WO2013092730A1 - Process for preparing a vinyl chloride polymer - Google Patents

Process for preparing a vinyl chloride polymer Download PDF

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Publication number
WO2013092730A1
WO2013092730A1 PCT/EP2012/076177 EP2012076177W WO2013092730A1 WO 2013092730 A1 WO2013092730 A1 WO 2013092730A1 EP 2012076177 W EP2012076177 W EP 2012076177W WO 2013092730 A1 WO2013092730 A1 WO 2013092730A1
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Prior art keywords
polymerization
complexing agent
vinyl chloride
reduction
water
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PCT/EP2012/076177
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French (fr)
Inventor
Séverine ROCHARD
François BIRAL
Frédéric BOSCHET
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Solvay Sa
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Publication of WO2013092730A1 publication Critical patent/WO2013092730A1/en

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    • 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
    • C08F14/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
    • C08F14/02—Monomers containing chlorine
    • C08F14/04—Monomers containing two carbon atoms
    • C08F14/06—Vinyl chloride

Definitions

  • the present invention relates to a process for preparing a vinyl chloride polymer (PVC).
  • PVC vinyl chloride polymer
  • the invention relates more particularly to a process for preparing such a polymer, including a polymerization step performed in aqueous dispersion, usually as an aqueous microsuspension.
  • the invention also relates to the vinyl chloride polymers obtained via this process.
  • microsuspension polymerization It is known practice to prepare vinyl chloride polymers via a process known conventionally as "microsuspension polymerization".
  • This process includes a step during which droplets of at least one monomer, which is vinyl chloride (VC), are finely and homogeneously dispersed in an aqueous medium, in the presence of liposoluble radical initiators (also known more simply as liposoluble initiators), by means of powerful stirring and the presence of emulsifiers, such as alkali metal or ammonium carboxylates and alkylsulfonates, optionally in combination with liposoluble cosurfactants, such as long-chain alcohols.
  • liposoluble radical initiators also known more simply as liposoluble initiators
  • emulsifiers such as alkali metal or ammonium carboxylates and alkylsulfonates
  • liposoluble cosurfactants such as long-chain alcohols.
  • the microsuspension polymerization of VC has a drawback: the start of the polymerization is relatively slow, which has the consequences of lengthening the polymer production cycles and of using relatively higher doses of liposoluble initiators.
  • this polymerization of exothermic nature is frequently performed in at least one reactor of tank type with mechanical stirring.
  • the heat exchange required for the thermal control then takes place advantageously by means of a jacket inside which circulates a heat- exchange fluid (water), generally counter-currentwise. Given the slow kinetics of the polymerization, the cooling capacity of the jacket is not used optimally during part of this polymerization.
  • polymerization kinetics via the "seeded microsuspension” method i.e. a microsuspension polymerization in which the reaction medium contains a "seed” which is in the form of an aqueous dispersion of PVC particles containing all of the liposoluble initiator necessary for the polymerization
  • an activating system is an organosoluble metal complex that is preformed or formed by reaction of a water- soluble metal salt with a complexing agent.
  • the complexing agent should be capable of modifying the water-soluble form of the metal salt into a VC-soluble form and of not having any inhibitory action on the polymerization or on the activation of the initiator by the metal.
  • Complexing agents that satisfy these conditions are monocarboxylic acids that are sparingly water-soluble; polycarboxylic acids and the corresponding anhydrides thereof; alkylphosphoric acids; lactones; ketones bearing, in the a or ⁇ position, groups that activate the carbonyl function; and carbazones.
  • the complexing agent is usually introduced gradually throughout the polymerization or during part of this polymerization, and its addition is usually stopped when a pressure drop is detected.
  • the salt may be introduced into the reaction zone before or during the polymerization. In the latter case, it is either in a mixture with the complexing agent or in the form of a separate aqueous solution.
  • the water-soluble metal salt used in practice is copper sulfate.
  • the present invention is directed towards providing a process for preparing
  • PVC which solves these problems by means of introducing, at a particular moment, into the polymerization medium, at least the complexing agent described above, making it possible to accelerate the decrease of the VC autogenous pressure and the self -heating, and improving the efficacy of removal of the residual VC.
  • the present invention thus relates mainly to a process for preparing a vinyl chloride polymer, comprising a step of polymerizing at least vinyl chloride, the said step being performed in aqueous dispersion in the presence of at least one liposoluble radical initiator and being continued up to the reduction of the autogenous pressure of vinyl chloride with introduction, into the polymerization medium, of an activating system comprising a water-soluble transition metal salt and a complexing agent, at least the complexing agent being introduced in total into the said polymerization medium from the start of the said pressure reduction.
  • liposoluble radical initiator will also be referred to more simply and without preference as the “liposoluble initiator” or the “initiator”.
  • chlorinated monomers such as vinylidene chloride, fluorinated monomers such as vinylidene fluoride, monomers containing both chlorine and fluorine such as
  • vinyl esters such as vinyl acetate, vinyl ethers such as methyl vinyl ether, dialkyl maleates such as dibutyl maleate, (meth)acrylic monomers such as n-butyl acrylate and methyl methacrylate, styrene monomers such as styrene, and olefinic monomers such as ethylene, propylene and butadiene.
  • vinyl chloride polymers preference is accorded to vinyl chloride homopolymers.
  • the polymerization step included in the process for preparing the VC polymer according to the invention is performed in aqueous dispersion in a stirred reactor. In the present description, the expression "polymerization...
  • polymerization in aqueous dispersion is intended to denote polymerizations performed according to a radical mechanism in dispersed medium with the intervention of at least one liposoluble initiator.
  • polymerizations include not only the polymerization conventionally known as “suspension” polymerization, but also polymerizations known as “microsuspension” and “seeded microsuspension” polymerization.
  • the polymerization step is performed in microsuspension or in seeded microsuspension.
  • the second constituent of the activating system is a complexing agent.
  • complexing agent is intended to denote any chemical compound that is capable of changing the transition metal from its water-soluble form to the form of a metal complex that is soluble in VC, without exerting any inhibitory action on the polymerization or on the activation exerted by the transition metal on the liposoluble initiator.
  • the presence of several water-soluble transition metal salts and/or of several complexing agents in the same activating system is not at all excluded from the scope of the invention.
  • the terms "water-soluble transition metal salt” and “complexing agent” are thus used indiscriminantly in the singular or in the plural.
  • the activating system comprises only one water-soluble transition metal salt and only one complexing agent.
  • An activating system comprising a water-soluble transition metal salt chosen from copper salts and zinc salts (advantageously zinc salts), preferably from copper sulfate and zinc sulfate (advantageously copper sulfate), and ascorbic acid as complexing agent, gave excellent results.
  • a water-soluble transition metal salt chosen from copper salts and zinc salts (advantageously zinc salts), preferably from copper sulfate and zinc sulfate (advantageously copper sulfate), and ascorbic acid as complexing agent, gave excellent results.
  • at least the complexing agent is introduced in total into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride.
  • this introduction may take place at any moment from the start (t x ) of the said pressure reduction up to the end of the polymerization step, brought about either by addition of an inhibitor (a base such as aqueous ammonia, phenol, etc.) or by raising the temperature (self- heating), preferably by raising the temperature (self-heating) in the case of aqueous microsuspension polymerization (seeded or unseeded).
  • an inhibitor a base such as aqueous ammonia, phenol, etc.
  • the complexing agent is preferably introduced in a single batch at any fraction of z between t x and t z including addition in a single batch at t x or continuously, over z or over a fraction of z between t x and t z , at a constant rate or at a decreasing rate.
  • the complexing agent is introduced in a single batch at any fraction of z between t x and t z including addition in a single batch at t x .
  • the complexing agent and the water-soluble transition metal salt are advantageously introduced, separately or together, in one of the ways below taken separately or in combination,
  • the complexing agent and the water-soluble transition metal salt are preferably both introduced in a single batch at any fraction of z between t x and t z , including addition in a single batch at t x or continuously, over z or over a fraction of z between t x and t z , at a constant rate or at a decreasing rate.
  • the complexing agent and the water-soluble transition metal salt are both introduced in a single batch at any fraction of z between t x and t z including addition in a single batch at t x .
  • the amount of salt, expressed on a weight basis relative to the weight of complexing agent, introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride is between 0.1 and 5. Preferably, it is between 0.15 and 3. Even more preferably, the amount of salt introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride, thus expressed, is between 0.2 and 2.
  • the expression “the water-soluble metal salt is introduced at least partly” is intended to denote that either the water-soluble metal salt is introduced partly, or the water-soluble metal salt is introduced in total, into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride.
  • the water-soluble metal salt is introduced in total into the
  • start of the polymerization step should be understood as meaning the moment (referred to as to) at which the polymerization temperature is reached (to within + 1°C).
  • the expression "introduced at the very latest at the start of the polymerization step” should be understood as meaning introduced at a moment between the introduction of the first of the constituents of the medium in which the polymerization step is performed and the moment 3 ⁇ 4.
  • the water-soluble transition metal salt of the activating system is thus advantageously introduced at any moment between the introduction of the first of the constituents of the medium in which the polymerization step is performed and the moment 3 ⁇ 4 at which the polymerization temperature is reached (to within + 1°C) (commonly referred to as "initial").
  • it is introduced with the other constituents of the medium in which the polymerization step is performed before raising the temperature.
  • the water-soluble transition metal may be introduced in solid form, in the form of an aqueous solution or as a mixture with an emulsifier solution. It is preferably introduced in solid form.
  • the water-soluble transition metal salt of the activating system may be introduced via the "seed".
  • the water-soluble transition metal salt is thus advantageously introduced from to and at the very latest up to t x ("delayed"). If we call x the time elapsed between the start of the polymerization step (moment 3 ⁇ 4 at which the polymerization temperature is reached (to within + 1 °C)) and the moment t x at which the reduction of the VC autogenous pressure starts, the water-soluble transition metal salt is thus advantageously introduced - in a single batch at any fraction of x between 3 ⁇ 4 and t x including addition in a single batch at t x ,
  • the water-soluble transition metal salt is particularly preferably introduced continuously, over x or over a fraction of x between 3 ⁇ 4 and t x , at a constant rate or at a decreasing rate.
  • the complexing agent is introduced with the water- soluble transition metal salt, at least partly, they may be introduced in the form of an aqueous solution containing them both (referred to hereinbelow as a mixture) or alternatively by mixing two aqueous solutions each containing one of the two constituents.
