THE JOURNAL OF THE

Societv of Dvers and Colourists J J

VOl. S8-No. 2 FEBRUARY 1942 I.¶& Monl?bl2l

Proceedings of the Society SCOTTISH SECTION

Dyeing with Sulphur Dyes with Special Reference to Khaki, Blue and Grey Shades

Meeting held a t St. Enoch Hotel, Glasgow, on 24th October, 1941, Mr. J. A. YOUNCt in the chair.

H. BOOTHROYD

Tn producing yarns and cloths for Service requiremcnts sulphur dyea have played, and continue to play, an im portant part and it seems to be opportune to review the many problems arising from the various forms of dyeing employed in producing matorials made exclusively from vegetable fibres, or from Inixtures of cotton and wool.

After the Battle of France i t became necossary to ac- celerate production of textile equipment and every suitable dyeing method was employed.

Although, in general, the actual dyeing technicpa is the sanie for Service reqaircments as for gencral P U I ~ O S ~ S , there are certain new factors to be considered in the former case.

The principal difference betwoen dyeing for Sorvice requirements and for general purposes is that the dyer is committed to a dohi to specification when engaged on Government Contracts, and the specification usually contains stipulatiom not encountered in rivilian require- ments.

Certain khaki equipment, for example, must withstand prolongcd treatment with such products as hydrogen peroxide, citric acid and lactic acid, in addition to the desired standard of fasfness to light, washing, perspiration, alkalis, etc. Furthermore, a certain standard of penetra- tion and a high degree of resistance to water are expected. The finished yarn must not be proofed with wax, oil. rubber or other fusible solid and yet must float on warm water for a specified per~orl.

Much speculation has been caused among dyers regarding the inclusion of fastness to lactic and citric acids in the specification, and, in the absence of official explanation, it would appear that the most likely reason for their inclusion is the fact that these products react on the dyod fibre in a similar manner to metal polish, RO that a dyeing which meets tho sperification would not be altered in shade by metal polish spilled by a recruit during the button cleaning process. It is obvious, therefore. that the first doviation from the normal method of producing a shade is the mlection of dyes to meet the relevant speci6cation, since combillat ions which are adequate for general pwposm may prove iineuitable in reapact of resistance to lactic arid or citric acid.

Selection of .&ee-Exarnination of the Society's Cobur Z d f x reveals that there B no homogeneous Sulphur Khaki. I t is necessary then to employ two or three dyes to produce the desired shade. The principal cornbinations employed are-

(1) (2) (3) Sulphur Yellow Sulphur Yellow- Sulphur Orango

Sulphur Brown Sulphur Brown Sulphur Black Bulphiir Black Sulphur Black Sulphur Brown

Olive

(if necesstlry) The firat combination contains Sulphur Ycllow which is the most, fugitive member of t,he range.

It is well-known, howevor, that when sulphur dyeing6 are aftsrtreated by the copper-dichromete method, their festness to light is increased. In this treatment, the dyeing8 are worked in a solution of l-l+yo sodium dichro- mate, l-ltyo acetic acid and 1-1)% copper sulphate crystals, on the weight of the goods, a t 120'-140°r. for periods varying from 1-20 min., according to the method of dyeing employed, e.g. warp dyeing, hank dyeing, etc. I n Borne fonns of dyeing this aftertreatment B conveniently effected. but in others. particularly raw Rtock dyeing, it muses serious loss of production and may give rim to difficulties in subsequent carding and spinning operations.

In spite of the poor fastness to light of Sulphur Yellows, they have been extensively employed owing to two main reasons. Firstly, during periods of supply difficulties, there hae always bean a plentiful supply and, secondly and more important, the fastness to light undergoes a remarkable change when aftortreatod, and becomes equal. if not slightly superior, to the alternative comhinations.

It follows, therefore, that if the goods can be conveniently aftertreated, the adoption of the firat recipe will give satisfactory results as regard8 light fastness.

The second and third combinations give satisfactory fastness ta light without any aftortreatment and are suitable for the forms of dyeing where aftertreatment is impracticable.

All these combinations moot the specified 8tandard of resistance to hydrogen peroxide, lactic acid and citric acid.

