EP1276783A1

EP1276783A1 - Method for producing polybutadiene latex with an optimized thermal current profile

Info

Publication number: EP1276783A1
Application number: EP01940359A
Authority: EP
Inventors: Sabine Oepen; Michael Breulmann; Norbert Güntherberg; Klaus-Dieter Hungenberg; Norbert Niessner; Bernhard Czauderna; Wil Duijzings
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2000-04-26
Filing date: 2001-04-24
Publication date: 2003-01-22
Also published as: US6852797B2; WO2001081438A1; KR20020091230A; MXPA02010049A; US20030162889A1

Abstract

The invention relates to a method for producing polybutadeine latex, according to which butadeine is polymerized in a radical emulsion polymerization in the presence of initiators and optionally dispersants and additional conventional auxiliary agents. Said polymerization is carried out in the presence of reactive comonomers, in such a way that a thermal current of 43 watts/kg solid content is not exceeded. The presence of reactive comonomers increases the reaction speed at the beginning of said reaction, thus achieving a flatter thermal current profile overall. The preferred reactive comonomer is styrol. The method is preferably carried out in the following semi-batch manner: (a) in a first step, a partial quantity of butadeine and at least one partial quantity of a reactive comonomer is prepared in the form of an aqueous solution with a thermally disintegrating initiator and optionally dispersants and additional conventional auxiliary agents and the polymerization is initiated, (b) in a second step, the residual quantity of butadeine and optionally the residual quantity of the reactive comonomer are added as an influent, undiluted or in aqueous solution, optionally with dispersants and optionally with additional conventional auxiliary agents.

Description

Process for the production of polybutadiene latex with an optimized heat flow profile

The invention relates to a ner process for the production of polybutadiene latex, the polybutadiene latex itself, a ner process for the production of a polybutadiene graft copolymer, the graft copolymer itself, molding compositions prepared therefrom and the use of the graft copolymers and molding compositions.

Polybutadiene rubber, which can be used as a basic stage for acrylonitrile / butadiene / styrene graft copolymers, is usually produced by

Emulsion polymerization in a semi-continuous ner process (semi-batch

Nerfahren) manufactured. In a first stage, a partial amount of butadiene with an initiator is initially introduced as an aqueous emulsion and polymerized, and in a second stage

Stage the remaining amount of butadiene undiluted or added as an aqueous emulsion as feed. The disadvantage of this ner driving is the slow reaction rate

Beginning of the inflow and therefore an overall unfavorable heat flow profile

Polymerization reaction. While at the beginning of the feed at low current

The addition of only a small amount of heat is evident

Heat flow profile in the further course of the polymerization reaction a pronounced peak.

This is undesirable, especially in large plants, since a large heat flow impairs the driving safety of the plant and high cooling capacities have to be provided for the reactor. In addition, with increasing reactor size, heat dissipation via the reactor wall becomes increasingly difficult due to the decreasing surface: volume ratio. Additional cooling capacity must therefore be provided by evaporative coolers or internal or external heat exchangers.

EP-A 0 834 518 describes a method and a device for producing homopolymers and copolymers in emulsion polymerization technology, in which the reaction mixture present as an emulsion is passed through an external circuit leading from and back to the reaction vessel with a heat exchanger. EP-A 0 486 262 describes a method of emulsion polymerization in which the feed rate is controlled by means of online reaction calorimetry so that a certain heat flow is not exceeded.

Heat peaks in the course of the reaction can be avoided by increasing the reaction rate at the beginning of the reaction, which flattens the heat flow profile of the reaction with constant overall heat of reaction.

EP-A 0 761 693 describes the use of redox initiator systems to increase the reaction rate at the beginning of the emulsion polymerization. A monomer emulsion is initially introduced and the initiator is metered in together with further monomer.

The object of the invention is to provide an easy to carry out process for the production of polybutadiene latex by emulsion polymerization, in which peaks in the heat flow profile of the polymerization reaction are avoided.

