DE3039543A1 - METHOD FOR PRODUCING PVC RESINS - Google Patents

Description

description

The invention relates to a method for the production of polyvinyl chloride resins (PVC resins) in the preamble of Claim 1 mentioned Art.

In particular, the invention relates to a process for the production of PVC resins by polymerization in aqueous suspension. The process is specifically designed to produce product polymers with improved heat resistance and reduced discoloration to create when giving shape. Vinyl chloride is preferably used as the monomer for the polymerization reaction, but it can a monomer mixture whose main component is vinyl chloride can also be used. In this process, the Effectiveness of the polymerization reaction itself can be significantly improved by the fact that the approach and the structure is largely suppressed by incrustations on the inner walls of the polymerization reactor.

Usually PVC resins are usually made by suspension polymerization of monomeric vinyl chloride in an aqueous medium. One of the most difficult technical problems in suspension polymerization of monomeric vinyl chloride in an aqueous polymerization medium is the build-up of polymer encrustations on the Inner walls of the polymerization reactor. When the suspension polymerization of the monomeric vinyl chloride in the aqueous phase is carried out in a polymerization reactor made of stainless steel or a corresponding material, encrustation occurs the inner walls of the reactor and the other inner surfaces of the plant that come into contact with the monomer

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long, which particularly affects agitators and heat exchangers. Such incrustations will not only is the product polymer yield reduced, but the cooling capacity of the reactor is also reduced. By this reduction in the cooling capacity of the reactor will reduce the overall productivity of the polymerization plant. In addition, flaking parts of the polymer scale get from the reactor walls into the resin product and reduce them so the quality of this product. In particular, parts of the polymer crust that have broken off occur in a product polymer the reactor walls contain homogeneity defects in increased concentration, namely the so-called "fish eyes", which are noticeable when the PVC resins are being molded. In addition, the must after each polymerization Crust to be removed from the reactor. This costs time and effort and thereby reduces productivity and at the same time increases costs. In addition, the cleaning of such tanks poses a significant health risk the cleaning of the polymerization reactors performing personnel, since the polymer crusts adhering to the inner walls of the polymerization reactor are still considerable Contain portions of the toxic and volatile monomeric vinyl chloride.

On the other hand, however, it is also known that numerous properties are decisive for the product polymer quality are influenced by a number of parameters of the polymerization reaction. So hang in particular the heat resistance and the initial discoloration of the resin after molding by injection molding or an analogous one Shaping process depends to a large extent on the type of polymerization initiator used, which is used in the polymerization reaction system is used. In the aqueous suspension polymerization of monomeric vinyl chloride is usually

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a polymerization initiator soluble in the monomer is used. It is clear to the person skilled in the art that such monomer-soluble polymerization initiators are either practically insoluble or hardly soluble in water. It should be noted, however, that even these polymerization initiators are not absolutely insoluble in water, but always have residual solubility in water, no matter how low. It is known that the water solubility of the polymerization initiator is one of the parameters which affect the heat resistance and the initial color of the product PVC resin made with such polymerization initiators. In this context, organic peroxides used as polymerization initiators have a relatively good solubility in water, which is, for example, in the range of at least 0.2% by weight at 20 ^° C. The use of such polymerization initiators can significantly improve the heat resistance and the initial discoloration of the product resins even compared to other organic peroxides which have a lower solubility in water than that specified above.

Despite the advantages described with regard to the thermal stability of the product resins with those organic Peroxides are produced as polymerization initiators, which have a relatively high solubility in water such relatively readily water-soluble organic peroxides for the technical-industrial production of PVC resins barely used. The reason for the astonishing fact is that when used it is relatively more water-soluble organic peroxides as polymerization initiators result in a much stronger polymer encrustation of the reactor walls occurs than is the case when using less readily water-soluble organic peroxides.

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To suppress the polymer encrustation of the reactor walls during the suspension polymerization of monomeric vinyl chloride Numerous processes are known in an aqueous medium, which in principle are based on two methods let, namely either on a method for coating the reactor walls before the start of the polymerization reaction with a coating material that protects against polymer incrustation is less susceptible, or a process in which the polymerization mixture during the reaction certain additives are added.

