US3461837A - Coating apparatus - Google Patents

Description

Aug. 19, 1969 p F DREHER COATING APPARATUS 2 Sheets-Sheet 1 Filed Oct. 24, 1965 I N VE N TOR. DONALD F. DFZEHER.

Aug. 19, 1969 D. F. DRE E- 1 3,461,837

COATING APPARATUS Filed Oct. 24, 1965 2 Sheets-Sheet 2 INVENTOR. DONALD F DREHEF2.

United States Patent US. Cl. 118-50 9 Claims ABSTRACT OF THE DISCLOSURE This application relates to web coating apparatus for paper and the like, and in particular describes:

(a) A reverse roll coater (FIGURE 1) having one roll instead of the customary three or four. Bearing support throughout its operative length permits relatively small diameter, and the support housing incorporates means for lateral distribution of coating composition and its final and precise metering.

(b) A trailing blade type of coater (FIGURE 3), fully enclosed, utilizing partial vacuum to eliminate air entrainment and to control coating thickness.

(0) Doctoring elements responsive to subatmospheric pressure differential, adaptable to a range of apparatus and utilized in the coaters above described.

CROSS REFERENCES TO RELATED APPLICATIONS Applications serially numbered 504,405 and 504,406, filed concurrently herewith on Oct. 24, 1965, disclose subject matter related in part to this application.

This invention relates to methods and apparatus for coating continuous webs of flexible material such as paper, film and the like, and more particularly relates to improvements by which such a web may be roller supported and the coating applied by reverse roll or by spreader and doctoring means thereagainst. The improvement basic to such accomplishment is described in my US. patent application, Ser. No. 504,405.

In the above identified patent application, there is disclosed new and novel means by which spreading force may be more reliably and uniformly applied oppositionally to a doctoring element. Essentially the method involves positioning the doctoring element in planar, rather than deflective, tensional engagement with the web and the development of spreading force as a function of differential air pressure operative against the web, this being accomplished by maintenance of subatmospheric pressure within the coating enclosure of which the downweb boundary comprises the doctoring element, over which the web and a deposited layer of coating composition are drawn and against which they are impinged by atmospheric pressure. In the present invention the web is roller supported and the doctoring or final metering is applied oppositionally to the roller, the force thereagainst controlled by subatmospheric pressure differential operative against the doctoring element per se. Although other means for primary application of the coating composition may be used if desired, fountaining means are preferred, these being similar to those described in the identified accompanying application.

Therefore,-the primary object of the present invention is to apply certain of the aforesaid teachings to the controllable application of metering or spreading force against a transfer roll or directly against a roller-supported web, and including therewith means for rarification of air contained within the web, thereby permitting controllable penetration or anchorage of the coating composition together with elimination of air bubble entrainment within the coating composition.

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In addition, the present invention provides means by which reverse roll coating may be accomplished without the need for massive structure and multiple precision roller apparatus, and eliminates innumerable problems connected with the operation of such equipment with which those who are skilled in the art are well acquainted.

A further object of the present invention is to permit the use of rotary doctoring elements in spreading applications such as that of the trailing blade.

Still another objective comprises full enclosure of the fluid circuitry and the elimination of integral coating tanks, reservoirs and hoppers generally associated therewith.

A fuller understanding of the means by which these objectives may be accomplished will be gained by reference to the accompanying drawings in which reference characters common to the several related patent applications convey similar meanings.

FIGURE 1 is a medial cross section showing transfer or reverse roll application of a coating composition to a traveling web.

FIGURE 2 is a part section of one of the distributing pockets shown in FIGURE 1.-

FIGURE 3 is a medial cross section showing a rotary doctoring element trailing downweb from a fountain, wherein the web is roller supported and the coating composition doctored in place thereagainst.

Referring to FIGURE 1, a tubular roller 84 is positioned rotatably in a machine-spanning housing 85 which provides bearing support 87 throughout the operative length of the roller. The separable sections 85a, 85b of the support are shown secured by means of bolts 22 and alignment pins 23, and spaced apart by an adjustable set of shims 86, thereby facilitating fabrication and maintenance, and permitting adjustment for clearance between the journal-like face of the roller '84 and its bearing support 87. Part of the roller surface is exposed and the Web 1 positioned in deflective engagement 1b with an arc segmental portion thereof. In operation the transfer roll 84 is reverse rotated R relative to the indicated forward motion of the web 1. The consequent wiping action therebetween may be enhanced vacuously D for which purpose a contiguous vacuum chamber 8 is positioned upweb, the incoming web support 2 providing a convenient boundary for such a chamber. Additionally, as taught in the copending application previously identified, the rarification of web-entrained air may be utilized advantageously to induce penetration of fluid coatings into porous or semiporous webs and to control the depth thereof. In order to complete the vacuous enclosure, especially when handling non-barriered webs such as ordinary paper, the use of an overlaid membrane 17 is preferred. Such a membrane may trail downweb from its upweb support 18, its downweb terminus maintained laterally by the enveloped rod 19, the ends of which may be drawn tensionally downweb U if necessary to prevent its being dislodged by marginal contact with the reverse-rotating transfer roll, it being feasible to provide suitable lubrication if necessary for such margins in order to minimize friction at the interface.

The coating composition 11 may be fed 70 either singly or plurally into a crossweb 33 formed in the upweb portion 85a of the supporting body, and therefrom meterably orificed 34 into distributing pockets 25 formed therein as further illustrated by the sectional drawing X--X comprising FIGURE 2. A superposed plate 6a completes the pressurable enclosure and its forward edge 74 makes intimate contact with the transfer roll 84, and may serve additionally as a cleaning scraper thereagainst. The coating composition 11 thus may be fonntained positively Q against the transfer roller and driven frictionally and pressurably through a myraid of ducts 24a formed in the surfaces of the supporting bearing 87, the ducts preferably may be made continuous by being formed matedly in the clearance shims 86. It also is preferable that the ducts 24a be formed in duplex helical segments, thereby permitting the surface of the transfer roll 84 to be abraded uniformly rather than grooved or ridged in consequence of wear occurring only at the points of support 88. The ducts 24a may be conveniently machined by boring mated assemblies or by internal finishing a full cylinder and thereafter segmenting and finishing the several faces. It will be apparent that the construction permits lapping the several parts in assembled position, with following maintenance considerably less involved than in traditional reverse roll equipment. It also will be apparent that the bearing 87 could comprise insertable tubular segments, thereby facilitating maintenance and permitting replacement, including interchangeability with mated roll and bearing insert assemblies. If further will be apparent that the coating composition 11 serves as lubricant for the bearing support '88, and therefore that the equipment as specifically illustrated could be limited in the handling of compositions which are excessively abrasive. This does not necessarily preclude its use therefor, since the coating composition can be fountained in the downweb portion of the support and thereby its direct introduction into the bearing avoided.

The coating composition 11 thence is carried by the transfer roll 84 into contact with the flexible squeegee 83, between which there is formed an impingement nip J and a metering restriction E quite in the manner described in the identified accompanying application. The squeegee or doctoring element 83 is mounted in passive radial relationship to the roll 84, permitting the metering or spreading force B to be controllable by the subatmospheric pressure differential operati e thereagainst by that of external atmosphere C applied to the outer surface of the squeegee 83 and a lesser absolute pressure D applied thereunder, thereby causing the fluid pressure of the coating composition as it is frictionally impacted by the transfer roll into the impingement nip J to increase from the absolute pressure D establshed therein by the vacuous chamber 9 to the pressure of one atmosphere C, thereby establishing pressure equilibrium at the final metering restriction E. The excess composition 1112 thereby shived from the incoming flow cascades down the inboard face of the coating chamber 9, therefrom is drawn into one or more sumps 39 and collected so as to be withdrawn 40 preferably in continuous liquid form, the rate of withdrawal being controllable by a liquid level control device or feedback 41. Subatmospheric pressure D may be held constant and controlled precisely by gaseous evacuation from the chamber 9, it being important that this com munication be uninterrupted by viscous involvement, for which purpose a flow diverter 43a may be provided adjacent the exhaust port 56. The techniques previously described in the accompanying application are equally ap plicable hereto, including the input 55 of saturate air into the control chamber in order to minimize evaporation of volatile ingredients and to propel the cascaded eXcesS composition 11b toward the sump(s) 39, thereby permitting the depth of the chamber 9 to be minimal and in consequence the apparatus to be made exceedingly compact and requiring little space. Thus this type of apparatus may be located in restrictive quarters and inserted in existing machine lines without need for major relocation of existing facilities.

Beyond the meterng nip the transfer roll functions identically as in traditional reverse roll equipment, except that I prefer so to control the webs contact with the transfer roll that the traditional forward rotating pressure roll may be eliminated, thereby avoiding problems associated with the frictional interface therebetween. In order successfully to accomplish final transfer of the coating composition to the traveling web, especially in the event that the prevacuum chamber 8 is not being utilized, such as could occur for example if the coating were to be overlaid upon the web surface in differentiation from its being penetratively deposited within its interstices, and thus relying solely upon defiecti-ve web tensioning to secure uniformity of the transfer nip, in such event it may be helpful to provide a suspended bar 3 proximate the nip, under which the web may be deflectively transited, such a bar being usable either with or without the interpositioned membrane.

With respect to the membrane as such, it may comprise a frictionally-trailing segment anchored upweb 18 as illustrated, or it may be semicontinuous and much longer in length, wound upon spools suspended overhead and permitted to creep at such rate as to permit its continuous replacement. It also may comprise an endless belt traversing the coating apparatus at the speed and tension desired. Such arrangements are disclosed in the second patent application hereinbefore identified as Ser. No. 504,406.

Certain of the margining techniques described in the accompanying patent applications are suitable for inclusion in the reverse roll apparatus herein disclosed. It first will be apparent that one of the reasons for providing individual distributing pockets 25 at closely spaced intervals across the width of the coater is to permit each to be closed by appropriate plugging or valving as described fully in the first accompanying application. Downstream from the first fluid contact Q with the transfer roll, the coating composition is ducted directionally and emerges into the impingement nip J as it was patterned originally on the transfer roll. Lateral flowout along this nip will tend to be a function of the proportionate excess of flow, and of course is affected by the physical characteristics of the specific composition. Once equilibrated, the lateral flowout tends to remain constant. Since the use of distributing pockets permits margining only at spaced intervals, it usually is advised to include adjustable scraperlike squeegees 89 at the margins, thereby deflecting the marginal flow away from the transfer roll upweb from the impingement nip. Striping applications similarly may be accomplished, and indeed the application of dissimilar compositions as described is described in the first accompanyng patent application.

By incorporating means for heating the several parts, the apparatus may serve ideally for application of heatfluidizable compositions, including preheating of the contacted web surface and means for controllable depth penetration thereinto. Whereas operation at elevated temperatures tends to imperfect critical clearances in traditional reverse roll equipment, this form of the present invention avoids such problems since only two clearance factors are involved, viz.: journal clearances and the metering nip, the first tending to be selfcompensative and the second flexibly independent. In addition it will be noted that external exposure of the coating composition occurs only downstream from the final metering nip and in an area so occluded as to be easily flooded with inert gas if such be necessary.

It also will be apparent that certain of the techniques herein described may be applicable to traditional reverse roll apparatus, wherein it may be found advantageous to provide means for ratification of the web entrained air for the reasons described hereinbefore and in the identified patent applications, or that fountaining means may be advantaged over pickup rolls or flooded nips, or that the described subatmospheric pressure differential may be utilized for final metering of the coating composition against the transfer roll in place of the roller nips usually provided. Thus many of the problems associated with operation of such apparatus may be circumvented without necessitating loss of the investment therein or requiring duplication of basic facilities in order to retain the equipment for the end purposes to which it admirably is suited.

Referring now to FIGURE 3, which similarly incorporates a subatmospherically controlled spreading or doctoring element, the web 1 in this instance is roller supported 90, against which the illustrated coating assembly is placed. The assembly comprises two independently controllable vacuous enclosures 8, 9, a fountaining section 6, 7 dividing the said chambers, and the final metering element positioned downmotion therefrom. Here shown is a rotatable doctoring element 71 journaled in a supporting holder 72b which preferably is flexible in relation to its radial contact B with the roller-supported web, for which reason it is lightly constructed and flexibly hinged 91 from the downweb face of the supporting vacuous chamber 9. Both chambers are sealed by contact with the main roller 90, preferably including its end faces, the upweb chamber 8 being similarly sealed to the idler roller 92, by the interposed web between the said rollers and by flexible seal 93 against the upweb face 2 of said chamber. The fountain 6, 7 in this instance is positioned close to the running Web surface so that a viscous fluid seal Q is provided between upweb and downweb vacuum chambers. Immediately upweb from the incoming flow of fountaining composition, rarification of the air D tends to minimize its being drawn into the coating composition 11 and therein entrained in the form of air bubbles. Although elaborate means may be provided for perfecting the closure of the vacuum chambers, the apparatus is operable with provision for exhaust volume adequate to permit such ports of entry to be restrictive rather than perfectly sealed. The fluid circuitry may be identical to that hereinbefore described, including the preferential separation of liquid efliuent 11b and gaseous exhaust 56 from the coating chamber 9, and the passage of air 55 therethrough so as to facilitate drainage 40 of the effluent and minimize the overall size of the apparatus.

It will be apparent that either rotary or stationary doctoring elements may be utilized in either of the forms of apparatus herein described, and that the design may differ from that illustrated, While still utilizing the basic techniques and the teachings related to their various applications. Margining techniques are similarly applicable, and a number of modifications are possible within the fountaining element itself. Such may include pressurable positioning against the roller, thereby permitting instant withdrawal either separately controlled or as a function of the pressure of the incoming composition. Physical contact with the web may be established by flexible accoudrements, both metallic and elastomeric, the latter resembling a duplex window-washing squeegee. It further will be ap parent that the fountain could indeed be replaced by a coating hopper into which a portion of the web and the roller were immersed, such arrangement permitting the use of vacuum chambers both up and downweb therefrom, but tending to preclude the possibility of their being differentially vacuum leveled.

Having thus described my invention, I claim:

1. In an apparatus for applying a coating composition to one surface of a traveling web of paper, said apparatus comprising a roller to support said Web, drive means for rotating said roller, means continuously supplying said composition adjacent the periphery of said roller, and doctoring means stressed resiliently in radial opposition to said periphery and spaced operatively therefromby frictional impaction of said composition to form a restrictive impingement nip to meter a continuous and uniform thickness of said cooating, the improvement in said apparatus which comprises, and in combination, an enclosure upstream from and freely communicative with said nip, vacuous means for maintaining gaseous subatmospheric pressure within said enclosure, and wherein said doctoring means is substantially passive structurally in said opposition but is responsive operatively to the pressure differential between the external atmosphere and said sub atmospheric pressure within said enclosure, thereby to effect the metering of said thickness as a function of said subatmospheric pressure.

2. The combination as claimed in claim 1, wherein said doctoring means comprises a rotatable rod.

3. The combination as claimed in claim 1, including a second and separate enclosure contiguous said roller, boundaried partially by an arc-segmental portion of said periphery, positioned upstream from said supply means to communicate with said web prior to web contact with said coating composition, and adapted to be maintained at subatmospheric pressure.

4. The combination as claimed in claim 3, wherein said supply means comprises a fountaining section interposed between said enclosures.

5. An apparatus for applying a coating composition to one surface of a traveling web of paper, said apparatus consisting principally of two transverse structural elements with ancillary functional components, one of said elements comprising an elongate roller having a precision cylindrical periphery to form an uninterrupted journal substantially throughout its entire length, the other said element comprising a mated bearing for said journal, said journal and bearing essentially coextensive in length with an arc-segmental portion of said periphery unshrouded by said bearing, said ancillary components including drive means for rotating said roller counter-directionally to said traveling web, distributive means for continuous flow of said composition selectively to a linear portion of said periphery, doctoring means to meter the thickness of said coating against said periphery downstream from said distributive means, web support means to position said web in deflective arc-segmental contact with said periphery, and web tension means to maintain wiping contact between said web surface and said periphery.

6. The coating apparatus as claimed in claim 5, wherein said distributive means is integral with said bearing element and comprises a system of interconnected ducts and parallel restrictive passages to distribute said flow uniformly and controllably to said linear portion of said periphery.

7. The coating apparatus as claimed in claim 6, wherein one set of said parallel restrictive passages comprises grooves in the bearing surface which are sized and spaced apart uniformly and preferably oriented helically in the manner of female threads formed on the inner wall of the cylinder.

8. The coating apparatus as claimed in claim 5, including an enclosure freely communicative with said doctoring means and adapted to be maintained at subatmospheric pressure, and wherein said doctoring means is mounted in passive radial relationship to said periphery but adapted to be responsive to the differential between said pressure and that extant externally from the apparatus.

9. The coating apparatus as claimed in claim 5, including a chamber positioned upweb contiguous an arc-segmental portion of said periphery, adapted to be communicative with the incoming web and to be maintained at subatmospheric pressure, and wherein a membrane overlays the web to effect the closure of said chamber.

References Cited UNITED STATES PATENTS 2,293,125 8/1942 Fanselow 118261 X 2,470,093 5/ 1949 Crowder et al 118261 2,721,534 10/ 1955 Lucas 118-258 X 3,044,396 7/1962 Aller 101-l57 3,116,688 1/1964 Ward et al.

1,536,511 5/1925 McLaren 118-261 2,218,112 10/ 1940 Kaufmann 118261 2,681,294 6/1954 Beguin 117-34 2,946,307 7/ 1960 Warner 118-1 19 ROBERT W. MICHELL, Primary Examiner ROBERT I. SMITH, Assistant Examiner US. Cl. X.R. 118-l19, 410

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