The object is achieved by a process for the preparation of polybutadiene latex, in which butadiene is polymerized in a radical emulsion polymerization reaction in the presence of initiator and optionally dispersing aids and other customary auxiliaries, which is characterized in that the polymerization is carried out in the presence of reactive comonomers in this way is that a heat flow of 43 watts / kg solids content of the polymerization mixture is not exceeded. A heat flow of 39 watts / kg, particularly preferably of 34 watts / kg, is preferably not exceeded.

The heat flow profile of the polymerization can generally be characterized as follows:

during a first period of 10 to 700 min, preferably 10 to 600 min, particularly preferably 10 to 400 min, the change in the heat flow per unit of time is 0.01

0.5 watt / (kg • min), preferably 0.01-0.4 watt / (kg • min);

during a second period of 0 to 600 min, preferably 100 to 500 min, particularly preferably 100 to 400 min following the first period Change in heat flow per unit of time -0.1 - 0.1 watt / (kg • min), preferably - 0.05 - 0.05 watt / (kg • min), particularly preferably -0.01 - 0.01 watt / (kg • min);

during a third period of 10-1000 min, preferably 100-800 min, particularly preferably 200-800 min, following the second period

Change in heat flow per unit of time <0 watt / (kg ^■ min).

The presence of reactive comonomers increases the reaction rate at the beginning of the reaction, which results in an overall flatter heat flow profile.

Suitable reactive comonomers are generally ethylenically unsaturated monomers, such as styrene, styrene derivatives which are nucleus-substituted with alkyl or halogen, α-methylstyrene, alkyl acrylates, such as n-butyl acrylate, acrylonitrile, methacrylonitrile or mixtures thereof. The preferred reactive comonomer is styrene.

The process according to the invention can be carried out continuously or semi-continuously. It is preferably carried out semi-continuously by

(a) in a first stage, a portion of butadiene and at least a portion of reactive comonomer are introduced as an aqueous emulsion with a thermally decomposing initiator and optionally dispersing aids and other customary auxiliaries and the polymerization is started;

(b) in a second stage, the residual amount of butadiene and, if appropriate, the residual amount of reactive comonomer are added undiluted or as an aqueous emulsion, if appropriate with dispersing auxiliaries and, if appropriate, other customary auxiliaries, as feed.

Suitable thermally decomposing initiators for starting the polymerization reaction are all radical formers which decompose at the selected reaction temperature, that is to say both those which decompose thermally alone and also redox initiators. Preferred initiators alone are thermally decomposing radical formers, for example peroxides, such as sodium or potassium persulfate, and azo compounds, such as azobisisobutyronitrile. However, redox systems, in particular those based on hydroperoxides such as cumene hydroperoxide, can also be used. In the first stage of the semi-continuous process, a portion of butadiene and at least a portion of reactive comonomer are initially introduced as an aqueous emulsion; the total amount of reactive comonomer is preferably initially introduced. As a rule, customary emulsifiers are also used as dispersants, for example alkali metal salts of alkyl or alkylarylsulfonic acids, alkyl sulfates, fatty alcohol sulfonates, salts of higher fatty acids with 10 to 30 carbon atoms, sulfosuccinates, ether sulfonates or resin soaps. Preferred emulsifiers are the Na and K salts of alkyl sulfonates or fatty acids with 10 to 18 carbon atoms. The emulsifiers are usually used in amounts of 0.5 to 5% by weight, preferably 0.3 to 3% by weight, based on the monomers used in the preparation of the polybutadiene latex.

