MXPA97005696A - A method and apparatus for covering substrates using a neumat blade - Google Patents

Abstract

The present invention relates to a method of coating a substrate (32) with numerous coating layers, characterized in that it comprises the steps of: moving the substrate (32) along a path through a coating station; at least a first coating fluid (34) and a second coating fluid (36), wherein the first coating fluid formulation differs from the second coating fluid formulation, forming a composite layer 48 comprising at least one first coating fluid and the second coating fluid, contacting the substrate (32) with the composite layer capable of flowing (48) to interpose the first coating fluid (34) between the substance (32) and the second fluid of coating (36) for applying an excess of the second coating layer on the substrate; scraping the composite layer with a gas (52) from a gas-operated blade (54) to remove some portion of the second coating layer (36) of the substrate to produce a multi-layer composite coating on the downward coil of the gas-operated blade substrate to leave a coating comprising numerous different superimposed layers of the first and second coating fluids.

Description

ÜH METPJO AND APPARATUS FOR COATING SUBSTRATES USING A PNEUMATIC KNIFE FIELD OF THE INVENTION The invention relates to the preparation of single layer or multilayer wet coatings of 0.01 to 1000 microns by means of simultaneous coating in a single step. In particular, the invention relates to improvements in the method and apparatus for coating a substrate with a pneumatic blade. This technology is particularly useful for the waterborne coating and paper coating industries.

BACKGROUND OF THE INVENTION Frequently, the layers of different compositions must be applied to a substrate. It is common to apply a primer coating under a paint to improve adhesion. In the manufacture of photographic film, as many as twelve layers of different compositions must be applied in a different layer ratio with narrow tolerances in terms of uniformity. The use of sequential coating operations can produce numerous different overlapping layers on REF: 25216 a substrate. However, this is expensive and time-consuming and may require a large investment in the sequential coating and drying stations. The methods for simultaneously applying multilayer coatings are discussed in the book: Cohen, E. D. and Gutoff, E. B., Editors, 1992, Modern Coating and Drying Technology, chapter 4, Editorial VCH, New York. Predosed, slotted or extruded matrix coaters are described in US Patent Nos. 2,761,419 and 2,761,791 and many improvements have been made over the years. With these coaters, the surface of the continuous coil or roll to be coated is brought into contact with or very close to the matrix and numerous superposed layers are deposited. Each coating composition is dosed in the coating matrix which deposits them as layers on the continuous roll or coil. However, the uniformity of the separation with respect to the continuous roll or coil limits the quality of the coatings and the maximum operating speed is limited. Another method of simultaneous multiple layer coating is curtain coating. U.S. Patent No. 3,508,947 teaches the use of this method with the coating of photographic elements. The curtain coating uses a curtain of liquid that falls vertically in a vertical manner that hits the coil or continuous roll through the coating station. This patent teaches a method for forming the curtain from numerous different layers to obtain a multi-layered coating on the continuous coil or roll. The separation between the coating matrix and the continuous coil or roll is much greater than in the previous methods and the application speeds are substantially higher. However, this method has set gauge and speed limitations. One limitation of the curtain coating is that for any formulation, there is a minimum flow rate below which a stable curtain can not be maintained. This avoids coating in thin layers at slow and moderate speeds. Since simultaneous multi-layer sliding and curtain methods were first introduced, many refinements have been invented. However, there is still a need for an improved method of coating low speed and high speed simultaneous layers. The single layer pneumatic knife coating technology is summarized in chapter II of the book Pulp and Paper Manufacture, Volume 8; Coating, Converting, and Specialty Processes; Michael Kouris, Technical Editor, 3 / a. Edition, 1990 published by The Joint Textbook Committee of the Paper Industry, TAPPI and CPPA, Atlanta, Georgia. An additional description is found in chapter 5 of the book by Cohen and Gutoff. The pneumatic knife coating is characterized by the application of an excess of a single coating fluid composition to a continuous coil or roll followed by the removal of a portion of this fluid by a jet of gas exiting a nozzle. There is a low speed application region where a low pressure gas is used in the nozzle. The excess coating is forced against the direction of movement of the continuous roll or coil and a controlled amount passes through the gas jet into the surface of the continuous roll or coil. This technology has been used by the photographic industry. There is a region of high speed operation employed by the paper coating industry and in the cast metal coating by hot-dip steel strip manufacturers. In this case, the gas pressures and the speeds of the coil or continuous roll are high and the excess fluid is frequently atomized by the jet. The two low speed and high speed techniques are known only as single layer coating methods using a simple coating fluid composition and have been practiced for more than fifty years. Both technologies have used coating applicator matrices to apply the excess coating to the substrate before passing the gas jet. These matrices are used to roughly apply the excess, and are used to apply only a simple coating fluid composition. The conventional pneumatic knife coating method suffers in the range of applicability mainly because it covers only one layer at a time and because it has limitations of the minimum coating size. To produce thin dry coatings, the mass of solids that passes through the gas stream per unit of substrate area and left on the substrate must be low. The gas velocity, the percentage of solids and the coating viscosity are the dominant variables that control the weight of the coating. Thinner coatings can be obtained by reducing the percentage of solids, reducing the viscosity or increasing the speed of the jet. There will always be economic and physical limitations in all this. If the percentage of solids is reduced, more liquid diluent must be added, increasing both the cost and the drying time. The reduction of the viscosity requires changing the formulation and may lead to an undesirable flow of the coating after passing the stream, and before drying or solidification. Increases in jet velocity are limited by numerous practical considerations including the cost and complexity of exceeding the velocity of sound with the jet, the disorder created by the nebulization of excess coating fluid and the noise of a high velocity jet. There is a need for a more versatile multilayer coating method and a multilayer pneumatic knife coater. There is also a need for an improved pneumatic knife coater for applying a single dry layer of a coating from a composite layer fluid. And there is a need for a new method that coats thin wet coatings at low speeds (25 microns at coil or continuous roll speeds of 10 m / min) as well as at high speeds.