  • An emulsifying agent may be added to these solutions or added in the form of a separate aqueous solution.
  • they are introduced in the form of an aqueous solution containing them both (referred to hereinbelow as a mixture).
  • the water-soluble transition metal salt is introduced at the very latest at 3 ⁇ 4 and the complexing agent is introduced from t x to t z ;
  • the water-soluble transition metal salt is introduced at the very latest at 3 ⁇ 4 and from to to t x and the complexing agent is introduced from t x to t z ; - the water-soluble transition metal salt is introduced from 3 ⁇ 4 to t x and the complexing agent is introduced from t x to t z .
  • the water-soluble transition metal salt is introduced at the very latest at 3 ⁇ 4 and from to to t x and a mixture of the water-soluble transition metal salt and of the complexing agent is introduced from t x to t z ;
  • the water-soluble transition metal salt is introduced from 3 ⁇ 4 to t x and a mixture of the water-soluble transition metal salt and of the complexing agent is introduced from t x to t z .
  • the amounts in which they are introduced may vary within a wide range.
  • the amount of water-soluble transition metal salt introduced is greater than or equal to 10 "5 mol of the said salt per mole of initiator.
  • the amount of water-soluble transition metal salt introduced, thus expressed is greater than or equal to 10 "4 mol of the said salt per mole of initiator.
  • the amount of water-soluble transition metal salt introduced, thus expressed is greater than or equal to 5x10 "3 mol of the said salt per mole of initiator.
  • the amount of water-soluble transition metal salt introduced is less than or equal to 50 mol of the said salt per mole of initiator.
  • the amount of water-soluble transition metal salt introduced, thus expressed is less than 5 mol of the said salt per mole of initiator.
  • the amount of water-soluble transition metal salt introduced, thus expressed is less than or equal to 0.5 mol of the said salt per mole of initiator.
  • the amount of water-soluble transition metal salt introduced is advantageously greater than or equal to 1 ppm and preferably greater than or equal to 5 ppm.
  • the amount of water-soluble transition metal salt introduced is advantageously less than or equal to 300 ppm and preferably less than or equal to 200 ppm.
  • the amount of complexing agent introduced is greater than or equal to 0.05 mol of complexing agent per mole of salt.
  • the amount of complexing agent introduced, thus expressed is greater than 0.1 mol of complexing agent per mole of salt. Even more preferably, the amount of complexing agent introduced, thus expressed, is greater than or equal to 0.5 mol of complexing agent per mole of salt.
  • the amount of complexing agent introduced is greater than or equal to 50 mol of complexing agent per mole of salt.
  • the amount of complexing agent introduced, thus expressed is less than or equal to 20 mol of complexing agent per mole of salt. Even more preferably, the amount of complexing agent introduced, thus expressed, is less than or equal to 5 mol of complexing agent per mole of salt.
  • the complexing agent and the water-soluble transition metal salt are preferably introduced in total into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride.
  • the present invention also relates to the vinyl chloride polymers obtained via a process comprising a step of polymerizing at least vinyl chloride, the said step being performed in aqueous dispersion in the presence of at least one liposoluble radical initiator and being continued up to the reduction of the autogenous pressure of vinyl chloride with introduction, into the polymerization medium, of an activating system comprising a water-soluble transition metal salt and a complexing agent, at least the complexing agent being introduced in total into the said polymerization medium from the start of the said pressure reduction.
  • the process according to the invention has the advantage of leading to the production of polymers that are characterized by a low residual VC content.
  • the process is also characterized by short polymerization times and the content of dry lumps and cakes observed after polymerization is significantly low.
  • the use of a zinc salt has the particular advantage of leading to polymers that are characterized by better thermal stability and a lower content of dry lumps and cakes after the polymerization, in other words to a better compromise in terms of polymerization kinetics/properties of the polymers obtained, than when a copper salt is used.
  • the second embodiment of the process according to the invention has advantages over the first enbodiment, namely it is characterized by a shorter polymerization time, a higher ⁇ maximum and a lower content of dry lumps and cakes, and the polymers obtained are characterized by a lower residual VC content and an improved yellow index.
  • the process according to the invention leads to the production of polymers that is characterized by a lower residual VC content and characterized by a shorter total polymerization time.
  • the process according to the invention also solves the characteristic problems of the process according to the prior art (slowness of the pressure reduction up to the self-heating).
  • a sample of latex was taken from the storage tank and its solids content was measured by densimetry: the solids content of the seed latex S was 34.1%.
  • the distribution of the elementary polymer particles of the seed latex was also determined by photosedimentometry using a CPS machine formed from a centrifugation unit, a detector and a control/analysis device: the distribution of the elementary polymer particles of the seed latex S was unimodal; the mean diameter of these elementary particles was 105 nm.
  • butylhydroxyanisole were then introduced.
  • the mixing autoclave was closed and the stirrer switched on.
  • the mixing autoclave was then placed under vacuum.
  • a high-pressure homogenizer connecting the mixing autoclave to the reactor was switched on.
  • the homogenization pressure was adjusted.
  • the contents of the mixing autoclave were transferred into the reactor via this homogenizer.
  • the operating conditions of the homogenizer were such that a fine aqueous dispersion of VC droplets comprising the liposoluble initiators and the peak suppressant was obtained at its outlet.
  • the contents of the reactor were brought to 46°C. Once this temperature was reached, 0.146 kg of an aqueous ammonia solution at 222.5 g/L was introduced into the reactor.
  • a purification treatment of the residual VC was performed.
  • the latex was emptied out and the reactor cleaned.
  • the latex was filtered through a screen with a mesh size of 1 mm.
  • the wet lumps retained on this screen were collected. After weighing, the wet lumps were dried in an oven. The dry lumps were in turn weighed.
  • a sample of latex was collected, the solids content was measured by densitometry and the distribution of the elementary particles was measured by sedimentometry.
  • the PVC latex was dried by atomization.
  • the dry PVC was recovered and ground.
  • a plastisol was manufactured by mixing 300 g of PVC resin, 120 g of diisononyl phthalate plasticizer, 36 g of benzyl butyl phthalate plasticizer, 9 g of a viscosity reducer (Viscobyk ® 5050) and 6 g of a stabilizer (Irgastab ® BZ505). This plastisol was then coated as a layer 0.5 mm thick onto transfer paper, which was placed in a Werner-Mathis coating oven under determined gelation conditions (temperature, time).
  • the yellow index obtained on the film was measured using a Luci 100 spectrocolorimeter from the company DR Lange GmbH, using the illuminant D65 and the 10° observation angle. The values measured in the defined colorimetric space were x, y and Y.
  • the ⁇ maximum corresponds to the largest temperature difference observed between the jacket and the reaction medium. It is representative of the exothermicity of the reaction, and thus of the polymerization rate.
  • Thermo Finnigan brand gas chromatograph (Trace GC) equipped with a flame ionization detector and an automatic headspace injector of the same brand (Triplus), having a stirring function and also a system for acquisition and processing of the chromatographic data (ChromCard).
  • the assay was performed by the external calibration method (calibration with VC samples of known concentration in N,N-dimethylacetamide (DMA)).
  • the residual VC content is expressed in mg/kg resin (ppm).
  • results collated in the table show the advantages obtained by means of the process according to the invention (substantial decrease in residual VC content of the polymers and reduction of the polymerization time). The content of dry lumps and cakes after the polymerization was also significantly lower.
  • Example 4R was repeated, except that:
  • dodecylbenzenesulfonate solution at 29.54% in water were used.
  • Example 4R The process was performed as described in Example 4R, except that 64.45 kg of demineralized water, 0.034 kg of a commercial sodium
  • dodecylbenzenesulfonate solution at 29.54% in water, and 12.34 kg of the seed latex S at 37.8% solids were used.
  • Example 7R was repeated, except that:
  • an aqueous zinc sulfate monohydrate solution at 0.01 g per kg of VC used was added, in a single batch, at the moment at which a pressure reduction ( ⁇ ) of 0.5 bar was detected relative to the mean pressure at which the polymerization step was performed.
  • the process was performed as described in Example 1R.
  • the solids content of the seed latex S was 37.9%
  • Example 4R The process was performed as described in Example 4R, except that 50.0 kg of demineralized water and 3.2 kg of a commercial sodium
  • dodecylbenzenesulfonate solution at 31.25% in water were used.
  • Example 4R The process was performed as described in Example 4R, except that 64.5 kg of demineralized water, 0.36 kg of a commercial sodium dodecylbenzenesulfonate solution at 31.25% in water, and 12.3 kg of the seed latex S at 38.0% solids were used.
  • the contents of the reactor were brought to 51 °C. Once this temperature was reached (to), 18.66 kg of VC were introduced into the reactor during the polymerization.
  • the thermal stability of the ground resin (0.5 g) was evaluated using a Thermomat PVC 763 constructed by the company Metrohm.
  • the PVC sample heated to 180°C breaks down with evolution of HC1, which is entrained by a gas stream (7 L/h of N 2 ) into a measuring cell where it is absorbed by ultrapure water.
  • the HC1 concentration of this water is measured continuously by conductimetry.
  • the conventional thermal stability was defined as the induction time of the dehydrochlorination reaction at a temperature of 180°C leading to an increase in conductimetry of 5 ⁇ 8/ ⁇ relative to the initial value. It is expressed in minutes and seconds. Evaluation of the yellow index
  • Example 10R was repeated, except that:
  • copper sulfate pentahydrate was added at a rate of 0.024 g per kg of VC (the mole ratio of copper sulfate to the initiator mixture was thus about 0.027);
  • an aqueous ascorbic acid solution at 0.022 g per kg of VC used (the mole ratio between the ascorbic acid and the copper sulfate was thus about 1.27) was introduced continuously at a constant rate from the start of the polymerization step (to) and up to the point at which a pressure reduction ( ⁇ ) of 0.4 bar was detected relative to the mean pressure at which the polymerization step was performed (moment at which the addition was stopped).
  • Example 12 Comparison of the results of Example 12 with those of Example 11R reveals that the process according to the invention leads to the production of polymers that are characterized by a lower residual VC content than the process according to the prior art in which the complexing agent is introduced from the start of the polymerization step (to) and at the very latest at the said pressure reduction. Furthermore, comparison of the data regarding the duration of the various polymerization phases reveals that the process according to the invention leads to a shorter total polymerization time and also solves the characteristic problems of the process according to the prior art (slowness of pressure reduction up to the self-heating).

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Abstract

Process for preparing a vinyl chloride polymer, comprising a step of polymerizing at least vinyl chloride, the said step being performed in aqueous dispersion in the presence of at least one liposoluble radical initiator and being continued up to the reduction of the autogenous pressure of vinyl chloride with introduction, into the polymerization medium, of an activating system comprising a water-soluble transition metal salt and a complexing agent, at least the complexing agent being introduced in total into the said polymerization medium from the start of the said pressure reduction.

