CH649737A5 - Microparticles made of expanded polystyrenes or polyolefins and process for the production thereof - Google Patents

Description

The invention relates to microparticles as such or in the form of their aqueous slurry of expanded thermoplastic polymer which is not brittle in its expanded state, selected from polymers of optionally substituted styrene and polyolefins from the group consisting of polyethylene, polypropylene, polybutene and polymethylpentene, and copolymers or mixtures the polymeric styrene or olefin; it also relates to processes for producing these microparticles from particles of the polymers mentioned.

The microparticles according to the invention have a length of 40 to 325 micrometers, a width of 20 to 325 micrometers, are substantially or completely free of intact cells, differ from one another in their shape and have a density of 85 to 100% of the density of the unexpanded one Polymers.

When viewed, for example, at a magnification of 161 times in transmitted light (see FIG. 1), the microparticles appear as tufts of randomly arranged fibers; at 360x and 380x magnification in the scanner electron microscope (abbreviated SEM, see Figs. 4 and 13), the microparticles resemble strongly irregularly shaped, separate sheets of writing paper, each of which has been roughly crumpled up by hand and then released again and because of it Elasticity tried to resume its original shape as far as possible.

Further SEM images at other magnifications, for example at a magnification of 1800 times in FIG. 3 of a part of the zone shown in FIG. 4, show formations that appear as exploded and deformed outlines of torn boundaries that have a honeycomb-like arrangement of hexagonal lines before being torn apart and formed pentagonal cross sections of cells; at a magnification of 4,000 times (Fig. 2) they appear as randomly bent and partially overlapping, not completely open rose petals. Other SEM images with magnifications of 500 to 5000 times show the microparticles as small coral formations (as at least in FIGS. 7 to 9), with a wave-like surface (at 100 times magnification in FIG. 10) and as a somewhat curled fluted formation (at 10 11x magnification in FIGS. 11 and 14 and at 20x magnification in FIGS. 12 and 15).

The term "styrene polymer" includes not only polystyrene itself, but also thermoplastic polymers of all polymerizable substituted styrenes as well as copolymers of styrene with one or more compatible polymerizable substances such as e.g. the nuclear alkylated or halogenated styrenes such as the ring methylated or chlorinated styrenes, or else alpha-methylstyrene, or with beta-unsaturated esters, ethers, amides or nitriles of acrylic acids and their homologues alkylated in the alpha position, with vinyl esters of aliphatic and aromatic carboxylic acids , N-vinyl compounds of N-vinylcar-bazole, N-vinylimidazole or N-vinylpyrrolidone.

Such thermoplastic copolymers of styrene should usually contain at least about 50% by weight of styrene, the styrene may be the predominant component, or

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the styrene should be at least as prevalent as any other terpolymer present in larger quantities. The styrene copolymers also include all of the various impact resistant polystyrenes made from a larger proportion of styrene and a smaller proportion of styrene-butadiene rubber (usually called SBR, and sometimes referred to as Buna-S) e.g. one obtained by emulsion polymerization of about 75 parts of butadiene and about 25 parts of styrene. Furthermore, the styrene polymers also include so-called styrene alloys (i.e. pressure or melt mixtures) of polystyrene with other compatible polymers, which were usually produced on the basis of ethylenically unsaturated monomers.

The term “polyethylene” generally refers to high molecular weight products (at least 6000) and by definition includes low density polyethylene (specific gravity below 0.92), high density polyethylene (specific gravity above 0.94, usually 0.941 to 0.965) , and medium density polyethylene (a blend of high density polyethylene with low density polyethylene), and so-called impregnable polyethylene (ie an extruded melt blend of 10% polystyrene polyethylene, also referred to as a polyethylene polystyrene alloy); all of these polyethylenes are available as flakes or cubes similar to the polystyrene pellets.

The term "plastic particles" encompasses all discrete free-flowing forms of any of the styrene polymers or the polyolefins mentioned, e.g. the different sizes of granules produced by cutting the extruded polymers to small lengths, which are usually referred to as pellets or crystals (e.g. in the case of styrene polymer) or pellets or cubes in a polyethylene polystyrene alloy, the different sizes of styrene polymer granules which can be obtained by suspension polymerization or otherwise, for example by casting, receives the particles obtained when comminuting these different polymer forms, and the so-called regrind, the coarsely ground cast polymer or waste from these polymers (in different sizes, for example 3.175 mm thick, 6.35 mm wide, and 9.525 mm length), and all other manifestations of small sizes of these polymers.

Expandable polystyrene polymer particles can be produced by known methods, for example according to US Pat. No. 2,983,692. Expandable polyethylene-polystyrene mixtures can be obtained in the same way.

