DE19547975A1 - Deep draw thermoplastic moulding materials for fibres, films or formed articles - Google Patents

Abstract

Prepn. of deep draw-modified thermoplastics (T) by mechanical dewatering of a wet elastomer component (A) contg. up to 50 wt.% residual water and mixing dewatered (A) with a thermoplastic polymer (B) in a screw - by adding (A) to a twin-screw extruder with 3-way rotating screws. This extruder contains the following sections (in the direction of flow): (1) feed for adding (A) to the extruder; (2) at least one crusher for dewatering (A) that contains one or more barriers each with an opening through which at least some of the water passes as a liq.; (3) at least one section to which molten (B) is added; (4) one or more sections with mixing, kneading and/or plasticising devices; (5) at least one degassing section with one or more gas outlets through which water is removed as steam; and (6) an exit zone. Also claimed are deep draw-modified moulding materials prepd. by this process.

Description

The present invention relates to a new method for manufacturing Provision of impact modified thermoplastics by mecha niche drainage of a water-moist, up to 50% by weight rest water-containing elastomer component A and mixing the dewatered elastomer component A 'with a thermoplastic Polymer B in a screw machine.

The invention also relates to specific embodiments of the mentioned method, including those using certain Components A and B, as well as the form produced by the process masses and the use of the molding compositions for the production of Films, fibers and moldings.

As elastomer components for the impact modification of thermoplastic or other plastics are common Particulate rubbers are used that are grafted or unsung can be grafted. Such rubbers are usually in aqueous systems, for example by emulsion or suspension polymerization. The suspension polymer tion or during the emulsion polymerization Add a coagulating precipitant to precipitated particles are usually washed with water and by a suitable Drainage process further drained.

Such methods are, for example, the partial chemical one Drying with a current or fluid bed dryer, one Spray drying and mechanical drainage using fil tration (also under vacuum), dehanting or centrifuging. Man always receives partially dewatered products.

Often used graft rubbers are with a Styrene-acrylonitrile copolymers (SAN) grafted polybutadiene and poly-n-butyl acrylate grafted with such a copolymer, or rubber based on several grafting stages of butadiene, styrene, n-butyl acrylate, methyl methacrylate and / or Acrylonitrile. Rubbers for other uses are also often used obtained by polymerization in the aqueous phase.

The residual water content of that obtained after partial drainage Rubber is up to 50 wt .-% and is usually by energy-consuming drying removed. The powder Dried rubber is finally used as a powder or  Granules present thermoplastic melted works, creating the end product. The rubber powder tends during drying and incorporation into the thermo plastic because of the fine dust content for self-ignition.

According to a proposal described in DE-A-20 37 784 one can partially dewatered graft rubber in a SAN melt under Ver vaporize the water and enter this graft rubber contain thermoplastics. This procedure requires a relatively high amount of electrical energy.

EP-A 534 235 teaches a method for producing impact tough modified thermoplastics by incorporation of mechanical partially dewatered rubber in a thermoplastic above the softening point of the thermoplastic, the incorporation happens in a main extruder and the partial drainage of the Rubber in a so-called. Side extruder is made. What remained in the rubber Residual water is removed during the incorporation by before and after Mixing point ent degassing openings as steam ent distant.

A disadvantage of this method is the need to restore it position of the impact-resistant thermoplastic operate two extruders have to. There is also drainage of the rubber in the sides Extruder not completely, so that a large amount of water in the Main extruder must be evaporated.

U.S. Patent 5,151,026 describes an extruder in which shredded and washed plastic waste, its water content is up to 50 wt .-%, are dewatered. For this purpose be can be found in the extruder screw, which is otherwise as usual Right-hand thread, short sections with a left-hand thread. The divisional application derived from this U.S. document US 5 232 649 describes the corresponding method.

Japanese script JP 22 86 208 teaches a twin screw extruders for dewatering thermoplastic molding compounds, whose right-hand screws each have two left-hand screws Have sections. The water flows fluidly through so-called Colander housing - sieve-like inserts in the extruder housing - and as Steam through vent openings. The colander housings tend however, blockages caused by escaping polymer material, as for example in DE 15 79 106 for Ent Watering synthetic rubber is described.  

JP 1-202 406 discloses a method in which moist, rubbery polymers in an extruder first in partially dewatered in an area provided with strainer housings den, and then the rest of the water in an atmospheric and three adjacent vacuum degassing zones removed becomes. This procedure includes the vulnerable colander still enclose a complex vacuum degassing area.