Alt>liough the second and third combinations potwtw satisfactory fastnew to light without Bftertreatment, most dyem carry out the process to ininimise alteration of shade on storage. In large scale dyeing, washing-off does not remove all the sodium sulphide which retards oxidation and development of the final shade. Corn- sequently, goods not aftertreated are more subject to alteration of shade on storago and, since somo parts of stored goods are more exposed to the atmosphere than others, shade differences may be obsorved a few daya after dyeing. The aftertreatment process removes all traces of rosidual sulphide and oxidises the dye i o approximately its final shade.

Alteration of shade on storage is not confined to goods dyed with sulphur dyes and is worthy of more attention. Many people, particularly dyers. have observed with considerable surprise variations of shade in battle dress worn by recruits. e.g. tunics which differ from trousers and even sleeves which differ from the rest of the tunir. In view of the exacting dornands for accurate ahade match- ing this observation seems inexplicable, hut it w probably due to the fact that the same shade obtained by differcnt recipes ages in different directions on storage and, owing to the practice of matching against previous deliveries, one contractor's standard may gradually become gwner,

BOOTHROYD--“DYEING - - - ~ - _- - _ _ 26

whilst another’s may become iedder, thm accounting for these variations.

For the production of blues, there are several hoirio- geneous SUl hur dyes of satisfactory fastness availabb and many or the shades for Service cloth van be obtained by using a homogeneous blue. I n other cases, a certain proportion of black is required, whilst in others it is necessary to employ a mixture of two homogeneous Sulphiir Blues.

The Air I+iirce grey may bc dyed froin a homogeneous Sulphur Black and, from a dyeing point of view, this shade presents fewer difficulties than any other Service shade. It is customary to aftertreat dyeinga of grey with acetic acid and dichromate to stabilim the shade and 80 mini- misc rhange in shade on storage.

MAIN DYEING MET~IOA)Y &~PLOY*D

(1) Raw ,Stork Dyeing-This method is chiefly employed for production of cotton yarns for webbing which has to withstand a great deal of abrasion, e.g. straps, belts and equipment worn on the body, and for yarns s un from mixtures of cotton and wool for warp cmd we$ of such rloths a8 iinion shirtings.

Owing to the fact that the cotton is dyed ~ I I a finely divided state, the yarns spun from cotton dycd in thie form do not show grey or undyed patches when chafed. The ootton is usually dyed in batches of about 000-700 Ib., although in some caw8 lot6 up to 1200 Ib. are dyed. The dye may be dissolved in the dye vessel itself with the requisite amount of sodium sulphide in about one-quarter to one-third of the total dye-liquor. After boiling for 5 niin., water is added up to the total dyeing volume of liquor and the solution raised to b.p. The cotton is then thrown in, a n operation which ueually takes 36-60 min.. and tho liquor circulated by steam injectors.

I t is very advantageous to enter the cotton &B speedily as possible in order to avoid differcncos in shado and depth between the firet and last portions of the cotton to he entered, and the addition of a wetting-out agent, which tames the ootton to sink quickly, is to be reoom- mended. A h it is better to have the ootton pulled boforo charging, as cotton taken directly from the bale sinks very slowly owing to its compiwsed state.

Tho object of speedy charging is to reduce the disparity of the period of immersion between the first, portion and the lust portion to be charged, ae a certain amount of dyeing takes place even beforo addition of salt; i t follows. therefore, that if there is an interval of 30 min. between the entry of the first and last portions of the batch, the first portion (at the bottom of the dye vcssel) will be dyed darker than the rest.

In dyeing khaki shades, wherc a mixture of dyes is being iiscd, the position is further complicated owing to the variation of dyeing spoeds of tho individual dye8. When charging is slow, a deficiency of the dye which has tho highest dyoing speed is created by the time charging is complete and the dye-liquor at this stage is slightly different in tone from the original.

