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Publication numberUS2952559 A
Publication typeGrant
Publication dateSep 13, 1960
Filing dateNov 1, 1956
Priority dateNov 1, 1956
Publication numberUS 2952559 A, US 2952559A, US-A-2952559, US2952559 A, US2952559A
InventorsNadeau Gale F
Original AssigneeEastman Kodak Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method of coating a liquid photographic emulsion on the surface of a support
US 2952559 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

Sept. 13, 1960 G. F. NADEAU 2,952,559 METHOD OF COATING A LIQUID PHOTOGRAPHIC EMULSION ON THE SURFACE OF A SUPPORT Filed Nov. 1, 1956 suhpoer GALE E NADEAU INVENTOR.

ATTORNEYS the support, or necking-in as it is known in the art.

United States Patent Office 2,952,559 Patented Sept. 13, 1960 METHOD OF COATING A LIQUID PHOTO- GRAPHIC EMULSION ON THE SURFACE OF A SUPPORT Gale F. Nadeau, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Nov. 1, 1956, Ser. No. 619,721 7 Claims. (Cl. 117-34) This invention relates to a coating method and, more particularly, to an improved method of coating liquid photographic emulsions on supports.

In the process of coating webs of materials such as photographic papers or film supports with liquid photographic emulsion, ditficulty is experienced as one attempts to increase the lineal coating speed of the web. This is especially true in those instances where either scraper, extrusion or roller coating methods of application are involved. One difficulty which frequently occurs is the tendency for the coating to pull away from the edge of The necking-in is aggravated by increases in the consistency and viscosity of the coating being applied. It is important from the practical aspect to eliminate the necking-in of the coating for the reason that excessive edging losses and problems with drying and curing the heavy edges are otherwise presented. Many suggestions have been offered for eliminating necking-in of the coating such as the use of special edge shoes to lead the applied coating to the desired width of the web and the addition of surfactants and other types of spreading agents to the solution being coated. While these proposals lead to satisfactory results in certain instances, their use is seriously limited in the manufacture of photographic products because of the photographic effects of such added materials. Furthermore, surfactants have not proven very efiective in systems comprising non-aqueous solvents. Another serious problem encountered in coating photographic emulsions on support materials is photographic mottle which results from the non-uniform thickness of the application of the photographic emulsion layer on the support. Because of the high surface resistivity of photographic support materials, it is possible to find relatively high static Charges which vary in intensity and sign, occupying areas closely adjacent to each other. As a result of this irregular static charge distribution on the surface of and in the support, disturbances in the coating bead frequently occur and the uniformity of the emulsion coating is therefore impaired.

It was in order to overcome or avoid these defects which occur with the coating methods of the known prior art, that the research and devolpment was carried on,

which led to the coating method of the present invention. The coating method comprises broadly the establishing of a uniform electrostatic charge between the support and the photographic emulsion and applying the emulsion to the support.

The primary object of the present invention is, therefore, to provide a method of coating a uniform thickness of photographic emulsion on a support, thereby eliminating photographic mottle.

Another object of the present invention is to provide a method of coating a uniform thickness of photographic emulsion on a support in which the tendency for the phoi 'tographic emulsion to pull away from the edges of the support is eliminated.

Still another object of the present invention is to provide a method of coating a uniform thickness of photographic emulsion on a support which comprises applying a uniform electrostatic charge on the surface of the support and an electrostatic charge of opposite polarity to the liquid photographic emulsion, and applying the charged emulsion to the charged support.

Yet another object of the present invention is to provide a method of coating a uniform thickness of photographic emulsion on a support which comprises rendering the support electrically neutral, applying a uniform electrostatic charge to the surface of the support, applying an electrostatic charge of opposite polarity to the photographic emulsion, and applying the charged photographic emulsion to the charged support.

Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following description with reference to the drawing.

As was mentioned above, photographic mottle results from the non-uniformity of the thickness of the photographic emulsion coating which is applied to the support. The non-uniformity is caused by an irregular electrostatic charge distribution in and on the surface of the support being coated which causes disturbances in the coating bead of the liquid emulsion as well as causing an uneven flowing of the liquid emulsion on the surface of the support. Thus the first step of the coating method of my invention is to render the surface of the support electri- Cally neutral. The electrostatic charges found to influence the coating bead are of two general types. One is an irregular charge which accumulates within the support as a result of a polarization of some of the molecules of the support and which Will be hereinafter referred to as the polarization charge. The polarization charge is removed from the support by intimately contacting a grounded conductor to the opposed surfaces of the support.