As a coating material for coating the reactor walls before the start of the polymerization reaction are, for example polar organic compounds, organic dyes and pigments known, in particular amines, quinones and Aldehydes (JP 45-30 343 B2 or JP 45-30 835 B2). The following substances are also used as coating material for the reactor walls known: polar organic substances or organic dyes treated with a metal salt (JP 52-24 953 B2), Mixtures of an electron donor with an electron acceptor (JP 53-28 347 B2) and certain inorganic salts and inorganic complex compounds (JP 52-24 070 B2).

Such coating processes are particularly effective when the polymerization initiator used is an azo compound or an organic peroxide with a long-chain alkyl group, i.e. extremely low water solubility, is. However, these coating methods are practically ineffective when the polymerization using a relatively highly water-soluble organic peroxide is carried out as a polymerization initiator. So in spite of it the numerous known processes for suppressing polymer incrustation on the reactor walls during polymerization of monomeric vinyl chloride is not a process that is effective even when a relatively highly water-soluble organic peroxide is used,

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for example a peroxide with a water solubility of at least approximately 0.2% by weight.

In view of this prior art, the invention is based on the object of creating a process for the production of PVC resins with improved heat resistance and reduced discoloration during molding, the polymerization being the suspension polymerization of monomeric vinyl chloride or monomeric vinyl chloride containing monomer mixtures as an essential component in one aqueous medium is to be carried out in the presence of a polymerization initiator which is a relatively readily water-soluble organic peroxide, especially an organic peroxide with a water solubility of at least 0.2% by weight at 20 ^° C.

A method of the type mentioned at the outset is used to solve this problem Kind created, which according to the invention has the features mentioned in the characterizing part of claim 1.

The invention thus provides an improved process for the suspension polymerization of monomeric vinyl chloride or of monomer mixtures, the main component of which is monomeric vinyl chloride, in an aqueous polymerization medium. An organic peroxide which is soluble in the monomer and whose solubility in water at 20 ^° C. is at least 0.2% by weight is used as the polymerization initiator. In this process, a coating is applied to the inner walls of the polymerization reactor before the polymerization reaction begins and before the polymerization reactor is charged with the polymerization mixture. The coating compound used is an aqueous coating solution which contains an organic dye which contains a sulfonic acid group-SO_H or a carboxyl group -COOH in the form of an alkali metal salt or ammonium salt, or an alkali metal salt or an ammonium salt.

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salt of an organic sulfonic acid or a carboxylic acid contains dissolved, which has at least one pair of conjugated double bonds in the molecule. After coating the Reactor walls with the aqueous solution, the coating is dried. In combination with this measure, the Polymerization system, that in the so coated polymerization reactor is polymerized, a water-soluble thiocyanate in a concentration of at least 1 ppm added based on the weight of the monomer or monomers. .

The method according to the invention for suspension polymerization of vinyl chloride monomer is not limited to homopolymerization only of vinyl chloride monomer applicable, but also to the copolymerization of monomeric vinyl chloride with at least one further copolymerizable ethylenically unsaturated monomer component as long as the main component of the monomer mixture is vinyl chloride. The main component in this context means that the monomer mixture is vinyl chloride contains in a concentration of about at least 50% by weight. As comonomers copolymerizable with vinyl chloride the following may be mentioned in particular: vinyl esters, in particular vinyl acetate and vinyl propionate, vinyl ethers, Acrylic acid and methacrylic acid and their esters, acrylonitrile, vinyl ketones, vinylidene halides, in particular vinylidene chloride and vinylidene fluoride, as well as olefins, in particular Ethylene and propylene.

The actual implementation of the polymerization can be carried out in a conventional manner and essentially as is known are, the essential difference to the invention from conventional polymerizations is that the reactor walls are coated in the manner described before the start of the polymerization reaction and at the same time the polymerization mixture in the one described above

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Way at least one thiocyanate is added. In particular, the polymerization system can use conventional dispersants contain as they usually contain for the suspension of the monomer or the monomer mixture in an aqueous medium can be used, for example water-soluble synthetic or natural polymers, in particular completely or partially saponified polyvinyl alcohol, cellulose ethers, in particular methyl cellulose or hydroxypropylmethyl cellulose, Polyacrylic acid, copolymers of vinyl acetate and maleic anhydride, gelatin and starch, nonionic Surface-active agents, in particular sorbitan monolaurate or sorbitan trioleate, and dispersion auxiliaries such as in particular Carboxymethyl cellulose.

