WO1998031721A1

WO1998031721A1 - Continuous process for producing thermoplastic moulding compounds

Info

Publication number: WO1998031721A1
Application number: PCT/EP1998/000065
Authority: WO
Inventors: Wolfgang Fischer; Michael BAUMGÄRTEL; Hermann Gausepohl; Norbert Hasenbein; Rolf Kick; Wolfgang Loth; Volker Warzelhan
Original assignee: Basf Aktiengesellschaft
Priority date: 1997-01-21
Filing date: 1998-01-08
Publication date: 1998-07-23
Also published as: TW363975B; AU5862298A; DE19701865A1

Abstract

The invention concerns a process for continuously producing impact-resistant modified thermoplastic moulding compounds which contain a rubber-elastic soft phase dispersed in a vinylaromatic hard matrix. In a first reaction zone the rubber necessary for forming the soft phase is polymerized anionically in solution substantially without re-mixing until the reaction is complete. The rubber is fed, directly or after the addition of a breaking or coupling agent, to a second reaction zone in which it is polymerized until the phases are inverted with the addition of an amount of vinylaromatic monomer sufficient for phase inversion and a further anionic initiator. In a third reaction zone polymerization is terminated anionically with as many vinylaromatic monomers as are required to form the impact-resistant modified thermoplastic moulding compound.

Description

Continuous process for the production of thermoplastic molding compounds

description

The invention relates to a process for the continuous production of impact-modified, thermoplastic molding compositions which contain a rubber-elastic soft phase dispersed in a vinylaromatic hard matrix, and to a device for producing impact-modified, thermoplastic molding compositions.

Various continuous and discontinuous processes in solution or suspension are known for producing impact-resistant polystyrene. In these processes, a rubber, usually polybutadiene, is dissolved in monomeric styrene, which is polymerized in a preliminary reaction up to a conversion of approximately 30%. The formation of polystyrene and simultaneous decrease in the monomeric styrene leads to a change in the phase coherence. During this process, known as "phase inversion", grafting reactions also occur on the polybutadiene, which together with the stirring intensity and the viscosity influence the setting of the disperse soft phase. The polystyrene matrix is built up in the subsequent main polymerization. Such processes carried out in different types of reactors are described, for example, in A. Echte, Handbuch der Technische Polymerchemie, VCH Verlagsgesellschaft Weinheim 1993, pages 484-489 and US Pat. Nos. 2,727,884 and 3,903,202.

In these processes, the separately produced rubber has to be comminuted and dissolved in a complex manner and the polybutadiene rubber solution thus obtained has to be filtered in styrene before the polymerization in order to remove gel particles.

Various attempts have therefore been made to produce the required rubber solution directly by anionically polymerizing styrene / butadiene to block copolymers in nonpolar solvents such as, for example, cyclohexane or ethylbenzene

(GB 1 013 205, EP-A-0 334 715 and EP-A-0 059 231. The block rubber thus produced must either be purified by precipitation or else the solvent and other volatile substances, in particular monomeric butadiene, must be distilled off. The monomer butadiene, which, due to the residence time spectrum in stirred tanks, can only be reduced in quantity by long post-polymerization times after the monomers have been added, would then radical polymerization of styrene lead to crosslinking. Due to the high solution viscosity, only relatively dilute rubber solutions can be handled, which means high solvent consumption, cleaning and energy expenditure.

Compared to these processes, in which the polystyrene matrix is produced by radical polymerisation, the processes with anionic polymerisation have much lower residual styrene contents. From US 4 153 647 and EP-A-0 595 120, the production of impact-modified styrene by anionic polymerization of the styrene / polybutadiene rubber and subsequent anionic polymerization of the styrene matrix is known. However, these processes do not work continuously. Large amounts of solvent and long reaction times are required for the polymerization in the stirred tank. The resulting space-time yields are low.

