GB2220209A

GB2220209A - Detackifying atactic polypropylene

Info

Publication number: GB2220209A
Application number: GB8909309A
Authority: GB
Inventors: J Nick Fowler
Original assignee: ORION DRILLING Inc
Current assignee: ORION DRILLING Inc
Priority date: 1988-04-26
Filing date: 1989-04-24
Publication date: 1990-01-04
Anticipated expiration: 2009-04-24
Also published as: GB8909309D0; JPH01317709A; IT1231464B; IT8947888A0; GB2220209B; JP2920640B2; CA1329687C; DE3913773C2; DE3913773A1

Description

1 PACKAGING AND/OR STORING ATACTIC POLYPROPYLENE OR OTHER OLEFINS 2220209

This invention relates to an improved method and apparatus for use in packaging and/or storing atactic polypropylene or other amorphous poly alpha olefins which are characterised by high surface tack and low thermal conductivity, and wherein large temperature reductions contribute only moderate increases in viscosity or form retaining ability.

Atactic polypropylene occurs in the form of a noncrystalline, naturally occurring by-product of polypropylene whose primary use is as an elastomer for roofing material. More recently, it has been found possible to manufacture atactic polypropylene in the form of an atactic copolymer of ethylene and propylene also known as atactic polyalpha-olefin. Polybutene may be added to this -manufactured atactic polypropylene to make it "adhesive grade", and thus to have broader usage in the adhesive industry.

Since this material is a natural adhesive which is so tacky, even when solid at room temperature, it sticks to itself as well as anything else it contacts, including Teflon. Moreover, it is difficult to supply to the consumer, whether as roofing material or otherwise, in a usable form or state. Thus, apart from the problem of transporting it, it is self insulating, and hence large and expensive facilities would have to be provided for maintaining large volumes of it in a molten state (about 375 F). Although 1 2 efforts have been made to package it in relatively small cardboard containers, as is done with asphalt, this is not only an expensive procedure, but also one which requires removal of the container from the atactic polypropylene itself before use by the consumer.

To my knav;ledge, it has also been proposed to package atactic polypropylene in relatively thin slabs which may be remelted without too much difficulty. 7-.pparently, the molten atactic polypropylene is poured onto a stainless steel belt under water which is thought to reduce the tendency for it to stick to the belt. The thin slabs are difficult to handle and transport, not only because of the4 ir shape and size, but also because of their tendency to stick %.o one another and anything else they contact.

It has also been proposed to extrude atactic polypropylene within a sheath of polypropylene which is not so sticky, and which is then cut into segments or pellets. Among other things, the coextrusion head is expensive, and the sheath is extruded at a relatively high temperature and must be cooled before being cut. Also, of course, the cut ends o.E the segments leave exposed sticky surLaces of atactic polypropylene.

An object of this invention is to nrovide atactic polypropylene in a form more suitable -Eor packaging and/or storage by the producer and consumer, and in particular to provide a method and apparatus of forming pellets of atactic to one another or anything polypropylene which do not stick t else, and which are of such composition and size that they or use by the consumer with a minimum of preparaare ready tion.

These and other objects are accomplished, in accordance with the illustrated embodiments of this invention, by a method and apparatus wherein a rod of molten atactic polyp.ropylene is extruded through an orifice of an extrusion head, a knJfe is moved across the outer end of the orifice to cut the rod into a succession of pellets, and the 3 pellets and k.,,ife are substantially covered with a dust-like material which is inert to the atactic polypropylene as -the knife cuts the rod into pellets. As a consequence, the pellets may be collected for packaging and/or storage without sticking to one another or to anything else which they may contact. Furthermor,:!, the extrusion orifice may be of such size and the knife operated at such speed as to form pellets of a size not only suitable for storage and/or packaging, but easily melted for use by the consumer. Still further, since the dust-like material is inert to t.he atactic polypropylene, its presence on the outside of the pellet does not in any way detract from the use of the product, and hence need not be removed therefrom.

In a first embodiment of the invention, the dust-like material is blown into an enclosure at the outlet end of the orifice, and that portion of the dust which does not stick to the pellets as they are collected is preferably recovered and recycled for blowing into the enclosure in order to substantially cover subsequently formed pellets. Thus, the apparatus includes a source of dust-like material, and means for blowing the material into the enclosure, together with means for recovering the material and returning it to the source.