U.S. Patent No. 4,802,769 describes an extruder in which 10 an aqueous suspension ("slurry") of a rubber polymer, and a styrene-acrylonitrile copolymer to form a thermoplastic are processed. The water passes through the colander housing liquid and through a three-stage degassing as vapor. As Disadvantages are - besides the clogged strainer housings - to mention NEN that the extruder part provided with strainer housings is heated and that in the degassing part a multiple pressure build-up Damming elements takes place, making the polymer material thermally and is mechanically stressed.

The object of the invention was to provide a method to deliver, which does not have the disadvantages described. In particular, a procedure should be created that the Her position of an impact-resistant thermoplastic from a water damp Elastomer component and a thermoplastic, brittle poly mer in a technically simple manner, if possible in a ver driving step, enables.

Accordingly, the process defined at the outset was found, where the elastomer component A with a twin-screw extruder feeds three-speed screws rotating in the same direction, essentially in the conveying direction

• - A metering section in which by means of a metering device Elastomer component A is fed to the extruder,
• - At least one squeeze serving for drainage section, the at least one damming element, as well as each contains at least one associated drainage opening,
• - At least one section in which the thermoplastic poly mere B is introduced into the extruder as a melt,
• - At least one with mixing, kneading and / or others Section provided with plasticizing elements,  
• - At least one with at least one vent opening provided degassing section, in which the remaining water is removed as steam, and
• - a discharge zone

is built up, and which from the drainage openings partially or completely entering water in the liquid phase is present.

In addition, special embodiments of the method have been developed visibly the design of the extruder and the used Components A and B made by the process thermoplastic molding compositions and the use of this mold masses for the production of foils, fibers and molded articles the.

The principle of the method and the preferred embodiments of the method are described below, the components of the extruder referred to as sections or zones not necessarily being identical to the individual components, such as housing parts, screw segments, from which the extruder is mounted. A section or zone usually consists of several components. The numbers given in the sections or zones refer to FIG. 1.

The water-moist, up to 50% by weight residual water-containing elastomer component A, for example a graft rubber obtained by precipitation of up to 50% by weight residual water by precipitation polymerisation, the partially dewatered gum rubber. B. by thermal drying, decanting or centrifuging - is fed to the metering section 2 of the extruder, the metering section usually consisting of an automatically operating metering device and the actual metering opening. The metering device is designed, for example, as a screw conveyor which conveys or pushes the material to be conveyed into the metering opening. By means of a suitable screw geometry in the metering section, component A is drawn in and vented. Optionally, trapped air can also escape through a vent section 1 , which is located upstream against the direction of conveyance of the extruder and typically has one or more vent openings.

The water-moist elastomer component is downstream in the promoted first squeeze section.  

In the first squeezing section 3 , a considerable part of the residual water contained in the elastomer component is mechanically removed. The material is conveyed against a damming element which acts as an obstacle and which is usually located at the end of the squeezing section. This creates a pressure that squeezes the water out of the elastomer component. Depending on the rheological behavior of the rubber, the pressure can be built up by arranging the screws, kneading elements or other accumulation elements differently.

Basically, the most diverse elements, one Cause pressure to be used. They form a so-called "Stowage zone", and are known to the specialist as commercially available components known.

For example, screw elements with a very low pitch direction in the conveying direction, kneading blocks with wide, non-conveying Kneading disks, kneading blocks whose kneading disks are offset in this way are arranged that an incline against the conveying direction results, or screw elements with an incline counter the direction of conveyance. It can also be two or several of the baffle elements can be combined. Soon if the congestion effect can be caused by the length of each congestion elements are adapted to the respective elastomer.

The squeezing section 3 preferably contains screw elements with an incline opposite to the conveying direction, or kneading blocks with a resulting incline opposite to the conveying direction, or a combination of these two accumulating elements.

In the first squeezing section, all constructions are preferred tive features and all operating parameters of the extruder coordinated with each other that at the selected screw speed the elastomer material is promoted and compressed, however not or only plasticized to a minor extent or is melted and not melted.

The one squeezed out of the elastomer material in the squeezing section Water leaves the extruder in the liquid phase and not as Steam. In a less preferred embodiment, up to 20% by weight of the water removed in this section as steam out.

The squeezing section is with one or more, as a rule drainage openings under normal pressure or overpressure Mistake. They are preferably located approximately in the middle of the Squeeze section and usually at the top of the  Extruders. Furthermore, the drainage openings are preferred provided with a device that the emergence of the conveyor Prevent elastomers A, which are usually under pressure. So-called retaining screws are particularly preferred turns.

The temperature of the exiting water is generally 20 to 50 ° C and preferably 25 to 40 ° C, measured at the outlet opening.

