MXPA97005695A - Method of coating with multip layers - Google Patents

Abstract

The present invention relates to a method for coating a substrate with a plurality of layers of coating fluid, characterized in that it comprises the steps of: moving the substrate along a path through a coating station, forming at least a first and second flowing layer of coating fluids; flowing at least one of the layers from an orifice in a slot of a kinetic jet coater at a rate that is sufficient to form a kinetic jet exiting the orifice; flows horizontally, continuously, placing the layers in face-to-face contact with each other to form a composite layer regardless of whether each of the layers flows individually at a rate that is sufficient to form a kinetic stream of fluid that flows continuously; the composite layer at a speed that is sufficient to cause the composite layer to form a kinetic stream that flows horizontally, continuously, at substrate by a coating width, and contacting the substrate with a kinetic jet of flowing composite layer, to deposit the coating fluids on the substrate in a plurality of overlapping layers other than the coating fluids; Substrate along a path through the coating station stage comprises separating the substrate from the beginning of the fluid kinetic jet by a distance greater than 10 times the thickness of the composite layer applied to the substrate.

Description

"METHOD OF COATING WITH MULTIPLE LAYERS" FIELD OF THE INVENTION The present invention relates to the preparation of multilayer coatings. More particularly, the present invention relates to a system for coating a substrate with a plurality of layers applied simultaneously.

BACKGROUND OF THE INVENTION Coating is the process of replacing the gas that contacts a substrate, usually a solid surface such as a web or network, by a fluid layer. Sometimes, multiple layers of a coating are applied on top of each other. After the deposition of a coating, a fluid such as in the application of lubricating oil to the metal in the processing of metal coils or in the application of chemical reagents to activate or chemically transform a surface of a substrate can remain. Alternatively, the coating can be dried if it contains a volatile fluid to leave a solid layer such as a paint, or it can be cured or solidified in some other way until a functional coating such as a release coating to which a coating is applied. Pressure sensitive adhesive will not stick.

Frequently to create the correct operation of a coated substrate, multiple layers of different compositions should be applied. There are many examples of this. It is common to apply a primer coating under a paint to improve adhesion. In the manufacture of color photographic film, as many as twelve layers of different compositions should be applied in a different layer placement relationship with narrow uniformity tolerances. The manufacture of magnetic recording tapes of high performance requires the coating of numerous layers of magnetic pigments of different compositions.

Sequential coating operations can produce numerous different layers superimposed on a substrate. However, this is expensive, time consuming and may require a large investment in the sequential coating and drying stations.

Methods for applying multiple layer coatings simultaneously are described in Cohen, ED and Gutoff, EB, Modern Coating and Drying Technology, chapter 4, VCH Publishers, New York, 1992. Predosed, slotted or extruded matrix coatings are they describe in US Patents 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 surface of the matrix and numerous superposed layers are deposited. Each coating composition is dosed in the coating matrix that deposits the layers on the continuous coil or roll. In these methods, the maximum operating speed is limited and the uniformity of the separation between the die and the continuous roll or coil limits the quality of the coatings.

Another method of simultaneous multilayer coating is curtain coating. U.S. Patent No. 3,508,947 teaches the use of this method with respect to photographic coating elements. The curtain coating uses a curtain of fluid that falls freely vertically that strikes the continuous coil or roll that passes through the coating station. This patent teaches a method for forming the curtain from numerous different layers to perform a multilayer coating on the continuous coil or roll. The separation between the coater matrix and the continuous coil or roll is much greater than other methods and the application rates are substantially higher. However, even this technique has limitations.

To create a multilayer fluid curtain of miscible layer compositions or coating compositions having an interfacial tension of zero or near zero, the flow of the layers must be kept laminar to avoid mixing. If the preferred slip geometry is used, the maximum unit flow rate is limited by the transition from laminar to turbulent flow in the slip. If the coating speed is set, this limits the maximum coating thickness that can be applied. If the thickness of the coating is set, the maximum speed at which the coating can be applied may be limited.

