KR100715166B1 - Electrostatically assisted coating method and apparatus with focused web charge field - Google Patents

Abstract

A system for applying a fluid coating onto a substrate includes forming a fluid wetting line by introducing a stream of fluid onto a first side of the substrate along a laterally disposed fluid-web contact area. The apparatus of the present invention comprises a coating fluid applicator which dispenses a stream of coating fluid onto a first surface of the substrate to form a fluid wetting line along a laterally disposed fluid contact area, an electrical field applicator which applies an electrostatic field at a location on the substrate adjacent the fluid wetting line to attract the coating fluid to the first surface of the substrate, and an acoustical field applicator which applies an acoustical field at a location on the substrate adjacent the fluid wetting line. Ultrasonics combined with electrostatic fields further enhances coating process conditions and coating uniformity.

Description

FIELD OF THE INVENTION Electrostatically assisted coating method and coating apparatus by a focused web charge field {{ELECTROSTATICALLY ASSISTED COATING METHOD AND APPARATUS WITH FOCUSED WEB CHARGE FIELD}

The present invention relates to electrostatically assisted coating methods and apparatus. More specifically, the present invention relates to achieving an improvement in the uniformity of the coating process using an electrostatic field at the point of contact of the movable web and the coating fluid.

Coating is a process that replaces a gas in contact with a substrate, typically a solid surface such as a web, with one or more fluid layers. The web is a relatively long and flexible substrate or sheet material, such as a plastic film, paper or synthetic paper, or a metal foil, separate product or sheet. The web may be a continuous belt. Functionally useful when the coating fluid is applied to the substrate surface. Examples of coating fluids include liquids for forming photosensitive emulsion layers, release layers, primary layers, base layers, protective layers, lubricating layers, magnetic layers, adhesive layers, decorative layers and colored layers.

After welding, the coating may remain fluid, such as the application of lubricating oil to the metal in the metal coil manufacturing process or the application of a chemical reagent to activate or chemically change the substrate surface. Alternatively, if the coating contains a volatile fluid, it may be dried to leave a solid coating such as paint, or it may be cured or solidified in some other way with a functional coating such as a release coating in which the pressure sensitive adhesive is not firmly fixed. Coatings can be coated by Cohen, ED and Gutoff, EB's "Modern Coating and Drying Technology" (VCH Publisher, New York 1992), and Satas, D.'s "Web Treatment and Preservation Technology". "Web Processing and Converting Technology and Equipment" (Van Vorstrand Reinhold Publishing Co., New York 1984).

In order to apply an accurate coating, the coating liquid is usually applied evenly on the substrate. In the web coating process, the moving web passes through a coating station where a layer of coating liquid is deposited on one web surface. The uniform application of the coating fluid on the web is influenced by many factors, including web speed, web surface properties, viscosity of the coating fluid, surface tension of the coating fluid and the thickness of the coating fluid applied on the web.

Electrostatic coating applications have been used in the printing and photography arts, where roll and slide coatings dominate and use low viscosity conductive fluids. Although the electrostatic force applied to the coating area can delay the onset of air incorporation and allow it to proceed at higher speeds, the electrostatic field that attracts the coating fluid to the web is quite wide. One known method of applying an electrostatic field employs precharging the web (applying charge to the web in front of the coating station). Another known method uses a voltage applied support roll below the web in the coating station. Precharged webs include corona wire charged and charged brushes. Methods of applying voltage to the support rolls include conductive high potential rolls, precharged nonconductive roll surfaces, and powered semiconductor rolls. While these methods carry an electrostatic charge to the coating area, there is no high concentration electrostatic field in the coating device. For example, in curtain coating with a precharged web, the fluid is attracted to the web and the equilibrium position of the fluid / web contact line (wet line) is determined by the balance of forces. The electrostatic field attracts the coating fluid onto the web and draws the coating fluid onto the web. The movement of the web generates a force that is likely to pull the wet line down the web. Thus, when other processing conditions remain constant, higher electrostatic forces or lower line speeds result in the wet line being pulled over the web. In addition, when some flow change is present in the flow of coating fluid across the web, the lower flow region is pulled further over the web as a whole, and the upper flow region is pulled further down the web as a whole. This situation reduces the uniformity of the coating thickness. In addition, since the fluid contact line (wet line) is not stabilized but depends on many factors, the stability of the process is less than the required value.

Many patents are disclosed relating to electrostatic auxiliary coatings. Some deal with coating properties, others deal with charge properties. Some representative patents are described below. U. S. Patent No. 3,052, 131 discloses an aqueous dispersant coating method using any of a roll charge or web precharge. U. S. Patent No. 2,952, 559 discloses slide coating the emulsion with web precharge, and U. S. Patent No. 3,206, 323 discloses coating the viscous fluid by precharging the web.

U.S. Patent 4,837,045 discloses the use of a low surface energy bottom coating layer for gelatinized DC voltage on a support roll. Coating fluids used in this method include gelatin, magnetic materials, lubricants, or adhesive layers of aqueous or organic nature. This coating method may include slide, roller bead, spray, extrusion or curtain coating.

EP 390774 B1 relates to a high speed curtain coating of a fluid at a speed of at least 250 cm / sec (490 ft / min), using a pre-applied electrostatic charge, wherein the charge magnitude versus speed (cm / sec) ( Volts) is at least 1: 1.

U. S. Patent No. 5,609, 923 discloses a method of curtain coating a movable support, which increases the maximum actual coating rate. The charge can be applied before or at the coating point by the backing roller. This patent refers to a technique for generating an electrostatic voltage as is known and suggests that the roll or corona charge below the coating point refers to an example of a previous patent where the coating occurs prior to coating. This patent also discloses corona charges. The disclosed technique is a technique of transferring charge to a web with a corona, roll, bristle brush in front of the coating point to form an electrostatic field on the web before the coating is added.

1 and 2 show known techniques of electrostatic auxiliary coating application. In FIG. 1, the web 20 moves past the coating station 24 in the longitudinal direction (arrow 22 direction). The web 20 has a first major side 26 and a second major side 28. At the coating station 24, the coating fluid applicator 30 distributes the stream of coating fluid laterally onto the first side 26 of the web 20. Thus, downstream of coating station 24, web 20 supports coating 34 of coating fluid 32.