These inequalities may be overcome by diwlving thr dye8 separately and feeding the solution to the dye veesel as charging proceeds. When fully charged, the liquor i N boiled, circulated and, after 20 min.. the requisite amount of salt is added and dyoing allowed to proceed for 4-1 hr. ”he dyc-liquor is then run off and the cotton washed well and dried. Owing to the fact that it is difficult for liquors to penetrate to the centre of a large wet maw of cotton, the washing-off ~ ~ O C C S E i rather slow; in fact. after washing-off for 1 hr., it is poraible to h i 1 patches which are quite hot in the interior of the dyed maw. These patches still contain exhaust, dye-liquor and therefore residual sulphide. If an attempt, were made to treat such mateiial by the copper-dichromate process, there would bn a tlanger of producing Htains due to the formation of copper sdphide and to tho precipitation of dye from sfJhti011. When such material is (tried it would give rise to dustiness in the subsequent carding operationa. Consequently. good waahing-off is essential and dyes should be employed which do not require thc copper- dichromate aftertreatment to meet the fastness to light and washing specifications. Cotton dyed by this method is never quite uniform in depth, but the fibres are 80 well mixed in carding and spinning that R uniform yarn is ohtained.

WlTH SULPHUR DYES” . . - _. E’eb . , I V 42

YARN DYEINQ C‘op and C h e w Dyeing-These inethoda have been

Hdopted principally for dyeing single yarns for the pro- duction of cloths and %fold and 5-fold yarns for webbing; they give much better penetration than is obtained in war? or hank dyeing. Webbing produced from yarns dyed by these methods does not show undyed or weakly dyed placea when subjected to abrasion.

The main points to be observed are selection of dyes free from insoluble matter and the omploynient of the west brands of sodium sulphide. Specially purified rands of sulphur dyes are available for this work.

Warp Dyeiw-Yarns dyed by this method have been used chiefly for cotton gabardines, cloths constructed of cotton warp and woollen weft or worsted warp and cotton weft, as well a8 for cotton linings and for the pro- duotion of tightly woven cotton cloths, e.g. nurses’uniforma. which require to show better penetration than is possible in the case of piece-dyed goods. Both warp and weft yarns are dyed by this method and, in addition to observing the same precautions regarding selection of dyes to meet the epecificntion. it is advisable, when dyeing combination shades, e.g. khaki, to cbhoose dyes possessing similar dyeing speeda.

A comparatively large yuantity of yarn is passed through a small volume of dye-liquor which is constantly replenished with fresh dye solution to balance the rate of absorption. Since the warps may be 4,000-5,000 yd. long, it is obvious that, in cases where 3 dyes of varying dyeing speeds are employed, the shade of the dye-liquor will gradually change. I n order to overcome this undesirable feature it ifi necessary to use dyes of similar dyeing speed, or to use dyes of known speed and make the neoewary adjustment in the feed-liquor to maintain the original shade. When the desired shade is obtained, the goods are passed through a bath containing acetic acid and dichromate to stabilise the shade. (C) Hank Dyeimg-The bulk of the yarns dycd by this

method for Service requirements arc 3/10s, Ti/%. 2/19,, or 2-fold, 3-fold and 5-fold.

There are 801110 particular feature8 of the yarns which merit attention, vic.-( l).Hard twist; (2) multifold nature of the yarn; (3) water resistance which must be premivd; and (4) variation in dyeing affinity in yarns from different sources, e.g. India, America, Egypt, etc.

Hard-twisted and multifold yarn is difficult to penetrate and, since the beet possible penetration is required, there is a tendency to seek mistance by wing wetting-out agents for the pretreatment of the hanks before dyeing. The yarns principally used ~ O S S ~ % S a high degree of reaist- ance to water, due to natural wax content, and the hard twist. It is possible to emulsify the natural wax and so promote penetration, but t,he serious drawback to this proccdure is that, after dyeing, the water repellency almost disappears and the yarn is so absorbent that it will not float on warm water for the E cified period. Similarly, if the yarn is wetted-out w i g hot alkalinn solutions, the procese requires absolutely exact adjustment or will mult in either insufficient, removal of natural wax, which gives a yarn still difficult to penetrate, or a yarn 80 ahsorbont that it does not POSSOSS the specified degree of wat.er-repellenry. Experience seams to show that the best r~sul ts have lieen obtained by kior-boiling the yarn with water only. The combination of high temperature and p i ~ i i r a procluces a yarn thoroughly wetted-out and ost,abli~hos a condition which ermits smooth entry of dye particles into the yarn. wh&t the latter still retain# fmfflcient natural wax to give the desired degree of water- resistance. This resistance to water is increased by the copper-dichromate aftertreatment. The bulk of this claw of work is carried out in Huesong machines and the technique is the same as for general p u p o m .

