JPS6129966B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a process for polymerizing halogen-containing vinyl monomers, such as vinyl chloride, in aqueous dispersions. Usually, halogen-containing vinyl monomers are polymerized in the form of droplets dispersed in water by mechanical agitation in the presence of emulsifiers or dispersants, and either oil-soluble polymerization initiators (suspension polymerization) or water-soluble polymerization initiators (emulsification Polymerization) is used. You can also use a paddle
It is customary to carry out the polymerization batchwise in a reactor having a steel kettle equipped with a stirrer and, if necessary, baffles. In this conventional polymerization process, more specifically in suspension polymerization, solid polymer precipitates, commonly called "crusts", adhere strongly to the inner surfaces of the reactor (kettle, stirrer, board). is formed during polymerization. This phenomenon is commonly referred to as "crust formation." Crust formation is extremely disadvantageous. In fact, the crust lining the inside of the kettle reduces the amount of heat that can be removed by the heat transfer liquid circulating in the double jacket that the reactor is commonly equipped with. As a result, productivity is reduced because a lower rate of polymerization must be used than without crust formation. Furthermore, during polymerization it often occurs that the crust partially separates and contaminates the resulting polymer, and the polymer is contaminated with infusible nodules, commonly referred to as "fish-eyes", which are attributed to this crust. (nodules). Finally, crust formation, which always occurs irregularly, makes the polymerization cycle more difficult to carry out and control. Obviously, it is common to clean the interior surfaces of the reactor after each polymerization cycle. This cleaning is often done by hand, but there are also more complex techniques using hot solvents or equipment that sprays water jets at high velocity. However, this cleaning is always a labor-intensive task, requiring expensive manual labor, power, and materials, and requiring long periods of time to shut down the polymerization reactor. For this reason, attempts have been made to prevent crust formation by adding to the polymerization mixture various additives that have an inhibitory effect on crust formation. Under the name of CHISSO Corporation, March 1976
German patent application No. 2518260, filed on April 4th, includes:
It has been proposed to use oxalic acid or oxalate salts for this purpose. However, the inhibitory effect of oxalic acid and its salts on crust formation is not complete. Therefore,
This inhibitor cannot carry out very long series of polymerization cycles without intermediate cleaning. The inventors have discovered a new class of crust formation inhibitors that are completely effective and have no undesirable side effects. The present invention therefore relates to a process for polymerizing halogen-containing vinyl polymers with a radical polymerization initiator in the presence of a crust formation inhibitor in an aqueous dispersion. The crusting inhibitor is selected from among the anions derived from organic hydroxycarboxylic acids. The anion used as a crust formation inhibitor according to the present invention has at least one carboxyl group -COOH as a substituent for a carbon atom in its molecule.
and one hydroxyl group -OH. Generally, anions derived from organic acids containing a total of 2 to 20 carbon atoms are used. Preferably, anions derived from organic acids containing 3 to 8 carbon atoms are used, with best results obtained with anions derived from acids containing 4 to 6 carbon atoms. Preferably, anions derived from organic acids containing at least two carboxyl groups per molecule are used as crust formation inhibitors according to the invention; The best results are obtained with anions derived from . Examples of anions that can be used according to the invention are hydroxyacetic acid (glycolic acid), hydroxyphenylacetic acid, hydroxybenzoic acid, hydroxybutanoic acid, hydroxybutenoic acid, hydroxycinnamic acid (coumaric acid), hydroxycyclohexanecarboxylic acid, hydroxy Hexanoic acid, hydroxypropanoic acid (lactic acid), leucinic acid, hydroxymalonic acid (taludronic acid), hydroxyoctanoic acid, hydroxypentanedioic acid, hydroxyphthalic acid, hydroxyphenylpropanoic acid, citric acid, and more specifically dihydroxybutanedioic acid. acid (tartaric acid),
It is an anion derived from dihydroxymaleic acid, gluconic acid, and citric acid. Of all the anions that can be used as crust formation inhibitors according to the present invention, the most effective are those derived from tartaric acid and citric acid.