BRIEF DESCRIPTION OF THE INVENTION The method of coating a substrate with numerous layers of coatings includes moving the substrate along a path through the coating station. A composite layer is formed and has at least a first coating fluid and a second miscible coating fluid. The substrate is contacted with the composite layer flowing to interpose the first coating fluid between the substrate and the second coating fluid. The composite layer is scraped with a gas to remove some portion of the composite layer from the substrate. First numerous coating fluids can be used. When using numerous first coating fluids, at least two of these first coating fluids may be immiscible. The first coating fluid may be the latex and the second coating fluid may be the water. Alternatively, both coating fluids may be latices having different compositions or percentages of solids or both. A multi-layer skid coater, a curtain coater, a jet coater, a flange coater, or an extrusion die coater can be used to apply the coating fluid to the substrate, or the layers of the first and second fluids of coating can be formed sequentially. The substrate can be moved through the coating station at speeds up to 1000 m / min.

• Also, the composite layer can be placed first on a transfer surface before being transferred to the substrate. The apparatus includes a die for ejecting a first coating fluid. The matrix can be a multi-layer coating matrix.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of a coating apparatus according to the present invention. Figure 2 is a schematic view of another embodiment of the coating apparatus according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION The copending US patent application Serial No. 08 / 382,962, entitled "Method and Apparatus for Applying Thin Fluid Coatings", in the name of Wi-lliara K. Leonard et al., Describes a method of applying a liquid coating creating a composite of two layers of coating fluid and a carrier fluid which is applied to a substrate as a layer composed of two layers, simultaneously, on the substrate followed by the removal of the carrier fluid which is left below the coating fluid. It is the object of this invention to coat a plurality of coating fluids simultaneously applied on a substrate in a coating station by a method of moving the substrate through the coating station, forming a composite layer of a plurality of fluid layers that they flow separately, from different but miscible compositions; depositing a composite layer on the surface of the substrate when it passes through the coating station; then remove a portion of the compound by the scraping action of a gas jet (pneumatic blade) which extends transversely through the path of the substrate. The substrates can be continuous coils or rolls running at speeds of 1 to 1,000 m / min through the coating station, or they can be discrete sheets or discrete pieces of rigid pieces or an array of parts or parts transported through the coating station. The respective layers can have different compositions and have a large variation in the viscosity, surface tension and thickness ratios. The coating fluids preferably have a combination of surface tension and viscosity so that they will not dehumidify from the surface of the substrate after they are spread over the surface within the transport time through the coating station. Examples of coating fluids applicable by this method are monomers, oligomers, solutions of dissolved solids, solid-liquid dispersions, liquid mixtures, emulsions and latices. The coating method will be better understood with reference to Figure 1 illustrating a coating station including a preferred apparatus of this invention. The coater matrix 10 is commonly known in the photographic industry as a sliding curtain coater. A first coating fluid 34 of a first composition is pumped at a precisely controlled flow rate from a tank 14 by a precision metering pump 16 through a filter 18 and a bubble trap 20 to the coating matrix 10. The coil or continuous roll 32 passes to the coating station and beyond the die 10 which is mounted transversely to the continuous coil or roll. A second coating fluid 36 of a second composition passes through a throttle valve 24 and flow meter 25 to a vacuum degassing vessel 26. The flow rate is measured when leaving the vacuum degassing vessel with another flow meter 27. Both flow meters can be rotometers. The flow from the container 26 is pumped by a pump of the continuous helical cavity type 28. From the pump 28, the second coating fluid 36 flows through a sealed compensation tank 29, through a fine filter 30, to through the