EP0563308B1 - Verbesserungen bei oder im zusammenhang mit der beschichtung - Google Patents

Verbesserungen bei oder im zusammenhang mit der beschichtung Download PDF

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Publication number
EP0563308B1
EP0563308B1 EP92904009A EP92904009A EP0563308B1 EP 0563308 B1 EP0563308 B1 EP 0563308B1 EP 92904009 A EP92904009 A EP 92904009A EP 92904009 A EP92904009 A EP 92904009A EP 0563308 B1 EP0563308 B1 EP 0563308B1
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EP
European Patent Office
Prior art keywords
curtain
support
coating
sheet
plane
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.)
Expired - Lifetime
Application number
EP92904009A
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English (en)
French (fr)
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EP0563308A1 (de
Inventor
Terence Desmond Blake
Kenneth J. Ruschak
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Kodak Ltd
Eastman Kodak Co
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Kodak Ltd
Eastman Kodak Co
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Publication of EP0563308A1 publication Critical patent/EP0563308A1/de
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05C—APPARATUS FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05C5/00—Apparatus in which liquid or other fluent material is projected, poured or allowed to flow on to the surface of the work
    • B05C5/007—Slide-hopper coaters, i.e. apparatus in which the liquid or other fluent material flows freely on an inclined surface before contacting the work
    • B05C5/008—Slide-hopper curtain coaters
    • 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
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05C—APPARATUS FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05C9/00—Apparatus or plant for applying liquid or other fluent material to surfaces by means not covered by any preceding group, or in which the means of applying the liquid or other fluent material is not important
    • B05C9/06—Apparatus or plant for applying liquid or other fluent material to surfaces by means not covered by any preceding group, or in which the means of applying the liquid or other fluent material is not important for applying two different liquids or other fluent materials, or the same liquid or other fluent material twice, to the same side of the work
    • 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
    • G03C2001/7407—Specific angles in extrusion head-slide hopper
    • 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
    • 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
    • G03C2001/747—Lateral edge guiding means for curtain coating
    • 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
    • G03C2001/7474—Impingement conditions curtain onto support

Definitions

  • This invention relates to coating supports, such as continuous webs or sheets, with liquid composition.
  • the apparatus therein described includes a hopper for forming a free-falling curtain of liquid photographic coating compositions.
  • the curtain includes a plurality of discrete contiguous layers.
  • the liquid flows down an upwardly facing inclined surface of the hopper and off a lip, at the lower end of the surface, to form a curtain.
  • the liquid may be extruded from one or more slit-like orifices in a downwardly facing portion of a hopper, to form a curtain.
  • the liquid in the curtain impinges on a continuous support, in the form of a web, where it is trained about a backing roll, and forms a coating, comprising discrete layers, on the web.
  • the sheet may be regarded as a curtain because its velocity just prior to impingement on the support is predominantly due to gravity.
  • the liquid composition may have free fallen from the lip of a slide hopper.
  • the support is moved downwardly through the coating zone and the plane of the curtain just prior to impingement is substantially vertical.
  • the plane of the support at the line of impingement of the curtain on the support is inclined at (90 - A)° to the horizontal. If the support is trained about a backing roller in the coating zone, it is the tangent to the support at the line of impingement which is inclined at (90 - A)° to the horizontal.
  • the sheet of liquid processing composition is formed by extrusion from a device, for example, an extrusion die, capable of forming a sheet of the liquid composition moving at such a velocity that just prior to impingement on the support it has a speed of at least about 200 cm per sec.
  • a device for example, an extrusion die
  • the positioning of the sheet and of the support may be independent of the direction of gravity.
  • the sheet may be horizontal or vertical with the liquid composition flowing upwards towards the support.
  • the height of the curtain is preferably in excess of 20 cm, this being the height necessary to give a velocity of about 200 cm per sec at impingement.
  • the line at which the impingement occurs is at (90-A)°, i.e. 30° to 60°, beyond top dead center.
  • the angle (90-A)° is termed the application angle.
  • Top dead center is the line on the support which is in a vertical plane which includes the axis of the backing roll about which the support is trained.
  • “beyond” means on the side of top dead center to which the support moves after passing through top dead center.
