EP0390774A1 - Procede et appareil de couchage au rideau a vitesse elevee. - Google Patents

Procede et appareil de couchage au rideau a vitesse elevee.

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Publication number
EP0390774A1
EP0390774A1 EP88900199A EP88900199A EP0390774A1 EP 0390774 A1 EP0390774 A1 EP 0390774A1 EP 88900199 A EP88900199 A EP 88900199A EP 88900199 A EP88900199 A EP 88900199A EP 0390774 A1 EP0390774 A1 EP 0390774A1
Authority
EP
European Patent Office
Prior art keywords
coating
web
charge
speed
curtain
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP88900199A
Other languages
German (de)
English (en)
Other versions
EP0390774B1 (fr
Inventor
Ronald L Hartman
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Eastman Kodak Co
Original Assignee
Eastman Kodak Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Eastman Kodak Co filed Critical Eastman Kodak Co
Publication of EP0390774A1 publication Critical patent/EP0390774A1/fr
Application granted granted Critical
Publication of EP0390774B1 publication Critical patent/EP0390774B1/fr
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
    • G03C1/00—Photosensitive materials
    • G03C1/74—Applying photosensitive compositions to the base; Drying processes therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
    • B65H23/00—Registering, tensioning, smoothing or guiding webs
    • B65H23/04—Registering, tensioning, smoothing or guiding webs longitudinally
    • B65H23/18—Registering, tensioning, smoothing or guiding webs longitudinally by controlling or regulating the web-advancing mechanism, e.g. mechanism acting on the running web
    • B65H23/188—Registering, tensioning, smoothing or guiding webs longitudinally by controlling or regulating the web-advancing mechanism, e.g. mechanism acting on the running web in connection with running-web
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65H—HANDLING THIN OR FILAMENTARY MATERIAL, e.g. SHEETS, WEBS, CABLES
    • B65H2301/00—Handling processes for sheets or webs
    • B65H2301/30—Orientation, displacement, position of the handled material
    • B65H2301/31—Features of transport path
    • B65H2301/311—Features of transport path for transport path in plane of handled material, e.g. geometry
    • B65H2301/3112—S-shaped
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
    • G03C1/00—Photosensitive materials
    • G03C1/76—Photosensitive materials characterised by the base or auxiliary layers
    • G03C1/91—Photosensitive materials characterised by the base or auxiliary layers characterised by subbing layers or subbing means
    • G03C1/915—Photosensitive materials characterised by the base or auxiliary layers characterised by subbing layers or subbing means using mechanical or physical means therefor, e.g. corona
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
    • G03C1/00—Photosensitive materials
    • G03C1/74—Applying photosensitive compositions to the base; Drying processes therefor
    • G03C2001/7433—Curtain coating

