GB1559804A

GB1559804A - Extruding plastics material

Info

Publication number: GB1559804A
Application number: GB34216/75A
Authority: GB
Original assignee: Courtaulds PLC
Current assignee: Akzo Nobel UK PLC
Priority date: 1976-11-17
Filing date: 1976-11-17
Publication date: 1980-01-30

Description

(54) EXTRUDING PLASTICS MATERIAL (71) We, COURTAULDS LIMITED, a British Company, of 18, Hanover Square, London, W1A 2BB, England, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following Statement:- This invention relates to the production of plastics net and in particular to an extrusion apparatus for producing plastics net, which apparatus comprises a die formed from two die members which are relatively rotatable transversely to the direction of extrusion through the die, which die members have confronting concentric surfaces in sliding contact with each other and each have circumferentially spaced extrusion orifices at or closely adjacent to the said confronting surfaces.

The circumferentially spaced extrusion orifices are generally grooves in the said confronting surfaces but can be apertures in the die members closely adjacent to the confronting surfaces. When the die members are rotated relative to one another during extrusion the apparatus forms an extruded plastics net or mesh as described in British Patent Specifications Nos.

836,555, 925,658, and 1,058,445. The extruded product is in tubular form and if a flat net is required a separate slitting step is necessary. However, the extruded tubular net cannot conveniently be slit to form a flat net with edges parallel to one of the sets of strands of the net.

Plastics net has also previously been produced by extrusion through a flat slit die combined with a reciprocating slotted die member. This process has the advantage that a flat web of net is produced with one of the sets of strands making up the net parallel to the edges of the net and the other set of strands at right angles to the first mentioned strands. Such a flat rectilinear web of net is desired for many uses, for example as a reinforcing scrim for nonwoven materials. However, this process is inherently slower than the process which employs relatively rotatable die members.

The present invention aims to provide an improved apparatus for producing plastics net which obviates the need for a separate slitting step.

According to the invention an apparatus for producing plastics net comprises a die formed from two die members which are relatively rotatable transversely to the direction of extrusion through the die, which die members have confronting concentric surfaces in sliding contact with each other and each has circumferentially spaced extrusion orifices at or closely adjacent to the said confronting surfaces, means for feeding thermoplastics material under pressure to the extrusion orifices in the die, means for rotating one of the said die members while the other die member remains fixed so that the sets of strands extruded through the extrusion orifices in the two die members cross each other to form a net, a blocking plate positioned so as to block any extrusion orifices in the rotatable die member which comes into radial alignment with it as the die members are rotated relative to one another, a guide positioned to receive the extruded net and means for collecting the net from the guide at an oblique angle to the axis of rotation of the extrusion apparatus.

The circumferentially spaced orifices are preferably formed by grooves in the confronting surfaces of the die members. The blocking plate can be conveniently mounted on the stationary die member, for example it may extend circumferentially between two of the extrusion orifices in the stationary die member. As rotation takes place the blocking plate blocks off successive extrusion orifices in the rotating die mem ber which become radially aligned with it.

This produces a web of net having a slit corresponding to the position of the blocking plate. The edge of the slit is parallel to one of the sets of strands making up the net, namely that set formed by extrusion through the orifices in the die member carrying the blocking plate.

The direction of formation of the strands extruded from the orifices in the rotating die member is at an angle to the axis of rotation of the extrusion apparatus. This angle is dependent on the angular velocity of the rotating die member and the rate of extrusion of the plastics material. The direction of formation of strands extruded from the stationary die member would of course be parallel to the axis of rotation of the extrusion apparatus in the absence of any special means for receiving and collecting the net. The means for collecting the net, preferably a reel, at an oblique angle to this axis constrains the strands extruded from the stationary die member to wrap helically around the guide. The collecting reel is positioned so that the direction of collection of the net diverges from the axis of rotation of the extrusion apparatus in the opposite sense from the direction of formation of the strands extruded from the orifices in the rotating die member so that it is the strands extruded from the stationary die member which are drawn in the collection direction, that is perpendicular to the collecting reel.

The grooves or other extrusion orifices in the stationary die member can be parallel to the axis of rotation of the extrusion apparatus. The collecting reel and guide will satisfactorily draw the strands extruded through these orifices away at the desired angle to the axis. Alternatively these grooves can be of helical configuration so as to assist extrusion of the strands in the direction in which they are to be drawn away from the die face. The grooves or other extrusion orifices in the rotating die member can also be of helical configuration of opposite direction to the helical grooves in the stationary die member.