  • Figure 11 is a schematic view which illustrates the text which says that it is not necessary that the plane of the free-falling curtain be oriented to intersect the axis of the supporting roll (i.e. impinge at top dead center) in order to satisfactorily coat a web passing therearound. It is further stated in the aforesaid patents that, if the web to be coated is directed to and from the supporting roll so as to leave sufficient supported area of the web accessible, then the free-falling curtain can be directed on or off axis of the roll.
  • the free-falling curtain should not be so far off axis that the direction of travel of the web at impingement is so far from horizontal as to detrimentally affect the coating operation.
  • curtain positions forward of top dead center and curtain positions backward of top dead center.
  • the Greiller patents are merely saying that the coating point does not have to be at top dead center. They do not teach that there is any advantage in having a coating point (the location where the curtain impinges on the support) other than top dead center. Specifically, they do not teach the importance of optimizing the position of the wetting line in maximizing speed and maintaining the uniformity of the coating.
  • the curtain must usually be positioned significantly beyond top dead center to optimize wetting line position.
  • puddling Another problem encountered with the prior art is often referred to as puddling.
  • the liquid composition has a tendency to move against the direction of travel of the support, until it is entrained by viscous shearing generated by the support.
  • impingement speed is high, the flowrate is high and/or viscosity is low, a "heel" develops at the foot of the curtain.
  • the heel may contain an an eddy which can trap air bubbles or debris. Such trapped bubbles or debris can produce streaks or lines in the coating.
  • the heel may oscillate and such oscillations produce non-uniformities in the coating.
  • the heel may promote mixing or a degree of mutual displacement of the materials in the different layers.
  • application angles of 30° or more are employed to control wetting line position, puddling is prevented. It can be appreciated that at such increased application angles, the direction of motion of the curtain at the time of impingement on the support, is closer to the direction of movement of the support, and hence there is less tendency for the liquid composition to move upstream on the support.
  • a short curtain is defined as 0.5 to 50 millimeters.
  • the short curtain is to impinge on the web at an angle of 30° to 90° past top dead center. It has been found that following the teachings of that earlier published patent application is detrimental to the problem of air entrainment.
  • the height of the curtain should be so selected that the free-falling curtain has adequate momentum at impingement to effectively penetrate or displace the air barrier and wet the moving support
  • increasing the curtain height may, in actual practice, result in little gain in coating speed before the onset of the above-mentioned problems associated with air being entrained between the support and the coating, unless the support is inclined downwardly as is achieved if the curtain impinges on the support on a line in the range of 30° to 60° beyond top dead center.
  • coating speeds may be increased by 50% or more by adopting the present invention, namely by having a curtain height of at least 20 cm and a coating point, for example, in the range of 30° to 60° beyond top dead center.
  • a curtain height of at least 20 cm and a coating point for example, in the range of 30° to 60° beyond top dead center.
  • the support is inclined at 30° to the horizontal.
  • the support is inclined at 60° when the coating point is at 60° beyond top dead center.
  • the liquid When the curtain impinges on the support, the liquid has a tendency to move both with and against the direction of movement of the support.
  • the motion of the support is transmitted to the liquid through viscous shearing. More specifically, a viscous boundary layer begins at the wetting line and extends to the downstream surface of the curtain.
  • the apparatus includes a coater including a backing roll 12 about which is trained support to be coated in the form of a web 14.
  • the web 14 is continuous.
  • the web may be formed of, for example, cellulose acetate, in known manner.
  • the roll 12 has an axis 16 of rotation which is very accurately at the geometric center of its very accurate circular cylindrical surface 18.
  • Preferably the axis 16 of rotation is horizontal.
  • a hopper 20, of known form, has a slide surface 22 to which extend a plurality of slots, only the uppermost one of which is visible and is designated 24.
  • liquid compositions are supplied to cavities within the hopper which communicate with the respective slots.
  • the various liquid compositions are supplied through conduits 26 in which are located pulsation dampeners 28.
  • the slide surface 22 is inclined so that liquids issuing from the slots flow down the slide surface forming a composite layer formed of a plurality of, in the illustrated example three, discrete layers.
  • the slide surface 22 has a lip 30 from which the composite layer falls cleanly into a sheet, in the form of a curtain 32, in known manner.