discharge flow meter 27 and towards the coater matrix 10. The internal cavities 12 and 22 distribute the flow of the coating fluids through the width of this coater matrix 10 by two-layer sliding curtain, so that they are distributed to the faces of the matrix 38 and 40 through distribution slots 42 and 44. The first and the second fluid are miscible, but have different compositions. These fluids may have identical constituents and vary only in the concentrations of the individual components, or these fluids may have different constituents. If the fluids are solutions, dispersions or emulsions, the main liquid components can be identical or different. The first coating fluid 34 flows on top of the second coating fluid 36 at the outlet of the slot 44, and then flows in a layer relationship with and on top of the second fluid descending the inclined plane towards the flange of the matrix 46 as a composite layer. From the flange, the composite liquid film falls in the form of a curtain 48 under the influence of gravity to make contact with the coil or continuous roll 32. The coil or continuous roll 32 is moved through the coating station and further beyond the transverse coater matrix 10 so that when the curtain of the composite layer makes contact with the continuous coil or roll, the first coating fluid is located adjacent to the surface of the coil or continuous coil and is interposed between the coil and the second coating fluid. The first coating fluid 34 will have an intimate contact with the continuous roll or coil 32 and the second coating fluid 36 will not have it. The individual layers remain different and unmixed. The curtain applying matrix is used here to apply an excess of the second coating fluid 36 to the substrate. Therefore, the composite layer is also said to be in excess. The excess amount is controlled by the dosing of the second fluid 36. Some portions thereof will subsequently be removed by the air knife blade as described below. Figure 1 also shows an interceptor baffle 60 that can be moved to intercept the curtain before it collides with the substrate 32. This can be coupled to facilitate start-stop procedures and generally allows to stop the coil coating operation or continuous roll without stopping the coil or fluxes of coating fluids. When the baffle 60 is coupled, as shown by the interrupted lines, the fluid will flow down the deflector and into a collecting tray 51. The combined wet thickness of the composite layer of coating fluids deposited on the moving substrate will be related to the thickness of the curtain of multiple layers just before hitting the substrate. The faster substrate speeds will produce thinner coatings. High substrate speeds are possible since the kinetic energy of the impact with the curtain is sufficient to displace the air on the surface of the substrate in a sufficiently uniform and stable manner. If the impact velocity is greater than the velocity of the substrate, the wet thickness of the layers on the substrate will be greater than the curtain immediately before impact. Depending on many factors, the impact of the curtain may cause a "fluid bead" to form on the upstream side of the substrate at the point of impact. When this becomes large, the quality of the coating layers can be altered or mixing can occur. Factors influencing this are the flow properties of the layers, the surface and interfacial tension of the capeas, the impact angle with the substrate, the external body forces and the external pressure gradients. The flow rates of the layers, the speed of the substrate, the distance of the coating matrix from the substrate and the angle of impact are the primary variables that the coating operator can change to stabilize the deposition. Also, there are many refinements of curtain coating techniques. All of these can benefit from the use of the sliding curtain matrix as an excess applicator of the composite coating fluid layer prior to the air knife 54. After the substrate passes the sliding curtain matrix and the composite layer has been applied in In excess, the substrate passes the gas jet nozzle which is also known as a pneumatic blade 54. This can be designed in accordance with the teachings of US Patent No. 2,135,406. This nozzle commonly uses air as the operating gas. The jet 52 coming out of the pneumatic blade 54 avoids either that some portion of the composite layer of the coating fluids in the continuous coil or roll approaching the air knife 54 passes beyond the position of the knife 54 or that blows some portion of the fluids of coating off the substratum as.yna mist depending on the volume and