The proportion of monomers (butadiene + reactive comonomer) in the total amount of monomers in the feed and feed is preferably 5 to 50% by weight, particularly preferably 8 to 40% by weight, in particular 10 to 30% by weight. The feed can contain the residual amount of butadiene and optionally the residual amount of reactive comonomer undiluted or also as an aqueous emulsion, optionally with dispersing agents. The feed preferably contains butadiene and the reactive comonomer in undiluted form. The feed is generally added within 1-18 hours, preferably 2-16 hours, particularly preferably 2-12 hours. The monomer feed can be added batchwise or continuously over the entire period. The water: monomer ratio is usually from 2: 1 to 0.7: 1. The feed and feed can contain further customary auxiliaries, such as molecular weight regulators or buffer substances. The dispersing agents and other auxiliaries can also be added separately from the monomer feed, for example divided into batches, or continuously during a certain time interval. Molecular weight regulators are, for example, ethylhexyl thioglycolate, n- or t-dodecyl mercaptan, terpinols or dimeric α-methylstyrene. Buffer substances are, for example, Na HPO ₄ / NaH ₂ P0 ₄ , sodium hydrogen carbonate or citric acid / citrate buffer.

The total amount of reactive comonomer in the forerun and optionally the feed is generally 3 to 20% by weight, preferably 5 to 10% by weight, of the total amount of monomer.

Polymerization is usually carried out at temperatures of 20 to 100 ° C., preferably 30 to 80 ° C. The polymerization reaction is carried out by heating the

Polymerization mixture started to the reaction temperature. In a preferred one

After the start of the reaction, the first step (a) submitted polymerization mixture polymerized (= partially polymerized) and only after a certain time with the addition of the remaining amount of monomer (step (b)) started. Polymerization is usually carried out for 0.1-3 hours, preferably 0.25-1 hour. After the end of the feed, polymerization is usually continued for a while until the desired monomer conversion is reached. The polymerization reaction is preferably terminated when approximately 90% monomer conversion is reached.

The present invention also relates to a polybutadiene latex which can be produced by one of the processes described above.

The present invention furthermore relates to a process for producing butadiene graft copolymers, in which a polybutadiene latex is produced in accordance with one of the processes described above and

(c) in a further step, a graft pad comprising at least one vinylaromatic monomer, acrylonitrile and optionally further ethylenically unsaturated monomers is grafted on.

In general, the graft is composed of 65 to 95, preferably 70 to 90 and particularly preferably 75 to 85% by weight of the vinylaromatic monomer, 5 to 35, preferably 10 to 30 and particularly preferably 15 to 25% by weight of acrylonitrile and 0 to 30 , preferably 0 to 20 and particularly preferably 0 to 15% by weight of the further ethylenically unsaturated monomer.

Suitable vinyl aromatic monomers are styrene and styrene derivatives such as α-methylstyrene. Styrene is preferred. Other monomers are in particular methyl methacrylate and acrylates, such as n-butyl acrylate, and N-phenyl maleimide. Methyl methacrylate is very particularly preferred in an amount of up to 20% by weight.

The graft pad can be produced in one or more process steps. For example, in a two-stage grafting, first styrene or α-methylstyrene alone and then styrene and acrylonitrile can be polymerized in two successive steps. It is advantageous to carry out the polymerization on the graft base again in an aqueous emulsion. It can be carried out in the same system as the polymerization of the graft base, it being possible to add further emulsifier and initiator. These do not have to be identical to the emulsifiers or initiators used to prepare the graft base. The Monomer mixture to be grafted on can be added to the reaction mixture all at once, batchwise in several stages or, preferably, continuously during the polymerization.

The graft polymerization can also be carried out in the presence or absence of a molecular weight regulator, such as one of the above-mentioned molecular weight regulators.

In general, the butadiene graft copolymers are prepared from 40 to 90% by weight of the polybutadiene latex according to the invention and 10 to 60% by weight of the monomers forming the graft pad.

The present invention also relates to butadiene graft copolymers which can be prepared by the process described above.

