EP0032142A1 - Process and device for the continuous production of polyurethane - Google Patents

Abstract

The process must allow polyaddition and continuous manufacture of polymethanes with consecutive granulation, which is suitable for machining on extruders, presses and extruders. This is obtained by injecting into the housing of a worm machine (16), at selected points (25), with metering pumps (17), of the various constituents (6, 7, 8) beforehand. heat. The worm machine (16) has a single axis and serves as a cascade reactor. Its construction is special: the threads of the worm are interrupted and the rotary shaft simultaneously performs a back-and-forth movement, so that pegs (25, 25) or teeth (27) arranged at the inside the housing of the worm can penetrate between the fins of the screw, through the gaps, to divide, knead and intensively mix the material transported. At the outlet of the worm machine (16), the polymerisat enters a short transfer screw (19) then exits through a nozzle with several holes (21) where it is cut to form the aggregate.

Description

 Process and device for the continuous production of polyurethanes.

The present invention relates to a method and a device according to the preceding claims. This is intended to avoid an untargeted crosslinking of the individual components during the addition polymerization, as a result of which the material properties would be adversely affected and incorrectly polymerized, jelly particles could also occur. Recipes, types of manufacture and use of polyurethanes are known from publications, for example from the plastics handbook. Volume VII, Vieweg-Höchtlen, Carl-Hanser Verlag. However, these ^• deal primarily with batch production using the casting process or on mixing rolling mills.

The possibility of continuously producing a polyurethane on screw machines has already been described in FR PS 956.605 and 961.756. Care was taken to ensure that the polymer which had not yet reacted completely was discharged in the liquid state before it reached the viscous-plastic state. However, the properties of the products produced did not reach the desired high values that can be achieved with the casting method. The experiments were unsatisfactory, the setting of the desired molecular weight was extremely difficult, and the molecular weight distribution was not sufficiently uniform. In addition, there were always jelly particles in the ejected melt, which are also referred to as nodules. It was concluded that it was not possible to adequately adapt a single-screw machine to the difficult reaction conditions of the various recipes and that only multi-screw extruders were suitable for the production of polyurethane; this goes under ^"alia from DE OS 24 47 368 25 49 372 26 08 280 and 26 10 980 forth. These all describe processes in which one seeks to prevent back mixing effect as possible.

- TJTC * _

O PI ^~ The investigation of the causes of the results, which are not entirely satisfactory, leads to the realization that the temperature and the point in time at which the components are polyadducted must be adapted precisely to the formulation and the process conditions in order to obtain polyurethanes with the desired properties. With continuous production, you also have to be careful to keep the reaction time short. If, for example, a short-chain diol is added as a so-called chain extender to the reaction between the long-chain bi-functional polyol and isocyanate, considerable difficulties can arise because the chain extender, preferably an diol, for example 1,4-butanediol, reacts on the one hand preferred due to its greater reactivity with the diisocyanates and, on the other hand, quickly separated from the polyols at the reaction temperatures. The distribution of the soft and hard segments in the chains is not carried out in the desired manner, and in extreme cases this can even lead to the formation of linear non-elastic polyurethanes if large amounts of the diisocyanate are consumed in the reaction with butanediol alone.

Small fluctuations in the proportion of the components available for the overall reaction can result in large fluctuations in the molecular weight of the polyaddition products; their continuous production is therefore not easy.

The inventive method and the device for this have the features listed in the characterizing part of claims 1 and 2. The object of the invention was to overcome the difficulties and disadvantages described above and describes a successful process in which the individual reaction components are separated into the screw housing of a single-shaft mixing and kneading machine, as described, for example, in DE PS 20 56 611 has been described, injected. f OMPI - 3 -

This mixing and kneading machine has an intensive mixing effect, both in the axial and in the radial direction, with clear backmixing between the individual kneading stages, which represent a progressive reactor cascade. This mixing effect is caused by the interaction of the individual worm wings and the knuckle teeth.