The drawing represents a diagrammatic view illustrating the apparatus used to practice the method of electrostatically applying a liquid photographic emulsion on the As indicated in the drawing, this is effected by passing the film support 21 between the grounded metal pressure rolls 23 and 25 which are mounted in opposed relation and biased. by means of springs 27 and 29 respectively into contact with the support 21. The other type of electrostatic charge found to influence the coating head, is the static charge which is present on the surface of the support. In order to discharge this surface charge, the film support coming from between the pressure rolls 23 and 25 is passed over idler roll 31 and between a pair of opposed devices 33 and 35 for generating and directing a flow of ionized air onto the surface of the support 21. Thus the surface of the support 21 as it leaves the vicinity of the ionized air generating devices 33 and 35 is uniformly electrically neutral in charge.

I have found that the tendency of the liquid photographic emulsion to pull away from the edge of the support is greatly reduced and practically eliminated by applying a uniform electrostatic charge between the support and the liquid emulsion to be coated on the support. The application of the electrostatic charge influcnces the flow characteristics of the liquid emulsion by bringing about a reduction in the surface tension thereof which is a direct result of a reduction in the cohesive tension within the liquid. This phenomenon is not limited to water and water solutions since any polarizable liquid responds in a similar manner including those liquids having a specific conductivity of the magnitude, 10 ohms per 3 cc. When the electrostatic charge is applied to the liquid emulsion, there is a tendency for the molecules within the liquid to repel each other. This has the effect of reducing the surface tension and increasing the flow rate of the liquid. Thus, when the charged liquid emulsion flows from an orifice onto the support, there is a strong tendency for the liquid particles to flow out to the edge of the support. The next step of the coating method of my invention is, therefore, to apply a uniform electrostatic charge between the surface of the support and the liquid photographic emulsion. As indicated in the drawing, this is effected by directing a flow of ionized air of the desired polarity onto the surface of the support 21 as by means of the device 37 which is similar to devices 33 and 35. A uniform electrostatic charge is thus distributed over the surface of the support 21 which remains on the support as it is conducted in contact with coating roll .39 to the position at which the liquid emulsion is coated thereon. An electrostatic charge of opposite polarity is applied to the liquid emulsion by connecting a source of potential 41 to the metal orifice 43 of the hopper 45 through hich the liquid emulsion 47 is passed for coating onto the support 21. The total potential difference existing between the charged support 21 and the .liquid emulsion 47 should be less than 10,000 volts in order to avoid any possibility of sparking which would cause fogging of the applied emulsions. I prefer to maintain a potential difference of about 7,000 volts which is quite sufficient to give very satisfactory results.

By way of summary, the coating method according to my invention in its more specific aspects comprises, first, discharging the polarization charge within the support by passing the support in contact with a pair of opposed grounded metal rolls, discharging the static surface charge on the support by directing a flow of ionized air onto the surface of the support, applying a uniform electrostatic charge to the support by directing a flow of ionized air of the desired polarity onto the surface of the support, applying an electrostatic charge of the opposite polarity to the liquid photographic emulsion, and applying the .charged photographic emulsion to the charged support.

It should be understood that the coating method of my invention can be readily utilized to coat any photographic emulsion on any known support including photographic plates, film base and photographic printing papers.

The utilization of a flow of ionized air to render a Web or other sheet material electrically neutral or to distribute an electrical charge on the surface thereof is well known in the art, and apparatus for generating such flows of onized air are disclosed in US. Patents 1,678,869 which was granted to M. Morrison on July 31, 1938, and

2,497,604 which was granted to P. Henry et al. on February 14, 1950.

While only one embodiment of the present invention has been illustrated and specifically described, many modifications and variations are possible and will be readily recognized by those skilled in the art and, therefore, the foregoing description is intended to be illustrative only and the scope of the invention is defined in the appended claims.

Having now particularly described my invention what I desire to secure by Letters Patent of the United States .and what I claim is:

l. A method of coating a liquid photographic emul- .sion on the surface of a support which comprises apply- .mg a uniform electrostatic charge to said surface to facilitate the even spreading of said liquid emulsion on said surface, applying an electrostatic charge of opposite polarity to a supply of said liquid emulsion to facilitate the flowing of said liquid emulsion on said surface, and flowing said'liquid emulsion in a continuous liquid mass from said supply directly onto said surface, the electric potential difference between said charge on said surface ;and said charge on said liquid Emulsion being less than:

that at which arcing occurs between said liquid emulsion and said surface.