Expanded styrene polymer particles can also be obtained from the expandable polystyrene by known methods. One method for producing expanded styrene polymer particles is heating with air or steam according to US Pat. No. 2,983,692 (column 4, lines 65-69) to a temperature above the softening point of the styrene polymer, as also in US Pat. No. 3,001 954 (column 3, lines 20-23). In this context, US Pat. No. 3,259,594 (column 2, lines 24-27) is also mentioned. Expanded particles of polyethylene polystyrene mixture can be produced in the same way.

Expanded particles made of polyethylene, polypropylene, polybutene or polymethylpentene can be prepared by known methods by adding a chemical blowing agent (a so-called pneumatogen, usually a complex organic nitrogen-containing compound, which is released at the extrusion temperature to the extrusion temperature) before extruding the specific polyolefin decomposed by nitrogen) and adjusts the extrusion temperature so that the pneumatogen decomposes when the polyolefin

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trusions nozzles, as briefly described in Plastics Extrusion Technology, by Allan L. Griff, Reinhold Publishing Cor., New York, (1968), on page 221, and then shreds or otherwise shreds the expanded polyolefin into particles.

Various physical properties of the microparticles according to the invention can be seen from the photomicrographs of the drawing, which represent dry microparticles, polystyrene microparticles being shown in FIGS. 1 to 9, 14 and 15 and low density polyethylene microparticles in FIGS. 10 to 13 . In the drawing, FIG. 1 is a microphotograph with a 161x magnification in transmitted light; 2 shows an SEM microphotograph at a magnification of 4000 times; FIG. 3 shows an SEM microphotograph with a 1800x magnification of the lower left quarter of the region shown in FIG. 4; 4 shows an SEM microphotograph with a 360 magnification; 5 shows a microphotograph with a 100x magnification; FIG. 6 shows a SEM microphotograph at a magnification of 500 times, which shows the zone in the central region of FIG. 5; FIG. 7 shows an SEM microphotograph with a magnification of 1,000 times in the region shown in FIG. 6; FIG. 8 shows a SEM microphotograph in which the protruding zone is magnified 2000 times in the right section of FIG. 7; FIG. FIG. 9 shows an SEM microphotograph with a magnification of 5,000 times the zone in the lower right quarter of FIG. 8; Fig. 10 is a SEM microphotograph of polyethylene microparticles at 100X magnification, showing the zone showing the lower left quarter of the upper right quarter of Fig. 13; 11 shows an SEM microphotograph at a magnification of 10 ×, which shows the fault zone which can be seen approximately in the middle of FIG. 10; FIG. 12 is a SEM microphotograph at 20,000 times magnification, which shows the fault zone which can be seen at a lower magnification approximately in the middle of FIG. 11; 13 is a SEM microphotograph of the polyethylene microparticles shown in FIGS. 10 to 12, magnified 380 times; 14 shows an SEM microphotograph of polystyrene microparticles at a magnification of 10,000; FIG. 15 is a SEM microphotograph at 20,000 magnifications, showing part of the fault zone shown in FIG. 14; 16 is a schematic representation of a system for removing the water retained by the microparticles according to the invention, the microparticles being obtained from the expanded plastic particles, as will be described in more detail according to Example 2 below, and the comminution device in the form of an aqueous slurry leave.

The process for producing the microparticles according to the invention is characterized in that coarse particles of expanded, thermoplastic polymer of the type defined in claim 1 are subjected to shear forces or impact forces in water such that microparticles are broken off and torn off several times from each particle of the starting polymer or are sheared off and the water supply is matched to the supply of the polymer particles in such a way that no temperature is reached during comminution at which the properties of the polymer with regard to the separation of microparticles are impaired and that an aqueous slurry of the microparticles defined in claim 1 is obtained , and that a comminution device is used to carry out the process, into which coarse polymer particles and water are fed and in which the mixture of polymer particles and water is moved several times on a circular path, repeatedly striking surfaces on said particles meet, which are arranged at a distance and rotate at 4700 to 8000 min "1 around the axis of the circular path and said particles against corner-shaped boundary edges of a plurality of circular openings with a diameter of 0.102 to 3.175 mm and / or practically rectangular openings with a Throw a width of 0.254 to 3.175 and a length of 3.81 to 12.7 mm, which are arranged in a sieve-like manner in a curved surface radially to the striking surfaces so that contact between the boundary edges of the openings and the striking surfaces is not possible.