The guide for receiving the extruded net is preferably a cylinder positioned with its longitudinal axis aligned with the axis of rotation of the extrusion apparatus. Its external circumference is preferably approximately the same as that of the confronting concentric surfaces of ffie die members.

The surface of the guied cylinder is axially separated by a short distance from the die orifice although the guide can be integral with the extrusion apparatus if it has a portion of substantially reduced diameter adjacent to the die face. This portion leaves a gap where the strands can be extruded and joined to form a net free from any supporting surface.

The guide cylinder is preferably helically grooved so that each groove in the guide cylinder receives a strand from a particular extrusion orifice in the stationary die member. The grooves in the guide cylinder help to keep the strands extruded through the orifices in the stationary die member separate and parallel and to prevent them wavering in direction. The surface of the guide cylinder is preferably a low-friction material, for example polytetrafluoroethylene. The bottom of the grooves can also be supplied with holes through which water can be passed from the interior of the guide cylinder. The water acts to cool and set the strands quickly and also to provide lubrication. Cooling water can also be applied externally to the guide cylinder, for example in the form of a shower or spray, and such cooling water cools and sets both sets of strands forming the net.

It is preferred that the two sets of strands forming the net should be perpendicular to each other. This allows subsequent stretching of the net in the two perpendicular directions to orientate the plastics material and strengthen the strands. In a preferred method of achieving perpendicular strands the direction of collection of the extruded product and hence of the strands extruded through the orifices in the stationary die member is at a predetermined angle. This angle is fixed by the orientation of the collecting reel and is preferably 300 to 60 to the axis of rotation of the extrusion apparatus. The angular velocity of the rotating die member is then adjusted relative to the rate of extrusion of the plastics material so that the strands extruded through the orifices in the rotating die member are perpendicular to the strands extruded by the stationary die member.

The net is most preferably collected on a reel arranged at an angle of 45" to the axis of rotation of the extrusion apparatus.

If the angular velocity of the rotating die member is then adjusted to make the two sets of strands forming the net perpendicular, the openings in the net are square rather than merely rectangular. The net as collected has a width ol

where C is the circumference of the confronting surfaces of the die.

The invention will now be described by way of example, with reference to the drawings accompanying the provisional specification, in which: Figure 1 is a side elevation of an apparatus according to the invention for the production of net, Figure 2 is a sectional elevation of part of the apparatus of Figure 1 on an enlarged scale, and Figure 3 is an inverted plan of the die face of the extrusion apparatus of Figures 1 and 2.

The apparatus of Figures 1 to 3 comprises an extruder 1, a guide cylinder 2 and a collecting reel 3. The extruder 1 has a rotatable outer die member 4 and a stationary inner die member 5 having confronting concentric surfaces 6 and 7, respectively. The confronting surfaces 6 and 7 are a sliding fit with each other, and they each have grooves 8 and 9, respectively, which act as die orifices. In the space between one pair of successive grooves 9a.

and 9b a blocking plate 10 is attached to the stationary die member 5. This blocking plate 10 projects outwardly from the stationary die member 5 and blocks any extrusion orifice (such as the groove 8a.

shown in dotted lines in Figure 3) which is radially aligned with it.

The stationary inner die member 5 forms the end portion of a heated chamber 11 containing a pressure screw 12. The inner die member 5 is formed with circumferentially spaced ports 13 for transmitting plastics material from the chamber 11.

Each port 13 leads from the chamber 11 both to a groove 9 with which it is associated and to an annular chamber 14 formed between the inner die member 5 and a channel in the rotatable outer die member 4. This annular chamber 14 communicates with the grooves 8 in the outer die member 4. In Figure 2 the extrusion apparatus is shown with the grooves 8 at the point in their rotation where they are radially aligned with the grooves 9. The outer die member 4 is formed with a gear wheel 15 which can be driven, by means not shown, to rotate the die member 4.

The guide cylinder 2 has an outer circumference the same as that of the inner die member 5 and is positioned in line with it and separated from it by a gap 16.

The collecting reel 3 (rotated by means not shown) is positioned at an angle of 45" to the axis of rotation of the die member 4 and offset from it.

When the apparatus is in operation the plastics material extruded through the grooves 9 of the stationary inner die member is initially in the form of strands such as 17 which form freely in the gap 16.

