US2842092A - Reverse roll coating machine with blade support for web - Google Patents

Description

A. W. POMPER July 8, 1958 REVERSE ROLL COATING MACHINE WITH BLADE SUPPORT FOR WEB- Filed March 2, 1955 E 00 ooooo 0000000 900000 o+ bb oooooao GUI:

O O Q 000 INVENTOR ANTI-ION) m POMPER BY M ATTORNEYS United States Patent fiice 2,842,092 Patented July 8, 1958 REVERSE ROLL \COATING MACHHNE Will"?! BLADE. SUPPORT FOR WEB Application March 2, B55, Serial No. 491,697

9 Claims. (Cl. 118---Z43) This invention relates toweb coating and particularly 7 to a method of and apparatus for web coating by the so-called roll transfer process wherein there is less penetration of the web.

it is a general object of the present invention to provide a novel method and apparatus for web coating.

A. more specific object of the invention consists in the provision of a novel method and apparatus for applying coating to a travelling web with minimum penetration or strike-through on porous or open mesh type web material.

An important object of the invention consists in the application of coating material to a travelling Web from a transfer roll in the absence of a resilient backing roll whereby penetration is materially reduced.

Another important object of the invention consists in the replacement of the usual resilient backing roll with a flexible blade of the doctor type whereby the included angle between the coating material approaching the web and the latter is substantially increased.

Still another important object of the invention consists in the substitution, in a reverse roll type coater for web material, of a flexible doctor blade and suitable web pulling means for the usual resilient backing roll whereby the coating transfer to the web is performed more rapidly and with less impregnating pressure.

Other and further objects of the invention will be more apparent to those skilled in the art upon a consideration of the following specification and accompanying. drawing wherein isdisclosed a single exemplary embodiment of the invention, with the understanding that such changes and modifications may be made therein as fall within the scope of. the appended claims Without departing from the spirit of the invention.

in said drawings:

Fig. l is a schematic and diagrammatic side elevation of a coating machine incorporating the present invention;

Fig. 2 is span view, partiallybroken away to illusirate the. suction blanket assembly usedin one. embodiment to apply the feeding motion to the Web to be coated;

Fig. 3 is a fragmentary side elevation of a second embodimentof the feed mechanism making use of a belt with card clothing;

Fig. 4 represents diagrammatically the operation of the. present invention showing the more obtuse angle and shorter delivery timeand distance contact at coating transfer; and.

Fig. 5 is a view similar to Fig. 4 showing the arrangement in a conventionalrcoater where. the angle is more acute and the time and distance of contact greater.

in the, field of coating papers, fabrics, plastics and like webs continuously with various types of relatively fluid materials suchas: coloring matters, varnishes, lacquers, adhesives, plastics and the like, development has resulted in many methods of coating and forrnsof coat ing devices, and among these may be mentioned brush coaters, roll coaters, hot melt coaters, spray coaters, knife coaters, dip bath coaters, air knife coaters, and many others, each having its proponents and its specific uses. However, one of the most versatile and effective of the coating devices is known as a reverse roll coater, and while this occurs in many forms, in essence, it includes at least two oppositely rotating, highly polished metal rolls to one of which coating material is applied before it meets the other. At the meeting the gap is sized to determine the thickness of coating which is allowed to remain on the so-called transfer roll by the operation of the metering roll. This layer of coating iaterial on the transfer roll is then delivered to the web which travels oppositely to the direction of movement of the cooperating transfer roll and wipes the coating from the latter, taking it on to itself in a layer whose thickness to some degree depends on the relative speeds of the transfer roll and the web.

Heretofore in reverse roll coaters the web to be coated has been universally drawn along the surface of the transfer roll to pick up its layer of coating material by means of a resilient backing roll, insuring contact throughout the full width of the web material at relatively uniform pressure in spite of slight inequalities in web thickness and uniformity.

One serious fault, however, occurs with machines of this character when working with certain types of webs and coating materials, and this is known in the industry as strike through. In other words, the coating material is forced through the web material and shows, at least, as unsightly splotches on the back face thereof. Obviously the condition is aggravated in various porous and absorbent web materials such as loosely woven fabrics and the like, and with relatively thin and highly penetrative liquid coatings.