Another limitation of the curtain coating is that the free fall curtain is accelerated by the force of gravity which is constant and limited. The kinetic energy gained in this free fall is used to displace air from the surface of the continuous coil or roll in a manner that prevents undesirable entrainment of air. The gain of kinetic energy in the free fall increases with the height of the curtain, but the increase in the height of the curtain increases the probability of disturbances in the fragile curtain. In practice, it is difficult to obtain a good coating quality with heights greater than 25 centimeters. This limits the range of thickness and coating speed. The desire for high curtains to obtain high speed, thin coatings and short curtains to obtain high quality coatings is contradictory and compromises must be made that limit the usefulness of this method. In addition, curtain coaters can not operate in low-gravity or zero-gravity environments.

Another limitation of the curtain coating is that the curtain always falls vertically. This limits the geometries of the coating station and the orientation of the coating station. Also, if the curtain coating is to be added to an existing manufacturing process, the process should be adapted to the restrictive vertical fall orientation of the curtain instead of orienting the coater and the apparatus to the path or path of the curtain. the existing continuous coil or roll of the existing process.

The axisymmetric coater of U.S. Patent No. 4,348,432 teaches how to form a multilayer radial expansion sheet from cylindrical cylindrical jets that collide in opposite ways, and how to translate a continuous coil or roll behind the device to effect a coating. multilayer, simultaneous. However, in addition to other limitations, this method is severely limited by the limitation of the maximum width of the continuous roll or coil, imposed by the dynamics of the fluids. Widths greater than 1 meter are prohibited and widths greater than 0.75 meters are impractical.

The application of single layer liquid jets coming out of grooves is already known in the paper industry both to apply an excess of coating liquid to a surface of the continuous roll before dosing with a knife coater or to apply a coater. Excess coating liquid to the parallel pitting wheel of a rotogravure or rotogravure coater.

However, the use of multilayer coatings is not known by applying them as a jet. There is a need for a system that can apply thin multilayer coatings, simultaneously, at higher speeds without the orientation, geometry and gravitational limitations of known coating methods. There is a need for an improved system that can simultaneously coat many layers on a substrate, which accurately doses and distributes each layer across the width of the substrate, while maintaining the substrate in a juxtaposed, controlled face-to-face relationship.

BRIEF DESCRIPTION OF THE INVENTION The system of the present invention coats numerous coating fluids applied simultaneously on a substrate. The substrate moves along a path through a coating station, and numerous layers of coating fluids are flowed in face-to-face contact with each other to form a composite layer. The composite layer flows as a high velocity jet at a velocity that is high enough to form a fluid bridge that flows continuously to the surface of the substrate across the width of the coating regardless of the direction of gravity. The flowing composite layer jet collides with the substrate to deposit the coating fluids onto the substrate. The composite jet fluid bridge has a length greater than the thickness or thickness of the wet paper of the applied coating fluid.

The system may also include the deposition of the composite layer on a transfer surface, such as a roller or tape, before it makes contact with the substrate. Also, the system may include an interceptor that interrupts the coating process by blocking the flow before it makes contact with the continuous spool or roll without stopping the substrate or suspending the other steps.

The fluid bridge can be accelerated by at least one of the gravitational, magnetic or electrostatic forces. However, this is not essential, and the coating can be carried out in a low-gravity environment. In various embodiments, it is possible to have at least one coating fluid that does not wet the substrate, or that is not miscible with an adjacent coating fluid, or that has a surface tension that differs from an adjacent coating fluid, or that is in a turbulent flow, or that is miscible with an adjacent coating fluid.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of a jet coater matrix. Figure 2 is a schematic view of a coating system of the present invention. Figure 3 is a schematic view of the coating system according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The jet coating device is best understood with reference to the illustration of FIG. 1 which shows a single layer matrix which can be used for jet coating. The matrix 10 has a simple cavity 12 in which the fluid can be pumped through an inlet (not shown). The cavity is connected to an outlet groove 14 which allows the fluid to exit the matrix through the orifice 16 formed where the groove 14 leaves the body of the die 10. Alternatively, the die and its grooved outlet could be formed by closing a side of the cavity with a thin metal sheet having a hole cut through it.

