KR820001786B1 - Process for the preparation of styrene-butadiene copolymers - Google Patents

Abstract

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Description

Method for preparing styrene-butadiene copolymer

The present invention relates to a process for producing styrene-butadiene copolymers having a styrene content of at least 80% by a continuous process.

Known styrene-butadiene copolymers are commonly used as mixtures with rubber (especially S. B. R.) in the production of shaped articles such as platy and platy. In the known art, the preparation of these copolymers is carried out by aqueous emulsions by discontinuous or semi-continuous processes in the presence of an emulsifier such as hydrogen peroxide and an inorganic peroxide catalyst such as alkali metal or ammonium persulfate, and an alkali metal soap of fatty acid or a disproportionate resin. It is carried out by polymerizing the monomer at. Such methods are described, for example, in US Pat. Nos. 2,835,645 and 2,615,206 and German Patent Publication No. 2,455,276.

In these methods, difficulties arise due to the incidence formed in the heat exchanger as well as in the liquid-vapor contact zone, in particular in the reactor. These phenomena due to the poor stability of the emulsions occur especially at the end of the polymerization reaction, when the inversion of the monomers is greatest.

In practice, the capstone reduces the useful volume of the reactor, so the operator must continuously adjust the feed rate and also acts as a growth point for other precipitations because it hinders heat exchange and polymerization control. Since styrene-butadiene copolymers have a high degree of crosslinking and are usually virtually insoluble in organic solvents, their capstones can only be removed by mechanical devices, ie only by prolonged tedious manipulations.

In addition, the instability of the latex obtained by conventional methods causes significant difficulties during the separation of unreacted monomers after the polymerization process. Another drawback arises from the fact that the production is carried out discontinuously or semi-continuously, which means that the production of copolymers with constant properties for a long time is difficult, in fact these properties can vary from lot to lot. have.

It is an object of the present invention to avoid the drawbacks of the prior art mentioned above in the preparation of styrene-butadiene copolymers having a styrene content of at least 80% by weight.

In particular according to the invention,

Concentrations of formaldehyde and alkali metal salts of naphthalene sulfonic acid and primary emulsifiers selected from molar, styrene and butadiene monomers, alkali metal or ammonium persulfates as catalysts and alkali metal soaps of fatty acids and / or alkali metal soaps of heterogeneous rosin An emulsification system consisting of a secondary emulsifier selected from the product is continuously fed to the first polymerization process carried out under isothermal conditions at a temperature of 60-75 ° C. until a monomer conversion of 30-45% is achieved.

The reaction mixture released from the first process is continuously fed to a second polymerization process which is carried out under adiabatic conditions at a temperature of 110-80 ° C. during the time when the monomers are completely converted into the copolymer.

The styrene-butadiene copolymer latex thus obtained is subsequently recovered from the second polymerization process.

First polymerization process

Styrene and butadiene are supplied to the first polymerization process.

The amount of styrene is 80-95 parts by weight relative to every 100 parts by weight of the total weight of the two monomers.

It is convenient to maintain the weight ratio of feed between water and monomer at least 1.3: 1, preferably 1.3: 1-1-1.7: 1. It is virtually inconvenient to reduce it below 1.3: 1 since the viscosity of the mixture undesirably increases. The weight ratio is not absolute but is chosen for inherently economic reasons.

Catalysts used for the purposes of the present invention are inorganic persulfates, especially persulfates of potassium and ammonium.

It is convenient to feed 0.1-0.5 parts by weight of catalyst with respect to every 100 parts by weight of monomer to the first process.

The process of the present invention requires the use of an emulsifying system containing a primary emulsifier consisting of an alkali metal soap of fatty acid or heterogeneous rosin, and a secondary emulsifier consisting of an alkali metal salt of naphthalene sulfonic acid and a concentrated product of formaldehyde.

Most preferred primary emulsifiers are salts of partially chlorinated natural fatty acids with an iodine number of 30-50 (preferably sodium or potassium salts). Typically these partially-chlorinated fatty acids have acid values (KOH / g) on the order of 190-210. Moreover, heterogeneous rosin means a modified product of natural rosin in the presence of an oxidation-reduction catalyst. It includes dihydroabitic acid, tetrahydrobietic acid and dehydroabietic acid as main components. Also preferred are sodium and potassium salts in this case.