In the first squeezing section, depending on the elastomer component and the initial residual water content, usually 5 to 90, preferably 5 to 80 wt .-% of the initial contained residual water removed.

If the elastomer component is a particulate rubber, so after passing the first congestion zone it is usually completely predominantly in powder form.

The partially dewatered elastomer component A is over the Congestion zones conveyed away and reaches the next extruder section.

In a preferred embodiment, the first squeeze section 3 just described is followed by a second squeeze section 3 ', which in turn consists of a conveying section and an effective stowage zone. With regard to this section, essentially the same statements apply as for the first squeezing section 3 .

In the second squeezing section, the elastomer component becomes wider dewatered, again up to 80, preferably 5 to 65% by weight of the water initially contained (before extrusion) is removed will. By being turned on by the rotating extruder screw brought mechanical energy increases the temperature of the elastomer component in the second squeezing section generally to values up to 250 ° C.

The water removed in this section occurs to 20 to 99% by weight as a liquid, the amount missing in 100% by weight as steam. However, the drainage openings are preferred in this way designed that the proportion of liquid escaping water is 70% by weight or more despite the high material temperature. For this, the geometries of the extruder screws and the back holding screws designed so that by building pressure in the off the water remains mostly liquid.  

As a rule, the water temperature is at the outlet opening at 40 to 130, preferably at 50 to 99 ° C.

In a particular embodiment, at least one associated drainage opening is operated under excess pressure in at least one of the squeezing sections. Preferably, the drainage openings of the second squeeze section 3 'and those of the subsequent squeeze sections - if present - are operated under excess pressure. An absolute pressure of up to 20 bar is usually set. The external pressure can be generated, for example, by a special degassing dome, provided with water drainage and discharge and pressure control valve, or a tightly meshing counter-rotating retention screw.

The partially dewatered elastomer component at the end of the second squeezing section 3 'can already be melted or melted to a greater extent and be in the form of larger melted agglomerates.

The extruder can contain further squeeze sections behind the second squeeze section 3 ', in particular when the initial residual water content of the elastomer component A is high.

After passing the last squeezing section, the elastomer component is freed from most of the residual water (component A ') and reaches a section 4 in which there are one or more supply openings for the thermoplastic polymer B. It is advantageous that the polymer B is fed in the form of its melt.

The supply of the melt of the polymer B can by means of a Extruders, but preferably by means of technically simple conveying facilities such as melt pumps or dosing screws.

In the area of section 4 , in which the melt of the thermoplastic polymer B is fed, the screw is expediently designed as a screw conveyor, which is able to homogenize the mixture of elastomer component A and the melt of the thermoplastic B only to a small extent.

At the section feeding the thermoplastic melt B is a section 5 , which is provided with mixing, kneading and / or other plasticizing elements ("plasticizing section").

The plasticizing elements homogenize the polymer mixture while melting the dewatered elastomer component A ', the heat required for plasticization energy by friction of the polymer mixture on the plastic tion elements is introduced.

The plasticizing elements are familiar to those skilled in the art Components into consideration, for example screw elements with small incline in the conveying direction, kneading blocks with narrow or wide, promoting or non-promoting kneading disks, screws elements with a slope opposite to the conveying direction, or a combination of such elements. The choice of plasticity tion elements in the plasticizing section with regard to their The type, number and dimensions depend on the components the polymer mixture, especially according to viscosity and expansion temperature and the miscibility of the components.

The extruder can, according to the described plasticizing section, contain one or more further plasticizing sections 5 if the homogenization and melting of the mixture in the first plasticizing section was incomplete or only with very intensive kneading and associated thermal damage to the polymer material due to the considerable frictional heat could have been done.

The same applies to the other plastication section (s) Explanations for the first plastication section accordingly.

In a preferred embodiment, the melt of the thermoplastic polymer B is fed to the extruder at the beginning of the plasticizing section. In this embodiment, the section of the thermoplastic feed 4 coincides with the beginning of the plasticizing section 5 .

In a further special embodiment of the extruder, one or more further plasticizing sections are located in front of section 4 , in which the melt of the thermoplastic polymer is fed, that is to say behind the last squeezing section. In this plasticizing section 5 '', the largely dewatered elastomer component A ', for example the rubber powder, is first homogenized and plasticized alone.

The melt of the thermoplastic polymer B is accordingly introduced in this embodiment into a viscous "melt" of the elastomer component A '. In this case, the mixture of melt B (section 4 ) following the plasticizing section 5 only serves to homogenize the mixture of the two components already in the plastic state and therefore generally contains fewer mixing elements than the previously described plasticizing sections.