Particularly preferred anions are those derived from tartaric acid. The above anions can be derived independently of all optical isomers of tartaric acid. Therefore, this anion is converted into dextrotartaric acid (d-tartaric acid or L
(+)-tartaric acid), levorotary tartaric acid (l-tartaric acid or D(-)-tartaric acid), mesotartaric acid (optically inactive due to internal compensation), and racemic tartaric acid (dl-tartaric acid). Preference is given to using natural tartaric acid (d-tartaric acid or L(+)-tartaric acid). The anions can be used in the method in the form of water-soluble compounds and compounds that dissociate in water to form the anions mentioned above. In particular, the anions can be generated from the corresponding organic hydroxycarboxylic acids and their salts. Among these, alkaline earth metal salts and also alkali metal salts, such as potassium or sodium salts and ammonium salts, are preferred. When using a salt, it is desirable to select a salt whose cations do not have an adverse effect on the polymerization reaction or the properties of the polymer. However, the best results are obtained by starting from the organic hydroxycarboxylic acid itself. The method of the present invention is applicable to the polymerization of halogen-containing vinyl monomers. The term halogen-containing vinyl monomer has terminal olefinic unsaturation and at least one
means all monomers that can be polymerized by radical polymerization and are substituted with halogens. Preferably, these monomers are selected from substituted derivatives of ethylene and contain only 2 carbon atoms. Examples of the above monomers include vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, chlorotrifluoroethylene, and tetrafluoroethylene. The invention is preferably applied to the polymerization of fluorine-containing and chlorine-containing vinyl monomers. The invention particularly relates to chlorine-containing monomers,
Furthermore, it is particularly suitable for the polymerization of vinyl chloride. The term polymerization refers to the homopolymerization of halogen-containing vinyl monomers and the copolymerization of said monomers with each other or with other monomers copolymerizable with said monomers. Examples of the latter include vinyl esters such as vinyl acetate, acrylic esters such as methyl acrylate and glycidyl methacrylate, unsaturated nitrites such as acrylonitrile and methacrylonitrile, unsaturated diesters such as dibutyl maleate, allyl acetate. Mention may be made of allyl esters such as, unsaturated amides such as acrylamide, styrene derivatives, α-olefins such as ethylene and propylene. However, it is preferred to apply the invention to the preparation of polymers containing in the polymer molecule at least 50 mole %, more particularly at least 80 mole %, of units derived from halogen-containing vinyl monomers. The present invention is a statistical copolymer (statistical copolymer).
copolymers) and block or graft copolymers. The process of the invention can be used in all polymerization processes in which halogen-containing vinyl monomers are dispersed in droplet form in a liquid aqueous phase. In particular, the method of the invention can be used in aqueous emulsion polymerization. Emulsifiers can be used in this case, especially anionic emulsifiers and nonionic emulsifiers, such as sodium benzylsulfonate or sodium dodecylbenzenesulfonate. Aqueous radical polymerization initiators, especially persulfates, can also be used. However, the problem of crust formation is particularly severe in aqueous suspension and microsuspension polymerization processes using oil-soluble polymerization initiators. In suspension polymerization, finely dispersed solids, gelatin,
Conventional dispersants such as water-soluble cellulose ethers, synthetic polymers such as polyvinylpyrrolidone, vinyl acetate/maleic anhydride copolymers, and mixtures thereof are generally used. A surfactant can also be used at the same time as a dispersant. The amount of dispersant used generally varies from 0.5 to 1.5% by weight, based on water. In microsuspension polymerization, sometimes referred to as homogenized aqueous dispersion polymerization, an emulsion of monomer droplets is created by intensive mechanical stirring, usually in the presence of the same type of emulsifier as mentioned above, and with the aid of an oil-soluble initiator. Carry out polymerization. Any oil-soluble initiator can be used in suspension or microsuspension polymerizations. For example,
butyl peroxide, lauroyl peroxide,
peroxides such as acetylcyclohexylsulfonyl peroxide, azo compounds such as azobisisobutyronitrile and azobis-2,4-dimethylvaleronitrile, diethyl, diisopropyl, dicyclohexyl, di-tert-butylcyclohexyl peroxydicarbonate. Examples include dialkyl peroxydicarbonates and alkyl boron compounds such as. Generally, the initiator is used in a proportion of 0.01 to 1% by weight based on the monomer. In addition to dispersants or emulsifiers and initiators, the polymerization mixture can also contain various additives commonly used in conventional aqueous dispersion polymerization processes. Examples of such additives include buffers, regulators of the diameter of the polymer particles, such as alkali metal polyphosphates, molecular weight regulators, stabilizers, plasticizers, dyes, and reinforcing agents or agents that facilitate the processing of the polymer. can be mentioned. In addition to the anion-generating compounds derived from organic hydroxycarboxylic acids, other inhibitors of crust formation can also be incorporated into the polymerization mixture. The operating conditions of the polymerization process according to the invention do not differ from those commonly used. Temperature is generally 35-80