Definitions

  • This invention relates in general to the process of curtain coating and in particular to the use of curtain coating in the manufacture of photographic materials such as photographic films and papers. More specifically, this invention relates to an improved curtain coating process which is especially adapted to high speed manufacturing operations that are capable of achieving the high degree of precision that is essential in the photographic field, and to apparatus for use in such process.
  • the curtain coating method in particular has many advantages in the manufacture of photographic materials that require the application of coated layers of a precise thickness, with regard to both widthwise and lengthwise uniformity, onto a continuously moving support material. It is recognized that many of the advantages achieved by the curtain coating method result from the fact that the free-falling curtain can be formed by a slide hopper which is not in close proximity to the application locus on the moving support.
  • the bead coating process continues to be in general use because it had become so highly developed before the advent of curtain coating in the manufacture of photographic materials. Investigation of bead coating for coating photographic materials was particularly directed to the coating zone where it was found that in order to establish an extremely stable process it was necessary to control two stabilizing forces which effected bead formation.
  • Control and stabilization of the bead formation permitted the use of a wide latitude of coating speeds, layer viscosities and layer thicknesses.
  • the stabilizing forces are first, a pressure differential (suction) applied across the coating bead at the application locus as disclosed in Beguin U. S. 2,681,294 and, secondly, an electrostatic charge differential applied just prior to the application locus as described in Nadeau, United States Patent No. 2,952,559 issued September 13, 1960.
  • a pressure differential and an electrostatic charge serve to hold the bead within the coating zone.
  • forces which act toward the web such as those provided by a pressure differential or an electrostatic charge, aid in stabilizing the bead and maintain it in wetting contact with the moving web.
  • the curtain In a curtain coating process, however, no bead is ever formed and the mechanism of the coating action is distinctly different.
  • the curtain In a curtain coating process, the curtain is free—falling and impinges on the moving support with considerable momentum to provide a sufficient force to stabilize the application locus and insure a uniform wetting line on the moving support.
  • the required momentum is obtained by appropriate selection of the curtain flow rate and the height of free fall.
  • the preferred method for obtaining a uniform electrostatic force at the coating application point in bead coating is to form a bound polar charge on the support at a uniform level. With a bound charge there are equal and opposite electrostatic charges on the two surfaces of the support.
  • the support be a dielectric material having a very high resistivity.
  • the side of the support adjacent to the coating roll mirrors a charge on the coating roll surface which effectively neutralizes the charge on the support in contact with the coating roll surface and creates the equivalent of a net charge on the surface of the support being coated. This creates an electrostatic field at the coating application locus between the surface of the support and the grounded hopper lip.
  • the coating defects encountered in curtain coating as the web speed is increased to very high levels result in part from the mechanism referred to herein as "insufficient viscous friction" force.
  • the effect of "insufficient viscous friction” force is characterized by a defect which results from a multitude of entrained air bubbles between the coating and the support and the presence of longitudinal bands which result when droplets of coating composition form upstream of the application locus and coat out to provide such bands.
  • the "insufficient viscous friction" force hypothesis is suggested by the inability to coat unifor ily, because the coating solution viscosity is too low, the flow rate is too high, or the support surface is too smooth.
  • a predetermined high level of electrostatic polar charge is utilized to solve these problems in high speed curtain coating, as contrasted with known use of electrostatic polar' charge in bead coating, which involves a distinctly different purpose, namely the purpose of stabilizing a coating bead.
  • a high level of electrostatic polar charge apparently contributes a substantial attractive force which acts, in the appropriate direction, in the region where the curtain impacts the web, and thereby substantially increases the speed at which coatings can be successfully applied by the curtain coating mechanism.
  • the high speed curtain coating process of this invention is carried out at web speeds which typically begin at about 250 centimeters per second or higher. Speeds of as high as about 1,000 centimeters per second, or more, can be effectively utilized with the aid of the appropriate level of electrostatic polar charge.
  • An object of the present invention is to provide a curtain coating process and apparatus for coating a moving object at very high coating speeds.
  • the above described object of the present invention can be attained by a process and apparatus for coating an object with liquid coating composition in which an object is advanced along a path through a coating zone, and a free-falling curtain which is comprised of one or more layers of liquid coating composition and extends transversely of said path is impinged within said coating zone on a surface of said moving object to form thereon a coating comprised of one or more-layers.
