Injector for feeding additives in a polymer melt stream

The invention comprises an injector for feeding additives into a polymer melt stream. The injector comprises a body with a curved surface and a longitudinal axis having an inlet opening for the additives in the upper portion, opening into a channel running along the longitudinal axis and having a 90 degree deflection to a side injector outlet and having two groove-shaped recesses in the outer wall arranged parallel to the channel on both sides at the level of the injector outlet.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention concerns an injector for feeding additives into a polymer
 melt stream.
 2. Summary of the Related Art
 Devices for feeding one liquid medium into another are known. U.S. Pat. No.
 5,176,448 describes a device for mixing fluid media in which a liquid
 additive is conveyed through a channel having a 90.degree. deflection to
 an outlet at the side. The side outlet opens directly into the middle of
 the countercurrent main stream of another liquid medium directly upstream
 of a biscuit located inside of the main stream conduit and forming an
 annular gap with it for the passage of the liquids.
 U.S. Pat. No. 4,753,535 describes a device for mixing two liquid media,
 whereby most of the main stream of the one liquid medium is conveyed
 through a flow channel containing static mixing elements and arranged at
 the center of the main stream conduit. At a right angle to the direction
 of flow, the second liquid medium is fed directly into the flow channel
 through a lateral feed port.
 E. Henglein, Lexikon Chemische Technik [Lexicon of Chemical Technology],
 1988, page 267, describes an injector for continuous mixing of two gases,
 where one component of the mixture is fed centrally into a mixing zone at
 a high rate while the second gas stream enters the zone through the
 remaining annular gap. Due to the high flow rate and the difference in
 flow rates at the point of entry, there is a great deal of turbulence
 prevailing in the mixing zone.
 European Patent Application No. 838,259 describes a device for adding
 additives to a stream of a highly viscous liquid having one feed element
 for each additive to be supplied. Each feed element has a feed channel for
 the additive running across the direction of flow that opens into a feed
 port of an annular tube sheet within the main stream conduit. The tube
 sheet serves as additive distributor.
 SUMMARY OF THE INVENTION
 The present invention comprises an injector for feeding of additives
 primarily into the center of a polymer melt stream and subsequent feeding
 of the polymer melt stream and additives into a static mixer where the
 additives and polymer melt are blended. Preferably, it is possible to
 mount the injector in the polymer melt stream relatively easily.

DETAILED DESCRIPTION OF THE INVENTION
 The injector according to the invention comprises a body having a curved
 exterior surface and a longitudinal axis. The body further has an inlet
 opening for additives in an upper face that opens into a channel running
 parallel to (preferably along) the longitudinal axis and having a
 90.degree. deflection to a side injector outlet. Two groove-shaped
 recesses are located on the exterior surface at the level of the injector
 outlet on opposite sides of and running parallel to the plane of the
 channel.
 The term "additives" is understood to include, for example, heat
 stabilizers and UV stabilizers, lubricants, copolymers or color
 concentrates.
 The injector body may be a straight circular cylinder or a straight
 circular cylinder cropped at an inclined angle or it may be a straight
 circular cone or a straight truncated cone. The injector is inserted into
 the polymer melt stream at a right angle to the direction of flow of the
 polymer melt stream, with the polymer melt stream flowing along the
 groove-shaped recesses on either side of the injector body. The size of
 the groove-shaped recesses should be selected with regard to the diameter
 of the flow channel of the polymer melt stream so that the edges of the
 groove-shaped recesses are in flush contact with the flow channel. It has
 surprisingly been found that by central feeding of additives into the
 polymer melt stream at the injector outlet the additives remain centered
 in the polymer melt stream downstream from the injector outlet.
 Symmetrical flow conditions result and are attributable to the fact that
 the groove-shaped recesses are arranged on both sides of and parallel to
 the plane of the injector channel and at the level of the injector outlet.
 The curved surface exterior of the injector facilitates relatively easy
 insertion and arrangement of the injector in a form-fitting manner in the
 flow channel of the polymer melt stream. In addition, the injector outlet
 can be positioned in the desired manner. Thus, for example, it is possible
 to arrange the injector outlet in such a way that the additives are fed
 into the polymer melt stream with or against the direction of flow of the
 polymer melt stream. With both alternatives, the additives are kept in the
 middle of the polymer melt stream and thus can be fed centrally to a
 static mixer, which is a condition for achieving a high degree of
 homogenity of the resulting mixture.