  • the curtain is guided by known vertical edge guides 34.
  • the lip 30 of the hopper 20 is parallel to the axis 16 of rotation of the backing roll 12.
  • the lip is so located that the curtain 32 falling vertically will impinge on the web 14 along a line 35 which is in a plane 36 containing the axis 16, at an angle (90-A)° in the range of 30° to 60°, in accordance with the present invention (see Fig. 2).
  • the plane 38 includes top dead center 40.
  • the roll 12 is rotating clockwise as seen in Figs. 1 and 2 so that the web 14 is moving upwards towards the left hand side of the roll 12 and is moving downwards through the coating point and away from the right hand side of the roll, having been coated with liquids from the curtain 32.
  • the coating point i.e. the line 35
  • (90 - A)° is termed the application angle.
  • the tangent to the web is inclined at (90 - A)° to the horizontal at the coating point.
  • Each of the pulsation dampeners 28 comprises a chamber closed in part by a diaphragm on the other side of which is a second chamber filled with gas.
  • the second chamber is in communication with a third chamber through a passage which presents a resistance to gas flow.
  • the first chamber is open to the conduit 26 so that hydraulic pressure pulsations which may occur in the delivery of the coating composition are applied to the diaphragm and are absorbed by the diaphragm and the gas in the second chamber.
  • the resistance which is selectable, in the passage from the second to the third chamber selectively dampens the system.
  • a baffle device 41 for applying slight suction over the side of the support which is to be coated, just before it reaches the coating point.
  • the application of suction at this location serves, in known fashion, to reduce the amount of air which is carried along with the fast moving support. The removal of such air assists in maintaining the curtain in its desired plane without air-motion-induced excursion out of that plane.
  • Fig. 3 there is illustrated a line 43 which is parallel to the plane of the support 14 at the line of impingement of the curtain 32 on the support. Also illustrated is a line 45 which is parallel to the plane of the curtain just prior to impingement on the support. The angle between the lines 43 and 45 is designated A. It will be observed that it is between the curtain and the uncoated support.
  • the curtain 32 has an upstream surface 42 and a downstream surface 44.
  • the line at which the liquids from the curtain actually wet the web 14, termed the wetting line, is indicated at 46 in Fig. 3. It will be seen that in the condition illustrated in Fig. 3 the wetting line 46 is just downstream of the plane of the upstream surface 42 of the curtain.
  • Liquid in the boundary layer 47 is entrained by the web through the action of viscosity and thereby comes to move in the same direction as the web.
  • the boundary layer is bounded approximately by a broken line 48 and, of course, by the surface of the web 14.
  • the plane of the downstream surface 44 of the curtain 32 is shown in Fig. 3 by a broken line 50. Downstream of the downstream end of the boundary layer, the velocity profile of the boundary layer gradually relaxes to the uniform velocity of the web 14.
  • the length of the boundary layer determines the position of the wetting line relative to the position of the downstream surface of the curtain.
  • the wetting line is remote from the curtain and the momentum of liquid in the curtain cannot be effective at promoting dynamic wetting and excluding air.
  • the wetting line is again not positioned to benefit to the maximum from the momentum in the curtain.
  • the momentum in the curtain has the most effect on avoiding air entrainment when the wetting line 46 is located approximately in the plane of the upstream surface 42 of the curtain 32.
  • the relative wetting line position quotient is the ratio of the distance L between the wetting line 46 and the intersection of the plane of the downstream surface 44 of the curtain 32 with the surface of the web 14, to the distance between the planes of the upstream and downstream surfaces of the curtain just above the region where the thickness of the curtain is affected by the impingement, measured in a plane parallel to the surface of the web.
  • the boundary layer length L can be measured by direct observation in some cases, but, more practically, can be estimated using boundary layer theory.
  • boundary layer theory reference is directed to Boundary-Layer Theory (seventh edition), H. Schlichting, McGraw-Hill, New York 1979, and to Boundary-Layer Behaviour on Continuous Solid Surfaces, B. C. Sakiadis, AIChE Journal, 1961, volume 7, page 26.
  • U the acceleration due to gravity
  • H curtain height, that is, the height of the lip 30 of the hopper 20 above the web 14, measured in the curtain 32.