Which of the described variants of supplying melt B, namely

• - in a promotional section before plasticizing section,
• - at the beginning of the plasticizing section,
• - in a promotional section between two plasticizers sections,

is chosen depends on the physical and chemical properties remove the components to be mixed. For example only be the viscosities of the melts of elastomer component A ′ and thermoplastic polymer B, the softening temperatures of the components, their thermal resilience or decomposition tendency at higher temperatures, the compatibility in the sense a miscibility or wettability of the components, the rest water content of the polymer mixture of elastomer component A 'and thermoplastic polymer B, and, in the case of a particle shaped rubber as elastomer component A, the particles called size and particle size distribution.

The last plasticizing section is followed by one or more degassing sections 6 and 6 ', each of which is provided with one or more degassing openings. In the degassing sections, the remaining water, which has not yet been mechanically removed in the squeezing sections, is partially or completely removed. Because of the temperatures of the polymer melt, which are usually above 100 ° C, most of the water escapes completely as steam. The energy required to evaporate the water has already been introduced in the plasticizing sections.

The degassing openings are preferably located on the top of the extruder. However, side or other arrangements are also possible possible.

The vent openings can be under normal pressure, under vacuum or operated under positive pressure, with all degassing openings can have the same or different pressure. In the case of a vacuum, the absolute pressure is usually 100 up to 500 mbar; in the case of degassing under excess pressure, the  Usually set up to 20 bar absolute pressure. It is preferred however, to operate the degassing sections under normal pressure.

The number of degassing sections as well as the number, arrangement and Dimensioning of the degassing openings depends on the Water content of the poly entering the degassing sections mer and the desired water content in the end product. In a preferred embodiment is an extruder with two ent gas sections used.

The degassing openings of the degassing sections can with Vor directions, e.g. B. retaining screws, provided an off the conveyed material through the openings from the Prevent extruders.

After a significant amount of the residual water contained in the elastomer component A has already been removed in the squeezing sections 3 and 3 ', in all degassing sections 6 and 6 ' taken together only about 10 to 60, preferably 20 to 50% by weight of the pre-extrusion in of the elastomer component A residual water removed.

The extruder screws are in the area of the degassing sections usually designed as a conventional screw conveyor.

The last section of the extruder is discharge zone 7 . It consists of a screw conveyor and a closed housing part, which is closed with a defined discharge opening. A nozzle head is preferably used as the discharge opening, which is designed, for example, as a nozzle plate or nozzle strip, the nozzles being circular (perforated nozzle plate), slot-shaped or in some other way. The product discharged as a strand in the case of a nozzle plate is, as usual, e.g. B. cooled in water and granulated. Cube pelletizing is possible especially when using a slot nozzle.

In a particular embodiment, instead of that described above lower nozzle bar with the otherwise usual combination of strand fume cupboard, water bath and granulator with a special nozzle head closing underwater pelletizing used. Here occurs the polymer melt through a nozzle plate with a preferably circular Round bores, arranged in a rotating manner Knives separated and cooled in water, adding the polymer more or less round, pearl-shaped grains solidified. In the However, the arrangement of the holes are also other than circular Arrangements and other than round hole shapes in use.  

In a further embodiment, instead of the discharge Nozzle bar, water bath cooling and pelletizing am hot cut process used, the emerging from the nozzle head Polymer melt not cooled by liquid, but after Leaving the nozzle head after a short air cooling while still hot Condition is crushed (granulated). The resulting granulate is then cooled further or cools during further processing if necessary. It is also the finishing conceivable when hot.

The water content of the discharged polymer (the "St rang moist ") is usually 0.1 to 1.2 wt .-%, based on this polymer. The temperature of the discharge opening emerging polymer melt is usually 180 to 350 ° C, each depending on the type of polymer used.

As is well known, the different zones can be one Extruders can be individually heated or cooled to run along to set an optimal temperature profile for the screw axis. It is also known to the person skilled in the art that the individual sections of the extruder can be of different lengths.

The temperatures and lengths to be selected in individual cases individual sections differ depending on the chemical and physical properties already mentioned in a playful manner properties of the components and their proportions.

The same applies to the screw speed, which can vary within a wide range. The speed of the extruder screws in the range from 100 to 350 min ^{−1 is} just one example.

It is advantageous to design and operate the extruder in such a way that average shear rates of 180 to 220 s ^-1 occur at a screw speed of 100 to 350 min ^-1 . However, depending on the type, amount and properties of the components used, it may be expedient to work at medium shear speeds outside of this range.

