beads will expand and the pressure in the vessel will move some of the liquid medium back into the expansion tank. Accord-ingly, the minimum pressure in the expansion tank for a certain blowing agent should be so high that no liquid medium will be moved back into the ;
tank. The necessary pressure for e.g. polystyrene beads having pentane as blowing agent is within the range of 500-2000 kPa at temperatures of 75-95C, while isobutane, having a boiling point of about -12C, requires a pressure within the range of 1000-2500 kPa at the same temperatures.
As examples of suitable water soluble initiators for ethylenically unsaturated monomers well known inorganic, free radical initiators, such po~~.~ t~
as hydrogen-peroxide and ~&~iXffl or ammonium persulfates, or organic, free radical initiators, such as hydroperoxides, cyclohexanonperoxide or methyl isobutyl ketone peroxide could be mentioned. It is also within the scope of the invention to add a mixture of water soluble initiators or a combin-ation of a water soluble and a monomer soluble initiator, such as peroxides, e.g. Iauroylperoxide, peroxidicarbonates, e.g. cetylperoxidicarbonate or a~o compounds. The amount of water soluble initiator can be within the interval of 0.01-5% and preferably 0.1-2%, counted on the weight of the charged monomer.
. , : .: ;..... . . . : :
: : ' :
Suitable liquid volatile blowing agents are: petroleum ether, pentane, isopentane, neo-pentane, hexane, heptane, cyclopentane, cyclohexane, iso-butylene, n-butane and iso-butane. The blowing agents are in a known manner used in amounts of 2-95, preferably 5-40 per cent by weight based on the monomers.
The process of the invention is applicable to all ethylenically un-- saturated monomers or mixtures of such monomers capable of forming polymer ~ beads containing blowing agents. As examples of such monomers can be men-rnet~h~ l ;c tioned styrene, vinylidene chloride, acrylic esters ~ *~e~ e esters, acrylonitrile and methacrylonitrile.
The process is preferably used for expandable beads of styrene and up to 40~ of its weight of copolymerizable ethylenically ~msaturated monomers, especially copolymerization of styrene with up to 40 per cent by weight of acrylonitrile, based on the styrene, or copolymerization of vinylidene chloride and up to 40 per cent by weight of acrylonitrile or vinyl chloride, based on the vinylidene chloride, expecially copolymerization of 65-90 per cent by weight of vinylidene chloride and 35-10 per cent by weight of acrylonitrile. Most preferably the beads are produced by copolymerization, one co-monomer being acrylonitrile or methacrylonitrile.
The essential feature of the process is the use of a vessel which is com-pletely filled with liquid medium during the temperature treatment. It will be obvious that all known polymerization recipes for producing of expand-able beads from the above monomers are applicable.
It is of course possible to keep the reactor filled up during the poly-merization, or the final part of ~he polymerization, by connecting the re-actor to an external pressure source or expansion tank which is partly filled with water, and which has suitable means for applying pressure to the water surface. According to one embodiment the polymerization of the beads is - .
. , , -~
.:
i;5~
lnterrupted after 70% conversion~ preferably 95%, whereafter the water soluble initiator is charged and the autoclave is filled and the temp-erature is raised according to the invention during the final polymerization.
Example 1 (comparing test) The polymerization experiment was performed in a 13 1 reactor equip-ped with a stirrer and a mantle for heating and cooling ~he reaction medium.
The reactor was connected to an external tank which was also used for charg-ing the monomer mixture to the reactor.
- The following recipe was used to evaluate the system:
Vinylidene chloride/acrylonitrile ratio 70:30 100.0 parts Blowing agent, pentane 10.0 parts Suspension agent, polyvinyl alcohol1.0 part Suspensiorl agent, colloid oE silica type 0.5 parts ; Initiator, lau*yl peroxide 1.0 part Water 400.0 parts The water, 8.0 1, with the suspension agents was charged to the re-actor, and the reactor was evacuated for 900 s. The vinylidene chloride, --acrylonitrile, pentane and initiator (totally 2.9 1) was charged to the re-actor from the external tank. The temperature was raised to 55C and kept for 12 hours. The reactor was disconnected to the external tank during the polymerization and under these conditions the pressure rose to about 500 kPa.
