Patent Application
20250144666
Gravure is a widely used method for coating where ink is metered onto an engraved or textured roll (e.g., a gravure roll) with an applicator, with any excess ink on the roll surface removed by a doctor blade. The use of a doctor blade ensures that the volume of ink transferred is proportional to the specification of the engraved pattern, such as cell depth, width, and spacing.
Briefly, in one aspect, the disclosure describes a method including applying a liquid material onto a receiving roll to form a liquid pattern. The method further includes transferring at least a portion of the liquid material in the liquid pattern either (i) from the receiving roll (as a web transfer roll) onto a major surface of a web to form a substantially continuous coating, (ii) from the receiving roll onto a web transfer roll and transferring the liquid material from the web transfer roll onto the major surface of the web to form a substantially continuous coating, or (iii) from the receiving roll onto one or more intermediate transfer rolls and then onto a web transfer roll and then transferring the liquid material from the web transfer roll onto a major surface of a web to form a substantially continuous coating. When applying the liquid material onto the receiving roll, a coating volume of the liquid material applied to the receiving roll is controlled to proportionally control a thickness for a given width of the continuous coating on the major surface of the web.
In another aspect, this disclosure describes a coating system including a receiving roll as a web transfer roll, an applicator configured to apply a liquid material onto the web transfer roll to form a liquid pattern, and a web engaging with the web transfer roll such that at least a portion of the liquid material in the liquid pattern from the web transfer roll is transferred onto a major surface of the web to form a substantially continuous coating. When applying the liquid material onto the web transfer roll, the applicator is configured to control a coating volume of the liquid material applied to the web transfer roll to proportionally control a thickness for a given width of the continuous coating on the major surface of the web.
In another aspect, this disclosure describes a coating system including a receiving roll, an applicator configured to apply a liquid material onto the receiving roll to form a liquid pattern, and a web transfer roll. Optionally, the coating system further includes one or more intermediate rolls between the receiving roll and the web transfer roll. The web transfer roll directly engages with the receiving roll, or indirectly engages with the receiving roll via the optional one or more intermediate rolls, to receive at least a portion of the liquid material from the receiving roll. A web engages with the web transfer roll such that at least a portion of the liquid material on the web transfer roll is transferred onto a major surface of the web to form a substantially continuous coating. When applying the liquid material onto the receiving roll, the applicator is configured to control a coating volume of the liquid material applied to the receiving roll to proportionally control a thickness for a given width of the continuous coating on the web transfer roll and the major surface of the web.
Various unexpected results and advantages are obtained in exemplary embodiments of the disclosure. Some advantages of exemplary embodiments of the present disclosure include: (i) the ability to vary or prescribe coating thickness by varying the volume of fluid deposited in a liquid pattern, eliminating the need for roll changes or precision engraved rolls, (ii) the ability to make ultrathin coatings that may not be reproducibly made by traditional coating methods using a gravure roll with a doctor blade for metering, and (iii) the ability to make coatings with improved uniformity over traditional gravure coating methods, in particular for extremely thin coatings where local variability in the cell engravings may significantly impact the uniformity of the coating.
Various aspects and advantages of exemplary embodiments of the disclosure have been summarized. The above Summary is not intended to describe each illustrated embodiment or every implementation of the certain exemplary embodiments of the present disclosure. The Drawings and the Detailed Description that follow more particularly exemplify certain preferred embodiments using the principles disclosed herein.
The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying drawings, in which:
In the drawings, like reference numerals indicate like elements. While the above-identified drawings, which may not be drawn to scale, sets forth various embodiments of the present disclosure, other embodiments are also contemplated, as noted in the Detailed Description. In all cases, this disclosure describes the presently disclosed disclosure by way of representation of exemplary embodiments and not by express limitations. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of this disclosure.
For the following Glossary of defined terms, these definitions shall be applied for the entire application, unless a different definition is provided in the claims or elsewhere in the specification.
Certain terms are used throughout the description and the claims that, while for the most part are well known, may require some explanation. It should be understood that:
In this application, the term “roll-to-roll process” refers to a process of manufacture that embeds, coats, prints, laminates, or imparts other transformative work on a flexible, rolled substrate material or materials as they are fed continuously from one roller to another.