The production of these microparticles from a styrene polymer or from one of the polyolefins mentioned, and thus also the process according to the invention, can be carried out in such a way that the expanded plastic particles from the plastics mentioned are comminuted in a comminution machine. Such a machine is manufactured, for example, by the Fitzpatrick Company, 832 Industriai Drive, Elmhurst, Illinois 60126, USA in accordance with its Bulletin No. 152, copyright 1968, where fixed knives (identified by code DS-225) are used instead of knives or other comminution elements ) are rotatably mounted in the shredding chamber model DAS06 (both components are shown on page 5 of this bulletin). The comminution chamber is covered in a liquid-tight manner, for example by a cover according to the code M44D6 or MA44D6 (upper half of page 3 of bulletin 152).

The comminution chamber according to the model DAS06 is rectangular in horizontal cross-section and has two mutually opposite parallel vertical walls, which are connected at each of their opposite ends by a vertical curved wall, the convex side of which is directed outwards and two curved walls are provided that face each other.

On a working shaft with free outer ends 16 mutually identical strip-like shredding arms are separately removably fixed, the shredding arms being arranged closely adjacent to one another, each gripping the working shaft with their feet and fastened there. The shredding arms extend radially from the working shaft (for example, the distance from the working shaft axis to the outer end of each arm is 127 mm), the first of a group of four successive shredding arms extending horizontally towards a curved wall, the second vertically above, the third extends horizontally towards the other curved wall and the fourth extends vertically downwards.

Each comminution arm has a rectangular cross section in a plane running through the entire length of the axis of the working shaft and through this arm or through all the arms offset by 180 ° to this arm. The outer end face of each shredding arm is at right angles on its two broader side faces (25.4 mm wide) and on its narrow face (width 9.525 mm), which leads in the direction of rotation. This narrow striking surface is still at right angles to the two broad sides of the striking arm, which run parallel to one another over a large part of their width, but are inclined towards one another in the last, trailing third, the trailing end of the shredding arm being designed as a knife-edge.

The free ends of the working shaft each extend through one of the two parallel vertical walls, with stuffing boxes being provided, and through a bearing which is carried by a pin connected to the machine foundation and is located outside the vertical walls. A drive pulley is also arranged outside the bearing journal at each end of the working shaft.

The bottom of the shredding chamber is an interchangeable perforated plate that is plate-shaped and convex downwards

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is curved and has an inner radius (measured from the axis of the working shaft), which corresponds to the length of a shredding arm plus 0.67 mm as a gap. The outside dimensions of the approximately rectangular perforated plate are selected so that the perforated plate can be attached to the bottom edges of the four walls of the comminution chamber in a liquid-tight and removable manner.

The perforated plate has mutually offset rows of, for example, circular openings, the diameter of which can be from 0.102 to approximately 3.175 mm, and which are arranged closely next to one another, but there is sufficient intermediate material that the perforated plate has sufficient stability during operation.

With the exception of the feed hopper arranged on one side for introducing the material to be treated, the rest of the cover of the shredding chamber is convexly curved upwards, the inner radius measured by the axis of the working shaft again being sufficient for one between the rotating shredding arms and the inward-facing surfaces A plurality (for example three) of pre-breaking bars (approximately 6.35 mm wide and approximately 20.32 cm long) which extend 3.175 mm deep into the interior of the comminution chamber over their entire length and are spaced apart from one another parallel to the axis extend the working shaft, a space of 0.762 mm remains.

The selected drive pulley on the working shaft is connected to the drive pulley of a drive motor via drive belts and can be driven at approximately 4700 to approximately 8000 rpm, preferably from approximately 5000 to approximately 7500 rpm.

Different batches of the microparticles according to the invention made of plastic, which had been produced, for example, in the comminution machine described with a perforated plate with circular openings, contain varying amounts of fibrous particles in small amounts of approximately up to 20% by weight, which are smaller than the particle size specified above , for example, have a width down to 15 or 10 microns. In general, the presence of these amounts of particles of smaller grain size does not have any disadvantages with regard to the particular use to which the microparticles are to be put.

If necessary, however, these smaller grain sizes can be removed by filtering out with conventional sieves or other suitable means, for example using the high-performance centrifugal sifter from Kason Corporation in Newark, N.J., USA. The microparticles are introduced uniformly via a screw conveyor into a helical paddle stirrer, which rotates in a horizontally arranged cylindrical viewing chamber, whereby the centrifugal force causes the movement of the microparticles against the sieve, which is arranged on its carrying basket so that the sieve can swing freely. accelerates. When the process according to the invention is carried out in practice, an increase in temperature of the divided batch of expanded plastic particles made of a styrene polymer or of a polyolefin can occur as a result of the working conditions. This fact can occur more clearly with some styrene polymers than with other polymers, so that with some of these polymers the temperature can reach a level at which even higher temperatures make the particles of styrene polymer no longer easily or satisfactorily by tearing off under the chosen working parameters - or shear forces form microparticles, but may show a tendency to stretch or in some other way the reaction of the treated material is changed so that the desired shear and tear effect

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the plastic particles used and the fragments already separated from them are adversely affected. This can e.g. this prevents more water with the plastic particles from being introduced into the separation chamber.

