Device for the granulation of a plastic molding compound which does not flow under gravity and the use of an extruder
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a device for the granulation of a plastic molding compound which does not flow under gravity, more particularly an enzyme concentrate suitable for detergents, comprising a granulating head which adjoins an extruder and which comprises a number of bore-like passages on its outlet side and a preliminary distributor in the form of a perforated plate arranged at a distance from the extruder screw and the bore-like passages on the extruder side. 
     Modern detergents contain enzyme granules, for example proteases, amylases, lipases. In the production of enzyme granules, it is important to obtain a dust-free product of homogeneous composition and uniform external appearance, including shape, color and general appearance. Since granules of the type in question must not disintegrate in the detergent powder, their particle sizes have to be comparable with the other granules. Accordingly, die plates having bore diameters of less than 0.8 mm have to be used where an extruder is employed for granulation. 
     Enzyme granules consist not only of the liquid enzyme concentrates, but also of fillers, zeolites, tripolyphosphates, starch, cellulose, methyl cellulose, carboxymethyl cellulose, waxes, water-soluble polymers, etc. 
     Another problem is the uniform distribution of the compound to be processed over the entire cross-section of the molding plates containing die plates. This problem is particularly serious when the cross-section of the molding plate, for example with 3,000 to 6,000 individual bores, is considerably larger than the cross-section of the outlet opening for the molding compound at the end of the extruder screw. Unless the molding compound to be processed is uniformly distributed over the entire cross-section of the moulding plate, the compound issues from the individual openings at different rates. Accordingly, the issuing strands are cut into granules of different length by the blade rotating in front of the moulding plate so that a uniform product cannot be obtained. 
     2. Discussion of Related Art 
     Although a device of the type mentioned at the beginning is known from DE-OS 25 57 166, only a few (about twenty at most) bore-like passages are provided in the known granulating head so that the above-mentioned problem of uniform distribution of the molding compound does not arise. In the known extruder, the molding compound is uniformly distributed for the simple reason that all the bores are arranged symetrically to one another and equidistantly from the central axis of the extruder. 
     Accordingly, the problem addressed by the present invention was to provide a granulating device of the type mentioned at the beginning which would enable the molding compound for processing to be uniformly distributed over the entire cross-section of the moulding plate even when the cross-section of the moulding plate was considerably larger than the cross-section of the outlet opening for the molding compound at the end of the extruder screw. 
     DESCRIPTION OF THE INVENTION 
     Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term &#34;about&#34;. 
     According to the invention, the solution to this problem is characterized in that, in a device of the type mentioned at the beginning, the preliminary distributor is preceded on the extruder side by a displacement cone and in that the bore-like passages are formed in a support plate and, at the front end of the support plate, each comprise a perforated disk of which the bores have an inlet-end zone of relatively large cross-section and an outlet-end zone of relatively small diameter, the transitional zone between these two zones being inclined at an angle of 55° to 65° relative to the longitudinal axis of the bores. 
     According to the invention, the ratio of length to diameter in the granules is the same over the entire cross-section section of the molding plate which is also referred to herein as the support plate. 
     In one particularly advantageous embodiment of the invention, the bore-like passages have substantially the same diameter as the perforated disks. Both here and in the following, the expressions &#34;substantially the same&#34; and &#34;substantially equal&#34; mean that the deviations are at most 10%. 
     In addition, uniform distribution of the molding compound is promoted in particular by a baffle plate which is arranged behind the displacement cone on the extruder side and of which the axial bore increases substantially from the diameter of the extruder screw to substantially the diameter of the preliminary distributor. This baffle plate provides the molding compound with a regular path via the displacement cone to the cross-sectional area of the preliminary distributor. 
     To avoid disturbances in the flow of the molding compound in the region of the displacement zone, the inner surfaces of the baffle plate all have rounded edges. 
     To ensure uniform flow of the moulding compound from the extruder screw between the baffle plate and the displacement cone, the distance between that surface of the displacement cone which faces the extruder and the opposite inner surface of the baffle plate is substantially constant. A more uniform flow also provides for more uniform distribution of the molding compound over the cross-section of the preliminary distributor facing the extruder. 