Description

Process for preparing a vinyl chloride polymer
This application claims priority to French application No. 1162282 filed on December 22, 2011, the whole content of this application being incorporated herein by reference for all purposes.
The present invention relates to a process for preparing a vinyl chloride polymer (PVC). The invention relates more particularly to a process for preparing such a polymer, including a polymerization step performed in aqueous dispersion, usually as an aqueous microsuspension. The invention also relates to the vinyl chloride polymers obtained via this process.
It is known practice to prepare vinyl chloride polymers via a process known conventionally as "microsuspension polymerization". This process includes a step during which droplets of at least one monomer, which is vinyl chloride (VC), are finely and homogeneously dispersed in an aqueous medium, in the presence of liposoluble radical initiators (also known more simply as liposoluble initiators), by means of powerful stirring and the presence of emulsifiers, such as alkali metal or ammonium carboxylates and alkylsulfonates, optionally in combination with liposoluble cosurfactants, such as long-chain alcohols. This process, which leads to polymer particles with a diameter of between 0.05 and 5 microns approximately, is particularly suitable for the manufacture of PVC plastisols.
However, the microsuspension polymerization of VC has a drawback: the start of the polymerization is relatively slow, which has the consequences of lengthening the polymer production cycles and of using relatively higher doses of liposoluble initiators. In addition, this polymerization of exothermic nature is frequently performed in at least one reactor of tank type with mechanical stirring. The heat exchange required for the thermal control (temperature regulation) then takes place advantageously by means of a jacket inside which circulates a heat- exchange fluid (water), generally counter-currentwise. Given the slow kinetics of the polymerization, the cooling capacity of the jacket is not used optimally during part of this polymerization.
It has already been proposed (see documents US-A-4 091 197 (I) and US-
A-4 331 788 (II), but also EP 0 826 703 Al (III)) to improve the VC
polymerization kinetics via the "seeded microsuspension" method (i.e. a microsuspension polymerization in which the reaction medium contains a "seed" which is in the form of an aqueous dispersion of PVC particles containing all of the liposoluble initiator necessary for the polymerization), via the addition, to the polymerization medium, of an activating system. This activating system is an organosoluble metal complex that is preformed or formed by reaction of a water- soluble metal salt with a complexing agent.
The complexing agent should be capable of modifying the water-soluble form of the metal salt into a VC-soluble form and of not having any inhibitory action on the polymerization or on the activation of the initiator by the metal. Complexing agents that satisfy these conditions are monocarboxylic acids that are sparingly water-soluble; polycarboxylic acids and the corresponding anhydrides thereof; alkylphosphoric acids; lactones; ketones bearing, in the a or β position, groups that activate the carbonyl function; and carbazones. For the practical implementation of these inventions, use is made of ascorbic acid, dihydroxymaleic acid, succinic acid, citric acid, tartaric acid, naphthenic acid or sulfosalicylic acid. The complexing agent is usually introduced gradually throughout the polymerization or during part of this polymerization, and its addition is usually stopped when a pressure drop is detected.
The salt may be introduced into the reaction zone before or during the polymerization. In the latter case, it is either in a mixture with the complexing agent or in the form of a separate aqueous solution. The water-soluble metal salt used in practice is copper sulfate.
The Applicant has found that although the activating systems described in documents (I) to (III) improve the VC polymerization kinetics in (seeded) microsuspension, other problems associated with this type of polymerization remain unresolved. In particular, the reduction in the autogenous pressure of the monomer (VC), which indicates that the polymerization is close to completion, is slow and the time to reach the phenomenon conventionally defined by the term "self-heating", which corresponds to an increase in temperature at the end of polymerization (the heat being supplied mainly by the heat of the polymerization itself), is also too slow; this lengthens the polymer production cycles. The slowness thus observed at the end of polymerization is especially detrimental towards the efficacy of removal of the unconsumed residual VC at the end of polymerization.
The present invention is directed towards providing a process for preparing
PVC, which solves these problems by means of introducing, at a particular moment, into the polymerization medium, at least the complexing agent described above, making it possible to accelerate the decrease of the VC autogenous pressure and the self -heating, and improving the efficacy of removal of the residual VC.
The present invention thus relates mainly to a process for preparing a vinyl chloride polymer, comprising a step of polymerizing at least vinyl chloride, the said step being performed in aqueous dispersion in the presence of at least one liposoluble radical initiator and being continued up to the reduction of the autogenous pressure of vinyl chloride with introduction, into the polymerization medium, of an activating system comprising a water-soluble transition metal salt and a complexing agent, at least the complexing agent being introduced in total into the said polymerization medium from the start of the said pressure reduction.
In the present description, the terms "monomer" and "polymer" are used indiscriminantly in the singular and in the plural. The liposoluble radical initiator will also be referred to more simply and without preference as the "liposoluble initiator" or the "initiator".
The polymer prepared according to the invention is a vinyl chloride polymer. In the present description, the term "vinyl chloride polymer", or "polymer" for short, is intended to denote any polymer containing at least 50% by weight, preferably at least 60% by weight, particularly preferably at least 70% by weight and most particularly preferably at least 85% by weight of monomer units derived from vinyl chloride (monomer), and thus both vinyl chloride homopolymers (containing 100% by weight of monomer units derived from vinyl chloride) and copolymers of vinyl chloride with one or more ethylenically unsaturated monomers. As examples of ethylenically unsaturated monomers that can be copolymerized with vinyl chloride, mention may be made of chlorinated monomers such as vinylidene chloride, fluorinated monomers such as vinylidene fluoride, monomers containing both chlorine and fluorine such as
chlorotrifluoroethylene, vinyl esters such as vinyl acetate, vinyl ethers such as methyl vinyl ether, dialkyl maleates such as dibutyl maleate, (meth)acrylic monomers such as n-butyl acrylate and methyl methacrylate, styrene monomers such as styrene, and olefinic monomers such as ethylene, propylene and butadiene. Among all the vinyl chloride polymers mentioned above, preference is accorded to vinyl chloride homopolymers. The polymerization step included in the process for preparing the VC polymer according to the invention is performed in aqueous dispersion in a stirred reactor. In the present description, the expression "polymerization... in aqueous dispersion" is intended to denote polymerizations performed according to a radical mechanism in dispersed medium with the intervention of at least one liposoluble initiator. These polymerizations include not only the polymerization conventionally known as "suspension" polymerization, but also polymerizations known as "microsuspension" and "seeded microsuspension" polymerization. Preferably, the polymerization step is performed in microsuspension or in seeded microsuspension.
The term "suspension polymerization" is intended to denote any polymerization process that is performed with stirring in an aqueous medium in the presence of at least one dispersant and of at least one liposoluble initiator.
The term "microsuspension polymerization" is intended to denote any polymerization process (already mentioned hereinabove) in which is used at least one liposoluble initiator and in which is prepared an emulsion, also known as a "fine dispersion", of monomer droplets by means of powerful mechanical stirring and the presence of at least one emulsifier, the nature of which will be specified later in the present description.
The mechanical stirring may be produced by a suitable mechanical means, for instance a colloidal mill, a rapid pump, a vibrating agitator, an ultrasonic generator, a high-pressure homogenizer, etc.
The term "seeded microsuspension polymerization" is understood to denote any microsuspension polymerization process performed in the presence of at least one "seeding product", which may be, as mentioned hereinabove, a dispersion of particles of vinyl chloride polymer with a diameter advantageously between 0.01 and 1 micron and preferably between 0.05 and 0.2 micron. This seed may itself be prepared by polymerization, for example by using water, VC and an optional comonomer, at least one emulsifier and the initiator.
In the present description, the term "medium" is intended to define the contents of the reactor, excluding the monomer(s) introduced and the polymer formed.
Constituents that are common to the media in which the polymerization step is performed are:
- water,
- VC and optionally at least one of the monomers mentioned above, - at least one liposoluble initiator, and
- an activating system.
When the polymerization is performed in suspension, the medium also contains at least one dispersant.
When the polymerization is performed in microsuspension or in seeded microsuspension, the respective media also contain at least one emulsifier. These media may also optionally contain at least one liposoluble cosurfactant. The medium in which the seeded microsuspension polymerization is performed also contains a seeding product (seed). The weight of the seeding product relative to the total weight of the monomer(s) is at least 1% and preferably at least 3%.
The weight of the seeding polymer(s) relative to the total weight of the monomer(s) is not more than 25% and preferably not more than 10%.
In the polymerization medium, the ratio of the weight of water to the weight of the monomer(s) is advantageously at least 0.4 and preferably at least 0.8.
In the polymerization medium, the ratio of the weight of water to the weight of the monomer(s) is advantageously not more than 2 and preferably not more than 1.5.
The media in which the polymerizations are performed may optionally contain additives other than the constituents mentioned above. They are then conventional additives, which make it possible, in a known manner, to improve the implementation of the process and/or the characteristics of the resulting polymer. Examples of such additives are chain-transfer agents, for instance chloroform, trichlorofluoromethane and C2-C5 dialkyl carbonates; chain extenders, for instance diallyl maleate and dialkyl phthalate; anticaking agents; antistatic agents; antifoams; cosolvents; and pH regulators, for instance ammonia, buffer salts, for example sodium phosphate, polyphosphate and hydrogen carbonate, and alkali metal carbonates, for example sodium carbonate, advantageously added to the polymerization medium at the start of the said polymerization.
The polymerization step included in the process for preparing the VC polymer according to the invention is performed with the intervention of at least one liposoluble initiator. These liposoluble initiators are advantageously organic peroxide compounds or liposoluble diazo compounds. Examples of organic peroxide compounds that may be mentioned include peroxides such as dilauryl peroxide, di-ieri-butyl peroxide or dibenzoyl peroxide; hydroperoxides such as ferf-butyl hydroperoxide; peresters such as ferf-butyl perpivalate, ferf-butyl peroxy-2-ethylhexanoate and ferf-butyl perneodecanoate; percarbonates such as diethyl, diisopropyl, diethylhexyl and dimyristyl peroxydicarbonate. Examples of diazo compounds that may be mentioned include azobisisobutyronitrile and 2,2'-azobis(methoxy-2,4- dimethylvaleronitrile). Preferred organic peroxide compounds are, in particular, dilauryl peroxide and percarbonates, in particular dimyristyl peroxydicarbonate. The amount of liposoluble radical initiator used ranges advantageously between 0.2%o and 3.5%o by weight and preferably between 0.8%o and 3%o by weight relative to the weight of monomer(s) used.
When the polymerization step included in the process for preparing the VC polymer according to the invention is performed in suspension, the
polymerization medium also contains at least one dispersant. Examples of dispersants that may be mentioned include water-soluble cellulose ethers and partially saponified polyvinyl alcohol, and mixtures thereof. Along with the dispersants, surfactants may also be used. The amount of dispersant used ranges advantageously between 0.7%o and 2.0%o by weight relative to the weight of monomer(s) used.