The cause of this strike through is believed to be the acute angle occurring between the surface of the web leaving the transfer roll, after picking up its coating,

and the corresponding and coated surface of this roll which subjects the web material to a continuous pressure of coating material for too long a time and over too long a space, it being remembered that the material and the transfer roll are travelling in opposite directions so that the first wipes coating from the other. If some way could be provided to render the angle more obtuse on the discharge of the web from the transfer roll, then the time and distance of contact pressure between the advancing coating on the transfer roll and the oppositely moving web could be materially reduced and the constriction of the coating at the transfer area lowered so that the material would not strike through nearly so readily. It is the purpose of the present invention to describe apparatus and methods for carrying out a system which produces these superior results.

Referring now to Fig. 5 which is a fragmentary representation of the manner of applying the coating in a reverse roll coater using a resilient backing roll, it should be noted that the transfer roll it) carrying its coating layer 11 of the material which is to be transferred to the web 12 travelling in the direction of the arrow, rotates in such a direction as to move its periphery contrary to that of the contacting surface of the web to be coated, thus wiping all of the coating onto the web in the narrow acute angle indicated by 13 which exists between the transfer roll 10 and the web material running over the surface of the resilient backing roll 14. It will be noted that as long as two rolls are used but little change in the acuteness of this angle can be effected. This acuteness produces a considerable area, from the actual meeting point 15 where the last of the coating material is wiped onto the traveling web, to the interior angle to Where there is a sharp change in direction between the moving coating material 11 on the transfer roll and that numbered 17 now moving with the web, in which the coating material 11 on the surface of the transfer roll is being driven or forced toward and through the material of the web at a velocity which is substantially the sum of the velocities of the two rolls. Likewise a time interval of considerable magnitude exists between the point 15 and the point 16 so that not only is the coating material thrust against the surface of the web at a high velocity but this occurs over considerable time and distance elements.

In accordance with the present invention the resilient backing roll is wholly eliminated and in its place, as seen inFig. 4 is supplied a thin, flexible, straight edged blade 20 having the major characteristics of the well known doctor blade used for scraping materials from the surface of travelling rolls. Here the web 21 advances transversely over the rounded edge 22 of the doctor blade and breaks away sharply at 23 from the surface of the transfer roll 10'. In this manner the included angle between the transfer roll and the leaving web is much more obtuse and the distance from 15 to 16 is considerably less whereby both the time and distance elements are shortened. Moreover, there is no suction effect as the web leaves the relatively thin edge of the doctor blade in contrast to that which exists when the coated web is pulled away from the surface of the resiliently covered backing roll, tending to create a suction or vacuum which draws the now still fluid coating material toward the back surface of the web. In any event the results are very much superior and very porous fabrics can be coated with relatively thin coating materials without strike through when used on apparatus, as diagrammatically illustrated in Fig. 4.

In the conventional reverse roll coater the resilient backing roll 14 provides the drive for feeding the web material through the coating machine and since no such drive is provided by the flexible doctor blade some auixiliary means for providing for the passage of the material through the coating machine is essential, and this is shown in Fig. 1 where all of the essential elements of the coating machine of the present invention are depicted.

In this machine there is illustrated the polished transfer roll 10" and its cooperating metering roll 9 rotating in the opposite direction and serving to wipe from the surface of the transfer roll all but the desired thickness of coating material which is supplied to it, in one man-- ner or another, in excess of the desired thickness. A favorite arrangement for supplying this material is by forming a fountain between and above the junction of rolls 9 and It)" by means of end dams and a back dam 31 whereby a quantity of the material to be coated is maintained in a reservoir in-open contact with the surface of the transfer roll in advance of its meeting with the metering roll. In keeping with the usual practice a doctor blade 32 wipes the material from the surface of the metering roll as it lifts from the fountain and lets this material run back therein. As shown by the arrow 33 the metering roll is adjustable toward or from the axis of the transfer roll to determine the thickness of coating which is delivered below the nip between the two rolls. The web guiding doctor blade is shown at 20" over whose straight edge the web 21 travels from a suitable supply source and guide roll 34 which determines the angle of approach to the transfer roll. As previously mentioned, the doctor blade is resilient and .by a suitable mounting, illustrated only in block form at 35, can be flexed against the surface of the roll at various angles as determined by the operator. The arrows 36 indicate the possibility of adjustment in either direction from the position shown, while the arrow 37 indi- 4 cates that adjustment from and toward the transfer roll may be effected by suitable means.