The term “applicator” is used to refer to any appropriate means of applying a coating fluid onto a gravure roll surface. Traditional applicators in the gravure coating literature include open pans, fountain rolls, and enclosed chamber systems. In the context of this application, an applicator is capable of applying or depositing a liquid material in a pattern to a roll surface by any appropriate means, including but not limited to, for example, inkjet printing, aerosol jet printing, spray coating, flexographic printing, gravure printing, etc.
The term “inkjet printing”, “inkjet printer”, or “inkjet printhead” refers to a controlled, non-contact printing method or device that uses a jetting mechanism to expel liquid drops onto a roll surface (e.g., a piezoelectric inkjet, a continuous inkjet, a thermal inkjet, a valve-jet inkjet, etc.). Control of the printhead may be through digital or analog signals. The term “non-contact” means that there is a gap (for example, 1 mm to 2 mm) between the printhead nozzle plate surface and the roll surface. Technical advantages of inkjet printing include, for example, (i) on-demand ability to control the deposited pattern of liquid, (ii) high spatial resolution in the machine direction and cross-web direction of the deposited pattern of liquid (e.g., commercial printhead resolutions greater than or equal to 360 dots per inch), and (iii) precision low volume throughput of liquid material (e.g., commercial printhead native drop volumes 2.5 to 70 picoliters). The ability to control the liquid deposition “on-demand” means that the inkjet droplet deposition can be varied with respect to position and/or time.
The term “gravure roll” is used to refer to a roll whose outer surface contains an array of cells, purposefully produced on that surface. These cells can be engraved in any shape, size, depth, or pattern that is appropriate for applying a continuous coating onto a web, produced by any means known in the art. It is to be noted that this definition of a gravure roll includes what are commonly known as “anilox rolls” in the flexographic printing industry.
The terms “liquid,” “liquid material,” or “liquid coating material” refers to any materials flowable at coating operation conditions described herein.
The term “speed ratio” refers to the absolute value of the ratio of the surface speed of a particular roll relative to a reference speed, which may be the web speed or the speed of an adjacent roll. For example, a speed ratio of 1 means a roll speed is equal to the reference speed. A speed ratio of +0.5 or −0.5 means a roll speed is 50% faster or 50% slower, respectively, than the reference speed. When a coated roll is nipped to another roll with speed ratio other than 1, smearing of the coating may take place in the nip. It is to be understood that the speed ratio is taken as an absolute value and it is always positive. For example, when a receiving roll has a surface speed 50% slower than a second roll, the speed ratio will be 0.5 regardless of whether the two rolls have the same direction of rotation (e.g., both clockwise), or opposite directions of rotation (i.e., one clockwise, and one counterclockwise).
A “pre-metered” coating system is one in which, for a given coating width and line speed, and in the absence of coating defects, the thickness of the applied coating is determined by the amount of coating solution supplied into the system, and not by the setup of the system. For example, when using a coating die one may adjust the gap between the die and a backing roll without impacting the coating thickness, or one may adjust the flowrate of solution into the die and obtain a proportional increase in the coating thickness without adjusting the gap (so long as no coating defects are generated which may cause the system to lose pre-metering). Typical pre-metered coating systems include die coaters, curtain coaters, and slide coaters.
A “self-metering” coating system is one in which the thickness of the applied coating is determined by the physics of that system, and not by the amount of coating solution supplied into that system. For example, in a roll coating nip the coating thickness may depend on various system properties such as gap between two rolls, the hardness of any rubber coverings that are present, the viscosity of the coating fluid, etc. In such a system one may adjust the flowrate of solution into the roll coating nip without seeing any substantial change to the coating thickness, or one may adjust the gap between the two rollers and see an appreciable change in thickness without adjust the flowrate of solution supplied to the system. Typical self-metering systems include roll coaters and gravure coaters.
In this application, by using terms of orientation such as “atop”, “on”, “over,” “covering”, “uppermost”, “underlying” and the like for the location of various elements in the disclosed coated articles, we refer to the relative position of an element with respect to a horizontally disposed, upwardly-facing substrate (e.g., web). However, unless otherwise indicated, it is not intended that the substrate (e.g., web) or articles should have any particular orientation in space during or after manufacture.
In this application, the term “machine direction” or “down-web direction” refers to the direction in which the substrate or web travels. Similarly, the term “cross-web direction” refers to the direction perpendicular to the machine direction (i.e., substantially perpendicular to the direction of travel for the web), and in the plane of the top surface of the web.