The amount of water introduced into the comminution chamber should be at least so high that the mixture of water and microparticles obtained becomes sufficiently flowable to flow through the openings in the perforated plate base of the comminution device. The weight of the water added should advantageously be about 55 to about 100 times the weight of the expanded microparticles produced, in particular if a styrene polymer is used.

Furthermore, it is advantageous to add a quantity of water to the expanded plastic particles made of a styrene polymer or of a polyolefin before they are introduced into the comminution chamber, which is sufficient to substantially completely wet the surface of these particles.

Furthermore, it is advantageous to carry out the method according to the invention in such a way that the plastic particles in the comminution zone alternately through the impact surfaces a) against corner-shaped edges of at least one pre-crushing or impact surface (at least one pre-breaker bar described above) which is arranged in the circumferential direction away from the opening is and in the radial direction, like the openings, lies outside the area of the striking surfaces, and b) are thrown against the openings.

Furthermore, it is advantageous if the striking arms are both offset from one another in the axial direction and angled toward one another in the radial direction.

The finished plastic microparticles emerging from the comminution device show the property of holding water up to 40 to 50 times their dry weight and, together with the retained water, forming a non-flowing plastic mass which is deformable and can roll, but does not become liquid. The water is not released from this mass by draining or ordinary filtering, but for this purpose the use of pressure or suction is necessary, the mass still containing a significant amount of water even after the use of these aids. For example, the application of fairly high pressure lowers the moisture content of the mass to only about 50% by weight.

For some uses, the styrene polymer or polyolefin microparticles can be used along with the amount of water held by them or with any lower amount of water that, after application of pressure and / or vacuum, to remove the desired proportion of the amount of water applied to them Way can be removed, remains.

In order to remove the remaining water when dry microparticles are desired, one possibility is to freeze the product after the partial removal of the water content by pressure and / or vacuum. Then the frozen microparticles are allowed to thaw or are heated to reach a temperature just above freezing or up to room temperature at which the water still held free then runs off. After the draining process has ended, the remaining water can be removed by squeezing and / or drawing off in vacuo, which is followed by final drying.

Another and more practical method for removing the water retained by the microparticles emerging from the comminution device is described below.

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ter described in more detail with reference to the device shown in Fig. 16 of the drawing.

In this method, in which lumps, cakes or mats of the microparticles are obtained with a dry grip from the highly water-containing slurry of microparticles in water which leaves the comminution device, a first permeable carrier becomes between the slurry of the microparticles and a vacuum source (for example, from wire mesh) and allowed to act through this support on the aqueous slurry under pressure to an extent that is at least sufficient to have a removably adhering layer or layer (practically usable thickness, for example about 3.2 mm) of on the support To provide microparticles with an intermittently reduced water content that is low enough that the layer maintains its continuity on this support, whereupon the free surface of the adherent layer of microparticles is brought into contact with a second permeable support so that the microparticle layer intervenes n is passed through both permeable carriers, then the free side of each permeable carrier is covered with a continuous layer of water-absorbent web material which has a greater water absorption capacity than that of the web made of microparticles; whereupon the five-layer structure obtained is then subjected to external pressure in order to enable the layers of water-absorbing web material to absorb the practically possible amount of water from the microparticle layer through the permeable carrier interposed thereafter, after which each layer of the water-absorbing web material is removed from the adjacent permeable carriers are separated and the permeable carriers are each separated from the intermediate layer of microparticles, which now has a reduced water content, whereupon this layer is ejected. A characteristic of this method is that this method can be carried out continuously, each permeable support and each water-absorbing web being endless, and a further process step is provided in which each individual web of water-absorbing material after the process step in which Pressure is applied, passed through a drying zone to remove absorbed water from these webs to an extent sufficient that these webs can in turn be used to withdraw water from the supplied microparticle mat beginning at the end of the vacuum application step.

Thus, since each permeable carrier is endless, the first carrier is returned to the starting slurry, from which it in turn receives an endless layer of microparticles deposited thereon under the action of negative pressure. At the same time, the second permeable support is returned to the end of the vacuum application zone, so that again the continuously formed layer of microparticles is passed between the two opposing permeable supports. Thereupon, in turn, each of the two endless water-absorbing webs is continuously brought into contact with the free surface of the permeable carrier assigned to it.