Salts of naphthalene sulfonic acid (particularly sodium and potassium) and concentrated products of formaldehyde are known substances. Examples of these materials are commercial products known as Daxad-15 (manufactured by Grace Company) and TamolN (manufactured by Rohm-Haas Company).

The amount of emulsifying system used is generally 4-7 parts by weight per 100 parts by weight of the monomers fed to the first process, and the weight ratio between the primary and secondary emulsifiers is preferably 1: 0.04-1: 0.16. When using an emulsifying system of 4 parts by weight or less based on every 100 parts by weight of the monomer, the polymerization reaction rate is gradually lowered and the particles are not sufficiently protected. The latex thus obtained is unstable and coagulation occurs very easily. It is difficult to control the reaction because the amount of the emulsion system above the upper limit causes a high polymerization rate. In addition, insufficiency of the latex may occur due to insufficient large particles forming the protection imparted by the emulsifier.

The first polymerization process is carried out under isothermal or virtually isothermal conditions, and the heat generated by the polymerization reaction is removed to maintain a temperature in the range of 60-75 ° C. Moreover, the residence time in this step is adjusted to achieve 30-45% conversion of the monomers fed.

According to a preferred embodiment, the first step is a styrene / butadiene weight ratio of 85:15, water / monomer weight ratio of 1.5: 1, 0.2-0.3 parts by weight of an ammonium persulfate catalyst, and a primary emulsifier and a secondary emulsifier based on 100 parts by weight of monomers. It is carried out by using an emulsifying system present at 5 and 0.5 parts by weight with respect to 100 parts by weight, temperature of about 65 ° C. and monomer conversion of about 40%, respectively.

According to a further preferred embodiment, an electrolyte such as sodium chloride and / or sodium chloride of potassium chloride and / or phosphoric acid is added to the first step to adjust the particle size. It is convenient to use these electrolytes in the amount of about 0.05 weight part with respect to 100 weight part of monomers, and it is convenient to add them in the form of aqueous solution with an emulsion system.

Other useful adducts are side chain regulators such as normal and tertiary mercaptans, such as tertiary dodecyl mercaptan, which are generally used in amounts of about 0.1 parts by weight with respect to 100 parts by weight of monomers. These side chain regulators are usually supplied in independent flows.

The first polymerization process can be carried out in an autoclave equipped with sufficient stirrer capable of assuring a reaction mass of at least 25,000 turbulences, evaluated as a heat exchanger and Reynoldnumber.

Finally, the first process can be carried out in a single reactor or several reactors in series. In the latter case all reagents are fed to the first reactor.

Second polymerization process

The reaction mixture released from the first process is continuously fed to a second polymerization process in which the conversion of the monomers is completed, or in fact completed.

The second process is carried out under adiabatic conditions where heat is not removed from the system, and heat removal is limited to losses due to the system itself. The conditions in each case are adjusted so that the maximum temperature is in the range of 80-110 ° C., preferably 85-100 ° C., preferably near the upper limit of this range.

Under this condition, complete conversion of butadiene is achieved quickly, and the residual content of free styrene in each case is about 500 ppm or less for latex. The term complete conversion of butadiene as used herein means conversion until the monomer content cannot be determined by conventional analytical methods.

In a preferred embodiment, the above-mentioned emulsifying system is also preferably supplied to the second process in an amount of about 1 part by weight based on 100 parts by weight of the monomer fed to the first process. Furthermore this improves the stability of the latex.

Appropriate apparatus for the second polymerization process is similar to that described for the first process except for the heat exchanger. The second process can also be carried out in several reactors in series.

The total polymerization time (first and second steps) is typically about 3 hours when the above operating conditions are used. The residence time in the first process is in this case about 60-70 minutes.

The latex is released from the second process with a dry content of about 40% by weight and a gel content of 80% or more (% crosslinking).

The latex obtained can be mixed with rubber latex rubber latex, in particular SBR, and the whole can be coagulated and dried by a known method. Usually the two latexes are mixed at a ratio of 185 parts of styrene-butadiene copolymer to 100 parts of styrene-butadiene rubber. Alternatively, the styrene-butadiene copolymer latex can be solidified and dried and the dry product can be mixed with the rubber in a solid state.