2. A method of coating a liquid photographic emul sion on the surface of a support which comprises rendering said surface electrically neutral, applying a uniform electrostatic charge to said surface to facilitate the even spreading of said liquid emulsion on said surface, applying an electrostatic charge of opposite polarity to a supply of said liquid emulsion to reduce the surface tension of said liquid emulsion and facilitate the flowing thereof on said surface, and transferring said liquid emulsion in a continuous liquid mass from said supply directly to said surface, the electric potential difference between said charge on said surface and said charge on said liquid emulsion being less than that at which arcing occurs between said liquid emulsion and said surface.

3. A method of coating a liquid photographic emulsion on the surface of a support carrying polarization charges therein which comprises neutralizing said polarization charges in said support by passing the support through the bite of a pair of opposed grounded metal rolls, rendering saidsurface electrically neutral by directing a flow of ionized air onto said surface, applying a uniform electrostatic charge to said surface to facilitate the even spreading of said liquid emulsion on said surface, applying an electrostatic charge of opposite polarity to a supply of said liquid emulsion to facilitate the flowing of said liquid emulsion on said surface, and transferring said liquid emulsion in a continuous liquid mass from said supply directly to said surface, the electric potential difference between said electrostatic charge on said surface and said electrostatic charge on said liquid emulsion being less than that at which arcing occurs between said liquid emulsion and said surface.

4. A method of coating a liquid photographic emulsion on the surface of a support which comprises first rendering said support electrically neutral, applying a uniform electrostatic charge to said surface by directing a flow of ionized air of a given polarity onto said surface and thereby facilitating the even spreading of saidliquid emulsion on said surface, applying an electrostatic charge of opposite polarity to a supply of said liquid emulsion to facilitate the flowing of said liquid emulsion on said surface, and flowing said liquid emulsion in a continuous liquid mass from said supply directly onto said surface, the electric potential difference between said charge on said surface and said charge on said liquid emulsion being less than that at which arcing occurs between said liquid emulsion and said'surface.

5. A method of coating a liquid photographic emulsion on the surface of a support carrying polarization charges and static surface charges thereon which comprises first discharging said polarization charges in said support by passing the support through the bite of a pair of opposed grounded metal rolls, rendering said static charges on said surface electrically neutral by directing a flow of ionized air onto said surface, applying a uniform electrostatic charge to said surface by directing a flow of ionized air of the desired polarity onto said surface to thereby facilitate the even spreading of said liquid emulsion on said surface, applying an electrostatic charge of opposite polarity to a supply of said liquid emulsion to facilitate the flowing of said liquid emulsion on said surface, and transferring said liquid emulsion in a continuous liquid mass from said supply directly to said surface, the electric potential difference between said electrostatic vcharge on said surface and the electrostatic charge on said liquid emulsion being less than that at which arcing occurs between said liquid emulsion and said surface. I

- port, the improvement which comprises applying to said surface a uniform electrostatic charge havinga'polarity different from the polarity of said liquid emulsiomand flowing the liquid emulsion from said supply in a continuous liquid mass onto said surface while maintaining said charge thereon, the electric potential difference between the charge applied to said surface and the potential of said liquid emulsion being less than that at which 5 arcing occurs between said liquid emulsion and said surface.

7. The further improvement in the method according to claim 6 in which a uniform electric potential difference is maintained between the charged surface and the 10 liquid emulsion.

References Cited in the file of this patent UNITED STATES PATENTS Morrison July 31, Chappell Aug. 25, Ransburg Nov. 1, Henry et al. Feb, 14, Hart et al. Oct. 24, Miller May 1, Ransburg July 27, Miller Sept. 20,