The slot 14 is shown oriented horizontally, perpendicular to the direction of gravity. At very small unit flow rates and in the absence of any substrate or obstruction near the orifice, the fluid exiting the orifice 16 will be attached to the lower face 20 of the matrix and will flow down therethrough a certain distance that can be measured. before escaping and falling vertically under the influence of gravity.

A jet coating device of this invention is created if the kinetic energy of the fluid exiting the orifice 16 is large. This occurs at high unit flow rates. At these flow rates, the fluid exiting the slotted hole will be attached or fixed only to the upper and lower edges 22, 24 of the orifice 16, escaping cleanly from the faces 18, 20 of the matrix and forming a horizontal jet. The jet is a band of fluid that is ejected horizontally at a certain visible distance. The high unit flow rate at which this jet first forms depends on the dimensions of the groove, the fluid density, the surface tension of the fluid and the Theological properties of the fluid. The spacing between the flanges of the coater, which defines the outlet of the groove 14, and the continuous coil or roll, may be greater than ten times the thickness of the fluid layer applied to the coil or continuous coil. Although this explanation describes a horizontal jet, jets can be created at any angle if the exit velocity of the orifice is sufficiently high. This is an advantage of jet coaters; the jets can be expelled upwards against the force of gravity at any angle and the jets can be created in an environment of zero gravity.

A multi-layer jet coater, which coats three layers of fluid simultaneously on a mobile substrate in a superposed layer ratio is shown in Figure 2. The substrate is a continuous roll 30 which is directed through the coating station by rollers 32, 34 supporting the coil or roll and directing the coil or roll substantially upwards.

A jet coater matrix 36 is located transversely to the path of the coil or roll. The coater matrix 36 possesses a first cavity 38 in which a first fluid coating 40 is pumped at a constant flow rate by a first dosing pump 42 through a first inlet 44 from a feed tank 41. The fluid coating 40 flows from the cavity 38 through a first elongate slot 40 to a common slot 48.

The coater matrix 36 also has a second cavity 50 in which a second fluid coating 52 is pumped at a constant flow rate by a second metering pump 54 through a second inlet 56 from the feed tank 51. The fluid coating 52 flows from the cavity 50 through a second elongated slot 58 to the common slot 48 where it joins the coating fluid 40 to form a fluid flow capable of flowing, of composite layer, into the slot 48. The coating matrix 36 has a third cavity 60 in which a third fluid coating 62 is pumped at a constant flow rate by a third metering pump 64 through a third inlet 66 from the feed tank 61. The fluid coating 62 flows from the cavity 60 through a third elongated slot 68 to the common slot 48 where it joins the coating fluids 40 and 52 to form a fluid stream capable flow, composite layer, in slot 48.

The coating fluids 40, 52, 62 flow through the common slot 48 in a layered juxtaposed face-to-face relationship, with a combined unit flow rate large enough to form a free fluid jet 70 in the form of layers , composite, having three different superposed layers 72, 74, 76 emerging from a slotted hole 78. The flow through each individual slot 46, 58, 68 may be sufficient to create a jet or these flows may be too small, while the flow through the common slot 48, due to the increased speed, is sufficient to create the jet. The jet coater 36 is oriented so that the slot 48 is perpendicular to the force of gravity. In alternative embodiments, the flow of the jet and the continuous coil or roll can be oriented in any direction including jets that flow up or down. The coating method can be used in a low gravity or zero gravity environment and is not altered by gravitational orientation. Surprisingly, the high unitary flow rate necessary to form the fluid jet does not cause the numerous layers to mix during impact with the continuous coil 30, and a multilayer coating can be produced.