The reaction progresses gradually in individual sections of the snail shell with a smooth transition. The individual reaction components can be adjusted individually or partially with reaction adaptation. premixed or even pre-reacted injected. In a known manner, fillers, extenders, colorants and auxiliaries can be added and kneaded homogeneously during or after the reaction. The melt is preferably discharged through a thread nozzle into a cooling bath and then granulated. However, it is also possible to granulate individual recipes directly by hot cutting on a multi-hole nozzle plate and collect them in a coolant flow. Water can be used as the coolant, which could react crosslinking with the still hot polymer, but the contact time in the cooling bath is usually sufficiently short so that the water evaporates immediately from the surface of the polymer. It is of course also possible to use substances which are known to not react with the polymer.

The method is described below using an example and illustrated on the accompanying drawings, as follows:

1 shows a system for carrying out the method in a schematic representation,

Fig. 2 shows three different kneading chicanes, which in the

Inner wall of the housing of the mixing and kneading machine can be used / ÜRE-AT? _"

OMPI Fig. 3 shows the mixing and kneading machine in side view

Fig. 4 is a front view of the flanged Trans ferschnecke.

The shaft of the mixing and kneading machine 16 is driven by the motor 1 by means of V-belts 15 and the gear 14. The housing of the machine 16 is equipped with kneading chicanes over its entire length without an inlet connection. Kneading teeth 27 can be used, which are secured against rotation with the pin 28 in the housing wall, or kneading bolts 25, 26. In the selected example, the machine is equipped with 126 bolts 26 and three bolts 25; the latter are pierced and are used to inject the reaction components. The bolts 25 can be used in any A number and at optimally chosen points instead of the bolts 26. The individual bolts form a cascade of 129 intermeshing processing chambers in the known To interact with the rotating and simultaneously reciprocating screw blades. In these, the product is mixed intensively, kneaded and divided by the screw wing edge. A smaller part is pushed back into the previous chamber, the larger part is pushed into the next subsequent chamber. The edges of the screw blades brush the inside wall of the housing and past the bolt, which in turn wipes the screw blades, so that the process is self-cleaning

Depending on the recipe, the reactants, an isocyanate 6, a polyol 7, which can be an unbranched or slightly branched polyester mixture, and a so-called chain extender are preheated in the boilers 9 provided with a heating jacket. The individual components are pumped by means of metering pumps 17 through heated pipelines 18 to the mixing and kneading machine 16 and injected through the bolts 25 into the kneading chambers.

OMPI The kneader housing has a length of 12 L / D from the first injection point. The average residence time of the components when passing through the 129 kneading cascades is 3-4 minutes. Due to the inclination of the screw blades, the excellent longitudinal and transverse mixing effect with partial recirculation is overlaid by a dominant plug flow in the exit direction, which means that the residence time can be shortened by increasing the speed. Kneader housing and shaft can be heated or cooled, which enables the temperature of the strongly exothermic reaction to be controlled. The mixture of the isocyanate with the polyol begins at 1 after one L / D length and is continued until close to 3 at three L / D lengths; the reaction already begins.

At 3, the chain extender is now added and takes part in the reaction, which is already quite advanced shortly after 5 at five L / D. Now the material is processed over a further seven L / D lengths in order to mature the reaction at a temperature. The resulting highly viscous melt is then ejected into a short transfer screw 19 with drive 20. The screw conveyor 19 builds up a uniform delivery pressure in order to push the melt through a right-angled thread nozzle 21 into a water bath 22. The threads drawn through the water bath are then cut into a granulator 23.

In some formulations, degassing the melt can be advantageous. For this purpose, a degassing nozzle 24 is provided on the kneader housing, which is closed by an insert when not in use.