The process of the invention can be used especially for the suspension polymerization of vinyl chloride in an aqueous medium, in which an organic peroxide which is soluble in the monomer and has a water solubility of at least 0.2% by weight at 20 ^° C. is used as the polymerization initiator. This is where the real advantages of the process lie. However, this does not mean that the process of the invention cannot be successfully applied even when an azo compound or an organic peroxide having a lower water solubility than that specified above is used as the polymerization initiator.

The following are preferably used as relatively readily water-soluble organic peroxides in the context of the invention: Di-2-ethoxyethyl peroxydicarbonate (hereinafter referred to as EEP), bis-3-methoxybutyl peroxydicarbonate (hereinafter referred to as MC) and dibutoxyethyl peroxydicarbonate (hereinafter referred to as BEP). Of course, within the scope of the invention other organic peroxides can also be used, as long as they have the minimum solubility mentioned. The three However, the above-mentioned peroxides are preferably used as being particularly suitable for a wide variety of reasons.

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The coating solution is applied to the inner walls of the polymerization reactor and, if appropriate, to the surfaces all other parts of the system, especially the agitator, applied with the monomer or monomers come into contact during the polymerization reaction. The coating solution is created by simply solving the opposite Alkali metal salts or ammonium salts of organic dyes or acids made in water.

As organic dyes having a sulfonic acid group or a carboxyl group, which are in the form of an alkali metal salt or an ammonium salt are present, the following preferably used dyes may be mentioned: CI. Direct yellow 1; C.I. Acid Yellow 3 8; C.I. Acid yellow 3; CI. Reactive Yellow 3; C.I. Direct orange 2; C.I. Direct orange 10; C.I. Direct red 1; CI. Acid red 2; CI. Acid red 18; C.I. Acid Red 52; C.I. Acid Red 73; CI. Direct red 186; CI. Direct red 92; C.I. Basic Red 2; CI. Direct violet 1; C.I. Direct violet 22; CI. Basic Violet 10; C.I. Acid Violet 11; C.I. Acid Violet 78; CI. Mordant Violet 5; C.I. Direct blue 6; C.I. Direct blue 71; C.I. Direct blue 106; C.I. Reactive blue 2; C.I. Reactive blue 4; CI. Reactive blue 18; C.I. Acid Blue 116; C.I. Acid Blue 158; Cl. Mordant Blue 1; C.I. Mordant Black 1; C.I. Mordant Black 5; C.I. Acid black 2; CI. Direct black 38; CI. Solubilized Vat Black 1; C.I. Fluorescent brightening agent 30; C.I. Fluorescent Brightening agent 32; C.I.-Azoic Brown 2. ·

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For the sake of clear identification of the substances the individual dyes in the list compiled above are cited in the form in which they are in the original edition of the Color Index are listed.

As organic sulfonic acids or carboxylic acids with at least one pair of conjugated double bonds in the molecule, the as another dissolved substance in the coating solution in the form of an alkali metal salt or an ammonium salt are used, the following preferably used substances may be mentioned: the toluidines, α-naphthalenesulfonic acid, Anthraquinonesulfonic acid, dodecylbenzenesulfonic acid, p-toluenesulfonic acid, Abietic acid, isonicotinic acid, benzoic acid, phenylglycine and 3-hydroxy-2-naphthoic acid.

To prepare the coating solution, those specified above are used Substances, namely at least one of the organic dyes and / or the organic sulfonic acids and / or the Carboxylic acids dissolved in water in the form of their salts. The concentration of the coating solution is not specific critical as long as it is suitable overall for producing the required coating on the inner walls of the reactor.

The coating solution prepared in the manner described above is usually more or less alkaline, so the pH value of the solution is preferably adjusted after complete :! Dissolution of the salts of the organic dyes and / or organic sulfonic acids and / or carboxylic acids by adding a small amount of acid adjusted to a value not greater than 7. Suitable acids for this purpose are the following, which are preferably used: sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid. Carbonic acid, perchloric acid, Molybdic acid, tungstic acid, formic acid, acetic acid, oxalic acid, lactic acid, maleic acid, glycolic acid, thioglycolic acid and phytic acid. These acids are preferably in the form

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their previously prepared aqueous solutions of the coating solution added.

The aqueous coating solution produced in this way is applied to the inner walls of the polymerization reactor and all other surfaces that come into contact with the monomer or monomers, in particular also to the surfaces of the stirrer. The aqueous coating solution can be applied in a manner known per se, for example by spraying, brushing or rolling. The surfaces that have been wet coated in this way are then thoroughly dried, if desired and necessary also with heating. Preferably, the heated surfaces to be coated before the wet coating to a temperature of about 40 to 100 ⁰ C. The surfaces coated and dried in one way or another can then be washed with water.