When the polymerization step included in the process for preparing the VC polymer according to the invention is performed in microsuspension or in seeded microsuspension, the polymerization medium also contains at least one emulsifier. These emulsifiers are advantageously ionic emulsifiers chosen from anionic emulsifiers, cationic emulsifiers and amphoteric emulsifiers. Preferably, these emulsifiers are chosen from anionic emulsifiers. Particularly preferably, these emulsifiers are chosen from the following anionic emulsifiers: alkyl sulfates, alkyl sulfonates, alkylaryl sulfonates, dialkyl sulfosuccinates and alkyl carboxylates. The salts may optionally be ethoxylated and may comprise, as counterion, a sodium, potassium, lithium, caesium or ammonium cation. These emulsifiers are most particularly preferably chosen from the following non- ethoxylated sodium salts: alkyl sulfates, for instance sodium dodecyl sulfate, alkyl sulfonates, for instance primary or secondary sodium alkyl sulfonates, alkylaryl sulfonates, for instance sodium dodecylbenzenesulfonate, dialkyl sulfosuccinates, for instance dioctyl sulfosuccinate, and alkyl carboxylates, for instance sodium ammonium myristates. The amount of emulsifier used ranges advantageously between 0.1 % and 3% by weight relative to the weight of monomer(s) used.
The polymerization medium intended for suspension, microsuspension or seeded microsuspension polymerization is heated under the autogenous pressure to a temperature determined by the molar mass that it is desired to obtain for the polymer.
The polymerization temperature is advantageously between 30 and 100°C, preferably between 30 and 90°C and more particularly between 45 and 85°C. The polymerization is advantageously performed at a pressure between 0.3 and 2.5 MPa and preferably between 0.5 and 1.5 MPa.
The polymerization step is advantageously continued until 60% to 98% by weight and preferably 80% to 95% by weight of the monomer(s) are converted, with concomitant reduction of the autogenous pressure of VC in the reactor.
The content of solid polymer in the aqueous dispersion obtained at the end of the polymerization step is advantageously between 20% and 55% by weight and preferably between 40% and 50% by weight.
As a consequence of incomplete conversion of the monomer, the amount thereof that remains in the aqueous dispersion obtained at the end of the polymerization step must be removed.
This removal may be performed conventionally by degassing the dispersion, which is usually performed in a depressurization tank,
advantageously followed by a distillation operation, steam entrainment of the residual monomer or, preferably, boiling under vacuum.
The solid polymer or the aqueous polymer dispersion derived from the abovementioned separation treatment may then be subjected to a final drying operation performed in any drying device known for this purpose. In the case of aqueous microsuspension or seeded aqueous microsuspension leading to the production of an aqueous dispersion (commonly known as a latex), the aqueous dispersion may be stored and used in this form without being dried.
The polymer synthesized by suspension polymerization is in the form of particles with a diameter advantageously between 50 and 150 microns.
The polymer synthesized by microsuspension or seeded microsuspension polymerization is in the form of elemental particles with a diameter
advantageously between 0.1 and 5 microns before drying and of particles with a diameter advantageously between 30 and 100 microns after drying. The medium in which the polymerization step included in the process for preparing the vinyl chloride polymer according to the invention is performed contains, during at least part of this polymerization (as will be specified later), an activating system comprising a water-soluble transition metal salt and a complexing agent.
According to the invention, the transition metal from which the water- soluble salt is derived is advantageously chosen from iron, copper, cobalt, nickel, zinc, tin, titanium, vanadium, manganese, chromium and silver. The water- soluble transition metal salt, which is the first constituent of the activating system, is thus preferably a water-soluble iron, copper, cobalt, nickel, zinc, tin, titanium, vanadium, manganese, chromium or silver salt. The water-soluble transition metal salt is particularly preferably a water-soluble iron, copper or zinc salt. The water-soluble transition metal salt is most particularly preferably a water-soluble copper or zinc salt. Since the latter salt leads to a better compromise in terms of polymerization kinetics/properties of the polymers obtained, it is in this respect particularly preferred.
Any water-soluble transition metal salt may be used as constituent of the activating system. These salts may be mineral or organic. Among the mineral water-soluble transition metal salts, mention may be made of the sulfates, chlorates, chlorides and nitrates of these metals. Among the organic water- soluble transition metal salts, mention may be made of the acetates of these metals. The mineral salts of these metals are preferred as constituents of the activating system, and, among these, the sulfates. Copper sulfate and zinc sulfate are particularly preferred. The water-soluble transition metal salt is thus most particularly preferably copper sulfate or zinc sulfate. Since the latter salt leads to a better compromise in terms of polymerization kinetics/properties of the polymers obtained, it is in this respect particularly preferred.
The second constituent of the activating system is a complexing agent. In the present description, the term "complexing agent" is intended to denote any chemical compound that is capable of changing the transition metal from its water-soluble form to the form of a metal complex that is soluble in VC, without exerting any inhibitory action on the polymerization or on the activation exerted by the transition metal on the liposoluble initiator.
Complexing agents that satisfy these conditions may be chosen especially from monocarboxylic acids, polycarboxylic acids, alkylphosphoric acids, lactones, ketones and carbazones. As monocarboxylic acids that may be used as complexing agents, mention may be made of those that are sparingly water-soluble, such as perfluorobutyric acid, a-bromolauric acid, sulfosalicylic acid, naphthenic acid and octanoic acid.
As polycarboxylic acids that may be used as complexing agents, mention may be made of succinic acid, tartaric acid, maleic acid and hydroxymaleic acid.
As alkylphosphoric acids that may be used as complexing agents, mention may be made of bis(2-ethyl)hexylphosphoric acid.
As lactones that may be used as complexing agents, mention may be made of ascorbic acid, its stereoisomer erythorbic acid, and esters thereof, and also γ- butyrolactone.
As ketones that may be used as complexing agents, mention may be made of ketones bearing, in the γ or β position, groups that activate the carbonyl function, such as acetylacetone, 1, 3 -dihydroxy acetone and benzoin.
As carbazones that may be used as complexing agents, mention may be made of diphenylthiocarbazone.
The complexing agent is preferably chosen from monocarboxylic acids, polycarboxylic acids and lactones. The complexing agent is particularly preferably chosen from lactones. The complexing agent is most particularly preferably chosen from ascorbic acid, its stereoisomer erythorbic acid, and esters thereof. The complexing agent is really most particularly preferably ascorbic acid.
The complexing agent may be introduced in solid form, in the form of an aqueous solution or as a mixture with an emulsifier solution. The complexing agent is preferably introduced in the form of an aqueous solution.
The presence of several water-soluble transition metal salts and/or of several complexing agents in the same activating system is not at all excluded from the scope of the invention. The terms "water-soluble transition metal salt" and "complexing agent" are thus used indiscriminantly in the singular or in the plural. Preferably, the activating system comprises only one water-soluble transition metal salt and only one complexing agent.
An activating system comprising a water-soluble transition metal salt chosen from copper salts and zinc salts (advantageously zinc salts), preferably from copper sulfate and zinc sulfate (advantageously copper sulfate), and ascorbic acid as complexing agent, gave excellent results. According to the invention, at least the complexing agent is introduced in total into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride.
For the purposes of the present description, the expression "at least the complexing agent is introduced" is intended to denote that either only the complexing agent is introduced, or the complexing agent and the water-soluble transition metal salt are introduced, at least partly for the latter, into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride.
According to a first embodiment of the process according to the invention, only the complexing agent is introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride.
According to a second embodiment of the process according to the invention, the complexing agent and the water-soluble transition metal salt are introduced, at least partly for the latter, into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride. In the latter case, the activating system comprising the water-soluble transition metal salt, at least partly, and the complexing agent, may be introduced into the polymerization medium either in the form of a preformed organosoluble organometallic complex resulting from the preliminary reaction of its two constituents, or in the form of its two distinct and separate constituents. The latter case is preferred insofar as it enables modification of the respective amounts of the two constituents. According to this case, an aqueous solution containing a mixture of water-soluble transition metal salt, at least partly, and of the complexing agent is preferably introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride.
The second embodiment of the process according to the invention affords additional advantages and, in this respect, is preferred.
For the purposes of the present description, the expression "from the start of reduction of the autogenous pressure of vinyl chloride" should be understood as meaning from the moment (tx) at which the reduction of the VC autogenous pressure starts.
The expression "reduction of the VC autogenous pressure" is intended to denote the pressure reduction generated taking into account the disappearance of VC in the gaseous phase (since it is consumed by the polymerization reaction). This reduction in the VC autogenous pressure is advantageously not induced by a reduction in the polymerization temperature.
The moment (tx) at which the reduction of the VC autogenous pressure starts may be detected by a pressure decrease advantageously of the order of at least 0.1 bar and preferably of the order of at least 0.2 bar, relative to the mean pressure at which the polymerization step is performed. Nevertheless, a person skilled in the art can recognize this moment tx beforehand for the polymerization recipes he has prepared previously and does not necessarily need to wait to observe the pressure reduction in order to commence the introduction of at least the complexing agent into the polymerization medium.
Preferably, the moment (tx) at which reduction of the VC autogenous pressure starts is detected by a pressure reduction advantageously of the order of at least 0.1 bar and preferably of the order of at least 0.2 bar, relative to the mean pressure at which the polymerization step is performed.
If, in the process according to the invention, at least the complexing agent is introduced in total into the polymerization medium from the start of the reduction of the autogenous pressure of vinyl chloride, this introduction may take place at any moment from the start (tx) of the said pressure reduction up to the end of the polymerization step, brought about either by addition of an inhibitor (a base such as aqueous ammonia, phenol, etc.) or by raising the temperature (self- heating), preferably by raising the temperature (self-heating) in the case of aqueous microsuspension polymerization (seeded or unseeded).
Thus, if we call tz the moment at which the polymerization is complete, at least the complexing agent is advantageously introduced in total into the polymerization medium from tx and at the very latest up to tz.
If we call z the time elapsed between the start of reduction of the autogenous pressure of vinyl chloride (tx) and the moment tz at which the polymerization is complete, according to the first embodiment of the process according to the invention, the complexing agent is advantageously introduced
- in a single batch at any fraction of z between tx and tz including addition in a single batch at tx,
- in several successive batches of the same weight or of uniformly decreasing weight distributed over the duration z,
- continuously over z at a constant rate,
- continuously over z at a decreasing rate,
- continuously over a fraction of z of between tx and tz at a constant rate, or - continuously over a fraction of z of between tx and tz at a decreasing rate.
According to this first embodiment of the process according to the invention, the complexing agent is preferably introduced in a single batch at any fraction of z between tx and tz including addition in a single batch at tx or continuously, over z or over a fraction of z between tx and tz, at a constant rate or at a decreasing rate. In a particularly preferred manner, the complexing agent is introduced in a single batch at any fraction of z between tx and tz including addition in a single batch at tx.
If we call z the time elapsed between the start of reduction of the autogenous pressure of vinyl chloride (tx) and the moment tz at which the polymerization is complete, according to the second embodiment of the process according to the invention, the complexing agent and the water-soluble transition metal salt, at least partly, are advantageously introduced, separately or together, in one of the ways below taken separately or in combination,
