US2995469A

US2995469A - Apparatus and process for coating a flexible web

Info

Publication number: US2995469A
Application number: US679342A
Authority: US
Inventors: Claire Charles Francis Le
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1957-08-21
Filing date: 1957-08-21
Publication date: 1961-08-08
Anticipated expiration: 1978-08-08
Also published as: DE1209467B; FR1209600A; BE570270A; GB855164A

Description

Aug. 8, 1961 c. F. LE CLAIRE 2,995,4

APPARATUS AND PROCESS FOR COATING A FLEXIBLE WEB Filed Aug. 21, 1957 CHILL HID UP AREA v21 INVENTOR CHARL ES FRANCIS (.eCLA/RE COATING STATION BY M ' ATTORNEY material onto supporting webs.

2,995,469 7 APPARATUS AND PROCESS FOR COATING A FLEXIBLE WEB Charles Francis Le Claire, Little Silver, NJ., assignor to E. l. du Pont de Nemours and Company, Wilmington, 'DeL, a corporation of Delaware Filed Aug. 21, I957, Ser. No. 679,342

' 9'Claims. (Cl. 117-102) This invention relates toweb coating apparatus and more particularly to apparatus for applying to continuous webs viscous aqueous solutions as layers of high uniform quality in the manufacture of photographic films. and

7 papers. Still more particularly, it relates tosuch apparacombination of such devices effects a surprising improvement in the smoothness and uniformity of quality of the appliedcoating. The apparatus according to this invention also unexpectedly permits an increase in coating speed by as much as 300% or more without sacrifice of quality. An object of this invention is to provide an improved coating apparatus for producing a smooth uniform coating of material onto a travelling web. Another object is to provide such apparatus that permits the coating'of viscous liquid materials ontocontinuous webs over a wide range of speeds; Yet another object is to provide such apparatus that is easily adjustable and accessible for cleaning and maintenance. A further object is to provide such apparatus that. eliminates the necessity for spray deflectors and baffles of prior art devices to prevent mist and flying particles from contaminating the coated area of the web. A still further object is to provide such apparatus whereby excess coating material is recycled, reducing the volume and expense of coating material required from the source of supply.

A particular object isto provide improved apparatus ,having a novel arrangement of component elements by which viscous water-permeable colloid silver halide dispersons can be coated continuously as a thin layer onto a continuous web at a coating speed 'as high as 400 feet per minute to produce a photographic film element of commercial quality and uniformity having satisfactory sensitometric and other photographic properties. Still other objects will be apparent from the following de scription of a preferred embodiment of the invention, which will now be detailed with reference to the accompanying drawing, wherein:

FIG. 1 is a side elevation view of the component parts of the apparatus in operational relationship, with a portion of the coating pan broken away for clarity; and

FIG. 2 is a schematic side elevation view illustrating the production of a coated photographic film utilizing the webcoating apparatus of FIG. 1.

FIG. 3 is a schematic side elevation view illustrating the relationship between certain parts of the web coating apparatus of FIG. 1.

Referring now to the drawing, the principal elements of the apparatus of this invention include an air knife 1, a metering device 2, a coating roll 3 and a coating pan 4, arranged to apply a thin layer of viscous liquid coating material 5 by the skim coating method to the flexible web 6 continuously advancing in the direction indicated by the arrows.

United States Patent 0 2,995,469 Patented Aug. 8, 1961 The air knife 1 is positioned on and secured to a suitable frame (not shown). The air knife is adjustable as in the prior art to impinge a planar stream of air at any. desired angle onto the coated web. A trunnion 7 is fastened at each end of end plate 8 of the air knife near the air oriffice 9. Trunnions- 7 extend ashort distance from the end plate 8 to hold upperbracketslfl of the adjusting mechanism for the metering device 2. The trunnions7 are threaded to receive nuts 11 for securing the upper brackets 10.