speed of the jet. It is preferred that the substrate pass up past the jet, so that gravity helps pull the excess down and away from the point of impact of the jet. The backflow of the excess accumulates a thick layer of the second coating fluid 62 under the jet 52 which is very irregular and whose movement is turbulent or chaotic. Unexpectedly, it has been found that despite this, it is possible to produce a two layer composite coating 64 on the underside of the continuous roll of the air knife 54 even when the first and second coating fluid are miscible. (The miscible fluids if placed together in a beaker and shaken, would mix and form a smooth fluid of uniform composition). Furthermore, and also surprisingly, it has been found that the air jet 52 can be adjusted so that a portion of the second fluid 36 is removed with the first fluid 34 remaining substantially undamaged and intact. This is most easily accomplished when the first coating fluid is more viscous than the second, such as when the viscosity of the first coating fluid is ten and even one hundred times larger than the viscosity of the second coating fluid. The composite layer 64 of two layers remains on the substrate after passing the pneumatic blade. Excessive coating fluid 62 drains and falls from the coil into tray 50. This excess can be discarded or reused if appropriate. After passing the air knife 54, the composite layer 64 can be dried, gelled or cured when necessary by the particular application. This would be followed by roller coiling, sheet cutting, or additional processing steps. Mechanical, vibratory, or magnetic smoothing of the wet composite coating could also be used. As shown, a coating matrix 10 is used by multi-layer sliding curtain to apply the excess. Other simultaneous multi-layer coating devices could be used, including matrixing devices for flanging, sliding, extrusion and jetting. The composite layer of the excess material can also be constructed by a sequence of simple layers deposited on the surface of the continuous coil or roll without the intervention of an excess removal or drying step. This simultaneous multilayer pneumatic knife coating technique is especially useful for producing solid coatings on latices substrates. Frequently, the commonly known single layer pneumatic knife coating method has problems when coating the latex. Thin coating with the conventional single layer method may require jet velocities that produce fog or foam, which creates quality and waste problems. This can be avoided using the multi-layer approach. The thin dry coatings of a latex can be applied using two compositions of different solids percentages of the same latex as shown in Figure 2. The advantage is that most solids can be dosed accurately with a first fluid coating with high solids content while the second fluid with a low solids content facilitates the deposition of the first fluid on the coil or continuous roll before passing the pneumatic blade. Additionally, after passing the air knife, the coating of the composite layer of a first layer of high viscosity fluid under a second layer of low viscosity fluid can make drying faster and promote smoothing of the surface of the fluid. dry coating. In Figure 2, a first latex coating fluid 104, of high solids content, is pumped at a precisely controlled flow rate from a tank 84 by a precision metering pump 85 through a filter 88 and a bubble trap 90 to the coater 110. The coil or continuous roll 102 passes to the coating station and when the die 110 which is mounted transversely to the coil has been passed. A second coating fluid 86 may be the first coating fluid 104 diluted with conditioned water to form a latex 86 of the second composition with a low content of 86 solids. The water is conditioned with any salt, pH adjuster, buffer agent, and surfactathat are necessary for dilution without causing coagulation of the latex. The second coating fluid 86 is supplied from a tank 94 by a precision metering pump 96 through a filter 98 and a bubble trap 100 to the coater 110. As with the apparatus of Figure 1, the cavities 82 and 92, the slots 112 and 144 and the faces 108 and 90 function to create a composite curtain 118, of layers, of the first 104 and second 86 coating fluids. These first and second coating fluids are miscible and differ primarily in the percentage of solids. Since the viscosity of the latex usually depends very strongly on the percentage of solids, the viscosities of the first and second fluids can differ by a factor of 2 to 1,000 or more, depending on the viscosity of the first one from which the second was produced by dilution .

