EP0019383B1

EP0019383B1 - Spinning process

Info

Publication number: EP0019383B1
Application number: EP80301366A
Authority: EP
Inventors: Paul Snowden
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1979-05-15
Filing date: 1980-04-25
Publication date: 1982-06-23
Also published as: NO801417L; NZ193641A; NO149357C; AU528448B2; EP0019383A1; DE3060576D1; FI65094B; CA1136366A; NO149357B; AU5822580A; FI65094C; FI801565A

Description

This invention relates to a spinning process and in particular to a process of producing fibres by centrifugal spinning from a solution containing a thermosetting aldehyde resin such as an amino- and/or phenol- aldehyde resin, particularly a urea- formaldehyde resin.
In our DE-A-28 10 535 we describe a process wherein the resin solution, containing a suitable curing catalyst, is centrifugally spun from a spinning cup rotating about a substantially vertical axis. A stream of cold, humid air is directed downwardly into and around the cup to retard evaporation of the solvent and curing of the resin while a stream of hot dry air is blown outwardly from beneath the cup so as to heat, and hence dry, the fibres spun from the cup and to transport them to a collecting zone.
In addition to retarding evaporation of the solvent and curing of the resin in the cup, the downward stream of cold, humid air into and around the cup provides an environment around the cup of cold humid conditions within which the fibres spun from the cup are attenuated prior to contact with the hot dry air.
In a preferred embodiment, the resin is spun through a series of perforations in the wall of the cup or from the rim thereof, entrained in a stream of the cold humid air thrown out of the cup by the rotation thereof. Where a perforated cup is used the resin flow rate is such that the perforations are not completely filled with the resin so that some of the cold, humid air flows through the perforations with the resin.
We have found that this stream of cold, humid air thrown out of the cup may provide the cold, humid environment for attenuation of the fibres, thus obviating the need for a downwardly directed cold, humid air stream around the outside of the cup. The spun fibres are thus attenuated while entrained in the cold, humid air stream emanating from the perforations of the cup. The attenuation is partly effected by the entraining air stream and partly by inertia effects, prior to contact with the hot, dry air stream.
However, in the absence of the downwardly directed stream of cold, humid air around the cup, the outwardly directed air stream having the fibres entrained therein emanating from the cup often gives rise to a torroidal vortex of cold, humid air of somewhat greater diameter than the spinning cup and located in a plane just above the spinning plane i.e. the plane of the fibres as they are spun from the cup. In some cases the fibres may be caught up by this vortex and become entangled and/or thrown up on to the underside of the top of the enclosure in which the spinning operation is conducted where, because the fibres are still only partially dried and hence are of a somewhat adhesive nature, they adhere and so are not transported to the collection zone. Eventually much adhering fibres interfere with the satisfactory spinning of the rest of the resin.
We have found that these problems may be overcome by spinning the fibres entrained in the outwardly directed stream of cold, humid air into an enclosure in which a stream of hot, dry air is flowing downwards and deflecting the outwardly directed stream of cold, humid air downwards. The downwardly directed stream of hot, dry air is utilised in addition to, or instead of, the upwardly and outwardly directed stream of hot, dry air from beneath the spinning cup.
Therefore according to the present invention we provide a process for the manufacture of fibres from a solution containing a thermosetting aldehyde resin and a curing catalyst therefor comprising

(i) feeding said solution to the interior of a spinning cup mounted within an enclosure and rotating about a substantially vertical axis,
(ii) feeding cold, humid air into the cup from whence it is pumped, by rotation of the cup, as an outwardly directed stream

(iii) providing in the enclosure a stream of hot, dry air at a temperature sufficient to dry the attenuated fibres, said stream being downwardly directed from above the spinning cup,
(iv) deflecting downwards the outwardly directed stream of cold, humid air having the fibres entrained therein,
(v) contacting said outwardly directed stream of air having attenuated fibres entrained therein with the stream of hot, dry air whereby said attenuated fibres are dried, and
(vi) transporting the attenuated fibres by said stream of hot, dry air to a collection zone.