Any polymer can be used as the elastomer component A, which has elastomeric properties and fed to an extruder can be. In particular, as mentioned at the beginning, particles become shaped rubbers used. Those are particularly preferred Rubbers that are a grafted shell from others in which Usually have non-elastomeric polymers. The extruder as partially dewatered gum rubber types  hold up to in a preferred embodiment of the invention 50, particularly preferably 25 to 40% by weight of residual water.

One embodiment of the invention consists in a method in the two or more stages as the elastomer component A. built graft rubbers are used, in which the elasto meren basic or graft stages by polymerization of one or several of the monomers butadiene, isoprene, styrene, alkylstyrene, C₁- to C₁₀ alkyl esters of acrylic acid or methacrylic acid and receive small amounts of other, also crosslinking monomers and where the hard grafting stages from one or several of the monomers styrene, alkylstyrene, acrylonitrile, methyl be polymerized methacrylate. Graft particles A are preferred from polymers based on butadiene / styrene / acrylonitrile, n-buty acrylate / styrene / acrylonitrile, butadiene / n-butyl acrylate / styrene / Acrylonitrile, n-butyl acrylate / styrene / methyl methacrylate, butadiene / Styrene / acrylonitrile / methyl methacrylate and butadiene / n-butyl acrylate / Methyl methacrylate / styrene / acrylonitrile.

In this embodiment, thermoplastic polymers B Styrene-acrylonitrile (SAN) copolymers, polystyrene, polymethylmeth acrylate, polyvinyl chloride or mixtures of these polymers set.

SAN polymers, polymethyl methacrylate (PMMA) or Mixtures of these polymers are preferred.

Furthermore, as thermoplastic polymers B, poly carbonate, polybutylene terephthalate, polyoxymethylene, polymethylme thacrylate, polyphenylene sulfide, polysulfones, polyether sulfones and Polyamides and mixtures of these thermoplastics are used.

Likewise, as component B, copolymers based on styrene / Maleic anhydride, styrene / imidated maleic anhydride, Styrene / maleic anhydride / imidated maleic anhydride, sty rol / methyl methacrylate, styrene / methyl methacrylate / maleic acid drid, methyl methacrylate / imidized maleic anhydride, styrene / imidated methyl methacrylate, imidated PMMA or mixtures use of these polymers.

In all of the thermoplastic polymers B mentioned, the styrene wholly or partly by α-methylstyrene or alkylated nucleus Styrene to be replaced.  

Of the latter polymers B, those based on α-methylstyrene / acrylonitrile, styrene / maleic anhydride, styrene / Methyl methacrylate and copolymers with imidized maleic acid anhydride preferred.

Known examples of the elastomer component A are polymers sate of conjugated dienes like butadiene, with an outer Graft shell based on a vinyl aromatic compound, e.g. B. SAN copolymers. Graft rubbers are also known Basis of crosslinked polymers from C₁ to C₁₀ alkyl esters Acrylic acid such as n-butyl acrylate or ethylhexyl acrylate, grafted with polymers based on vinyl aromatic compounds like SAN copolymers. Graft rubbers are also common Essentially a copolymer of conjugated dienes and C₁- to C₁₀ alkyl acrylates, for example a butadiene-n-butyl acrylate lat copolymer, and an outer graft made of SAN copolymer or PMMA included.

The production of such graft rubbers according to the usual Ver drive, especially by emulsion or suspension polymers sation, is known.

Graft rubbers based on SAN-grafted polybutadiene for example in the documents DE 24 27 960 and EP-A 258 741 described, those based on SAN-grafted poly-n-butyl acrylate in DE-AS 12 60 135 and DE-OS 31 49 358. More on SAN-grafted poly (butadiene / n-butyl acrylate) blend rubbers can be found in EP-A 62 901.

As thermoplastic polymers B in the case of the last Paragraph mentioned graft rubbers copolymers of styrene and Acrylonitrile is used. You are known and z. T. also commercial usual and usually have a viscosity number VZ (determined according to DIN 53 726 at 25 ° C, 0.5 wt .-% in dimethylformamide) of 40 to 160 ml / g, corresponding to an average molecular weight of about 40000 to 200000.

The thermoplastic polymers B are preferred by continuous Nuclear substance or solution polymerization produced, the melt obtained, optionally after removal of the Solvents, for example with a melt pump continuously Lich is fed directly to the extruder. However, there is also one Production by emulsion, suspension or precipitation polymers sation possible, whereby in an additional step Polymer is separated from the water phase.  

Details of the manufacturing process are e.g. B. in plastic manual, ed. R. Vieweg and G. Daumiller, Vol. V "Polystyrene", Carl-Hanser-Verlag, Munich, 1969, pp. 118 ff.