The substrate is moved through the coating station and until the transverse coater has been passed so that when the composite curtain 118 contacts the coil, the first coating fluid 104 is placed adjacent to the coil surface. the coil and is interposed between the coil 102 and the second fluid 86. The first coating fluid 104 will make intimate contact with the coil and the second coating fluid 86 will not. The flow rate of the first coating fluid 104 is initially chosen to equal that which is necessary to achieve the desired dry coating weight on the coil 102 at a given coil speed. If this flow is sufficient to form a continuous curtain from the rim 116 of the matrix without the use of the second fluid and if the curtain can be deposited on the coil without air entrainment or objectionable configurations, then this invention is not necessary and may be the conventional curtain coating is used to produce the desired coating weight. Unfortunately, this is not the case at low coil speeds or at very low flow rates of the first coating fluid 104. To produce the desired coating deposit on the continuous coil or roll, the second coating fluid 86 is used to produce a composite flow stream 118 which is stable and flowing at a flow rate that is deposited on the coil without dragging the coil. air and undesirable configurations. The second coating fluid 86 flows at a flow rate that differs from the flow rate of the first coating fluid 104. In preferred uses, this flow rate of the second coating fluid is greater than that of the first coating fluid, although there are some situations in which the flow rate of the second coating fluid is smaller. The composite layer 118 constitutes an excess of the compound that must be scraped with the pneumatic blade 124 to remove the excess. The removal of the excess can be controlled by changing the position of the pneumatic blade 124, the gas flow rate and the velocity of the gas. It is preferred that the viscosity ratio between the second 86 and the first coating fluid 104 is 0.1 or less. It is possible to adjust the operation of the pneumatic blade 124 to remove the excess of the second fluid and leave below a composite layer 144 of the first fluid and sufficient of the second to achieve the desired dry coating weight on the reel after drying. After initial testing, it may be necessary to adjust the flow rate of the first fluid to obtain the exact, desired dry coating weight of the composite layer 144. The adjustment is necessary to compensate for the mass of solid added to the composite layer 144 by the layer of the second fluid 86 left below since the pneumatic blade has removed the excess. At the end, the second coating fluid could be about 100% water. Here the final dry coating could be achieved by drying the composite layer applied by the curtain matrix without using the scraping by the pneumatic blade. However, the total heat load required would be large compared to anuella when a portion of excess water is removed using the air knife 124. The use of the air knife is therefore highly desirable. The production of a coating of the composite layer 144 wherein the first fluid 104, the latex, is close to the coil and the second fluid, the water, is stratified at the top of the first, may be useful for improving the quality of the coated product and improve drying speed. Beneath the pneumatic blade 124 in Figure 2, a tray 120 collects the excess fluid blown away or held back by the jet 122. This fluid will be primarily the second fluid 86 with a small amount of contamination of the first fluid 104. contamination comes from the diffusion of the material through of the interface of the layers and of the first fluid 104 on the heavy edge rims (not shown) at the ends of the curtain in the direction of the transverse coil. The pneumatic blade 124 normally removes the flanges from the edge and mixes them with the excess fluid 132 retained by the jet 122. The composition of the fluid 134 in the tray may differ from that in the supply tank 94 due to this and other factors such as evaporation. A recirculation pump 136 transports fluid 134 back to supply tank 94 through process line 148 for reuse. The percentage of solids, the viscosity, the pH, the surface tension and any other critical property of the fluid in the tray can be verified by a monitor 138 connected to a sensor 146 that samples the fluid 134. The monitor 138 sends control signals through a wire 150 to the control module 140 containing additional pumps for supplying water and conditioning agents (not shown) to the tray 120 as needed to adjust the fluid 134 to a composition as identical as possible to the fluid 86 in the supply tank 94. A Further variation of this invention could include forming a first layer of coating fluid as a composite of numerous layers of coating fluid. In this way, a multiple layer coating of more than two layers can be applied to the continuous roll.