  • the contribution to U due to the speed of the liquid as it left the hopper lip and entered the curtain can be neglected for curtains of greater than about 5 cm height, that is, for all curtains for which the present invention is concerned.
  • H is the effective height of the curtain, that is, the height of that curtain which, free-falling with zero initial vertical velocity, would create the same curtain velocity just prior to impact.
  • this representative shear rate in curtain coating can be 100,000 sec ⁇ 1, or more. More accurate means of calculation of the value of L can, of course, be used, but the above formulae are simple and useful in the practice of the invention. Also, they are readily generalized for the case where the different coating compositions in the different layers forming the curtain have significantly different viscosities. As is known, it is generally preferable for curtain coating uniformity that the viscosities of the different layers be substantially the same and that they be relatively high.
  • the speed at which air entrainment problems cease is generally less than that speed at which the problems started.
  • the term highest practical coating speed will be used herein for that speed which is just below the speed at which air entrainment problems cease as coating speed is decreased.
  • the highest practical coating speed depends on the total flowrate. In particular, there is a flowrate at which the highest practical coating speed is maximized, and this maximum highest practical coating speed will be referred to herein as S m .
  • S m the maximum highest practical coating speed.
  • the wet coating thickness desired is greater or smaller, then the highest practical coating speed for coating that thickness may be substantially less than S m .
  • the wet coating thickness corresponding to S m is in the neighborhood of 30 »m.
  • high surface tension is meant values of surface tension in the curtain just above the point of impingement in the range of approximately 60 to 70 dynes/cm, which includes aqueous solutions without added surfactant, such as aqueous solutions of gelatin.
  • low surface tension is meant values of the surface tension in the curtain just above the point of impingement in the range of approximatedly 24 to 40 dynes/cm, which includes aqueous solution to which a surfactant has been added, such as aqueous solutions of gelatin containing surfactants as commonly practiced in the coating of photographic products. While it is of greatest advantage to operate at the value of l m given by this expression, it has been found that highest practical coating speed will be at least 70% of S m when l m is in the range of 0.8 to 2.0 of the optimum value.
  • S m decreases as the application angle (90 - A)° is increased. More specifically, S m has been found to depend on the quantity curtain speed multiplied by the cosine of the application angle (90 - A)°, i.e. U x sin A. Away from the origin, S m depends on (U x sin A) raised to a power which is approximately 0.8.
  • curtain height can be increased to increase impingement speed U and partially or fully offset the effect due to increase in application angle (90 - A)°, i.e. decrease in angle A. It is for this reason that high curtains are preferred in the practice of coating at application angles significantly greater than 0° (i.e. values of A significantly less than 90°).
  • the relative wetting line position quotient is sensitive to the viscosity of the liquids being coated onto the web and to the angle of the web at the coating point.
  • wet coating thicknesses greater than 30 »m as is the case in many photographic products, application angles substantially larger than zero degrees have been found to be advantageous. It has been found that the thicker the coating and the lower the viscosity of the coating liquids, the greater is the optimum application angle for highest practical coating speed.
  • An advantage of calculating the relative wetting line position quotient is that, for any coating thickness and curtain speed, it leads to an application angle which is close to the optimum.
  • the method above of estimating the quotient in order to derive an application angle applies when the rheology of the coating liquids is Newtonian or pseudoplastic. For some coating compositions, it may be necessary to measure and include also other rheological effects. Some coating supports have substantial surface roughness and cannot be considered hydrodynamically flat.
  • the highest practical coating speed, as defined above, is considered, according to good practice, to be the practical speed limit and is the speed recorded and plotted.
  • the experiment was carried out at an application angle of 0° (i.e. an angle A of 90°) for curtain heights (c.h.) of 2, 6, 10 and 25 centimeters and at an application angle of 45° (i.e. an angle A of 45°) for curtain heights of 10 and 25 centimeters.
  • Fig. 4 The data for the 0° application angle experiments are shown in Fig. 4, wherein coating speed in cm/sec is plotted against flowrate of the coating liquid in cc/sec per centimeter of coated width.
  • the curves for the 10 cm and 25 cm heights have been truncated at approximately 5 cu cm per sec per cm of width above which the highest practical coating speed rapidly falls.