In this application, the terms “about” or “approximately” with reference to a numerical value or a shape means +/−five percent of the numerical value or property or characteristic, but expressly includes the exact numerical value.
In this application, the term “substantially” with reference to a property or characteristic means that the property or characteristic is exhibited to a greater extent than the opposite of that property or characteristic is exhibited.
In this application, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended embodiments, the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
As used in this application, the recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.8, 4, and 5). Various exemplary embodiments of the disclosure will now be described with particular reference to the Drawings. Referring to
In some embodiments, the first roll 110 may be rotating such that within the nip 4 the first roll 110 and the web 2 are travelling in the same direction (which may refer to a forward gravure configuration, or FWD), or in opposite directions (which may refer to a reverse gravure configuration, or REV). It is to be understood that the surface speed of the first roll 110 and of the web 2 may not need to have the same magnitude. In other words, there may be a speed differential between the surface speed of the first roll 110 and of the web.
The applicator 120 is positioned adjacent the first roll 110 and configured to apply a pattern of liquid material onto the first roll 110 when the first roll 110 rotates at a predetermined speed. In some embodiments, the applicator 120 includes an inkjet printer which allows a user to control a print pattern from a digital interface, e.g., making changes on-demand. The liquid pattern may include at least one of a regular or irregular pattern of dots, discontinuous lines, grids, or geometric shapes. In some embodiments, the pattern of liquid material can be conveniently present in the form of discrete quantities such as droplets including dots, short intermittent stripes, or any other appropriate shapes. In some embodiments, the liquid material in the liquid pattern 112 applied to the first roll 110 is discontinuous in at least one of the cross-web direction and the down-web direction. In some embodiments, the liquid pattern is discontinuous in both cross-web direction and down-web direction. In other words, at least some of the discrete quantities are disconnected with respect to each other with a gap between nearest neighbors in either or both machine direction and cross-web direction. In some embodiments, the gap may be, for example, no less than 1 time, no less than 2 times, no less than 5 times, or no less than 10 times the average lateral size of the discrete quantities (e.g., an average diameter of dots). In some embodiments, some of the droplets may slightly overlap with the nearest neighbors. It is to be understood that the inkjet printer 120 can be other suitable applicators. In general, any suitable applicators that can provide the liquid material onto a receiving roll in a liquid pattern can be used.
In the depicted embodiment of
In some examples, the printer 120 may include inkjet printheads which can deliver various droplet patterns to precisely control ink volumes. Exemplary printheads may include a piezoelectric inkjet printhead. Native drop volume may also be controlled by printhead selection. For example, piezoelectric inkjet printheads are commonly manufactured in small, medium, and large size corresponding to native drop volumes, which ranges from 2.4 to 70 picoliters or more. In some examples, the printer 120 may digitally control the volume of each droplet by in-flight (i.e., grey-scale printing) or on-impact coalescence of subsequent drops in a range, for example, from about 2.4 picoliter to about 1.0 microliter. In some examples, the printed pattern of liquid material is present in the form of discrete droplets each having an in-plane substantially round shape and a cross-sectional dome shape. The printed droplet diameter and droplet height may depend on the liquid volume and contact angle. A theoretical contact angle of a droplet on a roll surface may be greater than 5 degrees, greater than 10 degrees, greater than 20 degrees, or greater than 30 degrees. In some examples, a droplet may have a diameter greater than 20 micrometers, greater than 30 micrometers, greater than 40 micrometers, greater than 50 micrometers, or greater than 100 micrometers. The pattern of the droplets can be adjusted in the cross-web direction (“CW”) by arranging the nozzles 112 on the printer head 11 to adjust the cross-web nozzle spacing. The pattern of the droplets can be further adjusted in the machine direction (“DW”) by changing the firing frequency of the nozzles. The pattern of droplets can be adjusted in both the cross-web and machine directions by the print pattern itself, for instance, by selectively activating or deactivating nozzles. It is to be understood that, in some embodiments, the printed quantities of liquid material may be present as other shapes such as, for example, short intermittent stripes, squares, grids, etc. It is also to be understood that direct inkjet printing from the printer 120 onto a substrate or web may not be capable of achieving continuous ultrathin solvent-free coatings, even at the highest resolution and smallest drop volumes.
