US3539384A - Coating apparatus for coating a flexible web - Google Patents

Description

Nov. 10, 1970 F. P. KOLESINSKAS 3,539,384

COATING APPARATUS FOR COATING A FLEXIBLE WEB Filed June 30, 1967 PRIOR ART INVENTOQR. Frank P. Kolesinskus B) ATTORNEY United States Patent 3,539,384 COATING APPARATUS FOR COATING A FLEXIBLE WEB Frank P. Kolesinskas, Binghamton, N.Y., assignor to GAF Corporation, New York, N.Y., a corporation of Delaware Filed June 30, 1967, Ser. No. 650,422 Int. Cl. B05c 1/12 US. Cl. 117111 1 Claim ABSTRACT OF THE DISCLOSURE For applying a uniform coating layer to a web of diazotype film moving at high speed there is provided a pick-up roller having an annular surface rotatable in a liquid coating solution, a transfer roller having an annular surface rotatable in spaced relationship with that of the pick-up roller to thereby reverse, split and receive only a portion of the coating solution therefrom, and a moving film web the surface of which is spaced from that of the transfer roller, and also only a portion of the solution carried on the surface of the transfer roller. The smoothing return flow due to the splitting of the wet film on the transfer roller and on the pick-up roller, facilitates the uniform coating of a film web moving at high speed.

This invention relates to a method and apparatus for coating a flexible web and, in particular, for applying a uniform layer of coating solution to the surface of a continuously moving web of diazo-type film material.

The continuous and rapid increase in the production of diazo-type films, such as microfilm or the like, has stimulated the need for the development of efficient high speed methods and apparatus which are capable of applying high quality coating to the film. In essence, the coating process concerns itself primarily with the uniform application of a coating solution to diazo-type films without the necessity of providing the so-called solution flowout after application, to the film surface. Prior art methods and apparatus, in general, have proven themselves to be sloW in terms of production output and incapable of meeting present day industrial and technical demands.

Among presently used solution coating methods, which are described to be of the high speed production type, are those employing. air knives, gravure and reverse roll solution coating systems. These have proven themselves to be generally satisfactory when used in connection with commercial diazo-type film processing installations and systems, but are subject to some limitations. In particular, these limitations have been the relatively complex and expensive apparatuses which are required for the pneumatic devices employing air doctor blades or knives, and the poor coating results obtained at higher production speeds when using prior art devices incorporating gravure or reverse roll systems. At higher roller speeds, when using gravure or roller devices rotating in a trough containing a coating solution, waves and ridges are formed in the solution layer on the surfaces of the pick-up rollers. These irregularities in the solution thickness are transmitted to the film passing adjacent to the pick-up rollers, causing drastic deteriorations in the quality of the coated film, and at times, making the film completely unusuable. Consequently, it becomes quite evident that the prior art film coating methods and apparatuses are not sufiiciently suitable when applied to the large quantity, high speed production of sophisticated film products such as diazotype micro-film.

The novel and improved diazo-type film coating apparatus and method according to the present invention,

Patented Nov. 10, 1970 "ice overcomes the foregoing and other disadvantages encountered in the prior art, by providing a coating apparatus which includes a rotatable pick-up roller adapted to rotate at high speeds in a trough containing a diazo coating solution, a transfer roller rotatable in a predetermined relationship with the pick-up roller and which receives a portion of the coating solution from the latter, and a continuously moving web of film material adapted to receive the coating solution from the transfer roller. A primary advantage of the use of the transfer roller intermediate to the pick-up roller and the film web is that it has a smoothing eifect on the coating solution removed from the trough by the pick-up roller. In effect, a portion of the coating solution picked up by the pick-up roller is transferred to the surface of the transfer roller, while the remainder of the solution passes between the pick-up and transfer rollers and returns to the trough. The portion of the coating solution transferred to the transfer roller is then conveyed by the latter about an angular displacement of at least This will allow. the coating solution on the surface of the transfer roller to smooth itself under the action of gravity. Subsequently, the coating solution is deposited on the surface of a web of film material being conveyed past the transfer roller, and produces a smooth, high quality coating of the solution on the film. The utilization of intermediate transfer rollers will facilitate the high speed operation of reverse roll coating apparatuses, allowing the film to be satisfactorily coated at film speeds in excess of I00 feet/minute.

