CA1118974A - Production of formaldehyde resin fibres - Google Patents

Abstract

ABSTRACT

Formaldehyde resin fibres, in particular urea formaldehyde resin fibres, are produced by introducing a liquid formaldehyde resin and a catalyst into a spinning cup in the presence of cold humid air which inhibits drying and reaction, centrifugally spinning fibres from the cup into the path of hot air currents, at between 50°C and 100°C, which dry the fibres without curing them, and curing and chemically stabilising the dry fibres by heating at above 100°C until they are insoluble in cold water, The fibres are useful in paper-making,

Description

~ 29406 9~4 ~HE PRESE~ INVE~TI0~ RELATES to a proces~ for centrifugally apin-ning fibres from a liquid formaldehyde resin. ~he formaldehyde resin i~ preferably urea formaldehyde resin, but it may be melamine formalde-hyde reain, phenol formaldehyde resin, resorcinol formaldehyde resin, cre~ol formaldehyde resin, or a mixture of any two or more of the ~aid resins. ~he invention is hereinafter described with partioular refer-ence to the centrifu~al spinning of ~F resin.
A liquid ~F resin is used (for example an aqueous solution thereof) and its viscosity adjusted, if necessary, to a preaelected value between 5 and 300 poise, preferably between 15 and 75 poise. ~he resin is mixed with a liquid catalyst whi¢h allows the resin to ~f~ve a usefully long pot~life at room temperature but which, at temperat~res above 100C, partioularly above 120C, cures and ohemically stab:ilizes the resin and renders it inaolubIe in oold water.
~he liquid re~in and catalyst mixture (if de~i~ed with one or more additives, auoh a~ a ~pinning aid and/or a surfactallt) i~ fed at a pre-selected (but variable) ra-te into a spinning-cup or the like rotating at - a high pre~selected (but variable), ~peed. Rurely by way of example9 oup~
having diameters in the ran~e 3" to 5" have been uaed with rotational speeds of 3000 to 5000 rpm.
~he resin/catalyst mixture in the spinnin~ oup is located below and in the path of a downward flow of oold humid air, part o~ which enters the cup sub~tantially co-currently with the mixture and part of which may be deflected outwards by and away from the oup as outwardly-directed current~
f cold humid air. ~he purpose of the cold1 humid air i~ to inhibit dr~-ing or reaction of the resin/catalyst mixture at least whil~qt in the oup.
~sually ambient air may be used, but if nPcessary its temperature and humidity may be ad~usted as required~
The resin/cataly~t mixture, in the pre~ence of cold humid air9 flow~
over the inner surface and wall of the cup, and is ~pun centrifu~ally out-

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3 29406 ward~ wi-th the cold humid air, from the rim of th~3 oup or from a plurality of apertures provided at re~ular intervals in the circumferenoe of the wall of the oup, in the form of individual separat;e fibres. As the fibres spin outward~ from the cup in the presenoe of the oold humid air ourrent3 and before they are dried or oured, they oontinue to be drawn out and be-oome attenuated or stretohed into fibre~ Or smallB:~ diameterO When they have aohiev~d the desired diameter a~d befo~3 they have had a chanoe to develop into droplets or shot, they are dried and ;ohyaioally stabilized by heat, ~nd transported to a oolleoting zone.
The~e latter heating and transportin~ steps axe oarried out by hot, dry current3 of air flowin~ outwarda from below,ancl away from, the spin-ning oup. Eot, dry air may be oaused to flow from below the oup toward3 the bottom of the oup, which deflects it outwards. If nec3ssary, means may be provided on the bottom of the oup (for exam~lle an axial fan and/
or a radial propeller or the like) to ensure that the hot air is defleoted to foxm outwardly-flowing hot dry air ourrent~. Th!e hot air ia at a temp-erature whioh will heat the fibres above 50C but b~310w 100C, typioally to 65 C or 70C, at whioh temperature the fibres are dried and ph~æically atabilized without, however, cau~ing the oatalyst to oure and ohemioally stabilize them. ~ha hot dry air currents also ~erve the purpo~e of ~up-porting the fibres and oarr~in~ them to a oollectin,g zone whioh, in un-oonfined oondition~, would normally be in the form of an annulus havin~
the ~plnning oup a~ it3 oentre, but at some distanoe away from, and below, the oup.
The dried (but unoured) fibrss are remo~ed froDI the colleoting zone and then oured and ohemioally stabilized by the oataly~t, by heating (for example in an oven) at over 100 C, typioally at between 120C and 140C
until the oure is oomplete and the fibres are insoluble in oold waterO
~he pre3ent invention aooordingly provides a prv^oe3~ for centrifug-ally 3pinning formaldehyde flbre3 from a liquid forlDaldehyde re~in whioh - ~ 29~L06 g~L