Articles such as plates, sheets and tubes can be prepared from these mixtures by conventional extrusion and molding methods. Styrene-butadiene copolymers act as reinforcements in the product, and the product has particularly good stiffness and size stability.

Primarily, the process of the invention has the advantage of a continuous process over a discontinuous or semi-continuous process. This gives greater yield to the useful unit volume of the reactor, greater potential for the automatics of the machinery, and greater invariance of product properties.

Another basic advantage of the process of the present invention is that all monomers convert without the formation of capstone. Since the particles of the copolymer in the known process are insufficiently protected by the emulsifier used, the latex formed is very unstable, especially when high conversion of monomers is achieved. Thus, the dialysis occurs in particular during the end of the polymerization and during the separation of the monomers from the polymerized product. Also, as can be seen, in the conventional method, the conversion of monomers does not exceed 99% and is typically about 95%, which conversion is achieved only by using long-term polymerization.

According to the invention, the completion of the polymerization takes place at a relatively high temperature in the presence of a persulfate catalyst. Under the reaction conditions, it is believed that these persulfate catalysts are self-bonded to form a copolymer in the form of sulfur groups, which helps to give the desired stability to latex.

Whatever the mechanism, the total conversion of monomers (which is desired to achieve a high degree of crosslinking in the copolymerization) is achieved in the process of the invention, but it is true that the capstone can be avoided by the process of the invention.

Another important advantage is that the process of the invention does not require a monomer separation process. However, this monomer separation process is a complicated and cumbersome process.

Hereinafter, the present invention will be described in detail with reference to Examples.

EXAMPLE

The test was carried out in a laboratory process in which the first process was carried out continuously in two identical stainless-steel reactors equipped with a turbulent stirrer and a cooling jacket. The second process was carried out in a single reactor similar to that used in the first process but without the cooling jacket.

The following feed was introduced into the first reactor of the first process. In other words

Styrene 12.75 kg / hr;

Butadiene 2.25 kg / hr;

9.09 kg / hr solution containing 8.25% potassium salt of partially hydrogenated natural fatty acid of 43, 0.82% Daxad-15, 0.09% potassium chloride and 90.84% water;

Tertiary dodecyl mercaptan 0.015 kg / hr;

1.98 kg / hr aqueous solution of ammonium persulfate with 1.8% by weight of concentrate; And water 12.3 kg / hr;

The reaction was carried out in both reactors for a total of 70 minutes at a temperature of 65 ° C. and 40% of the monomers fed were converted.

This latex was continuously fed to the reactor of the second step together with 1.8 kg / hr of an aqueous solution containing fatty acid soap, Daxad-15 and potassium chloride used in the first step.

The second process was carried out adiabatically with a maximum temperature of about 100 ° C. and a residence time of 110 minutes.

Under these conditions, latex having the following characteristics was continuously released from the second process. In other words

Moreover, the gel content of the copolymer was 85% and the composition (weight) of the copolymer relative to the monomers it contained was 85% styrene and 15% butadiene. After 100 hours of operation, no capstone was found in the reactor and no capstone was found in any part of the plant.

Claims (1)

As described above in the text, water, styrene and butadiene monomers are subjected to a first polymerization process carried out under isothermal conditions at a temperature of 60-75 ° C. until the conversion of monomers is achieved at 30-45%; Alkali metal or ammonium persulfate as a catalyst; And an emulsifying system comprising a primary emulsifier selected from alkali metal soaps of fatty acids and / or disproportionated rosin, and a secondary emulsifier selected from condensation products of alkali metal salts and formaldehydes of naphthalene sulfonic acid; Continuously and the reaction mixture released from the first process is continuously fed to a second polymerization process carried out under adiabatic conditions and a maximum temperature of 80-110 ° C. for a period of time when the conversion of the monomers is fully achieved, A process for the continuous production of styrene-butadiene copolymers having a styrene content of at least 80% by weight, characterized by continuously recovering styrene-butadiene copolymer latex obtained from the polymerization step.