The object of the invention was to provide a continuous process for the preparation of impact-modified molding compositions with a low residual monomer content. Only monomeric feedstocks should be used in the process and high space-time yields should be made possible. Furthermore, a device for carrying out the method should be provided.

Accordingly, a process for the continuous preparation of impact-modified thermoplastic molding compositions which contain a rubbery soft phase disperse distribution in a vinyl aromatic resin matrix, found, which is marked in characterized ^¬ distinguished, is carried out that the entire process in at least three reac ^¬ tion zones, wherein

in a first reaction zone R1, the rubber required for the formation of the soft phase is polymerized anionically, essentially without backmixing, until complete conversion in solution,

the rubber is fed directly or after the addition of a stopping or coupling agent to a second reaction zone R2, in which the addition of an amount sufficient for the phase inversion of vinyl aromatic monomer and further anionic initiator is polymerized at least until the phase inversion and In a third reaction zone R3 with as much vinyl aromatic monomer as is required to form the impact-modified thermoplastic molding composition, the polymerization is carried out anionically.

The first reaction zone R1 for the production of the rubber component for the soft phase is shown schematically in FIG. 1. It essentially consists of N temperature-controlled mixer sections (1), N tube reactors (2) and N-1 heat exchangers (3) which are connected in series, where N is an integer> 1 and is advantageously between 2 and 8. The mixing sections can be designed, for example, as pipes which contain static mixers in order to promote radial mixing. So-called Kenics mixers or SMR reactors or so-called SMX or SMXL mixers as are marketed by Sulzer or in Chem. Eng. Techn. 13 (1990) pages 214-220. The tubular reactors (2) can optionally also contain mixing elements. The temperature-controlled mixer section and the tubular reactor can also be implemented as one unit. For example, a shell-and-tube heat exchanger or an SMR reactor can be used as the heat exchanger. After the last tubular reactor, before entering the second reaction zone R2, an inlet (7) is provided for a chain termination or coupling agent.

The second reaction zone R2 is designed as a temperature-controllable backmixing unit. It can be designed, for example, as a stirred tank with a heat exchanger or as a circulation reactor with static mixers. A hydraulically filled circuit reactor can be particularly advantageous when the reaction mass has higher viscosities. In this reaction zone, the hard phase, usually polystyrene, is polymerized until phase inversion and the desired morphology and particle size of the rubber-elastic phase are set. The necessary shear conditions are elements through the selected static mixing ^¬ and the flow rate of the polymerization - mass by adjusting the circulation ratio in the case of use of a circulation reactor, or by selecting suitable stirrer and the stirrer speed in the case of a stirred tank, preserver - technical th Detailed. embodiments of the reactors so ^¬ as the morphology and properties of the rubber-modified polystyrene is found of Industrial Chemistry, VCH, Weinheim 1993, pages 484 to A. True, manual - 489th

The third reaction zone R3 consists of the same elements and has the same structure as the first reaction zone. You can just ^¬ if consist of repetitive structures. Usually there is also no heat exchanger following the last tubular reactor and the reaction energy released can advantageously be used to remove the solvent. It contains at least one inlet 10 for metering the styrenic monomer and one inlet 11 for the chain terminator. The number of tubular reactors, heat exchangers and inlets depends on the desired temperature profile and the desired final temperature.

The initiator solution, the solvent and the vinyl aromatic monomer or diene monomer are fed to the first tubular reactor via the mixer section. Further comonomers can be metered in via the further mixing sections. If necessary, further initiator solution or solvent can also be metered in. The number N of tubular reactors depends on the structure and composition of the desired rubber. The reaction in the tubular reactors is essentially adiabatic, that is to say without targeted heat exchange and essentially without backmixing. In technical systems, however, a slight heat exchange with the environment and slight backmixing in limited areas can never be completely ruled out.

