EP0000620B1

EP0000620B1 - Process and apparatus for the manufacture of polymer fibrils

Info

Publication number: EP0000620B1
Application number: EP19780300087
Authority: EP
Inventors: Robert E. Boehme; Clarence R. Murphy
Original assignee: Champion International Corp; Gulf Oil Corp
Current assignee: Champion International Corp; Gulf Oil Corp
Priority date: 1977-07-01
Filing date: 1978-06-27
Publication date: 1981-11-11
Also published as: EP0000620A1; NO782282L; CA1101163A; JPS5434417A; US4125584A; DE2861309D1

Description

This invention relates to a process and apparatus for the manufacture of fibrils.
The Parrish patent U.S. 2,988,782 disclosed the manufacture of very fine polymer filaments that can be employed to manufacture water-laid sheets of synthetic paper. These synthetic filaments are of such a small diameter that they behave quite differently from spun filaments and have been characterized in the art as "fibrils" or "fibrids".
The Parrish process for preparing such fibrils involves preparing a solution of a polymer in a suitable solvent and adding the polymer solution to a vigorously-agitated solution of a liquid, which is a non-solvent for the polymer of interest. As the polymer solution is added to the vigorously-stirred nonsolvent liquid, the droplets of the polymer solution are subjected to sheer forces and attenuated while simultaneously being precipitated. Parrish discloses that the precipitation step is carried out in a high intensity mixer such as a Waring blender, while the Parrish process is suitable for making small laboratory quantities of such fibrils, the process is not well suited to make substantial quantities of the fibrils at an acceptable cost.
The Davis, et al, patent U.S. 4,013,751 discloses an alternate process for preparing fibrils by modified methods in which a hot polymer solution and coolant liquid are passed into a hammermill comprising a housing having a cylindrical internal surface, a hammer rotor in the housing including pivotal flails on hub discs, and a plurality of ports in the housing including an inlet port disposed centrally in a side wall of the housing to provide for axial flow of polymer solution into the housing, and a peripheral series of three ports opening from a segment of the cylindrical internal surface, namely, a pair of diametrically opposed inlet ports for coolant liquid and a fibril discharge port disposed midway between the pair of inlet ports. While this process provides good quality fibrils, the process is capital intensive and has higher manufacturing costs than is desired.
There is a need in the art for improved apparatus and processes for manufacturing fibrils at a lower cost.
It has now been discovered that by directing the liquids through a particular arrangement of ports in a cylindrical housing containing a centrifugal spinner in the form of a modified impeller, good quality fibrils can be produced at low cost.
According to the present invention we provide apparatus for the manufacture of polymer fibrils from a hot viscous solution of thermoplastic polymer, comprising a housing having an internal surface forming a cylindrical cavity, a centrifugal spinner mounted for rotation in the cavity, inlet means in the housing to provide for entry of the polymer solution and a coolant liquid into the cylindrical cavity, and a discharge port in the housing to provide for the removal of fibrils from the cylindrical cavity, characterised in that the centrifugal spinner includes central rotary driving means and a plurality of radially elongate blades rigidly connected to the driving means, said blades being disposed substantially in the plane of their rotation and having their tips in close proximity to the peripheral internal surface of the housing, the inlet means and the discharge port open from the internal surface of the housing at the periphery of the cavity, and the inlet means are positioned close to the discharge port and at the upstream side thereof when the discharge port is viewed with respect to the rotary movement of the blades away from and towards same, so that the liquids entering through the inlet means are swept by the blades away from the discharge port and through a major segment of the peripheral zone of the cavity.
Further according to the present invention we provide a process for preparing fibrils from a hot viscous solution of a thermoplastic polymer which consists essentially of:

a. rotating a centrifugal spinner in the cylindrical cavity of a housing at high speed, the spinner including central rotary driving means and a plurality of radially elongate blades rigidly connected to the driving means, said blades being disposed substantially in the plane of their rotation and having their tips in close proximity to the peripheral internal surface of the housing,
b. feeding a coolant liquid and a hot viscous solution of thermoplastic polymer into the peripheral zone of the cavity through inlet means opening from an internal surface of the housing at the periphery of the cavity so that said coolant liquid and polymer solutions are contacted by the outer end portions of said blades and are broken up into droplets and/or thin streams which flow over the surfaces of said blades whereby the polymer solution is subjected to high shear stresses and is attenuated to orient the solute polymer molecule in said polymer solution, and the blades are cooled and serve to cool the polymer solution in contact therewith so that fibrils are precipitated from the polymer solution, and
c. withdrawing a stream of fibrils, polymer solvent and coolant liquid from the peripheral zone of the cavity through a discharge port which opens from an internal surface of the housing at the periphery of the cavity and has the inlet means positioned close thereto at the upstream side thereof when the discharge port is viewed with respect to the rotary movement of the blades away from and towards same, so that the liquids entering through the inlet means are swept by the blades away from the discharge port and through a major segment of the peripheral zone of the cavity.

Preferably the polymer solution fed into the cavity is at a temperature of at least 100°C, has a viscosity in excess of 5 x 10-² Pa.s (50 centipoises), and is a hydrocarbon solution of a polymer selected from:

a. an olefin polymer having an intrinsic viscosity of at least 3.5 g/dl and selected from:
- (i) an ethylene homopolymer,
- (ii) a copolymer containing at least 90 weight percent of polymerized ethylene and the balance a polymerized olefin hydrocarbon containing at least 4 carbon atoms,
- (iii) a propylene homopolymer, and
- (iv) a copolymer containing at least 50 weight percent of polymerized propylene and the balance polymerized ethylene:
b. a mixture of olefin polymers of (a), and
c. a mixture of polymers containing at least 20 weight per cent of an olefin polymer of (a) and up to 80 weight percent of diluent polymer that is soluble at 100°C in the solvent employed in the process.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:-

Fig. 1 is an end view of centrifugal spinning apparatus, partially in section with parts broken away.
Fig. 2 is a view taken through lines 2-2 of Fig. 1.
Fig. 3 is a view of the rotating spinner blades as seen from the inner peripheral surface of the apparatus of Fig. 1 with the peripheral surface extended into a flat plane to show the pattern made by the rotating blades.
Fig. 4 is a view taken through lines 4-4 of Fig. 3.
Fig. 5 is a side plane view showing three pieces of the centrifugal spinning apparatus shown in Fig. 1 ganged together and driven by a common shaft.