The metering device 2 is positioned so that its metering lip 12 is parallel to the surface of the coating roll 3 and extends laterally across the roll for a distance at least as great as the width of the web 6 being coated. The metering device is of rigid construction and may be solid or hollow. Besides the metering lip 12, which is preferably a machined projecting portion adjacent the coating roll as illustrated, the metering device has uppersurface 13 and lower surface 14 for guiding excess coating ma: terial back into the coating pan. Upper surface 13 is shown sloping downwardly in an arcuateprojection 15 to further direct excess material off surface 13 into the coating pan. Trunnion 16 for-securing the metering device 2 to its adjusting mechanism is secured at each lateral end of the metering device by means of threads and nuts or, as illustrated, by pinch fits.

The adjusting mechanism is mounted on'the air knife so that the: precise location of the metering device can be adjusted independently of the air knife. .As illustrated in FIG. 3, it is important to be able to adjust accurately the distance Y of the metering lip 12 from the on-running web 6, the distance Z between the metering device and'the air orifice 9, and the angle 0 that the plane of theweb forms with the upper surface 13 of the metering device.

The adjusting mechanism in the illustrated embodiment has upper brackets 10 and lower brackets.- ..17 suitably interconnected. Adjusting screw or-screws 19 mount.- ed on the upper brackets enable preciseadvancing and retracting of the metering device to adjust'the distance Y of the lip 12 from the web. Adjusting screw or screws 19 similarly enable precise advancing and retracting of the metering device in a perpendicular direction to adjust the distance Z between the metering device and the air ori-- fice. Rotative adjustment of the metering device about its pivotal mount on trunnions 16 serves to regulate the desired angle 6 between the web and the upper surface 13 of the metering device. The angle is held by any suitable means such as adjusting screw 20.

The coating pan 4 can be of conventional design but is preferably divided into separate sections as shown. -,A reservoir of coating material 5 is supplied from any'suit-. able source such as through an inlet pressure feeding from a source outside the pan. The overflow of coating material over wier 21 flows into trough 22 which serves as a collecting container for the overflow over wier 21 as well as excess coating material flowing down

surfaces

13 and 14 of the metering device. The wier 21 is'par-allel to the surface of the coating roll 3 and is somewhat lower than the back edge 23 of the pan so overflow from the reservoir will occur only in the direction of travel ofthe web. Coating material collected in trough 22 is led by any suitable means (not shown) back into the flowof coating material feeding to the reservoir, thus eliminating waste and loss of material. The coating pan can be adjustable in a vertical direction and in a right and left direction to permit positioning of the coating pan at the precisely desired location during operation.

Maintenance of the variables referred to above critical defined limits of position to produce the surprising results herein described will now be set forth.

The coating pan must be in a position relative to web to apply a surface coating of the coating material within the.

I leaves the coating pan.

onto the web in a thickness of at least 200% of the final wet coating thickness X desired. It'is preferred that a thickness of coating material of from 450% to 550% of the final wet coating thickness be left on the web as it It is preferred that the thickness of the coating applied at the coating pan be controlled by using the wier or forward edge of the coating pan as a metering or doctoring blade.

The metering device 2 is preferably positioned with its metering lip 12 adjacent the web at the place where the web changes direction of forward travel from an arcuate path around the coating roll to a straight planar path leading to subsequent web handling equipment. In other words, it is preferred that the metering lip 12 be located immediately preceding the point at which the outrunning web leaves contact with the coating roll. In this preferred position, the jet from the orifice 9 impinges on the coating material on a portion of the web which is still in contact with coating roll 3.

It is essential that the metering lip 12 be positioned close enough to the web that the lip acts to remove a part of the freshly applied excess coating material. The outstanding results obtainable according to this invention require that there be no gap or space between the lip and the coating material on the web. It is important that no air, particularly from the air knife, be permitted to pass between the lip and the web. It has been found necessary to position the lip 12 so that it permits an excess of coating material to pass the lip 12. In particular, the amount of coating allowed to pass the lip as illustrated in FIG. 3 (or, in other words, the distance Y from the lip 12 to the web 6) must be 'at least 120%, and preferably 120% to 150%, of the final wet coating thickness X.

The material that is metered by the lip 12 flows down the lower surface 14 of the metering device 2 in a smooth stream to the trough 22. The angle of position of the lower surface 14 will depend on the shape and construction of the metering device and is not critical.