Alternatively, the coating fluids may be combined in a composite layer before the fluids enter the matrix which then creates the composite layer jet.

The jet of fluid 70 in the form of layers, composite, follows a route that does not need to be straight. The path is the resultant of the surface forces on their free surfaces, the viscous retarding forces due to the changes in the velocity profile when leaving the slot 48, the viscous forces resulting from the acceleration or deceleration of the jet and any forces external acting on the jet including magnetic, electrostatic, acoustic, pressure, gravitational and centrifugal forces. The collision of the composite fluid jet 70 on the continuous roll in motion 30 can occur without mixing the layers to deposit on the coil or continuous roll a coating of three different superposed layers 72, 74, 76. The correct adjustment of the distance from the hole 78 of the die to the continuous roll 30, and the angle of impact of the jet with the continuous roll or coil, is important to obtain continuous layer coatings Figure 2 also shows an inter-ceptor baffle 84 that can be moved upward by a pulse device (not shown) to intercept the jet 70 before it collides with the coil or continuous roll 30. The baffle 84 is used when the gravity It is present to facilitate the start and stop procedures and can stop the coating operation without stopping the coil or the flow of the coating fluids. When the baffle 84 intercepts the coating fluid jets 70 as shown by the interrupted lines, the coating fluid will run down over the baffle and into a collection tray 86.

In Figure 2, the combined unit flow rate of the layers forming the jet 70 for some fluids is generally greater than 1.5 cubic centimeters per second per centimeter of jet width. To maintain the different ratio of layers of the coating to the continuous roll 30, turbulence in the individual layers 72, 74, 76 should be avoided if the interfacial tensions are low or if the layers are miscible. If there is a large interfacial tension, some turbulence may occur without disturbing the interface.

The combined wet thickness of the layers 72, 74, 76 of the coating deposited on the continuous roll in motion will be the same thickness as the thickness of the multi-layer jet before the collision when the velocity of the surface of the coil 30 equals the speed of shock of the jet immediately before making contact. When the velocity of the substrate is greater than the impact velocity of the jet, the combined wet thickness of the deposited layers will be less than the thickness of the jet immediately before impact. Larger substrate speeds will produce thinner coatings. Very high substrate speeds are possible since the kinetic energy due to the impact of the jet is sufficient to displace the air on the surface of the coil in a sufficiently uniform and stable manner. When the substrate velocity is less than the jet crash speed, the combined wet thickness of the layers on the substrate will be greater than the thickness of the jet immediately before impact. Depending on many factors, the impact of the jet may cause a "fluid bead" to form on the near side (the side from which the coil or continuous roll approaches the jet) of the continuous coil or roll at the point of impact. When this becomes large, the coating quality of the coating may be altered or mixing may occur. The factors that influence this are the properties of the fluids of the layers, the surface and interfacial tension of the layers, the impact angle with the substrate, the forces external to the body and the external pressure gradients. The flow rates of the layers, the velocity of the substrate, the distance of the jet matrix from the substrate and the angle of impact are the primary variables that will be changed to stabilize the contact of the jet with the substrate.

Many different matrix geometries can be used to produce a multiple layer jet. The currents of various fluids can be brought together before entering a single die cavity and then spread in a stratified relationship within the cavity before leaving a single die groove. A fluid jet can be formed from a die groove with additional layers bonded externally with respect to the jet orifice shown in Figure 3. The jet can be either a single layer or a composite layer to which additional layers are added. externally. Also, the multiple jets of the separate orifices of one or more matrices can be combined in full air after having left the respective orifices to form composite jets. Also, the edges of the jet orifice may be deflected.