  • Also included in the graph are straight lines passing through the origin which represent wet coating thicknesses of 25, 50, 100 and 150 microns, respectively.
  • the data may also be used in the calculation of the relative wetting line position quotient.
  • Fig. 6 shows plots of relative wetting line position as a function of the ratio of actual highest practical coating speed S to the maximum highest practical coating speed S m .
  • S m maximum highest practical coating speed
  • the highest practical coating speed for each flow rate is normalized by dividing the speed for each data point on the curve by the value of S m for that curve.
  • the relative wetting line position quotient is calculated for each data point.
  • the viscosity of the gelatin solution is measured as a function of shear, on a rheometer.
  • the six plots define a master curve, within scatter which is reasonable for this type of measurement.
  • the relative wetting line position quotients corresponding to the greatest speed for each curve are plotted in Fig. 7 against the maximum highest practical coating speed for that curve. It is apparent that the relative wetting line position quotient corresponding to the maximum highest practical coating speed is about 0.63 in each case.
  • the maximum highest practical coating speed varies with the component (U sin A) of curtain impingement speed U, perpendicular to the web, as shown in Fig. 8.
  • the optimum application angle (90-A)° can be estimated for particular coating conditions.
  • the optimum coating thickness and corresponding maximum highest practical coating speed are both plotted against the application angle for the curtain height of 25 cm. It will be observed that above about 30 »m wet coverage thickness the optimum application angle is substantially different from 0° and that the optimum application angle increases with coating thickness. For 150 »m thickness, which is within the range of practical interest in the photographic industry, the optimum application angle is about 60° (i.e. the optimum value of angle A is 30°).
  • a suitable surfactant was added to reduce the surface tension to an estimated 31 mN/m.
  • Surfactants are often present in photographic coating compositions and are known to be useful in the practice of curtain coating.
  • Fig. 10 is a plot of flowrate per centimeter of curtain width against highest practical coating speed.
  • Curtain heights were 12 and 25 cm at application angles (90 - A)° of 0 and 45°.
  • the advantages of the present invention are apparent for coating thicknesses exceeding about 25 »m.
  • Increasing curtain height to 25 centimeters, or increasing application angle to 45° at the 12 centimeter height gives only slightly higher speeds.
  • Fig. 11 is a plot of 1 m , the best relative wetting line position quotient attainable, against 1/V a , the reciprocal of the apparent Newtonian viscosity, for aqueous solutions of polymers to which no surfactants have been added (high-surface-tension case).
  • the values are shown for fourteen different pseudoplastic materials, whose characteristics and coating parameters are given in the Table which is Fig. 12.
  • Fig. 13 is a similar plot for aqueous gelatin solutions to which surfactant has been added to lower the surface tension in the curtain (low-surface-tension case). Material properties and coating parameters are listed in the Table which is Fig. 14. In each case the base is polyethylene terephthalate, gelatin subbed unless otherwise indicated.
  • Two gelatin layers were curtain coated simultaneously at a speed of 200 cm/sec and with a curtain height of 25 centimeters.
  • the top layer had a wet thickness of 60 »m and a viscosity of 0.035 Pas [35 centipoise], while the bottom layer had a wet thickness of 40 »m and a viscosity of 0.003 Pas [3 centipoise].
  • viscosities considerably higher than 0.003 Pas [3 centipoise] are preferable in practice, this is not always possible in light of, for example, solubility constraints on components, or the rate at which a crosslinking agent added to the composition reacts with gelatin.
  • a suitable surfactant was added to the layers to reduce their surface tensions to an estimated 31 m/Nm.
  • Curtain height was 25 centimeters.
  • the top and middle layers comprised aqueous gelatin solutions having viscosities of 0.063 Pas [63 centipoise] and 0.067 Pas [67 centipoise], respectively, and a combined total wet thickness of 100 »m.
  • the bottom layer was demineralized water at 42.5°C with viscosity 0.00062 Pas [0.62 centipoise] and wet thickness 3.5 »m. Such a water layer may be used, for example, to obtain increased coating speed without air entrainment, or to deliver a hardening agent or other chemical which reacts with gelatin.