In FIG. 1, the electrostatic coating aid in the coating process results in electrostatic charge at the first side of the web 20 at a charge application station 36 disposed longitudinally spaced upstream from the coating station 24. 26, by means of which charge may be applied to the second side 28 of the web 20. In the charge application station 36, laterally disposed corona discharge wires 38 apply a positive (or negative) charge 39 to the web 20. This wire 38 may be on the first or second side of the web 20. The coating fluid 32 is grounded (in the same way as grounding the coating fluid applicator 30) and is electrostatically attracted to the charged web 20 at the coating station 24. Laterally arranged air dams 40 may be disposed upstream of the coating station 24 to reduce web boundary layer air interference at the coating fluid-web interface 41. The corona wire can be freely spaced along the web at intervals (see FIG. 1), or alternatively can be disposed adjacent to the first side of the web while the web is in contact with the backing roll at the coating station.

2 shows another known electrostatic auxiliary coating system. In this device, a relatively large diameter backing roll 42 supports the second side 28 of the web 20 at the coating station 24. The backing roll 42 may be a charged dielectric roll, a voltage rolled semiconductor roll, or a conductive roll. The conductive roll and the semiconductor roll are charged by the high voltage power supply. In the dielectric roll, the roll may be supplied with charge by any suitable means such as corona charging assembly 43. Regardless of the form of the backing roll 42 or its charging means, its outer cylindrical surface 44 is adapted to carry electrical charge 39 to the second side 28 of the web 20. As shown in FIG. 2, the electrical charge 39 of the backing roll 42 is positively charged and the coating fluid 32 is grounded by grounding the coating fluid applicator 30. Thus, the coating fluid 32 is electrostatically attracted by the charge remaining at the interface between the web 20 and the upper cylindrical surface 44 of the roll 42. Air dam 40 reduces web boundary layer-air interference at coating fluid-web interface 41.

Known electrostatic auxiliary coating apparatuses as shown in FIGS. 1 and 2 assist the coating process by delaying the onset of air incorporation and improving the wettability of the wet line of the coating. However, such a device applies charge to the web at a position almost upstream from the wet line and generates a fairly wide electrostatic field. This device is quite inefficient for maintaining a straight wet line in the presence of a change in flow across the web or a change in electrostatic field across the web. For example, if a localized deflection region of the coating fluid flow occurs in any position across the curtain in a curtain coating apparatus, the wet line in this deflection coating region may move downstream in response to the material or process variables. have. This results in a coating that is more biased in this area due to stresses and strains on the curtain, especially in fluids exhibiting elastic properties (more elastic fluids have greater elongational viscosity relative to shear). In addition, if the electrostatic field is not uniform (e.g., uneven corona web precharge), the low voltage region on the web will cause the wet line in this region to move downstream of the web. Will increase the coating weight. This effect is gradually dominant as the elasticity of the fluid increases. Thus, changes in fluid flow across the web and changes in the electrostatic field across the web result in nonuniformities in the wet line, resulting in nonuniform coating application on the web.

Any of the known methods and apparatus for electrostatically assisted coatings disclose a technique for applying a focused electric field from an electric field applicator to the web of the coating station to improve the properties of the fluid coating applied and also to achieve an improvement in processing conditions. I could not. There is a need for an electrostatically assisted coating technique that applies a more focused electric field to the web of the coating station.

The present invention relates to a method of applying a fluid coating on a substrate. The substrate has a first side and a second side. The method provides longitudinal relative motion between the substrate and the fluid coating station and directs the fluid stream onto the first side of the substrate at an angle of 0 ° to 180 ° along the laterally disposed fluid-web contact area at the coating station. Introducing to form a fluid wetting line. Electric forces are generated on the fluid from an effective electric field that arises from a predetermined location on the second side of the substrate substantially downstream of and in the fluid wetting line.

The electrical force can be generated by transferring electrical charge through the fluid medium and depositing the electrical charge onto the second side of the substrate, depositing the electrical charge transfer from the electrical charge source onto the second side of the substrate and In this case, the physical contact between some or all of the charge source and the substrate is used. When using a liquid medium, the electrical charge can be transferred from the laterally extending corona discharge source at a distance from the second side of the substrate at the fluid coating station. Transfer of electrical charge upstream from the fluid wet line can be further limited by providing an electrical barrier that shields the upstream portion of the web from the charge. This substrate may be supported on the second side adjacent the fluid coating station.

According to one embodiment of the invention, the electrical charge is formed as a first charge at a location remote from the substrate, and is transferred in a fluid wet line to a charge application region laterally disposed adjacent to the second side of the substrate, and substantially And to a location on the second side of the substrate downstream of and in the fluid wetting line to allow electrical force to be generated in the fluid.

The fluid stream may be formed with a coating fluid dispenser such as curtain coater, bead coater, extrusion coater, carrier fluid coating method, slide coater, knife coater, jet coater, notch bar, roll coater or fluid bearing coater. The stream of coating fluid may be introduced tangentially to the first surface of the substrate.

The electrical charge may have a first polarity and the method may include applying a charge of a second opposite polarity to the fluid.

According to another embodiment of the invention, a method of applying a fluid coating on a substrate, wherein the substrate has a first surface on a first side and a second surface on a second side, is provided with the substrate and the fluid coating station. Providing longitudinal relative movement of the liver. The method further includes forming a fluid wetting line by introducing a coating fluid stream onto the first side of the substrate at an angle of 0 ° to 180 ° along the laterally disposed fluid-web contact area at the coating station. . The invention further includes the step of exposing the effective electrostatic charge on the substrate to a fluid that is substantially only at a location on the substrate and downstream of the fluid wet line.

According to the method of the invention, the exposing step further comprises depositing an electrical charge on one of the first or second surfaces of the substrate at a position upstream of the web from the fluid coating station. The exposing step may further include imparting charge to an invalid charge as an electrostatic charge to the fluid until the electrical charge is at least substantially in the fluid wet line.

According to one embodiment, the exposing step of the method of the present invention comprises applying an electrical charge from the fluid wet line to the substrate upstream of the web, the electrical charge on the web until the electrical charge is at least substantially in the fluid wet line. Shielding any effective electrostatic attraction between the fluids.

In yet another embodiment, an electrical charge is applied to the first side of the substrate, the shielding step providing a ground surface adjacent thereto at a distance from the second surface of the substrate, the ground surface directly upstream of the fluid wetting line. Extends along the substrate from the fluid wet line at the trailing edge of to a more upstream and spaced leading edge.                 

The invention also relates to an apparatus for applying a fluid coating on a substrate, the substrate having a first surface on a first side and a second surface on a second side, and moving longitudinally with respect to the apparatus. The apparatus includes means for dispensing a coating fluid stream on the first surface of the substrate to form a fluid wetting line along the laterally disposed fluid-web contact region, and laterally extending the second side of the substrate. An electrical charge applicator. The electrical charge applicator is disposed on the first surface of the substrate, which is generally opposite the fluid wet line, to substantially charge the substrate at a location on the substrate that is substantially downstream of and in the fluid wet line.