It is between ℃. The absolute pressure is generally less than 15Kg/ ^cm2 . The PH is generally acidic, for example between 2 and 7. The amount of water used is generally such that the total weight of monomer represents 20-50% of the total weight of water and monomer. Generally, the polymerization of halogen-containing vinyl monomers is carried out in a discontinuous manner, with water being introduced first and then the various components of the reaction mixture (dispersant or emulsifier, initiator, monomer). According to a preferred embodiment of the invention, a crust formation inhibitor is introduced into the polymerization mixture before the halogen-containing vinyl monomer, and the best results are obtained when said inhibitor is introduced before the initiator. To do this, it is sufficient to add a crust formation inhibitor after the introduction of water, optionally simultaneously with a dispersant or emulsifier. Crust formation inhibitors can also be introduced into the polymerization mixture in several stages during the polymerization or continuously. To initiate the polymerization, the polymerization mixture is heated, for example, by means of a heat transfer liquid circulating through a double jacket with which the reactor is usually provided. Preferably, a crust formation inhibitor is introduced into the polymerization mixture at the heating initiator. When the polymerization is carried out continuously, it is also preferable to continuously introduce the crust formation inhibitor into the polymerization mixture. The amount of crusting inhibitor used can vary widely;
It is a function of the nature of the monomers used and the internal conditions of the reactor. Generally, an amount of crusting inhibitor is used such that the polymerization mixture contains at least 1 ppm of water. Preferably, the polymerization mixture contains at least 5 ppm inhibitor based on water. Best results are obtained when the polymerization mixture contains at least 10 ppm of crusting inhibitor based on water. There is no disadvantage to using large amounts of crust formation inhibitors. However, 10000ppm of water in the polymerization mixture
It is generally pointless to exceed the crusting inhibitor content of . most often, at most
A content of 1000ppm is sufficient. In practically all cases, a content equal to at most 200 ppm is quite sufficient. It was observed that some amount of crusting inhibitor was adsorbed on the inner metal surface of the polymerization reactor. For this reason, the polymerization mixture should contain an amount of crusting inhibitor of at least 1 mg, preferably at least 5 mg, per m ² of internal metal surface area. Also for this reason, a certain amount of crusting inhibitor remains adsorbed on the inner metal surface of the reactor at the end of the polymerization cycle and is available for action during the next cycle. Taking this amount into account, the amount added during the next cycle can be reduced. When starting to use this method in a particular reactor, it is worth first cleaning the internal surfaces with special care. To do this, it is possible to use particularly effective solvents of the crust-forming polymers, to carry out pyrolysis of the vessel walls, or to carry out descaling or refinishing. The new set of crust formation inhibitors that form the subject of the present invention are extremely effective. In fact, crust formation inhibitors previously considered effective in the art, such as oxalic acid and its salts, described in the above-mentioned German patent application no. For it to be noticeable, it needs to be used at a rate of about 50 ppm relative to water. The crust formation inhibitor according to the invention is fully effective already when using about 15 ppm based on water. Furthermore, the inhibitors of the present invention contain a number of compounds that do not exhibit adverse secondary effects on the appearance of the polymer, its odor, its heat and light stability, its ability to use food packaging. The polymers obtained according to the invention can be used in all the customary applications for products of this type, in particular for the production of articles such as bottles or profiles by the customary techniques of extrusion-blowing and extrusion. The following examples are illustrative of the invention, but are not intended to limit the invention to these examples. Examples 1, 2, 4 and 5 were carried out according to the invention. Example 3 (R) is shown for comparison. Examples 1-3 (R) A 3 capacity stainless steel laboratory reactor equipped with a double jacket through which the heat transfer liquid flows and a stainless steel, conventional agitator was used. The inner surface of the reactor was cleaned by washing with tetrahydrofuran and heating the vessel wall to 400° C. for 30 minutes for pyrolysis.