The pressure continuously applied to the five-day structure thus formed improves the continuous absorption of water from the microparticle layer by the endless, oppositely absorbing webs through the permeable supports. After the water-absorbing webs are carried away, each of these water-absorbing webs then being passed through a drying zone, and after the permeable supports are carried away, the continuous microparticle layer is continuously ejected from the drying device.

In Fig. 16, it can be seen that the microparticle slurry discharged from the grinder is placed in water in a slurry holding tank 10. At a distance from the bottom of the tank 10 and from its side surfaces, a cylindrical vacuum drum 11 is provided rotatably about a coaxial, horizontal shaft 12, the bearing of the shaft 12 outside the tank 10 by means of bearings, not shown, which are rotatably provided on supports, not shown , he follows. A first endless permeable carrier in the form of a filter web 13 made of wire mesh (with a mesh opening of, for example, 0.42 mm) is supported by free-running rollers 14 and 15 and is guided in the direction of arrow a down around the lower half of the vacuum drum 11, where that wire mesh 13 guided through the slurry absorbs a layer of microparticles with partially reduced water content from this slurry.

A second permeable carrier in the form of a further filter web 17 made of wire mesh (also with a 0.42 mm mesh opening is guided over rollers 18 and 19 and over the tensioning roller 20 and under the guide rollers 21 and 22 in the direction of arrow b, so that the the layer of microparticles adhering to the filter web 13 is guided between this web and the second filter web 17 in the manner of a sandwich.

Furthermore, an endless water-absorbing felt web 24 is guided over carrier rollers 25 and 26 in the direction of arrow c under the action of the tension roller 27 over the guide rollers 28 and 29. The section of the felt web 24 running between the guide rollers 28 and 29 covers the free surface of the filter network 13.

A second water-absorbing felt web 31 runs over the support rollers 32 and 33 in the direction of arrow d as well as over the free-running rollers 34 and 35 and over the tensioning roller 36, the felt web 31 in the section lying between the rollers 32 and 33 in contact with the free one Bottom of the filter network 17 is running. A five-layer structure is thus formed from the microparticle layer in this area, which is guided between the wire nets 13 and 17, these in turn being covered by the felt webs 24 and 31.

Between the two pairs of opposing free-running rollers 28 and 32 or 29 and 31, a pair of opposing pressure rollers 38 and 39 with a length of 56 cm is arranged, through which the five-layer structure is passed, and on this structure from the pressure rollers a total force of, for example, 4000 N, which corresponds to a linear pressure of 71.5 N / cm, is exerted.

After the felt webs 24 and 31 have been lifted off while the rollers 29 and 33 are rotating, the lower wire mesh 17 is first separated from the now three-layer structure when the free-running roller 19 rotates. The microparticle cake carried on the wire mesh 17, the solids content of which is now 84% by weight, is lifted from the wire mesh 17 by means of a separating knife 40 and falls into a receptacle 41. At the same time, the first, i.e. the upper filter net 13 is led away upwards around the free-running roller 42, any cake of microparticles adhering to this filter net being stripped off by an upper separating knife 43 and also falling into the container 41 for receiving the microparticle cake.

The system described above for reducing the water content is operated with a vacuum drum 11 which is 28 cm in diameter and 56 cm in length and rotates at 10 min −1, and from the comminution device

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11.41 / min of a slurry of microparticles from a styrene polymer in water with a solids content of 2% by weight, a moist, 3.175 mm thick layer of microparticles is obtained, and using the 71.5 N / cm pressure by the pressure rollers 38, 10.9 kg / h of a cake was obtained, which contained 84 wt .-% solid in the form of microparticles from a styrene polymer.

In the drying zones, which are not shown, the water-absorbing webs can be dried with hot air or in some other way, with the water-absorbing webs being passed between further pressure rollers for this purpose before drying for a correspondingly high water content in which a significant proportion of this water content can be squeezed out can be.

The system and apparatus described above for separating microparticles from water or from another liquid inert to them is not limited to the use described with respect to expanded polystyrene microparticles. The method and system can equally be applied to microparticles of other expanded styrene polymers as well as any polyolefins. Furthermore, the system is not limited to the dimensions or arrangements given above, as also described in the drawing, but can be modified with regard to a different production capacity, as it seems most practical, furthermore there is a variation in the arrangement of the different parts possible to take into account different circumstances regarding production capacity and spatial arrangement.

The system for withdrawing large amounts of water from the microparticles is also not limited to using a rotating vacuum drum to form a layer of microparticles with a high water content, which is then passed through pressure rollers 38, 39. It is thus possible to dispense with the slurry tank 10 and the vacuum drum 11 and its shaft, instead the rollers 18, 20 and 21 in FIG. 16 being shifted to the left in place of the tank 10, the filter network 17 being extended accordingly got to.