comprises the ~teps of feeding the resin and a resi~-curing catalyst, which at temperature3 above 100C will cure and chemically stabilize the resin and render lt in~oluble in cold water, into a rctating spin-ning cup, direoting downwardly towards the cup a flow of oold9 humid airJ at least part of which flow enters the cup with the resin/oat-alyst mixture, the temperature and humidity of the air being such that it inhibits dryin~ and reaction of the resin/catalyst mixture whilst in the oup, the rotation of the cup oausing the re~in/catalyst mlxture to flow as an even film over the inner surface of the oup, in the presence of the cold, humid air, and to be ~pun centrifugally from the outer wall of the oup, in the form of individual, separate fibIes whi¢h attenuate or qtretoh until they have achieved the desired diameter, providing from below the oup outwardly-directed current;s of hot dxy air at a temperature such as to heat the fibres to between 50C and 100C to dry the attenuated or stretohed fibres and transport them to a oolleotirlg zone, removing the : dry fibres from the collecting zone, and ourin~ and ohemioally stabilizing them by heating at above 100C until they are insoluble in cold waterO
Preferably, at leaat part oP the downwardly-direc-ted flow of cold~
humid air i~ defleoted outwardly by the oup to foxm outwardly direoted CUI' rent~ of oold humid air/ and the fibres are spun fro~ the oup into the path of the sald current~.
The invention iB hereinafter described with referenoe to the aooomp-anyin~ drawings, wherein:-Fig. 1 illustrates, ~chematioally, the pro¢ess aocorcLing to the inventio~
25 for centrifugally spi~ning and colleoting formaldehyd.e resin fibres by : introduoinOE a liquid resin (for example, an aqueous ~ea formaldehyde resin) into a rotating cup, Fig. 2 illustrate3 one form of cup, in whioh the ~ibres are spun oen-tri-fugally from the upper lip of the oup;
Fig. 3 illustrates an invexted oup, in which the fibres are spun oentrifug-l8~

ally from the lower lip of the cup;
Fig. 4 illu~trates another form of cup, in which the fibres are spun centri-fu~ally through hole~ provided in the circumference of the cup, and ~ig. 4a ~how~ the same cup in operation;
Fig. 5 illu~trates another form of cup, in which the fibres are spun centri-~ugally through ~lots provided in the circumference of the cup, and Fi~. 5a ~hows the same cup in operation; and ~ig. 6 illustrates an alternative form of cup, in which fibres are ~pun through groove~, serrations or the like provided in the upper rim of the cup.
Referring to ~ig. 1, aqueous ~F resin of viscosity 5 to 300 poise, preferably 10 to 100 poise, more preferably 15 to 75 poise, i~ introduoed ~ -at 1 into a mixer 2, where it is mixed with an aqueous solution of a resin-curing catalyst intr3duced at ~ he addition of a spinnin~ aid, such as polyethylene oxide ~olution, and/or of a surfactant, such as "Lissapol",to the mixer 2 is advantageou~ rom the mixer 2, the ~ resin mixture is introduced onto thc ba~e of a rotating cup 4 driven by a motor 5~ ~he resin ~pread~ over the base and the wall of the oup 4 as a thin film, and is spun from apertures 6 in the wall of the rotatin~ cup under such con-ditions a~ to produce a plurality of individual, separate fibres. ~he~e are allowed to attenuate or 3tretch to the diameter de3ired therefor, with-out drying or curing or disturbance from turbulent airl by first spinning them i~to a region of low temperature and high humidit;y. Such a region i~
provided by a downwardly-directed flow of oold, humid air which partly *lows through the apertures 6 with the fibres and which is partly deflected outwardly by the cup, to form outwardly directed currerlts of cold humid air as shown by the arraws A. The pumping action cau3ed b~y the rotation o~ the cup 4 causes the cold, humid air to be deflected outwaraly with, and in the same manner and direction as~ the fibres, thereby reducing the relati~e velo~ity between the cold, humid air and the re~in fib e~ during the attenu-* Trade Mark B ~:

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ation and stretching of the resin fibres ]:n most cases, ambient air will be suitable When the desired fibre diameter has been attained, the resin fibres are dried and transported to a fibre-collecting point by suitable outwardly-direc~ted currents of dry, hot air indicated by arrows B in Fic~. 1. These currents B may be created by a radial propellor 7 and an axial fan 8 fitted to the bottom of the cup 4. The hot dry air is at a temperature such as to heat the fibres to between 50C and 100C, for example about 6CioC or 70C.
After the spun fibres leave the CUp, they continue to be drawn out and attenuated or stretched into fibres of : smaller diameter, but they are physically stabilised b~
the heat of the dry, hot air currents B, during their free flight from the cup, after they have attained the desired diameter but before they have a chance to develop into droplets or shot.
After collection, the fibres are cured and chemically stabilized by heating, during which the catalyst not only cures them but renders them insoluble in cold water Suitable catalysts comprise acids or acid sallts, for example sulphuric acid, formic acid, ammonium salts ~for example ammonium sulphate), or mixtures thereof The curing is carried out at above 100C, preferably above ; 120C.
One suitable cup design for use in the invention is illustrated diagiamatically in Fig 2 of the accompanying drawings Liquid resin (e.g. a UF resin sol.ution) is fed through 9 with a liquid catalyst to the bott:om of the rotating cup 4; it flows radially across the~ cup and then up the walls of the cup, where flow irregulcsrities are smoot~ed under the centrifugal forces operat.ing in the rotating cup. At the correct flow rate, ibres are spun outwardly from the lip 10 of the cup. The height of the cup is such as to allow the flow rate to be smoothed and depends upon the diameter of the cup, its rotational speed, and the viscosity of the liquid resin being spun .. , ~ ~. ~

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The diameter of the cup and its rotational speed can be varied over quite large ranges, and are adjustable to gi~e the flow rates required by the process An alternative apparatus for use in the process of the invention is illustrated in Figure 3, in which the liquid resin and catalyst are through 11 fed onto a xotating disc 12 surroun~ed by a downwardly-extend annular wall 13, the wall and the disc forming an inverted cup The resin flows radially across the disc 12 and down the inner surface of the annular wall 13 where fibres are spun centri-fugally outwards from the bottom lip 14 thereof The throughput of the cup designs illustrated in Figs 2 and 3 is limited by the fact that, above a certain critical resin flow-rate (which depends, inter alia, upon the diameter and depth of the cup, its rotational speed, and the viscosity of the resin), the resin tends to leave the rim of the cup as a two-dimensional sheet before breaking up into irregular fibres, instead of leaving the rim of the cup as individual, separate fibres The effect of exceeding the critical resin flow~rate is illustrated in the Examples which follow hereunder.
Eowever, the limit to the resin flow-rate described above can be removed if the fibres are prevented from joining at the rim of the cup to form continuous two-dimensional liquid films. This can be achieved by the use of cups as shown in Figs. 4 and 4a, in which the cup wall 4 is provided with a plurality of equidistantly-spaced holes 15 extending into the interior of the cup. ~lhe embodiments of Fi~s. 4 and 4a are preferably operated at a resin flow rate such that the holes 15 are not completely filled with the liquid resin, but also allow the cold humid air to flow there-through together with the resin. The resin spins from the surfaces of the holes 15 as a film which collapses to form a fibre which generally has an elliptical cross-section.
The distance between adjacent holes 15 must be greater than that necessary to allow for the :

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., elastic expansion of the resin upon leaving the hole.
The holes 15 of Figs. 4 and 4a may be re~placed by equidistantly-spaced slots 16, as shown in Fiqs. 5 and 5a.
Cups with grooved, scalloped, serrated or castellated rims 17, as shown in Fig. 6, work in the same manner as the holed or slo-tted cups of Figs. 4, 4a, 5 and 5a, until the resin flow-rate is such as to cause the resin to flood over the top of the rim of the cup. At such a high flow rate, the fibres will join 1~ together as a two-dimensional sheet and the cup will have reached its useful limit for the production of good qualiky fibres, However, with the holed or slotted cups of Figs. 4, 4a, 5 and 5a, the useful limit is probably not reached until the holes or slots are full of liquid In the following Examples 1 to 9, exper;ments were carried out using aqueous urea formaldehyde resin, vary-ing in viscosity from 15 poise to 300 poise, 3"-diameter cups and 5"-diameter cups of the types shown :in Figs. 2 20 and ~ were used, rotating at between 3000 rpm and 5000 rpm, In Examples 1, 2, 4 to 6, the resim was not catalysed and so are not in accordance with the invention, and the physical quality of the fibres was merely inspected and judged at the collecting point.
In Examples 3 and 7 to 9, the resin was catal~sed, and the fibres were removed from the collecting point and cured and chemically stabilised as described. -The fibres were judged to be of good quality if the bulk of them were in the form of separate, individual 30 fibres, or as fibres sufficiently loosely stranded so as not to impede their subsequent separation, and if they were substantially free of "shot" li e non- ~, fibrous formaldehyde-resin material of a size greater than the diameter of the thickest of the fibres). Good quality fibres also had a mean diameter betwelsn l~u and 30~u, preferably between 2~u and 20 Ju, and an average strength of at least 50 mega-Newtons per square metre.
The mast obvious characteristic of poor quality fibres was the presence of a substantial amount of "shot".