  • the invention is directed to establishing an electrostatic polar charge, on the surface of said object to which said coating is applied, of a magnitude sufficient to insure the uniformity of said coating.
  • the invention is further directed to a process and apparatus for coating an object with liquid coating composition in which said object is advanced along a path through a coating zone, and a free—falling curtain which is comprised of one or more layers of liquid coating composition and extends transversely of said path is impinged within said coating zone on a surface of said moving object to form thereon a coating comprised of one or more layers; wherein said object is advanced at a speed of at least 400 centimeters per second and an electrostatic polar charge is established on the surface of said object to which said coating is applied, the magnitude of said charge being selected in accordance with the speed of said object so that the ratio of said charge at any point on said surface, measured in volts, to said speed, measured in centimeters per second, is at least 1 to 1.
  • the present invention is particularly suitable for the manufacture of a photographic element wherein a single layer or a plurality of layers of liquid photographic coating composition are formed into a free— alling curtain which extends transversely of a web advanced along a path and said curtain impinges within a coating zone on said web, to form a single or multi—layer coating.
  • the improvement comprises advancing said web at a speed of at least 400 centimeters per second and establishing an electrostatic polar charge on the surface of said web to which said coating is applied, the magnitude of said charge being selected in accordance with the speed of said web so that the ratio of said charge at any point on said surface, measured in colts, to said speed, measured in centimeters per second, is at least 1 to 1.
  • FIG. 1 is a schematic illustration of the apparatus for applying a predetermined level of electrostatic polar charge to the surface of a web and thereafter curtain coating the web surface with a liquid coating composition.
  • FIG. 2 is a graph relating electrostatic polar charge level and coating speed in a typical curtain coating process for the manufacture of a photographic material.
  • FIG. 3 is a graph relating flow rate of coating composition and coating speed in a typical curtain coating process for the manufacture of a photographic material. Description of the Preferred Embodiments
  • the invention is described herein with particular reference to the coating of photographic materials. This field of coating involves highly precise operations, so that the invention is especially beneficial in this field. However, the invention is in no way limited to use in the coating of photographic materials and can be advantageously employed in any curtain coating operation in which it is desired to achieve very uniform coating at very high rates of speed. Both single layer and multiple layer curtain coating processes benefit greatly from the electrostatic polar charge.
  • the curtain coating problems which this invention solves occurs only at very high coating speeds, such as at web speeds which are typically above 250 centimeters per second.
  • a predetermined high level of electrostatic polar charge is utilized to solve these problems in high speed curtain coating, as contrasted with the prior art use of electrostatic charge in bead coating, which involves the use of electrostatic charge for a distinctly different purpose, namely the purpose of stabilizing a coating bead.
  • the electrostatic polar charge at the application point obtained by using a support with a high level of bound or polar charge and a grounded coating roll.
  • Such use of a predetermined high level of electrostatic polar charge in curtain coating is frequently referred to herein, for convenience, as the use of "polar charge assist,” in the sense that it directly assists in achieving effective coating.
  • a high level of electrostatic polar charge apparently contributes a substantial attractive force which acts, in the appropriate direction, in the region where the curtain impacts the web, and thereby substantially increases the speed at which coatings can be successfully applied by the curtain coating mechanism.
  • More specifically, with the use of the appropriate level of electrostatic polar charge it is possible to operate at substantially higher coating speeds, with a particular set of operating parameters such as web texture, flow rate, coating composition viscosity, and curtain height, while still successfully meeting the very high quality standards of the photographic coating art.
  • the high speed curtain coating process of this invention is carried out at web speeds which are typically above 250 centimeters per second. Speeds of as high as about 1,000 centimeters per second, or more, can be effectively utilized with the aid of the appropriate level of electrostatic polar charge.
  • the coating apparatus can be a curtain coating hopper of the overflow weir type, the pressure extrusion type, the slide type, or the slide—extrusion type.
  • slide hoppers are particularly preferred, especially for photographic coating operations.
  • the coating apparatus can be adapted to carry out single-layer coating or it can be of the type with which a plurality of layers are simultaneously coated. It can be adapted to carry out full width coating or to carry out coating of abutting or non-abutting stripes as described, for example, in Research Disclosure, Item 17553, Volume 175, November, 1978.
  • the process of this invention can be utilized to coat any material or mixture of materials which can be put in liquid form, for example, in the form of a solution, a dispersion, or a suspension.