The electrical charge applicator may comprise laterally extending charged wire, a member of sharp edges, a conductive sheet of sharp edges, a series of needles, a brush, or a jack knife edge.

The electrical charge applicator can include an electrical charge source away from the second surface of the substrate and a fluid medium for generating the electrical charge as the first charge. The fluid medium transfers the first electrical charge from the electrical charge source to the laterally disposed charge application region in the fluid wet line and adjacent to the second surface of the substrate, and transfers the first electrical charge onto the second surface of the substrate. It is disposed between the electrical charge source and the second surface of the substrate for application. The electrical charge applicator may be evenly spaced from the second surface of the substrate.

The air bearing extends laterally across the substrate adjacent the electrical charge applicator to support and align the second side of the substrate with respect to the electrical charge applicator. The electrostatic field barrier may be placed near the substrate and the electrical charge applicator to shield the web upstream portion from the fluid wet line from the electrical charge from the electrical charge applicator.

The electrical charge from the electrical charge applicator can have a first polarity and can apply a charge of a second opposite polarity to the coating fluid.

1 is a schematic illustration of a known electrostatic coating apparatus for applying charge from a corona wire upstream of a web to a movable web before the movable web enters the coating station,

FIG. 2 is a schematic diagram of a known electrostatic coating apparatus for transferring charge from the backing roll below the movable web in the coating station to the movable web,

3 is a schematic illustration of one embodiment of an electrostatic auxiliary coating apparatus according to the present invention in which a corona source applies charge to a movable web in a coating area, FIG.

4 is an enlarged schematic view of a portion of FIG. 2 showing the applied electrostatic charge and its reverse line;

5 is an enlarged schematic view of a portion of FIG. 3 showing the electrostatic charge applied during the coating operation and its reverse line;

6 is a schematic illustration of another embodiment of an electrostatic auxiliary coating apparatus according to the present invention in which an air bearing assembly encloses a corona wire,

FIG. 7 is a schematic enlarged view of the air bearing assembly having the corona wire of FIG. 6, FIG.                 

8 is a schematic enlarged view of another air bearing assembly having a conductive strip;

9 is a schematic illustration of yet another embodiment of the electrostatic auxiliary coating apparatus of the present invention, illustrating one application of using the electrostatic auxiliary coating apparatus for tangential curtain coating,

10 and 11 schematically illustrate another embodiment of the electrostatic auxiliary coating apparatus of the present invention showing a remote location for an electrical charge source.

Some of the drawings show a preferred embodiment of the present invention, but also apply to other embodiments as is well known in the discussion. In all cases, it is disclosed that this invention is not restrictive but is representative of this invention. Numerous other modifications and embodiments falling within the scope of the invention may be devised by those skilled in the art.

The present invention includes coating apparatus and methods that use a more focused electrostatic field at the interface of a substrate to be coated (such as a web) with a fluid coating material applied on the substrate. The inventors have found that a more focused electrostatic field can improve the coating process by stabilizing and straightening and determining the placement of the coating wetting line to achieve a wider treatment window. For example, the present invention not only improves the uniformity of the coating in the direction across the web, but also the coating properties such as coating weight, coating speed, coating geometry, web properties such as dielectric strength, viscosity, surface tension and elasticity. It is possible to widen the fluid properties and the die to web gap. Additionally, for conductive fluids, lower energy systems (low currents) can be used as compared to systems using high potential conductive rolls. Low dielectric strength webs, such as paper, high voltages and coating rates can be used without dielectric breakdown of the webs. In curtain coating, the electrostatic coating aids enable lower curtain height (therefore the stability of the curtain) and enable the coating of elastic solutions that could not be coated without the entrained flow of air in the past. The focused magnetic field significantly improves the ability to transport the elastic coating fluid, because it more accurately determines the placement, linearity and stability of the wet line, resulting in improved stability of the processing process. In addition, thinner coatings can be produced even at lower line speeds than previously possible, which is important for processing processes with limited drying and curing rates.

In extrusion coating, electrostatics not only enable the use of larger coating gaps, but also enable the use of low elastic aqueous fluids (such as some aqueous emulsion adhesives) that cannot be extruded (in extrusion mode) without static electricity. Let's do it. During coating by the curtain coating method, the coating step involves the displacement of the boundary layer air with respect to the coating fluid, while the main force is based on the momentum, while in extrusion coating the main force is the associated elastic or surface tension. If you use static electricity, it can be the dominant static electricity. Thus, when electrostatics are used and become the predominant force in the coating step, the coater can be classified as an electrostatic coater rather than a curtain or extrusion coater. Therefore, as the gap of the extrusion coater increases, the gap may become indistinguishable in the operating principle using the curtain coater in which static electricity exists.

Although the present invention is described for smooth and continuous coatings, the present invention can also be used during the application of discontinuous coatings. For example, static electricity can be used to help coat a substrate having a macroscopic structure, such as a void filled with a coating, with or without continuity between coatings in adjacent pores. In this situation, the uniformity and improved wettability of the coating are maintained both in separate coating areas and in one area to another.

The substrate can be any surface of any material to be coated, including the web. The web can be any sheet-like material such as polyester, polypropylene, paper or nonwoven material. The improved wettability of the coating is particularly useful in rough tissues or porous webs, whether the pores are microscopic or macroscopic. Although the examples shown illustrate a web moving past a stationary coating applicator, while the web is stationary, the coating applicator may move, or both the web and the coating applicator may move relative to a fixed point. .

Generally speaking, the present invention relates to a method of applying a fluid coating on a substrate, such as a web, comprising providing longitudinal relative motion between the web and the fluid coating station. A stream of coating fluid is introduced onto the first side of the web along a laterally disposed fluid wetting line at the coating station. The coating fluid is introduced at any of angles between 0 ° and 180 °. The electric force is generated on the fluid from the electric field generated from the charge on the second side of the web and at a location on the web substantially downstream of and in the fluid wet line. The electric field can be generated by an electric charge carried by any method and deposited on the second side of the web. This charge can be transported by the second side or direct contact of the web through the fluid medium. According to all descriptions of the invention, negative or positive charges can be used to attract the coating fluid. Coating fluids may include solvent-based fluids, flowable melts of thermoplastic materials, emulsions, dispersants, flowable mixtures that are miscible or incompatible, inorganic fluids, and 100% solids fluids. Solvent-based coating fluids include any aqueous or organic solvent. Since electrostatic discharges can pose a hazard such as fire or explosion, certain safety precautions must be taken, for example when handling flammable volatile solvents. Such precautions are known and may include the use of an inert atmosphere in the region where electrostatic discharge occurs.