Accordingly, it is a primary object of the present invention to provide an improved and novel film coating apparatus facilitating the high speed, quality coating of diazo-type film Webs.

Another object of the present invention is to provide a novel film coating apparatus utilizing a rotatable pickup roller adapted to receive coating solution from a trough, a rotatable transfer roller cooperative with the pick-up roller so as to receive a portion of the coating solution therefrom, and a continuously moving web of film material which is coated with the coating solution carried by the transfer roller.

A further object of the present invention is to provide a novel method of coating a moving web of diazo-type film through the use of a reverse roller coating apparatus.

A more specific object of the present invention is to provide a novel method of applying a coating solution to the usrface of a moving web of diazo-type film by means of a transfer roller which receives the coating solution from a cooperative rotatable pick-up roller.

These and other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which:

FIG. 1 is a diagrammatic view of a prior art coating apparatus;

FIG. 2 is a diagrammatic view of a preferred embodiment of a diazo-type film coating apparatus according to the present invention;

FIG. 3 is a second embodiment of a coating apparatus according to the present invention;

FIG. 4 is a third embodiment of a coating apparatus according to the present invention;

FIG. 5 is a fourth embodiment of a coating apparatus according to the present invention; and

FIG. 6 is a fifth embodiment of a coating apparatus according to the present invention.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts through out the several views, FIG. 1 illustrates a prior art coating apparatus of the so-called two roll reverse roll bear type. A pick-up or applicator roller 1 is adapted to rotate in a trough 2 containing a quantity ofdiazotype film coating or developer solution. Applicator roller 1 picks up a portion of the coating solution on its surface, and conveys the solution into contact with a moving web of film material 3. Film material 3 is conveyed past applicator roller 1 by means of a conveyor roller 4 which rotates in the same direction as applicator roller 1. Consequently, the solution on applicator roller 1 is transferred to the surface of the film material 3 in a relatively smooth and uniform manner. Although the aforedescribed coating apparatus is satisfactory when utilized at relatively low film web and applicator roller speeds, diificulties have been encountered at higher speeds in excess of 23 linear feet/minute. When the applicator roller 1 is rotated at higher speeds, coating solution waves are generated in the trough, which result in an uneven application of coating solution on the surface of roller 1. Since the film web material 3 receives the coating solution directly from roller 1, the irregularities and waves in the thickness of the solution are transferred to the web. This, of course, res lts the formation of a low quality film coating wh ch is unacceptable in an industry requiring a high standard of coating quality.

The diazo-type film coating apparatus 4 according to the present invention, as shown in FIG. 2, includes a pick-up roller 5 rotating in trough 2 which contains a quantity of the developer or film coating solution. A transfer roller 6 is positioned in closely spaced relationship with pick-up roller 5, so as to provide a controllable gap '7 between the rollers. Transfer roller 6 is adapted to the rotated in the same direction as the direction of rotation of pick-up roller 5.

Film web 3 is entrained about a conveyor or backing roller 8, and is arranged to move past the surface of transfer roller 6 in closely spaced relationship, forming a gap 9 with transfer roller 6. Backing roller 8 is rotated in the same direction as the direction of rotation of transfer roller 6.

During operation, pick-up roller 5 is rotated in the trough 2 at relatively high speeds, in excess of to 30 linear feet/minute, picking up a quantity of developer or coating solution on its surface. At these high speeds, waves are generated in the solution in the trough 2, which in turn cause the solution on the surface of the pick-up roller to be uneven in thickness, and interspersed with waves and ridges. When the solution on pick-up roller 5 reaches the nip or gap 7 between the latter roller and transfer roller 6, a portion of the solution deposited on the surface of the transfer roller, while the remainder of the solution passes through the gap 7 and is returned to the trough 2 along the back portion of pick-up roller 5. The splitting or dividing of the coating solution between pick-up roller 5 and transfer roller 6 will tend to reduce the irregularities and waves in the coating solution transferred to the surface of transfer roller 6.

Concurrently, the solution on the surface of transfer roller 6 is rotated toward gap 9 between film web 3 and transfer roller 6, and is deposited onto the surface of the film web in a manner well known in the art. Inasmuch as the coating solution on the surface of the transfer roller 6 is rotated through an angular displacement of approximately 270, it will tend to level itself off under the influence of gravity during rotation. In effect, this will assure that a smooth coating of the solution will be deposited uniformly over the contacted surface of film web 3.

In order to avoid an excess of coating solution being deposited on the transfer roller 6 and film web 3, the transfer roller 6 is rotated at a greater linear peripheral speed than that of pick-up roller 5. Similarly, film web 3 may be moved at a greater linear speed tran the peripheral surface speed of transfer roller 6. This will permit the coating solution which is removed from trough 2 by pick-up roller 5 to be spread over a larger surface in an equal and uniformly distributed thickness. Typical speed ratios, which have been proven to be satisfactory in operation, are rotation of the pickup roller 5 at a linear surface velocity of 4 5 feet/minute, and the film web 3 at a linear velocity of 60 feet/minute. Essentially, the speed ratio between the transfer roller 6 and pick-up roller 5 may be in the order of 3:2, while similar ratios may be maintained between the film web 3 and transfer roller 6 depending upon the desired coating solution thickness on the film surface. In present diazo-type coatings, the above mentioned speed ratios, in conjunction with proper adjustments of roller gaps 7 and 9 produce final smooth film coatings of 2.5 cc./ square foot.

It is to be noted that the above mentioned speed ratios are given by way of example only, and that other speeds and combinations thereof may be employed for different types of developer and diazo-type coating solutions as required by the particular applications.

Referring now to the embodiments illustrated in FIGS. 3 to 6 of the drawings, these are in many essential respects quite similar to the embodiment of FIG. 2. Thus, FIGS. 3, 4 and 5 show the apparatuses wherein the backing rollers 8 are positioned at an angle of from the pick-up rollers 5 when measured about the circumference of the transfer rollers 6. However, in the embodiment of FIG. 3, the film web 3 which is entrained about backing roller 8 is conveyed at an angle relative to roller gap 9, whereas in FIG. 4 the film web extends in vertical parallel directions from the backing roller. In the embodiment of FIG. 5 the web diverges from backing roller 8. Aside from these constructional distinctions, which may be each particularly suitable for specific coating applications, the principle of operation is quite analogous to that of the apparatus emboided in FIG. 2 of the drawings.

Respecting the embodiment of the apparatus shown in FIG. 6, this is essentially similar to that of FIG. 2, in that it allows the coatin' solution conveyed by the transfer roller 6 to rotate through an angular displacement of 270. In this embodiment, however, the film web is moved parallel to the surface of transfer roller 6, and is directed over direction-changing idler rollers 10.

In addition to the foregoing, the diameters of pick-up roller 5, transfer roller 6 and backing roller 8 may be varied and used in different combinations in order to obtain the desired coating thickness and consistency.

In essence, the foregoing achieves the basic objective of the invention, by splitting the solution between the pick-up roller and transfer roller, and the subsequent deposit of the solution onto the film web surface; minimizes any disturbances occurring to the liquid meniscus in the solution trough 2; and accurately meters the solution over the web surface at relatively high speeds previ ously unattainable in the prior art.

It should also be understood that the foregoing relates to only a preferred embodiment of the invention, and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

1. A method of uniformly applying a liquid coating solution to the surface of a rapidly moving web of film material, comprising:

rotating the annular surface of a pick-up roller in a trough containing a quantity of said liquid coating solution,

split-transferring only a portion of the resulting film of said coating solution from the annular surface of said pick-up roller to that of a rotatable transfer roller,

conveying said web in the reverse direction in spaced relationship past the rotating surface of said transfer roller,

and thereby split-transferring only a portion of the liquid coating solution carried by the surface of said transfer roller to the reversely moving adjacent surface of said web of film material.

References Cited UNITED STATES PATENTS 6 FOREIGN PATENTS 788,939 1/1958 Great Britain.

RALPH S. KENDALL, Primary Examiner U.S. Cl. X.R.

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