Many dyers favour the 1188 of two or more homogeneous clyee for production of khakis, whilst others prefer a pre- pared mixture. Owing to variationa in yarn, with atten- dant variations in dyeing affinity, it. iR preferable to usc the individual dyes in order to make adjustments to tho shade when necessary. Since it is impossible to prepare a mixture to gib-e a definite shado on all types of yarn, diading is unctvoiclehle, and therofnre the former inethotl seems to be preferablo.

When the desired shade has been obtainod, it is very important to wash the goocb well to remove residual

( A )

( B ) E

~ - - -. _ _ _ _ - _ ~-

sodium sulphide. In all cases it is adviaable to add the acetic acid and dichromate first, and the copper sulphate last, in order to avoid preripitation of rnpper niilphide on the yarn.

PIECE DYEING)

In piece dyeing the princi a1 demands are (1) good penetration, ( 2 ) avoidance of SeTvedge marks, (3) avoidance of bronzing, and (4) uniformity of shade.

In the case of light weight cloths. there art) no special difficulties as regards penetration. With some of the heavy clotha, however, good penetration is not possible owing to the tight weave and hard twisted nature of the yarnn employed. The period of immersion in the hot liquor is not siiffirient for good penetration and the best rmiiltR fall far short of those obtained by produc.ing cloth from ByeJ )rams. This no doubt explains why such a rompara- 1 ivelgancrU pm rtion of heavy cloth is dyed in the piece.

Selwdge M a r g ! I ’ h m e are coilsod by local precipitation of dye mainly due to ilxidafion and cooling at, the edges of the piece. Throughout the dyeing proress the selvedges we exposed to atmosphoric oxidation and cooling, whilst the rest of the piece is protected, each lap being quickly covered by the succeeding one. In jig-dyeing there is a tendency for dye-liquor to be squeezed towards the selvedges and, since dye-liquor on oxidation and cooling precipitates the dye from eolution. local deposits dim to this cause may occur. Certain precautione may be taken to obviate this fault. Thus-(1) Whenever possible avoid mixing, or using mixtures of, the two different types of sulphur dyes, i.e. the direct type and the colourless leuco-type; ( 2 ) correct adjustment of ratio of sodium sulphide to dye in orderto permit rapid oxidation: and ( 3 ) avoid using dye-liquors so concentrated that some of the dye is in suspension.

When using the colourless leuco-type of dye, 0.g. Bulphur Sky Blues. Indigos and Greens, it is important to recogniae that the colourless leuco-dye is soluble in water and the oxidieed dye is insoluble. When a considerable exress of sodium sulphide is preaent. cloth which is carried out of the bath on to the roller is charged with dye-liquor rich in leuco-dye, which oxidisee slowly and, if any surplu~ liquor is squeezed towards the selvedges, it! meets con- ditions favourable for oxidation and cooling and yields the insoluble oxidiaed dye which is deposited locally. If, on the other hand, the sodium sulphide content is acijueted 80 that the insoluble oxidiaed dye ie formed immediately on leaving the bath, any liquor squeezed from the centre of the iece to the edges will have already yielded its dyes an tno local deposits are possible. When dyes of the two typea are employed together for the produotion of a shade, any local precipitation at the selvedges c a w s , in addition to darker stains, a change of shade at these places. due to a larger proportion of the colourless leuco-type of dyes being deposited. In other words, dyeing with a homogeneous colourless leuco-type dye may produce darker stains of the same tone, whilst mixtures of the two typae may also produce a change of shade. This fault is observed when attempts are made to shade a khaki with green, when green selvedge marks ueuelly appear. The dyer should use a combination which doea not require the addition of green, e.g. yellow, hlaok and, if required, brown or yellow-olive and black.

Broming-This fault is caused by deposition of dye perticlea on the cloth and may be general or local. The chief causes are an over-saturated dye solution, a deficiency of d u r n sulphide, an excess of salt in the dyebath, or oxidation and cooling of the dye solution. The principal Bulphur Blue used for navy shades, although readily Roluble to a certain extent, does not possess a high degree of solubility. Up to 2-3% of the dye dissolves completely, but beyond this concentration a portion of the dye remains III suepension. In works practice, the dye-liquor usually containa 4-6% of dye when dyeing full shades. Under these conditions, dye in suspension may be deposited evenly on the cloth, causing bronzinew. It is customary to run the cloth twice from roller to roller before adding any salt. During these preliminary runs some flxation takes place and this reduces the strength of the dye-liquor,

If, R“ owever, d t is added before the whole of the SUB nded dye is d h l v e d , bronzinese will occur, since the socbility of the dye falls in presence of salt. Premature addition

rmitting more of the suspended dye to dissolve.