Instead of using a preloaded or energized support roll system as is known, the invention extends linearly in a direction across the web where the wet line must occur on the side of the web opposite the coating fluid. A focused electric field source such as a narrow conductive electrode is used. In curtain coating application, a good wetting line is typically a gravity-determining curtain fluid wetting line (no electrostatics applied) when the web is stationary (or an initial coating fluid wetting line (electrostatic if the web is stationary) Not authorized). The narrow conductive electrode may be, for example, a continuous corona wire (such as the corona wire 50 of FIG. 3), discontinuously spaced needle points, a brush, or any member having a sharp edge that can generate corona discharge. have. The high electrostatic field gradient near the narrow electrode produces a corona discharge from the electrode, whose charge moves toward the conductive coating fluid, but is stopped by the dielectric barrier of the web. The source of electrical charge may also be disposed far away such that the charge subsequently transfers to the back side of the web and is focused substantially at or downstream of the wet line. Alternatively, the charge can be deposited directly on the back of the web from a solid structure in contact with the back of the web, such as, for example, a brush, conductive film, or a member having a small radius. Again, the charge is substantially concentrated at or downstream of the wet line. These charges on the back of the web produce a more focused electric field than conventional electrostatic assisted coating systems. Because this electric field does not extend far upstream of the web (such as conventional precharged webs or applied coating roll systems), the coating fluid is led to wet lines with sharper contours, and the direction across the web. To stabilize the wet line by maintaining a more linear profile and constraining the fluid in place. This means that the vertical balance of the forces that determine the location of the wet line is less important and the nonlinearity in the wet line becomes less apparent. Thus, process variations such as coating fluid velocity, coating uniformity in the direction across the web, web speed variation, charge variation of the incoming web and other process variations have less impact on the coating process.

An additional advantage of the non-contact electrostatic charge application system (eg, the system shown in FIG. 3) of the present invention is that it works well with low dielectric strength webs and conductive coating fluids. In systems such as conductive fluids, high potential conductive rolls used in conjunction with known electrostatic auxiliary coatings, since the rolls are close to the web surface, more current may be required to generate the desired attraction. This makes for a higher energy system and creates a greater risk of electric shock. In addition, arcing from the electrode to the coating fluid via the web is more likely to occur especially for materials of lower dielectric strength. In a non-contact system where the focused web charge is generated by transferring the fluid medium (eg air) to the second side of the web, a lower current is required and less arcing from the electrode to the coating fluid occurs. . This makes the device safer and allows you to drive at higher web speeds. Typically, the electrode to web gap is between 0.2 cm (0.10 in) and 5 cm (2 in). Preferably, the gap is 1.9 cm (0.75 in). However, closer gaps can increase aggression further, and larger gaps, that is, between 2.5 cm (1 in) and 5 cm (2 in), will further reduce arcing and improve the ability to drive low dielectric strength materials. Can be.

FIG. 3 illustrates an embodiment of an electrostatic assisted coating apparatus that uses a focused web charge field that can achieve better aggressiveness (eg, coating fluid web attraction at a desired wet line location) and wet line linearity than conventional devices. It is. The inventors have found that the magnetic field remains focused during arc generation and current reduction by placing the electrode at a distance from the web and using a small diameter wire to act as a corona wire. In this case, the magnetic field emanating from the wire itself does not create a major attraction in the coating fluid. This main attraction comes from the corona charge from the wire that is transported to the back of the web through air or other connecting media, and collects in the wet line. This charge on the back of the web creates a strong attraction in the coating fluid. In addition, the charge from the wire does not tend to be attracted to the web substantially upstream of the web in the wet line because the main attraction is directed to the coating fluid in the wet line. The magnetic field can be more highly focused by providing a barrier or shaped field to limit the flow of charge from the desired wet line to either upstream or downstream of the web.

According to the apparatus shown in FIG. 3, the laterally extending corona discharge wire 50 is arranged in the second direction of the web 20 in a longitudinal direction to a coating station 24 comprising a lateral coating wetting line 52. It is arranged at a distance from the side surface 28. This web 20 is supported by a coating station 24 between a pair of support rolls 54, 56. Alternatively, the web 20 may be supported to the coating station 24 by a support panel, slide, track or other support. Air dam 40 may be any suitable physical barrier that limits ambient air interference in the wet line. Figure 3 illustrates the method of the present invention with respect to curtain coating operations, but can also be applied to other geometric coatings.

The stream of coating fluid 32 is conveyed from the coating fluid applicator 30 onto the first surface on the first side 26 of the web 20. As shown, the coating fluid applicator 30 may be grounded to ground the coating fluid 32 against the charge 58 applied by the corona discharge wire 50 to the web 20. Alternatively, the opposite charge can be applied to the coating fluid 32 by means of a suitable electrode device or the like, and also the polarity of the charges applied to the coating fluid 32 and the web 20 can be reversed. This method can be particularly useful when using low electrically conductive coating fluids. For example, for low conductive coating fluids, charge may be applied to the coating fluid prior to coating via a die or by corona. This system can be used when insufficient electrostatic aggressiveness is seen due to the use of low conductivity coating fluids. For conductive coating fluids in which the conductive paths are isolated, the die potential can be raised to create the opposite polarity of the coating fluid. Alternatively, opposite polarities can be applied to the coating fluid anywhere along the isolated path of conduction.

When the corona discharge wire 50 becomes active, it applies an electrical charge 58 to the second side 28 of the web 20. According to one embodiment, the upstream shield 60 is corona discharged to prevent discharged ions from being drawn from the coating wet line 52 to the second side 28 of the web 20 upstream. Extend laterally adjacent to the wire 50. The upstream shield 60 is a non-conductive or insulating material, such as Delrin ^™ acetal resin, available from EI du Pont Nemours, Wilmington, Delaware, or a ground potential or elevated It may be formed of a semiconductive or conductive material held at a potential. The web upstream shield 60 is of any shape suitable for obtaining a desired electrical barrier for shielding the upstream portion of the web 20 from the electrical charge of the corona discharge wire 50. A web downstream shield can also be used, which can reduce excessive charges that are transported downstream of the web. The web upstream shield and the web downstream shield are preferably arranged at equal intervals from the wire, but other types of spacing may be applied. Although shields in the form of physical barriers are shown, other types of shields may be used, such as shields that resist electrostatic fields.

4 is an enlarged view of the prior art system of FIG. 2 and shows a reverse line 66 generated by electrostatic charge 39 with respect to the coating fluid 32. Typically, the desired wet line is a coating fluid wetting line (or initial coating fluid wetting line when the web is stationary) determined by gravity when the web is stationary, as shown in FIGS. 2 and 4. It becomes the top dead center of the rolled roll. However, the location of other wet lines is common and depends on the shape of the coating die, the fluid properties and the web path.