When the first coating fluid is a plurality of layers, the layer adjacent to the second coating fluid must be miscible with the second coating fluid. Also, these systems do not necessarily use a matrix. For example, a bucket or tundish for fluid that ends in a spill container can be used to create a curtain. The coating fluid is placed on the surface of the carrier fluid before a curtain is formed. The coating method of this invention is further illustrated by means of the following examples of its use.

EXAMPLE 1 Using the slide curtain coating matrix shown in Figure 1, a thin coating of a water soluble resin solution was applied to a coil or continuous roll of polyester. The coating fluid consisted of a Carbolpol 940 resin solution dissolved in tap water. This solution was prepared by first dissolving about 1.1 weight percent of the resin in water and then neutralizing the solution to a pH of 7 with a 5 weight percent sodium hydroxide solution. This created a viscous gel to which a saturated solution of Green Solvent dye 7 was added at a ratio of one part of dyeing solution per 100 parts of gel by weight. The gel was then diluted with water until a viscosity of 300 centipoises was obtained measured at 60 rpm with a spindle number 4 in a Brookfield viscometer model LVTDV-II. To the diluted solution was added 0.2 g of the Silwet 7200 surfactant per 100 g of solution. The surface tension of the resin solution was 23.5 dynes / cm, and it was completely miscible with the tap water used as the second coating fluid. The interfacial tension between the first and second coating fluids was zero due to its miscibility. The Carbolpol can be obtained from BF Goodrich Company of Cleveland, Ohio. The Green Solvent 7 tincture is available from Keystone-Ingham Corporation of Mirada, California. The Brookfield viscometer is a product of Brookfield Engineering Laboratories, Inc. of Stoughton, Massachusetts. The Silwet surfactant is manufactured by Union Carbide Chemicals and Plastics Company, Inc. of Danbury, Connecticut. The coil or continuous roll of polyester was a Scotchpar MR polyester film (6 inches) wide, 35.6 microns (1.4 thousandths of an inch), purchased from 3M of St. Paul, Minnesota.

. The second coating fluid used was tap water from the municipal water supply without additives modifying the surface tension. The water was supplied at a temperature of 13 ° C to a vacuum degassing vessel operated at a pressure of 200 mm absolute mercury and then pumped into the coating matrix. The delivery flow rate was 3000 ml / min. The viscosity of the vehicle fluid was estimated at 1.2 cp. The water flow rate was measured both at the inlet and outlet of the vacuum degassing vessel with two identical rotometers. These were model 1307EJ27CJ1AA meters, from 0.2 to 2.59 gpm, purchased from Brooks Instrument Corporation of Hatfield, Pennsylvania. The container flow was pumped by a pump of the continuous helical cavity type, model 2L3SSQ-AAA, Moyno MR pump from Robbins & Meyers Corporation of Springfield, Ohio. To obtain a vacuum seal through this pump, it was operated in reverse to its normal operation. That is, its rotor was rotated opposite to the standard direction and water was pumped from the vacuum vessel through the normal discharge opening of the Moyno MR, through the pump and out of the feed opening. From the pump, the water circulated through a one-liter, bubble-removing tank and pulsation damper, sealed through a thin filter, through the discharge rotometer and into the coating matrix. The input flow was adjusted manually by means of a throttle valve on the input rotometer. The water discharge rate of the vacuum vessel was controlled by the rotation speed of the Moyno MR pump and verified by the discharge rotometer. The inlet flow was adjusted manually with the throttle valve to make it match the indicated discharge speed. The filter used was a disposable filter capsule. This was purchased from Porous Media Corporation of St. Paul, Minnesota, and was identified with part number DFC1022Y050Y, adjusted to 5 microns. The vacuum for the degassing vessel was supplied by a water ring vacuum pump, model MHC-25 from Nash Engineering Corporation of Downers Grove, Illinois. During the coating, the sliding curtain coating matrix was placed above the roller 58. More specifically, it was placed so that the height of the curtain, h, was 3 mm and the curtain hit the coil on the roller at a 310 ° angular position measured clockwise from the top of the roller. The impact angle, a ^, was approximately 45 °. The face 90 of the die was inclined at an angle of 84 ° with respect to the horizontal. The width of the groove of the first coating fluid was 18.5 cm while the width of the groove of the second coating fluid was 21 cm. The separations of the distribution slots for the first and second coating fluids were 160 and 1100 microns respectively. The diameter of the coating roller 58 was 2.5 cm. The second fluid was drained simultaneously by gravity and the excess was removed by a pneumatic blade 54. The nozzle spacing of the pneumatic blade was 250 microns and the compressed air was supplied thereto at a pressure of 34 kilopascals. The first coating fluid was supplied at flow rates of 11, 21.5, 50 and 100 g / min. At these flow rates, a continuous descending curtain of the first coating fluid alone could not be produced. However, the aggregate flow of the second coating fluid produced a stable curtain. The speed of the continuous roll or coil was kept constant at 29 cm / sec. It was observed that after the pneumatic blade, both the first and second fluids were present in the coil. The second was present as a very thin low viscosity layer on the surface of the first fluid. A wet coating composed of multiple layers was created. The fluorescence of the undried coated samples was measured at 0.8, 1.4, 2.4 and 5.0 relative fluorescence units for the first four coating fluid pumping rates respectively. The coating weights as indicated by the fluorescence varied linearly with the pumping rate of the first coating fluid. This example illustrates that the coated thickness of the first fluid responds directly to the pumping flow rate of the first coating fluid and that it is not greatly affected by the use of the second fluid.