The butadiene graft copolymers according to the invention can be mixed with thermoplastic copolymers of at least one vinylaromatic monomer, acrylonitrile and optionally further ethylenically unsaturated monomers, such as commercially available SAN polymers and optionally further thermoplastic polymers "and conventional additives, to give thermoplastic molding compositions. Preferred molding compositions contain 5 to 80% by weight % Butadiene graft copolymers and 20 to 95% by weight of the thermoplastic copolymers, for example PSAN (polystyrene / acrylonitrile copolymer).

The butadiene graft copolymers according to the invention or the thermoplastic molding compositions containing them can be processed by the known methods of thermoplastic processing, such as extrusion, injection molding, calendering, blow molding, pressing or sintering.

The present invention also relates to the use of the butadiene graft copolymers and the molding compositions containing them for the production of moldings, films and fibers by extrusion, injection molding, calendering, blow molding, pressing or sintering.

The invention is illustrated by the examples below. Examples

Production of the basic butadiene stage

Comparative Examples a and b (preparation of the butadiene basic stage without styrene as comonomer)

66.14 liters of demineralized water, 339 g of potassium stearate, 177.0 g of sodium hydrogen carbonate and 124.5 g of potassium persulfate were placed in a 160 l autoclave and heated to 67.degree. 13.08 kg of butadiene were then added over the course of 30 minutes. 10 min after the start of this feed, 174.2 g of tert-dodecyl mercaptan were added. After the end of the first butadiene feed (monomer charge), polymerization was carried out for 30 min. Then 39.24 kg of butadiene were added within 9 hours. 4 hours after the start of this main feed, 174.2 g of dodecyl mercaptan were added. A further 174.2 g of dodecyl mercaptan were added 8 hours after the start of this main feed. After the main feed had ended, polymerization was continued until the conversion reached 90%. The pressure was then released, the mixture was cooled to 50 ° C. and the remaining butadiene was removed in vacuo. The dispersion was then drained into a keg.

Example b is the repetition of example a.

Example c (7% by weight of styrene, based on the total amount of monomers in the feed and feed, in the monomer charge

66.14 liters of demineralized water, 339 g of potassium stearate, 177.0 g of sodium hydrogen carbonate and 124.5 g of potassium persulfate were placed in a 160 l autoclave and heated to 67.degree. 9.42 kg of butadiene and 3.66 kg of styrene were then added over the course of 30 minutes. 10 min after the start of this feed, 174.2 g of tert-dodecyl mercaptan were added. After the end of the first butadiene feed (monomer charge), polymerization was carried out for 30 min. Then 39.24 kg of butadiene were added within 9 hours. 4 hours after the start of this main feed, 174.2 g of dodecyl mercaptan were added. A further 174.2 g of dodecyl mercaptan were added 8 hours after the start of this main feed. After the main feed had ended, polymerization was continued until the conversion reached 90%. The pressure was then released, the mixture was cooled to 50 ° C. and the remaining butadiene was removed in vacuo. The dispersion was then drained into a keg. Example d (3.5% by weight of styrene in monomer feed, 3.5% by weight in feed, in each case based on the total amount of monomers in the feed and feed

66.14 liters of demineralized water, 339 g of potassium stearate, 177.0 g of sodium hydrogen carbonate and 124.5 g of potassium persulfate were placed in a 160 l autoclave and heated to 67.degree. 11.25 kg of butadiene and 1.83 kg of styrene were then added over the course of 30 minutes. 10 min after the start of this feed, 174.2 g of tert-dodecyl mercaptan were added. After the end of the first butadiene feed (monomer charge), polymerization was carried out for 30 min. Then 37.41 kg of butadiene and 1.83 kg of styrene were added within 9 hours. 4 hours after the start of this main feed, 174.2 g of dodecyl mercaptan were added. A further 174.2 g of dodecyl mercaptan were added 8 hours after the start of this main feed. After the main feed had ended, polymerization was continued until the conversion reached 90%. The pressure was then released, the mixture was cooled to 50 ° C. and the remaining butadiene was removed in vacuo. The dispersion was then drained into a keg.