The liquid material can include any coatable material including, for example, water-based or solvent-based solutions, thermally curable solutions, radiation curable solutions, primers, adhesives, release materials, oils, waxes, hard coats, optical coatings, inks, dispersions, emulsions, combinations of any of these examples, etc. In some examples, a liquid material may include an inkjet-compatible liquid material where the ability to control spatial deposition is maintained. In some examples, a liquid material may include typical fluids for generating, for example, a pattern of droplets. Liquid materials of interest may be those with desirable properties for use as release liners or materials, low-adhesion backsize coatings, hardcoats, primers, optical coatings, adhesive coatings, etc.
Optimal properties for the liquid material may depend on the particular application method used to produce the desired pattern on a receiving roll. For example, when the pattern is produced via inkjet printing, the liquid material may have a viscosity below about 100 centipoise (cP), optionally between about 10 and 15 cP. For example, when the pattern is produced via flexographic printing, the liquid material may have a viscosity below about 10,000 cP, optionally between about 500 and 2,000 cP. The liquid material may be Newtonian or non-Newtonian, shear thinning or shear thickening, so long as it is able to produce the desired pattern. In some embodiments, the liquid material may have a surface tension below about 100 mN/m, preferably between 20 mN/m and 40 mN/m. In some embodiments, temperature may be employed to adjust the viscosity and/or surface tension of a material so that it is more readily patterned. For example, an ink may have a viscosity that is too high at room temperature, but that decreases to a range that is acceptable for printing at an elevated temperature. Physical properties of the liquid material, such as viscosity, surface tension, and density, are not meant to be limiting so long as the desired pattern can be achieved on a receiving roll via an applicator (e.g., an inkjet printer).
The web material may be any substrate capable of roll-to-roll web handling. In some embodiments, exemplary substrates may include but are not limited to thermoplastics such as polyesters (e.g., polyethylene terephthalate or polyethylene naphthalates), polyacrylates (e.g., polymethyl methacrylate or “PMMA”), poly(vinyl acetate) (“PVAC”), poly(vinylbutyral) (“PVB)”, poly(ethyl acrylate) (“PEA”), poly(diphenoxyphosphazene) (“PDPP”), polycarbonate (“PC”), polypropylene (“PP”), high density polyethylene (“HDPE”), low density polyethylene (“LDPE”), polysulfone (“PS”), polyether sulfone (“PES”), polyurethane (“PUR”), polyamide (“PA”), polyvinyl chloride (“PVC”), polyvinylidene fluoride (“PVdF”), polystyrene and polyethylene sulfide; and thermoset plastics such as cellulosic derivatives, polyimide, polyimide benzoxazole, polybenzoxazole, crosslinked acrylates, polyepoxide resins, and polydimethylsiloxane resins. Other suitable substrates may include papers such as cellulosic or synthetic paper, nonwoven, metal foil, glass, foam, etc. It should be understood that any suitable substrate may optionally be coated or treated by one or more coatings or treatments. It should also be understood that when the major surface 21 of web 2 includes interruptions (e.g., depressions, apertures, etc.), a substantially continuous liquid coating may form on the portions of the major surface 21 that come into contact with the first roll 110 as it passes through the impression nip 4. Conversely, the interruptions may not be directly coated with a liquid layer as it passes through the impression nip 4.
In some embodiments, useful substrates are typically in the form of a film. Depending on the method or methods used in making the film, the film may be smooth or may be structured on its major surface. Methods for making suitable smooth film substrates are well known in the art and include, for example, cast film extrusion and/or blown film extrusion. One example of a substrate having a structure is a “microreplicated” film. Methods for making microreplicated films are well known in the art and include, for example, continuous cast and cure processes. In one embodiment, a substrate may have a thickness value in the range from about one micrometer to about 25,000 micrometers. In another embodiment, the substrate film may have a thickness value in the range from about 12 micrometers to about 10,000 micrometers. In still another embodiment, the substrate film may have a thickness value in the range from about 50 micrometers to about 2000 micrometers.
In some embodiments, the major surface 21 of the web 2 may be interrupted by one or more structural features (e.g., depressions, apertures, etc.) that do not directly receive the transferred coating. A structured surface of a substrate may be a microstructured surface formed by an extrusion replication procedure utilizing a tool that imparts a negative structure in the polymer surface. The tooling can be in any of a variety of forms and materials. Typically, the tooling is a sheet, roll, belt, or roll of surface structured film made of metal or polymer. For metal tools, the metal is generally diamond-machined, embossed, knurled, sandblasted, etc. to form the surface structure. The structured polymer surface is generally formed by extrusion replication where a thermoplastic resin such as a fluoropolymer extruded through a die and into a nip with a machined metal tool roll and a rubber roll.