If the elastomer component A is a SAN-grafted polybutadiene, incorporating the SAN creates a molding compound that acts as ABS (Acrylonitrile / butadiene / styrene) is known. Is used as component A a SAN-grafted alkyl acrylate is used So-called ASA molding compounds (acrylonitrile / styrene / acrylate).

In another embodiment, graft rubbers with are 50% by weight of residual water based on polydienes and / or Polyalkyl acrylates as well as SAN and / or PMMA are used more than two graft stages have been set up. Examples of such multistage graft particles are particles that have a poly core dien and / or polyalkyl acrylate, as the first shell a SAN polymer and as a second shell another SAN polymer with a ver changed weight ratio styrene: acrylonitrile, or also particles containing a core made of polystyrene or SAN polymer, a first shell made of polydiene and / or polyalkyla crylate and a second sleeve made of SAN polymer. Further examples are graft rubbers made from a polydiene core, one or more Polyalkyl acrylate sleeves and one or more SAN polymer sleeves or analog graft rubbers with an acrylic core and poly service covers.

Copolymers with a multi-stage core-shell structure are also available from cross-linked alkyl acrylate, styrene, methyl methacrylate and one outer shell made of PMMA in use.

Such multi-stage graft rubbers are such. B. in DE-OS 31 49 046 described. Graft rubbers based on n-butyl acrylate / Styrene / methyl methacrylate with a shell made of PMMA z. B. in EP-A 512 333 described, each other also the state of the Technically appropriate construction of such graft rubbers possible is.

Such rubbers are used as an impact-resistant component for Polyvinyl chloride and preferably used for impact-resistant PMMA.

The thermoplastic polymers B are again preferred mentioned SAN copolymers and / or PMMA used.

Is the elastomer component A a multi-shell core / Shell polymer based on n-butyl acrylate / methyl methacrylate, and the polymer B PMMA, so you get impact-resistant PMMA.  

The diameter of the particulate graft rubbers is 0.05 to 20 µm. Is it the well-known graft small diameter rubbers, it is preferably 0.08 to 1.5 and particularly preferably 0.1 to 0.8 μm.

In the expediently by means of suspension polymerization large graft rubbers made is the diameter preferably 1.8 to 18 and in particular 2 to 15 μm. Such Graft rubbers of large diameter, for example, teach that DE-OS 44 43 886.

In this embodiment, preferred component 3 are the mentioned SAN copolymers and / or PMMA.

In addition to the elastomer component A and the thermoplastic poly Meren B can be made according to the inventive method provided molding materials still other components, in particular Additives such as lubricants and mold release agents, pigments, colors substances, flame retardants, antioxidants, stabilizers against Exposure to light, fibrous and powdery filling and reinforcement agents and antistatic agents in the amounts customary for these agents contain.

These other components can go directly through feed openings or together with the elastomer component A and the thermo plastic polymers B are introduced into the extruder.

The thermoplastic molding compositions produced by the process can be processed into moldings using the generally customary processes be prepared. Examples include extrusion (for pipes, profiles, Fibers, foils and plates), injection molding (for molded parts of all Type) as well as calendering and rolling (for plates and foils) called.

A major advantage of the method according to the invention is that a significant part of the residual water, which in the part watered elastomer component A is already contained in the Squeeze zones is removed mechanically, which is why in the after following extruder sections use less thermal energy Evaporation of the remaining water must be applied. It this results in significant energy savings.

Another advantage of the method according to the invention lies in that the extruder operated at low temperatures can be as for example according to that in EP-A 534 235 described method, so that the elastomer component A and that  from components A and B - and, if necessary, the others Components - existing polymers are processed more gently.

By incorporating a partially dewatered elastomer compo ent A in the melt of a thermoplastic polymer B tolerance or at least partial tolerance the elastomer component with the thermoplastic polymer and provided sufficient thermal resistance, rubber modified thermoplastic molding compounds of all kinds produce.

Compared to the methods known from the prior art the inventive method further has the advantage that none strainer housing susceptible to blockage.

The arrangement of the extruder according to the invention can be cost-saving with the help of commercially available extruder components after Modular principle can be built. Such components are in shape differently designed snail and associated Housing sections, so-called "shots", available and enable an exact adaptation of the extruder to the special confection nation problem.