The temperature of the mixing sections, the metering of the monomers so ^¬ as the amount of solvent are selected so that the temperature in the tubular reactors is not above 200 ° C, preferably not rise above 150 ° C and the reaction at the end of each tubular reactor na ^¬ hezu is complete. The temperature of the mixing sections is advantageously set so that the reaction mixture has a temperature of 30 ° C. to 60 ° C., preferably 40 ° C. to 55 ° C., when it enters the tubular reactor. The reaction mixture is cooled to 20 ° C. to 70 ° C., preferably to 30 ° C. to 60 ° C., via the heat exchanger (3). After the last tubular reactor in reaction zone 1, there is usually no cooling. A chain terminating or coupling agent can optionally be metered in via inlet 7 in order to terminate the chain ends or to link them to form multi-block or star polymers. The rubber solution can, however, also be fed directly to reaction zone 2 without termination. Their concentration can vary within wide limits. It is only limited by the solution viscosity. Because of the economy of the process, the highest possible concentration is desirable. In general, the concentration of the rubber solution before entering the second reaction zone is 5-60% by weight, preferably 10-45% by weight.

The rubbers produced in this way can be both polydienes and random linear block copolymers or star polymers with a sharp or smeared transition of the following type: (SB) _n , SBS, BSB, (SB) _m X, 5 (BS) _m X, (SBS) _m X, (BSB) _m X with n = 1 to 6 and m = 2 to 10, where

S is a block of vinyl aromatic monomer, preferably styrene 0 B is a polydiene block, preferably of butadiene or isoprene,

X is an m-functional coupling agent or m- functional ^¬ In itiator.

The block length of each individual block and the block sequences can be adjusted to the individual mixing sections via the initiator quantity, the monomer quantity and the metering method. Blocks S can also contain alkadiene monomers, blocks B also vinyl aromatic monomers in statistical order.

Statistical incorporation is achieved, for example, by adding small amounts of Lewis bases such as dimethyl ether, diethylene glycol dimethyl ether, tetrahydrofuran, alkali metal salts of primary, secondary and tertiary alcohols and tertiary amines such as pyridine and tributylamine. These are usually used in concentrations 5 from 0.1 to 5 vol .-% based on the initiator used, such as alkoxides used in Kaliumtetrahydrolinoleat 3-20 volume per ^¬ producers. The starting materials and process conditions are preferably chosen such that a 1,2-vinyl content in the diene block of less than 30% by weight, based on the diene block, results. The average molecular weights Mw of the blocks are generally in the range of 1,000 to 500,000, preferably in the Be ^¬ ranging from 20,000 to 300,000 g / mol. The total content of vinyl aromatic monomer ^¬ is in the range of 3 to 85 wt -.%, Preferably between 10 and 60 wt -.%, And most forthcoming

35 increases between 10 and 45%, based on the total rubber. The glass transition temperatures of the rubber-elastic blocks are below -20 ° C, preferably below -40 ° C.

The rubber solution produced in the first 40 reaction zone is fed continuously to the second reaction zone, and further styrenic monomer and initiator are fed in via feeds 8 and 9, in flow rates as are necessary to achieve phase inversion. In the second reaction ^zone , polymerization is usually carried out at temperatures from 50 to 120 ° C., preferably from 60 to 45 100 ° C. The reaction mass from zone 2 fed to the third reaction zone is heated to 20 to 70 ° C., preferably 30 to 60 ° C. Additional styrenic monomer and optionally further initiator are metered in via feed 10. The reaction mixture is polymerized in the tubular reactor without heat removal to complete conversion. After the live chain ends have been terminated with the chain terminating agent via feed 11, the polymerization solution can be worked up in a known manner in degassing extruders or degassing evaporators at temperatures of usually 190 to 320 ° C. The solvent obtained here is expediently returned to the process after distillation and appropriate drying.

To prepare the rubber solution in the first reaction zone, it is possible to use the customary anionically polymerizable vinylaromatic monomers and diene monomers which meet the usual purity requirements, in particular the absence of polar substances.