These strands 17 are drawn away from the die orifice by the collecting reel 3 and wrapped helically around the guide cylinder 2 as they pass to the reel 3. The plastics material extruded through the grooves 8 of the rotating outer die member 4 is initially in the form of strands such as 18 which emerge at an angle to the axis of rotation of the die member 4 and substantially perpendicular to the strands 17. As each groove 8 passes the blocking plate 10, for example groove 8 shown in Figure 3, the strand of plastics material extruded through the die orifice formed by that groove is broken.

The net produced thus has a slit 19 corresponding to the position of the blocking plate 10. This slit appears between the strands of plastics material 17a, 17b extruded through grooves 9a and 9b. When a groove 8 becomes radially aligned with a groove 9 an intersection of the strands 18 and the strands 17 is extruded. In the apparatus shown in Figures 1 to 3 all the grooves 8 and the grooves 9 become aligned simultaneously and at this point the blocking plate 10 is not aligned with any of the grooves 8. The strands of plastics material 17sir and 17b and the intersections extruded as grooves 9a and 9b become aligned with successive grooves 8 form the edges of the sheet of net. The collecting reel 3 is so positioned that the strand 174 passes substantially directly to the reel 3 whereas the strand 17b passes almost right around the guide cylinder 2 before it reaches the reel 3.

Extrusion can be started with the rotatable outer die member 4 stationary. Two sets of strands are produced and these can be collected at a waste godet in approximately the direction of collection used for the product until extrusion conditions have settled down. The rate of extrusion of plastics material, the rate of supply of cooling water on the guide cylinder 2 and the take-up speed of the collecting reel 3 can be adjusted relative to one another to produce the desired thickness of strands.

When rotation of the outer die member 4 is started, the strands extruded through the grooves 8 are broken as they pass the blocking plate 10 and the strands 18 subsequently emerge at an angle to the axis of rotation of the die member 4 which increases as the angular velocity of the die member increases. At a certain angular velocity relative to the rate of extrusion the direction of formation of the strands 18 is at 90" to the direction of the strands 17 and collection of the desired product can begin.

WHAT WE CLAIM IS: 1. An apparatus for producing plastics net comprising a die formed from two die members which are relatively rotatable transverse to the direction of extrusion through the die, which die members have confronting concentric surfaces in sliding contact with each other and each has circumferentially spaced extrusion orifices at or closely adjacent to the said confronting surfaces, means for feeding thermoplastics material under pressure to the extrusion orifices in the die, means for rotating one of the said die members while the other die member remains fixed so that the sets

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. of the apparatus of Figure 1 on an enlarged scale, and Figure 3 is an inverted plan of the die face of the extrusion apparatus of Figures 1 and 2. The apparatus of Figures 1 to 3 comprises an extruder 1, a guide cylinder 2 and a collecting reel 3. The extruder 1 has a rotatable outer die member 4 and a stationary inner die member 5 having confronting concentric surfaces 6 and 7, respectively. The confronting surfaces 6 and 7 are a sliding fit with each other, and they each have grooves 8 and 9, respectively, which act as die orifices. In the space between one pair of successive grooves 9a. and 9b a blocking plate 10 is attached to the stationary die member 5. This blocking plate 10 projects outwardly from the stationary die member 5 and blocks any extrusion orifice (such as the groove 8a. shown in dotted lines in Figure 3) which is radially aligned with it. The stationary inner die member 5 forms the end portion of a heated chamber 11 containing a pressure screw 12. The inner die member 5 is formed with circumferentially spaced ports 13 for transmitting plastics material from the chamber 11. Each port 13 leads from the chamber 11 both to a groove 9 with which it is associated and to an annular chamber 14 formed between the inner die member 5 and a channel in the rotatable outer die member 4. This annular chamber 14 communicates with the grooves 8 in the outer die member 4. In Figure 2 the extrusion apparatus is shown with the grooves 8 at the point in their rotation where they are radially aligned with the grooves 9. The outer die member 4 is formed with a gear wheel 15 which can be driven, by means not shown, to rotate the die member 4. The guide cylinder 2 has an outer circumference the same as that of the inner die member 5 and is positioned in line with it and separated from it by a gap 16. The collecting reel 3 (rotated by means not shown) is positioned at an angle of 45" to the axis of rotation of the die member 4 and offset from it. When the apparatus is in operation the plastics material extruded through the grooves 9 of the stationary inner die member is initially in the form of strands such as 17 which form freely in the gap 16. These strands 17 are drawn away from the die orifice by the collecting reel 3 and wrapped helically around the guide cylinder 2 as they pass to the reel 3. The plastics material extruded through the grooves 8 of the rotating outer die member 4 is initially in the form of strands such as 18 which emerge at an angle to the axis of rotation of the die member 4 and substantially perpendicular to the strands 17. As each groove 8 passes the blocking plate 10, for example groove 8 shown in Figure 3, the strand of plastics material extruded through the die orifice formed by that groove is broken. The net produced thus has a slit 19 corresponding to the position of the blocking plate 10. This slit appears between the strands of plastics material 17a, 17b extruded through grooves 9a and 9b. When a groove 8 becomes radially aligned with a groove 9 an intersection of the strands 18 and the strands 17 is extruded. In the apparatus shown in Figures 1 to 3 all the grooves 8 and the grooves 9 become aligned simultaneously and at this point the blocking plate 10 is not aligned with any of the grooves 8. The strands of plastics material 17sir and 17b and the intersections extruded as grooves 9a and 9b become aligned with successive grooves 8 form the edges of the sheet of net. The collecting reel 3 is so positioned that the strand 174 passes substantially directly to the reel 3 whereas the strand 17b passes almost right around the guide cylinder 2 before it reaches the reel 3. Extrusion can be started with the rotatable outer die member 4 stationary. Two sets of strands are produced and these can be collected at a waste godet in approximately the direction of collection used for the product until extrusion conditions have settled down. The rate of extrusion of plastics material, the rate of supply of cooling water on the guide cylinder 2 and the take-up speed of the collecting reel 3 can be adjusted relative to one another to produce the desired thickness of strands. When rotation of the outer die member 4 is started, the strands extruded through the grooves 8 are broken as they pass the blocking plate 10 and the strands 18 subsequently emerge at an angle to the axis of rotation of the die member 4 which increases as the angular velocity of the die member increases. At a certain angular velocity relative to the rate of extrusion the direction of formation of the strands 18 is at 90" to the direction of the strands 17 and collection of the desired product can begin. WHAT WE CLAIM IS:

1. An apparatus for producing plastics net comprising a die formed from two die members which are relatively rotatable transverse to the direction of extrusion through the die, which die members have confronting concentric surfaces in sliding contact with each other and each has circumferentially spaced extrusion orifices at or closely adjacent to the said confronting surfaces, means for feeding thermoplastics material under pressure to the extrusion orifices in the die, means for rotating one of the said die members while the other die member remains fixed so that the sets

of strands extruded through the extrusion orifices in the two die members cross each other to form a net, a blocking plate positioned so as to block any extrusion orifice in the rotatable die member which comes into radial alignment with it as the die members are rotated relative to one another, a guide positioned to receive the extruded net and means for collecting the net from the guide at an oblique angle to the axis of rotation of the extrusion apparatus.

2. An apparatus according to claim 1 in which the blocking plate is mounted on the stationary die member.

3. An apparatus according to claim 2 in which the blocking plate extends circumferentially between an adjacent pair of the extrusion orifices in the stationary die member.

4. An apparatus according to any of claims 1 to 3 in which the circumferentially spaced extrusion orifices are grooves ir tlie confronting concentric surfaces of the die members.

5. An apparatus according to claim 4 in which the grooves in the stationary die member are each of helical configuration so as to assist extrusion of the strands in the direction relative to the direction in which they are drawn away from the dies face by the collecting means.

6. An apparatus according to any of claims 1 to 5 in which the guide for receiving the extruded net is a cylinder with its longitudinal axis aligned with the axis of rotation of the extrusion apparatus.

7. An apparatus according to claim 6 in which the external circumference of the guide is substantially equal to that of one of said concentric surfaces.

8. An apparatus according to claim 6 or claim 7 in which the guide cylinder is helically grooved so that each groove in the guide cylinder receives a strand from a particular extrusion orifice in the stationary die member.

9. A process for producing plastics net in which thermoplastics material is extruded and collected using an apparatus as claimed in any of claims 1 to 8, the direction of collection of the extruded net being at an angle of 30 to 60 to the axis of rotation of the extrusion apparatus and the angular velocity of the rotating die member relative to the rate of extrusion of the plastics material being such that the strands extruded through the orifices in the rotating die member are perpendicular to the strands extruded through the orifices in the stationary die member.

10. A process according to claim 9 in which the direction of collection of the extruded net is at an angle of 45" to the axis of rotation of the extrusion apparatus.

11. An apparatus for producing plastics net substantially as hereinbefore described with reference to Figures 1, 2 and 3 of the drawings accompanying the provisional specification.