The thermosetting resin is preferably a condensate of an amino compound with an aldehyde such as formaldehyde. Some or all of the formaldehyde may be replaced by a higher aldehyde such as acetaldehyde. The amino compound is preferably a polyamine, particularly urea and/or melamine. In order that the resin is water soluble, so that water can be used as the solvent, the amino compound is preferably urea, alone or in admixture with up to 5% by weight of melamine. Some or all of the amino compound may be replaced by a phenol such as phenol, cresol or resorcinol.
It is preferred that the molar ratio of aldehyde to phenol and/or amino groups is between 0.6:1 and 1.5:1, preferably between 0.7:1 and 1.3:1.
The curing catalyst, which is preferably added to the resin solution just before the latter is fed to the spinning cup, may be a weak catalyst such as di(ammonium) hydrogen phosphate or ammonium formate, a moderate catalyst such as formic acid, ammonium sulphate, ammonium chloride or ammonium dihydrogen phosphate, or a strong catalyst such as phosphoric, sulphuric, sulphamic or hydrochloric acid. The amount of catalyst will generally be within the range 0.05 to 1% by weight of the resin solids.
In some cases, particularly where the fibres are to be used in the manufacture of paper, it may be desirable to incorporate an adhesion modifier into the resin. Such modifiers include certain inorganic oxyacid radicals which react with aldehydes. Examples of suitable radicals include sulphite, phosphite, and borate radicals. When used as adhesion modifiers, such radicals are incorporated into the resin during the condensation of the amino or phenol compound with the aldehyde.
Alternatively adhesion modifiers, such as carbohydrates, particularly formose, may be incorporated into the resin solution before, during, or after condensation of the amino or phenol compound with the aldehyde. The incorporation of modifiers is further described in our DE-A-2 754 525 and DE-A-2 819 461.
The solvent used to make the solution is preferably water, but alternatively may be any solvent which is relatively volatile at the temperatures to which the spun fibres are heated by the hot, dry air stream.
In order to improve the spinning properties of the resin solution, it is preferred to incorporate into the solution a small amount of a thermoplastic polymer that is soluble in the solvent employed. Examples of suitable water soluble polymers include polyvinyl alcohol and polyethyleneoxide. The amount of thermoplastic polymer used is preferably 0.01 to 5% by weight of the thermosetting resin solids. While the thermoplastic polymer may be incorporated before or during condensation of the amino and/or phenol compound with the aldehyde, it is conveniently added with the curing catalyst.
The resin solution, to which the curing catalyst has been added, is fed to a spinning cup. The cup, which is mounted for rotation about a substantially vertical axis, is a hollow vessel having one or more spinning surfaces. For example the cup may be open-ended and the spinning surface comprises the end of the open wall thereof. Alternatively the cup wall may be provided with a plurality of spinning surfaces in the form of perforations. The size and number of perforations will be determined by the cup diameter and rotational speed: however typically for a 12 cm diameter cup rotating at 5000 to 10,000 revolutions per minute, 24 perforations of 3 mm width are suitable. The perforations are preferably rectangular in configuration and the resin solution feed rate and cup rotational speed are preferably adjusted so that the resin solution is spun from part of the perimeter of the perforations.
The spinning, solution preferably has a viscosity between 5 and 100 poise (0.5 and 10 Pa.s) at room temperature as measured by British Standard 1733 using cup B6. The viscosity may be adjusted by concentration or dilution of the solution as necessary.
In order to prevent premature curing of the resin and evaporation of the solvent, cold, humid air is supplied to the interior of the cup from whence it is pumped, by rotation of the cup, along with the resin solution. Normally air from the external surroundings of the spinning apparatus may be employed, e.g. ambient air having a temperature below 30°C and a relative humidity in excess of 50% is suitable. The temperature and humidity of the cold, humid air may be modified as necessary to provide satisfactory spinning but generally the air temperature should be below 40°C and the air should have a relative humidity above 40%. It will be appreciated that as the air temperature is reduced, the relative humidity need not be so high in order to retard drying of the spun fibres.