Reverse line 66 does not focus well on charged rolls (similar to roll 42 in FIG. 2), and the charge does not force the force substantially upstream of the web of the wet line (eg, upstream of the web). Region 67] is applied to the coating fluid. For example, for charged rolls larger than 3 inches (7.5 cm) in diameter, a charge is applied to the coating fluid substantially upstream of the web from the desired wet line. However, as charge transfer to the web is more focused on a one-inch diameter roll given the same potential, the charge is functionally adversely affecting the uniformity of the wet line, from the wet line to the coating fluid substantially upstream of the web. It does not exert a force (ie, the charge on the web is invalid upstream of the web compared to the coating fluid).

FIG. 5 is an enlarged view of the inventive system of FIG. 3, showing that the charge transferred to the second surface on the second side of the web is further focused below the coating fluid and the web contact line. In this case, the back line 68 is more concentrated to create a sharper and more linear wet line, which stabilizes the wet line because it tends to confine the wet line in place across the web travel path. Let's do it. Additional focusing techniques such as shield 60 shown in FIG. 3 also improves focusing. Viscous and elastic fluids may require a higher degree of focusing because variations in the uniformity of the contact lines can result in greater variations in coating thickness than low viscosity and elastic fluids. 6 and 7 show yet another embodiment of the electrostatic auxiliary coating apparatus of the present invention. As shown in FIGS. 6 and 7, the laterally extending electrodes 100 extend along the second side 28 of the web 20. The electrode 100 may be formed of, for example, a continuous corona wire, discontinuously spaced needle points, a brush, or any member having a sharp edge that can cause corona discharge. Preferably, the electrode 100 is disposed in an adjacent web air bearing 102 that can act as a web upstream shield and a web downstream shield. This air bearing 102 stabilizes the position of the web and the vibration of the web, which can adversely affect the stability and uniformity of the coating. The air bearing 102 preferably includes a porous membrane 104 (porous polyethylene or the like) in fluid communication with the air manifold chamber 106. Compressed air is supplied to the air manifold chamber 106 as indicated by arrow 110 through one or more suitable inlets 108. Air flows through the air manifold chamber 106 and into the porous membrane 104. The porous membrane 104 has a relatively smooth and generally radial bearing surface 112 disposed adjacent the second side 28 of the web. Air exiting the bearing surface 112 supports the web 20 across the coating station 24 and the electrode 100, and between the electrode 100 and the second side 28 of the web 20. To form a media space (eg air). Although active air bearings are described (only the air boundary layer on the second side of the web as bearing medium) passive air bearings can be used at sufficiently high web speeds. Like the apparatus of the present invention shown in FIGS. 3 and 5, the embodiment shown in FIGS. 6 and 7 is narrowly distributed adjacent to the fluid wetting line that constrains the coating fluid / web wetting line in a desired position. Form an electrostatic field line. The electrostatic effect increases the coating fluid wettability on the web and "locks" the coating fluid / web contact line into a stable line extending laterally across the web.

Relative quantitative analysis was performed to evaluate the advantages of the electrostatic auxiliary coating apparatus of the present invention. According to a series of experiments, the range of webs 20 ranges from 0.005 inch thick paper backing to 0.0075 cm thick paper liners with a release layer on the second side, and coating fluid 32 ) Was an aqueous dispersant having a viscosity of about 850 centipoise. The flow rate of the coating fluid in the curtain was set to obtain a dry coating thickness of about 10.6 microns (0.0042 in) at the flow rate of the web of 111.25 m / mim (365 ft / min). Different curtain heights were evaluated from 5.72 cm (2.25 in) to less than 0.64 cm (0.25 in). Curtain coatings of such fluids without the aid of static electricity have resulted in very low line speeds with increasing air velocity and air entrainment and curtain breakage. Several electrostatic systems were tested to determine the best method for curtain coating of these fluids. Unless stated otherwise, the polarity of the above-mentioned voltage is positive. Using a system similar to that shown in FIG. 2 except that it has a conductive powder roll and a curtain about 0.5 inch high, the maximum web speed attainable without air incorporation is 15.25 m / min (50) without static charge. ft / min). In this condition, the curtain contact line was deflected at about 2.5 cm (1 inch) downstream of the web at the top dead center position on the support roll. Further increase in line speed caused damage to the curtain. When increasing the voltage of the supported support roll to increase the web speed, arcing through the web will occur at about 2,500 volts. A web speed of 112.78 m / min (370 ft / min) was obtained at 2,000 volts prior to dielectric breakdown of the web. When arcing occurs, the beneficial effects of static electricity are greatly reduced, which in turn limits the web speed. The use of a polymer carrier web or belt will cause less arcing, but residual web or belt charge can cause problems with coating uniformity. The precharge of the web in a manner similar to that shown in FIG. 1 was also investigated with very little ability to increase web speed when using paper backing as the web. The charge of the support roll covered with rubber or ceramic was also investigated. In this type of system, web speeds within 137.16 m / min (450 ft / min) were obtained by setting the corona charging device to 9-12 kilovolts. However, in such a system, charge nonuniformity on the incoming web or roll surface can affect the linearity of the contact line and the stability of the contact line.

By using the apparatus of the present invention shown in FIG. 3, the stability and linearity of the excellent contact lines were observed. The corona discharge wire was a tungsten wire of 0.0152 cm (0.006 in) in diameter and was usually placed below 1.9 cm (0.75 in) of the second side 28 of the web 20. The power supply was an EH series high voltage power supply manufactured by Glassman High Voltage, Inc. of Whitehouse Station, New Jersey. Delrin ^™ web upstream shield 60 was disposed from the corona discharge wire 50 at 1.27 cm (0.5 in) spacing. A web speed of less than 198.12 m / min (650 ft / min) was observed using 15 kilovolts. The curtain flow rate was doubled and a maximum web speed of 618.16 m / min (1700 ft / min) was obtained at 17 kilovolts. Current consumption was less than observed with a powered support roll system and was typically 15 microamps per inch wide. This system was the most suitable system and the process change was the least sensitive.

When the large discontinuities in the lateral direction intentionally occurred in the electrostatic field generated by the corona wire 50, the utility of the device of the present invention is further illustrated in such a system. A strip of 0.15 cm (0.06 in) wide 3M Type 33 electrical tape was placed on the wire to simulate the heavily contaminated wire. At 8 kV and a web speed of about 635 cm (250 ft / min) on the corona wire, the contact line is a 0.32 cm (0.125 in) wide curtain with only 0.076 cm (0.030 in) across the area of the tape strip on the wire. Deflected downstream and remained perfectly linear with only a narrow line of air entrainment occurring at that deflection point (the application of a high voltage on the wire tends to reduce or eliminate air entrainment). Apparently, the electrostatic charge generated from the wire adjacent to the tape strip moves to the second side of the web directly over the tape strip, thus generating the required electrostatic attraction between the web and the coating fluid in the coating area. The non-contact corona charging system of the present invention (eg, as shown in FIG. 3) applies a substantially uniform charge distribution across the web on the second side of the web in the coating fluid wetting line, but at the second side. A very sudden decrease provides an adaptation system that will charge the web upstream of the wet line.