  • the coating composition is an aqueous composition but other liquid vehicles, of either an organic or inorganic nature, can also be utilized and are fully within the contemplation of this invention.
  • the respective layers can be formed of the same or different liquid coating compositions and these coating compositions can be either miscible or immiscible with one another.
  • the process of this invention is especially useful in the photographic art for manufacture of multi-layer photographic elements, i.e., elements comprised of a support coated with a plurality of superimposed layers of photographic coating compositions.
  • the number of individual layers may be as high as ten or more.
  • the liquid coating compositions utilized are usually aqueous compositions but organic compositions can also be employed.
  • the individual layers applied in the manufacture of photographic elements must be exceedingly thin, i.e., a wet thickness which is a maximum of about 0.015 centimeter and generally is far below this value and may be as low as about 0.0001 centimeter.
  • the layers must be of extremely uniform thickness, with the maximum variation in thickness uniformity typically being plus or minus two percent and in some instances as little as plus or minus one—half percent.
  • Useful photographic supports include film base, e.g. , cellulose nitrate film, cellulose acetate film, polyvinyl acetal film, polycarbonate film, polystyrene film, polyethylene terephthalate film and other polyester films; paper; glass; cloth; metal; and the like, Paper supports coated with alpha—olefin polymers, as exemplified by polyethylene and polypropylene, or with other polymers, such as cellulose organic acid esters and linear polyesters, may also be used if desired.
  • the term "photographic” normally refers to a radiation—sensitive material, but not all of the layers applied to a support in the manufacture of photographic elements are, in themselves, radiation—sensitive.
  • subbing layers, pelloid protective layers, filter layers, antihalation layers, etc. are often applied separately and/or in combination and these particular layers are not radiation—sensitive.
  • the present invention relates also to the application bf such layers, and the term "photographic coating composition" as employed herein, is intended to include the composition from which such layers are formed.
  • the invention includes within its scope all radiation—sensitive materials, including electrophotographic materials and materials sensitive to invisible radiation as well as those sensitive to visible radiation.
  • the photographic layers are coated according to the process of this invention can contain light-sensitive materials such as silver halides, zinc oxide, titanium dioxide, diazonium salts, light-sensitive dyes, etc., as well as other ingredients known to the art for use in photographic layers.
  • surfactants can be used to modify the surface tension and coatability of photographic coating compositions in accordance with this invention.
  • useful surfactants include saponin; non-ionic surfactants such as polyalkylene oxides, e.g., polyethylene oxides, and the water—soluble adducts of glycidol and alkyl phenol; anionic surfactants such as alkylaryl polyether sulfates and sulfonates; and amphoteric surfactants such as arylalkyl taurines, N—alkyl and N—acyl beta—amino propionates; alkyl ammonium sulfonic acid betaines, etc.
  • Aqueous photographic coating compositions typically contain a hydrophilic colloid.
  • hydrophilic colloids include proteins, e.g. gelatin, protein derivatives; cellulose derivatives, polysaccharides such as starch; sugars, e.g., dextran; plant gums; etc.; synthetic polymers such as polyvinyl alcohol, polyacrylamide, and polyvinylpyrrolidone; and other suitable hydrophilic colloids such as are disclosed in U.S. patent No. 3,297,446. Mixtures of the aforesaid colloids may be used if desired.
  • the coating compositions are gelatin silver halide emulsions.
  • Emulsions containing a wide variety of silver salts can be used, such as silver bromide, silver iodide, silver chloride, or mixed silver halides such as silver chlorobromide, silver bromoiodide or silver chloroiodide.
  • Conventional addenda such as, for example, hardening agents, antifoggants, stabilizers, matting agents, plasticizers, developing agents, and the like, can be included in the emulsions.
  • the emulsions can contain color— orming couplers or can be emulsions adapted to be developed in solutions containing color—forming couplers or other color—generating materials.
  • Curtain coating hoppers employed in the practice of this invention are typically equipped with edge guides to guide the free—falling curtain and define its width.
  • Useful edge—guiding methods include the use of edge guides which ride on the web, as described in the aforesaid patents to Greiller and Hughes, and the use of "liquid edge—guiding " techniques as described in Research Disclosure, Item 17553, Volume 175, November, 1978.
  • the process of this invention involves the application of an electrostatic polar charge at a predetermined high level sufficient to be effective in enhancing the uniformity of coating which results from the action of a free—falling curtain of liquid coating composition impacting on the surface to be coated. It is thus clearly distinguishable from the curtain coating of a web or other object which may have acquired an irregular electrostatic charge pattern or a low level of electrostatic charge.
  • Such accumulation of irregular and/or low level electrostatic charge can result from various causes.
  • the conveyance of a web support over a series of rollers can result in the generation of an irregular elect.rostatic charge pattern on the web surface.
  • the corona—activation of the surface of a web for the purpose of promoting coatability can result in the acquisition by the web surface of an irregular electrostatic charge pattern.
