CS197313B2 - Process for preparing abs resins - Google Patents

Description

(54) Production method of ABS resins (11) (B2) (51) Int. CL ³

OJ C 08 F 279/04

The present invention relates to a process for the production of ABS resins obtained by polymerizing vinyl compounds, in particular a mixture of styrene and acrylonitrile, in the presence of an elastomer, in particular polished dense rubber. These resins consist of the rubber and acrylonitrile-styrene copolymers, some of which are grafted onto the rubber particles. Said resins have. good mechanical properties, in particular increased impact resistance, when at least 5% of styrene-acrylonitrile copolymers based on the weight of pure rubber are fixed to the rubber by grafting, the remainder of said copolymers forming a continuous phase in which the graft rubber particles are dispersed.

Conventional polymerization processes, i.e., in bulk, emulsion and slurry, can be used to produce these ABS resins. There are some difficulties in carrying out these processes, and therefore two-stage copolymerization is often used, namely bulk copolymerization followed by slurry copolymerization. Using this technique, ABS resin is obtained in the form of beads that can be easily separated from the reaction medium, washed and dried.

In practice, however, it has been found that performing in suspension is a delicate operation with respect to. the fact that the copolymer in the mass has a very high viscosity.

On the other hand, certain reagents used in the polymerization tend to react with each other, thereby deteriorating the properties of the final resin.

It is an object of the present invention to overcome these drawbacks.

The present invention provides a process for producing ABS resins by grafting styrene and unsaturated nitrile compounds selected from acrylonitrile and methacrylonitrile to a rubbery polymer in the presence of a chain transfer agent.

It is an object of the invention that the polymerization is carried out in the presence of dithiobis (benzothiazole) as a chain transfer agent.

The polymerization is carried out in bulk, in the absence of air or oxygen, wherein the styrene compound and the unsaturated nitrile selected from the group consisting of acrylonitrile and methacrylonitrile are copolymerized in the presence. of a rubbery polymer and in the presence of dithiobis (benzothiazole) as a chain transfer agent at a temperature of 75 to 125 ° C, until a mass having a viscosity of about 10,000 to 100,000 mPa. s measured at 65 ° C, the continuous phase of which consists of copolymers of styrene and acrylonitrile swollen in monomers, followed by suspension copolymerization by adding an aqueous dispersion of the suspending agent to the copolymer obtained in hm197313, followed by a surfactant compound and the mixture. Heat at 75 to 150 ° C with stirring.

The dithiobis (benzothiazole) is used in an amount of 0.001 to 1%, preferably 0.05 to 0.5 percent by weight of the total monomers and the rubbery polymer.

The copolymer obtained after the first stage of polymerization in the mass does not have such a high viscosity, which essentially facilitates suspension performance. In the process according to the invention, this viscosity is achieved in a reproducible manner.

The reaction mixture from which it is based most often consists of a mixture of monomers containing 65 to 90% by weight of styrene compounds, in particular styrene, and 35 to 10% of an unsaturated nitrile, in particular acrylonitrile, and further an amount of approximately 7 to 15 percent rubber. by weight of the monomer mixture.

Instead of styrene or a mixture with styrene, other aromatic hydrocarbons, such as α-alkylstyrene or halostyrene, for example ar-methylstyrene, p-chlorostyrene, etc., may be used. For ease of interpretation, these compounds or mixtures thereof are referred to as "styrene".

Acrylonitrile can also be replaced by methacrylonitrile or mixtures of both.

The rubber most often consists of a polymer

1,4-diene, especially polybutadiene, polyisoprene or a mixture of the two elastomers. Other rubber compounds or copolymers of butadiene and vinyl compounds, for example copolymers of butadiene and styrene, may also be used, starting rubber before becoming soluble in the mixture of styrene monomers and acrylonitrile.

The mixture of monomers and rubber forms a homogeneous phase which is subjected to partial copolymerization in the mass under intensive stirring. This copolymerization can be carried out in the presence of a free radical-providing catalyst, in particular in the presence of a peroxide or azo-type catalyst, for example benzoyl peroxide, lauryl peroxide, dicumyl peroxide, butylperacetates, α, α-azodiisohutyronitrile or mixtures thereof. The amount of catalyst is usually 0.01 to 2%, preferably 0.2% by weight, based on the total weight of rubber and monomers. This partial polymerization in the mass can also be carried out without catalyst, purely thermally, at a temperature of 75 to 125 ° C for 2 to 24 hours.

A chain length regulator or transfer agent is added to the reaction mixture. In the processes used hitherto, mainly mercaptan, in particular tert-dodecylmercaptan, is used as a chain transfer agent.

