Extrusion method and apparatus

Abstract

Improvements in the extrusion of thermohardenable materials are achieved by cooling the material in the initial zone of the extruder and reducing residence time by use of a prescribed length to diameter ratio and screw speed, particularly useful for intermittent application during robotically controlled mass production.

Claims

1. A process for extruding thermally activatable material on a substrate comprising: (a) feeding the thermally activatable material into an extruder via a feed section, wherein the feed section compresses and moves the thermally activatable material to an extrusion screw; (b) moving the thermally activatable material along the extrusion screw within a barrel of the extruder through a plurality of zones by rotating the extrusion screw and engaging the thermally activatable material with grooves of the barrel, wherein the grooves are equally spaced around an internal diameter of the barrel along a length of the extrusion screw, and wherein a length to diameter ratio of the barrel is 20 to 16 and the plurality of zones includes: (i) a first zone in which the thermally activatable material is cooled by a cooling fluid, wherein a length to diameter ratio of the barrel in the first zone is in the range of 2 to 5, and wherein at least a portion of the grooves is located in the first zone; (ii) a second zone in which the thermally activatable material is heated to a temperature above a melting point of the thermally activatable material but below an activation temperature of the thermally activatable material; (iii) a third zone; and (iv) a fourth zone, wherein the third zone and the fourth zone each further gradually heat the thermally activatable material to a temperature above the melting point but below the activation temperature; (c) passing the thermally activatable material from the extrusion screw through an extrusion die as a molten material, wherein the extrusion die is a single component with its own heating system, and the extrusion die is mounted to the barrel at a downward angle relative to the barrel; and (d) extruding the thermally activatable material onto the substrate at a temperature below the activation temperature where the thermally activatable material bonds to the substrate and cools, wherein the extrusion screw operates at 10 to 50 revolutions per minute, and the extrusion screw rotates in a clockwise direction and a counterclockwise direction to create a discontinuous pattern or array of the thermally activatable material having one or more gaps free of the thermally activatable material so that the one or more gaps are spot welded; wherein a residence time of the thermally activatable material within the extruder is less than 5 minutes and a compression ratio, defined as a channel depth at an end of the extruder located near the extrusion die divided by a channel depth of the extruder in the first zone is in a range of 1.5 to 2; and wherein the substrate is pre-treated, prior to extrusion, by heating, infra-red treatment, plasma treatment, or a combination thereof.

2. The process of claim 1, wherein the second zone, the third zone, and the fourth zone each have a separate heating system to heat the thermally activatable material in a controlled manner.

3. The process of claim 1, wherein the second zone is heated to a temperature in a range of 20° C. to 40° C.

4. The process of claim 1, wherein the third zone is heated to a temperature in a range of 40° C. to 80° C.

5. The process of claim 4, wherein the fourth zone is heated to a temperature in a range of 80° C. to 120° C.

6. The process of claim 1, wherein the first zone is cooled by a cooling jacket containing water as the cooling fluid and a temperature of the cooling fluid leaving the cooling jacket does not exceed 10° C.

7. The process of claim 6, wherein the thermally activatable material is conveyed as a solid through the first zone.

8. The process of claim 1, wherein the extrusion die is mounted in a heated block that attaches to the barrel of the extruder that further heats the thermally activatable material prior to extruding the thermally activatable material onto the substrate.

9. The process of claim 1, wherein the grooves extend along the extrusion screw along an entire length of the extrusion screw through the plurality of zones.

10. The process of claim 1, wherein a gap exists between an end of the extrusion screw and the substrate prior to the extrusion of the thermally activatable material onto the substrate, and the gap is filled immediately prior to commencement of the extrusion of the thermally activatable material onto the substrate.

11. The process of claim 10, wherein the thermally activatable material is sucked back into the gap when extrusion is to be terminated.

12. The process of claim 1, wherein the substrate includes a groove that receives the extruded thermally activatable material.