In this case, the largely liquid slurry originating from the comminution device is fed via a feed box (similar to the headbox through which the paper stock in the Fourdrinier machine reaches the circulating endless sieve), which is arranged somewhat to the right of the roller 18 above the filter network 17. brought to the filter network. The free water contained in the slurry of the microparticles flows down in the first section of the filter network 17 through this filter network. Before the filter network 17 is passed through the pressure rollers 38 and 39, it runs over a suction box (again as in the suction section of a Fourdrinier machine in papermaking), where a part of the water held by the microparticles is sucked down.

The roller 15 is shifted to the right so far that it is on the right above the roller 18. The filter net 13 is shortened, tensioned by a roller replacing the drum 11 and guided along the wire net 17 while it is being moved over the suction box. The layer of moist microparticles formed on the filter network 17 after passing through the roller 18 is held between the filter networks 13 and 17 and passed through the gap between the pressure rollers 38 and 39.

The water-absorbing webs 24 and 31 are advantageously made of cotton felt, but can also consist of any other suitable water-absorbing web material which has a greater affinity for water than the surface tension, which obviously holds the water to the microparticles.

The crushing plant is not limited to the embodiment described in detail above. For example, the number of shredding arms can be varied up to a number of 32 depending on the specific production conditions, and the shape of the housing can also be changed accordingly. A variation is also possible with regard to different parts of the shredding arms. The markings that are necessary for the actual shredding function should be retained, while design changes are possible in other areas of the shredding arms. Furthermore, the primary crusher bars are not limited, for example, in terms of their length or number, since both can be varied with regard to the specific production schedule, and in some cases the primary crusher bars can also be omitted.

The invention is subsequently described in more detail using a few non-limiting examples.

example 1

Microparticles made of pellets from expanded, extruded

Polystyrene.

4251 extruded polystyrene pellets (crystals) impregnated with a blowing agent, which had been expanded into substantially round pellets with a diameter of about 6.35 to about 12.7 mm and a bulk density of 12 g / 1, were in one above described crushing device, which was provided with a feeder with a length of 7.62 cm and a diameter of 10.16 cm and a curved perforated plate base with openings of 0.1016 mm in diameter. The rotor was set at a speed of 6000 min -1 and the feeder so that the particles of expanded polystyrene in an amount of 35.41 / 5 min, i.e. 4251 / h. The polystyrene particles introduced into the feeder were treated with enough water to substantially completely wet their outer surface. The wetted expanded polystyrene particles were now continuously introduced at the feed rate mentioned above, and at the same time injected into the comminution chamber through two injection nozzles with a diameter of 1.6 mm each at a feed rate of 7.571 / min.

The mixture of the obtained microparticles and water emerging from the perforated plate bottom of the comminution device was collected in open containers with bottom drains, with the free water settling on the bottom, and the microparticles made of polystyrene, 98 parts by weight per 2 parts by weight of polystyrene Hold water, float to the surface of free water due to the trapped air. After the free water had drained away, a plastic mass of microparticles made of expanded polystyrene remained in the water physically bound to these particles. This mass weighed 255.15 kg and contained 5.1 kg of microparticles, i.e. the bound amount of water was 250.05 kg.

27.24 kg of this plastic mass were then placed in a double tightly woven cotton sack and subjected to an external pressure until 92.711 water had been squeezed out. The remaining 4.08 kg mass, which contained 544 g microparticles of expanded polystyrene, were then dried on an open plate in a drying cabinet kept at 44 ° C.

The polystyrene microparticles produced according to Example 1 showed the following: Those for the production of the micro5

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expanded polystyrene particles used were made from polystyrene specially produced for this purpose,

no waste product with a density of 1.1. The microparticles had a density of 1.0, which is 90.9% of the density of the polystyrene crystals used before expanding to expanded polystyrene particles. This means that the density of the dry microparticles according to the invention is essentially the same as that of the base material used for producing the expanded plastic particles, from which the microparticles are then obtained by comminution.

Example 2

Microparticles made from expanded, impregnated polystyrene waste

Approximately 2.5 cm long pieces of impregnated polystyrene waste with a bulk density of 16 g / 1 were treated as in Example 1, but were fed to the comminution chamber in an amount of 28.321 / 6 min, with the rotor set to 6500 min -1, and in the same way gave a plastic mass similar to that obtained in Example 1, the color of which was a lighter gray pink than that of the impregnated waste used.