&/A. 1#f2 BOOTHNOYD -“DYEING WlTH SULPHUR UYES” 21 -

of‘ salt impedes the suspended dye from dissolving. Improved results are obt,ained by delaying t,he addition of salt until the pieces have run 4 endn. Bronzinwa due t,o the low solubility may also be avoided by employing a dye-liquor of lower concentration at t.he start of the dyeing proces~ and making addit.ions of dye as dyeing proceeds.

When dye-liquor rontaining some suspended dye is squeezed t,owards the selvedges, the deposition of un- dissolved dye is greater near the edges of the cloth, thus

Owing to the comparatively i w solubility of the clyo, some degree of bronziness is almost unavoidable, but t.he ahadas adopted in the trade are bronzy and cloths are acceptable. provided that the bronzineaa is quite even and general. The deposition of dye particles on the cloth showa the present method to Iwl uneconomical, and efforts are cont,inually being made to improve solubility and so eliminate the defect.. The dye principally employed is now available with perfect, solubility up to 4% concentration.

When using dye-liquors a t or near saturation point, it. is often advantageous to add very small quantit,it#l of sodium hydrosulphite to the batah.

Deflciency of sodium sulphide, exreas of salt, excessivc oxidation and cooling em all contributory factors, each producing a greater proportion of aurpanded dye and can- requently e greater degree of bronzing. When pieaeu are dyed in accordance with the above aiiggestions milch better fmtnese to washing and rubbing is obtainod.

Untformity of Shude-In jig dyeing i t is common practice to dholve half the required dye in tthe maohine and to run the piece through t.he solution. Then the remaining half of the dye, previoualy dissolved, is added to the bath and the piece run through it again in the reverse direction. Next, the requisite amount of salt is added and the pieces run through backwards and forwards until t,he desired shade is obtained. Although, in general, this met.hod Rives satiafact,ory results, it is not atrictly accurate since, in the first run, the cloth passes through half t,ha dye in solution, whilst in the second run the cloth peesea through helf the dye in solution plua the einount. left. in the bath after the initial riin.

In dyeing a ahade which requii*es two or three dyes, it in important to choose dyes possessing similar dyeing speeds. otherwise the ahadc of the dye solution will gradually change during the passage of the piece and the ends of the piece will be dyed a different shade from that of the middle. The dye with the higheat dyeing speed will dye the ends deeper t,han the middle of the piece, and the deficiency created in the latter pert gives the appearance. of the slower dye being fuller in the middle and weaker at the ends. The dyeing speed8 of the main homogeneous dyes are known and at.tention to thia point will be well rewarded.

Piece Dyeing for the Rubber Proofing Trade-In dyeing piece ~ o o d s which have subsequently to be proofed with rubber it is essentJial to avoid contamination with cert,ain metals and their salts, principally copper and manganese. The presence of thest. metala or their salts on the fibre causes deterioration of the rubber and may cause degra- dation of t.he cotton fibre. A special range of siiit.able dyes is available for dyeing goo& of thia type.

[Jince the presence of copper salts is objectionable, it is not possible to employ the copper-dichromete method of aWortreatment to improve fastness t#o light and wmhing. Consequently, only those dyes, which without after- t.reatment meet the fastness to light and washing demands of the specification, should be wed. (The Lecturer illzrelrared his remarks with more than 100

exhibila of dyeitage on raw cotton, y a m and clolha in all ntagee of mo,nufaoture; they inoludsd khaki and grey yarns and webbing for elrape. belts, rsepimtw covers, ankleta, 8lrekh.m Cloths, wagon covers, A.R.P. owralb, blue drilla, Union fitanel shirthgs, union twill shirtings, cap cloth, cotton shirtings. lininjp, ground sheeta (rubberproofed), aeuing cotton, nur8m’ uniforms. handkerchiefs, gym shurts, black- out cloths, gun covers, arnmun.ition cot:cre. cnmozrpage clotha, qnbnrdine trsnch coate, etc..)

roducing bronzy wdveclgm.