The reactor was then descaled with a fluoronitric acid bath and then rinsed five times with deionized water. 1500 g of deionized water and 10 mg of organic carboxylic acid were introduced into the reactor sequentially. Then 1.65 g of polyvinyl alcohol was introduced. Started the stirrer.
500 mg of di-tert-butylcyclohexyl peroxydicarbonate were then introduced as a powder.
Then, vacuum the reactor twice (100 mmHg, absolute pressure).
and the reactor was heated to 1360 mmHg between these two operations.
Flushed with industrial nitrogen at absolute pressure. Then 1000 g of vinyl chloride was introduced. Polymerization mixture at 1℃/
The mixture was heated to 61°C at a rate of 1 min. The polymerization mixture was kept at 61° C. with stirring until the absolute pressure dropped to 3.5 Kg/cm ² . Polymerization was then stopped by lowering the reactor pressure to evaporate unpolymerized vinyl chloride. The mixture was cooled and the polymer was collected by filtration and then dried. Table 1 shows the type of organic acid used and the results of an inspection of the reactor interior at the end of the polymerization cycle.

[Table] % covered.
Example 4 1500 g of deionized water, 10 mg of L(+)-tartaric acid and 10 mg of potassium iodide were introduced sequentially into the same reactor as used in the above example. Then 1.65 g of polyvinyl alcohol was introduced. Started the stirrer. Then diethyl peroxydicarbonate
200mg was introduced. The reactor was then evacuated twice (100 mm Hg absolute) and between the two operations the reactor was flushed with technical nitrogen at 1360 mm Hg absolute. Then 1000 g of vinyl chloride was introduced.
The polymerization mixture was heated to 61°C at a rate of 1°C/min. The polymerization mixture was kept at 61° C. with stirring until the absolute pressure decreased to 3.5 Kg/cm ² . Polymerization was then stopped by lowering the reactor pressure to evaporate unpolymerized vinyl chloride. The mixture was cooled and the polymer was collected by filtration and then dried. After polymerization, the inside surface of the reactor was inspected and found to be free of crust. Three similar polymerizations could be repeated before thorough cleaning of the reactor was required. Example 5 This example corresponds in all respects to Example 4, except that before introducing the polyvinyl alcohol
(+) - Tartaric acid 10 mg, potassium iodide 10 mg, sodium polymetaphosphate (sold under the name Metagon) 25 mg
were sequentially introduced into deionized water. After polymerization, the inside surface of the reactor was inspected and found to be free of crust. Ten similar polymerizations could be repeated before a thorough cleaning of the reactor was required. These examples demonstrate the superiority of the crust formation inhibitor according to the present invention, and more particularly the superiority of anions derived from tartaric acid over oxalic acid.

Claims (1)

[Scope of Claims] 1 The crust formation inhibitor is an anion derived from an organic hydroxycarboxylic acid containing 4 to 6 carbon atoms in the molecule (provided that copper salts, nickel salts, etc. of the corresponding organic hydroxycarboxylic acid) In the presence of a crust formation inhibitor, an oil-soluble radical polymerization initiator is essentially selected from A method for polymerizing vinyl chloride monomer using an initiator. 2. The method according to claim 1, wherein the anion is derived from an organic acid containing at least two carboxyl groups in the molecule. 3. The method according to claim 1, characterized in that the anion is derived from tartaric acid. 4. The method according to claim 1, wherein the anion is derived from citric acid. 5. The method according to any one of claims 1 to 4, characterized in that the anion is introduced into the polymerization mixture in the form of the corresponding organic acid or an alkali metal salt or ammonium salt of the corresponding organic acid. Method. 6. The method according to any one of claims 1 to 5, characterized in that the anion is introduced into the polymerization mixture before the halogen-containing vinyl monomer and the radical polymerization initiator. 7. Claims 1 to 7, characterized in that the anion is used in a proportion of at least 5 ppm and not more than 200 ppm based on the water present in the polymerization mixture.
The method described in any one of Item 6. 8 The anion is transferred to the inner metal surface area of the reactor of 1 m ²
8. A method according to claim 1, characterized in that a proportion of at least 5 mg per portion is used. 9. The method according to any one of claims 1 to 8, which is applied to suspension polymerization.