In the process of the present invention, the transfer agent consists of dithlobis (benzothiazole) and is hereinafter referred to as TBT and is used in an amount corresponding to about 0.001 to 1%, in particular 0.05 to 0.5% by weight of the total weight of monomers and rubber. It has been observed that the viscosity of the mass obtained after the first stage of the process, i.e. the polymerization in the mass, is much less increased when TBT is used in place of other transfer agents known to date. Acrylonitrile in the presence of basic compounds, which are often present as residual products in the rubbers used, while TBT is inert to acrylonitrile, and TBT has the added advantage of being insensitive to oxygen and air.

However, it is preferred that the copolymerization is carried out in a mass in an atmosphere free of air or oxygen. In fact, in the presence of air, the copolymerization reaction does not start sooner than after a rather long inhibition, which may be 2 to 3 hours at a temperature of the order of 100 [deg.] C., whereupon the reaction develops very vividly and uncontrollably. In the process according to the invention, the copolymerization is carried out under an inert atmosphere, preferably under a nitrogen atmosphere. The reaction starts rapidly and polymerization continues. Initially, the continuous phase consists of a solution of rubber in the monomers. After some degree of monomer conversion, phase inversion occurs and styrene-acrylonitrile copolymers grafted with monomers become a continuous phase.

Polymerization is continued until a conversion of 10 to 30% of the monomers is achieved. At this point, the viscosity of the reaction mixture is usually 10,000 to 100,000 mPa. s (measured at 65 ° C), the viscosity varying according to the rubber content of the mixture. These conditions are very advantageous for monitoring polymerization using a slurry polymerization technique.

The product obtained by the partial polymerization in the mass is mixed with water and an aqueous dispersion of the suspending agent or protective colloid. The suspending agent is preferably a water-insoluble inorganic type, for example, phosphate, aluminum oxide, zinc oxide, magnesium silicate, which can usually be easily and completely removed from the ABS resin. In particular, normal calcium phosphate, which can be prepared from normal sodium phosphate and calcium chloride, is used.

It is also preferred to carry out the polymerization in suspension in the presence of a surfactant compound, which is usually of the nonionic or anionic type. The amount of this compound varies according to the nature of the compound and the nature of the suspending agent. By way of illustration, when using normal calcium phosphate as a suspending agent and sodium dodecylbenzene sulfonate as a surfactant, the concentration of the surfactant is about 0.1 to 0.4 g per liter of water in the aqueous phase of the reaction mixture.

When the amount of surfactant is less than or above the critical values, ABS resin is formed in the form of beads with increased diameter, which is disadvantageous and, as a last resort, it is also possible to achieve conversion of the organic matter into an aqueous suspension.

To make the suspending agent particularly effective, the reaction mass obtained by the partial polymerization in the mass is mixed with water, an aqueous dispersion of the suspending agent is added, followed by a surfactant, for example sodium dodecylbenzenesulfonate, in the above amounts. Thus, the suspending agent is not found in the presence of an increased surfactant concentration, so that it does not adsorb the surfactant to a large extent and does not become too lipophilic, preventing its absorption within the organic matter.

The slurry polymerization is then carried out at a temperature of 75 to 150 ° C in the presence of a catalyst. with partial polymerization in the mass as thermal polymerization. The catalysts for this polymerization are of the same type as the catalysts previously used for bulk polymerization. According to one preferred embodiment, the slurry polymerization is carried out at a temperature of 75 to 125 ° C, then when the ABS resin beads acquire a density greater than that of the aqueous phase, the ambient temperature is increased from 15 to 25 ° C and polymerization is continued for 2 up to 4 hours.

The process according to the invention can be carried out in an apparatus commonly used for styrene polymerization or in the production of ABS resin. Both stages of the process can be carried out sequentially in the same reactor. One variation consists in the use of two reactors, one for bulk polymerization and the other for slurry polymerization.

In the following examples of thermal copolymerization of styrene and acrylonitrile in the presence of various chain transfer agents, the particular effect of TBT as a chain transfer agent is emphasized.

A solution containing 25% by weight of acrylonitrile and 75% by weight of styrene was used. This solution is divided into three pressure tubes to which the same molecular amount of the different carrier is added, and. as follows:

0.100% by weight target; Dodecyl mercaptan (TDM)

0.164% TBT

0.178% dithiobis-methylbenzothiazole) (or MTBT)

The polymerization is carried out under nitrogen for 1 hour at 100 ° C with stirring.

If the reactivity of styrene and acrylonitrile is known, it can be calculated that the theoretical molecular weight of the copolymers should be 200,000. The results of the experiments were as follows:

Chain Carrier

Conversion, %

Molecular weight

TDM 6,824 315,000

TBT 7,609 195,000

MTBT 6,629 550,000

The molecular weight obtained in the experiments with TDM and MTBT indicates that TDM and MTBT are clearly less effective than TBT as chain carriers.

Similar experiments with thermal polymerization of the following mixtures - 60% by weight of styrene,% methylstyrene and% acrylonitrile, - 75%. styrene,% acrylonitrile. % and methacrylonitrile,.