DI~CUSSION Mr. R. A. Peel said that the points dealt with by t.he

Lecturer would not be found in any’text-book. Looking through back numbere of the J o u d , it. would be found t,hat, rontrihut.ions on dyeing with sulphur dyes were

28 SALKELD-"SOME MODERN WAR-TIME FINISHEB" ~ ._ - ~

itmarkably fow . He Iiopetl, thereforti, that the lectiire would he published, as much of the information given would be of great value to inemborn. Could the Lecturer give information on the following points?

( 1 ) WaH sodium pOrkirat0 suitable for tho after- troatnient of blue and green clyeings?

The Locturer said that oxitlatioil treatnitwts W ~ P A necessary in most cases to prevent alteration of shade on storage and the perhorate mothod was useful in cases where thomaxirnum brightness was required, since thedichromate mothod invariably flattened the shade. Elevated tem- peraturea in tho perhoratc method were not advisable as the availablo oxygen was reloam1 too quickly to produce uniform oxidat ion ovw the whole piore. The perborate methoti did not increase fastnee8 to washing and I horefore wus not preferable to the tlic-hromate method for this piirpose.

(2) Hcr, Mr. Peel, coi~sidoretl thel one calm of stainod selvetlgocl wacl due to inrorrevt gulding of tho cloth on tho beam. Would covered j i p eliminute depnsitn on the srlvedges ?

The Locturor agreed that the piecw nhoiilrl hs c ~ o n ant1 straight on the roller, or unr\ wi (linlrihution o f dye-liquor would resiilt. T-kgniding rovc*rctl jig#, he said that it might I x r ~ ) i ) i - ~ i b I i ~ t o inii i imh local cooling at the selvedges, I m t it would hardly be possible to eliminate oxidation at these points.

(3) What was the best niothocl, i.e. the caustic soda. soda cteh or enzyme methotl, of' scouring pieres for such shntles as navy hlues?

The Lcc*titrei* said that, owing to the wide variatioiis in tiieing iuatoriula U B C ~ in the production of pioco gooch, it W~IH not postliblo to givo one method whivh woiild he best

for H I 1 cloths. Each batch of cloth had to he trrateal in accordance with practical oxperience.

12egai~ing the Lecturer's statement that mixtures of the direct and colourless leuco-types of mlphur dyes should be avoidotl, if possible, could he say whic-h type, when iised alone, gave the best rasnlts?

Tho Lortiiror stated that the direct typo gave tho bost results.

Mr. Praseranked if, when employing three dyes of different sulubility to produce a given shade, any advantage was to bo gained by dissolving the dym separately?

The Lecturor replied in the negative. Mr. Fraser also said that he had experienced cliiiioulty

in obtaining ronsistont rewilts with cliffctrent hatches when dyeing with a fixed recipe. Coiilcl the Lerturer offer an explanation?

The Lecturer said that if the question referred tn rrptvir- irig a shade after an interval of sevtwd I I I ~ * I I ~ ~ I + , tlio lemon for the difficultymiRht bo t lu( i Io l l i i b giatlual decomposition of one or i r i o i ' ( ' 01 1111, cwiibtituents, but if varying results wcro ohtoiiied at short intorvals, the cause would probably be clue to variations in dissolving the dyes.

The Chairman (Mr. J. A. Young) said that he had frequently observed that, when some operatives believed a solution to be boiling, the temperature was only 180°-200%. and this might account for one of tho variations likely to cause the inconsintenries mentioned.

Mr. 1'. J. Brown asked whethor any work W ~ R being done on t>he pad printing method L o pi*odwe better penetration of thick rlothsl

Tho Lwturer sttit1 that he did not know of any work prorooding on those lines, but the mothod wan worthy of invont iga tinn.

(4)

Meetsing held a t St. Xnoch Hotel, Olasgow. on 28th February, 1941, Mr. John Muir, jear. . in t.he chair.