Example e (10% by weight of styrene, based on the total amount of monomers in the feed and feed, in the monomer charge)

66.14 liters of demineralized water, 339 g of potassium stearate, 177.0 g of sodium hydrogen carbonate and 124.5 g of potassium persulfate were placed in a 160 l autoclave and heated to 67.degree. Then 7.85 kg of butadiene and 5.32 kg of styrene were added within 30 minutes. 10 min after the start of this feed, 174.2 g of tert-dodecyl mercaptan were added. After the end of the first butadiene feed (monomer charge), polymerization was carried out for 30 min. Then 39.24 kg of butadiene were added within 9 hours. 4 hours after the start of this main feed, 174.2 g of dodecyl mercaptan were added. A further 174.2 g of dodecyl mercaptan were added 8 hours after the start of this main feed. After the main feed had ended, polymerization was continued until the conversion reached 90%. The pressure was then released, the mixture was cooled to 50 ° C. and the remaining butadiene was removed in vacuo. The dispersion was then drained into a keg.

Examples a to e were repeated with correspondingly reduced amounts in a 2 liter heat flow calorimeter, the heat flow profile of the polymerization reactions being measured.

Table 1 shows the results of the tests. The heat form curves are shown in FIG. 1. With increasing styrene content of the template, a significantly flatter heat flow profile becomes apparent.

Figure 2 shows the corresponding sales / time curves.

Production of ABS graft copolymers and blending with PSAN (polystyrene / acrylonitrile copolymer) to ABS molding compounds.

Graft variant 1

Comparative example (VB) f and examples g - j

4427.8 g of a polybutadiene latex, prepared according to Example a-e, were placed in a 10 1 stirred flask and heated to 75 ° C. The solids content of the polybutadiene latex was 43.8% by weight. During the heating, 387.9 g of a 10% strength by weight dispersion of poly (ethyl acrylate-co-methacrylamide) were added at 65 ° C. Then 198.1 g of a mixture of 80 parts by weight of styrene and 20 parts by weight of acrylonitrile were added and the mixture was polymerized for 15 minutes. Thereafter, 990.5 g of the same monomer mixture were added within 3 hours. Two hours after the start of this feed, the temperature was raised to 80 ° C. After the end of the feed, 2.38 g of potassium persulfate were added and polymerization was continued for 1.5 hours. After cooling, a dispersion of an antioxidant was added to the dispersion.

Graft variant 2

Comparative Example k and Examples 1 - o

4427.8 g of a polybutadiene latex, produced according to Example a-e, and 5.9 g of tert-dodecyl mercaptan were placed in a 10 1 stirred flask and heated to 75 ° C. The solids content of the polybutadiene latex was 43.8% by weight. During the heating, 387.9 g of a 10% strength by weight dispersion of poly (ethyl acrylate-co-methacrylamide) were added at 65 ° C. Then 198.1 g of a mixture of 80 parts by weight of styrene and 20 parts by weight of acrylonitrile were added and the mixture was polymerized for 15 minutes. Thereafter, 990.5 g of the same monomer mixture were added within 3 hours. Two hours after the start of this feed, the temperature was raised to 80 ° C elevated. After the end of the feed, 2.38 g of potassium persulfate were added and polymerization was continued for 1.5 hours. After cooling, a dispersion of an antioxidant was added to the dispersion.

The properties of the rubber are shown in Tables 2 and 4.

The polybutadiene dispersions grafted according to graft variants 1 and 2 were precipitated in MgSO ₄ solution and made up to ABS molding compositions with 70% by weight PSAN.

The properties of the molding compositions are shown in Table 3.

Summarized in the tables below mean:

FG: solids content [%]

t (90% sales): time to reach 90% sales [h]

Q _max : maximum heat flow [watt / kg solids content] |

QI: swelling index

Gel: gel content [%]; the gel content gives the cross-linked portion of the

Rubber particles.

d ₅ o ". Weight-average particle diameter [nm]; of those

Particle diameter indicates in which 50% by weight of all particles have a larger and 50% by weight of all particles have a smaller particle diameter.