The aqueous coating solution can also be prepared using a mixed solvent, that is, under Use of a mixture of water with a water-miscible organic solvent, provided that the solubility thereby the substances to be dissolved in the solution is improved. In addition, solutions made using such dry mixed solvents are produced on the coated surfaces much faster than purely aqueous solvents Solutions. If mixed use agents are used, the one used for drying purposes can also often be referred to Heating can be dispensed with. As an organic solvent, which is added to the water for the preparation of the aqueous coating solution are added, the following are preferably used: alcohols, esters and ketones.

The coating solution is preferably used in such

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Amount applied to the surfaces to be coated so that the dried coating has a weight per unit area of at least 0.001 g / m ² . Such a layered or such a basis weight of the coating is in the range of those basis weights as are customary for other coatings known per se for the same purpose.

After the completion of the coating of the inner walls of the polymerization reactor carried out in the manner described above, the polymerization reaction is carried out in the usual manner carried out. The reactor is filled with the water used as the polymerization medium, the dispersant or suspension aid, the polymerization initiator and the monomeric Vinyl chloride or the monomers and, if appropriate, with other customary additives to such polymerization mixtures loaded. It is essential to the invention, however, that the reactor charge forming the polymerization system is also added contains at least one water-soluble thiocyanate.

Water-soluble thiocyanates for the purposes of the invention are preferred the thiocyanates of the alkali metals, in particular sodium thiocyanate, potassium thiocyanate and cesium thiocyanate, also ammonium thiocyanate and the thiocyanates of the alkaline earth metals, in particular magnesium thiocyanates, calcium thiocyanate, Strontium thiocyanate and barium thiocyanate. These thiocyanates can be added directly to the polymerization mixture are then dissolved in the aqueous phase of the polymerization mixture. Preferably be the water-soluble thiocyanates are added to the polymerization mixture before the start of the copolymerization reaction. Practically however, the same polymer scale suppressing efficiency can be obtained even if the water-soluble thiocyanates to the polymerization mixture only after the start of the polymerization reaction, if not too long after the start of the polymerization reaction

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~ ΙΟ -

will.

The thiocyanates are preferably added to the polymerization mixture in a concentration of at least 1 ppm, based on the weight of the monomeric vinyl chloride or the weight of the monomer mixture. The upper limit of the The concentration of the thiocyanate in the polymerization mixture is 500 ppm, preferably 100 ppm, always based on weight of the monomer or monomers. If these upper concentration limits or limits of the addition of the Thiocyanate to the polymerization mixture, the quality of the product resin is impaired, although at the same time none Improvement in the suppression of polymer encrustation on the reactor walls can be achieved more.

Even if the process of the invention is used specifically and primarily for the suspension polymerization of vinyl chloride in the aqueous phase in the presence of an organic peroxide as the polymerization initiator whose solubility in water at 20 ^° C. is at least 0.2% by weight, the process of the invention can also be used in such cases in which the water solubility is used as the polymerization initiator, organic peroxide at 20 ⁰ C.kleiner than 0.2 wt .-%. On the other hand, as is readily apparent to any person skilled in the art, the organic peroxide used as a polymerization initiator should also not have an excessively high solubility in water, since polymerizations carried out in a medium which contains an organic peroxide which is unusually readily water-soluble as a polymerization initiator are already essentially as Emulsion polymerizations take place and no longer lead to suspension polymers of polyvinyl chloride in the manner sought in the context of the invention. In this sense and for these reasons, the polymerization according to the invention is preferably carried out using an organic peroxide as the poly

merisationsinitiator performed, its water solubility is not greater than 10 wt .-%, preferably not greater than 5 wt .-% at 20 ⁰ C.

The invention is described below on the basis of exemplary embodiments explained in more detail.

Example 1 (experiments 1 to 29):

Using seven different monomer-soluble organic peroxides as polymerization initiators four series of polymerization tests were set up. The following organic peroxides are used: Di-2-ethylhexyl peroxydicarbonate (hereinafter referred to as OPP), lauroyl peroxide (hereinafter referred to as LPO) / 3,5,5-trimethylhexanoyl peroxide (hereinafter abbreviated to L-355) and ct-cumyl peroxyneodecanoate (hereinafter briefly L-188). In addition, the peroxides already mentioned above EEP, MC and BEP used.