Some Modern War-time Finishes C. H. RALKELD

C!ertsain typm of fiiilshes a8811ino increased iinportancv in war time. Examples are showerproof and waterproof finishes, mildew antl rotproof fmishos, firoproof finishes, and piginerit filled finishes-as usctl for blackout cloth, etc. Again, under war timo p I R H E U I ' 0 , entirely now types of finish may be demanded at very short notice. Tho present paper deal8 with threo t y p S of finish of particular interest now. One section covers in some detail the production of fabrics for which an entirely new type of finish suitable for making transparent weatherproof window replacements is needed. Another sectinn is clevotcd to a particular aaport of the application of modern textile synthetic resins in pigment-filled finishe6, and a third scction IE concerned with n new and simple mothod of rotproofing cellirlosir materials.

Wirir~ow I ic~plnc~mrnl Fabrics--d fabric of this typo cwnsist~ geiierally of a textile 01' wire foundation upon whirh is SllppOrtet~ a trunsparont film of matorial, which ulone would be too weak to bo of prnrtical utility. The four principal methods of procwsing in order to obtain stit isfuc~tcwy materials are-

(1) Bonding viscose film or cellulose acetate film to a netting foundation by means of rosin; (2) filling a netting or wire foundation completely with a rontinuous film of iinpermeablo resin; (3) filling n netting foundation com- pletuly with a continuous film of some water-soluble substanre which will give a transparent film and then coating the film with a protective layor of transparent resin; (4 ) inipregnating an ordinary, instead of a net, fabric with a resin or oil rlopo in ordor to give it a weather. proof trnnslucent finisli.

Suild~le Rcszns-From timong the raw materials essential for the above methods, the choice of a ra in 18 of primary importance. In genoral, it, should pOEEeEE the following propertios-( 1 ) It, must givo a transparent film of reasonablo strength; (2) the film must possess flexibility, dtliough opinions appear to differ considerably as to how much flexibility is desirable; (3) tho film must resist exposure to tho weather (wind, rain, sun. and frost, etc.); nntl (4) the film must be impermeable to rain.

Much work has heen carliod out on the problems of rnaking satisfactory window replacoment material, and

amongst tlie various siibsta,nccs t,hat have been exanlined for suitability aa filling media for netting, otc., t.he resin known as Beclafin 2001 has boen f ~ ~ u n t l to rneot satisfac- torily the reqnircments alroady noted.

I+opo,.i.ies of @hjh 2001-I3eclafin 2001 is a 40%, sollit ion of a thermo-hardening syrit het ic resin in Collosolve. When dried at, 60°-1000c., it, gives a transparent fairly hard film which tends to boconie opalescent, on wetting, but regains clarity on drying. Apart from this tendency to hecome opalescent. on wetting, tosts show that the film has satisfactory weatherproof properties. If t.he pre-dried film is heat-treated at from 100°-150"~., the resin cont.ent polynierises furtlier. producing a harder, somewhat more brit,t$le film. absolutely unaffeotod by exposure to rain. and remaining perfect,ly clear and 1,ransparont under all conditions. Although t,he pro-drying and baking pro. cesses above 100"o. jiroth~ce tho most sat'isfactory film, haking is not absolutely essential, since material which has been dried a t only 00"-100"~. is iinpormaahle to rain, t,he only defect heing tho opalesconce produccd on wett,ing. As the film becomes clear and t,ransparent. again on drying, t.he opalescent effoct is not, of importance. It is intoresting to note, however, that a resin film which has been dried below 100"~. will cont.inue to polymerise slowly by the action of sunlight and long exposure to air, 80 that the reversible clouding effect, will prohahly disappear in time.

Plaeticim'ng Agenta-Opinions differ regarding t,he degree of flexihi1it.y which is desirable in finished window- replacemant fabrics; in some cases, u flexible, easily bent product, which moulds itself readily to any givori stxuct)ure, is desired, whereas in otlior C ~ W R tlie materia,l should be as rigid as possible, i.e. as glass-like as possible. All ilemandn, howover. with regard to flexibility of the Bedafin 2001 film can bo readily mot hy incorporating a plasticher into the w i n The plaaticiser used is Bedafin 286X which ia an oily polymeric substanco miacible in d l proportions with Bcdafin 2001. The greater t.he proport.ion used, tho more pliahlo iR the resultant film, witliout impairing its clarit,y antl trans- parency. In this way, AexibiMy can be varied from tlie st,iff Alm produced hy the us0 of Redafin 2001 alone to