Preferred monomers are styrene, α-methylstyrene, p-methylstyrene, ethylstyrene, tert. -Butylstyrene, vinyltoluene, 1, 1-diphenylethylene and butadiene, isoprene, dimethylbutadiene, pentadiene-1, 3 or hexadienes-1, 3 or mixtures thereof.

The usual mono-, bi- or multifunctional alkali metal alkyls or aryls are used as initiators. Advantageously - organolithium compounds are used, such as ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert. -Butyl-, phenyl-, hexyldiphenyl-, hexamethylenedi-, butadienyl- or isopropenyllithium. The amount of initiator required results from the desired molecular weight and is generally in the range from 0.0002 to 5 mol percent, based on the amount of monomer.

Suitable chain terminators are proton-active substances or Lewis acids such as water, alcohols, aliphatic and aromatic carboxylic acids or their salts, and inorganic acids such as carbonic acid or boric acid.

Polyfunctional compounds such as polyfunctional aldehydes, ketones, esters, anhydrides or epoxides can be used to couple the rubbers.

The customary anionically polymerizable vinyl aromatic monomers which meet the usual purity requirements, such as, in particular, the absence of polar substances, can be used as the monomer for the preparation of the hard phase. Styrene, α-methylstyrene, p-methylstyrene, ethylstyrene, tert are preferred. -Butylstyrene, vinyltoluene, 1, 1-diphenylethylene or mixtures thereof are used.

As the solvent, the organization for the anionic Polymeri ^¬ conventional aliphatic, cycloaliphatic or aromatic hydrocarbons having 4 to 12 carbon atoms such as pentane, hexane, heptane, cyclohexane, methylcyclohexane, isooctane, benzene, alkylbenzenes such as toluene, xylene, ethylbenzene or decalin or suitable mixtures. The solvent must of course have the high purity required for the process. To remove proton-active substances, they can be dried, for example, over aluminum oxide or molecular sieve and distilled before use. The solvent from the process is preferably reused after condensation and the cleaning mentioned.

If necessary, customary auxiliaries and additives such as lubricants, stabilizers or mold release agents can be added to the molding composition.

The device described is also suitable for producing other multi-phase molding compositions. For this purpose, the polymer forming the soft phase is synthesized in reaction zone 1 and mixed in reaction zone 2 with further monomer or monomer mixtures which form the polymer of the hard phase and polymerized until phase inversion. The polymerization is completed in the third reaction zone.

Examples

An arrangement as shown in FIG. 1 was used for the examples, four tube reactors (2a, 2b, 2c, 2d) each having a length of 500 mm (DN 32-SMXL mixer from Sulzer) being used in the unit designated as reaction zone R1 ) were used, each of which had a temperature-controllable premixer (la, lb, lc, ld) each 350 mm long (DN 15 SMX mixer from Sulzer) with the corresponding feeds for monomers (feeds 1,4,5,6 ), Solvent (inlet 2) and initiator (inlet 3) upstream and in the case of tube reactors 2a to 2c each have a heat exchanger (3a, 3b, 3c), each consisting of a tube bundle with 3 DN 15 tubes and a length of 1000 mm, were downstream. For the reaction zone R2, a 10 1 stirred tank was used, which was equipped with an anchor stirrer and reflux condenser and the inlets for chain terminating or coupling agents (inlet 7), monomers (inlet 8) and initiator (inlet 9).

The reaction zone R3, consisting of a heat exchanger (3d) consisting of a 1000 mm long tube bundle with 3 DN 15 tubes, two 300 mm long mixers (le and lf) (DN 25 SMX mixer from Sulzer) with inlet 10 (for Monomers) or 11 (for chain terminating agent) and a 400 mm long, interposed tubular reactor (2e) (DN 50 SMXL mixer from Sulzer) was connected via a gear pump to the boiler outlet valve of the stirred reactor of reaction zone 2.

The total reaction volume of the arrangement was approximately 9.9 1, divided into 3.5 1 in reaction zone 1, 5 1 in reaction zone 2 (fill level of the stirred tank) and 1.4 1 in reaction zone 3.