Referring to Figs. 1 and 2, the centrifugal spinning apparatus includes a housing 20 having a cylindrical cavity 30 machined therein and having downwardly and outwardly extending lower discharge port 22 which terminates at its lowermost end in an opening 24. The ratio of diameter to depth in cavity 30 preferably is at least 5.0:1.0. Cavity 30 normally is covered and sealed by a removable front plate 32. Front plate 32 is held on the position on the front of housing 20 by means of a plurality of nuts 34 secured to the ends of bolts 36 which are pivotally mounted to housing 20 and extend through U-shaped slots 38. A centrifugal spinner consists of blading rigidly mounted within cavity 30 on a driving shaft 40. The blading consists of four double-bladed elements the two radially elongate blades of each element being shown as, respectively, 42a and 42b, 44a and 44b, 46a and 46b, and 48a, and 48b. The width of each blade is less than 2.54 cms. (one inch), and each narrow blade lies substantially in the plane of rotation. The elements are separated from each other by washers not shown and are locked in fixed positions by suitable keys not shown. The elements are offset from each other in fixed positions so that the blades 42a, 44a, 46a and 48a constitute one set of blades, each of which is offset substantially equidistant from each other, both in the rotational plane of the spinner and in the plane transverse thereto. In a like manner, the blades 42b, 44b, 46b and 48b constitute a second substantially-identical set of blades, with these blades also being offset sub- stantiaily equidistant from each other, both in the rotational plane of the spinner and in the plane transverse thereto. The spinner rotates in the direction of the arrow at high speed so that the tip speed of each of the blades is at least about 60 metres/second (200 feet per second) and preferably greater than 150 metres/second (500 feet per second).
Two inlet ports in the housing 20 at the periphery thereof include slots 50 and 52 of rectangular cross-section opening from the inner peripheral surface of cavity 30 and extending axially throughout substantially the entire depth of the inner peripheral surface in a plane transverse to the rotational plane of the spinner. The inlet ports include also openings 54A, 56A in the periphery of the housing 20, said openings communicating with the slots 50 and 52 and being tapped to receive liquid feed tubes 54 and 56. Thus, the three ports opening from the surface of cavity 30, being close together, extend over a minor segment of the peripheral surface of the cavity. Moreover, the inlet ports are at the upstream side of the discharge port when the discharge port is viewed with respect to the rotation of the spinner, so that the liquids entering the inlet ports are swept away from the discharge port. In operation of the process, it is customary to drive a plurality of units from a single shaft. Fig. 5 illustrates three units being ganged together for operation off one drive shaft.
While the apparatus illustrated in the draw- íngs represents the preferred embodiment of the invention as presently perceived by the applicants, a number of modifications can be made therein. The apparatus illustrated contains four blading elements of which the blades constitute two separate sets of blades. By increasing the ratio of the cylindrical cavity's depth to its diameter, it is possible to mount a significantly greater number of elements on the shaft. While the illustrated apparatus is mounted so that the spinner blades rotate in the earth's gravitational field, the apparatus can be rotated 90° so that the spinner rotates in a plane perpendicular to the earth's gravitational field. When operated in this mode, the product discharge port is in one side of the apparatus and the centrifugal force of the spinner blades transfers product into the discharge port.
In operation the spinner is rotated by an external motor at high speed to provide tip speeds in excess of 60 metres/sec. (200 ft./sec). At these speeds, the two tips of each element, e.g. 42a and 42b, 44a and 44b, etc., function essentially as one continuous knife blade. This action is shown in Fig. 3 in which rotation of the spinner blades is shown in an extended, flattened plane. A polymer solution, consisting of about 4 weight percent of a high molecular weight olefin polymer having an intrinsic viscosity of at least 3.5 dl/g dissolved in a kerosene-type hydrocarbon, heated to a temperature of about 190°C, is fed to cavity 30 through inlet port 50. Upon entering cavity 30, the polymer solution impinges upon the spinner blades and is broken up into a multiplicity of droplets which are carried by centrifugal forces around a major segment of the periphery of cavity 30 until they reach discharge port 22. Virtually all of the droplets of polymer solution will come into contact with the face of a spinner blade. When this occurs the droplets as indicated by 60 and 62 in Fig. 4 are attenuated by centrifugal force to form thin polymer streams as shown, this action having the effect of orienting the solute polymer molecules in the direction of the applied centrifugal force.
A coolant liquid, preferably water, is fed to cavity 30 through inlet port 52. The coolant liquid impinges upon the spinner blades and is carried to discharge port 22 by centrifugal forces in the manner previously described. Upon contacting the spinner blades, the coolant liquid removes heat from the blades which are thus cooled and the polymer solution in contact therewith to cause the polymer to precipitate from the solution in the form of fibrils.