Examples a) extruder

A ZSK 53 twin-screw extruder from Werner and Pfleiderer, Stuttgart, is used, which is built up from 14 shots. Their downstream arrangement is as follows (the name of the extruder section used in the description is given in brackets):

Shot 0: length 3 D, unheated, with ventilation opening on top (ventilation section 1 ).
Shot 1: Length 3 D, unheated, with a metering opening above, which is provided with a metering device ESB 45 from Werner and Pfleiderer (metering section 2 for elastomer component A).
Shot 2: Length 3 D, unheated, with drainage opening at the top, which is provided with a retaining screw (first squeezing section 3 , front part).
Shot 3: length 3 D, unheated, without openings, contains dam elements (first squeeze section 3 , rear part).
Shot 4: Length 3 D, unheated, without openings, with a conveying screw (second squeezing section 3 ', front part).
Shot 5: Length 3 D, unheated, with drainage opening at the top, which is provided with a degassing dome, retaining screw of the associated water drainage and pressure control valve (second squeezing section 3 ', middle part).
Shot 6: length 3 D, unheated, without openings, contains damming elements (second squeeze section 3 ', rear part).
Shot 7: Length 3 D, heated to 240 ° C, without openings, with a conveying screw (section 4 , in which the melt of the thermoplastic polymer B is fed, front part).
Shot 8: Length 3 D, heated to 240 ° C., with a side opening through which the polymer melt is introduced by means of a pipeline via a melt pump (section 4 , in which the melt of the thermoplastic polymer B is fed, rear part) and a screw section, which contains kneading blocks (first plasticizing section 5 ).
Shot 9: length 3 D, heated to 240 ° C, without openings, with a screw section containing kneading blocks (second plasticizing section 5 ').
Shot 10: Length 3 D, heated to 240 ° C., with a degassing opening at the top, provided with a retaining screw, and a screw conveyor, is operated under normal pressure (first degassing section 6 ).
Shot 11: length 3 D, heated to 240 ° C, without openings, with screw conveyor (second degassing section 6 ', front part).
Shot 12: Length 3 D, heated to 240 ° C, with degassing opening and screw conveyor above, is operated under normal pressure (second degassing section 6 ', rear part).
Shot 13: Length 3 D, heated to 240 ° C, without openings and with screw conveyor (discharge zone 7 , front part).
Finishing: Nozzle bar with cylindrical bores (discharge zone 7 , rear part).

The screw diameter is D = 53 mm and the screw is executed in three courses. "Snail" denotes the double snail, both snails.

b) polymer components used

The following graft rubbers were used as the elastomer component A. used:

A-1: Graft rubber type polybutadiene (core) / styrene-acrylonitrile (Bowl).

Butadiene was polymerized in emulsion, the latex obtained agglomerated, being a latex with a medium particle size d₅₀ of 238 nm, and then with a Mixture of styrene and acrylonitrile graft polymerized. Closeness res is DE-AS 24 27 960, column 6, line 17 to column 7, line 27, can be seen, but the precipitated graft polymer first decanted (not aspirated) and then using a power dryer to a residual water content was partially dewatered by 19% by weight.

A-2: Graft rubber type polybutyl acrylate (core) / styrene-acrylic nitrile (shell)

n-Butyl acrylate was treated with dihydrodicyclopentadienyl acrylate Polymerized in emulsion and the latex obtained, whose average particle size was d₅₀ 230 nm, with a Styrene-acrylonitrile mixture graft-polymerized. In detail was according to the in DE-AS 12 60 135, column 4, line 65 to 5, line 18, specified procedure, whereby the precipitated graft partially dried in an air stream has been. The residual water content was 28% by weight.  

A copolymer of 65 was used as the thermoplastic polymer B. % By weight of styrene and 35% by weight of acrylonitrile by the process of continuous solution polymerization, as in Kunststoff-Handbuch, ed. R. Vieweg and G. Daumiller, Vol. V "Poly styrene ", Carl Hanser Verlag, Munich 1969, pages 122 to 124, is described. Two polymers B-1 and B-2 with ver different degrees of polymerization. The viscosity number VZ (determined according to DIN 53 726 at 25 ° C, 0.5% by weight in dimethyl formamide) was 60 ml / g for the polymer B-1 and 90 ml / g for the Polymers B-2.

The SAN copolymer was fed to the extruder as a melt.

Components A-1 and B are used to produce molding compositions which are general are known as ABS (acrylonitrile / butadiene / styrene). The from the Components A-2 and B are products obtained as ASA molding compounds (Acrylonitrile / styrene / acrylic ester) common.

c) measurements

One of the graft rubbers A and one of the polymers B were the Extruder fed. The water discharge and the Rubber discharge in the first and second squeeze zones as well the strand moisture of the emerging end product. These measurements were carried out gravimetrically.