The fibres are entrained in the stream of cold humid air as they are spun from the spinning cup. While so entrained in the cold, humid environment the fibres are attenuated, partly by inertia and partly by the effect of the cold humid air stream. The fibres are preferably drawn out to a mean diameter of the order of 1 to 50 µm, particularly below 30 µm. To permit such attenuation it is necessary for the fibres to remain entrained in the cold, humid air stream for some distance from the spinning cup. Generally they should be so entrained until they have reached a distance of at least the diameter of the spinning cup from the axis of the cup.
The extent to which the fibres are attenuated depends on a number of factors, including the extent to which they remain entrained in a cold, humid environment, as indicated above. The stream of hot, dry air will eventually mix with the cold, humid air and dry the fibres thereby preventing further attenuation.
The extent of attenuation will therefore also depend on the relative velocities, positioning, temperature and humidity of the air streams.
In the process of the invention, the stream of cold, humid air emanating from the spinning cup is deflected downwards: it should be deflected downwards to such an extent that any torroidal vortex between the streams of hot, dry air and cold, humid air is eliminated to such an extent that the fibres entrained in the cold, humid air stream are not caught up in such a vortex. The cold, humid air stream may be deflected downwards by the downwardly directed hot air stream. Increasing the flow rate of the hot, dry air stream will reduce or eliminate completely such a vortex but at the same time will reduce the extent of attenuation of the fibres. However simple experimentation particularly aided by an inspection window in the casing of the spinning apparatus and suitable illumination, will reveal whether the fibres are being caught up in any vortex, while examination of the product will reveal whether the desired attenuation has been achieved. However where the design of the system is such that the downwardly directed hot air stream would deflect and mix with the outwardly directed cold air stream too early; i.e. before the fibres have attenuated sufficiently, the hot air stream may be deflected outwardly by a subsidiary stream of cold, humid air above the spinning cup. This subsidiary stream may have a downward component which causes some or all of the downward deflection of the stream of cold, humid air having the fibres entrained therein. The process is conveniently set up by fixing the temperature, humidity and flow rate of the cold, humid air stream(s), the resin feed rate, and the rotational speed of the cup, and then adjusting the flow rate and temperature of the hot, dry air to eliminate vortex formation and to give fibres having the desired degree of attenuation.
The temperature and rate of flow of the hot, dry air stream must be sufficient to dry the attenuated fibres to render them non-sticky. The temperature of the hot, dry air is preferably in the range 80 to 270°C, particularly 100 to 220°C. The relative humidity of the hot air is preferably below 5096. Conveniently the hot, dry air may simply be ambient air heated to the desired temperature without any drying step.
In some cases it may be found that a vortex is formed below the spinning cup. While it is not necessary to eliminate such a vortex, its removal may be desirable in some cases. It may be eliminated by the provision of an outwardly directed stream of air from below the cup and/or by the provision of a suitably shaped housing below the spinning cup to give streamlined flow of the air streams thereover.
The stream of hot, dry air serves to dry the fibres and to transport them to the collection zone. The hot, dry air may also serve to at least partially cure the resin. Further curing of the resin fibres may be effected, if desired, by heating, for example in an oven, at 80 to 250°C, preferably 100 to 200°C for a suitable period of time. The nature and amount of the catalyst, together with the spinning and post spinning heat treatment conditions will determine the degree of cure for any given resin. For some applications it may be desirable to only partially cure the resin. The degree of cure may conveniently be assessed by determining the proportion of fibre dissolved in water under specified conditions. A suitable procedure is as follows:

A sample (approx 5g) of the dry fibre is accurately weighed and then digested with 200 ml of water for 2 hours at 50°C. The undissolved fibre remaining is recovered by filtration and dried at 100°C in air for 2 hours and then reweighed. The (%) degree of cure is defined as

The use of certain partially cured resin fibres in paper manufacture is described in our European patent application 80.300016 & EP-A-14026.
Fibres produced by the process of the invention are of particular utility in paper manufacture either as the sole fibrous constituent or in admixture with cellulosic fibres, e.g. conventional mechanical or chemical pulp, or other synthetic fibrous materials, e.g. polyolefin fibres.
Two embodiments of the invention are illustrated by reference to the drawings in which Figure 1 is a vertical section through the apparatus of a first embodiment and Figure 2 is a vertical section through part of the apparatus of a second embodiment. In Figure 1 the spinning apparatus has an outer casing 1 on the top 2 of which is mounted a motor 3 driving a shaft 4 carrying a spinning cup 5. The cup 5 has a vertical side wall 6 in which there is provided a plurality of rectangular perforations 7. Resin solution, in admixture with a solution of a curing catalyst, and optionally a soluble thermoplastic polymer, is fed to the cup 5 via a feed pipe 8. Cold, humid, air is fed to the cup via an air feed pipe 9. On rotation of the cup, e.g. at 5000-10,000 revolutions per minute, the resin solution is spun from the lower edge of the perforations 7 as fibres 10 entrained in an outwardly directed stream 11 of cold, humid air pumped from the supply 9 through the perforations 7 by rotation of the cup 5. Between the top of cup 5 and casing 1 is a shroud 12 surrounding the drive shaft 4 and feed pipes 8, 9. A small gap 13, for example about 1 mm, is left between the bottom of shroud 12 and the top of cup 5. Rotation of cup 5 also causes an outwardly directed stream 14 of the cold, humid air to issue from gap 13. Hot, dry air is pumped to a plenum chamber 15 on the top 2 of the apparatus from whence it flows as a downwardly directed stream 16 through an annular orifice 17. This stream 16 of hot, dry air is deflected outwardly by the stream 14 of cold, humid air issuing from gap 13 and impinges on the stream 11 of cold, humid air issuing from the perforation 7 of the cup, deflecting the stream 11 downwards thereby eliminating the torroidal vortex 18 (shown dotted) which would form in the absence of the downwardly directed stream 16 of air. The shroud 12 may, if desired, be provided with vanes (not shown) to deflect the hot, dry air stream outwardly thus augmenting the radial deflection given by stream 14.
While the fibres 10 are entrained in the cold, humid, air stream 11 drying is retarded so that they are attenuated, partly by the effect of the cold, humid air stream 11.
The stream of hot, dry, air 16 eventually mixes with the stream of cold, humid air 11, dries the fibres 10, and transports them to a conveyor (not shown) at the bottom of the spinning apparatus.
Beneath cup 5 there is provided a housing 19 which serves to streamline the air flow. A hole 20 is provided in housing 19 beneath cup 5. The rotating cup 5 acts as an air pump drawing air in through hole 20 and expelling it radially as a stream 21. This air stream prevents the formation of a vortex below the spinning cup 5.
In Figure 2 the spinning cup 22 comprises a hollow vessel divided into upper and lower portions by an integral plate 23 having a plurality of perforations 24 therein. The cup is driven by a shaft 25. A resin feed supply tube 26 extends through the open upper end of cup 22 and supplies the resin on to plate 23 from whence it passes, through perforations 24, on to the interior wall 27 of the lower portion of cup 22. The resin flows down wall 27 and is spun as fibres 28, by centrifugal force, from the lower edge of wall 27.
Cup 22 is mounted for rotation within an enclosure, not shown, carrying a stationary shroud 29 surrounding the drive shaft 25 and the resin supply tube 26. Cold, humid air is pumped down the interior of shroud 29. Some of the cold, humid air flows into the upper portion of cup 22, through perforations 24 and out of the bottom of the cup as an outwardly directed air stream 30 having the fibres 28 entrained therein. A deflector ring 31 mounted under and rotatable with plate 23 is provided to limit the flow of cold, humid air and to direct it outwardly to entrain fibres 28.
The remainder of the cold, humid air flows outwardly as a stream 32 from between the bottom surface 33 of shroud 29 and the top surface 34 of cup 22. These bevelled surfaces 33, 34 impart a downward component to the air stream 32 flowing from therebetween.
Outside cup 22, but within the enclosure, is a downwardly directed stream 35 of hot, dry air. This stream 35 is deflected outwardly by the air stream 32 so that it does not meet the cold air stream 30 flowing out of the bottom of cup 22 with the fibres 28 entrained therein until the fibres have been attenuated to the desired degree. As cold air stream 32 has a downward, as well as outward, component it also serves to deflect the cold air stream 30 flowing out of the bottom of cup 22 downwards thus eliminating vortex formation.
As in the embodiment of Figure 1 a housing 36 is provided to smooth the air flows below the cup 22. This housing 36 is provided with an aperture 37 from which air is drawn, and thrown outwardly by the pumping action of the rotation of cup 22, as an air stream 38.
The invention is further illustrated by the following example.
An aqueous solution of a urea/formaldehyde resin having a urea:formaldehyde ratio of 1:2 and a solids content of 65% by weight was mixed with 16 ml, per 100g of the resin solution, of an aqueous solution containing 2.5% by weight of a polyethyleneoxide of mean molecular weight 600,000 and 0.44% by weight of ammonium sulphate as curing catalyst. The resultant solution, which had a viscosity of about 20 poise (2 Pa.s) at room temperature, was spun into fibres using apparatus of the type shown in Figure 1 but in which housing 19 was omitted.
The solution was fed at 20°C at a rate of 80 ml/min (approx 75g of resin per minute) to the spinning cup which had a diameter of 12 cm and 24 rectangular perforations of 3 mm width and 5 mm height in its sidewall. The rotational speed of the cup was 7000 revolutions per minute.
Air at 30°C and 70% relative humidity was fed to the cup at a rate of approximately 63 m³/hour. Dry air at 170°C (obtained by heating ambient air to 170°C without any drying step) was fed to the plenum chamber at 185 m³/h from whence it flowed via an annular gap of 20 cm outside diameter and 4 cm width, into the spraying chamber which had a diameter of 1.2 m. The resultant stream of hot, dry air deflected the stream of cold, humid air emanating from the spinning cup perforations and from the gas between the shroud and the top of the cup, downwards and carried the fibres, while drying them, to the collection zone. The resultant fibres had an average diameter of about 8 ,um.
The process was repeated varying the spinning conditions as set out in the following table.
In run 4 it is seen that the hot air flow rate was insufficient to prevent the fibres from being flung onto the vessel roof. In run 6 the hot air flow rate was too great and did not permit the fibres to remain entrained in the cold, humid air stream for a sufficient time.