The molten polymer is quenched while in contact with the tool surface which then releases from the tool roll and is wound on a roll. Another technique for making structured surfaces is to coat UV curable acrylate functional resins against a tool followed by removal of the cross-linked structured film from the tool. Yet another technique for making structured surfaces is to coat thermally curable urethane functional resins against a tool followed by removal of the cross-linked structured film from the tool. This polyurethane layer can be prepared from the condensation polymerization of a reaction mixture that includes a polyol, a polyisocyanate, and a catalyst.
In some embodiments, the first roll 110 may be a gravure roll, which refers to a roll that has an array of microwells (also called cells) used to carry the liquid material. The cells may be created by any suitable techniques or methods, such as mechanical engraving, laser engraving, or etching, which are well known in the industry. A gravure roll typically may have a rigid surface. The cells may have any suitable size, including cell depths ranging from 1 micrometer or less to greater than 100 micrometers, or cell widths ranging from 10 micrometers or less to greater than 500 micrometers. The cells may have any suitable centre-to-centre spacing, ranging from 100 cells per inch or less to greater than 2000 cells per inch. The cells may also have any suitable shape or arrangement, such as hexagonal, quadrangular, or trihelical. The size, shape, and arrangement of the cells defines the capacity for the roll to carry fluid, and is typically specified as the volume factor of the roll, given in units of BCM/in2 (Billion Cubic Microns per square inch). The volume factor of a roll is a geometrical parameter that is determined at the time of engraving.
In some embodiments, the first roll 110 may not include a pattern of cells. Instead, the first roll 110 may contain a random surface structure with peaks and valleys. Such random surface structures on a roll may be fabricated using any suitable method, and may be characterized by any suitable metric, such as an arithmetic mean roughness (commonly referred to as Ra), and root mean squared roughness (commonly referred to as Rq), an average maximum peak to valley within five sampling lengths (commonly referred to as Rz), parameters based on material ratio curves (common examples include Rk, Rpk, Rmr, tp, Rmr1, Rvk, Rmr2), parameters based on probability models such as plateau root mean squared roughness (commonly referred to as Rpq), valley root mean squared roughness (commonly referred to as Rvq), and plateau-valley transition bearing ratio (commonly referred to as Rmq), and other suitable metrics for quantifying surface finish. Typical values for Ra may be, for example, about 1,000 nm or less, about 500 nm or less, about 100 nm or less, or about 50 nm or less. A volume factor for such a roll may still be defined by the volume per unit area of liquid that can be carried between the peaks and valleys on the surface of the roll. An example of a random surface structure is an abraded, honed, or plateau honed surface.
Referring again to
In some examples, the coating thickness and uniformity of the coating 22 on the web surface 21 can be controlled by controlling the pattern of liquid material on the first roll 110. For example, as shown in
In some embodiments, the use of an inkjet printer may allow the position of the droplets to be changed dynamically, allowing an operator to adjust the down-web and/or cross-web coating thickness profile to meet any desired criteria (e.g., to improve the uniformity, to purposefully introduce coating thickness variations, etc.) without stopping the machine. In some embodiments, the use of an inkjet printer may allow the volume of the droplets to be changed dynamically, allowing an operator to adjust the down-web and/or cross-web coating thickness profile to meet any desired criteria.
In a traditional gravure coating system, while the thickness of the coating can be primarily determined by the specifications of the engraving on the gravure roll, in some cases the coating thickness and uniformity may be additionally adjusted by controlling the ratio of the surface speed of the gravure roll to the speed of the web (or, in the case of transfer coating, to the surface speed of the transfer roll). This can be understood by noting that while the BCM sets the volume of coating solution carried into the nip by each cell, when the gravure roll speed is increased relative to the substrate speed, the number of cells carried into the nip per unit length of substrate may increase, resulting in a larger flowrate of liquid into the coating nip, and thus a thicker coating on the substrate. It is to be understood that this may not be a linear effect, as the pickout (which is commonly defined as the percentage of the coating solution that is transferred from a given gravure cell to the web) may depend on roll speed ratio. This coupling makes the impact of roll speed ratio on coating thickness difficult to understand, as well as system dependent. For example, one may modify the viscosity of the coating solution or the geometry of the gravure cells and observe a substantial change in the pickout, resulting in substantially different coating thickness and/or a change in the way thickness varies as a function or roll speed ratio.