  • the top and bottom layers contained suitable surfactants to promote spreading on the middle layer, and the resulting surface tensions were 24.4 mN/m for the top layer, 46.3 mN/m for the middle layer, and 19.3 mN/m for the bottom layer. Because a relatively thin and low viscosity layer is difficult to deliver as a bottom layer on a slide surface without waves and other instabilities developing in the layers, the arrangement of the hopper relative to direction of web movement was such that the bottom layer (in the sense of the layer which contacts the web) was the top layer on the slide surface, an arrangement which gives more latitude for slide instabilities. Although it is preferable that the layers have similar high viscosities to promote uniform flow on the slide and overall coating quality, this is not always consistent with other objectives.
  • the curtain may be created in other ways.
  • an extrusion hopper with its orifice facing downwardly may extrude a curtain of liquid.
  • the curtain may have a starting velocity substantially other than zero at the top of the curtain, but does not have to. It is for such a reason that reference is made herein to the curtain having a velocity equal to that attained by a curtain free-falling from a specified height and in such an expression the curtain is assumed to have a starting velocity of substantially zero.
  • the curtain height need be less than that of a curtain created by liquid falling from the lip of a slide hopper, in order for the velocity at impact to be the same in the two cases.
  • the angle A has been considered above, it being described as the angle included between the plane of the sheet of liquid composition just prior to impingement on the support and the tangent to the support at the line of impingement, the angle being measured at the side of the sheet facing the uncoated support. It has also been pointed out, with reference to Figure 2, that (90 - A)° is the angle of inclination of the plane 36 to the plane 38 and has been termed the application angle in those embodiments which include a curtain and a backing roll.
  • the liquid composition is given most of its speed just prior to impingement on the support, by gravity. This is because the liquid composition, when it falls off the lip of the slide hopper, has only a small speed.
  • the present invention may be embodied in systems in which the speed of the liquid composition just prior to impingement on the support is entirely or very largely due to the velocity it is given in exiting an extrusion die.
  • the liquid composition may be in the form of a sheet which is directed horizontally or even vertically upwards or at other inclinations to the vertical.
  • the liquid composition in such embodiments, when moving through space towards the support, should be termed a sheet rather than a curtain.
  • the term sheet may be regarded as including the more specific term curtain.
  • the distance between the apparatus and the support may be quite short or, indeed, long, because the distance is not determinative of the speed.
  • gravity does affect velocity during the flight of the liquid composition between the apparatus projecting it and the support, and such effect on both the direction and speed aspects of the velocity should be taken into account.
  • Fig. 15 diagrammatically represents a backing roll 12′ having an axis of rotation 16′.
  • a support, in the form of a web 14′ is trained about the backing roll 12′ which is rotating counterclockwise as seen in Fig. 15 and as is indicated by the arrow.
  • An extrusion hopper 130 has a slot 132 from which is directed a sheet 134 of liquid composition at a velocity in excess of 200 cm per sec.
  • the extrusion slot 132 is parallel to the axis of rotation 16′ of the backing roll 12′.
  • the distance between the mouth of the extrusion hopper slot and the support may be quite small, of the order of 1 cm or less.
  • the plane of the sheet 134 just prior to impingement of the liquid composition on the support is indicated by the line 45′.
  • a plane tangential to the support at the line of impingement of the liquid composition on the support is indicated by the line 43′ in Fig. 15.
  • the above-discussed angle A is, again, the angle between the planes 43′ and 45′, just as it is the angle between the planes 43 and 45 in Fig. 3. It will be recognized that in the immediately preceding description relating to Fig. 15, there is no implicit reference to the direction of gravity.
  • liquid composition as used herein is to be understood as including a plurality of compositions contained in a plurality of layers.
  • the viscosities of such multiple layers may be the same or different.
  • liquid coated in accordance with the present invention may be Newtonian or non-Newtonian, with non-Newtonian including, but not limited to, pseudoplastic liquids.