The web is drawn from its contact with the transfer roll and the blade edge at a desired angle in accordance with the position of roll 39 which may be spaced at appropriate distance from the contacting surface so that the coating has partially set, hardened or dried by the time it reaches this roll. Roll 39 and its companion roll 40, driven. at any suitable speed by any desired source of power, such as indicated by the motor 41, form the pulleys for a belt system 42 used for drawing the fabric or web through the coating machine. If the web is of more or less air impervious material this belt may be a suction type rubber belt such as shown in Fig. 2 and having a plurality of longitudinal rows of through holes 44 as seen. The upper reach of the belt travels over the face of a suction box 45 wherein a vacuum is maintained by means not illustrated. As seen in Fig. 2 slits in the upper face of the vacuum box at 46 register continuously with the under sides of the holes 44, in the upper reach of the belt, so that a suction is provided for causing adherence of the web 21 to the upper face of the traveling suction belt. If the web is sufiiciently non-porous it will be drawn at the desired speed as set by the drive motor 42. Release is effected as the holes 44 successively reach the ends of the slots and are deprived of their vacuum.

In an alternative form of the feeding device illustrated in Fig. 3, where corresponding parts have their reference characters primed, the belt system instead of being perforated rubber, is covered with card clothing 50 so that it has an appropriate surface for cooperating with the fibers of woven web material to drag it through the machine in an obvious manner. The latter form of feed is for use with textiles and the like where porosity prevents adequate suction or such suction might tend to increase the coating penetration.

. I claim:

1. A web coating apparatus comprising in combination, a continuously driven transfer roll, means to advance a web into line contact with said roll in opposition to its direction of rotation, means to supply said roll with a uniform layer of coating material of a predetermined thickness in advance of its engagement with said web, and a flexible blade having a straight edge adapted to engage the under surface of the web at the contact line and urge it into said roll contact.

2. The apparatus of claim 1 in which means guides the web to leave the roll at an angle more obtuse than the angle of tangency.

3. The apparatus of claim 1 in which said blade is non-radially positioned in respect to the roll.

4. The apparatus of claim 3 in which the blade is angled so that its plane passes to the side of the roll axis of rotation in the direction of web travel.

5. In a web coating apparatus of the type described, a continuously driven coating transfer roll, a source of coating material, delivery and metering means to provide said roll continuously with a layer of said material of predetermined thickness, means to advance a web at fixed velocity past said roll in a direction opposite to the adjacent roll periphery and means to resiliently press one face of the web against the surface of the roll in substantially line contact to remove substantially all of said material therefrom, said last mentioned means comprising a thin, resilient blade having a straight edge engaging the opposite face of the web.

6. The apparatus as defined in claim 5 in which the general plane of the blade is angled toward the advancing roll periphery whereby the breakaway angle between the web and the coating delivery are of the roll may be 1 increased to reduce penetration of the web by the coating material.

7. The apparatus of claim 5 in which the web advancing means comprises a continuous suction type belt engaging the said opposite face of the web beyond the said roll.

8. The apparatus of claim 5 in which the web advancing means comprises a continuously driven belt having a card clothing surface engaging the said opposite face of the web beyond the said roll.

9. Apparatus for coating a relatively porous web with a highly penetrative material, in combination, a coating transfer roll driven at a constant speed and provided with a continuous, constant thickness layer of coating material, means to advance a Web at fixed velocity contra to the adjacent roll periphery, guide means for said web, one ahead of and one following said roll, a common tangent to said guide means being spaced a substantial distance from said periphery, and a flexible blade having a straight edge parallel to the roll axis positioned to urge the web reach between said guide means into line contact with said roll to wipe the coating material therefrom, said blade being positioned to provide a more obtuse angle of Web separation than angle of web approach to the roll surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,135,406 MacDonald Nov. 1, 1938 2,205,557 Fisher et al. June 25, 1940 2,308,024 Piker Jan. 12, 1943 2,383,964 Grupe Sept. 4, 1945 2,556,954 Zeigler et al. June 12, 1951 2,729,192 Warner Jan. 3, 1956 FOREIGN PATENTS 925,376 France Mar. 31, 1947

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