Furthermore, the temperature of the in the squeeze zones was off water measured in the usual way. The steam out The amount of water entered was determined by subtracting the initial residual water content and the sum of the leaked river water.

From the discharges of water, steam and rubber in kg / h Percentages calculated. The% values given are% by weight and for water and steam refer to the water content of the Extruder fed rubber (line marked with *), the was set equal to 100, and for rubber on the throughput of the wet rubber (line marked with **), which is 100 was set. The strand moisture is on the end product obtained based.  

table

The examples show that 6 to 59 wt .-% of the initially in part dewatered rubber contained residual water already in the first Squeeze section and 14 to 53 wt .-% in the second squeeze bar cut as liquid water. Only 27 to 41% by weight, i.e. the smaller part of the residual water, is in the Degassing sections discharged as steam.

The rubber discharge is moist with a maximum of 3% by weight of the amount Rubber in the first and maximum 1% by weight in the second squeeze section low.

Claims (16)

1. A process for the preparation of impact-modified thermoplastic by mechanical dewatering of a water-moist, up to 50 wt .-% residual water-containing elastomer component A and mixing the dewatered elastomer component A 'thus obtained with a thermoplastic polymer B in a screw machine, characterized in that the elastomer component A is fed to a twin-screw extruder with co-rotating, three-flight screws in each case, essentially in the conveying direction

• a metering section into which the elastomer component A is fed to the extruder by means of a metering device,
• at least one squeezing section serving for dewatering, which contains at least one damming element and at least one associated drainage opening,
• at least one section in which the thermoplastic polymer B is introduced as a melt into the extruder,
• at least one section provided with mixing, kneading and / or other plasticizing elements,
• at least one degassing section provided with at least one degassing opening, in which the remaining water is removed as steam, and
• - a discharge zone

is built up, and that from the drainage openings escaping water partially or completely in liquid Phase is present. 2. The method according to claim 1, characterized in that the Drainage openings, each with a retaining screw are provided. 3. The method according to claim 1 and 2, characterized in that the discharge zone is closed by a nozzle head.   4. The method according to claim 1 to 3, characterized in that the extruder is heated in the discharge zone. 5. The method according to claim 1 to 4, characterized in that the extruder between the last squeezing section and the Section in which the melt of the thermoplastic polymer Ren B is supplied, at least one with mixing, Kneading and / or other plasticizing elements provided Section. 6. The method according to claim 1 to 5, characterized in that the extruder between the last squeezing section and the first degassing section at least one supply opening for the melt of the thermoplastic polymer B, and mind at least one following and given this feed opening if at least one preceding this feed opening Mixing section. 7. The method according to claim 1 to 6, characterized in that in at least one of the squeeze sections of the extruder at least one associated drainage opening under About pressure is operated. 8. The method according to claim 1 to 7, characterized in that the extruder is driven at a screw speed of 100 to 350 min ^-1 and average shear rates of 180 to 220 s ^-1 be. 9. The method according to claim 1 to 8, characterized in that as elastomer component A with at least one graft rubber a residual water content of up to 50% by weight is used. 10. The method according to claim 1 to 9, characterized in that as an elastomer component A built up in two or more stages ter graft rubber, containing a basic stage from a or more of the monomers butadiene, isoprene, styrene, alkyl styrene, alkyl acrylate, alkyl methacrylate and small amounts other, also crosslinking monomer and a graft Styrene, alkylstyrene, acrylonitrile, methyl methacrylate or Mixtures of these monomers, is used and as thermo plastic polymer B a styrene-acrylonitrile copolymer, Polystyrene, polymethyl methacrylate, polyvinyl chloride or Mixtures of these polymers is used. 11. The method according to claim 1 to 10, characterized in that as elastomer component A a graft rubber based on Polybutadiene and / or polyalkyl acrylate as a basic step and  a copolymer of styrene and acrylonitrile as a graft stage, and as thermoplastic polymer B a styrene-acrylonitrile Copolymer is used. 12. The method according to claim 1 to 11, characterized in that as an elastomer component A built up in two or more stages ter graft rubber is used, which consists essentially of Polyalkyl acrylate and a copolymer of styrene and acrylic nitrile exists, and as a thermoplastic polymer B. Styrene-acrylonitrile copolymer is used. 13. The method according to claim 1 to 12, characterized in that the graft rubber has a diameter of 0.05 to 20 µm. 14. Impact-modified thermoplastic molding compositions obtained Lich by the method according to claims 1 to 13. 15. Use of molding compositions according to claims 1 to 14 for Manufacture of films, fibers and moldings.