One benefit of some embodiments in this disclosure is that, by using an inkjet printer to vary the amount of coating solution applied on a gravure roll, the coating thickness can be directly controlled and adjusted. In other words, the coating system in some embodiments of this disclosure may be described as a pre-metered system in that changes to the amount of fluid supplied onto the gravure roll result in clear and predictable changes to the thickness of the coating on the web. To explain this benefit, it is helpful to note that it is known in the literature that a roll coating nip has a maximum flowrate of liquid allowed through for a given condition (for an explanation of this effect, see Coyle, Macosko, and Scriven, 1986, “Film-Splitting Flows in Forward Roll Coating”, Journal of Fluid Mechanics, vol. 171, pp. 183-207), and supplying fluid in excess of this critical value has very little impact on the resulting coating thickness. This in turn implies that this excess fluid is rejected by the roll coating nip, most typically via what is known as a rolling bank. The rejection of fluid and the configuration-dependent flowrate are why a roll coating nip is commonly referred to as self-metering. Further evidence of the self-metering nature of roll coaters is that they are most commonly operated using a pan or some other system to supply a large excess of fluid to the roll nip, with much of that excess rejected by the nip. In contrast, when the flowrate of liquid entering the nip is kept below this critical value, it is possible to pre-meter the nip, enabling the coating operator to make predictable changes in the coating thickness. What is particularly surprising is that some embodiments of this disclosure can achieve a pre-metered and continuous coating with a pattern of liquid material, without any substantial levelling or merging of the pattern prior to the point where the liquid material is transferred. Although one might expect a priori that any condition that operates in a starved mode would be incapable of sufficiently spreading a pattern of liquid droplets into a continuous layer without losing pre-metering, it is shown in some examples that the equivalent volume of the input layer can be varied by an order of magnitude without losing the pre-metering capability.
In some examples, the coating thickness and uniformity of the coating 22 on the web 2 can be controlled by controlling the surface roughness of the first roll 110. For example, a polished roll surface with a random roughness may improve drop spreading on the web when the web 2 engage with the first roll 110 under an impression force, as compared to a gravure roll surface with a well-defined cell structure engraving.
In some examples, the coating thickness and uniformity of the coating 22 on the web 2 can be controlled by controlling an impression force between the first roll 110 and the web 2. For example, the nip engagement can be adjusted such that a coating changes from discontinuous to continuous.
For gravure coating using the system 100′ of
During a traditional coating operation such as shown in
There are several primary drawbacks to the approach as shown in
Referring to
An applicator 220 is positioned adjacent the receiving roll 210 and configured to apply a pattern of liquid material onto the receiving roll 210 when the receiving roll 210 rotates at a predetermined speed. In the depicted embodiment of
In some embodiments, the pattern of liquid material can be conveniently present in the form of discrete quantities such as droplets including dots, short intermittent stripes, or any other shapes. At least some of the discrete quantities are disconnected with respect to each other with a gap between nearest neighbors in either or both machine direction and cross-web directions. In some embodiments, the gap may be, for example, no less than 1 time, no less than 2 times, no less than 5 times, or no less than 10 times the average lateral size of the discrete quantities (e.g., an average diameter of dots). In some embodiments, some of the droplets may slightly overlap with the nearest neighbors.
In some embodiments, the receiving roll 210 may be a gravure roll, which refers to a roll that has an array of microwells (also called cells) used to carry the liquid material. The cells can be produced with various shapes by any suitable techniques or methods, all of which are well known in the coating and printing industries. It is to be understood that in some embodiments, the receiving roll 210 may be the same as the first roll 110 of
In the depicted embodiment of
Referring again to
In various examples, the coating thickness and uniformity on a web surface can be controlled by controlling a roll speed ratio. For example, in the case of a two-roll system such as the system 100 of
In some examples, the coating thickness and uniformity of the coating 32 on the web surface can be controlled by controlling the surface roughness of the receiving roll 210 and the surface roughness of the web transfer roll 240. For example, a polished roll surface with a random roughness may improve drop spreading on the web when the web 2 engage with the web transfer roll 240 under an impression force. While it is common in the roll coating space for the impression force between two rolls in a nip to be adjusted as a means of tuning the coating thickness, in some embodiments of this disclosure the impression force at any nip within the coater may not significantly impact the coating thickness. Typical means of adjusting the impression force may include either controlling the force directly between the two rolls (for example, using air cylinders to engage one roll into the other), or controlling the position of one roll relative to the other (for example, using a leadscrew, or pressing the roll with a high force against a set of stops, with adjustment of the stops used to precisely control the roll(s) relative position to each other or the substrate). In either case, the impression force may be conveniently quantified by the footprint, which is a measure of the machine direction length over which the two rolls are in contact. Typical values for the footprint may be less than 1 mm, less than 3 mm, less than 5 mm, less than 10 mm, or less than 15 mm, with a preferred value less than 5 mm. In some embodiments a larger footprint may improve spreading of adjacent droplets, assisting the formation of a uniform and continuous coating, though it is usually desirable to run the smallest footprint possible.