In a second embodiment of the invention, the dust-like material is contained within a liquid slurry which is supplied to the pellets and knife, the slurry containing at least 75%-by volume of particles of the dust-like material and a surfactant. Thus, the apparatus includes a container C for the slurry together with means for drawing -slurry from the container and delivering it to pellets and knife through hoses, as well as means for recovering in the 11--ank slurry and particles which do not stick to the pellets and knife.

In its preferred and illustrated embodiment, t- h e extrusion head has a plurality of orifices through which rods are simultaneously extruded and cut into pellets by the to knife, and valves which connect with each orifice so as t maintain subs tantially uniform rates of flow of atac-,,-ic 4 polypropylene therethrough. Also, the knife has an opening through which the extruded rods are passed, and cutting edges on opposite sides of the opening in order to sever the rods as the knife reciprocates in each opposite direction.

The apparatus of each of the embodiments includes, in addition to the extruding head, means in which solid atactic polypropylene may be heated to render it molten and then cooled to a temperature at which it is semisolid as it leaves the extrusion head. More particularly, it includes a heater for receiving and melting the solid atactic polypropylene, a scraped wall heat exchanger in whi ch the molten atactic polypropylene may be cooled to a temperature of about 1800-210"F, and means for pumping the molten atactic polypropylene from the heater to the heat exchanger and from the heat exchanger to the extrusion head. -.

Thus, the apparatus contemplated by the present invention enables the use of substantially standard equipment, such as heater tanks, scraped wall heat exchangers, extrusion heads, as well as suitable conduits connecting them, and blowers, tanks, hoses, etc. for handling the dust-like material, whether in air or a liquid slurry.

In the drawings, wherein like referenced characters are used throughout; to designate like parts:

Fig. 1 is a diagrammatic view of apparatus constructed and arranged in accordance with the first embodiment of the present invention; Fig. 2 is an enlarged view, partly in elevation and partly in section, of the extrusion head and the means by which dust-like material is blown into an enclosure adjacent the extruded rod and knife; Fig. 3 is a top plan view of the extrusion head of Fig. 2, as seen along broken lines 3-3 of Fig. 2; Fig. 4 is a end view of the extrusion head as seen from broken lines 4-4 of Fig. 2;' and Fig. 5 is a diagrammatic view of a portion of apparatus constructed and arranged in accordance with the second embodiment of the invention.

With reference now to the details of the above described drawings, the overall apparatus constructed in accordance with the first embodiment is shown in Fig. 1 to include a tank 20 in which solid atactic polypropylene may be received and heated to 375F. or above in order to render "' the tank it molten. Nitrogen may be supplied to 1-he top o. through a line 211 to provide a blanket of nitrogen over the top of the molten atactic pclypropylene. When heated to the desired temperature, the molten atactic polypropylene is fed to a scraped wall heat exchanger 22 through conduit 23 connecting the tank toward its lower end with the upstream or right hand end of the heat exchanger. The conduit 23 includes a valve 24 for opening and closing it and a gear type pump 25 for pumping the molten atactic polypropylene into the heat exchanger.

The heat exchanger includes an inner cylindrical shell 26 in which the atactic polypropylene is received, and a plurality of scrapers 27 mounted on a central shaft 28 in position to scrape the inside wall of the shell 26 upon rotation of the shaft by means of a moil-or 29. Thus, the molten ataclic polypropylene is prevented from sticking to the inner wall of the shell as it is pumped from the inlet end to the outlet end of the shell, where it exits from the heat exchanger through a conduit 30.

The heat exchanger 22 also includes an outer shell 31 which surrounds the inner shell to form an annular space 32 in which a coolant may be circulated so as to lower the temperature of the molten atactic polypropylene i-rom approximately 375F. at which it enters the heat exchanger about 1800-2100 at which it leaves the heat exchanger to enter the conduit 30. For this purpose, a suitable coolant is stored within a tank 33 disposed within a conduit connecting the annular space at the right hand end of the outer shell of the heat exchanqer with the annular space at the downstream or left hand thereof. More particularly, coollanit is pumped through the conduit and the annular space by means of a pu,--p 35, the d_4rection of flow being preferably in the directicn 6 indicated by the arrows in the line 34. The coolant is cooled before return to the container 33 by means of a fan 36 for circulating air over a coil 37 in the conduit.