In another test, the web 20 was made with a 0.0036 cm (0.0014 in) polyester backing coated using the system apparatus of the present invention similar to that shown in FIG. In this test, an air bearing 102a (see FIG. 8) supporting the electrode 100a was used. The electrode 100a is approximately 0.94 cm disposed laterally by attaching the web upstream and downstream web edges of the conductive strip to the bearing surface 112a of the air bearing 102a (to prevent corona discharge at these edges). It was set as the electroconductive strip of (0.37in) length (web run direction). The coating fluid 32 is an aqueous emulsion having a viscosity of about 800 centipoise and a dry coating thickness of about 19 microns (0.00075 in) at a flow rate of web of 304.8 m / mim (1000 ft / min). Was adjusted to obtain. The coating curtain height was 13.34 cm (5.25 in) and the maximum web speed obtained (before the uniformity of the coating fell) was about 121.92 m / min (400 ft / min) without the use of static electricity. When operating the electrostatic system, the maximum web speed obtained was about 487.68 m / min (1600 ft / min) at an electrode voltage of 5 kilovolts. Driving the web at higher speeds causes air bubbles. However, a major concern with the system is that it requires a very high level of current (about 500 microamps per inch of coating width). As the voltage across the electrode 100a increases to make the web speed higher, higher levels of current are required and arcing can occur.

The electrostatic auxiliary coating apparatus of the present invention shown in FIG. 3 is described in the above-described example [with the web 20 being 0.0036 cm (0.0014 in) of polyester backing and the coating fluid 32 having a viscosity of about 800 centipoise. With an aqueous emulsion having a coating fluid and a polyester substrate. The coating curtain flow rate was adjusted to yield a dry coating thickness of 19 microns (0.00075 in) at a web speed of 914.1 m / min (3000 ft / cm) with the coating curtain height set at 19.37 cm (7.625 in). . Delrin ^™ web upstream shield 60 was disposed from the corona discharge wire 50 at a spacing of 0.635 cm (0.25 in). A web downstream shield was also used for the test and placed 0.635 cm (0.25 in) apart from the corona discharge wire 50. By operating the electrostatic system at 19 kilovolts, a web speed of 914.1 m / min (3000 ft / min) was achieved with a linear, stable wet line and no air entrainment. Current draw was typically as low as 10 microamps per inch.

In use, the electrostatic auxiliary coating apparatus shown in FIG. 3 was more aggressive than expected, and the coating wet line was linear and stable. The interaction between the grounded conductive coating fluid 32 and the corona discharge wire 50 suddenly causes electrical charges 58 on the second side 28 of the web 20 along the desired lateral fluid wetting line. Strong application was made (see FIG. 5). The use of web upstream shielding further increases the thermal insulation of the magnetic field. High density charge attraction (and progressively lower in the upstream direction) to the second side 28 of the web 20 opposite the first surface 26 of the web 20 that the coating fluid 32 contacts. The density of the lost charge) produces a significantly focused electrostatic field line. The linearity of the contact line of the coating system shown in FIG. 3 was better than that of the known dielectric backing roll system as shown in FIG. The device shown in FIG. 3 is stretchable and self-compensating, producing an electrostatically focused electrostatic field gradient. This system is simpler, more stable (because it uses lower current levels), and is less susceptible to dielectric breakdown of the web than known systems.

The system shown in FIG. 3 also eliminates the need for high current when using aqueous or conductive fluids. Typically, a current of 98.43 microamps per square centimeter (of web) (250 microamps per inch) is required when using a conductive voltage applied backing roll for known electrostatic auxiliary coatings when coating at very high web speeds. can do. However, in the corona discharge wire of FIG. 3, the current requirement for generating an electrostatic charge generally decreases below 9.843 microamps per centimeter (25 microamps per inch). Thus, the system shown in FIG. 3 is safer with very low risk of electric shock. To further improve this low electric shock system, an appropriately sized resistor (or other current limiting system) can be used in series with the high voltage supply to the corona discharge wire. This reduces the maximum current flow in the discharge and spreads the capacitive energy of the power supply over a long period of time (reducing the peak current in the discharge).

According to the electrostatic auxiliary coating apparatus of the present invention shown in FIG. 3, the corona discharge wire 50 is closely spaced to the second side 28 of the web 20. This corona discharge wire 50 must be installed at a predetermined distance from the second side 28 of the web 20 to provide an air gap to obtain an effective corona discharge effect. Wire and web spacing is determined by a number of factors including, for example, web thickness and dielectric strength, conductivity of the coating fluid, and web speed. The spacing is preferably in the range of 0.08 cm (0.031 in) to 5.1 cm (3 in), more preferably in the range of 1.58 cm (0.625 in) to 1.9 cm (0.75 in).

The interval between the upstream shield 60 from the corona discharge wire 50 is preferably 0.15 cm (0.06 in) to 7.7 cm (3.0 in). The side shield may also be installed at a similar distance downstream from the corona discharge wire 50 to further limit the loss of charge from the corona discharge effect. This prevents unnecessary charges from going downstream of the desired coating wetting line.

The corona discharge wire 50 may be positioned directly below the initial wet line of the coating fluid 32 on the web 20. Movement of the web, surface tension, boundary layer effects on the first side of the web 20 and the elasticity of the coating fluid 30 may move the coating wet line downstream of the web. Because of the strong electrostatic attraction that can be achieved with the present invention, the location of the corona discharge wire 50 will determine the operating location of the coating wet line when this coating auxiliary corona discharge wire 50 is activated. Thus, the position of the corona discharge wire 50 (upstream or downstream from the initial coating wetting line) can cause corresponding movement of the contact line because the contact line tends to align with the opposing electrical charge being drawn. Preferably, the corona discharge wire 50 is disposed below 2.54 cm (1 in) downstream or upstream from the line where the initial wet line is not affected by charge.