- in a single batch at any fraction of z between tx and tz including addition in a single batch at tx,
- in several successive batches of the same weight or of uniformly decreasing weight distributed over the duration z,
- continuously over z at a constant rate,
- continuously over z at a decreasing rate,
- continuously over a fraction of z of between tx and tz at a constant rate, or
- continuously over a fraction of z of between tx and tz at a decreasing rate.
According to this second embodiment of the process according to the invention, when the introduction is performed in a single batch or in several successive batches, the complexing agent and the water-soluble transition metal salt, at least partly, may be introduced both at tx or both at tx and then both simultaneously at least once at at least a fraction of z, or both at tx and then both simultaneously at least once at at least a fraction of z, ending with an
introduction of the complexing agent at a fraction of z closer to tz.
According to this second embodiment of the process according to the invention, the complexing agent and the water-soluble transition metal salt, at least partly, are preferably both introduced in a single batch at any fraction of z between tx and tz, including addition in a single batch at tx or continuously, over z or over a fraction of z between tx and tz, at a constant rate or at a decreasing rate. In a particularly preferred manner, the complexing agent and the water-soluble transition metal salt are both introduced in a single batch at any fraction of z between tx and tz including addition in a single batch at tx.
Irrespective of the embodiment of the process according to the invention, the amount of complexing agent introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride, expressed on a weight basis relative to the weight of initiator present in the polymerization step, is advantageously greater than or equal to 0.5 per thousand, preferably greater than or equal to 1 per thousand. Even more preferably, the amount of complexing agent introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride, thus expressed, is greater than or equal to 3 per thousand.
Advantageously, the amount of complexing agent introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride, expressed on a weight basis relative to the weight of initiator present in the polymerization step, is less than or equal to 50 per thousand and preferably less than or equal to 40 per thousand. Even more preferably, the amount of complexing agent introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride, thus expressed, is less than or equal to 30 per thousand.
In the case of the second embodiment of the process according to the invention, the amount of salt, expressed on a weight basis relative to the weight of complexing agent, introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride, is between 0.1 and 5. Preferably, it is between 0.15 and 3. Even more preferably, the amount of salt introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride, thus expressed, is between 0.2 and 2.
In the case of the second embodiment, for the purposes of the present description, the expression "the water-soluble metal salt is introduced at least partly" is intended to denote that either the water-soluble metal salt is introduced partly, or the water-soluble metal salt is introduced in total, into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride. Preferably, the water-soluble metal salt is introduced in total into the
polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride.
In other words, the process according to the invention is advantageously not limited solely to the introduction of the water-soluble metal salt into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride. Thus, other modes of introduction of the water-soluble metal salt described below, combined with one of the two embodiments described above, form the subject of variants of the process according to the invention.
According to the variants mentioned above, the water-soluble transition metal salt is introduced either at the very latest at the start of the polymerization step and/or from the start of the polymerization step and at the very latest up to the reduction of the autogenous pressure of vinyl chloride.
For the purposes of the present description, the expression "start of the polymerization step" should be understood as meaning the moment (referred to as to) at which the polymerization temperature is reached (to within + 1°C).
For the purposes of the present description, the expression "introduced at the very latest at the start of the polymerization step" should be understood as meaning introduced at a moment between the introduction of the first of the constituents of the medium in which the polymerization step is performed and the moment ¾.
The water-soluble transition metal salt of the activating system is thus advantageously introduced at any moment between the introduction of the first of the constituents of the medium in which the polymerization step is performed and the moment ¾ at which the polymerization temperature is reached (to within + 1°C) (commonly referred to as "initial"). Preferably, it is introduced with the other constituents of the medium in which the polymerization step is performed before raising the temperature.
In this case, the water-soluble transition metal may be introduced in solid form, in the form of an aqueous solution or as a mixture with an emulsifier solution. It is preferably introduced in solid form.
In the case of a seeded microsuspension polymerization, the water-soluble transition metal salt of the activating system may be introduced via the "seed".
For the purposes of the present description, the expression "introduced from the start of the polymerization step and at the very latest up to the reduction of the autogenous pressure of vinyl chloride" is intended to denote from the moment to at which the polymerization temperature is reached (to within + 1 °C) defined above and not later than up to the moment tx at which the reduction of the VC autogenous pressure starts (commonly referred to as "delayed").
The water-soluble transition metal salt is thus advantageously introduced from to and at the very latest up to tx ("delayed"). If we call x the time elapsed between the start of the polymerization step (moment ¾ at which the polymerization temperature is reached (to within + 1 °C)) and the moment tx at which the reduction of the VC autogenous pressure starts, the water-soluble transition metal salt is thus advantageously introduced - in a single batch at any fraction of x between ¾ and tx including addition in a single batch at tx,
- in several successive batches of the same weight or of uniformly decreasing weight distributed over the duration x,
- continuously over x at a constant rate,
- continuously over x at a decreasing rate,
- continuously over a fraction of x of between ¾ and tx at a constant rate, or
- continuously over a fraction of x of between ¾ and tx at a decreasing rate.
The water-soluble transition metal salt is preferably introduced
continuously, over x or over a fraction of x between ¾ and tx, at a constant rate or at a decreasing rate. The water-soluble transition metal salt is particularly preferably introduced continuously, over x or over a fraction of x between ¾ and tx, at a constant rate or at a decreasing rate.
In the case where the complexing agent is introduced alone, it may be introduced in solid form, in the form of an aqueous solution or as a mixture with an emulsifier solution. Preferably, it is in the form of an aqueous solution.
In the case where the complexing agent is introduced with the water- soluble transition metal salt, at least partly, they may be introduced in the form of an aqueous solution containing them both (referred to hereinbelow as a mixture) or alternatively by mixing two aqueous solutions each containing one of the two constituents. An emulsifying agent may be added to these solutions or added in the form of a separate aqueous solution. Preferably, they are introduced in the form of an aqueous solution containing them both (referred to hereinbelow as a mixture).
Examples of combinations of the first embodiment of the process according to the invention with one of the other modes of introduction of the water-soluble metal salt (variants) are thus:
- the water-soluble transition metal salt is introduced at the very latest at ¾ and the complexing agent is introduced from tx to tz;
- the water-soluble transition metal salt is introduced at the very latest at ¾ and from to to tx and the complexing agent is introduced from tx to tz; - the water-soluble transition metal salt is introduced from ¾ to tx and the complexing agent is introduced from tx to tz.
Examples of combinations of the second embodiment of the process according to the invention with one of the other modes of introduction of the water-soluble metal salt (variants) are thus:
- the water-soluble transition metal salt is introduced at the very latest at ¾ and a mixture of the water-soluble transition metal salt and of the complexing agent is introduced from tx to tz;
- the water-soluble transition metal salt is introduced at the very latest at ¾ and from to to tx and a mixture of the water-soluble transition metal salt and of the complexing agent is introduced from tx to tz;
- the water-soluble transition metal salt is introduced from ¾ to tx and a mixture of the water-soluble transition metal salt and of the complexing agent is introduced from tx to tz.
When the constituents of the activating system are introduced according to the abovementioned variants, the amounts in which they are introduced may vary within a wide range.
Advantageously, the amount of water-soluble transition metal salt introduced, expressed on a weight basis relative to the amount of initiator present in the polymerization step, is greater than or equal to 10"5 mol of the said salt per mole of initiator. Preferably, the amount of water-soluble transition metal salt introduced, thus expressed, is greater than or equal to 10"4 mol of the said salt per mole of initiator. Even more preferably, the amount of water-soluble transition metal salt introduced, thus expressed, is greater than or equal to 5x10"3 mol of the said salt per mole of initiator.
Advantageously, the amount of water-soluble transition metal salt introduced, expressed on a weight basis relative to the amount of initiator present in the polymerization step, is less than or equal to 50 mol of the said salt per mole of initiator. Preferably, the amount of water-soluble transition metal salt introduced, thus expressed, is less than 5 mol of the said salt per mole of initiator. Even more preferably, the amount of water-soluble transition metal salt introduced, thus expressed, is less than or equal to 0.5 mol of the said salt per mole of initiator.
When expressed on a weight basis relative to the amount of VC present in the polymerization step, the amount of water-soluble transition metal salt introduced is advantageously greater than or equal to 1 ppm and preferably greater than or equal to 5 ppm.
When expressed on a weight basis relative to the amount of VC present in the polymerization step, the amount of water-soluble transition metal salt introduced is advantageously less than or equal to 300 ppm and preferably less than or equal to 200 ppm.
Advantageously, the amount of complexing agent introduced, expressed on a weight basis relative to the amount of water-soluble transition metal salt introduced into the polymerization step, is greater than or equal to 0.05 mol of complexing agent per mole of salt. Preferably, the amount of complexing agent introduced, thus expressed, is greater than 0.1 mol of complexing agent per mole of salt. Even more preferably, the amount of complexing agent introduced, thus expressed, is greater than or equal to 0.5 mol of complexing agent per mole of salt.
Advantageously, the amount of complexing agent introduced, expressed on a weight basis relative to the amount of water-soluble transition metal salt introduced into the polymerization step, is greater than or equal to 50 mol of complexing agent per mole of salt. Preferably, the amount of complexing agent introduced, thus expressed, is less than or equal to 20 mol of complexing agent per mole of salt. Even more preferably, the amount of complexing agent introduced, thus expressed, is less than or equal to 5 mol of complexing agent per mole of salt.
According to the second embodiment of the process according to the invention, the complexing agent and the water-soluble transition metal salt are preferably introduced in total into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride.
The present invention also relates to the vinyl chloride polymers obtained via a process comprising a step of polymerizing at least vinyl chloride, the said step being performed in aqueous dispersion in the presence of at least one liposoluble radical initiator and being continued up to the reduction of the autogenous pressure of vinyl chloride with introduction, into the polymerization medium, of an activating system comprising a water-soluble transition metal salt and a complexing agent, at least the complexing agent being introduced in total into the said polymerization medium from the start of the said pressure reduction. The process according to the invention has the advantage of leading to the production of polymers that are characterized by a low residual VC content. The process is also characterized by short polymerization times and the content of dry lumps and cakes observed after polymerization is significantly low.