(d ₉ o-dιo) / d ₅ o: the d ₁₀ value indicates the particle diameter at which the 10th

% By weight of all particles have a smaller and 90% by weight a larger diameter. Accordingly, the d ₉ o value indicates that particle diameter at which 90 wt .-% of all particles have a smaller, and 10 wt .-% have a larger diameter. The quotient (d ₉₀ - d ₁₀ ) / d ₅ o characterizes the

Width of the particle size division. The smaller this value, the narrower the distribution. a _κ : Charpy impact strength [U / m ² ]; this was determined on standard small bars by impact bending tests according to ISO 179-2 / 1 eA (S) at room temperature (RT) or -40 ° C.

Vicat B: Vicat B temperature [° C]; the heat resistance according to Vicat was determined on pressed platelets according to 150306 / B with a load of 50 N and a heating rate of 50 K / h.

a _D : penetration work; this was determined according to ISO 6603-2 on round or rectangular discs 40 • 40 mm by the plastic test at 23 ° C.

Glass transition temperature [° C].

MVR: Melt index according to DIN 53735/30 at 220 ° C and 10 kg load

Table 1:

Table 2:

Table 3:

The mechanical properties of the blends are at a constant level.

Table 4:

The glass transition temperature of the rubber increases only disproportionately in relation to the styrene content, which indicates a heterogeneous structure of the graft rubber particles.

Claims

claims

1. A process for the preparation of polybutadiene latex, in which butadiene is polymerized in a radical emulsion polymerization reaction in the presence of initiator and optionally dispersing aids and other customary auxiliaries, characterized in that the polymerization is carried out in the presence of reactive comonomers in such a way that a heat flow of 43 watts / kg solids content of the polymerization mixture is not exceeded.

2. The method according to claim 1, characterized by a heat flow profile with

- During a first period of 10 - 700 min, a change in the heat flow per unit of time of 0.01 - 0.5 watt / (kg • min)

- During a subsequent second period of 0 - 600 min, a change in the heat flow per unit of time of -0.1 - 0.1 watt / (kg • min)

- During a subsequent third period of 10-1000 min, a change in the heat flow per unit of time of <0 watt / (kg • min).

3. The method according to claim 1 or 2, characterized in that the polymerization is carried out semi-continuously by

(a) in a first stage, a subset of butadiene and at least one

Subset of reactive comonomer as an aqueous emulsion with a thermally decomposing initiator and optionally dispersing aids and other customary auxiliaries and the polymerization is started,

Method according to one of claims 1 to 3, characterized in that the total amount of reactive comonomer is initially charged.

5. The method according to any one of claims 1 to 4, characterized in that the total amount of reactive comonomer is 3 to 20 wt .-% of the total amount of monomer (butadiene + reactive comonomer).

6. The method according to any one of claims 1 to 5, characterized in that the reactive comonomer is styrene.

7. polybutadiene latex, producible by the method according to any one of claims 1 to 6.

8. A process for the preparation of butadiene graft copolymers, in which a polybutadiene latex is produced as a graft base according to the process according to one of claims 1 to 6

9. .Nerfahren according to claim 8, characterized in that step (c) is carried out in the presence or in the absence of a molecular weight regulator.

10. butadiene graft copolymers, producible according to the ner process according to one of claims 1 to 9.

11. ABS molding compounds containing

(a) 5 to 80 wt .-% butadiene graft copolymers according to claim 10 as component A and

(b) 20 to 95% by weight of thermoplastic copolymers of at least one vinylaromatic monomer, acrylonitrile and optionally further ethylenically unsaturated monomers.

12. Use of the butadiene graft copolymers according to claim 10 and the molding compositions according to claim 11 for the production of moldings, films and fibers.