Claims

1. A process for the manufacture of fibres from a solution containing a thermosetting aldehyde resin and a curing catalyst therefor, comprising

(I) feeding said solution to the interior of a spinning cup (5;22) mounted withirr an enclosure and rotating about a substantially vertical axis,

(ii) feeding cold, humid air into the cup from whence it is pumped, by rotation of the cup, as an outwardly directed stream (11,30; 14,32) whereby said resin solution is spun from the cup into said enclosure as fibres (10;28) entrained in said outwardly directed stream (11;30) of air wherein said fibres are attenuated,

(iii) providing in the enclosure a stream (16;35) of hot, dry air at a temperature sufficient to dry said attenuated fibres,

(iv) contacting said outwardly directed stream (11;30) of air having attenuated fibres entrained therein with the stream (16;35) of hot, dry air, whereby said attenuated fibres are dried, and

(v) transporting the attenuated fibres (10;28) by said stream (16;35) of hot, dry air to a collection zone, characterised in that the outwardly directed stream (11;30) of cold, humid air having the fibres (10;28) entrained therein is deflected downwards and contacted with the stream (16;35) of hot, dry air which is directed downwards from above the spinning cup (5;22).

2. A process according to claim 1 characterised in that the stream (16;35) of hot, dry air is deflected outwards by a subsidiary outwardly directed stream (14;32) of cold, humid air above the spinning cup.

3. A process according to claim 2 characterised in that the stream (11 ;30) of cold, humid air having the fibres (10:28) entrained therein is deflected downwards by said subsidiary stream of cold, humid air which subsidiary stream (32) has a downward component in addition to its outwards component.

4. A process according to any one of claims 1 to 3 characterised in that the outwardly directed stream (11;30) of cold, humid air having the fibres (10;28) entrained therein is not contacted with the stream (16;35) of hot, dry air until the fibres have reached a distance from the axis of the spinning cup at least equal to the spinning cup diameter.

5. A process according to any one of claims 1 to 4 characterised in that a further stream (21:38) of hot, dry air is provided outwardly directed from below the spinning cup.

6. A process according to any one of claims 1 to 5 characterised in that the resin solution is spun as fibres from perforations (7) in the wall of the spinning cup (5).

7. A process according to claim 6 characterised in that the resin solution is spun from part of the perimeter of each perforation (7) with the outwardly directed stream of cold, humid air flowing through the remainder of said perforation.

8. A process according to any one of claims 1 to 7 characterised in that the fibres are spun from an aqueous solution of a resin formed from formaldehyde and an amino compound component comprising urea and 0 to 5% by weight, based on the weight of said amino compound component, of melamine.

9. A process according to any one of claims 1 to 8 characterised in that the fibres are spun from an aqueous solution of said thermosettinq aldehyde resin, said solution containing 0.01 to 5% by weight, based on the weight of the resin solids, of a water soluble thermoplastic polymer.