Although the abovementioned advantages may be obtained both with a zinc salt and with a copper salt, the use of a zinc salt has the particular advantage of leading to polymers that are characterized by better thermal stability and a lower content of dry lumps and cakes after the polymerization, in other words to a better compromise in terms of polymerization kinetics/properties of the polymers obtained, than when a copper salt is used.
The second embodiment of the process according to the invention has advantages over the first enbodiment, namely it is characterized by a shorter polymerization time, a higher ΔΤ maximum and a lower content of dry lumps and cakes, and the polymers obtained are characterized by a lower residual VC content and an improved yellow index.
When compared with the process according to the prior art in which the complexing agent is introduced from the start of the polymerization step (to) and at the very latest at the said pressure reduction, the process according to the invention leads to the production of polymers that is characterized by a lower residual VC content and characterized by a shorter total polymerization time.
The process according to the invention also solves the characteristic problems of the process according to the prior art (slowness of the pressure reduction up to the self-heating).
Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.
The following examples are intended to illustrate the invention without however limiting the scope thereof.
Example 1R (comparative)
Preparation of the seed latex (seed latex S)
A PVC latex (seed latex S) was prepared via an emulsion polymerization step performed conventionally (emulsifier: solution of dodecylbenzenesulfonate at 180 g/kg; water-soluble initiator: aqueous ammonium persulfate solution at 66.5 g/L) in a 300L reactor equipped with a stirrer and a jacket. The latex was emptied from the reactor. The latex was filtered through a screen with a mesh size of 1 mm. The latex was placed in a storage tank.
A sample of latex was taken from the storage tank and its solids content was measured by densimetry: the solids content of the seed latex S was 34.1%.
The distribution of the elementary polymer particles of the seed latex was also determined by photosedimentometry using a CPS machine formed from a centrifugation unit, a detector and a control/analysis device: the distribution of the elementary polymer particles of the seed latex S was unimodal; the mean diameter of these elementary particles was 105 nm.
Preparation of the fine dispersion (1st part)
47.28 kg of demineralized water were first placed in a 300 L mixing autoclave equipped with a stirrer and a jacket, and maintained at 17°C. 0.529 kg of an aqueous sodium dioctylsulfosuccinate solution at 717.3 g/kg, 90.90 g of dilauroyl peroxide (PL) (99.4% pure), 138.1 g of dimyristyl peroxydicarbonate (MYPC) (97.5% pure), 142.8 g of dioctyl adipate and 0.542 g of
butylhydroxyanisole were then introduced. The mixing autoclave was closed and the stirrer switched on. The mixing autoclave was then placed under vacuum.
Loading the reagents into the reactor (1st part)
78.75 kg of demineralized water, 0.983 kg of a solution of sodium dioctylsulfosuccinate at 717.3 g/kg and 4.875 kg of the seed latex S (at 370.7 g/kg of PVC in water) were successively introduced into a 300 L reactor equipped with a stirrer and a jacket, and maintained at 17°C. The reactor was closed and the stirrer switched on. The reactor was then placed under vacuum.
Preparation of the fine dispersion (2nd part)
31.62 kg of VC were placed in the mixing autoclave and vigorous stirring was maintained in order to constitute a homogeneous aqueous dispersion of vinyl chloride droplets comprising the mixture of liposoluble initiators and the peak suppressant (butylhydroxyanisole).
Loading the reagents into the reactor (2nd part)
58.73 kg of VC were placed in the reactor.
Preparation of the fine dispersion (3rd part) and loading of the reagents into the reactor (3rd part)
A high-pressure homogenizer connecting the mixing autoclave to the reactor was switched on. The homogenization pressure was adjusted. The contents of the mixing autoclave were transferred into the reactor via this homogenizer. The operating conditions of the homogenizer were such that a fine aqueous dispersion of VC droplets comprising the liposoluble initiators and the peak suppressant was obtained at its outlet.
Polymerization
The contents of the reactor were brought to 46°C. Once this temperature was reached, 0.146 kg of an aqueous ammonia solution at 222.5 g/L was introduced into the reactor.
During the polymerization, 2 x 9.036 kg of VC were introduced into the reactor.
After the time tx (in this case corresponding to a pressure reduction (ΔΡ) of 0.2 bar relative to the average pressure at which the polymerization step was performed), once a pressure reduction (ΔΡ) of 0.5 bar was detected, the contents of the reactor were brought to a higher temperature (self-heating), the polymerization time elapsed from ¾ up to this moment (ΔΡ = 0.5 bar) was recorded, and 45.5 g of a commercial solution of antifoam (Tego® KS53 sold by Evonik) were added.
End operations
A purification treatment of the residual VC was performed.
The latex was emptied out and the reactor cleaned.
The wet cake present inside the reactor, especially on the walls and on the blades of the stirrer, was collected. After weighing, the wet cake was dried in an oven. The dry cake was in turn weighed.
The latex was filtered through a screen with a mesh size of 1 mm. The wet lumps retained on this screen were collected. After weighing, the wet lumps were dried in an oven. The dry lumps were in turn weighed.
A sample of latex was collected, the solids content was measured by densitometry and the distribution of the elementary particles was measured by sedimentometry.
Drying of the latex and recovery of the resin
The PVC latex was dried by atomization. The dry PVC was recovered and ground.
Evaluation of the yellow index
A plastisol was manufactured by mixing 300 g of PVC resin, 120 g of diisononyl phthalate plasticizer, 36 g of benzyl butyl phthalate plasticizer, 9 g of a viscosity reducer (Viscobyk® 5050) and 6 g of a stabilizer (Irgastab® BZ505). This plastisol was then coated as a layer 0.5 mm thick onto transfer paper, which was placed in a Werner-Mathis coating oven under determined gelation conditions (temperature, time).
The yellow index obtained on the film was measured using a Luci 100 spectrocolorimeter from the company DR Lange GmbH, using the illuminant D65 and the 10° observation angle. The values measured in the defined colorimetric space were x, y and Y. The yellow index (YI) was defined by the formula YI = 100*((Cx*X)-Cz*Z)/Y with:
X = Y * x / y
Z = ((l-x-y)/y)*Y
Cx=1.3013
Cz=1.1498
Example 2 (according to the invention)
The procedure followed was identical to that of Example 1 , with the exception that an aqueous solution containing a mixture of zinc sulfate monohydrate and ascorbic acid (ascorbic acid/mixture of initiators (PL and MYPC mass ratio): 6%; zinc sulfate/ascorbic acid mass ratio: 0.5) was injected in a single batch at time tx (ΔΡ = 0.2 bar).
Example 3 (according to the invention)
The procedure followed was identical to that of Example 1 , except that the zinc sulfate was introduced at the start into the mixing autoclave (the mole ratio of zinc sulfate to the mixture of initiators (PL and MYPC) was 76 x 10"4). The aqueous ascorbic acid solution was injected in the same proportions as in Example 2, as a single batch at time tx (ΔΡ = 0.2 bar)
The table below collates the results of Examples 1R, 2 and 3.
Table
Figure imgf000023_0001
(*) The ΔΤ maximum corresponds to the largest temperature difference observed between the jacket and the reaction medium. It is representative of the exothermicity of the reaction, and thus of the polymerization rate.
(§) The residual VC content was measured on a Thermo Finnigan brand gas chromatograph (Trace GC) equipped with a flame ionization detector and an automatic headspace injector of the same brand (Triplus), having a stirring function and also a system for acquisition and processing of the chromatographic data (ChromCard). The assay was performed by the external calibration method (calibration with VC samples of known concentration in N,N-dimethylacetamide (DMA)).
The latex sample (1 ml) to be analysed dispersed in a water/DMA mixture (40/60 by weight, 5 ml) contained in a hermetically sealed penicillin-type flask was placed on the chromatograph sampler and subjected to incubation with stirring for 30 minutes at a temperature of 70°C. After this equilibration, the headspace was analysed by chromatography on a packed semicapillary column, divinylbenzene type (20 μιη), commercial name RT-Q Bond, 30 m long and 0.53 μιη inside diameter of the abovementioned chromatograph.
The residual VC content is expressed in mg/kg resin (ppm).
The results collated in the table show the advantages obtained by means of the process according to the invention (substantial decrease in residual VC content of the polymers and reduction of the polymerization time). The content of dry lumps and cakes after the polymerization was also significantly lower.
Comparison of the results of Example 2 with those of Example 3 reveals the advantages obtained by means of the second embodiment of the process over the first embodiment (shorter polymerization time, higher ΔΤ maximum, lower content of dry lumps and cakes, lower residual VC content and improved yellow index).
Example 4R (comparative)
Preparation of the seed latex (seed latex S)
The process was performed as described in Example 1R. The solids content of the seed latex S was 37.0%
Preparation of the fine dispersion (1st part)
50.1 kg of demineralized water were first placed in a 300 L mixing autoclave equipped with a stirrer and a jacket. The following were then placed in the mixing autoclave: 3.135 kg of a commercial solution of sodium
dodecylbenzenesulfonate at 32.15% in water, a mixture of liposoluble initiators comprising 78.1 g of dilauryl peroxide (PL) and 111.2 g of dimyristyl peroxydicarbonate (MYPC), 168.0 g of dioctyl adipate and 0.56 g of butylhydroxyanisole. The mixing autoclave was closed and the stirrer switched on. The mixing autoclave was then placed under vacuum.
Loading the reagents into the reactor (1st part)
64.23 kg of demineralized water, 0.35 kg of a commercial solution of sodium dodecylbenzenesulfonate at 32.15% in water, 12.60 kg of the seed latex S containing 37.0% solids and 34.0 g of sodium carbonate were successively introduced into a 300 L reactor equipped with a stirrer and a jacket. The reactor was closed and the stirrer switched on. The reactor was then placed under vacuum.
Preparation of the fine dispersion (2nd part)
The process was performed as described in Example 1R, introducing 37.33 kg of VC into the mixing autoclave.
Loading the reagents into the reactor (2nd part)
56.0 kg of VC were placed in the reactor.
Preparation of the fine dispersion (3rd part) and loading of the reagents into the reactor (3rd part)
The process was performed as described in Example 1R. Polymerization
The contents of the reactor were brought to 51°C. Once this temperature was reached (to), 18.66 kg of VC were introduced into the reactor during the polymerization.
After time tx (in this case corresponding to a pressure reduction (ΔΡ) of 0.2 bar relative to the average pressure at which the polymerization step was performed), once a pressure reduction (ΔΡ) of 0.4 bar was detected, the contents of the reactor were brought, 1 hour after this time, to a higher temperature (self- heating), the polymerization time elapsed from tD up to this point (ΔΡ = 0.4 bar + 1 hour) was recorded, and 56.4 g of a commercial solution of antifoam (Tego® KS 53 sold by Evonik) were added.
End operations
The process was performed as described in Example 1R.
Drying of the latex and recovery of the resin
Latex was coagulated, filtered and dried in an oven under vacuum at 50°C for evaluation of the thermal stability.
Evaluation of the thermal stability
The thermal stability of the dried latex (0.5 g) was evaluated using a Thermomat PVC 763 constructed by the company Metrohm.
The PVC sample heated to 180°C breaks down with evolution of HC1, which is entrained by a gas stream (7 L/h of N2) into a measuring cell where it is absorbed by ultrapure water. The HC1 concentration of this water is measured continuously by conductimetry.
The conventional thermal stability was defined as the induction time of the dehydrochlorination reaction at a temperature of 180°C leading to an increase in conductimetry of 5 μ8/αη relative to the initial value. It is expressed in minutes and seconds.
Determination of the residual monomer in the latex
The process was performed as described in Example 1R.
In this example:
- the polymerization lasted 286 minutes;
- the ΔΤ maximum was 25.0°C;
- the amount of dry lumps and cakes (expressed as a percentage of the VC introduced) was 0.46;
- the thermal stability of the resin sample obtained was 7 minutes 12 seconds;
- the residual monomer content in the latex was 119.6 ppm. Example 5 (according to the invention)
Example 4R was repeated, except that:
after time tx, once a pressure reduction (ΔΡ) of 0.5 bar was detected, the contents of the reactor were brought, 1 hour after this time, to a higher temperature (self-heating), the polymerization time elapsed from to up to this point (ΔΡ = 0.5 bar + 1 hour) was recorded, and 56.4 g of a commercial solution of antifoam (Tego® KS 53 sold by Evonik) were added; and in the polymerization step, an aqueous solution containing a mixture of copper sulfate pentahydrate at a rate of 0.0108 g per kg of VC used (the mole ratio of copper sulfate to the mixture of initiators was thus about 0.012) and of ascorbic acid at a rate of 0.0100 g per kg of VC used (the mole ratio between the ascorbic acid and the copper sulfate was thus about 1.31) was added in a single batch, at the moment at which a pressure reduction (ΔΡ) of 0.5 bar was detected relative to the mean pressure at which the polymerization step was performed.
The results of this example were as follows:
the polymerization lasted 322 minutes;
the ΔΤ maximum was 23.6°C;
the amount of dry lumps and cakes (expressed as a percentage of the VC introduced) was 0.25;
the thermal stability of the resin sample obtained was 4 minutes 48 seconds; the residual monomer content in the latex was 34.3 ppm.
Example 6 (according to the invention)
Example 4R was repeated, except that:
after time tx, once a pressure reduction (ΔΡ) of 0.5 bar was detected, the contents of the reactor were brought, 1 hour after this time, to a higher temperature (self-heating), the polymerization time elapsed from tO up to this point (ΔΡ = 0.5 bar + 1 hour) was recorded, and 56.4 g of a commercial solution of antifoam (Tego® KS 53 sold by Evonik) were added; and in the polymerization step, an aqueous solution containing a mixture of zinc sulfate monohydrate at a rate of 0.005 g per kg of VC used (the mole ratio of zinc sulfate to the mixture of initiators was thus about 0.0084) and of ascorbic acid at a rate of 0.010 g per kg of VC used (the mole ratio between the ascorbic acid and the zinc sulfate was thus about 1.83) was added in a single batch, at the moment at which a pressure reduction (ΔΡ) of 0.5 bar was detected relative to the mean pressure at which the polymerization step was performed.
The results of this example were as follows:
- the polymerization lasted 355 minutes;
- the ΔΤ maximum was 22.0°C;
- the amount of dry lumps and cakes (expressed as a percentage of the VC introduced) was 0.17;
- the thermal stability of the resin sample obtained was 10 minutes 12 seconds;
- the residual monomer content in the latex was 40.3 ppm.
Comparison of the results of Example 4R with those of Examples 5 and 6 reveals that the process according to the invention led to the production of polymers characterized by a lower residual VC content. The content of dry lumps and cakes after the polymerization was also significantly lower.
Comparison of the results of Examples 5 and 6 itself reveals that, although the abovementioned advantages were obtained both with a zinc salt and with a copper salt, the use of a zinc salt has the particular advantage of leading to a polymer which is characterized by better thermal stability and a lower content of dry lumps and cakes after the polymerization, in other words to a better compromise in terms of polymerization kinetics/properties of the polymers obtained, than when a copper salt is used.
Example 7R (comparative)
Preparation of the seed latex (seed latex S)
The process was performed as described in Example 1R. The solids content of the seed latex S was 37.8%
Preparation of the fine dispersion (1st part)
The process was performed as described in Example 4R, except that 49.9 kg of demineralized water and 3.4 kg of a commercial sodium
dodecylbenzenesulfonate solution at 29.54% in water were used.
Loading the reagents into the reactor (1st part)
The process was performed as described in Example 4R, except that 64.45 kg of demineralized water, 0.034 kg of a commercial sodium
dodecylbenzenesulfonate solution at 29.54% in water, and 12.34 kg of the seed latex S at 37.8% solids were used.
Preparation of the fine dispersion (2nd part)
The process was performed as described in Example 4R.
Loading the reagents into the reactor (2nd part)
The process was performed as described in Example 4R. Preparation of the fine dispersion (3rd part) and loading of the reagents into the reactor (3rd part)
The process was performed as described in Example 1R.
Polymerization
The contents of the reactor were brought to 51°C. Once this temperature was reached (to), 18.66 kg of VC were introduced into the reactor during the polymerization.
After time tx (in this case corresponding to a pressure reduction (ΔΡ) of 0.2 bar relative to the average pressure at which the polymerization step was performed), once a pressure reduction (ΔΡ) of 1 bar was detected, the contents of the reactor were brought to a higher temperature (self -heating), the
polymerization time elapsed from ¾ up to this point (ΔΡ = 1 bar) was recorded, and 56.0 g of a commercial solution of antifoam (Tego® KS 53 sold by Evonik) were added.
End operations
The process was performed as described in Example 1R.
Drying of the latex and recovery of the resin
The process was performed as described in Example 1R.
Determination of the residual monomer in the latex
The process was performed as described in Example 1R.
In this example:
- the polymerization lasted 355 minutes;
- the ΔΤ maximum was 21.0°C;
- the amount of dry lumps and cakes (expressed as a percentage of the VC introduced) was 0.27;
- the residual monomer content in the latex was 10.0 ppm.
Example 8R (comparative)
Example 7R was repeated, except that:
- after time tx, once a pressure reduction (ΔΡ) of 0.5 bar was detected, the contents of the reactor were brought, 1 hour after this time, to a higher temperature (self-heating), the polymerization time elapsed from tO up to this point (ΔΡ = 0.5 bar + 1 hour) was recorded, and 56.0 g of a commercial solution of antifoam (Tego® KS 53 sold by Evonik) were added; and
- in the polymerization step, an aqueous ascorbic acid solution at 0.01 g per kg of VC used was added, in a single batch, at the moment at which a pressure reduction (ΔΡ) of 0.5 bar was detected relative to the mean pressure at which the polymerization step was performed.
The results of this example were as follows:
- the polymerization lasted 335 minutes;
- the ΔΤ maximum was 21.0°C;
- the amount of dry lumps and cakes (expressed as a percentage of the VC introduced) was 0.42;
- the residual monomer content in the latex was 25.0 ppm.
Example 9R (comparative)
Example 7R was repeated, except that:
- in the polymerization step, an aqueous zinc sulfate monohydrate solution at 0.01 g per kg of VC used was added, in a single batch, at the moment at which a pressure reduction (ΔΡ) of 0.5 bar was detected relative to the mean pressure at which the polymerization step was performed.
The results of this example were as follows:
- the polymerization lasted 398 minutes;
- the ΔΤ maximum was 22.0°C;
- the amount of dry lumps and cakes (expressed as a percentage of the VC introduced) was 0.51;
- the residual monomer content in the latex was 10.9 ppm.
Comparison of the results of Examples 8R and 9R with those of Example
7R reveals that the addition of only one of the components of the activating system from the start of the reduction of the VC autogenous pressure does not lead to the production of polymers that are characterized by a lower residual VC content.
Example 10R (comparative)
Preparation of the seed latex (seed latex S)
The process was performed as described in Example 1R. The solids content of the seed latex S was 37.9%
Preparation of the fine dispersion (1st part)
The process was performed as described in Example 4R, except that 50.0 kg of demineralized water and 3.2 kg of a commercial sodium
dodecylbenzenesulfonate solution at 31.25% in water were used.
Loading the reagents into the reactor (1st part)
The process was performed as described in Example 4R, except that 64.5 kg of demineralized water, 0.36 kg of a commercial sodium dodecylbenzenesulfonate solution at 31.25% in water, and 12.3 kg of the seed latex S at 38.0% solids were used.
Preparation of the fine dispersion (2nd part)
The process was performed as described in Example 4R.
Loading the reagents into the reactor (2nd part)
The process was performed as described in Example 4R.
Preparation of the fine dispersion (3rd part) and loading of the reagents into the reactor (3rd part)
The process was performed as described in Example 1R.
Polymerization
The contents of the reactor were brought to 51 °C. Once this temperature was reached (to), 18.66 kg of VC were introduced into the reactor during the polymerization.
After time tx (in this case corresponding to a pressure reduction (ΔΡ) of 0.2 bar relative to the average pressure at which the polymerization step was performed), once a pressure reduction (ΔΡ) of 1 bar was detected, the contents of the reactor were brought to a higher temperature (self-heating), the
polymerization time elapsed from ¾ up to this point (ΔΡ = 1 bar) was recorded, and 56.4 g of a commercial solution of antifoam (Tego® KS 53 sold by Evonik) were added.
End operations
The process was performed as described in Example 1R.
Drying of the latex and recovery of the resin
The process was performed as described in Example 1R.
Evaluation of the thermal stability
The thermal stability of the ground resin (0.5 g) was evaluated using a Thermomat PVC 763 constructed by the company Metrohm.
The PVC sample heated to 180°C breaks down with evolution of HC1, which is entrained by a gas stream (7 L/h of N2) into a measuring cell where it is absorbed by ultrapure water. The HC1 concentration of this water is measured continuously by conductimetry.
The conventional thermal stability was defined as the induction time of the dehydrochlorination reaction at a temperature of 180°C leading to an increase in conductimetry of 5 μ8/αη relative to the initial value. It is expressed in minutes and seconds. Evaluation of the yellow index
The process was performed as described in Example 1R.
Determination of the residual monomer in the latex
The process was performed as described in Example 1R.
In this example:
- the polymerization lasted 404 minutes;
- the ΔΤ maximum was 21.0°C;
- the amount of dry lumps and cakes (expressed as a percentage of the VC introduced) was 0.15;
- the yellow index was 1.9 after 90 seconds of gelation at 180°C;
- the thermal stability of the resin sample obtained was 9 minutes 36 seconds;
- the residual monomer content in the latex was 38.7 ppm.
Example 11R (comparative)
Example 10R was repeated, except that:
- in the step of loading the reagents into the reactor (1st part), copper sulfate pentahydrate was added at a rate of 0.024 g per kg of VC (the mole ratio of copper sulfate to the initiator mixture was thus about 0.027);
- in the polymerization step, an aqueous ascorbic acid solution at 0.022 g per kg of VC used (the mole ratio between the ascorbic acid and the copper sulfate was thus about 1.27) was introduced continuously at a constant rate from the start of the polymerization step (to) and up to the point at which a pressure reduction (ΔΡ) of 0.4 bar was detected relative to the mean pressure at which the polymerization step was performed (moment at which the addition was stopped).
The results of this example were as follows:
- the polymerization lasted 384 minutes, namely 242 minutes from ¾ up to the moment at which ΔΡ =0.4 bar and 142 minutes between the latter moment and the moment at which ΔΡ = 1 bar;
- the ΔΤ maximum was 27.3°C;
- the amount of dry lumps and cakes (expressed as a percentage of the VC introduced) was 0.34;
- the yellow index was 2.0 after 90 seconds of gelation at 180°C;
- the thermal stability of the resin sample obtained was 6 minutes 54 seconds;
- the residual monomer content in the latex was 17.6 ppm. Example 12 (according to the invention)
Example 10R was repeated, except that:
- in the step of loading the reagents into the reactor (1st part), copper sulfate pentahydrate was added at a rate of 0.024 g per kg of VC (the mole ratio of copper sulfate to the initiator mixture was thus about 0.0027);
- in the polymerization step, an aqueous ascorbic acid solution at 0.022 g per kg of VC used (the mole ratio between the ascorbic acid and the copper sulfate was thus about 1.27) was introduced in a single batch at the moment at which a pressure reduction (ΔΡ) of 0.4 bar was detected relative to the mean pressure at which the polymerization step was performed.
The results of this example were as follows:
- the polymerization lasted 285 minutes, namely 283 minutes from ¾ up to the moment at which ΔΡ =0.4 bar and 2 minutes between the latter moment and the moment at which ΔΡ = 1 bar;
- the ΔΤ maximum (measurement of the exothermic nature of the
polymerization) was 21.4°C;
- the amount of dry lumps and cakes (expressed as a percentage of the VC introduced) was 0.34;
- the yellow index was 1.9 after 90 seconds of gelation at 180°C;
- the thermal stability of the resin sample obtained was 5 minutes 24 seconds;
- the residual monomer content in the latex was 10.1 ppm.
Comparison of the results of Example 12 with those of Example 10R reveals that the process according to the invention leads to the production of polymers which are characterized by a much lower residual VC content and is characterized by a much shorter polymerization time.
Comparison of the results of Example 12 with those of Example 11R reveals that the process according to the invention leads to the production of polymers that are characterized by a lower residual VC content than the process according to the prior art in which the complexing agent is introduced from the start of the polymerization step (to) and at the very latest at the said pressure reduction. Furthermore, comparison of the data regarding the duration of the various polymerization phases reveals that the process according to the invention leads to a shorter total polymerization time and also solves the characteristic problems of the process according to the prior art (slowness of pressure reduction up to the self-heating).