- 70% styrene,

In the presence of dithiobis (benzothiazole) (TBT) and under the above conditions, 5% w / w of p-chlorostyrene and% acrylonitrile gave molecular weights which were of the order of 95% of the theoretical molecular weight.

The application of the process of the invention is further illustrated by the following examples without limiting the invention thereto.

Example

22.77 kg of styrene, 9.50 kg of acrylonitrile, 4.92 kg of rubber (Stereon 703A from Firestone Tire and Rubber Co.), 0.0069 kg of glacial acetic acid and 0.475 kg of water are charged into the reactor. The mixture was melted at 70 rpm under a nitrogen atmosphere at room temperature (about 20 ° C) overnight.

0.070 kg of dithiobis (benzothiazole) and 0.50 kg of styrene are added before mass polymerization is started. Thus, the amount of TBT corresponds to 0.19% of the total weight of the rubbers and monomers used. The thermal polymerization in the mass is then carried out under a nitrogen atmosphere at 98 ° C with stirring at 220 rpm.

After 7 hours, the reaction mixture has a viscosity of 8,200 mPa · s (measured at 65 ° C) and consists of a uniform phase of styrene-acrylonitrile copolymers swollen with the corresponding monomers in which the graft rubber particles have been dispersed.

By mixing 15.4 kg of water, 0.6 kg of normal sodium phosphate and 0.8 kg of calcium chloride at 65 ° C, a dispersion of the reagent for slurrying the reaction mixture was prepared in a separate vessel.

30.8 kg of water was added to the reaction mixture obtained by mass polymerization, followed by a dispersion of the reagent, 0.29 kg of a 2.5 percent sodium dodecylbenzene sulphate solution and then 0.0324 kg of a 40 percent cumene peroxide.

The slurry polymerization was carried out at 116 ° C and once the styrene-acrylonitrile-elastomer copolymer beads began to settle, the temperature was maintained at 135 ° C for 3 hours.

The beads formed were separated from the reaction medium, washed with water and dried. They had the following granulometric composition:

24 mesh sieve 0.20% 32 mesh sieve 0.30% 42 mesh sieve 18.50% 60 mesh sieve 28.50% 80 mesh sieve 39.70% residue on 115 mesh sieve 9,70% fraction passing through 115 mesh sieve 3,10%

The resin obtained had the following properties:

notched Izod toughness (ASTM D 256) 423.4 J / cm Vicat deformation temperature (ASTM D 1525) 98.3 ° C tensile strength (ASTM 638) 43.04 MPa tensile strength (ASTM 638) 36.38 MPa flexural strength (ASTM D 790) 76.81 MPa flexural modulus (ASTM D 790) 2517.6 MPa

For comparison, experiments are performed which are practically identical; the only difference is that

(a) tert-butylmerpheaptane is used instead of dithiobis (benzophthazole): the viscosity of the substance after polymerization in the mass is 120,000 mPa · s (measured at 65 ° C), making it practically impossible to suspend the substance;

(b) 0.35 g of dithlobis (benzothiazole) is used: the viscosity of the substance after prepolymerisation in the mass is also higher than 100 Θ0Ο mPa. with;

e) 0.35 kg, i.e. 9.93 percent of the total weight of monomers and rubber, are also used; the viscosity of the substance after the prepolymerization in the mass is also of the order of 8000 mPa. with.

These comparative experiments show that the dihiobis (benzothiazole j) must be used in an amount greater than 0.001% of the total weight of monomers and rubber, but greater than 1% must be avoided in any case, since the mechanical properties of the polymer tend to be worse: notch toughness In addition, the resin composed of styrene-acrylonitrile copolymers and rubber, which obtains suspension polymerization, contains a larger amount of residual monomers, preferably dithiobis (benzothiazole) is used in amounts of between about 0.05 and about 0.5. 5% of the total weight of monomers and rubber.

Claims (3)

SUBJECT CLAIMS 1. A process for the production of ABS resins by grafting polymerization of styrene and unsaturated nitrile compounds selected from acrylonitrile and methacrylonitrile to a rubbery polymer in the presence of a chain transfer agent, characterized in that the polymerization is carried out in the presence of dithiobis (benzothiazole j as chain transfer agents). 2. The process according to claim 1, wherein the graft polymerization is carried out in the mass in the absence of air or oxygen at a temperature of 75 to 125 [deg.] C. until a mass having a viscosity of 10,000 to 100,000 mBa is formed. s measured at 65 ° C, the continuous phase of which is OF THE INVENTION consists of styrene-acrylonitrile copolymers swollen in monomers, followed by suspension copolymerization by adding to the mass copolymers an aqueous dispersion of the suspending agent, then a surfactant compound and heating the mixture at 75-150 ° C with continuous stirring. 3. Process according to claim 1, characterized in that the dithiobis (benzothiazole) is used in an amount of 0.001 to 1%, preferably 0.05 to 0.5%, of the total weight of the monomers and of the rubbery polymer.