When the polymer solvent, precipitated fibrils and coolant liquid come to the discharge port 22, they leave the centrifugal spinning apparatus via opening 24 and are collected for further processing and recovery. Typically, the product will be treated and recovered in the manner as illustrated and discussed in U.S. 4,013,751. Specifically, the product will be passed through a wringer to express the bulk of the liquid from the polymer solids which then will be beaten one or more times in isopropanol to remove the remainder of the solvent and coolant liquid from the fibrils. The fibrils then are filtered and dried for use.
The process of the invention can be employed to prepare fibrils from essentially any polymer solution in which the difference in polymer solubility between the two operating temperatures is sufficiently large. The quality of the fibrils produced, of course, will be importantly influenced by the polymer from which they are prepared.
Fibrils of optimum properties are prepared from olefin polymers having a very high molecular weight such that the polymer has an intrinsic viscosity of at least 3.5 dl/g. One species of such polymers consists of ethylene polymers containing, on a weight basis, at least 90% of polymerized ethylene. Such ethylene polymers will be ethylene homopolymers or ethylene copolymers containing small quantities of C₄ or higher olefin comonomer such as butene, hexene, styrene, a conjugated diene such as butadiene, or the like. A second species of such olefjn polymers consists of propylene polymers containing, on a weight basis, at least 50% of polymerized propylene. Such propylene polymers will be propylene homopolymers, or propylene copolymers containing up to 50% of copolymerized ethylene.
In the preparation of the fibrils of this invention, fibrils having a highly satisfactory combination of overall properties are obtained when the polymer employed in the process consists entirely of an olefin polymer as described above. It has been observed, however, that fibrils of generally satisfactory properties can be obtained when a mixture of polymers is employed in the process, provided that the olefin polymer as described above, constitutes at least about 20 weight % and preferably at least 35 weight % of the total polymer employed in the fibril-manufacturing process.
Where polymers other than an olefin polymer, as described above, are employed as a part of the polymer used in the fibril-manufacturing process, the other polymers employed may be employed for either of two principal purposes. For one, such other polymers can be employed principally to lower the raw material cost of the fibrils to be prepared. In some cases, such other polymers can be employed to modify specific properties of the fibrils themselves, or the water-laid, paper-like sheets prepared therefrom. Regardless of the purpose for which such other polymers are employed, for convenience of description, the polymers employed in the fibril-manufacturing process, in addition to the olefin polymers described above, will be referred to as "diluent polymers". Diluent polymers suitable for this purpose are those set forth in U.S. 4,013,751.
The solvent to be employed in the process of the invention may be any liquid which will completely dissolve the olefin polymer employed in the process at an elevated temperature. It is highly desirable that the solvent employed have a significantly different capacity to dissolve the olefin polymer at different temperatures. The ideal solvents are those having a very low solubility for the olefin polymer at ambient temperature, but having a high degree of solvent power for the olefin polymer at temperatures above 140°C. Hydrocarbon solvents such as kerosene, mineral spirits, tetraline and aromatic hydrocarbons such as xylenes, have excellent characteristics for use in the invention and are the preferred solvents to be employed in the invention. Other solvents, however, such as certain of the chlorinated hydrocarbons, also can be employed if desired. The solvents employed should be liquids at ambient temperature and preferably should have atmospheric boiling points above 150°C and preferably above 180°C.
In a preferred process the polymer solutions employed should be heated to temperatures of at least 100°C and preferably 150°C or higher, and should have a viscosity in excess of 5 x 10-² Pa.s (50 centipoises). Polymer concentrations of 2 weight % or higher should be employed.
By reason of the process by which the fibrils of the invention are prepared, it is possible to make many modifications of the fibrils, which improve their utility in the manufacture of waterlaid sheets. By way of example, certain inorganic pigments, fillers, and the like can be incorporated into the polymer solution and remain physically encapsulated within the polymer filaments when they are precipitated from the fine polymer streams in the cooling step. Typical of the pigments that can be employed for this purposes include titanium dioxide, silica, calcium carbonate, calcium sulfate, and the like. In another variation of the invention, cellulosic papermaking fibres can be incorporated into the polymer solution and are encapsulated within the monofilaments in the cooling step. Waterlaid sheets prepared from such modified fibrils have enhanced opacity, improved printing characteristics, high water resistance, and the like.