  • charge patterns are not effective in overcoming the curtain coating problems solved by this invention, since the solution of these problems requires the presence of electrostatic polar charge on the surface to be coated which is at a level equal to or greater than what was known to be an effective minimum level — typically a level of at least 400 volts — at substantially all points on the surface of the support to be coated.
  • the web, or other object to be coated is advanced through the coating zone at a speed of 400 centimeters per second or higher and an electrostatic polar charge is established on the surface to be coated at a level such that the ratio of the charge at any point on the surface, measured in volts, to the speed, measured in centimeters per second, is at least 1 to 1.
  • an electrostatic polar charge is established on the surface to be coated at a level such that the ratio of the charge at any point on the surface, measured in volts, to the speed, measured in centimeters per second, is at least 1 to 1.
  • a charge level that is at least 400 volts, but could be well above 400 if necessitated by other factors such as, for example, the use of a support which has a surface texture with which it is especially difficult to achieve coating uniformity.
  • the level of electrostatic polar charge in volts, is made equal to or greater than the web speed in centimeters per second plus 200 volts, e.g., for a 400 cm/sec web speed a polar charge level of 600 volts or more.
  • the upper limit to the level of polar charge that can be utilized is dictated by practical considerations involved in the design and construction of the charge generating apparatus and by the requirement that the level not be so great as to have detrimental effects on the photographic emulsion or other coating composition.
  • a level of polar charge is established which is substantially uniform over the entire web surface.
  • the web is adapted to extend beyond the edges of the coating roll, i.e., the web is wider than the width of the coating roll and therefore overhangs it. This may be done, for example, to reduce the tendency for the coating roll to become fouled with coating composition. In these processes, a problem can arise in achieving uniform coating on the overhanging regions of the web.
  • polar charge is less effective on the overhanging regions of the web than on the remainder of the web surface, apparently because, in the overhanging regions, there is no coating roll behind the web to provide an electrical ground. For this reason, it is desirable to establish a higher level of polar charge over the regions of the web which overhang the coating roll than over the remainder of the web surface.
  • This can be readily accomplished in the process of this invention by providing supplementary charging means which apply supplementary polar charge to only the regions of the web which overhang the coating roll.
  • a charging means which applies polar charge over the entire surface thereof, and before it receive the coating composition, it is passed beneath a second charging means which applies polar charge only to the regions of the web which will overhang the coating roll.
  • the charge applied in these regions must be of the same polarity as that applied over the entire web surface and is preferably at a voltage level that is two to three times as great.
  • the supplementary polar charge applied to the overhanging regions is advantageously about 1600 to about 2400 volts.
  • An alternative technique for use in processes in which the web overhangs the coating roll is to charge the entire web surface, including the overhanging regions, to a uniform polar charge level that is substantially higher than that needed for the particular coating speed, and coating condition employed, to thereby provide a level of polar charge which is adequate to ensure uniform coating on the overhanging web regions as well as over the remainder of the web surface. This means, of course, that there will be a higher level of polar charge over the remainder of the web surface than the minimum level that is needed, but this is usually not objectionable.
  • FIG. 1 schematically illustrates the coating process of this invention utilizing a multiple—slide hopper to simultaneously coat three layers of liquid coating composition on a web support.
  • web 10 is unwound from supply roll 12 and then passes around tension roller 14 and over grounded metal roll 16 where it receives a uniform electrostatic polar charge of the appropriate level.
  • the apparatus for generating the electrostatic polar charge is of ' the grid—controlled ionizer type.
  • a first such ionizer comprises grid elements 18 in association with a series of conductive elements 20, such as tungsten rods or wires. Grid 18 is connected to DC power supply 22 while conductive elements 20 are connected to DC power supply 24.
  • a second ionizer comprises a grid 26 connected to DC variable power supply 28 and conductive elements 30 connected to DC variable power supply 32. The function of the first ionizer is to eliminate any variations in polar charge on the surface of the incoming web.
  • a high voltage direct current power supply provides a 15,000 volt potential to conductive elements 20. This high voltage ionizes the atmosphere and the charged ions are accelerated toward web 10 through grid 18. Web 10 is charged to a uniform level determined by the power supply voltage to grid 18.
  • the second ionizer serves to boost the uniform potential to a higher level and controls this level. This function is accomplished using variable output power supplies.
  • the output voltage is controlled electrically with a feedback loop comprising an electrostatic voltmeter 34 which measures the voltage on the web. By means of control circuits 36, this voltage is compared to a reference voltage and the power supply output voltage is either raised or lowered automatically to keep a constant voltage level on web 10.