The use of spaced corona discharge wires from the web adjacent to the wet line also aids in tangential fluid coating. A tangential coating apparatus using air bearings surrounding the electrostatic coating auxiliary corona wire is shown in FIG. 9 (using an air bearing / electrode assembly as shown in FIG. 7). The width “w” (see FIG. 7) of the channel in the air bearing 102 surrounding the corona wire is preferably 0.635 cm (0.25 in) to 1.9 cm (0.75 in) but larger or at least better. Tangential curtain coatings can generally flow coating fluids having a higher stretchable viscosity than is possible with horizontal curtain coating geometries. The tangential coating apparatus shown in FIG. 9 mitigates the change in coating curtain orientation in the wet line, and if breakage of the web 20 occurs, the corona discharge wire 50 is not easily contaminated with the coating fluid 32. It offers the advantages of additional production. Modification of the device to include continuous or intermittent movement of the corona discharge wires ensures clean wires. In addition, air flow is provided around the wire to prevent particles from adhering to the wire, which is desirable in view of long term production durability.

FIG. 10 illustrates another embodiment of a focused web charge electrostatic auxiliary coating apparatus. In this embodiment, the electrostatic charge applied to the web 20 is generated by a charge generator away from the web and then transported by a suitable medium to the second side 28 of the web 20. As with the system shown in FIG. 3, this embodiment defines the location of the coating wetting line, minimizes the air boundary layer, and increases acceptable process parameters.

In FIG. 10, the laterally extending corona discharge wires 80 are disposed in the drum 82. The corona discharge wire 80 is at least 3.0 inches away from the web 20. This drum 82 can be conductively shielded adjacent to the web 20 as done by shields 84 and 86. The shields 84 and 86 are grounded or rise to a desired potential. The shields 84, 86 are separated by laterally extending slots 88, and the cylindrical wall of the drum 82 is laterally extending slots generally aligned with the slots 88 ( 90). Thus, the interior of the drum 82 is open to the outside through the slots 88 and 90. The drum 82 may also cooperate with the inlet 91 for the air flow through the drum 82. The ions or electric charges 92 discharged from the corona discharge wire 80 are received in the drum 82 and can exit the drum 82 only through the slots 88 and 90 (adjacent to the top). . The web upstream edge of the slot 88 is typically aligned to be adjacent to the initial wet line 52. The charge 92 from the corona discharge wire 80 is only applied to the second side 28 of the web 20 via the slots 88, 90. There is no contact between the charge generator and the web 20. The system provides a rapid, highly focused, laterally disposed application to the web 20 even when the charge 92 is generated away from the web 20 without any contact between the charge generator and the web 20. Will be created. Although a drum is shown, other geometries for the application of remotely generated charges, such as rectangular or triangular structures in which current is supplied by ion blowers or charged wires, are also contemplated.

Another embodiment of an electrostatic auxiliary coating apparatus is shown in FIG. 11, which shows another means for providing electrical charge at a location remote from the coating station 24. The laterally extending electrical charge applicator (such as corona discharge wire 130) is spaced upstream from the coating station 24, preferably on the first side 26 of the web 20. have. The corona discharge wire 130 (or other suitable electrode) is connected to electrical charges on the first side 26 of the web 20 at the charge application station 134 disposed longitudinally upstream from the coating station 24. 132) is applied. In this system, the grounded surface or plate 136 is aligned along and away from the second side 28 of the web 20 upstream from the coating station 24. Corona wire 130 may be located at a point on grounded plate 136 (not shown) or further upstream from tip 137 of grounded plate 136. The rear end 138 of the exposed grounded plate 136 terminates its extension in the substantially upstream web in the initial lateral coating wetting line 52. The position of the trailing edge 138 will form a wet line over much of the static electricity as it is activated. Preferably, the trailing edge 138 is in one side of the initial wet line. Plate 136 may extend downstream the web past the initial wet line as long as it is effectively shielded to form the trailing edge of the plate. Corona discharge wire 130 applies electrical charge 132 to first side 26 of web 20. The electrostatic attraction of charge on the web 20 directed to the plate 136 is such that the trailing edge 138 of the plate 136, in particular, until the charge 132 is closer to the ground fluid 32 than the ground plate 136. The attraction of charge 132 to ground coating fluid 32 is greater (due to the proximity of the plate towards the web). At this point, the ground fluid 32 is then attracted to the charge 132 in the web 20 and is electrostatic in the formation of the wet line in a highly focused manner in accordance with the present invention and its additional advantages as described above. Will be assisted. The upstream web electrostatic charge 132 is " masked " or near the trailing end 138 of the grounded plate 136, at which point the electrostatic charge 130 on the web 20 is in accordance with the principles of the present invention. Thus an attractive force on the coating fluid 32 imparts forcelessness to the coating fluid 32 up to an effective (ie attractive) charge on the coating fluid 32 to electrostatically assist in forming the wet line. . In addition, if plate 136 is well grounded, it may be sufficient to provide a plate or surface with a slightly elevated potential, provided that the electrical charge on the helpless web until the electrical charge reaches the coating fluid contact line. As long as it is used for the purpose of providing a charge deposit. Preferably, the potential of the plate is electrically opposite to the potential of charge 132. Additionally, although FIG. 11 illustrates the use of corona discharge wire 130 to carry charge 132 to first side 26 of web 20, charge may be applied to the web by any suitable charge transport means. May even be deposited on the second side 28 of the web 20. Regardless of how the web 20 is charged, the present invention substantially makes the charge effective for the purpose of providing electrostatic attraction to the fluid wet line and only downstream of the web.

Relative coating flows were performed (using glycerin as coating fluid) to demonstrate the effectiveness and performance of charge shielding to create a more focused magnetic field. The system used was similar to the system of FIG. 11 except that the step of precharging the web was done on an idle roll upstream of the web of the coating station. The clearance between the web charged wire and a 7.62 cm (3 in) diameter idle roll was about 1.8 cm (0.7 in). The grounded plate was made of aluminum, and the length of the surface facing the web was 10.8 cm (4.25 in) and the width was 30.5 cm (12 in). The gap between the grounded plate and the web at the coating station was about 0.32 cm (0.125 in). Plate edges were covered with 3M Type 33 electrical tape to prevent corona discharge from the edges of the plates. The die position is adjusted at the trailing edge coated with the tape of the grounded plate without static and static webs such that a curtain of coating fluid falling vertically contacts the web at the leading edge of the tape. The gap between the web and the die was 1.43 cm (0.56 in). The polyester web was made to have a thickness of 0.00356 cm (0.0014 in) and a width of 30.48 cm (12 in). The die was a slide curtain die having a coating width of 25.4 cm (10 in) and a 0.076 cm (0.030 in) die slot thickness. The coating fluid was Milsolv ^™ glycerin (99.7% purity) commercially available from Minnesota Corporation. The height of the curtain was set to 1.9 cm (0.75 in). The measured viscosity of the coating fluid was about 1060 centipoise and the surface tension thereof was about 46 dyn / cm. The flow rate of glycerin was set to obtain a wet coating thickness of 51 microns (0.002 in) at a web speed of 30.5 m / min (100 ft / min).