Claims

1. Apparatus for the manufacture of polymer fibrils from a hot viscous solution of thermoplastic polymer, comprising a housing having an internal surface forming a cylindrical cavity, a centrifugal spinner mounted for rotation in the cavity, inlet means in the housing to provide for entry of the polymer solution and a coolant liquid into the cylindrical cavity, and a discharge port in the housing to provide for the removal of fibrils from the cylindrical cavity, characterised in that the centrifugal spinner includes central rotary driving means and a plurality of radially elongate blades rigidly connected to the driving means, said blades being disposed substantially in the plane of their rotation and having their tips in close proximity to the peripheral internal surface of the housing, the inlet means and the discharge port open from the internal surface of the housing at the periphery of the cavity, and the inlet means are positioned close to the discharge port and at the upstream side thereof when the discharge port is viewed with respect to the rotary movement of the blades away from and towards same, so that the liquids entering through the inlet means are swept by the blades away from the discharge port and through a major segment of the peripheral zone of the cavity.

2. Apparatus according to claim 1, wherein each blade has a width of less than 2.54 cms (one inch).

3. Apparatus according to claim 1 or 2, wherein the blades are spaced from one another peripherally and axially.

4. Apparatus according to claim 3, wherein the blades are arranged in at least two substantially identical sets each having its blades offset substantially equidistantly from one another both peripherally and axially.

5. Apparatus according to any one of claims 1 to 4, wherein the inlet means include first and second inlet ports opening from the peripheral internal surface of the housing.

6. Apparatus according to claim 5, wherein the inlet ports include slots extending axially over substantially the entire axial length of said surface.

7. Apparatus according to any one of claims 1 to 6, including means for feeding the different liquids to the first and second inlet ports.

8. Apparatus according to any one of claims 1 to 7, wherein the ratio of the peripheral internal sur^face's diameter to its axial length is at least 5.0:1.0.

9. Apparatus according to any one of claims 1 to 8, including means for rotating the spinner at a speed such that the tip speed of the blades is at least 60 metres/second (200 ft. per second).

10. A process for preparing fibrils from a hot viscous solution of a thermoplastic polymer which consists essentially of:

a. rotating a centrifugal spinner in the cylindrical cavity of a housing at high speed, the spinner including central rotary driving means and a plurality of radially elongate blades rigidly connected to the driving means, said blades being disposed substantially in the plane of their rotation and having their tips in close proximity to the peripheral internal surface of the housing,

b. feeding a coolant liquid and a hot viscous solution of thermoplastic polymer into the peripheral zone of the cavity through inlet means opening from an internal surface of the housing at the periphery of the cavity so that said coolant liquid and polymer solution are contacted by the outer end portions of said blades and are broken up into droplets and/or thin streams which flow over the surfaces of said blades whereby the polymer solution is subjected to high shear stresses and is attenuated to orient the solute polymer molecule in said polymer solution, and the blades are cooled and serve to cool the polymer solution in contact therewith so that fibrils are precipitated from the polymer solution, and

c. withdrawing a stream of fibrils, polymer solvent and coolant liquid from the peripheral zone of the cavity through a discharge port which opens from an internal surface of the housing at the periphery of the cavity'and has the inlet means positioned close thereto at the upstream side thereof when the discharge port is viewed with respect to the rotary movement of the blades away from and towards same, so that the liquids entering through the inlet means are swept by the blades away from the discharge port and through a major segment of the peripheral zone of the cavity.

11. A process according to claim 10, in which the polymer solution fed into the cavity is at a temperature of at least 100°C, has a viscosity in excess of 5 x 10-² Pa.s (50 centipoises), and is a hydrocarbon solution of a polymer selected from:

a. an olefin polymer having an intrinsic viscosity of at least 3.5 g/dl and selected from:

(i) an ethylene homopolymer,

(ii) a copolymer containing at least 90 weight percent of polymerized ethylene and the balance a polymerized olefin hydrocarbon containing at least 4 carbon atoms,

(iii) a propylene homopolymer, and

_'(iv) a copolymer containing at least 50 weight percent of polymerized propylene and the balance polymerized ethylene:

b. a mixture of olefin polymers of (a), and

c. a mixture of polymers containing at least 20 weight % of an olefin polymer of (a) and up to 80 weight % of a diluent polymer that is soluble at 100°C in the solvent employed in the process.

12. A process according to claim 10 or 11, in which the coolant liquid is water.

13. A process according to claim 10 or 11 or 12, wherein the tip speed of the rotating blades is at least 60 metres/sec. (200 ft. per second).