The composite layer can be deposited on a transfer surface, such as a roller or tape, before the step of contacting the substrate. Figure 3 shows a two layer coating apparatus simultaneously. The coating fluid 88 passes through the matrix 90. A coating station 92 is placed next to the die 90. A continuous roll 94 passes through the coating station 92 and around a driven roller 96 with a coating. of elastic rubber. A transfer roller 98 rotates counterclockwise and is in rotary contact with the driven roller 96. The cover matrix 90 has an internal cavity 100 which is connected to a slot 102 and a hole 104. This cavity 100 is connected to a tank 106 by a precision metering pump 108 through a filter 110 and a bubble trap 112.

The second coating fluid 114 is supplied from a tank 116 and is metered by a pump 110 through a filter 120 and a bubble trap 122 to a cavity 124 in the die 90. From the cavity 124, it flows through a slot 126 and leaves the die 90 through the slotted hole 128. The coating fluid 88 flows from the cavity 100 through the slot 102 and exits in a hole 104 on the face 130 of the die. The unit flow rate of the fluid 88 from the orifice 104 is not large enough to form a free jet, so it flows down the face 130 of the matrix and on top of the fluid 114 in the orifice 128. The fluid 114 it is flowing at a high flow rate and is combined with the fluid 90 to form a free-flowing, two-layer jet 132, which includes the layers 134, 136. The layer 136 of the fluid 114 is attached to the matrix 90 only at the edges of the orifice 128. The composite jet 132 traverses the space towards the driven transfer roller 98 and deposits a two-layer coating on its surface. If the slot 126 is horizontal and no obstruction is present, the jet 132 could pass through a perpendicular plane spaced 1.5 millimeters to the right of the hole 128.

The transfer roller 98 rotates counterclockwise and carries the composite fluid layer 138 on its surface towards the line of contact between the driven roller 96 and the transfer roller 98. The transfer roller 98 carries the Continuous roll or coil 94 through the nip in such a manner that it contacts the surface of the transfer roll 98. The bobbin removes the composite layer and this is deposited on the surface of the continuous roll or coil.

The substrate can be a continuous coil or roll that moves at speeds of 10 to 3,000 meters per minute through the coating station, or it can be a discrete sheet, a discrete rigid part part or a set of parts or parts transported through the coating station. The coating layers can be of different compositions and have a large variation in the viscosity, surface tension and thickness ratios. The composite layer will have a combination of surface tensions and viscosities so that it will not dehumidify the surface of the substrate after contacting the surface within the transport time through the coating station. Examples of coating fluids that can be coated by this method are monomers, oligomers, solutions of dissolved solids, solid-liquid dispersions, liquid mixtures and emulsions.

Because both curtain coating and jet coating involve the use of unsupported, free moving fluid sheets, many of the devices and apparatus used to take advantage of the curtain coating can be used in the spray coating. . These include edge guides, air deflectors, air dampers and flange removal devices.

This method can be used in various fields such as to create photographic materials on paper or similar substrates or to create tapes, discs and other items of magnetic media.

It is noted that in relation to this date, the best method known to 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 (15)

1. A method for coating a substrate 30, 94 with several layers 72, 74, 76, 134, 136 of coating fluid, characterized in that it comprises the steps of: moving the substrate along a path through a coating station; forming at least one first and second layers that can flow 72, 74, 76, 134, 136 of the coating fluid; flowing at least one of the layers from a slotted hole 78, 128 of a slot 48, 126 of a kinetic jet coater 36, 90 at a speed that is sufficient to form a kinetic jet exiting the orifice, which flows horizontally, continuous; placing the layers in contact face to face with each other to form a composite layer 138 regardless of whether each layer is flowing individually at a rate that is sufficient to form a kinetic jet of continuously flowing fluid; flowing the composite layer at a rate that is sufficient to cause the composite layer to form a kinetic jet that flows horizontally, continuously, with respect to the substrate, for a width of the coating; and contacting the substrate 30, 94 with the kinetic jet 138 of the composite layer that is flowing, to deposit the coating fluids on the substrate in several different superimposed layers of the coating fluids.