For gravure coating using the system 200′ of
In the gravure coating configuration shown in
Some embodiments of the present disclosure use an inkjet printer instead of a standard applicator in gravure coating, which eliminates the need to manufacture gravure rolls with very precise cell structures, in particular as it pertains to shallow/narrow cells that are difficult to engrave accurately using existing technology. An inkjet printer enables precision metering to ultra-low coating volumes not achievable with typical gravure roll machining. An inkjet printer also enables digital control of the coating volume as well as the coating pattern.
Unless otherwise indicated, all numbers expressing quantities or ingredients, measurement of properties and so forth used in the specification and embodiments are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and more particularly the Listing of Exemplary Embodiments and the claims can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings of the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claimed embodiments, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Exemplary embodiments of the present disclosure may take on various modifications and alterations without departing from the spirit and scope of the present disclosure. Accordingly, it is to be understood that the embodiments of the present disclosure are not to be limited to the following described exemplary embodiments, but are to be controlled by the limitations set forth in the claims and any equivalents thereof.
Exemplary embodiments are listed below. It is to be understood that any one of the embodiments 1-15, 16-20, 21-23, and 24-26 can be combined.
Embodiment 1 is a method comprising:
Embodiment 2 is the method of embodiment 1, further comprising forming a nip between the web and the web transfer roll.
Embodiment 3 is the method of embodiment 1 or 2, further comprising applying an impression force to press the web to engage with the web transfer roll.
Embodiment 4 is the method of embodiment 3, wherein applying the impression force further comprises pressing the web via a backup roll, or wrapping a free span of the web around the web transfer roll.
Embodiment 5 is the method of any one of embodiments 1-4, further comprising controlling the coating volume of the liquid material applied to the receiving roll such that the continuous coating has a coating thickness in a range from 10 nm to 100 micrometers.
Embodiment 6 is the method of embodiment 5, wherein controlling the coating volume of the liquid material further comprises controlling the liquid pattern on the receiving roll.
Embodiment 7 is the method of any one of embodiments 1-6, wherein applying the liquid material onto the receiving roll further comprises inkjet printing the liquid material to form the liquid pattern.
Embodiment 8 is the method of any one of embodiments 1-7, wherein the liquid pattern comprises at least one of a regular or irregular pattern of dots, discontinuous lines, grids, or geometric shapes.
Embodiment 9 is the method of any one of embodiments 1-8, wherein the liquid material in the liquid pattern is discontinuous in at least one of a cross-web direction and a down-web direction.
Embodiment 10 is the method of any one of embodiments 1-9, wherein applying the liquid material onto the receiving roll further comprises at least one of flexographic printing, or gravure printing.
Embodiment 11 is the method of any one of embodiments 1-10, further comprising controlling a uniformity of the continuous coating when transferring the liquid material from the web transfer roll onto the major surface of the web.
Embodiment 12 is the method of embodiment 11, further comprising controlling the liquid pattern of the liquid material applied to the receiving roll to control the uniformity.
Embodiment 13 is the method of embodiment 11 or 12, further comprising controlling a roll speed ratio to control the uniformity.
Embodiment 14 is the method of any one of embodiments 11-13, further comprising controlling a surface roughness of the receiving roll to control the uniformity.
Embodiment 15 is the method of any one of embodiments 11-14, further comprising controlling an impression force of the web transfer roll and the web to control the uniformity.
Embodiment 16 is a coating system comprising:
Embodiment 17 is a coating system comprising:
Embodiment 18 is the system of embodiment 16 or 17, further comprising a backup roll to press the web to engage with the web transfer roll.