To determine the solubility of these peroxides in water, the peroxides mentioned are dispersed in water at 20 ⁰ C individually in excess. After the solution equilibrium has been established, the dispersion is centrifuged. The clear solution obtained after centrifugation is titrated iodometrically. The following solubilities are determined in this way for the peroxides used. OPP 0.04% by weight, LPO 0.003% by weight, L-355 0.05% by weight, L-188 0.01% by weight, EEP 0.41% by weight, MC 0, 24 wt% and BEP 0.20 wt%.

Three different coating solutions are made for each polymerization batch:

ORIGINAL INSPECTED

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Coating solution A: 0.1 wt% C.I. Solvent Black 7

dissolved in methyl alcohol.

Coating solution B: 0.1 wt% sodium thiocyanate

dissolved in methyl alcohol.

Coating solution C: 0.1 wt% C.I. Acid Black 2

dissolved in water, the pH being adjusted by adding sulfuric acid is set to a value of 3.0.

A stainless steel reactor with a capacity of 1000 l and equipped with a stirrer is used as the polymerization reactor. The inner walls of this polymerization reactor and the surface of the entire stirrer in the reactor are each coated with one of the three above-mentioned coating solutions. The wet-coated surfaces are heated ^{to 90 ° C. for 10 minutes to dry.} In all cases, the coating produced in this way has a weight per unit area of 0.1 g / m ² after drying.

The surface-coated polymerization reactor prepared in this way is with 500 kg of water containing 150 g of a partially saponified polyvinyl alcohol with one of the above-mentioned organic peroxides, in the case of LPO in an amount of 500 g and in all other cases in an amount of 100 g, and charged with 250 kg of monomeric vinyl chloride. In the polymerizations carried out according to the process of the invention, the charge also contains 2.5 g of ammonium thiocyanate; in the comparative experiments, no ammonium thiocyanate is added. The polymerization itself is carried out in the usual way at 50 ^° C. for 10 hours. After the polymerization reaction has ended, the polymer slurry is discharged from the reactor. After emptying the polymerization reactor, the weight per unit area of the poly

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Merisatkrust determined, which is on the inner wall of the reactor has formed. For comparison, a polymerization approach is also carried out in the same way as described above, but with the modification that the reactor walls remain uncoated. The results obtained are in the Table 1 compiled.

Table 1

Weight per unit area of the polymer crust (g / m ² )

Coating
solution • ammonium
thiocyanate organic peroxide LPO L-355 L-188 EEP MC BEP A. with OPP 2 1 3 450 400 250 B. with 1 18th 25th 33 550 600 320 C. with 12th 2 1 4th 0 0 0 C. without 1 3 3 8th 300 100 85 without without 1 - - 1500 - - -

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In Table 1, the polymerization batches with the organic peroxides EEP, MC and BEP are used of the coating solution C and, in the presence of the ammonium thiocyanate in the polymerization system, the process the invention. All other approaches serve as comparative experiments. The data presented in Table 1 show that when using the peroxides EEP, MC and BEP as polymerization initiators, an incrustation of the polymer the reactor walls can then and only be practically completely suppressed if both the reactor walls with the coating solution of the invention are coated and at the same time the thiocyanate is the polymerization medium is added.

Example 2 (experiments 30 to 41).

Various aqueous coating solutions are prepared by dissolving the coating substances listed in Table 2 in a concentration of 1% by weight and then adjusting the pH to 4.0 by adding acetic acid. The inner walls of a 1000 liter stainless steel polymerization reactor and the surface of the stirrer arranged in this reactor are each coated with one of the coating solutions thus prepared, in such a way that the weight per unit area of the dried coating is 0.1 g / m ² . After the wet coating is dried 10 min at 90 ⁰ C. After drying, the coating is washed with water.

The polymerization reactor coated in the manner described above is mixed with 400 kg of water, 250 g of partially saponified polyvinyl alcohol, 25 g of hydroxypropylmethyl cellulose, 75 g EEP and 200 kg monomer! Vinyl chloride charged. The

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Ammonium thiocyanate is added to the polymerization mixtures in the amount shown in Table 2. The polymerization batches in which no ammonium thiocyanate is added are used for comparison purposes. The polymerization is carried out in the usual way at 57 ^° C. for 12 h.