A degassing extruder was installed downstream of the arrangement.

The monomers and solvents used for the polymerization were dried over A1 ₂ 0 ₃ (ethylbenzene) or molecular sieve (butadiene) and distilled (styrene, ethylbenzene) before use. A 1.2% solution of sec-butyllithium in n-hexane / ethylbenzene (10/90% by weight) was used as the initiator.

The molar masses Mp (peak maximum) of the styrene matrix were determined by means of gel permeation chromatography (GPC) against narrowly distributed polystyrene standards.

The notched impact strength was determined on notched standard bodies in accordance with DIN 53453. The yield stress was determined on test specimens produced according to ISO 3167 according to DIN 53455.

Example 1-3

Examples 1-3 were carried out in the apparatus described above using the process parameters listed in Table 1. The examples show, in particular, low residual monomer contents and very high space-time yields, which are between 0.08 and 0.2 kg / (hx 1) in the technical plants usually used for the production of impact-resistant polystyrene. Table 1

Claims

claims

1. A process for the continuous production of impact-modified thermoplastic molding compositions which comprise a rubber-elastic soft phase dispersed in a vinyl aromatic hard matrix, characterized in that the entire process is carried out in at least three reaction zones, where

in a first reaction zone the rubber required for the formation of the soft phase is anionically polymerized without backmixing until complete conversion in solution,

the rubber is fed directly or after the addition of a termination or coupling agent to a second reaction zone in which the addition of an amount sufficient for the phase inversion of vinyl aromatic monomer and further anionic initiator is carried out at least up to the phase inversion and

in a third reaction zone, the polymerization is carried out anionically with an amount of vinylaromatic monomer required to form the impact-modified thermoplastic molding composition.

2. The method according to claim 1, characterized in that in the first reaction zone at least a part of the starting materials for the production of the rubber are mixed and preheated in a first pipe section provided with permanently installed mixing elements, in a subsequent pipe section with possibly other ones built-in mixing elements is implemented non-isothermally and is cooled in a further pipe section with a heat exchanger and, if appropriate, further parts of the starting materials are mixed, converted and cooled in further pipe sections in the same way to the reaction solution.

3. The method according to claim 1, characterized in that the second reaction zone is designed as a back-mixing unit.

4. The method according to claim 3, characterized in that a circulation reactor with static mixers or a stirred tank with a heat exchanger is present as the back-mixing unit.

5. Process according to claims 1 to 4, characterized in that styrene and butadiene are used as monomers to form the rubber.

6. Process according to claims 1 to 5, characterized in that water, a mixture of carbon dioxide and water, an alcohol or a carboxylic acid or salts thereof are used as the terminating agent.

7. Process according to claims 1 to 6, characterized in that styrene or styrene / diphenylethylene mixtures are used as vinyl aromatic monomers.

8. Device for the continuous production of impact modified thermoplastic molding compositions, characterized in that the device consists of at least three interconnected reaction zones, wherein

the first reaction zone R1 has at least one tube reactor (a), consisting of at least one first temperature-controlled tube section (1) which has mixing elements in the form of fixed internals and at least one inlet, at least one further tube section (2) without a heat exchanger, which optionally contains mixing elements Has the form of fixed internals and has at least one further pipe section (3) with a heat exchanger,

the second reaction zone R2 consists of a circulation reactor with static mixers or a stirred tank with a heat exchanger (3) and at least one feed,

the third reaction zone R3 has at least one heat exchanger (3d), followed by at least one tube reactor (e) consisting of at least one first temperature-controlled tube section (1), the mixing elements in

Has fixed installations and at least one inlet, has at least one further pipe section (2) without a heat exchanger with optionally further permanently installed mixing elements and a further mixing element (f) with an inlet.

9. The device according to claim 8, characterized in that the third reaction zone is followed by a degassing unit.