Claims

C L A I M S
1. Process for preparing a vinyl chloride polymer, comprising a step of polymerizing at least vinyl chloride, the said step being performed in aqueous dispersion in the presence of at least one liposoluble radical initiator and being continued up to the reduction of the autogenous pressure of vinyl chloride with introduction, into the polymerization medium, of an activating system comprising a water-soluble transition metal salt and a complexing agent, characterized in that at least the complexing agent is introduced in total into the said polymerization medium from the start of the said pressure reduction.
2. Process according to Claim 1, characterized in that the polymerization step is performed in microsuspension or in seeded microsuspension.
3. Process according to Claim 1 or 2, characterized in that the water- soluble transition metal salt is a water-soluble copper or zinc salt.
4. Process according to any one of Claims 1 to 3, characterized in that the complexing agent is chosen from lactones.
5. Process according to Claim 4, characterized in that the complexing agent is ascorbic acid.
6. Process according to any one of Claims 1 to 5, characterized in that only the complexing agent is introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride.
7. Process according to Claim 6, characterized in that if we call z the time elapsed between the start of reduction of the autogenous pressure of the vinyl chloride (tx) and the moment tz at which the polymerization is complete, the complexing agent is introduced in a single batch at any fraction of z between tx and tz including addition in a single batch at tx, in several successive batches of the same weight or of uniformly decreasing weight distributed over the duration z, continuously over z at a constant rate, continuously over z at a decreasing rate, continuously over a fraction of z of between tx and tz at a constant rate, or continuously over a fraction of z of between tx and tz at a decreasing rate.
8. Process according to any one of Claims 1 to 5, characterized in that the complexing agent and the water-soluble transition metal salt are introduced, at least partly for the latter, into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride.
9. Process according to Claim 8, characterized in that, if we call z the time elapsed between the start of reduction of the autogenous pressure of vinyl chloride (tz) and the moment tz at which the polymerization is complete, the complexing agent and the water-soluble transition metal salt are introduced separately or together, in one of the ways below, taken separately or in combination:
- in a single batch at any fraction of z between tx and tz including addition in a single batch at tx,
- in several successive batches of the same weight or of uniformly decreasing weight distributed over the duration z,
- continuously over z at a constant rate,
- continuously over z at a decreasing rate,
- continuously over a fraction of z of between tx and tz at a constant rate, or
- continuously over a fraction of z of between tx and tz at a decreasing rate.
10. Process according to Claim 8 or 9, characterized in that the amount of salt, expressed on a weight basis relative to the weight of complexing agent introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride, is between 0.15 and 3.
11. Process according to any one of Claims 1 to 10, characterized in that the amount of complexing agent introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride, expressed on a weight basis relative to the weight of initiator present in the polymerization step, is greater than or equal to 1 per thousand.
12. Process according to any one of Claims 1 to 11, characterized in that the amount of complexing agent introduced into the polymerization medium from the start of reduction of the autogenous pressure of vinyl chloride, expressed on a weight basis relative to the weight of initiator present in the polymerization step, is less than or equal to 40 per thousand.
13. Vinyl chloride polymers obtained via a process comprising a step of polymerizing at least vinyl chloride, the said step being performed in aqueous dispersion in the presence of at least one liposoluble radical initiator and being continued up to the reduction of the autogenous pressure of vinyl chloride with introduction, into the polymerization medium, of an activating system comprising a water-soluble transition metal salt and a complexing agent, at least the complexing agent being introduced in total into the said polymerization medium from the start of the said pressure reduction.
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20200048132A (en) * 2018-10-29 2020-05-08 주식회사 엘지화학 Method for preparing vinyl chloride based polymer
EP3875498A4 (en) * 2018-11-02 2021-12-01 Lg Chem, Ltd. Composition for preparing vinyl chloride-based polymer and method for preparing vinyl chloride-based polymer using same
EP3875499A4 (en) * 2018-11-02 2021-12-08 Lg Chem, Ltd. Method for preparing vinyl chloride-based polymer
WO2023180317A1 (en) 2022-03-21 2023-09-28 Inovyn Europe Limited Process for producing pvc and pvc product

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4091197A (en) 1973-06-08 1978-05-23 Nicolas Fischer Process for polymerization of vinyl chloride micro-suspension with metal compounds
US4331788A (en) 1979-08-28 1982-05-25 Chloe Chimie Process of polymerizing vinyl chloride in seeded microsuspension
EP0826703A1 (en) 1996-08-27 1998-03-04 Elf Atochem S.A. Latex with two-particle size populations of vinylchloride polymers, manufacturing method thereof and use in plastisols

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4091197A (en) 1973-06-08 1978-05-23 Nicolas Fischer Process for polymerization of vinyl chloride micro-suspension with metal compounds
US4331788A (en) 1979-08-28 1982-05-25 Chloe Chimie Process of polymerizing vinyl chloride in seeded microsuspension
EP0826703A1 (en) 1996-08-27 1998-03-04 Elf Atochem S.A. Latex with two-particle size populations of vinylchloride polymers, manufacturing method thereof and use in plastisols

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20200048132A (en) * 2018-10-29 2020-05-08 주식회사 엘지화학 Method for preparing vinyl chloride based polymer
CN112272678A (en) * 2018-10-29 2021-01-26 株式会社Lg化学 Process for producing vinyl chloride polymer
EP3875500A4 (en) * 2018-10-29 2021-12-01 Lg Chem, Ltd. Method for preparing vinyl chloride-based polymer
KR102381870B1 (en) 2018-10-29 2022-04-04 주식회사 엘지화학 Method for preparing vinyl chloride based polymer
US11952442B2 (en) 2018-10-29 2024-04-09 Lg Chem, Ltd. Method for preparing vinyl chloride-based polymer
EP3875498A4 (en) * 2018-11-02 2021-12-01 Lg Chem, Ltd. Composition for preparing vinyl chloride-based polymer and method for preparing vinyl chloride-based polymer using same
EP3875499A4 (en) * 2018-11-02 2021-12-08 Lg Chem, Ltd. Method for preparing vinyl chloride-based polymer
US11760818B2 (en) 2018-11-02 2023-09-19 Lg Chem, Ltd. Method of preparing vinyl chloride-based polymer
US11952443B2 (en) 2018-11-02 2024-04-09 Lg Chem, Ltd. Composition for preparing vinyl chloride-based polymer and method of preparing vinyl chloride-based polymer using the same
WO2023180317A1 (en) 2022-03-21 2023-09-28 Inovyn Europe Limited Process for producing pvc and pvc product

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