The air knife must be positioned to direct a stream of air against the coated web at an angle, measured from the plane of the outrunning web (or from the plane of tangents to the roll through the line of impingement of the air stream, if applicable), of from 35 to 90, and preferably from 45 to 55. This angle is measured counterclockwise from the plane of the outrunning web.

The distance Z from the line of impingement of the air stream to the lip 12 may vary depending on such variables as the viscosity of the coating material and the coating speed, and can readily be determined by persons in the art in accordance with the teachings set forth herein. The distance Z for most coating operations generally will be from 1.0 to 5.0 times. and preferably from 2.0 to 3.0

times, the final wet coating thickness.

The angle formed by the upper surface 13 of the metering device 2 and the plane of the web at the line of metering by lip 12 has been found to be critical. This angle is measured counter-clockwise from the upper surface 13 and is herein referred to as the angle between the upper surface of the metering device and the plane of the web. It is important that this angle between the upper surface of the metering device and the plane of the web be at least as large, and preferably to 15 larger, than the angle at which air impinged on the coating material is reflectedaway from the coated surface of the web. Operating in this relative position insures the stability of the flow of air and excess coating material, which is passing downwardly over surface 13. It should be pointed out that the angle of impingement of air from the air knife will not necessarily be equal to the angle of reflection of the air stream.

In operation, the flexible web is passed around the coating roll, coating material to be applied is delivered aqueous photographic materials.

in the coating of aqueous silver halide dispersions in the to the coating pan, and the various elements of the apparatus are positioned as described above to effect the coating of a thin layer on the web. With the wier acting partially as a doctor blade, coating material metered by it remains in the coating pan. Coating material metered by the lip 12 flows smoothly and steadily downwardly on surface 14 into the trough. Excess coating metered by the air stream from the air knife, which in prior art air knife coating installations may run back down the web or fly from the webas' a spray, mist or fog-of particles, is returned to the coatingpanin a smooth stream flowing downwardly along the upper surface 13 of the metering device. The possibilities of streaks being formed by the coating material running down the web and the spray, mist or fog settling on and injuring the smoothed portion of the coating are eliminated by this invention.

This invention is particularly useful in the coating of It is especially useful various types of natural and synthetic water-permeable colloids as binding agents for the light-sensitive silver halide grains, including gelatin, albumin, agar-agar, water-permeablepolyamides, polyvinyl alcohol, partially hydrolyzed polyvinyl esters, hydrophilic polyvinyl acetals including those containing color-former nuclei, and other types of viscous aqueous solutions, particularly those containing colloids.

A preferred use for this invention is in the coating of gelatino silver halide emulsions. FIG. 2 of the drawing schematically represents a convenient arrangement of operations conventionally used for such coating.

Referring to FIG. 2, a supply of web, e.g., film base or paper, from unwind source 24 travels around guide roller 25 in the direction indicated, around the coating roll 3.at the coating station (see FIG. 1), past guide roller 26, through a conventional chill area 27 where the emulsion is set, around guide roller 28, through a conventional dryer 29, and then to windup 30 or other processing operation. Other airangements may of course be used, as will be readily understood by persons in the art.

While not wishing to be limited by the following explanation, it is believed that the reason for the outstanding results obtainable under the conditions outlined above is that the air stream from the air knife, after it has cu off the last excess coating material, is stabilized by the metering device 2 after the air is reflected from the coating and travels in a-smooth non-turbulent stream along the upper surface 13 of the metering device. This appears to effect the holding of the excess coating material on the upper surface 13 and directs the flow of the material evenly and smoothly into the trough of the coating pan.

An additional reason for the excellent results, particularly at high coating speeds, is believed due to the fact that, as the excess coating material is cut from the web by the air stream from the air knife, a small puddle or head of material is formed at the upper part of the juncture between the outrunning web and the upper edge of the metering device. This puddle in effect serves as a reservoir supplying material to any voids which exist in I the coating. In this manner, a uniform surface of coat- 'minute i 'Ili'erinvention;will;beefurther explained. but is not intended .to tber-limited -by;:the=;:fllowifig examples:

Example; I

Apparatus as illustrated ,lll'l'i' F-IG. 1 of the drawing is arranged with' the air streann dir'ected .to impinge on the coated "Web at: an angles ofwabouttSZ. from the plane oft'ithe outrunning webi 'Ili'e air:knifeispositioned'0.1 inch from the :web. The :air; tkniferpressuretis '5 :78 inches of L'Water "using an orificeeof 0;.025 inchi The metering device is adjusted withitherrnetering lip; 12Jat a distance oft t 0.013 inch; from the :webi That-distance. between the line at whichitthexair streamztfrom the-:airiknife' :impinges onrthe coatinggand the upper edge of the lipof the meter-. irigidwic'edsiOiOBO inchl" Theangle'formed between the planeof ith'e:aveb*i(asfdefined above) and: the upper surfa'cecofl thermetering ,device :is about i 68 A cellulose acetate z fil'ihr. base :12 moving; at a speed of 220 feet per oatedrwithbm galati'rio silver bromochloridc light-sensititie photographic emulsion v "havin g a a viscosity of- .10.6 F centistokes wat Latemperaturerof "100 F;' and a solids-:content iof 516%,] by aweig'htr, A coating got about l39img." of solids per tsquareadecimeter -is obtained. The result'antzremulsion coatedtflm vhas excellentnquality and uniformitiywof .sensitbthetricizand.iother :propertiess.

Example. II t Eiramplewl Eis zrepeatedlexcept that' theair knife pres-.-

inches: ofifwater; the: distance between the:

sure is 3n :andth :web: device A ang e. .:with"respect:ttoothe web is. about. 65

graphic emulsion of the Xray;.type:havingaaviscosity of 26=Tcentistokes atla temperatureeofil 00 9 andta "16% by weight solids content-rt istcoatedliontoa gelatin :subbed polyethylene rterephthalatawebkrnoving ,at. about :1 50 feet I pertrninutex; A'tcoating'zof i'about;:227 7mg: of solids per square "decimeter havingsexcellent; quality and properties isobtainedzasxiriz'liiiample Ex'amplellll 1 Estampletl ."is repeated 'except 'that ltheudistance betwcen the metering elip and the=.webis-.-0OO7 inch. A'web ofpapersoft. the-slight: weight: document. stock type moving att ab'outi ISO-"feet per minute is. coated with 1a .gelatino ample 1L Tlie a.coating ".operationris notuliinited to skim coating; methods but iszalsotusefuli wherein thetapplicationof'the coatingumaterial t to: the awebi is' :accomplished f by other methodsv utilizing zan a extrusion coating;v etc.

In additio'ntto" silver halide :emulsions,- the invention is useftibfim-the;applicationeofisuch coating materials as gelatin sublayeis; gelatint'fil'tervlayers; antiabrasion layers,

antistatic-z layers, etcr Th'einventionis also useful in" applying pigmented layers tofilihs andpaper webs. Other useswillireadily occur topersons in the art.

lt'fiwill beunderstoodthat meet the apparatus of this invention,andequivalentapparatus inthe herein described manneryis,directed toasnovel process for coating a con-- tinuous flexible .wcb'to 'apply' a'coatcd layer of coating material having a .pre'selectedztlesired final thickness (cone veniently -referredetotas-measuredtwhile wet; although dry thicknessrcalculations couldz'ireadily' be used :with" corre-' spondihgtchanges'=inx therranges=zset forth below)$ The process comprises =applyirigvto'i-the moving web coating; materialt im atrelativ'ely -thick layer having a "thickness of knife. 0- elfect' smoothing of the: coating;v In tadditionntorskim coating, such methods. iri cludecdip, coating .nip rolLfcoating; reverse roll coating,"

'.020 inch, and theunetering An' aqueous 'gelatino-sil'ver iodoeo'romidedightrsensitive photo-- at lenti 00%; and preferablyt450%- to.550%";of.;the*

desiredofinal ;wet thickness metering at a first line-:tr'ans;

verse acrossthe .web the relatively thick layer to a3lesser thickness of-at least Y%, and preferably 120% to of -tli'e :desir'ed 'final wet thickness; impinging at asecond linewtr'ansversetacross the web a stream of *air against the clayer'of:lesser' thickness at'an'angleof 35.?" to 90, and preferably-45. to .50", measured fromathe plane of the'web at the secondtransverseline IQS dOCtOE-T the layer of lesser .thicknessttoithe desired final thickness,-e. the second trnnsverseliriecbeingat a distanceifrom the first": transverse line ofaboutr-LO to 5.0 times, and preferablyfrom 2.0 to 3.-O-times,"therdesired final wet thickness, and

guiding the-air stream reflected from the second transverse line away from the web'tzat. an angle measured froniath'e': plane of the web atthe first transverse '-line..o.at.:least as large, and preferably 5? to 15 larger, than thezanglesof ithe reflected "air stream also tmeasureddfromxtheeplane of thetweb atr the -first transverse-line; whil'enpreventin'g-aa the-passage of any air from theimpingin'gwr'reflectedii stream from eftectingtcontact directly withftthe inrunningg;

prevention of the Hcoating-Jrnaterial .beinggimetereda from. the web:.by the metering device. from. returning along athea surface :of the web; thus obviating a.defectof zprior tartfi coatingapparatus'and methods, namely, theidefect :which-i, appearsas bands ofcoatingmaterial ofatthickness heavier: than desired. running .in the. direction of the. weblztravelzi By carrying; out the .present inventionp these 'longitudiiialai bands t orstripes are eliminated' Another radvantage-cuis that by, controlling .;the -:path=. of=:the rcoatinggmaterialsdoci-- toredzby the. air 'knife,: .not material: is thrown: fromnthel web atshigh speeds as spray,- mist lor;fog,-t .thus "-reducinggi, the-danger 'of coating. material. contaminating'i andfior s' otherwise injut'ing-thczsmoothed' coating surface; Yet any other advantage resides in the fact that. coatings-can; made-over a :wide range of speeds by' apparatus th'at easily adjustable and accessible for'cleaning.andnmaiti e. nancer Afurther advantage is that=exeess coating-material); is not 'wastc dtbut can be conveniently recycled; thus (re ducing the amount neededandtheexpense .of;complicated salvaging equipment. A stillfurther:advantage-isthatth air stream from-z-theair knife isscompletelydeflected? 0- that it. cannot disturb the surfaceof thetcoatingrmateria'l in .the:.coatingpan at thcspoint at.which'.the'-weba' c011= tacts thecoating:material..inithetpan;

An additional advantage is thnttheair streamis'ista'bi-ilizccl, eliminating air. jet. chatter :by the proximitytof the upper surface ot the metering -.device .to the lineiof fima pingement of the air stream,vand.by maintaining-thethick I; ness of the layer .to beair' doctored relatively constant. b'yl: the :action of the meteringdevice.:- Yetaafurtherradvanl-r tage is .th at the .entire smoothing apparatus can; be iconveniently moved out of operating position and returned? to operatingtposition with the-air knife in 'a SiHgIG'HIOtiOIiE- A particu lar advantage resides inthefact. that light sen si tive photographic emulsions can"besapplie'd top l 1oto-'- graphic .film base at spcedsias high as 400feet per minute-i to obtain coated photographic filihsof'outstanding smoothE-i ness and uniformity; of 'quality;.withl satisfactory-tsenst-i tometric and other photographicproperties. still 'lotherl" advantages will be apparent fr'omthe above-z descriptions: of the invention.

An advantage of the present; invention; residesinsthe The invention claimed is:

1. A process of web coating comprising applying to a flexible moving web coating material in a relatively thick layer having a thickness of at least 200% of the desired final wet thickness, metering at a first transverse line across the web said relatively thick layer to a lesser thickness of at least 120% of said desired wet thickness, impinging at a second transverse line across said web a stream of air against said layer of lesser thickness at an angle of 35 to 90 measured from the plane of said web through said second transverse line to dostor said layer of lesser thickness to said desired wet thickness, said second transverse line being at a distance from said first transverse line of about 1.0 to 5.0 times said desired wet thickness, and guiding said air stream reflected from said second transverse line away from said web at an angle, measured from the plane of said web at said first transverse line, at least as large as the angle of said reflected air stream measured from the plane of said web at said second transverse line, while preventing the passage of air from said impinging-stream and said reflected stream from effecting contact with the inrun'ning web at any portion of said web preceding said first transverse line.

2. A process as set forth in claim I wherein said coating material is a viscous aqueous solution of a waterpermeable colloid.

3.. A process as set forth in claim 2 wherein said coating material is an aqueous gelatino silver halide dispersion.

s 4. A process as set forth in claim 1 wherein said relatively thick layer has a thickness of 450% to 550% of said desired wet thickness.

5. A process as set forth in claim 1 wherein said layer of lesser thickness has a thickness of 120% to 150% of said desired wet thickness 6. A process as set forth in claim 1 wherein said angle of said stream of air is 45 to 55.

7. A process as set forth in claim 6 wherein said distance is 2.0 to 3.0 times said desired wet thickness.

8. A process as set forth in claim 6 wherein said guiding is at an angle of to 15 greater than the angle of said reflected air stream.

9. In an apparatus for coating a moving flexible web to a desired wet thickness (X) comprising a coating roll layer of coating material, arotatably mounted air knife doctor having an air orifice adjacent to the traveling web for directing a stream of air against the coated layer at an impingement line transverse to the direction of web travel, said angle of impingement ranging from 35 to from the plane of the outrunning web at the impingement line, the combination with said air knife doctor of a metering device, said metering device being connected .to said air knife doctor and beinglocated between said coating means and said air knife doctor, the metering device comprising an upper fluid deflecting surface and a lower liquid smoothing surface having a lip portion adjacent and parallel to the surface of the web, said lip portion forming an apex with the upper fluid deflecting surface, said metering device being precisely adjustable horizontally, vertically and rotatively in relation to the web independently of the air knife doctor by an adjusting mechanism having separate screw adjustments, said, adjusting mechanism being mounted on the air knife doctor whereby the distance (Y) of the metering lip from the web, the distance (Z) from the apex of the metering device and the air orifice of the air knife doctor range from 1.2X to 1.5X and X to 5X, respectively, and the angle 0 measured from the said upper fluid deflecting surface counterclockwise to the plane of the web as the web passes the metering lip is at'least as great as the angle of the air being deflected from the coated surface of the web.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain Ian. 9, 1930

Claims

1. A PROCESS OF WEB COATING COMPRISING APPLYING TO A FLEXIBLE MOVING WEB COATING MATERIAL IN A RELATIVELY THICK LAYER HAVING A THICKNESS OF AT LEAST 200% OF THE DESIRED FINAL WET THICKNESS, METERING AT A FIRST TRANSVERSE LINE ACROSS THE WEB SAID RELATIVELY THICK LAYER TO A LESSER THICKNESS OF AT LEAST 120% OF SAID DESIRED WET THICKNESS, IMPINGING AT A SECOND TRANSVERSE LINE ACROSS SAID WEB A STREAM OF AIR AGAINST SAID LAYER OF LESSER THICKNESS AT AN ANGLE OF 35* TO 90* MEASURED FROM THE PLANE OF SAID WEB THROUGH SAID SECOND TRANSVERSE LINE TO DOCTOR SAID LAYER OF LESSER THICKNESS TO SAID DESIRED WET THICKNESS, SAID SECOND TRANSVERSE LINE BEING AT A DISTANCE FROM SAID FIRST TRANSVERSE LINE OF ABOUT 1.0 TO 5.0 TIMES SAID DESIRED WET THICKNESS, AND GUIDING SAID AIR STREAM REFLECTED FROM SAID SECOND TRANSVERSE LINE AWAY FROM SAID WEB AT AN ANGLE, MEASURED FROM THE PLANE OF SAID WEB AT SAID FIRST TRANSVERSE LINE, AT LEAST AS LARGE AS THE ANGLE OF SAID REFLECTED AIR STREAM MEASURED FROM THE PLANE OF SAID WEB AT SAID SECOND TRANSVERSE LINE, WHILE PREVENTING THE PASSAGE OF AIR FROM SAID IMPINGING STREAM AND SAID REFLECTED STREAM FROM EFFECTING CONTACT WITH THE INRUNNING WEB AT ANY PORTION OF SAID WEB PRECEDING SAID FIRST TRANSVERSE LINE.