After the polymerization reaction has ended, the polymer slurry is discharged from the reactor. The basis weight of the Polymer crust that has formed on the inner walls of the reactor is determined. Also, be part of that in everyone The fisheye concentration and heat resistance of the dried product PVC obtained in each individual batch were tested. The results are shown in Table 2. The test methods are detailed below. As can be seen from the test results given in Table 2, the heat resistance is the last The PVC resin obtained in the polymerization batch is less good than the heat resistance obtained in the other batches Products. This result shows that the heat resistance of the product resins due to the addition of too large amounts of thiocyanate to the polymerization system is adversely affected.

The determination of the fisheye concentration is carried out as follows:

A molding composition is made from 100 parts by weight of the product resin, 50 parts by weight of dioctyl phthalate, 1 part by weight of dibutyltin dilaurate, 1 part by weight of cetyl alcohol, 0.25 part by weight of titanium dioxide and 0.05 part by weight of carbon black manufactured. For this purpose, the individual components are 7 min at 150 ⁰ C on a roller mixer homogeneously kneaded together. The homogeneously mixed molding compound is then shaped into a 0.2 mm thick film. The defects that occur in these films, usually referred to as "fish eyes"

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places are counted in transmitted light over an area of 100 cm ^2.

The heat resistance of the product resins is tested as follows:

100 parts by weight of the product resin, -1 parts by weight of stearic acid and 1 part by weight of dibutyltin 10 at 170 ⁰ C on a two roll mill having a nip of 0.7 mm min to give a homogeneous molding composition kneaded. A film with a thickness of 0.7 is then molded from this homogeneous molding compound. Test specimens cut from this film are then heated ^{to 180 ° C. in a Geer oven.} The time required for the test object to remain in the oven until the test object is blackened is measured. The measured residence time in minutes serves as a measure of the heat resistance of the product resin.

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Table 2

Coating substance Ammonium -
thiocyanate
(ppm) fish
eyes
(100
cm ' Warmth-
persistent
age
(min) Polymer
crust
(g / m ² ) without without 60 120 1600 without 10 55 120 1500 C.I. Acid Blue 116 without 40 120 350 C.I. Acid Blue 116 10 .8th 120 0 Airenonium abbey 10 10 120 3 Na-a-naphthalene sulfonate
CI Direct blue 6 10
20th 10
6th 120
120 ■ 2
0 C.I. Acid Violet 78 1 10 120 3 C.I. Acid Violet 78 10 6th 120 1 C.I. Acid Violet 78 50 4th 120 0 C.I. Acid Violet 78 100 4th 120 0 C.I. Acid Violet 78 1000 4th 80 0

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The concentration of ammonium thiocyanate additive is based on the weight of the monomer.

Example 3 (experiments 42 to 48):

The coating substances given in Table 3 are dissolved in water in a concentration of 1% by weight. The aqueous solutions are then adjusted to a pH of 2.5 by adding phosphoric acid. The inner walls and the agitator surfaces of a stainless steel polymerization reactor with a capacity of 100 l are coated with the aqueous coating solutions thus produced. The coating is then dried for 10 min bie 90 ⁰ C. After drying, it is washed with water. The washed and dried coating has a weight per unit area of 0.1 g / m ² .

The polymerization reactor coated in this way is then charged with 40 kg of water, 17 kg of monomeric vinyl chloride, 3 kg of monomeric vinyl acetate, 12 g of partially saponified polyvinyl alcohol, 4 g of hydroxypropylmethyl cellulose, 6 g of MC and 200 g of trichlorethylene. A thiocyanate of the type and amount shown in Table 3 is also added to the feed. In addition, two comparative approaches are carried out without the addition of thiocyanate. The feed mixture is initially stirred for 15 minutes. The polymerization is then carried out in the usual way at 58 ^{° C. for 12 h.}

After the polymerization reaction has ended, the polymer becomes cloudy discharged from the reactor. The weight per unit area is then the adhering to the inner walls of the reactor Determined polymer crust. The results are shown in Table 3.

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Table 3

Coating substance Thiocyanate polymer
crust (ppm) (g / m ² ) -without without 1800 without
CI Acid Black 2 Ammonium thiocyanate
(10)
without 1600
1300 C.I. Acid Black 2 Ammonium thiocyanate
(10) 3 CI. Acid Red 2 Sodium thiocyanate
(2'O) 2 C.I. Acid Yellow 38 Calcium thiocyanate
(20) 1 CI. Direct Red 1 Potassium thiocyanate
(10) 1

The stated concentration for the addition of thiocyanate relates in turn to the weight of the monomers in the polymerization mixture .