     To guarantee minimal differences between the pressures under which the molding compound is introduced into the bores of the preliminary distributor, the displacement cone is designed in such a way that the lengths of the paths of the molding compound to be granulated to the bores of the preliminary distributor which are situated nearest the longitudinal axis of the granulating head and to those situated furthest away are substantially the same. 
     In addition, it is favorable to a uniform feed pressure of the molding compound into the bores of the preliminary distributor if the distance between the outer cross-sectional area of the preliminary distributor on the extruder side and the opposite surface of the displacement cone is at least 3% of the diameter of the preliminary distributor. 
     The shape of the capillaries in the perforated disk is important to the production of uniform granules. To this end, it is proposed that the diameter of the outlet-end zone of the bores in the perforated disk should be between 0.5 and 1.0 mm. In another advantageous embodiment, the length of the bores in the perforated disk is between 1.5 and 2 times the diameter of the outlet-end zone. In another advantageous embodiment, the diameter of the inlet-end zone of the bores in the perforated disk is between 1.7 and 3 times the diameter of the outlet-end zone. 
     The invention also relates to the use of an extruder of the above-mentioned type for granulating enzyme concentrates for detergents. An extruder of the type in question is particularly suitable for such an application. In this case, it is further proposed that the enzyme concentrate should be forced through the granulating head under pressures of 80 to 200 bar and preferably under pressures of 110 to 150 bar. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One example of embodiment of the invention is described in detail in the following with reference to the accompanying drawings, wherein: 
     FIG. 1 is a longitudinal section through a granulating head of a device according to the invention. 
     FIG. 2 is a longitudinal section through a bore in the perforated disk according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-section through a granulating head according to the invention. The longitudinal axis of the granulating head is shown at (17). The molding compound enters the granulating head at (20), passes through the baffle plate (11), flows along that plate and the displacement cone (2) onto the rear cross-section (18) of the preliminary distributor (3). The molding compound is forced through the orifices of the preliminary distributor (3), the bores (16), into an empty space (21) between the preliminary distributor (3) and the support plate (1). This support plate (1) is referred to elsewhere as the molding plate. At its outlet-end front, it comprises a number of perforated disks (5) of which the bores (6) have the longitudinal section shown in FIG. 2. Arranged behind the support plate (1) is a rotating blade (not shown) which cuts the thin strands issuing into granules. 
     The support plate (1) comprises a plurality of bore-like passages (4) which are arranged in concentric circles around the longitudinal axis of the granulating head and at the outlet-end orifices of which the perforated disks (5) are arranged. The illustrated support plate contains 75 such bore-like passages (4), each of which is closed at its front end by perforated disks (5) each comprising 87 capillary-like bores (6). 
     The bores (6) shown in FIG. 2 have a narrow front outlet-end zone (8) and an inlet-end zone (7). The length data in FIG. 2 are in mm. The outlet-end zone (8) has a diameter of 0.7 mm while the inlet-end zone (7) has a diameter of 1.2 mm. The length of the outlet-end zone (8) is 1.4 mm while the length of the inlet-end zone (7) is 4.5 mm. In the transitional zone (9), the inclination of the wall relative to the longitudinal axis (10) is 60°. 
     When the molding compound coming from the extruder flows through the axial bore (12), it impinges on the displacement cone (2) and flows between that surface (15) of the displacement cone (2) which faces the extruder and the opposite inner surface (13) of the baffle plate (11) onto the cross-section (18) of the preliminary distributor (3) facing the extruder. This passage should neither narrow nor widen. To ensure uninterrupted flow, the inner surfaces (13) of the baffle plate (11) all have rounded edges (14). 
     At the outer cross-sectional area (18) of the preliminary distributor (3) facing the extruder, the molding compound then passes through the orifices (16) into the space (21) between the preliminary distributor (3) and the support plate (1). That surface of the displacement cone (2) which faces the outer cross-sectional area (18) of the preliminary distributor (3) is shown at (19). 
     The diameter of the plate as a whole is 30 cm. The displacement cone (2) is fixedly connected to the preliminary distributor (3) at (22) by a screwthread.