The conduit 30 -o an I leads from the heat exchanger extrusion head 40 so as to supply the atactic polypropylene to the extrucion head in its semi-solid state. The space between the heat exchanger and extrusion head may be quite small, and in fact they may be adjacent one another, thereby insuring that the molten atactic polypropylene is maintained at the desired temperature suitable for extrusion purposes. Another conduit 41 connects the conduit 30 with the heater tank 20, and valves 42 and 43 are connected in the conduit 41 and in the conduit 30 intermediate the conduit 41 and the extrusion head 40, respectively. Thus, when the extrusion process is occurring, the valve 42 will be closed and the valve 43 opened. On the other hand, when the extrusion vrocess is discontinued, the valve 43 is closed and the valve 42 opened to permit the molten polypropylene to be recirculated and thus reheated back through the tank 20.

As best shown in Figs. 2 to 4, the extrusion head 40 includes a laterally elongate box 44 to the right-hand side of which the conduit 30 is connected, and four conduits 45 extending between holes in the left hand end of the box and holes forming orifices in a common wall 46 mounted to the f the box. A valve 47 is ins- left o.9 L-alled in each conduit 45 to control the size of the passageway through the conduit, and thus insure subs 'Cantial ly uniform flow of atactic f the conduits. In any event, polypropylene through each o.& with the valves opened, four rods of atactic polypropylene are extruded from the extrusion head in laterally spaced apart, side-by-side relation.

The apparatus further includes a kni-Pe 48 which extends laterally across the left hand end of the wall and is mounted for reciprocation transversely of the direction of -'-he rods. More particularly, fe is extrusion oz - the knif mounted within guides 49 for reciprocation adjacent the orifices so as to cut the rods into segments as they leave 7 the orifices. Thu.,, as best shown in Fig. 4, the knife has a wide opening 50 therethrough which, in a neutral vertical position, permits the rods to be extruded therefrom, and cutting edges 51 and 52 along the upper and lower edges of the opening so as to simultaneously cut the rods into segments upon both the downstroke and upstroke of the knife.

As shown in Figs. 2 and 4, the knife is in the process of moving down so as to sever a pellet P from the rod, as indicated in the broken lines of Fig. 2. As previously indicated, the rate of extrusion and timing of the reciprocation of the rod may be controlled to cut a pellet of desired size. As also shown in Figs. 2 to 4, the knife is adapted to be reciprocated by means of an air cylinder 53 mounted on the extrusion head by means of bracket 54 and connected to the upper edge oil the knifle by means of a clevis 55.

As shown in Fig. 1, an enclosure 60'is mounted on the extrusion head so as to substantially enclose a space about the orifices in the head and the cutter knife. This enclosure may be formed of any suitable material, such as a cloth or plastic bag. Dust-like material is adapted to be blown into the enclosure from a source of the dust within a container 61 and a hose 62 leading into the enclosure. As shown, the ends of the hoses are mounted adjacent the outer ends of the orifices and thus in the position to substantially cover the pellets as they are cut as well as the cutting edges of the cutting knife.

As shown in Fig. 1, the pellets P drop from the outer ends of the orifices in the extrusion head onto a screen 63 on the upper side of a shaker 64. Thus, excess dust-like material which drops off of the pellets falls into the shaker 64, where it is picked up in a conduit 65 leading from the shaker back to the container 61. As shown, a pumn 66 is disposed in the conduit 65 for circulating the dust-like material back to the container, and then drawing it from the container through the hoses 62 into the enclosure to thereby recycle it.

8 As previously described, the dust may be any material which is inert to atactic polypropylene, such as talc, polvethylene or polypropylene. In each case, the dust has fine fibers which tend to overlap and thus substantially cover the outer sticky surface of the pellets. A 400 mesh size of talc has been found satisfactory ffor this purpose.

As the pellets P fall downwardly over the end of thc screen 63, they drop into a bath of quenching liquid within a container 67. From that point, the hardened pellets may be collected for packaging and/or storage, as previously described.

Fig. 5 illustrates only a portion oil the second embodiment of the invention since much of it is identical to the first embodiment. To the extent it differs, the second embodiment includes a tank 70 to contain water to which the dust-like material is added to form a slurry. The slurry is drawn from the tank by means of pump 66 within conduit 65 connecting the tank with hoses 62 having nozzles on t.Leir ends and arranged to apply the slurry to the pellets and knife as the rod is cut into pellets to substantially cover the Dellets and knife with the material..

The slurry falls through the screen 63 of the shaker which separates the pellets, and then through holes in the shaker back into the tank 70. Additional dust-like material is added to the tank as needed to maintaln the slurry at a desired density. Thus, as previously noted, the slurry should contain at least 75% by volume of particles of dust-like material. The 'resulting pasty composition of the slurry, as well as the addition of a surfactant, is helpful in maximizing adherence of the particles to the surface of the pellets and knife.