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Claims (13)

  1. Verfahren zum Beschichten eines Trägermaterials mit einer flüssigen Masse mit folgenden Schritten:
    - Bewegen des Trägers durch eine Beschichtungszone;
    - Erzeugen einer aus der flüssigen Masse bestehenden und sich fortbewegenden Bahn;
    - Positionieren von Bahn und Trägermaterial derart, daß die Bahn auf das in der Beschichtungszone befindliche Trägermaterial in einem spitzen Winkel A zwischen 30 und 60° auftrifft;
    dadurch gekennzeichnet, daß der zwischen der Ebene der Bahn kurz vor deren Auftreffen und einer an der Auftrefflinie der Bahn tangential zum Trägermaterial verlaufenden Ebene gebildete Winkel A aus der Gleichung l = L/[W/sin A]
    Figure imgb0013
     errechnet wird, wobei
    l der Bereich zwischen 0,8 und 2 des durch die Beziehung l = 0,25 + K/Va
    Figure imgb0014
     vorgegebenen Werts l ist, wobei
    Va   die momentane Viskosität in Pas,
    L   den seitlichen Abstand der Benetzungslinie zur Ebene der Bahnvorderseite,
    W   die Bahndicke kurz vor deren Auftreffen auf dem Trägermaterial darstellen, und
    K   bei hoher Oberflächenspannung 0,015 und bei niedriger Oberflächenspannung 0,010 ist,
    mit der Vorgabe, daß die Bahn kurz vor ihrem Auftreffen auf dem Trägermaterial mit einer Geschwindigkeit von mindestens 2 m/s bewegt.
  2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das Trägermaterial nach unten durch die Beschichtungszone abwärtsbewegt wird, und daß der Schritt zur Erzeugung einer bewegten Bahn durch Bilden eines aus der flüssigen Masse bestehenden freifallenden Vorhangs erfolgt, wobei der zwischen der Ebene der Bahn kurz vor deren Auftreffen und einer an der Auftrefflinie der Bahn tangential zum Trägermaterial verlaufenden Ebene gebildete Winkel der spitze Winkel A ist.
  3. Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß das Trägermaterial eine Bahnform besitzt.
  4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, daß die Trägerbahn um eine drehbar um eine Horizontalachse angeordnete Stützrolle geführt wird, der Vorhang so ausgerichtet ist, daß seine Ebene parallel zur Drehachse der Stützrolle verläuft und auf dem auf der Stützrolle befindlichen Trägerbahnabschnitt entlang einer Linie auftrifft, die in einer die Achse der Stützrolle einschließenden Ebene liegt, welche sich in einem Winkel von (90 - A)° zu der die Drehachse der Stützrolle einschließenden senkrechten Ebene erstreckt, wobei die Linie an der Seite der senkrechten Ebene verläuft, zu der sich die Trägerbahn nach ihrem Durchgang durch die senkrechte Ebene hinbewegt.
  5. Verfahren nach Anspruch 4, dadurch gekennzeichnet, daß der Vorhang gebildet wird, indem die flüssige Masse so durch einen Beschichtungstrichter bewegt wird, daß sie als Bahn über die geneigte Gleitfläche des Trichters abwärtsfließt um danach von dessen Traufkante zufallen.
  6. Verfahren nach Anspruch 5, dadurch gekennzeichnet, daß der Beschichtungstrichter eine Vielzahl von Schlitzen aufweist und die flüssige Masse durch jeden der Schlitze bewegt wird, wodurch ein aus mehreren Schichten bestehender Vorhang gebildet wird.
  7. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, daß die flüssige Masse zur Bildung einer oder mehrerer Schichten für fotografische Filme oder Papiere geeignet ist.
  8. Verfahren nach Anspruch 4, gekennzeichnet durch einen Gießtrichter solcher Ausrichtung daß sein Gießschlitz parallel zur Drehachse der Stütztrolle verläuft, wobei die Masse so durch den Gießtrichter bewegt wird, daß sie aus dem Gießschlitz mit einer Geschwindigkeit austritt, die kurz vor dem Auftreffen der Bahn auf dem Trägermaterial mindestens 2 m/s beträgt.
  9. Verfahren nach Anspruch 8, dadurch gekennzeichnet, daß die Ebene der Bahn bis kurz vor deren Auftreffen auf dem Trägermaterial senkrecht verläuft.
  10. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß sich der Wert von L auf Beobachtungen stützt.