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Claims (6)

JABGBR, GRAMS & PONTANI DIPL.CHEM. DR. KLAUS JAEGER DIPL.-INS. KLAUS D. GRAMS DR.-ING. HANS H. PONTANI GAUTING BERGSTR. 48Vi Θ031 STOCKDORF. KREUZWES 34 8702 KLEINOSTHEIM · DEER PATH SHI-80 Shin-Etsu Chemical Co., Ltd. 6-1, Otemachi 2-chome, Chiyoda-ku, Tokyo, Japan Process for the production of polyvinyl chloride resins Claims 1. A process for the production of polyvinyl chloride resins (PVC resins) by suspension polymerization of monomeric vinyl chloride or a monomer mixture which consists essentially of vinyl chloride monomer in an aqueous polymerization medium which contains a suspending agent and a polymerization initiator which is soluble in the monomer or monomers, namely an organic peroxide which is at least 0.2% by weight soluble in water at 20 ^{° C.,} TELEPHONE: (O89) 850203d; * V4 «Ö * j * (cfecH! 77« 3Ϊ? 5. TELEX: 521777! Sard characterized , (a) that before the start of the polymerization, the inner walls of the polymerization reactor in which the polymerization is carried out, be coated with an aqueous coating solution, the at least one organic dye whose molecules have at least one sulfonic acid group or one carboxyl group in Contain the form of an alkali metal or ammonium salt, and / or at least one alkali metal salt or an ammonium salt of an organic sulfonic acid and / or at least one carboxylic acid with at least one pair of conjugated double bonds per molecule is dissolved contains, and that the wet coated with this solution inner walls are then dried, and (b) that the polymerisation mixture which is polymerised in the polymerisation reactor thus coated should, at least one water-soluble thiocyanate is added. 2. The method according to claim 1, characterized in that the aqueous coating solution by adding a Acid is adjusted to a pH of not greater than 7. 3. The method according to claim 1, characterized in that the inner walls of the polymerization reactor are coated with the aqueous coating solution in such a way that the coating, after drying, has a weight per unit area of at least 0.001 g / m ² . 130037/0606 4. The method according to any one of claims 1 to 3, characterized in that that one of the following thiocyanates is used as the water-soluble thiocyanate: an alkali metal thiocyanate, Ammonium thiocyanate and / or an alkaline earth metal thiocyanate. 5. The method according to any one of claims 1 to 4, characterized in that that the water-soluble thiocyanate is added to the polymerization mixture in a concentration of 1 to 500 ppm is added, based on the weight of the monomeric vinyl chloride or the monomer mixture. 6. The method according to any one of claims 1 to 5, characterized , (a) That as the organic dye, any of the following Dyes are used which, for the sake of readability, are included in the designation of the "Color Index": C.I. Direct yellow 1, C.I. Acid yellow 38, C.I. Acid Orange 2, C.I. Direct orange 10, C.I. Direct Red 1, C.I. Acid Red 2, C.I. Acid red 18, C.I. Acid Red 52, C.I. Acid red 73, C.I. Direct red 186, C.I. Direct Red 92, C.I. Basic Red 2, C.I. Direct violet 1, C.I. Direct violet 22, C.I. Basic Violet 10, C.I. Acid Violet 11, C.I. Acid Violet 78, C.I. Mordant Violet 5, C.I. Direct blue 6, C.I. Direct Blue 71, C.I. Direct blue 106, C.I. Reactive Blue 2, CI. Reactive Blue 4, C.I. Reactive Blue CI. Acid Blue 116, CI. Acid blue 158, C.I. Mordant Black 1, CI. Mordant Black 5, C.I. Acid Black 2, CI. Direct black 38, C.I. Solubilized Vat Black 1, C.I. Fluorescent Brightening Agent 30, C.I. Fluorescent Brightening Agent 32 and C.I. Azoic Brown 2; and 130037/0606 b) that the organic sulfonic acid or the carboxylic acid with at least one pair of conjugated double bonds is one of the following substances: Toluidine, α-naphthalenesulfonic acid, anthraquinonesulfonic acid, Dodecylbenzenesulfonic acid, p-toluenesulfonic acid, Abietic acid, isonicotinic acid, benzoic acid, phenylglycine or 3-hydroxy-2-naphthoic acid. 130037/0606