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EXA~IE 1.
"Aerolite 300" U/~ resin ~upplied by Ciba-Geigy was used. (Aerolite 300"
i8 an aqueous ~/F re~in prepared by condensin~ a mixture of urea and form-aldehyde in a ~:~ molar ratio of about 1.95:1, followed by concentration to a solids c~ntent of about 65% by wei~ht. It has a viscosi~y, depending upon its a~e, of about 40 to 200 poise at room temperature, and a water tolerance of about 18~/o). ~he resin was adjusted to a viscosity of abou~
75 poise, by the addition of water, and then fed to the bottom of a 3"
dia~eter cup shaped accordin~ to ~ig. 2, and rotating at a speea of 3000 rpm. At a feed rate of about 75 ml/minute, good quality fibre was prod-uced, ha~ing an average diameter of about 15 ~. ~t a feed rate of 200 mlj min., the resin wa~ spun from the ri~ of the cup aa a continuous two-dimen~ional sheet and gave poor quality fibre~.
blXAMPLE2.
~he experiment outlined in Example 1 was repeated usin~ "Aerolite 300"
diluted to abo~t 25 poise viscosity and with 2/~ "Lissapol" solution added.
Good fibrillation waa obtai~ed over a range of flow rates of about 60 ml/
~in~ to about 190 ml/min. At higher flow rate~, the fibres were o~ poorer, unacceptable quality.
EXAMPLE 3.
~ "Ae~ollte 300" re~i~, diluted to a viscosity of about 35 poi~e, was mixed ; with 6% by weight of a 2.4% aqueous solution of polyet;hylene oxide and ~fo - by wei~ht of a 3~% solution of ammonium sulphate in water, and then ~ed to a 24-holed 3"-diameter rotating cup of the type shown in Figo 4. At a feed rate of about 75 ml/min., good quality fibres of average diameter about 12 ~ were produced at a rotational speed of 5000 rpm, ~he fibres were removed from the collectin~ point, and cured by heating i~ an o~en at between 120 C ana 140 C for about 4 hours~ Thi~ ~t~bili3ed t~em Ghem-ically, and rendered them insoluble in cold water. ~nlike Example 1, gOoa ~0 fibrlllation waB still obtained at flow rates in exce~ of 12 Kg/min.
* Trade Mark ~B g ,:, ; .

(approx g litres/min). ~ L89'79~

"Aerolite 300" diluted with water to give a solution with viscasity 75 poise was spun from a 5"-diameteE~cup~ f the type shown in Fig~ 2, and rotating at 3000 rpm, Good fibres were produced at rat~s between about 50 and 200 ml~min _X MPLE 5 ~he experiment outlined in Example 4 was repeated using "Aerolite 300" resin with a viscosity of about 15 poise, Good fibrillation was obtained at flow rates between about lO0 and 250 ml/min, EXAMP~E 6 The experiment outlined in Example 4 was repeated, using "Aerolite 30Q" diluted to a viscosity of 25 poise with water, with the addition of 2% by weight of "Lissapol" solution, Good fibrillation was obtained at resin flow rates between about lO0 and 250 ml/min.

"Aerolite 300" resin, diluted with water to about 35 poise viscosity, was mixed with 6% by weight of a 2.4% solution of polyethylene oxide and 2% by weight of a 30% aqueous solution of ammonium sulphate, This was then fed to a 24-holed 5"-diameter rotating cup of the type shown in Fig. 4, At a `I speed of about 5000 rpm, good fibres of average di.~meter about 10 ~ were obtained at a feed rate of about 75 ml/min.
As in Example 3, good fibrillation was also observed at very ~, much higher feed rates, The fibres were removed from the collecting point, and cured by heating at between 120C and ~ 140C for about 4 hours. This stabilized them chemically, ~, - 30 and rendered them insoluble in cold water.