An advantage to this second embodiment of the invention is that the water, even at room temperature, acts as a L. %..

coolant to cause the skin of the self-insulating pellets to harden and thereby prevent penetration of the par-'Licles which would contaminate the pellets. At the same time, the coolannt promotes adherence of the particles to the skin, 9 rather than melting and building up on the skin, which might otherw-'Lse occur when the particles are instead carried in air. 1-urthermore, containment of the particles in a slurry prevents them from contaminating the atmosphere, and the enclosure illustrated in Fig. 5 is instead for the purpose of containing splash from the slurry.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and oh-jects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Claims

1. In a method for use in packaging and/or storing atactic polypropylene or other amorphous poly alpha olefins which are characterised by high surface tack and low thermal conductivity, and wherein large temperature reductions contribute only moderate increases in viscosity or form retaining ability, the steps of extruding a rod of molten atactic polypropylene through an orifice of an extrusion head, moving a knife across the outer end of the orifice to cut the rod into a succession of pelletsf and substantially covering the pellets and knife with a dustlike material which is inert to the atactic polypropylene.

2. In a method of the character defined in claim 1, wherein the dust-like material is blown into an enclosure at the outlet end of the orifice.

3. In a method of the character defined in claim 2, the further step of recovering dust-like material which does not stick to the pellets and/or knife and blowing it into the enclosure to substantially cover additional pellets and the knife.

4. In a method of the character defined in claim 1, wherein the dust-like material is contained with a liquid slurry which is applied to the pellets and knife.

5. In a method of the character defined in claim 4, wherein the slurry contains at least 75% by volume of particles of the dust-like material and a surfactant.

6. In a method of the character defined in claim 1, wherein the dust-like material is talc.

7. In a method of the character defined in claim 1, wherein the dust-like material is polypropylene.

8. In a method of the character defined in claim 11 1, wherein the dust-like material is polyethylene.

9. In a method of the character defined in claim 1, the further steps of heating a solid mass of atactic polypropylene to about 375 OF to render it molten and maintaining it at about 200 OF as it is extruded through the orifice.

10. In apparatus for use in packaging and/or storing atactic polypropylene or other amorphouspoly alpha olefins which are characterised by high surface tack and low thermal conductivity, and wherein large temperature reductions contribute only moderate increases in viscosity or form retaining ability, means including an extrusion head having an orifice through which a rod of atactic polypropylene may be extruded, a knife mounted for reciprocation across the outer end of the orif ice in order to cut the rod into a succession of pellets, and means for substantially covering the pellets and knif e with dust-like material which is inert to the atactic polypropylene as the knife cuts the rod into pellets.

11. In apparatus of the character defined in claim 10, an enclosure adjacent the head to surround the extruded rod and knife, and means for blowing the material into the enclosure.

12. In apparatus of the character defined in claim 11, means for recovering the dust-like material which does not stick to the pellets and/or knife and returning it to the source.

13. In apparatus of the character defined in claim 10, includinq - 1 c 12 means for containing the material in a liquid slurry and applying the slurry to the pellets and knife as the rod is cut into pellets.

wherein In apparatus of the character defined in claim 10, the knife has an opening through which the rod is extruded and oppositely facing b_1ades for cutting a pellet during each stroke of its reciprocation.

15. In apparatus of the character defined in claim 10, means in which solid atactic polypropylene may be heated to render it molten and then cooled to a temperature of about 1800-2100 as it is pumped into the extrusion head.

16. In apparatus of the character defined in claim 15, wherein said lastmentioned means includes a heater for receiving the solid atactic polypropylene, a scraped wall heat exchanger in which the molten atactic POlvPropylene may be cooled, and means for 'Dumping molten atactic polypropylene from the heater to the heat exchanger.

17. In apparatus of the character defined in claim 16, first conduit means connecting the heat exchanger with the extrusion head, second conduit means connecting the heater to the first conduit means, and valve means enabling molten atactic polypropylene to be returned from the heat exchanger to the heater during shut down of the extrusion process.

-er defined in claim 10,

18. In apparatus of the cha-ract 1 wherein 1 13 the extrusion head has a plurality of orifices through which rods are simultaneously extruded and cut into pellets by the knife, and valves connecting vith each orifice to maintain substantially uniform rates of flow of atactic polypropylene therethrough.

0 Published 1989 at The Patent Office, State House. 56171 High Holborn. London WClR4TP. Further copies maybe obtainedfrom. The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1187