The reactor was cooled from 55C to about 25C. The produced bead suspension did not contain pre-expanded beads and the amount of waste col-lected on a screen DIN 60 was about 15 g per 1000 g charged monomer.
The amounts of residual monomers in the beads were: Acrylonitrile 3200 mg/kg and vinylidene chloride 29000 mg/kg. The amount of acrylo-nitrile monomer in the process water was 1~10 mg/kg.
'' ~' '' ', "' ' ' .` : ~
56~ ;
Example ? ~comparing test) The polymerization was performed with the same recipe and the same procedure as in example l. ~lowever, after 12 hours of pol~llerization, 1.0 part of potassium persulphate in a water solution was charged to the reactor and the temperature raised to 75C and kept for 4 hours. The amount of waste was more than 100 g per 1000 g charged monomer.
The amounts of residual monomers in the beads were: Acrylonitrile 50 mg/kg and vinylidene chloride 1500 mg/kg and the amount of acrylo-nitrile in the process water was 30 mg/kg. As can be seen from this example the monomer content in the beads and the process water was considerably reduced, but the amount of pre-expanded beads was unacceptabLy high.
~xample 3 The polymerization was performed with the same recipe and the same pro-cedure as in example 1. However, after 12 hours of polymerization, 1.0 part of potassium persulphate in a water solution was charged to the reactor.
The reactor was connected to the external tank and was kept completely filled up with water from the tank at a pressure of 850 kPa. The temperature was raised to 75C and kept for 4 hours.
The amount of waste was 15 g per 1000 g charged monomer. The amount of residual monomer in the beads was: Acrylonitrile 50 mg/kg and vinylidene chloride 1450 mg/kg. The amount of acrylonitrile in the process water was 25 mg/kg.
By keeping the reactor completely filled with water according to the invention the monomer content in the beads and the process water could be considerably reduced and the amount of pre-expanded beads could be kept at a minimum.
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Process for reducing the monomer content in expandable thermoplastic beads produced by polymerizing an ethylenically unsaturated monomer or mixture of monomers in aqueous suspension in the presence of a blowing agent, wherein at least a part of an obtained slurry of expandable beads and water, in the presence of a water soluble initiator for ethylenically unsaturated monomers, is warmed to a temperature above 65°C in a vessel which is completely filled with liquid medium, until an essential part of the monomer content is reduced.
2. Process according to claim 1, characterized in that the vessel is the polymerizing autoclave.
3. Process according to claim l in which the temperature is within the range of about 65-150°C.
4. Process according to claim 1, characterized in that the temperature is within the range of about 70-120°C.
5. Process according to claim 1, characterized in that the liquid medium is water.
6. Process according to claim 1, characterized in that at least one monomer is acrylonitrile.
7. Process according to claim 1 wherein the obtained slurry of expandable beads is polymerized to a conversion exceeding 70% before the addition of the water soluble initiator.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7806665-1 | 1978-06-08 | ||
| SE7806665A SE429238B (en) | 1978-06-08 | 1978-06-08 | SET TO REDUCE MONOMER CONTENT IN EXPANDABLE TERMOPLASTES |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1105650A true CA1105650A (en) | 1981-07-21 |
Family
ID=20335152
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA329,252A Expired CA1105650A (en) | 1978-06-08 | 1979-06-07 | Process for reducing the monomer content in expandable beads of thermoplastic materials |