Example 1 :

In a test reactor with D = 46 mm and 11 L / D length, a premix of polyol plus glycol and catalyst was injected into the beginning of the screw reactor. The premix was melted by heating to approx. 70 ° C until it only

OMPI still had a medium viscosity. In the case of 2 L / D, the liquid di- isoc.yanate was injected through a kneading pin, the ratio between the premix and the diisocyanate was kept at approx. 2.4: 1. The worm shaft and the three separately heatable housing zones were heated to 178 ° C. After the onset of the reaction, the product temperature rose briefly to 182 ° C. and then decreased again. The screw speed in the reaction kneader was 85 rpm and was tempered to 70 ° C., so that the viscous product could be knocked off hot immediately after leaving the multi-hole nozzle plate and quickly cooled in a conveying air stream. The result was a polyurethane with good thermoplastic behavior and in regular granular form. Small traces of catalyst solvent vapors were sucked off through the degassing nozzle at 9 L / D. The average residence time in the reactor 1 a at 3 minutes.

Example 2: •

In the same device used for Example 1, a polyurethane was continuously prepared from three individual metered components. For this purpose, however, the drilled kneading pins were inserted into the reactor housing as follows in accordance with the recipe. One at the beginning at zero D, 1 D and 4 D. A long-chain polyol mixture with a relative molecular weight of about 16O0 to 50 ° C was premelted and injected into the reactor at zero D. An injection of diisocyanate followed at 1 D and 1,4 butanediol as a chain extender at 4 D. The three zones of the reactor housing were tempered at 120 ° C., then 100 ° C. and 60 ° C., the screw shaft at 100 ° C. The production temperature jumped to 120 ° C and then at 4 D to 140 ° C, before slowly falling again. The screw speed was kept at 40 rpm and 4.2 kg / h of product was produced.

f OM Example 3;

In the kneading reactor of a production plant with a diameter of 100 mm and a length of 12 l / d, a mixture of a hydroxyl group-containing, only weakly branched polyester plus 1,4 butanediol, preheated to 95 ° C., is injected at zero D. At 3 D, isocyanate is injected. The worm shaft and housing zones are tempered from 175 ° C to 205 ° C. The temperature of the reaction product rises to 195 ° C.

The method disclosed above offers numerous advantages; For example, the installation of pierced kneading pins at freely selected locations, which can be found on the circumference or length of the reactor housing, enables a very good adaptation to the known recipes. This also makes it possible to shorten the length of the reaction zones. The large number of successive reactor stages in a cascade brings about thorough mixing and advantageous homogenization of the reaction. The speed and the shear rate in the kneading reactor can be selected so that the reaction product is not overheated and thermally damaged. The worm shaft consists of a shaft core with slid-on screw wing bushes, which are interchangeable. The screw wing geometry can _. be selected so that the speed can be regulated independently of the throughput, and the reactor remains filled. The reaction products in granular form have the same excellent properties as could previously only be achieved using the pouring method; they are free of jellyfish or nodules. The reactor can also be used at high temperatures without modification.

Claims

PATENT CLAIMS 1. Continuous process for the production of polyurethanes by polyaddition and shaping into regular pieces which are suitable for further processing, characterized in that the components, individually or partially premixed, are fed directly into a closed reaction cascade in locally separated locations, in which si kneaded and mixed in the case of partial remixing and, as the conveyance progresses, linger until the ration has matured, after which the polyurethane formed is ejected into a screw conveyor which pushes it through a multi-hole nozzle plate, after which the product is cooled and chopped. 2. Device for carrying out the method according to claim 1, characterized in that it uses a kneading and mixing device with a reciprocating shaft as a closed reaction cascade, which carries screw blades, which with the inner wall of the housing of the mixing ^' and kneading machines used kneading chicanes work together in such a way that each one of them, with the associated screw blades, represents a reactor stage in which mixing, kneading and partial backmixing is carried out, individual kneading chicanes being pierced and serving to supply the reaction components, and the polymer is ejected into a screw conveyor, conveyed through it and pushed through a multi-hole nozzle plate, after which the strands thus shaped are fitted with a cutting device. f O