Description

(1) The invention is illustrated by reference to the accompanying drawings in which

(2) FIG. 1 is a longitudinal cross section of an extruder according to the invention.

(3) FIG. 2 is a plot showing the operation of the process of the present invention during one cycle of intermittent operation.

(4) FIG. 3 is a plot showing the effect on material flow rate of providing grooves in the initial section of the extruder barrel.

(5) FIG. 4 is a cross sectional view of the extruder nozzle and die.

(6) FIG. 5 shows how the extruder may be used to apply material to a series of substrates.

(7) FIG. 6 illustrates how the invention may be used to produce an automotive hem flange on an assembly line.

(8) FIG. 1 is a cross section of an extruder according to the invention showing an extruder barrel (1) divided into four zones (2), (3), (4) and (5). The extruder screw is designated as (6) and the extrusion die at (7). (8) is the feed hopper and (9) is the motor that drives the extruder screw.

(9) Zone (1) is a cooling zone and heaters are provided in zones (2), (3) and (4) to gradually increase the temperature along the barrel, the lines (10) and (11) indicate the grooves formed in the initial cooled section of the barrel of the extruder.

(10) FIG. 2 is a plot of a typical temperature profile along the barrel of the extruder. The X axis being the distance along the barrel and the Y axis is the temperature of the material.

(11) In FIG. 3 Q is the flow rate of the material within the extruder and RPM is the speed of rotation of the screw of the extruder. The two curves provide a comparison that illustrates the impact of the grooves.

(12) FIG. 4 shows the extrusion die (7) provided with heaters and mounted in a heated block for attachment to the barrel of the extruder.

(13) FIG. 5 shows how the extruder may be mounted and automatically controlled to apply an extrudate to a series of substrates. In FIG. 5 the extruder is mounted on a stand (13), (14) and a movement system (15), and (16) is provided. A series of substrates (18), (19) etc can be moved to be below the extrusion die (7) and when in position material can be extruded from the die (7) onto the substrate and the extruder may be moved in a programmed manner to provide the desired pattern of extrudate on the substrate. The section (6) of the extruder is cooled and the temperatures of the three heating zones (3), (4) and (5) are maintained by the controller LC.

(14) Pellets of material may be fed to the hopper (9) of the extruder from bulk storage (12).

(15) FIG. 6 shows how an extrudate may be applied directly to a vehicle body on an automobile assembly line. The extruder (1) being movable above the car components (20, (21) and the component positioned beneath the extruder so that an extrudate of a thermohardenable adhesive may be provided for example for bonding of the roof panel. As shown in FIG. 7 a groove (22) may be provided in the car body panel for receipt of the extrudate (23).

(16) FIG. 8 shows how an extruder of the present invention may be employed to deliver an extrudate to materials on a conveyer belt line (24) moving from right to left, a series of metal components (as substrates) such as (25) may be moved along the conveyor line and thermoactivatable material extruded onto the component as it passes the extrusion die (7). A device (26) for pretreating the components such as with hot air to improve adhesion to the extrudate is also shown.

(17) The invention is further illustrated by comparison with the use of the method and apparatus described in United States Patent Publication US 2003/0140671. A thermohardenable material comprising a thermoactivable epoxy resin was employed in the apparatus of United States Patent Publication US 2003/0140671 having a heated initial section of the extruder and a length to diameter ratio of 12 with the extruder screw operating at 3 RPM and extruding the material at 90° C. After a few minutes material had built up within the extruder barrel, the extrusion was irregular and it was not possible to operate for more than 20 minutes without the need to stop and clean the extruder.

(18) By comparison when employing the techniques of the present invention with the thermoactivable epoxy resin in which the initial section of the extruder was provided with grooves and was cooled with water to below 15° C. and the length/diameter ratio of the extruder was 20 and the extruder operated at 15 RPM. It was possible to run continuously for at least 40 hours without product build up and blockages.