EXAMPLE 2 Using the revealing curtain coating matrix and a recirculation system of a second coating fluid similar to that shown in Figure 2, a coating composed of a water-based latex having a first fluid with many solids and a coating was applied. second fluid with few solids, to a coil or continuous roll of polyester. The first coating fluid 104 consisted of a Sequabond DW-1 latex with a solids content of 45% by weight. The second coating fluid 86 also consisted of the same latex with a content of the solids composition of 3.1% by weight prepared by dilution with deionized water of the first fluid with a high solids content. The Sequabond MR DW-1 is available from Sequa Chemicals, Inc. of Chester, South Carolina. The polyester coil was a Scotchpar MR polyester film .2 cm (6 inches) wide, 35.6 microns (1.4 mils), purchased from 3M St. Paul, Minnesota. The second coating fluid was pumped to the coating application matrix by a pump of the progressive helical cavity type, Model 2L3SSQ-MR AAA, Moyno pump from Robbins & Meyers Corporation of Springfield, Ohio. From the pump, the fluid flowed through a one-liter pulsation, sealing, and bubble-absorbing tank, through a filter and into the coater matrix. The filter used was a disposable filter capsule. This was purchased from Porous Media Corporation of St. Paul, Minnesota and was identified with part number DFC1022Y050Y, adjusted to 50 microns. During the coating, the sliding curtain coater was placed above the roller 58. More specifically, it was placed so that the curtain hit the coil on the roller at an angular position of 310 ° measured in the clockwise direction from the top of the roller. The impact angle was approximately 45 °. The width of the groove of the first coating fluid was 25.2 cm while the width of the groove of the second coating fluid was 25.8 cm. The spacings of the distribution slots for the first and second coating fluids were 254 and 500 microns respectively. The diameter of the coating roller 58 was 2.5 cm. The second fluid was drained simultaneously by gravity and subjected to the action of the pneumatic blade 124 to remove a portion of the second fluid. The separation of the nozzle from the pneumatic blade was 250 microns and the compressed air was supplied to it at a pressure of 21 kilopascals. The outlet of the pneumatic blade slot was placed at approximately 2 mm from the surface of the continuous roll or coil. The first coating fluid was supplied at a flow rate of 0.15 g / sec. At these flow rates, a curtain of continuous falling of the first coating fluid alone could not be produced. However, the aggregate flow of the second coating fluid of 16 g / sec produced a stable curtain. The speed of the coil was kept constant at 25 cm / sec. It was observed that after removing the excess of the second fluid with the pneumatic blade, both the first and second fluids were present in the coil. A composite coating was achieved. The second was present as a thin, low viscosity layer on the surface of the first fluid. The combined dry coatings of the first and second fluids were measured at a combined weight of 0.14 milligrams / cm2. At a flow rate of the first fluid of 4.9 g / sec, a flow rate of the second fluid of 30 g / sec, a second fluid with solids at 4.3%, the combined dry coating of the first and second fluids was measured at a combined weight of 3.7 milligrams / cm 2 It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following

Claims (16)

CLAIMS • ».

1. A method of coating a substrate 32 with numerous coating layers, characterized in that it comprises the steps of: moving the substrate 32 along a path through a coating station; dosing at least a first coating fluid 34 and a second coating fluid 36, wherein the first formulation of the coating fluid differs from the second formulation of the coating fluid; forming a composite layer 48 comprising at least a first coating fluid and the second coating fluid; contacting the substrate 32 with the composite layer capable of flowing 48 to interpose the first coating fluid 34 between the substrate 32 and the second coating fluid 36 to apply an excess of the second coating layer on the substrate; scraping the composite layer with a gas 52 of a blade actuated with an ace 54 to remove some portion of the second coating layer 36 from the substrate to produce a composite coating of multiple layers on the downward coil of the substrate of the cuchi-11a aconated by gas to leave a coating comprising numerous different superposed layers of the first and second coating fluids.

2. The method according to claim 1, characterized in that it further comprises the step of adjusting the gas 52 of the gas driven blade 54 to remove only the second rewind fluid 36 leaving the first coating fluid 34 substantially intact on the substrate 32 changing one of: a position of the gas driven blade, a gas flow rate and a gas velocity.