Patent Citations
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US1678869 *Dec 1, 1922Jul 31, 1928Montford MorrisonStatic dissipator
US2052131 *Oct 10, 1933Aug 25, 1936Us Rubber CoSpreading, extruding, or like operations
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US2497604 *Jul 15, 1947Feb 14, 1950British Cotton Ind Res AssocMethod of and means for eliminating electrostatic charges in industrial processes
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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3206323 *Jun 12, 1962Sep 14, 1965Eastman Kodak CoCoating high viscosity liquids
US3250620 *Jan 18, 1962May 10, 1966Eastman Kodak CoSilver halide emulsions having chill-setting properties
US3323934 *Aug 5, 1963Jun 6, 1967M E S Sa De Machines ElectrostElectrostatic coating process and apparatus
US3335026 *Jul 16, 1963Aug 8, 1967Gevaert Photo Prod NvMethod for coating liquid compositions employing electrostatic field
US3462286 *Jul 16, 1963Aug 19, 1969Gevaert Photo Prod NvMethod of coating webs with photographic emulsions or other liquid compositions utilizing an electric field
US3501330 *Oct 22, 1965Mar 17, 1970Agfa Gevaert NvManufacture of electrophotographic materials
US3522080 *Jul 18, 1968Jul 28, 1970Bayer AgProcess for hardening the surfaces of synthetic materials
US3645735 *Oct 16, 1969Feb 29, 1972Eastman Kodak CoCoating bead modulation and recording thereby
US3645773 *Feb 10, 1969Feb 29, 1972Agfa Gevaert AgProcess for coating substrates in strip-form with photographic emulsion
US3663292 *Feb 10, 1969May 16, 1972Agfa Gevaert AgProcess for coating strip-form substrates
US3916043 *Nov 15, 1971Oct 28, 1975Eastman Kodak CoMethod of coating a spliced web
US4517143 *Oct 3, 1983May 14, 1985Polaroid CorporationMethod and apparatus for uniformly charging a moving web
US4810432 *Dec 28, 1987Mar 7, 1989Polaroid CorporationMethod and apparatus for establishing a uniform charge on a substrate
US4835004 *Jul 18, 1988May 30, 1989Fuji Photo Film Co., Ltd.Method and apparatus for applying a coating liquid to a moving web
US5049404 *Dec 9, 1988Sep 17, 1991Polaroid CorporationMethod and apparatus for applying ultra-thin coatings to a substrate
US5798146 *Sep 14, 1995Aug 25, 1998Tri-Star TechnologiesSurface charging to improve wettability
US6368675Apr 6, 2000Apr 9, 20023M Innovative Properties CompanyElectrostatically assisted coating method and apparatus with focused electrode field
US6406541 *May 26, 2000Jun 18, 2002The Regents Of The University Of CaliforniaMethod and apparatus for adhering and centering particles to the tacky areas on a surface containing an array of tacky and non-tacky areas
US6475572Apr 6, 2000Nov 5, 20023M Innovative Properties CompanyElectrostatically assisted coating method with focused web-borne charges
US6666918Jul 26, 2002Dec 23, 20033M Innovative Properties CompanyElectrostatically assisted coating apparatus with focused web charge field
US6716286Jan 22, 2002Apr 6, 20043M Innovative Properties CompanyElectrostatically assisted coating method and apparatus with focused electrode field
US7255769 *Dec 19, 2002Aug 14, 2007Fujifilm Manufacturing Europe B.V.Method for splicing and coating webs as well as a web obtained with such methods
US7942495Jan 5, 2009May 17, 20113M Innovative Properties CompanyMethod of and apparatus for ink jet printing using an electrostatic field
US8570703Jun 3, 2008Oct 29, 20133M Innovative Properties CompanyApparatus and methods for modification of electrostatic charge on a moving web
US8605406Dec 16, 2008Dec 10, 20133M Innovative Properties CompanyApparatus and methods for altering charge on a dielectric material
US20030152740 *Dec 19, 2002Aug 14, 2003Fuji Photo Film B.V.Method for splicing and coating webs as well as a web obtained with such methods
US20090174755 *Jan 5, 2009Jul 9, 20093M Innovative Properties CompanyMethod of and apparatus for ink jet printing using an electrostatic field
US20100182728 *Jun 3, 2008Jul 22, 2010Jendrejack Richard MApparatus and methods for modification of electrostatic charge on a moving web
DE19617724C1 *May 3, 1996Jun 19, 1997Agfa Gevaert AgPhotographic recording material manufacturing method
EP0055982A2 *Jan 4, 1982Jul 14, 1982Polaroid CorporationMethod and apparatus for coating semiconductive materials
EP0055982B1 *Jan 4, 1982Nov 12, 1986Polaroid CorporationMethod and apparatus for coating semiconductive materials
EP0055983A2 *Jan 4, 1982Jul 14, 1982Polaroid CorporationElectrostatically assisted coating gap
EP0055983B1 *Jan 4, 1982May 6, 1987Polaroid CorporationElectrostatically assisted coating gap
EP0136606A2 *Sep 14, 1984Apr 10, 1985Polaroid CorporationMethod and apparatus for uniformly charging a moving web
EP0136606A3 *Sep 14, 1984Sep 10, 1986Polaroid CorporationMethod and apparatus for uniformly charging a moving web
Classifications
U.S. Classification427/472, 427/533, 427/209, 427/482, 118/638
International ClassificationG03C1/74
Cooperative ClassificationG03C1/74
European ClassificationG03C1/74