The following table sets out the formulation oE different resins and the conditions which were used to produce good quality fibres; in all cases a 3" cup with 24 holes was used at a rotation ~peed of 4500 rpm. The hot air r~emperature was ` , 1 ':
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75C. All the resins contained 1.6% by weight of a 2.4%
polyethylene oxide solution and 7% by weight of a 30%
ammonium sulphate solution. All the percentages hereunder are percentages by weight.
Resin Resin Viscosity Resin Feed Rake (poise) (g/min) 1. F:U ratio 1.95:1 Solids content 55% with 10%
glycerol added 25 78 10 2, As (1) except 10% ethylene glycol instead of glycerol 15 "
3 F:U ratio 1,95:1 Solids content 65%, 5%
melamine added 50 "

4. As (3) but 10% melamine added to the resin 50 ""

5. As (4) but melamine substituted by 10% resorcinol added to the resin 50 "
20 6. As (4) but melamine substituted by 10% cresol added to the resin 50 "
7. As (4) but melamine substituted by 10% p~enol added to the ~:
resin ~0 "

The following I~F resins were fibrillatecl using a 5"
diameter cup with 24 holes, rotating at 4500 rExm and using the same catalyst, spinning aid and hot air temperature as above.
30 Resin Resin Viscosity Resin Feed Rate (poise) (g/min) ::
F:U ratio 1.2:1 35 50 F:U 1,6:1 50 50 , .

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' ., , ~8974 All fibres produced were of good quality, and were cured at 120C for 3 hours.
The fibres produced in accordance with the present invention are particularly useful for use in paper-making, as described in our UK Patent Serial ~o, 1573115. ~~ ~ ~~

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Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for centrifugally spinning formaldehyde fibres from a liquid thermosetting formaldehyde resin which comprises the steps of feeding a mixture of the resin and a resin-curing catalyst, which at temperatures above 100°C
will cure and stabilize the resin to render it insoluble in cold water, into a rotating spinning cup, directing a stream of cold, humid air downwards towards the cup so that at least part of the stream enters the cup with the resin/
catalyst mixture, the temperature and humidity of the air being such that it inhibits drying and reaction of the resin/catalyst mixture whilst in the cup, the rotation of the cup causing the resin/catalyst mixture to flow as an even film over the inner surface of the cup, in the presence of the cold, humid air, and to be spun centrifugally from the outer wall of the cup, in the form of individual, separate fibres entrained in said cold humid air wherein the fibres attenuate until they have achieved the desired diameter, contacting the attenuated fibres with a stream of hot dry air to dry the attenuated fibres and to transport them to a collecting zone without causing curing of the fibres to the cold water insoluble condition, removing the dry fibres from the collecting zone, and thereafter heating the fibres at above 100°C to cure and chemically stabilize them until they are insoluble in cold water.

2. A process as claimed in Claim 1 wherein at least part of the downwardly-directed stream of cold, humid air is deflected outwardly by the cup to form outwardly-directed currents of cold humid air, and the fibres are spun from the cup into the path of the said currents.

3. A process as claimed in Claim 1, wherein the viscosity of the formaldehyde resin is adjusted to a pre-selected value within the range 5 to 300 poise.

4. A process as claimed in claim 1, wherein the catalyst comprises an acid or an acid salt.

5. A process as claimed in claim 1, wherein the resin/catalyst mixture contains a spinning aid.

6. A process as claimed in claim 1, wherein the fibres are spun from the upper lip of the cup.

7. A process as claimed in claim 1, wherein the resin and catalyst are fed onto a rotating disc surrounded by a downwardly-extending annular wall forming, with the disc, an inverted cup, so that rotation of the disc and wall cause the resin/catalyst mixture to flow radially across the disc and down the inner surface of the annular wall, and the fibres to be spun from the lower lip of the inverted cup.

8. A process as claimed in claim 1, wherein the lip of the cup is provided with a plurality of serrations equidistantly spaced around its circumference, and the fibres are spun through the said serrations.

9. A process as claimed in claim 1, wherein the outer wall of the cup is provided with a plurality of apertures equidistantly spaced around its circumference and extending inwardly to the inner wall of the cup, and the fibres are spun through the said apertures.

10. A process as claimed in claim 9 wherein the resin/
catalyst mixture flow rate is such that the apertures are not completely filled with the resin/catalyst mixture so that the cold, humid, air flows through the apertures with the resin/catalyst mixture.

11. A process as claimed in claim 1 wherein the liquid thermosetting formaldehyde resin is an aqueous solution of a urea-formaldehyde resin.