  • web 10 After web 10 has been brought to a desired uniform level of electrostatic polar charge, it passes around guide rolls 40, 42, 44, 46 and 48 and then over a grounded coating roll 50 where it is coated with a three-layer coating of liquid coating composition, e.g., three different photographic emulsions, by means of multiple—slide curtain coating hopper 52 which receives the emulsions from a suitable supply source (not shown) and generates free-falling curtain 54 that impinges on web 10.
  • a suitable supply source not shown
  • free-falling curtain 54 that impinges on web 10.
  • web 10 After passing over coating roll 50, web 10 is directed through drying chamber 56, where the emulsion layers are dried by contact with air or other gaseous medium maintained at an elevated temperature, and then directed around guide roll 58 and wound onto take-up roll 60.
  • FIG. 2 relates the level of electrostatic polar charge required to give uniform coating with the coating speed for a typical curtain coating process in which a gelatin silver halide photographic emulsion is coated on the surface of a web.
  • the curve shown in FIG. 2 is representative for the coating conditions which follow, whereas a different set of coating conditions would result in a shift in the curve:
  • curtain height 12.5 centimeters
  • Curtain flow rate 1.5 to 6 grams per second per centimeter of curtain width
  • Viscosity of coating composition 60 centipoise
  • Web surface glossy polyethylene Application point — minus 15 degrees.
  • Uniform coating is achieved in the region to the left of the curve, while a non—uniform coating that would not be useful in photographic manufacturing operations results in the region to the right of the curve.
  • the curve represents the transition between satisfactory coating and coating failure.
  • no polar charge assist is required to prevent coating failure at coating speeds up to about 250 cm/sec.
  • the curve indicates a gradually increasing need for polar charge assist.
  • no polar charge assist is applied at speed levels between 250 and about 400 cm/sec because other means would be used to achieve satisfactory coating uniformity.
  • the slope of the curve decreased with further increase in coating speed.
  • the ratio of the charge, measured in volts, to the speed, measured in centimeters per second must be at least 1 to 1 to achieve uniform coating over a speed range of 400 to 800 cm/sec with the particular coating conditions employed.
  • the preferred embodiment of the invention may require additional electrostatic charge on the order of an additional 200 volts, e.g., for a 400 cm/sec web speed a polar charge level of 600 volts or more may be necessary.
  • FIG. 3 relates to the flow rate of coating composition per unit width of curtain with the coating speed. It describes a uniform coating region bounded by identifiable regions in which poor quality coating occurs. The size and shape of the uniform coating region is dependent upon the curtain height, the coating composition viscosity, the application point, the nature of the web surface, and the level of electrostatic polar charge assist.
  • the unstable curtain region is the region where curtain flow rate per unit width is too low to produce a stable curtain. In this region, the curtain will split into a number of strands and thereby render the formation of a uniform coating impossible.
  • the puddling region represents conditions where the velocity of the curtain at the coating application point is greater than the web velocity. As a result, coating composition builds up behind the curtain and produces longitudinal streaks.
  • the uniform coating region can be substantially extended, for a given set of operating conditions, by the use of electrostatic polar charge assist, i.e., by the application'of a sufficiently high level of electrostatic polar charge to the web surface.
  • electrostatic polar charge assist i.e., by the application'of a sufficiently high level of electrostatic polar charge to the web surface.
  • EXAMPLE I By the bead coating method: A multiple slide bead coating hopper similar to that shown in U. S. 2,761,791 was used except that.the hopper was set up to coat 7 layers simultaneously ' . The product coated was Ektacolor Paper which contains 7 separate layers. The wet thickness and viscosity of the 7 layers are tabulated in Table I.
  • the glossy surface support a polar charge was not required to achieve satisfactory coatability at a speed greater than 400 cm/sec. Note that the glossy surface support can generally be coated at approximately
  • Glossy 300 At least
  • the matte surface curtain coating data recorded in Table III should be compared with the matte surface bead coating data recorded in Table II. Whereas with bead coating it was necessary to use a polar charge of 350 volts to coat at a maximum speed of 400 cm/sec it was shown that such a speed could be achieved with the curtain coating method without the use of polar charge assist.
  • Table III shows that a maximum coating speed of only 300 cm/sec could be achieved for a glossy surface support using a 26 centipoise bottom layer when no polar charge assist was used.
  • Table II relating to the bead coating method shows that for a glossy surface a maximum coating speed of 400 cm/sec could be achieved without use of a polar charge.
  • the glossy surface support could be curtain coated at a speed of at least 500 cm/sec. This amounts to an increase in the achievable curtain coating speed for the glossy support surface of at least 67% over that obtainable when no polar charge was used. Coating at higher speeds is possible when increasingly higher levels of polar charge are used as shown in Figure 2.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
  • Coating Apparatus (AREA)