  11. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß bei einer pseudoplastischen- oder Newton'schen Flüssigkeit der Wert L aus der Gleichung L = 3s[3s + 2cos A] x RxD 20[s + 2cos A]²
    Figure imgb0015
     errechnet wird, in der
    s = S/U ist, wobei
    S   die Geschwindigkeit des Trägermaterials,
    U   die Geschwindigkeit des Vorhangs kurz vor dessen Auftreffen,
    D   die Benetzungsdicke der Bschichtung unmittelbar im Anschluß an den Vorhang, und
    R   die als R = dq/V definierte Reynoldszahl der Flüssigkeit des Vorhangs darstellen, wobei
    d   die Flüssigkeitsdichte,
    q   die gesamtvolumetrische Durchflußrate pro Einheit der Vorhangbreite, und
    V   die Newton-Viskosität oder momentane Viskosität Va im Falle einer pseudoplastischen Flüssigkeit bei einem durch [S-U cosA]/D gegebenen Scherungskoeffizienten bedeuten.
  12. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das Trägermaterial durch die Beschichtungszone abwärts bewegt wird und die Ebene der Emulsionsschicht senkrecht verläuft.
  13. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die flüssige Masse zur Bildung einer oder mehrerer Schichten für fotografische Filme oder Papiere geeignet ist.
EP92904009A 1990-12-20 1991-12-18 Verbesserungen bei oder im zusammenhang mit der beschichtung Expired - Lifetime EP0563308B1 (de)

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WOPCT/US90/07559 1990-12-20
PCT/US1990/007559 WO1992011571A1 (en) 1990-12-20 1990-12-20 Improvements in or relating to coating
PCT/US1991/009527 WO1992011572A1 (en) 1990-12-20 1991-12-18 Improvements in or relating to coating

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Cited By (1)

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EP1314485A2 (de) 2001-11-26 2003-05-28 Eastman Kodak Company Start-Vorhang-Auftragsvorrichtung

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GB9027676D0 (en) * 1990-12-20 1991-02-13 Kodak Ltd Coating processes
GB9503849D0 (en) * 1995-02-25 1995-04-19 Kodak Ltd Improvements in or relating to curtain coating
US5700524A (en) * 1996-07-30 1997-12-23 Eastman Kodak Company High speed coating starts using a shear thinning top layer
US6171658B1 (en) * 1998-02-06 2001-01-09 Eastman Kodak Company Coating method using electrostatic assist
US6099913A (en) * 1998-10-20 2000-08-08 Eastman Kodak Company Method for curtain coating at high speeds
US6103313A (en) * 1998-10-20 2000-08-15 Eastman Kodak Company Method for electrostatically assisted curtain coating at high speeds
US6368675B1 (en) 2000-04-06 2002-04-09 3M Innovative Properties Company Electrostatically assisted coating method and apparatus with focused electrode field
US6475572B2 (en) 2000-04-06 2002-11-05 3M Innovative Properties Company Electrostatically assisted coating method with focused web-borne charges
BRPI0515107B1 (pt) * 2004-09-09 2018-06-12 Avery Dennison Corporation Método e sistema de revestimento por cortina
FI117175B (fi) * 2005-01-27 2006-07-14 Metso Paper Inc Tuentajärjestely paperi-/kartonkirainan verhopäällystyksessä

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US3632374A (en) * 1968-06-03 1972-01-04 Eastman Kodak Co Method of making photographic elements
DE3424884C1 (de) * 1984-07-06 1986-02-20 Du Pont de Nemours (Deutschland) GmbH, 4000 Düsseldorf Vorrichtung zum Auftragen mindestens einer Giessschicht und Verfahren zum Betrieb dieser Vorrichtung
CN85100851B (zh) * 1985-04-01 1988-03-30 王仲钧 垂直拉帘涂布的方法

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1314485A2 (de) 2001-11-26 2003-05-28 Eastman Kodak Company Start-Vorhang-Auftragsvorrichtung

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DE69109695D1 (de) 1995-06-14
WO1992011571A1 (en) 1992-07-09
JP2619190B2 (ja) 1997-06-11
WO1992011572A1 (en) 1992-07-09
DE69109695T2 (de) 1996-01-25
EP0563308A1 (de) 1993-10-06
JPH08510679A (ja) 1996-11-12

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