Country Status (15)
| Country | Link |
|---|---|
| JP (1) | JPS5835618B2 (en) |
| AT (1) | AT379162B (en) |
| AU (1) | AU512761B2 (en) |
| BE (1) | BE876836A (en) |
| CA (1) | CA1105650A (en) |
| CH (1) | CH642384A5 (en) |
| DE (1) | DE2923310B2 (en) |
| DK (1) | DK238379A (en) |
| FI (1) | FI65793C (en) |
| FR (1) | FR2428057A1 (en) |
| GB (1) | GB2025429B (en) |
| IT (1) | IT1116551B (en) |
| NL (1) | NL177497C (en) |
| NO (1) | NO151663C (en) |
| SE (1) | SE429238B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4550003A (en) * | 1983-12-13 | 1985-10-29 | Asahi Kasei Kogyo Kabushiki Kaisha | Vinylidene chloride type resin expandable particles, foam particles, in-mold foam molding by use thereof and process for producing them |
| KR102418722B1 (en) | 2014-11-26 | 2022-07-07 | 마쓰모토유시세이야쿠 가부시키가이샤 | Thermally expandable microspheres and use of same |
| CN109456506A (en) * | 2018-11-07 | 2019-03-12 | 西能化工科技(上海)有限公司 | The heat-expandable microsphere and preparation method thereof of low residual monomer content |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1160184B (en) * | 1961-08-22 | 1963-12-27 | Oldrich Marek | Process for the production of foamable thermoplastic polymers |
| US3425966A (en) * | 1965-03-01 | 1969-02-04 | Dow Chemical Co | Three stage suspension polymerization process for vinyl aryl monomers |
| FR1480502A (en) * | 1965-05-13 | 1967-05-12 | Foster Grant Co Inc | Process for preparing expandable plastic particles |
| DE2511315A1 (en) * | 1975-03-19 | 1976-09-23 | Sealed Air Corp | METHOD OF MANUFACTURING FOAMABLE STYLE POLYMER PIECES |
| DE2734607A1 (en) * | 1977-08-01 | 1979-02-15 | Basf Ag | PROCESS FOR THE MANUFACTURING OF SPHERICAL EXPANDABLE STYRENE POLYMERIZES |
-
1978
- 1978-06-08 SE SE7806665A patent/SE429238B/en not_active IP Right Cessation
- 1978-06-09 FI FI781847A patent/FI65793C/en not_active IP Right Cessation
-
1979
- 1979-05-18 AU AU47200/79A patent/AU512761B2/en not_active Expired
- 1979-05-28 AT AT0386279A patent/AT379162B/en not_active IP Right Cessation
- 1979-06-06 JP JP54070017A patent/JPS5835618B2/en not_active Expired
- 1979-06-06 IT IT49329/79A patent/IT1116551B/en active
- 1979-06-06 NL NLAANVRAGE7904447,A patent/NL177497C/en not_active IP Right Cessation
- 1979-06-07 BE BE0/195626A patent/BE876836A/en not_active IP Right Cessation
- 1979-06-07 NO NO791908A patent/NO151663C/en unknown
- 1979-06-07 CA CA329,252A patent/CA1105650A/en not_active Expired
- 1979-06-07 FR FR7914526A patent/FR2428057A1/en active Granted
- 1979-06-08 DE DE2923310A patent/DE2923310B2/en not_active Ceased
- 1979-06-08 GB GB7920135A patent/GB2025429B/en not_active Expired
- 1979-06-08 CH CH538979A patent/CH642384A5/en not_active IP Right Cessation
- 1979-06-08 DK DK238379A patent/DK238379A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| NO151663B (en) | 1985-02-04 |
| SE7806665L (en) | 1979-12-09 |
| NL7904447A (en) | 1979-12-11 |
| DE2923310B2 (en) | 1980-12-11 |
| AU4720079A (en) | 1979-12-13 |
| SE429238B (en) | 1983-08-22 |
| AT379162B (en) | 1985-11-25 |
| ATA386279A (en) | 1985-04-15 |
| AU512761B2 (en) | 1980-10-23 |
| GB2025429A (en) | 1980-01-23 |
| DE2923310A1 (en) | 1979-12-13 |
| JPS54163966A (en) | 1979-12-27 |
| NL177497C (en) | 1985-10-01 |
| BE876836A (en) | 1979-12-07 |
| NL177497B (en) | 1985-05-01 |
| FR2428057B1 (en) | 1984-09-14 |
| NO151663C (en) | 1985-05-15 |
| FR2428057A1 (en) | 1980-01-04 |
| CH642384A5 (en) | 1984-04-13 |
| JPS5835618B2 (en) | 1983-08-03 |
| GB2025429B (en) | 1982-12-01 |
| FI65793C (en) | 1984-07-10 |
| FI65793B (en) | 1984-03-30 |
| IT1116551B (en) | 1986-02-10 |
| DK238379A (en) | 1979-12-09 |
| FI781847A (en) | 1979-12-09 |
| IT7949329A0 (en) | 1979-06-06 |
| NO791908L (en) | 1979-12-11 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |