US3220877A

US3220877A - Method of coating strip material

Info

Publication number: US3220877A
Application number: US203036A
Authority: US
Inventors: Herschel R Johnson
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1962-06-18
Filing date: 1962-06-18
Publication date: 1965-11-30
Anticipated expiration: 1982-11-30

Description

Nov. 30, 1965 H. R. JOHNSON 3,220,377

METHOD OF COATING STRIP MATERIAL Filed June 18, 1962 VACUUM 11 SOURCE \j'g. 5

Herschel R. Johnson INVENTOR.

United States Patent C) ice 3,220,877 METHOD OF COATING STRIP MATERIAL Herschel R. Johnson, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed June 18, 1962, Ser. No. 283,036 9 Claims. (Cl. 117-120) This invention relates to improvements in the method of applying liquid compositions or coating materials to a moving strip of material to be coated.

It has been customary heretofore to utilize dip roll coating or applicator roll coating, with or without a doctor blade to apply a liquid composition to a moving strip material or web so as to coat one or both surfaces of the material. The liquid composition has also been applied to a moving strip material by pumping the composition through a slot in a hopper to coat the material. These methods have been satisfactory in that uniform and usable coatings have been produced but the speed of application is very limited. It is also very diflicult to attain a very thin coating by such methods. These disadvantages and limitations are of a very serious nature in the photographic industry where many types of precise coatings on relatively nonporous supports are required. In making color films which require multilayer coatings, the above methods have not only been time consuming but also difiicult to utilize because of the number of coatings required.

In US. Patent 2,681,294, a method of coating a moving 9 strip material is disclosed which overcomes many of the disadvantages of the earlier methods as well as permitting the coating speed to be greatly increased. The method disclosed in this patent includes flowing a ribbon of the liquid composition in a stream between a coating device and a surface to be coated while maintaining a greater pneumatic or other gaseous pressure on that side of the ribbon from which the coated material moves away than on that side toward which the material to be coated approaches. Yet this method presents certain difficulties in starting a coating which results in a considerable loss of coated material. As the method is practiced, the coating device in which the coating composition is contained is usually positioned several inches from the material to start the flow of the composition. The device is then moved toward the material and at the same time the suction is applied. The device is moved almost into contact with the material and held in this position until the coating bead is formed. Once the head has been properly formed, the device is moved away from the material to a normal coat position. Observation of the coated material at the start of coating made in this way indicates that there is an excessive laydown of the composition on the material at the instant of wetting and such excess of the liquid composition can extend for everal feet longitudinally of the material. This thicker layer does not dry as quickly as a layer of normal thickness and subsequently tracks oil onto the rollers for supporting the material as it is moved through its drying or curing path. The portion of the material coated with the thicker layer as well as those portions of the material which have picked up streaks of the coating composition from the support rolls cannot be used, and hence, must be cut out of the roll and scrapped. The thicker layer is formed whenever the coating device is moved forward to start a new coating operation, and Whenever the coating device is moved out of its normal coat position to restart the coating operation or to permit passage of a splice in the material.

In Observing the flow of the coating compositions and particularly the flow at the lip of the coating device or 3,220,877 Patented Nov. 30, 1965 bead point, it was noted that an abnormally large welt or ridge of the coating composition forms at the lip, this welt or ridge apparently being drawn up by surface tension forces and the nonwettable character of the surfaces of the coating device. The disadvantages of the method described above have been overcome by utilizing a surge of higher than normal suction as the coating device approaches the moving strip material. This higher suction is maintained until the ribbon of coating composition forms the necessary bead with the strip material and is then reduced to the normal suction as the coating device is moved to its coat position. As the lip of the coating device approaches the moving strip material, a high velocity throat is formed with the strip material and a corresponding higher velocity of air flow through the throat results therefrom. The higher suction and the corresponding higher velocity of air flow over the lip pulls the large welt or bead of coating composition that has accumulated on the lip down over the lip and carries it away in the air stream. The head that is formed as the coating composition is then moved into contact with the moving strip material immediately produces a uniform coating of the desired thickness, the thicker layer normally prevalent at the start of a coating being completely eliminated with the removal of the accumulation of the coating composition at the lip of the coating device.

The primary object of the invention is, therefore, to provide a method of applying a liquid composition to a moving strip material by which a uniform layer of the liquid composition is immediately applied to the material.

A further object of the invention is to provide a method of applying a liquid composition to a moving strip material by which the coating starts are without any uncontrolled or abnormal layer of the composition.

Another object of the invention is to provide a method of applying a liquid composition to a moving strip material by which any accumulation of the composition on the lip of the coating device is removed before the composition is applied to the material.

And stil anothelr object of the invention is to provide a method of applying a liquid composition to a moving strip material by which any accumulation of the composition on the lip of the coating device is removed by the air stream produced by different pressures on each side of the lip of the coating device.

These and other objects and advantages will be ap parent to those skilled in the art by the description which follows.

Reference is now made to the accompanying drawing wherein like reference numerals designate like parts and wherein:

FIG. 1 is a diagrammatic side elevation partially in section of a form of apparatus by which the improved method can be carried out;

FIG. 2 is an enlarged fragmentary sectional view showing the accumulation of the liquid composition on the lip of the coating device just prior to removal thereof; and

FIG. 3 is an enlarged fragmentary sectional view showing the formation of the high velocity throat and the removal of the composition accumulation by the air stream moving through the throat just prior to formation of the coating bead.

With reference particularly to FIG. 1, the strip material ll), such as film or paper, is drawn from a supply source (not shown) and partially wrapped around the roll or drum 11 for movement past the coating station 12, the roll 11 being keyed or fixed to shaft 13 which is continuously rotated at a desired rate (feet per minute) in accordance with the liquid composition to be applied to the strip material. Thus, as the uncoated material 10 is moved into the coating station, the liquid composition 14 is applied thereto and then passes away from the roll 11 for the necessary drying operations.

The coating device 15 can be of a type disclosed in US. Patents 2,761,419 and 3,005,440 in which a fluid composition 16 is continuously pumped by a constant discharge pump 17 into a cavity 18 at a given rate, the composition being forced through a narrow distributing slot 19 in the form of a ribbon and onto a downwardly inclined slide surface 20. The ribbon flows by gravity in the form of a layer 21 .to the point where it forms a coating bead 22 between the lip 23 of surface and the moving strip material 10. A second fluid composition 25 is pumped into cavity 26 by another constant discharge pump 27 and is forced through the distributing slot 28 in the form of a ribbon and onto the inclined slide surface 29. As the layer 30 reaches the layer 21, it flows thereover and the two layers then flow down surface 20 and into the coating bead 22.

The coating device 15 extends axially with respect to roll 11 and is mounted on plate 32 which, in turn, is pivotally mounted on cross shaft 33. By means of wheel 34 and lead screw 35, which is pivotally connected to extension 36 on plate 32, the coating device can be moved toward and away from material 10 and roll 11.

A casing 40 having end walls 41 together with coating device 15 and a portion of roll 11 form a chamber 42. A vacuum source or pump 43 is connected to chamber 42 by pipe 44 which is provided with a regulating valve 45. The pressure within chamber 42 can be indicated by means, of the manometer 46 which is connected to chamber 42 by means of line 47.

When starting a coating operation, the coating device 15 is moved or tilted to a Start Coat position in which the lip 23 is separated by several inches from the material 10 and roll 11. In this position the fluid compositions must be pumped into the

cavities

18 and 26 in order that the

layers

21 and 30 of the compositions can be formed for flowing toward the lip 23 of the coating device. In accordance with the method taught by US. Patent 2,681,294, the pressure within chamber 42 is reduced so that it is subatmospheric with a pressure differential of the order of 0.1 inch to 5.00 inches of water depending on the fluid composition and the material to be coated. Since it is desirable to have

layers

21 and 30 at the lip 23 when the coating device is positioned relative to material 10 to form bead 22, the coating device is not moved toward the material 10 until the

layers

21 and 30 are at the lip. During the interval that the coating device 15 is moved toward material 10, a welt 50 of the fluid compositions accumulates at lip 23, as shown in FIG. 2. Although the air pressure on the side of the fluid compositions toward which the material 10 approaches is subatmospheric and on the opposite side of the fluid compositions is atmospheric, the differential in pressures is not great enough to create an air flow in the throat formed by lip 23 and material 10 as the layers approach material 10 which is sufficient to remove the welt 50 from the lip..

In the present invention, the coating device 15 is in the Start Coat position, as described above, for forming the

layers

21 and 30. At this time, the pressure differential between chamber 42 and the atmosphere is equivalent to that for the normal coating operation. However, as the coating device 15 is moved toward material 10 and roll 11, valve is turned to increase the vacuum so as to increase the pressure differential. The initial pressure differential as well as the increased pressure differential will vary in accordance with the fluid compositions, the material to be coated and the rate at which the material is moved. The air pressure differential must, however, be great enough to provide an air flow between lip 23 and material 10, as the coating device 15 approaches material 10, so that the welt will be removed from lip 23, as shown in FIG. 3, and carried by the air stream into chamber 42. The increased air pressure differential is maintained until coating device 15 has been moved sufliciently close to material 10 so as to form bead 22 with

layers

21 and 30 and the moving strip material 10. After the bead 22 has been formed transversely of material 10 and layers 21 and 30 are being applied uniformly to material 10, the coating device is then moved away from material 10 into the Coat position. At this time, the valve 45 is readjusted so the air pressure differential is reduced to that normally used for the coating operation. The position of lip 23 relative to the moving strip material for forming the bead 22 and for maintaining a uniform coating application will also be dependent on the fluid composition, the material to be coated and the rate of movement of the material.

In order to more clearly illustrate the applicability of the invention with respect to particular coating applications, several specific examples are described hereinafter. It is to be understood, of course, that the invention is not to be limited to the materials nor the various factors set forth in these examples.

Example 1.--C0atir1g a single layer color filter This was a dispersion in aqueous solution which was applied to a dry subbed safety support from a coating device such as shown in FIG. 1. The speed of coating was 120 feet per minute. The air pressure differential used for coating was equal to approximately 0.35 inch of water. The total amount of solution coated was 0.012 pound per square foot. The viscosity was approximately four centipoise at F. The increased air pressure differential introduced during the start of coating and beadmaking was 1.5 inches of water which was maintained for a brief period of time until the coating device was moved to Coat position. The air pressure differential was then reduced to 0.35 inch of water and held.

Example 2 .-C0at1'ng an anti-halatz'on layer A water solution of gelatin containing a spreading agent, such as saponin, and a suitable dye was coated as an anti-halation layer on the back of a safety support at 90 feet per minute. The viscosity of the solution was approximately 10 centipoise at F. This solution was applied from a coating device such as shown in FIG. 1. The total amount of solution applied was 0.0235 pound per square foot of support. The air pressure differential at the coating bead was 0.5 of water. The increased air pressure differential introduced just before and during the start of coating and bead-making was 1.5 inches of water which was maintained for a brief period of time until the coating device was moved to Coat position. The air pressure differential was then dropped back to 0.5 inch of water.

In addition to the above examples, reference can also be made to the examples set forth in US. Patent 2,681,294 wherein various initial air pressure differentials are disclosed for coating other materials with different fluid compositions. The increased air pressure differential to be used in these examples will again be dependent on the material, composition and rate of movement of the material. While the improved method of coating a moving strip material described herein can be utilized for many other applications, the invention is not to be limited to the disclosed examples but is of a scope as defined by the appended claims.

I claim:

1. A method of applying a liquid composition to a relatively moving strip material carried by a support which comprises:

forming a flowing stream of said liquid composition;

subjecting the flowing stream of liquid composition to an initial differential air pressure, the lesser air pressure being on the side of the flowing stream toward which the moving strip material approaches; increasing the initial differential air pressure as the flowing stream of liquid composition approaches the U moving strip material to remove any accumulation of the liquid composition at the end of the stream prior to engagement of the stream with the moving strip material; maintaining the increased differential air pressure until a bead of liquid composition has been formed transversely of an area of the moving strip material; and

decreasing the differential air pressure to the initial differential air pressure after the head has been formed.

2. A method of applying a liquid composition to a relatively moving strip material carried by a support which comprises:

forming a flowing stream of the liquid composition;

subjecting the flowing stream of liquid composition to and initial differential air pressure, the pressure on the side of the flowing stream toward which the moving strip material approaches being subatmospheric and the pressure on the opposite side being atmospheric;

increasing the initial differential air pressure as the flowing stream of liquid composition approaches the moving strip material to remove any accumulation of the liquid composition at the end of the stream prior to engagement of the stream with the moving strip material;

maintaining the increased differential air pressure until a bead of liquid composition has been formed transversely of an area of the moving strip material; and decreasing the differential air pressure to the initial differential air pressure after the bead has been formed. 3. A method of applying a liquid composition to a relatively moving strip material carried by a support which comprises:

forming a flowing stream of the liquid composition; subjecting the flowing stream of liquid composition to a greater air pressure on that side from which the coated strip leaves the flowing stream and to a lesser air pressure on the other side, the air pressure differential being of the order of .1" to 5.00" of Water;

increasing the initial differential air pressure as the flowing stream of liquid composition approaches the moving strip material to remove any accumulation of the liquid composition at the end of the stream prior to engagement of the stream with the material;

maintaining the increased differential air pressure until a bead of liquid composition has been formed transversely of an area of the moving strip material; and

decreasing the differential air pressure to the initial differential air pressure after the head has been formed. 4. A method of applying a liquid composition to a relatively moving strip material carried by a support which comprises:

forming a flowing stream of said liquid composition; subjecting the flowing stream of liquid composition to an initial differential air pressure, the lesser air pressure being on the side of the flowing stream toward which the moving strip material approaches;

decreasing the lesser air pressure to obtain a differential air pressure 2 to 15 times that of the initial differential air pressure as the flowing stream of liquid composition approaches the moving strip material to remove any accumulation of the liquid composition prior to engagement of the stream with the material;

decreasing the increased differential air pressure to the initial differential air pressure after the bead has been formed.

5. A method of applying a liquid composition to a relatively moving strip material carried by a support which comprises:

forming a flowing stream of the liquid composition;

subjecting the flowing stream of liquid composition to a greater air pressure on that side from which the coated strip leaves the flowing stream and to a lesser air pressure on the other side, the air pressure differential being of the order of .1" to 5.00" of water;

decreasing the lesser air pressure to obtain a differential air pressure 2 to 15 times that of the initial differential air pressure as the flowing stream of liquid composition approaches the moving strip material to remove any accumulation of the liquid composition prior to engagement of the stream with the material; maintaining the increased differential air pressure until a bead of liquid composition has been formed transversely of an area of the moving strip material; and

6. A method of applying a liquid composition contained in a coating device to a relatively moving strip material carried by a support which comprises:

moving the coating device toward said moving strip material; subjecting that side of the lip of the coating device toward which the strip of material approaches to an initial subatmospheric pressure while maintaining atmospheric pressure on the opposite side thereof;

decreasing the initial subatmospheric pressure so as to obtain a greater pressure differential with respect to the atmospheric pressure as said coating device approaches the moving strip material for removing any accumulated liquid composition from the lip of the coating device;

maintaining the greater pressure differential until a bead of said liquid composition has been formed transversely of an area of the moving strip material; moving said coating device away from the moving strip material after a formation of the bead to a position for providing a uniform coating of the liquid composition on the moving strip material; and increasing the subatmospheric pressure to the initial subatmospheric pressure and maintaining the initial subatmospheric pressure while the liquid composition is being applied to the moving strip material.

7. A method of applying a liquid composition contained in a coating device to a relatively moving strip material carried by a support which comprises:

flowing a thin layer of said liquid composition to the lip of the coating device;

moving the coating device toward the moving strip material;

subjecting the flowing layer of liquid composition at the lip of the coating device to an initial differential air pressure, the lesser air pressure being on the side of the flowing layer toward which the moving strip material approaches;

increasing the initial differential air pressure as the flowing layer approaches the moving strip material to remove any accumulation of the liquid composition on the lip of the coating device; maintaining the increased differential air pressure as a bead of liquid composition is being formed transversely of an area of the moving strip material;

moving the coating device away from the moving strip material after formation of the bead to a position for for applying a uniform coating of the liquid composition to the moving strip material; and

decreasing the differential air pressure to the initial differential air pressure after the coating device has been moved into the applying position and maintaining the initial differential air pressure while the liquid composition is being applied to the moving strip material.

8,220,877 71 8 8. A method of applying a liquid composition contained in a coating device to a relatively moving strip tained in a coating device to a relatively moving strip l Carried by a Support which comprises material arried by a support hi h comprises; flowing a thin layer of said hquid composition to the flowing a thin layer of said liquid composition to the lip of the coating device;

lip f the Coating device; moving the coating device toward the moving strip t n ma eria 232; coating device toward the movmg Stnp subjecting the layer of the liquid composition at the subjecting the layer of said liquid composition at the hp of.the coatmg Slevlce to a greatei all-Pressure on lip of the coating device to an initial differential air that.s1de from whlch the coaied strip W111 leave pressure, the pressure on the side of the layer to- -g lay-er and to a -i g on the otder ward which the moving strip material approaches be- $1 'E alr Bressure eremla mug of the or er of .1 to 5.00 of water, silbasmosphenc the Pressure the OPPO decreasing the lesser air pressure to obtain a differenslte 0f h P =5 tial air pressure 2 to times that of the initial difincreasing the 1n1t1al differential air pressure as the 15 f ti l air pressure as the fl i layer f liquid coating device approaches the moving Strip material composition approaches the moving strip material material to remove any accumulation of the liquid to remove any accumulation of the liquid composicomposition on the lip of the coating device; tion or the lip of the coating device; maintaining the increased ditferential air pressure as a maintaining the increased differential air pressure as head of liquid composition is being formed transa bead of liquid composition is being formed transversely of an area of the moving strip material; versely of an area of the moving strip material; moving the coating device away from the moving strip moving the coating devhfe y from the moving h p material after formation of the bead to a position material 'f forlhatlon of F bead Positlon for applying a uniform coating of the liquid com- }PP a P cqfltmg the hquld position to the moving strip material; and I posit on to the moving str p material; and I increasing the subatmospheric pressure to the initial mcreasmg the ubatmosphenc pressure 9 the 1 subatrnospheric pressure after the coating device is figig gig g gfiiig gP223 g s g igi i ggg ig gg moved into the applying position and maintaining the initial subatmospheric pressure while the liquid comlnitial subatmospheric pressure while the liquid composition is being applied to the moving Strip materiaL position is being applied to the moving strip material. 9. A method of applying a liquid composition con- No references cited.

RICHARD D. NEVIUS, Primary Examiner.

Claims

1. A METHOD OF APPLYING A LIQUID COMPOSITION TO A RELATIVELY MOVING STRIP MATERIAL CARRIED BY A SUPPORT WHICH COMPRISES: FORMING A FLOWING STREAM OF SAID LIQUID COMPOSITION; SUBJECTING THE FLOWING STREAM OF LIQUID COMPOSITION TO AN INITIAL DIFFERENTIAL AIR PRESSURE, THE LESSER AIR PRESSURE BEING ON THE SIDE OF THE FLOWING STREAM TOWARD WHICH THE MOVING STRIP MATERIAL APPROACHES; INCREASING THE INITIAL DIFFERENTIAL AIR PRESSURE AS THE FLOWING STREAM OF LIQUID COMPOSITION APPROACHES THE MOVING STRIP MATERIAL TO REMOVE ANY ACCUMULATION OF THE LIQUID COMPOSITION AT THE END OF THE STREAM PRIOR TO ENGAGEMENT OF THE STREAM WITH THE MOVING STRIP MATERIAL; MAINTAINING THE INCREASED DIFFERENTIAL AIR PRESSURE UNTIL A BEAD OF LIQUID COMPOSITION HAS BEEN FORMED TRANSVERSELY OF AN AREA OF THE MOVING STRIP MATERIAL; AND DECREASING THE DIFFERENTIAL AIR PRESSURE TO THE INITIAL DIFFERENTIAL AIR PRESSURE AFTER THE BEAD HAS BEEN FORMED.