At 1.53 m / min (5 ft / min), the wet line itself, without static electricity, is aligned about 0.9 cm (2.3 cm) downstream of the web in the vertical curtain position with a large amount of air entrained. Higher speeds further move the contact line downstream of the web, causing curtain failure. By electrostatically precharging the web at 12 kilovolts without a charge shielding plate, the wet line moves upstream of the web but becomes very nonlinear, with a space between the ribs of about 2.5 to 5 cm (1 to 2 inches). You will have large, unstable lips. The lip extends about 0.64 cm (0.25 in) into the upstream web in a vertical position and about 1.27 cm (0.5 in) into the downstream web, giving about ± 0.97 cm (0.38 in) of linearity. The lower applied voltage moves the wet line to the downstream web while the higher applied voltage moves the contact line to the more upstream web, creating a more unsafe wet line. Increasing the web speed causes greater instability and curtain breakage.

Although using the same system to precharge the web, substantial improvements have been made by using a grounded plate to shield the incoming web upstream charge. By precharging the same 12 kilovolt upstream web, the wet line showed safety at a web speed of 1.53 m / min (5 ft / min) with a linearity of ± 0.32 cm (0.125 in) at approximately a vertical position. Further increasing the voltage did not move the wet line upwards, resulting in increased linearity. This system also increased web speed. At 24.4 m / min (80 ft / min), the wet line was stable at approximately vertical position with a visual linearity of about ± 0.08 cm (1/32 in) at 20 kilovolts. At this rate entrained air of less than about 0.127 cm (0.050 in) diameter was noticed.

For the purpose of comparison, a system as shown in FIG. 3 was used. This system was performed in the same manner as the test described above with the curtain height of about 1.9 cm (0.75 in), except that the web was not precharged or grounded. With a voltage of 12 kilovolts applied to the electrode (corona discharge wire) and the speed of the web at 1.53 m / min (5 ft / min), the wet line is at 0.32 cm (0.125 in) downstream of the web in a vertical position and entrained in air. It is linear and stable without. At both 15 and 20 kilovolts, the wet line position was vertical (just above the wire). The web speed was then increased from 20 kilovolts to 30.48 m / min (100 ft / min), and the wet line had a linear, safe wet line and was maintained in a vertical position without visual air incorporation. The measurement of the wet line position and the linearity of the contact line were generally evaluated visually.

These tests showed that the systems of FIGS. 3 and 11 can focus magnetic fields to produce linear and stable wet lines and to allow higher coating speeds. In addition, it can be seen that the system of FIG. 3 is designed to have a more aggressive and wider operating window. The system shown in FIG. 11 may function requiring less aggressive electrostatic assistance.

Shielding the charge is another way to create a more focused magnetic field. Many other methods may also be implemented, including applying magnetic field formation techniques using a counter-magnetic or charge source or any system that forms a magnetic field.

3, 6, 9, 10 and 11 show some variations of the device for applying an electrical charge to the second side of the web at the coating station. Numerous other devices for achieving the improved process operation of the present invention will become apparent to those skilled in the art within the spirit and scope of the present invention. A major advantage of generating electrical resistance at a location remote from the coating station and then transferring its charge through the fluid medium (air, etc.) to the web is to simplify the structure to facilitate maintenance and manipulation. This electrical charge generator does not need to be adjacent to the coating fluid applicator and even need not be at the coating station. Moreover, if the web breaks, contamination of the electrical charge generator by the coating fluid can be minimized or prevented. This advantage leads to saving of operating time and improvement of productivity.

Various changes and modifications can be made in the present invention without departing from the spirit and scope of the invention. For example, any method can be used to generate a focused web charge field. Additionally, as noted above, numerous coating processes (including roll coating) may be advantageous in more concentrated electrostatic fields. For example, in a kiss coating, the magnetic field focused on the initial wetting line can improve aggressiveness, wettability, and process stability.

Energy to form coating discontinuously laterally to coat only a particular web downstream strip of coating fluid onto the web, or to start coating in any region to create an isolated region of the coating fluid or a pattern of coating fluid on the web May be supplied or may not be energized to stop the coating in any area. To produce non-linear contact lines and non-uniform coatings, for example, a laterally non-linear corona source can be used to form the electrostatic field non-linearly. Thus, if the electrode has a curvature downstream of the web in a particular region that is laterally disposed, the coating in that region may be thicker compared to the region adjacent thereto. All citations are incorporated herein by reference.

Claims (21)

A method of applying a fluid coating onto a substrate having a first surface on a first side and a second surface on a second side, Providing longitudinal relative motion between the substrate and the fluid coating station; Forming a fluid wetting line by introducing a coating fluid stream onto the first surface of the substrate at an angle of 0 degrees to 180 degrees along the laterally disposed fluid-substrate contact region at the coating station; Generating an electrical force on the fluid from the focused electric field resulting from the electrical charge on the second side of the substrate Wherein the electrical force is substantially effective in and downstream of the fluid wetting line. A method of applying a fluid coating onto a substrate having a first surface and a second surface, Providing longitudinal relative motion between the substrate and the fluid coating station; Forming a fluid wetting line by introducing a coating fluid stream onto the first surface of the substrate at an angle of 0 degrees to 180 degrees along the laterally disposed fluid-substrate contact region at the coating station; Exposing the effective electrostatic charge on the substrate to a fluid at only a predetermined location on the substrate Wherein the predetermined location is substantially in and downstream of the fluid wetting line. A method of applying a fluid coating onto a substrate having a first side and a second side, Providing longitudinal relative motion between the substrate and the fluid coating station; Forming a fluid wetting line by introducing a coating fluid stream onto the first side of the substrate along a laterally disposed fluid-substrate contact region at the coating station; Drawing fluid to the first side of the substrate by an electric force from an effective electric field generated at a location on the second side of the substrate Wherein the predetermined location is substantially in and downstream of the fluid wetting line. A method of applying a fluid coating onto a substrate having a first surface and a second surface, Providing longitudinal relative motion between the substrate and the fluid coating station; Forming a fluid wetting line by introducing a coating fluid stream onto the first side of the substrate at an angle of 0 degrees to 180 degrees along the laterally disposed fluid-substrate contact region at the coating station; Forming a charge as a first charge at a predetermined position away from the substrate; Moving the first charge from the remote predetermined location to a portion of the second surface of the substrate so as to be adjacent to the second surface of the substrate in the fluid-substrate contact region; Thereafter, applying the first charge to the second surface of the substrate to generate an electrical force that is substantially at and downstream of the fluid wet line. How to include. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

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