2. The method according to claim 1, characterized in that the step of placing the layers comprises placing the first and second layers 72, 74, 76, 134, 136 in face-to-face contact with each other to form a composite layer 138 within the slot 48, 126 at a speed that is sufficient to cause the composite layer to form a kinetic jet that flows horizontally, continuously, with respect to the substrate, for the width of the coating.

3. The method according to claim 1, characterized in that the step of placing the layers comprises, after flowing at least a first layer of coating fluid 76, 136 through the groove and out of the groove, applying to the less a second layer 134 of coating fluid on the first layer of coating fluid to form a kinetic jet of the composite layer without destroying the kinetic jet of the first layer.

4. The method according to claim 3, characterized in that the step of flowing the composite layer comprises continuously dosing the second coating fluid 74 through a slot of the kinetic jet coater and flowing the second fluid along a face of the coater.

5. The method according to claim 3, characterized in that it further comprises the step of selecting a unitary flow rate for the first layer 76, 136 that is flowing, of the coating fluid in combination with the dimensions of the groove, a fluid density, a surface tension of the fluid, and a rheological property of the fluid to form a kinetic jet.

6. The method according to claim 1, characterized in that the step of flowing the composite layer comprises forming each layer in a groove 102, 126 of a separate matrix of a kinetic jet coater and forming the composite outer layer to the grooves of the matrix as the confluence of the various single layer kinetic jets emerging from the respective matrix portions.

7. The method according to claim 1, characterized in that at least one of the coating fluids does not wet the substrate.

8. The method according to the claim 1, characterized in that at least one of the coating fluids is not miscible with an adjacent coating fluid.

9. The method according to the claim 1, characterized in that at least one of the coating fluids has a different surface tension from that of an adjacent coating fluid.

10. The method according to the claim 1, characterized in that at least one of the coating fluids is in turbulent flow.

11. The method according to claim 1, characterized in that moving the substrate 30, 94 along a path through a coating station step comprises separating the substrate from the beginning of the fluid kinetic jet a distance greater than ten times. the thickness of the composite layer 138 applied to the substrate.

12. A kinetic jet coating apparatus for coating a substrate 30, 94 with multiple layers of coating fluid, characterized in that it comprises: a die 36, 90 having a first passageway communicating a source of coating fluid with a die outlet; means for moving the substrate 30, 94 at a distance spaced from the die outlet; means for flowing a first coating fluid 76, 136 from the outlet of the matrix to a flow rate that is large enough to cause the coating fluid to exit the matrix outlet and form a kinetic jet of continuously flowing fluid that establishes a bridge to the substrate for a coating width; means for flowing at least a second layer of coating fluid 74, 134 in face-to-face contact with the kinetic jet of coating fluid to form a kinetic jet of the composite layer that bridges the substrate for the coating width .

13. The apparatus according to claim 16, characterized in that the second layer of the coating fluid 74, 134 flows together with the first coating fluid 76, 136 through the outlet of the matrix.

14. The apparatus according to claim 16, characterized in that the matrix comprises: a first cavity 60 for receiving the first coating fluid 76, wherein the first passage is a slot 68 communicating between the first cavity and a first slot exit; a second cavity 50 for receiving the second coating fluid 74; and a second groove 58 communicating between the second cavity and a second groove outlet; and a third slot 48 for receiving the first and second coating fluids of the respective first and second outputs of the slot and communicating with the die outlet; wherein the first and second fluids form a composite layer within the third groove 48 and wherein the third groove is dimensioned so that the composite layer flows at a flow rate that is high enough to cause the composite layer to leave the outlet of the matrix and it comes off cleanly from the surfaces of the matrix without contacting more than the edges of the matrix groove outlets without taking into account whether the flow rate of the first and second individual fluids in their respective first and second grooves is sufficient to form a kinetic jet of fluid.

15. The apparatus according to claim 16, characterized in that the flow means comprise means for flowing at least one layer of coating fluid through the matrix and means for applying at least one layer of additional coating fluid on the layers of liquid. coating fluid that have come out of the matrix.