Abstract

Dans un procédé de couchage par projection, l'utilisation de vitesses élevées de couchage est facilitée par l'application sur la surface de l'objet à coucher, d'un haut niveau prédéterminé de charge polaire électrostatique. Le niveau de charge efficace pour favoriser l'obtention de l'uniformité voulue de couchage avec un minimum de formation de défauts de couchage est directement fonction de la vitesse de couchage, de sorte qu'il faut des niveaux de charge de plus en plus élevés à mesure qu'augmente la vitesse de couchage. Ledit procédé est particulièrement utile pour le couchage de matières photographiques telles que des pellicules et des papiers photographiques multicouches.
EP88900199A 1987-12-03 1987-12-03 Procede et appareil de couchage au rideau a vitesse elevee Expired - Lifetime EP0390774B1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US1987/003190 WO1989005477A1 (fr) 1987-12-03 1987-12-03 Procede et appareil de couchage par projection a vitesse elevee

Publications (2)

Publication Number Publication Date
EP0390774A1 true EP0390774A1 (fr) 1990-10-10
EP0390774B1 EP0390774B1 (fr) 1992-07-15

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Application Number Title Priority Date Filing Date
EP88900199A Expired - Lifetime EP0390774B1 (fr) 1987-12-03 1987-12-03 Procede et appareil de couchage au rideau a vitesse elevee

Country Status (4)

Country Link
EP (1) EP0390774B1 (fr)
JP (1) JP2509316B2 (fr)
DE (1) DE3780472T2 (fr)
WO (1) WO1989005477A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
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US6511711B2 (en) 2000-12-21 2003-01-28 Eastman Kodak Company Slide bead coating method
US6517909B1 (en) * 1998-12-16 2003-02-11 Eastman Kodak Company Method for using a patterned backing roller for curtain coating a liquid composition to a web
US6572516B2 (en) 1998-12-23 2003-06-03 Eastman Kodak Company Device to reduce electrostatic pattern transfer in coating processes
US6638576B2 (en) 2001-04-25 2003-10-28 Eastman Kodak Company Apparatus and method of coating a web

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6517909B1 (en) * 1998-12-16 2003-02-11 Eastman Kodak Company Method for using a patterned backing roller for curtain coating a liquid composition to a web
US6572516B2 (en) 1998-12-23 2003-06-03 Eastman Kodak Company Device to reduce electrostatic pattern transfer in coating processes
US6399157B1 (en) * 2000-04-28 2002-06-04 Eastman Kodak Company Method and apparatus for controllable electrical charging of a web support
US6511711B2 (en) 2000-12-21 2003-01-28 Eastman Kodak Company Slide bead coating method
US6638576B2 (en) 2001-04-25 2003-10-28 Eastman Kodak Company Apparatus and method of coating a web

Also Published As

Publication number Publication date
DE3780472D1 (de) 1992-08-20
WO1989005477A1 (fr) 1989-06-15
DE3780472T2 (de) 1993-03-11
JPH03501702A (ja) 1991-04-18
JP2509316B2 (ja) 1996-06-19
EP0390774B1 (fr) 1992-07-15

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