If the expanded polystyrene particles used as starting material according to Examples 1 and 2 are replaced by other amounts of particles of expanded polystyrene produced for this purpose or as a waste product, or by any expanded styrene-acrylic copolymer or by any other expanded styrene polymer or any applicable polyolefin described above If the steps described in the examples are replaced and the same or slightly different water components or different rotor speeds are repeated, the corresponding, relatively similar microparticles are obtained from the plastics used. The corresponding additional examples in this regard are to be regarded as explicitly stated; the abbreviated information is used to avoid extensive descriptions.

If the bottom perforated plate of the shredding device described above is replaced by a perforated plate with the same outer dimensions, but which shows rectangular openings with a length of 12.7 mm and a width of 0.254 mm in a herringbone arrangement, and with the shredding device modified in this way, Examples 1 and 2 is repeated, the expanded plastic particles of a styrene polymer or of a polyolefin used as the starting material give the same type of microparticles as the end product in the same way, these microparticles being essentially or 100% of a width of 5 to 15 micrometers and many different ones Have lengths up to about 325 microns and are substantially or completely free of intact cells.

A substantial proportion of the at least 98% by weight of water in the slurry of microparticles of styrene polymer or polyolefin in water emerging from the comminution device, such as is obtained if any example 1 or example 2 is carried out, can be removed to a substantial extent , whereby lumps, cakes or mats of the microparticles are obtained which have a dry feel and contain, for example, up to 84% by weight or more solids, for which purpose a water elimination method using a system schematically described in Fig. 16 is used.

From the type of comminution process and the appearance of the microparticles (as for example in FIGS. 1 to 5) it follows that the individual microparticles do not show any remarkable uniformity with regard to their shape.

The fact that the styrene polymers and polyolefins used as starting material, from polyethylene to polymethylpentene, from which expanded particles are first formed and then converted into microparticles, are thermoplastic materials, means that these materials can also be extruded.

The indication that the microparticles according to the invention have a dry grip despite a considerable water content (for example up to 80% by weight) means that when the microparticles are touched by hand, neither the fingers nor the balls of the hands become wet.

The microparticles according to the invention can be used in various ways, for example for filtering and improving the properties of flowable media, such as liquid and gaseous media. This is done, for example, by adding the selected microparticles from a styrene polymer or from a polyolefin to the liquid, the properties of which are to be improved, and then filtering off these microparticles, or by filtering the liquid to be improved through a bed of these microparticles. The microparticles according to the invention remove invisible dissolved or invisibly suspended organic substances from the liquid and usually no such substances are formed in the liquid even after a long period of standing.

For example, tap water from Matawan, New Jersey, USA, was filtered through Whatman No. 2 filter paper in an amount of 473.2 ml in a first pure 946.3 ml Mason vessel, which was then tightly sealed. 0.4 g of microparticles according to the invention, which had been produced from expanded plastic particles made of polystyrene, were wetted with about 20 ml of the same tap water and mixed with about 473.2 ml of this water and then mixed into a corresponding filter using another Whatman No. 2 filter paper filtered pure 946.33 ml Mason jar, which was then tightly closed. A week later, a slight yellow turbidity was found in the first vessel, while the water mixed with the microparticles was still completely clear in the second vessel. The yellow turbidity in the first vessel increased in quantity and density, after which it settled on the bottom of the vessel while the vessel was observed for three months. The water in the second vessel, which had been filtered through the polystyrene microparticles, was still completely clear after this observation period.

As examples of the use of the microparticles according to the invention for filtering and improving the properties of gases, these polymeric microparticles can also be used as a filling in air filters, for which purpose they are mixed with suitable fibers for papermaking and processed into webs or plates which can be used in air filter frames.

With microparticles made of polyethylene, comparable results can be achieved when filtering gases and liquids. Microparticles from other polyolefins also provide corresponding results.

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Claims (24)