Embodiment 19 is the system of any one of embodiments 16-18, wherein the applicator includes an inkjet printer.
Embodiment 20 is the system of any one of embodiments 16-19, wherein the applicator is configured to control the liquid pattern applied onto the receiving roll to control the coating volume.
Embodiment 21 is a method comprising:
Embodiment 22 is the method of embodiment 21, wherein transferring the liquid material comprises directly transferring at least a portion of the liquid material from the receiving roll onto the major surface of the web.
Embodiment 23 is the method of embodiment 21 or 22, wherein transferring the liquid material further comprises transferring the liquid material from the receiving roll onto a web transfer roll, and from the web transfer roll to the major surface of the web.
Embodiment 24 is the method of any one of embodiments 21-23, wherein transferring the liquid material further comprises transferring the liquid material from the receiving roll onto one or more intermediate transfer rolls and then onto a web transfer roll and then transferring the liquid material from the web transfer roll onto the major surface of the web.
Embodiment 25 is a coating system comprising:
Embodiment 26 is the coating system of embodiment 25, further comprising a web transfer roll engaging with the receiving roll, wherein the liquid material in the liquid pattern is transferred from the receiving roll onto the web transfer roll, and from the web transfer roll to the major surface of the web.
Embodiment 27 is the coating system of embodiment 26, further comprising one or more intermediate rolls between the receiving roll and the web transfer roll, transferring the liquid material from the receiving roll onto one or more intermediate transfer rolls and then onto the web transfer roll.
The operation of the present disclosure will be further described with regard to the following detailed examples. These examples are offered to further illustrate the various specific and preferred embodiments and techniques. It should be understood, however, that many variations and modifications may be made while remaining within the scope of the present disclosure.
These Examples are merely for illustrative purposes and are not meant to be overly limiting on the scope of the appended claims. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the present disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
All examples were coated using a flexographic printing deck manufactured by Retroflex Inc. (Wrightstown, WI, USA) on a roll-to-roll webline. The flexographic printing deck was set up in direct (
The web was loaded onto the flexographic printing line and put under 1 pound per linear inch of tension. The line was run at about 10 feet per minute to transport the web through the flexographic printing deck. A dot array of liquid material was applied to the Roll #1 using the pattern applicator with the patterned applicator gapped to the receiving roll surface set at 2 mm. The coated liquid material exiting the flexographic printing deck was cured using a UV cure oven available from Xeric Web Drying Systems (Neenah, WI, USA). The cured coating of liquid material was subsequently wound up into a roll.
1. Thickness versus Roll Speed Ratio
The flexographic printing deck was run in offset configuration (
The input rate of liquid was varied by changing the speed ratio of Roll #1 (210 in
Alternatively, the input rate of liquid was held constant while changing the roll speed ratio of Roll #1 to Roll #2 when the drop spacing was referenced to the speed of Roll #2 in Table 2. Note that Roll #2 and Roll #3 (230 in
Samples 1 to 10 were coated with Liquid Material A. Coating thickness was measured using X-ray fluorescence.
2. Thickness versus Drop Spacing
The flexographic printing deck was run in offset configuration (
The flexographic printing deck was run in direct configuration (
The flexographic printing deck was run in direct configuration and reverse mode with all other conditions equal for comparison.
The flexographic printing deck was run in offset configuration (
Reference throughout this specification to “one embodiment,” “certain embodiments,” “one or more embodiments” or “an embodiment,” whether or not including the term “exemplary” preceding the term “embodiment,” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the certain exemplary embodiments of the present disclosure. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the certain exemplary embodiments of the present disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.
While the specification has described in detail certain exemplary embodiments, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, may readily conceive of alterations to, variations of, and equivalents to these embodiments. Accordingly, it should be understood that this disclosure is not to be unduly limited to the illustrative embodiments set forth hereinabove. In particular, as used herein, the recitation of numerical ranges by endpoints is intended to include all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5). In addition, all numbers used herein are assumed to be modified by the term “about.”
Furthermore, all publications and patents referenced herein are incorporated by reference in their entirety to the same extent as if each individual publication or patent was specifically and individually indicated to be incorporated by reference. Various exemplary embodiments have been described. These and other embodiments are within the scope of the following claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2023/051055 | 2/6/2023 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63311335 | Feb 2022 | US |