 In a preferred embodiment of the present invention, the cross section of
 the injector at the level of the injector outlet is droplet-shaped with
 the injector outlet opening into the narrow, tapered part of the
 droplet-shaped cross section. This optimizes the flow conditions at the
 groove-shaped recesses, where the direction of flow of the polymer melt
 stream is oriented toward the injector outlet, facilitating a central feed
 of the additives into the polymer melt stream.
 Preferably, the inlet opening of the injector is designed in a funnel
 shape. This measure simplifies the feeding of additives into the injector.
 According to another preferred embodiment of this invention, the injector
 body is a straight truncated cone with the wider end as the upper part
 having the inlet opening for the additives. Due to the conical shape of
 the injector, an especially good seal is achieved between the injector and
 the channel of the polymer melt stream.
 In another embodiment of this invention, the injector body has a 5 to
 15.degree. cone angle, i.e., a 5 to 15.degree. angle of inclination
 .alpha. between surface segments on opposite sides of the injector body. A
 surface segment is defined to be a straight line running on the outer
 surface of the injector body in a plane with the longitudinal axis of the
 injector body. A cone angle of 5 to 15.degree. yields the optimum sealing
 of the injector with the polymer melt stream channel. Leakage of the
 polymer melt would result in harmful damage to the polymer due to
 degradation products from the leaking polymer, but that is avoided by the
 aforementioned structure of the injector.
 According to another preferred embodiment of this invention, the injector
 has a groove centrally located in the bottom face. This measure
 facilitates installation and dismantling of the injector and the correct
 positioning of the injector outlet.
 This invention is explained in greater detail below on the basis of the
 drawings (FIGS. 1 and 2).
 FIG. 1 shows the injector (1) for feeding additives into a polymer melt
 stream, in a sectional view (FIG. 1A) together with the side view (FIG.
 1B) and the respective cross section (1C). The injector (1) is in the form
 of a straight truncated cone with an angle of inclination .alpha. (the
 cone angle) formed between two precisely opposing surface segments on the
 outside of the injector (1). The angle of inclination .alpha. is
 advantageously in the range between 5.degree. and 15.degree.. An inlet
 opening (2) for the additives is located on the upper surface of the
 injector (1) and opens into a channel (3) running in the longitudinal axis
 of the injector. The channel (3) has a 90.degree. deflection to the side
 injector outlet (6). In the middle area of the injector (1), groove-shaped
 recesses (4) are arranged on the outside on both sides parallel with the
 plane of the channel (3) at the level of the injector outlet (6). The size
 of the groove-shaped recesses (4) is selected with regard to the diameter
 of the flow channel (8) of the polymer melt so that the edges of the
 groove-shaped recesses (4) are in flush contact with the flow channel (8)
 thereby preventing zones of reduced melt flow. When the injector (1) is
 installed, the polymer melt stream flows around it symmetrically through
 the groove-shaped recesses (4). At the level of the injector outlet (6),
 the cross section of the injector (1) exterior surface forms a droplet
 shape with the injector outlet (6) opening into the tapered part of the
 droplet-shaped cross section. Therefore there is central feed of the
 additives into the polymer melt stream at the injector outlet (6). A
 groove (5) is arranged on the middle of the bottom face (9) of the
 injector (1). The groove (5) serves for additional fixation of the
 injector (1) in the device containing the flow channel (8) for the polymer
 melt stream.
 FIG. 2 shows the injector (1) for feeding additives into a polymer melt
 stream in the installed state. Section A--A (FIG. 2B) shows the injector
 (1) in a cross-sectional view 90.degree. from that in FIG. 2A. Because of
 the conical shape of the injector (1), which is designed as a straight
 truncated cone, a tight, form-fitting mounting of the injector (1) is
 guaranteed. The upper face of the injector (1) together with the inlet
 opening (2) for the additives advantageously can border on the metering
 pump (7) for the additives. The pump (7) can thus be positioned relatively
 closely to the outlet (6) of the injector (1). The polymer melt stream
 flows directly along the groove-shaped recesses (4) of the injector (1) in
 the flow channel (8), thus arriving directly at the injector outlet (6),
 resulting in immediate central feed of additives into the polymer melt
 stream. The additives fed into the polymer melt stream in this way remain
 at the center of the polymer melt stream during the remaining conveyance
 through an acceleration zone (10), which leads directly to the downstream
 static mixer (11). As shown by section A--A, the injector outlet (6) is
 positioned so that the additives are fed into the polymer melt stream in
 the direction of flow of the stream. It is also possible, however, to
 rotate the injector (1) by 180.degree. so that the additives can be fed
 into the polymer melt stream against the direction of flow of the stream.
 Positioning of the injector outlet (6) in the devices having the channel
 for the polymer melt stream can thus be optimized relatively easily.