3. The method according to any of claims 1 and 2, characterized in that it further comprises the steps of flowing the first coating fluid 34 to a first flow rate which will reach a desired dry coating weight on the substrate 32 at a substrate speed. Dadaist; and flowing the second coating fluid 34 to a second flow rate that differs from the flow rate of the first coating fluid and that will produce a continuous, stable fall curtain of the composite layer 48 of the first and second fluids, regardless of the first flow rate is unable to produce a curtain of continuous, stable fall of the first fluid alone.

4. The method according to any of claims 1, 2 and 3, characterized in that the forming step comprises forming a composite layer 48 comprising numerous first coating fluids 34 in different superposed layers and a second coating fluid 36.

5. The method according to claim 1, characterized in that the dosing step comprises dosing the first and second coating fluids 34, 36 that are miscible with each other.

6. The method according to claim 1, characterized in that the dosing step comprises dosing the first and second fluids 34, 36 that have wetting properties that allow some of the second fluid to remain as a continuous film covering the surface of the first layer of fluid after the fluid layers are applied on the substrate and after the scraping step.

7. The method according to claim 6, characterized in that the dosing step comprises dosing the first and second coating fluids 34, 36 which are immiscible with each other.

8. The method according to claim 5, characterized in that the forming step comprises forming a composite layer 48 of a first coating fluid 34 comprising latex and a second miscible coating fluid 36, comprising water.

9. The method according to claim 5, characterized in that the forming step comprises forming a composite layer 48 of at least one first coating fluid 34 comprising a first latex and a second miscible coating fluid 36 comprising a second latex which It has a composition and percentage of solids, one of which differs from the first latex.

10. The method according to claim 7, characterized in that at least one of the first coating fluids 34 and the second coating fluid 36 are immiscible.

11. The method according to claim 1, characterized in that the movement step comprises moving the substrate 32 through a coating station at speeds up to 1,000 n / min.

12. The method according to claim 1, characterized in that it further comprises the steps of: contacting a transfer surface with the composite layer capable of flowing 48 to interpolate the second coating fluid between the transfer surface and the first fluid of coating 34; and transferring some portion of the coating fluid to the substrate 32 from the transfer surface to interpose the first coating fluid 34 between the substrate and the second coating fluid 36 to apply an excess of the second coating layer onto the substrate 32. .

13. An apparatus for coating a substrate with numerous layers of coating, characterized in that it comprises; means for bringing together a first coating fluid 34 and a second coating fluid 36 to create numerous layers of fluid capable of flowing, dosed, in face-to-face contact with each other to form a composite layer 48, wherein the formulation of the first coating fluid differs from the formulation of the second coating fluid; means for moving the substrate 32 at a spaced apart distance from the means for bringing the two fluids together, to allow the composite layer 48 to form a fluid bridge flowing continuously to the substrate, along the coating width and for depositing the coating layer on the substrate to interpose the first coating fluid 34 between the substrate 32 and the second coating fluid 36 to apply an excess of the second coating layer on the substrate; and a gas-operated blade 54 scraping the composite layer 48 with a gas 52 to remove some portion of the second coating layer from the substrate and to produce a multi-layer composite coating on the downward roll of the driven blade substrate. by gas to leave a coating comprising numerous overlapping layers different from the first and second coating fluids.

14. The apparatus according to claim 13, characterized in that it further comprises means for adjusting the gas driven blade 54 to remove only the second coating fluid, leaving the first coating fluid substantially intact on the substrate.

. The apparatus according to claim 13, characterized in that the means for bringing the two fluids together comprises: means for flowing the first coating fluid 34 to a first flow rate which will reach a desired dry coating weight on the substrate 32 a a given substrate speed; and elements for flowing the second coating fluid 36 to a second flow rate that differs from the flow rate of the first coating fluid and that will produce a continuous, stable fall curtain of the composite layer 48 of the first and second fluids regardless of the first flow rate is unable to produce a curtain that falls continuously, stable from the first fluid only.

16. The apparatus according to claim 13, characterized in that the means for bringing together the two fluids comprises a matrix 10 having a face 38, 40, a groove 42, 44 communicating with the face and a flange 46, wherein one of the first and second coating fluids 34, 36 leaves the groove on the face and flows along the face towards the flange, where the deposition means deposits the other of the first and second coating fluids on one of the first and second coating fluids flowing along the face, and wherein the composite layer 48 is conveyed along the face of the matrix towards the die flange.