649 737 PATENT CLAIMS 1. microparticles as such or in the form of their aqueous slurry of expanded, thermoplastic polymer which is not brittle in the expanded state, selected from polymers of optionally substituted styrene and polyolefins from the group consisting of polyethylene, polypropylene, polybutene and polymethylpentene or from copolymers or mixtures of the polymer Styrenes or olefins, with a length of the particles of 40 to 325 (xm and a width of 20 to 325 µm, essentially or completely free of intact cells, practically free of any uniformity of the shape of the individual particles and with a density between 85 % and 100% of the density of the underlying, unexpanded polymer. 2. Microparticles according to claim 1 made of a styrene polymer. 3. Microparticles according to claim 2 made of polystyrene. 4. Microparticles according to claim 3 made of waste polystyrene. 5. Microparticles according to claim 1 made of a polyolefin. 6. microparticles according to claim 5 made of a polyethylene. 7. Microparticles according to one of claims 1 to 6 made of a melt mixture of polyethylene with a content of about 10 wt .-% polystyrene. 8. Microparticles according to claim 5 made of polypropylene. 9. microparticles according to claim 5 made of a copolymer of polypropylene and 20 to 30 wt .-% polyethylene, based on the copolymer. 10. Microparticles according to claim 5 made of a polyolefin melt mixture of polypropylene and a copolymer of polyethylene with up to 30 wt .-% polyvinyl acetate, based on the copolymer, the polypropylene making up at least 50 wt .-% of the melt mixture. 11. microparticles in the form of their aqueous slurry according to any one of claims 1 to 10, which contains 1 to 2 wt .-% microparticles. 12. The microparticle of claim 11, wherein the slurry contains microparticles made from a styrene polymer. 13. The microparticle of claim 12, wherein the slurry contains polystyrene microparticles. 14. Microparticles according to one of claims 1 to 10 with a dry handle and a content of 16 to 100 wt .-% solid, the rest consisting of water. 15. Microparticles according to claim 14 made of a styrene polymer. 16. Microparticles according to claim 15 made of polystyrene. 17. A process for producing an aqueous slurry of microparticles according to claim 1, characterized in that coarse particles of expanded, thermoplastic polymer of the type defined in claim 1 are subjected to shear forces or impact forces in water such that each particle of the starting poly- Microparticles are repeatedly broken off, torn off or sheared off and the water supply is matched to the supply of the polymer particles in such a way that no size is reached during comminution, at which the properties of the polymer with regard to the separation of microparticles are impaired, and that an aqueous slurry of the Microparticles defined in claim 1, and that one uses a comminution device for carrying out the process, into which coarse polymer particles and water are fed and in which the mixture of polymer particles and water is moved several times on a circular path, repeatedly on said n particles hit striking surfaces which are arranged at a distance and rotate at 4700 to 8000 min ~ 1 around the axis of the circular path and the mentioned particles against corner-shaped boundary edges of a plurality of circular openings with a diameter of 0.102 to 3.175 mm and / or practically rectangular Throw openings with a width of 0.254 to 3.175 mm and a length of 3.81 to 12.7 mm, which are arranged in a sieve-like manner in a curved surface radially to the striking surfaces so that there is no contact between the boundary edges of the openings and the striking surfaces is possible. 18. The method according to claim 17, characterized in that the surfaces of the polymer particles are moistened with water before being introduced into the comminution device. 19. The method according to any one of claims 17 and 18, characterized in that the polymer particles in the crushing device by the striking surfaces alternately a) against corner-shaped edges of at least one preliminary breaking surface, which is circumferentially between the inlet and the openings at a distance from the openings and outside the face area is arranged and b) are thrown against the boundary edges of the openings. 20. The method according to claim 19, characterized in that the polymer particles are thrown against a plurality of elongated primary crushing surfaces which are arranged parallel to the axis of the circular path and about this axis at a distance from one another over the width of the size reduction zone. 21. The method according to any one of claims 17 to 20, characterized in that an aqueous slurry, which contains at least 1 wt .-% microparticles as a solid, is drawn off from the comminution device and the slurry is then vacuum filtered in order to reduce the solids content to at least 16 wt. -% increase. 22. The method according to any one of claims 17 to 21, characterized in that the microparticles are continuously drawn off from the comminution device as a slurry in water, the slurry is continuously applied to one side of a continuously moving endless belt made of non-absorbent, permeable material and so on a continuous, adhesion-adhering layer of partially dewatered microparticles is formed on this side, a negative pressure is applied to the other side of the endless belt, and water is sucked out of the microparticle layer through the endless belt and then the free surface of the microparticle layer is extracted with a second continuously moving endless belt non-absorbent, permeable material is covered, so that the microparticle layer between the two endless belts is covered with an endless web of absorbent material that has a higher absorbency for water than the surface tension g, which holds the water to the microparticles, and that the 51-layer structure thus obtained is then passed through a pressure roller pinch joint in such a way that further water from the microparticle layer gets into the absorbent endless layers, and a moist one after exiting the nip Product removed from the permeable continuous webs containing 50 to 90% by weight of microparticles. 23. The method according to claim 22, characterized in that the microparticle slurry is continuously fed to a liquid container, while suction is continuously carried out by the vacuum drum, so that a continuous layer of wet microparticles is formed on the outside of the endless belt, which is applied after leaving the liquid container the second permeable endless belt is brought in and transported in contact with the two endless belts between them. 24. The method according to any one of claims 22 and 23, characterized in that after removing the Mikro2 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 Particles from the space between the two endless belts water is removed from the absorbent endless webs before they are brought back into contact with the permeable endless belts to absorb water again.